Comparison of hydrogen and methane as coolants in regeneratively cooled panels

Comparison of hydrogen and methane as coolants in regeneratively cooled panel

The AF structure of non commutative toroidal Z/4Z orbifolds

For any irrational theta and rational number p/q such that q|qtheta-p|<1, a projection e of trace q|qtheta-p| is constructed in the the irrational rotation algebra A_theta that is invariant under the Fourier transform. (The latter is the order four automorphism U mapped to V, V mapped to U^{-1}, where U, V are the canonical unitaries generating A_theta.) Further, the projection e is approximately central, the cut down algebra eA_theta e contains a Fourier invariant q x q matrix algebra whose unit is e, and the cut downs eUe, eVe are approximately inside the matrix algebra. (In particular, there are Fourier invariant projections of trace k|qtheta-p| for k=1,...,q.) It is also shown that for all theta the crossed product A_theta rtimes Z_4 satisfies the Universal Coefficient Theorem. (Z_4 := Z/4Z.) As a consequence, using the Classification Theorem of G. Elliott and G. Gong for AH-algebras, a theorem of M. Rieffel, and by recent results of H. Lin, we show that A_theta rtimes Z_4 is an AF-algebra for all irrational theta in a dense G_delta.Comment: 35 page

Solidification in soft-core fluids: disordered solids from fast solidification fronts

Using dynamical density functional theory we calculate the speed of solidification fronts advancing into a quenched two-dimensional model fluid of soft-core particles. We find that solidification fronts can advance via two different mechanisms, depending on the depth of the quench. For shallow quenches, the front propagation is via a nonlinear mechanism. For deep quenches, front propagation is governed by a linear mechanism and in this regime we are able to determine the front speed via a marginal stability analysis. We find that the density modulations generated behind the advancing front have a characteristic scale that differs from the wavelength of the density modulation in thermodynamic equilibrium, i.e., the spacing between the crystal planes in an equilibrium crystal. This leads to the subsequent development of disorder in the solids that are formed. For the one-component fluid, the particles are able to rearrange to form a well-ordered crystal, with few defects. However, solidification fronts in a binary mixture exhibiting crystalline phases with square and hexagonal ordering generate solids that are unable to rearrange after the passage of the solidification front and a significant amount of disorder remains in the system.Comment: 18 pages, 14 fig

Quantum dynamics of the avian compass

The ability of migratory birds to orient relative to the Earth's magnetic field is believed to involve a coherent superposition of two spin states of a radical electron pair. However, the mechanism by which this coherence can be maintained in the face of strong interactions with the cellular environment has remained unclear. This Letter addresses the problem of decoherence between two electron spins due to hyperfine interaction with a bath of spin 1/2 nuclei. Dynamics of the radical pair density matrix are derived and shown to yield a simple mechanism for sensing magnetic field orientation. Rates of dephasing and decoherence are calculated ab initio and found to yield millisecond coherence times, consistent with behavioral experiments

Cartesian Bicategories II

The notion of cartesian bicategory, introduced by Carboni and Walters for locally ordered bicategories, is extended to general bicategories. It is shown that a cartesian bicategory is a symmetric monoidal bicategory

Forest Decline and Tree Mortality in a Southeastern Ohio Oak-Hickory Forest

Author Institution: Department of Environmental and Plant Biology, Ohio UniversityMany forests throughout the central Appalachians have been suspected, or observed, to be in declining health. Few studies have examined the vitality of southeastern Ohio's forests. The purpose of our study was to evaluate the health of a representative southeastern Ohio oak-hickory forest. Thirty-two 0.1 ha plots were sampled in August 1995 on the 550 ha Waterloo Wildlife Experiment Station (ODNR) in Athens County, OH. Data were collected for all living and dead stems with a DBH >10 cm (1,891 stems sampled). For living trees, a decline index (DI) was determined to evaluate the percentage of branch dieback, undersized leaves, and chlorosis. Dead trees were identified and categorized by mortality class (log vs. snag). Quercus spp. and Carya spp. accounted for 68% of all stems sampled (83% living). Among the live trees, only three species (Juglans nigra, Sassafras albidum, and Cornus florida) exhibited nonhealthy DI values. All other species were observed to be healthy or exhibiting only trace symptoms of decline. In contrast to decline, high mortality was observed for S. albidum (29.1%), Liriodendron tulipifera (21.7%), and Prunus serotina (21.6%). Quercus spp. (17.0%), and Carya spp. (16.2%) exhibited moderate mortality. Acer spp. had the highest vitality among the dominant species. Most of the observed patterns can be explained by successional dynamics and known pathogenic processes. Various incongruities emphasize the need for long-term studies of forest dynamics and forest health monitoring

The effect of bedrest on various parameters of physiological function. part v- dietary requirements

Effect of bedrest on various parameters of physiological function - nutritional requiremen