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  • 2015-2019
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  • 1
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    Supporting Global Numerical Optimization of Rational Functions by Generic Symbolic Convexity Tests (2010)
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    Publikationsdatum: 2020-12-11
    Beschreibung: Convexity is an important property in nonlinear optimization since it allows to apply efficient local methods for finding global solutions. We propose to apply symbolic methods to prove or disprove convexity of rational functions over a polyhedral domain. Our algorithms reduce convexity questions to real quantifier elimination problems. Our methods are implemented and publicly available in the open source computer algebra system REDUCE. Our long term goal is to integrate REDUCE as a workhorse'' for symbolic computations into a numerical solver.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 2
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    Fault-Tolerant and Decentralized Lease Coordination in Distributed Systems (2010)
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    Publikationsdatum: 2016-06-30
    Beschreibung: Applications which need exclusive access to a shared resource in distributed systems require a fault-tolerant and scalable mechanism to coordinate this exclusive access. Examples of such applications include distributed file systems and master/slave data replication. We present Flease, an algorithm for decentralized and fault-tolerant lease coordination in distributed systems. Our algorithm allows the processes competing for a resource to coordinate exclusive access through leases among themselves without a central component. The resulting system easily scales with an increasing number of nodes and resources. We prove that Flease ensures exclusive access, i.e. guarantees that there is at most one valid lease at any time.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 3
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    Robust Tail Assignment (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: We propose an efficient column generation method to minimize the probability of delay propagations along aircraft rotations. In this way, delay resistant schedules can be constructed. Computational results for large-scale real-world problems demonstrate substantial punctuality improvements. The method can be generalized to crew and integrated scheduling problems.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 4
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    State Trajectory Compression for Optimal Control with Parabolic PDEs (2010)
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    Publikationsdatum: 2022-01-07
    Beschreibung: In optimal control problems with nonlinear time-dependent 3D PDEs, full 4D discretizations are usually prohibitive due to the storage requirement. For this reason gradient and quasi-Newton methods working on the reduced functional are often employed. The computation of the reduced gradient requires one solve of the state equation forward in time, and one backward solve of the adjoint equation. The state enters into the adjoint equation, again requiring the storage of a full 4D data set. We propose a lossy compression algorithm using an inexact but cheap predictor for the state data, with additional entropy coding of prediction errors. As the data is used inside a discretized, iterative algorithm, lossy coding maintaining an error bound is sufficient.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 5
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    A simple mathematical model of the bovine estrous cycle: follicle development and endocrine interactions (2010)
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    Publikationsdatum: 2020-03-11
    Beschreibung: Bovine fertility is the subject of extensive research in animal sciences, especially because fertility of dairy cows has declined during the last decades. The regulation of estrus is controlled by the complex interplay of various organs and hormones. Mathematical modeling of the bovine estrous cycle could help in understanding the dynamics of this complex biological system. In this paper we present a mathematical model of the bovine estrous cycle that includes the processes of follicle and corpus luteum development and the key hormones that interact to control these processes. Focus in this paper is on development of the model, but also some simulation results are presented, showing that a set of equations and parameters is obtained that describes the system consistent with empirical knowledge. Even though the majority of the mechanisms that are included are only known qualitatively as stimulatory or inhibitory effects, the model surprisingly well features quantitative observations made in reality. This model of the bovine estrous cycle could be used as a basis for more elaborate models with the ability to study effects of external manipulations and genetic differences.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 6
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    Rapid Learning for Binary Programs (2010)
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    Publikationsdatum: 2022-03-14
    Beschreibung: Learning during search allows solvers for discrete optimization problems to remember parts of the search that they have already performed and avoid revisiting redundant parts. Learning approaches pioneered by the SAT and CP communities have been successfully incorporated into the SCIP constraint integer programming platform. In this paper we show that performing a heuristic constraint programming search during root node processing of a binary program can rapidly learn useful nogoods, bound changes, primal solutions, and branching statistics that improve the remaining IP search.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 7
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    Models for Line Planning with Transfers (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: We propose a novel integer programming approach to transfer minimization for line planning problems in public transit. The idea is to incorporate penalties for transfers that are induced by “connection capacities” into the construction of the passenger paths. We show that such penalties can be dealt with by a combination of shortest and constrained shortest path algorithms such that the pricing problem for passenger paths can be solved efficiently. Connection capacity penalties (under)estimate the true transfer times. This error is, however, not a problem in practice. We show in a computational comparison with two standard models on a real-world scenario that our approach can be used to minimize passenger travel and transfer times for large-scale line planning problems with accurate results.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 8
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    Adaptive Timestep Control for the Contact-Stabilized Newmark Method (2010)
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    Publikationsdatum: 2016-06-09
    Beschreibung: The aim of this paper is to devise an adaptive timestep control in the contact--stabilized Newmark method (CONTACX) for dynamical contact problems between two viscoelastic bodies in the framework of Signorini's condition. In order to construct a comparative scheme of higher order accuracy, we extend extrapolation techniques. This approach demands a subtle theoretical investigation of an asymptotic error expansion of the contact--stabilized Newmark scheme. On the basis of theoretical insight and numerical observations, we suggest an error estimator and a timestep selection which also cover the presence of contact. Finally, we give a numerical example.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 9
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    Railway capacity auctions with dual prices (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: Railway scheduling is based on the principle of the construction of a conflict-free timetable. This leads to a strict definition of capacity: in contrast with road transportation, it can be said in advance whether a given railway infrastructure can accommodate - at least in theory - a certain set of train requests. Consequently, auctions for railway capacity are modeled as auctions of discrete goods -- the train slots. We present estimates for the efficiency gain that may be generated by slot auctioning in comparison with list price allocation. We introduce a new class of allocation and auction problems, the feasible assignment problem, that is a proper generalization of the well-known combinatorial auction problem. The feasible assignment class was designed to cover the needs for an auction mechanism for railway slot auctions, but is of interest in its own right. As a practical instance to state and solve the railway slot allocation problem, we present an integer programming formulation, briefly the ACP, which turns out to be an instance of the feasible assignment problem and whose dual problem yields prices that can be applied to define a useful activity rule for the linearized version of the Ausubel Milgrom Proxy auction. We perform a simulation aiming to measure the impact on efficiency and convergence rate.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 10
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    Solving Optimal Control Problems with the Kaskade 7 Finite Element Toolbox (2010)
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    Publikationsdatum: 2022-01-07
    Beschreibung: This paper presents concepts and implementation of the finite element toolbox Kaskade 7, a flexible C++ code for solving elliptic and parabolic PDE systems. Issues such as problem formulation, assembly and adaptivity are discussed at the example of optimal control problems. Trajectory compression for parabolic optimization problems is considered as a case study.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 11
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    Aggregation Methods for Railway Networks (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: In this paper a bottom-up approach of automatic simplification of a railway network is presented. Starting from a very detailed, microscopic level, as it is used in railway simulation, the network is transformed by an algorithm to a less detailed level (macroscopic network), that is sufficient for long-term planning and optimization. In addition running and headway times are rounded to a pre-chosen time discretization by a special cumulative method, which we will present and analyse in this paper. After the transformation we fill the network with given train requests to compute an optimal slot allocation. Then the optimized schedule is re-transformed into the microscopic level and can be simulated without any conflicts occuring between the slots. The algorithm is used to transform the network of the very dense Simplon corridor between Swiss and Italy. With our aggregation it is possible for the first time to generate a profit maximal and conflict free timetable for the corridor across a day by a simultaneously optimization run.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 12
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    Merging solutions of non-linear algebraic systems (2010)
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    Publikationsdatum: 2020-12-11
    Beschreibung: In solving large polynomial algebraic systems that are too big for standard Gröbner basis techniques one way to make progress is to introduce case distinctions. This divide and conquer technique can be beneficial if the algorithms and computer programs know how to take advantage of inequalities. A further hurdle is the form of the resulting general solutions which often have unnecessarily many branches. In this paper we discuss a procedure to merge solutions by dropping inequalities which are associated with them and, if necessary, by re-parametrizing solutions. In the appendix the usefulness of the procedure is demonstrated in the classification of quadratic Hamiltonians with a Lie-Poisson bracket $e(3)$. This application required the solution of algebraic systems with over 200 unknowns, 450 equations and between 5000 and 9000 terms.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 13
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    A Dynamical Systems Approach for Static Evaluation in Go (2010)
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    Publikationsdatum: 2020-12-11
    Beschreibung: In the paper arguments are given why the concept of static evaluation (SE) has the potential to be a useful extension to Monte Carlo tree search. A new concept of modeling SE through a dynamical system is introduced and strengths and weaknesses are discussed. The general suitability of this approach is demonstrated. A Remark: Among users of the Internet Go server KGS the abbreviation SE is used for 'Score Estimator'. Although different from 'Static Evaluation' a score estimator is easily obtained from static evaluation by adding up probabilities of chains to be alive at the end of the game or points to be owned by White or Black
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 14
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    Classification of integrable quadratic Hamiltonians on e(3) (2010)
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    Publikationsdatum: 2020-12-11
    Beschreibung: Linear Poisson brackets on e(3) typical of rigid body dynamics are considered. All quadratic Hamiltonians of Kowalevski type having additional first integral of fourth degree are found. Quantum analogs of these Hamiltonians are listed.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 15
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    Classification of integrable super-systems using the SsTools environment (2010)
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    Publikationsdatum: 2020-12-11
    Beschreibung: A classification problem is proposed for supersymmetric %scaling\/-\/in\-va\-ri\-ant evolutionary PDE that satisfy the assumptions of nonlinearity, nondegeneracy, and homogeneity. Four classes of nonlinear coupled boson\/-\/fermion systems are discovered under the weighting assumption $|f|=|b|=|D_t|=\oh$. The syntax of the \Reduce\ package \SsTools, which was used for intermediate computations, and the applicability of its procedures to the calculus of super\/-\/PDE are described.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 16
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    N=2 supersymmetric a=4-KdV hierarchy derived via Gardner's deformation of Kaup-Boussinesq equation (2010)
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    Publikationsdatum: 2020-12-11
    Beschreibung: We consider the problem of constructing Gardner's deformations for the $N{=}2$ supersymmetric $a{=}4$--\/Korteweg\/--\/de Vries equation; such deformations yield recurrence relations between the super\/-\/Hamiltonians of the hierarchy. We prove the non\/-\/existence %P.~Mathieu's Open problem on constructing for of supersymmetry\/-\/invariant %Gardner's deformations that %solutions, retract to Gardner's formulas for the KdV equation %whenever it is assumed that, under the %respective component reduction. % in the $N{=}2$ super\/-\/field. the solutions . At the same time, we propose a two\/-\/step scheme for the recursive production of the integrals of motion for the $N{=}2$,\ $a{=}4$--\/SKdV. First, we find a new Gardner's deformation of the Kaup\/--\/Boussinesq equation, which is contained in the bosonic limit of the super\/-\/%$N{=}2$,\ $a{=}4$--\/SKdV hierarchy. This yields the recurrence relation between the Hamiltonians of the limit, whence we determine the bosonic super\/- /Hamiltonians of the full $N{=}2$, $a{=}4$--\/SKdV hierarchy.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 17
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    The Quickest Path to the Goal (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: We provide an introduction into the mathematics of and with paths. Not on the shortest, but hopefully on an entertaining path!
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 18
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    Linienoptimierung - reif für die Praxis? (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: Wir stellen in dieser Arbeit ein mathematisches Optimierungsmodell zur Bestimmung eines optimalen Linienplans vor, das sowohl die Fahrzeiten und die Anzahl der Umstiege berücksichtigt als auch die Kosten des Liniennetzes. Dieses Modell deckt wichtige praktische Anforderungen ab, die in einem gemeinsamen Projekt mit den Verkehrsbetrieben in Potsdam (ViP) formuliert wurden. In diesem Projekt wurde der Linienplan 2010 für Potsdam entwickelt. Unsere Berechnungen zeigen, dass die mathematische Optimierung in nichts einer "Handplanung" des Liniennetzes nachsteht. Im Gegenteil, mit Hilfe des Optimierungsprogramms ist es möglich, durch Veränderung der Parameter mehrere verschiedene Szenarien zu berechnen, miteinander zu vergleichen und Aussagen über minimale Kosten und Fahrzeiten zu machen.
    Schlagwort(e): ddc:510
    Sprache: Deutsch
    Materialart: reportzib , doc-type:preprint
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  • 19
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    Positions in the Game of Go as Complex Systems (2010)
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    Publikationsdatum: 2020-12-11
    Beschreibung: The paper gathers evidence showing different dimensions of the game of Go: the continuous and discrete nature of the game and different types of relations between state variables happening on ultra local, local, regional, and global scales. Based on these observations a new continuous local model for describing a board position is introduced. This includes the identification of the basic variables describing a board position and the formulation and solution of a dynamical system for their computation. To be usable as a static evaluation function for a game playing program at least group-wide (regional)aspects will have to be incorporated.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 20
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    Railway Track Allocation by Rapid Branching (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: The track allocation problem, also known as train routing problem or train timetabling problem, is to find a conflict-free set of train routes of maximum value in a railway network. Although it can be modeled as a standard path packing problem, instances of sizes relevant for real-world railway applications could not be solved up to now. We propose a rapid branching column generation approach that integrates the solution of the LP relaxation of a path coupling formulation of the problem with a special rounding heuristic. The approach is based on and exploits special properties of the bundle method for the approximate solution of convex piecewise linear functions. Computational results for difficult instances of the benchmark library TTPLIB are reported.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 21
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    Optimizing the Simplon Railway Corridor (2010)
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    Publikationsdatum: 2020-08-05
    Beschreibung: This paper presents a case study on a railway timetable optimization for the very dense Simplon corridor, a major railway connection in the Alps between Switzerland and Italy. Starting from a detailed microscopic network as it is used in railway simulation, the data is transformed by an automatic procedure to a less detailed macroscopic network, that is sufficient for the purpose of capacity planning and amenable to state-of-the-art integer programming optimization methods. In this way, the macroscopic railway network is saturated with trains. Finally, the corresponding timetable is re-transformed to the microscopic level in such a way that it can be operated without any conflicts among the slots. Using this integer programming based micro-macro aggregation-disaggregation approach, it becomes for the first time possible to generate a profit maximal and conflict free timetable for the complete Simplon corridor over an entire day by a simultaneous optimization of all trains requests. This also allows to to undertake a sensitivity analysis of various problem parameters.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 22
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    Analysis of a multi-scale asymptotic model for internal gravity waves in a moist atmosphere (2010)
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    Publikationsdatum: 2016-06-09
    Beschreibung: The thesis presents the analysis of a reduced model for modulation of internal gravity waves by deep convective clouds. The starting point for the derivation are conservation laws for mass, momentum and energy coupled with a bulk micro-physics model describing the evolution of mixing ratios of water vapor, cloud water and rain water. A reduced model for the identified scales of the regime is derived, using multi-scale asymptotics. The closure of the model employs conditional averaging over the horizontal scale of the convective clouds. The resulting reduced model is an extension of the anelastic equations, linearized around a constant background state, which are well-known from meteorology. The closure of the model is achieved purely by analytical means and involves no additional physically motivated assumptions. The essential new parameter arising from the coupling to a micro-physics model is the area fraction of saturated regions on the horizontal scale of the convective clouds. It turns out that this parameter is constant on the employed short timescale. Hence the clouds constitute a constant background, modulating the characteristics of propagation of internal waves. The model is then investigated by analytical as well as numerical means. Important results are, among others, that in the model moisture (i) inhibits propagation of internal waves by reducing the modulus of the group velocity, (ii) reduces the angle between the propagation direction of a wave-packet and the horizontal, (iii) causes critical layers and (iv) introduces a maximum horizontal wavelength beyond which waves are no longer propagating but become evanescent. The investigated examples of orographically generated gravity waves also feature a significant reduction of vertical momentum flux by moisture. The model is extended by assuming systematically small under-saturation, that is saturation at leading order. The closure is similar to the original case but requires additional assumptions. The saturated area fraction in the obtained model is no longer constant but now depends nonlinearly on vertical displacement and thus on vertical velocity.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: doctoralthesis , doc-type:doctoralThesis
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  • 23
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    A Constraint Integer Programming Approach for Resource-Constrained Project Scheduling (2010)
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    Publikationsdatum: 2022-03-14
    Beschreibung: We propose a hybrid approach for solving the resource-constrained project scheduling problem which is an extremely hard to solve combinatorial optimization problem of practical relevance. Jobs have to be scheduled on (renewable) resources subject to precedence constraints such that the resource capacities are never exceeded and the latest completion time of all jobs is minimized. The problem has challenged researchers from different communities, such as integer programming (IP), constraint programming (CP), and satisfiability testing (SAT). Still, there are instances with 60 jobs which have not been solved for many years. The currently best known approach, lazyFD, is a hybrid between CP and SAT techniques. In this paper we propose an even stronger hybridization by integrating all the three areas, IP, CP, and SAT, into a single branch-and-bound scheme. We show that lower bounds from the linear relaxation of the IP formulation and conflict analysis are key ingredients for pruning the search tree. First computational experiments show very promising results. For five instances of the well-known PSPLIB we report an improvement of lower bounds. Our implementation is generic, thus it can be potentially applied to similar problems as well.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 24
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    Coupling Meshbased and Meshfree Methods by a Transfer Operator Approach (2010)
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    Publikationsdatum: 2023-11-03
    Beschreibung: In contrast to the well known meshbased methods like the finite element method, meshfree methods do not rely on a mesh. However besides their great applicability, meshfree methods are rather time consuming. Thus, it seems favorable to combine both methods, by using meshfree methods only in a small part of the domain, where a mesh is disadvantageous, and a meshbased method for the rest of the domain. We motivate, that this coupling between the two simulation techniques can be considered as saddle point problem and show the stability of this coupling. Thereby a novel transfer operator is introduced, which interacts in the transition zone, where both methods coexist.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 25
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    Diskrete Mathematik und ihre Anwendungen: Auf dem Weg zu authentischem Mathematikunterricht (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: Das heutige Leben ist durchdrungen von komplexen Technologien. Ohne Kommunikationsnetze, Internet, Mobilfunk, Logistik, Verkehrstechnik, medizinische Apparate, etc. könnte die moderne Gesellschaft nicht funktionieren. Fast alle dieser Technologien haben einen hohen Mathematikanteil. Der "normale Bürger"' weiss davon nichts, der Schulunterricht könnte dem ein wenig abhelfen. Einige mathematische Aspekte dieser Technologien sind einfach und sogar spielerisch intuitiv zugänglich. Solche Anwendungen, die zusätzlich noch der Lebensumwelt der Schüler zugehören, können dazu genutzt werden, die mathematische Modellierung, also die mathematische Herangehensweise an die Lösung praktischer Fragen, anschaulich zu erläutern. Gerade in der diskreten Mathematik können hier, quasi "nebenbei" mathematische Theorien erarbeitet und Teilaspekte (Definitionen, Fragestellungen, einfache Sachverhalte) durch eigenständiges Entdecken der Schüler entwickelt werden. Wir beginnen mit einigen Beispielen.
    Schlagwort(e): ddc:510
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    Wegeprobleme der Graphentheorie (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: Den kürzesten Weg in einem Graphen zu finden ist ein klassisches Problem der Graphentheorie. Über einen Vortrag zu diesem Thema beim Tag der Mathematik 2007 von R. Borndörfer kam ich in Kontakt mit dem Konrad-Zuse-Zentrum (ZIB), das sich u.a. mit Wegeoptimierung beschäftigt. Ein Forschungsschwerpunkt dort ist im Rahmen eines Projekts zur Chipverifikation das Zählen von Lösungen, das, wie wir sehen werden, eng mit dem Zählen von Wegen zusammenhängt. Anhand von zwei Fragen aus der Graphentheorie soll diese Facharbeit unterschiedliche Lösungsmethoden untersuchen. Wie bestimmt man den kürzesten Weg zwischen zwei Knoten in einem Graphen und wie findet man alle möglichen Wege? Nach einer Einführung in die Graphentheorie und einer Konkretisierung der Probleme wird zunächst für beide eine Lösung mit auf Graphen basierenden Algorithmen vorgestellt. Während der Algorithmus von Dijkstra sehr bekannt ist, habe ich für das Zählen von Wegen einen eigenen Algorithmus auf der Basis der Tiefensuche entwickelt. Im zweiten Teil der Arbeit wird das Konzept der ganzzahligen Programmierung vorgestellt und die Lösungsmöglichkeiten für Wegeprobleme, die sich darüber ergeben. Schließlich wurden die vorgestellten Algorithmen am Beispiel des S- und U-Bahnnetzes von Berlin implementiert und mit Programmen, die die gleichen Fragen über ganzzahlige Programmierung lösen, verglichen.
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    A Perturbation Result for Dynamical Contact Problems (2008)
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    Publikationsdatum: 2016-06-09
    Beschreibung: This paper is intended to be a first step towards the continuous dependence of dynamical contact problems on the initial data as well as the uniqueness of a solution. Moreover, it provides the basis for a proof of the convergence of popular time integration schemes as the Newmark method. We study a frictionless dynamical contact problem between both linearly elastic and viscoelastic bodies which is formulated via the Signorini contact conditions. For viscoelastic materials fulfilling the Kelvin-Voigt constitutive law, we find a characterization of the class of problems which satisfy a perturbation result in a non-trivial mix of norms in function space. This characterization is given in the form of a stability condition on the contact stresses at the contact boundaries. Furthermore, we present perturbation results for two well-established approximations of the classical Signorini condition: The Signorini condition formulated in velocities and the model of normal compliance, both satisfying even a sharper version of our stability condition.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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    An Integer Programming Algorithm for Routing Optimization in IP Networks (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: Most data networks nowadays use shortest path protocols to route the traffic. Given administrative routing lengths for the links of the network, all data packets are sent along shortest paths with respect to these lengths from their source to their destination. In this paper, we present an integer programming algorithm for the minimum congestion unsplittable shortest path routing problem, which arises in the operational planning of such networks. Given a capacitated directed graph and a set of communication demands, the goal is to find routing lengths that define a unique shortest path for each demand and minimize the maximum congestion over all links in the resulting routing. We illustrate the general decomposition approach our algorithm is based on, present the integer and linear programming models used to solve the master and the client problem, and discuss the most important implementational aspects. Finally, we report computational results for various benchmark problems, which demonstrate the efficiency of our algorithm.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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    The Line Connectivity Problem (2008)
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    Publikationsdatum: 2020-12-15
    Beschreibung: This paper introduces the "line connectivity problem", a generalization of the Steiner tree problem and a special case of the line planning problem. We study its complexity and give an IP formulation in terms of an exponential number of constraints associated with "line cut constraints". These inequalities can be separated in polynomial time. We also generalize the Steiner partition inequalities.
    Schlagwort(e): ddc:510
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    Using Model Counting to Find Optimal Distinguishing Tests (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: Testing is the process of stimulating a system with inputs in order to reveal hidden parts of the system state. In the case of non-deterministic systems, the difficulty arises that an input pattern can generate several possible outcomes. Some of these outcomes allow to distinguish between different hypotheses about the system state, while others do~not. In this paper, we present a novel approach to find, for non-deterministic systems modeled as constraints over variables, tests that allow to distinguish among the hypotheses as good as possible. The idea is to assess the quality of a test by determining the ratio of distinguishing (good) and not distinguishing (bad) outcomes. This measure refines previous notions proposed in the literature on model-based testing and can be computed using model counting techniques. We propose and analyze a greedy-type algorithm to solve this test optimization problem, using existing model counters as a building block. We give preliminary experimental results of our method, and discuss possible improvements.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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    On the Effects of Minor Changes in Model Formulations (2008)
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    Publikationsdatum: 2021-08-05
    Beschreibung: Starting with the description of the Traveling Salesmen Problem formulation as given by van Vyve and Wolsey in the article Approximate extended formulations'', we investigate the effects of small variations onto the performance of contemporary mixed integer programming solvers. We will show that even minor changes in the formulation of the model can result in performance difference of more than a factor of 1000. As the results show it is not obvious which changes will result in performance improvements and which not.
    Schlagwort(e): ddc:510
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    Detecting Orbitopal Symmetries (2008)
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    Publikationsdatum: 2022-03-14
    Beschreibung: Orbitopes can be used to handle symmetries which arise in integer programming formulations with an inherent assignment structure. We investigate the detection of symmetries appearing in this approach. We show that detecting so-called orbitopal symmetries is graph-isomorphism hard in general, but can be performed in linear time if the assignment structure is known.
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    Optimization and Identification in Regional Hyperthermia (2008)
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    Publikationsdatum: 2019-01-29
    Beschreibung: Regional hyperthermia is a cancer therapy aiming at heating tumors using phased array applicators. This article provides an overview over current mathematical challenges of delivering individually optimal treatments. The focus is on therapy planning and identification of technical as well as physiological quantities from MR thermometry measurements.
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    On Efficiency and Accuracy in Cardioelectric Simulation (2008)
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    Publikationsdatum: 2019-05-10
    Beschreibung: Reasons for the failure of adaptive methods to deliver improved efficiency when integrating monodomain models for myocardiac excitation are discussed. Two closely related techniques for reducing the computational complexity of linearly implicit integrators, deliberate sparsing and splitting, are investigated with respect to their impact on computing time and accuracy.
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    Models for Periodic Timetabling (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: We investigate the computation of periodic timetables for public transport by mixed integer programming. After introducing the problem, we describe two mathematical models for periodic timetabling, the PERIODIC EVENT SCHEDULING PROBLEM (PESP) and the QUADRATIC SEMI-ASSIGNMENT PROBLEM. Specifically, we give an overview of existing integer programming (IP) formulations for both models. An important contribution of our work are new IP formulations for the PESP based on time discretization. We provide an analytical comparison of these formulations and describe different techniques that allow a more efficient solution by mixed integer programming. In a preliminary computational study, on the basis of standard IP solvers, we compare different formulations for computing periodic timetables. Our results justify a further investigation of the time discretization approach. Typically the timetable is optimized for the current traffic situation. The main difficulty with this approach is that after introducing the new timetable the passengers’ travel behavior may differ from that assumed for the computation. Motivated by this problem, we examine an iterative timetabling procedure that is a combination of timetable computation and passenger routing. We discuss the algorithmic issues of the passenger routing and study properties of the computed timetables. Finally, we confirm our theoretical results on the basis of an own implementation.
    Beschreibung: Wir untersuchen die Berechnung von Taktfahrplänen für den öffentlichen Verkehr mit gemischt-ganzzahliger Programmierung (MIP). Im Anschluss an die Problembeschreibung, stellen wir zwei mathematische Modellierungen vor, das PERIODIC EVENT SCHEDULING PROBLEM (PESP) und das QUADRATIC SEMI-ASSIGNMENT PROBLEM. Wichtiger Bestandteil ist ein Überblick über existierende ganzzahlige Formulierungen beider Modelle. Wir entwickeln neue ganzzahlige Formulierungen für das PESP auf der Basis von Zeitdiskretisierung. Diese werden analytisch miteinander verglichen und wir beschreiben verschiedene Techniken, die eine effizientere Lösung der Formulierungen mit gemischt-ganzzahliger Programmierung ermöglichen. In einer ersten Rechenstudie, unter Verwendung gängiger MIP-Löser, vergleichen wir verschiedene ganzzahlige Formulierungen zur Berechnung von Taktfahrplänen. Unsere Ergebnisse rechtfertigen eine weitere Untersuchung des Zeitdiskretisierungsansatzes. In der Regel werden Fahrpläne mit Bezug auf die gegenwärtige Verkehrssituation optimiert. Dies birgt jedoch folgendes Problem. Wenn der neue Fahrplan eingeführt wird, ist es möglich, dass die Passagiere ein anderes Fahrverhalten zu Tage legen, als für die Berechnung des Fahrplans angenommen wurde. Vor diesem Hintergrund behandeln wir ein iteratives Verfahren zur Berechnung von Taktfahrplänen. Dieses ist eine Kombination aus Fahrplanberechnung und Passagierrouting. Neben den algorithmischen Details des Passagierroutings untersuchen wir Eigenschaften der berechneten Fahrpläne. Abschließend bestätigen wir unsere theoretischen Ergebnisse auf Grundlage einer eigenen Implementierung des Verfahrens.
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    Sprache: Englisch
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    Experiments with nonlinear extensions to SCIP (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: This paper describes several experiments to explore the options for solving a class of mixed integer nonlinear programming problems that stem from a real-world mine production planning project. The only type of nonlinear constraints in these problems are bilinear equalities involving continuous variables, which enforce the ratios between elements in mixed material streams. A branch-and-bound algorithm to handle the integer variables has been tried in another project. However, this branch-and-bound algorithm is not effective for handling the nonlinear constraints. Therefore state-of-the-art nonlinear solvers are utilized to solve the resulting nonlinear subproblems in this work. The experiments were carried out using the NEOS server for optimization. After finding that current nonlinear programming solvers seem to lack suitable preprocessing capabilities, we preprocess the instances beforehand and use an heuristic approach to solve the nonlinear subproblems. In the appendix, we explain how to add a polynomial constraint handler that uses IPOPT as embedded nonlinear programming solver for the constraint programming framework SCIP. This is one of the crucial steps for implementing our algorithm in SCIP. We briefly described our approach and give an idea of the work involved.
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    Tiefensuche: Bemerkungen zur Algorithmengeschichte (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: Dieser kurze Aufsatz zur Algorithmengeschichte ist Eberhard Knobloch, meinem Lieblings-Mathematikhistoriker, zum 65. Geburtstag gewidmet. Eberhard Knobloch hat immer, wenn ich ihm eine historische Frage zur Mathematik stellte, eine Antwort gewusst – fast immer auch sofort. Erst als ich mich selbst ein wenig und dazu amateurhaft mit Mathematikgeschichte beschäftigte, wurde mir bewusst, wie schwierig dieses „Geschäft“ ist. Man muss nicht nur mehrere (alte) Sprachen beherrschen, sondern auch die wissenschaftliche Bedeutung von Begriffen und Symbolen in früheren Zeiten kennen. Man muss zusätzlich herausfinden, was zur Zeit der Entstehung der Texte „allgemeines Wissen“ war, insbesondere, was seinerzeit gültige Beweisideen und -schritte waren, und daher damals keiner präzisen Definition oder Einführung bedurfte. Es gibt aber noch eine Steigerung des historischen Schwierigkeitsgrades: Algorithmengeschichte. Dies möchte ich in diesem Artikel kurz darlegen in der Hoffnung, dass sich Wissenschaftshistoriker dieses Themas noch intensiver annehmen, als sie das bisher tun. Der Grund ist, dass heute Algorithmen viele Bereiche unserer Alltagswelt steuern und unser tägliches Leben oft von funktionierenden Algorithmen abhängt. Daher wäre eine bessere Kenntnis der Algorithmengeschichte von großem Interesse.
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    State constrained optimal control problems with states of low regularity (2008)
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    Publikationsdatum: 2016-06-09
    Beschreibung: We consider first order optimality conditions for state constrained optimal control problems. In particular we study the case where the state equation has not enough regularity to admit existence of a Slater point in function space. We overcome this difficulty by a special transformation. Under a density condition we show existence of Lagrange multipliers, which have a representation via measures and additional regularity properties.
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    Properties of Reduced Reversible Markov Chains (2008)
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    Publikationsdatum: 2016-06-09
    Beschreibung: The enormous time lag between fast atomic motion and complex pro- tein folding events makes it almost impossible to compute molecular dy- namics on a high resolution. A common way to tackle this problem is to model the system dynamics as a Markov process. Yet for large molec- ular systems the resulting Markov chains can hardly be handled due to the curse of dimensionality. Coarse graining methods can be used to re- duce the dimension of a Markov chain, but it is still unclear how far the coarse grained Markov chain resembles the original system. In order to answer this question, two different coarse-graining methods were analysed and compared: a classical set-based reduction method and an alternative subspace-based approach, which is based on membership vectors instead of sets. On the basis of a small toy system, it could be shown, that in con- trast to the subset-based approach, the subspace-based reduction method preserves the Markov property as well as the essential dynamics of the original system.
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    Line Planning on Paths and Tree Networks with Applications to the Quito Trolebus System (2008)
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    Publikationsdatum: 2021-02-19
    Beschreibung: Line planning is an important step in the strategic planning process of a public transportation system. In this paper, we discuss an optimization model for this problem in order to minimize operation costs while guaranteeing a certain level of quality of service, in terms of available transport capacity. We analyze the problem for path and tree network topologies as well as several categories of line operation that are important for the Quito Trolebus system. It turns out that, from a computational complexity worst case point of view, the problem is hard in all but the most simple variants. In practice, however, instances based on real data from the Trolebus System in Quito can be solved quite well, and significant optimization potentials can be demonstrated.
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    On the optimality of Least Recently Used (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: It is well known that competitive analysis yields too pessimistic results when applied to the paging problem and it also cannot make a distinction between many paging strategies. Many deterministic paging algorithms achieve the same competitive ratio, ranging from inefficient strategies as flush-when-full to the good performing least-recently-used (LRU). In this paper, we study this fundamental online problem from the viewpoint of stochastic dominance. We show that when sequences are drawn from distributions modelling locality of reference, LRU is stochastically better than any other online paging algorithm.
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    Angebotsplanung im öffentlichen Nahverkehr (2008)
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    Publikationsdatum: 2020-12-15
    Beschreibung: Die Angebotsplanung im öffentlichen Nahverkehr umfasst die Aufgaben der Netz-, Linien-,Fahr- und Preisplanung. Wir stellen zwei mathematische Optimierungsmodelle zur Linien- und Preisplanung vor. Wir zeigen anhand von Berechnungen für die Verkehrsbetriebe in Potsdam(ViP), dass sich damit komplexe Zusammenhänge quantitativ analysieren lassen. Auf diese Weise untersuchen wir die Auswirkungen von Freiheitsgraden auf die Konstruktion von Linien und die Wahl von Reisewegen der Passagiere, Abhängigkeiten zwischen Kosten und Reisezeiten sowie den Einfluss verschiedener Preissysteme auf Nachfrage und Kostendeckung.
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    Constraint Integer Programming: a New Approach to Integrate CP and MIP (2008)
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    Publikationsdatum: 2022-03-14
    Beschreibung: This article introduces constraint integer programming (CIP), which is a novel way to combine constraint programming (CP) and mixed integer programming (MIP) methodologies. CIP is a generalization of MIP that supports the notion of general constraints as in CP. This approach is supported by the CIP framework SCIP, which also integrates techniques from SAT solving. SCIP is available in source code and free for non-commercial use. We demonstrate the usefulness of CIP on two tasks. First, we apply the constraint integer programming approach to pure mixed integer programs. Computational experiments show that SCIP is almost competitive to current state-of-the-art commercial MIP solvers. Second, we employ the CIP framework to solve chip design verification problems, which involve some highly non-linear constraint types that are very hard to handle by pure MIP solvers. The CIP approach is very effective here: it can apply the full sophisticated MIP machinery to the linear part of the problem, while dealing with the non-linear constraints by employing constraint programming techniques.
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    An Extended Mathematical Framework for Barrier Methods in Function Space (2008)
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    Publikationsdatum: 2016-06-09
    Beschreibung: An extended mathematical framework for barrier methods for state constrained optimal control compared to [Schiela, ZIB-Report 07-07] is considered. This allows to apply the results derived there to more general classes of optimal control problems, in particular to boundary control and finite dimensional control.
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    Counting solutions of integer programs using unrestricted subtree detection (2008)
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    Publikationsdatum: 2021-08-05
    Beschreibung: In the recent years there has been tremendous progress in the development of algorithms to find optimal solutions for integer programs. In many applications it is, however, desirable (or even necessary) to generate all feasible solutions. Examples arise in the areas of hardware and software verification and discrete geometry. In this paper, we investigate how to extend branch-and-cut integer programming frameworks to support the generation of all solutions. We propose a method to detect so-called unrestricted subtrees, which allows us to prune the integer program search tree and to collect several solutions simultaneously. We present computational results of this branch-and-count paradigm which show the potential of the unrestricted subtree detection.
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    On the cardinality constrained matroid polytope (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: Edmonds showed that the so-called rank inequalities and the nonnegativity constraints provide a complete linear description of the matroid polytope. By essentially adding Grötschel's cardinality forcing inequalities, we obtain a complete linear description of the cardinality constrained matroid polytope which is the convex hull of the incidence vectors of those independent sets that have a feasible cardinality. Moreover, we show how the separation problem for the cardinality forcing inequalities can be reduced to that for the rank inequalities. We also give necessary and sufficient conditions for a cardinality forcing inequality to be facet defining.
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    On solving large systems of polynomial equations appearing in Discrete Differential Geometry (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: The paper describes a method for solution of very large overdetermined algebraic polynomial systems on an example that appears from a classification of all integrable 3-dimensional scalar discrete quasilinear equations $Q_3=0$ on an elementary cubic cell of the lattice ${\mathbb Z}^3$. The overdetermined polynomial algebraic system that has to be solved is far too large to be formulated. A probing' technique which replaces independent variables by random integers or zero allows to formulate subsets of this system. An automatic alteration of equation formulating steps and equation solving steps leads to an iteration process that solves the computational problem.
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    Sprache: Englisch
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    Invertible Mappings of Nonlinear PDEs to Linear PDEs Through Admitted Conservation Laws (2008)
    Details
    Publikationsdatum: 2020-08-05
    Beschreibung: An algorithmic method using conservation law multipliers is introduced that yields necessary and sufficient conditions to find invertible mappings of a given nonlinear PDE to some linear PDE and to construct such a mapping when it exists. Previous methods yielded such conditions from admitted point or contact symmetries of the nonlinear PDE. Through examples, these two linearization approaches are contrasted.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 49
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    Classification of 3-dimensional integrable scalar discrete equations (2008)
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    Publikationsdatum: 2021-02-26
    Beschreibung: We classify all integrable 3-dimensional scalar discrete affine linear equations $Q_3=0$ on an elementary cubic cell of the lattice ${\mathbb Z}^3$. An equation $Q_3=0$ %of such form is called integrable if it may be consistently imposed on all $3$-dimensional elementary faces of the lattice ${\mathbb Z}^4$. Under the natural requirement of invariance of the equation under the action of the complete group of symmetries of the cube we prove that the only ontrivial(non-linearizable) integrable equation from this class is the well-known dBKP-system.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 50
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    About a Computer Algebra based online Mathtest (2008)
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    Publikationsdatum: 2020-12-11
    Beschreibung: The article describes the online mathematics test {\tt http://lie.math.brocku.ca/mathtest}, its typical applications and experiences gathered.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 51
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    TTPLIB 2008 - A Library for Train Timetabling Problems (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: We introduce (TTPlib), a data library for train timetabling problems that can be accessed at http://ttplib.zib.de. In version 1.0, the library contains data related to 50 scenarios. Most instances result from the combination of macroscopic railway networks and several train request sets for the German long distance area containing Hannover, Kassel and Fulda, short denoted by Ha-Ka-Fu. In this paper, we introduce the data concepts of TTPlib, describe the scenarios included in the library and provide a free visualization tool TraVis.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 52
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    The Parametric Solution of Underdetermined linear ODEs (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: The purpose of this paper is twofold. An immediate practical use of the presented algorithm is its applicability to the parametric solution of underdetermined linear ordinary differential equations (ODEs) with coefficients that are arbitrary analytic functions in the independent variable. A second conceptual aim is to present an algorithm that is in some sense dual to the fundamental Euclids algorithm, and thus an alternative to the special case of a Gr\"{o}bner basis algorithm as it is used for solving linear ODE-systems. In the paper Euclids algorithm and the new dual version' are compared and their complementary strengths are analysed on the task of solving underdetermined ODEs. An implementation of the described algorithm is interactively accessible at http://lie.math.brocku.ca/crack/uode.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 53
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    Probabilistic analysis of Online Bin Coloring algorithms via Stochastic Comparison (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: This paper proposes a new method for probabilistic analysis of online algorithms that is based on the notion of stochastic dominance. We develop the method for the Online Bin Coloring problem introduced by Krumke et al. Using methods for the stochastic comparison of Markov chains we establish the strong result that the performance of the online algorithm GreedyFit is stochastically dominated by the performance of the algorithm OneBin for any number of items processed. This result gives a more realistic picture than competitive analysis and explains the behavior observed in simulations.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 54
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    Models for Fare Planning in Public Transport (2008)
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    Publikationsdatum: 2020-12-15
    Beschreibung: The optimization of fare systems in public transit allows to pursue objectives such as the maximization of demand, revenue, profit, or social welfare. We propose a non-linear optimization approach to fare planning that is based on a detailed discrete choice model of user behavior. The approach allows to analyze different fare structures, optimization objectives, and operational scenarios involving, e.g., subsidies. We use the resulting models to compute optimized fare systems for the city of Potsdam, Germany.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 55
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    Solving Pseudo-Boolean Problems with SCIP (2008)
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    Publikationsdatum: 2022-03-14
    Beschreibung: Pseudo-Boolean problems generalize SAT problems by allowing linear constraints and a linear objective function. Different solvers, mainly having their roots in the SAT domain, have been proposed and compared,for instance, in Pseudo-Boolean evaluations. One can also formulate Pseudo-Boolean models as integer programming models. That is,Pseudo-Boolean problems lie on the border between the SAT domain and the integer programming field. In this paper, we approach Pseudo-Boolean problems from the integer programming side. We introduce the framework SCIP that implements constraint integer programming techniques. It integrates methods from constraint programming, integer programming, and SAT-solving: the solution of linear programming relaxations, propagation of linear as well as nonlinear constraints, and conflict analysis. We argue that this approach is suitable for Pseudo-Boolean instances containing general linear constraints, while it is less efficient for pure SAT problems. We present extensive computational experiments on the test set used for the Pseudo-Boolean evaluation 2007. We show that our approach is very efficient for optimization instances and competitive for feasibility problems. For the nonlinear parts, we also investigate the influence of linear programming relaxations and propagation methods on the performance. It turns out that both techniques are helpful for obtaining an efficient solution method.
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 56
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    Planung von öffentlichem Personenverkehr (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: Millionen von Menschen werden allein in Deutschland täglich von Bussen, Bahnen und Flugzeugen transportiert. Der öffentliche Personenverkehr (ÖV) ist von großer Bedeutung für die Lebensqualität einzelner aber auch für die Leistungsfähigkeit ganzer Regionen. Qualität und Effizienz von ÖV-Systemen hängen ab von politischen Rahmenbedingungen (staatlich geplant, wettbewerblich organisiert) und der Eignung der Infrastruktur (Schienensysteme, Flughafenstandorte), vom vorhandenen Verkehrsangebot (Fahr- und Flugplan), von der Verwendung angemessener Technologien (Informations-, Kontroll- und Buchungssysteme) und dem bestmöglichen Einsatz der Betriebsmittel (Energie, Fahrzeuge und Personal). Die hierbei auftretenden Entscheidungs-, Planungs- und Optimierungsprobleme sind z.T. gigantisch und "schreien" aufgrund ihrer hohen Komplexität nach Unterstützung durch Mathematik. Dieser Artikel skizziert den Stand und die Bedeutung des Einsatzes von Mathematik bei der Planung und Durchführung von öffentlichem Personenverkehr, beschreibt die bestehenden Herausforderungen und regt zukunftsweisende Maßnahmen an.
    Schlagwort(e): ddc:510
    Sprache: Deutsch
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  • 57
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    Development and test of a numerical model for pulse thermography in civil engineering (2008)
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    Publikationsdatum: 2019-05-10
    Beschreibung: Pulse thermography of concrete structures is used in civil engineering for detecting voids, honeycombing and delamination. The physical situation is readily modeled by Fourier's law. Despite the simplicity of the PDE structure, quantitatively realistic numerical 3D simulation faces two major obstacles. First, the short heating pulse induces a thin boundary layer at the heated surface which encapsulates all information and therefore has to be resolved faithfully. Even with adaptive mesh refinement techniques, obtaining useful accuracies requires an unsatisfactorily fine discretization. Second, bulk material parameters and boundary conditions are barely known exactly. We address both issues by a semi-analytic reformulation of the heat transport problem and by parameter identification. Numerical results are compared with measurements of test specimens.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 58
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    Barrier Methods for Optimal Control Problems with Convex Nonlinear Gradient Constraints (2008)
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    Publikationsdatum: 2016-06-09
    Beschreibung: In this paper we are concerned with the application of interior point methods in function space to gradient constrained optimal control problems, governed by partial differential equations. We will derive existence of solutions together with first order optimality conditions. Afterwards we show continuity of the central path, together with convergence rates depending on the interior point parameter.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 59
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    Interior Point Methods in Function Space for State Constraints - Inexact Newton and Adaptivity (2008)
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    Publikationsdatum: 2016-06-09
    Beschreibung: We consider an interior point method in function space for PDE constrained optimal control problems with state constraints. Our emphasis is on the construction and analysis of an algorithm that integrates a Newton path-following method with adaptive grid refinement. This is done in the framework of inexact Newton methods in function space, where the discretization error of each Newton step is controlled by adaptive grid refinement in the innermost loop. This allows to perform most of the required Newton steps on coarse grids, such that the overall computational time is dominated by the last few steps. For this purpose we propose an a-posteriori error estimator for a problem suited norm.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 60
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    Fair Ticket Prices in Public Transport (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: Ticket pricing in public transport usually takes a welfare or mnemonics maximization point of view. These approaches do not consider fairness in the sense that users of a shared infrastructure should pay for the costs that they generate. We propose an ansatz to determine fair ticket prices that combines concepts from cooperative game theory and integer programming. An application to pricing railway tickets for the intercity network of the Netherlands demonstrates that, in this sense, prices that are much fairer than standard ones can be computed in this way.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 61
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    A sharp interface finite volume method for elliptic equations on Cartesian grids (2008)
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    Publikationsdatum: 2014-02-26
    Beschreibung: We present a second order sharp interface finite volume method for the solution of the three-dimensional poisson equation with variable coefficients on Cartesian grids. In particular, we focus on interface problems with discontinuities in the coefficient, the source term, the solution, and the fluxes across the interface. The method uses standard piecewiese trilinear finite elements for normal cells and a double piecewise trilinear ansatz for the solution on cells intersected by the interface resulting always in a compact 27-point stencil. Singularities associated with vanishing partial volumes of intersected grid cells are removed by a two-term asymptotic approach. In contrast to the 2D method presented by two of the authors in [M.~Oevermann, R.~Klein: A Cartesian grid finite volume method for elliptic equations with variable coefficients and embedded interfaces, J.~Comp.~Phys.~219 (2006)] we use a minimization technique to determine the unknown coefficients of the double trilinear ansatz. This simplifies the treatment of the different cut-cell types and avoids additional special operations for degenerated interface topologies. The resulting set of linear equations has been solved with a BiCGSTAB solver preconditioned with an algebraic multigrid. In various testcases -- including large coefficient ratios and non-smooth interfaces -- the method achieves second order of accuracy in the L_inf and L_2 norm.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 62
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    Cardinality Constrained Combinatorial Optimization: Complexity and Polyhedra (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: Given a combinatorial optimization problem and a subset $N$ of natural numbers, we obtain a cardinality constrained version of this problem by permitting only those feasible solutions whose cardinalities are elements of $N$. In this paper we briefly touch on questions that addresses common grounds and differences of the complexity of a combinatorial optimization problem and its cardinality constrained version. Afterwards we focus on polytopes associated with cardinality constrained combinatorial optimization problems. Given an integer programming formulation for a combinatorial optimization problem, by essentially adding Grötschel's cardinality forcing inequalities, we obtain an integer programming formulation for its cardinality restricted version. Since the cardinality forcing inequalities in their original form are mostly not facet defining for the associated polyhedra, we discuss possibilities to strengthen them.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 63
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    On the complexity of column generation in survivable network design with path-based survivability mechanisms (2008)
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    Publikationsdatum: 2020-08-05
    Beschreibung: This survey concerns optimization problems arising in the design of survivable communication networks. It turns out that such problems can be modeled in a natural way as non-compact linear programming formulations based on multicommodity flow network models. These non-compact formulations involve an exponential number of path flow variables, and therefore require column generation to be solved to optimality. We consider several path-based survivability mechanisms and present results, both known and new, on the complexity of the corresponding column generation problems (called the pricing problems). We discuss results for the case of the single link (or node) failures scenarios, and extend the considerations to multiple link failures. Further, we classify the design problems corresponding to different survivability mechanisms according to the structure of their pricing problem. Finally, we show that almost all encountered pricing problems are hard to solve for scenarios admitting multiple failures.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 64
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    On the Line Planning Problem in Tree Networks (2008)
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    Publikationsdatum: 2021-02-19
    Beschreibung: We introduce an optimization model for the line planning problem in a public transportation system that aims at minimizing operational costs while ensuring a given level of quality of service in terms of available transport capacity. We discuss the computational complexity of the model for tree network topologies and line structures that arise in a real-world application at the Trolebus Integrated System in Quito. Computational results for this system are reported.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 65
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    Line Planning on Paths and Tree Networks with Applications to the Quito Trolebus System (Extended Abstract) (2008)
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    Publikationsdatum: 2021-02-19
    Beschreibung: Line planning is an important step in the strategic planning process of a public transportation system. In this paper, we discuss an optimization model for this problem in order to minimize operation costs while guaranteeing a certain level of quality of service, in terms of available transport capacity. We analyze the problem for path and tree network topologies as well as several categories of line operation that are important for the Quito Trolebus system. It turns out that, from a computational complexity worst case point of view, the problem is hard in all but the most simple variants. In practice, however, instances based on real data from the Trolebus System in Quito can be solved quite well, and significant optimization potentials can be demonstrated.
    Schlagwort(e): ddc:510
    Sprache: Englisch
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  • 66
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    Meshless Methods in Confirmation Dynamics (2006)
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    Publikationsdatum: 2016-06-09
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: doctoralthesis , doc-type:doctoralThesis
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  • 67
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    Kombinatorische Optimierung –Inhalte und Methoden für einen authentischen Mathematikunterricht (2006)
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    Publikationsdatum: 2020-08-05
    Beschreibung: wird nachgereicht
    Schlagwort(e): ddc:510
    Sprache: Englisch
    Materialart: doctoralthesis , doc-type:doctoralThesis
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  • 68
    Digitale Medien
    Digitale Medien
    Production of polysaccharide with Xanthomonas campestris (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 51-63 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Industrially important polysaccharides are now primarily obtained from plant sources. One exception is the exocellular bacterial polysaccharide, dextran. A survey at the Northern Laboratory revealed that many other microbial polysaccharides could be synthesized by the action of micro-organisms on starch-derived saccharides. Previous publications from this laboratory describe the production of the microbial polymer, phosphomannan, synthesized by the yeast Hansenula holstii. This paper describes the production of another polysaccharide, synthesized by the bacterium Xanthomonas campestris NRRL B-1459.Fermentation of media containing 3 per cent dextrose, seeded with 5 per cent inoculum of X. campestris NRRL B-1459 and cultured aerobically at 28°C, is complete in 96 h. A light tan polymer is recovered in yields of 50 per cent, based on commercial dextrose, from the viscous fermentation broth by precipitation with methanol in the presence of an electrolyte. The viscosities of aqueous re-solutions containing 1 and 2 per cent of the polymer were 3,000 cP and 11,000 cP respectively.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030107
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  • 69
    Digitale Medien
    Digitale Medien
    Ion-exchange chromatography of the streptomycin complex (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 79-85 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Various studies have revealed the presence of several maltolproducing compounds in streptomycin preparations. These previous studies have utilized the techniques of counter-current distribution, column chromatography, paper chromatography, and electrophoresis. A system of cation-exchange chromatography has been reported which separates, at least partially, six components of the streptomycin complex. This technique involves the use of a gradient elution procedure.In addition to five maltol-producing compounds, another member of the complex is reported. The possible significance of such a compound is discussed.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030109
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  • 70
    Digitale Medien
    Digitale Medien
    Percentage estimation of denitrifying bacteria (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 115-117 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030113
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  • 71
    Digitale Medien
    Digitale Medien
    Masthead (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961) 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030401
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  • 72
    Digitale Medien
    Digitale Medien
    The chemical sterilization of liquid media with beta-propiolactone and ethylene oxidePresented at the 138th National Meeting, American Chemical Society, New York, September 1960. (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 311-323 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The effectiveness of beta-propiolactone (BPL) and ethylene oxides as sterilants for liquid microbiological media was studied. Preliminary tests against heavy suspensions of B. coagulans in various media confirmed the sterilizing levels found by earlier investigators. In actinomycin fermentation tests, both compounds were found to sterilize effectively at concentrations up to 0·5 per cent without significant effects on the growth-promoting qualities of the medium. At the concentrations required to sterilize large numbers of spores (0·5-1·0 per cent), however, both agents exhibit inhibitory effects on the fermentation. In these cases BPL is less damaging than ethylene oxide.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030308
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  • 73
    Digitale Medien
    Digitale Medien
    Dihydroxyacetone: Production and usesPresented at the 140th National Meeting of the American Chemical Society, Chicago, Illinois, September 1961. (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 351-355 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Based on numerous reports in the literature, it appeared that the commerical production of dihydroxyacetone by microbial fermentation was not feasible due to the comparatively long duration of fermentation and the low total yield that could be obtained per fermentor. A new study has indicated that by adjusting environmental conditions and by modifying mash ingredients, commerical production of dihyroxyacetone via microbial oxidation of glycerol is practicable. The effect of these variables on the rate and extent of dihydroxyacetone production is discussed. The commerical and pharmaceutical uses of dihydroxyacetone and its derivatives is presented.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030404
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  • 74
    Digitale Medien
    Digitale Medien
    Small-scale studies of microbiological oxidation of hydrocarbons to long-chain fatty acids (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 219-233 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Several strains of Pseudomonas, Nocardia and incompletely identified soil isolates have been grown in a mineral salts plus hydrocarbon medium, and the fatty acids produced by the organisms have been isolated, identified and estimated. The results of an estimation of the percentage conversion to these acids under varying experimental conditions is discussed in relation to the metabolic systems involved. Some indication has been obtained that the hydrocarbon breakdown pathway by these organisms is that of ω oxidation followed by β oxidation. Preliminary experiments carried out with one strain of organism, Pseudomonas aeruginosa 5940, indicate that there may be some difference in the utilization of odd- and even-chain hydrocarbons by this organism. An improvement of 3 ·8-fold was obtained by using nitrate instead of ammonium nitrogen; 13-fold by using continuous instead of batch operation; and 8-fold by the use of liquid instead of solid paraffins, giving a total improvement of yield of 400-fold.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030302
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  • 75
    Digitale Medien
    Digitale Medien
    Adsorption method for measuring the specific and average areas of cells (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 235-240 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: This paper presents a method for measuring the specific area (area/mass) of micro-organisms and the average area of cells, based on the adsorption of dyes.
    Zusätzliches Material: 1 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030303
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  • 76
    Digitale Medien
    Digitale Medien
    Redox potential changes in the 2-keto-L-gulonic acid fermentation - I. Correlation between redox potential and dissolved-oxygen concentrationData presented in this paper were taken from a thesis, submitted in June, 1961, to St. John's University, New York, as partial fulfilment of the requirement for the degree of Doctor of Philosophy. (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 241-253 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The redox potential changes in the oxidative fermentation of L-sorbose to 2-keto-L-gulonic acid were investigated, using a mutant strain of Pseudomonas. The growth medium contained sorbose as the sole carbohydrate source. It was found that the redox potential curve of the fermenting system indicated qualitatively the existing oxygen demand of the culture. Increasing aeration rates led to higher oxygen demand and lower redox potentials. A comparison of the redox potential curves revealed that although the amount of dissolved oxygen directly affected the respiration of the culture, it did not necessarily mean respiratory insufficiency. The redox potential difference between the aerated and the deoxygenated (nitrogen flushed) fermentation broth was found to be linearly proportional to the logarithm of the dissolved-oxygen concentration. This observation served as the basis of a new quantitative method of dissolved-oxygen measurement, for which the name differential redoxymetry was proposed.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030304
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  • 77
    Digitale Medien
    Digitale Medien
    Inhibition of microbiological breakdown of Δ1,4-androstadienedione with cyclic compounds (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 325-329 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030309
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  • 78
    Digitale Medien
    Digitale Medien
    Mathematical models for the product accumulation in microbiolgical processes (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 95-109 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A production model consisting of one or more exponential decay functions is proposed to represent the rate of accumulation of a product per unit weight of cell. This, together with a cell age distribution function, is used to describe the product accumulation in a fermentation process.This postulate offers a unified concept applicable to both batch and continuous processes as well as problems arising from environmental changes. The idea is compatible with the current understanding of microbial physiology. It offers an interpretation for the controversy over cell-product ratios observed in some batch and continuous fermentations when treated as conventional chemical reaction. The proposed postulate fits reasonably well with the lysine and lactic acid processes.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030111
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  • 79
    Digitale Medien
    Digitale Medien
    Masthead (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961) 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030201
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  • 80
    Digitale Medien
    Digitale Medien
    Masthead (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961) 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030101
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  • 81
    Digitale Medien
    Digitale Medien
    Cation exchangers on a sugar-beet pulp base. Application for decontaminating radioactive waste water (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 7-20 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A cation exchanger suitable for decontaminating low and medium radioactive waste water was sought. Regeneration being considered undesirable, the exchange material had to be cheap and readily obtainable. Sugar-beet pulp, a weakly acidic cation exchanger, satisfies these conditions. Its capacity is about 0·62 mg eq. per gram of dry matter. In order to study the selectivity of the sugar-beet pulp exchanger, the equilibrium curve of the reaction was determined.This curve was found to have the shape of the hyperbola proposed by Waterman and Weber for the characterization of the course of simultaneous reactions. Sugar-beet pulp adsorbs the salts of the alkaline earth metals selectively in the presence of both Na+ and La+++. Sugar-beet pulp was used to decontaminate a solution containing 140BaCl2 and 140LaCl3 and having an activity of about 10-2 μc/ml. The results were satisfactory.By treating sugar-beet pulp with formaldehyde and hydrochloric acid, the amount of water bound to the pulp is very much decreased. By this treatment a cation exchanger is produced having a capacity per unit volume about six times greater than that of sugar-beet pulp. The capacity of this exchanger is about 0·5 mg eq. per gram of dry matter. The selective behaviour of sugar-beet pulp treated with formaldehyde is similar to that of unmodified sugar-beet pulp.By treating sugar-beet pulp with formaldehyde, hydrochloric acid and dilute sulphuric acid, a cation exchanger with very good mechanical and filtration properties is obtained. This exchanger has a capacity of about 1·3 mg eq. per gram of dry matter.It seems possible to employ the cation exchangers obtained by treatment of sugar-beet pulp with either formaldehyde and HCl or formaldehyde, HCl and H2SO4 also for purposes other than the removal of radioactive cations from water.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030103
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  • 82
    Digitale Medien
    Digitale Medien
    The prediction of oxygen transfer rates in the presence of mould mycelium (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 1-6 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: An empirical relationship of oxygen transfer rate and mould viscosity is discussed, which leads to equations for predicting the OTR of mould fermentations.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030102
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  • 83
    Digitale Medien
    Digitale Medien
    The disintegration of bacteria and other micro-organisms by the M.S.E.-Mullard Ultrasonic disintegrator (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 405-433 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Two commercially available ultrasonic instruments are described, in which micro-organisms and other cells may be disintegrated.Sound waves (20 kc/s) are generated in the cell suspension by means of titanium velocity transformers (probes) coupled to a magnetostriction transducer. One instrument operating at 500 W will disintegrate from 2 to 500 ml, the other operating at 50 W from 1 ml to 30 ml.Yeast was used as a test organism but results on some other organisms are also given. Cell rupture is shown to be independent of sonically generated free radicals, but enzyme inactivation (alcohol dehydrogenase) is accelerated by free radicals. Increasing the viscosity, decreasing surface tension of the suspending medium, or the presence of CO2 decreases disintegration. The addition of solid nuclei such as powdered glass, as well as small air bubbles, increases disintegration.This is consistent with disintegration being due to cavitation, but does not indicate the precise mechanism of cell rupture. Some effects of sonic disruption are compared with disruption by other methods.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030408
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  • 84
    Digitale Medien
    Digitale Medien
    An improved pH electrode assembly for pilot plant and plant fermentorsPresented 138th National Meeting, American Chemical Society, New York, N.Y., September, 1960. (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 125-137 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A modified pH electrode assembly is desccribed which is capable of steam sterilization and which can be installed in steel fermentors of all sizes in a variety of ways. Its design is such that electrode life is prolonged and contamination hazards are reduced.
    Zusätzliches Material: 8 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030203
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  • 85
    Digitale Medien
    Digitale Medien
    A method for the preparation of undigested bacterial cell wallsThe work reported in this paper was made possible through Research Grant (E-2690) from the National Institutes of Health, United States Public Health Service, Bethesda, to the University of Pennsylvania. (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 151-159 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The combination of low-temperature disintegration with gradient and pile centrifugation makes possible the preparation of bacterial cell walls under conditions preventing digestion.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030205
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  • 86
    Digitale Medien
    Digitale Medien
    Bacterial sulphide production from sulphate-enriched spent distillery liquor - II (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 181-197 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Accumulation of volatile acids produced during anaerobic fermentation of distillery-spent liquor decreased the activity of Desulphovibrio desulphuricans employed in previously communicated studies; this caused a decrease in the reduction of sulphates to sulphides. An enriched strain of Desulphovibrio rubentschikii made in a synthetic mineral medium (NH4Cl, 1·0 g; MgSO4·7H2O, 2·0 g; NaCl, 10·0 g; CaSO4, 1·0 g; calcium acetate, 1·0 g; K2HPO4, 0·5 g; Mohrs' salt, trace in 1 l.) using calcium acetate as the substrate and carbon from the tap-water was gradually built up to a 3-1. volume. The amount of hydrogen sulphide in this medium was found to be 225 mg/l. The fermentation was next carried out in a synthetic medium containing volatile acids from distillery-spent liquor as the only substrate. A 3-1. fermentation set up with diluted distillery-spent liquor (300 ml or raw liquor in 3,000 ml of water), neutralized with NaOH to pH 7·2 and supplemented with calcium sulphate and 0·1 per cent urea, showed sulphide productions (calculated as milligrams of hydrogen sulphide per litre of raw distillery-spent liquid) of 2,000, 4,000 and 6,000 with 0·1, 1·0 and 2·0 per cent calcium sulphate in the charge respectively. The volatile acid content, expressed as acetic acid, was 18,564 mg/litre of raw distillery-spent liquor on an average throughout the study. The ratio of hydrogen sulphide produced per litre of raw distillery-spent liquor to the amount of volatile acids developed expressed in milliequivalents per litre of raw liquor during fermentation increased gradually from 0·1367 to 0·5567 in the presence of 0·1 to 2·0 per cent of calcium sulphate in the charge.
    Zusätzliches Material: 7 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030208
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  • 87
    Digitale Medien
    Digitale Medien
    Measurement of dissolved oxygen in fermentationsPublished with the approval of the Director of the Wisconsin Agricultural Experiment Station. Supported in part by funds from Abbott Laboratories, North Chicago, Illinois. (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 261-275 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Two methods have been investigated for the measurement of dissolved oxygen in fermentations: the tubing method and the probe method. The sensing elements for both methods are steam-sterilizable and measure only the oxygen tension in the liquid phase. The tubing method is probably the most accurate and reliable method available for measurement of dissolved oxygen in fermentations but it requires extensive ancillary apparatus.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030306
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  • 88
    Digitale Medien
    Digitale Medien
    A rapid estimation of prednisolone produced by fermentative oxidation (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 119-123 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: An analytical method has been devised for the rapid determination of prednisolone produced in a fermentative oxidation process. It allows frequent checking of concentrations of the prednisolone formed during the oxidation of hydrocortisone.The estimation of prednisolone in the presence of hydrocortisone is based upon the diversity of colour shown by the chromogens produced from these steroids by sulphuric acid and ethanol. Using the optimal reagent mixture and conditions, the interference of hydrocortisone is negligible. The steroids are extracted from the fermentation broth with ethyl acetate. One test takes about 20 min.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030202
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  • 89
    Digitale Medien
    Digitale Medien
    Miso - I. Preparation of soybeans for fermentation (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 161-174 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The preparation of soybeans for fermentation is a very important part of the process for making miso, a traditional Japanese food. In general, soybeans from the United States are smaller and more pigmented than Japanese soybeans. Twenty-eight American varieties, four Japanese varieties and one Chinese variety have been studied with respect to absorption of water and cooking. A variety of soaking and cooking conditions have been investigated. Some U.S. varieties absorb water and cook unevenly. Unevenness in cooking is not associated with the size of the beans within a variety.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030206
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  • 90
    Digitale Medien
    Digitale Medien
    Die technische Herstellung von klinischem dextran durch gelenkte synthese in wachsender Kultur (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 199-218 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A process is described for the production of a specific-molecular-weight dextran, e.g. clinical dextran, by using a modified form of controlled synthesis. The synthesis is carried out directly in a medium containing appropriate amounts of sucrose and low-molecular-weight dextran after inoculation with a culture of actively growing bacteria. The importance of an inoculum substantially freed from substances affecting the synthesis of dextran is demonstrated. The technique appears to offer a decided advantage over other well-known procedures. Technical details of the process and equipment are given.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030209
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  • 91
    Digitale Medien
    Digitale Medien
    A preliminary study of depth filtration at a constant rateThis paper was presented before the ACS meeting held in New York, September 1960. (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 139-150 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The constant-rate operation of a system utilizing asbestos filter-pads for the cold sterilization of a tissue culture medium is described. Filtration theory is briefly reviewed with regard to the constant-rate process, and the results of several data treatment methods are reported. The standard law of Hermans and Bredée4, 5 best describes the constant-rate data. Computation of the data, when plotted by the standard-law method, results in two straight lines divided by a transition zone. The second region is characterized by a slower plugging rate and a plot of the standard-law slopes versus the initial filtration pressures shows a linear relation. The constant-rate method is compared with the constant-pressure method and is found to yield equivalent overall filtrate rates at lower operating pressures.The observed filtration behaviour is discussed, and available data are presented to indicate the sterilization capability of the filter.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030204
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  • 92
    Digitale Medien
    Digitale Medien
    The disintegration of yeast with dry ice and some properties of the extract (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 175-180 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A simple procedure for the disintegration of yeast cells, by which litre quantities of cell extract (approximately 11 per cent dry weight) may be obtained, is described. The fresh yeast cake is treated with dry ice in a high speed electric homogenizer after which it is left to thaw out at 0°. No addition of buffer has to be made, and the cell juice obtained after centrifugation of the resulting slurry appears to contain different subcellular particles and various enzymes in a relatively native state.When the extract is incubated at higher temperatures, proteolysis will rapidly change the electrophoretic and enzymatic properties, which indicates that procedures involving autolysis may be dangerous when information about the chemical composition of the native enzymes is desired.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030207
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  • 93
    Digitale Medien
    Digitale Medien
    Production of concentrated cell suspensions: The sponge fermentor (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 339-350 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A novel fermentor is described in which aerobic microorganisms are grown on solid medium. Cellulose sponges support a nutrient-agar medium, resulting in a large surface area for growth within a relatively small volume. The sponges are alternately squeezed and relaxed within a piston-and-cylinder-type apparatus during fermentation. Provision is made for inoculation, harvesting, and for supplying air during operation. The apparatus has been operated semicontinuously in that there are enough cells left in the sponges after harvest to inoculate fresh medium. Cell concentrations of Serratia marcescens up to 84 × 1010 per ml have been recovered. A growth curve for this micro-organism is given and sample data on semicontinuous operation are presented.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030403
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  • 94
    Digitale Medien
    Digitale Medien
    Continuous cultivation of micro-organisms: A new approach and possibilities for its use (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 357-376 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: When trying to turn a batch fermentation process into a continuous process, many important factors must be repected. A new approach is presented by means of which it is possible to reproduce in a continuous system those changes (both inside the cells and in the environment) which are functions of elapsed time (lag-type changes, sudden changes occurring at a constant growth rate of the micro-organisms, etc.). Special attention is paid to lag-type changes. In the hitherto described apparatuses for continuous cultivation it was difficult to follow changes which are functions of time. The use of a multi-stage apparatus is therefore suggested, and a method of cultivation, which through adjusting retention times in individual cultivation vessels allows a detailed study of such changes, is proposed. Basic equations concerning the growth of microorganisms in the described apparatus are derived and some examples of the possible practical use of the new approach are presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030405
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  • 95
    Digitale Medien
    Digitale Medien
    Chemical separation methods for common microbes (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 395-403 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: To collect microbes from suspensions by a process other than centrifugation, it has been found effective to add inorganic and organic electrolytes in the colloidal state. The addition of electrolytes causes a neutralization of charges on the particles in suspension resulting in their coagulation and precipitation. High-molecular-weight compounds which form micelles also promote coagulation and precipitation. It is believed that chemical collection is an extremely efficient method of treatment for the mass production of microbial suspensions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030407
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  • 96
    Digitale Medien
    Digitale Medien
    Neue apparatur zur Herstellung von Schüttelkulturen von Mikroorganismen (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 331-338 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A simple apparatus for preparing shake cultures of microorganisms on a laboratory scale is described. Using a series of special shaking vessels, each of a capacity of 1-10 l., a total volume of 20-200 l. of culture can be produced in one run. The rate of aeration is similar to the one observed in shake flasks.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030402
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  • 97
    Digitale Medien
    Digitale Medien
    Volume increase of wheat kernels accompanying absorption of liquid water (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 377-393 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: The purposes of this investigation were to determine the relationship between weight and volume increases which take place when wheat kernels are immersed in water, to develop an equation for the volume increase, and to test experimentally its validity.It was shown that the volume increase was practically equal to the weight increase divided by the fluid density. In view of this, the following equation was obtained by analogy to the diffusion equation derived by Becker.1 \documentclass{article}\pagestyle{empty}\begin{document}$$ 1 - \bar V = \frac{2}{{\sqrt \pi }}\frac{S}{V}\sqrt {D_\upsilon \theta } $$\end{document} where 1 - V̄ is the relative volume increase, and Dv is the coefficient of volume increase.The average coefficients of volume increase are given by the Arrhenius relation as: \documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l@{\quad}l} D_\upsilon = 1{\cdot}068\ e^{ - 10,129/RT} & \hbox{for Ponca wheat} \\ D_\upsilon = 1{\cdot}240\ e^{ - 11,030/RT} & \hbox{for Seneca wheat} \end{array} $$\end{document}The results obtained in this investigation provide useful information for designing the steeping vessels.
    Zusätzliches Material: 10 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030406
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  • 98
    Digitale Medien
    Digitale Medien
    Rapid determination of 17-α-oxy-11-desoxy-corticosterone in the course of biological fermentative oxidations (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 21-28 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A rapid analytical method has been developed to follow the biological oxidation of 17-α-oxy-11-desoxy-corticosterone (Reichstein compound S) to hydrocortisone. Paper chromatography is too slow to follow the progress of a preparative microbiological steroid transformation. However, 17-α-oxy-11-desoxy-corticosterone can be separated in a sufficiently pure state for photometric assay by a simple extraction from fermentation broths containing several steroids. This extraction, coupled with the formation of a sulphuric acid chromogen, permits estimation of the steroid in fermentation liquors. The steady decrease of the 17-α-oxy-11-desoxy-compound thus estimated proved to be a true indication of the progress of the oxidation process, allowing it to be stopped at the most favourable time.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030104
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  • 99
    Digitale Medien
    Digitale Medien
    The formation of magnetic iron sulphide by bacterial reduction of iron solutions (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 29-39 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: Laboratory scale experiments have been carried out with sulphate-reducing bacteria growing under anaerobic conditions to investigate the removal of iron from iron-containing solutions. The complete removal of iron, as the insoluble sulphide, has been achieved from both ferrous and ferrous-ferric sulphate solutions. It has been found that under certain conditions a magnetic iron sulphide is produced. This aggregates under the influence of a magnetic field and settles at a rate of some 30 in./min. The magnetic sulphide has only been obtained from intermittent continuous cultures. With the system employed, rates of removal of up to 150 mg of iron per litre of culture vessel per hour have been obtained.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030105
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  • 100
    Digitale Medien
    Digitale Medien
    The recovery of staphylococcal enterotoxin from bacterial culture supernatants by ion exchangeThis work was supported by contributions from various companies and associations of the food industries. (1961)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Biochemical and Microbiological Technology and Engineering 3 (1961), S. 41-50 
    Details
    ISSN: 0368-1467
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A method has been developed for the recovery of enterotoxin from bacterial culture supernatants of staphylococcus strain S-6 by use of the ion-exchange resin Amberlite XE-64 (IRC-50). The enterotoxin from 200 ml of bacterial culture supernatant diluted with one volume of water and adjusted to pH 6 can be removed with 1 g of resin pretreated with 0·02 M sodium phosphate, pH 6·2. The enterotoxin is recovered from the resin with 0·2 M sodium phosphate, pH 6·2, with subsequent precipitation with EtOH at -10°C, dialysis, and freeze drying. Partially purified preparations containing 1 emetic dose per 50μg were obtained.
    Zusätzliches Material: 4 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/jbmte.390030106
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