No abstract

This paper investigates the interaction of an initially uniform magnetic field with an electrically conducting slab that moves perpendicularly to the magnetic field with arbitrary time-dependent velocity. It is demonstrated that the problem of determining the time-dependent Lorentz force and the time-dependent Joule heat in the slab is mathematically equivalent to solving a 1-D heat diffusion problem with time-dependent boundary conditions and to submitting the solution to a nonstandard postprocessing procedure. For the particular case of an impulsively driven slab we exploit the mathematical analogy between magnetic diffusion and heat diffusion by translating a textbook solution of the corresponding heat-transfer problem into exact and previously unknown relations for Lorentz force and Joule heat. Moreover, we use a 1-D finite-difference code to investigate more general time dependencies of the velocity including smooth accelerations and random velocity changes. Our numerical determination of reaction times (T 98) of the Lorentz force in the case of smooth accelerations provides a useful design tool for the development of Lorentz force flowmeters with short reaction times.

No abstract

The European guideline 74/60/EWG specifications currently pertaining to closing force restriction do not eliminate the risk of potentially serious injury to children's fingers in motor vehicle power windows.

Knowledge of the elastic properties of children's fingers is very important to understand the potential hazard for jamming injuries that exists in modern motor vehicles with automatic power-operated windows. This study determined the elastic resistance and the point of onset of bone/joint deformation at each of 5 different jam positions of a child's finger under continuous dorsal-palmar compression. An unembalmed finger that recently had been surgically removed from a polydactylic 8 month-old girl was jammed in a custom hydraulic test apparatus. A subminiature force sensor and an electrometric path sensor measured force and deflection values. To visualise the respective point of onset of bone/joint deformation, jamming of the finger was performed under fluoroscopy. The mean force at the point of onset of bone/joint deformation was 78.4 N. The current statutory limit of 100 N for the maximum closing force of an automatic power-operated motor vehicle window is thus well beyond the point at which finger injuries can occur in children. Assuming finger injuries in children can occur at a jamming force below approximately 80 N, a reduction of the statutory limit to us higher than 50 N is reasonable.