Using an optimized queueing network model to support wafer fab design

We develop an Optimized Queueing Network (OQNet) capacity planning tool for supporting the design of new and reconfigured semiconductor fabrication facilities that makes use of queueing network approximations and an optimization routine. The basic problem addressed by this tool is to minimize the facility cost required to meet specified volume and cycle time targets. Features common to semiconductor environments, such as batch processes, re-entrant flows, multiple product classes, and machine setups, are incorporated into the model. Comparisons with simulation show that the queueing and other approximations are reasonably accurate. Tests of the optimization routine demonstrate that it can find good solutions quickly.     

The part mix and routing mix problem in FMS: a coupling between an LP model and a closed queueing network

In the near future many companies will face the problem of the optimal use of newly installed manufacturing technology (e.g. a flexible manufacturing system or FMS). Very often this will involve decisions on what parts to produce using the new system (the part mix problem) and how to produce these parts (the routing mix problem). We show that traditional operational research tools such as linear programming and queueing network theory are well suited to tackle these problems. In particular, LP models are combined with queueing network models in an iterative procedure. As such the strengths of both techniques can be exploited in making optimal use of the part mix and routing mix flexibility of the FMS.     

Measurement of processing and queuing delays introduced by an open-source router in a single-hop network

Measurement of the main contributions to the single-hop delay introduced by an open-source router is dealt with. A new method is proposed, which is capable of distinguishing the time interval during which a generic packet stays in either input or output queue (queuing delay) of the router under analysis and the time interval characterizing the effective routing process (processing delay) the packet undergoes. Thanks to proper measurement probes, i.e., kernel-layer functions, the method makes the occurring time of events of interest available at the application layer, thus giving the possibility of separately evaluating the aforementioned delays and, ultimately, pursuing a deeper insight of the considered router. After brief remarks concerning various delays a packet experiences when passing through a generic router, the measurement principle underlying the method is presented in detail. Particular emphasis is put on its capability of locally monitoring the transit of each packet from the input to the output port of an open-source router along with main features and implementation issues of the proposed measurement probes. Results obtained in many experiments carried out on a suitable test bed in different operating conditions are then given in order to highlight the method's reliability and effectiveness.     

The contagious nature of imprisonment: an agent-based model to explain racial disparities in incarceration rates

We build an agent-based model of incarceration based on the susceptible–infected–suspectible (SIS) model of infectious disease propagation. Our central hypothesis is that the observed racial disparities in incarceration rates between Black and White Americans can be explained as the result of differential sentencing between the two demographic groups. We demonstrate that if incarceration can be spread through a social influence network, then even relatively small differences in sentencing can result in large disparities in incarceration rates. Controlling for effects of transmissibility, susceptibility and influence network structure, our model reproduces the observed large disparities in incarceration rates given the differences in sentence lengths for White and Black drug offenders in the USA without extensive parameter tuning. We further establish the suitability of the SIS model as applied to incarceration by demonstrating that the observed structural patterns of recidivism are an emergent property of the model. In fact, our model shows a remarkably close correspondence with California incarceration data. This work advances efforts to combine the theories and methods of epidemiology and criminology.     

Using an improvement model to reduce adverse drug events in VA facilities

BACKGROUND: Adverse drug events cause significant morbidity and mortality in health care. Many adverse drug events are due to medication errors and are preventable. In 1999 and 2000 the Patient Safety Center of Inquiry collaborated with the Institute for Healthcare Improvement (IHI) to implement a quality improvement (QI) project designed to reduce medication errors within the Veterans Administration system. METHODS: During a 6- to 9-month period, interdisciplinary teams that want to achieve much higher levels of performance work on a common aim, under the guidance of faculty, and come together for three 2-day educational and planning sessions. Between these sessions, teams implement some of the suggested changes, measure the results of those changes, and report back to the larger group. RESULTS: During the formal project, teams collected allergy information on more than 20,000 veterans and averted 1,833 medication errors that had the potential to cause adverse events. At 6-month follow-up, the majority of teams remained intact, continued to collect data, and maintained their gains, approximately doubling the results obtained during the formal project. Half of the teams expanded their efforts to other settings, and one-third of the teams expanded beyond their original topics. Returns on investment in the QI effort were substantial. CONCLUSIONS: The results suggest that gains made in organized QI efforts can be maintained for 6 months without additional external support or coaching if team structure and leadership support remain intact. Facilitators of QI efforts should focus on teams that are having difficulty learning new techniques. Finally, this effort appeared to generate cost savings.     

Using a constructive residue theorem to increase computational efficiency in systems for transmission and processing of telemetric information

We present a constructive residue theorem whose use in computations and information transmission in a system of residue classes eliminates many shortcomings of practical use of its classical version. Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–13, April, 1997.     

Weekly scheduling in the service industry: an application to mail processing and distribution centers

This paper addresses the midterm planning problem that arises at various service facilities staffed by full-time and part-time employees. In response to updated demand forecasts, expected leave, training assignments, and other contingencies, weekly adjustments are often required to better match available personnel with demand over the planning horizon. Unlike manufacturing where uniform 8-hour shifts are the rule, service organizations may experience several busy periods during the day that do not fit a standard shift. In such cases, supervisors must adjust employee schedules by assigning overtime, increasing the number of part-time hours, and calling in temporary workers. The situation is complicated by union contracts, labor rules, and company policies. To find solutions that can be implemented in a real-world environment, a two-phase approach was developed. In the first phase, the adjustment problem is formulated as a large-scale integer program and solved with a commercial code for those cases in which demand increases are limited to no more than 10% above the baseline. For the more general case, a new target-based heuristic was designed with the goal of finding good feasible solutions. In the second phase, the shift schedules are post-processed to provide daily assignments for each worker. An analysis of the problem arising in the first phase is presented for an application involving weekly scheduling at a mail processing and distribution center. The results indicate that high quality solutions can be obtained within a matter of minutes.     

An approach to integrate production-transportation planning and scheduling in an aluminium supply chain network

This article is based on a real-life problem of a global aluminium supply chain network driven by an aluminium smelter. At each echelon of the aluminium supply chain network, several members are involved which are scattered around the world. Producing aluminium begins with bauxite mining. Next, aluminium oxide is made from bauxite and finally aluminium is produced from aluminium oxide. A novel type of mixed-integer decision-making model, including a time-continuous representation of the planning period, is presented. The model enables coordination of production quantities and times of all supply chain members in order to minimise production and transportation costs of the whole supply chain minus bonus payments for early deliveries which are stipulated between the supply chain network and its customers. Material flows can take place with or without temporary storage of intermediate products at supplying and/or receiving sites. Furthermore, relax-and-fix heuristics are presented. A number of randomly generated scenarios are presented to demonstrate that the heuristics can find nearly optimal solutions along with drastically reduced computation times. The relax-and-fix heuristic enables iterative planning between centralised and decentralised decision makers.     

Using strain gages to investigate subsonic dynamic interfacial fracture in an isotropic-isotropic bimaterial

In this experimental study, strain fields were used to investigate the behavior of subsonic interfacial crack propagation in a bimaterial system. Strain field equations were derived from the available stress field equations and critically evaluated in a parametric study. The feasibility of using strain gages was then demonstrated in model experiments in which values of the dynamic complex stress intensity factor (CSIF), , were obtained. Experiments were conducted using a PSM-1/aluminum bimaterial system subjected to quasi-static loading to determine and mixity φ. The first-order analysis of the strain gage data, which was conducted using two-gage and three-gage methods, resulted in values for CSIF, which compared very well to values of obtained from higher-order photoelastic analysis. Finally, a design curve was prepared to facilitate the analysis of dynamic interfacial crack propagation problems using strain gage techniques.     

Using Writing Assignments to Improve Self‐Assessment and Communication Skills in an Engineering Statics Course

This study explores the use of writing as a tool for metacognition in the engineering classroom. We used the “explain‐a‐problem” type of assignment in the Engineering Statics course for four terms. The objectives associated with the assignments were grouped under student self‐assessment, student communication, and administration. Performance on each of four grading criteria for each assignment was tracked throughout the terms. The data indicate that explain‐a‐problem does help students achieve the self‐assessment and communication objectives, although the impact on overall course performance was not as significant as hoped. The assignment evolved to the point that the administrative objectives were also met.     

Using an MQE chart based on a self-organizing map NN to monitor out-of-control signals in manufacturing processes

Control charts are recognized as one of the most important tools for statistical process control (SPC), used for monitoring any abnormal deviations in the state of manufacturing processes. However, the effectiveness of control charts is strictly dependent on statistical assumptions that in real applications are frequently violated. In contrast, neural networks (NNs) have excellent noise tolerance in real time, requiring no hypothesis on the statistical distribution of monitored processes. This feature makes NNs promising tools for quality control. In this paper, a self-organizing map (SOM)-based monitoring approach is proposed for enhancing the monitoring of processes. It is capable of providing a comprehensive and quantitative assessment value for the current process state, achieved by minimum quantization error (MQE) calculation. Based on MQE values over time series, a novel MQE chart is developed for monitoring process changes. The aim of this research is to analyse the performance of the MQE chart under the assumption that predictable abnormal patterns are not available. To this aim, the performance of the MQE chart in manufacturing processes (including non-correlated, auto-correlated and multivariate processes) is evaluated. The results indicate that the MQE chart may be a promising tool for quality control.     

Using queuing theory and simulated annealing to design the facility layout in an AGV-based modular manufacturing system

An automated guided vehicle-based flow production system is used for manufacturing prefabricated bathroom units. One unit can occupy a space of more than 10?m². Due to large time deviations in sequential processes, queues are formed and greater plant space is needed. Reducing work-in-progress helps to save plant space but renders manufacture less efficient. The research explores better workstation arrangements. An open queuing network (OQN) model was used to approximate the flow production system. Since the problem of workstation arrangement is a combinatorial optimisation problem, simulated annealing (SA) was applied to search for a good solution. The combination of an OQN model and SA provides a powerful tool to solve the facility layout problem for a stochastic flow production system. The experimental results show that the proposed approach has the potential to guide industrial layout design and practice.     

Using the lorentz transformation to simulate terahertz-range superradiance of picosecond electron bunches moving in an undulator field

The possibility of generating multimegawatt pulses of radiation in the terahertz range based on the phenomenon of superradiance of picosecond electron bunches moving in an undulator magnetic field is demonstrated by means of numerical simulations using a particle-in-cell (PIC) code. The analysis has been carried out in a reference system K?? moving with electrons, followed by a reverse transition to the laboratory reference system K, which significantly simplifies the simulation procedure due to the commensurate character of all spatial scales in the K?? system, including the radiation wavelength, electron bunch length, and duration of a pumping pulse train (into which the undulator field is transformed).     

Using the online and offline change model to improve efficiency for fast-track patients in an emergency department

BACKGROUND: In 1998 the emergency department (ED) Work Group at Johns Hopkins Bayview Medical Center (Baltimore) worked to reinvigorate the fast-track program within the ED to improve throughput for patients with minor illnesses and injuries who present for care. There had been two prior unsuccessful attempts to overhaul the fast-track process. METHODS: The work group used a change model intended to improve both processes and relationships for complex organizational problems that span departments and functional units. Before the first work group meeting, the work group evaluated the institutional commitment to address the issue. The next step was to find data to fully understand the issues and establish a baseline for evaluating improvements--for example, patients with minor illnesses and injuries had excessively long total ED (registration to discharge) times: 5 hours 57 minutes on average for nonacute patients. ONLINE AND OFFLINE MEETINGS: The work group identified process problems, but relationship barriers became evident as the new processes were discussed. Yet offline work was needed to minimize the potential for online surprises. The work group leaders met separately in small groups with nursing staff, lab staff, x-ray staff, registrars, and physician's assistants to inform them of data, obtain input about process changes, and address any potential concerns. The group conducted four tests of change (using Plan-Do-Study-Act cycles) to eliminate the root causes of slow turnaround identified previously. RESULTS: Total ED time decreased to an average of 1 hour 47 minutes; the practice of placing nonacute patients in fast track before all higher-acuity patients were seen gained acceptance. The percentage of higher-acuity patients sent to fast track decreased from 17% of all patients seen in fast track in January 1998 to 8.5% by February 1999. Patients with minor illnesses and injuries no longer had to wait behind higher-acuity patients just to be registered. The average wait for registration decreased from 42 minutes in January 1998 to 14 minutes in February 1999. Physician's assistant, nursing, and technician staff all report improved working relationships and feeling a team spirit. DISCUSSION: The offline component of the integrated model helped to improve organizational relationships and dialogue among team members, thereby facilitating the effectiveness of online efforts to improve processes. This model has also been applied to improve patient registration (revenue recovery) and the emergency transfer and admissions process.     

Using post-breakdown conduction study in a MIS structure to better understand the resistive switching mechanism in an MIM stack

We apply our understanding of the physics of failure in the post-breakdown regime of high-κ dielectric-based conventional logic transistors having a metal-insulator-semiconductor (MIS) structure to interpret the mechanism of resistive switching in resistive random-access memory (RRAM) technology metal-insulator-metal (MIM) stacks. Oxygen vacancies, gate metal migration and metal filament formation in the gate dielectric which constitute the chemistry of breakdown in the post-breakdown stage of logic gate stacks are attributed to be the mechanisms responsible for the SET process in RRAM technology. In this paper, we draw an analogy between the breakdown study in logic devices and filamentation physics in resistive non-volatile memory.     

On the Effect of Dielectric Breakdown in UD CFRPs Subjected to Lightning Strike Using an Experimentally Validated Model

Applied Composite Materials - To meet worldwide increases in energy demands Wind Turbine (WT) manufacturers are producing turbines with longer blades to generate more electrical energy. To...