How to measure the impact of environmental factors in a nonparametric production model

The measurement of technical efficiency allows managers and policy makers to enhance existing differentials and potential improvements across a sample of analyzed units. The next step involves relating the obtained efficiency estimates to some external or environmental factors which may influence the production process, affect the performances and explain the efficiency differentials. Recently introduced conditional efficiency measures (,  and ), including conditional FDH, conditional DEA, conditional order-m and conditional order-α, have rapidly developed into a useful tool to explore the impact of exogenous factors on the performance of Decision Making Units in a nonparametric framework. This paper contributes in a twofold fashion. It first extends previous studies by showing that a careful analysis of both full and partial conditional measures allows the disentangling of the impact of environmental factors on the production process in its two components: impact on the attainable set and/or impact on the distribution of the efficiency scores. The authors investigate these interrelationships, both from an individual and a global perspective. Second, this paper examines the impact of environmental factors on the production process in a new two-stage type approach but using conditional measures to avoid the flaws of the traditional two-stage analysis. This novel approach also provides a measure of inefficiency whitened from the main effect of the environmental factors allowing a ranking of units according to their managerial efficiency, even when facing heterogeneous environmental conditions. The paper includes an illustration on simulated samples and a real data set from the banking industry.     

Field procedures to assess soils and waste disposals

The aim of this research was the development of rapid analytical test methods for arsenic, lead, cadmium, chromium(VI), copper, nickel, and zinc to classify waste materials into waste classes and assess contaminated soils for purification purposes. In order to estimate the danger potentials of contaminated soils, a rapid ecotoxicological method was developed (A. Götzl, H. Malissa, W. Riepe, FACT 3 (6) (1999) 329.). These rapid analytical and ecotoxicological tests offer an instrument to comprehensively assess soils and wastes. The developed rapid methods are suitable for the elution of different soils and wastes, the analysis of the eluates and also for waste waters with concentrations greater than 0.1 mg l⁻¹ arsenic, 0.5 mg l⁻¹ lead, 0.01 mg l⁻¹ cadmium, 0.1 mg l⁻¹ chromium(VI), 0.3 mg l⁻¹ copper, 0.5 mg l⁻¹ nickel and 0.1 mg l⁻¹ zinc in the eluate. Our developed rapid analytical test methods described below can be implemented on site, are of low cost and are not time-consuming (about 30 min). They also do not need to be carried out by highly qualified specialists only, they can also be easily applied by persons with some experience. The comparability of results obtained using the developed rapid test method and standardised methods was tested with various matrices.     

Capacitated dynamic lot sizing problems in closed-loop supply chain

In this paper, we address the capacitated dynamic lot sizing problem arising in closed-loop supply chain where returned products are collected from customers. These returned products can either be disposed or be remanufactured to be sold as new ones again; hence the market demands can be satisfied by either newly produced products or remanufactured ones. The capacities of production, disposal and remanufacturing are limited, and backlogging is not allowed. A general model of this problem is formulated, and several useful properties of the problem are characterized when cost functions are concave. Moreover, this problem is analyzed and solved to optimality using dynamic programming algorithms under different scenarios. It is shown that the problem with only disposal or remanufacturing can be converted into a traditional capacitated lot sizing problem and be solved by a polynomial algorithm if the capacities are constant. A pseudo-polynomial algorithm is proposed for the problem with both capacitated disposal and remanufacturing. The problem with capacitated production and remanufacturing and the problem with uncapacitated production and capacitated remanufacturing are also analyzed and solved. Through numerical experiments we show that the proposed algorithms perform well when solving problems of practical sizes. From the experimental results also indicates that it is worthwhile to expand the remanufacturing capacity only when returned products exist in a relatively long planning horizon, and production capacities have little effect on the remanufacturing plan when the demand is mainly satisfied by the production.     

Directional distances and their robust versions: Computational and testing issues

Directional distance functions provide very flexible tools for investigating the performance of Decision Making Units (DMUs). Their flexibility relies on their ability to handle undesirable outputs and to account for non-discretionary inputs and/or outputs by fixing zero values in some elements of the directional vector.  and  indicate how the statistical properties of Farrell–Debreu type of radial efficiency measures can be transferred to directional distances. Moreover, robust versions of these distances are also available, for conditional and unconditional measures. B?din, Daraio, and Simar (2012) have shown how conditional radial distances are useful to investigate the effect of environmental factors on the production process. In this paper we develop the operational aspects for computing conditional and unconditional directional distances and their robust versions, in particular when some of the elements of the directional vector are fixed at zero. After that, we show how the approach of B?din et al. (2012) can be adapted in a directional distance framework, including bandwidth selection and two-stage regression of conditional efficiency scores. Finally, we suggest a procedure, based on bootstrap techniques, for testing the significance of environmental factors on directional efficiency scores. The procedure is illustrated through simulated and real data.     

Corrosion of AGR Fuel Pin Steel Under Conditions Relevant to Permanent Disposal

Fuel pins from the UK's Advanced Gas-cooled Reactors (AGR) consist of ceramic UO₂ fuel encased in a 20/25/Nb stainless steel cladding. Spent AGR fuel is currently reprocessed, but the option of direct disposal of spent fuel in a sealed, underground Geological Disposal Facility (GDF) is now under examination. It is assumed that over several thousand years groundwater from the environment will penetrate these barriers and come into contact with the fuel surface and steel cladding.Electrochemical studies on unsensitised samples of 20/25/Nb steel in simulant groundwater electrolytes have been performed, and show low corrosion currents, typically of the order μA/cm2, at the oxidative potential stresses found in such repositories. Whilst the cladding may therefore be considered to be passive short time periods, the very long timescales involved in a GDF project mean that these currents are sufficient to cause corrosion of the full thickness of the clad in a matter of decades.Furthermore, an increase in electrochemical potential from that expected of less than 50 mV is sufficient to initiate severe pitting corrosion in a matter of hours. It can therefore be assumed that there is a risk of cladding corrosion in a repository environment, and the corrosion products created may have implications for the chemistry of the spent fuel ceramic.     

A continuous review replenishment–disposal policy for an inventory system with autonomous supply and fixed disposal costs

In this study, we analyze an inventory system facing stochastic external demands and an autonomous supply (independent return flow) in the presence of fixed disposal costs and positive lead times under a continuous review replenishment–disposal policy. We derive the analytical expressions of the operating characteristics of the system; and, construct the objective function to minimize the total expected costs of ordering, holding, purchasing and disposal per unit time subject to a fill rate constraint. An extensive numerical analysis is conducted to study the sensitivity of the policy parameters and the benefit of employing a policy which allows for disposal of excess stock in this setting. We model the net demand process as the superposition of normally distributed external demand and inflows, which is expressed as a Brownian motion process. Our findings indicate that the disposal option results in considerable savings even (i) in the presence of non-zero fixed disposal costs, (ii) large actual demand rates with high return ratios (resulting in small net demands) and (iii) for moderate return ratios with high demand variability.     

A production–recycling–inventory system with imprecise holding costs

This paper presents an optimal control recycling production inventory system in fuzzy environment. The used items are bought back and then either put on recycling or disposal. Recycled products can be used for the new products which are sold again. Here, the rate of production, recycling and disposal are assumed to be function of time and considered as control variables. The demand inversely depends on the selling price. Again selling price is serviceable stock dependent. The holding costs (for serviceable and non-serviceable items) are fuzzy variables. At first we define the expected values of fuzzy variable, then the system is transferred to the fuzzy expected value model. In this paper, an optimal control approach is proposed to optimize the production, recycling and disposal strategy with respect so that expected value of total profit is maximum. The optimum results are presented both in tabular form and graphically.     

ATM-PON系统中信元定界的并行处理

基于异步传输模式(ATM)的无源光网络(PON-Passive Optical Network)系统传输汇聚层(TC)层的实现是通过VHDL语言,采用现场可编程门阵列(FPGA)芯片来完成的根据国际电信联盟(ITUT)关于无源光接入网的G.983.1协议,ATMPON(APON)系统采用对称的155M速率传输数据,为避免高速率下进行校验定界对ATMPON提出苛刻的要求,以及系统可能产生的不稳定性,在设计中采用了并行循环冗余校验(CRC)算法,并且采用了并行的处理技术本文具体介绍了TC层芯片设计过程中采用的几种并行处理技术.