Purpose -The purpose of this paper is to present an eight-step simulation model development process (SMDP) for the design, implementation, and evaluation of logistics and supply chain simulation models, and to identify rigor criteria for each step. Design/methodology/approach -An extensive review of literature is undertaken to identify logistics and supply chain studies that employ discrete-event simulation modeling. From this pool, studies that report in detail on the steps taken during the simulation model development and model more than one echelon in logistics, supply chain, or distribution systems are included to illustrate rigor in developing such simulation models. Findings -Literature review reveals that there are no preset rigor criteria for publication of logistics and supply chain simulation research, which is reflected in the fact that studies published in leading journals do not satisfactorily address and/or report the efforts taken to maintain the rigor of simulation studies. Although there has been a gradual improvement in rigor, more emphasis on the methodology required to ensure quality simulation research is warranted.Research limitations/implications -The SMDP may be used by researchers to design and execute rigorous simulation research, and by reviewers for academic journals to establish the level of rigor when reviewing simulation research. It is expected that such prescriptive guidance will stimulate high quality simulation modeling research and ensure that only the highest quality studies are published. Practical implications -The SMDP provides a checklist for assessment of the validity of simulation models prior to their use in practical decision making. It assists in making practitioners better informed about rigorous simulation design so that, when answering logistics and supply chain system questions, the practitioner can decide to what extent they should trust the results of published research. Originality/value -This paper develops a framework based on some of the most rigorous studies published in leading journals, provides rigor evaluation criteria for each step, provides examples for each step from published studies, and illustrates the SMDP using a supply-chain risk management study.
N-(1-Pyrenyl)iodoacetamide has been used to introduce fluorescent probes into Escherichia coli RNA polymerase. After an incubation time of 15 min, approximately 2 pyrene equiv was introduced per enzyme molecule. There was no further increase in modification after more extended periods of incubation. Neither calf thymus DNA nor nucleotides protected the holoenzyme from modification. Thus, the sites of modification do not appear to involve the binding sites for polynucleotides or the ribonucleoside triphosphates. From the isolation and analysis of the individual subunits, it was found that sigma contained approximately 1 pyrene equiv, beta contained 0.6, beta' contained 0.6, and alpha less than 0.1. Spectral and Stern-Volmer analyses indicate that the covalently attached pyrene molecules are in comparable apolar microenvironments. On the basis of CD analyses, the introduction of pyrene molecules into RNA polymerase alters its secondary structure. This alteration in secondary structure manifests itself by a reduction in overall enzymatic activity. Transcript analysis of the products obtained by using a linearized plasmid containing the A1 promoter and the Te terminator of bacteriophage T7 indicates that the pyrenyl derivative is capable of producing full-length transcripts and that it has an efficiency of chain termination comparable to the native enzyme. Analysis of tau plots for the interaction of the pyrenyl derivative and the native enzyme, respectively, with the A1 promoter yielded comparable values for the isomerization constant in the conversion of the closed complex to an open one. Comparable values were also obtained for the association constant. The rate of chain elongation for the pyrenyl derivative, however, is approximately 54% of that observed for the native enzyme. Thus, the decrease in overall transcriptional activity observed with the pyrenyl derivative is not due to a decrease in the efficiency of initiation or premature termination, but rather to a decrease in the rate of chain elongation.
A common issue faced by physician groups is how to schedule 24-7 coverage for hospital units such as an emergency department. The first step is to determine the shifts to be covered. The second step, assigning physicians to specific shifts, is complicated because shifts vary with respect to duration, day of week, time of day, and desirability. To ensure workload fairness, physician groups often create “equality” schedules in which they evenly divide shifts, by type, among physicians. This problem can be readily modeled and solved via optimization. This paper presents a novel approach that incorporates individual physician shift-type preference and seeks, for each physician, a schedule that is superior to his or her equality schedule. We formulate and solve the problem as a binary, mixed-integer program designed to maximize relative gains in individual physician preference. We describe the methodology and real-world implementation within a neonatal intensive care group, and present a hybrid version of the model that is capable of simultaneously accommodating physicians who prefer an equality schedule and physicians willing to deviate from the equality schedule in pursuit of a schedule that better fits their shift preferences. Increases in schedule preference for the latter group ranged from 6.3 to 8.5 percent.
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