Publications

This peper presents a parallel algorithm for optimal control problems. The parallelism is applied at the algorithmic level, which suggests the use of a real-time parallel programming language of high level as for example Ada. The algorithm is formulated as number of rules which control the execution of its main tasks: the "gradient" tasks and the "object function" tasks, to be run concurrently. Simulation experiments are used to compare the performance of the proposed algorithm with that of the corresponding sequential one. ©IEEE

Process hierarchy and inheritance make it possible to add new properties to existing objects of simulation models. Thus, the user can construct complex models using a code developed earlier. This feature is discussed and its implementation in the language PASION is pointed out. Examples are given. ©SAGE

The Queuing Model Generator (QMG), described in this article, is a module of the environment of the simulation language PASION. It contains a block-diagram editor which permits the user to define the structure of the model, and a program generator which generates the corresponding PASION code. This code is automatically translated to PASCAL. QMG is transpar ent, (i.e. the languages PASION and PASCAL are not visible for "non-program mer" users.) However, if the user knows PASION or PASCAL, then he can work with the resulting code, creating more complex models. An application in flexible manufacturing systems design is described.

It is pointed out that a major limitation of graphical user interfaces for simulation is that users such as managers and decision makers need to know too much. The author examines the weaknesses inherent in graphical user interfaces to support these users of simulation for short-term situation assessment and scenario evaluation, a style of problem-solving characteristic of military and factory command-and-control. He then presents Shoptalk, a factory command-and-control system with an interface integrating direct manipulation and natural-language processing, and demonstrates how the Shoptalk style of interaction can overcome these limitations.

The productivity of present day industrial robots may be hampered by phenomena such as vibrations and deformations which appear whenever they are made to move at high speeds or to carry heavy payloads. To address this problem, many researchers have studied the flexibility of robot arms. Most works, however, rely on simple one or two-link flexible arms made with extremely flexible beams which operate at very slow speeds. Thus their results may prove difficult to apply to more realistic situations. The CEIT flexible robot is a lightweight three degree of freedom flexible arm which has been built to bridge this gap between flexible and industrial robots. The structural behavior of this robot is investigated through experimental modal analysis. The procedure and results of the analysis are described in this paper.< >

Using low conversion bulk copolymerization experimental data and the apparent rate constant model, the monomer chain cross‐transfer rate constants and the cross‐termination coefficient were evaluated. It was found that the dependence of the cross‐termination coefficient on composition is a function of initiator efficiency and that monomer chain cross‐transfer rate constant are relevant for the theoretical estimation of the molecular weights and molecular weight distributions.

Two examples of models formulated in terms of the Ordinary Differential Equations (ODE) are given. It is pointed out that, in certain situations, the ODE- based models commonly used in system dynamics may be completely wrong. Even in some very simple models of the dynamics of populations it is not certain that any finite state vector of the system exists, which means that the corresponding finite ODE model does not exist. If the modeled system is nonlinear, the existence of solutions to the ODE model is important. The mapping from the space of disturbances to the space of corresponding trajectories may be discontinuous, even if the right-hand sides of the equations are continuous. This may cause errors when simplified models are used. A possible application of the discrete event and object-oriented simulation instead of the ODE models is suggested.

New TiB2-based cermets have been consolidated by hot isostatic pressing of powder mixtures of TiB2 and metallic alloys based on Fe, Ni and Co additions. Relevant thermodynamic aspects of the systems B-Ti-Ni, B-Ti-Fe and B-Ti-Co, essential for avoiding the formation of extremely brittle secondary borides, especially the secondary boride M23B6, are discussed in this work. The role of contaminants like oxygen, carbon and nitrogen, which can also lead to the formation of these compounds is also explained. The hardness, toughness and cutting behaviour of the cermets produced with these new binder phases are comparable with the highest commercial WC-Co grades.

No abstract available.

There is no doubt that this century has witnessed great technological innovations and a great deal of industrial progress, all of which has modified in an important manner life on this planet. This progress has brought many great benefits; on the other hand, there have been some changes in our environment that are harmful to our health in both the short and long run. In order to reduce these problems, some programs have been started all around the world. At the labor level, this industrial progress has increased worker exposure to different chemical and physical agents, some of which have a known noxious effect. Generally, knowledge of these harmful actions and the consequences of exposure to these industrial agents has been acquired only after serious accidents in the workplace that have exposed the problem and are the basis for the preventative measures that have to be taken to keep new cases from occurring.

Abstract For an analysis of the acoustical properties of a multistage gear mechanism, a technique was used that combines a dynamic calculation of the mechanism as multimass multicoupling system and the SEA method for the calculation of acoustical energy. The dynamic calculation was used to determine the energy introduced into the mechanism’s gear meshes and the energy transmitted to the housing. The SEA method was used for the calculation of propagation of acoustical energy in the structure and its radiation in the surrounding space. Such a combination permits us to utilize the advantage of dynamic calculation accurately describing the mechanism’s performance and the SEA method for describing an acoustical model having the elements of high mode density in a wide frequency range. Some useful results were obtained which permit us to reduce noise level of the mechanism.

Object-oriented simulation is an excellent tool while treating models of complex systems. The model can be decomposed into several submodels and the structure of the simulation program can be similar to the structure of the real system. In this article the problem of simulation and control of a set of interconnected induction motors is considered. Models of such kind can be useful while working on control problems for complex mechanisms driven by multiple motors, such as belt or chain conveyers or some transport facilities. In particular, an application of the simulation system PASION™ is described. Possible applications of the model in control problems related to the system stability and performance are pointed out.

Abstract An analysis of possibilities for the selection of tool geometry parameters was made to reduce tooth profile errors during grinding of gears by different methods. The selection of parameters was based on the analysis of the grid diagram of a gear and a rack. Some formulas and graphs are presented for the selection of the pressure angle, module and addendum of the rack-tool. The results of grinding of experimental gears confirm the theoretical analysis.

No abstract available.

El desgaste de materiales en el horno alto puede realizarse bajo la consideración de mecanismos estrictamente abrasivos o con el predominio de las componentes químicas y erosivas resultantes de la circulación de fluidos sobre el refractario. No obstante, aunque en determinadas situaciones, la abrasión o las componentes químicas pueden resultar los mecanismos controlantes, es necesario considerar que todos ellos (abrasión, erosión, desgaste químico, adhesión y desgaste térmico-choque térmico) "cooperan" en la degradación del refractario del horno, Para cualquiera de los mecanismos que intervenga en el desgaste de los materiales, resulta conveniente conocer el valor de la temperatura a lo largo de las intercaras del refractario con los sólidos, líquidos o gases presentes en el horno. En la ponencia será desarrollada de forma específica, la importancia que tiene la temperatura en la intercara refractario-arrabio sobre el desgaste de los materiales del crisol. Se discutirán las diferentes hipótesis de transporte (energía, cantidad de movimiento y materia) más adecuadas para la obtención de la temperatura de intercara.

In Barrett's esophagus, stratified squamous mucosa of the lower third of the esophagus is replaced by columnar mucosa, as a complication of chronic gastroesophageal reflux. The presence of Barrett's esophagus appears to be a major factor in the progression to adenocarcinoma of the lower third of the esophagus. Therefore it is crucial to identify the subset of patients at risk for the development of adenocarcinoma. Dysplasia is an important histologic feature to evaluate because it identifies those patients who require follow-up. The diagnosis of biopsies with lesser degrees of abnormalities, however, makes microscopic evaluation less helpful in identifying patients who need more frequent endoscopic biopsy surveillance. DNA ploidy and the use of monoclonal antibodies, such as suppressor gene product p53, oncogene cerbB-2, and Ki-67, have added dramatically to our understanding of the biology of Barrett's metaplasia and have given us objective indicators to predict the presence of an increased risk of developing cancer. © Lippincott-Raven Publishers

We present a case of a 48-year-old woman with a solitary fibrous tumor localized in the carotid bifurcation clinically simulating a chemodectoma. The tumor was composed of spindle cells with abundant intercellular collagen. These spindle cells were positive for CD34 and negative for chromogranin, S-100 protein, NSE, GFAP, and cytokeratin. This is the first solitary fibrous tumor reported in this location, in the English literature. © International Journal of Surgical Pathology