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  • 101
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    The maximum diversity assortment selection problem (2021)
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    Publikationsdatum: 2024-03-06
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: 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)
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    Publikationsdatum: 2024-03-18
    Sprache: Englisch
    Materialart: researchdata , doc-type:ResearchData
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  • 103
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    cmdtools (2021)
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    Publikationsdatum: 2024-03-18
    Beschreibung: Python implementation of severals tools (PCCA, AJC, SQRA, P/Q estimation) for the analysis of dynamical systems from the transfer operator perspective.
    Sprache: Englisch
    Materialart: 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)
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    Publikationsdatum: 2024-03-18
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: 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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    Publikationsdatum: 2024-03-18
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: article , doc-type:article
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  • 106
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    Combining XOR and Partner Checkpointing for Resilient Multilevel Checkpoint/Restart (2021)
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    Publikationsdatum: 2024-04-05
    Sprache: Englisch
    Materialart: 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)
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    Publikationsdatum: 2024-04-05
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: masterthesis , doc-type:masterThesis
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  • 108
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    On the Regression Model for Generalized Normal Distributions (2021)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: 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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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: 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)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: 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)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 112
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    Deep learning for spatio-temporal supply anddemand forecasting in natural gas transmission networks (2021)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: 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)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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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)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: article , doc-type:article
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  • 115
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    Robust Approximation of Chance Constrained DC Optimal Power Flow under Decision-Dependent Uncertainty (2021)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: article , doc-type:article
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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)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: 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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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: article , doc-type:article
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  • 118
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    Optimization of Stationary Expansion Planning and Transient Network Control by Mixed-Integer Nonlinear Programming (2021)
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    Publikationsdatum: 2024-04-26
    Sprache: Englisch
    Materialart: 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)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 120
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    CMAP-LAP: Configurable Massively Parallel Solver for Lattice Problems (2021)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
    Materialart: conferenceobject , doc-type:conferenceObject
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  • 121
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    CMAP-LAP: Configurable Massively Parallel Solver for Lattice Problems (2021)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
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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)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
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  • 123
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    Massively parallel sharing lattice basis reduction (2021)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
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  • 124
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    Interface stability of compressible fluids in porous media (2021)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
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  • 125
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    Effect of water depth on Kelvin - Helmholtz instability in a shallow-water flow (2021)
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    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
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    Instability of a tangential discontinuity surface in a three-dimensional compressible medium (2021)
    Details
    Publikationsdatum: 2024-04-26
    Beschreibung: 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.
    Sprache: Englisch
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    Faster algorithms for Steiner tree and related problems: From theory to practice (2021)
    Details
    Publikationsdatum: 2024-04-26
    Sprache: Englisch
    Materialart: doctoralthesis , doc-type:doctoralThesis
    Format: application/pdf
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    Inference of historical influence networks (2021)
    Details
    Publikationsdatum: 2024-05-16
    Beschreibung: 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.
    Sprache: Deutsch
    Materialart: conferenceobject , doc-type:conferenceObject
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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
    Publikationsdatum: 2024-06-13
    Sprache: Englisch
    Materialart: article , doc-type:article
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    Grundlagen der Eingruppierung TVöD und TV-L : das aktuelle Eingruppierungsrecht im öffentlichen Dienst (2021)
    Berlin :Walhalla und Praetoria Verlag,
    Details
    Titel: Grundlagen der Eingruppierung TVöD und TV-L : das aktuelle Eingruppierungsrecht im öffentlichen Dienst
    Autor: Richter, Achim
    Beteiligte Person(en): Gamisch, Annett , Mohr, Thomas
    Ausgabe: 7., aktualisierte Auflage, Bearbeitungsstand: Juni 2017
    Verlag: Berlin :Walhalla und Praetoria Verlag,
    Erscheinungsjahr: 2021
    Seiten: 112 Seiten
    ISBN: 978-3-8029-1599-4
    Materialart: Buch
    Sprache: Deutsch
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    Crashkurs BWA : betriebswirtschaftliche Auswertungen erstellen, lesen und verstehen (2021)
    Details
    Titel: Crashkurs BWA : betriebswirtschaftliche Auswertungen erstellen, lesen und verstehen
    Autor: Träger, Elisabeth
    Ausgabe: 1. Auflage
    Erscheinungsjahr: 2021
    Seiten: 180 Seiten
    ISBN: 978-3-648-13768-0
    Materialart: Buch
    Sprache: Deutsch
    URL: Inhaltstext
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    Schwierige Geschäftsvorfälle richtig buchen / (2021)
    Freiburg im Breisgau :Haufe-Lexware,
    Details
    Titel: Schwierige Geschäftsvorfälle richtig buchen /
    Autor: Thomsen, Iris
    Beteiligte Person(en): Zöllner, Nikolaus
    Ausgabe: 15. Auflage
    Verlag: Freiburg im Breisgau :Haufe-Lexware,
    Erscheinungsjahr: 2021
    Seiten: 413 Seiten
    ISBN: 978-3-648-14840-2
    Materialart: Buch
    Sprache: Deutsch
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    Erfurter Kommentar zum Arbeitsrecht (2021)
    München :C.H. Beck,
    Details
    Titel: Erfurter Kommentar zum Arbeitsrecht
    Beteiligte Person(en): Müller-Glöge, Rudi , Preis, Ulrich , Gallner, Inken
    Ausgabe: 22. Auflage
    Verlag: München :C.H. Beck,
    Erscheinungsjahr: 2021
    Seiten: 3100 Seiten
    ISBN: 978-3-406-77038-8
    Materialart: Buch
    Sprache: Deutsch
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    Programming Rust : fast, safe systems development (2021)
    Beijing ; Boston ; Farnham ; Sebastopol :O'Reilly,
    Details
    Titel: Programming Rust : fast, safe systems development
    Autor: Blandy, Jim
    Beteiligte Person(en): Orendorff, Jason , Tindall, Leonora
    Ausgabe: Second edition
    Verlag: Beijing ; Boston ; Farnham ; Sebastopol :O'Reilly,
    Erscheinungsjahr: 2021
    Seiten: xix, 711 Seiten
    ISBN: 9781492052562
    Materialart: Buch
    Sprache: Englisch
    Paralleltitel: 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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    Git für Dummies / (2021)
    Weinheim :Wiley-VCH,
    Details
    Titel: Git für Dummies /
    Autor: Kaufmann, Michael
    Beteiligte Person(en): Binkle, Harald
    Verlag: Weinheim :Wiley-VCH,
    Erscheinungsjahr: 2021
    Seiten: 417 Seiten
    ISBN: 978-3-527-71697-5
    Materialart: Buch
    Sprache: Deutsch
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    Git Handbuch für Einsteiger : Der leichte Weg zum Git-Experten (2021)
    Landshut :BMU Media Verlag,
    Details
    Titel: Git Handbuch für Einsteiger : Der leichte Weg zum Git-Experten
    Autor: Fuchs, Paul
    Verlag: Landshut :BMU Media Verlag,
    Erscheinungsjahr: 2021
    Seiten: 307 Seiten
    ISBN: 978-3-96645-119-2
    Materialart: Buch
    Sprache: Deutsch
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    Linear Algebra : Theory, Intuition, Code (2021)
    Sincxpress Bv,
    Details
    Titel: Linear Algebra : Theory, Intuition, Code
    Autor: Cohen, Mike X
    Verlag: Sincxpress Bv,
    Erscheinungsjahr: 2021
    Seiten: 548 S.
    ISBN: 978-90-831366-0-8
    Materialart: Buch
    Sprache: Deutsch
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    HTML und CSS : das umfassende Handbuch (2021)
    Bonn :Rheinwerk Verlag,
    Details
    Titel: HTML und CSS : das umfassende Handbuch
    Autor: Wolf, Jürgen
    Ausgabe: 4., aktualisierte und überarbeitete Auflage
    Verlag: Bonn :Rheinwerk Verlag,
    Erscheinungsjahr: 2021
    Seiten: 1158 Seiten
    ISBN: 978-3-8362-8117-1
    Materialart: Buch
    Sprache: Deutsch
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    Forschungsdatenmanagement und Recht : Datenschutz-, Urheber- und Vertragsrecht (2021)
    Feldkirch/Düns :Neugebauer,
    Details
    Titel: Forschungsdatenmanagement und Recht : Datenschutz-, Urheber- und Vertragsrecht
    Autor: Baumann, Paul
    Beteiligte Person(en): Krahn, Philipp , Lauber-Rönsberg, Anne
    Verlag: Feldkirch/Düns :Neugebauer,
    Erscheinungsjahr: 2021
    Seiten: 304 Seiten
    ISBN: 978-3-85376-328-5
    Materialart: Buch
    Sprache: Deutsch
    URL: Inhaltsverzeichnis
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    ¬The¬ science of science / (2021)
    Cambridge :Cambridge University Press,
    Details
    Titel: ¬The¬ science of science /
    Autor: Wang, Dashun
    Beteiligte Person(en): Barabási, Albert-László
    Verlag: Cambridge :Cambridge University Press,
    Erscheinungsjahr: 2021
    Seiten: x, 303 Seiten
    ISBN: 978-1-108-71695-6
    Materialart: Buch
    Sprache: Englisch
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    Introduction to Quantum Computing / (2021)
    Basel :Springer International Publishing,
    Details
    Titel: Introduction to Quantum Computing /
    Autor: LaPierre, Ray
    Verlag: Basel :Springer International Publishing,
    Erscheinungsjahr: 2021
    Seiten: 368 Seiten
    ISBN: 978-3-030-69317-6
    Materialart: Buch
    Sprache: Englisch
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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
    Titel: Handbuch Prüfung ortsfester elektrischer Anlagen und Betriebsmittel : Prüfabläufe, Grenz- und Richtwerte gem. DIN VDE 0100-600 und 0105-100 für die Prüfung vor Ort
    Autor: Donath, Karl [Verfasser]
    Beteiligte Person(en): Rottmann, Rainer [Verfasser] , Orgel, Christian [Verfasser]
    Ausgabe: 4. überarbeitete Auflage
    Verlag: Forum Verlag Herkert,
    Erscheinungsjahr: 2021
    Seiten: 374 Seiten
    Materialart: Buch
    Sprache: Deutsch
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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
    Titel: Handbuch Prüfung ortsveränderlicher elektrischer Geräte : Prüfabläufe, Grenz- und Richtwerte gem. DIN VDE 0701-0702 für die Prüfung vor Ort
    Beteiligte Person(en): Donath, Karl [Verfasser] , Rottmann, Rainer [Verfasser] , Gavrancic, Milan [Verfasser] , Orgel, Christian [Verfasser]
    Ausgabe: 4. überarbeitete Auflage
    Verlag: Forum Verlag Herkert,
    Erscheinungsjahr: 2021
    Seiten: 311 Seiten
    ISBN: 978-3-96314-615-2
    Materialart: Buch
    Sprache: Deutsch
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    Docker : das Praxisbuch für Entwickler und DevOps-Teams (2021)
    Details
    Titel: Docker : das Praxisbuch für Entwickler und DevOps-Teams
    Autor: Öggl, Bernd
    Beteiligte Person(en): Kofler, Michael
    Ausgabe: 3. Aufl.
    Erscheinungsjahr: 2021
    Seiten: 496 S. : , Illustrationen, Diagramme
    ISBN: 978-3-8362-8634-3
    Materialart: Buch
    Sprache: Deutsch
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    Götzendämmerung : Kunst und Künstliche Intelligenz (2021)
    Bielefeld :transcript,
    Details
    Titel: Götzendämmerung : Kunst und Künstliche Intelligenz
    Beteiligte Person(en): Dotzler, Bernhard J. , Karpat, Berkan
    Verlag: Bielefeld :transcript,
    Erscheinungsjahr: 2021
    Seiten: 154 Seiten
    ISBN: 978-3-8376-5976-4
    Materialart: Buch
    Sprache: Deutsch
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    Muster : Theorie der digitalen Gesellschaft (2021)
    München :C.H. Beck,
    Details
    Titel: Muster : Theorie der digitalen Gesellschaft
    Autor: Nassehi, Armin
    Ausgabe: 1. Auflage
    Verlag: München :C.H. Beck,
    Erscheinungsjahr: 2021
    Seiten: 352 Seiten
    ISBN: 978-3-406-76786-9
    Materialart: Buch
    Sprache: Deutsch
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    Liberating structures : Entscheidungsfindung revolutionieren (2021)
    München :Verlag Franz Vahlen GmbH,
    Details
    Titel: Liberating structures : Entscheidungsfindung revolutionieren
    Autor: Steinhöfer, Daniel
    Verlag: München :Verlag Franz Vahlen GmbH,
    Erscheinungsjahr: 2021
    Seiten: 120 Seiten
    ISBN: 978-3-8006-5929-6
    Materialart: Buch
    Sprache: Deutsch
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    Crashkurs Internes Kontrollsystem für Buchhaltung und Steuern / (2021)
    Details
    Titel: Crashkurs Internes Kontrollsystem für Buchhaltung und Steuern /
    Autor: Alves, Winfried
    Ausgabe: 2. völlig überarbeitete und erweiterte Auflage
    Erscheinungsjahr: 2021
    Seiten: 167 Seiten
    ISBN: 978-3-648-14049-9
    Materialart: Buch
    Sprache: Deutsch
    URL: Inhaltstext
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    Quasinormal mode solvers for resonators with dispersive materials (2019)
    Details
    Publikationsdatum: 2021-02-26
    Sprache: Englisch
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    Decomposition of scattered electromagnetic fields into vector spherical wave functions on surfaces with general shapes (2019)
    Details
    Publikationsdatum: 2021-01-08
    Sprache: Englisch
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    Benchmarking five global optimization approaches for nano-optical shape optimization and parameter reconstruction (2019)
    Details
    Publikationsdatum: 2021-01-08
    Sprache: Englisch
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    Structure-driven fix-and-propagate heuristics for mixed integer programming (2019)
    Details
    Publikationsdatum: 2022-03-14
    Beschreibung: Primal heuristics play an important role in the solving of mixed integer programs (MIPs). They often provide good feasible solutions early and help to reduce the time needed to prove optimality. In this paper, we present a scheme for start heuristics that can be executed without previous knowledge of an LP solution or a previously found integer feasible solution. It uses global structures available within MIP solvers to iteratively fix integer variables and propagate these fixings. Thereby, fixings are determined based on the predicted impact they have on the subsequent domain propagation. If sufficiently many variables can be fixed that way, the resulting problem is solved first as an LP, and then as an auxiliary MIP if the rounded LP solution does not provide a feasible solution already. We present three primal heuristics that use this scheme based on different global structures. Our computational experiments on standard MIP test sets show that the proposed heuristics find solutions for about 60 % of the instances and by this, help to improve several performance measures for MIP solvers, including the primal integral and the average solving time.
    Sprache: Englisch
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    Intersection cuts for factorable MINLP (2019)
    Details
    Publikationsdatum: 2020-08-05
    Beschreibung: Given a factorable function f, we propose a procedure that constructs a concave underestimor of f that is tight at a given point. These underestimators can be used to generate intersection cuts. A peculiarity of these underestimators is that they do not rely on a bounded domain. We propose a strengthening procedure for the intersection cuts that exploits the bounds of the domain. Finally, we propose an extension of monoidal strengthening to take advantage of the integrality of the non-basic variables.
    Sprache: Englisch
    Materialart: conferenceobject , doc-type:conferenceObject
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    Parallel PIPS-SBB: Multi-Level Parallelism For Stochastic Mixed-Integer Programs (2019)
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    Publikationsdatum: 2020-12-14
    Beschreibung: PIPS-SBB is a distributed-memory parallel solver with a scalable data distribution paradigm. It is designed to solve MIPs with a dual-block angular structure, which is characteristic of deterministic-equivalent Stochastic Mixed-Integer Programs (SMIPs). In this paper, we present two different parallelizations of Branch & Bound (B&B), implementing both as extensions of PIPS-SBB, thus adding an additional layer of parallelism. In the first of the proposed frameworks, PIPS-PSBB, the coordination and load-balancing of the different optimization workers is done in a decentralized fashion. This new framework is designed to ensure all available cores are processing the most promising parts of the B&B tree. The second, ug[PIPS-SBB,MPI], is a parallel implementation using the Ubiquity Generator (UG), a universal framework for parallelizing B&B tree search that has been successfully applied to other MIP solvers. We show the effects of leveraging multiple levels of parallelism in potentially improving scaling performance beyond thousands of cores.
    Sprache: Englisch
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    Presolve Reductions in Mixed Integer Programming (2019)
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    Publikationsdatum: 2021-08-05
    Beschreibung: Mixed integer programming has become a very powerful tool for modeling and solving real-world planning and scheduling problems, with the breadth of applications appearing to be almost unlimited. A critical component in the solution of these mixed-integer programs is a set of routines commonly referred to as presolve. Presolve can be viewed as a collection of preprocessing techniques that reduce the size of and, more importantly, improve the ``strength'' of the given model formulation, that is, the degree to which the constraints of the formulation accurately describe the underlying polyhedron of integer-feasible solutions. As our computational results will show, presolve is a key factor in the speed with which we can solve mixed-integer programs, and is often the difference between a model being intractable and solvable, in some cases easily solvable. In this paper we describe the presolve functionality in the Gurobi commercial mixed-integer programming code. This includes an overview, or taxonomy of the different methods that are employed, as well as more-detailed descriptions of several of the techniques, with some of them appearing, to our knowledge, for the first time in the literature.
    Sprache: Englisch
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    An Easy Way to Build Parallel State-of-the-art Combinatorial Optimization Problem Solvers: A Computational Study on Solving Steiner Tree Problems and Mixed Integer Semidefinite Programs by using ug[SCIP-*,*]-libraries (2019)
    Details
    Publikationsdatum: 2020-08-05
    Beschreibung: Branch-and-bound (B&B) is an algorithmic framework for solving NP-hard combinatorial optimization problems. Although several well-designed software frameworks for parallel B&B have been developed over the last two decades, there is very few literature about successfully solving previously intractable combinatorial optimization problem instances to optimality by using such frameworks.The main reason for this limited impact of parallel solvers is that the algorithmic improvements for specific problem types are significantly greater than performance gains obtained by parallelization in general. Therefore, in order to solve hard problem instances for the first time, one needs to accelerate state-of-the-art algorithm implementations. In this paper, we present a computational study for solving Steiner tree problems and mixed integer semidefinite programs in parallel. These state-of-the-art algorithm implementations are based on SCIP and were parallelized via the ug[SCIP-*,*]-libraries---by adding less than 200 lines of glue code. Despite the ease of their parallelization, these solvers have the potential to solve previously intractable instances. In this paper, we demonstrate the convenience of such a parallelization and present results for previously unsolvable instances from the well-known PUC benchmark set, widely regarded as the most difficult Steiner tree test set in the literature.
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
    Format: application/pdf
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  • 157
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    What you extract is what you see: Optimising the preparation of water and wastewater samples for in vitro bioassays (2019)
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    Publikationsdatum: 2019-07-08
    Beschreibung: The assessment of water quality is crucial for safeguarding drinking water resources and ecosystem integrity. To this end, sample preparation and extraction is critically important, especially when investigating emerging contaminants and the toxicity of water samples. As extraction methods are rarely optimised for bioassays but rather adopted from chemical analysis, this may result in a misrepresentation of the actual toxicity. In this study, surface water, groundwater, hospital and municipal wastewater were used to characterise the impacts of common sample preparation techniques (acidification, filtration and solid phase extraction (SPE)) on the outcomes of eleven in vitro bioassays. The latter covered endocrine activity (reporter gene assays for estrogen, androgen, aryl-hydrocarbon, retinoic acid, retinoid X, vitamin D, thyroid receptor), mutagenicity (Ames fluctuation test), genotoxicity (umu test) and cytotoxicity. Water samples extracted using different SPE sorbents (Oasis HLB, Supelco ENVI-Carb+, Telos C18/ENV) at acidic and neutral pH were compared for their performance in recovering biological effects. Acidification, commonly used for stabilisation, significantly altered the endocrine activity and toxicity of most (waste)water samples. Sample filtration did not affect the majority of endpoints but in certain cases affected the (anti-)estrogenic and dioxin-like activities. SPE extracts (10.4 × final concentration), including WWTP effluents, induced significant endocrine effects that were not detected in aqueous samples (0.63 × final concentration), such as estrogenic, (anti-)androgenic and dioxin-like activities. When ranking the SPE methods using multivariate Pareto optimisation an extraction with Telos C18/ENV at pH 7 was most effective in recovering toxicity. At the same time, these extracts were highly cytotoxic masking the endpoint under investigation. Compared to that, extraction at pH 2.5 enriched less cytotoxicity. In summary, our study demonstrates that sample preparation and extraction critically affect the outcome of bioassays when assessing the toxicity of water samples. Depending on the water matrix and the bioassay, these methods need to be optimised to accurately assess water quality.
    Sprache: Englisch
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  • 158
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    An auxiliary field approach for computing optical resonances in dispersive media (2019)
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    Publikationsdatum: 2020-03-09
    Sprache: Englisch
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  • 159
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    DPI: The Data Processing Interface for Modern Networks (2019)
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    Publikationsdatum: 2021-02-01
    Beschreibung: As data processing evolves towards large scale, distributed platforms, the network will necessarily play a substantial role in achieving efficiency and performance. Increasingly, switches, network cards, and protocols are becoming more flexible while programmability at all levels (aka, software defined networks) opens up many possibilities to tailor the network to data processing applications and to push processing down to the network elements. In this paper, we propose DPI, an interface providing a set of simple yet powerful abstractions flexible enough to exploit features of modern networks (e.g., RDMA or in-network processing) suitable for data processing. Mirroring the concept behind the Message Passing Interface (MPI) used extensively in high-performance computing, DPI is an interface definition rather than an implementation so as to be able to bridge different networking technologies and to evolve with them. In the paper we motivate and discuss key primitives of the interface and present a number of use cases that show the potential of DPI for data-intensive applications, such as analytic engines and distributed database systems.
    Sprache: Englisch
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  • 160
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    From interacting agents to density-based modeling with stochastic PDEs (2019)
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    Publikationsdatum: 2021-11-02
    Beschreibung: Many real-world processes can naturally be modeled as systems of interacting agents. However, the long-term simulation of such agent-based models is often intractable when the system becomes too large. In this paper, starting from a stochastic spatio-temporal agent-based model (ABM), we present a reduced model in terms of stochastic PDEs that describes the evolution of agent number densities for large populations. We discuss the algorithmic details of both approaches; regarding the SPDE model, we apply Finite Element discretization in space which not only ensures efficient simulation but also serves as a regularization of the SPDE. Illustrative examples for the spreading of an innovation among agents are given and used for comparing ABM and SPDE models.
    Sprache: Englisch
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  • 161
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    Linearizable State Machine Replication of State-Based CRDTs without Logs (2019)
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    Publikationsdatum: 2021-02-01
    Beschreibung: General solutions of state machine replication have to ensure that all replicas apply the same commands in the same order, even in the presence of failures. Such strict ordering incurs high synchronization costs due to the use of distributed consensus or a leader. This paper presents a protocol for linearizable state machine replication of conflict-free replicated data types (CRDTs) that neither requires consensus nor a leader. By leveraging the properties of state-based CRDTs—in particular the monotonic growth of a join semilattice—synchronization overhead is greatly reduced. In addition, updates just need a single round trip and modify the state ‘in-place’ without the need for a log. Furthermore, the message size overhead for coordination consists of a single counter per message. While reads in the presence of concurrent updates are not wait-free without a coordinator, we show that more than 97 % of reads can be handled in one or two round trips under highly concurrent accesses. Our protocol achieves high throughput without auxiliary processes such as command log management or leader election. It is well suited for all practical scenarios that need linearizable access on CRDT data on a fine-granular scale.
    Sprache: Englisch
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  • 162
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    Dispersion-engineered nanocomposites enable achromatic diffractive optical elements (2019)
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    Publikationsdatum: 2020-03-09
    Sprache: Englisch
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  • 163
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    A Three-Phase Heuristic for Cyclic Crew Rostering with Fairness Requirements (2019)
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    Publikationsdatum: 2020-08-05
    Beschreibung: In this paper, we consider the Cyclic Crew Rostering Problem with Fairness Requirements (CCRP-FR). In this problem, attractive cyclic rosters have to be constructed for groups of employees, considering multiple, a priori determined, fairness levels. The attractiveness follows from the structure of the rosters (e.g., sufficient rest times and variation in work), whereas fairness is based on the work allocation among the different roster groups. We propose a three-phase heuristic for the CCRP-FR, which combines the strength of column generation techniques with a large-scale neighborhood search algorithm. The design of the heuristic assures that good solutions for all fairness levels are obtained quickly, and can still be further improved if additional running time is available. We evaluate the performance of the algorithm using real-world data from Netherlands Railways, and show that the heuristic finds close to optimal solutions for many of the considered instances. In particular, we show that the heuristic is able to quickly find major improvements upon the current sequential practice: For most instances, the heuristic is able to increase the attractiveness by at least 20% in just a few minutes.
    Sprache: Englisch
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  • 164
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    BEAM-ME: Ein interdisziplinärer Beitrag zur Erreichung der Klimaziele (2019)
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    Publikationsdatum: 2020-08-05
    Sprache: Deutsch
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  • 165
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    KOBV Jahresbericht 2010 (2019)
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    Publikationsdatum: 2019-10-24
    Beschreibung: Der KOBV-Jahresbericht informiert rückblickend im 2-Jahres-Rhythmus über die bibliothekarisch-fachlichen Entwicklungen im Verbund und die Projekte des Kooperativen Bibliotheksverbunds Berlin-Brandenburg (KOBV).
    Sprache: Deutsch
    Materialart: annualzib , doc-type:report
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  • 166
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    Deterministic integration of quantum dots into on-chip multi-mode interference couplers via in-situ electron beam lithography (2019)
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    Publikationsdatum: 2020-03-09
    Sprache: Englisch
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  • 167
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    Separation of cycle inequalities in periodic timetabling (2019)
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    Publikationsdatum: 2021-04-14
    Beschreibung: Cycle inequalities play an important role in the polyhedral study of the periodic timetabling problem in public transport. We give the first pseudo-polynomial time separation algorithm for cycle inequalities, and we contribute a rigorous proof for the pseudo-polynomial time separability of the change-cycle inequalities. Moreover, we provide several NP-completeness results, indicating that pseudo-polynomial time is best possible. The efficiency of these cutting planes is demonstrated on real-world instances of the periodic timetabling problem.
    Sprache: Englisch
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  • 168
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    Correlation of circular differential optical absorption with geometric chirality in plasmonic meta-atoms (2019)
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    Publikationsdatum: 2022-01-07
    Sprache: Englisch
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  • 169
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    Structural characterization of synthetic peptides using electronspray ion mobility spectrometry and molecular dynamics simulations (2019)
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    Publikationsdatum: 2020-11-16
    Beschreibung: Electrospray ionization-ion mobility spectrometry was employed for the determination of collision cross sections (CCS) of 25 synthetically produced peptides in the mass range between 540–3310 Da. The experimental measurement of the CCS is complemented by their calculation applying two different methods. One prediction method is the intrinsic size parameter (ISP) method developed by the Clemmer group. The second new method is based on the evaluation of molecular dynamics (MD) simulation trajectories as a whole, resulting in a single, averaged collision cross-section value for a given peptide in the gas phase. A high temperature MD simulation is run in order to scan through the whole conformational space. The lower temperature conformational distribution is obtained through thermodynamic reweighting. In the first part, various correlations, e.g. CCS vs. mass and inverse mobility vs. m/z correlations, are presented. Differences in CCS between peptides are also discussed in terms of their respective mass and m/z differences, as well as their respective structures. In the second part, measured and calculated CCS are compared. The agreement between the prediction results and the experimental values is in the same range for both calculation methods. While the calculation effort of the ISP method is much lower, the MD method comprises several tools providing deeper insights into the conformations of peptides. Advantages and limitations of both methods are discussed. Based on the separation of two pairs of linear and cyclic peptides of virtually the same mass, the influence of the structure on the cross sections is discussed. The shift in cross section differences and peak shape after transition from the linear to the cyclic peptide can be well understood by applying different MD tools, e.g. the root-mean-square deviation (RMSD) and the root mean square fluctuation (RMSF).
    Sprache: Englisch
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  • 170
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    Achiral, Helicity Preserving, and Resonant Structures for Enhanced Sensing of Chiral Molecules (2019)
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    Publikationsdatum: 2021-01-08
    Sprache: Englisch
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  • 171
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    SLCV – A Supervised Learning - Computer Vision combined strategy for automated muscle fibre detection in cross sectional images (2019)
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    Publikationsdatum: 2020-11-24
    Beschreibung: Muscle fibre cross sectional area (CSA) is an important biomedical measure used to determine the structural composition of skeletal muscle, and it is relevant for tackling research questions in many different fields of research. To date, time consuming and tedious manual delineation of muscle fibres is often used to determine the CSA. Few methods are able to automatically detect muscle fibres in muscle fibre cross sections to quantify CSA due to challenges posed by variation of bright- ness and noise in the staining images. In this paper, we introduce SLCV, a robust semi-automatic pipeline for muscle fibre detection, which combines supervised learning (SL) with computer vision (CV). SLCV is adaptable to different staining methods and is quickly and intuitively tunable by the user. We are the first to perform an error analysis with respect to cell count and area, based on which we compare SLCV to the best purely CV-based pipeline in order to identify the contribution of SL and CV steps to muscle fibre detection. Our results obtained on 27 fluorescence-stained cross sectional images of varying staining quality suggest that combining SL and CV performs signifi- cantly better than both SL based and CV based methods with regards to both the cell separation- and the area reconstruction error. Furthermore, applying SLCV to our test set images yielded fibre detection results of very high quality, with average sensitivity values of 0.93 or higher on different cluster sizes and an average Dice Similarity Coefficient (DSC) of 0.9778.
    Sprache: Englisch
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  • 172
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    An unexpected connection between Bayes A-optimal designs and the group lasso (2019)
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    Publikationsdatum: 2020-08-05
    Beschreibung: We show that the A-optimal design optimization problem over m design points in R^n is equivalent to minimizing a quadratic function plus a group lasso sparsity inducing term over n x m real matrices. This observation allows to describe several new algorithms for A-optimal design based on splitting and block coordinate decomposition. These techniques are well known and proved powerful to treat large scale problems in machine learning and signal processing communities. The proposed algorithms come with rigorous convergence guarantees and convergence rate estimate stemming from the optimization literature. Performances are illustrated on synthetic benchmarks and compared to existing methods for solving the optimal design problem.
    Sprache: Englisch
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  • 173
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    Linear Programming using Limited-Precision Oracles (2019)
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    Publikationsdatum: 2021-02-01
    Beschreibung: Linear programming is a foundational tool for many aspects of integer and combinatorial optimization. This work studies the complexity of solving linear programs exactly over the rational numbers through use of an oracle capable of returning limited-precision LP solutions. It is shown that a polynomial number of calls to such an oracle and a polynomial number of bit operations, is sufficient to compute an exact solution to an LP. Previous work has often considered oracles that provide solutions of an arbitrary specified precision. While this leads to polynomial-time algorithms, the level of precision required is often unrealistic for practical computation. In contrast, our work provides a foundation for understanding and analyzing the behavior of the methods that are currently most effective in practice for solving LPs exactly.
    Sprache: Englisch
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  • 174
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    On the Relation between the Extended Supporting Hyperplane Algorithm and Kelley’s Cutting Plane Algorithm (2019)
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    Publikationsdatum: 2020-08-05
    Beschreibung: Recently, Kronqvist et al. (2016) rediscovered the supporting hyperplane algorithm of Veinott (1967) and demonstrated its computational benefits for solving convex mixed-integer nonlinear programs. In this paper we derive the algorithm from a geometric point of view. This enables us to show that the supporting hyperplane algorithm is equivalent to Kelley's cutting plane algorithm applied to a particular reformulation of the problem. As a result, we extend the applicability of the supporting hyperplane algorithm to convex problems represented by general, not necessarily convex, differentiable functions that satisfy a mild condition.
    Sprache: Englisch
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  • 175
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    Nanocomposites – A Route to better and smaller optical Elements? (2019)
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    Publikationsdatum: 2020-03-09
    Sprache: Englisch
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  • 176
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    Strategic Planning of Rolling Stock Rotations for Public Tenders (2019)
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    Publikationsdatum: 2022-03-14
    Beschreibung: Since railway companies have to apply for long-term public contracts to operate railway lines in public tenders, the question how they can estimate the operating cost for long-term periods adequately arises naturally. We consider a rolling stock rotation problem for a time period of ten years, which is based on a real world instance provided by an industry partner. We use a two stage approach for the cost estimation of the required rolling stock. In the first stage, we determine a weekly rotation plan. In the second stage, we roll out this weekly rotation plan for a longer time period and incorporate scheduled maintenance treatments. We present a heuristic approach and a mixed integer programming model to implement the process of the second stage. Finally, we discuss computational results for a real world tendering scenario.
    Sprache: Englisch
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  • 177
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    New Perspectives on PESP: T-Partitions and Separators (2019)
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    Publikationsdatum: 2020-11-16
    Beschreibung: In the planning process of public transportation companies, designing the timetable is among the core planning steps. In particular in the case of periodic (or cyclic) services, the Periodic Event Scheduling Problem (PESP) is well-established to compute high-quality periodic timetables. We are considering algorithms for computing good solutions for the very basic PESP with no additional extra features as add-ons. The first of these algorithms generalizes several primal heuristics that had been proposed in the past, such as single-node cuts and the modulo network simplex algorithm. We consider partitions of the graph, and identify so-called delay cuts as a structure that allows to generalize several previous heuristics. In particular, when no more improving delay cut can be found, we already know that the other heuristics could not improve either. The second of these algorithms turns a strategy, that had been discussed in the past, upside-down: Instead of gluing together the network line-by-line in a bottom-up way, we develop a divide-and-conquer-like top-down approach to separate the initial problem into two easier subproblems such that the information loss along their cutset edges is as small as possible. We are aware that there may be PESP instances that do not fit well the separator setting. Yet, on the RxLy-instances of PESPlib in our experimental computations, we come up with good primal solutions and dual bounds. In particular, on the largest instance (R4L4), this new separator approach, which applies a state-of-the-art solver as subroutine, is able to come up with better dual bounds than purely applying this state-of-the-art solver in the very same time.
    Sprache: Englisch
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  • 178
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    Visible points, the separation problem, and applications to MINLP (2019)
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    Publikationsdatum: 2020-08-05
    Beschreibung: In this paper we introduce a technique to produce tighter cutting planes for mixed-integer non-linear programs. Usually, a cutting plane is generated to cut off a specific infeasible point. The underlying idea is to use the infeasible point to restrict the feasible region in order to obtain a tighter domain. To ensure validity, we require that every valid cut separating the infeasible point from the restricted feasible region is still valid for the original feasible region. We translate this requirement in terms of the separation problem and the reverse polar. In particular, if the reverse polar of the restricted feasible region is the same as the reverse polar of the feasible region, then any cut valid for the restricted feasible region that \emph{separates} the infeasible point, is valid for the feasible region. We show that the reverse polar of the \emph{visible points} of the feasible region from the infeasible point coincides with the reverse polar of the feasible region. In the special where the feasible region is described by a single non-convex constraint intersected with a convex set we provide a characterization of the visible points. Furthermore, when the non-convex constraint is quadratic the characterization is particularly simple. We also provide an extended formulation for a relaxation of the visible points when the non-convex constraint is a general polynomial. Finally, we give some conditions under which for a given set there is an inclusion-wise smallest set, in some predefined family of sets, whose reverse polars coincide.
    Sprache: Englisch
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  • 179
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    Learned Clause Minimization in Parallel SAT Solvers (2019)
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    Publikationsdatum: 2021-03-03
    Beschreibung: Learned clauses minimization (LCM) let to performance improvements of modern SAT solvers especially in solving hard SAT instances. Despite the success of LCM approaches in sequential solvers, they are not widely incorporated in parallel SAT solvers. In this paper we explore the potential of LCM for parallel SAT solvers by defining multiple LCM approaches based on clause vivification, comparing their runtime in different SAT solvers and discussing reasons for performance gains and losses. Results show that LCM only boosts performance of parallel SAT solvers on a fraction of SAT instances. More commonly applying LCM decreases performance. Only certain LCM approaches are able to improve the overall performance of parallel SAT solvers.
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  • 180
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    Ein System zur deterministischen Wiedergabe von verteilten Algorithmen auf Anwendungsebene (2019)
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    Publikationsdatum: 2021-01-21
    Sprache: Deutsch
    Materialart: masterthesis , doc-type:masterThesis
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  • 181
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    A Graph- and Monoid-based Framework for Price-Sensitive Routing in Local Public Transportation Networks (2019)
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    Publikationsdatum: 2020-08-05
    Beschreibung: We present a novel framework to mathematically describe the fare systems of local public transit companies. The model allows the computation of a provably cheapest itinerary even if prices depend on a number of parameters and non-linear conditions. Our approach is based on a ticket graph model to represent tickets and their relation to each other. Transitions between tickets are modeled via transition functions over partially ordered monoids and a set of symbols representing special properties of fares (e.g. surcharges). Shortest path algorithms rely on the subpath optimality property. This property is usually lost when dealing with complicated fare systems. We restore it by relaxing domination rules for tickets depending on the structure of the ticket graph. An exemplary model for the fare system of Mitteldeutsche Verkehrsbetriebe (MDV) is provided. By integrating our framework in the multi-criteria RAPTOR algorithm we provide a price-sensitive algorithm for the earliest arrival problem and assess its performance on data obtained from MDV. We discuss three preprocessing techniques that improve run times enough to make the algorithm applicable for real-time queries.
    Sprache: Englisch
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  • 182
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    Linear Programming using Limited-Precision Oracles (2019)
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    Publikationsdatum: 2021-02-01
    Beschreibung: Since the elimination algorithm of Fourier and Motzkin, many different methods have been developed for solving linear programs. When analyzing the time complexity of LP algorithms, it is typically either assumed that calculations are performed exactly and bounds are derived on the number of elementary arithmetic operations necessary, or the cost of all arithmetic operations is considered through a bit-complexity analysis. Yet in practice, implementations typically use limited-precision arithmetic. In this paper we introduce the idea of a limited-precision LP oracle and study how such an oracle could be used within a larger framework to compute exact precision solutions to LPs. Under mild assumptions, it is shown that a polynomial number of calls to such an oracle and a polynomial number of bit operations, is sufficient to compute an exact solution to an LP. This work provides a foundation for understanding and analyzing the behavior of the methods that are currently most effective in practice for solving LPs exactly.
    Sprache: Englisch
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  • 183
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    Linear Programming using Limited-Precision Oracles (2019)
    Details
    Publikationsdatum: 2021-02-01
    Beschreibung: Since the elimination algorithm of Fourier and Motzkin, many different methods have been developed for solving linear programs. When analyzing the time complexity of LP algorithms, it is typically either assumed that calculations are performed exactly and bounds are derived on the number of elementary arithmetic operations necessary, or the cost of all arithmetic operations is considered through a bit-complexity analysis. Yet in practice, implementations typically use limited-precision arithmetic. In this paper we introduce the idea of a limited-precision LP oracle and study how such an oracle could be used within a larger framework to compute exact precision solutions to LPs. Under mild assumptions, it is shown that a polynomial number of calls to such an oracle and a polynomial number of bit operations, is sufficient to compute an exact solution to an LP. This work provides a foundation for understanding and analyzing the behavior of the methods that are currently most effective in practice for solving LPs exactly.
    Sprache: Englisch
    Materialart: reportzib , doc-type:preprint
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  • 184
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    Pinpoint Data Races via Testing and Classification (2019)
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    Publikationsdatum: 2021-03-03
    Sprache: Englisch
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  • 185
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    A Cut Separation Approach for the Rolling Stock Rotation Problem with Vehicle Maintenance (2019)
    Details
    Publikationsdatum: 2020-08-05
    Beschreibung: For providing railway services the company's railway rolling stock is one if not the most important ingredient. It decides about the number of passenger or cargo trips the company can offer, about the quality a passenger experiences the train ride and it is often related to the image of the company itself. Thus, it is highly desired to have the available rolling stock in the best shape possible. Moreover, in many countries, as Germany where our industrial partner DB Fernverkehr AG (DBF) is located, laws enforce regular vehicle inspections to ensure the safety of the passengers. This leads to rolling stock optimization problems with complex rules for vehicle maintenance. This problem is well studied in the literature for example see [Maróti and Kroon, 2005; Gábor Maróti and Leo G. Kroon, 2007], or [Cordeau et al., 2001] for applications including vehicle maintenance. The contribution of this paper is a new algorithmic approach to solve the Rolling Stock Rotation Problem for the ICE high speed train fleet of DBF with included vehicle maintenance. It is based on a relaxation of a mixed integer linear programming model with an iterative cut generation to enforce the feasibility of a solution of the relaxation in the solution space of the original problem. The resulting mixed integer linear programming model is based on a hypergraph approach presented in [Ralf Borndörfer et al., 2015]. The new approach is tested on real world instances modeling different scenarios for the ICE high speed train network in Germany and compared to the approaches of [Reuther, 2017] that are in operation at DB Fernverkehr AG. The approach shows a significant reduction of the run time to produce solutions with comparable or even better objective function values.
    Sprache: Englisch
    Materialart: conferenceobject , doc-type:conferenceObject
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    Modeling of Multivalent Ligand-Receptor Binding Measured by kinITC (2019)
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    Publikationsdatum: 2022-02-17
    Beschreibung: In addition to the conventional Isothermal Titration Calorimetry (ITC), kinetic ITC (kinITC) not only gains thermodynamic information, but also kinetic data from a biochemical binding process. Moreover, kinITC gives insights into reactions consisting of two separate kinetic steps, such as protein folding or sequential binding processes. The ITC method alone cannot deliver kinetic parameters, especially not for multivalent bindings. This paper describes how to solve the problem using kinITC and an invariant subspace projection. The algorithm is tested for multivalent systems with different valencies.
    Sprache: Englisch
    Materialart: article , doc-type:article
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    pKa of opioid ligands as a discriminating factor for side effects (2019)
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    Publikationsdatum: 2020-01-17
    Beschreibung: The non-selective activation of central and peripheral opioid receptors is a major shortcoming of currently available opioids. Targeting peripheral opioid receptors is a promising strategy to preclude side effects. Recently, we showed that fentanyl-derived μ-opioid receptor (MOR) agonists with reduced acid dissociation constants (pKa) due to introducing single fluorine atoms produced injury-restricted antinociception in rat models of inflammatory, postoperative and neuropathic pain. Here, we report that a new double-fluorinated compound (FF6) and fentanyl show similar pKa, MOR affinity and [35S]-GTPγS binding at low and physiological pH values. In vivo, FF6 produced antinociception in injured and non-injured tissue, and induced sedation and constipation. The comparison of several fentanyl derivatives revealed a correlation between pKa values and pH-dependent MOR activation, antinociception and side effects. An opioid ligand's pKa value may be used as discriminating factor to design safer analgesics.
    Sprache: Englisch
    Materialart: article , doc-type:article
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    Restarting Frank-Wolfe (2019)
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    Publikationsdatum: 2020-02-14
    Sprache: Englisch
    Materialart: conferenceobject , doc-type:conferenceObject
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  • 189
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    Effect of disorder and polarization sequences on two-dimensional spectra of light harvesting complexes (2019)
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    Publikationsdatum: 2020-08-04
    Beschreibung: Two-dimensional electronic spectra (2DES) provide unique ways to track the energy transfer dynamics in light-harvesting complexes. The interpretation of the peaks and structures found in experimentally recorded 2DES is often not straightforward, since several processes are imaged simultaneously. The choice of specific pulse polarization sequences helps to disentangle the sometimes convoluted spectra, but brings along other disturbances. We show by detailed theoretical calculations how 2DES of the Fenna-Matthews-Olson complex are affected by rotational and conformational disorder of the chromophores.
    Sprache: Englisch
    Materialart: article , doc-type:article
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  • 190
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    Transformationsprodukte im Klärwerk: Mathematische Ansätze der Bewertung (2019)
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    Publikationsdatum: 2020-01-16
    Sprache: Deutsch
    Materialart: article , doc-type:article
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  • 191
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    Modeling of Drug Diffusion Based on Concentration Profiles in Healthy and Damaged Human Skin (2019)
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    Publikationsdatum: 2020-01-28
    Beschreibung: Based on experimental drug concentration profiles in healthy as well as tape-stripped ex vivo human skin, we model the penetration of the antiinflammatory drug dexamethasone into the skin layers by the one-dimensional generalized diffusion equation. We estimate the position-dependent free-energy and diffusivity profiles by solving the conjugated minimization problem, in which the only inputs are concentration profiles of dexamethasone in skin at three consecutive penetration times. The resulting free-energy profiles for damaged and healthy skin show only minor differences. In contrast, the drug diffusivity in the first 10 μm of the upper skin layer of damaged skin is 200-fold increased compared to healthy skin, which reflects the corrupted barrier function of tape-stripped skin. For the case of healthy skin, we examine the robustness of our method by analyzing the behavior of the extracted skin parameters when the number of input and output parameters are reduced. We also discuss techniques for the regularization of our parameter extraction method.
    Sprache: Englisch
    Materialart: article , doc-type:article
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  • 192
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    Blended Matching Pursuit (2019)
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    Publikationsdatum: 2020-08-05
    Sprache: Englisch
    Materialart: conferenceobject , doc-type:conferenceObject
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  • 193
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    Structured Robust Submodular Maximization: Offline and Online Algorithms (2019)
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    Publikationsdatum: 2020-02-14
    Sprache: Englisch
    Materialart: conferenceobject , doc-type:conferenceObject
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  • 194
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    Affine Reductions for LPs and SDPs (2019)
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    Publikationsdatum: 2020-05-14
    Sprache: Englisch
    Materialart: article , doc-type:article
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  • 195
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    Transport of a colloidal particle driven across a temporally oscillating optical potential energy landscape (2019)
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    Publikationsdatum: 2021-02-01
    Beschreibung: A colloidal particle is driven across a temporally oscillating one-dimensional optical potential energy landscape and its particle motion is analysed. Different modes of dynamic mode locking are observed and are confirmed with the use of phase portraits. The effect of the oscillation frequency on the mode locked step width is addressed and the results are discussed in light of a high-frequency theory and compared to simulations. Furthermore, the influence of the coupling between the particle and the optical landscape on mode locking is probed by increasing the maximum depth of the optical landscape. Stronger coupling is seen to increase the width of mode locked steps. Finally, transport across the temporally oscillating landscape is studied by measuring the effective diffusion coefficient of a mobile particle, which is seen to be highly sensitive to the driving velocity and mode locking.
    Sprache: Englisch
    Materialart: article , doc-type:article
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  • 196
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    Computing Optical Resonances in Plasmonic Systems Using a Contour Integral Method (2019)
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    Publikationsdatum: 2020-03-09
    Sprache: Englisch
    Materialart: conferenceobject , doc-type:conferenceObject
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  • 197
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    Line Broadening Mechanisms in Hybrid Plasmonic Systems for Strong Coupling (2019)
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    Publikationsdatum: 2020-03-09
    Sprache: Englisch
    Materialart: conferenceobject , doc-type:conferenceObject
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  • 198
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    Spectral Expansion of the Scattering Response of Resonant Nanostructures (2019)
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    Publikationsdatum: 2021-01-08
    Sprache: Englisch
    Materialart: conferenceobject , doc-type:conferenceObject
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  • 199
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    Automating PCCA+ applied to Eye-Tracking Data (2019)
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    Publikationsdatum: 2020-02-27
    Sprache: Englisch
    Materialart: masterthesis , doc-type:masterThesis
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    Numerical methods for simulation and optimization of the extraction efficiency from quantum-dot based single-photon emitters (2019)
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    Publikationsdatum: 2020-03-09
    Sprache: Englisch
    Materialart: conferenceobject , doc-type:conferenceObject
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