Peter Wallace Johnson

In North America, Hispanic migrant farmworkers are being exposed to occupational ergonomic risks. Due to cultural differences in the perception and reporting of effort and pain, it was unknown whether standardized subjective ergonomic assessment tools could accurately estimate the directly measured their physical effort. This study investigated whether the subjective scales widely used in exercise physiology were associated with the direct measures of metabolic load and muscle fatigue in this population. Twenty-four migrant apple harvesters participated in this study. The Borg RPE in Spanish and the Omni RPE with pictures of tree-fruit harvesters were used for assessing overall effort at four time points during a full-day 8-h work shift. The Borg CR10 was used for assessing local discomfort at the shoulders. To determine whether there were associations between the subjective and direct measures of overall exertion measures, we conducted linear regressions of the percentage of heart rate reserve (% HRR) on the Borg RPE and Omni RPE. In terms of local discomfort, the median power frequency (MPF) of trapezius electromyography (EMG) was used for representing muscle fatigue. Then full-day measurements of muscle fatigue were regressed on the Borg CR10 changes from the beginning to the end of the work shift. The Omni RPE were found to be correlated with the % HRR. In addition, the Borg RPE were correlated to the % HRR after the break but not after the work. These scales might be useful for certain situations. In terms of local discomfort, the Borg CR10 were not correlated with the MPF of EMG and, therefore, could not replace direct measurement.

The basic principle of operation of a novel engine, which combines a thermosyphon with a Rankine engine, is introduced. The proposed configuration is a vertical sealed cylinder functioning as a combination of an evaporator, an insulated section and a condenser. An axial flow turbine is installed towards the upper end of the cylinder. The diameter of the turbine is less than the internal diameter of the cylinder to provide space for a jacket for the collection of the condensed fluid. The height difference between this liquid reservoir and the level of the liquid in the evaporator section provides the head required to return the liquid from the condenser to the evaporator. The turbine drives an electric generator which is directly coupled to it. Two wires through a sealed gland transfer the electric power to the external electrical load. The main applications of this combined thermosyphon and Rankine Engine, abbreviated to TSR Engine, are for power production from solar ponds and for waste heat utilisation. The theoretical formulation, as well as results from computer simulations and the experimental results on a prototype unit, is presented.

A heat pipe is a heat transfer device characterised by very high effective thermal conductivity up to 500 times greater than that of a solid copper bar of the same length and outer diameter. The focus of this paper will be on phase-change from liquid to vapour in the evaporator sections of heat pipes. The boiling phenomena in heat pipes and thermosiphons are analysed in relation to the general boiling correlation presented by Rohsenow [35] and experimentally observed by Nukiyama [32]. Different specific correlations developed for boiling in thermosiphons are compared with the general theory. The transition from nucleate boiling to film boiling has been experimentally observed and analysed by the authors. Future work is needed to develop a general theory of boiling in heat pipes and thermosiphons.

An automotive seat is a key component which not only provides restraint and support for its occupant, but also mitigates vibration. Since an automotive seat is in constant contact with the vehicle occupant, its dynamic comfort is of great importance in automotive seat designs. In this study, three automotive seats with different foam firmnesses were evaluated to understand how the foam firmness, through different foam formulations, affected the seat vibration performance and perceived dynamic comfort in a laboratory (study 1) and field setting (study 2). In a repeated-measures laboratory based study, whole-body vibration (per ISO 2631-1), self-reported body discomfort, and seating comfort were measured and compared among the three automotive seats while participants were exposed to tri-axial, field-measured, automotive vibration and X-Y-Z axis 1–30 Hz sine sweeps. In a subsequent ride-and-drive field study, the two seats that received the highest comfort ratings from the laboratory study were installed in two identical vehicles and whole body vibration (WBV) and self-reported seating comfort were evaluated by the participants. The results showed that the foam firmness significantly affected WBV measures and self-reported comfort (p < 0.05). This study demonstrated that altering foam formulation can be an effective way of further improving dynamic vibration and seat comfort performance.

Alternative techniques to assess physical exposures, such as prediction models, could facilitate more efficient epidemiological assessments in future large cohort studies examining physical exposures in relation to work-related musculoskeletal symptoms. The aim of this study was to evaluate two types of models that predict arm-wrist-hand physical exposures (i.e. muscle activity, wrist postures and kinematics, and keyboard and mouse forces) during computer use, which only differed with respect to the candidate predicting variables; (i) a full set of predicting variables, including self-reported factors, software-recorded computer usage patterns, and worksite measurements of anthropometrics and workstation set-up (full models); and (ii) a practical set of predicting variables, only including the self-reported factors and software-recorded computer usage patterns, that are relatively easy to assess (practical models). Prediction models were build using data from a field study among 117 office workers who were symptom-free at the time of measurement. Arm-wrist-hand physical exposures were measured for approximately two hours while workers performed their own computer work. Each worker’s anthropometry and workstation set-up were measured by an experimenter, computer usage patterns were recorded using software and self-reported factors (including individual factors, job characteristics, computer work behaviours, psychosocial factors, workstation set-up characteristics, and leisure-time activities) were collected by an online questionnaire. We determined the predictive quality of the models in terms of R² and root mean squared (RMS) values and exposure classification agreement to low-, medium-, and high-exposure categories (in the practical model only). The full models had R² values that ranged from 0.16 to 0.80, whereas for the practical models values ranged from 0.05 to 0.43. Interquartile ranges were not that different for the two models, indicating that only for some physical exposures the full models performed better. Relative RMS errors ranged between 5% and 19% for the full models, and between 10% and 19% for the practical model. When the predicted physical exposures were classified into low, medium, and high, classification agreement ranged from 26% to 71%. The full prediction models, based on self-reported factors, software-recorded computer usage patterns, and additional measurements of anthropometrics and workstation set-up, show a better predictive quality as compared to the practical models based on self-reported factors and recorded computer usage patterns only. However, predictive quality varied largely across different arm-wrist-hand exposure parameters. Future exploration of the relation between predicted physical exposure and symptoms is therefore only recommended for physical exposures that can be reasonably well predicted.

Laboratory studies have shown that exposure to whole-body vibration (WBV) increases physical and mental fatigue, which are common issues professional drivers face. The objective of this study was to determine whether altering WBV exposures had any effect on driver vigilance and discomfort. A repeated measures crossover design of five truck drivers with regular 10-h routes was used. Active and passive suspension truck seats were evaluated. For each seat, WBV exposures were measured. Participants completed a discomfort questionnaire and a reaction time task before and after their shift for two weeks, one week per seat. Compared with the passive seat, the active seat significantly reduced WBV exposures, decrements in the optimal and mean reaction times (p=0.02, 0.047, respectively), and discomfort in the lower back and wrist(s)/forearm(s) (p<0.01, 0.01, respectively). Study results indicated that reducing WBV helps reduce discomfort and maintain vigilance, which may improve drivers' health and reduce the risk of truck collisions.Practitioner Summary: The active suspension seat used in this study reduced truck drivers' exposure to whole-body vibration (WBV) by over 33% in relation to their current industry standard passive suspension seat. This study demonstrated that reducing truck drivers' exposure to WBV reduced fatigue and discomfort development over a workday.