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  • 101
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    The maximum diversity assortment selection problem (2021)
    Details
    Publication Date: 2024-03-06
    Description: In this article, we introduce the Maximum Diversity Assortment Selection Problem (MDASP), which is a generalization of the two-dimensional Knapsack Problem (2D-KP). Given a set of rectangles and a rectangular container, the goal of 2D-KP is to determine a subset of rectangles that can be placed in the container without overlapping, i.e., a feasible assortment, such that a maximum area is covered. MDASP is to determine a set of feasible assortments, each of them covering a certain minimum threshold of the container, such that the diversity among them is maximized. Thereby, diversity is defined as the minimum or average normalized Hamming distance of all assortment pairs. MDASP was the topic of the 11th AIMMS-MOPTA Competition in 2019. The methods described in this article and the resulting computational results won the contest. In the following, we give a definition of the problem, introduce a mathematical model and solution approaches, determine upper bounds on the diversity, and conclude with computational experiments conducted on test instances derived from the 2D-KP literature.
    Language: English
    Type: article , doc-type:article
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  • 102
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    Simulation data: Data-driven model reduction of agent-based systems using the Koopman generator (2021)
    Details
    Publication Date: 2024-03-18
    Language: English
    Type: researchdata , doc-type:ResearchData
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  • 103
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    cmdtools (2021)
    Details
    Publication Date: 2024-03-18
    Description: Python implementation of severals tools (PCCA, AJC, SQRA, P/Q estimation) for the analysis of dynamical systems from the transfer operator perspective.
    Language: English
    Type: software , doc-type:Other
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  • 104
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    Data-driven model reduction of agent-based systems using the Koopman generator (2021)
    Details
    Publication Date: 2024-03-18
    Description: The dynamical behavior of social systems can be described by agent-based models. Although single agents follow easily explainable rules, complex time-evolving patterns emerge due to their interaction. The simulation and analysis of such agent-based models, however, is often prohibitively time-consuming if the number of agents is large. In this paper, we show how Koopman operator theory can be used to derive reduced models of agent-based systems using only simulation or real-world data. Our goal is to learn coarse-grained models and to represent the reduced dynamics by ordinary or stochastic differential equations. The new variables are, for instance, aggregated state variables of the agent-based model, modeling the collective behavior of larger groups or the entire population. Using benchmark problems with known coarse-grained models, we demonstrate that the obtained reduced systems are in good agreement with the analytical results, provided that the numbers of agents is sufficiently large.
    Language: English
    Type: article , doc-type:article
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  • 105
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    Agent-based modeling: Population limits and large timescales (2021)
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    Publication Date: 2024-03-18
    Description: Modeling, simulation and analysis of interacting agent systems is a broad field of research, with existing approaches reaching from informal descriptions of interaction dynamics to more formal, mathematical models. In this paper, we study agent-based models (ABMs) given as continuous-time stochastic processes and their pathwise approximation by ordinary and stochastic differential equations (ODEs and SDEs, respectively) for medium to large populations. By means of an appropriately adapted transfer operator approach we study the behavior of the ABM process on long time scales. We show that, under certain conditions, the transfer operator approach allows to bridge the gap between the pathwise results for large populations on finite timescales, i.e., the SDE limit model, and approaches built to study dynamical behavior on long time scales like large deviation theory. The latter provides a rigorous analysis of rare events including the associated asymptotic rates on timescales that scale exponentially with the population size. We demonstrate that it is possible to reveal metastable structures and timescales of rare events of the ABM process by finite-length trajectories of the SDE process for large enough populations. This approach has the potential to drastically reduce computational effort for the analysis of ABMs.
    Language: English
    Type: article , doc-type:article
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  • 106
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    Combining XOR and Partner Checkpointing for Resilient Multilevel Checkpoint/Restart (2021)
    Details
    Publication Date: 2024-04-05
    Language: English
    Type: conferenceobject , doc-type:conferenceObject
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  • 107
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    Registration-based Tracking of Regions Defined by Level Sets of Time-dependent Scalar Fields (2021)
    Details
    Publication Date: 2024-04-05
    Description: This thesis is concerned with the wide field of feature tracking in time-dependent data. Many solutions already exist for the tracking of various features in scalar fields that are given as discrete time steps. In the field of meteorology, recently published precipitation data of the COSMO-REA2 reanalysis system gave rise to the analysis of precipitation at a convective scale for which a tracking of precipitation cells over time is desired. A previous study indicated that a tracking based on the widely used overlap criterion does not perform well for the reanalysis data. Based on a novel set of requirements, a new approach to the tracking of regions in time-dependent scalar fields is developed in the course of this thesis and applied in a prototypical study to example datasets of the COSMO-REA2 system. Despite the concrete motivation of using the developed method for subsequent studies of precipitation, the tracking approach is designed to be applicable for arbitrary scalar quantities that can conceptually be given on uniform grids of arbitrary dimensions. Based on a detailed description of the utilized methods, this thesis presents a novel tracking solution whose correspondence identification is based on image registration of successive time steps in combination with a hierarchical watershed segmentation by means of which features are extracted. The proposed implementation allows for an efficient generation of tracking results under the premise that the registration-based correspondence information has been precomputed.
    Language: English
    Type: masterthesis , doc-type:masterThesis
    Format: application/pdf
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  • 108
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    On the Regression Model for Generalized Normal Distributions (2021)
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    Publication Date: 2024-04-26
    Description: The traditional linear regression model that assumes normal residuals is applied extensively in engineering and science. However, the normality assumption of the model residuals is often ineffective. This drawback can be overcome by using a generalized normal regression model that assumes a non-normal response. In this paper, we propose regression models based on generalizations of the normal distribution. The proposed regression models can be used effectively in modeling data with a highly skewed response. Furthermore, we study in some details the structural properties of the proposed generalizations of the normal distribution. The maximum likelihood method is used for estimating the parameters of the proposed method. The performance of the maximum likelihood estimators in estimating the distributional parameters is assessed through a small simulation study. Applications to two real datasets are given to illustrate the flexibility and the usefulness of the proposed distributions and their regression models.
    Language: English
    Type: article , doc-type:article
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  • 109
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    Controlling transient gas flow in real-world pipeline intersection areas (2021)
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    Publication Date: 2024-04-26
    Description: Compressor stations are the heart of every high-pressure gas transport network. Located at intersection areas of the network they are contained in huge complex plants, where they are in combination with valves and regulators responsible for routing and pushing the gas through the network. Due to their complexity and lack of data compressor stations are usually dealt with in the scientific literature in a highly simplified and idealized manner. As part of an ongoing project with one of Germany's largest Transmission System Operators to develop a decision support system for their dispatching center, we investigated how to automatize control of compressor stations. Each station has to be in a particular configuration, leading in combination with the other nearby elements to a discrete set of up to 2000 possible feasible operation modes in the intersection area. Since the desired performance of the station changes over time, the configuration of the station has to adapt. Our goal is to minimize the necessary changes in the overall operation modes and related elements over time, while fulfilling a preset performance envelope or demand scenario. This article describes the chosen model and the implemented mixed integer programming based algorithms to tackle this challenge. By presenting extensive computational results on real world data we demonstrate the performance of our approach.
    Language: English
    Type: article , doc-type:article
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  • 110
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    Distribution System Planning with Battery Storage using Multiperiod Optimal Power Flow (2021)
    Details
    Publication Date: 2024-04-26
    Description: The ongoing energy transition introduces new challenges for distribution networks and brings about the need to expand existing power grid capacities. In order to contain network expansion and with it economic costs, utilization of various flexibility options to reduce expansion needs is discussed. This paper proposes a multiperiod optimal power flow (MPOPF) approach with a new continuous network expansion formulation to optimize the deployment of flexibility options under the objective of minimizing network expansion costs. In a comparison of the newly proposed continuous network expansion formulation with an existing mixed integer formulation and a continuous interpretation of the latter the here proposed formulation is shown to be useful in order to obtain a solvable problem and contain computational efforts. The presented MPOPF including the flexibility options storage units and curtailment is then assessed on synthetic medium voltage grids and applied to evaluate the benefit of a combined vs. a stepwise optimization of these flexibility options. It is demonstrated that using a local solver the proposed approach is applicable and yields a solution in reasonable time. Furthermore, it is shown that the combined optimization generally leads to a more efficient utilization of the considered flexibility options and therefore lower grid expansion costs than the stepwise consideration.
    Language: English
    Type: conferenceobject , doc-type:conferenceObject
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  • 111
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    Modeling and forecasting gas network flows with multivariate time series and mathematical programming approach (2021)
    Details
    Publication Date: 2024-04-26
    Description: With annual consumption of approx. 95 billion cubic me-ters and similar amounts of gas just transshipped through Germany toother EU states, Germany’s gas transport system plays a vital role inEuropean energy supply. The complex, more than 40,000 km long high-pressure transmission network is controlled by several transmission sys-tem operators (TSOs) whose main task is to provide security of supplyin a cost-efficient way. Given the slow speed of gas flows through the gastransmission network pipelines, it has been an essential task for the gasnetwork operators to enhance the forecast tools to build an accurate andeffective gas flow prediction model for the whole network. By incorpo-rating the recent progress in mathematical programming and time seriesmodeling, we aim to model natural gas network and predict gas in- andout-flows at multiple supply and demand nodes for different forecastinghorizons. Our model is able to describe the dynamics in the network bydetecting the key nodes, which may help to build an optimal manage-ment strategy for transmission system operators.
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 112
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    Deep learning for spatio-temporal supply anddemand forecasting in natural gas transmission networks (2021)
    Details
    Publication Date: 2024-04-26
    Description: Germany is the largest market for natural gas in the European Union, with an annual consumption of approx. 95 billion cubic meters. Germany's high-pressure gas pipeline network is roughly 40,000 km long, which enables highly fluctuating quantities of gas to be transported safely over long distances. Considering that similar amounts of gas are also transshipped through Germany to other EU states, it is clear that Germany's gas transport system is essential to the European energy supply. Since the average velocity of gas in a pipeline is only 25km/h, an adequate high-precision, high-frequency forecasting of supply and demand is crucial for efficient control and operation of such a transmission network. We propose a deep learning model based on spatio-temporal convolutional neural networks (DLST) to tackle the problem of gas flow forecasting in a complex high-pressure transmission network. Experiments show that our model effectively captures comprehensive spatio-temporal correlations through modeling gas networks and consistently outperforms state-of-the-art benchmarks on real-world data sets by at least 21%. The results demonstrate that the proposed model can deal with complex nonlinear gas network flow forecasting with high accuracy and effectiveness.
    Language: English
    Type: article , doc-type:article
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  • 113
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    Deep learning for spatio-temporal supply and demand forecasting in natural gas transmission networks (2021)
    Details
    Publication Date: 2024-04-26
    Description: Germany is the largest market for natural gas in the European Union, with an annual consumption of approx. 95 billion cubic meters. Germany's high-pressure gas pipeline network is roughly 40,000 km long, which enables highly fluctuating quantities of gas to be transported safely over long distances. Considering that similar amounts of gas are also transshipped through Germany to other EU states, it is clear that Germany's gas transport system is essential to the European energy supply. Since the average velocity of gas in a pipeline is only 25km/h, an adequate high-precision, high-frequency forecasting of supply and demand is crucial for efficient control and operation of such a transmission network. We propose a deep learning model based on spatio-temporal convolutional neural networks (DLST) to tackle the problem of gas flow forecasting in a complex high-pressure transmission network. Experiments show that our model effectively captures comprehensive spatio-temporal correlations through modeling gas networks and consistently outperforms state-of-the-art benchmarks on real-world data sets by at least 21$\%$. The results demonstrate that the proposed model can deal with complex nonlinear gas network flow forecasting with high accuracy and effectiveness.
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 114
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    A hierarchical optimization approach to robust design of energy supply systems based on a mixed-integer linear model (2021)
    Details
    Publication Date: 2024-04-26
    Description: In designing energy supply systems, designers should heighten the robustness in performance criteria against the uncertainty in energy demands. In this paper, a robust optimal design method using a hierarchical mixed-integer linear programming (MILP) method is proposed to maximize the robustness of energy supply systems under uncertain energy demands based on a mixed-integer linear model. A robust optimal design problem is formulated as a three-level min-max-min MILP one by expressing uncertain energy demands by intervals, evaluating the robustness in a performance criterion based on the minimax regret criterion, and considering relationships among integer design variables, uncertain energy demands, and integer and continuous operation variables. This problem is solved by evaluating upper and lower bounds for the minimum of the maximum regret of the performance criterion repeatedly outside, and evaluating lower and upper bounds for the maximum regret repeatedly inside. Different types of optimization problems are solved by applying a hierarchical MILP method developed for ordinary optimal design problems without and with its modifications. In a case study, the proposed approach is applied to the robust optimal design of a cogeneration system. Through the study, its validity and effectiveness are ascertained, and some features of the obtained robust designs are clarified.
    Language: English
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  • 115
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    Robust Approximation of Chance Constrained DC Optimal Power Flow under Decision-Dependent Uncertainty (2021)
    Details
    Publication Date: 2024-04-26
    Description: We propose a mathematical optimization model and its solution for joint chance constrained DC Optimal Power Flow. In this application, it is particularly important that there is a high probability of transmission limits being satisfied, even in the case of uncertain or fluctuating feed-in from renewable energy sources. In critical network situations where the network risks overload, renewable energy feed-in has to be curtailed by the transmission system operator (TSO). The TSO can reduce the feed-in in discrete steps at each network node. The proposed optimization model minimizes curtailment while ensuring that there is a high probability of transmission limits being maintained. The latter is modeled via (joint) chance constraints that are computationally challenging. Thus, we propose a solution approach based on the robust safe approximation of these constraints. Hereby, probabilistic constraints are replaced by robust constraints with suitably defined uncertainty sets constructed from historical data. The ability to discretely control the power feed-in then leads to a robust optimization problem with decision-dependent uncertainties, i.e. the uncertainty sets depend on decision variables. We propose an equivalent mixed-integer linear reformulation for box uncertainties with the exact linearization of bilinear terms. Finally, we present numerical results for different test cases from the Nesta archive, as well as for a real network. We consider the discrete curtailment of solar feed-in, for which we use real-world weather and network data. The experimental tests demonstrate the effectiveness of this method and run times are very fast. Moreover, on average the calculated robust solutions only lead to a small increase in curtailment, when compared to nominal solutions.
    Language: English
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  • 116
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    Effect of model reduction by time aggregation in multiobjective optimal design of energy supply systems by a hierarchical MILP method (2021)
    Details
    Publication Date: 2024-04-26
    Description: The mixed-integer linear programming (MILP) method has been applied widely to optimal design of energy supply systems. A hierarchical MILP method has been proposed to solve such optimal design problems efficiently. In addition, a method of reducing model by time aggregation has been proposed to search design candidates accurately and efficiently at the upper level. In this paper, the hierarchical MILP method and model reduction by time aggregation are applied to the multiobjective optimal design. The methods of clustering periods by the order of time series, by the k-medoids method, and based on an operational strategy are applied for the model reduction. As a case study, the multiobjective optimal design of a gas turbine cogeneration system is investigated by adopting the annual total cost and primary energy consumption as the objective functions, and the clustering methods are compared with one another in terms of the computation efficiency. It turns out that the model reduction by any clustering method is effective to enhance the computation efficiency when importance is given to minimizing the first objective function, but that the model reduction only by the k-medoids method is effective very limitedly when importance is given to minimizing the second objective function.
    Language: English
    Type: article , doc-type:article
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  • 117
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    Modeling functional time series and mixed-type predictors with partially functional autoregressions* (2021)
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    Publication Date: 2024-04-26
    Description: In many business and economics studies, researchers have sought to measure the dynamic dependence of curves with high-dimensional mixed-type predictors. We propose a partially functional autoregressive model (pFAR) where the serial dependence of curves is controlled by coefficient operators that are defined on a two-dimensional surface, and the individual and group effects of mixed-type predictors are estimated with a two-layer regularization. We develop an efficient estimation with the proven asymptotic properties of consistency and sparsity. We show how to choose the sieve and tuning parameters in regularization based on a forward-looking criterion. In addition to the asymptotic properties, numerical validation suggests that the dependence structure is accurately detected. The implementation of the pFAR within a real-world analysis of dependence in German daily natural gas flow curves, with seven lagged curves and 85 scalar predictors, produces superior forecast accuracy and an insightful understanding of the dynamics of natural gas supply and demand for the municipal, industry, and border nodes, respectively.
    Language: English
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  • 118
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    Optimization of Stationary Expansion Planning and Transient Network Control by Mixed-Integer Nonlinear Programming (2021)
    Details
    Publication Date: 2024-04-26
    Language: English
    Type: doctoralthesis , doc-type:doctoralThesis
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  • 119
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    Statistical analysis and modeling for detecting regime changes in gas nomination time series (2021)
    Details
    Publication Date: 2024-04-26
    Description: As a result of the legislation for gas markets introduced by the European Union in 2005, separate independent companies have to conduct the transport and trading of natural gas. The current gas market of Germany, which has a market value of more than 54 billion USD, consists of Transmission System Operators (TSO), network users, and traders. Traders can nominate a certain amount of gas anytime and anywhere in the network. Such unrestricted access for the traders, on the other hand, increase the uncertainty in the gas supply management. Some customers’ behaviors may cause abrupt structural changes in gas flow time series. In particular, it is a challenging task for the TSO operators to predict gas nominations 6 to 10 hours ahead. In our study, we aim to investigate the regime changes in the time series of nominations to predict the 6 to 10 hours ahead of gas nominations.
    Language: English
    Type: reportzib , doc-type:preprint
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  • 120
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    CMAP-LAP: Configurable Massively Parallel Solver for Lattice Problems (2021)
    Details
    Publication Date: 2024-04-26
    Description: Lattice problems are a class of optimization problems that are notably hard. There are no classical or quantum algorithms known to solve these problems efficiently. Their hardness has made lattices a major cryptographic primitive for post-quantum cryptography. Several different approaches have been used for lattice problems with different computational profiles; some suffer from super-exponential time, and others require exponential space. This motivated us to develop a novel lattice problem solver, CMAP-LAP, based on the clever coordination of different algorithms that run massively in parallel. With our flexible framework, heterogeneous modules run asynchronously in parallel on a large-scale distributed system while exchanging information, which drastically boosts the overall performance. We also implement full checkpoint-and-restart functionality, which is vital to high-dimensional lattice problems. Through numerical experiments with up to 103,680 cores, we evaluated the performance and stability of our system and demonstrated its high capability for future massive-scale experiments.
    Language: English
    Type: conferenceobject , doc-type:conferenceObject
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  • 121
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    CMAP-LAP: Configurable Massively Parallel Solver for Lattice Problems (2021)
    Details
    Publication Date: 2024-04-26
    Description: Lattice problems are a class of optimization problems that are notably hard. There are no classical or quantum algorithms known to solve these problems efficiently. Their hardness has made lattices a major cryptographic primitive for post-quantum cryptography. Several different approaches have been used for lattice problems with different computational profiles; some suffer from super-exponential time, and others require exponential space. This motivated us to develop a novel lattice problem solver, CMAP-LAP, based on the clever coordination of different algorithms that run massively in parallel. With our flexible framework, heterogeneous modules run asynchronously in parallel on a large-scale distributed system while exchanging information, which drastically boosts the overall performance. We also implement full checkpoint-and-restart functionality, which is vital to high-dimensional lattice problems. Through numerical experiments with up to 103,680 cores, we evaluated the performance and stability of our system and demonstrated its high capability for future massive-scale experiments.
    Language: English
    Type: reportzib , doc-type:preprint
    Format: application/pdf
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  • 122
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    Blending hydrogen into natural gas: An assessment of the capacity of the German gas grid; Technical Report (2021)
    Details
    Publication Date: 2024-04-26
    Description: In the transition towards a pure hydrogen infrastructure, utilizing the existing natural gas infrastructure is a necessity. In this study, the maximal technically feasible injection of hydrogen into the existing German natural gas transmission network is analysed with respect to regulatory limits regarding the gas quality. We propose a transient tracking model based on the general pooling problem including linepack. The analysis is conducted using real-world hourly gas flow data on a network of about 10,000 km length.
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  • 123
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    Massively parallel sharing lattice basis reduction (2021)
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    Publication Date: 2024-04-26
    Description: For cryptanalysis in lattice-based schemes, the performance evaluation of lattice basis reduction using high-performance computers is becoming increasingly important for the determination of the security level. We propose a distributed and asynchronous parallel reduction algorithm based on randomization and DeepBKZ, which is an improved variant of the block Korkine-Zolotarev (BKZ) reduction algorithm. Randomized copies of a lattice basis are distributed to up to 103,680 cores and independently reduced in parallel, while some basis vectors are shared asynchronously among all processes via MPI. There is a trade-off between randomization and information sharing; if a substantial amount of information is shared, all processes will work on the same problem, thereby diminishing the benefit of parallelization. To monitor this balance between randomness and sharing, we propose a metric to quantify the variety of lattice bases. We empirically find an optimal parameter of sharing for high-dimensional lattices. We demonstrate the efficacy of our proposed parallel algorithm and implementation with respect to both performance and scalability through our experiments.
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  • 124
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    Interface stability of compressible fluids in porous media (2021)
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    Publication Date: 2024-04-26
    Description: The stability of flows in porous media plays a vital role in transiting energy supply from natural gas to hydrogen, especially for estimating the usability of existing underground gas storage infrastructures. Thus, this research aims to analyze the interface stability of the tangential-velocity discontinuity between two compressible gases by using Darcy's model to include the porosity effect. The results shown in this research will be a basis for considering whether underground gas storages in porous material can be used to store hydrogen. We show the relation between the Mach number M, the viscosity \mu, and the porosity \epsilon on the stability of the interface. This interface stability affects gases' withdrawal and injection processes, thus will help us to determine the velocity which with gas can be extracted and injected into the storage effectively. By imposing solid walls along the flow direction, the critical values of these parameters regarding the stability of the interface are smaller than when considering no walls. The consideration of bounded flows approaches the problem more realistically. In particular, this analysis plays a vital role when considering two-dimensional gas flows in storages and pipes.
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  • 125
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    Effect of water depth on Kelvin - Helmholtz instability in a shallow-water flow (2021)
    Details
    Publication Date: 2024-04-26
    Description: It is well known that the interface between two regions of an incompressible ideal fluid flow moving in a relative motion is necessarily destabilized, regardless of the velocity difference's strength. This phenomenon is the so-called Kelvin-Helmholtz instability (KHI). However, a large number of works demonstrated a surprising result that the instability is suppressed for shallow water flows; the interface is stabilized if the Froude number, defined by the velocity difference's ratio to the gravity wave's speed, is sufficiently large. In a limited way, these authors have been used the shallow-water equations without the higher-order effect of the dispersive terms. Thus, this investigation aims to examine these higher-order dispersive effects to analyze the interface stability problem of tangential-velocity discontinuity in shallow-water flows. In particular, we use the Green-Naghdi equations to introduce the dispersive terms related to the depth and the depth-averaged horizontal velocities of the fluid. We show that the interface stability depends on the Froude number (i.e., the velocity difference's strength) and the water depth. A critical value of the Froude number to stabilize the interface is smaller than the case of no dispersive terms, and the flow in a deeper region is more stable than in a shallower one. We also consider the distribution of kinetic and potential energy to clarify a feature characteristic of a large class of instabilities in shallow water flow. The instability of flows is caused by the decrease in the kinetic energy during the perturbation of waves. This phenomenon is known as negative energy modes and plays a vital role in applying the model to industrial equipment. A conclusion is that the equipartition of energies occurs if and only if the velocity difference is zero and the water depth is shallow enough to ignore the dispersive terms.
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  • 126
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    Instability of a tangential discontinuity surface in a three-dimensional compressible medium (2021)
    Details
    Publication Date: 2024-04-26
    Description: Compressible flows appear in many natural and technological processes, for instance, the flow of natural gases in a pipe system. Thus, a detailed study of the stability of tangential velocity discontinuity in compressible media is relevant and necessary. The first early investigation in two-dimensional (2D) media was given more than 70 years ago. In this article, we continue investigating the stability in three-dimensional (3D) media. The idealized statement of this problem in an infinite spatial space was studied by Syrovatskii in 1954. However, the omission of the absolute sign of cos θ with θ being the angle between vectors of velocity and wave number in a certain inequality produced the inaccurate conclusion that the flow is always unstable for entire values of the Mach number M. First, we revisit this case to arrive at the correct conclusion, namely that the discontinuity surface is stabilized for a large Mach number with a given value of the angle θ. Next, we introduce a real finite spatial system such that it is bounded by solid walls along the flow direction. We show that the discontinuity surface is stable if and only if the dispersion relation equation has only real roots, with a large value of the Mach number; otherwise, the surface is always unstable. In particular, we show that a smaller critical value of the Mach number is required to make the flow in a narrow channel stable.
    Language: English
    Type: article , doc-type:article
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  • 127
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    Faster algorithms for Steiner tree and related problems: From theory to practice (2021)
    Details
    Publication Date: 2024-04-26
    Language: English
    Type: doctoralthesis , doc-type:doctoralThesis
    Format: application/pdf
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  • 128
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    Inference of historical influence networks (2021)
    Details
    Publication Date: 2024-05-16
    Description: We study the romanization process of northern Africa from 50 BC till 300 AD. Our goal is to infer the communication strength between different subregions, based on the evolution of the status of cities. Herefore, we use the general inverse infection model, that infers the weights of a known underlying network, given observations of the spreading on this network. As infection process we choose the SI metapopulation model, where I stands for a city with a Roman status. To solve the minimization problem we use the particle swarm optimization algorithm with a specific choice of parameters.
    Language: German
    Type: conferenceobject , doc-type:conferenceObject
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  • 129
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    Prediction of Covid-19 spreading and optimal coordination of counter-measures: From microscopic to macroscopic models to Pareto fronts (2021)
    Details
    Publication Date: 2024-06-13
    Language: English
    Type: article , doc-type:article
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  • 130
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    Grundlagen der Eingruppierung TVöD und TV-L : das aktuelle Eingruppierungsrecht im öffentlichen Dienst (2021)
    Berlin :Walhalla und Praetoria Verlag,
    Details
    Title: Grundlagen der Eingruppierung TVöD und TV-L : das aktuelle Eingruppierungsrecht im öffentlichen Dienst
    Author: Richter, Achim
    Contributer: Gamisch, Annett , Mohr, Thomas
    Edition: 7., aktualisierte Auflage, Bearbeitungsstand: Juni 2017
    Publisher: Berlin :Walhalla und Praetoria Verlag,
    Year of publication: 2021
    Pages: 112 Seiten
    ISBN: 978-3-8029-1599-4
    Type of Medium: Book
    Language: German
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  • 131
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    Forschungsdatenmanagement und Recht : Datenschutz-, Urheber- und Vertragsrecht (2021)
    Feldkirch/Düns :Neugebauer,
    Details
    Title: Forschungsdatenmanagement und Recht : Datenschutz-, Urheber- und Vertragsrecht
    Author: Baumann, Paul
    Contributer: Krahn, Philipp , Lauber-Rönsberg, Anne
    Publisher: Feldkirch/Düns :Neugebauer,
    Year of publication: 2021
    Pages: 304 Seiten
    ISBN: 978-3-85376-328-5
    Type of Medium: Book
    Language: German
    URL: Inhaltsverzeichnis
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  • 132
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    Handbuch Prüfung ortsveränderlicher elektrischer Geräte : Prüfabläufe, Grenz- und Richtwerte gem. DIN VDE 0701-0702 für die Prüfung vor Ort (2021)
    Forum Verlag Herkert,
    Details
    Title: Handbuch Prüfung ortsveränderlicher elektrischer Geräte : Prüfabläufe, Grenz- und Richtwerte gem. DIN VDE 0701-0702 für die Prüfung vor Ort
    Contributer: Donath, Karl [Verfasser] , Rottmann, Rainer [Verfasser] , Gavrancic, Milan [Verfasser] , Orgel, Christian [Verfasser]
    Edition: 4. überarbeitete Auflage
    Publisher: Forum Verlag Herkert,
    Year of publication: 2021
    Pages: 311 Seiten
    ISBN: 978-3-96314-615-2
    Type of Medium: Book
    Language: German
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  • 133
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    Muster : Theorie der digitalen Gesellschaft (2021)
    München :C.H. Beck,
    Details
    Title: Muster : Theorie der digitalen Gesellschaft
    Author: Nassehi, Armin
    Edition: 1. Auflage
    Publisher: München :C.H. Beck,
    Year of publication: 2021
    Pages: 352 Seiten
    ISBN: 978-3-406-76786-9
    Type of Medium: Book
    Language: German
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  • 134
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    ¬The¬ science of science / (2021)
    Cambridge :Cambridge University Press,
    Details
    Title: ¬The¬ science of science /
    Author: Wang, Dashun
    Contributer: Barabási, Albert-László
    Publisher: Cambridge :Cambridge University Press,
    Year of publication: 2021
    Pages: x, 303 Seiten
    ISBN: 978-1-108-71695-6
    Type of Medium: Book
    Language: English
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  • 135
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    Book
    Erfurter Kommentar zum Arbeitsrecht (2021)
    München :C.H. Beck,
    Details
    Title: Erfurter Kommentar zum Arbeitsrecht
    Contributer: Müller-Glöge, Rudi , Preis, Ulrich , Gallner, Inken
    Edition: 22. Auflage
    Publisher: München :C.H. Beck,
    Year of publication: 2021
    Pages: 3100 Seiten
    ISBN: 978-3-406-77038-8
    Type of Medium: Book
    Language: German
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  • 136
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    Handbuch Prüfung ortsfester elektrischer Anlagen und Betriebsmittel : Prüfabläufe, Grenz- und Richtwerte gem. DIN VDE 0100-600 und 0105-100 für die Prüfung vor Ort (2021)
    Forum Verlag Herkert,
    Details
    Title: Handbuch Prüfung ortsfester elektrischer Anlagen und Betriebsmittel : Prüfabläufe, Grenz- und Richtwerte gem. DIN VDE 0100-600 und 0105-100 für die Prüfung vor Ort
    Author: Donath, Karl [Verfasser]
    Contributer: Rottmann, Rainer [Verfasser] , Orgel, Christian [Verfasser]
    Edition: 4. überarbeitete Auflage
    Publisher: Forum Verlag Herkert,
    Year of publication: 2021
    Pages: 374 Seiten
    Type of Medium: Book
    Language: German
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  • 137
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    Book
    Programming Rust : fast, safe systems development (2021)
    Beijing ; Boston ; Farnham ; Sebastopol :O'Reilly,
    Details
    Title: Programming Rust : fast, safe systems development
    Author: Blandy, Jim
    Contributer: Orendorff, Jason , Tindall, Leonora
    Edition: Second edition
    Publisher: Beijing ; Boston ; Farnham ; Sebastopol :O'Reilly,
    Year of publication: 2021
    Pages: xix, 711 Seiten
    ISBN: 9781492052562
    Type of Medium: Book
    Language: English
    Parallel Title: Erscheint auch als Druck-Ausgabe 978-1-492-05259-3
    URL: https://search.ebscohost.com/login.aspx?direct=true&db=nlebk&AN=2949563&site=ehost-live
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  • 138
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    Götzendämmerung : Kunst und Künstliche Intelligenz (2021)
    Bielefeld :transcript,
    Details
    Title: Götzendämmerung : Kunst und Künstliche Intelligenz
    Contributer: Dotzler, Bernhard J. , Karpat, Berkan
    Publisher: Bielefeld :transcript,
    Year of publication: 2021
    Pages: 154 Seiten
    ISBN: 978-3-8376-5976-4
    Type of Medium: Book
    Language: German
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  • 139
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    Book
    Docker : das Praxisbuch für Entwickler und DevOps-Teams (2021)
    Details
    Title: Docker : das Praxisbuch für Entwickler und DevOps-Teams
    Author: Öggl, Bernd
    Contributer: Kofler, Michael
    Edition: 3. Aufl.
    Year of publication: 2021
    Pages: 496 S. : , Illustrationen, Diagramme
    ISBN: 978-3-8362-8634-3
    Type of Medium: Book
    Language: German
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  • 140
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    Git Handbuch für Einsteiger : Der leichte Weg zum Git-Experten (2021)
    Landshut :BMU Media Verlag,
    Details
    Title: Git Handbuch für Einsteiger : Der leichte Weg zum Git-Experten
    Author: Fuchs, Paul
    Publisher: Landshut :BMU Media Verlag,
    Year of publication: 2021
    Pages: 307 Seiten
    ISBN: 978-3-96645-119-2
    Type of Medium: Book
    Language: German
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  • 141
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    Book
    Crashkurs BWA : betriebswirtschaftliche Auswertungen erstellen, lesen und verstehen (2021)
    Details
    Title: Crashkurs BWA : betriebswirtschaftliche Auswertungen erstellen, lesen und verstehen
    Author: Träger, Elisabeth
    Edition: 1. Auflage
    Year of publication: 2021
    Pages: 180 Seiten
    ISBN: 978-3-648-13768-0
    Type of Medium: Book
    Language: German
    URL: Inhaltstext
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  • 142
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    Book
    Crashkurs Internes Kontrollsystem für Buchhaltung und Steuern / (2021)
    Details
    Title: Crashkurs Internes Kontrollsystem für Buchhaltung und Steuern /
    Author: Alves, Winfried
    Edition: 2. völlig überarbeitete und erweiterte Auflage
    Year of publication: 2021
    Pages: 167 Seiten
    ISBN: 978-3-648-14049-9
    Type of Medium: Book
    Language: German
    URL: Inhaltstext
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  • 143
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    Schwierige Geschäftsvorfälle richtig buchen / (2021)
    Freiburg im Breisgau :Haufe-Lexware,
    Details
    Title: Schwierige Geschäftsvorfälle richtig buchen /
    Author: Thomsen, Iris
    Contributer: Zöllner, Nikolaus
    Edition: 15. Auflage
    Publisher: Freiburg im Breisgau :Haufe-Lexware,
    Year of publication: 2021
    Pages: 413 Seiten
    ISBN: 978-3-648-14840-2
    Type of Medium: Book
    Language: German
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  • 144
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    Introduction to Quantum Computing / (2021)
    Basel :Springer International Publishing,
    Details
    Title: Introduction to Quantum Computing /
    Author: LaPierre, Ray
    Publisher: Basel :Springer International Publishing,
    Year of publication: 2021
    Pages: 368 Seiten
    ISBN: 978-3-030-69317-6
    Type of Medium: Book
    Language: English
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  • 145
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    Book
    Git für Dummies / (2021)
    Weinheim :Wiley-VCH,
    Details
    Title: Git für Dummies /
    Author: Kaufmann, Michael
    Contributer: Binkle, Harald
    Publisher: Weinheim :Wiley-VCH,
    Year of publication: 2021
    Pages: 417 Seiten
    ISBN: 978-3-527-71697-5
    Type of Medium: Book
    Language: German
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  • 146
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    Book
    Linear Algebra : Theory, Intuition, Code (2021)
    Sincxpress Bv,
    Details
    Title: Linear Algebra : Theory, Intuition, Code
    Author: Cohen, Mike X
    Publisher: Sincxpress Bv,
    Year of publication: 2021
    Pages: 548 S.
    ISBN: 978-90-831366-0-8
    Type of Medium: Book
    Language: German
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  • 147
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    Book
    HTML und CSS : das umfassende Handbuch (2021)
    Bonn :Rheinwerk Verlag,
    Details
    Title: HTML und CSS : das umfassende Handbuch
    Author: Wolf, Jürgen
    Edition: 4., aktualisierte und überarbeitete Auflage
    Publisher: Bonn :Rheinwerk Verlag,
    Year of publication: 2021
    Pages: 1158 Seiten
    ISBN: 978-3-8362-8117-1
    Type of Medium: Book
    Language: German
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  • 148
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    Book
    Liberating structures : Entscheidungsfindung revolutionieren (2021)
    München :Verlag Franz Vahlen GmbH,
    Details
    Title: Liberating structures : Entscheidungsfindung revolutionieren
    Author: Steinhöfer, Daniel
    Publisher: München :Verlag Franz Vahlen GmbH,
    Year of publication: 2021
    Pages: 120 Seiten
    ISBN: 978-3-8006-5929-6
    Type of Medium: Book
    Language: German
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  • 149
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    Die Wissensberechnungsmaschine Wolfram|Alpha (2009)
    Details
    Publication Date: 2020-12-11
    Description: Im Mai 2009 wurde Wolfram|Alpha gestartet, ein Service, der seinen Namen von seinem Entwickler, dem britischen Mathematiker Stephen Wolfram, ableitet. Dem Benutzer soll nicht nur eine Liste von Webseiten als Ergebnis auf Anfragen geliefert werden, sondern Antworten auf konkrete Fragen geben. In diesem Report soll gezeigt werden, warum sichWolframjAlpha von Suchmaschinen abgrenzt und was die Berechnung von Antworten auf natürlichsprachliche Fragen möglich machen kann.
    Description: Wolfram|Alpha was started in May 2009 and it's a service whose name derives from the british mathematician Stephen wolfram. As a result for a request the user is not just supported with a list of websites but with answers for concrete questions. In this report it will be shown why Wolfram|Alpha seperates from search engines and moreover what makes the computation of answers for natural language queries possible.
    Keywords: ddc:004
    Language: German
    Type: reportzib , doc-type:preprint
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  • 150
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    Barrier methods for a control problem from hyperthermia treatment planning (2009)
    Details
    Publication Date: 2019-01-29
    Description: We consider an optimal control problem from hyperthermia treatment planning and its barrier regularization. We derive basic results, which lay the groundwork for the computation of optimal solutions via an interior point path-following method. Further, we report on a numerical implementation of such a method and its performance at an example problem.
    Keywords: ddc:510
    Language: English
    Type: reportzib , doc-type:preprint
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  • 151
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    Transparent boundary conditions for Maxwell's equations: Numerical concepts beyond the PML method (2009)
    Details
    Publication Date: 2016-06-09
    Description: Optical technologies are ubiquitously used in hi-tech devices. As a common feature of such devices one finds structures with dimensions in the order of the wavelength of the used light. To design and produce such devices, the wave nature of light must be taken into account. Accordingly, robust simulation tools are required which are based on rigorously solving Maxwell's equations, the governing equations of light propagation within macroscopic media. This thesis contributes to the modeling and the numerical computation of light scattering problems: Light scattering problems are typically posed on the entire space. The Perfectly-Matched -Layer method (PML) is widely used to restrict the simulation problem onto a bounded computational domain. We propose an adaptive PML method which exhibits a good convergence even for critical problems where standard PML implementations fail. Besides the computation of the near field, that is the electromagnetic field within the computational domain, it is of major interest to evaluate the electromagnetic field in the exterior domain and to compute the far field. So far, this was numerically only possible for simple geometries such as homogeneous exterior domains or layered media. To deal with more complicated devices, for example with waveguide inhomogeneities, we develop an evaluation formula based on the PML solution which allows for an exterior domain field evaluation in a half space above the device. Finally, we generalize the PML method to problems with multiply structured exterior domains. The term “multiply structured exterior domain” is defined in this thesis and means that the exterior domain exhibits several half-infinite structures. Mathematically, this gives rise to various complications. For example, no analytical solutions to Maxwell's equations for standard light sources are available in the exterior domain, which are needed to describe the incoming field in a light scattering problem. To tackle this we propose a new light scattering problem formulation which fits well into the PML method framework and which may be regarded as an extension of classical contributions by Sommerfeld, Wiener and Hopf. An exterior domain evaluation formula for multiply structured exterior domains with an extended illumination is derived as well.
    Keywords: ddc:510
    Language: English
    Type: doctoralthesis , doc-type:doctoralThesis
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    The Coolest Path Problem (2009)
    Details
    Publication Date: 2020-08-05
    Description: We introduce the coolest path problem, which is a mixture of two well-known problems from distinct mathematical fields. One of them is the shortest path problem from combinatorial optimization. The other is the heat conduction problem from the field of partial differential equations. Together, they make up a control problem, where some geometrical object traverses a digraph in an optimal way, with constraints on intermediate or the final state. We discuss some properties of the problem and present numerical solution techniques. We demonstrate that the problem can be formulated as a linear mixed-integer program. Numerical solutions can thus be achieved within one hour for instances with up to 70 nodes in the graph.
    Keywords: ddc:510
    Language: English
    Type: reportzib , doc-type:preprint
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    Format: application/zip
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  • 153
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    The MCF-Separator -- Detecting and Exploiting Multi-Commodity Flow Structures in MIPs (2009)
    Details
    Publication Date: 2021-08-05
    Description: Given a general mixed integer program (MIP), we automatically detect block structures in the constraint matrix together with the coupling by capacity constraints arising from multi-commodity-flow formulations. We identify the underlying graph and generate cutting planes based on cuts in the detected network. Our implementation adds a separator to the branch-and-cut libraries of SCIP and CPLEX. We make use of the complemented mixed integer rounding framework (cMIR) but provide a special purpose aggregation heuristic that exploits the network structure. Our separation scheme speeds-up the computation for a large set of MIPs coming from network design problems by a factor of two on average.
    Keywords: ddc:510
    Language: English
    Type: reportzib , doc-type:preprint
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    Format: application/postscript
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    Co-Reservation of Resources in the Grid (2009)
    Details
    Publication Date: 2016-06-30
    Description: Executing applications in the Grid often requires access to multiple geographically distributed resources. In a Grid environment, these resources belong to different administrative domains, each employing its own scheduling policy. That is, at which time an activity (e.g., compute job, data transfer) is started, is decided by the resource's local management system. In such an environment, the coordinated execution of distributed applications requires guarantees on the quality of service (QoS) of the needed resources. Reserving resources in advance is an accepted means to obtain QoS guarantees from a single provider. The challenge, however, is to coordinate advance reservations of multiple resources. This work presents a system architecture and mechanisms to coordinate multiple advance reservations -- called co-reservations -- for delivering QoS guarantees to complex applications. We formally define the co-reservation problem as an optimization problem. The presented model supports three dimensions of freedom: the start time, the duration and the service level of a reservation. Requests and resources are described in a simple language. After matching the static properties and requirements of either side in a mapping, the reservation mechanism probes information about the future status of the resources. The versatile design of the probing step allows the efficient processing of requests, but also lets the resources express their preferences among the myriads of reservation candidates. Next, the best mapping is found through an implementation of the formal co-reservation model. Then, the mapping has to be secured, i.e., resources need to be allocated to a co-reservation candidate with all-or-nothing semantics. We study several goal-driven sequential and concurrent allocation mechanisms and define schemes for handling allocation failures. Finally, we introduce the concept of virtual resources for seamlessly embedding co-reservations into Grid resource management.
    Description: Die Ausführung von Anwendungen erfordert oft mehrere, geographisch verteilte Ressourcen. In Grid-Umgebungen gehören diese Ressourcen zu verschiedenen administrativen Organisationen, wobei jede ihre eigene Schedulingregeln verwendet. Das bedeutet, zu welcher Zeit eine Aktivität gestartet wird (z.B. ein Rechenjob), wird vom lokalen Ressourcenmanagementsystem entschieden. Die koordinierte Ausführung von verteilten Anwendungen erfordert Dienstgütegarantien für die benötigten Ressourcen. Das Reservieren von Ressourcen im Voraus ist ein Mittel, um Dienstgütegarantien von einem einzelnen Ressourcenanbieter zu erhalten. Die Herausforderung in dieser Arbeit ist, Vorausreservierungen von mehreren Ressourcen zu koordinieren. Es wird ein System für die Koordinierung mehrerer Vorausreservierungen -- Co-Reservierungen genannt -- für die Bereitstellung von Dienstgütegarantien vorgestellt. Wir definieren das Co-Reservierungsproblem als Optimierungsproblem. Das vorgestellte Modell unterstützt drei Freiheitsgrade: die Startzeit, die Dauer und die Dienstgüte einer Reservierung. Anfragen und Ressourcen werden in einer einfachen Sprache beschrieben. Nachdem statische Eigenschaften und Anforderungen beider Seiten überprüft wurden, ermittelt der Reservierungsmechanismus Informationen über den zukünftigen Zustand der Ressourcen. Dieser Schritt ist so allgemein gehalten, daß er sowohl ein effizientes Bearbeiten der Anfragen erlaubt als auch den Ressourcen ermöglicht ihre Präferenzen auszudrücken. Im Anschluss wird die optimale Zuweisung von Anfragen zu Ressourcen ermittelt. Im letzten Schritt muss diese Zuweisung umgesetzt werden, d.h., entweder alle oder keine Ressource wird allokiert. Es werden mehrere sequentielle und parallele Allokationsverfahren vorgestellt sowie deren Auswirkung auf verschiedene Metriken untersucht. Die Einbettung von Co-Reservierungen in das Grid-Ressourcenmanagement wird anhand des Konzeptes der virtuellen Ressource dargestellt.
    Keywords: ddc:004
    Language: English
    Type: doctoralthesis , doc-type:doctoralThesis
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    Veränderungen der Publikations- und Kommunikationswelt: Open Access, Google, etc. (2009)
    Details
    Publication Date: 2020-12-11
    Description: Vorbemerkung Beim Schreiben dieses Artikels, der auf Veränderungen der Kommunikations- und Publikationstechniken und ihre Bedeutung hinweist, ist uns mehr als je zuvor bewusst geworden, wie beschränkt das Medium Papier ist. Es gibt z. B. keine Hyperlinks, durch die man unmittelbar das Erwähnte erleben oder überprüfen kann. Ein schneller Wechsel vom Wort zum Bild, zum Ton oder Video ist nicht möglich. Wer will schon lange URLs abtippen und Medienbrüche erleiden? Wir haben uns daher entschlossen, eine textidentische Version dieses Artikels mit allen URLs – sie liegt Ihnen hier vor – elektronisch anzubieten und in der für die "Gegenworte" (BBAW) gekürzten Fassung nur durch [URL] anzudeuten, dass der Leser an dieser Stelle einfach in der elektronischen Version einen Klick ins Internet machen sollte. Und damit sind wir bereits mitten im Thema.
    Keywords: ddc:020
    Language: German
    Type: reportzib , doc-type:preprint
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  • 156
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    A Priori Tabulation of Turbulent Flame Speeds via a Combination of a Stochastic Mixing Model and Flamelet Generated Manifolds, Extended to Incorporate Strain Effects (2009)
    Details
    Publication Date: 2016-06-09
    Description: In this paper we revisit the a priori turbulent flame speed tabulation (TFST) technique for a given parameter space within the region of flamelet combustion-regimes. It can be used as a subgrid-scale (SGS) model in Large Eddy Simulation (LES). In a first step, stationary laminar flamelets are computed and stored over the progress variable following the ideas of flamelet generated manifolds (FGM). In a second step, the incompressible one-dimensional Navier-Stokes equations supplemented by the equation for the progress variable are solved on a grid that resolves all turbulent scales. Additionally, turbulent transport is implemented via the linear eddy model (LEM). The turbulent flame structures are solved until a statistically stationary mean value of the turbulent flame speed has been reached. The results are stored in a table that could be used by large scale premixed combustion models, e.g. front tracking schemes. First results are compared quantitatively with direct numerical simulations (DNS) taken from literature. Then it is illustrated in one example how the new method could help to fix constants in algebraic models for turbulent flame speeds. Further it is shown how the technique can be extended to incorporate turbulent strain effects. Finally we investigate the effect of the use of detailed and tabulated chemistry under unsteady conditions.
    Keywords: ddc:620
    Language: English
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    Nonlinear pseudo-Boolean optimization: relaxation or propagation? (2009)
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    Publication Date: 2022-03-14
    Description: Pseudo-Boolean problems lie on the border between satisfiability problems, constraint programming, and integer programming. In particular, nonlinear constraints in pseudo-Boolean optimization can be handled by methods arising in these different fields: One can either linearize them and work on a linear programming relaxation or one can treat them directly by propagation. In this paper, we investigate the individual strengths of these approaches and compare their computational performance. Furthermore, we integrate these techniques into a branch-and-cut-and-propagate framework, resulting in an efficient nonlinear pseudo-Boolean solver.
    Keywords: ddc:510
    Language: English
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    The Steiner Connectivity Problem (2009)
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    Publication Date: 2020-12-15
    Description: The Steiner connectivity problem is a generalization of the Steiner tree problem. It consists in finding a minimum cost set of simple paths to connect a subset of nodes in an undirected graph. We show that polyhedral and algorithmic results on the Steiner tree problem carry over to the Steiner connectivity problem, namely, the Steiner cut and the Steiner partition inequalities, as well as the associated polynomial time separation algorithms, can be generalized. Similar to the Steiner tree case, a directed formulation, which is stronger than the natural undirected one, plays a central role.
    Keywords: ddc:000
    Language: English
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  • 159
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    Ergebnisse aus dem BVB-KOBV-Entwicklungsprojekt "Literaturverwaltungsprogramme": Handreichung für Bibliotheken (2009)
    Details
    Publication Date: 2020-12-11
    Description: Zwischen dem Bibliotheksverbund Bayern (BVB) und dem Kooperativen Bibliotheksverbund Berlin-Brandenburg (KOBV) besteht seit Ende 2007 eine Strategische Allianz, die auf zwei Säulen beruht: einer langfristigen Entwicklungspartnerschaft einerseits und der Kooperation im Dienstleistungsbereich mit der Integration der Verbundkataloge andererseits. Ende 2008 wurde das erste Entwicklungsprojekt "Literaturverwaltungsprogramme" abgeschlossen, dessen Ergebnisse in dieser Handreichung in Form von Handlungsempfehlungen für Bibliotheken vorgestellt werden. Ziel des Projekts war es, den Datenaustausch zwischen den Bibliotheks- und Verbundkatalogen des BVB und KOBV und gängigen Literaturverwaltungsprogrammen zu optimieren. Neben Handlungsempfehlungen für die Implementierung neuer Exportschnittstellen und die Verbesserung bestehender Exportmöglichkeiten werden Hinweise auf verbesserte Nutzerführung gegeben. Die Empfehlungen beziehen sich vorwiegend auf den Datenaustausch zwischen den Bibliothekssystemen Aleph 500, MetaLib und WebOPAC/InfoGuide und den Literaturverwaltungsprogrammen Citavi, EndNote, RefWorks und Zotero.
    Keywords: ddc:020
    Language: German
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  • 160
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    Planning Problems in Public Transit (2009)
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    Publication Date: 2020-08-05
    Description: Every day, millions of people are transported by buses, trains, and airplanes in Germany. Public transit (PT) is of major importance for the quality of life of individuals as well as the productivity of entire regions. Quality and efficiency of PT systems depend on the political framework (state-run, market oriented) and the suitability of the infrastructure (railway tracks, airport locations), the existing level of service (timetable, flight schedule), the use of adequate technologies (information, control, and booking systems), and the best possible deployment of equipment and resources (energy, vehicles, crews). The decision, planning, and optimization problems arising in this context are often gigantic and “scream” for mathematical support because of their complexity. This article sketches the state and the relevance of mathematics in planning and operating public transit, describes today’s challenges, and suggests a number of innovative actions. The current contribution of mathematics to public transit is — depending on the transportation mode — of varying depth. Air traffic is already well supported by mathematics. Bus traffic made significant advances in recent years, while rail traffic still bears significant opportunities for improvements. In all areas of public transit, the existing potentials are far from being exhausted. For some PT problems, such as vehicle and crew scheduling in bus and air traffic, excellent mathematical tools are not only available, but used in many places. In other areas, such as rolling stock rostering in rail traffic, the performance of the existing mathematical algorithms is not yet sufficient. Some topics are essentially untouched from a mathematical point of view; e.g., there are (except for air traffic) no network design or fare planning models of practical relevance. PT infrastructure construction is essentially devoid of mathematics, even though enormous capital investments are made in this area. These problems lead to questions that can only be tackled by engineers, economists, politicians, and mathematicians in a joint effort. Among other things, the authors propose to investigate two specific topics, which can be addressed at short notice, are of fundamental importance not only for the area of traffic planning, should lead to a significant improvement in the collaboration of all involved parties, and, if successful, will be of real value for companies and customers: • discrete optimal control: real-time re-planning of traffic systems in case of disruptions, • model integration: service design in bus and rail traffic. Work on these topics in interdisciplinary research projects could be funded by the German ministry of research and education (BMBF), the German ministry of economics (BMWi), or the German science foundation (DFG).
    Keywords: ddc:510
    Language: English
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    Jahresbericht 2008 (2009)
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    Publication Date: 2019-10-24
    Keywords: ddc:080
    Language: German
    Type: annualzib , doc-type:report
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  • 162
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    Solving Steel Mill Slab Problems with Branch and Price (2009)
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    Publication Date: 2020-08-05
    Description: The steel mill slab design problem from the CSPLib is a binpacking problem that is motivated by an application of the steel industry and that has been widely studied in the constraint programming community. Recently, several people proposed new models and methods to solve this problem. A steel mill slab library was created which contains 380 instances. A closely related binpacking problem called multiple knapsack problem with color constraints, originated from the same industrial problem, were discussed in the integer programming community. In particular, a simple integer programming for this problem has been given by Forrest et al. [3]. The aim of this paper is to bring these different studies together. Moreover, we adopt the model of [3] for the steel mill slab problem. Using a state of the art integer program solver, this model is capable to solve all instances of the steel mill slab library, mostly in less than one second, to optimality. We improved, thereby, the solution value of 76 instances.
    Keywords: ddc:510
    Language: English
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  • 163
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    On the Hardness of Finding Small Shortest Path Routing Conflicts (2009)
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    Publication Date: 2020-08-05
    Description: Nowadays most data networks use shortest path protocols such as OSPF or IS-IS to route traffic. Given administrative routing lengths for the links of a network, all data packets are sent along shortest paths with respect to these lengths from their source to their destination. One of the most fundamental problems in planning shortest path networks is to decide whether a given set of routing paths forms a valid routing and, if this is not the case, to find a small subset of the given paths that cannot be shortest paths simultaneously for any routing lengths. In this paper we show that it is NP-hard to approximate the size of the smallest shortest path conflict by a factor less than 7/6.
    Keywords: ddc:510
    Language: English
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  • 164
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    A Binary Quadratic Programming Approach to the Vehicle Positioning Problem (2009)
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    Publication Date: 2020-08-05
    Description: The Vehicle Positioning Problem (VPP) consists of the assignment of vehicles (buses, trams or trains) of a public transport or railway company to parking positions in a depot and to timetabled trips. Such companies have many different types of vehicles, and each trip can be performed only by vehicles of some of these types. These assignments are non-trivial due to the topology of depots. The parking positions are organized in tracks, which work as one- or two-sided stacks or queues. If a required type of vehicle is not available in the front of any track, shunting movements must be performed in order to change vehicles' positions, which is undesirable and should be avoided. In this text we present integer linear and non-linear programming formulations for some versions of the problem and compare them from a theoretical and a computational point of view.
    Keywords: ddc:510
    Language: English
    Type: reportzib , doc-type:preprint
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  • 165
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    Statistical Error Estimation and Grid-free Hierarchical Refinement in Conformation Dynamics (2009)
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    Publication Date: 2020-03-11
    Description: The understanding of geometric structures and dynamical properties of molecular conformations gives insight into molecular long-term behavior. The identification of metastable conformations together with their life times and transition patterns is the intention of conformation dynamics. Conformation dynamics is a multi-scale approach that leads to a reduced description of the dynamical system in terms of a stochastic transition probability matrix. The present thesis deals with the error analysis of computed matrices and the resulting matrix functions. Since conformational membership vectors, as they are computed by the Robust Perron Cluster Analysis (PCCA+), form an invariant subspace of the transition matrix, subspace-based error estimators are of particular interest. The decomposition of the state space into basis functions and the approximation of integrals by Monte-Carlo quadrature give rise to row-wise correlated random matrices, for which stochastic norms are computed. Together with an appropriate statistical model for the distribution of matrix rows, this allows for the calculation of error bounds and error distributions of the invariant subspace and other variables of interest. Equilibration of errors among the basis functions can be achieved by enhanced sampling in regions where the trajectories are mixing slowly. Hierarchical refinement of such basis functions systematically improves the clustering into metastable conformations by reducing the error in the corresponding invariant subspace. These techniques allow for an evaluation of simulation results and pave the way for the analysis of larger molecules. Moreover, the extension of PCCA+ to non-reversible Markov chains, verified by the corresponding perturbation theory, and the modification of the objective function for the case of soft membership vectors represent a further generalization of the clustering method, thus continuing the development from PCCA over PCCA+ to PCCA++. The methods developed in this thesis are useful for but not limited to conformation dynamics. In fact, they are applicable to a broader class of problems which combine domain decomposition with Monte-Carlo quadrature. Possible application areas may include the chemical master equation or quantum dynamical systems.
    Description: Das Verständnis von geometrischen Strukturen und dynamischen Eigenschaften molekularer Konformationen ist essentiell für die Vorhersage des Langzeitverhaltens von Molekülen. Die Identifikation metastabiler Konformationen sowie die Bestimmung von Übergangswahrscheinlichkeiten und Haltezeiten sind Bestandteil der Konformationdynamik. Dabei handelt es sich um eine Mehrskalenmethode, die auf eine reduzierte Beschreibung des Systems mittels einer stochastischen Übergangsmatrix führt. In der vorliegenden Dissertation wurde untersucht, wie man die Genauigkeit der Matrizen sowie der daraus berechneten Größen quantifizieren kann. Im Mittelpunkt stehen dabei Fehlerschätzer für den invarianten Unterraum, da die rechten Eigenvektoren als Grundlage der Robusten Perron Cluster Analyse (PCCA+) zur Identifizierung der metastabilen Konformationen dienen. Die Zerlegung des Zustandsraumes in Basisfunktionen sowie die Approximation der Matrixeinträge mittels Monte-Carlo-Quadratur führen zu zeilenweise korrelierten Zufallsmatrizen. Mit Hilfe einer stochastischen Norm sowie einem geeigneten statistischen Modell für die Verteilung der Matrixzeilen können u.a. Fehlerschranken und -verteilungen für den invarianten Unterraum brechnet werden. Eine Equilibrierung des Fehlers zwischen den Basisfunktionen kann durch erweitertes Sampling in solchen Regionen erreicht werden, in denen die Trajektorien nur langsam mischen.Eine hierarchische Zerlegung dieser Basisfunktionen verbessert systematisch die Zerlegung in metastabile Konformationen, indem sie den Fehler im invarianten Unterraum reduziert. Diese Techniken gestatten eine Evaluierung der Simulationsergebnisse und ebnen den Weg zur Behandlung komplexerer Moleküle. Desweiteren wurden Verallgemeinerungen der PCCA+ untersucht. Die Erweiterung der PCCA+ auf nicht-reversible Markov-Ketten sowie die Modifizierung der Zielfunktion für den Fall der weichen Clusterung setzen die Entwicklung von der PCCA über PCCA+ zu PCCA++ fort. Somit können neue Anwendungsfelder für dieses Cluster-Verfahren erschlossen werden. Die Methoden wurden zwar in Rahmen der Konformationsdynamik entwickelt, jedoch lassen sie sich auf eine weite Problemklasse anwenden, in der Gebietszerlegungsverfahren mit Monte-Carlo-Quadratur kombiniert werden. Mögliche Anwendungsgebiete umfassen die chemische Master-Gleichung oder quantenchemische Systeme.
    Keywords: ddc:510
    Language: English
    Type: doctoralthesis , doc-type:doctoralThesis
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    Hyperdeterminants as integrable discrete systems (2009)
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    Publication Date: 2020-12-11
    Description: We give the basic definitions and some theoretical results about hyperdeterminants, introduced by A.~Cayley in 1845. We prove integrability (understood as $4d$-consistency) of a nonlinear difference equation defined by the $2 \times 2 \times 2$ - hyperdeterminant. This result gives rise to the following hypothesis: the difference equations defined by hyperdeterminants of any size are integrable. We show that this hypothesis already fails in the case of the $2\times 2\times 2\times 2$ - hyperdeterminant.
    Keywords: ddc:000
    Language: English
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    A new generalized domain decomposition strategy for the efficient parallel solution of the FDS-pressure equation. Part I: Theory, Concept and Implementation (2009)
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    Publication Date: 2016-06-09
    Description: A world-wide used program for the simulation of fire-induced flows is the Fire Dynamics Simulator (FDS) which originally was developed for a purely serial execution on single-processor computing systems. Due to steadily increasing problem sizes and accuracy requirements as well as restrictions in storage capacity and computing power on single-processor systems, the efficient simulation of the considered fire scenarios can only be achieved on modern high-performance systems based on multi-processor architectures. The transition to those systems requires the elaborate parallelization of the underlying numerical methods which must guarantee the same result for a given problem as the corresponding serial execution. Unfortunately, one fundamental serial serial solver of FDS, the pressure solver, only possesses a low degree of inherent parallelizm. Its current parallelization may cause additional numerical errors, casually leading to significant losses of accuracy or even numerical instabilities. In order to ensure that the parallelization errors are limited by the leading error of the numerical scheme such that second order convergence for the whole method can be acchieved, optimized parallelization concepts must be designed. With respect to these considerations this articles gives an overview of the current parallel pressure solver as well as the problems related to it and presents an alternative method, SCARC, to overcome the existing complicacies. Part I explains the theory, concept and implementation of this new strategy, whereas Part II describes a series of validation and verification tests to proof its correctness.
    Keywords: ddc:620
    Language: English
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    A new generalized domain decomposition strategy for the efficient parallel solution of the FDS-pressure equation. Part II: Verification and Validation (2009)
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    Publication Date: 2016-06-09
    Description: Because CFD programs, like FDS, generally consist of a large number of different components representing the variety of participating numerical algorithms and chemical / physical processes, it is nearly impossible to verify such codes in their entirety, for example with comparisons of fire tests. Instead, a careful verification and validation with respect to the underlying mathematical conditions and applied numerical schemes is indispensable. In particular, error cancelations between single program components can only be detected by such detailed component-level tests. In part I of this article series a conceptual deficiency of the FDS program package with regard to multi-mesh computations was illustrated and an alternative domain decomposition strategy FDS-ScaRC was introduced. In this second part we will present the structure of a comprehensive test concept and the needs for a more mathematically and numerically orientated test procedure that is much more suited for a reliable evaluation than only a simple visual comparison of the numerical results with experimental fire tests. After a general introduction of our test concept we will demonstrate the high potential of the new FDS-\scarc{} technique compared to the FDS-FFT technique which is used in the FDS program package as yet. Based on this concept, we will present a comprehensive set of analytical and numerical test results.
    Keywords: ddc:620
    Language: English
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    A Set Partitioning Approach to Shunting (2009)
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    Publication Date: 2020-08-05
    Description: The Vehicle Positioning Problem (VPP) is a classical combinatorial optimization problem in public transport planning. A number of models and approaches have been suggested in the literature, which work for small problems, but not for large ones. We propose in this article a novel set partitioning model and an associated column generation solution approach for the VPP. The model provides a tight linear description of the problem. The pricing problem, and hence the LP relaxation itself, can be solved in polynomial resp. pseudo-polynomial time for some versions of the problems.
    Keywords: ddc:510
    Language: English
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  • 170
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    Solving Large-scale Open Pit Mining Production Scheduling Problems by Integer Programming (2009)
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    Publication Date: 2020-08-05
    Description: Since the initial application of mathematical optimisation methods to mine planning in 1965, the Lerchs-Grossmann algorithm for computing the ultimate pit limit, operations researchers have worked on a variety of challenging problems in the area of open pit mining. This thesis focuses on the open pit mining production scheduling problem: Given the discretisation of an orebody as a block model, determine the sequence in which the blocks should be removed from the pit, over the lifespan of the mine, such that the net present value of the mining operation is maximised. In practise, when some material has been removed from the pit, it must be processed further in order to extract the valuable elements contained therein. If the concentration of valuable elements is not sufficiently high, the material is discarded as waste or stockpiled. Realistically-sized block models can contain hundreds of thousands of blocks. A common approach to render these problem instances computationally tractable is the aggregation of blocks to larger scheduling units. The thrust of this thesis is the investigation of a new mixed-integer programming formulation for the open pit mining production scheduling problem, which allows for processing decisions to be made at block level, while the actual mining schedule is still computed at aggregate level. A drawback of this model in its full form is the large number of additional variables needed to model the processing decisions. One main result of this thesis shows how these processing variables can be aggregated efficiently to reduce the problem size significantly, while practically incurring no loss in net present value. The second focus is on the application of lagrangean relaxation to the resource constraints. Using a result of Möhring et al. (2003) for project scheduling, the lagrangean relaxation can be solved efficiently via minimum cut computations in a weighted digraph. Experiments with a bundle algorithm implementation by Helmberg showed how the lagrangean dual can be solved within a small fraction of the time required by standard linear programming algorithms, while yielding practically the same dual bound. Finally, several problem-specific heuristics are presented together with computational results: two greedy sub-MIP start heuristics and a large neighbourhood search heuristic. A combination of a lagrangean-based start heuristic followed by a large neighbourhood search proved to be effective in generating solutions with objective values within a 0.05% gap of the optimum.
    Keywords: ddc:510
    Language: English
    Type: masterthesis , doc-type:masterThesis
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    Moisture-Gravity Wave Interactions in a Multiscale Environment (2009)
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    Publication Date: 2016-06-09
    Description: Starting from the conservation laws for mass, momentum and energy together with a three species, bulk microphysic model, a model for the interaction of internal gravity waves and deep convective hot towers is derived by using multiscale asymptotic techniques. From the resulting leading order equations, a closed model is obtained by applying weighted averages to the smallscale hot towers without requiring further closure approximations. The resulting model is an extension of the linear, anelastic equations, into which moisture enters as the area fraction of saturated regions on the microscale with two way coupling between the large and small scale. Moisture reduces the effective stability in the model and defines a potential temperature sourceterm related to the net effect of latent heat release or consumption by microscale up- and downdrafts. The dispersion relation and group velocity of the system is analyzed and moisture is found to have several effects: It reduces energy transport by waves, increases the vertical wavenumber but decreases the slope at which wave packets travel and it introduces a lower horizontal cutoff wavenumber, below which modes turn into evanescent. Further, moisture can cause critical layers. Numerical examples for steadystate and timedependent mountain waves are shown and the effects of moisture on these waves are investigated.
    Keywords: ddc:000
    Language: English
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    1D-Reduktion thermal signifikanter Aderstränge in der Hyperthermie-Modellierung (2009)
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    Publication Date: 2019-01-29
    Description: In dieser Arbeit wird ein neuer Ansatz zur Modellierung von thermal signifikanten Gefäßsträngen im Hyperthermie-Kontext betrachtet. Ausgehend von einer Konvektions-Diffusions-Gleichung wird durch Reskalierung des Massenflussterms eine Reduktion des Adergebietes auf eine 1D-Struktur erreicht. Nach numerischen Vorbetrachtungen wird die Grenzgleichung innerhalb einer verallgemeinerten Sobolev-Algebra formuliert. Die Untersuchung der Lösungsfamilie in klassischen Funktionenräumen zeigt, dass deren schwacher Grenzwert die Lösung der korrespondierenden Diffusions-Gleichung ist. Die Diskretisierung einer formalen Grenzgleichung mit Linienstromanteil stellt jedoch eine gute Approximation an die Diskretisierung des ursprünglichen Problems dar, wenn man die lokale Maschenweite an die Gefäßradien koppelt und bei erhöhtem Genauigkeitsbedarf auf ein vollständiges 3D-Modell umschaltet.
    Keywords: ddc:510
    Language: German
    Type: masterthesis , doc-type:masterThesis
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    Guiding properties of chirped photonic crystal fibers (2009)
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    Publication Date: 2020-05-06
    Language: English
    Type: article , doc-type:article
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  • 174
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    Simulation method improves accuracy for optical metrology and nanooptics design (2009)
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    Publication Date: 2020-03-09
    Language: English
    Type: article , doc-type:article
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  • 175
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    Numerical Investigation of Silicon-on-Insulator 1D Photonic Crystal Microcavities (2009)
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    Publication Date: 2020-03-20
    Language: English
    Type: conferenceobject , doc-type:conferenceObject
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    Magnetization waves in split-ring-resonator arrays (2009)
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    Publication Date: 2020-08-20
    Language: English
    Type: article , doc-type:article
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    Comparison of electromagnetic field solvers for the 3D analysis of plasmonic nano antennas (2009)
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    Publication Date: 2020-09-25
    Language: English
    Type: conferenceobject , doc-type:conferenceObject
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    Reduction of the influence of skin marker artefacts using the optimal common shape technique (2009)
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    Publication Date: 2020-03-09
    Language: English
    Type: conferenceobject , doc-type:conferenceObject
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  • 179
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    A Perturbation Result for Dynamical Contact Problems (2009)
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    Publication Date: 2016-06-09
    Language: English
    Type: article , doc-type:article
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  • 180
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    Accurate simulation of light transmission through subwavelength apertures in metal films (2009)
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    Publication Date: 2020-03-20
    Language: English
    Type: article , doc-type:article
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  • 181
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    Fast Light and Focusing in 2D Photonic Quasicrystals (2009)
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    Publication Date: 2020-03-09
    Language: English
    Type: article , doc-type:article
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  • 182
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    Adaptive Finite Element Simulation of Ventricular Dynamics (2009)
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    Publication Date: 2020-11-16
    Language: English
    Type: article , doc-type:article
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  • 183
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    Mathematical modeling and simulation of the female menstrual cycle (2009)
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    Publication Date: 2020-02-04
    Language: English
    Type: doctoralthesis , doc-type:doctoralThesis
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    Non-invasive Assessment of Skeletal Kinematics (2009)
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    Publication Date: 2020-03-09
    Language: English
    Type: conferenceobject , doc-type:conferenceObject
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    Language: English
    Type: article , doc-type:article
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    Language: English
    Type: article , doc-type:article
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    Language: English
    Type: article , doc-type:article
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    Language: English
    Type: conferenceobject , doc-type:conferenceObject
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    Type: article , doc-type:article
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    Type: article , doc-type:article
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    Language: English
    Type: article , doc-type:article
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    Language: English
    Type: bookpart , doc-type:bookPart
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    Language: English
    Type: article , doc-type:article
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    Type: article , doc-type:article
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    Type: masterthesis , doc-type:masterThesis
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    Type: masterthesis , doc-type:masterThesis
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