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311.
Unit‐load warehouses store and retrieve unit‐loads, typically pallets. When storage and retrieval operations are not coordinated, travel is from a pickup and deposit (P&D) point to a pallet location and back again. In some facilities, workers interleave storage and retrieval operations to form a dual‐command cycle. Two new aisle designs proposed by Gue and Meller (“Improving the unit‐load warehouse.” In Progress in Material Handling Research: 2006. Material Handling Industry of America, Charlotte, NC, 2006) use diagonal aisles to reduce the travel distance to a single pallet location by approximately 10 and 20[percnt] for the two designs, respectively. We develop analytical expressions for travel between pallet locations for one of these—the fishbone design. We then compare fishbone warehouses that have been optimized for dual‐command to traditional warehouses that have been optimized in the same manner, and show that an optimal fishbone design reduces dual‐command travel by 10–15%. © 2009 Wiley Periodicals, Inc. Naval Research Logistics 54: 389–403, 2009 相似文献
312.
A natural extension of the bucket brigade model of manufacturing is capable of chaotic behavior in which the product intercompletion times are, in effect, random, even though the model is completely deterministic. This is, we believe, the first proven instance of chaos in discrete manufacturing. Chaotic behavior represents a new challenge to the traditional tools of engineering management to reduce variability in production lines. Fortunately, if configured correctly, a bucket brigade assembly line can avoid such pathologies. © 2009 Wiley Periodicals, Inc. Naval Research Logistics 2009 相似文献
313.
A general model for the failure of fibrous composite materials is described. It is shown to contain some of the well-known models in the literature. The composite material is viewed as a coherent system of independent identically distributed component strengths. Under the assumption that the applied load is redistributed “homotonically” to the unfailed components upon the failure of a component (an individual fiber segment) and that the distributions of component strengths are IFRA, it is shown that the system (composite) strength distribution is also IFRA. Examples are given using carbon reinforced composite data to illustrate the IFRA property. 相似文献
314.
We present techniques for classifying Markov chains with a continuous state space as either ergodic or recurrent. These methods are analogous to those of Foster for countable space chains. The theory is presented in the first half of the paper, while the second half consists of examples illustrating these techniques. The technique for proving ergodicity involves, in practice, three steps: showing that the chain is irreducible in a suitable sense; verifying that the mean hitting times on certain (usually bounded) sets are bounded, by using a “mean drift” criterion analogous to that of Foster; and finally, checking that the chain is such that bounded mean hitting times for these sets does actually imply ergodicity. The examples comprise a number of known and new results: using our techniques we investigate random walks, queues with waiting-time-dependent service times, dams with general and random-release rules, the s-S inventory model, and feedback models. 相似文献
315.
D. E. Matthews 《海军后勤学研究》1977,24(3):457-462
A simple method is presented for deriving the mean and variance of the queueing time distribution in an M/G/1 queue when the priorities assigned to customers have an assignment probability distribution. Several examples illustrate the results. The mean and variance of the queueing time distribution for the longest service time discipline are derived, and its disadvantages are discussed. 相似文献
316.
Satya D. Dubey 《海军后勤学研究》1969,16(1):37-40
Logistic distribution is widely used in describing biological, engineering, industrial, and various other types of data. In this paper it is shown that this distribution is a special case of a compound generalized extreme value distribution which is derived by compounding a generalized extreme value distribution with a gamma distribution. The paper contains several useful results relevant to these distribution functions. 相似文献
317.
Adam Mount 《The Nonproliferation Review》2014,21(3-4):399-410
President Barack Obama's 2009 commitment to pursue a world without nuclear weapons struck some as incredible given political resistance to arms control treaties and unilateral reductions. This viewpoint describes steps that can demonstrate a commitment to nuclear disarmament that do not rely on warhead dismantlement. These steps include the collation and release of nuclear data; the renovation and construction of facilities to new transparency standards; and the selective modification of conventional weapon systems. The steps may make a disarmament agreement more likely by assuaging the difficulty the United States will have committing to a verification scheme, given its capacity to circumvent such a scheme. A more credible disarmament pledge could also secure substantial fiscal and diplomatic gains. 相似文献
318.
方丁酉 《国防科技大学学报》1989,11(3):11-15
喷管面积比的选择和气动型面的设计是喷管设计中的一个重要课题。本文应用二维两相喷管流场计算程序和直接优化法,对喷管面积比及扩张段型面进行了二维寻优计算。计算表明:考虑二维两相流损失的推力最大的面积比要明显小于理论最佳面积比;对于锥形喷管,能量最佳面积比大于冲重比最大的面积比,而对于特性喷管,只是稍大一些;特性喷管的最优型面,就是最佳面积比下的最佳型面。 相似文献
319.
We examine the validity of the guns-versus-butter hypothesis in the pre-Arab Spring era. Using panel data from 1995 to 2011 – the eve of the Arab uprisings – we find no evidence that increased security needs as measured by the number of domestic terrorist attacks are complemented by increased military spending or more importantly ‘crowd out’ government expenditure on key public goods such as health care. This suggests that both expenditure decisions were determined by other considerations at the government level. 相似文献
320.