柔性轮对结构振动对车辆动力学性能的影响

为研究轮对柔性对车辆动力学的影响,建立高速列车轮对的有限元模型,对轮对进行自由模态分析.通过模态综合法获取柔性轮对模态信息,应用多体系统动力学理论建立柔性轮对-刚性轨道接触力学模型;建立包含高速旋转柔性轮对的车辆-轨道耦合动力学模型,研究高速列车在直线和曲线通过时轮对结构振动对车辆动力学性能的影响.结果表明:轮对的结构振动对轮轨接触点位置、蠕滑率、蠕滑力和脱轨因数等均产生较明显的影响,但是对轮重减载率影响较小,因此应采用更加精确的柔性轮轨耦合模型研究轮轨相互作用、轮轨滚动接触疲劳和轮轨噪声等.     

A screening tool for occupations requiring a high level of attentional performance

Vigilance tasks with a high level of attentional demand are becoming more frequent in daily work. High levels of attentional demand are required in critical systems, such as air traffic control, crowd monitoring, visual quality inspection, or sports.In a previous study, we introduced an ecologically valid test for screening visual attention in the general working population. The test requires participants to complete a visual search task at a moderate level of difficulty. In the present work, we increased the test's level of difficulty to enable accurate screening of high levels of attentional skills. To establish reference data, attentional skills were recorded in 60 participants, ranging in age from 19 to 40, performing the test at both, moderate and high levels of difficulty.Increasing the difficulty level of the test resulted in a lower test performance score. Furthermore, an increased level of difficulty reduced the ceiling effects caused by highly-skilled participants. In the present report, we provide normative performance score data and evidence for the reliability of the developed test. Adapting the level of difficulty enables our attention test to effectively screen for attention in occupations requiring moderate or elevated attentional skills.Relevance to industryDemands for visual attention are increasing in a variety of industries. Therefore, screening for attentional performance is becoming more important in accident prevention and quality of work. A previously-reported ecologic test for screening visual attention at a moderate level of attention was adapted to enable screening at an elevated level of attentional demands.     

Comparative Analysis of the Design Techniques for Low Leakage SRAMs at 32nm

This paper presents a comprehensive overview of leakage reduction techniques prevailing in Static Random Access Memories (SRAMs) by classifying them in three categories namely latch, bitline and read port. The performance of the techniques are evaluated in terms of leakage reduction capability along with the impact on read performance and hold stability through extensive simulative investigations at 32 nm technology node by taking conventional SRAM cell as reference. Further, as SRAMs are susceptible to inter-die as well as intra-die process variations, the performance at different PVT corners is also captured to demonstrate the efficacy of each technique under PVT variations. It is found that among the techniques used for reducing latch leakages, Multi-threshold CMOS technique possess the highest leakage reduction capabilities followed by Drowsy mode and Substrate-bias techniques. The results also indicate that Negative word line technique is more effective at low supply voltages whereas the Leakage biased bitline technique is more effective at high supply voltages for reducing bitline leakages. Amongst the read port leakage reduction techniques, Stack-effect and Dynamic control of power supply rail techniques are capable of suppressing the leakages at high voltages whereas Virtual cell ground technique is more efficacious at low voltages. The impact of technology scaling on SRAM cell performance with leakage reduction techniques is also studied. For the sake of completeness, suggestions are put forward for adopting a particular technique to address leakages at latch, bitline and read port levels.     

Adaptation of performance during a week of simulated night work

This study aimed to provide a comparative index of the performance impairment associated with the fatigue levels frequently experienced in workplaces that require night work. To do this, we equated fatigue-related impairment with the impairment resulting from varying levels of alcohol intoxication. Fifteen young individuals participated in two counterbalanced conditions which required them to (1). 'work' seven consecutive 8-h night shifts, and (2). consume an alcoholic beverage at hourly intervals until their blood alcohol concentration (BAC) reached 0.10%. In each condition, performance was measured at hourly intervals using a 10-min psychomotor vigilance task (PVT). Analysis indicated that as BAC increased, performance impairment significantly increased. Similarly, response times significantly increased during the first six simulated night-shifts, and lapse frequency significantly increased during the first two shifts. Equating the two conditions indicated that the first simulated night shift was associated with the greatest degree of performance impairment. In general, the impairment at the end of this shift was greater than that observed at a BAC of 0.10%. During the second and third simulated night shifts, the performance impairment was less than on the first night, but greater than that observed at a BAC of 0.05%. For the final four nights, the performance decrements generally did not exceed those observed at a BAC of 0.05%. This suggests that during a week of consecutive night shifts, adaptation of performance occurs.     

Adaptation of performance during a week of simulated night work

This study aimed to provide a comparative index of the performance impairment associated with the fatigue levels frequently experienced in workplaces that require night work. To do this, we equated fatigue-related impairment with the impairment resulting from varying levels of alcohol intoxication. Fifteen young individuals participated in two counterbalanced conditions which required them to (1) ‘work’ seven consecutive 8-h night shifts, and (2) consume an alcoholic beverage at hourly intervals until their blood alcohol concentration (BAC) reached 0.10%. In each condition, performance was measured at hourly intervals using a 10-min psychomotor vigilance task (PVT). Analysis indicated that as BAC increased, performance impairment significantly increased. Similarly, response times significantly increased during the first six simulated night-shifts, and lapse frequency significantly increased during the first two shifts. Equating the two conditions indicated that the first simulated night shift was associated with the greatest degree of performance impairment. In general, the impairment at the end of this shift was greater than that observed at a BAC of 0.10%. During the second and third simulated night shifts, the performance impairment was less than on the first night, but greater than that observed at a BAC of 0.05%. For the final four nights, the performance decrements generally did not exceed those observed at a BAC of 0.05%. This suggests that during a week of consecutive night shifts, adaptation of performance occurs.     

The effects of fatigue on performance in simulated nursing work

Fatigue is associated with increased rates of medical errors and healthcare worker injuries, yet existing research in this sector has not considered multiple dimensions of fatigue simultaneously. This study evaluated hypothesised causal relationships between mental and physical fatigue and performance. High and low levels of mental and physical fatigue were induced in 16 participants during simulated nursing work tasks in a laboratory setting. Task-induced changes in fatigue dimensions were quantified using both subjective and objective measures, as were changes in performance on physical and mental tasks. Completing the simulated work tasks increased total fatigue, mental fatigue and physical fatigue in all experimental conditions. Higher physical fatigue adversely affected measures of physical and mental performance, whereas higher mental fatigue had a positive effect on one measure of mental performance. Overall, these results suggest causal effects between manipulated levels of mental and physical fatigue and task-induced changes in mental and physical performance.

Statement of Relevance: Nurse fatigue and performance has implications for patient and provider safety. Results from this study demonstrate the importance of a multidimensional view of fatigue in understanding the causal relationships between fatigue and performance. The findings can guide future work aimed at predicting fatigue-related performance decrements and designing interventions.     

The effects of fatigue on performance in simulated nursing work

Fatigue is associated with increased rates of medical errors and healthcare worker injuries, yet existing research in this sector has not considered multiple dimensions of fatigue simultaneously. This study evaluated hypothesised causal relationships between mental and physical fatigue and performance. High and low levels of mental and physical fatigue were induced in 16 participants during simulated nursing work tasks in a laboratory setting. Task-induced changes in fatigue dimensions were quantified using both subjective and objective measures, as were changes in performance on physical and mental tasks. Completing the simulated work tasks increased total fatigue, mental fatigue and physical fatigue in all experimental conditions. Higher physical fatigue adversely affected measures of physical and mental performance, whereas higher mental fatigue had a positive effect on one measure of mental performance. Overall, these results suggest causal effects between manipulated levels of mental and physical fatigue and task-induced changes in mental and physical performance. STATEMENT OF RELEVANCE: Nurse fatigue and performance has implications for patient and provider safety. Results from this study demonstrate the importance of a multidimensional view of fatigue in understanding the causal relationships between fatigue and performance. The findings can guide future work aimed at predicting fatigue-related performance decrements and designing interventions.     

Influence of fatigue time and level on increases in postural sway

The purpose of this study was to investigate the influence of fatigue time and fatigue level on the increases in postural sway during quiet standing. Centre of pressure-based measures of postural sway were collected both before and after fatiguing participants using three different fatigue levels and two different fatigue times. Results showed increasing fatigue time increased sway velocity and sway area, and increasing fatigue level increased sway velocity. Fatigue time effects are important to consider when applying laboratory-based findings to the field given that the fatigue time can differ substantially between the two. Fatigue level effects imply a dose - response relationship between localized muscle fatigue and risk of falling that can have important implications in work/rest cycle scheduling for occupations at risk of injurious falls.     

Influence of fatigue time and level on increases in postural sway

The purpose of this study was to investigate the influence of fatigue time and fatigue level on the increases in postural sway during quiet standing. Centre of pressure-based measures of postural sway were collected both before and after fatiguing participants using three different fatigue levels and two different fatigue times. Results showed increasing fatigue time increased sway velocity and sway area, and increasing fatigue level increased sway velocity. Fatigue time effects are important to consider when applying laboratory-based findings to the field given that the fatigue time can differ substantially between the two. Fatigue level effects imply a dose – response relationship between localized muscle fatigue and risk of falling that can have important implications in work/rest cycle scheduling for occupations at risk of injurious falls.     

CORRIGENDUM

The aim of this study was to assess the effects of four hours' continuous ‘ driving ’ in a ear simulator on (a) performance (number of steering errors and brake reaction time), (6) subjective fatigue, ( c) pulse rate, respiratory rate, skin resistance and neck muscle tension, ( d) intra-subject correlations between the latter variables and performance over time. An additional aim was to study these psychological and physiological measures when arousal was stimulated by the pairing of an electric shock with steering errors.

To control training effects the Ss repeated the experiment twice. The results showed that all subjects had a progressive performance decrement over time in parallel with increased feelings of fatigue. There was also a decrease in pulse rate and respiratory rate. Skin resistance showed continuous increment over time. Covariations over time between performance variables and physiological variables were rather high in most individuals; e.g. for pulse rate with frequency of steering errors, and EJ1G with frequency of steering errors. The expectation of an electric shock in connection with steering errors yielded higher subjective and autonomic arousal, slower performance decrement over time, and also lowered variability, both within and between subjects for all the variables recorded.     

The use of expert knowledge in the development of simulations for train driver training

The current study was undertaken to inform the development of simulations for improving train driver’s decision making under degraded track conditions. Trains are sophisticated heavy machinery and their performance is ever increasing resulting in the driving task becoming more complex and progressively dominated by cognitive and perceptual skills. A critical part of reducing the potential for train driver error and of increasing performance lies in the appropriate design of simulation training. In the current study a cognitive task analysis, using the critical decision method (CDM) was undertaken using a focus group research design. The process resulted in increased knowledge of expert train driver decision-making processes. Across four major incidents analyzed 11 decision points, 17 cues, 30 essential responsive actions and 45 possible errors where identified. The use of these results for supporting the design of simulation training and associated performance measures is discussed.     

灰色预测模糊自适应PID控制的城轨列车智能驾驶系统研究

为提高城轨列车驾驶系统的智能化程度，将灰色预测控制与模糊自适应PID控制技术相结合，应用到城轨列车驾驶系统中。在对城轨列车驾驶系统进行需求分析的基础上，针对其对各种性能指标的要求，提出了基于灰色预测模糊自适应PID控制的城轨列车智能驾驶系统的设计方案。将灰色预测控制与模糊自适应控制应用到经典PID控制中，设计出了系统的智能控制器，有效满足了城轨列车在运行时对跟踪误差、准点率、停车误差、舒适度和节能性等多个性能指标的要求。仿真结果表明：采用灰色预测模糊自适应PID算法的控制系统具有良好的控制精度且系统的智能化程度得到了相应的提升。     

Decision on economical rail grinding interval for controlling rolling contact fatigue

Rail players around the world have been increasing axle loads to improve the productivity of freight and heavy haul operations. This has increased the risk of surface cracks at curves because of rolling contact fatigue. Rail grinding has been considered an effective process for controlling these cracks and reducing risks of rail breaks. The complexity of deciding the optimal rail grinding intervals for improving the reliability and safety of rails is because of insufficient understanding of the various factors involved in the crack initiation and propagation process. This paper focuses on identifying the factors influencing rail degradation, developing models for rail failures and analyzing the costs of various grinding intervals for economic decision making. Various costs involved in rail maintenance, such as rail grinding, downtime, inspection, rail failures and derailment, and replacement of worn‐out rails, are incorporated into the total cost model developed in this paper. Field data from the rail industry have been used for illustration.     

The effect of work pace on workload, motor variability and fatigue during simulated light assembly work

This study investigated the effect of work pace on workload, motor variability and fatigue during light assembly work. Upper extremity kinematics and electromyography (EMG) were obtained on a cycle-to-cycle basis for eight participants during two conditions, corresponding to "normal" and "high" work pace according to a predetermined time system for engineering. Indicators of fatigue, pain sensitivity and performance were recorded before, during and after the task. The level and variability of muscle activity did not differ according to work pace, and manifestations of muscle fatigue or changed pain sensitivity were not observed. In the high work pace, however, participants moved more efficiently, they showed more variability in wrist speed and acceleration, but they also made more errors. These results suggest that an increased work pace, within the range addressed here, will not have any substantial adverse effects on acute motor performance and fatigue in light, cyclic assembly work. STATEMENT OF RELEVANCE: In the manufacturing industry, work pace is a key issue in production system design and hence of interest to ergonomists as well as engineers. In this laboratory study, increasing the work pace did not show adverse effects in terms of biomechanical exposures and muscle fatigue, but it did lead to more errors. For the industrial engineer, this observation suggests that an increase in work pace might diminish production quality, even without any noticeable fatigue being experienced by the operators.     

UK rail workers' perceptions of accident risk factors: An exploratory study

Although non-fatal injuries remain a frequent occurrence in Rail work, very few studies have attempted to identify the perceived factors contributing to accident risk using qualitative research methods. This paper presents the results from a thematic analysis of ten interviews with On Track Machine (OTM) operatives. The inductive methodological approach generated five themes, of which two are discussed here in detail, ‘Pressure and fatigue’, and ‘Decision making and errors’. It is concluded that for companies committed to proactive accident risk reduction, irrespective of current injury rates, the collection and analysis of worker narratives and broader psychological data across safety-critical job roles may prove beneficial.     

Associations between errors and contributing factors in aircraft maintenance

In recent years cognitive error models have provided insights into the unsafe acts that lead to many accidents in safety-critical environments. Most models of accident causation are based on the notion that human errors occur in the context of contributing factors. However, there is a lack of published information on possible links between specific errors and contributing factors. A total of 619 safety occurrences involving aircraft maintenance were reported using a self-completed questionnaire. Of these occurrences, 96% were related to the actions of maintenance personnel. The types of errors that were involved, and the contributing factors associated with those actions, were determined. Each type of error was associated with a particular set of contributing factors and with specific occurrence outcomes. Among the associations were links between memory lapses and fatigue and between rule violations and time pressure. Potential applications of this research include assisting with the design of accident prevention strategies, the estimation of human error probabilities, and the monitoring of organizational safety performance.     

ERRORS IN THE PERCEPTION OP RAILWAY SIGNALS

This paper is based upon observations of train drivers at work, and defines certain kinds of errors which may be made by drivers in perceiving railway signals. It discusses hypotheses relating incidence of error to various factors. It is suggested that the investigation of hypotheses of this kind, derived from the observation of the normal performance of the operative, is a valid method of accident study.     

Temporal strategy and performance during a fatiguing short-cycle repetitive task

This study investigated temporal changes in movement strategy and performance during fatiguing short-cycle work. Eighteen participants performed six 7-min work blocks with repetitive reaching movements at 0.5 Hz, each followed by a 5.5-min rest break for a total duration of 1 h. Electromyography (EMG) was collected continuously from the upper trapezius muscle, the temporal movement strategy and timing errors were obtained on a cycle-to-cycle basis, and perceived fatigue was rated before and after each work block. Clear signs of fatigue according to subjective ratings and EMG manifestations developed within each work block, as well as during the entire hour. For most participants, timing errors gradually increased, as did the waiting time at the near target. Changes in temporal movement strategy were negatively correlated with changes in the level and variability of EMG, suggesting that an adaptive temporal strategy offset the development of unstable motor solutions in this fatiguing, short-cycle work. PRACTITIONER SUMMARY: Sustained performance of operators is essential to maintain competitiveness. In this study of repetitive work, participants gradually changed their temporal movement strategy, for possibly alleviating the effects of fatigue. This suggests that in order to effectively counteract fatigue and sustain performance, industrial production should allow extensive spatial and temporal flexibility.     

Ergonomic stress levels, personal characteristics, accident occurrence and sickness absence among factory workers

This study was designed to evaluate the association of a single, integrated measure of simultaneous exposure to a number of adverse work and environmental conditions, termed the Ergonomic Stress Level (E-S-L), on workers' accident and sickness absence rates. The factors determining the E-S-L were body motion and posture, physical effort, active hazards and environmental stressors. E-S-L evaluation was based on 'walk-through' hazard inventories, direct observations, measurements and interviews. Workers were assigned to one of four stress levels ranging from low (A) to high (D). Subjects were 729 males, aged 20-67 years, employed in five factories in Israel. A linear relationship between E-S-L AND accident incidence was found, increasing from the lowest to the highest E-S-L. Moreover, workers more sensitive to environmental stressors, as indicated by their reported subjective annoyance, showed higher accident rates across all the ergonomic stress levels, a tendency which was statistically significant at levels C and D. On the other hand, sickness absence was significantly related to the overall subjective stress experienced, as manifested by reported job dissatisfaction and somatic complaints, and not directly to E-S-L. These findings highlight the role of aggregate work stress, coupled with individual sensitivity to environmental stressors, in increasing the risk of accidents.     

Assessment and monitoring of mental workload in subway train operations using physiological,subjective, and performance measures

Subway train operation is a complex, sociotechnical system that involves a variety of cognitively demanding tasks. The train operators are responsible for continuously monitoring the surrounding environment, maintaining awareness, processing information, and making decisions under risk. The resulting mental strain on operators can negatively affect their performance and the interaction of the human–machine system. The objective of this study was to evaluate if physiological, subjective, and performance measures could identify the level of mental workloads arising from routine and nonroutine operations in the subway system. A total of 11 subway train operators underwent different driving scenarios in a high‐fidelity simulator. The simulated tasks were divided into two categories: routine operations (preparing to drive and driving between stations without interruptions or emergencies) and nonroutine operation (responding to a tunnel fire, dealing with a high density of passengers, encountering a passenger/technician on the track, and responding to train failure). The mental workload was monitored and evaluated in these tasks using an electrocardiogram, subjective self‐rating scales, and driving performance. Both heart rate variability and performance measures (including reaction time and error rate) detected mental workload variations in the different operations. On the other hand, the subjective ratings (including NASA‐TLX) assessed the overall mental workload associated with a task, without explaining the mental demand variations within the task over time. Subway train drivers experienced different levels of mental workload during routine and nonroutine driving conditions. The findings of this study can be used to extract mental workload limits to optimize workload levels during train operations.