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  • 1
    Publication Date: 2014-11-10
    Description: Graphs with circular symmetry, called webs, are relevant w.r.t. describing the stable set polytopes of two larger graph classes, quasi-line graphs and claw-free graphs. Providing a decent linear description of the stable set polytopes of claw-free graphs is a long-standing problem. However, even the problem of finding all facets of stable set polytopes of webs is open. So far, it is only known that stable set polytopes of webs with clique number $\leq 3$ have rank facets only while there are examples with clique number $〉4$ having non-rank facets.
    Keywords: ddc:000
    Language: English
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  • 2
    Publication Date: 2014-02-26
    Description: The bio-heat transfer equation is a macroscopic model for describing the heat transfer in microvascular tissue. In [{\sl Deuflhard, Hochmuth 2002}] the authors applied homogenization techniques to derive the bio-heat transfer equation as asymptotic result of boundary value problems which provide a microscopic description for microvascular tissue. Here those results are generalized to a geometrical setting where the regions of blood are allowed to be connected. Moreover, asymptotic corrector results are derived.
    Keywords: ddc:000
    Language: English
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  • 3
    Publication Date: 2014-11-10
    Description: Stable multi-sets are an evident generalization of the well-known stable sets. As integer programs, they constitute a general structure which allows for a wide applicability of the results. Moreover, the study of stable multi-sets provides new insights to well-known properties of stable sets. In this paper, we continue our investigations started in [{\sl Koster and Zymolka 2002}] and present results of three types: on the relation to other combinatorial problems, on the polyhedral structure of the stable multi-set polytope, and on the computational impact of the polyhedral results. First of all, we embed stable multi-sets in a framework of generalized set packing problems and point out several relations. The second part discusses properties of the stable multi-set polytope. We show that the vertices of the linear relaxation are half integer and have a special structure. Moreover, we strengthen the conditions for cycle inequalities to be facet defining, show that the separation problem for these inequalities is polynomial time solvable, and discuss the impact of chords in cycles. The last result allows to interpret cliques as cycles with many chords. The paper is completed with a computational study to the practical importance of the cycle inequalities. The computations show that the performance of state-of-the-art integer programming solvers can be improved significantly by including these inequalities.
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  • 4
    Publication Date: 2014-02-26
    Description: In this paper, first solutions of the dust moment equations developed in [{\sl Woitke & Helling 2002}] for the description of dust formation and precipitation in brown dwarf and giant gas planet atmospheres are presented. We consider the special case of a static brown dwarf atmosphere, where dust particles continuously nucleate from the gas phase, grow by the accretion of molecules, settle gravitationally and re-evaporate thermally. Applying a kinetic description of the relevant microphysical and chemical processes for TiO$_2$-grains, the model makes predictions about the large-scale stratification of dust in the atmosphere, the depletion of molecules from the gas phase, the supersaturation of the gas in the atmosphere as well as the mean size and the mass fraction of dust grains as function of depth. Our results suggest that the nucleation occu in the upper atmosphere where the gas is cool, strongly depleted, but nevertheless highly supersaturated ($S\!\gg\!1$). These particles settle gravitationally and populate the warmer layers below, where the in-situ formation (nucleation) is ineffective or even not possible. During their descent, the particles grow up to radii $\approx\!0.3\,\mu{\rm m}\,...\,150\,\mu{\rm m}$, depending gas around the cloud base. The particles finally sink into layers which are sufficiently hot to cause their thermal evaporation. Hence, an effective transport mechanism for condensable elements exi considered solid/liquid material. In the stationary case studied here, this downward directed element transport by precipitating dust grains is balanced by an upward directed flux of condensable elements from the deep interior of the star via convective mixing (no dust without mixing). We find a self-regulation mechanism which leads to an approximate phase equilibrium ($S\!\approx\!1$) around the cloud base. The mass fraction of dust present in the atmosphere results be to approximately given by the mass fraction of condensable elements in the gas being mixed up.
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    Language: English
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  • 5
    Publication Date: 2020-03-09
    Description: Analysis of phenomena that simultaneously occur on quite different spatial and temporal scales require adaptive, hierarchical schemes to reduce computational and storage demands. For data represented as grid functions, the key are adaptive, hierarchical, time-dependent grids that resolve spatio-temporal details without too much redundancy. Here, so-called AMR grids gain increasing popularity. For visualization and feature identification/tracking, the underlying continuous function has to be faithfully reconstructed by spatial and temporal interpolation. Well designed interpolation methods yield better results and help to reduce the amount of data to be stored. We address the problem of temporal interpolation of AMR grid data, e.g.\ for creation of smooth animations or feature tracking. Intermediate grid hierarchies are generated by merging the cells on all refinement levels that are present in the key frames considered. Utilizing a clustering algorithm a structure of nested grids is induced on the resulting collection of cells. The grid functions are mapped to the intermediate hierarchy, thus allowing application of appropriate interpolation techniques.
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  • 6
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    Publication Date: 2020-03-09
    Description: An improved general-purpose technique for the visualization of symmetric positive definite tensor fields of rank two is described. It is based on a splatting technique that is built from tiny transparent glyph primitives which are capable to incorporate the full directional information content of a tensor. The result is an information-rich image that allows to read off the preferred directions in a tensor field at each point of a three-dimensional volume or two-dimensional surface. It is useful for analyzing slices or volumes of a three-dimensional tensor field and can be overlayed with standard volume rendering or color mapping. The application of the rendering technique is demonstrated on general relativistic data and the diffusion tensor field of a human brain.
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  • 7
    Publication Date: 2014-11-10
    Description: Graphs with circular symmetry, called webs, are relevant for describing the stable set polytopes of two larger graph classes, quasi-line graphs [{\sl Giles and Trotter 1981, Oriolo 2001}] and claw-free graphs [{\sl Galluccio and Sassano 1997, Giles and Trotter 1981}]. Providing a decent linear description of the stable set polytopes of claw-free graphs is a long-standing problem [{\sl Grötschel, Lov\'asz, and Schrijver 1988}]. However, even the problem of finding all facets of stable set polytopes of webs is open. So far, it is only known that stable set polytopes of webs with clique number $\leq 3$ have rank facets only [{\sl Dahl 1999, Trotter 1975}] while there are examples with clique number $\geq 4$ having non-rank facets [{\sl e.g. Liebling et al. 2003, Oriolo 2001, P\^echer and Wagler 2003}]. In this paper, we provide a construction for non-rank facets of stable set polytopes of webs. We use this construction to prove, for several fixed values of $\omega$ including all odd values at least 5, that there are only finitely many webs with clique number $\omega$ whose stable set polytopes admit rank facets only.
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  • 8
    Publication Date: 2020-11-13
    Description: We present an algorithm that constructs parametrizations of boundary and interface surfaces automatically. Starting with high-resolution triangulated surfaces describing the computational domains, we iteratively simplify the surfaces yielding a coarse approximation of the boundaries with the same topological type. While simplifying we construct a function that is defined on the coarse surface and whose image is the original surface. This function allows access to the correct shape and surface normals of the original surface as well as to any kind of data defined on it. Such information can be used by geometric multigrid solvers doing adaptive mesh refinement. Our algorithm runs stable on all types of input surfaces, including those that describe domains consisting of several materials. We have used our method with success in different fields and we discuss examples from structural mechanics and biomechanics.
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  • 9
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    Publication Date: 2020-08-05
    Description: This article investigates a certain class of combinatorial packing problems and some polyhedral relations between such problems and the set packing problem.
    Keywords: ddc:000
    Language: English
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  • 10
    Publication Date: 2014-02-26
    Description: We construct non-constructible simplicial $d$-spheres with $d+10$ vertices and non-constructible, non-realizable simplicial $d$-balls with $d+9$ vertices for $d\geq 3$.
    Keywords: ddc:000
    Language: English
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  • 11
    Publication Date: 2014-11-11
    Description: We consider the problem of designing a network that employs a non-bifurcated shortest path routing protocol. The network's nodes and the set of potential links are given together with a set of forecasted end-to-end traffic demands. All relevant hardware components installable at links or nodes are considered. The goal is to simultaneously choose the network's topology, to decide which hardware components to install on which links and nodes, and to find appropriate routing weights such that the overall network cost is minimized. In this paper, we present a mathematical optimization model for this problem and an algorithmic solution approach based on a Lagrangian relaxation. Computational results achieved with this approach for several real-world network planning problems are reported.
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  • 12
    Publication Date: 2014-02-26
    Description: We investigate the impact of link and path restoration on the cost of telecommunication networks. The surprising result is the following: the cost of an optimal network configuration is almost independent of the restoration concept if (i) the installation of network elements (ADMs, DXCs, or routers) and interface cards, (ii) link capacities, and (iii) working and restoration routings are simultaneously optimized. We present a mixed-integer programming model which integrates all these decisions. Using a branch-and-cut algorithm (with column generation to deal with all potential routing paths), we solve structurally different real-world problem instances and show that the cost of optimal solutions is almost independent of the used restoration concept. In addition, we optimize spare capacities for given shortest working paths which are predetermined with respect to different link metrics. In comparison to simultaneous optimization of working and restoration routings, it turns out that this approach does not allow to obtain predictably good results.
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  • 13
    Publication Date: 2020-11-13
    Description: In the dial-a-ride-problem (DARP) objects have to be moved between given sources and destinations in a transportation network by means of a server. The goal is to find a shortest transportation for the server. We study the DARP when the underlying transportation network forms a caterpillar. This special case is strongly NP-hard in the worst case. We prove that in a probabilistic setting there exists a polynomial time algorithm which almost surely finds an optimal solution. Moreover, with high probability the optimality of the solution found can be certified efficiently. We also examine the complexity of the DARP in a semi-random setting and in the unweighted case.
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  • 14
    Publication Date: 2019-01-29
    Description: The paper presents a new affine invariant theory on asymptotic mesh independence of Newton's method in nonlinear PDEs. Compared to earlier attempts, the new approach is both much simpler and more natural from the algorithmic point of view. The theory is exemplified at collocation methods for ODE boundary value problems and at finite element methods for elliptic PDE problems.
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  • 15
    Publication Date: 2014-02-26
    Description: In this paper we introduce the notion of smoothed competitive analysis of online algorithms. Smoothed analysis has been proposed by [{\sl Spielman and Teng} STOC 2001] to explain the behaviour of algorithms that work well in practice while performing very poorly from a worst case analysis point of view. We apply this notion to analyze the Multi-Level Feedback (MLF) algorithm to minimize the total flow time on a sequence of jobs released over time when the processing time of a job is only known at time of completion. The initial processing times are integers in the range $[1,2^K]$. We use a partial bit randomization model, where the initial processing times are smoothened by changing the $k$ least significant bits under a quite general class of probability distributions. We show that MLF admits a smoothed competitive ratio of $O(max((2^k/\sigma)^3, (2^k/\sigma)^2 2^K-k))$, where $\sigma$ denotes the standard deviation of the distribution. In particular, we obtain a competitive ratio of $O(2^K-k)$ if $\sigma = \Theta(2^k)$. %The analysis holds for an oblivious as well as for a stronger adaptive %adversary. We also prove an $\Omega(2^{K-k})$ lower bound for any deterministic algorithm that is run on processing times smoothened according to the partial bit randomization model. For various other smoothening models, including the additive symmetric smoothening model used by [{\sl Spielman and Teng}], we give a higher lower bound of $\Omega(2^K)$. A direct consequence of our result is also the first average case analysis of MLF. We show a constant expected ratio of the total flow time of MLF to the optimum under several distributions including the uniform distribution.
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  • 16
    Publication Date: 2014-11-11
    Description: For the general G/G/1 processor sharing (PS) system a sample path result for the sojourn times in a busy period is proved, which yields a relation between the sojourn times under PS and FCFS discipline. In particular, the result provides a formula for the mean sojourn time in G/D/1-PS in terms of the mean sojourn time in the corresponding G/D/1-FCFS, generalizing known results for GI/M/1 and M/GI/1. Extensions of the formula provide the basis for a two-moment approximation of the mean sojourn time in G/GI/1-PS in terms of a related G/D/1-FCFS.
    Keywords: ddc:000
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  • 17
    Publication Date: 2014-02-26
    Description: The paper surveys recent progress in the mathematical modelling and simulation of essential molecular dynamics. Particular emphasis is put on computational drug design wherein time scales of $msec$ up to $min$ play the dominant role. Classical long-term molecular dynamics computations, however, would run into ill-conditioned initial value problems already after time spans of only $psec=10^{-12} sec$. Therefore, in order to obtain results for times of pharmaceutical interest, a combined deterministic-stochastic model is needed. The concept advocated in this paper is the direct identification of metastable conformations together with their life times and their transition patterns. It can be interpreted as a {\em transfer operator} approach corresponding to some underlying hybrid Monte Carlo process, wherein short-term trajectories enter. Once this operator has been discretized, which is a hard problem of its own, a stochastic matrix arises. This matrix is then treated by {\em Perron cluster analysis}, a recently developed cluster analysis method involving the numerical solution of an eigenproblem for a Perron cluster of eigenvalues. In order to avoid the 'curse of dimension', the construction of appropriate boxes for the spatial discretization of the Markov operator requires careful consideration. As a biomolecular example we present a rather recent SARS protease inhibitor.
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  • 18
    Publication Date: 2021-02-01
    Description: The operative planning problem in natural gas distribution networks is addressed. An optimization model focusing on the governing PDE and other nonlinear aspects is presented together with a suitable discretization for transient optimization in large networks by SQP methods. Computational results for a range of related dynamic test problems demonstrate the viability of the approach.
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  • 19
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    Publication Date: 2014-02-26
    Description: This article presents a new computational approach to the three-dimensional (3D) modeling of ribonucleic acid (RNA) sequences with unknown spatial structure. The main concept is a mapping of the query sequence onto the 3D structures of a suitable template RNA molecule. This technique called \textit{threading} has originally been developed for the modeling of protein 3D structures. The application to RNA systems bridges the information gap between the growing mass of RNA sequence data and the relatively limited number of available 3D structures. The new RNA threading method is demonstrated on a tRNA model system because sufficient representative 3D structures have experimentally been elucidated and deposited in the public databases. Nevertheless, the method is in principle transferable on all other RNA species. Algorithms are developed that decompose these template structures into their secondary structure elements and gather this information in a specific template database. The best template is chosen with public alignment and secondary structure prediction tools which are integrated in the RNA modeling module. The structural information gathered from the template and the best alignment is combined to establish a comprehensive 3D model of the query sequence. A range of complete tRNA structures has successfully been modeled with the RNA threading method. The prototype module visualizes the models and provides convenient access to the proposed 3D structures. Therefore, the method could give new insight into a variety of RNA systems which in the recent years have become increasingly important as potential new pharmaceutical agents.
    Keywords: ddc:000
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  • 20
    Publication Date: 2014-02-26
    Description: Collection of abstracts of the Korean-German Bilateral Symposium on Scientific Computing, Berlin January 15/16, 2004
    Keywords: ddc:000
    Language: English
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  • 21
    Publication Date: 2014-11-11
    Description: Beim Entwurf und Ausbau von Informations- und Kommunikationsnetzwerken m{ü}ssen zahlreiche interdependente Entscheidungen getroffen und gleichzeitig mannigfaltige Bedingungen ber{ü}cksichtigt werden. Die verf{ü}gbaren technischen und organisatorischen Alternativm{ö}glichkeiten sind normalerweise so vielf{ä}ltig und komplex, dass eine manuelle Planung praktisch nicht m{ö}glich ist. In diesem Artikel wird das Potential und die Methodik der mathematischen Optimierung bei der kostenoptimalen Planung von Kommunikationsnetzen vorgestellt. Als Ausgangspunkt wird exemplarisch eine typische praktische Aufgabe, die Struktur- und Konfigurationsplanung mehrstufiger Telekommunikationsnetzwerke, dargestellt. Anschließend werden kurz die wesentlichen Modellierungstechniken und Verfahrensans{ä}tze der mathematischen Optimierung skizziert. Abschließend gehen wir auf die Planung einer ad{ä}quaten Informations- und Kommunikations- Infrastruktur f{ü}r ein dezentrales Energieversorgungsnetz ein.
    Keywords: ddc:000
    Language: German
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  • 22
    Publication Date: 2020-08-05
    Description: Point-to-Multipoint systems are one kind of radio systems supplying wireless access to voice/data communication networks. Such systems have to be run using a certain frequency spectrum, which typically causes capacity problems. Hence it is, on the one hand, necessary to reuse frequencies but, on the other hand, no interference must be caused thereby. This leads to the bandwidth allocation problem, a special case of so-called chromatic scheduling problems. Both problems are NP-hard, and there exist no polynomial time approximation algorithms with a guaranteed quality. One kind of algorithms which turned out to be successful for many other combinatorial optimization problems uses cutting plane methods. In order to apply such methods, knowledge on the associated polytopes is required. The present paper contributes to this issue, exploring basic properties of chromatic scheduling polytopes and several classes of facet-defining inequalities.
    Keywords: ddc:000
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  • 23
    Publication Date: 2020-02-11
    Description: The UMTS radio network planning problem poses the challenge of designing a cost-effective network that provides users with sufficient coverage and capacity. We describe an optimization model for this problem that is based on comprehensive planning data of the EU project MOMENTUM. We present heuristic mathematical methods for this realistic model, including computational results.
    Keywords: ddc:000
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  • 24
    Publication Date: 2014-02-26
    Description: Relaying -- allowing multiple wireless hops -- is a protocol extension for cellular networks conceived to improve data throughput. Its benefits have only been quantified for small example networks. For assessing its general potential, we define a complex resource allocation\slash{}scheduling problem. Several mathematical models are presented for this problem; while a time-expanded MIP approach turns out intractable, a sophisticated column generation scheme leads to good computational results. We thereby show that for selected cases relaying can increase data throughput by 30\% on the average.
    Keywords: ddc:000
    Language: English
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  • 25
    Publication Date: 2014-02-26
    Description: Finding conflict-free wavelength assignments with a minimum number of required conversions for a routing of the lightpaths is one of the important tasks within the design of all-optical networks. We consider this problem in multi-fiber networks with different types of WDM systems. We give a detailed description of the problem and derive its theoretical complexity. For practical application, we propose several sequential algorithms to compute appropriate wavelength assignments. We also perform computational experiments to evaluate their performance. For the iterative algorithms, we identify characteristic patterns of progression. Two of these algorithms qualify for application in practice.
    Keywords: ddc:000
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  • 26
    Publication Date: 2014-09-30
    Description: A recently developed algorithm allows Rigid Body Docking of ligands to proteins, regardless of the accessibility and location of the binding site. The Docking procedure is divided into three subsequent optimization phases, two of which utilize rigid body dynamics. The last one is applied with the ligand already positioned inside the binding pocket and accounts for full flexibility. Initially, a combination of geometrical and force-field based methods is used as a Coarse Docking strategy, considering only Lennard-Jones interactions between the target and pharmaceutically relevant atoms or functional groups. The protein is subjected to a Hot Spot Analysis, which reveals points of high affinity in the protein environment towards these groups. The hot spots are distributed into different subsets according to their group affiliation. The ligand is described as a complementary point set, consisting of the same subsets. Both sets are matched in $\mathrm{I\!R}^{3}$, by superimposing members of the same subsets. In the first instance, steric inhibition is nearly neglected, preventing the system's trajectory from trapping in local minima and thus from finding false positive solutions. Hence the exact location of the binding site can be determined fast and reliably without any additional information. Subsequently, errors resulting from approximations are minimized via finetuning, this time considering both Lennard-Jones and Coulomb forces. Finally, the potential energy of the whole complex is minimized. In a first evaluation, results are rated by a reduced scoring function considering only noncovalent interaction energies. Exemplary Screening results will be given for specific ligands.
    Keywords: ddc:000
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  • 27
    Publication Date: 2014-02-26
    Description: We suggest a new model for the design of telecommunication networks which integrates decisions about the topology, configuration of the switching hardware, link dimensioning, and protected routing of communication demands. Applying the branch-and-cut-algorithm implemented in our network planning and optimization tool DISCNET, we demonstrate that real-world based network planning instances of such an enhanced model can be solved.
    Keywords: ddc:000
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  • 28
    Publication Date: 2020-02-11
    Description: Dieser Bericht beschreibt die Erfahrungen und Schlussfolgerungen,die im Rahmen der VDS-Vorstudie bei der Speicherung der vom Friedrich-Althoff-Konsortium lizenzierten Zeitschriften des Kluwer-Verlages gewonnen wurden.
    Keywords: ddc:000
    Language: German
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  • 29
    Publication Date: 2020-11-13
    Description: Der KOBV setzt für die endnutzerbasierte Online-Fernleihe den Sisis ZFL-Server (Zentraler Fernleih-Server) ein. Mit dem Einsatz des ZFL-Servers können in den Bibliotheken echte Rationalisierungseffekte erzielt werden: Der Server ist in der Lage, Fernleih-Bestellungen an lokale Systeme zu übergeben, so dass sie im lokalen System automatisch - ohne Eingreifen von Bibliotheksmitarbeitern - weiterverarbeitet werden können. Im KOBV können derzeit Sisis- und Aleph-Lokalsysteme diese Schnittstelle voll bedienen. Andere Bibliothekssysteme im KOBV, die diese Schnittstelle nicht bedienen können, werden mittels eines E-Mail-Verfahrens in die Online-Fernleihe integriert. Die vorliegende Kurzbeschreibung der Online-Fernleihe im KOBV soll - im Gegensatz zur Spezifikation, die möglichst vollständig sein sollte - einen leicht verständlichen Einblick in die Abläufe der Online-Fernleihe vermitteln. Nach einem Überblick über zu erwartende Rationalisierungseffekte ist der Ablauf einer Online-Fernleih-Bestellung - veranschaulicht durch eine Graphik mit dem technischen Aufbau im KOBV - kurz dargestellt. \vspace{6mm} {\it Hinweis:} Die von einer Arbeitsgruppe des KOBV erstellte Spezifikation zur Online-Fernleihe ist als ZIB Report 02-30 auf dem Preprint-Server des ZIB veröffentlicht. Siehe: Monika Kuberek (Red.) {\begin{rawhtml} 〈a href="http://www.zib.de/Publications/Reports/ZR-02-30.pdf"〉 〈i〉 Spezifikation für eine Verbund-Fernleih-Software im KOBV〈/i〉 〈/a〉 \end{rawhtml}}
    Keywords: ddc:000
    Language: German
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  • 30
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    Publication Date: 2014-02-26
    Description: The problem of clustering data can often be transformed into the problem of finding a hidden block diagonal structure in a stochastic matrix. Deuflhard et al. have proposed an algorithm that state s the number $k$ of clusters and uses the sign structure of $k$ eigenvectors of the stochastic matrix to solve the cluster problem. Recently Weber and Galliat discovered that this system of eigenvectors can easily be transformed into a system of $k$ membership functions or soft characteristic functions describing the clusters. In this article we explain the corresponding cluster algorithm and point out the underlying theory. By means of numerical examples we explain how the grade of membership can be interpreted.
    Keywords: ddc:000
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  • 31
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    Publication Date: 2014-02-26
    Description: Mit der Entwicklung des KOBV-Informationsportals soll den Benutzern in der Region Berlin-Brandenburg ein verbesserter Zugang zu Informationsressourcen geboten werden. Einen wesentlichen Anteil diese Auf der Grundlage der Analyse der Rahmenbedingungen werden Anforderungen an die Zugriffskontrolle im KOBV definiert und Lösungsmöglichkeiten auf der Ebene allgemeiner Modelle diskutiert.
    Keywords: ddc:000
    Language: German
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  • 32
    Publication Date: 2014-02-26
    Description: The KOBV Informationsportal aims to be a universal gateway to the sources of information hosted by the partner libraries from the Berlin-Brandenburg area. Due to the large number of these sources, an intuitive navigation is an essential component of the portal. The navigation-component should preserve the partner libraries? independence and overcome their administrative and technical differences. This paper proposes a collection-level navigation with four dimensions: the sources? subject areas (e.g. the first two levels of DDC), the sources? type (e.g. e-journals, databases, OPACs, etc.), the sources? location (e.g. Berlin, Brandenburg) / the library that hosts that source and the sources? accessing state (e.g. free, restricted, etc.).
    Keywords: ddc:000
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  • 33
    Publication Date: 2014-02-26
    Description: Our main result is that every n-dimensional polytope can be described by at most (2n-1) polynomial inequalities and, moreover, these polynomials can explicitly be constructed. For an n-dimensional pointed polyhedral cone we prove the bound 2n-2 and for arbitrary polyhedra we get a constructible representation by 2n polynomial inequalities.
    Keywords: ddc:000
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  • 34
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    Publication Date: 2020-02-11
    Description: The NETLIB has now served for 18 years as a repository of LP problem instances. From the beginning to the present day there was some uncertainness about the precise values of the optimal solutions. We implemented a program using exact rational arithmetic to compute proofs for the feasibility and optimality of an LP solution. This paper reports the \emph{exact} optimal objective values for all NETLIB problems.
    Keywords: ddc:000
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  • 35
    Publication Date: 2014-02-26
    Description: Based on the knowledge gained from direct numerical simulations which are only possible in the microscale regime, a concept of driven turbulence is presented which allows to enter the mesoscopic scale regime. Here, dust formation under stochastic hydro- and thermodynamic conditions is studied: constructively superimposed stochastic waves initiate dust formation by the creation of singular nucleation events. It, hence, results a varying mean grain size and dust density in space and time. The newly formed dust changes the thermodynamic behavior from almost isotherm to adiabatic and chemically depletes the gas phase.
    Keywords: ddc:000
    Language: English
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  • 36
    Publication Date: 2014-11-11
    Description: Der scharfe Wettbewerb innerhalb der Telekommunikationsbranche zwingt die Netzbetreiber dazu, ihre Investitionen genau zu planen und immer wieder Einsparungsmanahmen durchzuführen. Gleichzeitig ist es jedoch wichtig, die Qualität der angebotenen Dienste zu verbessern, um neue Kunden zu gewinnen und langfristig an sich zu binden. Die mathematische Optimierung bietet sich für viele solcher Aufgabenstellungen als hervorragend geeignetes Planungswerkzeug an. Ziel dieses Artikels ist es, ihre Methodik und ihre Anwendung speziell zur Kosten- und Qualitätsoptimierung in Kommunikationsnetzen vorzustellen. Anhand von vier konkreten Planungsaufgaben aus dem Bereich der Festnetzplanung wird aufgezeigt, wie sich komplexe Zusammenhänge in flexiblen mathematischen Modellen abbilden lassen und welche Verfahren zur automatisierten Bearbeitung der Probleme eingesetzt werden können. Die hier vorgestellten Methoden zeichnen sich insbesondere dadurch aus, dass sie neben hochwertigen Lösungen auch eine Qualittsgarantie liefern, mit der sich die Lsungen fundiert bewerten lassen. Die dokumentierten Ergebnisse aus verschiedenen Industrieprojekten belegen die Eignung und Güte der mathematischen Optimierung für die Praxis.
    Keywords: ddc:000
    Language: German
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  • 37
    Publication Date: 2014-02-26
    Description: Dust formation {in brown dwarf atmospheres} is studied by utilizing a model for driven turbulence in the mesoscopic scale regime. We apply a pseudo-spectral method where waves are created and superimposed {within} a {limited} wavenumber interval. The turbulent kinetic energy distribution follows the Kolmogoroff spectrum which is assumed to be the most likely value. Such superimposed, stochastic waves may occur in a convectively active environment. They cause nucleation fronts and nucleation events and thereby initiate the dust formation process which { continues until} all condensible material is consumed. Small disturbances {are found to} have a large impact on the dust forming system. An initially dust-hostile region, which may originally be optically thin, becomes optically thick in a patchy way showing considerable variations in the dust properties during the formation process. The dust appears in lanes and curls as a result of the interaction with waves, i.e. turbulence, which form larger and larger structures with time. Aiming on a physical understanding of the variability of brown dwarfs, related to structure formation in substellar atmospheres, we work out first necessary criteria for small-scale closure models to be applied in macroscopic simulations of dust forming astrophysical systems.
    Keywords: ddc:000
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  • 38
    Publication Date: 2014-02-26
    Description: Substellar atmospheres are observed to be irregularly variable for which the formation of dust clouds is the most promising candidate explanation. The atmospheric gas is convectively unstable and, last but not least, colliding convective cells are seen as cause for a turbulent fluid field. Since dust formation depends on the local properties of the fluid, turbulence influences the dust formation process and may even allow the dust formation in an initially dust-hostile gas. A regime-wise investigation of dust forming substellar atmospheric situations reveals that the largest scales are determined by the interplay between gravitational settling and convective replenishment which results in a dust-stratified atmosphere. The regime of small scales is determined by the interaction of turbulent fluctuations. Resulting lane-like and curled dust distributions combine to larger and larger structures. We compile necessary criteria for a subgrid model in the frame of large scale simulations as result of our study on small scale turbulence in dust forming gases.
    Keywords: ddc:000
    Language: English
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  • 39
    Publication Date: 2019-01-24
    Description: The solution of scattering problems described by the Helmholtz equation on unbounded domains is of importance for a wide variety of applications, for example in electromagnetics and acoustics. An implementation of a solver for scattering problems based on the programming language Matlab is introduced. The solver relies on the finite-element-method and on the perfectly-matched-layer-method, which allows for the simulation of scattering problems on complex geometries surrounded by inhomogeneous exterior domains. This report gives a number of detailed examples and can be understood as a user manual to the freely accessible code of the solver HelmPole.
    Keywords: ddc:000
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  • 40
    Publication Date: 2020-03-09
    Description: \noindent The size of data sets produced on remote supercomputer facilities frequently exceeds the processing capabilities of local visualization workstations. This phenomenon increasingly limits scientists when analyzing results of large-scale scientific simulations. That problem gets even more prominent in scientific collaborations, spanning large virtual organizations, working on common shared sets of data distributed in Grid environments. In the visualization community, this problem is addressed by distributing the visualization pipeline. In particular, early stages of the pipeline are executed on resources closer to the initial (remote) locations of the data sets. \noindent This paper presents an efficient technique for placing the first two stages of the visualization pipeline (data access and data filter) onto remote resources. This is realized by exploiting the ``extended retrieve'' feature of GridFTP for flexible, high performance access to very large HDF5 files. We reduce the number of network transactions for filtering operations by utilizing a server side data processing plugin, and hence reduce latency overhead compared to GridFTP partial file access. The paper further describes the application of hierarchical rendering techniques on remote uniform data sets, which make use of the remote data filtering stage.
    Keywords: ddc:000
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  • 41
    Publication Date: 2014-02-26
    Description: Relaying is a protocol extension for cellular wireless computer networks; in order to utilize radio resources more efficiently, several hops are allowed within one cell. This paper investigates the principle potential of relaying by casting transmission scheduling as a mathematical optimization problem, namely, a linear program. We analyze the throughput gains showing that, irrespective of the concrete scheduling algorithm, performance gains of up to 30\% on average for concrete example networks are achievable.
    Keywords: ddc:000
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  • 42
    Publication Date: 2014-02-26
    Description: We call an edge $e$ of a perfect graph $G$ critical if $G-e$ is imperfect and call $e$ anticritical if $G+e$ is imperfect. The present paper surveys several questions in this context. We ask in which perfect graphs critical and anticritical edges occur and how to detect such edges. The main result by [{\sl Wagler, PhD thesis 2000}] shows that a graph does not admit any critical edge if and only if it is Meyniel. The goal is to order the edges resp.~non-edges of certain perfect graphs s.t. deleting resp.~adding all edges in this order yields a sequence of perfect graphs only. Results of [{\sl Hayward 1985}] and [{\sl Spinrad & Sritharan 1995}] show the existence of such edge orders for weakly triangulated graphs; the line-perfect graphs are precisely these graphs where all edge orders are perfect [{\sl Wagler 2001}]. Such edge orders cannot exist for every subclass of perfect graphs that contains critically resp.~anticritically perfect graphs where deleting resp.~adding an arbitrary edge yields an imperfect graph. We present several examples and properties of such graphs, discuss constructions and characterizations from [{\sl Wagler 1999, Wagler PhD thesis 2000}]. An application of the concept of critically and anticritically perfect graphs is a result due to [{\sl Hougardy & Wagler 2002}] showing that perfectness is an elusive graph property.
    Keywords: ddc:000
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  • 43
    Publication Date: 2014-02-26
    Description: Hasenbusch has proposed splitting the pseudo-fermionic action into two parts, in order to speed-up Hybrid Monte Carlo simulations of QCD. We have tested a different splitting, also using clover-improved Wilson fermions. An additional speed-up between 5 and 20\% over the original proposal was achieved in production runs.
    Keywords: ddc:000
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  • 44
    Publication Date: 2014-11-10
    Description: A set of vertices $S\subseteq V$ is called a safe separator for treewidth, if $S$ is a separator of $G$, and the treewidth of $G$ equals the maximum of the treewidth over all connected components $W$ of $G-S$ of the graph, obtained by making $S$ a clique in the subgraph of $G$, induced by $W\cup S$. We show that such safe separators are a very powerful tool for preprocessing graphs when we want to compute their treewidth. We give several sufficient conditions for separators to be safe, allowing such separators, if existing, to be found in polynomial time. In particular, every minimal separator of size one or two is safe, every minimal separator of size three that does not split off a component with only one vertex is safe, and every minimal separator that is an almost clique is safe; an almost clique is a set of vertices $W$ such that there is a $v\in W$ with $W-\{v\}$ a clique. We report on experiments that show significant reductions of instance sizes for graphs from proba! bilistic networks and frequency assignment.
    Keywords: ddc:000
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  • 45
    Publication Date: 2019-01-29
    Description: A primal-dual interior point method for optimal control problems is considered. The algorithm is directly applied to the infinite dimensional problem. Existence and convergence of the central path are analyzed, and linear convergence of a short step pathfollowing method is established.
    Keywords: ddc:000
    Language: English
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  • 46
    Publication Date: 2014-02-26
    Description: We explicitly construct small triangulations for a number of well-known $3$-dimensional manifolds and give a brief outline of some aspects of the underlying theory of $3$-manifolds and its historical development.
    Keywords: ddc:000
    Language: English
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  • 47
    Publication Date: 2016-06-30
    Description: Peer-to-Peer (P2P) Systeme werden u.a. zur Verwaltung von großen Datenmengen benutzt, die auf verschiedene Rechner verteilt sind. Benutzern soll damit der Zugriff auf Daten innerhalb des Systems leicht ermöglicht werden. Damit in P2P Systemen die Daten effizient verteilt und gesucht werden können, existieren Distributed Hash Tables. Distributed Hash Tables (DHT) sind eine Methode, um globale Informationen persistent speichern zu können. Der Wertebereich der Hashfunktion, welche die zu veröffentlichenden Einträge auf Werte abbildet, wird in Abschnitte aufgeteilt, die einzelnen Knoten zugeteilt werden. Die meisten DHTs haben aber ein Problem bei der Verteilung der Last. Die verschiedenen DHT Systeme beruhen meist auf einem identischen Ansatz der Lastverteilung. Die Last wird nur mit Hilfe einer Hashfunktion verteilt. Es wird davon ausgegangen, dass diese Funktion die Last gleichmäßig verteilt. Im Rahmen dieser Arbeit wurde ein Verfahren zur Last Verteilung entwickelt, simuliert und implementiert. Bei dem Verfahren wird die Last wie bei der Verteilung von Wärme an die Umgebung abgegeben. Es wird mit existierenden Lastbalancierungsalgorithmen verglichen. Mit diesem neuen Verfahren ist es möglich, Last in DHTs besser zu verteilen ohne große Änderungen an den DHTs vorzunehmen. Es wird gezeigt, wie mit dem Verfahren zusätzlich die Fehlertoleranz des P2P Systems erhöht werden kann.
    Description: One of the many uses of Peer-to-Peer (P2P) systems is the administration of large data sets that are distributed across different computers, with the goal of facilitating user access to files within the system. Distributed Hash Tables (DHT) are designed to enable the efficient distribution and search of files, by allowing global information to be persistently stored. The range of values of the hash function (the possible entries in the published hash table) are assigned to individual nodes. Most DHTs, however, have a problem with load distribution. The various DHT systems usually operate by distributing load equally among nodes. Thus the load is distributed using the help of the hash function. One assumes this function distributes the load evenly. In the context of this work a method of distributing load has been developed, simulated and implemented. With this method load is transferred in a fashion analogous to the dissipation of heat into the environment. Comparisons with existing algorithms for load balancing are drawn. With the new procedure it is possible to better distribute load in DHTs without requiring major changes to the DHTs themselves. It is shown that with the procedure the fault tolerance of P2P systems may also be increased.
    Keywords: ddc:000
    Language: German
    Type: masterthesis , doc-type:masterThesis
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  • 48
    Publication Date: 2014-02-26
    Description: The key to molecular conformation dynamics is the direct identification of metastable conformations, which are almost invariant sets of molecular dynamical systems. Once some reversible Markov operator has been discretized, a generalized symmetric stochastic matrix arises. This matrix can be treated by Perron cluster analysis, a rather recent method involving a Perron cluster eigenproblem. The paper presents an improved Perron cluster analysis algorithm, which is more robust than earlier suggestions. Numerical examples are included.
    Keywords: ddc:000
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  • 49
    Publication Date: 2014-11-11
    Description: In this paper, a new shared protection mechanism for meshed optical networks is presented. Significant network design cost reductions can be achieved in comparison to the well-known 1+1 protection scheme. Demand-wise Shared Protection (DSP) bases on the diversification of demand routings and exploits the network connectivity to restrict the number of backup lightpaths needed to provide the desired level of prorection. Computational experiments approve the benefits of the concept DSP for cost efficient optical network designs.
    Keywords: ddc:000
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  • 50
    Publication Date: 2019-05-10
    Description: The correlation of the inner architecture of bone and its functional loading was already stated by Wolff in 1892. Our objective is to demonstrate this interdependence in the case of the human mandible. For this purpose, stress/strain profiles occuring at a human lateral bite were simulated. Additionally, by a combination of computer graphics modules, a three--dimensional volumetric visualization of bone mineral density could be given. Qualitative correspondences between the density profile of the jaw and the simulated stress/strain profiles could be pointed out. In the long run, this might enable the use of the simulation for diagnosis and prognosis. The solution of the underlying partial differential equations describing linear elastic material behaviour was provided by an adaptive finite element method. Estimates of the discretization errors, local grid refinement, and multilevel techniques guaranteed the reliability and efficiency of the method.
    Keywords: ddc:000
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  • 51
    Publication Date: 2014-02-26
    Description: UMTS is a 3rd generation mobile telecommunication system which enables multi-service and multi-bit rate communication going beyond the possibilities of previous systems. The simulator MoDySim models UMTS in great detail. Characteristics of UMTS such as soft hand-over and the interdependency of load and capacity among neighbouring cells are challenges for the parallelisation of such a system. In this paper we explain how the software was parallelised and present performance results of a UMTS simulation for the city of Berlin.
    Keywords: ddc:000
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  • 52
    Publication Date: 2014-02-26
    Description: We report on a numerical reinvestigation of the Aoki phase in lattice QCD with two flavors of Wilson fermions where the parity-flavor symmetry is spontaneously broken. For this purpose the Hybrid Monte Carlo algorithm was used and an explicit symmetry-breaking source term $h\bar{\psi} i \gamma_{5} \tau^{3}\psi$ was added to the Wilson fermion action. The order parameter $\langle\bar{\psi}i\gamma_{5}\tau^{3}\psi\rangle$ was studied at several values of $(\beta,\kappa,h)$ on lattices of sizes $4^4$ to $12^4$. Our largest lattices can be considered as infintely large allowing to extrapolate to $h=0$. The existence of a parity-flavor-breaking phase can be confirmed at $\beta=4.0$ and $\beta=4.3$ while we find no sign of parity-flavor-breaking at $\beta=4.6$ and $\beta=5.0$.
    Keywords: ddc:000
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  • 53
    Publication Date: 2014-02-26
    Description: In this paper we interpret clustering as a mapping of data into a simplex. If the data itself has simplicial struture this mapping becomes linear. Spectral analysis is an often used tool for clustering data. We will show that corresponding singular vectors or eigenvectors comprise simplicial structure. Therefore they lead to a cluster algorithm, which consists of a simple linear mapping. An example for this kind of algorithms is the Perron cluster analysis (PCCA). We have applied it in practice to identify metastable sets of molecular dynamical systems. In contrast to other algorithms, this kind of approach provides an a priori criterion to determine the number of clusters. In this paper we extend the ideas to more general problems like clustering of bipartite graphs.
    Keywords: ddc:000
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  • 54
    Publication Date: 2016-06-09
    Keywords: ddc:000
    Language: German
    Type: masterthesis , doc-type:masterThesis
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  • 55
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    Publication Date: 2019-10-24
    Keywords: ddc:000
    Language: German
    Type: annualzib , doc-type:report
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  • 56
    Publication Date: 2022-04-11
    Description: The Web of the future will provide a huge amount of information. We need better ways for dealing with and managing the information. A qualified semantic annotation of the information plays a key role for the Web of the future. This article gives an overview about the efforts of the mathematical community to build up a distributed and open information and communication system for mathematics: the Math-Net. The Math-Net Initiative has developed metadata schemas for some classes of Web resources which are relevant in mathematics. Math-Net Services process this information and enable the user to efficiently search and access the information.
    Keywords: ddc:000
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  • 57
    Publication Date: 2022-07-07
    Description: In this paper we propose a new finite element realization of the Perfectly Matched Layer method (PML-method). Our approach allows to deal with arbitrary shaped polygonal domains and with certain types of inhomogeneous exterior domains. Among the covered inhomogeneities are open waveguide structures playing an essential role in integrated optics. We give a detailed insight to implementation aspects. Numerical examples show exponential convergence behavior to the exact solution with the thickness of the PML sponge layer.
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  • 58
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Es wird der Versuch unternommen, die Wärmeübergangszahl einer in einem senkrechten Verdampferrohr umlaufenden und siedenden Flüssigkeit in Abhängigkeit von den maßgebenden Einflüssen anzugeben. Zu diesem Zwecke wurden die Rohrwandtemperatur und die Flüssigkeitstemperatur im Rohr gemessen. Für die verwendeten Rohrabmessungen läßt sich die Wärmeübergangszahl durch eine einfache Potenzfunktion wiedergeben. Über sie wird im folgenden berichtet.Die Versuche wurden durchgeführt mit der dankenswerten Unterstützung des Vereins Deutscher Ingenieure durch Zuschüsse aus ERP-Mitteln, ferner der DECHEMA, Frankfurt a. M.; BASF, Ludwigshafen a. Rh.; B. Müller, Weidenau; C. Canzler, Düren, und Deutsche Forschungsgemeinschaft, Bad Godesberg.Meinen beiden Mitarbeitern Dipl.-Ing. R. Baumann und Dipl.-Ing. W. Busch danke ich für ihre Unterstützung bei der Durchführung und Auswertung der Versuche. Ferner waren mit den Versuchen beschäftigt die Herren cand. chem. ing. Hunke Schwarze, Boger, Canzler, Hummel, Ernst u. George.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 59
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Die Verfahrenstechnik benutzt vielfach Methoden der Vakuumtechnik als Hilfsmittel. Ein Hauptproblem bei Verfahren im Druckgebiet unter 10 Torr ist der Transport großer Gas- und Dampfvolumina. Es wird eine Apparatur beschrieben, mit der man unter Ausnutzung dieser Tatsache sehr kleine Gasgehalte in Flüssigkeiten bestimmen kann.
    Additional Material: 10 Ill.
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  • 60
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Es wird eine Auswahl neuer Anwendungen beschrieben, die sich auf die Theorie der Flammenfortpflanzung, auf rheologische Flüssigkeiten, die Strömung geschmolzenen Glases in der Schmelzwanne, die Bewegung des flüssigen Stahls im Konverter, den Einfluß pulsierender Strömung auf die Kohfenstaubverbrennung und die Heizgasströmung bei Eckenfeuerung beziehen. Am Beispiel des Gesetzes von Avogadro und des Wienschen Verschiebungsgesetzes wird schließlich gezeigt, daß die Bedeutung der Ähnlichkeitstheorie wesentlich tiefer als nur in der Anwendung liegt.
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  • 61
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 51-55 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 5 Ill.
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  • 62
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Es wurde die Wärmeleitzahl verschiedener Flüssigkeiten in einer näher beschriebenen Apparatur untersucht, in der gleichzeitig ein hohes elektrisches Feld angelegt werden konnte. Es zeigte sich, daß das Wärmeleitvermögen unter dem Einfluß des Gleichspannungsfeldes auf das 2- bis 5fache des normalen Wertes ansteigt. Wie Schlierenaufnahmen beweisen, wird dieser mit steigender Temperatur zunehmende Effekt durch Konvektionsbewegungen der Flüssigkeiten hervorgerufen.
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  • 63
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 56-56 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 64
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 72-74 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Technische Kornverteilungen werden meist mit Hilfe der Rosin-Rammler-Sperling-Gleichung in einem doppelt-logarithmisch geteilten Körnungsnetz dargestellt. Im folgenden wird gezeigt, daß diese Verteilungsfunktion unter bestimmten Bedingungen auch Normalverteilungen erfaßt. Diese Tatsache erweitert den Anwendungsbereich der RRS-Gleichung und läßt manche Darstellungen im Körnungsnetz sinnfälliger deuten.
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  • 65
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 81-83 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Für elektrophoretische Trennungen von Substanzgemischen (Eiweißhydrolysaten, Gerbstoffgemischen) wurde ein Stromversorgungsgerät entwickelt, welches elektronisch - stabilisierte Gleichspannungen von 0 bis 1500 V liefert.
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  • 66
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Der Transport von Gasen und Dämpfen in Papier wird unter Verwendung einer Strömungsmethode untersucht. Die für die Luftdurchlässigkeit maßgebenden Faktoren können auf bekannte Gesetze zurückgeführt werden, so daß man die Durchlässigkeit für jedes permanente Gas aus einer Messung der Luftdurchlässigkeit für einen beliebigen mittleren Druck berechnen kann.  -  Der Wasserdampftransport in Papier und Folien kann, sofern er nicht nach den bekannten Gesetzen durch das freie Porenvolumen vonstatten geht, unter Berücksichtigung von Adsorptionsisothermen quantitativ erfaßt werden. Aus den theoretischen und experimentellen Untersuchungen folgt, daß das Oberflächenkonzentrationsgefälle sowie die Oberflächenkonzentration selbst von maßgeblichem Einfluß sind. Es wird damit die Möglichkeit aufgezeigt, Aussagen über die Wasserdampfdurchlässigkeit unter allen praktisch vorkommenden klimatischen Bedingungen zu machen.
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  • 67
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 97-100 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Außer der für die Selbstzündung von Gasen und Dämpfen maßgebenden Temperatur, dem „Gaszündpunkt“, findet man bei vielen brennbaren chemischen Substanzen noch einen  -  meist sehr viel niedriger liegenden  -  „Tropfzündpunkt“, bei dem sich die flüssige Phase der betreffenden Substanz beim Auftreffen auf eine heiße Fläche entzündet. Die Merkmale der beiden Zündpunkte werden einander gegenübergestellt und Folgerungen für explosionsgefährdete Räume gezogen; weiterhin wird eine empirische Formel für die Berechnung des Tropfzündpunktes in einzelnen chemischen Gruppen angegeben.
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  • 68
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 113-113 
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    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 69
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 101-106 
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    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 70
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 114-116 
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    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 71
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 118-120 
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    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 72
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    Chemie Ingenieur Technik - CIT 26 (1954) 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 73
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 129-131 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Es wird ein Verfahren und die zugehörige Apparatur für die kontinuierliche Kurzweg-Fraktionierung beschrieben. Die Apparatur ist aus kontinuierlich abgestuften Elementen der einfachen Destillation zusammengesetzt und hat als wesentlichsten Bestandteil eine Heizwanne mit einem Temperaturgradienten. Die Leistungsfähigkeit des Verfahrens wird am Beispiel eines Zweistoffgemisches mit einer gewöhnlichen Fraktionierung aus einem Claisenkolben verglichen.
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  • 74
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An einigen Beispielen wird erläutert, wie man durch strömungstechnische Maßnahmen in Trocknern eine gleichmäßige Trocknung und geringe Verluste an Strömungsenergie erreichen kann. Ferner wird dargelegt, wie sich die Strömung vor und hinter Lüftern sowie in Querschnittsänderungen und Umlenkungen ordnen und lenken läßt, und wie man die Luft auf mehrere Kanäle genügend gleichmäßig verteilen kann.
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  • 75
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 157-163 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 76
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Es werden die Bedingungen für die Entstehung eines Quertriebs (Auftriebs), der von der Magnus-Kraft herrührt, beschrieben und zunächst an sedimentierenden Teilchenschüttungen verschiedener Größe und verschiedenen Materials geprüft. Dabei wird die Zahl der sedimentierenden Teilchen im wandnahen Bereich mit der im achsennahen Bereich verglichen. Es ergab sich eine Anreicherung der Teilchen im achsennahen Bereich bis zu 25%. Bei sedimentierenden Schüttungen mit Teilchen zweier Größenklassen reichern sich dagegen die größeren im Strömungsmaximum bis zu 40% an.Im II. Teil dieser Arbeit wird die Wirkung der Magnus - Kraft in strömenden Elektrolytlösungen und Gasgemischen erörtert.
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  • 77
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 163-168 
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    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 8 Ill.
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  • 78
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 171-172 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 79
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 175-176 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 80
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 236-236 
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    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 81
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 237-238 
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    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 82
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 239-244 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 83
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 259-264 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Wenn man die Meßwerte für die reduzierte (d. h. auf den kritischen Zustand bezogene) Dichte aesättigter Flüssigkeiten in Abhängigkeit von der reduzierten Temperatur aufträgt, so erhält man, ähnlich wie beim Dampfdruck, keine einheitliche Kurve, wie es das Theorem der übereinstimmenden Zustände in der üblichen Fassung verlangt, sondern eine einparametrige Kurvenschar. Für diese wird eine der Erfahrung angepaßte Gleichung aufgestellt, die den auch für die Dampfdruckkurve maßgebenden „kritischen Parameter“ enthält. Durch Einführung der Nullpunktsdichte statt der kritischen Dichte ergibt sich eine vom kritischen Parameter weitgehend unabhängige Funktion, die tabellarisch wiedergegeben wird und deren Anwendungsmöglichkeiten diskutiert und an Hand von Zahlenbeispielen erläutert werden. Das auf den absoluten Nullpunkt extrapolierte Molvolumen zeigt bei Kohlenwasserstoffen präzise Zusammenhänge mit der Struktur der Molekeln. Zur Abschätzung des kritischen Volumens organischer Verbindungen wird eine Zusammenstellung der Meßwerte und ein System von Substitutionsinkrementen angegeben.
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  • 84
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 281-284 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Nach einer grundsätzlichen Betrachtung des Ausmauerungs-Problems werden allgemeine Formeln zur Ermittlung der Spannungen und Dehnungen angegeben, die in einer Kugelschale unter dem Einfluß des Druckes und eines Temperaturgefälles auftreten. Hieraus wird für den ausgemauerten, kugelförmigen Behälter eine Bedingung hergeleitet, deren Erfüllung gewährleistet, daß sich das Mauerwerk vom Eisenmantel nicht ablöst. Die Verwendung von quellendem Kitt bringt Vorteile. Abschließend werden die im Mauerwerk und im Eisenmantel auftretenden Spannungen ermittelt.
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  • 85
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    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Im I. Teil wurde der Quertrieb in sedimentierenden Teilchenschüttungen untersucht. Nachfolgend wird gezeigt, daß auch in laminar strömenden wäßrigen Elektrolytlösungen ein Quertrieb entsteht, infolgedessen die größeren lonen bevorzugt in den Bereich höherer Strömungsgeschwindigkeit, also in den achsennahen Bereich diffundieren. Diese Versuche lassen Schlüsse auf die lonenhydratation zu. Außerdem wurde der Quertrieb in laminar strömender Luft mit sehr hoher Strömungsgeschwindigkeit, z. B. im Wirbelrohr, beobachtet. Auch dort ergibt sich für die größeren Molekeln eine Anreicherung im achsennahen Bereich, d. h. eine O2-Anreicherung im Kaltgasanteil. Abschließend werden die Ergebnisse in den einzelnen Aggregatzuständen miteinander verglichen.
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  • 86
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 287-289 
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    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 8 Ill.
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  • 87
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 291-291 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 88
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 349-349 
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    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 2 Ill.
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  • 89
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 413-418 
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    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 11 Ill.
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  • 90
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 425-428 
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    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
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  • 91
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 533-538 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Für verschiedene Verfahren der chemischen Technik, insbesondere bei der Glasherstellung und in der Eisenindustrie, werden Werkstoffe gebraucht, die bei Temperaturen von etwa 1500 °C und darüber beständig sind. Hierfür kommen vor allem keramische Materialien in Betracht. Es werden daher im folgenden Baustoffe und Rohstoffe behandelt, welche zur Herstellung von Silica-, Sillimanit-, Korund-, Magnesit-, Chrommagnesit-, Dolomit-, Siliciumcarbid- und Zirkon-Steinen dienen. Anwendungsgrenzen, Wärmedehnung, Temperaturwechselbeständigkeit, Wärmeleitung und die chemische Beständigkeit dieser Materialien bei Temperaturen um 1500 °C werden besprochen.
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  • 92
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 548-554 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Es wird ein Überblick über die Eigenschaften und die Verwendungsmöglichkeiten von Kunststoff-Folien und kunststoffbeschichteten Papieren und Pappen als Verpackungswerkstoffe in der chemischen Industrie gegeben, wobei deren Vor- und Nachteile einander gegenübergestellt werden.
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 543-547 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Der Packstoffverbrauch entfällt zu einem großen Teil auf Aluminiumfolien, vor allem in der Nahrungsund Genußmittel-Industrie. In der chemischen und pharmazeutischen Industrie dagegen ist er verhältnismäßig gering. Im folgenden wird ein Überblick über die für Verpackungszwecke wichtigen Eigenschaften von Aluminiumfolien gegeben unter besonderer Berücksichtigung der Möglichkeiten zu ihrer Veredelung.
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 555-561 
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    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Die Badische Anilin- & Soda-Fabrik A.G. hat gemeinsam mit der Firma Dr. F. Raschig GmbH., Ludwigshafen am Rhein, für die chemische Technik den neuen Werkstoff BascodurEingetragenes Warenzeichen der BASF. entwickelt, der geeignet ist, Lücken innerhalb der heute bekannten nichtmetallischen Apparatebaustoffe zu schließen. Nach kurzen Angaben über Eigenschaften und Verarbeitung des Materials werden an Hand zahlreicher Bilder insbesondere Anwendungsbeispiele aus dem chemischen Apparatebau besprochen.
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 568-575 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 643-643 
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    Source: Wiley InterScience Backfile Collection 1832-2000
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    Chemie Ingenieur Technik - CIT 26 (1954), S. 647-648 
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    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 98
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 26 (1954), S. 667-669 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Im In- und Ausland nimmt die Anwendung dimensionsloser Kennzahlen auf dem Gebiet der Wärmeübertragung immer mehr zu. Diese Entwicklung läßt sich nicht durch den Einwand aufhalten, daß dimensionslose Darstellungen unanschaulich seien, denn in Wirklichkeit lassen sich alle wichtigen Kennzahlen als Verhältnisse gleichartiger Größen in anschaulicher Form darstellen und bei der Berechnung von Wärmeübertragern verwenden.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
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  • 99
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Das Problem der automatischen Zählung und Größenanalyse mikroskopischer Teilchen wird besonders in den USA und England seit einigen Jahren intensiv bearbeitet, während in Deutschland auf diesem Gebiet praktisch noch kein Schrifttum vorliegt. Es sollen deshalb hier der Stand der Entwicklung und die bekanntgewordenen Geräte diskutiert werden. Allen beschriebenen Methoden ist das Ziel gemeinsam, jedes Teilchen einzeln zu messen und zu zählen. Dies führt zwangsläufig zu elektronischen Mitteln, da nur diese hinreichende Zählgeschwindigkeiten ermöglichen. -  Im ersten Teil der Arbeit werden Verfahren zur automatischen Größenanalyse von Aerosolen behandeit, während im zweiten Teil automatische Methoden zur Auszählung von mikroskopischen Präparaten und Mikrophotographien beschrieben werden.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 100
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemie Ingenieur Technik - CIT 26 (1954), S. 673-676 
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Nachdem im ersten Teil das Anheizen flüssigkeitsgefüllter Behälter behandelt wurde, werden nun der Temperaturverlauf und die Wärmeverluste beim Abkühlen derartiger Behälter berechnet. Dabei wird sowohl der Abkühlungsvorgang aus dem stationären Zustand heraus behandelt als auch der Fall, daß vor Erreichen des stationären Zustands die Wärmezufuhr im Innern des Behälters aufhört. Die Resultate für den Abkühlungsvorgang lassen sich ohne neue Schwierigkeiten aus den schon in Teil I gewonnenen Ergebnissen für das Anheizen herleiten. Es wird ferner das Anheizen und die Abkühlung gasgefüllter Behälter untersucht. Zwei Beispiele zeigen die Anwendung der gewonnenen Gleichungen und der daraus entwickelten Diagramme.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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