Influence Of Time Effects Research Articles

Implication of scaling hierarchy associated with nonequilibrium: field and particulate

The advent of nanotechnology has necessitated a better understanding of how material microstructure changes at the atomic level would affect the macroscopic properties that control the performance. Such a challenge has uncovered many phenomena that were not previously understood and taken for granted. Among them are the basic foundation of dislocation theories which are now known to be inadequate. Simplifying assumptions invoked at the macroscale may not be applicable at the micro- and/or nanoscale. There are implications of scaling hierrachy associated with inhomegeneity and nonequilibrium of physical systems. What is taken to be homogeneous and equilibrium at the macroscale may not be so when the physical size of the material is reduced to microns. These fundamental issues cannot be dispensed at will for the sake of convenience because they could alter the outcome of predictions. Even more unsatisfying is the lack of consistency in modeling physical systems. This could translate to the inability for identifying the relevant manufacturing parameters and rendering the end product unpractical because of high cost. Advanced composite and ceramic materials are cases in point. Discussed are potential pitfalls for applying models at both the atomic and continuum levels. No encouragement is made to unravel the truth of nature. Let it be partiuclates, a smooth continuum or a combination of both. The present trend of development in scaling tends to seek for different characteristic lengths of material microstructures with or without the influence of time effects. Much will be learned from atomistic simulation models to show how results could differ as boundary conditions and scales are changed. Quantum mechanics, continuum and cosmological models provide evidence that no general approach is in sight. Of immediate interest is perhaps the establishment of greater precision in terminology so as to better communicate results involving multiscale physical events.

Single-side microelectromechanical capacitive accelerometer

The advent of nanotechnology has necessitated a better understanding of how material microstructure changes at the atomic level would affect the macroscopic properties that control the performance. Such a challenge has uncovered many phenomena that were not previously understood and taken for granted. Among them are the basic foundation of dislocation theories which are now known to be inadequate. Simplifying assumptions invoked at the macroscale may not be applicable at the micro- and/or nanoscale. There are implications of scaling hierrachy associated with inhomegeneity and nonequilibrium of physical systems. What is taken to be homogeneous and equilibrium at the macroscale may not be so when the physical size of the material is reduced to microns. These fundamental issues cannot be dispensed at will for the sake of convenience because they could alter the outcome of predictions. Even more unsatisfying is the lack of consistency in modeling physical systems. This could translate to the inability for identifying the relevant manufacturing parameters and rendering the end product unpractical because of high cost. Advanced composite and ceramic materials are cases in point.Discussed are potential pitfalls for applying models at both the atomic and continuum levels. No encouragement is made to unravel the truth of nature. Let it be partiuclates, a smooth continuum or a combination of both. The present trend of development in scaling tends to seek for different characteristic lengths of material microstructures with or without the influence of time effects. Much will be learned from atomistic simulation models to show how results could differ as boundary conditions and scales are changed. Quantum mechanics, continuum and cosmological models provide evidence that no general approach is in sight. Of immediate interest is perhaps the establishment of greater precision in terminology so as to better communicate results involving multiscale physical events.

Influence of time effects on instability of granular materials

Results of previously performed series of triaxial compression tests designed to expose the type of behavior displayed by granular materials have shown that materials that exhibit non-associated flow do not obey the stability postulates by Drucker and by Hill. Triaxial tests on fully and partly saturated specimens of sand have been performed under drained and undrained conditions to study the regions of stable and unstable behavior. Granular materials may become unstable inside the failure surface if the state of stress is located between the instability line and the failure surface for the material. Presented here are three series of experiments conducted on sands that compress during shear. In one series, experiments are performed to study the effect of strain rate on the location of the instability line. In the second series, the sand is allowed to creep under drained conditions resulting in outwards movement of the yield surface, and the sand consequently becomes suffer in the region above the stress point. Increasing amounts of creep therefore require increasingly high stress differences to render the sand unstable. In the third series of experiments, the saturated sand is allowed to creep under undrained conditions, and this results in increasing pore pressures and possible instability because the stresses may be brought into the region of potential instability. Thus, time effects play important roles in the stability of soils.

Zur Frequenz- und Temperaturabh�ngigkeit der Koerzitivkraft d�nner polykristalliner Nickelschichten bei Wechselfeldmagnetisierung

The magnetoresistance is used for measuring the coercivityH c of nickel thin films, which have been condensed onto glass substrates at temperatures of 200°C and 400°C. TheH c -data obtained at various measuring temperatures using an alternating magnetic field in the frequency range from 40 cps to 10 kc permit an extra-polation to the results obtained with a Wheatstone bridge and galvanometer (i.e. with a nearly “static” method). With decreasing film thickness or reduction of the average grain size of the samples an increased influence of time effects is directly observed. This may essentially be attributed to thermal fluctuation effects. Thus the decrease of coercivity in the thickness range below about 100 A, as it has been found at the type of films used in this investigation, may mainly be explained.