M. Jeya Chandra

The effects of inflation and the time value of money on some inventory systems

Abstract The effects of inflation and the time value of money on the optimal policies of the order-level system and the economic lot-size system are examined. Two different inflation rates, one for the internal and the other for the external costs, are assumed. The objective is to minimize the present value of the total costs per unit time.

Consistency check of a house of quality chart

Quality function deployment (QFD) is a cross‐functional planning tool which ensures that the voice of the customer is systematically deployed throughout the product planning and design stages. One of the common mistakes in QFD is to perform analysis using an inconsistent house of quality (HOQ) chart. An inconsistent HOQ chart is one in which the information from the roof matrix is inconsistent with that from the relationship matrix. This paper develops a systematic procedure to check the consistency of information contained in an HOQ chart. The proposed consistency check can be performed prior to QFD’s main analysis to ensure the validity of the final results. A procedure for identifying the source of the inconsistency, if the HOQ chart should fail the consistency test, is also developed. The proposed procedures are illustrated through examples.

The Impact of Visual Layout Factors on Performance in Web Pages: A Cross-Language Study:

Visual layout has a strong impact on performance and is a critical factor in the design of graphical user interfaces (GUIs) and Web pages. Many design guidelines employed in Web page design were inherited from human performance literature and GUI design studies and practices. However, few studies have investigated the more specific patterns of performance with Web pages that may reflect some differences between Web page and GUI design. We investigated interactions among four visual layout factors in Web page design (quantity of links, alignment, grouping indications, and density) in two experiments: one with pages in Hebrew, entailing right-to-left reading, and the other with English pages, entailing left-to-right reading. Some performance patterns (measured by search times and eye movements) were similar between languages. Performance was particularly poor in pages with many links and variable densities, but it improved with the presence of uniform density. Alignment was not shown to be a performance-enhancing factor. The findings are discussed in terms of the similarities and differences in the impact of layout factors between GUIs and Web pages. Actual or potential applications of this research include specific guidelines for Web page design.

On a machine interference problem with several types of machines attended by a single repairman

We consider a machine interference problem with several types of machines attended by a single repairman. Assuming exponentially distributed time to failures, generally distributed repair times arid head of the line non-preemptive priority repair discipline, an imbedded Markov chain model is formulated. Using this Markov chain model and a discrete state level crossing analysis the steady state probability distribution of the number of machines in failed state at an arbitrary time epoch is derived. An algorithm is developed to compute these probabilities and some numerical results illustrating some basic features of this machine interference problem is also presented

An economic selective assembly procedure for two mating components with equal variance

An economic procedure of selective assembly is proposed when a product is composed of two mating components. The major quality characteristic of the product is the clearance between the two components. The components are divided into several classes prior to assembly. The component characteristics are assumed to be independently and normally distributed with equal variance. The procedure is designed so that the proportions of both components in their corresponding classes are the same. A cost model is developed based on a quadratic loss function and methods of obtaining the optimal class limits as well as the optimal number of classes are provided. Formulas for obtaining the proportion of rejection and the unavailability of mating components are also provided. The proposed model is compared with the equal width and the equal area partitioning methods using a numerical example.

A factorial design analysis of a biomass to ethanol production system.

Abstract A least cost, dynamic programming solution was derived by an algorithm for ethanol production from woody biomass. Conversion of the feedstock was based on an enzymatic hydrolysis/fermentation process. The final cost of ethanol from this system, prior to any sensitivity analysis, was

Analysis of robot positioning error

0.45 L −1 . A sensitivity analysis, using a factorial design, compared the relative impact of various model parameters on production costs. The factorial design analysis can be used as a guide for lowering final product costs. Three factors were incorporated into the first factorial design: the size of the manufacturing facility, storage retention, and the price of alternative feedstocks. Each of the main factors had an impact on the solution cost. Facility size had the largest effect, representing 45.3% of total cost variability. Storage deterioration and the price of alternative feedstocks had lower effects of 17.4% and 17.6%, respectively. The largest interaction effect, at 17.4%, illustrated that storage deterioration and facility size have a joint effect on production costs. The second factorial design employed five factors. Ethanol yield from the woody feedstock accounted for 44.0% of the total variability in final product cost. Harvesting equipment capability placed a 36.8% effect on the final product cost. The third largest effect, at 8.7%, was plantation yield. Although plantation yields are of key importance to feedstock prices, they had a lesser impact than the other factors on the final product cost over an entire production process. Storage retention and facility size had a reduced impact on total costs when considered in combination with other design factors. Based on this study the focus for research and technological improvements should be on conversion yields from wood, harvester equipment capabilities, and plantation yields.

Approximate Solutions for Some Two-Stage Tandem Queues, Part 1: Individual Arrivals at the Second Stage

Positioning errors of robots used for material handling and assembly can be sufficiently large to cause problems. These errors are due to imperfect repeatability of the robots, and their effects can be ameliorated or exacerbated by tolerances on the workpieces and on the jigs and fixtures. In this paper, a model for characterizing the positioning errors of robots is developed. A statistical analysis of positioning error data is performed to make inferences about the stochastic nature of the robotic system. The basic issue is whether the positioning errors of the robot are state dependent or state invariant.

Optimal tool inspection intervals using a process control approach

The analysis of tandem queues in which the output of each stage immediately becomes the input to the next is, in general, quite difficult. Although the analytic solution for the steady-state departure distribution from an M/M/N queue is well-known and that of an M/G/1 queue can be obtained if the analyst is willing to view it through a “Laplacian curtain,” the list of existing analytic solutions is not long. Some analytic “tricks” exist, but their utility is usually limited to the single-server queue. The treatment of tandem queues not fitting into these categories has been largely left to simulation. Yet this approach has its drawbacks. It is expensive and involves difficulties in designing and analyzing the simulation experiment. Approximation techniques are beginning to emerge as a wiser, faster, cheaper, and less troublesome alternative to simulation. In this paper we develop approximate solutions for average steady-state queue length in four different but related tandem queues that arise in connectio...

The assignment of minimum crews among bases in an airlift operation

SUMMARY In machining operations, it is often necessary to remove a cutting tool for inspection and maintenance to reduce the probability of failure during machining. In this paper, a tool replacement model patterned after a cost model for the design of control charts is developed which yields inspection intervals of equal length.