A Numerical Approach to Stability of Multiclass Queueing Networks

The Multi-class Queueing Network (McQN) arises as a natural multi-class extension of the traditional (single-class) Jackson network. In a single-class network subcriticality (i.e. subunitary nominal workload at every station) entails stability, but this is no longer sufficient when jobs/customers of different classes (i.e. with different service requirements and/or routing scheme) visit the same server; therefore, analytical conditions for stability of McQNs are lacking, in general. In this note we design a numerical (simulation-based) method for determining the stability region of a McQN, in terms of arrival rate(s). Our method exploits certain (stochastic) monotonicity properties enjoyed by the associated Markovian queue-configuration process. Stochastic monotonicity is a quite common feature of queueing models and can be easily established in the single-class framework (Jackson networks); recently, also for a wide class of McQNs, including first-come-first-serve (FCFS) networks, monotonicity properties have been established. Here, we provide a minimal set of conditions under which the method performs correctly. Eventually, we illustrate the use of our numerical method by presenting a set of numerical experiments, covering both single and multi-class networks

C-MOS array design techniques: SUMC multiprocessor system study

The current capabilities of LSI techniques for speed and reliability, plus the possibilities of assembling large configurations of LSI logic and storage elements, have demanded the study of multiprocessors and multiprocessing techniques, problems, and potentialities. Evaluated are three previous systems studies for a space ultrareliable modular computer multiprocessing system, and a new multiprocessing system is proposed that is flexibly configured with up to four central processors, four 1/0 processors, and 16 main memory units, plus auxiliary memory and peripheral devices. This multiprocessor system features a multilevel interrupt, qualified S/360 compatibility for ground-based generation of programs, virtual memory management of a storage hierarchy through 1/0 processors, and multiport access to multiple and shared memory units

Stability of preemptive EDF queueing networks

We show stability of preemptive, strictly subcritical EDF networks with Markovian routing. To this end, we prove that the associated fluid limits satisfy the first-in-system, first-out (FISFO) fluid model equations and thus, by an extension of a result of Bramson (2001), the corresponding fluid models are stable. We also demonstrate that in a preemptive multiclass EDF network, after a time large enough to process all the initial customers to completion, the maximal number of partially served customers in the system over a finite time horizon converges to zero in $L^1$ under fluid scaling

Control-friendly scheduling algorithms for multi-tool, multi-product manufacturing systems

textThe fabrication of semiconductor devices is a highly competitive and capital intensive industry. Due to the high costs of building wafer fabrication facilities (fabs), it is expected that products should be made efficiently with respect to both time and material, and that expensive unit operations (tools) should be utilized as much as possible. The process flow is characterized by frequent machine failures, drifting tool states, parallel processing, and reentrant flows. In addition, the competitive nature of the industry requires products to be made quickly and within tight tolerances. All of these factors conspire to make both the scheduling of product flow through the system and the control of product quality metrics extremely difficult. Up to now, much research has been done on the two problems separately, but until recently, interactions between the two systems, which can sometimes be detrimental to one another, have mostly been ignored. The research contained here seeks to tackle the scheduling problem by utilizing objectives based on control system parameters in order that the two systems might behave in a more beneficial manner. A non-threaded control system is used that models the multi-tool, multi-product process in a state space form, and estimates the states using a Kalman filter. Additionally, the process flow is modeled by a discrete event simulation. The two systems are then merged to give a representation of the overall system. Two control system matrices, the estimate error covariance matrix from the Kalman filter and a square form of the system observability matrix called the information matrix, are used to generate several control-based scheduling algorithms. These methods are then tested against more tradition approaches from the scheduling literature to determine their effectiveness on both the basis of how well they maintain the outputs near their targets and how well they minimize the cycle time of the products in the system. The two metrics are viewed simultaneously through use of Pareto plots and merits of the various scheduling methods are judged on the basis of Pareto optimality for several test cases.Chemical Engineerin

Optimization of multiclass queueing networks : polyhedral and nonlinear characterization of achievable performance

Includes bibliographical references (p. 48-50).Supported by the National Science Foundation. ECS-8552419 Supported by the Presidential Young Investigator Award. DDM-9158118 Supported by the Draper Laboratory and by the Leaders for Manufacturing Program at MIT. Supported by the ARO. DAAL03-92-G0309Dimitris Bertsimas, Ioannis Ch. Paschalidis, John N. Tsitsiklis

The Operations Research Approach for an Effective Management Information System

This report serves as an overview to the design of an effective Management Information System (MIS) by incorporating the modeling techniques of an Operations Research (OR) approach. It will be shown that the consideration of OR input requirements mixed with the information requirements for a data base existing at the everyday accounting and operational level creates a responsible management control and decision-making tool. This mix of OR and everyday information approach varies as a function of the managerial activities and the organizational level of effort. In lieu of designing a total MIS system, MIS designers should structure a loosely connected federation of MIS sub-systems using the appropriate mix which, for each of the operations, controlling, and planning activities, meets the problem-solvers\u27 requirements. A discussion of the background, definitions, and attributes of MIS and OR will be made in Chapters I and II prior to merging these two entities into a unified concept. Chapter III will develop this concept. A manufacturing organization environment will serve as a point of reference for the formulation of models in the application areas of sales forecasting, production, manpower planning, inventory control, and machine center utilization. I am not proposing a pipedream non-realistic approach to a MIS system design that will solve all of management\u27s problems. However, by planting the seeds of OR modeling techniques in the early phase of the design and development, the MIS system will, like a tree, in 3 to 5 years bear the fruit of today\u27s careful planning

Nondestructive Evaluation of Additive Manufacturing State-of-the-Discipline Report

This report summarizes the National Aeronautics and Space Administrations (NASA) state of the art of nondestructive evaluation (NDE) for additive manufacturing (AM), or "3-D printed", hardware. NASA's unique need for highly customized spacecraft and instrumentation is suited for AM, which offers a compelling alternative to traditional subtractive manufacturing approaches. The Agency has an opportunity to push the envelope on how this technology is used in zero gravity, an enable in-space manufacturing of flight spares and replacement hardware crucial for long-duration, manned missions to Mars. The Agency is leveraging AM technology developed internally and by industry, academia, and other government agencies for its unique needs. Recent technical interchange meetings and workshops attended by NASA have identified NDE as a universal need for all aspects of additive manufacturing. The impact of NDE on AM is cross cutting and spans materials, processing quality assurance, testing and modeling disciplines. Appropriate NDE methods are needed before, during, and after the AM production process

Semantics and logics for signals

In operating systems such as Unix, processes can interact via signals. Signal handling resembles both exception handling and concurrent interleaving of processes. The handlers can be installed dynamically by the main program, but signals arrive non-deterministically; therefore, a handler may interrupt a program at any point. However, the interleaving of actions is not symmetric, in that the handler interrupts the main program, but not conversely. This thesis presents operational semantics and program logic for an idealized form of signal handling. To make signal handling logically tractable, we define handling to be block-structured. To reason about the interleaving of signal handlers, we adopt the idea of binary relations on states from rely-guarantee logics, imposing rely conditions on handlers. Given the one-way interleaving of signal handlers, the logic is less symmetric than rely-guarantee. We combine signal and exception handlers in the same language to investigate their interactions, specifically whether a handler can run more than once or is linearly used. We prove soundness of the program logic relative to a big-step operational semantics for signal handling. Then, we introduce and discuss reentrancy in various domains. Finally, we present our work towards logic with Reentrancy Linear Type System