A Note on the Role of Peripheral Vision in Static Balancing

The ability to balance statically using minimal visual cues was investigated experimentally. It was found that sighted levels of proficiency wore not consistently achiovod in tho absence of background structure.     

Book Review

Six unilateral above-knee amputees using prostheses with quadrilateral sockets of the ischial-bearing typo, who were otherwise able-bodied persons, were evaluated economically by subjecting them to the physical exercise of walking on level ground with graded loads by shoulder pack or rucksack method

During tests, the energy expenditure, oxygen consumption, pulmonary ventilation and peak heart rate were measured for each subject. Performances of the teat group subjects were compared with those of a control group comprising six normal, healthy, adult males of sedentary habits

Results showed a consistently high rise in all the physiological parameters for the test group even when walking without loads and with graded loads as compared to the corresponding values from control subjects. In other words the tasks undertaken by the test group subjects appeared to be heavy according to the existing norms of heaviness of work. Thus the tasks which may be ‘ light ‘ for normal individuals may become ‘ heavy ’ or ‘ very heavy ’ for the above-knee amputees and encroach greatly on their physiological reserves

This study has shown that evaluative tests combining both static and dynamic muscular work in addition to the usual leg work involved in a routine lower extremity activity, render diminutive effects to personal factors contributing variability in the performance of above-knee amputees fitted with prostheses. From this point of view the present study and the mode of tasting have proved to be an improvement over the methods employed by Ganguli et al. (1974), thus setting up norms for above-knee rehabilitee performance.     

Changes in the body size of UK and US children over the past three decades

The major sources of published anthropometric data on children are now over two decades old. Due to concern being expressed regarding the continued validity of such data, changes in the body sizes of the UK child population over the past three decades have been considered. Comparisons were also made between the size of the current UK child population to the current US child population, and to the most comprehensive source of measured data on US children (but which are now over 20 years old). The growth of children in the UK and US over the past three decades was assessed for an indication of secular growth trends. Stature increases were found to have generally been less than body weight increases (as a percentage) at 5th percentile, mean and 95th percentile levels for UK children, and UK children were found to be closer in size to US children now than they were 30 years ago.     

Mismatch between classroom furniture and anthropometric measures in Chilean schools

Children spend about five hours per day sitting down while doing their school work. Considering this as well as the potential inadequate use of school furniture, it is likely that some anatomical-functional changes and problems in the learning process may occur. The aim of this study was to compare furniture sizes within three different schools with the anthropometric characteristics of Chilean students in the Valparaíso region, in order to evaluate the potential mismatch between them. The sample consisted of 195 volunteer students (94 male, 101 female) of the 8th grade, ranging from 12.5 to 14.5 years of age from 3 different schools. Regarding the methodology, 6 anthropometric measures (Stature, Popliteal height, Buttock-popliteal length, Elbow height while sitting, Hip width, Thigh thickness and Subscapular height) were gathered, as well as 8 dimensions from the school furniture. For the evaluation of classroom furniture a match criterion equation was defined. After considering the existing classroom furniture dimensions in each match criterion equation, the anthropometric characteristics of the considered population were compared in order to determine the mismatch between them. Results indicated that seat height, which should be considered as the starting point for the design of classroom furniture, was appropriate for students' popliteal height in only 14% of the 2 out of the 3 schools, and 28% in the third. Seat to desk height was too high and mismatched 99% of the students in one school and 100% in the others. Therefore, it was possible to conclude that the classroom's furniture was inadequate in almost all the analyzed cases and subjects. It is possible that the high mismatch percentage found between furniture and students' anthropometry can be associated to the fact that the acquisition and selection of the furniture was made without any ergonomic concern or criteria.     

The Role of Static Pedestrian Groups in Crowded Spaces

It was hypothesized that groups of static pedestrians would play an important role in determining pattorns of movement in crowded spaces. This was investigated in five ticket halls in the London Underground. Queues, groups of people using automatic ticket machines, and other types of static groups were observed. The location of these groups was related to the layout of the space, and their general effects on movement through the space were assessed. It was found that under certain conditions static groups impede movement and diminish the effective width of key movoment channels. Although the study was exploratory, the results suggest a number of ways in which the layout of certain types of space might be optimized in terms of the criteria considered.     

DRIVERS' GALVANIC SKIN RESPONSE AND THE RISK OF ACCIDENT

Galvanic skin responses of 20 drivers were measured in two studies covering a wide range of roads and road conditions. Accident histories wore obtained for the roads in one of the studies. It is shown that the level of GSR activity does not depend primarily on the nature of the road or conditions. Consistent sources of variation in the GSR are observed, one of them apparently being the subject's experience of driving. The distribution of GSR per unit distance travelled was found to be similar to the distribution of accidents per unit total distance of vehicle travel (the accident rate). The results support a view that driving is a self-paced task governed' by the level of emotional tension or anxiety which the driver wishes to tolerate. The possible effects of this on the distribution of accidents is discussed.     

Warning signal words: connoted strength and understandability by children,elders, and non-native English speakers

Signal words, such as DANGER, WARNING and CAUTION, are commonly used in sign and product label warnings for the purpose of conveying different levels of hazard. Previous research has focused on whether people's perceptions of connoted hazard are consistent with the levels suggested by design standards and guidelines. Most investigations have used college students to evaluate the terms; other populations who may be at greater risk have not been adequately studied. One purpose of the present research was to determine whether young children, the elderly, and non-native English speakers perceive similar connoted hazard levels from the terms as undergraduates and published guidelines. A second purpose was to assess the terms' comprehensibility using various metrics such as missing values (i.e. ratings left blank) and understandability ratings. A third purpose was to develop a list of potential signal words that probably would be understandable to members of special populations. In the first experiment, 298 fourth- to eighth-grade students and 70 undergraduates rated 43 potential signal words on how careful they would be after seeing each term. The undergraduates also rated the terms on strength and understandability. In the second experiment, 98 elders and 135 non-native English speakers rated the same set of terms. The rank ordering of the words was found to be consistent across the participant groups. In general, the younger students gave higher carefulness ratings than the undergraduates. The words that the younger children and the non-native English speakers frequently left blank were given lower understandibility ratings. Finally, a short list of terms was derived that 95% or 99% of the youngest students (fourth- and fifth-graders) and 80% of the non-native English speakers understood. Implications of hazard communication are discussed.     

Plenary Discussion: Relevance of Physiological and Psychological Criteria to Man-Machine Systems: The Present State of the Art

Abstract

Ergonomics seems to be more physiologically-oriented than does human factors engineering, its American counterpart. Quantitative support for this view is provided by content analyses of papers presented at certain meetings of two European and one American professional society, and of papers published in the journals Ergonomics and Human Factors. Several possibilities are adduced to account for this divergent emphasis placed on the use of physiological and psychological criteria. More serious than such differences is that it is not immediately apparent how most criteria used in ergonomic and human factors research relate to the criteria that are used for the design and evaluation of systems. If we are to have a viable technology we need to be able to show the relationship between the criteria used in experimental work and those used in the practical world.     

域间动态角色转换中的静态互斥角色约束违反

安全互操作是实现跨管理域的资源共享与保护的关键技术. Kapadia等人的IRBAC2000模型提供了一种灵活的通过角色关联和动态角色转换实现安全互操作的方法..廖俊国等人指出该模型可能违反静态互斥角色约束,对问题的原因进行了分析,提出了约束违反检测算法和添加角色关联的先决条件.首先指出廖俊国等人关于约束违反原因的分析是片面的,其检测算法和先决条件也不能保证系统不会违反约束;然后指出在给定角色关联的前提下,外域的用户/角色分配是造成约束违反的根本原因;进而提出动态角色转换违反静态互斥角色约束的充要条件和约束违反检测算法;给出了添加角色关联和用户/角色分配的先决条件,保证了模型状态始终满足静态互斥角色约束.     

The ergonomics of different tyres and tyre pressure during wheelchair propulsion

It is believed that the newer solid tyres on wheelchairs perform as well as pneumatic tyres along with less cost and time for maintenance. The questions are: (1) do solid tyres perform as well as pneumatic tyres and (2) what is the critical level of pneumatic tyre pressure before wheeling efficiency decreases? Part one measured the rolling resistance differences of five commonly used wheelchair tyres (three pneumatic and two solid) under four different tyre pressures (100, 75, 50 and 25 of inflation). Part two measured the oxygen consumption in 15 participants with paraplegia, during wheelchair propulsion, comparing the same four levels of tyre inflation. The solid tyres performed worse than all three pneumatic tyres even when tyres were under-inflated to 25% of tyre pressure. Two of the pneumatic tyres showed significant decreases in rolling between 100 and 50%, but there were no significant differences in rolling distance between 100 and 75% pressure. The physiological study showed that energy expenditure increased significantly at 50% of tyre-inflation. Health care facilities are finding ways to decrease cost by using solid tyres on all wheelchairs. This study shows that benefits to clients and staff using pneumatic tyres far outweigh the minimal cost in time to maintain adequate tyre inflation.     

基于链式SVG三相不平衡负荷的平衡补偿方法的仿真分析

本文对链式静止无功发生器的工作原理进行了分析,在深入研究三相不平衡负荷的平衡化补偿原理的基础上,提出了一种基于链式静止无功发生器在不平衡补偿时的分相补偿控制方法.该方法是通过对静止无功发生器各相输出电压与电网电压的相角差δ进行调节来控制各相输出电流,从而可以有效地对三相负载不平衡的系统进行平衡补偿.对所提出的补偿方法进行了仿真研究,仿真结果表明运用分相控制方法补偿三相不平衡负载,具有比较好的稳态补偿效果,补偿后电网电流三相平衡,各相电流与电压基本同相位并且幅值成相同的比例,达到了负载功率平衡和无功补偿的目的.     

Computing Vision Points in Polygons

We consider a restricted version of the art gallery problem within simple polygons in which the guards are required to lie on a given one-dimensional object, a watchman route. We call this problem the vision point problem . We prove the following: • The original art gallery problem is NP-hard for the very restricted class of street polygons. • The vision point problem can be solved efficiently for the class of street polygons. • A linear time algorithm for the vision point problem exists for the subclass of street polygons called straight walkable polygons. Received June 6, 1996; revised September 12, 1997.     

Risk and effectiveness criteria for using on-product warnings

A variety of potential hazards can be identified for nearly any consumer product, often more than can be practically or effectively addressed with warning labels. Published standards and guidelines for warnings do not offer a reasonable basis for limiting the number and length of warning labels. This paper proposes criteria for the use and design of warning labels based on effectiveness research, accident data, and product-associated risk.     

Arm strength and impulse generation: Initiation of wheelchair movement by the physically disabled

The initiation of wheelchair movement is a function of starting technique, upper extremity strength and the stabilizing potential of the trunk musculature. This study examined the relation between arm strength, activity level, degree of disability and the maximum impulse generated from a resting position while seated in a wheelchair. Two starting techniques were examined using a force platform.

Sixteen male paraplegic adults (age 28·1 ±6·9 year, supine length l·62±0·16m, total body mass 61·2±16·2 kg) performed three grab starts and three strike starts on a Kistler force platform. For each technique, the processed data were averaged together and impulse in the forward/backward and vertical directions was determined. Isokinetic shoulder flexion and elbow extension moments of force were measured at an angular velocity of 60 degs^?1. Peak power and average power were calculated from digitized values of the moment of force-time curves.

Subjects were classified as highly active (HA, >2 exercise periods per week, N = 8) or less active (LA, N = 8). In addition, the site of spinal cord injury was quantified as a high level lesion (HL, above T10, N = 7) or low level lesion (LL, N = 9). There were no differences (p>0·05) between activity or lesion level groups with respect to age, height, total body mass or skinfold thicknesses. Nor were there significant differences between groups for shoulder and elbow power values. However, shoulder flexion scores for the combined groups were greater than those scores for elbow extension (peak power, 72·9 W versus 49·5 W; average power, 51·8 W versus 37·2 W). The grab start produced more forward impulse (the integral of forward force × time) (152·6 N s) than the strike start (119·5 N s, p < 0·05), but the magnitude of this difference was similar for the several groups. Wheelchair impulse scores were well correlated with strength values in both HA and LA subjects (r=0·74 to 0·89). However, the intercepts of the regression lines were dissimilar between activity groups, suggesting an interaction between activity pattern, muscle force and impulse.     

比例伺服阀静动态特性仿真建模

建立准确的比例伺服阀静动态特性仿真模型,对研究液压伺服系统具有重要的意义。由于比例伺服阀的静动态特性随输入信号的幅值变化而变化,难以用单一数学公式准确表达,而且样本所提供的性能数据往往有限,给比例伺服阀准确的仿真建模带来不便。以产品样本为依据,利用比例伺服阀仿真建模的方法,首先建立了比例伺服阀详细的数学模型,通过对产品样本的分析,分析了比例伺服阀静动特性的组成形式;利用MATLAB软件,建立了仿真模型;将仿真结果性能曲线数据化,并运用仿真模型中相关参数进行了辨识。仿真结果表明,模型的幅相频曲线和流量曲线与产品样本上的性能参数基本一致;说明仿真建模的方法是可行的。     

Mathland: The Role of Mathematics in Virtual Architecture

This paper is dedicated to some arguments that could be of interest both for students and practicing architects. A short adventure in the reign of mathematics and culture. The example that I have chosen is that of the idea of space, how this idea and the perception of space around us has changed up to the point where it has arrived to the form of virtual architecture.     

Static Frequency Assignment in Cellular Networks

A cellular network is generally modeled as a subgraph of the triangular lattice. In the static frequency assignment problem, each vertex of the graph is a base station in the network, and has associated with it an integer weight that represents the number of calls that must be served at the vertex by assigning distinct frequencies per call. The edges of the graph model interference constraints for frequencies assigned to neighboring stations. The static frequency assignment problem can be abstracted as a graph multicoloring problem. We describe an efficient algorithm to multicolor optimally any weighted even or odd length cycle representing a cellular network. This result is further extended to any outerplanar graph. For the problem of multicoloring an arbitrary connected subgraph of the triangular lattice, we demonstrate an approximation algorithm which guarantees that no more than 4/3 times the minimum number of required colors are used. Further, we show that this algorithm can be implemented in a distributed manner, where each station needs to have knowledge only of the weights at a small neighborhood. Received May 13, 1997; revised August 24, 1998.     

Errors of visual judgement in precision measurements

Abstract

Measurement is one of the most widely practiced social activities of people, and in many instances, measurements are made manually by individuals. On the other hand, automation of measurement has made rapid progress in recent years, but is not always advantageous. For example, even automatic measuring instruments are calibrated manually in many instances, and manual calibration will still be needed in the future. One of the problems to be considered in conjunction with manual measurement is error in measurement, especially personal error, which varies in degree according to the individual.

This paper is concerned with the causes of personal error in precision measurements which require strict control of errors, especially those of measurements involving visual judgements by observers of measuring instruments. What is called visual judgement can be divided into (i) judgement by the presence or absence of a stimulus, (ii) judgement by the intensity of the stimulus and (iii) judgement by comparison of the stimulus; we have conducted experiments on measurements involving these three. The results show that in case (i) where judgement relies on the coincidence between the corner of the image and the reference line, individual differences in visual ability are reflected in personal error, and the simpler the visual ability required for judgement, the smaller the degree of personal error in measurement; in the case of (ii)where judgement relies on the observation of outline of the pattern, i.e. judgement through the measurement of the dimensions of an indistinct image, the standards of the judgement of the observer is reflected in personal error; and in the case of (iii), where judgement relies on the visual interpolation of distance between two scale lines, the optical illusion of distance between the lines causes personal error.