Measurements of Grain Motion in a Dense, Three-Dimensional Granular Fluid

We have used an NMR technique to measure the short-time, three-dimensional displacement of grains in a system of mustard seeds vibrated vertically at 15g. The technique averages over a time interval in which the grains move ballistically, giving a direct measurement of the granular temperature profile. The dense, lower portion of the sample is well described by a recent hydrodynamic theory for inelastic hard spheres. Near the free upper surface the mean free path is longer than the particle diameter and the hydrodynamic description fails.Comment: 4 pages, 4 figure

Cold quarks in medium: an equation of state

We derive a compact, semi-algebraic expression for the cold quark matter equation of state (EoS) in a covariant model that exhibits coincident deconfinement and chiral symmetry restoring transitions in-medium. Along the way we obtain algebraic expressions for: the number- and scalar-density distributions in both the confining Nambu and deconfined Wigner phases; and the vacuum-pressure difference between these phases, which defines a bag constant. The confining interaction materially alters the distribution functions from those of a Fermi gas and consequently has a significant impact on the model's thermodynamic properties, which is apparent in the EoS.Comment: 5 pages, 5 figure

Phase diagram and critical endpoint for strongly-interacting quarks

We introduce a method based on the chiral susceptibility, which enables one to draw a phase diagram in the chemical-potential/temperature plane for strongly-interacting quarks whose interactions are described by any reasonable gap equation, even if the diagrammatic content of the quark-gluon vertex is unknown. We locate a critical endpoint (CEP) at (\mu^E,T^E) ~ (1.0,0.9)T_c, where T_c is the critical temperature for chiral symmetry restoration at \mu=0; and find that a domain of phase coexistence opens at the CEP whose area increases as a confinement length-scale grows.Comment: 4 pages, 3 figure

Scanning probe microscopy study of thin film solar cells

textThin film solar cells, such as CdTe, CuIn [subscript x] Ga [subscript 1-x] Se₂ (CIGS), Cu₂ZnSnS₄ (CZTS) and Cu₂ZnSnSe₄ (CZTSe), have been intensively studied for their unique features and excellent prospect of mass production in industry. The p-n junction is the most critical part of the thin film solar cell and greatly influences the performance. In this thesis work, the p-n junctions and the device layers of multiple kinds of thin film solar cells have been studied by using scanning probe microscopy based techniques. The scanning spreading resistance microscopy (SSRM) has been developed on the cross-section of CdTe solar cells to study the resistance and carrier concentration distribution in different layers of the device. The CdTe sample was cleaved and milled with the argon ion beam to get a flat cross-section. The multiple device layers of the device were identified by the resistance mapping. A high-resistance region around the junction on the CdTe side due to carrier depletion was measured. With the AFM laser illumination, the resistance in the deep depletion region dropped and the resistance across the entire CdTe layer became relatively uniform due to domination of photo-excited carriers. With carriers injected by applying a forward-bias voltage to the working device, the resistance in the deep depletion region decreased and the region moved toward the CdS/CdTe interface. These observed trends and observations are consistent with device physics. We also measured the surface potential and the electric field across the junction using scanning Kelvin probe force microscopy (SKPFM) in the cross-section of the standard CIGS, ZnS(O,OH)/CIGS and the standard CZTSe devices. Both the heterojunction and homojunction situations of the three solar cells were simulated using the PC1D software. The simulation results were compared with the experimental results to analyze the properties of the junction. The comparison results provided the possible ranges of the thickness and carrier concentration of n-CIGS/n-CZTSe layer.Physic

Exact solution at integrable coupling of a model for the Josephson effect between small metallic grains

A model is introduced for two reduced BCS systems which are coupled through the transfer of Cooper pairs between the systems. The model may thus be used in the analysis of the Josephson effect arising from pair tunneling between two strongly coupled small metallic grains. At a particular coupling strength the model is integrable and explicit results are derived for the energy spectrum, conserved operators, integrals of motion, and wave function scalar products. It is also shown that form factors can be obtained for the calculation of correlation functions. Further, a connection with perturbed conformal field theory is made.Comment: 12 pages, latex, no figure