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  • 2000-2004  (218)
  • 1890-1899
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  • 2003  (57)
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  • ddc:000  (117)
  • Analytical Chemistry and Spectroscopy  (101)
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  • 2000-2004  (218)
  • 1890-1899
  • 1810-1819
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  • 1
    Publikationsdatum: 2014-11-10
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 2
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 3
    Publikationsdatum: 2014-11-10
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 4
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 5
    Publikationsdatum: 2020-03-09
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 6
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    Unbekannt
    Publikationsdatum: 2020-03-09
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 7
    Publikationsdatum: 2014-11-10
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 8
    Publikationsdatum: 2020-11-13
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 9
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    Publikationsdatum: 2020-08-05
    Beschreibung: This article investigates a certain class of combinatorial packing problems and some polyhedral relations between such problems and the set packing problem.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 10
    Publikationsdatum: 2014-02-26
    Beschreibung: We construct non-constructible simplicial $d$-spheres with $d+10$ vertices and non-constructible, non-realizable simplicial $d$-balls with $d+9$ vertices for $d\geq 3$.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 11
    Publikationsdatum: 2014-11-11
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 12
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 13
    Publikationsdatum: 2020-11-13
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 14
    Publikationsdatum: 2019-01-29
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 15
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 16
    Publikationsdatum: 2014-11-11
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 17
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 18
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    Publikationsdatum: 2021-02-01
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 19
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    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 20
    Publikationsdatum: 2014-02-26
    Beschreibung: Collection of abstracts of the Korean-German Bilateral Symposium on Scientific Computing, Berlin January 15/16, 2004
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 21
    Publikationsdatum: 2014-11-11
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Deutsch
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  • 22
    Publikationsdatum: 2020-08-05
    Beschreibung: 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.
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    Sprache: Englisch
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  • 23
    Publikationsdatum: 2020-02-11
    Beschreibung: 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.
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    Sprache: Englisch
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  • 24
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
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    Sprache: Englisch
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  • 25
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
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    Sprache: Englisch
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  • 26
    Publikationsdatum: 2014-09-30
    Beschreibung: 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.
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    Sprache: Englisch
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  • 27
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
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    Sprache: Englisch
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  • 28
    Publikationsdatum: 2020-02-11
    Beschreibung: 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.
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    Sprache: Deutsch
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  • 29
    Publikationsdatum: 2020-11-13
    Beschreibung: 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}}
    Schlagwort(e): ddc:000
    Sprache: Deutsch
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  • 30
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    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 31
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    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Deutsch
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  • 32
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.).
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 33
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 34
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    Publikationsdatum: 2020-02-11
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 35
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 36
    Publikationsdatum: 2014-11-11
    Beschreibung: 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.
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  • 37
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 38
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 39
    Publikationsdatum: 2019-01-24
    Beschreibung: 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.
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    Sprache: Englisch
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  • 40
    Publikationsdatum: 2020-03-09
    Beschreibung: \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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 41
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 42
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 43
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 44
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    Publikationsdatum: 2014-11-10
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 45
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    Publikationsdatum: 2019-01-29
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 46
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 47
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    Publikationsdatum: 2016-06-30
    Beschreibung: 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.
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Deutsch
    Materialart: masterthesis , doc-type:masterThesis
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  • 48
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
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    Sprache: Englisch
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  • 49
    Publikationsdatum: 2014-11-11
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 50
    Publikationsdatum: 2019-05-10
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 51
    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 52
    Publikationsdatum: 2014-02-26
    Beschreibung: 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 $\beta=5.0$.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 53
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    Publikationsdatum: 2014-02-26
    Beschreibung: 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.
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    Sprache: Englisch
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  • 54
    Publikationsdatum: 2016-06-09
    Schlagwort(e): ddc:000
    Sprache: Deutsch
    Materialart: masterthesis , doc-type:masterThesis
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  • 55
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    Publikationsdatum: 2019-10-24
    Schlagwort(e): ddc:000
    Sprache: Deutsch
    Materialart: annualzib , doc-type:report
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  • 56
    Publikationsdatum: 2022-04-11
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
    Format: application/postscript
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  • 57
    Publikationsdatum: 2022-07-07
    Beschreibung: 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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
    Format: application/postscript
    Format: application/pdf
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  • 58
    ISSN: 0935-6304
    Schlagwort(e): Capillary HPLC ; gradient elution ; temperature programming ; phenolic compounds ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---This paper describes a liquid chromatographic method using a reversed phase capillary column coupled to an UV detector for the quantitation of thirteen pollutant phenols. Chromatographic separation was carried out with gradient elution at 25.0 ± 0.1°C. The two major anisocratic elution modes (gradient elution and temperature programming) were evaluated. The detection limit range was 10-81 pg (100 nL injected). The chromatographic method combined with liquid-liquid extraction was applied to analysis of these compounds in river water. Recoveries of 75-103% were achieved for most of them.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 59
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 389-392 
    ISSN: 0935-6304
    Schlagwort(e): Capillary SFC ; zinc dialkyldithiophosphates ; lubricating oils ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 60
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 393-396 
    ISSN: 0935-6304
    Schlagwort(e): Supercritical fluid chromatography (SFC) ; micropacked capillary columns ; waxes ; restoring ; objects of art ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 61
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 379-385 
    ISSN: 0935-6304
    Schlagwort(e): Aroma ; “lulo del Chocó” ; Solanum topiro ; volatiles ; glycosidically bound volatiles ; glycoside TFA derivatives ; enantioselective gas chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---The volatile constituents of lulo del Chocó (Solanum topiro) fruit pulp obtained by liquid-liquid extraction were analyzed by capillary GC and capillary GC-MS. In total, 30 components were identified with methyl salicylate, hexadecanoic acid, hexanal, guaiacol, ethyl butanoate, and ethyl acetate being the major components. Chirospecific MDGC analysis revealed the predominance of (R)-ethyl-3-hydroxybutanoate (ee 40%) and the presence of racemic mixtures both of δ-octalactone and of δ-decalactone. For γ-hexalactone, γ-octalactone, and γ-decalactone enantiomeric distributions of 22.4 : 77.6, 22.9 : 77.1, and 20.0 : 80.0, (R) : (S), respectively, were determined. Glycosidically bound aroma compounds were identified by capillary GC and capillary GC-MS after isolation of the glycosidic fraction obtained by Amberlite XAD-2 adsorption and methanol elution followed by hydrolysis with a commercial pectinase enzyme. In total 13 bound aroma compounds (aglycones) were identified. These aglycones mainly consisted of compounds exhibiting aromatic structures. Additionally, with the aid of capillary GC and capillary GC-MS (EI and NCI) of trifluoroacetylated derivatives we identified eight glucosides: the novel 3,6-epoxy-7-megastigmen-5,9-diol β-D-glucopyranoside and the hexyl, benzyl, linalyl oxide (furanic), 2-phenylethyl, vomifolyl (isomer 1), (6S,9R)-vomifolyl, and scopoletin β-D-glucopyranosides.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 62
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 409-412 
    ISSN: 0935-6304
    Schlagwort(e): Cyclodextrin ; capillary electrophoresis ; system peak ; CHES 1 ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Using a running buffer containing cyclodextrins (CDs) and 2-[N-cyclohexylamino]-ethanesulfonic acid (CHES), positive system peaks were observed in the analysis of a ganglioside mixture by CE-UV. These system peaks were related to CDs in the running buffer because these peaks were also detected when a plug of solution devoid of CDs but having the same CHES concentration and pH as the running buffer was injected. Neutral CDs were separated owing to the formation of inclusion complexes with the anionic CHES ion. One possible explanation for the positive system peaks is that the anionic CD-CHES inclusion complex is displaced by co-ions with higher UV absorptivity.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 63
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 565-566 
    ISSN: 0935-6304
    Schlagwort(e): Liquid chromatography ; zinc dithiocarbamate ; vulcanization accelerator ; rubber gloves ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 64
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 603-608 
    ISSN: 0935-6304
    Schlagwort(e): Solvation parameter model ; ystem constants for poly(dimethyldiphenylsiloxane) HP-5 and poly(ethylene glycol) HP-INNOWax stationary phases ; temperature ; molecular interaction ; retention models ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---No abstract
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 65
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 561-564 
    ISSN: 0935-6304
    Schlagwort(e): Retention factors ; Cinnamomi ramulus ; high-performance liquid chromatography ; capillary electrophoresis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---No abstract
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 66
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 590-594 
    ISSN: 0935-6304
    Schlagwort(e): Ion chromatography ; graphitic carbon stationary phases ; anions ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---Inorganic anions could be separated on porous graphitic carbon stationary phases in ion chromatography. Ion exchange between eluent anions and sample anions on the stationary phase was confirmed by the retention behavior and the possibility of indirect photometric detection. The elution order of anions was different from that observed for commercially available anion exchangers. Chloride, nitrate, and sulfate contained in tap water could be determined in 7 min.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 67
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 485-488 
    ISSN: 0935-6304
    Schlagwort(e): Pyrethroids ; solid-phase microextraction ; water analysis ; temperature ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---Synthetic pyrethroids are increasingly being used for insect control on field crops because of their advantageous environmental properties such as short field life, broad spectrum of insecticide activity, and relatively low mammalian toxicity. In the present work, experimental conditions were optimized for trace analysis of pyrethroids in water by using solid-phase microextraction followed by capillary gas chromatography. Effects of temperature, SPME-fiber diameter, and matrix were studied. SPME used off-line with a gas chromatograph electron-capture detection (GC-ECD) showed a linear response over a wide concentration range. Our results showed a strong temperature effect on pyrethroid extraction yield. The detection limit after 5 min of SPME-fiber exposure to the samples changed from 1 ppb (at 30°C) to 0.1 ppt (at 90°C), which is a 10000 increase in pyrethroid detection. The standard deviations of the analyte peak area ratios were typically in the range of 1-7% at 30°C and of 3 to 15% at 90°C. Best conditions for pyrethroids analysis were achieved using high temperature solution and a 100 μm polydimethylsiloxane fiber. No matrix (river water) influence was observed on detection of the investigated pyrethroids.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 68
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 19-26 
    ISSN: 0935-6304
    Schlagwort(e): Microfabrication ; monolith ; electrochromatography ; peptides ; reactive ion etching ; reversed phase ; nanocolumns ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Monolith columns are generally fabricated by polymerization of monomers within a column. This paper reviews an alternative strategy in which the bed is microfabricated in an inorganic material by ablation. Channels of 1.5 μm width and 10 μm depth were sculpted in quartz by deep reaction ion etching. Using this approach chromatographic beds were constructed in which cubic support structures were created and arranged in rows to mimic particles in a conventional column. Beds ranging from hundreds of thousands to millions of “particles” with volumes of 15 nL to 15 μL were produced. Columns that had been derivatized with an octadecyl silane stationary phase were used to separate both low molecular weight analytes and peptides in the CEC mode. Plate height in the CEC mode was 1.2 μm at maximum efficiency.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 69
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 39-43 
    ISSN: 0935-6304
    Schlagwort(e): Monoliths ; CIM® monolithic column ; dynamic binding capacity ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The characterization of CIM® DEAE monolithic columns in terms of dynamic binding capacity is presented in this paper. Breakthrough experiments were performed for capacity determination. Bovine serum albumin (BSA) was used as a model protein. It is shown that CIM® monolithic columns have good batch-to-batch reproducibility as well as long-term stability. The experiments performed under different linear velocities demonstrated that the dynamic capacity is unaffected at least up to a linear velocity of 2450 cm/h. Furthermore, the breakthrough curve slope is constant, indicating that the capacity would remain constant at even higher linear velocities. The adsorption isotherm of BSA dissolved in 20 mM Tris-HCl buffer shows a constant capacity of around 30 mg/mL of support down to a concentration of 20 μg/mL. The capacity is substantially influenced by the ionic strength; however, 20% of the maximal capacity is still preserved at 0.3 M NaCl.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 70
    ISSN: 0935-6304
    Schlagwort(e): Monolith ; factor VIII ; affinity chromatography ; combinatorial peptide library ; peptide synthesis ; recombinant proteins ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: FVIII is a very complex molecule of great therapeutic significance. It is purified by a sequence of chromatographic steps including immunoaffinity chromatography. A peptide affinity chromatography method has been developed using peptides derived from a combinatorial library. Spot technology using cellulose sheets has been applied for this purpose. The dual positional scanning strategy was used for identification of the amino acids in random positions. Approximately 5000 possible candidates found in the first screening round were reduced to a panel of 36. Six candidates have been selected empirically. Five peptides seem to be directed against the light chain of FVIII, one peptide seems to be directed against the heavy chain. The peptides have been immobilized on conventional beaded material and CIM polymethacrylate monoliths. Much better performance with respect to capacity and selectivity has been observed with the monolithic material. Exposure of the ligand and its ensuing accessibility are responsible for these properties.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 71
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 67-72 
    ISSN: 0935-6304
    Schlagwort(e): Capillary electrochromatography ; monolithic column ; electroosmotic flow ; retention mechanism ; aromatic compound ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A new kind of monolithic capillary electrochromatography column with poly(styrene-co-divinylbenzene-co-methacrylic acid) as the stationary phase has been developed. The stationary phase was found to be porous by scanning electron microscopy and the composition of the continuous bed was proved by IR spectroscopy to be the ternary polymer of styrene, divinylbenzene, and methacrylic acid. The effects of operating parameters, such as voltage, electrolyte, and organic modifier concentration in the mobile phase on electroosmotic flow were studied systematically. The retention mechanism of neutral solutes on such a column proved to be similar to that of reversed-phase high performance liquid chromatography. In addition, fast analyses of phenols, chlorobenzenes, anilines, isomeric compounds of phenylenediamine and alkylbenzenes within 4.5 min were achieved.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 72
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 73-80 
    ISSN: 0935-6304
    Schlagwort(e): Continuous-bed ; sol-gel ; octadecylsilica ; mixed-mode stationary phase ; large-pore ; column technology ; capillary electrochromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---Sol-gel bonded packing materials in continuous-bed columns have been prepared for capillary electrochromatography (CEC). Three packing materials were investigated: small-pore Spherisorb ODS1 (3 μm, 80 Å) with octadecyl as stationary phase, small-pore mixed-mode Spherisorb ODS/SCX (3 μm, 80 Å) with octadecyl and propyl sulfonic acid as stationary phases, and large-pore Nucleosil ODS (7 μm, 1 400 Å) with octadecyl as stationary phase. The characteristics of these columns were compared in terms of electroosmotic flow, efficiency, inertness, and retention factors. In contrast to columns containing sol-gel bonded ODS, columns containing sol-gel bonded mixed-mode ODS/SCX generated nearly pH independent electroosmotic flow (EOF) over pH 2-9. Columns containing sol-gel bonded large-pore ODS produced nearly three times lower reduced plate height than those containing small-pore ODS. Efficiencies of 220,000 plates per meter and 175,000 plates per meter were obtained from columns containing sol-gel bonded 7 μm, 1 400 Å ODS and columns containing sol-gel bonded 3 μm, 80 Å ODS, respectively, which are among the highest reported efficiencies for continuous-bed columns. In CEC, over one million plates per meter and pH independent EOF are expected from continuous-bed columns containing sol-gel bonded 1.5 μm particles with large pores and mixed-mode stationary phases.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
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  • 73
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 81-88 
    ISSN: 0935-6304
    Schlagwort(e): Monolithic chromatography columns ; capillary electrochromatography (CEC) ; micro high performance liquid chromatography ; sol-gel based columns for chromatography ; fritless capillary chromatography columns ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---Particle-loaded (3 μm, octadecylsilica) monolithic sol-gel columns have been prepared and selected characteristics measured. Several electrical properties may be calculated from simple current measurements in the column as a whole. Resistivity in the packed segment is approximately three times that in open segments, resulting in a 60% increase in field strength in the packed regions compared to the capillary with no packing. The surprisingly high specific permeability of these sol-gel columns is characteristic of 8-μm particles, which allows their operation in the microLC mode at pressures as low as 69 kPa where their efficiency is about 50,000 plates per meter and in the CEC mode where efficiency is about 106,000 plates per meter at 5 kV. There is a relatively rapid loss of efficiency with increasing linear velocity beyond 0.2 mm/s in microLC mode, which may be due to additional diffusion processes in the inter-particulate voids. A rapid loss of efficiency above 0.5 mm/s is also observed in the CEC mode, for the same reasons. Chromatographic retention behavior in either separation mode is characteristic of conventional octadecylsilica particles, indicating that analytes have significant access to the surface within the pores of the immobilized bonded phase.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 74
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 89-92 
    ISSN: 0935-6304
    Schlagwort(e): Capillary electrochromatography ; packed columns ; fritless columns ; stationary phases ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---Fritless packed silica gel columns were prepared using sol-gel technology. A part of a 75 μm i.d. fused silica capillary was filled with a mixture of tetramethoxysilane and poly(ethylene glycol). After gelling at 40°C and heating at 300°C, the resultant silica gel was derivatized with dimethyloctadecylchlorosilane. A scanning electron micrograph of a cross-section of the capillary column showed that the gel took the form of a spherical particle aggregate and adhered to the column inner wall. The column performance was evaluated for electrochromatography using acetonitrile-50 mM HEPES buffer (pH 6.6) (60/40 or 40/60, v/v) as the mobile phase. An electroosmotic flow of 1.0 mm/s was generated with (60/40, v/v) acetonitrile/HEPES buffer at a field strength of 546 V/cm. Using a sol-gel-derived packed column at an electroosmotic flow of 0.5 mm/s, efficiencies of up to 1.1×105 plates/m were obtained for retained solutes.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 75
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 93-99 
    ISSN: 0935-6304
    Schlagwort(e): HPLC ; monolithic column ; silica rod column ; fast separations ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---The application of a new silica-based, monolithic-type HPLC-column for fast separations is presented. The column is prepared according to a new sol-gel process, which is based on the hydrolysis and polycondensation of alkoxysilanes in the presence of water soluble polymers. The method leads to “rods” made of a single piece of porous silica with a defined pore structure, i. e. macro- and mesopores. The main feature of silica rod columns is a higher total porosity, about 15% higher than of conventional particulate HPLC columns. The resulting column pressure drop is therefore much lower, allowing operation at higher flow rates including flow gradients. Consequently, HPLC analysis can be performed much faster, as it is demonstrated by various applications.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
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  • 76
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 3-18 
    ISSN: 0935-6304
    Schlagwort(e): Capillary electrochromatography ; monolithic columns ; synthetic polymers ; stationary phase ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Monolithic materials have quickly become a well-established stationary phase format in the field of capillary electrochromatography (CEC). Both the simplicity of their in situ preparation method and the large variety of readily available chemistries make the monolithic separation media an attractive alternative to capillary columns packed with particulate materials. This review summarizes the contributions of numerous groups working in this rapidly growing area, with a focus on monolithic capillary columns prepared from synthetic polymers. Various approaches employed for the preparation of the monoliths are detailed, and where available, the material properties of the resulting monolithic capillary columns are shown. Their chromatographic performance is demonstrated by numerous separations of different analyte mixtures in variety of modes. Although detailed studies of the effect of polymer properties on the analytical performance of monolithic capillaries remain scarce at this early stage of their development, this review also discusses some important relationships such as the effect of pore size on the separation performance in more detail.
    Zusätzliches Material: 16 Ill.
    Materialart: Digitale Medien
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  • 77
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 100-105 
    ISSN: 0935-6304
    Schlagwort(e): Preparative chromatography ; silica monoliths ; PrepROD™ ; productivity ; SMB-chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---The use of monolithic silica sorbents for the isolation of substances by preparative liquid chromatography is demonstrated. Preparative liquid chromatography is recognized as a valuable technique for the isolation and purification of substances in the pharmaceutical and fine chemicals industry. The system technology has meanwhile reached a high standard, and the greatest future improvements are expected to arise from new and improved adsorbents. Monolithic silica sorbents offer some unique features for preparative liquid chromatography. They exhibit high efficiencies even at high flow rates due to their fast convective mass transfer and can therefore be used at very high mobile phase velocities, leading to high productivity and hence to maximum process economy. The benefits of this new type of adsorbent are illustrated for an example in batch-chromatographic mode and an example using the continuous simulated moving bed (SMB) technology.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 78
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 106-110 
    ISSN: 0935-6304
    Schlagwort(e): Silica ; monolithic column ; aging ; mesopores ; pore size distribution ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---Mesopore formation in silica gels having continuous macropores has been investigated. The macroporous wet silica gel prepared by the sol-gel process including phase separation was aged in a basic solvent making use of hydrolysis of urea in a closed condition. The mesopore structure was finally obtained by subsequent evaporation drying of solvent and heat-treatment at 600°C for 2 h. The dissolution-reprecipitation kinetics at the interfaces between wet gel skeletons and an external solvent affected the size and volume of pores formed within the skeletons. Below 120°C, mesopores suitable for various chromatographic applications have been formed typically within 24 h. On the other hand, at 200°C, the pore size attained the macropore dimensions (〉50 nm), and the whole macroporous morphology was significantly modified.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 79
    ISSN: 0935-6304
    Schlagwort(e): Monolithic column ; silica monolith ; HPLC ; capillary liquid chromatography ; capillary electrochromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---Two types of monolithic silica columns derivatized to form an ODS phase, one prepared in a fused silica capillary (SR-FS) and the other prepared in a mold and clad with an engineering plastic (poly-ether-ether-ketone) (SR-PEEK), were evaluated. The column efficiency and pressure drop were compared with those of a column packed with 5-μm ODS-silica particles and of an ODS-silica monolith prepared in a mold and wrapped with PTFE tubing (SR-PTFE). SR-FS gave a lower pressure drop than a column packed with 5-μm particles by a factor of 20, and a plate height of 20 μm at a linear velocity below 1 mm/s. SR-PEEK showed higher flow-resistance than the other monolithic silica columns, but they still showed a minimum plate height of 8-10 μm and a lower pressure drop than popular commercial columns packed with 5-μm particles. The evaluation of SR-FS columns in a CEC mode showed much higher efficiency than in a pressure-driven mode.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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  • 80
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 119-126 
    ISSN: 0935-6304
    Schlagwort(e): Gas chromatography ; retention volume ; real gas carrier ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The problem of the calculation and interpretation of the net retention volume with a real gas as carrier is revisited. The properties of the carrier are described by a first order virial equation of state. The net retention volume of a solute is related to the mean flow rate of the carrier, therefore determination of the mean flow rate of a real gas carrier is reviewed. It is shown that the mean flow rate cannot be calculated from the mean column pressure. With a real gas carrier the local capacity factor depends on the local pressure of the real gas. The basic relationship between the net retention volume and the function describing this pressure dependence is also reviewed. Precise formulae as well as practical approximations are presented for the calculation of the mean flow rate, of the mean column pressure, and of a representative pressure related to the mean capacity factor.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
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  • 81
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 127-130 
    ISSN: 0935-6304
    Schlagwort(e): Chemiluminescence ; diol compound ; oxalate ; post-column reaction ; ruthenium complex ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---In this paper we propose a new post-column detection method for polyols containing 1,2-diol, 1,3-diol, and saccharides. The polyols are oxidized in a photochemical reactor to yield oxalate with subsequent chemiluminescence detection using [Ru(III)(bpy)3]3+. A mixing solution of eluate and oxidizing reagent is delivered to a reaction coil, which is then irradiated with ultraviolet light to promote the oxidation reaction. The detection limits for 1,2-ethanediol (ethylene glycol) and 1,3-propanediol were 38 pmol and 23 pmol, respectively.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 82
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 131-137 
    ISSN: 0935-6304
    Schlagwort(e): On-line coupled LC-GC ; nitrogen selective detection ; NPD ; carbazoles ; PANH ; personal exposure measurement ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A coupled LC-GC method for the analysis of carbazole-type PANH has been developed and evaluated. Group separation and isolation of carbazoles from interfering acridines in a complex sample matrix was accomplished by using a back-flush technique and an in situ end-capped dimethylaminopropyl silica column in the HPLC part of the system. On-line injection of the carbazole fraction into the GC column was performed with a loop-type interface utilizing concurrent solvent evaporation technique. An LOD of 1-3 pg of individual carbazole compounds was achieved by nitrogen selective detection using an NPD. The method is shown to be robust and is demonstrated by application to personal exposure measurement in an aluminum reduction plant.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 83
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 138-142 
    ISSN: 0935-6304
    Schlagwort(e): Capillary electrochromatography ; nucleosides ; short-end injection ; phenyl-bonded silica ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---The influence of several experimental parameters (pH, ionic strength, organic modifier content of hydro-organic buffer) upon EOF, migration time, and retention factor has been studied in CEC with a phenyl-bonded silica column on a model mixture of five nucleosides. This paper illustrates the current interest in CEC as a method of resolving complex mixtures of neutral and ionic solutes and demonstrates the potential of the short-end injection method as a means of reducing analysis time.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 84
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 143-148 
    ISSN: 0935-6304
    Schlagwort(e): Analysis of anthraquinones ; capillary electrophoresis ; high-performance liquid chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---The separation and determination of twelve anthraquinones, viz. anthraquinone 1, chrysphanol 2, aloe-emodin 3, alizarin 4, anthraquinone-2-carboxylic acid 5, purpurin 6, sennoside B 7, sennoside A 8, emodin 9, quinalizarin 10, rhein 11, and anthraflavic acid 12, were achieved by capillary electrophoresis (CE) and high-performance liquid chromatography (HPLC). Detection at 260 nm with a buffer solution containing 30 mM sodium borate (adjusted to pH = 10.56 with 0.05N NaOH) and acetonitrile (9 : 1) in CE or with a linear gradient elution containing 20 mM KH2PO4 with 0.05% phosphoric acid (pH = 2.91) and methanol in HPLC was found to be the most suitable approach for this separation. Contents of six components (2, 3, 7, 8, 9, 11) in crude Rhei Rhizoma extract could easily be determined within 39 min by CE or 63 min by HPLC. The effects of buffers on this separation and the validation of the two methods were studied.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 85
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 156-157 
    ISSN: 0935-6304
    Schlagwort(e): Capillary gas chromatography ; trichlorophenols ; ammonia ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---No abstract
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
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  • 86
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 149-155 
    ISSN: 0935-6304
    Schlagwort(e): Capillary GC ; fast GC ; on-column injection ; narrow-bore column ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---In this work a fast gas chromatography set-up with on-column injection was optimized and evaluated with a model mixture of C8-C28 n-alkanes. Usual injection volumes when using narrow-bore (e. g., 0.1 mm i.d.) analytical columns are ca. 0.1 μL. The presented configuration allows introduction of 10-30-fold larger sample volumes without any distortion of peak shapes. In the set-up a normal-bore retention gap (1 m×0.32 mm i. d.) was coupled to a narrow-bore (4.8 m×0.1 mm i. d.×0.4 μm film thickness) analytical column using a low dead volume column connector. The effects of the experimental conditions such as inlet pressure, sample volume, initial injection temperature, and oven temperature on a peak focusing are discussed. H-u curves for helium and hydrogen are used to compare their suitability for high speed gas chromatography and to show the dependence of separation efficiency on the carrier gas velocity at high inlet pressures. In the fast gas chromatography system a baseline separation of C10-C28 n-alkanes was achieved in less than 3 minutes.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 87
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 182-188 
    ISSN: 0935-6304
    Schlagwort(e): Comprehensive two-dimensional gas chromatography ; GC×GC ; thermal modulation ; oil analysis ; petroleum analysis ; analysis of middle-distillate oil fractions ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---Comprehensive two-dimensional gas chromatography (GC×GC) is an utterly suitable separation technique for the analysis of complex samples, such as oil fractions. Once the two columns and the operating conditions are properly tuned, the technique is able to provide a detailed characterization of such materials. Some considerations applying to the tuning of a GC×GC system for a specific separation are presented and discussed. The authors present a number of different column sets and conditions which allow the separation of a non-aromatic hydrocarbon solvent, a kerosene, the light end of a crude oil, and an olefinic fraction, respectively. The highly structured GC×GC chromatograms, together with chemical knowledge about the samples, provide a much more comprehensive characterization of the samples than hitherto possible.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 88
    ISSN: 0935-6304
    Schlagwort(e): Comprehensive two-dimensional gas chromatography ; thermal desorption modulator ; temperature programming ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---In comprehensive two-dimensional gas chromatography, two individual separations are coupled by means of a rotating thermal desorption modulator interface. The injection pulse introduced via the interface onto the second column should be as short as possible. Parameters affecting the modulator operation are studied. In the set-up used in this study, the temperature of the second column can be programmed independently from that of the first column. Optimization of the second-dimension separation to minimize peak broadening and maximize resolution is discussed and an elegant approach to determine second-dimension retention times using a non-constant modulation frequency is demonstrated. The high separation power of the comprehensive system is demonstrated by the analysis of technical and biota samples containing chlorinated biphenyls and toxaphene.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
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  • 89
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 197-201 
    ISSN: 0935-6304
    Schlagwort(e): Multidimensional gas chromatography ; comprehensive two-dimensional gas chromatography ; GC×GC ; oxygenates ; MTBE ; reformulated gasoline ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---Comprehensive two-dimensional gas chromatography (GC×GC) has been applied to the quantitation of oxygenates in reformulated gasoline. Target oxygenates were C1-C4 alcohols, tert-pentanol, methyl tert-butyl ether (MTBE), diisopropyl ether (DIPE), ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME). These were separated from the gasoline matrix using a volatility-based selectivity in the first chromatographic dimension, followed by a mixed-phase polarity/shape selectivity in the second dimension. The high resolving power of this stationary phase combination completely separated all oxygenates except DIPE, ETBE, and TAME, which exhibited coelution with other nonpolar gasoline components. Oxygenates quantitation was achieved with the use of an internal standard, an FID detector, and calibration curves. Quantitation results are in good agreement with ASTM and EPA standard methods. When coupled with our previous method for BTEX and aromatics, a single GC×GC method can now quantitate MTBE, alcohols, BTEX, and aromatics in a one-hour analysis.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 90
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 474-478 
    ISSN: 0935-6304
    Schlagwort(e): Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---Solid-phase extraction, on-line derivatization, and measurement by ion trap mass spectrometry (ITD-MS) were used to investigate the biological degradation of pharmaceutical residues (clofibric acid, ibuprofen, diclofenac). The results of the single steps of sample pretreatment and analytical determination are reported. MS/MS measurements were performed on an ITD-MS by selecting collision induced dissociation of the molecular ions (M+) as parent ions to defined daughter ions. A pilot sewage plant and biofilm reactors operating under oxic and anoxic conditions were run as model systems with synthetic sewage water containing 10 to 50 mg/L dissolved organic carbon (DOC) and pharmaceuticals in concentrations of 10 μg/L. Clofibric acid displayed its persistent character in all cases. The pilot sewage plant and the oxic biofilm reactor showed comparable results for diclofenac and ibuprofen, which both were partly degraded. These results can explain the occurrence of these substances in sewage effluents and in the aquatic environment. A high degree of degradation was found especially for ibuprofen in the oxic biofilm reactor, which was attributed to adaptation of the biofilm to the residue. Two metabolites of ibuprofen could be identified on the basis of their mass spectra and comparison with literature data, viz. hydroxyibuprofen and carboxyibuprofen.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
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  • 91
    ISSN: 0935-6304
    Schlagwort(e): Silicone oil ; supercritical fluid chromatography (SFC) ; micropacked columns ; MALDI-TOF ; GC/MS ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---No abstract
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 92
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 511-514 
    ISSN: 0935-6304
    Schlagwort(e): CZE ; indirect UV detection ; metal ions ; ecological samples ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---No abstract
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 93
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 297-303 
    ISSN: 0935-6304
    Schlagwort(e): Sample preparation ; gas extraction techniques ; membrane-type techniques ; water analysis ; soil analysis ; gas chromatography ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---This review focuses on the role of so-called solventless methods of sample preparation in contemporary environmental analysis. The basic classification of this group of methods as well as the principal features and advantages of the techniques in current use are discussed.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
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  • 94
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 253-258 
    ISSN: 0935-6304
    Schlagwort(e): Comprehensive gas chromatography ; cryogenic modulation ; semi-volatile aromatics ; thermal sweeper ; peak widths ; peak asymmetries ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---The two current technologies for achieving comprehensive gas chromatography (GC×GC) - the thermal sweeper and the cryogenic modulator - are compared in an interlaboratory study using a multicomponent semi-volatile aromatic compound sample. The same column set (phases, film thickness, dimensions of columns) and conditions of oven temperature program were used. Carrier gas flow settings however were different for the data reported here. The thermal sweeper has a longer overall length due to the extra ca. 30 cm length of narrow bore tubing used for the modulator/accumulator section. Data reveal that the two methods behave in an analogous manner in respect of delivering GC×GC results, with key peak parameters of peak widths and symmetry measures showing good correlation. Retention time dissimilarity on the first dimension columns in the two systems arises from different flow rates used, however the second column retention is similar, and this is due to the resulting different elution temperatures that peaks elute on the first dimension in each system. Overall, the two approaches to GC×GC appear to produce equivalent results within the scope of the application studied. Each system does have its experimental limitations; the thermal sweeper has what may be called a ‘thick film effect’, where at high temperature it can be difficult to sufficiently trap the migrating bands in the accumulator column, and the pulsing of solutes in the cryogenic system may suffer from a ‘thick wall effect’ if a column with too thick a wall dimension is used at low oven temperature.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 95
    ISSN: 0935-6304
    Schlagwort(e): Proteomics ; protein analysis ; multidimensional HPLC ; ion-exchange chromatography ; reversed phase chromatography ; comprehensive HPLC ; two-dimensional HPLC ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---The interactive modes of High Performance Liquid Chromatography (HPLC) of proteins provide a platform for the construction of a multidimensional HPLC system coupled to mass spectrometry. We present a system composed of both anion and cation exchanger columns, in the first dimension, and n-octadecyl bonded 1.5 μm nonporous silica columns in the second dimension. Both columns are operated under gradient conditions. A system suitability test with standard proteins showed that the total analysis can be performed within about 20 minutes. The fractions taken from the ion exchanger column are directly analyzed within one minute on the reversed phase column at a high flow rate. Two reversed phase columns are applied and operated alternatively: while the first column performs the separation within one minute, the analytes leaving the first dimension are enriched in an on-column focusing mode on top of the second column. The sample clean-up and enrichment is performed on a novel type of restricted access cation exchanger column with internal sulfonic acid groups and external diol groups. The columns exhibit a molecular weight exclusion limit for globular proteins of about 15 kDa. Our next studies will be directed towards the analysis of proteins and peptides from extracts of fibroblasts.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
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  • 96
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 343-347 
    ISSN: 0935-6304
    Schlagwort(e): SPME ; desorption ; fiber conditioning ; field sampling ; sample preparation ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: No abstract
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
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  • 97
    ISSN: 0935-6304
    Schlagwort(e): Silver ion high-performance liquid chromatography (Ag-HPLC) ; conjugated linoleic acid (CLA) ; p-methoxyphenacyl derivatives ; single-column Ag-HPLC ; fatty acid analysis ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---No abstract
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 98
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 360-366 
    ISSN: 0935-6304
    Schlagwort(e): Artemisia palustris ; Asterothamnus centrali-asiaticus ; capillary gas liquid chromatography ; Compositae (Asteraceae) ; Heteropappus hispidus ; seed oil ; silver ion thin layer chromatography ; trans-fatty acids ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---Seed oils from the Compositae plant family are known to contain a variety of unusual fatty acids. Subsequent to the recent discovery of γ-linolenic acid in Saussurea and Youngia, further Mongolian Compositae species were investigated for their seed oil fatty acid composition. A number of δ3trans-fatty acids (16 : 1δ3t, 18 : 1δ3t and 18 : 3δ3t, 9c, 12c) were found in the seed oils of Heteropappus hispidus and Asterothamnus centrali-asiaticus. The latter fatty acid, but not the trans-monoenes, was also found in one species of Artemisia. These unusual fatty acid isomers were characterized by capillary gas-liquid chromatographic (GLC) separations in combination with other chromatographic techniques (analytical thin layer chromatography, TLC and preparative argentation TLC), and infrared spectrocsopy (IR). Their identity was further confirmed by co-chromatography with other seed oils known to contain these trans-fatty acids. The fact that within the Compositae plant family there are apparently two or three distinct groups of genera containing δ3trans-fatty acids is discussed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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  • 99
    ISSN: 0935-6304
    Schlagwort(e): 2H/1H ratio analysis ; HRGC-P-IRMS ; stable isotopes ; benzaldehyde ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: ---Isotope ratio monitoring gas chromatography-mass spectrometry of the 2H/1H ratio by pyrolysis isotope ratio mass spectrometry (P-IRMS) was used to analyze benzaldehyde originating from various sources. Based on the δ2HSMOW value of an authentic reference sample determined with an elemental analyzer (EA), the range of reproducibility and linearity was checked. Correct (EA related) and reproducible data were obtained for sample amounts 〉0.6 μg benzaldehyde (on column). In another series of experiments, the influence of sample preparation, i. e. simultaneous distillation-extraction (SDE) was found to be negligible. The following ranges of δ2HSMOW values were determined for benzaldehyde using five types of samples, i. e. (i) synthetic (δ2HSMOW -78 to -85‰, ex benzal chloride; +420 to +668‰, ex toluene) and ‘natural’ (including ‘ex-cassia’) references (δ2HSMOW -83 to -144‰); (ii) bitter almond oils (δ2HSMOW -113 to -148‰); (iii) fruits (δ2HSMOW -111 to -146‰); (iv) kernels (δ2HSMOW -115 to -188‰); and (v) leaves (δ2HSMOW -165 to -189‰).
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
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  • 100
    Digitale Medien
    Digitale Medien
    Weinheim : Wiley-Blackwell
    Journal of High Resolution Chromatography 23 (2000), S. 373-378 
    ISSN: 0935-6304
    Schlagwort(e): Open tubular columns ; capillary electrochromatography ; column efficiency ; injected volume ; applied voltage ; Chemistry ; Analytical Chemistry and Spectroscopy
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: The effect of some instrumental parameters on column efficiency in open tubular capillary electrochromatography (OTCEC) has been evaluated. First, it was investigated whether band broadening due to the sample injection process is within a tolerable range when an open tubular column (OTC) of about 10 μm i. d. is used. As a result of the small injection profile factor (K2 = 1.3), injected volumes must be sufficiently small (less than 10 pL) to avoid a significant efficiency loss (〉5%) when hydrodynamic injection by siphoning is employed. Secondly, the kinetic performance of OTCs in a CEC system was estimated from the variation of the reduced plate height (h) with the reduced linear velocity (ν) which was controlled by the voltage applied. Reasonable agreement was obtained between the theoretical h versus ν curve and the experimental values for a group of polycyclic aromatic hydrocarbons used as test compounds. Values of 0.25 for minimum h at an optimum ν of 16 are estimated, which permit separations with around 400,000 plates per meter to be obtained in less than 5 min. Finally, the possibility of estimating the diffusion coefficients of the solutes in the mobile phase from the plot of the height of a theoretical plate versus electroosmotic flow velocity is shown.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
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