Supplier managed inventory in the OEM supply chain: the impact of relationship types on total costs and cost distribution

We investigate the impact of four variants of supplier managed inventory on total costs and cost distribution in a capital goods supply chain consisting of a parts supplier who delivers parts to an original equipment manufacturer’s assembly plant. The four supplier managed inventory variants differ in the components of inventory costs that the supplier has to carry. The performance of the supplier managed inventory relationships is benchmarked with the situation where the assembly plant manages the inventories. Interesting managerial insights follow from this comparison.     

The impact of quality considerations on material flow in two-stage inventory systems

Supply chain management literature calls for coordination between the different members of the chain. Inventory models achieve this coordination along a supply chain by making the lot size at an upstream entity an integer multiplier of the lot size at the adjacent downstream entity. Such models assume that all components produced are of acceptable quality and may cause suppliers to produce larger quantities than what is optimal. In this paper, we formulate and solve two-stage supply chain inventory models in which the proportion of defective products increases with increased production lot sizes. We show that quality considerations can lead to significant reduction in production lot sizes. In addition, the models show that most benefits to the supply chain are attained from the suppliers producing on a just-in-time basis rather than delivering to their customers just-in-time. We derive closed-form expressions for the optimal lot sizes for a two-stage supply chain under deterministic and then stochastic demand and illustrate the models with numerical examples.     

The impact of restricting the flow of inventory in serial production systems

This research uses simulation technique to compare the output performance of pull production systems with different inter-station storage capacities (ISSC) under various levels of total inventory (INV) in the system, station coefficient of variation (CV), and station down-time (DT). There are two primary findings from this study. First, it shows pull systems with larger ISSC yield a significantly higher output at all levels of INV in the system, station CV, and station DT. Second, it shows that lines using a strict kanban-based pull system can increase output while decreasing WIP inventory simply by allowing the inventory to flow freely between stations. These are major findings considering that the modifications necessary in the system to achieve these results are fairly uncomplicated and should require minimal investment.     

The effect of the number of parallel DNA molecules on electric charge transport through 'standing DNA'

We present morphological and electrical characterization of double-stranded DNA (dsDNA) molecules covalently bound to two metal electrodes: an underlying gold surface and a gold nanoparticle (GNP). Conductive atomic force microscope (cAFM) with a metallized tip is used to perform current-voltage (I-V) measurements through dsDNA molecules, connected to GNPs of different diameters 5, 10 and 20?nm. The number of DNA molecules coating the GNP is expected to vary with the surface area of the GNP. This number and the portion of the GNP surface area enabling hybridization of the DNA determine the number of DNA molecules connecting the GNP to the gold surface. The larger the diameter of the GNP the higher the expected number of dsDNA molecules connecting it to the gold surface and thus the expected current. Our results show similar currents for all three GNP sizes, indicating that current flows through the same number of molecules regardless of the diameter of the measured GNP. The measured currents, 220 nA at 2?V, are in accordance with our previous reports (Cohen et al 2005 Proc. Natl Acad. Sci. USA 102 11589-93; Cohen et al 2006 Faraday Discuss. 131 367-76) in which we demonstrated the validity of the experimental system. In particular, for the 5?nm GNP, we conclude that the current possibly flows through two to three molecules, likely only one, and that a single short dsDNA molecule can support at least ～70?nA, and probably 220?nA.     

Cellular manufacturing: its impact on the total factory

This paper compares a factory structured as a traditional job shop with the same factory structured as a hybrid factory containing a cellular manufacturing unit. The comparison is based on job shop simulation using differing combinations of capacities, allocations of jobs between the cell and the rest of the factory and levels of productivity improvements achieved in the cell. Performance is evaluated in terms of flow times and delays for the cell, the non-cell remainder of the factory and for the normal functional factory. The simulation model was designed to eliminate possible confounding issues of machine reliability, operator skill, unique manufacturer specific part characteristics, factory layout and different scheduling techniques. The result is a systematic evaluation of cellular manufacturing, some general conclusions as to the particular circumstances that favour the use of cells and a set of implications for management practice.     

图的测地全控制数

将图的测地集与全控制集的概念结合,引入图的测地全控制集的定义,得到测地全控制数与测地数、测地控制数关系的一个基本结论:设图G为最小度δ≥2的任意图.如果图G的围长至少为6,则g(G)≤gγt(G)=tγ(G);给出路与圈上的测地全控制数的确定值,并证明弦图上的测地全控制集问题是NP-完全的.     

The impact of strategic inventory and procurement strategies on green product design in a two-period supply chain

This study analyses the impact of power structures and strategic inventory on the development-intensive and marginal-cost-intensive green product types under three procurement strategies. The results suggest that (i) in the manufacturer-Stackelberg game, the retailer retains strategic inventory to earn higher profits. The retailer's decision improves profit for the manufacturer and greening level of the product; (ii) for the marginal-cost-intensive green product, the power structures and procurement strategies cannot make any impact on the greening level and the retailer cannot build up strategic inventory under retailer-Stackelberg game; (iii) under the Nash game, the procurement decision creates conflict between the supply chain members for marginal-cost-intensive green products; (iv) if the retailer does not maintain strategic inventory or procures product in a single lot, then the manufacturer prefers to produce marginal-cost-intensive products and retailer prefers to sale development-intensive products to receive maximum profits under manufacturer-Stackelberg game. The optimal preferences are concurrent under retailer-Stackelberg game, but not under the Nash game; (v) single-period equilibrium solutions may exhibit sub-optimal characteristics, but two-period planning can lead to exemplary outcomes in the perspective of the greening level and profits of the supply chain members.     

The impact of total quality management on supply chain management and firm's supply performance

This research investigates the relationships among total quality management practices (TQMP), supply chain management practices (SCMP) and firm's supply performance (FSP) in the automotive industry in Thailand. The measurement instruments for SCMP, TQMP and FSP were developed based on an extensive literature review and verified by experts, pilot test and various statistical techniques to ensure reliability and validity in structural equation modeling constructs. The hypothesized model was tested through a path analysis. Qualitative case studies of two large first-tier automotive suppliers were conducted to obtain more in-depth information. We found that the set of SCMP, TQMP and FSP measures are reliable and valid for Thailand's automotive industry. TQMP not only has a significant direct positive impact on SCMP and on FSP but also a significant indirect positive impact on FSP through SCMP.     

Scheduling jobs on unrelated parallel machines to minimize regular total cost functions

In this paper we consider unrelated parallel machine scheduling problems that involve the minimization of regular total cost functions. We first present some properties of optimal solutions and then provide a lower bound. These mechanisms are tested on the well-known practical problem of minimizing total weighted flow time on unrelated parallel machines. In doing so, we design a branch and bound algorithm incorporating the mechanisms derived for the general total cost function along with the ones derived specifically for the total weighted flow time criterion. Computational experience indicates that incoiporating reduction and bounding mechanisms significantly improves the performance of the branch and bound algorithm.     

Highly parallel modular multiplication in the residue number system using sum of residues reduction

A new algorithm for modular multiplication in the residue number system (RNS) is presented. Modular reduction is performed using a sum of residues. As all of the residues can be evaluated simultaneously, the algorithm permits a highly parallel implementation and is suitable for performing public-key cryptography operations with very low latency.     

The effect of the number of conveyor belt carrying idlers on the failure of an impact place: A failure analysis

The article deals with the failure analysis of a conveyor belt related to the place of impact where material lands. It studies how the number of conveyor carrying idlers influences the belt compression stress in the place of impact. The landing material is represented by an impactor of 500 kg landing from the height of 4 m. The analyses are grounded in mathematical modelling of the transport belt and experimentally determine the quantities vital for the simulations. The place of impact under examination is the critical site of the whole facility as it is subject to extreme stress. The failure analysis considers two variants of idler number in the place of material impact. The results clearly demonstrate that the construction making use of a higher number of idlers is more suitable due to lower deformations of the belt. The conclusions presented in the article may thus lead to conveyor belt construction optimisations, and thus contribute to their longer life. At the same time, there is a great potential for further research, as the topic of longer conveyor belt life via changing the number of carrying idlers at the place of impact has not been widely investigated.     

Minimising total weighted earliness and tardiness on parallel machines using a hybrid heuristic

Scheduling jobs with different processing times and distinct known due dates on parallel machines (which may be idle) so as to minimise the total weighted earliness and tardiness is NP-hard. It occurs frequently in industrial settings with a just-in-time production environment. Here, small instances of this problem are tackled via an exact mixed-integer program, whereas larger instances are approximately solved using hybrid algorithms. The computational investigation discerns what makes a difficult instance, and demonstrates the efficiency of the approach.     

相对冲击位置和补片层数对胶接修理CFRP复合材料层合板抗冲击性能的影响

本文针对碳纤维增强聚合物（CFRP）复合材料修补结构,基于连续损伤力学和粘结单元模型,在ABAQUS软件中对低速冲击载荷下不同冲击位置和补片层数的CFRP复合材料层合板内部和层间损伤进行了数值分析,并与试验结果进行了对比。选择相对冲击位置为0 mm、10 mm、20 mm、30 mm和40 mm时对应的五种修补结构,通过数值计算和试验,获得了修补结构在低速冲击过程中的冲击力、冲击能量等数据。在保持补片单层厚度不变的前提下,使补片层数从1层增加到5层,计算获得了修补结构的低速冲击响应。研究结果表明:冲头接触修补结构时会对补片造成较大的损伤,补片可以提高含孔损伤母板的抗冲击性能;冲击点离修补结构损伤孔越近,结构受冲击所产生的分层损伤越严重;增加补片的层数可以提高修补结构的抗冲击性能;通过对补片层数进行优化,得到优化层数为2,其对应的修补结构与无修补结构相比分层损伤面积减少了19.9%,较好地提升了母板的抗冲击性能。      

Effects of number of layers and adhesive ductility on impact behavior of laminates

Laminated composites are made using different routes, including adhesive bonding. In this investigation, Aluminum layers are bonded together using epoxy adhesive (neat, rubber-modified and filled-epoxy). In phase one of this investigation, the influence of number of layers and adhesive ductility have been studied on dynamic behavior of composites. The results of impact behavior of laminates indicate that the impact energy increases with the number of layers. Also, it can be concluded that there is much more sensitivity of the impact energy of the composite to the number of the layers than that to the adhesive composition.     

The single-machine scheduling problem to minimize total tardiness subject to minimum number of tardy jobs

We consider the scheduling problem to minimize the total tardiness of a job set keeping the number of tardy jobs to its minimum value. A simple algorithm is presented to obtain an optimal sequence when the set of tardy jobs is specified. A set of properties is presented that explores the structure induced by the minimum number of tardy jobs requirement. The general problem is solved optimally by employing an efficient Branch & Bound (B&B) search that takes advantage of the theory developed. We identify special cases where the Moore-Hodgson algorithm can be applied to find the optimal tardy job set. Computational experiments show that the B&B algorithm solves relatively large instances in just a few seconds, on a personal computer.     

P-RnaPredict--a parallel evolutionary algorithm for RNA folding: effects of pseudorandom number quality

This paper presents a fully parallel version of RnaPredict, a genetic algorithm (GA) for RNA secondary structure prediction. The research presented here builds on previous work and examines the impact of three different pseudorandom number generators (PRNGs) on the GA's performance. The three generators tested are the C standard library PRNG RAND, a parallelized multiplicative congruential generator (MCG), and a parallelized Mersenne Twister (MT). A fully parallel version of RnaPredict using the Message Passing Interface (MPI) was implemented on a 128-node Beowulf cluster. The PRNG comparison tests were performed with known structures whose sequences are 118, 122, 468, 543, and 556 nucleotides in length. The effects of the PRNGs are investigated and the predicted structures are compared to known structures. Results indicate that P-RnaPredict demonstrated good prediction accuracy, particularly so for shorter sequences.     

Minimizing makespan subject to minimum total absolute deviation of completion time on identical parallel machines

This study addresses the identical parallel machine scheduling problem with the objective of minimizing makespan subject to minimum total absolute deviation of job completion time (TADC). An optimization algorithm is first proposed to solve TADC on an identical parallel machine and an iterative procedure based on a polynomial binary integer programming model is then proposed to minimize makespan. Computational experiments show that the proposed algorithm is efficient. The worst case performance, which refers to the largest average execution for each scenario of the experiments, is 229.10 seconds for the problem with n=200, m=30 and p _j from a uniform [1, 100].     

Fracture of parallel strand lumber (PSL) under impact loading

The behavior of Parallel Strand Lumber (PSL) subjected to impact loading was studied. Eighteen 100 mm ×100 mm×650 mm flexural specimens were tested under both static and impact loading conditions. It was found that the failure modes of PSL were similar under both loading conditions with the specimens failing mostly by a combination of shear and flexural modes. PSL also exhibited stress rate sentitive characteristics; however, the rate sensitivity was affected by the localized damage at the contact surface.

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Résumé Le comportement de composites unidirectionnels à base de bois (PSL) soumis à des tests d'impact a été étudié. Dix-huit éprouvettes de 100×100×650 mm ont été testées en mode statique et en mode impact. Le mode de rupture observé pour chaque type d'essais était similaire: une combinaison d'effets de cisaillement et de flexion. La sensibilité du composite unidirectionnel PSL au taux de déformation a également été vérifiée. Toutefois, cet effet tend à s'amenuiser en raison de l'endommagement localisé aux surfaces de contact.

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Editorial Note Prof. Sidney Mindess is a RILEM Senior Member and a Member of the Board to Editors of the journal Materials and Structures.