A unique pure mechanical system revealing dipole repulsion

We study multiple elastic collisions of a block and a ball against a rigid wall in one dimension. The complete trajectory of the block is solved as an analytic function of time. Near the turning point of the block the force carried by the ball is proportional to 1/x^3, where x is the distance between the wall and the block, in the limit that the block is sufficiently heavier than the ball. This is a unique pure mechanical system that reveals dipole-like repulsion.Comment: 20 pages, 3 figures, 1 table, version published in Am. J. Phy

Nondestructive evaluation techniques for nickel-cadmium aerospace battery cells

The ac impedance characteristics of Ni-Cd cells as an in-situ, nondestructive means of determining cell lifetime, particularly with respect to the probability of premature failure were evaluated. Emphasis was on evaluating Ni-Cd cell impedance over a wide frequency range (10,000 to 0.0004 Hz) as the cells were subjected to charge/discharge cycle testing. The results indicate that cell degradation is reflected in the low frequency (Warburg) impedance characteristics associated with diffusion processes. The Warburg slope (W) was found to steadily increase as a function of cell aging for completely discharged cells. In addition, based on data for two cells, a high or rapidly increasing value for W signals imminent cell failure by one mechanism. Degradation by another mechanism is apparently reflected in a fall-off (roll-over) of W at lower frequencies. As a secondary result, the frequency dependence of the absolute cell impedance at low frequencies (5 - 500 mHz) was found to be a good indication of the cell state-of-charge

Routine dipstick urinalysis in daily practice of Belgian occupational physicians

BACKGROUND: Little work has been done to assess the quality of health care and the use of evidence-based methods by occupational physicians in Belgium. Therefore, the main objective is to describe one aspect of occupational health assessments, namely the common use of dipstick urinalysis, and to compare the current practice with international guidelines. METHODS: A self-administered questionnaire was mailed to 211 members of the Scientific Association of Occupational Medicine in the Dutch speaking part of Belgium. RESULTS: A total of 120 occupational physicians responded, giving a response rate of 57%. Dipstick urinalysis was a routine investigation for the vast majority of physicians (69%). All test strips screened for protein and in 90% also for blood. Occupational health services offered clinical tests to satisfy customer wants as international guidelines do not recommend screening for haematuria and proteinuria in asymptomatic adults. A lack of knowledge concerning positive testing and referral criteria was demonstrated in almost half of the study participants. CONCLUSIONS: Belgian occupational physicians still routinely perform dipstick testing although there is no evidence to support this screening in healthy workers. To practice evidence-based medicine, occupational physicians need more instruction and training. Development and implementation of more guidelines is not only of use for the individual practitioner, it may also enhance professionalization and efficiency of occupational health care