Sharp upper bound for the first non-zero Neumann eigenvalue for bounded domains in rank-1 symmetric spaces

In this paper, we prove that for a bounded domain in a rank- symmetric space, the first non-zero Neumann eigenvalue where denotes the geodesic ball of radius such that

and equality holds iff . This result generalises the works of Szego, Weinberger and Ashbaugh-Benguria for bounded domains in the spaces of constant curvature.

     

Nano-assembly of manganese peroxidase and lignin peroxidase from P. chrysosporium for biocatalysis in aqueous and non-aqueous media

Development, characterization, and activity studies of nano-assemblies of lignin peroxidase (LiP), and manganese peroxidase (MnP) from Phanerochaete chrysosporium on flat surfaces as well as colloidal particles have been investigated. These assemblies of LiP and MnP were fabricated with polyelectrolytes-poly(ethylenimine) (PEI), poly(dimethyldiallylammonium chloride) (PDDA), and poly(allylamine) (PAH)-using a layer-by-layer self-assembly technique (LbL). Characterization of these assemblies on flat surfaces was monitored using quartz crystal microbalance (QCM), while assemblies on microparticles such as melamine formaldehyde (MF) were carried out with zeta potential analyzer (ZPA). A unique dynamic adsorption-desorption of the enzyme layers is observed during the assembly. All the nano-assemblies of LiP and MnP can effectively oxidize veratryl alcohol (VA) to its aldehyde for an extended period of time. The effect of different polyions and the number of polyion layers on the activities of LiP and MnP nano-assembly was also examined. It is observed that drying of enzyme layer during the assembly and the use of non-aqueous media, such as acetone can significantly reduce the activity of the enzymes. Enzyme activity reaches a minimum when the concentration of acetone is increased to 30%; however, the activity can be restored to its original value by increasing the concentration of aqueous media. Preliminary studies using assemblies of LiP and MnP on MF microparticles further demonstrate the feasibility of developing potential systems for degradation of environmental pollutants.     

Interactions of organic halides with a polyurethane elastomer

Interactions of halogen-substituted organic penetrants have been studied with a polyurethane membrane over the temperature interval of 25-60°C. Transport parameters such as diffusivity, solubility, and permeability have been measured. A temperature dependence of these quantities has been used to predict activation parameters for the transport mechanism. Equilibrium sorption data were used to estimate the entropy and Gibbs energy for the sorption process by using the Van't Hoff relationship. Furthermore, a phenomenological treatment has been suggested to estimate the classical Flory-Huggins interaction parameter for polyurethane-solvent pairs. These data were used to calculate the molar mass between crosslinks of the polyurethane network. For all the penetrants, the transport mechanism was found to be anomalous.     

INTERACTIONS OF ORGANIC SOLVENTS WITH POLYURETHANE

Abstract

Polyurethane elastomers [1] are linear block copolymers of the type in which one of the two blocks is typically a polyether or a polyester diol with a molar mass between 300 to 6000. These blocks comprise the soft segments because at the service temperature they exist in a rubbery or a viscous state and impart elastomeric properties. The other segments are composed of aromatic diisocyanates extended with low diols to produce blocks with molar mass ranging from 500 to 3000. These blocks comprise the hard segments because at the service temperature they exist in the glassy (or semicrystalline) state. Dimensional stability is imparted through microphase separation of the hard segments into domains which act as a reinforcing filler and multifunctional crosslinks. Polyurethanes are mainly thermoplastics because heating above the hard segment glass transition temperature (T_g) will allow the material to flow.