Determination of Aggregation Parameters of Hexadecyltrimethylammonium Bromide from Probe Absorption

The mean aggregation number (n) and the critical micelle concentrations (CMC) of reverse micelles formed by hexadecyltrimethylammonium bromide have been determined by means of an optical absorption probe (acridine orange). The procedure to obtain these quantities from absorption spectrophotometric measurements is described. The CMC and mean aggregation number are in satisfactory agreement with published results obtained from more sophisticated methods.     

Absorption and Flourescence of a Rigidly-Bridged Donor-Acceptor Molecule in Langmuir-Blodgett Mixed Films

Thermodynamic analysis of the pressure-area isotherms, of solutions of rigidly-bridged donor-acceptor molecule, D(10)A, in arachidic acid, indicates that the solutions behave ideally at low concentrations. The surface area per molecule at high dilutions (mf ≤ 0.02) approximates to 27 Ų from which it is evident that the long axis of the D(10)A molecule is oriented vertically, and the short axis of the 1,4-dimethoxynaphthalene moiety parallel to the monolayer surface at 25 mN m^?1 surface pressure Evidence from electronic absorption, static and time-resolved fluorescence spectra led us to conclude that D(10)A molecules form ground-state dimers, intermolecular excimers with very short lifetimes which do not photodimerize in Langmuir-Blodgett films, and give long-Jived (τ₃ ≈ 29±3ns) charge-transfer emissions at 440 nm.     

Enthalpy Change of Allosteric Transition in Human Haemoglobin A

Oxygen equilibria of haemoglobin were analysed according to a binding isotherm proposed by Amire ( Bull. Chem. Soc. Jpn. 1994, 67, 7 )¹ to obtain the intrinsic oxygen association constants to the molecule. Two sets of binding sites in haemoglobin were identified, which were ascribed to R₂ and T forms of the molecule. The average intrinsic association constants determined as a function of temperature gave a heat of oxygenation of‐76 ± 4 kJ mol^?;1 (tetramer). A microcalorimetrically determined heat of deoxygenation of oxyhaemoglobin by dithionite gave ?267 ± 10 kJ mol^?1 (tetramer). From these results, the heat of allostery of ?234 ± 24 kJ mol^?1 for haemoglobin tetramer was obtained, yielding allosteric energy per salt bridge of‐29 ± 3 kJ. This result suggests that salt‐bridge may, in fact, be thermochemically equivalent to hydrogen bonds.     

Improvement of Raman amplifier bandwidth by means of slow light in photonic crystal based waveguide structure

In this paper, we investigate the enhancement of Raman amplification bandwidth with self phase modulation (SPM) effect in silicon based photonic crystal waveguides. The Maxwell equations are solved using finite difference time domain method considering two photon absorption, free carrier absorption, Kerr and SPM effects. We also study the effects of shape, width and average power on the Raman amplification bandwidth. Then by changing the photonic crystal geometrical parameters, pump and signal group velocity are reduced to achieve higher Raman bandwidth.     

Stable high optical power in quantum well lasers with profiled reflection and tapered structures

A comprehensive model is presented to study quantum well tapered lasers and quantum well stripe lasers with profiled reflectivity output facets and to obtain lateral stability in high power semiconductor laser. Simulation of semiconductor lasers is performed by numerically solving space-dependent coupled partial differential equations for the complex optical forward and backward waves, carrier density distribution and temperature distribution. The coupled equations are solved by finite difference beam propagation method. The effect of nonlinear parameters like Kerr and linewidth enhancement factors, and precise dependence of linewidth enhancement factor and gain factor on the carrier density and temperature are considered in this paper. We use modal reflector in stripe lasers to confine the lateral mode to the stripe centre and provide the stable operation. We also use unpumped window to reduce the facet temperature and improve the catastrophic optical mirror damage level of tapered lasers.     

Characterization of pathogenic races of the sugarcane smut fungus by neutron activation analysis

Representative samples of five major races of Ustilago scitaminea, the causal organism of the smut disease of sugarcane, were obtained from infected sugarcane fields in the western hemisphere. The variations in concentration of 10 elements (Na, Mg, Al, Cl, K, Ca, Mn, Fe, Co, and Zn) in the sporidial yeast-like cells of this fungal pathogen were analyzed by neutron activation analysis. Comparative analysis of the elemental compositions in the different races of the fungus showed that the five pathogenic races of Ustilago scitaminea may be distinguished from each other on the basis of elemental compositions.