Mathematical models for analysis and synthesis of spatial mechanisms—III Six-link spatial mechanismsMathematische modelle zur analyse und synthese von räumlichen mechanismen. Teil 3: räumliche mechanismen mit sechs gelenken

In this paper the decomposition method for kinematic synthesis and analysis is extended to all 6-link, single-loop spatial mechanisms. This is accomplished by solving sets of equations which can be used to describe mathematical models of all 6-link spatial mechanisms. These sets of equations are solved sequentially in an organised way by subdividing the sets of equations into groups of equations which describe the intersection of two planes with a unit radius sphere (computer programme PREB3), and the intersection of a plane and a unit radius sphere (computer programme PREB2). By way of examples mathematical models for RRRTRR, RRPRTR, RTRPRP, RRPPRC spatial mechanisms are described which are representative of the 130 distinct 6-link spatial mechanisms.     

Periodic cycling of plate columns: Analytical solution

An analytical solution of the equations for periodic cycling of plate columns has been obtained in a closed form which is suitable for rapid calculation on a computer. The solution covers a wide range of parameters including the slope of the equilibrium and operating lines, plate efficiency, fraction of the liquid holdup transferred per cycle and the number of plates in the column. It is shown that under certain conditions improvements of more than 100% in the separating ability of plate columns are theoretically possible when the column is operated in the periodic cycling mode.     

Statistical Prediction Model for EMC. Analysis of Out-of-Band Phased Array Antennas

A statistical model was developed for predicting and describing the out-of-band pattern characteristics of phased arrays containing ferrite phase shifters. Statistical analysis techniques are necessary because experimental investigations showed that the propagation of higher-order modes at out-of-band frequencies cause phased arrays containing ferrite phase shifters not only to respond differently at out-of-band frequencies but also to exhibit random behavior. Equations were derived which relate the out-of-band pattern scanning properties, relative gain levels, median gain, and standard deviation to the in-band scan angle and the ferrite phase shifter statistics. Computer algorithms were written to both compute and graphically display the out-of-band antenna patterns. Experimentally derived phase-shift data were used as inputs to the model. The results of these investigations show that statistical analysis techniques are potentially very useful in an EMC context for characterizing out-of-band responses of phased array antennas     

Effects of training and experience on perception of hazard and risk

This study was designed to show how those proficient at a machining task, where proficiency was gained through both training and past experience, influence the perceived hazard and risk when observing Computer Numerical Control (CNC) machining. The study was also designed to determine whether the impact of the visual and auditory cues can be isolated during diagnosis of the hazard. In a study that included 40 participants, results show that trained observers can perceive more correctly a hazardous condition which is different from what one would predict based on psychophysics. The results also show that trained participants relied strongly on the auditory cues to diagnose the potential hazard and risk correctly whereas the untrained participants who had access to both auditory and visual senses perceived the potential hazard more incorrectly than those trained and more similarly to a traditional Stevens' psychophysical curve. Untrained subjects who had only auditory input had the most difficulty in distinguishing differences in the perception of hazard. This is important considering recent dialogue about whether there is a need to train for tasks that will be automated. The idea of training, especially for automated tasks, is important in allowing better recognition of hazard and risk in unusual circumstances. Additional research may help to improve the diagnosis of hazard and risk and may enable generalization of the results to other training scenarios in the manufacturing and services industries.     

Review of Work motivation: History, theory, research, and practice.

Reviews the book, Work motivation: History, theory, research, and practice by Gary Latham (see record 2006-11764-000). The reviewer commends Latham for writing an empirically comprehensive and "personal" book on work motivation. Included is a history of work motivation studies throughout the last 100 years, directions for future research, and the author's reflections on what he has learned about the field on his own professional and personal journey through life. The reviewer praises the author's style highly, and recommends this book to all. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Validation of a Three-Dimensional Transmission Line Matrix (TLM) Model Implementation of a Mode-Stirred Reverberation Chamber

Reverberation chambers are attractive electromagnetic compatibility test facilities, both economically and technically. Careful design and analysis of these facilities are important, if the results obtained are to be treated with a high level of confidence. Numerical modeling is an important part of the process of reverberation chamber design and analysis. Hence, it is important that the modeling techniques to be used are appropriately validated. Much of the published work to date takes either a statistical or a deterministic view of validation. This paper provides validation evidence for a low-resolution transmission line matrix (TLM) model of a reverberation chamber in a manner approximating the way in which the chamber is used, i.e., validating based on the effects of a simple device under test. A variety of statistical and heuristic approaches have been used to quantify the level of agreement, intending to set the likely lower bound for the quality of comparisons between simulations and measurements. While not drawing any "universal" conclusions about the veracity of the TLM technique, the paper concludes that a relatively simple model of a reverberation chamber provides a useful analysis of the chamber with close comparisons between modeled and measured data.     

Toward a hybrid model for usability resource allocation in industrial software product development

The organizational aspects of user‐centered software development in a financial services company are presented. The financial services industry sector is one of the industrial sectors to embark on the development of computer software as a consumer product. The nature of business in the service sector predisposes it to encounter difficulties in developing software aimed at meeting customer demands. Lack of familiarity and experience with the product design and implementation processes, as well as reliance on usability for acceptance, are major obstacles encountered. Difficulties, insights, and lessons learned regarding organizational ergonomics issues faced by a user‐centered design group are provided, and a hybrid resource distribution model is proposed to guide other service sector companies in their future software development efforts. © 2007 Wiley Periodicals, Inc. Hum Factors Man 17: 245–262, 2007.     

Exploring minimal scenarios to produce transversely bright electron beams using the eigen-emittance concept

Next generation hard X-ray free electron lasers require electron beams with low transverse emittance. One proposal to achieve these low emittances is to exploit the eigen-emittance values of the beam. The eigen-emittances are invariant under linear beam transport and equivalent to the emittances in an uncorrelated beam. If a correlated beam with two small eigen-emittances can be produced, removal of the correlations via appropriate optics will lead to two small emittance values, provided non-linear effects are not too large. We study how such a beam may be produced using minimal linear correlations. We find it is theoretically possible to produce such a beam, however, it may be more difficult to realize in practice. We identify linear correlations that may lead to physically realizable emittance schemes and discuss promising future avenues.     

Understanding the mechanisms behind coking pressure: Relationship to pore structure

During carbonisation coal undergoes both physical and chemical changes that result in the generation of gas and tar and the formation of an intermediate plastic state. This transformation is known to generate high internal gas pressures for some coals during carbonisation that translate to high pressures at the oven wall. In this study, three low volatile coals A, B and C with oven wall pressures of 100 kPa, 60 kPa and 20 kPa respectively were investigated using high-temperature rheometry, ¹H NMR, thermogravimetric analysis and SEM, with the primary aim to better understand the mechanisms behind the coking pressure phenomenon. Rheometer plate displacement measurements (ΔL) have shown differences in the expansion and contraction behaviour of the three coals, which seem to correlate with changes in rheological properties; while SEM images have shown that the expansion process coincides with development of pore structure. It is considered that the point of maximum plate height (ΔL_max) prior to contraction may be indicative of a cell opening or pore network forming process, based on analogies with other foam systems. Such a process may be considered important for coking pressure since it provides a potential mechanism for volatile escape, relieving internal gas pressure and inducing charge contraction. For coal C, which has the highest fluidity ΔL_max occurs quite early in the softening process and consequently a large degree of contraction is observed; while for the lower fluidity coal B, the process is delayed since pore development and consequently wall thinning progress at a slower rate. When ΔL_max is attained, a lower degree of contraction is observed because the event occurs closer to resolidification where the increasing viscosity/elasticity can stabilise the expanded pore structure. For coal A which is relatively high fluidity, but also high coking pressure, a greater degree of swelling is observed prior to cell rupture, which may be due to greater fluid elasticity during the expansion process. This excessive expansion is considered to be a potential reason for its high coking pressure.     

Complexity analysis of a decentralised graph colouring algorithm

Colouring a graph with its chromatic number of colours is known to be NP-hard. Identifying an algorithm in which decisions are made locally with no information about the graph's global structure is particularly challenging. In this article we analyse the complexity of a decentralised colouring algorithm that has recently been proposed for channel selection in wireless computer networks.