Steklov Spectral Geometry for Extrinsic Shape Analysis

We propose using the Dirichlet-to-Neumann operator as an extrinsic alternative to the Laplacian for spectral geometry processing and shape analysis. Intrinsic approaches, usually based on the Laplace-Beltrami operator, cannot capture the spatial embedding of a shape up to rigid motion, and many previous extrinsic methods lack theoretical justification. Instead, we consider the Steklov eigenvalue problem, computing the spectrum of the Dirichlet-to-Neumann operator of a surface bounding a volume. A remarkable property of this operator is that it completely encodes volumetric geometry. We use the boundary element method (BEM) to discretize the operator, accelerated by hierarchical numerical schemes and preconditioning; this pipeline allows us to solve eigenvalue and linear problems on large-scale meshes despite the density of the Dirichlet-to-Neumann discretization. We further demonstrate that our operators naturally fit into existing frameworks for geometry processing, making a shift from intrinsic to extrinsic geometry as simple as substituting the Laplace-Beltrami operator with the Dirichlet-to-Neumann operator.Comment: Additional experiments adde

Production of Polyhydroxyalkanoates, a bacterial biodegradable polymers

There has been considerable interest in the development and production of biodegradable polymer to solve the current problem of pollution caused by the continuous use of synthetic polymer of petroleum origin. Polyhydroxyalkanoates (PHAs) are known to be accumulated as intracellular inclusion in some bacteria. The materials properties exhibited by PHAs, ranging from stiff, brittle to rubber-like makes it a close substitute for the synthetic plastic. The high cost of PHAs production has restricted its applications. The possibility of producing this polymer commercially and at comparable cost has been the main focus in this area. Key Words: Polyhydroxyalkanoates, biodegradable polymer, bioplastic, poly(3-hydroxybutyrate), biosynthesis. African Journal of Biotechnology Vol.3(1) 2004: 18-2

Using Elastin-Like Polypeptides for Better Retention of Biofuels

Elastin-like polypeptides (ELPs) are synthetic molecules that exhibit an interesting property of inverse temperature phase transition; they exist as soluble monomers at low temperatures and form insoluble aggregates at higher temperatures. The transition temperature depends on the pH, salt concentration, and the amino acid sequence of the ELP. This unique and reversible behavior, along with their high biocompatibility has made them a strategic tool for various biomedical applications. However, their hydrophobic properties also make them a prime candidate for biofuel production. As high levels of many commercially important organic solvents are toxic to the cells that make them, ELPs can potentially alleviate the strain on cells by aggregating around the hydrophobic product. ELP’s are simply purified by exploiting their phase transition property and through serial centrifugation at different temperatures. The retention of various bio-products and the cell survivability was analyzed for E. coli containing ELPs both in vivo and in vitro. Confocal microscopy and fluorescence measurements were used to verify the results. The present study provides proof of principle that ELPs have high affinity with certain commercially important biologics and can be a strategic tool to increase their yield

Astronomy: Starbursts near and far

Observations of intensely bright star-forming galaxies both close by and in the distant Universe at first glance seem to emphasize their similarity. But look a little closer, and differences emerge.Comment: 6 pages including 1 figur

HCN Observations of Dense Star-Forming Gas in High Redshift Galaxies

We present here the sensitive HCN(1-0) observations made with the VLA of two submillimeter galaxies and two QSOs at high-redshift. HCN emission is the signature of dense molecular gas found in GMC cores, the actual sites of massive star formation. We have made the first detection of HCN in a submillimeter galaxy, SMM J16359+6612. The HCN emission is seen with a signal to noise ratio of 4$\sigma$ and appears to be resolved as a double-source of \approxlt 2'' separation. Our new HCN observations, combined with previous HCN detections and upper limits, show that the FIR/HCN ratios in these high redshift sources lie systematically above the FIR/HCN correlation established for nearby galaxies by about a factor of 2. Even considering the scatter in the data and the presence of upper limits, this is an indication that the FIR/HCN ratios for the early Universe molecular emission line galaxies (EMGs) deviate from the correlation that fits Galactic giant molecular cloud cores, normal spirals, LIRGs, and ULIRGs. This indicates that the star formation rate per solar mass of dense molecular gas is higher in the high-$z$ objects than in local galaxies including normal spirals LIRGs and ULIRGs. The limited HCN detections at high-redshift show that the HCN/CO ratios for the high-$z$ objects are high and are comparable to those of the local ULIRGs rather than those of normal spirals. This indicates that EMGs have a high fraction of dense molecular gas compared to total molecular gas traced by CO emission.Comment: 14 pages including 4 figures; ApJL accepte

Morphology and melt rheology of nylon 11/clay nanocomposites

Nylon 11 (PA11)/clay nanocomposites have been prepared by melt-blending, followed by melt-extrusion through a capillary. Transmission electron microscopy shows that the exfoliated clay morphology is dominant for low nanofiller content, while the intercalated one is prevailing for high filler loading. Melt rheological properties of PA11 nanocomposites have been studied in both linear and nonlinear viscoelastic response regions. In the linear regime, the nanocomposites exhibit much higher storage modulus (G') and loss modulus (G'') values than neat PA11. The values of G' and G'' increase steadily with clay loading at low concentrations, while the G' and G'' for the sample with 5 wt % clay show an inverse dependence and lie between the modulus values of the samples with 1 and 2 wt % of clay. This is attributed to the alignment/orientation of nanoclay platelets in the intercalated nanocomposite induced by capillary extrusion. In the nonlinear regime, the nanocomposites show increased shear viscosities when compared with the neat resin. The dependence of the shear viscosity on clay loading has analogous trend to that of G' and G''. Finally, a comparison has been made between the complex and steady viscosities to verify the applicability of the empirical Cox-Merz rule

HI observations of luminous infrared galaxy mergers

A total of 19 luminous infrared galaxy mergers, with L_IR~2 10^11 L_sun for H_0=75 km/s/Mpc, have been observed in the HI line at Nancay and four of them were observed at Arecibo as well. Of these 19, ten had not been observed before. Six were clearly detected, one of which for the first time. The objective was to statistically sample the \HI gas mass in luminous infrared mergers along a starburst merger sequence where the molecular CO gas content is already known.Comment: 11 pages, accepted for Astron. Astrophys., 22/12/200

Entanglement dynamics of two-bipartite system under the influence of dissipative environments

An experimental scheme is suggested that permits a direct measure of entanglement in a two-qubit cavity system. It is realized in the cavity-QED technology utilizing atoms as flying qubits. With this scheme we generate two different measures of entanglement, namely logarithmic negativity and concurrence. The phenomenon of sudden death entanglement (ESD) in a bipartite system subjected to dissipative environment is examined. We show that the sudden death time of the entangled states depends on the initial preparation of the entangled state and the temperature of the reservoir.Comment: 21 pages, 13 figure

Coexisting Kondo singlet state with antiferromagnetic long-range order: A possible ground state for Kondo insulators

The ground-state phase diagram of a half-filled anisotropic Kondo lattice model is calculated within a mean-field theory. For small transverse exchange coupling $J_{\perp}<J_{\perp c1}$, the ground state shows an antiferromagnetic long-range order with finite staggered magnetizations of both localized spins and conduction electrons. When $J_{\perp}>J_{\perp c2}$, the long-range order is destroyed and the system is in a disordered Kondo singlet state with a hybridization gap. Both ground states can describe the low-temperature phases of Kondo insulating compounds. Between these two distinct phases, there may be a coexistent regime as a result of the balance between local Kondo screening and magnetic interactions.Comment: four pages, Revtex, one figure; to be published in Phys. Rev. B, 1 July issue, 200

Tetra-μ-acetato-κ8 O:O′-bis­{[2-(2-fur­yl)-1-(2-furylmeth­yl)-1H-benzimidazole-κN 3]copper(II)}

The title complex, [Cu2(CH3COO)4(C16H12N2O2)2], forms a dimer of the paddle-wheel type located on a crystallographic inversion centre. The two CuII atoms [Cu⋯Cu = 2.7254 (11) Å] are bridged by four acetate anions. The geometry of the polyhedron around the metal centre can be described as tetra­gonal-pyramidal derived from the calculation of the value τ = 0.0018. The apical positions of the tetra­gonal-pyramidal copper coordination polyhedra are occupied by the N atoms of 2-(2-fur­yl)-1-(2-furylmeth­yl)-1H-benzimidazole ligands. In the crystal structure, mol­ecules are linked into a chain by inter­molecular C—H⋯O hydrogen bonds parallel to [010]. Two furan rings are disordered over two positions in ratios of 0.55:0.45 and 0.69:0.31