Professor Sivaramakrishna Chandrasekhar,FRS

Abstract

Optical microscopy in mixtures of di-octylazoxybenzene (8AB) and di-nonylazoxybenzene (9AB) reveals that a smectic A-nematic-isotropic triple point occurs at 71·5±0·5°C and 38±2wt% 8AB. Although this concentration induced triple point is different from the pressure induced triple point known to exist in pure 9AB at elevated pressure, analysis of the data from both the mixing and pressure experiments reveals that the phase transition surfaces in temperature-pressure-concentration space for this system are nearly planar.     

Speckle observation of pulsed laser-induced dynamics in a guest-host smectic A liquid crystal system

Abstract

Using a pulsed, pump-probe experimental arrangement, we have investigated the speckle generated by a 100 μm path length cell of smectic A liquid crystal 4-cyano-4′-octylbiphenyl doped with 0·1 wt% dichroic dye. Upon irradiation, the guest-host system undergoes a phase transition from an initially transparent condition to a scattering state. We show that the statistical theory of speckle can be used to describe the evolution of scattering domains and estimate an rms refractive index variation of 0·0021 within the irradiated region for one case. Dynamic response as a function of molecular anchoring conditions was also investigated.     

p-Alkoxy- and p-alkylbenzoates of α, a'-bi-p-hydroxytoluene. New series of liquid-crystalline compounds

Abstract

Six p-alkoxy and eight p-alkylbenzoates of 1,2-(p-hydroxyphenyl)ethane were synthesized for potential use as stationary phases in gas-liquid chromatography. All the p-alkoxy derivatives were nematic. The first five members of the alkyl series were nematic and the rest exhibited both smectic and nematic character. Most possess the desired combination of a wide liquid-crystalline temperature range and a high mesomorphic-isotropic transition temperature. The nematic-isotropic transition temperatures and entropies show the usual alternations characteristic of a high-melting series.     

Exploring background variability of a low-level (quartz) gas proportional counter using pulse shape and distribution analysis

The NIST low-level beta counting system is designed to capture digitally and timestamp each event for retrospective analysis. As a result, low and stable backgrounds are achieved and lead to extremely low detection and quantification limits for measuring, e.g., ¹⁴C of atmospheric gases and aerosol. The objective here is to explore the variability of the background count rate (counts per day) of several small (1 mL) freshly-assembled gas proportional counters (GPCs). The mean is 14.0 day^?1 with 95 % confidence limits 11.2–16.8 day^?1. The raw count per day data was non-normal and so a Log transformation was applied to achieve normality and to rigorously compute normal tolerance limits. Back in the original space such (95 % confidence, 95 % coverage) tolerance limits were 2.5–47.8 day^?1. These limits are taken as acceptance criteria for any GPCs assembled in the future.     

Biodegradation of Phenol by the Yeast Candida tropicalis: An Investigation by NMR Spectroscopy

The process of phenol biodegradation by the yeast Candida tropicalis NCIM 3556 in aqueous medium was studied by ¹H, ¹³C, and DOSY NMR techniques. Samples at regular intervals were centrifuged to separate the cells, and ¹H spectral data were collected at 400 MHz. Though a gradual decrease in the concentration of phenol was observed, after an incubation period of ~8 h, formation of any intermediate products could not be detected. Experiments carried out with uniformly ¹³C-labeled phenol also failed to detect formation of any carboxylic acid intermediates during degradation. The studies indicated that the phenol was completely degraded to carbon dioxide and water in approximately 20 h. Self-diffusion coefficient measurements showed that the lifetime of phenol in the bound form is too small to impart any change in its diffusion behavior and the intermediates formed are converted to carbon dioxide and water at a very fast rate.     

The photodetection process under the conditions of an imperfect measurement device

There may be a link between the quantum properties of the vacuum and the parameters describing the properties of light propagation, culminating in a sum over all types of elementary particles existing in Nature weighted only by their squared charges and independent of their masses. The estimate for that sum is of the order of 100.     

Synthesis of Amino Acid Derivatives of Neamine and 2-Deoxystreptamine to be used as Mutasynthons

ABSTRACT

6′-N derivatives of neamine with alanine, phenylalanine and lysine were synthesized either using an active esters method in one step under controlled conditions, or using a mixed anhydride method after blocking every functional group of neamine and leaving the 6′-amino group free to react. Similarly N,N′-diamino acid and monoamino acid derivatives of 2-deoxystreptamine were synthesized.     

Modification of Glycosylation as A Therapeutic Strategy

1. INTRODUCTION

Glycoconjugates play important roles in many cellular and physiological processes, including development, differentiation, cell to cell contact, formation of the intracellular matrix, recognition of microorganisms, macromolecules and small molecules and intracellular transport of proteins.^2,3