A column generation and partitioning approach for multi-commodity flow problems

Multi-commodity network flow problems, prevalent in transportation, production and communication systems, can be characterized by a set of commodities and an underlying network. The objective is to flow the commodities through the network at minimum cost without exceeding arc capacities. In this paper, we present a partitioning solution procedure for large-scale multi-commodity flow problems with many commodities, such as those encountered in the telecommunications industry. Using a cycle-based multi-commodity formulation and column generation techniques, we solve a series of reduced-size linear programs in which a large number of constraints are relaxed. Each solution to a reduced-size problem is an improved basic dual feasible solution to the original problem and, after a finite number of steps, an optimal multi-commodity flow solution is determined. Computational experience is gained in solving randomly generated test problems and message routing problems in the communications industry. The tests show that the procedure solves large-scale multi-commodity flow problems significantly faster than existing linear programming or column generation solution procedures.     

为大众谋求个性化——维也纳的住宅建设

我们能把住宅看成是准确无误地实现我们愿望的一些机器吗？虽然维也纳目前的住宅建设都在通过类型学和主题设计方面试图满足各种各样需求。但同时，所谓的“实验性的”理念或投资于未尝试过事物的愿望看起来正在收缩。有人会说，越来越多的服务型住宅都在以极其低廉的成本在建造，但这不是对住宅主题进行概念研究的一个理想基础。     

Analytical Solutions for Stress Intensity Factor,T-Stress and Weight Function for the Edge-Cracked Half-Space

An analytical solution for the linear-elastic problem of an edge-cracked semi-infinite body was given already in 1957. For the numerical evaluation of this solution an iteration procedure had to be applied. This might be the reason why the related analysis was not commonly used. By means of powerful mathematical tools developed in the last years it is now possible to evaluate highly-precise stress intensity factors, T-stress terms, weight functions etc. This will be shown in this paper in detail.     

Changes in medial prefrontal cortical dopamine levels associated with response-contingent food reward: an electrochemical study in rat

Voltammetry was used to monitor in rats changes in medial prefrontal cortex (PFC) dopamine (DA) levels associated with response-contingent presentation of a condensed milk reward. During two initial training sessions, minor DA signal fluctuations were seen when animals consumed a standard 30 sec (0.2 ml) meal earned on a continuous reinforcement schedule. There was no evidence of experience-dependent changes in these fluctuations. Under delayed reinforcement conditions, lever-presses were followed by DA signal increases that were time-locked to the delay duration, and these were followed by signal decreases when animals eventually received the reward. Such decreases became more pronounced when the standard rate of milk delivery was tripled, but were attenuated when milk delivery was reduced to half the usual rate. Withholding earned milk resulted in signal increases. In contrast, DA signal increases were observed during milk consumption when the standard meal duration was unexpectedly shortened to 15 sec or lengthened to 60 or 90 sec. Orderly changes in DA signal were also observed under partial reinforcement conditions. Unreinforced responses were associated with DA signal decreases, whereas transient increases were seen during the 30 sec meal that followed reinforced responses. These findings indicate that response-contingent reward presentation elicits synchronous changes in PFC DA transmission. They also suggest that the DA input to PFC is activated when rewards are presented under conditions that deviate from those that the animals had come to expect, particularly so when the temporal structure of learned associations is altered.     

Experimental mechanical characterization of plastic-bonded explosives

This article deals with the characterization of the static mechanical behavior of an energetic material. Due to its constituents (crystals and a polymeric binder), the behavior is complicated to model. A specific experimental protocol has been proposed in this article. It involves uniaxial tensile and compressive tests, compression under confinement and dynamic mechanical analysis. A constitutive law has been developed. The behavior is described using a Maxwell’s model, in which all the components are influenced by an isotropic damage. The first component takes into account an elasto-plastic behavior. The yield stress evolution is described using a parabolic criterion and an isotropic hardening law. The plastic flow rule is non-associated. A linear visco-elastic behavior is used for the other components. Numerical simulations show that experimental data are quite well reproduced. The last part of the article is devoted to a discussion highlighting the future improvements.     

Kinematic FE homogenized limit analysis model for masonry curved structures strengthened by near surface mounted FRP bars

Masonry curved structures, as for instance arches, domes and vaults, are very diffused in historical and existing structures and usually require seismic upgrading and/or rehabilitation.     

Predicting solvent effects on the 1‐dodecene hydroformylation reaction equilibrium

Solvent effects on the reaction equilibrium of the 1‐dodecene hydroformylation in a decane/N,N‐dimethylformamide solvent system is investigated. The reaction was performed at different decane/N,N‐dimethylformamide ratios and at temperatures between 368 K and 388 K. The equilibrium concentrations of all reactants and products were determined experimentally. The enthalpy and Gibbs energy of this reaction at the ideal‐gas standard state were determined by quantum‐chemical calculations in good agreement with literature data. Moreover, quantum‐chemically calculated standard Gibbs energies of reaction at infinite dilution in liquid decane/DMF‐solvent mixtures allowed a qualitative prediction of the solvent effect on the equilibrium concentrations. Based on the standard Gibbs energy of reaction at the ideal‐gas standard state and on fugacity coefficients calculated using the Perturbed‐Chain Statistical Associating Fluid Theory, the equilibrium concentrations of reactants and products for the 1‐dodecene hydroformylation performed in decane/N,N‐dimethylformamide mixtures of different compositions could be predicted in very good agreement with experimental data. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4576–4585, 2017