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  • 2005-2009  (54)
  • 1990-1994  (706)
  • 2006  (54)
  • 1990  (706)
  • Chemical Engineering  (674)
  • Electronic commerce, Management
  • composting
  • ddc:000
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  • 2005-2009  (54)
  • 1990-1994  (706)
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  • 1
    Keywords: Electronic books ; Electronic commerce, Management ; Information technology, Management ; Technological innovations, Management
    Pages: 1 v. (various pagings)
    ISBN: 1-591-40631-5
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  • 2
    ISSN: 1572-9729
    Keywords: composting ; crude oil ; olive mill wastewater ; olive oil mills ; olive tree branches ; olive tree leaves ; sludge ; woodchips
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The aim of this paper was to evaluate the use of different bulking agents in different ratios as a means to control, optimise and eventually reduce the duration of the thermophilic period in two-phase olive oil mill sludge (OOMS) composting. The bulking agents used were: (i) olive tree leaves (OTL), (ii) olive tree shredded branches (OTB) and (iii) woodchips (WDC). The selection of these materials was based on their abundance and availability on the island of Crete, the southernmost point of Greece. The ratios studied were: Pile 1, OOMS:OTL in 1:1 v/v; Pile 2, OOMS:WDC in 1:1.5 v/v; Pile 3, OOMS:OTL in 1:2 v/v; Pile 4, OOMS:OTL:OTB in 1:1:1 v/v; and Pile 5, OOMS:OTL:OTB in 1:1:2 v/v. The composting system used was that of windrows with the volume of each pile approximately 20–25 m3. The experiments took place over two consecutive years. A composting turner was used and turnings were performed at one and two week intervals. In each pile a variety of physiochemical parameters were monitored. Temperature remained high in all five trials. Piles 1, 2, 3, 4 and 5 temperatures recorded values of above 50 °C for 106, 158, 160, 175 and 183 days, respectively. Volumes were reduced by approximately 67%, 62%, 63%, 80% and 84%, respectively. Temperature remained high, mainly due to the presence in large amounts of oily substances which during their complete oxidation release important amounts of energy and aid the cometabolism of more stable molecules such as lignin. This process is better described as the slow “burning” of a “fuel” mixture in an “engine” than composting. This approach is based on the extensive similarities of this process to that of crude oil sludge or similar waste composting.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-9729
    Keywords: bioremediation ; composting ; ecotoxicity ; oil sludge
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The present work attempts to ascertain the efficacy of low cost technology (in our case, composting) as a bioremediation technique for reducing the hydrocarbon content of oil refinery sludge with a large total hydrocarbon content (250–300 g kg−1), in semiarid conditions. The oil sludge was produced in a refinery sited in SE Spain The composting system designed, which involved open air piles turned periodically over a period of 3 months, proved to be inexpensive and reliable. The influence on hydrocarbon biodegradation of adding a bulking agent (wood shavings) and inoculation of the composting piles with pig slurry (a liquid organic fertiliser which adds nutrients and microbial biomass to the pile) was also studied. The most difficult part during the composting process was maintaining a suitable level of humidity in the piles. The most effective treatment was the one in which the bulking agent was added, where the initial hydrocarbon content was reduced by 60% in 3 months, compared with the 32% reduction achieved without the bulking agent. The introduction of the organic fertiliser did not significantly improve the degree of hydrocarbon degradation (56% hydrocarbon degraded). The composting process undoubtedly led to the biodegradation of toxic compounds, as was demonstrated by ecotoxicity tests using luminescent bacteria and tests on plants in Petri dishes.
    Type of Medium: Electronic Resource
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  • 4
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    Publication Date: 2019-10-24
    Keywords: ddc:000
    Language: German
    Type: annualzib , doc-type:report
    Format: application/pdf
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  • 5
    Publication Date: 2014-02-26
    Description: We propose a variant of the control reduced interior point method for the solution of state constrained problems. We show convergence of the corresponding interior point pathfollowing algorithm in function space. Morever, we provide error bounds for the iterates.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 6
    Publication Date: 2014-02-26
    Description: This paper aims at presenting the complex coupled network of the human menstrual cycle to the interested community. Beyond the presently popular smaller models, where important network components arise only as extremely simplified source terms, we add: the GnRH pulse generator in the hypothalamus, receptor binding, and the biosynthesis in the ovaries. Simulation and parameter identification are left to a forthcoming paper.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 7
    Publication Date: 2014-02-26
    Description: This work explores two applications of a classical result on the continuity of Nemyckii operators to optimal control with PDEs. First, we present an alternative approach to the analysis of Newton's method for function space problems involving semi-smooth Nemyckii operators. A concise proof for superlinear convergence is presented, and sharpened bounds on the rate of convergence are derived. Second, we derive second order sufficient conditions for problems, where the underlying PDE has poor regularity properties. We point out that the analytical structure in both topics is essentially the same.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 8
    Publication Date: 2014-02-26
    Description: In this paper, we study the efficiency of Nash equilibria for a sequence of nonatomic routing games. We assume that the games are played consecutively in time in an online fashion: by the time of playing game $i$, future games $i+1,\dots,n$ are not known, and, once players of game $i$ are in equilibrium, their corresponding strategies and costs remain fixed. Given a sequence of games, the cost for the sequence of Nash equilibria is defined as the sum of the cost of each game. We analyze the efficiency of a sequence of Nash equilibria in terms of competitive analysis arising in the online optimization field. Our main result states that the online algorithm $\sl {SeqNash}$ consisting of the sequence of Nash equilibria is $\frac{4n}{2+n}$-competitive for affine linear latency functions. For $n=1$, this result contains the bound on the price of anarchy of $\frac{4}{3}$ for affine linear latency functions of Roughgarden and Tardos [2002] as a special case. Furthermore, we analyze a problem variant with a modified cost function that reflects the total congestion cost, when all games have been played. In this case, we prove an upper bound of $\frac{4n}{2+n}$ on the competitive ratio of $\sl {SeqNash}$. We further prove a lower bound of $\frac{3n-2}{n}$ of $\sl {SeqNash}$ showing that for $n=2$ our upper bound is tight.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 9
    Publication Date: 2016-06-09
    Description: To approximate convolutions which occur in evolution equations with memory terms, a variable-stepsize algorithm is presented for which advancing $N$ steps requires only $O(N\log N)$ operations and $O(\log N)$ active memory, in place of $O(N^2)$ operations and $O(N)$ memory for a direct implementation. A basic feature of the fast algorithm is the reduction, via contour integral representations, to differential equations which are solved numerically with adaptive step sizes. Rather than the kernel itself, its Laplace transform is used in the algorithm. The algorithm is illustrated on three examples: a blow-up example originating from a Schrödinger equation with concentrated nonlinearity, chemical reactions with inhibited diffusion, and viscoelasticity with a fractional order constitutive law.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 10
    Publication Date: 2020-11-13
    Description: This paper deals with MIP-based primal heuristics to be used within a branch-and-cut approach for solving multi-layer telecommunication network design problems. Based on a mixed-integer programming formulation for two network layers, we present three heuristics for solving important subproblems, two of which solve a sub-MIP. On multi-layer planning instances with many parallel logical links, we show the effectiveness of our heuristics in finding good solutions early in the branch-and-cut search tree.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 11
    Publication Date: 2019-05-10
    Description: The dynamics of ventricular fibrillation caused by irregular excitation is simulated in the frame of the monodomain model with an action potential model due to Aliev-Panfilov for a human 3D geometry. The numerical solution of this multiscale reaction-diffusion problem is attacked by algorithms which are fully adaptive in both space and time (code library {\sc Kardos}). The obtained results clearly demonstrate an accurate resolution of the cardiac potential during the excitation and the plateau phases (in the regular cycle) as well as after a reentrant excitation (in the irregular cycle).
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 12
    Publication Date: 2020-12-15
    Description: The topic of this paper are integer programming models in which a subset of 0/1-variables encode a partitioning of a set of objects into disjoint subsets. Such models can be surprisingly hard to solve by branch-and-cut algorithms if the permutation of the subsets of the partition is irrelevant. This kind of symmetry unnecessarily blows up the branch-and-cut tree. We present a general tool, called orbitopal fixing, for enhancing the capabilities of branch-and-cut algorithms in solving this kind of symmetric integer programming models. We devise a linear time algorithm that, applied at each node of the branch-and-cut tree, removes redundant parts of the tree produced by the above mentioned permutations. The method relies on certain polyhedra, called orbitopes, which have been investigated in (Kaibel and Pfetsch (2006)). However, it does not add inequalities to the model, and thus, it does not increase the difficulty of solving the linear programming relaxations. We demonstrate the computational power of orbitopal fixing at the example of a graph partitioning problem motivated from frequency planning in mobile telecommunication networks.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 13
    Publication Date: 2014-11-10
    Description: In this paper, we discuss the relation of unsplittable shortest path routing (USPR) to other routing schemes and study the approximability of three USPR network planning problems. Given a digraph $D=(V,A)$ and a set $K$ of directed commodities, an USPR is a set of flow paths $\Phi_{(s,t)}$, $(s,t)\in K$, such that there exists a metric $\lambda=(\lambda_a)\in \mathbb{Z}^A_+$ with respect to which each $\Phi_{(s,t)}$ is the unique shortest $(s,t)$-path. In the \textsc{Min-Con-USPR} problem, we seek for an USPR that minimizes the maximum congestion over all arcs. We show that this problem is hard to approximate within a factor of $\mathcal{O}(|V|^{1-\epsilon})$, but easily approximable within min$(|A|,|K|)$ in general and within $\mathcal{O}(1)$ if the underlying graph is an undirected cycle or a bidirected ring. We also construct examples where the minimum congestion that can be obtained by USPR is a factor of $\Omega(|V|^2)$ larger than that achievable by unsplittable flow routing or by shortest multi-path routing, and a factor of $\Omega(|V|)$ larger than by unsplittable source-invariant routing. In the CAP-USPR problem, we seek for a minimum cost installation of integer arc capacities that admit an USPR of the given commodities. We prove that this problem is $\mathcal{NP}$-hard to approximate within $2-\epsilon$ (even in the undirected case), and we devise approximation algorithms for various special cases. The fixed charge network design problem \textsc{Cap-USPR}, where the task is to find a minimum cost subgraph of $D$ whose fixed arc capacities admit an USPR of the commodities, is shown to be $\mathcal{NPO}$-complete. All three problems are of great practical interest in the planning of telecommunication networks that are based on shortest path routing protocols. Our results indicate that they are harder than the corresponding unsplittable flow or shortest multi-path routing problems.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 14
    Publication Date: 2014-11-11
    Description: In this paper, we investigate the connection availabilities for the new protection scheme Demand-wise Shared Protection (DSP) and describe an appropriate approach for their computation. The exemplary case study on two realistic network scenarios shows that in most cases the availabilities for DSP are comparable with that for 1+1 path protection and better than in case of shared path protection.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 15
    Publication Date: 2016-06-30
    Description: THESEUS, the ZIB threading environment, is a parallel implementation of a protein threading based on a multi-queued branch-and-bound optimal search algorithm to find the best sequence-to-structure alignment through a library of template structures. THESEUS uses a template core model based on secondary structure definition and a scoring function based on knowledge-based potentials reflecting pairwise interactions and the chemical environment, as well as pseudo energies for homology detection, loop alignment, and secondary structure matching. The threading core is implemented in C++ as a SPMD parallization architecture using MPI for communication. The environment is designed for generic testing of different scoring functions, e.g. different secondary structure prediction terms, different scoring matrices and information derived from multiple sequence alignments. A validaton of the structure prediction results has been done on the basis of standard threading benchmark sets. THESEUS successfully participated in the 6th Critical Assessment of Techniques for Protein Structure Prediction (CASP) 2004.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 16
    Publication Date: 2014-02-26
    Description: We consider a multi-queue multi-server system with $n$ servers (processors) and $m$ queues. At the system there arrives a stationary and ergodic stream of $m$ different types of requests with service requirements which are served according to the following $k$-limited head of the line processor sharing discipline: The first $k$ requests at the head of the $m$ queues are served in processor sharing by the $n$ processors, where each request may receive at most the capacity of one processor. By means of sample path analysis and Loynes' monotonicity method, a stationary and ergodic state process is constructed, and a necessary as well as a sufficient condition for the stability of the $m$ separate queues are given, which are tight within the class of all stationary ergodic inputs. These conditions lead to tight necessary and sufficient conditions for the whole system, also in case of permanent customers, generalizing an earlier result by the authors for the case of $n$=$k$=1.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 17
    Publication Date: 2014-02-26
    Description: In order to compute the thermodynamic weights of the different metastable conformations of a molecule, we want to approximate the molecule's Boltzmann distribution in a reasonable time. This is an essential issue in computational drug design. The energy landscape of active biomolecules is generally very rough with a lot of high barriers and low regions. Many of the algorithms that perform such samplings (e.g. the hybrid Monte Carlo method) have difficulties with such landscapes. They are trapped in low-energy regions for a very long time and cannot overcome high barriers. Moving from one low-energy region to another is a very rare event. For these reasons, the distribution of the generated sampling points converges very slowly against the thermodynamically correct distribution of the molecule. The idea of ConfJump is to use $a~priori$ knowledge of the localization of low-energy regions to enhance the sampling with artificial jumps between these low-energy regions. The artificial jumps are combined with the hybrid Monte Carlo method. This allows the computation of some dynamical properties of the molecule. In ConfJump, the detailed balance condition is satisfied and the mathematically correct molecular distribution is sampled.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 18
    Publication Date: 2020-02-11
    Description: "`Volkssport Sudoku"' titelt der Stern in seiner Ausgabe vom 24. Mai2006. In der Tat traut sich derzeit kaum noch eine Zeitung, ohne Sudoku zu erscheinen. Die Begeisterung am Lösen dieser Zahlenrätsel offenbart eine unvermutete Freude am algorithmischen Arbeiten. Mathematisch kann man Sudokus als lineare diophantische Gleichungssysteme mit Nichtnegativitätsbedingungen formulieren. Solche ganzzahligen linearen Programme sind die wichtigsten Modellierungswerkzeuge in zahlreichen Anwendungsgebieten wie z.B. der Optimierung von Telekommunikations- und Verkehrsnetzen. Moderne Verfahren zur Lösung dieser Optimierungsprobleme sind durch Sudokus allerdings deutlich weniger zu beeindrucken als Zeitungsleser.
    Keywords: ddc:000
    Language: German
    Type: reportzib , doc-type:preprint
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  • 19
    Publication Date: 2020-02-11
    Description: This article surveys mathematical models and methods used for physical PCB layout, i.e., component placement and wire routing. The main concepts are briefly described together with relevant references.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 20
    Publication Date: 2020-12-15
    Description: We study online multicommodity minimum cost routing problems in networks, where commodities have to be routed sequentially. Arcs are equipped with load dependent price functions defining the routing weights. We discuss an online algorithm that routes each commodity by minimizing a convex cost function that depends on the demands that are previously routed. We present a competitive analysis of this algorithm showing that for affine linear price functions this algorithm is $4K/2+K$-competitive, where $K$ is the number of commodities. For the parallel arc case this algorithm is optimal. Without restrictions on the price functions and network, no algorithm is competitive. Finally, we investigate a variant in which the demands have to be routed unsplittably.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 21
    Publication Date: 2021-03-16
    Description: Perfect graphs constitute a well-studied graph class with a rich structure, reflected by many characterizations w.r.t different concepts. Perfect graphs are, e.g., characterized as precisely those graphs $G$ where the stable set polytope STAB$(G)$ coincides with the clique constraint stable set polytope QSTAB$(G)$. For all imperfect graphs STAB$(G) \subset$ QSTAB$(G)$ holds and, therefore, it is natural to measure imperfection in terms of the difference between STAB$(G)$ and QSTAB$(G)$. Several concepts have been developed in this direction, for instance the dilation ratio of STAB$(G)$ and QSTAB$(G)$ which is equivalent to the imperfection ratio imp$(G)$ of $G$. To determine imp$(G)$, both knowledge on the facets of STAB$(G)$ and the extreme points of QSTAB$(G)$ is required. The anti-blocking theory of polyhedra yields all {\em dominating} extreme points of QSTAB$(G)$, provided a complete description of the facets of STAB$(\overline G)$ is known. As this is typically not the case, we extend the result on anti-blocking polyhedra to a {\em complete} characterization of the extreme points of QSTAB$(G)$ by establishing a 1-1 correspondence to the facet-defining subgraphs of $\overline G$. We discuss several consequences, in particular, we give alternative proofs of several famous results.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 22
    Publication Date: 2014-11-10
    Description: We give experimental and theoretical results on the problem of computing the treewidth of a graph by exact exponential time algorithms using exponential space or using only polynomial space. We first report on an implementation of a dynamic programming algorithm for computing the treewidth of a graph with running time $O^\ast(2^n)$. This algorithm is based on the old dynamic programming method introduced by Held and Karp for the {\sc Tra veling Salesman} problem. We use some optimizations that do not affect the worst case running time but improve on the running time on actual instances and can be seen to be practical for small instances. However, our experiments show that the space use d by the algorithm is an important factor to what input sizes the algorithm is effective. For this purpose, we settle the problem of computing treewidth under the restriction that the space used is only polynomial. In this direction we give a simple $O^\ast(4^n)$ al gorithm that requires {\em polynomial} space. We also show that with a more complicated algorithm, using balanced separators, {\sc Treewidth} can be computed in $O^\ast(2.9512^n)$ time and polynomial space.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 23
    Publication Date: 2014-03-10
    Description: The dynamic behavior of molecules can often be described by Markov processes. From computational molecular simulations one can derive transition rates or transition probabilities between subsets of the discretized conformational space. On the basis of this dynamic information, the spatial subsets are combined into a small number of so-called metastable molecular conformations. This is done by clustering methods like the Robust Perron Cluster Analysis (PCCA+). Up to now it is an open question how this coarse graining in space can be transformed to a coarse graining of the Markov chain while preserving the essential dynamic information. In the following article we aim at a consistent coarse graining of transition probabilities or rates on the basis of metastable conformations such that important physical and mathematical relations are preserved. This approach is new because PCCA+ computes molecular conformations as linear combinations of the dominant eigenvectors of the transition matrix which does not hold for other clustering methods.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 24
    Publication Date: 2014-02-26
    Description: Das deutschsprachige Bibliothekswesen verfügt mit den \glqq Regeln für den Schlagwortkatalog \grqq (RSWK) unter Verwendung der \glqq Schlagwortnormdatei \grqq (SWD) über ein Instrumentarium, welches zusammen mit einem \glqq Faceted Browsing \grqq das bisher bestehende Angebot für ein Information Retrieval optimal ergänzen kann. Die Verbindung zwischen Standardvokabular (SWD) und Kettenbildung (RSWK) einerseits und eine nach Facetten-Eigenschaften gegliederte Navigation andererseits unterstützt bestmöglich eine inhaltlich bezogene Recherche. Die Stärken und Schwächen der RSWK/SWD werden erörtert und auch Klassifikationen (DDC und RVK) als mögliche Facetten diskutiert.
    Keywords: ddc:000
    Language: German
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  • 25
    Publication Date: 2016-06-09
    Keywords: ddc:000
    Language: English
    Type: masterthesis , doc-type:masterThesis
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  • 26
    Publication Date: 2022-03-14
    Description: A lot of problems arising in Combinatorial Optimization and Operations Research can be formulated as Mixed Integer Programs (MIP). Although MIP-solving is an NP-hard optimization problem, many practically relevant instances can be solved in reasonable time. In modern MIP-solvers like the branch-cut-and-price-framework SCIP, primal heuristics play a major role in finding and improving feasible solutions at the early steps of the solution process. This helps to reduce the overall computational effort, guides the remaining search process, and proves the feasibility of the MIP model. Furthermore, a heuristic solution with a small gap to optimality often is sufficient in practice. We investigate 16 different heuristics, all of which are available in SCIP. Four of them arise from the literature of the last decade, nine are specific implementations of general heuristic ideas, three have been newly developed. We present an improved version of the feasibility pump heuristic by Fischetti et al., which in experiments produced solutions with only a third of the optimality gap compared to the original version. Furthermore, we introduce two new Large Neighborhood Search (LNS) heuristics. Crossover is an LNS improvement heuristic making use of similarities of diverse MIP solutions to generate new incumbent solutions. RENS is an LNS rounding heuristic which evaluates the space of all possible roundings of a fractional LP-solution. This heuristic makes it possible to determine whether a point can be rounded to an integer solution and which is the best possible rounding. We conclude with a computational comparison of all described heuristics. It points out that a single heuristic on its own has only a slight impact on the overall performance of SCIP, but the combination of all of them reduces the running time by a factor of two compared to a version without any heuristics.
    Keywords: ddc:000
    Language: English
    Type: masterthesis , doc-type:masterThesis
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  • 27
    Publication Date: 2014-02-26
    Description: We present a finite volume method for the solution of the two-dimensional Poisson equation $ \nabla\cdot( \beta( {\mbox{\boldmath $x$}}) \nabla u({\mbox{\boldmath $x$}})) = f(\mbox{\boldmath $x$}) $ with variable, discontinuous coefficients and solution discontinuities on irregular domains. The method uses bilinear ansatz functions on Cartesian grids for the solution $u({\mbox{\boldmath $x$})$ resulting in a compact nine-point stencil. The resulting linear problem has been solved with a standard multigrid solver. Singularities associated with vanishing partial volumes of intersected grid cells or the dual bilinear ansatz itself are removed by a two-step asymptotic approach. The method achieves second order of accuracy in the $L^\infty$ and $L^2$ norm.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 28
    Publication Date: 2014-11-11
    Description: In this article we aim at an efficient sampling of the stationary distribution of dynamical systems in the presence of metastabilities. In the past decade many sophisticated algorithms have been inven ted in this field. We do not want to simply add a further one. We address the problem that one has applied a sampling algorithm for a dynamical system many times. This leads to different samplings which more or less represent the stationary distribution partially very well, but which are still far away from ergodicity or from the global stationary distribution. We will show how these samplings can be joined together in order to get one global sampling of the stationary distribution.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 29
    Publication Date: 2014-02-26
    Description: The concept of jump system, introduced by Buchet and Cunningham (1995), is a set of integer points with a certain exchange property. In this paper, we discuss several linear and convex optimization problems on jump systems and show that these problems can be solved in polynomial time under the assumption that a membership oracle for a jump system is available. We firstly present a polynomial-time implementation of the greedy algorithm for the minimization of a linear function. We then consider the minimization of a separable-convex function on a jump system, and propose the first polynomial-time algorithm for this problem. The algorithm is based on the domain reduction approach developed in Shioura (1998). We finally consider the concept of M-convex functions on constant-parity jump systems which has been recently proposed by Murota (2006). It is shown that the minimization of an M-convex function can be solved in polynomial time by the domain reduction approach.
    Keywords: ddc:000
    Language: English
    Type: reportzib , doc-type:preprint
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  • 30
    Publication Date: 2020-12-15
    Description: We introduce orbitopes as the convex hulls of 0/1-matrices that are lexicographically maximal subject to a group acting on the columns. Special cases are packing and partitioning orbitopes, which arise from restrictions to matrices with at most or exactly one 1-entry in each row, respectively. The goal of investigating these polytopes is to gain insight into ways of breaking certain symmetries in integer programs by adding constraints, e.g., for a well-known formulation of the graph coloring problem. We provide a thorough polyhedral investigation of packing and partitioning orbitopes for the cases in which the group acting on the columns is the cyclic group or the symmetric group. Our main results are complete linear inequality descriptions of these polytopes by facet-defining inequalities. For the cyclic group case, the descriptions turn out to be totally unimodular, while for the symmetric group case, both the description and the proof are more involved. The associated separation problems can be solved in linear time.
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  • 31
    Publication Date: 2014-11-21
    Description: The standard computational methods for computing the optimal value functions of Markov Decision Problems (MDP) require the exploration of the entire state space. This is practically infeasible for applications with huge numbers of states as they arise, e.\,g., from modeling the decisions in online optimization problems by MDPs. Exploiting column generation techniques, we propose and apply an LP-based method to determine an $\varepsilon$-approximation of the optimal value function at a given state by inspecting only states in a small neighborhood. In the context of online optimization problems, we use these methods in order to evaluate the quality of concrete policies with respect to given initial states. Moreover, the tools can also be used to obtain evidence of the impact of single decisions. This way, they can be utilized in the design of policies.
    Keywords: ddc:000
    Language: English
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  • 32
    Publication Date: 2014-11-21
    Description: Wir beschäftigen uns mit dem Problem der Betriebsplanung von Laserschweißrobotern im Karosseriebau. Gegeben ist eine Menge von Schweißnähten, die innerhalb einer Fertigungszelle an einem Karosserieteil gefertigt werden müssen. Die Schweißnähte werden durch mehrere parallel betriebene Roboter bearbeitet. Die Aufgabe besteht darin, für jeden Roboter eine Reihenfolge und eine zeitliche Koordinierung seiner Bewegungen zu finden, so dass alle Schweißnähte innerhalb der Taktzeit der Fertigungszelle bearbeitet werden und so wenig Laserquellen wie möglich eingesetzt werden. Dabei müssen einige Nebenbedingungen berücksichtigt werden. Für dieses spezielle Schweißproblem haben wir eine Formulierung als gemischt-ganzzahliges lineares Programm entwickelt, welches sich für die untersuchten praktischen Fälle sehr schnell lösen lässt.
    Keywords: ddc:000
    Language: German
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  • 33
    Publication Date: 2021-08-05
    Description: Modern applications of mathematical programming must take into account a multitude of technical details, business demands, and legal requirements. Teaching the mathematical modeling of such issues and their interrelations requires real-world examples that are well beyond the toy sizes that can be tackled with the student editions of most commercial software packages. We present a new tool, which is freely available for academic use including complete source code. It consists of an algebraic modeling language and a linear mixed integer programming solver. The performance and features of the tool are in the range of current state-of-the-art commercial tools, though not in all aspects as good as the best ones. Our tool does allow the execution and analysis of large real-world instances in the classroom and can therefore enhance the teaching of problem solving issues. Teaching experience has been gathered and practical usability was tested in classes at several universities and a two week intensive block course at TU Berlin. The feedback from students and teachers has been very positive.
    Keywords: ddc:000
    Language: English
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  • 34
    Publication Date: 2014-11-21
    Description: The Bottleneck Shortest Path Problem is a basic problem in network optimization. The goal is to determine the limiting capacity of any path between two specified vertices of the network. This is equivalent to determining the unsplittable maximum flow between the two vertices. In this note we analyze the complexity of the problem, its relation to the Shortest Path Problem, and the impact of the underlying machine/computation model.
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  • 35
    Publication Date: 2014-02-26
    Description: We introduce a new and rich class of graph coloring manifolds via the Hom complex construction of Lov\´{a}sz. The class comprises examples of Stiefel manifolds, series of spheres and products of spheres, cubical surfaces, as well as examples of Seifert manifolds. Asymptotically, graph coloring manifolds provide examples of highly connected, highly symmetric manifolds.
    Keywords: ddc:000
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  • 36
    Publication Date: 2014-02-26
    Description: We give coordinate-minimal geometric realizations in general position for 17 of the 20 vertex-minimal triangulations of the orientable surface of genus 3 in the 5x5x5-cube.
    Keywords: ddc:000
    Language: English
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  • 37
    Publication Date: 2014-02-26
    Description: Biochemical interactions are determined by the 3D-structure of the involved components - thus the identification of conformations is a key for many applications in rational drug design. {\sf ConFlow} is a new multilevel approach to conformational analysis with main focus on completeness in investigation of conformational space. In contrast to known conformational analysis, the starting point for design is a space-based description of conformational areas. A tight integration of sampling and analysis leads to an identification of conformational areas simultaneously during sampling. An incremental decomposition of high-dimensional conformational space is used to guide the analysis. A new concept for the description of conformations and their path connected components based on convex hulls and {\em Hypercubes}is developed. The first results of the {\sf ConFlow} application constitute a 'proof of concept' and are further more highly encouraging. In comparison to conventional industrial applications, {\sf ConFlow} achieves higher accuracy and a specified degree of completeness with comparable effort.
    Keywords: ddc:000
    Language: English
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  • 38
    Publication Date: 2014-02-26
    Description: We consider linear inverse problems where the solution is assumed to fulfill some general homogeneous convex constraint. We develop an algorithm that amounts to a projected Landweber iteration and that provides and iterative approach to the solution of this inverse problem. For relatively moderate assumptions on the constraint we can always prove weak convergence of the iterative scheme. In certain cases, i.e. for special families of convex constraints, weak convergence implies norm convergence. The presented approach covers a wide range of problems, e.g. Besov- or BV-restoration for which we present also numerical experiments in the context of image processing.
    Keywords: ddc:000
    Language: English
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  • 39
    Publication Date: 2014-03-10
    Description: Whenever the invariant stationary density of metastable dynamical systems decomposes into almost invariant partial densities, its computation as eigenvector of some transition probability matrix is an ill-conditioned problem. In order to avoid this computational difficulty, we suggest to apply an aggregation/disaggregation method which only addresses wellconditioned sub-problems and thus results in a stable algorithm. In contrast to existing methods, the aggregation step is done via a sampling algorithm which covers only small patches of the sampling space. Finally, the theoretical analysis is illustrated by two biomolecular examples.
    Keywords: ddc:000
    Language: English
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  • 40
    Publication Date: 2016-02-29
    Description: \noindent We give a partial description of the $(s,t)-p$-path polytope of a directed graph $D$ which is the convex hull of the incidence vectors of simple directed $(s,t)$-paths in $D$ of length $p$. First, we point out how the $(s,t)-p$-path polytope is located in the family of path and cycle polyhedra. Next, we give some classes of valid inequalities which are very similar to inequalities which are valid for the $p$-cycle polytope, that is, the convex hull of the incidence vectors of simple cycles of length $p$ in $D$. We give necessary and sufficient conditions for these inequalities to be facet defining. Furthermore, we consider a class of inequalities that has been identifie d to be valid for $(s,t)$-paths of cardinality at most $p$. Finally, we transfer the results to related polytopes, in particular, the undirected counterpart of the $(s,t)-p$-path polytope.
    Keywords: ddc:000
    Language: English
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  • 41
    Publication Date: 2020-11-13
    Description: The numerical integration of dynamical contact problems often leads to instabilities at contact boundaries caused by the non-penetration condition between bodies in contact. Even a recent energy dissipative modification due to Kane et al. (1999), which discretizes the non-penetration constraints implicitly, is not able to circumvent artificial oscillations. For this reason, the present paper suggests a contact stabilization which avoids artificial oscillations at contact interfaces and is also energy dissipative. The key idea of this contact stabilization is an additional $L^2$-projection at contact interfaces, which can easily be added to any existing time integration scheme. In case of a lumped mass matrix, this projection can be carried out completely locally, thus creating only negligible additional numerical cost. For the new scheme, an elementary analysis is given, which is confirmed by numerical findings in an illustrative test example (Hertzian two body contact).
    Keywords: ddc:000
    Language: English
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  • 42
    Publication Date: 2016-06-30
    Keywords: ddc:000
    Language: German
    Type: masterthesis , doc-type:masterThesis
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  • 43
    Publication Date: 2014-02-26
    Description: We discuss different approaches for the enumeration of triangulated surfaces. In particular, we enumerate all triangulated surfaces with 9 and 10 vertices. We also show how geometric realizations of orientable surfaces with few vertices can be obtained by choosing coordinates randomly.
    Keywords: ddc:000
    Language: English
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  • 44
    Publication Date: 2014-02-26
    Description: The concept of L##-convexity is introduced by Fujishige--Murota (2000) as a discrete convexity for functions defined over the integer lattice. The main aim of this note is to understand the difference of the two algorithms for L##-convex function minimization: Murota's steepest descent algorithm (2003) and Kolmogorov's primal algorithm (2005).
    Keywords: ddc:000
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  • 45
    Publication Date: 2014-02-26
    Description: In this survey on combinatorial properties of triangulated manifolds we discuss various lower bounds on the number of vertices of simplicial and combinatorial manifolds. Moreover, we give a list of all known examples of vertex-minimal triangulations.
    Keywords: ddc:000
    Language: English
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  • 46
    Publication Date: 2020-02-11
    Description: This paper concerns the problem of operating a landside container exchange area that is serviced by multiple semi-automated rail mounted gantry cranes (RMGs) that are moving on a single bi-directional traveling lane. Such a facility is being built by Patrick Corporation at the Port Botany terminal in Sydney. The gantry cranes are a scarce resource and handle the bulk of container movements. Thus, they require a sophisticated analysis to achieve near optimal utilization. We present a three stage algorithm to manage the container exchange facility, including the scheduling of cranes, the control of associated short-term container stacking, and the allocation of delivery locations for trucks and other container transporters. The key components of our approach are a time scale decomposition, whereby an integer program controls decisions across a long time horizon to produce a balanced plan that is fed to a series of short time scale online subproblems, and a highly efficient space-time divisioning of short term storage areas. A computational evaluation shows that our heuristic can find effective solutions for the planning problem; on real-world data it yields a solution at most~8\% above a lower bound on optimal RMG utilization.
    Keywords: ddc:000
    Language: English
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  • 47
    Publication Date: 2014-02-26
    Description: We describe an algorithm for the enumeration of (candidates of) vertex-transitive combinatorial $d$-manifolds. With an implementation of our algorithm, we determine, up to combinatorial equivalence, all combinatorial manifolds with a vertex-transitive automorphism group on $n\leq 13$ vertices. With the exception of actions of groups of small order, the enumeration is extended to 14 and 15 vertices.
    Keywords: ddc:000
    Language: English
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  • 48
    Publication Date: 2014-02-26
    Description: We give coordinate-minimal geometric realizations in general position of all 865 vertex-minimal triangulations of the orientable surface of genus 2 in the 4x4x4-cube.
    Keywords: ddc:000
    Language: English
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  • 49
    Publication Date: 2014-02-26
    Description: We give a complete enumeration of combinatorial 3-manifolds with 10 vertices: There are precisely 247882 triangulated 3-spheres with 10 vertices as well as 518 vertex-minimal triangulations of the sphere product $S^2 x S^1$ and 615 triangulations of the twisted sphere product $S^2 \underline{x} S^1$. An analysis of the 3-spheres with up to 10 vertices shows that all these spheres are shellable, but that there are 29 vertex-minimal non-shellable 3-balls with 9 vertices.
    Keywords: ddc:000
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  • 50
    Publication Date: 2019-05-10
    Description: Adaptive numerical methods in time and space are introduced and studied for linear poroelastic models in two and three space dimensions. We present equivalent models for linear poroelasticity and choose both the {\em displacement--pressure} and the {\em stress--pressure} formulation for our computations. Their discretizations are provided by means of linearly implicit schemes in time and linear finite elements in space. Our concept of adaptivity opens a way to a fast and reliable simulation of different loading cases defined by corresponding boundary conditions. We present some examples using our code {\sf Kardos} and show that the method works efficiently. In particular, it could be used in the simulation of some bone healing models.
    Keywords: ddc:000
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  • 51
    Publication Date: 2016-06-30
    Description: During the last few years more and more functionalities of RNA have been discovered that were previously thought of being carried out by proteins alone. One of the most striking discoveries was the de tection of microRNAs, a class of noncoding RNAs that play an important role in post-transcriptional gene regulation. Large-scale analyses are needed for the still increasingly growing amount of sequen ce data derived from new experimental technologies. In this paper we present a framework for the detection of the distinctive precursor structure of microRNAS that is based on the well-known Smith-Wat erman algorithm and various filtering steps. We conducted experiments on real genomic data and we found several new putative hits for microRNA precursor structures.
    Keywords: ddc:000
    Language: English
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  • 52
    Publication Date: 2014-02-26
    Description: Wir erleben zu Beginn des aufkommenden Informationszeitalters mit dem Siegeszug von Google und anderen Internet-Technologien einen Wandel im Verhalten von Wissenschaftlern und Studenten, der mit dem Einsatz von {\sl Google Scholar} und {\sl Google Book Search} einen Paradigmenwechsel für Bibliotheken und Informationsversorger gleichkommt. Der Artikel untersucht die technischen Hintergründe für den Erfolg dieser besonderen Art des Information Retrievals: Fulltext Indexing und Citation Ranking als besondere Form des Information Minig. Er diskutiert Stärken und auch Schwächen des Google-Ansatzes. Der Autor stellt sich auch der Frage, unter welchen Bedingungen es möglich ist, ein zu {\sl Google Scholar} und der {\sl Google Book Search} konkurrenzfähiges Retrieval in der Landschaft der Bibliotheken und Bibliotheksverbünde zu entrichten. Die These ist, dass dieses unter Einsatz des {\sl Open Source} Indexierers {\sl Lucene} und des Web-Robots {\sl Nutch} möglich ist. Bibliotheken können durch gezielten Einsatz solcher Internet-Technologien dem Nutzer die Leistungen, welche Google uns mit seinen Tools im {\sl Visible Web} und mit Referenzen auf {\sl Citations} in der Welt der Literatur zur Verfügung stellt, in vergleichbarer Art auch für ihre eigenen durch Lizenzen geschützten digitalen Journale und ihre speziellen lokal verfügbaren Ressourcen, auf die Internet-Suchmaschinen keine Zugriff haben, anbieten. Es besteht die Hoffnung, dass Nutzer dann nicht - wie in einer kürzlichen Studie des OCLC konstatiert - überwiegend im Internet verbleiben, sondern bei ihrer Suche auch den Weg zu den Angeboten der örtlichen Bibliothek attraktiv finden.
    Keywords: ddc:000
    Language: German
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  • 53
    Publication Date: 2014-02-26
    Description: We consider a system where the arrivals form a Poisson process and the required service times of the requests are exponentially distributed. According to the generalized processor sharing discipline, each request in the system receives a fraction of the capacity of one processor which depends on the actual number of requests in the system. We derive systems of ordinary differential equations for the LST and for the moments of the conditional waiting time of a request with given required service time as well as a stable and fast recursive algorithm for the LST of the second moment of the conditional waiting time, which in particular yields the second moment of the unconditional waiting time. Moreover, asymptotically tight upper bounds for the moments of the conditional waiting time are given. The presented numerical results for the first two moments of the sojourn times in the $M/M/m-PS$ system show that the proposed algorithms work well.
    Keywords: ddc:000
    Language: English
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  • 54
    Publication Date: 2022-07-07
    Description: We present a domain decomposition approach for the computation of the electromagnetic field within periodic structures. We use a Schwarz method with transparent boundary conditions at the interfaces of the domains. Transparent boundary conditions are approximated by the perfectly matched layer method (PML). To cope with Wood anomalies appearing in periodic structures an adaptive strategy to determine optimal PML parameters is developed. We focus on the application to typical EUV lithography line masks. Light propagation within the multi-layer stack of the EUV mask is treated analytically. This results in a drastic reduction of the computational costs and allows for the simulation of next generation lithography masks on a standard personal computer.
    Keywords: ddc:000
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  • 55
    Electronic Resource
    Electronic Resource
    Springer
    Nutrient cycling in agroecosystems 24 (1990), S. 141-148 
    ISSN: 1573-0867
    Keywords: Ammonia volatilization ; animal manures ; composting ; forms of nitrogen ; Kjeldahl nitrogen ; poultry ; total nitrogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Kjeldahl nitrogen (N), total N and forms of inorganic N (ammoniacal (NH4)-N, nitrate (NO3)-N and nitrite (NO2)-N) were measured in a range of animal manures. The manures include fresh samples of poultry manure, sheep manure, horse manure, dairy slurry and pig slurry and composted poultry manure. Kjeldahl N was measured by standard micro-Kjeldahl digestion. For total N measurements, NO3-N and NO2-N were recovered during Kjeldahl digestion by pretreatments with various oxidizing and reducing agents. Inorganic forms of N were measured by extraction with 2M KCl solution. Kjeldahl digestion alone allowed measurement only of organic N and NH4-N. Amongst various modifications to the Kjeldahl, pretreatment with either acidified (H2SO4) Zn-CrK(SO4)2 or acidified (H2SO4) reduced Fe achieved complete recovery of NO3-N. Nitrite N was only recovered by first oxidising the NO 2 - to NO 3 - with KMnO4 followed by reduction to NH4-N with acidified (H2SO4) reduced Fe. More than 95% of the total N in fresh animal manure was present as organic N and NH4-N which were recovered by the standard Kjeldahl digestion. In the case of fresh manures there was no difference between the amount of total N measured by the Kjeldahl digestion and its modified methods. However composting of poultry manure or drying of poultry manure, pig slurry and dairy slurry resulted in an increase in NO3-N which was not recovered during Kjeldahl digestion alone. Under these conditions the total N could be measured by pretreating the samples with KMnO4 and reduced Fe prior to Kjeldahl digestion. Drying of animal manures caused a decrease in organic N and NH4-N, especially in poultry, pig and dairy manures. There was a slight increase in NO3-N; but most of the decrease in N content with drying was attributed to the volatilization loss of ammonia (NH3). Amongst various drying methods examined air drying caused maximum loss of N as NH3 whereas freeze drying caused minimum loss of N. This suggests that fresh animal manures can be freeze dried for analysis of N which causes minimum loss of N.
    Type of Medium: Electronic Resource
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  • 56
    ISSN: 1573-5117
    Keywords: digester ; composting ; Europe ; methanization ; phycocolloid extraction ; residues ; seaweed ; stranded macroalgae ; Ulva
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Proliferation of macroalgae is a world-wide problem with 50,000 m3 of drift Ulva harvested per year in Brittany and about 1.0 to 1.2 million tons growing in the Venice lagoon. This biomass may be treated by bioconversion (aerobic or anaerobic fermentation) to give useful products (gas, fertilizers or others) and to remove a source of environmental pollution. Such a treatment also may be applied to cultivated or harvested seaweds and to seaweed industry residues. Studies of seaweed methanization showed Laminaria an especially good substrate and Ulva a possible substrate. Research led to a defined way of treating drift algae, encompassing natural hydrolysis and pressing with methanization of the juices. The most advanced full-scale realization for algal biomass utilization is the C.A.T.-Quatre-Vaulx composting plant in Saint-Cast-Le-Guildo (Brittany, France). It produced from seaweed, wood and animal dung a biological quality compost that is competitive with the traditional market products.
    Type of Medium: Electronic Resource
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  • 57
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 22-29 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polymer blends of nylon 66 and thermotropic polyester with long flexible spacers in the main chains were prepared by melt mixing. The samples were made as single filaments by passing the polymer blend through a small and round die of a capillary rheometer. Mechanical properties of blends showed that the modulus and strength of nylon 66 could be improved without reduction of extensibility. The morphology of fractured surfaces was observed by a scanning electron microscope (SEM). It showed that the microfibrillar structure of a thermotropic polyester was formed by extensional flow while the spherical and ellipsoidal particles in the nylon 66 (matrix polymer) were produced by shear flow. The polyester particles were occasionally covered with adhering matrix polymer because of good adhesion between these two polymers. They were highly elongated by tensile stress without loss of elongational characteristics of blends. This fact was explained by very good adhesion between the two phases.
    Additional Material: 8 Ill.
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  • 58
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 83-89 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The physical behavior of the diglycidyl ether of bisphenol A, cured with different concentrations of 2-ethyl-4-methylimidazole, was examined with dynamic mechanical and dielectric analyses, differential scanning calorimetry, and solvent extraction studies, ‘The network formation process was shown to depend strongly on the imidazole concentration’. At high imidazole concentrations, the gel point was characterized by a decrease in sol fraction, the crossover of the dynamic moduli and a rapid increase in viscosity. At low imidazole concentrations, the viscosity remained low until the sol fraction approached zero. For this system, the gel point, which occurred prior to the dynamic moduli crossover, was characterized by comparing the thermal properties of the network with the viscosity and dielectric behavior of the resin system during cure.
    Additional Material: 12 Ill.
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  • 59
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 108-117 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We examine several practically important problems, related to the mechanical behavior of dual coated optical fibers: low temperature microbending, evaluation of spring constant due to coating layers, strength of the end portions of fibers clamped in terminal fixtures, and prediction of stresses caused by the misalignment of the openings in the frame and in the terminal fixture. The developed formulas are simple, easy-to-use, and clearly indicate the role of the major factors affecting the mechanical behavior of the fibers. The obtained results can be of help in physical design of dual coated fibers and optical interconnections.
    Additional Material: 7 Ill.
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  • 60
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 129-133 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The “Efficiency of Energy Absorption” (or “Efficiency”) and “Ideality” parameters were evaluated for several plastic foams and were found to be very useful in choosing an appropriate cushion for the protection of a specific product. The maxima in these parameters were found to be in the same range of stresses, when derived from dynamic measurements or from predicted stress-strain curves based on previously proposed “Reference” and “Modified Boltzman Superposition” Models. For the rate independent foams the maxima in these parameters do not change with strain rate and can therefore be derived from slow, constant rate (“static”) experiments. For rate dependent foams however, the maxima from “static” measurements were found to be in a lower range of stresses than those derived from dynamic ones. As a result, slow rate compressive measurements do not predict well the behavior of the foams during impact and the use of the “Reference” and “Modified Boltzman Superposition” Models is required for good predictions. It was found that the suffer PS and PE foams attain maximum Efficiency and Ideality at higher stresses than the more flexible PUR foams.
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  • 61
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 96-107 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Sudden changes of compressive strain-rate on glassy poly(methyl methacrylate) lead to the conclusion that the post-yield state under a constant stress is a state of steady flow in the polymer. Non-linearity between the stress divided by temperature and the logarithm of strain rate for this steady plastic flow can successfully be analyzed using the Eyring equation with structural factors variable depending on stress and temperature. This analysis gives a unique functional relationship between the activation entropy and the activation enthalpy, which agrees fairly well with that for the melt derived from the WLF equation. This agreement provides a direct evidence verifying structural change of the glass into liquid-like structure and enables us to recognize the conformational arrangement as an essential structural parameter controlling molecular mobility. Another experimental relation between the Eyring factors - the activation volume and the activation enthalpy - permits us to estimate the magnitude of an elementary volume for the molecular movement in the melt as a function of temperature. Moreover, the experimental finding of the steady flow in the glassy polymer motivated us to propose a transition mechanism from elastic deformation to plastic flow in which the internal viscosity or the activation volume is introduced as a single parameter representing the transient state of the structure.
    Additional Material: 16 Ill.
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  • 62
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 118-123 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An apparatus was designed and assembled to study the solvent removal from solution-cast thin polymer films. The computer interfacing of a thermogravimetric analyzer, spectrophotometer, electronic flowmeters, and control valves for the apparatus enabled the preprogramming of the carrier gas velocity, carrier gas solvent content, and temperature profiles to simulate the environment experienced in large parallel flow industrial driers. The apparatus has also been designed and operated to enable the visual observation of the drying film with an optical microscope. Initial experimental studies conducted with the apparatus involved the effect of temperature on solvent removal. The results indicate that high dryer gas temperatures can apparently cause skinning of the film surface resulting in slower solvent removal rates. The skin formation can be suppressed by higher solvent concentration in the carrier gas. The visual observations revealed the formation of standing waves in the film surface during drying at high gas velocities (〉2OO cm/min). The wave formation at least partially overcomes the effect of skinning by increasing the surface area of the film, and may be the manifestation of flow instabilities involving circulation within the film.
    Additional Material: 9 Ill.
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  • 63
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 147-152 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Ultrasonically induced bubble formation for the production of thermoplastic foam was investigated experimentally and theoretically as a basic study. A general purpose polystyrene and blends of low density polyethylene and polyethylene wax were saturated with nitrogen gas under various pressures and the ultrasonic excitation was applied to the polymer system upon release of gas pressure. The ultrasonic nucleation of bubbles in the polymer matrix was modeled by utilizing the classical nucleation theory. The negative pressure generated by the ultrasonic excitation was considered as the environmental pressure at the moment of nucleation. The experimental results showed that the heterogeneous nucleation must be used for ultrasonic foaming of the viscous fluid and the homogeneous nucleation for the low viscosity fluid. The theoretical analysis also indicated that the ultrasonic nucleation can be applied to the production of thermoplastic foam if the ultrasonic excitation generates large enough negative pressure.
    Additional Material: 10 Ill.
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  • 64
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 7-12 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Extrusion measurements have been carried out on blends of nylon 6 and a liquid-crystalline copolyesteramide (LCP). The flow curves at low temperature show a behavior similar to that of pure LCP with a rapid rise of the viscosity at low shear rates. At high shear rates the viscosity is lower than that for each of the two components. This minimum has been attributed to the lack of interactions between the two phases and to the formation of fibrils of the LCP phase. The SEM analysis shows, indeed, that fibrils of the LCP phase are produced in the convergent flow at the inlet of the capillary at high shear rates. These fibrils are lost during the flow in the long capillary.
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  • 65
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 124-128 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Rheological studies of an experimental liquid crystalline (LC) copolyester were carried out using a capillary rheometer and a cone and plate rheometer. Rheological characteristics of the polymer in the nematic state were observed. The nematic melt was found to be pseudoplastic and the degree of pseudoplasticity varied with shear rate. Melt viscosity was found to decrease with shear rate. Negative die swelling was observed at the exit of the capillary rheometer at temperatures marginally above the solid-nematic transition temperature of the polymer and was also found to be a function of shear rate. The dynamic mechanical properties of the polymer were studied as a function of temperature. The activation energies of flow and of dynamic mechanical deformation were calculated.
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  • 66
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 137-141 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Ion beam mixing was used to improve the adhesion between deposited Cu film (400 Å) and polyimide (PI) substrate. Ar+ ion with the energy levels between 180 and 200 keV, and the dose between 1014 to 4 × 1016 ions/cm2 were used. The surface analyses were carried out by Rutherford Backscattering Spectroscopy (SEM). RBS analysis, using 2 MeV He+ ions, showed mixing of Cu and FI and the mixing depended on the Ar+ energy and dose. The X-ray study showed a very broad halo for deposited Cu film but the (111) peak appeared after the Ar+ implantation and the peak increased with Ar+ ion dose. Optical micrographs showed that Cu film formed circular bubbles after many thermal cycles when adhesion was poor and fracture cracks when adhesion was good.
    Additional Material: 7 Ill.
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  • 67
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 153-161 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The general domain in which this work resides is that of mixing in creeping flows. Mixing, in this context, refers to the stretch of an interfacial line, or area in a strain field. The advancement of mixing technology is applied to the design of continuous mixers used in polymer processing. The geometric designs included single screw extruders, static motionless mixers, and co- and counter-rotating twin screw extruders. The co-rotating twin screw extruder was chosen to be studied in detail since it enjoys wide applications and, for which, little understanding of the contribution to mixing in the different screw geometries is known. In order to evaluate the rate of mixing for the non-uniform strain history flows, the method for measuring mixing had to be reexamined and broadened. An automated method has been developed which incorporates a digital camera and a computer to analyze the cross-sections of interest. Two measures of mixing - the correlation function and the distribution function - are developed to describe mixing in these regimes. These measures are applied successfully to the mixer geometries revealing subtle differences as to the nature of mixing in each.
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  • 68
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    Polymer Engineering and Science 30 (1990), S. 175-186 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper describes the shear imposed interfacial segregation of release systems for the facilitated attenuation of polyurethane (PU) adhesion to metal coun-terfaces using a RI-RIM system. It is shown that the migration rate of the dispersed release additives due to a shear imposed stress in the resin fluid is much greater than that arising from Fickian diffusion, thereby removing a vital constraint from conventional practice. The novel rotary injection RIM system is presented to simulate the on-line injection and shear induced interfacial segregation in model PU/abherent systems. A wide range of recipes comprising single (liquids or solids) and multicomponent (liquid-liquid and solid-liquid) release materials were injected into the polymerizing resin mixture to provide cohesively weak and friable “particle” boundary layer assemblies at the PU/metal interface. An instrumented Blister Test was employed to evaluate the quality of the molded interfaces in terms of adhesion and the concentration distribution of the injected species in the final cured moldings was determined through high pressure liquid chromatography (HPLC). A comparison of the results on the shear modified and the compounded interfaces confirm an accentuated lateral migration of the additives to the interface resulting in an appreciable diminution in the adhesion of the system. Finally, transport models are suggested to account for the observed augmented transport.
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  • 69
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 70
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    Polymer Engineering and Science 30 (1990), S. 197-201 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: It is the purpose of the present publication to show that most of the phenomenological viscoelastic theories developed for bulk polymers can be readily adapted to plastic foams in order to evaluate their mechanical properties. In addition it will be demonstrated how the mechanical properties of open cell plastic foams can be predicted from a few simple compression and relaxation experiments.
    Additional Material: 7 Ill.
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  • 71
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    Polymer Engineering and Science 30 (1990), S. 211-218 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We have extended the essential work of fracture technique to allow for the determination of the plane-strain essential work of fracture. The new technique is to measure the specific work of fracture as a function of ligament length in deeply double edge notched samples. This type of data is then experimentally corrected to remove the plastic work of fracture and leave only the essential work of fracture as a function of ligament length. By extrapolating the essential work of fracture to zero-ligament length, we claim to be measuring the plane-strain essential work of fracture. This new technique was applied to two rubber toughened nylons and to a series of polyethylenes. The plane-strain essential work of fracture was found to be independent of thickness. Where comparison can be made to J-integral testing, the plane-strain essential work of fracture was similar to the critical J-integral, JIc.
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  • 72
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    Polymer Engineering and Science 30 (1990), S. 228-234 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The objective of this work has been to study composite systems in which carbon fibers are dispersed in a liquid crystal polymer matrix. The fundamental point of interest here has been the interfacial response that fiber surfaces can potentially induce in self-ordering polymers. The matrix material used was a thermotropic liquid crystal polyester synthesized in our laboratory from the monomers p-acetoxybenzoic acid, diacetoxyhydroquinone, and pimelic acid. The aromatic-aliphatic polymer was characterized by NMR as a chemically disordered polymer of the three structural units which exhibits a nematic phase at temperatures above 150°C. Breadline proton NMR above the solid to liquid crystal transition was used to measure the rate of magnetic alignment of molecules in the matrix and polarized optical microscopy was used to analyze interfacial zones in composite samples. Fiber surfaces were found to influence the orientation and orientational dynamics of a liquid crystal polymer matrix. This was revealed by enhanced rates of magnetic orientation in the polymer melt when carbon fibers are dispersed in the medium. Fiber surfaces were also found to stabilize nematic ordering of the polymer as the melt was heated towards complete isotropization. The phenomena discovered here may originate in the development of zones around fibers with a common molecular orientation anchored by the carbon surface.
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  • 73
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    Polymer Engineering and Science 30 (1990), S. 241-248 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A series of impact tests are described in which the plane strain fracture toughness, Kc1, of five different polymers is measured using a three point bend specimen at striker speeds up to 5m/s. At low speeds Kc1 is determined using the maximum load and a static analysis, but at speeds greater than 1 m/s the dynamic effects render the load signal unusable. For the higher speeds the fracture is timed using contact and crack propagation gages and the analysis is performed using the striker displacement at fracture. A dynamic analysis is used to convert this measurement to the true specimen displacement and Kc1 is determined from this. The apparent downward trends in the Kc1 results obtained, especially at speeds above 3m/s, are discussed.
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  • 74
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 75
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    Polymer Engineering and Science 30 (1990), S. 385-393 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We have developed a new method to measure the true temperature of the polymer melt and its three-dimensional distribution of a shot stored in the reservoir during injection. By means of this method, it is demonstrated that the temperature distribution of the polymer melt stored in the reservoir is strongly dependent on the setup molding conditions, the polymer investigated, and the geometry of the screw used. Further, it is noted qualitatively that there are two major effects of screw geometry on the temperature distribution of polymer melts. One, which governs strongly the temperature in the high temperature zone, is shear heat generated within the polymer itself in the metering zone of the screw during the transporting process. The second is the ability to preheat and plasticate the polymer in the compression zone, which is indispensable for uniform plastication.
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  • 76
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The breaking strength, strain at break, and work to rupture of perfect fibers prepared with polymers of finite molecular weight are calculated by treating the perfect fiber as a stressed crystal undergoing a crystal-melt phase transition. In this view, a tensile load destabilizes the crystal and depresses its melting point. When the load is sufficient to lower the melting temperature to the ambient condition the fiber melts - i.e., fails. The theoretical equations (extremely simple) are applied to several common polymer fibers. The maximum tensile strength of polyethylene, for example, is calculated to be 7 to 9 GPa, in good agreement with current experimental results.
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  • 77
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Vinyl polymers containing pendant acetal groups were synthesized using (2,2-dimethyl-l,3-dioxolan-4-yl)methyl acrylate (DMA) and (2,2-dimethyl-l,3-dioxo-lan-4-yl)methyl methacrylate (DMM), and were evaluated as negative electron beam (EB) resists. It was found that the EB sensitivity of polymers containing acetal groups in the side chain was higher than that of polymers containing acetal groups in the main chain. A high sensitivity of 3.6 × 10-8 C/cm2 was observed. Copolymers of DMA or DMM with styrene were also synthesized in order to improve the durability for dry etching process. It was found that the copolymers had an excellent dry etching durability and were adaptable to EB lithography.
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  • 78
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    Polymer Engineering and Science 30 (1990), S. 453-458 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The thermal behavior of poly(etheretherketone)(PEEK) film heated in an open differential scanning calorimetry (DSC) pan at 20°C/min is distorted by relaxation of the strained film. PEEK film in a closed pan or quenched PEEK in open or closed pans shows a glass-transition temperature (Tg) around 144°C, cold crystallization (∼22 J/g) at 177°C, melt-temperature (Tm) peaking at 335-340°C, with an enthalpy of fusion of 32-34 J/g, and recrystallization on cooling at 285°C, with a crystallization exotherm of about 40 J/g. The enthalpy of fusion decreases with increasing heating rate from 2-100°C/min and approaches the enthalpy of cold crystallization. With increasing heating rate, further crystallization of PEEK during the DSC scan is suppressed. With increasing cooling rate, PEEK melt crystallizes at larger supercoolings to a lesser extent. Crystallization on cooling the melt was more complete than cold crystallization and annealing on heating.
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  • 79
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    Polymer Engineering and Science 30 (1990), S. 459-468 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The electrical and dielectric properties of compression-molded segregated polyethylene-carbon black mixtures are described in the frequency range between 10 and 8000 kHz as a function of frequency, temperature, and carbon black loading. The segregated systems investigated exhibit insulator-conductor transitions in the range 0.25-0.65% (volume/volume) carbon black. The dielectric constant and the dissipation factor of the conductive samples are relatively very high in the frequency range studied. The dielectric constant increased sharply with the carbon black concentration, and then increased moderately beyond the insulator-conductor transition. The dissipation factor-concentration curves for different carbon blacks show maximum values in the vicinity of the critical concentration values. The dielectric properties of these systems are discussed in terms of interfacial Maxwell-Wagner polarization effects.
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  • 80
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    Polymer Engineering and Science 30 (1990), S. 476-479 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The heat capacities of isotactic polypropylene and its composite with glass fiber have been measured at high pressure, up to 7 MPa, in the melt state by high pressure differential scanning calorimetry (HPDSC). The values also have been calculated from the data of specific volume (V) measured by dilatometry and thermal conductivity (κ) and thermal diffusivity (α) measured by a compensating hot wire method. The values of the heat capacity measured from HPDSC are consistent with those from the calculation method. The heat capacities of molten polypropylene and its composite increase linearly with temperature at a constant pressure and decrease with pressure at a constant temperature. It was found that the heat capacity of polypropylene is insensitive to molecular weight. The heat capacities of molten polypropylene composites are found to be predicted by an additive rule from the weight fractions of heat capacities of polypropylene and glass fiber.
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  • 81
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    Polymer Engineering and Science 30 (1990), S. 480-484 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The mutual diffusion coefficients for styrene-butadiene rubber (SBR)-ethylbenzene systems were measured using a sorption apparatus with a quartz spring at 100 and 130°C for mass fractions of ethylbenzene ranging from 0 to 0.17. The mutual diffusion coefficients were correlated with good agreement by the free-volume theory.
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  • 82
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    Polymer Engineering and Science 30 (1990) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 83
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    Polymer Engineering and Science 30 (1990), S. 485-489 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polymers were prepared from saturated (HMDS) and unsaturated (AN) monomers in a radio frequency discharge (plasma). The effect of selected parameters such as electrode type (such as Cu, Zn, Ni, Al), reactor type, and substrate temperature (other parameters constant) on chemical structure and the rate of polymer deposition was examined by Fourier transform infrared (FTIR) spectroscopy. Differences in the nature of electrodes and reactor types were found to yield similar plasma products with similar rates of deposition for two monomers. In the tubular reactor used, deposition rates were observed to decrease with increasing substrate temperatures showing different dependencies on temperature for the monomers tested.
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  • 84
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    Polymer Engineering and Science 30 (1990), S. 469-475 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The dielectric and magnetic properties of polystyrene composites containing barium or nickel-zinc ferrites were studied as function of the ferrite concentration and field frequency. The composites were prepared by methods yielding a random distribution of the ferrite particles or segregated structures. Barium ferrite-poly-styrene composites exhibited a typical insulator behavior, and only above 60% ferrite were high values of the dielectric properties noted at the lower frequencies, decreasing gradually with frequency to the low values typical of the higher frequencies. The mode of barium ferrite particle distribution did not affect the dielectric properties. The nickel-zinc ferrite systems demonstrated a conductor type behavior. An apparent insulator-conductor transition was observed, having lower values for segregated than for random distributions. The magnetic permability of barium ferrite-polystyrene composites above 10% ferrite increases with the ferrite concentration, whereas the magnetic dissipation factor steeply increases with concentration above 40% ferrite.
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  • 85
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    Polymer Engineering and Science 30 (1990), S. 493-510 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Morphology and properties of polymer alloys can be controlled by thermody-namlcally reversible (structure freeze-in) or irreversible (structure lock-in) processes by simultaneously manipulating miscibility, mechanisms of phase separation, glass transition temperature (structural relaxation), and cure kinetics of polymer systems. Using phase diagrams consisting of binodal and spinodal curves, the morphology of epoxy/CTBN (carboxyl-terminated butadiene acryloni-trile copolymer) systems can be controlled by the mechanism of nucleation and growth or by spinodal decomposition via simultaneously manipulating the kinetic processes of phase separation and curing reactions. We have found that the particle size of the rubber reinforcement in epoxies is affected by the mechanisms of phase separation. Phase separation by nucleation and growth gives larger rubber particles than the corresponding phase separation by spinodal decomposition. This contrast in the morphology development is the consequence of controlling phase separation through chemorheological behavior. Medication of the phase separation kinetics in epoxy/CTBN systems was extremely effective at altering both morphology and properties of these alloys. This technique offers a means to shift the glass transition temperature of the rubber-rich phase drastically without reducing the glass transition temperature of the epoxy-rich phase significantly. Such control over morphology is the key to ultimately controlling material properties. This morphology manipulation allows us to tailor the mechanical properties of alloy systems.
    Additional Material: 16 Ill.
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  • 86
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 511-518 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Blends of polypropylene (PP) and ethylene-propylene rubber (EPR) and blends of polystyrene (PS) and styrene-butadiene rubber (SBR) were prepared in a laboratory-scale internal mixer at various blend compositions and rotor rates. Blend morphology was studied by means of electron microscopy. For each blend pair under the given processing conditions, the phase inversion process occurred progressively with respect to the variation in blend composition; it is within this composition range of phase inversion that dual-phase continuity was observed. In addition, Characteristic torque values of blends were found to deviate negatively from a linear additivity rule; the composition range of maximum deviation from linear additivity corresponded approximately to the composition range where dual-phase continuity was observed. Sperling's predictive scheme was found to yield acceptable (although not completely satisfactory) estimates for compositions of dual-phase continuity in the present systems. It was also observed that partial cross-linking of SBR during the mechanical blending process, as suggested by the appearance of a cure peak in the torque curve and supported by infrared spectroscopic evidence, resulted in morphological features drastically different from those of the uncured blends.
    Additional Material: 10 Ill.
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  • 87
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 519-526 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Blends of an engineering thermoplastic, poly(ethylene terephthalate) (PET), and two liquid crystalline polymers (LCPs) viz., copolyesters of PET and parahydrox-ybenzoic acid (PHB) in 40/60 mole percent (LCP60) and in 20/80 mole percent (LCP80) were prepared. A blend of LCP60 and LCP80 in 50/50 weight percent (LCP60-80) was blended with PET. Both flat films and rods were extruded and their properties examined. The morphology of the films investigated using Scanning Electron Microscopy (SEM) revealed that the LCP phase remained as dispersed droplets in the PET matrix. In spite of the lack of fibrillation in these films, the mechanical properties were enhanced to some extent with a maximum at 10 weight percent of the LCP phase. However, in the case of the rods thin fibrils of the LCP phase of the order of 1 μm in diameter were observed provided the composition of the LCP was 20 weight percent or greater. This success In achieving fibrillation is through to be due to the extensional flow fields present at the entrance of the capillary die and the fact that a short L/D ratio die was used. Differential Scanning Calorimetry (DSC) thermograms of the extruded films indicated that the LCP phase may act as a nucleating agent for the crystallization of PET. Rheology of the blends revealed that the complex viscosity of the blends is not much different from that of pure PET. This is attributed to the partial miscibility of the two components. Based on the DSC results and residence times in the extruder, it is concluded that no significant transesterification reactions appear to have: taken place in the blends. The rheology is studied further with respect to the cooling behavior of the pure components and factors important to the fibrillation of the LCP phase and the formation of in-situ reinforced composites are discussed.
    Additional Material: 7 Ill.
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  • 88
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 618-618 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 89
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Eight commercial semiconductor grade epoxy compounds that are used to encapsulate 1C (integrated circuit) devices have been evaluated for their ability to minimize the development of thermal stresses which can cause failure during device temperature cycling. Thermal expansion, dynamic modulus and adhesion studies are used to describe the mechanical interaction between the plastic package and the silicon device it surrounds. A “figure of merit” is defined for the development of stress on the 1C device as it is cooled after the packaging process. The stress is shown to be proportional to the product of three terms: (αp-αs) Ep (Tanch-T) where αp and αs are the expansion coefficients for the plastic and silicon, respectively, Ep is the modulus of the epoxy and Tanch is the temperature at which the epoxy becomes anchored to the silicon device during transfer molding. In addition, the importance of good adhesion between the epoxy encapsulant and the silicon device to prevent package cracking has been demonstrated by finite element analysis and a novel adhesion test.
    Additional Material: 16 Ill.
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  • 90
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 603-608 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Covalent grafting of mesogenic chains on carbon fiber surfaces was attempted as part of a study on composite materials containing liquid crystal polymer matrices. Grafting in these composite systems is viewed not only as a mechanism to achieve interfacial bonding but also as an approach to modify the interphase physical structure. The synthetic approach to grafting involved the in-situ polymerization of monomers in the presence of functionalized fibers in order to grow chains covalently attached to the fibers. The chemical mechanism may be viewed as the “transesterification of car boxy lated fibers” with acetylated monomers. The monomers used were pimelic acid, p-acetoxybenzoic acid and diacetoxy hydroquinone which are known to yield upon condensation a chemically aperiodic nematic polymer. Evidence for grafting was obtained from X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis on fibers retrieved from composite samples. Interestingly, SEM micrographs of fractured composite specimens containing the mesogen-grafted fibers reveal excellent wetting and interfacial bonding of a liquid crystalline matrix on the carbon surfaces. Based on theoretical considerations for end-adsorbed macromolecules and the nematogenic nature of the grafted chains we infer that dense layers of adsorbed polymer may form at the interfaces studied. From a materials point of view the in situ growth of liquid crystal polymer chains on fibers may offer mechanisms to control composite properties through both bonding and molecular orientation in interfacial regions.
    Additional Material: 9 Ill.
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  • 91
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We present chain structure, phase morphology, and toughness relationships in thermoplastic polymers and polymer/rubber blends. In neat polymers, molecular aspects of craze/yield behavior are controlled by two chain parameters: entanglement density νe and characteristic ratio C∞. The crazing stress is proportional to νe1/2, and the yield stress is proportional to C∞. The dispersed rubber toughens a polymer/rubber blend mainly by promoting energy dissipation of the matrix. The toughening efficiency correlates with the rubber phase morphology and the chain structure of the matrix.
    Additional Material: 7 Ill.
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  • 92
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    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 762-768 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The positron annihilation lifetime spectroscopy (PALS) technique is used to measure volume relaxation in physically aged glassy polycarbonate. The relaxation times and activation energy calculated for the isothermal relaxations in the aged polycarbonate are greater than those parameters calculated for unaged polycarbonate. The activation energy of 8.2 kcal/mol in the aged polycarbonate is used to identify the phenyl group motion or the cooperative carbonate-phenyl interaction as the molecular features responsible for the thermally induced open volume relaxations. It is postulated that the open volume relaxation kinetics as measured by PALS can be used as a nondestructive indication of property differences between aged and unaged polycarbonate.
    Additional Material: 6 Ill.
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  • 93
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 769-775 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of added silica on the spherulite radial growth rates of isotactic poly(propylene oxide) (i-PPrO) has been investigated by optical photomicroscopy. Two different i-PPrO samples were used of different molecular weights and isotacticity, 87 and 100% as determined by 13C NMR. The addition of fine particle silica, an effective nucleating agent, depresses the spherulite growth rates throughout the entire temperature range, but the effect is more dramatic for the i-PPrO of lower isotacticity. For a given sample, the retardation increases as the quantity of filler increases. The growth rate-temperature behavior is analyzed in terms of the classical Hoffman-Lauritzen equation, modified to take into account the polymer-filler interaction.
    Additional Material: 4 Ill.
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  • 94
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 835-840 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effects of different cure procedures on the structure and properties of epoxy samples made from diglycidyl ether of bisphenol A (DGEBA) and mixtures of two linear aliphatic diamines were studied. The elastic modulus, fracture toughness, impact resistance, and glass transition temperature were determined for various cure schemes. The morphologies of the cured resins were characterized with small angle X-ray scattering. The results show that samples with the same average morphology (molecular network structure) have similar elastic moduli and glass transition temperatures. If some heterogeneity is introduced in the molecular network structure without changing the average structure, however, the experiments indicate that the toughness can be increased without significantly sacrificing other properties.
    Additional Material: 6 Ill.
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  • 95
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 841-847 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Viscoelastic properties of polypropylene melts filled with small (0.15 μm) and large (4.0 μm) CaCO3 particles have been measured. The effects of particle size, loading, and rheological history on the dispersion of particles have been investigated. The dispersion of particles was found to decisively influence the viscoelastic properties of these filled polymers. The systems filled with large particles exhibit a relatively stable viscoelastic behavior. The small particle-filled polymers with low loading are stable similarly to the large particle-filled system. For the system filled with 30 wt% small particles, there appears a “second plateau” in the storage modulus G′ curve in low frequency region and the height of the second plateau depends strongly on the rheological history. The results are interpreted in terms of the formation of an internal structure of particles. It was found that the internal structure of particles is broken up by a steady shear flow and the dispersion of particles is changed.
    Additional Material: 10 Ill.
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  • 96
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 829-834 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Three copolymeric perfluoroethers with the structure CF3[(OCF2CF2)p(OCF2)q] OCF3, having different p/q ratios, have been fractionated. The fractions obtained have been characterized by Gel Permeation Chromatography and 19F-NMR. The viscosity η the specific volume v and the glass transition temperature, Tg have been measured by standard techniques for all the above samples as well as for some other perfluorinated polyethers.The temperature dependence of viscosity of the unfractionated samples is described by the W.L.F. equation. The values of fg (fractional free-volume at Tg) and of af (free-volume expansion coefficient) are independent of composition, for p/q ratios from 0.53 to 1.15. The critical molecular weight, Mc, is of the order of 8-9,000. From the molecular weight dependence of specific volume, the contribution to the molar volume of the in-chain CF2 group and the excess molar free volume of the chain ends have been determined. The limiting value of Tg for an infinite molecular weight polymer was found to depend linearly on the compositional ratio O/C and the extrapolated values for polytetrafluoroethylene and for the homopolymer (CF2O)n were found to be respectively 200 K and 120 K.
    Additional Material: 7 Ill.
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  • 97
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 1146-1150 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Divalent metal (I.e.) Ba(2+), Ca(2+i), Mg(2+), Mn(2+), Cd(2+), Zn(2+), Pb(2+), and Sn(2+) salts of monovalent organic acids (i.e. p-methoxycinnamic, cinnamic, p-methoxybenzoic, and 4-n-butoxybenzoic) were synthesized via the double decomposition reaction from aqueous solution. Optical microscopy and differential scanning calorimetry (DSC) analysis showed that this series of salts formed nematic liquid crystals. DSC thermograms were characterized by broad nematic-to-isotropic transitions indicative of biphasic regions in which the nematic and isotropic phases coexist. These liquid crystalline salts were polymeric when melted due to ionic crosslinking which took place through the coordination of the divalent metal ion. Except Sn (2+) and Pb(2+), all the liquid crystalline halato-polymers were spun into fibers.
    Additional Material: 2 Ill.
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  • 98
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 1158-1164 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The steady shear viscosity and dynamic moduli, at 180 and 200°C, of polystyrene composites, containing cross-linked monodisperse polystyrene beads varying in diameter from 0.2 to 0.8 μm, are independent of bead size and cross-link density, but increase with the volume fraction of beads. Steady shear viscosities exhibit power-law regions up to 40% concentration of beads, but no yield stress. Storage and loss moduli are initially linear with frequency, on double logarithmic plots, with limiting slopes of 1.3 and 0.9, respectively. Uncross-linked beads and beads cross-linked with 0.1% divinylbenzene are destroyed by thermomechanical dispersion in the melt.
    Additional Material: 10 Ill.
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  • 99
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 1140-1145 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Room temperature mechanical properties, such as flexural strength and impact resistance, of epoxies and graphite/epoxy composites go through a maximum as a function of epoxy conversion. For tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM)-4,4′-diamlnodiphenylsulfone (DDS) formulations, the recommended cure cycle prescribes a maximum temperature close to 177°C. The maximum extent of reaction that may be obtained at this temperature is determined from the vitrification curve. At this maximum conversion, balanced mechanical and physical properties are attained in the partially cured specimen. However, if the standard cycle is used to cure thick parts, the maximum temperature inside the sample increases beyond 177°C. This leads to a complete conversion in most of the part and a consequent impairment of resulting physical and mechanical properties. It is shown how numerical solutions of differential energy and mass balances may be used to propose alternative cure cycles such that the maximum conversion at every point remains bounded by the vitrification curve. An illustration for a particular thickness is provided.
    Additional Material: 9 Ill.
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  • 100
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 30 (1990), S. 1165-1170 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Thermal lithography on poly(ethylene terephthalate) (PET) is carried out by inducing crystallization through selective exposure of amorphous films to Infrared radiation. The obtained images can be smaller than the wavelength of the CO2 laser light. This circumvention of the diffraction limit is accomplished by taking advantage of the non-linear temperature dependence of the crystallization rate. The optical marking process is reversible through simple melting of the crystalline images. The complementary process, selective melting of an initially crystalline film, can also be accomplished. The use as a heat sink of a mask which forms the image pattern is demonstrated.
    Additional Material: 5 Ill.
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