A survey of variants and extensions of the resource-constrained project scheduling problem

The resource-constrained project scheduling problem (RCPSP) consists of activities that must be scheduled subject to precedence and resource constraints such that the makespan is minimized. It has become a well-known standard problem in the context of project scheduling which has attracted numerous researchers who developed both exact and heuristic scheduling procedures. However, it is a rather basic model with assumptions that are too restrictive for many practical applications. Consequently, various extensions of the basic RCPSP have been developed. This paper gives an overview over these extensions. The extensions are classified according to the structure of the RCPSP. We summarize generalizations of the activity concept, of the precedence relations and of the resource constraints. Alternative objectives and approaches for scheduling multiple projects are discussed as well. In addition to popular variants and extensions such as multiple modes, minimal and maximal time lags, and net present value-based objectives, the paper also provides a survey of many less known concepts.     

A systematic procedure to evaluate an automobile manufacturer–distributor partnership

Automobile manufacturer–distributor partnerships are fundamental to the success of automobile companies. The complexity of the overall partnership model often causes difficulties in partnership study. This paper presents a systematic procedure to evaluate an automobile manufacturer–distributor partnership consisting of a large number of system variables. Firstly, Interpretive Structure Modeling (ISM) is used to sort system variables into groups of various characteristics. This sorting process provides an effective means to develop a three-stage hierarchic/network model of the partnership, including Stage I: partnership selection, Stage II: partnership establishment, and Stage III: partnership maintenance. Secondly, Analytic Hierarchy Process (AHP)/Analytic Network Process (ANP) are applied to partnership evaluation based on as many as 20 system variables. Relative importance weight of all variables is quantitatively determined. The most investment-worthy variables found are management strength and power. Finally, this paper makes a comparison between the optimum distributors identified by the present procedure and in practical cases. The usefulness and efficiency of the proposed procedure are ascertained with highly consistent results in the comparison.     

A study about the existence of the leverage effect in stochastic volatility models

The empirical relationship between the return of an asset and the volatility of the asset has been well documented in the financial literature. Named the leverage effect or sometimes risk-premium effect, it is observed in real data that, when the return of the asset decreases, the volatility increases and vice versa.Consequently, it is important to demonstrate that any formulated model for the asset price is capable of generating this effect observed in practice. Furthermore, we need to understand the conditions on the parameters present in the model that guarantee the apparition of the leverage effect.In this paper we analyze two general specifications of stochastic volatility models and their capability of generating the perceived leverage effect. We derive conditions for the apparition of leverage effect in both of these stochastic volatility models. We exemplify using stochastic volatility models used in practice and we explicitly state the conditions for the existence of the leverage effect in these examples.     

Comparison of gas-phase mechanisms applied to RDX combustion model

Two detailed gas-phase chemical mechanisms for RDX – Yetter and coworkers, herein ‘Y2’ [K. Prasad, R.A. Yetter, M.D. Smooke, Combust. Sci. Technol. 124 (1997) p. 35.]; Cal. Tech. group, herein ‘CTM’ [(a) A.D. Chakraborty, R.P. Muller, S. Dasgupta, W.A. Goddard, III, J. Phys. Chem. A 104 (2000) 2261. (b) D. Chakraborty, R.P. Muller, S. Dasgupta, W.A. Goddard, III, J. Comput. Aided Mater. Des. 8 (2001) 203. (c) D. Chakraborty, R.P. Muller, S. Dasgupta, W.A. Goddard, III, Available from: http://www.wag.caltech.edu/home/rpm/projects/hedm/] – have been tested using a recently developed combustion model. The results are compared with each other and experimental data. Burning rates predicted using CTM are about 15% higher than Y2, but both compare well with experimental data across a wide pressure range. Also, majority species profiles are in reasonable agreement with data from a 0.5 atm pressure experiment. However, comparison of predicted trace species profiles to experiments indicates neither mechanism reproduces all measured trace species well; furthermore, most of these trace species occur along main reaction pathways. Detailed chemical analysis indicates the main initial RDX reaction is surprisingly very different for the two mechanisms. NO₂ scission dominates using Y2, but HONO elimination dominates using CTM, in spite of the NO₂ scission reaction having by far the largest RDX decomposition rate coefficient in each mechanism. Analysis shows the unexpected result using CTM is due to a curious global kinetics phenomenon arising in the product pathway: the ring-opening reaction, RDXR → RDXRO, where RDXR is the cyclic radical formed upon NO₂ scission, has a much smaller rate coefficient in CTM compared to Y2. This causes the reaction to be a bottleneck, and so the NO₂ scission reaction goes into partial equilibrium rather than being forwards. Tests were performed to see how the predicted burning rates would be affected by changes in some of the most sensitive rate parameters. Some of the key parameters leading to the differing predictions have been identified. These results will help guide future efforts to understand and develop an accurate representation of the actual RDX combustion chemistry.     

基于VRML的虚拟管网漫游系统的研究与实现

通过对虚拟现实技术的研究,探索一条适合于互联网上进行管网虚拟漫游系统的开发方法和手段,为管网系统的安全管理,设计决策以及虚拟教学提供一种直观、有效的方法。     

关于机电系统建模、仿真与控制研究的探讨

介绍了机电系统建模、仿真与控制的历史与发展状况,分析了当今系统仿真与传统控制理论技术所具有的局限性以及面临的挑战,通过对当今研究和探索方向的探讨,提出了完善和改进系统仿真和控制理论技术的方法,指出在进一步发展过程中不断克服可能遇到困难和问题后,机电系统建模、仿真与控制有着良好的发展和应用前景。     

Novel multistage solid–liquid circulating fluidized bed: Hydrodynamic characteristics

The present work proposes a novel radially cross-flow multistage solid–liquid circulating fluidized bed (SLCFB). The SLCFB primarily consists of a single multistage column (having an inner diameter of 100 mm and length of 1.40 m), which is divided into two sections wherein both the steps of utilization or loading (e.g., adsorption and catalytic reaction) and regeneration of the solid phase can be carried out simultaneously in continuous mode. The hydrodynamic characteristics were studied using ion exchange resin as the solid phase and water as the fluidizing medium. The loading and flooding states were determined for three particle sizes; i.e., 0.30, 0.42, and 0.61 mm. The effects of the superficial liquid velocity and solid feed rate on the solid hold-up were investigated under loading and flooding conditions. The solid hold-up increases with an increase in the solid feed rate and decreases with an increase in the superficial liquid velocity. An artificial-intelligence formalism, namely the multilayer perceptron neural network (MLPNN), was employed for the prediction of the solid hold-up. The input space of MLPNN-based model consists of four parameters, representing operating and system parameters of the proposed SLCFB. The developed MLPNN-based model has excellent prediction accuracy and generalization capability.     

Organic insulator layer influence on the electrical properties of N,N’-di (2-ethylhexyl) - 3, 4, 9, 10-perylene diimide organic thin-film transistors: Experiment and modeling

In this work, n- type organic thin film transistors (OTFTs) based on different kinds of organic dielectrics were fabricated, characterized and theoretically investigated. Three kinds of organic insulators were applied as dielectric gate which are: divinyl tetramethyl disiloxane-bis (benzo-cyclobutene) (BCB), poly(vinylalcohol) (PVA) and poly (4-vinyl phenol) (PVP). Analytical model was applied to describe the electrical behavior of the fabricated OTFTs and to explain the absence of saturation of the drain current for the device based on PVA dielectric. In addition, Meyer–Neldel rule-grain boundary model was applied for the calculation of total resistance of OTFTs based on different dielectrics materials. The theoretical results of output characteristics and total resistance showed an excellent agreement with the experimental measurements. The experimental and theoretical calculations revealed that the n-channel OTFTs based on BCB as an insulator layer exhibited superior electrical characteristics in terms of threshold voltage, mobility and drain current compared with the devices based on PVA and PVP as a gate insulator layer. The device based on BCB organic insulator layer has the largest mobility of 4?×?10^?3 cm² V^?1 s^?1, the smallest leakage current relative to the devices based on PVA and PVP. While, the device fabricated with PVP organic insulator gate has a large trap density on the PVP-EHPDI interface which causes a pronounced decrease in field effect mobility and consequently drain current.     

The multiplicative meaning conveyed by visual representations

Research and practitioner articles advocate the use of visual representations in scaffolding elementary students’ learning of multiplication and division. Prior research suggests students use different strategies when provided with different visualized representations of multiplication and division. However, there is relatively little study examining how children’s multiplicative reasoning corresponds with different representations. The present study collected data from 182 elementary students responding to set, area, and length representations of multiplication/division. Rasch modeling was used to estimate item difficulty statistics to measure differences between visual representations. Results suggest that visual representations differed primarily in how unit was represented and quantified, and not regarding the form of representation (set, area, length).     

Boundary regularity for the [`(?)] b - Neumann\bar \partial _b - Neumann problem, Part 2

We adapt the results of Part 1 to include the unit ball in the Heisenberg group, the model domain with characteristic boundary points. In particular, we construct function spaces on which the Kohn Laplacian with the boundary conditions is an isomorphism. As an application, we establish sharp regularity for a canonical solution to the inhomogenous equation on the unit ball.