Time-gated optical imaging through turbid media using stimulated Raman scattering: Studies on image contrast

In this paper, we report the development of experimental set-up for time-gated optical imaging through turbid media using stimulated Raman scattering. Our studies on the contrast of time-gated images show that for a given optical thickness, the image contrast is better for sample with lower scattering coefficient and higher physical thickness, and that the contrast improves with decreasing value of anisotropy parameters of the scatterers. These results are consistent with time-resolved Monte Carlo simulations.     

β-Cyclodextrin Mediated Synthesis of Syndiotactic-rich Polystyrene

Stereoregular polystyrene (PS) was prepared using various molarequivalents of -cyclodextrin (-CD) by polymerisingstyrene in the presence of -CD. Stereoregular (isotactic,atactic and syndiotactic) distributions of the preparedpolystyrene polymers were determined from terminal modelBernoullian statistics using ¹³C NMR data. Inclusioncomplexation of styrene by -cyclodextrin was detected byUV-Visible spectroscopy, which gave a binding constant value of31606 ± 3350 M^-1 for the 1 : 1 complex. With anincrease in the styrene : -CD ratios, the proportionof syndiotactic polymers increased. The glass transitiontemperature (T_g) of the polymer also increased along withmelting temperature (T_m) at higher styrene : -CDratios. In addition, the molecular weight of the polymers prepareddecreased with increase in the -CD concentration.     

Computation of scattering from N spheres using multipole reexpansion

A computational technique for the solution of problems of wave scattering from multiple spheres is developed. This technique, based on the T-matrix method, uses the theory for the translation and reexpansion of multipole solutions of the Helmholtz equation for fast and exact recursive computation of the matrix elements. The spheres can have prescribed radii, impedances, and locations. Results are validated by comparison with boundary element calculations, and by convergence analyses. The method is much faster than numerical methods based on discretization of space, or of the sphere surfaces. An even faster method is presented for the case when the spheres are aligned coaxially.     

Isolation,Purification and Characterisation of an Organic Solvent-Tolerant Ca2+-Dependent Protease from Bacillus megaterium AU02

A new organic solvent-tolerant strain Bacillus megaterium AU02 which secretes an organic solvent-tolerant protease was isolated from milk industry waste. Statistical methods were employed to achieve optimum protease production of 43.6 U/ml in shake flask cultures. The productivity of the protease was increased to 53 U/ml when cultivated under controlled conditions in a 7-L fermentor. The protease was purified to homogeneity by a three-step process with 24 % yield and specific activity of 5,375 U/mg. The molecular mass of the protease was found to be 59 kDa. The enzyme was active over a wide range of pH (6.0–9.0), with an optimum activity at pH 7.0 and temperature from 40 to 70 °C having an optimum activity at 50 °C. The thermal stability of the enzyme increased significantly in the presence of CaCl₂, and it retained 90 % activity at 50 °C for 3 h. The K _m and V _max values were determined as 0.722 mg/ml and 0.018 U/mg respectively. The metalloprotease exhibited significant stability in the presence of organic solvents with log P values more than 2.5, nonionic detergents and oxidising agent. An attempt was made to test the synthesis of aspartame precursor (Cbz-Asp-Phe-NH₂) which was catalysed by AU02 protease in the presence of 50 % DMSO. These properties of AU02 protease make it an ideal choice for enzymatic peptide synthesis in organic media.     

How Many Timesteps for a Cycle? Analysis of the Wisdom-Holman Algorithm

The Wisdom-Holman algorithm is an effective method for numerically solving nearly integrable systems. It takes into account the exact solution of the integrable part. If the nearly integrable system is the solar system, for example, the Wisdom-Holman algorithm uses the solution consisting of Keplerian orbits obtained when the interplanetary interactions are ignored. The effectiveness of the algorithm lies in its ability to take long timesteps. We use the Duffing oscillator and Kepler's problem with forcing to deduce how long those timesteps can be. For nearly Keplerian orbits, the timesteps must be at least six per orbital period even when the orbital eccentricity is zero. High eccentricity of the Keplerian orbits constrains the algorithm and forces it to take shorter timesteps. The analysis is applied to the solar system and other problems.     

Structural Studies on Inclusion Compounds of β-Cyclodextrin with Some Substituted Phenols

A detailed structural study of the inclusion compounds of some substituted phenols such as catechol, guaiacol, protocatechuic aldehyde, vanillin, caffeic acid, ferulic acid and eugenol with -cyclodextrin (CD) was carried out by using UV-visible, fluorescence, 1H and solid-state 13C NMR spectroscopic and potentiometric investigations. Based on these studies guaiacol, catechol and eugenol were found to exhibit identical orientations - with the phenyl ring within the cavity and the hydroxyl and methoxyl groups projecting outside; protocatechuic aldehyde, caffeic acid, ferulic acid and vanillin display a different orientation - with the phenol part within the cavity and the aldehyde or carboxyl part projecting outside.     

Indirect spectrophotometric methods for the determination of antibiotics with iodine or periodate, and metol and sulphanilamide

Two spectrophotometric methods are described for the determination of antibiotics. In the first method, penicillins, cephalosporins, streptomycin and griseofulvin are estimated by oxidizing them under neutral or slightly acidic conditions, after alkaline hydrolysis, by means of a known and excessive quantity of iodine solution. The excess of iodine is determined at pH 3.0 with metol and sulphanilamide. In the second method, dihydrostreptomycin, framycetin and the acid hydrolysis product of chloramphenicol are determined by a method involving oxidation with sodium metaperiodate, masking the excess of periodate with sodium molybdate, and using metol and sulphanilamide at pH 3.0 to determine the iodate formed. In both methods the absorbance of the resulting p-N-methylbenzoquinonemonoimine sulphanilamide charge-transfer complex is measured at 520 nm.     

Disposition of copper(II) inβ-cyclodextrin

Distances of glucose protons in-cyclodextrin (BCD) from copper(II) in copper(II)--cyclodextrin have been determined from¹H NMR spin-lattice relaxation time (T ₁) measurements for the first time. Very lowT _1p /T _2p values indicated the dipolar mechanism to be the most dominant one in determining the paramagnetic contribution to relaxation. The distances of copper(II) from BCD glucose protons indicated copper(II) to be present almost in the centre, inside the cavity in the same plane as H-1 and H-4. An average distance of about 5.0–5.9 Å was obtained for copper(II) from the H-2, H-3, H-1, H-4 and H-6 a and b protons in BCD.