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  • 1
    facet.materialart.
    Unbekannt
    Publikationsdatum: 2014-02-26
    Beschreibung: Zeitschriften und andere Medien werden in wachsendem Maße elektronisch publiziert. Hier entsteht für die Bibliotheken, welche diese Online-Publikationen ihren Lesern zur Verfügung stellen, ein neuer Bereich der Informationsvermittlung. Mit dem aufkommenden Standard der OpenURL ergeben sich neue Möglichkeiten, dem Benutzer weiterführende Links und Dienste anzubieten. Das Document-Linking-System SFX der Firma Ex Libris ist die erste und bekannteste Anwendung, die ein Managementsystem fr die Auswertung der OpenURL implementiert. Im Rahmen eines Projektes hat die Zentrale des Kooperativen Bibliotheksverbundes Berlin-Brandenburg (KOBV) eine Evaluation von SFX durchgeführt. Als Ergebnis der Evaluation sollten Einsatzmöglichkeiten von SFX für die KOBV-Suchmaschine und in den lokalen Bibliothekssystemen und Informationsportalen aufgezeigt werden. Im Verlauf des Projektes hat sich das Produkt SFX als eine stabile Anwendung erwiesen, die dem Benutzer interessante zusätzliche Dienste bieten kann.
    Schlagwort(e): ddc:000
    Sprache: Deutsch
    Materialart: reportzib , doc-type:preprint
    Format: application/postscript
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  • 2
    Publikationsdatum: 2014-02-26
    Beschreibung: In this work we present an approach for the sensitivity analysis of linearly-implicit differential-algebraic equation systems. Solutions for both, states and sensitivities are obtained by applying an extrapolated linearly implicit Euler discretization scheme. This approach is compared to the widely used sensitivity extensions of multi-step BDF methods by means of case studies. Especially, we point out the benefit of this method in the context of dynamic optimization using the sequential approach.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 3
    Publikationsdatum: 2014-09-30
    Beschreibung: Decomposition of the high dimensional conformational space of bio-molecules into metastable subsets is used for data reduction of long molecular trajectories in order to facilitate chemical analysis and to improve convergence of simulations within these subsets. The metastability is identified by the Perron-cluster cluster analysis of a Markov process that generates the thermodynamic distribution. A necessary prerequisite of this analysis is the discretization of the conformational space. A combinatorial approach via discretization of each degree of freedom will end in the so called ''curse of dimension''. In the following paper we analyze Hybrid Monte Carlo simulations of small, drug-like biomolecules and focus on the dihedral degrees of freedom as indicators of conformational changes. To avoid the ''curse of dimension'', the projection of the underlying Markov operator on each dihedral is analyzed according to its metastability. In each decomposition step of a recursive procedure, those significant dihedrals, which indicate high metastability, are used for further decomposition. The procedure is introduced as part of a hierarchical protocol of simulations at different temperatures. The convergence of simulations within metastable subsets is used as an ''a posteriori'' criterion for a successful identification of metastability. All results are presented with the visualization program AmiraMol.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 4
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    Unbekannt
    Publikationsdatum: 2019-05-10
    Beschreibung: The adaptive finite element code {\sc Kardos} solves nonlinear parabolic systems of partial differential equations. It is applied to a wide range of problems from physics, chemistry, and engineering in one, two, or three space dimensions. The implementation is based on the programming language C. Adaptive finite element techniques are employed to provide solvers of optimal complexity. This implies a posteriori error estimation, local mesh refinement, and preconditioning of linear systems. Linearely implicit time integrators of {\em Rosenbrock} type allow for controlling the time steps adaptively and for solving nonlinear problems without using {\em Newton's} iterations. The program has proved to be robust and reliable. The user's guide explains all details a user of {\sc Kardos} has to consider: the description of the partial differential equations with their boundary and initial conditions, the triangulation of the domain, and the setting of parameters controlling the numerical algorithm. A couple of examples makes familiar to problems which were treated with {\sc Kardos}. We are extending this guide continuously. The latest version is available by network: {\begin{rawhtml} 〈A href="http://www.zib.de/Numerik/software/kardos/"〉 〈i〉 Downloads.〈/i〉〈/a〉 \end{rawhtml}}
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 5
    Publikationsdatum: 2016-06-09
    Beschreibung: This article studies the relation of the two scientific languages Chemistry and Mathematics via three selected comparisons: (a) QSSA versus dynamic ILDM in reaction kinetics, (b) lumping versus discrete Galerkin methods in polymer chemistry, and (c) geometrical conformations versus metastable conformations in drug design. The common clear message from these comparisons is that chemical intuition may pave the way for mathematical concepts just as chemical concepts may gain from mathematical precisioning. Along this line, significant improvements in chemical research and engineering have already been possible -- and can be further expected in the future from the dialogue between the two scientific languages.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 6
    Publikationsdatum: 2014-11-10
    Beschreibung: Several sets of reductions rules are known for preprocessing a graph when computing its treewidth. In this paper, we give reduction rules for a weighted variant of treewidth, motivated by the analysis of algorithms for probabilistic networks. We present two general reduction rules that are safe for weighted treewidth. They generalise many of the existing reduction rules for treewidth. Experimental results show that these reduction rules can significantly reduce the problem size for several instances of real-life probabilistic networks.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 7
    Publikationsdatum: 2014-02-26
    Beschreibung: Signaling is crucial to the operation of modern telecommunication networks. A breakdown in the signaling infrastructure typically causes customer service failures, incurs revenue losses, and hampers the company image. Therefore, the signaling network has to be highest reliability and survivability. This in particular holds for the routers in such a network, called \textit{signaling transfer points\/} (STPs). The robustness of an STP can be improved by equally distributing the load over the internal processing units. Several constraints have to be taken into account. The load of the links connected to a processing unit changes over time introducing an imbalance of the load. In this paper, we show how integer linear programming can be applied to reduce the imbalance within an STP, while keeping the number of changes small. Two alternative models are presented. Computational experiments validate the integer programming approach in practice. The GSM network operator E-Plus saves substantial amounts of time and money by employing the proposed approach.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 8
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    Unbekannt
    Publikationsdatum: 2019-10-24
    Schlagwort(e): ddc:000
    Sprache: Deutsch
    Materialart: annualzib , doc-type:report
    Format: application/pdf
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  • 9
    Publikationsdatum: 2020-11-13
    Beschreibung: In the problem of \emph{Online Call Admission in Optical Networks}, briefly called \textsc{oca}, we are given a graph $G=(V,E)$ together with a set of wavelengths~$W$ and a finite sequence $\sigma=r_1,r_2,\dots$ of calls which arrive in an online fashion. Each call~$r_j$ specifies a pair of nodes to be connected and an integral demand indicating the number of required lightpaths. A lightpath is a path in~$G$ together with a wavelength~$\lambda \in W$. Upon arrival of a call, an online algorithm must decide immediately and irrevocably whether to accept or to reject the call without any knowledge of calls which appear later in the sequence. If the call is accepted, the algorithm must provide the requested number of lightpaths to connect the specified nodes. The essential restriction is the wavelength conflict constraint: each wavelength is available only once per edge, which implies that two lightpaths sharing an edge must have different wavelengths. Each accepted call contributes a benefit equal to its demand to the overall profit. The objective in \textsc{oca} is to maximize the overall profit. Competitive algorithms for \textsc{oca} have been known for the special case where every call requests just a single lightpath. In this paper we present the first competitive online algorithms for the general case of larger demands.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 10
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    Unbekannt
    Publikationsdatum: 2020-11-13
    Beschreibung: Traditional optimization techniques assume, in general, knowledge of all data of a problem instance. There are many cases in practice, however, where decisions have to be made before complete information about the data is available. In fact, it may be necessary to produce a part of the problem solution as soon as a new piece of information becomes known. This is called an \emph{online situation}, and an algorithm is termed \emph{online}, if it makes a decision (computes a partial solution) whenever a new piece of data requests an action. \emph{Competitive analysis} has become a standard yardstick to measure the quality of online algorithms. One compares the solution produced by an online algorithm to that of an optimal (clairvoyant) offline algorithm. An online algorithm is called $c$-competitive if on every input the solution it produces has cost'' at most $c$~times that of the optimal offline algorithm. This situation can be imagined as a game between an online player and a malicious adversary. Although competitive analysis is a worst-case analysis and henceforth pessimistic, it often allows important insights into the problem structure. One can obtain an idea about what kind of strategies are promising for real-world systems and why. On the other hand there are also cases where the offline adversary is simply too powerful and allows only trivial competitiveness results. This phenomenon is called hitting the triviality barrier''. We investigate several online problems by means of competitive analysis. We also introduce new concepts to overcome the weaknesses of the standard approach and to go beyond the triviality barrier.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: doctoralthesis , doc-type:doctoralThesis
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  • 11
    Publikationsdatum: 2014-02-26
    Beschreibung: The paper deals with the two-class priority M/M/1 system, where the prioritized class-1 customers are served under FCFS preemptive resume discipline and may become impatient during their waiting for service with generally distributed maximal waiting times but finite expectation. The class-2 customers have no impatience. The required mean service times may depend on the class of the customer. As the dynamics of class-1 customers are related to the well analyzed M/M/1+GI system, our aim is to derive characteristics for class-2 customers and for the whole system. The solution of the balance equations for the partial probability generating functions of the detailed system state process is given in terms of the weak solution of a family of boundary value problems for ordinary differential equations. By means of this solution formulae for the joint occupancy distribution and for the sojourn and waiting times of class-2 customers are derived generalizing results recently obtained by Choi et al. in case of deterministic maximal waiting times. For deterministic maximal waiting times partially new explicit formulae are given.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 12
    Publikationsdatum: 2016-06-09
    Beschreibung: The bio-heat transfer equation is a macroscopic model for describing the heat transfer in microvascular tissue. So far the deduction of the Helmholtz term in the bio-heat transfer equation is not co role. In view of a future numerical application of this new mathematical model to treatment planning in hyperthermia we derive asymptotic estimates for first and second order correctors.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 13
    Publikationsdatum: 2021-08-05
    Beschreibung: Mixed integer programs ($MIPs$) are commonly solved with branch and bound algorithms based on linear programming. The success and the speed of the algorithm strongly depends on the strategy used to select the branching variables. Today's state-of-the-art strategy is called \emph{pseudocost branching} and uses information of previous branchings to determine the current branching. We propose a modification of \emph{pseudocost branching} which we call \emph{history branching}. This strategy has been implemented in $SIP$, a state-of-the-art $MIP$ solver. We give computational results that show the superiority of the new strategy.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 14
    Publikationsdatum: 2020-11-13
    Beschreibung: We consider the design of transparent optical networks from a practical perspective. Network operators aim at satisfying the communication demands at minimum cost. Such an optimization involves three interdependent planning issues: the dimensioning of the physical topology, the routing of lightpaths, and the wavelength assignment. Further topics include the reliability of the configuration and sparse wavelength conversion for efficient use of the capacities. In this paper, we investigate this extensive optical network design task. Using a flexible device-based model, we present an integer programming formulation that supports greenfield planning as well as expansion planning on top of an existing network. As solution method, we propose a suitable decomposition approach that separates the wavelength assignment from the dimensioning and routing. Our method in particular provides a lower bound on the total cost which allows to rate the solution quality. Computational experiments on realistic networks approve the solution approach to be appropriate.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 15
    Publikationsdatum: 2020-11-13
    Beschreibung: Today's telecommunication networks are configured statically. Whenever a connection is established, the customer has permanent access to it. However, it is observed that usually the connection is not used continuously. At this point, dynamic provisioning could increase the utilization of network resources. WDM based Optical Transport Networks (OTNs) will shortly allow for fast dynamic network reconfiguration. This enables optical broadband leased line services on demand. Since service requests competing for network resources may lead to service blocking, it is vital to use appropriate strategies for routing and wavelength assignment in transparent optical networks. We simulate the service blocking probabilities of various dynamic algorithms for this problem using a well-founded traffic model for two realistic networks. One of the algorithms using shortest path routings performs best on all instances. Surprisingly, the tie-breaking rule between equally short paths in different wavelengths decides between success or failure.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 16
    Publikationsdatum: 2020-11-13
    Beschreibung: Nachdem mit der KOBV-Suchmaschine die Online-Recherche in den wichtigsten Berliner und Brandenburgischen Bibliotheken realisiert ist, gehört der Aufbau der Online-Fernleihe als einer neuen, nutzerfreundlichen Dienstleistung zu den drängendsten Desideraten des KOBV. Dem Nutzer soll ein komfortabler Service geboten werden, der ihm im Anschluss an eine erfolgreiche Recherche die nahtlose - per Knopfdruck ausgelöste - Fernleih-Bestellung auf das gewünschte Medium erlaubt. Gleichzeitig trägt die Ablösung des traditionellen, per Post und Bücherauto versandten Roten Fernleihscheines durch eine sekundenschnelle Online-Kommunikation zu einer erheblichen Beschleunigung des Fernleih-Verfahrens bei. Der KOBV beteiligt sich an der Initiative der deutschen Bibliotheksverbünde zur Automatisierung und Beschleunigung der Fernleihe. Die Realisierung soll im KOBV in einem zweistufigen Verfahren erfolgen: (1) verbundinterne Fernleihe im KOBV und (2) verbundübergreifende Fernleihe in der Zusammenarbeit mit den anderen Verbünden. Eine Verbund-Fernleih-Software für den KOBV muss insbesondere den KOBV-spezifischen Gegebenheiten genügen, die in dieser Form in den anderen deutschen Verbünden nicht anzutreffen sind. Im Jahre 2001 hat eine KOBV-Arbeitsgruppe Spezifikationen für eine Verbund-Fernleih-Software erarbeitet, in der die Besonderheiten des KOBV mit berücksichtigt sind. Beim Aufbau der automatisierten Fernleihe als einer regulären KOBV-Dienstleistung geht es nicht allein darum, einen schnellen, komfortablen Service für Nutzer einzurichten, sondern darüber hinaus um eine weitreichende Rationalisierung innerhalb der Bibliotheken. Das vorliegende Spezifikationspapier zielt auf beide Faktoren ab, indem es die Fernleihe als integrierten Dienst entwirft, der von der Bestellung bis zur Bereitstellung des Mediums in der gebenden Bibliothek automatisiert - ohne manuelles Eingreifen der Fernleihstelle - abläuft: die jetzige manuell durchgeführte Fernleihe wird durch die automatisierte Fernleihe abgelöst.
    Schlagwort(e): ddc:000
    Sprache: Deutsch
    Materialart: reportzib , doc-type:preprint
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  • 17
    Publikationsdatum: 2020-12-14
    Beschreibung: In the online traveling salesman problem $OLTSP$ requests for visits to cities arrive online while the salesman is traveling. We study the $F{\_max}-OLTSP$ where the objective is to minimize the maximum flow time. This objective is particularly interesting for applications. Unfortunately, there can be no competitive algorithm, neither deterministic nor randomized. Hence, competitive analysis fails to distinguish online algorithms. Not even resource augmentation which is helpful in scheduling works as a remedy. This unsatisfactory situation motivates the search for alternative analysis methods. We introduce a natural restriction on the adversary for the $F{\_max}-OLTSP$ on the real line. A \emph{non-abusive adversary} may only move in a direction if there are yet unserved requests on this side. Our main result is an algorithm which achieves a constant competitive ratio against the non-abusive adversary.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 18
    Publikationsdatum: 2016-06-30
    Beschreibung: While attribute-value pairs are a popular method to name objects, information retrieval from those attribute-based namespaces is not an easy task. The user has to recall correct attribute names and values and master the syntax and semantics of query formulation. This paper describes hierarchical structures in attribute-based namespaces, shows how to extract them efficiently and evaluates the quality of these structures in an user experiment. It proposes an user interface for browsing attribute-named object sets which makes this task resemble todays file-system browsers and compares the usability of this interface to normal form-based methods in an user study.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 19
    Publikationsdatum: 2014-02-26
    Beschreibung: In this paper, we quantify and discuss the physical and surface chemical processes leading to the formation, temporal evolution and sedimentation of dust grains in brown dwarf and giant gas planet atmospheres: nucleation, growth, evaporation and gravitational settling. Considering dust particles of arbitrary sizes in the different hydrodynamical regimes (free molecular flow, laminar flow, turbulent flow), we evaluate the equilibrium drift velocities (final fall speeds) and the growth rates of the particles due to accretion of molecules. We show that a depth-dependent maximum size of the order of $a_{\rm max}\!\approx\!1\,\mu{\rm m\,(upper\ regions)} \ldots 100\,\mu{\rm m\,(lower\ regions)}$ exists, which depends on the condensate and the stellar parameters, beyond which gravitational settling is faster than growth. Larger particles can probably not be formed and sustained in brown dwarf atmospheres. We furthermore argue that the acceleration towards equilibrium drift is always very fast and that the temperature increase of the grains due to the release of latent heat during the growth process is negligible. Based on these findings, we formulate the problem of dust formation coupled to the local element depletion/enrichment of the gas in brown dwarf atmospheres by means of a system of partial differential equations. These equations state an extension of the moment method developed by Gail\plus Sedlmayr\,(1988) with an additional advective term to account for the effect of size-dependent drift velocities of the grains. A dimensionless analysis of the new equations reveals a hierarchy of nucleation $\to$ growth $\to$ drift $\to$ evaporation, which characterises the life cycle of dust grains in brown dwarf atmospheres. The developed moment equations can be included into hydrodynamics or classical stellar atmosphere models. Applications of this description will be presented in a forthcoming paper of this series.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 20
    Publikationsdatum: 2021-01-21
    Beschreibung: Global grid environments do not only provide massive aggregated computing power but also an unprecedented amount of distributed storage space. Unfortunately, dynamic changes caused by component failures, local decisions, and irregular data updates make it difficult to efficiently use this capacity. In this paper, we address the problem of improving data availability in the presence of unreliable components. We present an analytical model for determining an optimal combination of distributed replica catalogs, catalog sizes, and replica servers. Empirical simulation results confirm the accuracy of our theoretical analysis. Our model captures the characteristics of highly dynamic environments like peer-to-peer networks, but it can also be applied to more centralized, less dynamic grid environments like the European {\em DataGrid}.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 21
    Publikationsdatum: 2021-01-22
    Beschreibung: Das Management von großen Datenmengen spielt eine immer wichtigere Rolle, wie aktuelle Entwicklungen in der Hochenergiephysik [2] zeigen. Für das DataGrid-Projekt zum Beispiel ist es notwendig, große Datenmengen auf mehrere Rechenzentren in Europa zu verteilen und die Daten untereinander zu synchronisieren. Auch innerhalb von Clustern gewinnen mit zunehmender Anzahl der Knoten Werkzeuge zur effizienten Synchronisation und Verteilung von Daten an Bedeutung. Im Rahmen dieser Arbeit wurde ein effizientes Verfahren zur Synchronisation von verteilten Verzeichnisstrukturen entwickelt und implementiert. Mit diesem Verfahren ist es möglich, unabhängige Änderungen an beliebigen Repositories gleichzeitig durchzuführen. Das Verfahren benötigt keine zentrale Instanz, wodurch eine gegenüber vielen existierenden Verfahren verbesserte Skalierbarkeit erreicht werden konnte. Dabei wurden Erkenntnisse aus der Graphentheorie eingesetzt und weiterentwickelt, um die Netzwerktopolo-gie und -handbreiten zwischen den Rechnern zu berücksichtigen. Durch die Verwendung einer Offline-Synchronisation werden Änderungen erst dann an andere Rechner propagiert, wenn der Nutzer dies anstößt. Das kann zum Beispiel nach einer abgeschlossenen Transaktion, die Änderungen an mehreren Dateien beinhaltet, angemessen sein.
    Beschreibung: Current developments in high energy physics [2] show that the management of large datasets plays an important role. For the DataGrid project it is necessary to distribute large datasets over several computing centers all over Europe and to synchronize these datasets. Within clusters tools for efficient synchronization and distribution of data become more important, too. In this thesis, a method to synchronize distributed directory structures was developed and implemented which makes it possible to perform independent changes to arbitrary repositories simultaneously. This method needs no central instance and therefore the presented system achieves a better scalability than many existing systems. Knowledge from graph theory was used and improved to take the network topology and the network bandwidth between the computers into account. By using offline synchronization, changes will only be propagated when the user initiates it. This can be reasonable after a completed transaction which consists of changes on several files.
    Schlagwort(e): ddc:000
    Sprache: Deutsch
    Materialart: masterthesis , doc-type:masterThesis
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  • 22
    Publikationsdatum: 2020-11-17
    Beschreibung: An instance of the \emph{maximum coverage} problem is given by a set of weighted ground elements and a cost weighted family of subsets of the ground element set. The goal is to select a subfamily of total cost of at most that of a given budget maximizing the weight of the covered elements. We formulate the problem on graphs: In this situation the set of ground elements is specified by the nodes of a graph, while the family of covering sets is restricted to connected subgraphs. We show that on general graphs the problem is polynomial time solvable if restricted to sets of size at most~$2$, but becomes NP-hard if sets of size~$3$ are permitted. On trees, we prove polynomial time solvability if each node appears in a fixed number of sets. In contrast, if vertices are allowed to appear an unbounded number of times, the problem is NP-hard even on stars. We finally give polynomial time algorithms for special cases where the subgraphs form paths and the host graph is a line, a cycle or a star.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 23
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    Unbekannt
    Publikationsdatum: 2014-02-26
    Beschreibung: Hinter der für den Uneingeweihten etwas kryptischen Frage "P = NP?" verbirgt sich das derzeit wichtigste Problem der Komplexitätstheorie. Dieser Artikel erläutert einige Aspekte der Theorie und erklärt informell, was "P = NP?" bedeutet. Es geht nicht nur um komplizierte algorithmische Mathematik und Informatik, sondern um grundsätzliche Fragen unserer Lebensumwelt. Kann man vielleicht beweisen, dass es für viele Probleme unseres Alltags keine effizienten Lösungsmethoden gibt?
    Schlagwort(e): ddc:000
    Sprache: Deutsch
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  • 24
    Publikationsdatum: 2020-03-11
    Beschreibung: The Cooperative Library Network Berlin-Brandenburg (KOBV) has set the development of a genuine library information portal for the two German Lander (federal states) Berlin and Brandenburg as its main task for the next years. This joined effort is driven by the vision of an user friendly Internet information portal which is accessible anytime, from anywhere in the world. The idea of a regional information portal can be understood as the logically consistent development of the basic ideas of the KOBV. Starting in 1997, the consortia has set the implementation of a virtual OPAC instead of a physical union catalogue as its goal. The result was the KOBV-Search Engine which already has some qualities of a portal itself. The paper begins with initial remarks about the German library world, which do form the background for the project and its initiator - the KOBV consortia. After this preliminary part, different types of portals are introduced. The basic features of the KOBV-Search Engine as one of the cornerstones of the future portal are discussed in the following. The information portal will be much richer in content and services for the end-user. Two aspects are focused on in more detail: the presentation of resources, which becomes a compelling requirement because of the broader range of content and the personalization of services, as one important feature to suit user's individual needs.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 25
    Publikationsdatum: 2019-01-29
    Beschreibung: The paper presents a particle method framework for resolving molecular dynamics. Error estimators for both the temporal and spatial discretization are advocated and facilitate a fully adaptive propagation. For time integration, the implicit trapezoidal rule is employed, where an explicit predictor enables large time steps. The framework is developed and exemplified in the context of the classical Liouville equation, where Gaussian phase-space packets are used as particles. Simplified variants are discussed shortly, which should prove to be easily implementable in common molecular dynamics codes. A concept is illustrated by numerical examples for one-dimensional dynamics in double well potential.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 26
    Publikationsdatum: 2019-01-29
    Beschreibung: The paper deals with three different Newton algorithms that have recently been worked out in the general frame of affine invariance. Of particular interest is their performance in the numerical solution of discretized boundary value problems (BVPs) for nonlinear partial differential equations (PDEs). Exact Newton methods, where the arising linear systems are solved by direct elimination, and inexact Newton methods, where an inner iteration is used instead, are synoptically presented, both in affine invariant convergence theory and in numerical experiments. The three types of algorithms are: (a) affine covariant (formerly just called affine invariant) Newton algorithms, oriented toward the iterative errors, (b) affine contravariant Newton algorithms, based on iterative residual norms, and (c) affine conjugate Newton algorithms for convex optimization problems and discrete nonlinear elliptic PDEs.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 27
    Publikationsdatum: 2014-02-26
    Beschreibung: In Analogie zu den Elektrizitätsnetzen electricity grid), von denen die technische Revolution ausging, wurde der Begriff Computational Grid (kurz Grid) geprägt. Ein wichtiger Bestandteil des Systems liegt im benutzerfreundlichen Zugang und der koordinierten Nutzung der weltweit verteilten Speicherressourcen und Rechnerkapazitäten. Bei der Entwicklung dazu notwendiger Technologien und Software (Middleware) profitiert man von Kenntnissen und Erfahrungen bei der Entwicklung verteilter Algorithmen, dem Software-Engineering und dem Supercomputing.
    Schlagwort(e): ddc:000
    Sprache: Deutsch
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  • 28
    Publikationsdatum: 2020-02-11
    Beschreibung: In this article we study the problem of designing a nation-wide communication network. Such networks usually consist of an access layer, a backbone layer, and maybe several intermediate layers. The nodes of each layer must be connected to those of the next layer in a tree-like fashion. The backbone layer has to satisfy certain survivability and routing constraints. Given the node locations, the demands between them, the possible connections and hardware configurations, and various other technical and administrational constraints, the goal is to decide, which node is assigned to which network level, how the nodes are connected, what hardware must be installed, and how traffic is routed in the backbone. Mixed integer linear programming models and solution methods are presented for both the access and the backbone network design problem. The focus is on the design of IP-over-SDH networks, but the access network design model and large parts of the backbone network design models are general and also applicable for other types of communication networks. Results obtained with these methods in the planning of the German research network are presented.
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    Sprache: Englisch
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  • 29
    Publikationsdatum: 2021-02-19
    Beschreibung: We present an online algorithm for a real-world vehicle dispatching problem at ADAC, the German Automobile Association.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 30
    Publikationsdatum: 2020-03-11
    Beschreibung: Eine fremddatengestützte Katalogisierung bedeutet für die einzelne Bibliothek unbestritten eine Zeit- und Kostenersparnis. Dieser Report beleuchtet die unterschiedlichen Faktoren technischer und organisatorischer Natur, die die Fremddatennutzung in der dezentralen Struktur des Kooperativen Bibliotheksverbundes Berlin-Brandenburg (KOBV) beeinflussen. Die Ausführungen stützen sich im Wesentlichen auf eine Umfrage, die die Autoren im Mai / Juni 2002 unter KOBV-Mitgliedsbibliotheken zum Thema Fremddatennutzung durchgeführt haben. Dargelegt wird, wie komfortabel die in den KOBV-Bibliotheken eingesetzten Bibliotheksinformationssysteme eine fremddatengestützte Katalogisierung erlauben. Diskutiert wird zudem die Software ZACK, die sich als Alternative zu einem eigenen Z39.50-Client zur Datenübernahme anbietet. Erstmals seit Bestehen des Verbundes werden Zahlen veröffentlicht über den Anteil der Bibliotheken, die Fremddaten nutzen und denjenigen, die dieses Angebot nicht wahrnehmen. Dabei wird die Fremddatenutzung differenziert sowohl für den Bereich der Neuaufnahmen als auch für die Retrokatalogisierung. In der weiteren Analyse werden zusätzliche Aspekte betrachtet wie z.B. die verfügbaren bzw. gewünschten Datenbanken im Verhältnis zum sprachlichen Spektrum des erworbenen Katalogisierungsgutes. Eingegangen wird auch auf die von den Bibliotheken genannten Hauptproblemen und die gewünschten zusätzlichen Serviceleistungen auf Seiten der KOBV-Verbundzentrale. Als Ergebnis dieses Status-Quo-Berichts legt das Autorenteam eine Reihe von Empfehlungen vor, die darauf abzielen, auch für KOBV-Bibliotheken in Zukunft eine Fremddatennutzungsquote von 70 - 75 % zu erreichen.
    Schlagwort(e): ddc:000
    Sprache: Deutsch
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  • 31
    facet.materialart.
    Unbekannt
    Publikationsdatum: 2014-02-26
    Beschreibung: Substellar atmospheres are cool and dense enough that dust forms very efficiently. As soon as these particles are formed, they sizedependently precipitate due to the large gravity of the objects. Arriving in hot atmospheric layers, the dust evaporates and enriches the gas by those elements from which it has formed. The upper atmospheric layers are depleted by the same elements. Non-continuous and spatially inhomogeneous convective element replenishment, generating a turbulent fluid field, completes the circuit of dust. The formation of dust in substellar atmosphere is described by extending the classical theory of Gail\plus Sedlmayr for the case of different gas and dust velocities. Turbulence is modeled in different scale regimes which reveals turbulence as trigger for dust formation in hot environments. Both mechanisms cause the dust to be present in else wise dust-hostile region: precipitation transports the dust into hot regions, and turbulence allows the formation of dust in there.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 32
    Publikationsdatum: 2014-02-26
    Beschreibung: The talk given by the author at the CRM workshop on Superintegrability in Sep.\ 2002 and this related paper report on work in two subjects. One is the collaboration with Vladimir Sokolov and Takayuki Tsuchida in an effort to classify polynomial integrable vector evolution equations. The other is the computer algebra package {\sc Crack} which did the main computations in solving large bi-linear algebraic systems. Although originally designed to solve over-determined systems of partial differential equations a number of extensions made {\sc Crack} a powerful tool for solving systems of bi-linear algebraic equations. Such systems turn up in many different classification problems some of which were investigated by other participants of this workshop. Two additional applications are outlined. In the talk on which this article is based a method to reduce the length of equations was presented which proved to be useful in solving the bi-linear algebraic systems. Due to numerous asked questions about the computer program, a more complete overview is given in the appendix.
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    Sprache: Englisch
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  • 33
    Publikationsdatum: 2020-11-13
    Beschreibung: Die KOBV-Suchmaschine hat seit ihrer Inbetriebnahme Ende 1999 entscheidend zur Verbesserung der Informationsinfrastruktur in Berlin und Brandenburg beigetragen. Auf der Basis der offenen Plattform KOBV-Suchmaschine wird die KOBV-Zentrale gemeinsam mit den Bibliotheken in den nächsten Jahren das Dienstleistungsangebot des KOBV und seiner Bibliotheken kontinuierlich erweitern. Dabei sollen die Prinzipien des KOBV - Offenheit, Heterogenität und Dezentralität auf technischer und organisatorischer Ebene - gewahrt bleiben. Die einzelnen KOBV-Bibliotheken werden sich mit ihren Angeboten in unterschiedlicher Weise im Web positionieren. Die Integration auf regionaler Ebene kann und soll die lokalen Angebote nicht künstlich vereinheitlichen. Das kooperative Portal, das in der Region aufgebaut wird, ist als System geplant, in dem zentrales Portal und lokale Portale nicht hierarchisch einander zugeordnet, sondern miteinander vernetzt sind. Das \glqq KOBV-Informationsportal \grqq soll in der KOBV-Zentrale im Rahmen eines wissenschaftlichen Projektes von Mitte 2001 bis Ende 2003 aufgebaut werden. Das vorliegende Papier gibt einen ersten allgemeinen Einblick, welche Funktionen das \glqq KOBV-Informationsporta \grqq umfassen soll und stellt die Teilprojekte der 1. Stufe vor.
    Schlagwort(e): ddc:000
    Sprache: Deutsch
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  • 34
    Publikationsdatum: 2014-11-10
    Beschreibung: Oriented matroids are combinatorial structures that encode the combinatorics of point configurations. The set of all triangulations of a point configuration depends only on its oriented matroid. We survey the most important ingredients necessary to exploit oriented matroids as a data structure for computing all triangulations of a point configuration, and report on experience with an implementation of these concepts in the software package TOPCOM. Next, we briefly overview the construction and an application of the secondary polytope of a point configuration, and calculate some examples illustrating how our tools were integrated into the {\sc polymake} framework.
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    Sprache: Englisch
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  • 35
    Publikationsdatum: 2014-11-10
    Beschreibung: For all perfect graphs, the stable set polytope STAB$(G)$ coincides with the fractional stable set polytope QSTAB$(G)$, whereas STAB$(G) \subset$ QSTAB$(G)$ holds iff $G$ is imperfect. Padberg asked in the early seventies for ``almost'' perfect graphs. He characterized those graphs for which the difference between STAB$(G)$ and QSTAB$(G)$ is smallest possible. We develop this idea further and define three polytopes between STAB$(G)$ and QSTAB$(G)$ by allowing certain sets of cutting planes only to cut off all the fractional vertices of QSTAB$(G)$. The difference between QSTAB$(G)$ and the largest of the three polytopes coinciding with STAB$(G)$ gives some information on the stage of imperfectness of the graph~$G$. We obtain a nested collection of three superclasses of perfect graphs and survey which graphs are known to belong to one of those three superclasses. This answers the question: which graphs are ``almost'' perfect?
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 36
    Publikationsdatum: 2020-11-13
    Beschreibung: Die Automatisierung von innerbetrieblicher Logistik erfordert -- über die physikalische Steuerung von Geräten hinaus -- auch eine effiziente Organisation der Transporte: ein Aufgabenfeld der kombinatorischen Optimierung. Dieser Artikel illustriert anhand von konkreten Aufgabenstellungen die Online-Problematik (unvollständiges Wissen) sowie die Echtzeit-Problematik (beschränkte Rechenzeit), auf die man in der innerbetrieblichen Logistik trifft. Der Text gibt einen Überblick über allgemeine Konstruktionsprinzipien für Online-Algorithmen und Bewertungsmethoden, die bei der Entscheidung helfen, welche Algorithmen für eine vorliegende Problemstellung geeignet sind.
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    Sprache: Deutsch
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  • 37
    facet.materialart.
    Unbekannt
    Publikationsdatum: 2014-11-10
    Beschreibung: \We discuss a nested collection of three superclasses of perfect graphs: near-perfect, rank-perfect, and weakly rank-perfect graphs. For that, we start with the description of the stable set polytope for perfect graphs and allow stepwise more general facets for the stable set polytopes of the graphs in each superclass. Membership in those three classes indicates how far a graph is away from being perfect. We investigate for webs and antiwebs to which of the three classes they belong. We provide a complete description of the facets of the stable set polytope for antiwebs (with help of a result due to Shepherd on near-bipartite graphs). The main result is that antiwebs are rankperfect.
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    Sprache: Englisch
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  • 38
    Publikationsdatum: 2021-01-21
    Beschreibung: \textsf{\itshape{GuiGen}} is a comprehensive set of tools for creating customized graphical user interfaces (GUIs). It draws from the concept of computing portals, which are here seen as interfaces to application-specific computing services for user communities. While \textsf{\itshape{GuiGen}} was originally designed for the use in computational grids, it can be used in client/server environments as well. Compared to other GUI generators, \textsf{\itshape{GuiGen}} is more versatile and more portable. It can be employed in many different application domains and on different target platforms. With \textsf{\itshape{GuiGen}}, application experts (rather than computer scientists) are able to create their own individually tailored GUIs.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 39
    Publikationsdatum: 2014-02-26
    Beschreibung: The purpose of the paper is to formulate and use syzygies for systems of linear PDEs. The computation of an equivalent of a GCD for linear partial differential operators will save us their factorization which is otherwise only possible algorithmically in special cases. After showing the computation with the new and the traditional method and comparing both in the next three sections, the algorithm is explained in general and an overview is given.
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    Sprache: Englisch
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  • 40
    Publikationsdatum: 2020-11-13
    Beschreibung: Telekommunikation ist seit Jahren \glqq in\grqq. Zunächst gab es einen enormen Aufschwung; neue Technologien und Dienste haben eine überwältigende, nicht vorhersehbare Akzeptanz gefunden. Derzeit ist -- ausgelöst durch die UMTS-Lizenzversteigerungen, Rezessions- und Sättigungstendenzen -- eine Krise zu verzeichnen. Viele (auch wir) sind davon überzeugt, dass technischer Fortschritt und nützliche Dienste demnächst die Stimmung wieder ändern werden. Wenigen ist allerdings bewusst, welche Rolle Mathematik bei der Entwicklung und dem effizienten Einsatz vieler der neuen Kommunikationstechnologien spielt. In diesem Artikel soll kein Überblick über diesen umfangreichen Themenkreis gegeben werden. Wir zeigen lediglich an einem konkreten Beispiel aus dem Mobilfunk, der Frequenzplanung in GSM-Funknetzen, was man durch geeignete Modellierung der praktischen Fragestellung und den Einsatz problemadäquater Algorithmen erreichen kann.
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    Sprache: Deutsch
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  • 41
    Publikationsdatum: 2020-03-09
    Beschreibung: Wir beschreiben einen Ansatz zur integrierten Umlauf- und Dienstplanung im öffentlichen Nahverkehr. Der Ansatz zielt auf die Verbesserung des Gesamtwirkungsgrades dieser beiden Planungsschritte und auf die besondere Planungsproblematik im Regionalverkehr. Wir entwickeln dazu mathematische Optimierungstechniken für den Einsatz in den Planungssystemen MICROBUS II und DIVA.
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    Sprache: Deutsch
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  • 42
    Publikationsdatum: 2014-02-26
    Beschreibung: A graph property is called elusive (or evasive) if every algorithm for testing this property has to read in the worst case $n\choose 2$ entries of the adjacency matrix of the given graph. Several graph properties have been shown to be elusive, e.g. planarity (Best et al) or $k$-colorability (Bollobas). A famous conjecture of Karp says that every non-trivial monotone graph property is elusive. We prove that a non-monotone but hereditary graph property is elusive: perfectness.
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    Sprache: Englisch
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  • 43
    Publikationsdatum: 2014-02-26
    Beschreibung: Recently, a novel approach for the analysis of molecular dynamics on the basis of a transfer operator has been introduced. Therein conformations are considered to be disjoint metastable clusters within position space of a molecule. These clusters are defined by almost invariant characteristic functions that can be computed via {\em Perron Cluster} analysis. The present paper suggests to replace crisp clusters with {\em fuzzy} clusters, i.e. to replace characteristic functions with membership functions. This allows a more sufficient characterization of transiton states between different confor conformations and therefore leads to a better understanding of molecular dynamics. Fur thermore, an indicator for the uniqueness of metastable fuzzy clusters and a fast algorithm for the computation of these clusters are described. Numerical examples are included.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 44
    Publikationsdatum: 2019-01-29
    Beschreibung: The paper provides a detailed analysis of a short step interior point algorithm applied to linear control constrained optimal control problems. Using an affine invariant local norm and an inexact Newton corrector, the well-known convergence results from finite dimensional linear programming can be extended to the infinite dimensional setting of optimal control. The present work complements a recent paper of Weiser and Deuflhard, where convergence rates have not been derived. The choice of free parameters, i.e. the corrector accuracy and the number of corrector steps, is discussed.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 45
    Publikationsdatum: 2017-02-21
    Beschreibung: Pseudo--transient continuation methods are quite popular for the numerical solution of steady state problems, typically in PDEs. They are based on an embedding into a time dependent initial value problem. In the presence of dynamical invariants the Jacobian matrix of the nonlinear equation system is bound to be singular. The paper presents a convergence analysis which takes this property into account -- in contrast to known approaches. On the basis of the new analysis adaptive algorithms are suggested in detail. These include a variant with Jacobian approximations as well as inexact pseudo--transient continuation, both of which play an important role in discretized PDEs. Numerical experiments are left to future work.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 46
    Publikationsdatum: 2014-02-26
    Beschreibung: A beautiful result of Bröcker and Scheiderer on the stability index of basic closed semi-algebraic sets implies, as a very special case, that every $d$-dimensional polyhedron admits a representation as the set of solutions of at most $d(d+1)/2$ polynomial inequalities. Even in this polyhedral case, however, no constructive proof is known, even if the quadratic upper bound is replaced by any bound depending only on the dimension. Here we give, for simple polytopes, an explicit construction of polynomials describing such a polytope. The number of used polynomials is exponential in the dimension, but in the 2- and 3-dimensional case we get the expected number $d(d+1)/2$.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 47
    Publikationsdatum: 2014-11-10
    Beschreibung: TOPCOM is a package for computing triangulations of point configurations and oriented matroids. For example, for a point configuration one can compute the chirotope, components of the flip graph of triangulations, enumerate all triangulations. The core algorithms implemented in TOPCOM are described, and implentation issues are discussed.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 48
    Publikationsdatum: 2020-11-13
    Beschreibung: A model for the optimisation of the location and configuration of base stations in a UMTS network is described. The focus is primarily on modelling the configuration problem sufficiently accurate using mixed-integer variables and (essentially) linear constraints. These constraints reflect the limited downlink code capacity in each cell, the interference limitations for successful up- and downlink transmissions, the need for sufficiently strong (cell) pilot signals, and the potential gain for mobiles from being in soft(er) hand-over. It is also explained how to use the model as a basis for rating network configurations.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 49
    Publikationsdatum: 2016-06-09
    Beschreibung: Computational drug design studies molecular recognition in the {\em virtual lab}. The arising Hamiltonian dynamics is known to be chaotic and ill-conditioned already after picoseconds, whereas times are $msec$ up to $min$. Classical molecular dynamics with long term trajectory computation gives, at best, information about time and statistical ensemble averages. The present paper surveys a recent new modeling approach called {\em conformational dynamics}, which is due to the author and Ch. Schütte. This approach achieves information about the dy time scales by telescoping a short term deterministic model with a statistical model. Examples of small biomolecules are included.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 50
    Publikationsdatum: 2021-02-19
    Beschreibung: Combinatorial online optimization is an area with lots of applications and potential for significant progress, both in theory and practice. In this short note we sketch the ADACproblem, a typical large-scale online optimization problem, discuss some theoretical and pratical issues coming up, and explain, very briefly, how we approach this problem mathematically. Online problems are a battlefield of heuristics with many strong claims about their solution quality. We indicate that a stronger problem orientation and the use of a little more mathematics may yield.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 51
    Publikationsdatum: 2014-02-26
    Beschreibung: A subset ${\cal C}$ of the power set of a finite set $E$ is called cardinality homogeneous if, whenever ${\cal C}$ contains some set $F$, ${\cal C}$ contains all subsets of $E$ of cardinality $|F|$. Examples of such set systems ${\cal C}$ are the sets of circuits and the sets of cycles of uniform matroids and the sets of all even or of all odd cardinality subsets of $E$. With each cardinality homogeneous set system ${\cal C}$, we associate the polytope $P({\cal C})$, the convex hull of the incidence vectors of all sets in ${\cal C}$, and provide a complete and nonredundant linear description of $P({\cal C})$. We show that a greedy algorithm optimizes any linear function over $P({\cal C})$, give an explicit optimum solution of the dual linear program, and provide a polynomial time separation algorithm for the class of polytopes of type $P({\cal C})$.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 52
    facet.materialart.
    Unbekannt
    Publikationsdatum: 2014-02-26
    Beschreibung: Die Bibliotheken des KOBV haben im Jahr 2001 die Entwicklung der KOBV-Suchmaschine zu einem gemeinsamen Informationsportal Berlin-Brandenburg und den Aufbau lokaler Bibliotheksportale als Hauptentwicklungsziele des KOBV definiert. Diese Informationsportale sollen mit Standardsoftware realisiert werden. Um die Auswahl eines Systems zu unterstützen, wurde in der Zentrale des KOBV ausgewählte Systeme untersucht. In der Arbeit werden zahlreiche Kriterien vorgestellt, auf Grund derer die betreffenden Systeme beurteilt werden. Die Kriterien umfassen sowohl Aspekte aus der Sicht der Benutzer als auch Kriterien aus der Sicht der Betreiber eines solchen Systems. Wesentliche Funktionen und die Realisierung von verschiedenen Merkmalen werden im Bericht ausführlich beschrieben. Daneben liefert eine Tabelle mit allen betrachteten Kriterien eine Übersicht über vorhandene Merkmale und der Art der Realisierung.
    Schlagwort(e): ddc:000
    Sprache: Deutsch
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  • 53
    Publikationsdatum: 2021-03-16
    Beschreibung: In the cake cutting problem, $n\ge2$ players want to cut a cake into $n$ pieces so that every player gets a ``fair'' share of the cake by his own measure. We describe a protocol with $n-1$~cuts in which each player can enforce to get a share of at least~$1/(2n-2)$. Moreover we show that no protocol with $n-1$~cuts can guarantee a better fraction.
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    Sprache: Englisch
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  • 54
    Publikationsdatum: 2022-07-07
    Beschreibung: We present a new efficient algorithm for the solution of direct time-harmonic scattering problems based on the Laplace transform. This method does not rely on an explicit knowledge of a Green function or a series representation of the solution, and it can be used for the solution of problems with radially symmetric potentials and problems with waveguides. The starting point is an alternative characterization of outgoing waves called \emph{pole condition}, which is equivalent to Sommerfeld's radiation condition for problems with radially symmetric potentials. We obtain a new representation formula, which can be used for a numerical evaluation of the exterior field in a postprocessing step. Based on previous theoretical studies, we discuss the numerical realization of our algorithm and compare its performance to the PML method.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 55
    Publikationsdatum: 2022-07-07
    Beschreibung: The aim of this paper is to develop fast methods for the solution of nonlinear Schrödinger type equations in fiber optics. Using the method of lines we have to solve a stiff system of ordinary differential equations where the eigenvalues of the Jacobian are close to the imaginary axis. This is usually done by a Split Step method. Here we consider the extrapolation of Split Step methods with adaptive order and step size control. For more complicated nonlinearities, in particular stimulated Raman scattering, Split Step methods are less efficient since symmetry is either destroyed or requires much additional effort. In this case we use implicit Runge Kutta formulas of Gauß type. The key point for the efficient implementation of these methods is that the system of nonlinear algebraic equations can be solved without setting up the Jacobian. The proposed methods are compared to other methods, in particular exponential integrators, the method of Marcuse, and the method of Blow and Wood.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 56
    Publikationsdatum: 2022-07-07
    Beschreibung: The work presents a new approach to the numerical solution of time-harmonic and time-dependent scattering problems. We replace Sommerfeld's radiation condition valid for the Helmholtz equation by a more general concept called pole condition. The pole condition is based on the Laplace transform of the exterior solution and allows a characterization of outgoing waves. Both new insight into the analysis of scattering problems as well as new numerical algorithms are obtained.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: doctoralthesis , doc-type:doctoralThesis
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  • 57
    ISSN: 1435-604X
    Schlagwort(e): Brain tumour ; Rat ; Detection ; Fluorescence ; Laser ; Haematoporphyrin derivative
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract Laser-induced fluorescence has been used for the identification of brain tumours in rats, which have been previously given tumour-seeking haematoporphyrin derivative. A pulsed nitrogen laser (λ=337 nm) was used in conjunction with an optical multichannel analyzer. For both inoculated RG-2 and TCVC rat-brain-tumour models, the blue autofluorescence was strongly reduced in the tumour compared with normal brain tissue, and at the same time the characteristic red-drug signal increased. The contrast between tumour and normal tissue was strongly enhanced by forming the ratio between the two signals. Implications for possible improvement of tumour delineation in brain tumour surgery are discussed.
    Materialart: Digitale Medien
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  • 58
    Digitale Medien
    Digitale Medien
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 339 (1989), S. 178-183 
    ISSN: 1432-1912
    Schlagwort(e): Rat ; Urinary bladder ; Somatovesical inhibitory response ; Colovesical inhibitory response ; Capsaicin sensitive afferents
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary (1) The effect of perineal pinching and distension of a balloon inserted into the colon on motility of the urinary bladder has been investigated in adult urethane-anesthetized rats pretreated with capsaicin (50 mg/kg s.c.) or its vehicle 4 days before the experiments. (2) At bladder volumes which were sufficient to elicit reflex micturition, perineal pinching or colonic distension transiently inhibited the ongoing bladder voiding contraction. The somato-vesical inhibitory response was markedly reduced or even abolished by division of pudendal nerves. Neither the somato-vesical nor the colovesical inhibitory response were modified by desensitization with systemically administered capsaicin. (3) Intraurethral administration of capsaicin produced a transient inhibition of the reflexly-activated bladder contractions. A second administration of the drug was less effective, indicating desensitization. Intravenously administered capsaicin had a similar inhibitory effect on bladder motility. (4) The vesico-inhibitory response produced by intraurethral administration of capsaicin was not affected by phentolamine, propranolol, guanethidine, picrotoxin or naloxone, while it was greatly reduced or even abolished by bilateral section of the pudendal nerves. (5) These findings provide evidence that capsaicin-sensitive chemoreceptors in the rat urethra are involved in generating a vesico-inhibitory response via pudendal nerves. On the other hand, no evidence was found for the participation of capsaicin-sensitive nerves in the generation of the somato- or colo-vesical inhibitory response.
    Materialart: Digitale Medien
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  • 59
    ISSN: 1432-1912
    Schlagwort(e): Rat ; Forebrain ischemia ; Local cerebral blood flow ; Neuronal damage ; Emopamil
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The effects of the calcium entry blocker emopamil on physiological variables, local cerebral blood flow (LCBF) and on hippocampal cell damage were evaluated after 10 min of forebrain ischemia in the rat. LCBF was determined with the 14C-iodoantipyrine technique after 2, 10, and 60 min of postischemic recirculation. Histological evaluation was performed 7 days after ischemia in cortical and hippocampal tissue by determination of the percentage of necrotic neurons. Preischemic application of emopamil [4 mg/kg racemate or 2 mg/kg (S)-emopamil; i.v.] caused increases in LCBF in cortical areas but did not alter blood flow in the hippocampus at 2 min of recirculation. After 10 and 30 min of flow resumption no differences in LCBF between drug-treated and control animals were observed. In the histological series (S)-emopamil was applied at doses of 2, 4 or 6 mg/kg before the induction of ischemia. After 7 days of postischemic recovery, neuronal damage was significantly reduced by the calcium antagonist in hippocampal CA 1 sector at all doses tested, the most prominent effects being observed with the lowest dose. At this dose cell loss in the Ca3 sector was also reduced. In cortical tissue the number of necrotic cells remained unchanged by emopamil treatment. It is concluded that the calcium antagonist emopamil can reduce ischemia-induced neuronal cell damage. The compound improves circulation in cortical tissue only during early recovery but not at later phases of reflow, i.e. the period of delayed hypoperfusion. These increases in blood flow are not of crucial importance for ultimate neuronal death in this area. The ameliorative action of emopamil on the survival of hippocampal neurons is not associated with blood flow changes and therefore seems to reflect a direct effect on cerebral parenchyma.
    Materialart: Digitale Medien
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  • 60
    Digitale Medien
    Digitale Medien
    Springer
    Archives of gynecology and obstetrics 244 (1989), S. 151-155 
    ISSN: 1432-0711
    Schlagwort(e): Placenta ; Glycogen ; Triglyceride ; Cold ; Fasting ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The effect of exposure to cold (+2°C, 3 and 24 h) and fasting (1, 2 and 3 days) on placental glycogen and triglyceride content was investigated in rats pregnant for 20 days. The stimuli did not affect the level of glycogen in the placenta. The level of triglycerides remained unchanged in the rats exposed to cold. It rose after only one day of fasting and then levelled out on the 2nd and 3rd days. Fasting, but not exposure to cold produced hypoglycemia and elevation of the plasma free fatty acids level. We conclude that activation of the adrenergic system during exposure to cold does not interfere with the glycogen and triglyceride content of the placenta. Prolonged hypoglycemia also does not affect the placental glycogen level although it increases the accumulation of neutral fat.
    Materialart: Digitale Medien
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  • 61
    ISSN: 1432-1432
    Schlagwort(e): Carcinoembryonic antigen ; Evolution ; Gene family ; Human ; Rat ; Synonymous substitutions ; Silent molecular clock ; Evolutionary trees
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary Various rodent and primate DNAs exhibit a stronger intra- than interspecies cross-hybridization with probes derived from the N-terminal domain exons of human and rat carcinoembryonic antigen (CEA)-like genes. Southern analyses also reveal that the human and rat CEA gene families are of similar complexity. We counted at least 10 different genes per human haploid genome. In the rat, approximately seven to nine different N-terminal domain exons that presumably represent different genes appear to be present. We were able to assign the corresponding genomic restriction endonuclease fragments to already isolated CEA gene family members of both human and rat. Highly similar subgroups, as found within the human CEA gene family, seem to be absent from the rat genome. Hybridization with an intron probe from the human nonspecific cross-reacting antigen (NCA) gene and analysis of DNA sequence data indicate the conservation of noncoding regions among CEA-like genes within primates, implicating that whole gene units may have been duplicated. With the help of a computer program and by calculating the rate of synonymous substitutions, evolutionary trees have been derived. From this, we propose that an independent parallel evolution, leading to different CEA gene families, must have taken place in, at least, the primate and rodent orders.
    Materialart: Digitale Medien
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  • 62
    ISSN: 1432-2307
    Schlagwort(e): Hyperoxia ; Lung broncho-vascular reaction ; Electron microscopy ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary In order to clarify the early phenomena involved in the lung reaction to hyperoxia, twenty adult male rats were exposed to 100% oxygen at 1 ATA. Morphological pulmonary lesions were detectable after only 24 h hyperoxia, and included vasoconstriction and perivascular oedema, bronchiolar constriction, and pericyte reaction. The lesions were irregularly scattered within the lung parenchyma and occurred preferentially in areas centred on bronchiolo-vascular stems. Even at the latest stages, pulmonary heterogeneity was obvious, from the coexistence of areas damaged at different times. Neuro-epithelial-bodies were found under the bronchiolar epithelium; the morphological aspect of the neuro-endocrine cells observed was consistent with hyperoxia-induced modulation of their secretory activity. Taken together, our findings show the speed of development of hyperoxia-induced pulmonary changes and raise some pathogenic considerations.
    Materialart: Digitale Medien
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  • 63
    ISSN: 1432-2307
    Schlagwort(e): Keratin ; Mammary neoplasms ; Mouse ; Rat ; Immunohistochemistry
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Using immunoperoxidase staining of monoclonal antibody 312C8-1 against 51 000 dalton human keratin polypeptide, immunolocalization was observed in frozen sections of normal tissue and mammary tumours of adult female mice and rats. In normal tissue, the epitope was recognized in myoepithelial cells of the mammary, sweat and salivary glands, and in basal and suprabasal cells of the epidermis. However, the antibody did not react with luminal epithelial cells of the above glands or with mesenchymal cells. In spontaneous mammary tumours of mice, marker-positive tumour cells were distributed only in the outer layer of adenocarcinoma Type A, while they were scattered in some foci of adenocarcinoma Type B, and encircled the epithelial foci of pregnancy dependent tumours (plaque). All layers of epidermoid structures in adenoacanthoma revealed positivity. In rat mammary tumours induced by local dusting with 7, 12-dimethylbenz(α)anthracene (DMBA) powder, the staining pattern of benign tumours was comparable to that of the normal mammary gland. But, in addition to basally situated cells, marker-positive tumour cells were found scattered in the foci of adenocarcinoma, and were not restricted to basal cells in squamous cell carcinoma. The marker was not found in sarcomatous tissue. This antibody can therefore also be applied to rodents, and the staining pattern can be used to identify the epithelial subclass specific marker in normal tissue and in mammary tumours.
    Materialart: Digitale Medien
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  • 64
    Digitale Medien
    Digitale Medien
    Springer
    Research in experimental medicine 189 (1989), S. 281-287 
    ISSN: 1433-8580
    Schlagwort(e): Serotonin ; Tryptophan ; Small intestine ; Rat ; Pargyline
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary To investigate the release of serotonin from intestinal enterochromaffin cells, we used an in vitro technique which allows studies excluding overlapping influences from outside the gut. The entire small intestine of rats fed a standard or tryptophan-enriched (3% of total) diet was totally isolated by ligatures with the exception of the superior mesentric artery and portal vein that supply and drain the intestine. Simultaneously to the vascular perfusion (Krebs-Ringer bicarbonate buffer, 0,4% human albumin, 5 mM glucose, 0.6 mM glutamine) the gut lumen was infused (buffer or 0.1 N HCL). Acidification of the gut lumen resulted in an increment of venously released tryptophan and serotonin. After feeding tryptophan-enriched food the release of tryptophan was increased. However, the total amount of released serotonin after tryptophan diet did not differ as compared to that after standard diet. Addition of a monoamino-oxidase inhibitor (pargyline) to the arterial perfusate enhanced the released amount of serotonin 3-fold in the portal venous effluent (at a concentration of 1 mM but not 0.1 mM). Recovery studies done by arterial infusions of serotonin (1 µM, 10µM) and evaluation of the amounts venously released revealed a high loss of infused serotonin (40%–70%). Our data suggest gut-born serotonin to more likely play a paracrine role than a role as a classical hormone.
    Materialart: Digitale Medien
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  • 65
    ISSN: 1433-8580
    Schlagwort(e): Rat ; Liver cirrhosis ; Hypoxia ; Redox state ; Mitochondrial oxidative phosphorylative activity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The influence of hypoxia on hepatic mitochondrial function and energy status was studied in normal and carbon tetrachloride (CCl4)-induced cirrhotic rats. Under hypoxemia of 50 mm Hg-PaO2, hepatic energy status was suppressed both in normal and cirrhotic rats. After the reversal of hypoxia, it was completely restored in normal rats concomitant with a rapid elevation of hepatic mitochondrial redox state (overshoot phenomenon) and increase in the mitochondrial oxidative phosphorylative activity. By contrast, in cirrhotic rats, such an enhancement of mitochondrial function was not observed. It was clarified that cirrhotic liver mitochondria have little capacity to respond to the hypoxic stress. A lower resistance to hypoxic episode in cirrhotics might be attributable to the absence of mitochondrial enhancement which is a compensatory mechanism for the deranged energy metabolism of the liver.
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  • 66
    Digitale Medien
    Digitale Medien
    Springer
    Research in experimental medicine 189 (1989), S. 321-329 
    ISSN: 1433-8580
    Schlagwort(e): Fibronectin ; Nerve fibrosis ; Fibrin adhesives ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Although the fibrin adhesion enjoys increasing success in many areas of surgery, it has not, however, become fully established in nerve anastomosis. It was in this area particularly that significant advantages were expected, especially by the avoidance of suture granulomas. As the fibrin clot dissolved prematurely, however, and dehiscences ensued, antifibrinolytic substances had to be added to the adhesive. Fibroses occurred frequently as a result, which to date encumber nerve adhesive. We examined fibronectin for its fibrosis-inducing effect, comparing both presently available fibrin adhesive systems, because one contained up to 5 times more fibronectin per milliliter than the other. On the basis of a test grouping using 100 and 1000 KIU aprotinin/ml, we were able to establish that fibronectin in fibrin adhesives possesses a fibrosis-promoting effect.
    Materialart: Digitale Medien
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  • 67
    Digitale Medien
    Digitale Medien
    Springer
    Acta neuropathologica 78 (1989), S. 264-269 
    ISSN: 1432-0533
    Schlagwort(e): Skeletal muscle ; Regeneration ; Growth factors ; Growth hormone ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Against the background of the importance of growth hormone (GH) for normal muscle growth, a study was performed to investigate whether lack of GH after hypophysectomy affects the cell proliferation and the local production of insulin-like growth factor-I (IGF-I) in the early stages of muscle regeneration in adult rats. The level of IGF-I in the serum of hypophysectomised rats was reduced to about 30% of that of controls. The incorporation of [methyl-3H]thymidine into the regenerating muscle showed a peak 6 days after the operation and then gradually declined to the end of the period of study 30 days after initiation of regeneration by ischemic necrosis. The DNA content rose to a maximum level after 6–8 days, and remained high after 30 days. There was no major difference in the incorporation of [3H]thymidine in regenerating muscle of hypophysectomised and control rats, but the DNA concentration in the regenerating muscles of hypophysectomised rats was significantly reduced after 30 days. There was a corresponding reduction in the number of nuclei per muscle fibre, indicating that hypophysectomy has a small effect on the cell proliferation during the early stages of muscle regeneration. Immunohistochemical demonstration of IGF-I in the regenerating muscle revealed the transient presence of immunoreactive material in satellite cells and myotubes after 6 to 8 days of regeneration but no immunoreactivity after 30 days. No obvious difference was observed between hypophysectomised and control rats, indicating that the endogenous production of IGF-I in regenerating skeletal muscle can occur independently of GH.
    Materialart: Digitale Medien
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  • 68
    ISSN: 1432-0568
    Schlagwort(e): Melatonin synthesis ; Pineal gland ; Rat ; “Synaptic” ribbons ; Sympathetic stimulation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Melatonin metabolism in the mammalian pineal gland is under the clear influence of sympathetic fibers originating in the superior cervical ganglia (SCG). Previous studies suggested that pineal “synaptic” ribbons (SR) as well are regulated by the gland's sympathetic innervation. To gain more insight into the mechanisms involved, we examined the effects of sympathetic stimulation on SR number and on the activity of melatonin forming enzymes, serotonin N-acetyltransferase (NAT) and hydoxyindole-O-methyltransferase (HIOMT). The SCG in adult male rats were stimulated electrically during daytime for either 15 or 120 min. Immediately following stimulation, the glands were removed and processed for electron microscopy and for the determination of NAT and HIOMT activities. No differences in pineal SR number, size or location were found in rats stimulated with either parameters when compared with sham-stimulated or control animals. While the activity of HIOMT remained unchanged, the activity of NAT was also unaltered following 15 min of stimulation, but was augmented approximately three-fold in animals stimulated for 120 min. It is concluded that if SR in the rat pineal gland are under sympathetic control, the regulation is different from that involved in melatonin formation.
    Materialart: Digitale Medien
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  • 69
    ISSN: 1432-0568
    Schlagwort(e): Pyramidal tract ; Rat ; Development ; Axon loss ; Myelination
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary A quantitative electron microscopic analysis was undertaken of the development of the pyramidal tract, at the level of the third cervical spinal segment, in rats ranging in age from the day of birth to three months old. The axon number was calculated as the product of axon density, determined in a systematic random sample of electron micrographs, and tract area. During the first postnatal week the tract contains thin unmyelinated axons and growth cones. Growth cones are abundant in neonatal rats, but can still be observed occasionally at the end of the first postnatal week, indicating a continuous addition of pyramidal tract axons during the first postnatal week. Myelination starts around P10. By the end of the first postnatal month approximately 50% of the axons have already been myelinated. Myelination proceeds during further maturation, but in the three month old rat 28% of the axons are still unmyelinated. The total number of axons increases rapidly after birth up to 153 000 at the fourth postnatal day. Subsequently, the number of axons is reduced by nearly 50% to 79 000 in the adult rat. The axon loss is most prominent during the second postnatal week, when 32 000 axons are climinated, but continues for several weeks at a slower rate.
    Materialart: Digitale Medien
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  • 70
    ISSN: 1432-0533
    Schlagwort(e): Somatostatin ; Immunohistochemistry ; Aganglionosis ; Man ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The distribution of somatostatin-like immunoreactive (SOM-LI) nerves was elucidated immunohistochemically in the gut tissues from patients with Hirschsprung's disease and congenital aganglionosis rats. In the normoganglionic human colon, SOM-LI nerve cell bodies were found to a greater extent in the submucous plexus and to a lesser extent in the myenteric plexus. However, they were rarely observed in both the plexuses of the oligoganglionic segment. SOM-LI nerve fibres were widely distributed in the aganglionic bowel. The circular muscle layer of the distal aganglionic segment was densely innervated by SOM-LI nerve fibres which are probably derived from the extrinsic, hypertrophic nerve bundles. A decreased number of the intramuscular nerves fibres were seen in the proximal aganglionic segment. In the colon and rectum from adult and 21-day-old rats, SOM-LI cell bodies were numerous in both plexuses. On the other hand, enteric neurons were completely lacking from the colon and rectum of congenital aganglionosis rats of 21 days old. No neuronal elements staining for SOM were disclosed in these aganglionic segments of mutant rats. A possible origin and pathophysiological role of the extrinsic nerve fibres containing SOM in the diseased bowel are discussed. It is concluded that SOM-LI nerves in the human distal colon comprise both intrinsic and extrinsic elements, while SOM nerves in the rat colon and rectum are of only intrinsic origin.
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  • 71
    Digitale Medien
    Digitale Medien
    Springer
    Anatomy and embryology 179 (1989), S. 449-456 
    ISSN: 1432-0568
    Schlagwort(e): Corticospinal tract ; Development ; Myelination ; Pyramidal tract ; Anterograde tracing ; Electronmicroscopy ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Horseradish-peroxidase was used to anterogradely label and thus to trace the growth of corticospinal axons in rats ranging in age from one day to six months. Three to eight HRP-gels were implanted in the left cerebral hemisphere of the cortex. In each spinal cord three levels were studied, the cervical intumescence (C5), the mid-thoracic region (T5) and the lumbar enlargement (L3). The methodology employed for the electron microscopic visualization of HRP has been described previously (Joosten et al. 1987a). The outgrowth of labelled unmyelinated corticospinal tract axons in the rat spinal cord primarily occurs during the first ten postnatal days. The outgrowth of the main weve of these fibres is preceded by a number of pathfinding axons, characterized by dilatations at their distal ends, the growth cones. By contrast, later appearing unmyelinated axons, which presumably grow along the pathfinding axons, do not exhibit such growth cones. The first labelled pioneer axons can be observed in the cervical intumescence at postnatal day one (P1), in the mid-thoracic region at day three (P3) and in the lumbar enlargement at day five (P5). Prior to the entrance of the axons, the prospective corticospinal area or the pre-arrival zone is composed of fascicles consisting of unlabelled, unmyelinated fibres surrounded by lucent amorphous structures. During the outgrowth phase of the corticospinal fibres some myelinated axons could be observed within the outgrowth area even before day 14. These axons, however, were never labelled. These findings strongly suggest that the outgrowth area, which is generally denoted as the pyramidal tract, contains other axons besides the corticospinal fibres (and glial cells). The process of myelination of the labelled corticospinal tract axons in the rat spinal cord starts rostrally (C5) at about day 14 and progresses caudally during the third and fourth postnatal weeks. Although myelination seems to be largely complete at day 28 at all three spinal cord levels, some labelled unmyelinated axons are still present in the adult stage.
    Materialart: Digitale Medien
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  • 72
    Digitale Medien
    Digitale Medien
    Springer
    Anatomy and embryology 180 (1989), S. 207-212 
    ISSN: 1432-0568
    Schlagwort(e): Thyrotroph (TSH cell) ; Anterior pituitary ; Immunogold electron microscopy ; Postnatal development ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Thyrotrophs (TSH cells) of the rat anterior pituitary identified by immunogold electron microscopy were classified into three subtypes according to their morphological characteristics: Immature type TSH cells are oval with a few small secretory granules (50–100 nm in diameter) and poorly developed cell organelles. These cells are frequently found in the neonatal stage between birth and 10 days of age. The intermediate type is polygonal or stellate, containing a moderate number of medium sized secretory granules (80–120 nm in diameter) and moderately or well developed cell organelles. Cells of this type are often found between 10 and 30 days of age. Mature type cells are large and polygonal in shape, and contain many large secretory granules (120–180 nm in diameter) and well developed cell organelles. Cells of the last type are frequently found at more than 30 days of age. At 45 days of age the mature type TSH cells make up about 70% of all TSH cells. The proportion of immature type cells was shown to decrease while the proportion of the mature type TSH cells increases, as the animal grows.
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  • 73
    Digitale Medien
    Digitale Medien
    Springer
    Anatomy and embryology 180 (1989), S. 243-257 
    ISSN: 1432-0568
    Schlagwort(e): Dorsal lateral geniculate nucleus ; Synapse formation ; Synaptic glomerulus ; Rat ; Electron microscopy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Synapse formation and maturation were examined in the rat dorsal lateral geniculate nucleus (dLGN) from birth to adulthood. Examination of animals, whose ages were closely spaced in time, showed that the maturation of the synaptic organization of the nucleus takes place chiefly during the first 3 weeks of postnatal life. This period of maturation may be divided into 3 broad stages. During the first stage, which spans the first 4 days of life, there are only a few immature synapses scattered throughout the nucleus; occasionally aggregates of 3 or 4 synapses are encountered. Dendrodendritic synapses first appear at the end of this stage. The second stage, which lasts from the end of the first stage through day 8, is characterized by intensive synaptogenesis as well as extensive growth and degeneration. For the first time, large boutons resembling retinal terminals form multiple synaptic contacts with dendrites and dendritic protrusions; these synaptic arrangements are partially covered by glial processes. A feature characteristic of the developing dLGN during the first 2 postnatal weeks, and particularly during the second stage, is the presence of membrane specializations that resemble vacant postsynaptic densities. These specializations, which may be unapposed or opposite another neuronal process, decrease in frequency as the number of synapses increases. It is not known whether these densities are converted to synapses or whether they result from loss of presynaptic elements. The third stage in the process of synaptogenesis, which spans a period between days 10 and 20, is characterized by myelination and by the diminution of growth cones, degenerating profiles and vacant postsynaptic densities. There is also a very significant increase in the number and maturation of synapses including synaptic glomeruli. However, it is not until the end of this stage that synapses appear qualitatively indistinguishable from synaptic arrangements identified in adult animals.
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  • 74
    Digitale Medien
    Digitale Medien
    Springer
    Anatomy and embryology 179 (1989), S. 221-226 
    ISSN: 1432-0568
    Schlagwort(e): GABA ; Immunocytochemistry ; Gastrointestinal tract ; Epithelium ; Enteroendocrine cells ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Frozen sections of the corpus ventriculi, antrum pyloricum, duodenum, jejunum, ileum and colon from animals perfusion fixed with glutaraldehyde were treated with an antiserum specific for glutaraldehyde-fixed GABA and processed by the peroxidase antiperoxidase method. Semithin plastic sections from the antrum pyloricum were treated similarly. Stained cells appeared in the epithelium of all segments examined except the corpus ventriculi. The highest density of cells was observed along the major curvature of the antrum pyloricum. Here they were located in the bottom half of the gastric glands. Many of the cells showed a process extending towards the glandular lumen. No significant staining in the epithelium appeared when the antiserum was preincubated with glutaraldehyde-GABA complexes, nor when the anti-GABA serum was exchanged with anti-glycine or preimmune serum. The present findings and previous physiological data suggest that GABA may play a role in gut endocrine regulation.
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  • 75
    Digitale Medien
    Digitale Medien
    Springer
    Acta neuropathologica 79 (1989), S. 149-153 
    ISSN: 1432-0533
    Schlagwort(e): Lead ; Rat ; Cerebellum ; Particle-induced X-ray emission (micro-PIXE)
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The distribution of lead in the cerebellum of suckling Sprague-Dawley rats was examined using a nuclear microprobe for elemental mapping of tissue sections (particle-induced X-ray emission, 3-μm beam of 2.5 MeV protons; micro-PIXE). The rats were injected intraperitoneally with a lead-containing vehicle or vehicle only from ages 1 to 14 days. The calculated doses were 7.8 (low-dose) and 15.6 (high-dose) μg lead/g body weight. The rats were killed at 20 days of age. The vascular system was rinsed quickly with 0.15 M ammonium acetate to obtain determinations of intra-parenchymal lead with minimal influence of lead bound to erythrocytes and plasma proteins. Brains were frozen in propane/propylene in liquid nitrogen. Cryostat sections, 15 μm thick, were air dried on formvar coats that covered a hole, 15 mm in diameter, in a plastic disc, and were used for lead analysis by micro-PIXE. Very low concentrations of lead were found in the brain of controls. Lead levels in homogenates from cerebrum and cerebellum measured by atomic absorption spectrometry (AAS) were: low-dose 1.2–2.2 μg/g wet weight and high-dose 1.4–2.4 μg/g wet weight. The lead levels measured with the micro-PIXE method were in good agreement with the levels found with AAS. Lead was present in the cerebellar white matter in two to three times higher amounts than in the cortical grey (low-dose white matter 11–18 μg/g dry weight, grey matter 2.0–5.5 μg/g dry weight). This was true for both low and high dose exposed rats. Lead concentrations in rats subjected the high-dose lead exposure were approximately 60% higher than those in low-dose exposed rats. Concentrations were lower in the Purkinje cell layer than in other parts of the cortex. These new findings on the distribution of lead in suckling rats are discussed in relation to the pathogenesis of experimental lead encephalopathy.
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  • 76
    Digitale Medien
    Digitale Medien
    Springer
    Aquatic sciences 51 (1989), S. 108-128 
    ISSN: 1420-9055
    Schlagwort(e): Chemistry ; mountain lakes ; silica ; acidity ; sediment
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Alpine lakes in siliceous catchments of Tyrol and Carinthia (Austria) show signs of acidification. About 9% of the studied lakes have no alkalinity, more than 20% are below pH 6. About two thirds of all lakes have acid neutralizing capacities below 100 μeq 1−1. In spite of moderate precipitation acidity, some lakes show considerable concentrations of dissolved reactive aluminum during or shortly after snowmelt. High altitude lakes of the Alps are definitely more acidic than high mountain lakes in remote areas. Large differences in water and soil chemistry of nearby situated lakes were attributed to heterogeneities of bedrock geology. Paleolimnological investigations on former pH values of five lakes, based on diatom assemblages in the sediment, showed different developments: recent and past acidification, stable conditions, and alkalinization.
    Materialart: Digitale Medien
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  • 77
    ISSN: 1432-1106
    Schlagwort(e): Collateral sprouting ; Nerve regeneration ; Mechanoreceptors ; C-fibers ; Plasma extravasation ; Evans blue ; Skin ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The capacity of the saphenous nerve for collateral sprouting was examined by electrophysiological recordings of the activity of low threshold mechanoreceptors and plasma extravasation after C-fiber stimulation in rats. When the sciatic nerve was sectioned neonatally or in adults little evidence was obtained for collateral sprouting of either mechanoreceptors or fibers involved in plasma extravasation in the intact saphenous nerve0 In rats where the sciatic nerve was sectioned and the saphenous nerve was crushed either neonatally or in adults, expansive regenerative reinnervation by thin fibers, but not mechanoreceptors, was observed particularly in glabrous skin. Saphenous crush alone did not cause expansive regenerative reinnervation. The results indicate that much of the collateral sprouting or regenerative reinnervation of the skin observed in morphological studies may represent the presence of fibers not responding to the stimuli used in the present study. It is also suggested that some observations of collateral sprouting may represent changes in responsiveness to stimulation of skin areas with overlapping innervation territories.
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  • 78
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 76 (1989), S. 239-245 
    ISSN: 1432-1106
    Schlagwort(e): Hippocampus ; Noradrenaline ; Habenula ; Microdialysis ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Hippocampal extracellular levels of noradrenaline (NA) were monitored with the microdialysis technique during electrical stimulation of the lateral habenula (LHb) in halothane anaesthetized rats. The steady state NA level was 20.8±4.6 fmole/15 min of perfusion (mean ± SEM). Electrical stimulation of the LHb for 15 min (15 Hz, 0.5 mA) induced an immediate 228±48% increase in hippocampal NA release, compared to the pre-stimulation baseline (p〈0.05). A second stimulation 90 min later induced a similar increase. The effect of LHb stimulation was completely abolished by a knife cut transecting the dorsal NA bundle either immediately rostral to the locus coeruleus or at the level of the parafascicular nucleus. This suggests that the effect was dependent on nerve impulses flow in the coeruleo-hippocampal NA neurons, and was not mediated, e.g., by a local spread of electricity into the hippocampus. Since the LHb has previously been shown to be a powerful activator of the mesencephalic raphe nuclei we tested whether the effect was mediated via the serotonergic system. However, the effect of LHb stimulation on hippocampal NA release persisted after 5,7-di-hydroxytryptamine treatment and after complete radiofrequency lesions of the dorsal and central superior raphe nuclei. The present data suggest that electrical stimulation of the LHb can increase hippocampal NA release through an activation of the locus coeruleus, and that this effect is not dependent on the mesencephalic raphe nuclei. The results support the role of the LHb as a link for limbic and striatal forebrain activation of brain stem monoaminergic systems.
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  • 79
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 76 (1989), S. 369-385 
    ISSN: 1432-1106
    Schlagwort(e): Cobalt experimental epilepsy ; Motor cortex ; GABA ; Immunocytochemistry ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The distribution of GABA-immunoreactive cell bodies and terminals was studied using an anti-GABA serum during the development of chronic focal epilepsy induced by cobalt deposits onto the motor cortex of the rat. Cell counts of GABA-positive neurons were carried out in the epileptogenic area and correlated with the electrophysiological activity of the cobalt focus. In normal control rats, we identified GABA-immunoreactive somata and processes in the motor agranular cortex; they were multipolar or bipolar but never pyramidal and were present in all layers, especially in layer II. GABA-immunoreactive terminals were widely scattered in the neuropil and surrounded the unlabelled cell bodies. In the cobalt-treated animals, changes in the GABAergic innervation were observed during the development of the epileptic focus: decreases in the GABA-positive cell density and in the number of GABA-positive terminals were present before the onset of epileptic discharges and became more marked during the period of maximal spiking activity; a progressive return to normal values of GABA-positive cell density (except in the deep layers) as well as the reappearance of GABA positive terminals were associated with the extinction of the epileptic syndrome. Our observations suggest that the impaired inhibitory neurotransmission mediated by GABA plays a role in the development of the cobalt-induced epilepsy; moreover the recovery of GABAergic function which occurs during the extinction of the epileptic syndrome might imply a capacity for axonal regeneration of the GABAergic neurons.
    Materialart: Digitale Medien
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  • 80
    ISSN: 1432-1106
    Schlagwort(e): Calcitonin gene-related peptide (CGRP) ; Bed nucleus of the stria terminalis ; Central nucleus of the amygdala ; Ultrastructure ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Light and electron microscopic analysis of calcitonin gene-related peptide (CGRP)-like immunoreactive (LI) terminals in the bed nucleus of the stria terminalis (BST) and the central nucleus of the amygdala (Ce) was carried out using the peroxidase-antiperoxidase method. CGRP-LI fibers were densely distributed in the dorsal subdivision of the lateral BST (BSTL) and the lateral and lateral capsular subdivisions of the Ce, where the CGRP-LI terminals formed symmetrical and asymmetrical axo-dendritic, and symmetrical axosomatic synapses. One of the most characteristic features of the CGRP-LI terminals was the presence of large, long boutons, each of which surrounded a cell soma and made many synaptic contacts. These findings suggest that CGRP exerts a significant influence on neurons in the BSTL and Ce.
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  • 81
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 77 (1989), S. 499-506 
    ISSN: 1432-1106
    Schlagwort(e): Temporal/entorhinal area ; Memory processing ; Neurotransmitters ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The purpose of the present study was to investigate whether effects of temporo-entorhinal disconnections on acquisition and retention of a visual discrimination task might be associated with neurochemical dysfunctions. The results revealed that the present lesions impaired both acquisition and retention of the discrimination task. This impairment was accompanied by decreased glutamergic activity in both temporal and entorhinal cortices. No changes were seen in levels of acetylcholine or GABA. Further, the distribution of glutamate/ aspartate was related to both regional and hemispheric differences. The results are discussed in terms of a highly integrative role of the lateral entorhinal cortex and in terms of other putative neurotransmitter systems involved in the function of memory.
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  • 82
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 77 (1989), S. 569-576 
    ISSN: 1432-1106
    Schlagwort(e): Ventrobasal thalamic neurones ; Noxious mechanical stimulation ; Orofacial receptive fields ; Trigeminal sensory complex ; Tractotomy ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Single units were recorded, using extra-cellular glass microelectrodes, in the ventrobasal complex of the thalamus of rats under halothane-nitrous oxide anaesthesia. The animals had previously undergone a large bilateral section of the trigeminal sensory complex just above the obex to deprive the caudal part of the trigeminal sensory complex (subnucleus caudalis) of its trigeminal afferents. As observed on frontal slices our lesions impaired the whole descending tract and, in most cases, the intratrigeminal pathways between the rostral and the caudal part of the complex. Forty-seven units responding to a somatic mechanical noxious stimulation applied to the trigeminal area were recorded in these conditions. Forty-two of these had a receptive field (or at least a part of it) in or around the oral and nasal cavities, and 5 in the peripheral part of the face. These data confirm the hypothesis that the rostral part of the trigeminal sensory complex participates in pain sensory pathways, as a first relay site between nociceptive primary afferents coming from oral, perioral and perinasal areas, and the ventrobasal complex of the thalamus. In addition, they suggest that the intra-trigeminal pathways are not essential for the transmission of these nociceptive inputs, to the lateral thalamus.
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  • 83
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 78 (1989), S. 233-242 
    ISSN: 1432-1106
    Schlagwort(e): Hoppocampus ; Granule cells ; Long lasting inhibition ; Frequency habituation ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary In paired pulse stimulation experiments the mechanism underlying frequency habituation of postsynaptic potentials in dentate granule cells of rat hippocampal slices was studied by measuring extra and intracellular potentials as well as changes in extracellular calcium ([Ca2+]0) and potassium concentrations ([K+]0). Orthodromic stimulation of the perforant path induced in most granule cells a late, slow hyperpolarization (SH), lasting for up to 1.2 s. During the SH the membrane conductance was increased by up to 40%. The reversal potential of the SH was around -90 mV and varied with the [K+]0. Frequency habituation was seen in all cells with the SH, whereas cells which display frequency potentiation had no SH. Lowering of [Ca2+]0 reversed paired pulse induced frequency habituation into frequency potentiation at [Ca2+]0 levels where the SH disappeared. Phaclofen blocked the SH and reversed frequency habituation into frequency potentiation. Elevating [Mg2+]0 also reversed frequency habituation into frequency potentiation and reduced the SH. We conclude that the SH represents a late, slow IPSP which is responsible for frequency habituation in dentate granule cells. We noted that during repetitive stimulation the SH soon started to fade. This effect can in part be attributed to extracellular K+-accumulation as suggested by the K+-dependence of the slow IPSP and the observations of changes in [K+]0 during repetitive stimulation. This could explain why frequency habituation reverses into frequency potentiation during repetitive stimulation.
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  • 84
    ISSN: 1432-1106
    Schlagwort(e): Extincton ; Nonreward ; Adrenoceptor ; Noradrenaline ; Stress ; Sympathetic nervous system ; 6-hydroxydopamine ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary We tested whether the stress of nonreward has neurochemical effects on noradrenergic neurones which resemble those reported for other forms of stress. Rats trained to run in a straight runway for food reward were subjected to either 1 or 10 extinction trials. Half the rats in each group were injected before the start of acquisition with IP 6-hydroxydopamine to deplete peripheral noradrenaline stores. All animals were killed immediately after their final test in the runway, together with untrained controls. Noradenaline depletion had no behavioural or neurochemical effects. The rate of extinction in the 10-trial group, which was indexed by the slope of the linear regression of running time on trial, correlated negatively with both alpha2 and beta-adrenoceptor number (Bmax). There were no differences between groups in cerebral cortical noradrenaline content, or alpha2 or beta-adrenoceptor binding. These results substantially conflict with those predicted from Stone's hypothesis relating beta-adrenoceptor sensitivity to the behavioural response to stress. A further finding was that alpha2, but not beta-adrenoceptor number, negatively correlated with levels of noradrenaline in the tissue, suggesting that noradrenaline is less involved in the regulation of beta than in that of alpha2-adrenoceptors.
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  • 85
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 76 (1989), S. 141-152 
    ISSN: 1432-1106
    Schlagwort(e): Abducens motoneurones ; Intracellular recordings ; HRP staining ; Membrane properties ; Somato-dendritic organization ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The electrical and morphological properties of abducens motoneurones were investigated in the rat with intracellular recordings and intracellular HRP-staining. Motoneurones were identified by their antidromic response to electrical stimulation of the lateral rectus muscle. The antidromic action potential was followed by a delayed depolarization and an after hyperpolarization lasting 20 ms to 45 ms. The whole neurone input resistance (RN) calculated from I/V curves, was found to lie between 2 MΩ and 15 MΩ with a bimodal distribution (mean values 4.9 MΩ and 12 MΩ). In some cases, anomalous rectification was observed with low current intensities. Prolonged hyperpolarizing current pulses revealed the presence of a time dependant inward rectification and slow rebound depolarization. The intensity/frequency curves suggest the existence of three ranges of discharge. The average intensity frequency slope during the steady state was 43 imp/s/ nA. Eight abducens motoneurones were intracellularly labelled with HRP and fully reconstructed. The soma (23 μm to 40 μm in diameter) gave off 5 to 7 primary dendrites. The general organization and extension of the dendritic trees depended on the location of the soma within the abducens nucleus. The mean diameter of primary dendrites was 4.17 μm with similar average values in all motoneurones. The soma size of abducens motoneurones was not correlated with either the size of the proximal tree or the whole neurone input resistance.
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  • 86
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 76 (1989), S. 646-650 
    ISSN: 1432-1106
    Schlagwort(e): Glutamate binding sites ; Autoradiography ; Vestibular nuclei ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Quantitative autoradiography has been used to characterize l-[3H] glutamate binding sites and to describe their distribution in frozen sections of rat vestibular nuclei. Scatchard plots and Hill coefficients of glutamate binding suggest that glutamate interacts with a single population of sites having a KD of about 126 nM and a capacity of 2.5 pmol/mg of protein. Although the level of glutamate binding was not very high compared to the highest levels described for some other brain regions, it was nonetheless substantial. The sites were distributed unevenly in the four vestibular nuclei and their distribution correlated well with the projection areas of the vestibular nerve, which has been described as a glutamate-mediated pathway. The highest numbers of glutamate binding sites were observed in the medial vestibular nuclei. This technique provides a very sensitive assay for characterizing the pharmacological subtypes of glutamate binding in the vestibular nuclei and for analyzing changes in these sites during development or after deafferentation of the vestibular nuclei.
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  • 87
    ISSN: 1432-1106
    Schlagwort(e): Somatosensory cortex ; Differential development ; Lectin binding ; Vibrissae ; Forepaw ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Physiological studies have demonstrated a highly organized somatotopic representation of the body surface in SI cortex of rat. This representation is correlated morphologically with the presence of barrel-shaped structures in layer IV. Conventional staining techniques reveal barrels in the latter part of the first postnatal week. Recently, the peroxidase conjugates of lectins, which recognize glycosylated molecules, have been used to study barrel field formation. Con A, for example, has been shown to bind primarily to prospective barrel sides and septa as early as postnatal day 3 (PND-3) in mouse. To date, investigations of SI cortex using the lectin (Arachis hypogaea) peanut agglutinin (PNA) have been confined to the study of the barrel field representation of the face and mystacial vibrissae in the mouse. In the present study we extend these findings to the development of the representation of the entire body surface called the rattunculus. Rats ranging from PND-1 (first 24 h after birth) to PND-12 were anesthetized with Nembutal and perfused with 4% paraformaldehyde and 2% glutaraldehyde in 0.2 M sodium cacodylate buffer. Brains were removed, flattened tangentially, and sectioned on a vibratome at 30–120 microns. Sections were blocked in TRIS-buffered saline (TBS) plus 2% bovine serum albumin and incubated in peanut lectin at 4° C. Following incubation, sections were washed with TBS and processed using peroxidase histochemistry. Lectin binding in the prospective forelimb representation was apparent by PND-5 whereas lectin binding to the prospective face-mystacial vibrissae representation occurred before PND-4. These results suggest that body part representations show individual variations during early pattern formation. In rat, the representation of the limbs may lag behind the representation of the face-mystacial vibrissae during early postnatal development. This developmental gradient within the cortex may reflect a differential expression of lectin receptors.
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  • 88
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 78 (1989), S. 646-648 
    ISSN: 1432-1106
    Schlagwort(e): Hippocampus ; Experimental epilepsy ; Paroxysmal depolarization shift ; Afterpotential ; Penicillin ; Ca2+-activated potassium ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Penicillin-induced paroxysmal depolarization shifts (PDS) are followed by prolonged afterhyperpolarizations of about 2 seconds duration. Intracellular injection of EGTA blocked a late component of the afterhyperpolarizations; an early one lasting up to one second was only slightly reduced by EGTA. It is concluded that afterhyperpolarizations following penicillininduced PDS comprise different components: an initial one lasting up to one second which is not Ca2+-dependent and a slow one lasting up to two seconds which is caused by a Ca2+-dependent K+ current.
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  • 89
    ISSN: 1432-1106
    Schlagwort(e): Inhibition ; Hippocampal formation ; Development ; GABAergic neurons ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Glutamate decarboxylase (GAD)-positive and Golgi impregnated local circuit neurons of the hippocampal formation of five day old rats were examined in light and electron microscopic preparations. The ultrastructural features of these neurons were similar in both the dentate gyrus and CA1 area of Ammon's horn. Somata displayed a perikaryal cytoplasm rich in organelles but lacked organized Nissl bodies. Most nuclei showed intranuclear infoldings of varying degrees but no intranuclear sheets or rods were found. Somata and dendrites were contacted by relatively immature axon terminals that formed mainly symmetric synapses. The axons of local circuit neurons in both the dentate gyrus and Ammon's horn formed symmetric synapses with somata and dendrites of the principal neurons in these regions. Thus, both GAD-positive and Golgi-impregnated terminals of local circuit neurons were observed to form synapses with pyramidal and granule cells. These terminals were usually small and contained relatively few pleomorphic synaptic vesicles. The results show that a circuitry for inhibition is established in the 5 day old dentate gyrus and Ammon's horn, even though the local circuit neurons lack some of the typical adult ultrastructural features at this age.
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  • 90
    ISSN: 1432-1106
    Schlagwort(e): Steroid receptor ; CRF ; Neurotensin ; Enkephalin ; CCK ; PHI ; VIP ; Somatostatin ; TRH ; Dopamine ; Immunohistochemistry ; Arcuate nucleus ; Hormones ; Neurosecretion ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The paraventricular nucleus (PVN) of male albino rats was analyzed for the presence of glucocorticoid receptor-like immunoreactivity (GR-LI) in neuropeptide containing neurons. Using immunohistochemistry, coronal sections trough the entire PVN were double-stained with a mouse monoclonal antibody against GR and one of the following antisera: rabbit antiserum to corticotropin releasing factor (CRF), neurotensin (NT), enkephalin (ENK), cholecystokinin (CCK), thyrotropin releasing hormone (TRH), galanin (GAL), peptide histidine isoleucine (PHI), vasoactive intestinal polypeptide (VIP), somatostatin (SOM) or tyrosine hydroxylase (TH). For comparison the occurrence of GR-LI in NT-, SOM-, NPY- or TH-positive neurons of the arcuate nucleus was also studied. Our results indicate that GR-LI is present in the parvocellular part of the PVN but not in its magnocellular portion. Virtually every parvocellular neuron in the PVN containing one of the above mentioned peptides was also positive for GR, with the exception of SOM neurons, of which only about two thirds showed detectable levels of GR-LI. All TH-positive, presumably dopamine neurons in the PVN were GR-positive. In the arcuate nucleus all TH- and NPY-positive neurons as well as a large proportion of the SOM- and NT-immunoreactive neurons contained GR-LI. The results indicate that in the PVN, in addition to the CRF neurons, certain peptidergic neurons in the parvocellular part of the PVN, without any established role in the control of ACTH synthesis and release, may also be under glucocorticoid control. This seems to be the case also for most arcuate neurons.
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  • 91
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 78 (1989), S. 164-173 
    ISSN: 1432-1106
    Schlagwort(e): Glia ; GFAP ; Brainstem ; Spinal cord ; Immunocytochemistry ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The topographical mapping of glial fibrillary acidic protein (GFAP)-immunoreactivity was performed in coronal serial sections of the rat mesencephalon, rhombencephalon and spinal cord. Relative to a background of poor or moderate overall staining of the mesencephalon, the interpeduncular nucleus, substantia nigra and the periaqueductal grey matter were prominent by their intense GFAP-immunoreactivity. The pons and particularly the medulla contained more GFAP-labelled elements compared with the mesencephalon. The spinal trigeminal nucleus and Rolando substance were distinguished by their intense staining. Large fibre tracts were usually poor in immunoreactive GFAP. In a concluding discussion, findings relevant to the GFAP-mapping of the whole rat CNS are evaluated with regard to possible reasons underlying the observed differential distribution of GFAP-immunoreactivity.
    Materialart: Digitale Medien
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  • 92
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 78 (1989), S. 185-192 
    ISSN: 1432-1106
    Schlagwort(e): Cardiopulmonary vagal reflex ; Bezold-Jarisch reflex ; Excitatory amino acid ; Caudal ventrolateral medulla ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The importance of the caudal ventrolateral medulla (CVLM) in mediating vagal cardiopulmonary (Bezold-Jarisch reflex) reflex activity was studied in urethane-anaesthetized rats. Unilateral electrolytic lesion of the CVLM markedly attenuated Bezold-Jarisch reflex responses (hypotension and bradycardia) elicited by intravenous injections of 5-HT. Bilateral lesion of the CVLM virtually abolished the reflex responses. Microinjection of the excitatory amino acid (EAA) receptor antagonist kynurenate (KYN), but not the inactive analogue xanthurenate, into the CVLM markedly attenuated the reflex responses to 5-HT. The N-methyl-D-aspartate (NMDA) receptor antagonist, MK-801 also markedly attenuated reflex activity. Furthermore, lesions, KYN and MK-801 all tended to elevate resting blood pressure and to reduce resting heart rate. These findings support the hypothesis that the CVLM is an important medullary locus mediating cardiovascular reflex integration and that an EAA synapse in the CVLM is important in the cardiopulmonary reflex arc.
    Materialart: Digitale Medien
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  • 93
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 78 (1989), S. 358-368 
    ISSN: 1432-1106
    Schlagwort(e): Neurotensin ; Frontal cortex ; In vitro slice preparation ; Intracellular recording ; Single-electrode-voltage-clamp ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The actions of neurotensin (NT) on frontal pyramidal neurons were studied in vitro in slices of rat cerebral cortex using current clamp and single electrode voltage clamp (SEVC) techniques. Bath application of NT (0.1 μM–10 μM) induced a depolarization (2–13 mV) in 88% of the pyramidal cells, this effect was associated with a decrease in input conductance of 5–35% and its reversal potential was estimated at -88 +/-9.7mV. Typically, this depolarizing effect of NT was transient, since no cell responded to a second application of the peptide within 20 min after the first one. NT also induced an increase in the rate of firing of pyramidal cells evoked by direct stimulation, even when an hyperpolarizing current was applied to prevent the depolarization induced by NT. This effect could neither be explained by a decrease of the post-spike after-hyperpolarization, nor by an increase of the persistent sodium current which sustains the spiking of pyramidal cells, since the former was not affected consistently by NT and the later was insensitive to the peptide. This excitation of pyramidal neurons by NT persisted after blockade of synaptic transmission. On the other hand, NT also enhanced the synaptic noise recorded in pyramidal cells in standard perfusing medium. Furthermore, dopaminergic antagonists and noradrenergic antagonists failed to block these effects of NT. Finally, the inactive fragment of the peptide, NT(1–8), did not affect membrane properties of pyramidal cells. All together, these results suggest that NT excites frontal cortical neurons through the activation of specific NT receptors.
    Materialart: Digitale Medien
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  • 94
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 74 (1989), S. 41-46 
    ISSN: 1432-1106
    Schlagwort(e): Cortico-cortical neurons ; Sensorimotor cortex ; Glutamate and aspartate immunoreactivity ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Retrograde transport of tracers and immunocytochemistry have been used to determine if association and callosal neurons in the primary motor and somatosensory cortex of rats contain high levels of glutamate or aspartate and may, thus, use these amino acids as neurotransmitter. After tracer injections in these areas, about 65% of the retrogradely labeled neurons in layer V in the ipsilateral or contralateral hemisphere are immunopositive for glutamate. Lower percentages of double-labeled neurons are found in layers III, VI, and II. Similar results are obtained when sections are processed for aspartate immunoreactivity. About 90% of retrogradely labeled neurons are immunopositive in sections incubated with a mixture of both glutamateand aspartate antisera. These results suggest that a large fraction of cortico-cortical neurons are immunoreactive for either one amino acid but not for both. It is proposed that neurons with high levels of one amino acid use this as neurotransmitter; high levels of glutamate and aspartate are likely to be present in a fraction of neurons which may release both amino acids or a substance closely related to these.
    Materialart: Digitale Medien
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  • 95
    ISSN: 1432-1106
    Schlagwort(e): α-melanocyte ; stimulating hormone ; Dopamine receptors ; Rat ; Hypothalamus
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Release of alpha-melanocyte-stimulating hormone (α-MSH) from slices of rat hypothalamus superfused with artificial cerebro-spinal fluid (ACSF) was quantified by radioimmunoassay. Addition of 10-6 M quinpirole, a D2-dopamine receptor agonist, to the superfusion medium caused a significant (P 〈 0.001) reduction in the amount of α-MSH released upon depolarisation with 50 mM potassium from 319 ±37% to 110 ±16% of basal release in normal ACSF (mean ±S.E.M.). Basal peptide release in the presence of quinpirole was unaffected. Sulpiride, a D2-dopamine receptor antagonist, at a concentration of 10-6 M, induced a significant (P 〈 0.05) increase of both basal and potassium-stimulated α-MSH release to 203 ±21% and 447 ±88% of basal release in normal ACSF respectively. The latter increases were abolished when sulpiride and quinpirole were added in combination. SK&F 38393-A and SCH 23390, a D1-dopamine agonist and antagonist respectively, had no significant effect on either basal or potassiumstimulated α-MSH release. It is proposed that endogenous dopamine exerts an inhibitory control on α-MSH release from the rat hypothalamus via D2-dopamine receptors and that in isolated hypothalamic slices there is a tonic inhibition of peptide release due to the activity of this system.
    Materialart: Digitale Medien
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  • 96
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 75 (1989), S. 441-445 
    ISSN: 1432-1106
    Schlagwort(e): Hippocampal mossy fibers ; GABAergicneurons ; GABAergic inhibition ; EM immunocytochemistry ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Mossy fibers are known to form excitatory synapses on pyramidal neurons in regio inferior of the hippocampus. This study demonstrates that the mossy fibers also establish synaptic contacts with glutamate decarboxylase-immunoreactive, supposedly GABAergic inhibitory neurons in the CA3 region. The observed connection provides a morphological basis for feed-forward inhibition of the pyramidal cells.
    Materialart: Digitale Medien
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  • 97
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 75 (1989), S. 543-554 
    ISSN: 1432-1106
    Schlagwort(e): Intralaminar nuclei ; Cortical projection ; Arousal ; Pain ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Cortical surface potentials evoked from thalamic intralaminar nuclei have been studied in rats anaesthetized with chloralose. Stimulation with low current intensity in central lateral nucleus (CL), evoked potentials in large areas of the rat isocortex. In the posterior parietal cortex responses with a short latency negativity were evoked which followed high frequency repetitive stimulation. Its latency and ability to follow high frequency stimulation indicated a monosynaptic connection from CL to this part of the cortex. The short latency potential was followed by a second negativity with longer latency and varying amplitude. This second negativity did not follow repetitive stimulation exceeding 10 Hz, and was also reduced by supplementary doses of anaesthetics, indicating a polysynaptic origin. Stimulation at different CL sites elicited cortical potentials with short latency in a topographical pattern. Laminar analysis in the parietal and motor cortex suggested both a superficial and a deep layer termination of afferents from CL. Similar topografical relations and afferent layer distributions have previously been found in cats. The role of the thalamocortical projection from CL to parietal cortex in arousal, attention and pain mechanisms is discussed.
    Materialart: Digitale Medien
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  • 98
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 76 (1989), S. 417-423 
    ISSN: 1432-1106
    Schlagwort(e): Choline acetyltransferase ; Cerebral cortex ; Immunohistochemistry ; Development ; Transient expression ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary The cholinergic innervation of the rat cerebral cortex was examined in pre- and postnatal life using immunohistochemistry with a monoclonal antibody directed against choline acetyltransferase (ChAT). Our observations show that there are two separate phases in the development of the cholinergic innervation of the rat neocortex. The first, a transient phase, occurs in the late stages of gestation and in the perinatal period. During this time, ChAT-labelled cells (neuroblasts, as well as immature pyramidal and non-pyramidal neurons) are present throughout the entire rostro-caudal extent of the primordial cortex. The fate of these cells, which are not visible shortly after birth, is unknwon as is their functional role in the developing cortex. The second phase in the development of the cholinergic innervation begins in the middle of the second postnatal week. At this stage only a few faintly stained neurons and fibres appear in the cortex. Their numbers and staining intensity increase gradually until the fifth postnatal week when ChAT-labelled neurons and axonal arbours appear indistinguishable from their adult counterparts. The pattern of development observed in the second phase parallels closely that shown in a recent analysis of cortical ChAT activity during postnatal life.
    Materialart: Digitale Medien
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  • 99
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 76 (1989), S. 656-661 
    ISSN: 1432-1106
    Schlagwort(e): Central chemoreceptor ; Carbon dioxide ; Nucleus tractus solitarius ; Nucleus ambiguus ; Cardiopulmonary control ; Brain slice ; Intracellular recording ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary To identify central sites of potential CO2/H+-chemoreceptive neurons, and the mechanism responsible for neuronal chemosensitivity, intracellular recordings were made in rat tissue slices in two cardiopulmonary-related regions (i.e., nucleus tractus solitarii, NTS; nucleus ambiguus, AMBc) during exposure to high CO2. When the NTS was explored slices were bisected and the ventral half discarded. Utilizing such “dorsal” medullary slices removed any impinging synaptic input from putative chemoreceptors in the ventrolateral medulla. In the NTS, CO2-induced changes in firing rate were associated with membrane depolarizations ranging from 2–25 mV (n = 15). In some cases increased e.p.s.p. activity was observed during CO2 exposure. The CO2-induced depolarization occurred concomitantly with an increased input resistance ranging from 19–23 MΩ (n = 5). The lower membrane conductance during hypercapnia suggests that CO2-induced depolarization is due to a decreased outward potassium conductance. Unlike neurons in the NTS, AMBc neurons were not spontaneously active and were rarely depolarized by hypercapnia. Eleven of 12 cells tested were either hyperpolarized by or insensitive to CO2. Only 1 neuron in the AMBc was depolarized and it also showed an increased input resistance during CO2 exposure. Our findings suggest that CO2/H+-related stimuli decrease potassium conductance which depolarizes the cell and increases firing rate. Although our in vitro studies cannot guarantee the specific function of these cells, we believe they may be involved with brain pH homeostasis and cardiopulmonary regulation.
    Materialart: Digitale Medien
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  • 100
    Digitale Medien
    Digitale Medien
    Springer
    Experimental brain research 77 (1989), S. 283-294 
    ISSN: 1432-1106
    Schlagwort(e): Intracellular recordings ; Membrane potential ; Input impedance ; Hippocampal pyramidal cells ; Theta rhythm ; Urethane ; Rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin
    Notizen: Summary Intracellular recordings were made from hippocampal pyramidal cells identified by their depths and their responses to commissural stimulation. Recordings were made during spontaneous bouts of hippocampal theta rhythm in urethane anesthetized rats. Membrane potentials (V m) of pyramidal cells varied with the phase of the theta rhythm, that is, there was an “intracellular theta rhythm”. The changes in V m averaged about 2 mV peak to peak. Averaged intracellular theta waves showed that CA1 pyramids were most depolarized at the time of the positive peak of the extracellular theta rhythm recorded in (and superficial to) the CA1 pyramidal cell layer (CA1 theta). Peak depolarizations for CA3/4 pyramids were more broadly distributed, but occurred mainly in the interval just before the positive peak to just before the negative peak of the CA1 theta. Input impedance minima that were measurable at frequencies as high as 100 Hz occurred at about the same phases of the extracellular theta rhythm as the peak depolarizations (positive-going zero crossing to negative-going zero crossing of the CA1 theta). Such impedance changes imply conductance changes on the soma. The magnitude and localization of the conductance changes suggests that somatic IPSPs make major contributions to the intracellular theta rhythm. The phase relation between the intracellular and extracellular theta rhythms could be reversed by long duration current pulses that depolarized the cells slightly. This implies that either the intracellular theta-related IPSPs are depolarizing potential changes, or that they occur simultaneously with EPSPs. The phase of the intracellular theta rhythm was generally unaffected by long duration hyperpolarizing current pulses. Chloride leakage that reversed the evoked IPSPs usually had no effect on the phase of the intracellular theta rhythm, although in one case it appeared to cause its amplitude to increase.
    Materialart: Digitale Medien
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