The impact of two-product joint lifecycles on capacity planning of remanufacturing networks

Capacity planning in the reverse channel of closed-loop supply chains (CLSCs) involves complex issues due to the different lifecycles of product offerings in combination with the variability regarding product usage time, quality level of used products and return patterns. (Georgiadis, P., Vlachos, D., Tagaras, G., 2006. The impact of product lifecycle on capacity planning of closed-loop supply chains with remanufacturing. Production and Operations Management 15; 514–527) developed a system dynamics (SD) model to study a CLSC with remanufacturing for a single product which incorporates a dynamic capacity modeling approach. We extend this SD model for two sequential product-types under two alternative scenarios regarding the market preferences over the product-types; in the first scenario, the market is considered showing no preferences, while in the second scenario, the demand over a product-type can be satisfied only by providing units of the specific type. We study how the joint lifecycles of two product-types, entry time of the second product-type to the market and used product return patterns affect the optimal policies regarding expansion and contraction of collection and remanufacturing capacities. The results of extensive numerical investigation are tested for their statistical significance using analysis of variance (ANOVA). In the first scenario, the results show that the system performs best when the two lifecycles form a trapezoid pattern for total demand while in the second scenario, when the two lifecycles form a triangular pattern.     

Scheduling with pairwise XORing of packets under statistical overhearing information and feedback

We study the problem of scheduling packets from several flows traversing a given node which can mix packets belonging to different flows. Practical wireless network coding solutions depend on knowledge of overhearing events which is obtained either by acknowledgments or statistically. In the latter case, the knowledge about each packet improves progressively with feedback from the transmissions. We propose a virtual network mechanism in order to characterize the throughput region of such a system for the case where we allow only pairwise XORing. We also provide the policy which achieves the stability region and compare it to simple heuristics. The derived policy is a modification of the standard backpressure policy, designed to take into account the fact that in the proposed virtual network the destination of a transmitted packet is known only probabilistically. We demonstrate simulation results according to which scheduling with statistical information can provide significant throughput benefits even for overhearing probabilities as small as 0.6.     

Resolution of 2,3-Dideoxy-DL-2-Enopyranos-4-Uloses Via Chromatographic Separation of their Diastereomeric O-tert-Butyloxycarbonyl-L-Alanyl Esters. A Convenient Synthesis of L- and D-Aculose

ABSTRACT

A simple and effective procedure for the resolution of 2,3-dideoxy-DL-2-enopyranos-4-uloses is presented. This procedure is based on column chromatographic separation of their diastereomeric O-(N-tert-butyloxycarbonyl)-L-alanyl esters, followed by mild acidic cleavage of the ester function. L-Aculose, 2,3,6-trideoxy-L-glycero-hex-2-enopyranos-4-ulose, is also prepared in satisfactory yield.     

Ring chain transformation of γ-keto-δ-crotonolactones: A convenient synthesis of 1,4-piperazinones, 1,4-thiazinones and 1,4-diazepinones

A new procedure for the efficient synthesis of 1,4-piperazinones, 1,4-thiazinones and 1,4-diazepinones is presented. The reaction is based on a ring chain transformation of γ-keto-δ-crotonolactones induced by 1,2- or 1,3-diamino- (or thiamino-) binucleophiles. The reaction sequence of this transformation is also discussed.     

Algorithms for precomputing constrained widest paths and multicast trees

We consider the problem of precomputing constrained widest paths and multicast trees in a communication network. Precomputing and storing of the relevant information minimizes the computational overhead required to determine an optimal path when a new connection request arrives. We evaluate algorithms that precompute paths with maximal bandwidth (widest paths), which in addition satisfy given end-to-end delay constraints. We analyze and compare both the worst case and average case performance of the algorithms. We also show how the precomputed paths can be used to provide computationally efficient solutions to the constrained widest multicast tree problem. In this problem, a multicast tree with maximal bandwidth (widest multicast tree) is sought, which in addition satisfies given end-to-end delay constraints for each path on the tree from the source to a multicast destination.     

Mode III Stress-intensity factors in cracked orthotropic plates—An analogy with propagating cracks in isotropic media

In this paper, the method of reflected caustics—which was used to evaluate Mode III SIF's in stationary cracks in isotropic plates—was extended to deal with stationary cracks in orthotropic plates. Furthermore, a correspondence between the anisotropic stationary case and the case of a Mode III dynamic crack, traversing an isotropic plate, is developed by analyzing appropriately the governing equations of the two problems. For this purpose the singulardisplacement field for rectilinearly orthotropic cracked bodies was combined with either Yoffé's model for steady-state, or Broberg's model for transient-crack propagation. Graphs are given where the equivalence between these cases can be established. In this way, the dynamic problem of the propagating crack in an isotropic medium can be readily simulated by considering the experimentally easier anisotropic stationary case.     

Multicast tree structure and the power law

In this paper, we investigate structural properties of multicast trees that give rise to the so-called multicast power law. The law asserts that the ratio R(n) of the average number of links in a multicast tree connecting the source to n destinations to the average number of links in a unicast path, satisfies asymptotically R(n)/spl ap/cn/sup /spl phi//, 0相似文献   

Distributed channel allocation for PCN with variable rate traffic

We consider the design of efficient channel allocation algorithms in personal communication networks (PCN) where the cells have varying traffic loads. A common communication channel is to be dynamically shared between the cells. We propose a distributed intercell channel allocation policy that is easy to implement through the use of simple signaling between neighboring cells. For cells arranged in a line, we show that the proposed policy achieves maximum throughput. The same is true when the cells are arranged in a circle and the frequency reuse distance is 2, while for larger reuse distances and planar hexagonal arrays, the policy may not always achieve maximal throughput. For general circular arrays, we enhance the policy to achieve maximal throughput asymptotically as the number of cells increases. For planar hexagonal arrays, we show that the policy can guarantee throughputs which are fairly close to maximal     

Ozone countergradients over wheat

Summary The gradient method for measuring dry deposition of ozone on short vegetation was employed in a field experiment in Italy's Po Valley. Ozone countergradients involving time periods of about two hours were measured in the morning.