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  • 2010-2014
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  • 2000-2004  (57)
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  • 1
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    On Non-Rank Facets of Stable Set Polytopes of Webs with Clique Number Four (2003)
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    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
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    Multiscale Analysis for the Bio-Heat Transfer Equation (2003)
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    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
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    Polyhedral Investigations on Stable Multi-Sets (2003)
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    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
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    Formation and structure of quasi-static cloud-layers in brown dwarf atmospheres (2003)
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    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
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    Visualization of Time-Dependent Adaptive Mesh Refinement Data (2003)
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    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
    Materialart: reportzib , doc-type:preprint
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  • 6
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    Tensor Splats (2003)
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    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
    Materialart: reportzib , doc-type:preprint
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  • 7
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    A construction for non-rank facets of stable set polytopes of webs (2003)
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    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
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    Automatic Construction of Boundary Parametrizations for Geometric Multigrid Solvers (2003)
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    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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    Combinatorial Packing Problems (2003)
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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
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    Small Examples of Non-Constructible Simplicial Balls and Spheres (2003)
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    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
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    A Lagrangian Approach for Integrated Network Design and Routing in IP Networks (2003)
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    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
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    Comparing Restoration Concepts using Optimal Network Configurations with Integrated Hardware and Routing Decisions (2003)
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    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
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    Average Case Analysis of a Hard Dial-a-Ride Problem (2003)
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    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
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    Asymptotic Mesh Independence of Newton's Method Revisited (2003)
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    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
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    Smoothening Helps: A Probabilistic Analysis of the Multi-Level Feedback Algorithm (2003)
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    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
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    A sample path relation for the sojourn times in G/G/1-PS systems and its applications (2003)
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    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
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    Molecular Conformation Dynamics and Computational Drug Design (2003)
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    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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    Nonlinear Optimization in Gas Networks (2003)
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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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    RNA 3D-Modeling (2003)
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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
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    Korean-German Bilateral Symposium on Scientific Computing (2003)
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    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
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    Planung kostenoptimaler Informations- und Kommunikations-Infrastrukturen (2003)
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    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
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    Chromatic Scheduling Polytopes coming from the Bandwidth Allocation Problem in Point-to-Multipoint Radio AccessSystems (2003)
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    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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 23
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    Optimization Methods for UMTS Radio Network Planning (2003)
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    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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 24
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    Assessing Capacity Improvements by Relaying in Cellular Networks (2003)
    Details
    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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 25
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    Minimum Converter Wavelength Assignment in All-Optical Networks (2003)
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    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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 26
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    Rigid body docking for Virtual Screening (2003)
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    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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 27
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    Integrated Optimization of Hardware Configuration and Capacity. Dimensioning in SDH and opaque WDM networks (2003)
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    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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 28
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    Verteilter Dokumenten-Speicher, Erfahrungen mit den Kluwer-Daten des Friedrich-Althoff-Konsortiums (2003)
    Details
    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.
    Schlagwort(e): ddc:000
    Sprache: Deutsch
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  • 29
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    Endnutzerbasierte Online-Fernleihe im KOBV - Kurzbeschreibung (2003)
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    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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    Improved Perron Cluster Analysis (2003)
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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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    Zur Zugriffskontrolle im KOBV (2003)
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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
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    Navigation in the KOBV-Informationsportal Conceptual View (2003)
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    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
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    Polynomial Inequalities Representing Polyhedra (2003)
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    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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    The final NETLIB-LP results (2003)
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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.
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    Sprache: Englisch
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  • 35
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    Dust formation in brown dwarf atmospheres under conditions of driven turbulence (2003)
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    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
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    Kosten- und Qualitätsoptimierung in Kommunikationsnetzen (2003)
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    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.
    Schlagwort(e): ddc:000
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  • 37
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    Dust in Brown Dwarfs IV. Dust formation and driven turbulence on mesoscopic scales (2003)
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    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
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    The multi-scale dust formation in substellar atmospheres (2003)
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    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
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    HelmPole - A finite element solver for scattering problems on unbounded domains: Implementation based on PML (2003)
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    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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 40
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    Progressive Retrieval and Hierarchical Visualization of Large Remote Data (2003)
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    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
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    The Potential of Relaying in Cellular Networks (2003)
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    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
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    Critical and Anticritical Edges with respect to Perfectness (2003)
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    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
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    Accelerating Hasenbusch's Acceleration of Hybrid Monte Carlo (2003)
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    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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    Safe separators for treewidth (2003)
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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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    Interior Point Methods in Function Space (2003)
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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
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    Triangulated Manifolds with Few Vertices: Geometric 3-Manifolds (2003)
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    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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    Lastbalancierung in Peer-to-Peer Systemen (2003)
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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
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    Robust Perron Cluster Analysis in Conformation Dynamics (2003)
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    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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 49
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    Demand-wise Shared Protection for Meshed Optical Networks (2003)
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    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
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    Simulation of the Human Mandible: Comparison of Bone Mineral Density and Stress/Strain Profiles due to Masticatory Muscles' Traction (2003)
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    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
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    MoDySim - A parallel dynamical UMTS simulator (2003)
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    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
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    A numerical reinvestigation of the Aoki phase with $N_f=2$ Wilson fermions at zero temperature (2003)
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    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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    Clustering by using a simplex structure (2003)
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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.
    Schlagwort(e): ddc:000
    Sprache: Englisch
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  • 54
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    Ein neues Verfahren zur Lösung des Streuproblems der Maxwell-Gleichungen (2003)
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    Publikationsdatum: 2016-06-09
    Schlagwort(e): ddc:000
    Sprache: Deutsch
    Materialart: masterthesis , doc-type:masterThesis
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  • 55
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    Jahresbericht 2002 (2003)
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    Publikationsdatum: 2019-10-24
    Schlagwort(e): ddc:000
    Sprache: Deutsch
    Materialart: annualzib , doc-type:report
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  • 56
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    Semantic Annotation in Mathematics and Math-Net (2003)
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    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
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  • 57
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    A new Finite Element realization of the Perfectly Matched Layer Method for Helmholtz scattering problems on polygonal domains in 2D (2003)
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    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
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  • 58
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    Dynamics of macromolecular chains. III. Time-dependent fluorescence polarization studies of local motions of polystyrene in solution (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 11-27 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Fluorescence anisotropy decay experiments are described for polystyrene in various ethylacetate-tripropionin mixtures. Decay curve trends agree with the proposed theoretical autocorrelation function. Study of the effects of viscosity shows that the mean relaxation time varies according to a nonlinear law for low viscosities and that the relaxation time θ, reflecting the effects of the possible departures from the motions permitted by an ideal tetrahedral lattice, obeys a law of the type: θ = α + bη. Furthermore, the effects of the direction of the fluorophore transition moment are examined.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140102
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  • 59
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    Quasielastic scattering by dilute polymer solutionsA summary of this work was presented at the IUPAP International Conference on Statistical Physics, August 25-29, 1975. (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1-10 
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    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The scattering law S(k,w) for dilute polymer solutions is obtained from Kirkwood's diffusion equation via the projection operator technique. The width Ω(k) of S(k,w) is obtained for all k without replacing the Oseen tensor by its average (as is done in the Rouse-Zimm model) using the “spring-bead” model ignoring memory effects. For small (ka\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt N $ \end{document} ≪ 1) and large (ka ≫ 1) values of k we find Ω = 0.195 k2/β α η0 \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt N $ \end{document} and Ω = k2/βξ, respectively, indicating that the width is governed mainly by the viscosity η0 for small k values and by the friction coefficient ξ for large k values. For intermediate k values which are of importance in neutron scattering we find that in the Rouse limit Ω = k4a2/12βξ. When the hydrodynamic effects are included, Ω(k) becomes 0.055 k3/βη0. Using the Rouse-Zimm model, it is seen that the effect of pre-averaging the Oseen tensor is to underestimate the half-width Ω(k). The implications of the theoretical predictions for scattering experiments are discussed.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140101
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  • 60
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    Digitale Medien
    Ion recombination luminescence in polymer glasses induced by electron irradiation. I. High-vinyl polybutadiene (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 437-449 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The luminescence of 1,2-polybutadiene was measured during and following irradiation with 1.4-MeV electrons at 90 °K. Measured under isothermal conditions, the light intensity at first increases sharply on start-up of irradiation, and then reaches a plateau after several seconds. The equilibrium value was found to be linearly dependent on the dose rate employed. The postirradiation luminescence decay measured at 90°K follows second-order kinetics.The light emitted by the irradiated sample during warm-up to room temperature is characterized by the appearance of four intensity maxima at 118, 168, 223, and 261 °K. The first three peaks are attributable to the onset of local motion, whereas the peak at 223 °K is caused by the long-range motion occurring at the glass-to-rubber transition. A preirradiation of the polymer in vacuo causes an increase in these four peaks as well as the formation of a new maximum at 143 °K.Intermittent exposure of the irradiated sample to light of wavelengths λ 〉 450 nm causes the isothermal luminescence decay to be interrupted by a burst of light emitted by the sample during and shortly following the light exposure. This treatment also results in considerably reduced intensity maxima during warm-up to room temperature. An interpretation of the findings reported is given on the basis of reactions involving primary and secondary transient species produced during irradiation and on the molecular parameters of the polybutadiene.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140306
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  • 61
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    Digitale Medien
    Piezoelectric properties of oriented films of poly(γ-methyl D-glutamate) (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 401-414 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The dynamic piezoelectric stress constant e*25 of drawn films of poly(γ-methyl D-glutamate) (PMDG) cast from solutions in α-helix-promoting solvents 1,2-dichloroethane (DCE) and chloroform and from the nonhelicogenic solvent dichloroacetic acid (DCA) was measured from -180°C to 200°C at 110 Hz. The drawn and annealed films cast from chloroform show a small peak for the real part of piezoelectric stress constant -e′25 in the temperature range of the mechanical α2-crystalline relaxation, which is caused by the distortion motion of the backbone chain of the α-helix. On the other hand, drawn films cast from DCE show the peak of the real part of the piezoelectric stress constant, whose magnitude decreases in the range of the mechanical α1-crystalline relaxation or the β-relaxation processes, which were previously ascribed, respectively, to mutual slipping of α-helices and to the micro-Brownian motion of disordered regions. Also, -e′25 becomes virtually zero near 180°C where the α2-relaxation is located. These results suggest that the polarization change induced by applied strain is caused by distortion of the backbone chains in the α-helix. Near 0°C, the temperature range of the side-chain mechanical relaxation, -e′25 exhibits a marked peak both for films cast from chloroform and from DCE. The maximum value of -e′25 and the orientation function of the α-helix axis are linearly related and extrapolation of -e′25,max to unit orientation function gives 1.3 × 104 cgs esu which corresponds to 2.4 Debye per residue. This value corresponds reasonably to the value of 3.71 Debye for the permanent dipole moment of NHCO bond if the correction for crystallinity is made. This result also indicates the piezoelectric properties of PMDG arise from distortion of the backbone chain of the α-helix induced by applied strain.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140303
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  • 62
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    An anomalous transition to a lower activation energy for dc electrical conduction above the glass-transition temperature (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 955-957 
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    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140516
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  • 63
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    Digitale Medien
    Quantitative information from x-ray diffraction of nylon-6 yarns. II. Physical aspects of some quantitative parameters (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 941-954 
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    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A mathematical model developed in an earlier paper describes the experimental x-ray profiles of equatorial nylon-6 reflections in terms of Pearson VII functions. The present paper deals with the physical aspects and interpretations of the interrelations of the parameters obtained and the relation between these parameters and the results of other types of measurements. It was found that the growth of the crystallites perpendicular to the chain axis is not isotropic, the strongest growth being in the direction of the hydrogen bonds. Growth and perfection of the crystallites are found to be highly correlated. Large crystals are related to short distances between the planes containing the hydrogen bonds and so to densely packed, i.e., perfect unit cells. This correlation forms the basis for the observed similarity between our quantification technique and the method of the crystal perfection index introduced by Statton. Curve resolution, however, makes the method better applicable for poorly crystallized samples. Comparison of the results with those of small-angle x-ray scattering gave a high degree of consistency with respect to the determined crystal size. In the literature mention is made of a relation between the dimensions and the melting point of the crystals; this relation is confirmed by comparing the appropriate x-ray parameters with DTA results of methoxymethylated nylon 6-yarns.Information about the γ-phase can be obtained from equatorial and meridional reflections. The expected relationship between the relevant peak areas was established. This reported evidence shows the physical validity of the parameters obtained using the Pearson VII model for the analytical description of x-ray reflections of nylon-6 yarns.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140515
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  • 64
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    Digitale Medien
    Glass transitions of ethyl acrylate-based ionomers (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1201-1209 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The glass-transition temperatures of a series of copolymers of ethyl acrylate and acrylic acid neutralized with various cations were investigated. It was found that a plot of Tg as a function of ion content, for every type of ion investigated here, gives an unusual sigmoidal curve, which can be correlated with the onset of the failure of time-temperature superposition in viscoelastic studies, as will be shown in a future publication. Also, all of the Tg versus concentration curves for the various counterions can be superposed if the plots are made against cq/a, where c is the metal acrylate content, q the cation charge, and a the distance between centers of charge. Furthermore, in one region of water content, a linear relation is obtained between the glass transition and the water content (in weight-%) independent of the ion concentration over wide ranges of ion content. Finally, above an ion concentration of 12 mole-%, the rate of change in Tg per water molecule per ion pair at constant ion content, (∂Tg/∂n)c is linear but with different slopes above and below two water molecules per ion pair.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140705
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  • 65
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    Digitale Medien
    Enthalpy relaxation of rigid poly(vinyl chloride) (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1087-1095 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The changes which take place on annealing rigid PVC in the vicinity of the glass transition have been followed by differential scanning calorimetry. The changes appear as an increase in the glass-transition temperature and a decrease in the enthalpy with time of annealing. For annealing at 75°C, the enthalpy after 50-100 hr approaches the value characteristic of the equilibrium liquid state. The results obtained for annealing at 65°C and 75°C are in accord with those expected for the relaxation of an amorphous material, and are at variance with those expected on the basis of crystallization taking place on annealing. The enthalpy relaxation process is characterized by a distribution of activation energies centered about 18.8 kcal mole-1, and seems to reflect a multiplicity of molecular processes.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140611
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  • 66
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    Digitale Medien
    Newtonian behavior of a styrene-butadiene-styrene block copolymer (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1149-1156 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The melt rheological behavior of an anionically polymerized styrene-butadiene-styrene (SBS) block copolymer sample (S: 7 × 103 and B: 43 × 103) was studied using a Weissenberg rheogoniometer. Highly non-Newtonian behavior, high viscosity and high elasticity, which are characteristics of ABA type block copolymers, were observed at 125°C, 140°C, and 150°C. The data at these temperatures superimposed well onto a master curve giving a constant flow activation energy. However, the data at 175°C indicated a marked change in the flow mechanism between 150°C and 175°C. At 175°C, the sample showed Newtonian behavior, negligible elasticity, and deviation from the master curve. These findings may be considered as an indication that the SBS block copolymer sample undergoes a structural change from a multiphase structure at low temperatures into a homogeneous structure at some temperature between 150°C and 175°C.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140616
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  • 67
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    Digitale Medien
    Isotactic poly(pentene-1): Form III (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1161-1167 
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    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A new crystalline form of isotactic poly(pentene-1) was obtained from dilute solution in amyl acetate. We have designated it as form III. The morphology and structure of isothermally crystallized samples were investigated by electron microscopy and electron and x-ray diffraction. This crystalline modification can be indexed on an orthorhombic unit cell (cell dimensions: a = 21.20 ± 0.05 Å, b = 11.48 ± 0.05 Å, c = 14.39 ± 0.05 Å (fiber axis) and probable space group P212121).
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140701
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  • 68
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    Digitale Medien
    Phase equilibrium and glass-transition temperatures in plasticized amorphous bisphenol-A polycarbonate (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1187-1199 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Glass-transition temperatures and phase separation have been studied in amorphous bisphenol-A polycarbonate plasticized with pentaerythritol tetranonanoate (PETN), trimellitic acid, tridecyloctyl ester (TMDO), and tritolyl phosphate. (TTP). Phase separations occur with partially compatible plasticizers like PETN or TMDO. With PETN, for compositions situated in the miscibility gap, the system is composed of a pure plasticizer phase and of a plasticized polymeric phase characterized by a transition temperature of 110°C. In the case of TMDO and additional phase separation occurs below 55°C and two plasticized polycarbonate phases are observed. In compositions falling in the region where the could point curve crosses the glass-transition diagram the phase separation may be delayed by quick cooling. TTP is completely compatible with polycarbonate and the variation of the glass-transition temperature follows a Gordon and Taylor equation.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140704
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  • 69
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    Digitale Medien
    Thermal expansion and compressibility in the chain direction of a polydiacetylene single crystal (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1235-1240 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: An x-ray back-reflection rotating camera has been used to measure the lattice constant, thermal expansion, and compressibility in the polymer chain direction of a polydiacetylene, poly[bis(p-toluene sulfonate) of 2,4-hexadiyne 1,6-diol]. The thermal expansion coefficient of the polymer chain is small and positive (0.9 ± 0.2 × 10-6 °K-) at 300°K, but negative below about 70°K. Application of 3.43 kbar hydrostatic pressure at 299°K changed the unit cell dimension in the polymer chain direction by less than 10 ppm.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140708
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  • 70
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    Digitale Medien
    Persistence vectors for polypropylene, polystyrene, and poly(methyl methacrylate) chains (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1425-1431 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Persistence vectors a ≡ 〈r〉 are calculated for polypropylene, polystyrene, and poly(methyl methacrylate) chains as functions of chain length and stereochemical constitution. Differences between the progressions of a with chain length for these vinyl polymers are related to their conformational characteristics. The preferences of the syndiotactic chains for the tt dyad conformation are manifested most strikingly in the behavior of this vector.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140806
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  • 71
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    Digitale Medien
    Small-angle x-ray and light scattering studies of the morphology of blends of poly(∊-caprolactone) with poly(vinyl chloride)Abstracted in part from a Thesis for the Ph.D. degree submitted by F.B.K. in the Polymer Science and Engineering Program, University of Massachusetts. (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1391-1424 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Solvent-cast films of blends of poly(∊-caprolactone) (PCL) with poly(vinyl chloride) (PVC) were examined by low-angle x-ray scattering and by small-angle light scattering. X-ray scattering from crystalline compositions were analyzed using the Tsvankin-Buchanan technique and led to values of the repeat period of the lamellar structure and the thickness of the crystalline and amorphous layers. With increasing content of PVC, the amorphous layer thickness increased sufficiently to accommodate the PVC, leading to values of the linear crystallinity consistent with macroscopic measurements by density and DSC techniques up to about 50% PVC by weight. Above this concentration, the lamellar structure no longer appeared to be volume filling. At high concentration of PCL, the polymer consisted of volume-filling spherulites containing the lamellar substructure. Spherulite sizes were measured by light scattering and absolute light scattering intensities were consistent with calculations based upon the degree of crystallinity and anisotropy of the spherulites. Compositions containing more than 60% PVC were amorphous. Low-angle x-ray scattering was interpreted in terms of the Debye-Bueche theory which leads to values for a correlation distance lc and the mean-square electron density fluctuation 〈η2〉 (which was also obtained from the invariant). By the method of Porod, the correlation distances were resolved into persistence lengths within the two phases, which were determined as a function of composition. The fluctuation 〈η2〉 was analyzed in terms of a two-phase model to show that its value was somewhat larger than would be obtained if the phases were composed of the pure components. It was not possible to uniquely determine their compositions. The data were consistent with the existence of a transition zone of the order of 30 Å thick between phases.
    Zusätzliches Material: 23 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140805
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  • 72
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    Digitale Medien
    The determination of the molecular weight distribution of amylose by gel permeation chromatography (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1485-1493 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The universal calibration for gel permeation chromatography (GPC) has been applied to amylose and dextrans. The molecular weight distribution of amylose has been measured starting from known data on dextrans. The agreement found between the molecular weight averages resulting from GPC and those obtained by other methods justifies the procedure followed. The GPC measurements were performed with dimethylsulfoxide as the elution solvent and deactivated silica gel (Porasil) as the column-filling material.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140810
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  • 73
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    Digitale Medien
    Changes in light scattering from poly(ethylene terephthalate) and nylon 6 films upon stretching in relation to the deformation mechanism (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1495-1512 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Unoriented T-die flat films of nylon 6 and PET films annealed at 90°C were stretched in water at 80°C. Amorphous PET films were stretched in water at 65-75°C. Changes in the light scattering patterns from these samples upon stretching were investigated. One of the observed LS patterns from the stretched samples is the Hv eight-leaf pattern consisting of four lobes and streaks. In the nylon 6 and heat-treated PET showing this pattern, spherulitic patterns can be seen in polarization microscopy. The microscopic spherulitic superstructure may possibly be the factor responsible for producing the lobe-and-streak pattern. On the other hand, many microscopic eight-leaf patterns can be observed in amorphous unannealed PET showing the lobe-and-streak pattern. These microscopic patterns are due to retardation at stress concentrations around impurities and nuclei. The superstructure giving these microscopic patterns must be the origin of the lobe-and-streak pattern from unannealed PET. Another scattering pattern, the Vv cruciform pattern, was observed in both stretched nylon 6 and unannealed PET. This pattern is due to an orientation change across the slip lines observed under a polarizing microscope. It is noted (1) that the appearance of the slip lines in PET coincides with the occurrence of oriented crystallization on stretching, (2) that the lobe-and-streak pattern from PET in which orientation crystallization has taken place is fairly stable to heat treatment and does not disappear until just before melting, and (3) that the superstructures produced at low stretching seem to be deformed on further stretching, in accordance with affine deformation theory.
    Zusätzliches Material: 17 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140811
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  • 74
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    Digitale Medien
    A kinetic effect in the environmental stress cracking of polyethylene due to liquid viscosity (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1567-1573 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: An Interesting kinetic effect in the environmental stress cracking (E.S.C.) of polyethylene has been observed, in which the liquid viscosity plays an important role. E.S.C. of a low density, high melt index polyethylene due to silicone oils has been studied using constant load creep experiments. For relatively low stresses, it has been found that the time to fracture is independent of the viscosity of the silicone oil, all other factors being approximately equal. However, at high stresses, the time to fracture increases with increasing viscosity for a given stress. This effect has been shown to be due to the relative ease with which the liquid penetrates a growing crack and thus always be at the crack front. Times to fracture for viscous liquids at high stresses are longer since crack propagation continues partially with and partially without liquid contact, fracture rate being much slower when not in the presence of the liquid.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140904
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  • 75
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    Digitale Medien
    Directional anisotropy of dielectric β-relaxation in oriented poly(ethylene terephthalate) (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1591-1599 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The dielectric β-relaxation in oriented poly(ethylene terephthalate) was investigated over wide ranges of frequency and temperature, with the electric field applied at inclinations of 0°, 45°, and 90° to the draw direction. Pronounced directional anisotropy is observed over the entire range of temperature and frequency. With the external field parallel to the draw direction the dielectric loss is considerably smaller than the value obtained with the field normal to the draw direction. The value obtained with the electric field at 45° to the draw direction is intermediate between the other two. On the other hand, the activation energy is largest for 0° inclination and smallest for 90° inclination. It is suggested that motions of the dipoles involve localized rocking of the molecular chain backbone, particularly when the external electric field is parallel to the chain direction.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140906
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  • 76
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    Digitale Medien
    Mechanical relaxations in γ-ray-polymerized polyethylene (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1659-1669 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Dynamic mechanical properties of cold-compacted films of polyethylene prepared by γ-ray-induced polymerization in bulk at 30°C are discussed in connection with the fine structure. The cold-compacted films show a broad α-relaxation at a lower temperature than do single-crystal mats or melt-crystallized polymer. From the effects of annealing and swelling by carbon tetrachloride on the relaxation, it is concluded that the α-relaxation, like the α-relaxation in the single-crystal mats, originates from molecular motions within lamellar crystals. This is consistent with the finding that these films are composed of stacked small irregular lamellar crystals. The γ-relaxation is also similar to that in crystal mats.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140911
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  • 77
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    Digitale Medien
    The drawing behavior of linear polyethylene. I. Rate of drawing as a function of polymer molecular weight and initial thermal treatment (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1641-1658 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The drawing behavior of a series of linear polyethylene homopolymers with weight-average molecular weight (M̄w) ranging from 67,800 to ∼3,500,000 and variable distribution (M̄w/M̄n = 5.1-20.9) has been studied. Sheets were prepared by two distinct routes: either by quenching the molten polymer into cold water or by slow cooling below the crystallization temperature (∼120°C) followed by quenching into cold water.When the samples (2 cm long) were drawn in air at 75°C using a crosshead speed of 10 cm/min it was found that for low M̄w polymers the initial thermal treatment has a dramatic effect on the rate at which the local deformation proceeds in the necked region. At high M̄w such effects are negligible. An important result was that comparatively high draw ratios (λ 〉 17) and correspondingly high Young's moduli could be obtained for a polymer with M̄w as high as 312,000. It is shown how some of the structural features of the initial materials (mainly studied by optical microscopy, small-angle x-ray scattering and low-frequency laser Raman spectroscopy) can be interpreted in terms of the molecular weight and molecular weight distribution of the polymers. Although crystallization and morphology can be important at low M̄w, it suggested that the concept of a molecular network which embraces both crystalline and noncrystalline material is more helpful in understanding the drawing behavior over the whole range of molecular weights.
    Zusätzliches Material: 9 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140910
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  • 78
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    Digitale Medien
    Carbon-13 NMR spin-lattice relaxation times of isotactic and syndiotactic sequences in amorphous polypropylene (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1693-1700 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Spin-lattice relaxation times (T1) for methyl, methylene, and methine carbons in an amorphous polypropylene have been measured as a function of temperature from 46 to 138°C. The carbons from isotactic sequences characteristically exhibited the longest T1's of those observed. The T1 differences increased with temperature with the largest difference occuring for methine carbons where a 32% difference was observed. Activation energies were determined for the motional processes affecting T1's for isotactic and syndiotactic sequences with essentially no dependence upon configuration noted.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140914
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  • 79
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    Digitale Medien
    Design considerations for measurement of gas sorption in polymers by pressure decay (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1903-1907 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141014
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  • 80
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    Digitale Medien
    Epitaxial crystallization of cellulose II on valonia cellulose (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1913-1916 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141016
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  • 81
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    Digitale Medien
    Extensional infrared orientation (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1921-1929 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: In evaluating molecular orientation by dynamic infrared techniques, it is shown, subject to certain restrictions, that an extensional mechanism plays an important role in the measured orientation. Dichroic measurements can indicate a change in segmental orientation without any change occurring in the chain axis orientation. Extensional orientation was evaluated for a general helical molecule in terms of singular and coupled vibrational modes. Significant orientation changes can occur by the extensional mechanism, the sign and magnitude of which depend on the components of the transition moment vector.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141101
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  • 82
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    Digitale Medien
    A method for the evaluation of the activation energy from relaxation experiments (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1801-1812 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A method is proposed for calculating the activation energy over the entire temperature range from relaxation measurements at two frequencies as a function of temperature by taking into account the entire experimental curve. The method is independent of the distribution of relaxation times, but assumes the validity of the time-temperature superposition principle.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141006
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  • 83
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    Digitale Medien
    The effect of sorbed oxygen on the γ and δ dielectric relaxations in polystyrene (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1871-1875 
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    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The γ and δ relaxations of polystyrene (PS) are rendered more active dielectrically by sorbed oxygen. This effect, coupled with comparative work on molecularly similar systems has led to the assignment of the γ relaxation to a rotational libration of the phenyl ring in PS. Specific interactions of the pendant phenyl ring with molecular oxygen to induce off-axis dipole moments in the phenyl moiety is proposed. It is concluded that this interaction is strong enough to influence the dielectric relaxation strength of other relaxations in PS. It is further concluded that because of the interactions occuring in aromatic polymers containing sorbed oxygen, care must be taken to exclude oxygen or to vary its content, in order that intrinsic motions in the polymer system can be studied.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141011
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  • 84
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    Digitale Medien
    Brillouin scattering from amorphous poly(ethylene terephthalate) (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1909-1912 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141015
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  • 85
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    Digitale Medien
    Broadline NMR study of plasma-polymerized styrene (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1917-1919 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141017
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  • 86
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    Digitale Medien
    High-resolution gel-permeation chromatography of high molecular weight polymers (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 2105-2108 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141115
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  • 87
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    Digitale Medien
    Phenoxy single crystal aggregates (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 2109-2112 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141116
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  • 88
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    Digitale Medien
    Characterization of polystyrene networks by small-angle neutron scattering (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 2119-2128 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Polystyrene networks prepared by anionic polymerization have been characterized by small-angle neutron scattering. Two kinds of systems have been examined:(A) networks with labelled branch points allowing characterization of the spatial distribution of crosslinking points; (B) networks containing a low proportion of chains labelled with perdeuterated polystyrene in order to characterize the conformation of individual elastic chains of the polymeric network. The dependence of the results on swelling and uniaxial extension is discussed.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141201
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  • 89
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    Digitale Medien
    Birefringence and stress relaxation in polyisobutyleneThis work was part of the research program of the Rheology Research Center, University of Wisconsin, Madison, Wis. (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 2129-2136 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Relaxation of birefringence and stress in simple extension has been studied for polyisobutylene at -26.0°C and 25.0°C for extension ratios ranging from about 1.2 to 2.0. The dependence of both the stress and birefringence on the extension ratio, for a given time, is well described by equations of the Mooney-Rivlin form. The Mooney-Rivlin treatment of the birefringence experiments was found to reinforce but not add to information available from the stress-relaxation experiments alone. At 25.0°C, the stress-optical coefficient is found to be stress dependent. Possible explanations of this behavior are discussed. An experiment is also reported in which the birefringence is observed under zero stress immediately after cutting a strained sample. The zero stress birefringence is believed to be due to regions of stress-induced crystallization taking a finite time to melt after the stress is removed.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141202
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  • 90
    Digitale Medien
    Digitale Medien
    Environmental effects on the mechanical properties of reconstituted collagen hollow fiber membranes (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 2195-2209 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The lateral swelling, changes in length and tensile stress-strain curve of reconstituted collagen hollow fibers, crosslinked with uv irradiation, were measured as a function of the pH and ionic strength of their aqueous environment. From pH 5 to pH 10 the lateral swelling and length are constant; at lower and higher pH the lateral swelling increases rapidly while the fiber shrinks in length. Corresponding to these changes, a pronounced toe develops in the stress-strain curve and extends to a higher strain in more acid (or basic) media. This toe is attributed to the straightening of a microcrimp in the collagen fibrils; the microcrimp is accentuated by the repulsion between the charged fibrils in acid or basic media. Direct small-angle x-ray evidence of these microcrimp structure changes at low pH is presented. Increasing the ionic strength of an acid solution by adding NaCl decreases the lateral swelling, increases the length, and decreases the extent of the toe on the stress-strain curve. These changes result from an increased screening of the charge on neighboring fibrils at higher ionic strengths thus decreasing the repulsion between fibrils and the resulting microcrimp. Although the zigzag elastica model of the crimp developed by Diamant et al. [Proc. Roy. Soc., Ser. B, 180, 293 (1972)] provides a good empirical fit to the stress-strain data, it is shown to be inappropriate where the crimp results from repulsive forces between fibrils. A new model taking these forces into account is developed and is shown to be in reasonable agreement with the experimental results.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141205
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  • 91
    Digitale Medien
    Digitale Medien
    Dipole moments of poly(ethylene oxide) and poly(hexamethylene oxide) chains (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 2231-2240 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The mean-square dipole moments of poly(ethylene oxide) and poly(hexamethylene oxide) chains have been determined from dielectric constant measurements on dilute solutions of the polymers in benzene. The values obtained are in good agreement with those predccted using the rotational isomeric state models for these chains. In addition, the unperturbed dimensions of poly(hexamethylene oxide) have been calculated as a function of molecular weight, using the isomeric state theory.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141208
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  • 92
    Digitale Medien
    Digitale Medien
    The theory of phase transition kinetics with growth site impingement. II. Heterogeneous nucleation (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 2253-2257 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: The kinetics of phase transformation are treated for heterogeneous nucleation, where all nuclei are simultaneously initiated, and where initiation follows first-order kinetcs. The phase transformation curves are sigmoid. For simultaneous initiation in two dimensions, a(t)/(1 - a(t)) ∝ t2. For first-order initiation, we have, approximately, a(t)/(1 - a(t)) ∝ t2.85, and v(t)/(1 - v(t)) ∝ t3.74.
    Zusätzliches Material: 2 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141210
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  • 93
    Digitale Medien
    Digitale Medien
    Effects of inorganic salts on the properties of aqueous poly(ethylene oxide) solutions (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 2241-2251 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Cloud-point curves have been determined for aqueous solutions of poly(ethylene oxide) (PEO) at several concentrations for a variety of inorganic salts (sulfates, carbonates, nitrates, and chlorides). From these, theta conditions have been determined. The resulting dependences of the critical temperature θ (mostly between 300 and 360°K) on the molar concentrations (or ionic strengths) of the salts in solution cannot wholly be summarized in sequences of ion effects. The major findings are that sulfates and carbonates are much more effective in reducing θ than the chlorides and nitrates at the same concentrations. The trends found depend on salt concentration, i.e., certain plots of the data cross over, but they broadly agree with those found for comparable systems by other workers. Exceptional are the chlorides of Group II and LiCl which show minima when θ is plotted against molar salt concentration. While interpretations based on solvent structure-breaking are not adequate, there are similarities in behavior with the structure-breaking attributes of the ions based on independent studies (infrared). The results are briefly discussed in terms of current postulates: a more detailed discussion will accompany further experimental studies on these systems.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141209
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  • 94
    Digitale Medien
    Digitale Medien
    Mechanical relaxations in some ionene polymers. II. Influence of counterions and absorbed water (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 2273-2284 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Six 6,10-ionenes with different counterions were prepared by ion exchange reactions in aqueous solutions. The counterions were Br, I, CIO4, BF4, SCN, and B(C6H5)4. The dynamic mechanical properties of these polymers were investigated by use of a torsional braid analyser. Three relaxations α (25-140°C), β (-30-0°C), and γ (-140-120°C) were observed at the frequencies of 0.3-0.8 Hz. The temperature of the α and β relaxations were largely dependent on the size of counterions, but those of the γ relaxations had little variation. The effects of electrostatic forces in the polymers on each relaxation was discussed. The influence of absorbed water on the α, β, and γ relaxations was examined. The absorbed water in the polymers greatly depressed the temperature of the α relaxations and this phenomenon was interpreted to be the result of the specific hydration on ionic portions.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141212
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  • 95
    Digitale Medien
    Digitale Medien
    Rapid small-angle and wide-angle x-ray studies of crystallization behavior in polymers (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 2291-2311 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Small-angle and wide-angle x-ray scattering measurements, using a position-sensitive detector, were made during melt-crystallization of linear polyethylenes and PEO-PS-PEO triblock copolymer. The scattering measurements indicated that the triblock copolymer grew by the enlargement of regions in which lamellae are regularly stacked. During primary crystallization at higher temperatures similar behavior is observed in two linear polyethylenes. At lower temperatures, changes in the shape of small-angle scattering curves during the primary stage of crystallization indicate that amorphous gaps within the lamellar stacking become filled in. During secondary crystallization at higher temperatures new crystallites appear to grow between those formed in the primary stage. Concurrent decrease of the overall scattered intensity leads to the conclusion that secondary crystallization has two components: crystallization of new lamellae behind the spherulite growth front and the thickening of existing lamellae.
    Zusätzliches Material: 18 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141214
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  • 96
    Digitale Medien
    Digitale Medien
    A crystallographic study of polymers exhibiting side-chain crystallization (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1241-1255 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Fibers were drawn from polymers of octadecyl acrylate, octadecyl methacrylate, N-octadecylacrylamide, and a series of N-substituted acrylamides with a second amide group in the side chain as well as from copolymers of octadecyl and methyl esters of acrylic and methacrylic acid. Wide-angle and small-angle x-ray diffraction patterns were recorded for these materials. The interpretation of the characteristic difference between the behavior of the polycrylates and polymethacrylates, as proposed by Platé and his collaborators, is found to be inconsistent with a number of features of the experimental evidence. In the case of poly(octadecyl methacrylate) the data allow the estimation of two parameters of the electron density distribution in the side-chain crystallites. With polyacrylamide derivatives, a second amide group in the side chain is found to destabilize the side chain crystallites. The bahavior of the copolymers is very complex and exhibits, in one case, evidence for a long periodicity parallel to the fiber axis.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140709
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  • 97
    Digitale Medien
    Digitale Medien
    Surface properties of styrene-ethylene oxide block copolymers (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1287-1295 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Hydrophobic-hydrophilic block copolymers were prepared by “living” anionic polymerization. They consist of polystyrene and poly(ethylene oxide) blocks, and are soluble in water. Their interfacial properties were investigated, employing aqueous solutions. The block copolymers lowered the surface tension of water in analogy with the low molecular weight surfactants such as sodium lauryl sulfate and heptaethylene oxide n-dodecyl ether. Their aqueous solutions exhibited solubilization properties differing from those of polyethylene glycol. Therefore, it is thought that the polystyrene blocks produce solubilization phenomena. In samples of the same styrene content, the precipitation temperature of a high molecular weight copolymer in water was lower than that of a low molecular weight copolymer at the same concentration in the same solvent. The surface tension and precipitation temperature of aqueous solutions seem to be influenced by molecular weight and composition.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140712
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  • 98
    Digitale Medien
    Digitale Medien
    Potentiometric titration of polyelectrolyte gels equilibrated with a solution of a strong polyelectrolyte: Influence of gel swelling (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1317-1324 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A weak acid gel (carboxylmethyldextran) was titrated with sodium hydroxide while equilibrated with a solution sodium poly(vinyl sulfate), a salt of a strong acid polyelectrolyte.It was found that the quantity \documentclass{article}\pagestyle{empty}\begin{document}$$ S = {\rm pH} - {\rm pNa} + \log (V/V_0) $$\end{document} in which V/V0 is the volume of gel relative to its volume in acid form in pure water, is independent of the concentration Cp of the polyelectrolyte solution and of the relative volume of gel.The relation \documentclass{article}\pagestyle{empty}\begin{document}$$ S - \log \left({\frac{{\alpha ^2}}{{1 - \alpha}}} \right) = {\rm pK'} + \log \gamma _{{\rm Na}}^{\rm g} + \log (v/V_0) $$\end{document} where α is the degree of ionization, pK′ is the apparent pK of the gel, γnAG is the activity coefficient of the counterion in the gel phase, and v is the number of ionizable groups, is found to be constant for all values of Cp and for 0.1 〈 α 〈 0.9. These results can be extended to highly crosslinked ionexchange resins.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180140716
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  • 99
    Digitale Medien
    Digitale Medien
    Isothermal and nonisothermal creep of lightly crosslinked cis-1,4 polybutadiene (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1891-1901 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: A nonisothermal creep experiment has been analyzed to ascertain its suitability for determining the temperature dependence of low activation energy viscoelastic processes in elastomers far above Tg. The nonisothermal method was employed to determine the activation energy for creep near 35°C in a lightly crosslinked cis-1,4 polybutadiene elastomer at small strains within the linear viscoelastic region, and at various large deformations up to rupture. The observed activation energy was essentially independent of the level of strain, and the value of ΔHa (∼11 kcal/mole) determined via the nonisothermal creep method was in good agreement with the result (∼12 kcal/mole) obtained via time-temperature superposition of isothermal linear viscoelastic creep data. The nonisothermal data allowed for an estimate of the volume of the “flow unit” associated with the controlling viscoelastic creep mechanism, attributed here to slippage of entanglements within the lightly crosslinked network.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141013
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  • 100
    Digitale Medien
    Digitale Medien
    Studies of molecular relaxation of poly(propylene oxide) solutions by dielectric relaxation and brillouin scattering (1976)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 14 (1976), S. 1877-1890 
    Details
    ISSN: 0098-1273
    Schlagwort(e): Physics ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Physik
    Notizen: Dielectric relaxation and Brillouin scattering are jointly used in studying molecular relaxation in poly(propylene oxide) (PPO) and its solutions in methylcyclohexane. The dielectric method was applied to the more concentrated (100%, 80%, 60%, by volume) solutions over a wide temperature and frequency range (30 Hz to 8 GHz) in order that the variation in activation energy characteristic of a glass-forming substance could be delineated. The present work extends previous work on the undiluted polymer to higher frequencies so that range of 12 decades in the dielectric loss maximum fmax as a function of temperature is now available. The “Antoine” equation is found to represent the behavior of log fmax, of the bulk concentrated solutions very well. The more dilute (40%, 20%) solutions were studied only in the high-frequency (GHz) region since phase separation occurred at low temperatures. Both the temperature and dilution effects were interpreted in terms of free-volume theory. Brillouin scattering spectra were obtained at several scattering angles and a wide range of temperatures. A maximum in the curve of hypersonic attenuation versus temperature was observed in each polymer solution. The attenuation maximum shifts toward lower temperature upon dilution, in agreement with the dielectric relaxation result. The Brillouin scattering follows different activation parameters and evidences a more rapid process than does the dielectric relaxation. It is speculated that it monitors a secondary or subglass relaxation, due perhaps, to damped torsional oscillations.
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/pol.1976.180141012
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