On ratings of comfort and exertion by visual display unit users and ratings of workplace layout and working posture by expert ergonomists

Data sets comparing ratings of comfort and perceived exertion by visual display unit (VDU) users with ratings of workplace layout and working posture by expert ergonomists were published by Lindeg?rd et al. [2005. Concordance between VDU-users' ratings of comfort and perceived exertion with experts' observations of workplace layout and working postures. Appl. Ergon. 36, 319-325]. The present paper corrects the conclusions that were drawn. Users' and experts' ratings were very largely independent of each other. It is also noted that polychoric correlation is often an appropriate statistic for summarising the association in ordered tables of frequencies.     

Psychophysically determined symmetric and asymmetric lifting capacity of Chinese males for one hour's work shifts

A laboratory experiment was conducted to determine the effects of asymmetric lifting on psychophysically determined maximum acceptable weight of lift (MAWL) and the resulting heart rate, oxygen uptake and rating of perceived exertion. Thirteen male college students were recruited as participants. Each participant performed 12 different lifting tasks involving three lifting frequencies (one-time maximum, 1 and 4 lifts/min) and four twisting angles (including the sagittal plane and three different angles of asymmetry, i.e., 0, 30, 60, and 90°) from the floor to a 76 cm high pallet for one hour's work shift using a free-style lifting technique. The results showed that: (1) The MAWLs were significantly lower for asymmetric lifting than for symmetric lifting in the sagittal plane. The MAWL decreased with an increase in the angle of asymmetry, however, the heart rate, oxygen uptake and RPE remained unchanged; (2) Lifting frequency had no significant effect on the percentage decrease in MAWL from the sagittal plane values. Correction factors of 4, 9, and 13% for MAWL at 0, 30, 60, and 90°of asymmetric lifting, respectively, are recommended; (3) Both the physiological costs (heart rate and oxygen uptake) and rating of perceived exertion increased with an increase in lifting frequency though maximum acceptable weight of lift decreased. The most stressed body parts were the lower back and the arm; and (4) The percentage decrease in MAWL with twisting angle for the Chinese participants was somewhat lower than those of the Occidental participants. In addition, even though there was a decrease in MAWL, heart rate and RPE increased with an increase in the angle of a symmetric lifting for the Occidental participants, it was different from that of the Chinese participants.

Relevance to industry

It is generally believed that asymmetric lifting involving torso twisting is more harmful to back spine than symmetric lifting. However, the previous studies were conducted in Europe and North America, and the data were obtained from the Caucasian populations. This work, therefore, aims to investigate the influence of asymmetric lifting on the lifting capacity of the Chinese participants, and to compare the differences with the Occidental populations.     

Simplifying Proofs in Fitch-Style Natural Deduction Systems

We present an algorithm for simplifying Fitch-style natural-deduction proofs in classical first-order logic. We formalize Fitch-style natural deduction as a denotational proof language,, with a rigorous syntax and semantics. Based on that formalization, we define an array of simplifying transformations and show them to be terminating and to respect the formal semantics of the language. We also show that the transformations never increase the size or complexity of a deduction – in the worst case, they produce deductions of the same size and complexity as the original. We present several examples of proofs containing various types of superfluous “detours,” and explain how our procedure eliminates them, resulting in smaller and cleaner deductions. All of the transformations are fully implemented in SML-NJ, and the complete code listing is available on the Web.