Excess-entropy scaling of dynamics for a confined fluid of dumbbell-shaped particles

We use molecular simulation to study the ability of excess entropy scaling relationships to describe the kinetic properties of a confined molecular system. We examine a model for a confined fluid consisting of dumbbell-shaped molecules that interact with atomistically detailed pore walls via a Lennard-Jones potential. We obtain kinetic, thermodynamic, and structural properties of the system at three wall-fluid interaction strengths and over a temperature range that includes sub-and super-critical conditions. Four dynamic properties are considered: translational and rotational diffusivities, a characteristic relaxation time for rotational motion, and a collective relaxation time stemming from analysis of the coherent intermediate scattering function. We carefully consider the reference state used to define the excess entropy of a confined fluid. Three ideal-gas reference states are considered, with the cases differentiated by the extent to which one-body spatial and orientational correlations are accounted for in the reference state. Our results indicate that a version of the excess entropy that includes information related to the one-body correlations in a confined fluid serves as the best scaling variable for dynamic properties. When adopting such a definition for the reference state, to a very good approximation, bulk and confined data for a specified dynamic property at a given temperature collapse onto a common curve when plotted against the excess entropy.National Science Foundation CBET-0828979Welch Foundation F-1696David and Lucile Packard FoundationChemical Engineerin

Centre Commissioned External Review (CCER) of the IWMI-TATA Water Policy Research Program

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Appearance Potential Spectroscopy of Solid Surfaces

Among the techniques utilized for the study of unfilled density of states above the Fermi level in a system, appearance potential spectroscopy (APS) has emerged as one of the simplest. Some review papers on APS have appeared in the last decade. Since then APS has been applied to several interesting systems, the studies of which have been limited by other experimental techniques available. This paper reviews some of these applications of APS. We discuss briefly the one-electron theory describing the APS process and outline the basic experimental set-ups used by workers in this field. We then survey some important applications of this technique to simple, as well as, multi-component systems. The results of the applications cited are compared with those from other techniques wherever available. The electronic structure of transition metals, rare earths and their intermetallics as obtained from APS spectra are discussed. The phenomena of adsorption and fine structure which are dependent on the surface sensitivity of APS are also dealt with by including some interesting applications. Finally, we take into account the strengths and limitations of this technique and outline the prospects of this spectroscopy in attaining its importance among the various surface spectroscopies

Enhancement of drought-induced senescence by the reproductive sink in fertile lines of wheat and Sorghum

The leaf senescence pattern was examined in water-stressed male sterile and fertile lines of wheat (Triticum aestivum) and sorghum (Sorghum vulgare). The study was conducted at the seedling stage and during grain development. The loss of leaf area and chlorophyll content induced by water stress was similar in the male sterile and fertile lines of wheat at the seedling stage. At the grain filling stage, leaf senescence occurred at a faster rate in the fertile lines as compared to sterile lines of both wheat and sorghum. The study indicates that a reproductive sink accentuates drought-induced leaf senescence

Broad boron sheets and boron nanotubes: An ab initio study of structural, electronic, and mechanical properties

Based on a numerical ab initio study, we discuss a structure model for a broad boron sheet, which is the analog of a single graphite sheet, and the precursor of boron nanotubes. The sheet has linear chains of sp hybridized sigma bonds lying only along its armchair direction, a high stiffness, and anisotropic bonds properties. The puckering of the sheet is explained as a mechanism to stabilize the sp sigma bonds. The anisotropic bond properties of the boron sheet lead to a two-dimensional reference lattice structure, which is rectangular rather than triangular. As a consequence the chiral angles of related boron nanotubes range from 0 to 90 degrees. Given the electronic properties of the boron sheets, we demonstrate that all of the related boron nanotubes are metallic, irrespective of their radius and chiral angle, and we also postulate the existence of helical currents in ideal chiral nanotubes. Furthermore, we show that the strain energy of boron nanotubes will depend on their radii, as well as on their chiral angles. This is a rather unique property among nanotubular systems, and it could be the basis of a different type of structure control within nanotechnology.Comment: 16 pages, 17 figures, 2 tables, Versions: v1=preview, v2=first final, v3=minor corrections, v4=document slightly reworke

Packing Fractions and Maximum Angles of Stability of Granular Materials

In two-dimensional rotating drum experiments, we find two separate influences of the packing fraction of a granular heap on its stability. For a fixed grain shape, the stability increases with packing fraction. However, in determining the relative stability of different grain shapes, those with the lowest average packing fractions tend to form the most stable heaps. We also show that only the configuration close to the surface of the pile figures prominently.Comment: 4 pages, 4 figure