Development a distributed simulation environment on a cluster of workstations

Simulation has traditionally been used for analyzing the behavior of complex real world problems. Even though only some features of the problems are considered, simulation time tends to become quite high even for common simulation problems. Parallel and distributed simulation is a viable technique for accelerating the simulations. The success of parallel simulation depends heavily on the combination of the simulation application, algorithm and message population in the simulation is sufficient, no additional delay is caused by this environment. In this thesis a conservative, parallel simulation algorithm is applied to the simulation of a cellular network application in a distributed workstation environment. This thesis presents a distributed simulation environment, Diworse, which is based on the use of networked workstations. The distributed environment is considered especially hard for conservative simulation algorithms due to the high cost of communication. In this thesis, however, the distributed environment is shown to be a viable alternative if the amount of communication is kept reasonable. Novel ideas of multiple message simulation and channel reduction enable efficient use of this environment for the simulation of a cellular network application. The distribution of the simulation is based on a modification of the well known Chandy-Misra deadlock avoidance algorithm with null messages. The basic Chandy Misra algorithm is modified by using the null message cancellation and multiple message simulation techniques. The modifications reduce the amount of null messages and the time required for their execution, thus reducing the simulation time required. The null message cancellation technique reduces the processing time of null messages as the arriving null message cancels other non processed null messages. The multiple message simulation forms groups of messages as it simulates several messages before it releases the new created messages. If the message population in the simulation is suffiecient, no additional delay is caused by this operation A new technique for considering the simulation application is also presented. The performance is improved by establishing a neighborhood for the simulation elements. The neighborhood concept is based on a channel reduction technique, where the properties of the application exclusively determine which connections are necessary when a certain accuracy for simulation results is required. Distributed simulation is also analyzed in order to find out the effect of the different elements in the implemented simulation environment. This analysis is performed by using critical path analysis. Critical path analysis allows determination of a lower bound for the simulation time. In this thesis critical times are computed for sequential and parallel traces. The analysis based on sequential traces reveals the parallel properties of the application whereas the analysis based on parallel traces reveals the properties of the environment and the distribution.

Integrated engineering workstations in electrical engineering laboratories

This paper provides a description of integrated engineering workstations (IEW’s) used in undergraduate electrical engineering laboratories. The IEW’s are used for the design, analysis, and testing of engineering systems. Examples of laboratory experiments and software programs are presented.

Children's Postures While Playing at Computer Workstations

There has been a significant increase in the incidence of musculoskeletal disorders (MSD) and the costs associated with these are predicted to increase as the popularity of computer use increases at home, school and work. Risk factors have been identified in the adult population but little is known about the risk factors for children and youth. Research has demonstrated that they are not immune to this risk and that they are self reporting the same pain as adults. The purpose of the study was to examine children’s postures while working at computer workstations under two conditions. One was at an ergonomically adjusted children’s workstation while the second was at an average adult workstation. A Polhemus Fastrak™ system was used to record the children’s postures and joint and segment angles were quantified. Results of the study showed that children reported more discomfort and effort at the adult workstation. Segment and joint angles showed significant differences through the upper limb at the adult workstation. Of significance was the strategy of shoulder abduction and flexion that the children used in order to place their hand on the mouse. Ulnar deviation was also greater at the adult workstation as was neck extension. All of these factors have been identified in the literature as increasing the risk for injury. A comparison of the children’s posture while playing at the children’s workstation verses the adult workstation, showed that the postural angles assumed by the children at an adult workstation exceeded the Occupational Safety and Health Association (OSHA) recommendations. Further investigation is needed to increase our knowledge of MSD in children as their potential for long term damage has yet to be determined.

Safe maintenance guidelines for robotic workstations /

Mode of access: Internet.

A mathematical model for assembly line balancing model to consider disordering sequence of workstations

Purpose – A binary integer programming model for the simple assembly line balancing problem (SALBP), which is well known as SALBP-1, was formulated more than 30 years ago. Since then, a number of researchers have extended the model for the variants of assembly line balancing problem.The model is still prevalent nowadays mainly because of the lower and upper bounds on task assignment. These properties avoid significant increase of decision variables. The purpose of this paper is to use an example to show that the model may lead to a confusing solution. Design/methodology/approach – The paper provides a remedial constraint set for the model to rectify the disordered sequence problem. Findings – The paper presents proof that the assembly line balancing model formulated by Patterson and Albracht may lead to a confusing solution. Originality/value – No one previously has found that the commonly used model is incorrect.

Children's Postures While Playing at Computer Workstations

There has been a significant increase in the incidence of musculoskeletal disorders (MSD) and the costs associated with these are predicted to increase as the popularity of computer use increases at home, school and work. Risk factors have been identified in the adult population but little is known about the risk factors for children and youth. Research has demonstrated that they are not immune to this risk and that they are self reporting the same pain as adults. The purpose of the study was to examine children’s postures while working at computer workstations under two conditions. One was at an ergonomically adjusted children’s workstation while the second was at an average adult workstation. A Polhemus Fastrak™ system was used to record the children’s postures and joint and segment angles were quantified. Results of the study showed that children reported more discomfort and effort at the adult workstation. Segment and joint angles showed significant differences through the upper limb at the adult workstation. Of significance was the strategy of shoulder abduction and flexion that the children used in order to place their hand on the mouse. Ulnar deviation was also greater at the adult workstation as was neck extension. All of these factors have been identified in the literature as increasing the risk for injury. A comparison of the children’s posture while playing at the children’s workstation verses the adult workstation, showed that the postural angles assumed by the children at an adult workstation exceeded the Occupational Safety and Health Association (OSHA) recommendations. Further investigation is needed to increase our knowledge of MSD in children as their potential for long term damage has yet to be determined.

Integrating the age factor in designing industrial environments and workstations in the workforce ageing era

As people spend a third of their lives at work and, in most cases, indoors, the work environment assumes crucial importance. The continuous and dynamic interaction between people and the working environment surrounding them produces physiological and psychological effects on operators. Recognizing the substantial impact of comfort and well-being on employee satisfaction and job performance, the literature underscores the need for industries to implement indoor environment control strategies to ensure long-term success and profitability. However, managing physical risks (i.e., ergonomic and microclimate) in industrial environments is often constrained by production and energy requirements. In the food processing industry, for example, the safety of perishable products dictates storage temperatures that do not allow for operator comfort. Conversely, warehouses dedicated to non-perishable products often lack cooling systems to limit energy expenditure, reaching high temperatures in the summer period. Moreover, exceptional events, like the COVID-19 pandemic, introduce new constraints, with recommendations impacting thermal stress and respiratory health. Furthermore, the thesis highlights how workers' variables, particularly the aging process, reduce tolerance to environmental stresses. Consequently, prolonged exposure to environmental stress conditions at work results in cardiovascular disease and musculoskeletal disorders. In response to the global trend of an aging workforce, the thesis bridges a literature gap by proposing methods and models that integrate the age factor into comfort assessment. It aims to present technical and technological solutions to mitigate microclimate risks in industrial environments, ultimately seeking innovative ways to enhance the aging workforce's comfort, performance, experience, and skills. The research outlines a logical-conceptual scheme with three main areas of focus: analyzing factors influencing the work environment, recognizing constraints to worker comfort, and designing solutions. The results significantly contribute to science by laying the foundation for new research in worker health and safety in an ageing working population's extremely current industrial context.

Ergonomic Planned Supply in an Automotive Assembly Line

The objective of this research is to identify the benefits of ergonomic improvements in workstations and in planned parts supply in an automotive assembly line. Another aim is to verify to what extent it is possible to create competitive advantages in the manufacturing area with reduction in vehicle assembly time by using technological investments in ergonomics with benefits to the worker and to the company. The Methods Time Measurement (MTM) methodology is chosen to measure the process time differences. To ensure a reliable comparison, a company in Brazil that has two different types of assembly line installations in the same plant was observed, and both assembly lines were under the same influences in terms of human resources, wages, food, and educational level of the staff. In this article, the first assembly line is called ""new"" and was built 6 years ago, with high investments in ergonomic solutions, in the supply system, and in the process. The other is called ""traditional"" and was built 23 years ago with few investments in the area. (C) 2010 Wiley Periodicals, Inc.

Determination of particle concentration in the breathing zone for four different types of office ventilation systems

Many factors affect the airflow patterns, thermal comfort, contaminant removal efficiency and indoor air quality at individual workstations in office buildings. In this study, four ventilation systems were used in a test chamber designed to represent an area of a typical office building floor and reproduce the real characteristics of a modern office space. Measurements of particle concentration and thermal parameters (temperature and velocity) were carried out for each of the following types of ventilation systems: (a) conventional air distribution system with ceiling supply and return; (b) conventional air distribution system with ceiling supply and return near the floor; (c) underfloor air distribution system; and (d) split system. The measurements aimed to analyse the particle removal efficiency in the breathing zone and the impact of particle concentration on an individual at the workstation. The efficiency of the ventilation system was analysed by measuring particle size and concentration, ventilation effectiveness and the indoor/outdoor ratio. Each ventilation system showed different airflow patterns and the efficiency of each ventilation system in the removal of the particles in the breathing zone showed no correlation with particle size and the various methods of analyses used. (C) 2008 Elsevier Ltd. All rights reserved.

Visual Display Height

We examined the influence of backrest inclination and vergence demand on the posture and gaze angle that-workers adopt to view visual targets placed in different vertical locations. In the study 12 participants viewed a small video monitor placed in 7 locations around a 0.65-m radius arc (from 650 below to 300 above horizontal eye height). Trunk posture was manipulated by changing the backrest inclination of an adjustable chair. Vergence demand was manipulated by using ophthalmic lenses and prisms to mimic the visual consequences of varying target distance. Changes in vertical target location caused large changes in atlantooccipital posture and gaze angle. Cervical posture was altered to a lesser extent by changes in vertical target location. Participants compensated for changes in backrest inclination by changing cervical posture, though they did not significantly alter atlanto-occipital posture and gaze angle. The posture adopted to view any target represents a compromise between visual and musculoskeletal demands. These results provide support for the argument that the optimal location of visual targets is at least 15 below horizontal eye level. Actual or potential applications of this work include the layout of computer workstations and the viewing of displays from a seated posture.

Fungal and microbial volatile organic compounds exposure assessment in a waste sorting plant

In the management of solid waste, pollutants over a wide range are released with different routes of exposure for workers. The potential for synergism among the pollutants raises concerns about potential adverse health effects, and there are still many uncertainties involved in exposure assessment. In this study, conventional (culture-based) and molecular real-time polymerase chain reaction (RTPCR) methodologies were used to assess fungal air contamination in a waste-sorting plant which focused on the presence of three potential pathogenic/toxigenic fungal species: Aspergillus flavus, A. fumigatus, and Stachybotrys chartarum. In addition, microbial volatile organic compounds (MVOC) were measured by photoionization detection. For all analysis, samplings were performed at five different workstations inside the facilities and also outdoors as a reference. Penicillium sp. were the most common species found at all plant locations. Pathogenic/toxigenic species (A. fumigatus and S. chartarum) were detected at two different workstations by RTPCR but not by culture-based techniques. MVOC concentration indoors ranged between 0 and 8.9 ppm (average 5.3 ± 3.16 ppm). Our results illustrated the advantage of combining both conventional and molecular methodologies in fungal exposure assessment. Together with MVOC analyses in indoor air, data obtained allow for a more precise evaluation of potential health risks associated with bioaerosol exposure. Consequently, with this knowledge, strategies may be developed for effective protection of the workers.

Balanceamento de linhas de produção usando algoritmos genéticos

Aquando da definição de um layout por fluxo de produto, ou linha de produção, é necessário proceder-se à melhor selecção de combinações de tarefas a serem executadas em cada estação / posto de trabalho para que o trabalho seja executado numa sequência exequível e sejam necessárias quantidades de tempo aproximadamente iguais em cada estação / posto de trabalho. Este processo é chamado de balanceamento da linha de produção. Verifica-se que as estações de trabalho e equipamentos podem ser combinados de muitas maneiras diferentes; daí que a necessidade de efectuar o balanceamento das linhas de produção implique a distribuição de actividades sequenciais por postos de trabalho de modo a permitir uma elevada utilização de trabalho e de equipamentos e a minimizar o tempo de vazio. Os problemas de balanceamento de linhas são tipicamente problemas complexos de tratar, devido ao elevado número de combinações possíveis. Entre os métodos utilizados para resolver estes problemas encontram-se métodos de tentativa e erro, métodos heurísticos, métodos computacionais de avaliação de diferentes opções até se encontrar uma boa solução e métodos de optimização. O objectivo deste trabalho passou pelo desenvolvimento de uma ferramenta computacional para efectuar o balanceamento de linhas de produção recorrendo a algoritmos genéticos. Foi desenvolvida uma aplicação que implementa dois algoritmos genéticos, um primeiro que obtém soluções para o problema e um segundo que optimiza essas soluções, associada a uma interface gráfica em C# que permite a inserção do problema e a visualização de resultados. Obtiveram-se resultados exequíveis demonstrando vantagens em relação aos métodos heurísticos, pois é possível obter-se mais do que uma solução. Além disso, para problemas complexos torna-se mais prático o uso da aplicação desenvolvida. No entanto, esta aplicação permite no máximo seis precedências por cada operação e resultados com o máximo de nove estações de trabalho.