On the Thermodynamics of Granular Media

A thermodynamic formulation for moving granular material is proposed. The fluctuations due to the constant flux and dissipation of energy are controlled in a `granular' ensemble by a pressure $\wp$ (`compression') which is conjugate to a contact volume (`contactopy'). The corresponding response function (`dissipativity') describes how dissipation increases with $\wp$ and should serve to identify the fluidization transition and 1/f noise. In the granular ensemble one can consider the granular medium as a gas of elastically colliding particles and define a ``granular'' temperature and other standard thermodynamic quantities. PACS: 05.70, 46.10Comment: 11 p., no figs., plain Te

Quantum properties of two-dimensional electron gas in the inversion layer of Hg1−xCdxTe bicyrstals

The electronic and magnetotransport properties of conduction electrons in the grain boundary interface of p-type Hg1−xCdxTe bicrystals are investigated. The results clearly demonstrate the existence of a two-dimensional degenerate n-type inversion layer in the vicinity of the grain boundary. Hydrostatic pressure up to 103 MPa is used to characterize the properties of the two-dimensional electron gas in the inversion layer. At atmospheric pressure three series of quantum oscillations are revealled, indicating that tthree electric subbands are occupied. From quantum oscilations of the magnetoresistivity the characteristics parameters of the electric subbands (subband populations nsi, subband energies EF−Ei, effective electron masses m*ci) and their pressure dependences are established. A strong decrease of the carrier concentration in the inversion layer and of the corresponding subband population is observed when pressure is applied A simple theoretical model based on the triangular-well approximation and taking into account the pressure dependence of the energy band structure of Hg1−xCdxTe is use to calculate the energy band diagram of the quantum well and the pressure dependence of the subband parameters

Sedimentation of Oblate Ellipsoids at low and Moderate Reynolds numbers

In many applications to biophysics and environmental engineering, sedimentation of non-spherical particles for example: ellipsoids, is an important problem. In our work, we simulate the dynamics of oblate ellipsoids under gravity. We study the settling velocity and the average orientation of the ellipsoids as a function of volume fraction. We see that the settling velocity shows a local maximum at the intermmediate densities unlike the spheres. The average orientation of the ellipsoids also shows a similar local maximum and we observe that this local maximum disappears as the Reynolds number is increased. Also, at small volume fractions, we observe that the oblate ellipsoids exhibit an orientational clustering effect in alignment with gravity accompanied by strong density fluctuations. The vertical and horizontal fluctuations of the oblate ellipsoids are small compared to that of the spheres