瓷和玻璃绝缘子人工污秽交流闪络特性及有效爬电系数的比较

人工污秽绝缘子的闪络电压、污闪电压梯度和有效爬电系数均与其材质和型式有关。国内虽对污闪特性研究较多，但对不同绝缘子的有效爬电系数研究不多。文中在人工雾室中对五种典型结构的瓷和玻璃绝缘子的污闪特性进行了试验研究。根据试验结果分析和计算了五种典型绝缘子的闪络电压、闪络电压梯度、有效爬电系数。结果表明：在人工污秽试验条件下，不同型式绝缘子的污闪电压有较大差异，盐密对不同型式绝缘子的闪络电压的影响程度也有差异；三伞型绝缘子和玻璃绝缘子具有较高的闪络电压；不同绝缘子的有效爬电系数与其结构型式和材质有关，玻璃绝缘子的有效爬电系数高于瓷绝缘子，且玻璃绝缘子的有效爬电系数随污秽程度的增加而增加，而瓷绝缘子的有效爬电系数随污秽程度的增加而减小。     

Work organization and Low back pain in nursing personnel

Nursing personnel are at a high risk from occupational low back injury. Work organization has been suggested as one factor playing a part in the aetiology of occupational low back pain. Baseline data for a prospective epidemiology study were gathered by means of a questionnaire. One part of the questionnaire elicited characteristics of work organization, perceived autonomy, the relationship with head nurse and satisfaction in the relationship with co-workers. Information on history of musculoskeletal problems, reported frequency of lifting and personal characteristics was also gathered. Of 787 nursing staff at two acute care hospitals, 154 (19-6%) reported troublesome low back pain occurring within the previous 6 months. From univariate analyses, such characteristics of work organization as shift, type of schedule and primary versus functional nursing were not associated with low back pain. The relationship with head nurse and perceived autonomy of the job also were not related to recent back pain. Recent low back pain was significantly associated with younger age, the job category ‘registered nurse’ and greater satisfaction in relationships with co-workers. These associations were confirmed in multivariate analysis. None of the work organization factors examined, with the exception of satisfaction with co-workers, were associated with back pain in this study. Moreover, the positive association of satisfaction with coworkers suggests that interventions to improve working relationships may not be helpful in prevention programmes. To some extent, these results are susceptible to biases resulting from selective attrition from nursing and selective participation in the study.     

Participation in workplace design with reference to low back pain: a case for the improvement of the police patrol car

Thirty Canadian police officers, divided into six groups, participated in the redesign of the interior of the patrol car. Three of the groups consisted of individuals having a history of low back disease. The effect of participating in a design process on the characteristics of the final design and on the perception of the low back pain was studied in a semi-experimental setting. The participants developed a strong commitment to the participatory design process, which was reflected in their productions. The differences between participants with and without a history of a low back disease was not marked. The former tended to stress posture-related elements in their analysis and design.     

Simulation analysis of the effects of a back surface field on a p-a-Si:H/n-c-Si/n+-a-Si:H heterojunction solar cell

In order to investigate the effects of a back surface field（BSF） on the performance of a p-doped amorphous silicon（p-a-Si：H）/n-doped crystalline silicon（n-c-Si） solar cell,a heterojunction solar cell with a p-a-Si：H/n-c-Si/n^＋-a-Si：H structure was designed.An n^＋-a-Si：H film was deposited on the back of an n-c-Si wafer as the BSF.The photovoltaic performance of p-a-Si：H/n-c-Si/n^＋-a-Si：H solar cells were simulated.It was shown that the BSF of the p-a-Si：H/n-c-Si/n^＋-a-Si：H solar cells could effectively inhibit the decrease of the cell performance caused by interface states.     

The influence of skill and low back pain on trunk postures and low back loads of shearers

Shearing is a rural occupation developing considerable spinal loads and carrying a high risk of low back pain (LBP). Although the workforce has a skill structure, interaction between skill, spinal loads and LBP is unknown. We examined whether skill and LBP influenced trunk postures and loads within a sample of 80 shearers representing shear skill levels. A progression from junior to open class demonstrated a 100% increase in productivity, less time in severe flexion, more time in neutral lateral bend, and more time in axially twisted postures, with no increase in cumulative compressive and anterior shear forces. LBP prevalence increased linearly from 10% for junior through to 76% for open class shearers. Shearers with a history of LBP generated greater cumulative right medio-lateral shear forces, greater left lateral bend and left axial twist moments. Skill-based training that reduces asymmetric forces may help reduce such high prevalence levels of LBP.

Statement of Relevance: Shearing is an important and physically demanding rural occupation. It requires sustained flexed postures that generate considerable spinal loads and a high risk of LBP. This research examines how skill and a history of LBP it carries interact to influence trunk postures and spinal loads within a sample of shearers.     

The influence of lift frequency,lift duration and work experience on discomfort reporting

Discomfort surveys are commonly used to assess risk in the workplace and prioritize jobs for interventions before an injury or illness occurs. However, discomfort is a subjective measure and the relationship of discomfort to work-related factors is poorly understood. The objective of this study was to understand how reports of discomfort relate to work-related risk factors for the low back. A total of 12 novice and 12 experienced manual materials handlers performed repetitive, asymmetric lifts at different load levels and at six different lift frequencies throughout an 8-h exposure period. Discomfort was recorded hourly throughout the day. Analyses were performed to determine which experimental factors influenced reporting of discomfort and if discomfort trends matched spine loading trends. Novice lifters reported significantly higher discomfort levels than experienced subjects. They also reported increases in discomfort as moment exposure increased and as the exposure time increased. Novices lifting at 8 Nm load moment level reported increased discomfort from 0.07 to 0.63 by the end of the day, at 36 Nm they reported an increase from 0.04 to 0.40 and at 85 Nm they reported an increase from 0.37 to 3.06. Experienced subjects, on the other hand, reported low levels of discomfort regardless of moment exposure, lift frequency or exposure duration. The reported discomforts were generally unrelated to the biomechanical loading on the spine. Discomfort reporting appears to be more a reflection of experience than of work risk factor exposure. Experienced subjects may have more efficient motor patterns, which reduce spinal load and thus discomfort. Novice subjects seemed to have a lower threshold of discomfort. Caution is needed when using discomfort reporting as a means to identify jobs in need of interventions, in that biomechanical loading may not be accurately represented. Discomfort should only be used as a supplement to objective measures, such as spinal loading, to assess the risk of low back disorders.     

Evaluation of artificial neural network modelling to predict torso muscle activity

Owing to the complexities involved in obtaining direct measures of in vivo muscle forces, validation of predictive models of muscle activity has been difficult. An artificial neural network (ANN) model had been previously developed for the estimation of lumbar muscle activity during moderate levels of static exertion. The predictive ability of this model is evaluated in this study using several techniques, including comparison of response surfaces and composite statistical tests of values derived from model output, with multiple EMG experimental datasets. ANN-predicted activation levels were accurately modelled to within 3% across a range of experiments and levels of combined flexion/extension and lateroflexion loadings. The results indicate both a high degree of consistency in the averaged muscle activity measured in several different experiments, and substantiate the ability of the ANN model to predict generalized recruitment patterns. It also is suggested that the use of multiple comparison methods provides a better indication of model behaviour and prediction accuracy than a single evaluation criterion.     

Research to reality: a critical review of the validity of various criteria for the prevention of occupationally induced low back pain disability

Criteria have been suggested to reduce the incidence, or severity of low back pain disability. Five underlying theories for such criteria have been identified in the literature, and a critical review of the validity of these criteria has been carried out. Despite attributions elsewhere, peer-reviewed validation of the various criteria range from modest to nil. The need for a validation criterion for use in workplace design in order to reduce low back pain disability, or severity, is identified and the need for an international protocol to allow cross-study validation of present and future criteria is suggested.     

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.     

Margin of safety for the human back: a probable consensus based on published studies

Despite numerous efforts to control occurrences of work-related low back pain, it continues to be a significant problem. Since the causation of low back pain is under multifactorial control, it is suggested that the factor most vulnerable at any given time will determine the safety. Epidemiological, biomechanical, physiological, and psychophysical information presented in published literature has been analysed. The data available are related to injuries and the projected margin of safety. This paper therefore, is an integrative, inferential synthesis of the published work to discern the margin of safety. An attempt has been made to conclude, on the basis of objective evidence, an all encompassing criterion to ensure the safety of the back. The psychophysical approach appears to integrate biomechanical and physiological variables on a short term basis in the studies surveyed. However, it remains to be proven that the sensory conditioning due to prolonged and repetitive occupational tasks will remain responsive to cumulative load and fatigue failures.