An Analysis of Scheduling Policies In Multiechelon Production Systems

Results of a simulation study of the economics of frequency of rescheduling Material Requirements Planning (MRP) systems are presented for a single-product, two-stage system in which demand is uncertain. The results indicate that for systems with moderate demand uncertainty, frequent rescheduling to maintain customer service may be uneconomical when compared with the alternative of more stable schedules in conjunction with safety stock. This result arises primarily because the cost of “emergency” production setups which occur when rescheduling is frequent exceeds the cost of safety stock required to “protect” stable schedules.     

HEURISTIC APPROACHES FOR LOADING PROBLEMS IN FLEXIBLE MANUFACTURING SYSTEMS

Flexible manufacturing systems (FMSs) are able to process a wide variety of operations, but the specific mix of operations that can be performed at any point in time depends upon the combination of tools loaded onto the machines. The machines have tool magazines with finite capacities. We consider the problem of assigning operations and their associated tools to machines (or groups of machines) to maximize the throughput for a specified steady-state mix of orders. Since this objective is difficult to deal with directly, we use an intermediate objective of meeting workload targets for each machine group as closely as possible. A certain form of this intermediate objective has been shown to correlate highly with the original objective.

Since it is computationally intractable to find optimal solutions for problems with more than 20 operations, fast heuristic algorithms are developed. These algorithms are adapted from multi-dimensional bin-packing algorithms. Computational results are reported.     

Planned Leadtimes For Serial Production Systems

We investigate the problem of setting planned leadtimes in serial production systems when the actual leadtimes are stochastic. The objective is to minimize the sum of inventory holding costs, rescheduling costs arising from tardiness at intermediate stages of production, and tardiness of delivery to the customer.

A single-pass algorithm is developed which finds optimal solutions. The analytical models underlying the algorithm and extensive computational experience indicate that it is never optimal to have planned leadtimes of zero when there are rescheduling costs at intermediate stages of production. This also implies that unconditional immediate dispatching is not optimal under these conditions.     

Sustainable end-of-life vehicle recycling: R&;D collaboration between industry and the U.S. DOE

Approximately 15 million cars and trucks reach the end of their useful life in the United States each year. More than 75% of the materials from end-of-life vehicles are profitably recovered and recycled by the private sector; automotive materials recycling is a success story. To achieve greater fuel efficiency and safety, today’s cars incorporate an increasing share of innovative light-weight materials. While these materials greatly enhance efficiency during vehicle use, they can present special challenges for recycling. These challenges will persist as automotive designs and the mix of materials used in vehicles continue evolving to further improve safety and performance. To meet the challenges of automotive materials recycling, the U.S. Department of Energy has recently expanded its collaborative research with industry in this area. This article discusses this collaborative government/industry approach to sustainable end-of-life vehicle recycling. For more information, contact Edward J. Daniels, Argonne National Laboratory, 9700 S. Cass Avenue, Building 362, Room C393, Argonne, IL 60439-4815; (630) 252-5279; fax (630) 252-1342; e-mail edaniels@anl.gov.     

A framework for capacity planning and machine configuration in flexible assembly systems

We consider the problem of simultaneously determining the number of machines (and/or workers), the assignment of tasks (and related tools and components) to these machines, and the number of jobs circulating in a flexible assembly system (FAS), to satisfy steady-state throughput requirements for a family of similar products at minimum cost. We focus on situations where there are precedence relations among the various tasks, as is common in assembly systems. We present a framework for solving this problem based on a heuristic decomposition approach which involves the solution of only a few types of sub-problems. We demonstrate the efficiency and effectiveness of the overall procedure using a number of example problems.     

High-speed high-resolution gas-phase Raman spectroscopy

A new Raman spectrometer has been developed that can produce a complete high-resolution gas-phase vibrational spectrum during the time period of a single laser pulse. Conventional gas-phase Raman spectroscopy uses a single narrow-band laser to produce signals that are weak, requiring relatively long collection times. This spectrometer uses a degenerate OPO as a broad-band source that covers a continuous range of >3000 cm(-1). When a beam from this broad-band source is added to a narrow-band laser beam, the intensity of the Raman signal is amplified by the nonlinear optical effect. The resulting instrument can generate spectra with high-spectral (<1 cm(-1)), spatial (<0.05 mm2), and temporal resolution (<1 s).     

Optimizing dock configuration and staffing in decentralized receiving

In manufacturing facilities, shipping and receiving traditionally have been concentrated in one or two areas of the building. The widespread introduction of just-in-time shipping policies in US manufacturing companies during the past 15 years, as well as the common use of decentralized receiving in the Japanese automobile industry, has motivated the consideration (and occasionally the adoption) of dock configurations to support decentralized receiving (also known as perimeter receiving). By providing multiple access points along the perimeter of the building, decentralized receiving generally reduces the time and cost associated with moving purchased parts to the locations within the facility where they are used, but also results in increased cost of construction, maintenance, and operation for docks and associated truck access/egress, as well as additional interior floorspace requirements. We develop an optimization-based procedure to determine which of several possible dock areas to construct, how many doors or gates each should have, how many unloading and internal material handling staff should be assigned to each group, and which inbound materials each group should handle. We consider the amortized cost of constructing and equipping the docks, the amortized cost of material handling equipment to support the unloaders and material handlers, the cost of operating the material handling equipment, and labor costs for both unloading and internal material handling.     

Reflex facilitation of the rabbit nictitating membrane response by an auditory stimulus as a function of interstimulus interval.

The ability of an auditory stimulus to facilitate the amplitude and latency of the unconditioned nictitating membrane (NM) response in rabbits was investigated over a wide range of interstimulus intervals (ISIs) for both delay (Experiments 1–4) and trace (Experiments 3 and 4) procedures. The auditory stimulus was a 1000-Hz tone (T) at either 85 or 95 dB, and the reflex-eliciting stimulus was a 2.0 psi (pounds per square inch) corneal air puff. The results indicate that (a) robust facilitation of the NM response, as measured by an increased amplitude and a reduced latency, can be obtained at long ISIs (2,000–32,000 ms); (b) increasing the tone intensity can increase reflex facilitation of the peak amplitude; (c) at comparable ISIs, delay procedures produce more facilitation of both amplitude and latency than do trace procedures; and (d) when trace procedures are used, amplitude and latency facilitation by a 125-ms tone follows an inverted U-shaped ISI function in which facilitation peaks between 125 and 500 ms, rapidly decreases between 1,000 and 2,000 ms, and disappears by 4,000 ms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Aging and Enhancement Effects on Quality Characteristics of Beef Strip Steaks

ABSTRACT: Strip loins were removed 48 h postmortem from beef sides ( n = 20 pairs) to assess the effects of enhancement before or after aging on quality attributes of beef strip steaks. Strip loins were enhanced to 108% of original weight to contain 0.4% alkaline phosphate, 0.3% salt, 0.1% natural flavoring (on a final weight basis), and added water for comparison with non-enhanced samples. Regardless of when enhancement occurred relative to aging, enhanced samples were more tender, juicy, and salty than their non-enhanced counterparts. Enhanced samples were lighter, less red and less yellow, and had lower L *, a *, and b * values than non-enhanced samples; however, they generally had lower hue angles indicating that their color was closer to the true red axis of the color scale. Samples enhanced before aging achieved maximum tenderness after 14 d, whereas those enhanced after aging experienced no tenderness changes. Warner- Bratzler shear values were lower and pH values were higher in enhanced steaks than in controls.