Studies on the effect of extraction of isophorone diisocyanate-based segmented polyurethanes

Linear segmented polyurethane was synthesised, using isophorone diisocyanate (IPDI), poly(tetramethylene oxide) glycol (PTMG) and 1,4 butanediol, for use in biomedical applications. The chemical stability of this polyurethane in hot methanol during Soxhlet extraction was studied by viscosity measurements, thermal studies, mechanical tests, ultraviolet and infrared spectral studies, and gel permeation chromatography. Hot methanol degrades the polymer at the allophanate linkages, while extracting low molecular weight polyurethane fractions. More urea linkages are formed in the extracted polymer.     

Riesz means for the sublaplacian on the Heisenberg group

The uniform boundedness of the Riesz means for the sublaplacian on the Heisenberg groupH ⁿ is considered. It is proved thatS _R ^α are uniformly bounded onL ^p(Hⁿ) for 1≤p≤2 provided α>α(p)=(2n+1)[(1/p)−(1/2)].     

Revisiting Hardy's theorem for the Heisenberg group

We establish several versions of Hardy's theorem for the Fourier transform on the Heisenberg group. Let be the Fourier transform of a function f on and assume where is the heat kernel associated to the sublaplacian. We show that if then whenever . When we replace the condition on f by where is the Fourier transform of f in the t-variable. Under suitable assumptions on the ‘spherical harmonic coefficients’ of we prove: (i) when a=b; (ii) when a > b there are infinitely many linearly independent functions f satisfying both conditions on and . Received: 9 January 2001 / in final form: 17 April 2001 Published online: 1 February 2002     

Weyl multipliers for invariant Sobelev spaces

A concrete characterization for theL ^P -multipliers (1<p<∞) for the Weyl transform is obtained. This is used to study the Weyl multipliers for Laguerre Sobolev spacesW ^m,p (? ⁿ ). A dual space characterization is obtained for the Weyl multiplier classM _W (W _L ^m,1 (? ⁿ )).     

Uncertainty principles on certain Lie groups

There are several ways of formulating the uncertainty principle for the Fourier transform on ? ⁿ . Roughly speaking, the uncertainty principle says that if a functionf is ‘concentrated’ then its Fourier transform $\tilde f$ cannot be ‘concentrated’ unlessf is identically zero. Of course, in the above, we should be precise about what we mean by ‘concentration’. There are several ways of measuring ‘concentration’ and depending on the definition we get a host of uncertainty principles. As several authors have shown, some of these uncertainty principles seem to be a general feature of harmonic analysis on connected locally compact groups. In this paper, we show how various uncertainty principles take form in the case of some locally compact groups including ? ⁿ , the Heisenberg group, the reduced Heisenberg groups and the Euclidean motion group of the plane.     

Selective Determination of Catechol in the Presence of Hydroquinone at Bare Indium Tin Oxide Electrodes via Peak‐Potential Separation and Redox Cycling by Hydrazine

The electrochemical, selective determination of catechol (CT) in the presence of hydroquinone (HQ) is not readily achieved, because the formal potentials of two phenolic compounds are very close. Here, we have developed a simple electrochemical method for the selective determination of CT by using bare indium tin oxide electrodes and employing CT redox cycling by hydrazine. The cyclic voltammetry of CT and HQ was investigated in Tris buffer (pH 9.0), phosphate buffered saline buffer (pH 7.4), and acetate buffer (pH 4.5). Especially in Tris buffer, the anodic peak potential of CT is much lower than that of HQ, resulting in a large difference between two peak potentials (ca. 0.4 V). The difference allows the selective determination of CT in the presence of excess HQ. The anodic current of CT is amplified using CT redox cycling by hydrazine, which also helps to stabilize CT and HQ in Tris buffer for several hours. The detection limits of CT in Tris buffer containing 0.1 mM HQ are 1 μM and 10 μM in the presence and absence of hydrazine, respectively.     

Energy material - the role of silicotungstic acid and fly ash in sulfonated poly (ether sulfone) composites for PEMFC applications

The composite polymer electrolyte membranes were prepared from sulfonated poly (ether sulfone) (SPES), silicotungstic acid (STA) and fly ash (FA). Post sulfonation process was adopted to synthesize SPES using sulphuric and chlorosulfonic acid. The prepared electrolyte membranes were examined by water uptake capacity, swelling ratio, ion-exchange ability, proton conductivity, thermal stability and electrochemical performance for evaluating the pertinence of these membranes in fuel cell applications. As such the pristine membrane restricts with the proton conductivity of 0.042?S cm^?1 at 30?°C and 0.060?S cm^?1 at 90?°C while the polymer composite membrane, SP-STA-FA-10 reveals the maximum conductivity of 0.054?S cm^?1 at 30?°C and 0.073?S cm^?1 at 90?°C. It also exhibits good thermal stability than that of the pure membrane. The membrane electrode assemblies (MEAs) have been successfully developed from SPES as well as SP-STA-FA-10 membranes and their electrochemical performance were studied the wide range of current density. Herein, the composite membranes derived from SPES, STA and FA can be viable candidates for fuel cell applications.     

On the structure of analytic vectors for the Schr?dinger representation

This article deals with the structure of analytic and entire vectors for the Schr?dinger representations of the Heisenberg group. Using refined versions of Hardy’s theorem and their connection with Hermite expansions we obtain very precise representation theorems for analytic and entire vectors.     

On the structure of analytic vectors for the Schr?dinger representation

This article deals with the structure of analytic and entire vectors for the Schr?dinger representations of the Heisenberg group. Using refined versions of Hardy??s theorem and their connection with Hermite expansions we obtain very precise representation theorems for analytic and entire vectors.