A generalized design and performance analysis model for end-of-aisle order-picking systems

In this paper we present an analytical design algorithm to determine the near-minimum number of pickers required in an end-of-aisle order-picking operation based on a miniload automated storage/retrieval system. The algorithm is based on an approximate analytical model we developed to estimate the expected picker utilization (and the storage/retrieval machine utilization) for general system configurations with two or more pick positions per aisle and/or two or more aisles per picker. For systems with two pick positions, we also investigate the possibility of improving the picker utilization by sequencing container retrievals within each order.     

Simultaneous defocusing of the aperture and medium on a spectroholographic storage system

In a spectroholographic storage system the defocusing method is often used to obtain spectrum uniformity and improve the quality of the recorded information. However, defocusing introduces vignette and stronger interpixel cross talk in the marginal field of view. We report a method that defocuses the aperture and medium together. Based on the pixel spread function, two inequalities are introduced to estimate the upper and lower bounds of the energy received at the CCD. We balance the spectrum uniformity with interpixel cross talk and vignette and then allow the designer to select optimal structure values of the defocusing spectroholographic storage system, i.e., the defocusing value, aperture size, and fill factors for the spatial light modulator and CCD.     

Container packing problem with balance constraints

This paper presents a new hybrid algorithm that addresses current limitations of container packing problems (CPPs) to increase the efficiency of oceanic transport. The proposed algorithm considers not only the balance constraints, but also the trade-off between volume utilization and weight balance. We also present a mixed integer programming model which features upper and lower bounds for the three-dimensional CPP. The computational results show that our algorithm can efficiently and realistically help shippers make decisions between volume utilization and weight balance and thereby achieve a high rate of volume utilization.     

Information theoretic limits to the capacity of volume holographic optical memory

We derive the information theoretic limit to storage capacity in volume holographic optical memories for the limiting cases of dominant intensity noise (Gaussian noise) and dominant field noise (Rician noise). These capacity bounds are compared with the performance achievable using simple Reed-Solomon error-correcting codes.     

Production Rate of Transfer Lines Without Buffer Storage

We consider transfer lines without buffer storage in between the machines and with synchronous transfer. The processing time of each machine is a constant but machines are unreliable. Our analysis is based on the overall completion time of the transfer line, which is the time between successive transfers of parts within the line. Two techniques are presented. The first one provides lower and upper bounds on the production rate. These bounds can be made as tight as desired. The second technique provides an approximation of the production rate. It is based on the approximation of some distributions by simpler distributions having the same mean and coefficient of variation. We first consider the case of transfer lines with identical processing times and exponential times to failure and times to repair. Extensions to different processing times and general repair times are also discussed.     

Interleaving models for the analysis of twin shuttle automated storage and retrieval systems

A system of state equations is formulated for describing the dynamic behaviour of the queue of storage and retrieval transactions in a storage aisle served by twin shuttle storage and retrieval (S/R) machines. Using estimates of order picking cycle times in conjunction with storage and retrieval transaction demand levels, an estimate of the probability distribution of storage queue states is derived for a given storage aisle. System performance measures under an opportunistic interleaving discipline including S/R machine utilization, transaction queue lengths, average cycle times and expected transaction waiting times are approximated using the state probability distribution. The modelling tools are demonstrated using sample problems where the performance of twin versus single shuttle systems is contrasted for alternative combinations of storage and retrieval machine travel speeds, storage rack configurations, and transactions demand scenarios.     

The allocation of storage space for transshipment in vehicle distribution

We address the planning of transportation and storage capacity over time. In intermodal transshipment terminals, finished vehicles are assigned to yard locations for intermediate storage. The evolutionary algorithm proposed evolves a period-oriented capacity utilization strategy. This capacity utilization strategy then controls a construction heuristic which assigns vehicle movements to periods and vehicles to storage locations. It is aimed at efficient operations and at a balanced distribution of vehicle movements over the periods of the planning horizon.     

基于RFID技术的仓储管理系统的优化与设计

针对仓储管理存在的物流信息处理效率低以及出入库盘点不准确等问题,提出了一种基于RFID 技术的仓储管理系统优化设计方案,可实现对仓储操作全方位监控管理、仓储过程数据信息自动化处理、准确存储、按时分配、有效利用仓储空间以及节约仓储成本.     

Performance analysis of automatic storage/retrieval systems by stochastic modelling

This study considers an automated storage/retrieval system that performs either single or dual commands and analyses it as a queuing system with two waiting spaces and one server. It is assumed that the storage and retrieval commands arrive at the system according to Poisson processes with different rates and that the service times of single and dual commands are distributed differently. The steady-state probability distribution of the number of commands in the system at the service completion epochs is derived; subsequently, the semi-Markov process is employed to obtain the distribution at an arbitrary time. Several performance measures are derived and include the expected number of commands in the system, the expected waiting time, the probability that an arbitrary command cannot enter the system (the ‘blocking probability’) and the utilization of the storage/retrieval machine.     

直接蓄冷混合供冷的水蓄冷中央空调系统分析

为实现移峰填谷,在中央空调系统改造中,设计人员越来越重视水蓄冷技术的应用。本文针对常规水蓄冷中央空调系统存在的弊端,提出直接蓄冷混合供冷的水蓄冷中央空调系统。分析结果表明,利用峰谷电价差值,合理地匹配水蓄冷系统与中央空调系统,能耗成本可节约15%～20%。但过高地要求峰谷电价比,并不能明显提高系统的经济性,反而会制约水蓄冷技术的应用。本文的分析将为水蓄冷系统的实际工程应用提供理论参考。     

Interleaving dynamics in autonomous vehicle storage and retrieval systems

A state equation model is proposed for predicting the proportion of dual command cycles in autonomous vehicle storage and retrieval systems that use interleaving. This proportion is used to estimate storage and retrieval cycle times, system utilization and throughput capacity for alternative system design profiles defined by the number of storage aisles, storage rack height and depth, the vehicle fleet size and the number of lifts used for vertical movement. The state equation model enables the user to explicitly trade off model accuracy and computational complexity in the pre-engineering or 'concepting' stage of system development. A sample problem is used to demonstrate the model.     

双分层水箱太阳能喷射制冷循环特性

本文提出一种采用双分层水箱的太阳能喷射制冷循环,分层水箱热分层显著,颇具可用能储存优势,结合大小水箱各自的优势弥补因太阳日辐射量波动而导致太阳能利用率不高、太阳能驱动的喷射制冷效率较低等问题。采用逐时冷负荷分析法分析了双分层水箱太阳能喷射制冷系统特性,结果表明:该制冷循环高品位能耗约为普通机械压缩制冷循环的1/5,较传统水箱太阳能喷射制冷循环全天工作时间约多4 h,日产冷量提高36.8%,且分层水箱喷射制冷系统的逐时制冷量与办公室逐时冷负荷更吻合。     

A Sequential Bounding Approach for Optimal Appointment Scheduling

This study is concerned with the determination of optimal appointment times for a sequence of jobs with uncertain durations. Such appointment systems are used in many customer service applications to increase the utilization of resources, match workload to available capacity, and smooth the flow of customers. We show that the problem can be expressed as a two-stage stochastic linear program that includes the expected cost of customer waiting, server idling, and a cost of tardiness with respect to a chosen session length. We exploit the problem structure to derive upper bounds that are independent of job duration distribution type. These upper bounds are used in a variation of the standard L-shaped algorithm to obtain optimal solutions via successively finer partitions of the support of job durations. We present new analytical insights into the problem as well as a series of numerical experiments that illustrate properties of the optimal solution with respect to distribution type, cost structure, and number of jobs.     

碳中和背景下氢能利用关键技术及发展现状

氢能作为一种二次能源,因其绿色、灵活、来源广泛等特点,将在可再生能源占主导的未来能源体系中发挥重要作用。决定氢能产业大规模发展的核心是实现低廉、高效的原料来源和储运。为此,从可再生能源电解水制氢和储氢运输2个方面,对实现氢能清洁和高效利用的关键技术进行了综述。总结了欧洲和日本作为氢能利用的领先国家在氢能发展方面的一些思路与进展,也对氢能的成本因素进行了讨论。分析了我国氢能发展的趋势,对于未来我国氢能产业发展的前景,提出以下建议:建立健全法规与政策体系;重视氢源供应及储运的发展;积极探索发展各类氢能利用方式。     

The development of metal hydrides using as concentrating solar thermal storage materials

Metal hydrides high temperature thermal heat storage technique has great promising future prospects in solar power generation, industrial waste heat utilization and peak load regulating of power system. This article introduces basic principle of metal hydrides for thermal storage, and summarizes developments in advanced metal hydrides high-temperature thermal storage materials, numerical simulation and thermodynamic calculation in thermal storage systems, and metal hydrides thermal storage prototypes. Finally, the future metal hydrides high temperature thermal heat storage technique is been looked ahead.     

Rule of thumb heuristics for configuring storage racks in automated storage and retrieval systems design

A well-known rule of thumb for evaluating storage rack configurations in automated storage and retrieval (ASR) systems is modified to avoid the need for two key assumptions. These are the proportion of single and dual command order picking cycles used in operating a system and the total storage capacity requirements when randomized versus dedicated storage is used. Procedures for generating ASR system cost estimates are also directly coupled with models for estimating the utilization of storage and retrieval machines. Additional performance criteria for evaluation of alternative rack configurations are proposed. The modified rules of thumb are also designed for implementation on PC-level hardware, but with adequate computational efficiency for analysing a broad range of rack design alternatives in large-scale applications. They are demonstrated using a realistic sample problem.     

Approximate Fiducial Bounds for the Reliability of a Series System for Which Each Component has an Exponential Time-to-Fail Distribution

The computation of exact confidence limits on the reliability of systems using sample data on components turns out to be a very involved process or one requiring very extensive Monte Carlo runs on computers. We suggest here a simple, straight-forward procedure for approximating the fiducial probability bounds on the true system reliability which may be used as approximations to confidence bounds for the reliability of a series system for which each component has an exponential time-to-fail distribution.     

氢能的研究进展

随着可再生能源和生物制氢在氢源的开发、制氢源的开发和制氢技术中的不断拓展,高密度固体储氢材料的进一步研发,以及受燃料电池研究的驱动,氢能系统已经成为洁净能源研究的热点。综述了氢能系统中氢源的开发和制氢、储氢、输氢以及氢能利用5个技术领域的最新研究进展,旨在明确这些技术领域研究中的关键问题及主要研究方向。     

中国冷库现状及节能途径

随着人们生活水平的不断提高,对食品冷冻冷藏的要求,冷库行业的发展势在必行。本文从冷库的容积、利用率、制冷系统维修措施以及自动化控制程度等方面,论述了目前中国冷库行业发展中存在的问题,提出了一些有关冷库节能的途径。     

Lower bounds for arithmetic networks II: Sum of Betti numbers

We show lower bounds for the parallel complexity of membership problems in semialgebraic sets. Our lower bounds are obtained from the Euler characteristic and the sum of Betti numbers. We remark that these lower bounds are polynomial (an square root) in the sequential lower bounds obtained by Andrew C.C. Yao.Partially supported by 92-0498-C02-01, PB93-0472-C02-02 and POSS, ESPRIT-BRA 6846.