Showing papers in "Interfaces in 1998"
TL;DR: Some of the common pitfalls users encounter and remedies available in the latest version of Microsoft Excel are described, which have great impact in industry and education.
Abstract: In designing the spreadsheet optimizer that is bundled with Microsoft Excel, we and Microsoft made certain choices in designing its user interface, model processing, and solution algorithms for linear, nonlinear, and integer programs. We describe some of the common pitfalls users encounter and remedies available in the latest version of Microsoft Excel. The Solver has many applications and great impact in industry and education.
539 citations
TL;DR: The model adequately describes STD prevalences and the time-trend of HIV prevalence measured in Nairobi and shows model predictions of the effects of improved STD care and increased condom use on the prevalence and incidence of HIV.
Abstract: STDSIM is a dynamic stochastic simulation model for decision support in attempts to control sexually transmitted diseases (STDs). It describes the mechanisms responsible for the transmission of five STDs, including HIV/AIDS, at the level of individuals. A large variety of outcome measures (for example, STD prevalence, incidence, and mortality) can be calculated for different groups of the population (for example, adolescents, prostitutes, pregnant women, and migrants) to evaluate the effects of alternative STD control interventions. We designed the model to support decision making for different settings in developing countries, with Nairobi (Kenya) as its first application area. The model adequately describes STD prevalences and the time-trend of HIV prevalence measured in Nairobi. As an illustration of the possibilities of the model, we show model predictions of the effects of improved STD care and increased condom use on the prevalence and incidence of HIV.
80 citations
TL;DR: A gray linear-programming (GLP) model is used for the regional municipality of Hamilton-Wentworth, Ontario to address questions of waste-flow allocation and bring uncertain information into the optimization process and resulting solutions, permitting feasible decision alternatives to be generated.
Abstract: The materials in trash, or municipal solid waste (MSW), may be recycled, composted, incinerated, or landfilled. Transporting these materials to waste-management facilities consumes part of the operating budget of a municipality. Many factors, the majority uncertain, may influence the planning of waste-flow allocation. MSW managers want to know (1) whether the existing pattern is close to the optimal, and (2) if not, what is the optimal? We used a gray linear-programming (GLP) model to address these questions for the regional municipality of Hamilton-Wentworth, Ontario. This approach can effectively reflect the interactive relationships between uncertain system components. It can also bring uncertain information into the optimization process and resulting solutions, permitting feasible decision alternatives to be generated. The region's waste managers have used the results to verify or adjust the existing waste-flow allocation pattern. They may also be used to formulate related local policies.
71 citations
TL;DR: Societe Nationale des Chemins de Fer Francais (SNCF), in partnership with SABRE Technology Solutions, has developed RailPlus, a strategic schedule planning system, and RailCap, a tactical capacity-adjustment system to meet the new challenges of the rail business.
Abstract: Because of the upcoming deregulation and the advent of high-speed rail networks, European passenger railroads are battling for customers among themselves and with other means of transportation. To maintain a competitive advantage, they rely on the scheduling process as a key factor in winning market share. Societe Nationale des Chemins de Fer Francais (SNCF), in partnership with SABRE Technology Solutions, has developed RailPlus, a strategic schedule planning system, and RailCap, a tactical capacity-adjustment system, to meet the new challenges of the rail business. The heart of these systems is a set of advanced operations research models that enable analysts to take a global approach to decision making. The two systems combined provide 110 million francs in incremental revenue per year and substantially reduce operating costs. In addition, the two systems have become the foundation for the reorganization of SNCF/TGV.
68 citations
TL;DR: A simple linear programming model solves the problem of allocating resources to the home-care service provided to AIDS patients in the city of Rome, Italy, which include medical assistance provided by nurses and doctors and social assistance and accompaniment of patients provided by social workers.
Abstract: In allocating resources to health-care services, the main difficulties derive from uncertainty concerning the number of patients who need the service and the level of care required by each patient who is entitled to receive it. I deal with the problem of allocating resources to the home-care service provided to AIDS patients in the city of Rome, Italy, which include medical assistance provided by nurses and doctors and social assistance and accompaniment of patients provided by social workers. A simple linear programming model solves the problem for single organizations, which provide assistance within a given budget, and for public-health authorities, which have to evaluate the results of tentative budgets assigned to home care.
66 citations
TL;DR: In 1988, Taco Bell introduced six core-menu items for the reduced price of 59 cents and offered free drink refills and has since continued to change and innovate.
Abstract: Taco Bell Corporation has approximately 6,490 company-owned, licensed, and franchised locations in 50 states and a growing international market. Worldwide yearly sales are approximately $4.6 billion. In 1988, Taco Bell introduced six core-menu items for the reduced price of 59 cents and offered free drink refills. Taco Bell has since continued to change and innovate. Its new strategy meant restructuring the business to become more efficient and cost-effective. To do this, the company relied on an integrated set of operations research models, including forecasting to predict customer arrivals, simulation to determine the optimum labor required to provide desired customer service, and optimization to schedule and allocate crew members to minimize payroll. Through 1997, these models have saved over $53 million in labor costs.
60 citations
TL;DR: Assessment of the potential impact of using a prophylactic vaccine when one subtype of HIV is endemic and a second subtype is introduced into the community finds that both subtypes coexist.
Abstract: We developed and used mathematical models to assess vaccine programs for controlling two subtypes of HIV, both for developing countries where more than one subtype is present and for countries where only one subtype is present but other subtypes may invade. We began by formulating a model of the intrinsic transmission dynamics of the two HIV subtypes and then extended this model to include the effects of a prophylactic vaccine that provides a degree of protection against infection by one subtype and vaccine-induced cross-immunity against infection by the second subtype. Using these models, we assessed the potential impact of using a prophylactic vaccine when one subtype of HIV is endemic and a second subtype is introduced into the community. In each case, mass vaccination could result in one of four possible outcomes: (1) both subtypes are eradicated, (2) the endemic subtype persists and the invading subtype is eradicated, (3) the endemic subtype is eradicated and the invading subtype persists, or (4) both subtypes coexist.
58 citations
TL;DR: MIT researchers used analytical methods to predict capacity and to determine the sizes and locations of buffers that would increase capacity at the cost of a minor increase in inventory that yielded incremental revenues of about $280 million in printer sales and additional revenues from ancillary products, replacement ink-jet cartridges, media, and related items.
Abstract: As Hewlett-Packard Corporation installed a system for manufacturing ink-jet printers in Vancouver, Washington, in 1993, it realized that the system would not be fast enough or reliable enough to meet its production goals. At the time, the market for ink-jet printers was exploding, and any incremental printer shipments would translate directly into market share and revenue gains. The company undertook a simulation project to develop recommendations for design changes to improve the system performance but concluded that that project would take too long to be useful. MIT researchers used analytical methods to predict capacity and to determine the sizes and locations of buffers that would increase capacity at the cost of a minor increase in inventory. HP's implementation of this work yielded incremental revenues of about $280 million in printer sales and additional revenues from ancillary products, replacement ink-jet cartridges, media, and related items. Productivity increased about 50 percent, making the assembly of the print engine cost competitive. Finally, HP developed a method of creating rapid and effective system designs in the future.
52 citations
TL;DR: A study to improve the running of hospital outpatient clinics that were regularly overbooked, overrun, and had excessive patient waiting times found that a flexible and open-minded approach is adopted.
Abstract: We undertook a study to improve the running of hospital outpatient clinics that were regularly overbooked, overrun, and had excessive patient waiting times. The methodology adopted entailed a mixture of qualitative and quantitative approaches, but was problem-driven and so only emerged as the project developed. We generated a number of proposals for the improved running of the clinics during the project, some implemented and some not. For future studies we would recommend that a flexible and open-minded approach is adopted. This may well involve an initial, mainly qualitative, study followed by the application of a series of modest models-occasionally more sophisticated modeling may be appropriate. We would also recommend that the benefits of such studies are not judged solely in terms of one-off implementation leading to measurable improvements in performance. They should also be seen as part of an overall process of improving health care practices.
42 citations
TL;DR: The results imply that the primal simplex method using the basis-partitioning approach can now efficiently solve the extremely large multicommodity-flow models found in industry.
Abstract: The multicommodity-flow problem arises in a wide variety of important applications. Many communications, logistics, manufacturing, and transportation problems can be formulated as large multicommodity-flow problems. During the last few years researchers have made steady advances in solving extremely large multicommodity-flow problems. This improvement has been due both to algorithmic and to hardware advances. At present the primal simplex method using the basis-partitioning approach gives excellent solution times even on modest hardware. These results imply that we can now efficiently solve the extremely large multicommodity-flow models found in industry. The extreme-point solution can also be quickly reoptimized to meet the additional requirements often imposed upon the continuous solution. Currently practitioners are using EMNET, a primal basis-partitioning algorithm, to solve extremely large logistics problems with more than 600,000 constraints and 7,000,000 variables in the food industry.
41 citations
TL;DR: Two deterministic and stochastic models were used to compare three intervention strategies for preventing heterosexual transmission of the human immunodeficiency virus and found that combined interventions were more effective than single interventions.
Abstract: We compared three intervention strategies for preventing heterosexual transmission of the human immunodeficiency virus (HIV) using deterministic and stochastic models to simulate the epidemic of acquired immunodeficiency syndromes (AIDS). We estimated demographic, biological, and behavioral parameters for a severely affected east African city early in the epidemic, and used these parameter values in computing the spread of HIV under five scenarios: (1) a baseline scenario with no public health interventions; three single-intervention scenarios with strategies to (2) reduce the number and rate of change of sex partners, (3) increase condom use, or (4) improve treatment of sexually transmitted diseases (STD); and a (5) combined-intervention scenario. The rankings were the same in both models-decreasing partner change was most effective, followed by condom use and STD treatment. Combined interventions were more effective than single interventions. They interacted to produce impacts that varied with the trajectory of the epidemic at the onset of the interventions. Their timely, targeted, and sustained implementation appears critical to slow the epidemic significantly.
TL;DR: The Santa Fe Intermodal business unit has developed an innovative approach to designing its service offerings that shows the potential to improve global service by four percent while reducing costs by six percent over the existing operating plan.
Abstract: Santa Fe Railway's intermodal business unit has developed an innovative approach to designing its service offerings. The operating-plan model (OPM) minimizes the schedule-related costs of service subject to rail-operating capabilities while meeting customers' expectations for service. The algorithm produces a weekly train timetable and assigns traffic to trains. Because of the problem's size and complexity, a combination of genetic and tabu searches is used to search for successively better operating plans. The OPM shows the potential to improve global service by four percent while reducing costs by six percent over the existing operating plan. Santa Fe Intermodal has realized savings by applying the OPM to more narrowly focused problems.
TL;DR: In-depth analysis in one firm indicates that product profiling is a valuable tool to uncover the origins of misalignments that occur over time and to illustrate the phenomenon to executives.
Abstract: As companies choose among process alternatives, they need a clear understanding of the changing alignment between manufacturing and the needs of their markets. Assessing how well existing processes fit these market requirements and making choices to meet future needs are critical strategic responsibilities for manufacturing. Product profiling can be used to examine the degree of alignment between the needs of a company's markets and the characteristics of its existing manufacturing process and infrastructure investments. We compare product profiling with another tool, the product-process matrix, and examine the applicability of both in a typical mismatch situation. In-depth analysis in one firm indicates that product profiling is a valuable tool to uncover the origins of misalignments that occur over time and to illustrate the phenomenon to executives.
TL;DR: A dynamic model of HIV transmission is developed to evaluate the costs and benefits of HIV-vaccine programs in a population of homosexual men and it is found that the effect of reductions in condom use is more important for therapeutic vaccines than for preventive vaccines.
Abstract: We developed a dynamic model of HIV transmission to evaluate the costs and benefits of HIV-vaccine programs in a population of homosexual men. We examined how changes in high-risk sexual behavior and the growth pattern of the epidemic influence the cost-effectiveness of preventive vaccines and of therapeutic vaccines. We found that the effect of reductions in condom use is more important for therapeutic vaccines than for preventive vaccines. Therapeutic vaccines may increase HIV seroprevalence in the population, unless the vaccine program is accompanied by increased condom use. Epidemic growth patterns also influence the cost-effectiveness of both vaccines, but the effects are more pronounced for preventive vaccines, which are more cost-effective in an early-stage epidemic than in a late-stage epidemic.
TL;DR: The author argues that the reason for this is in that the MBA curriculum is increasingly driven by a need to please students, who view themselves as consumers.
Abstract: Many observers of the management science scene believe that the traditional management science course is in serious decline in MBA programs throughout the United States. This trend, if prolonged, could reduce the number of academic jobs for OR/MS PhDs and, more important, could cause one or more generations of MBA graduates to have no appreciation of the power and scope of the management science approach. The author argues that the reason for this is in that the MBA curriculum is increasingly driven by a need to please students, who view themselves as consumers.
TL;DR: The results indicate that soft and hard OR methods can be combined to good effect to produce tangible results.
Abstract: In 1994, RTZ Corporation plc, the world's largest mining company, tried to reconcile (a) the desire of central management to compare performance across mine sites with (b) the desire of local management to judge performance in their own terms. The company began a project to establish a method of measuring open-pit productive capacity, to spread best practice, and to motivate higher performance. Initially we saw the solution as a simple model of equipment availability using hard OR derived using a participative process based on soft OR. Trials in Australia, Southern Africa, and North America showed that we needed to combine various hard and soft OR methods and to move the emphasis to achieving breakthroughs in performance. The latest trial resulted in an increase in production of over 25 percent in the first year. The results indicate that soft and hard OR methods can be combined to good effect to produce tangible results.
TL;DR: A five-level hierarchic structure distributing the clients among the sales promoters in the levels of greater aggregation and assigning shops to individual drivers in the level with the greatest detail corresponds to a version of the traveling salesman problem with time windows.
Abstract: We designed and implemented a decision support system to organize the delivery network for the products of a large dairy. To deal with this complex problem, we employed a five-level hierarchic structure distributing the clients among the sales promoters in the levels of greater aggregation and assigning shops to individual drivers in the level with the greatest detail, which corresponds to a version of the traveling salesman problem with time windows. We implemented the model on a microcomputer, importing the necessary data from the company mainframe.
TL;DR: In this article, cognitive psychologists suggest that instructors should design learning activities according to the type and difficulty of the specific knowledge to be learned to increase students' understanding and retention of knowledge by creating more opportunities for active learning.
Abstract: Instructors increase their students' understanding and retention of knowledge by creating more opportunities for active learning. According to cognitive psychologists, instructors should design learning activities according to the type and difficulty of the specific knowledge to be learned. Ten cognitive strategies, related to three types of knowledge, can be used to generate active learning.
TL;DR: A dynamic production-simulation model and probabilistic assessments of schedule, production capacity, and availability risks were combined to predict the production behavior of each alternative over 40 years, and the secretary of energy decided to pursue both the commercial-reactor and accelerator alternatives.
Abstract: Nuclear weapons require the periodic replacement of tritium, a radioactive gas that decays at approximately 5.5 percent per year. Currently no tritium-supply facility exists in the US, and due to the decay, the tritium inventory will fall below the required reserve level in 2011. To decide how to fill this projected gap, the US Department of Energy assessed 10 tritium-supply alternatives, including several types of new reactors, an accelerator, and the use of commercial reactors. The DOE compared the alternatives with respect to three objectives: production assurance, cost, and environmental impacts. We combined a dynamic production-simulation model and probabilistic assessments of schedule, production capacity, and availability risks to predict the production behavior of each alternative over 40 years. We also assessed the cost and environmental risks. The secretary of energy decided to pursue both the commercial-reactor and accelerator alternatives, based, in part, on the results of this analysis.
Journal Article•
TL;DR: In this paper, a retorica da perda: os discursos do patrimonio cultural no Brasil de Jose Reginaldo Santos Goncalves are presented.
Abstract: Resenha do Livro A retorica da perda: os discursos do patrimonio cultural no Brasil de Jose Reginaldo Santos Goncalves
TL;DR: An introduction to stochastic-tree modeling and techniques involved in their application to medical-treatment decisions are offered and an application of these tools to the analysis of the decision to undergo a total hip replacement is described.
Abstract: The stochastic tree is a recently introduced generalization of the decision tree which allows the explicit depiction of temporal uncertainty while still employing the familiar rollback procedure for decision trees. We offer an introduction to stochastic-tree modeling and techniques involved in their application to medical-treatment decisions. We also describe an application of these tools to the analysis of the decision to undergo a total hip replacement from the perspectives of an individual patient (via utility analysis) and of society (via cost-effectiveness analysis).
TL;DR: A computer-based system to replace an existing manual system for assigning proctors, freeing up valuable staff time in the overloaded scheduling office and combines some problem-specific heuristics, a genetic-algorithm framework, and a simple user interface based on readily available software tools.
Abstract: Carleton University needs proctors during examination sessions to oversee the students as they write their final examinations. The process of assigning proctors to examinations is quite complex because of the sheer number of examinations and various complex constraints on allowable assignments. We developed a computer-based system to replace an existing manual system for assigning proctors, freeing up valuable staff time in the overloaded scheduling office. Our system combines some problem-specific heuristics, a genetic-algorithm framework, and a simple user interface based on readily available software tools.
TL;DR: Techniques for screening mathematical-programming formulations for structural problems pre- and postsolution for linear programming are developed and computerized in association with GAMS.
Abstract: Mathematical-programming formulations can yield faulty answers. Models can be unbounded, infeasible, or optimal with unrealistic answers. I develop techniques for screening mathematical-programming formulations for structural problems pre- and postsolution. The presolution approaches identify problems within single variables and constraints. The postsolution techniques may require model augmentation and relyon theory-based examination of primal and dual solutions. I demonstrate these approaches in the context of linear programming and have computerized them in association with GAMS. They are freely distributed through a web page.
TL;DR: A survey of firms in Mexico shows that many companies make limited use of modern forecasting methods, and the most commonly used methods are the judgmental.
Abstract: A survey of firms in Mexico shows that many companies make limited use of modern forecasting methods. The forecasting techniques used in the US and included in the survey are little known or used by the reporting Mexican companies. This is in spite of the fact that business forecasting has been taught in colleges and universities in Mexico for many years. The most commonly used methods are the judgmental. A likely explanation is the unstable business situation suffered by companies in Mexico since the December 1994 devaluation. Economic instability will make it very difficult to use historical information for forecasting purposes.
TL;DR: A simulation procedure is developed to obtain forecasts of the HIV/AIDS epidemic and used to estimate the characteristic regional parameters of the epidemic in Italy, based on a hybrid compartmental model, suitable for policy making.
Abstract: Short- and medium-term projections of the HIV/AIDS epidemic indicators are of great interest to those evaluating the needs for health care and prevention interventions We developed a simulation procedure to obtain forecasts of the HIV/AIDS epidemic and used it to estimate the characteristic regional parameters of the epidemic in Italy The simulation procedure is based on a hybrid compartmental model, in which the epidemic evolves via nonrandom mixing patterns Because of its structure, the model is suitable for policy making; in particular, for evaluating prevention campaigns, alternate forms of health care for people with AIDS, and drug supply needs The model will also be used to estimate the number of intravenous drug users in Italy and the number of AIDS cases not reported or reported with a delay to the Italian surveillance system
TL;DR: Computer software that uses mathematical optimization rather than trial-and-error methods to estimate the nutrient content of commercial food products was able to estimate nutrient values four times faster than conventional methods with the same degree of accuracy.
Abstract: We developed, evaluated, and deployed computer software that uses mathematical optimization rather than trial-and-error methods to estimate the nutrient content of commercial food products. Linear programming (LP) and quadratic programming (QP) optimization methods were evaluated by comparing nutrient values estimated for 31 commercial products with known values for these nutrients. The optimization software was able to estimate nutrient values four times faster than conventional methods with the same degree of accuracy, although the QP method was slightly slower than LP. Nutritionists found the software easy to learn and use. The Nutrition Coordinating Center at the University of Minnesota now uses the LP version of the software as a decision support tool to maintain a food composition database.
TL;DR: The authors used OR-based models to estimate HIV prevalence and incidence in the United States, understand the pathophysiology of HIV, evaluate costs and benefits of HIV screening programs, evaluate the effects of needle exchange programs, and determine policies for HIV/AIDS care in California.
Abstract: The AIDS epidemic is a serious, growing public health problem worldwide, but resources for treating HIV-infected patients and for combating the spread of the virus are limited. Governments, public-health agencies, and healthcare providers must determine how best to allocate scarce resources for HIV treatment and prevention among different programs and populations. OR-based models have influenced-and can influence-AIDS policy decisions. Mathematical modeling has had an effect on AIDS policy in a number of areas, including estimating HIV prevalence and incidence in the United States, understanding the pathophysiology of HIV, evaluating costs and benefits of HIV-screening programs, evaluating the effects of needle-exchange programs, and determining policies for HIV/AIDS care in California. Further work is needed to model a range of programs using comparable methods, to model overall epidemic control strategy, and to improve the usefulness of OR-based models for policy making.
TL;DR: This simple application saved Welch's between $130,000 to $170,000 during the first year and formulated the problem as a linear program model and used spreadsheet optimization to incorporate the model in daily decision making.
Abstract: Welch's, a large grape-processing company owned by a grower cooperative, faced complex logistics in planning recipes for products sold in retail stores. The recently installed integrated MRP and cost-accounting systems did not include ways to calculate recipes at optimal cost based on plant-raw-material and capacity constraints. An imbalance of supply and demand further complicated this problem in raw-materials management. The cross-functional team in charge of managing raw materials spent increasing a mounts of time deciding what recipes to use at each plant. We formulated the problem as a linear program model and used spreadsheet optimization to incorporate the model in daily decision making. The company has run the model each month since 1994 to provide senior management with information on the optimal logistics plan. This simple application saved Welch's between $130,000 to $170,000 during the first year.
TL;DR: In April 1997, the United States Army announced that savings had finally overtaken costs in closing or realigning 803 of its installations worldwide, in the ninth year of a 13-year program approved by Congress and Presidents Reagan, Bush, and Clinton.
Abstract: In April 1997, the United States Army announced that savings had finally overtaken costs in closing or realigning 803 of its installations worldwide. This milestone occurred in the ninth year of a ...
TL;DR: An optimization model that considers multiple weather scenarios in determining a supply portfolio and has been used to restructure supply portfolios, saving the Peoples Gas Light and Coke Company more than $50 million annually.
Abstract: A gas utility's profits depend on its portfolio of gas supply and storage contracts and their effective utilization. The Peoples Gas Light and Coke Company serves the Chicago market. Demand for natural gas depends on temperature, which is difficult to forecast. We developed an optimization model that considers multiple weather scenarios in determining a supply portfolio. We originally developed it to support filings of integrated least-cost supply plans with the Illinois Commerce Commission. With deregulation of the natural gas industry, the company has used the model to restructure supply portfolios, saving more than $50 million annually.