The single-mode rate equations for semiconductor lasers with thermal effects

A mathematical model describing the coupling of electrical,optical and thermal effects in semiconductor lasers is introduced.Numerical and asymptotic solutions are derived, including expressionsfor key physical quantities such as the initial time delay,the frequency of spike oscillation and the temperature rise,together with its influence on the photon density, the electronconcentration and the threshold current. The consequences ofthermal effects in reducing efficiency are thus quantified.     

Construction of high-quality narrow-band holographic filters

We have studied the factors limiting the quality of holographic notch filters. We have employed a novel recording scheme in which the sample is translated during exposure, eliminating flare due to reflections at the boundaries, and simultaneously reducing the scatter of the final hologram. We have also refined a gravity-settling dichromated gelatine (DCG) deposition technique and incorporated hardening of the DCG layers during the drying stage. With this, we have produced high optical quality, uniform, flare-free DCG filters with an optical density, OD > 5, bandwidth < 20 nm and scatter almost as low as that for state of the art dielectric notch filters.     

Structural and rheological properties of hydrophobically modified alkali‐soluble emulsion solutions

Scattering and rheological experiments were carried out on hydrophobically modified alkali‐soluble emulsion solutions at pH ～ 7.3 as a function of the polymer concentration. The light scattering experiments revealed the existence of a liquidlike order for concentrations below approximately 0.1 × 10^?2g cm^?3 corresponding approximately to the close packing of microgels particles. Above this concentration, the zero‐shear viscosity rose sharply, whereas the ordering disappeared progressively. The results are discussed within the framework of gelation models of associating polymers. Diffusing wave spectroscopy experiments provided estimates of the high‐frequency modulus. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1985–1994, 2002     

Genetic optimization of modulation characteristics for two twisted nematic liquid crystal spatial light modulators

A single twisted nematic liquid crystal spatial light modulator may suffer from coupled amplitude modulation and a phase modulation capability of less than 2, although almost all panels can achieve . Two twisted nematic liquid crystal panels can be combined in an optical system to produce a total phase modulation of at least 2, and a minimal coupled amplitude modulation. A genetic algorithm is used to optimize the combined modulation characteristics of two liquid crystal panels in a multiplicative architecture. Simulation results and experimental verification are presented which show a substantial reduction in the combined amplitude modulation, and a total phase modulation of 2.     

Impact of methanol and acetonitrile on separations based on pi-pi interactions with a reversed-phase phenyl column

Studies were performed to investigate the roles of methanol and acetonitrile on the retention mechanism of an active pharmaceutical ingredient (API) and related compounds with a reversed phase phenyl column. Different retention orders were observed depending upon whether acetonitrile or methanol was used as the organic modifier. We propose that acetonitrile impedes the selective pi-pi interactions between the analyte molecules and the phenyl groups in the stationary phase. Further study with 1-naphthoic acid and 1-naphthol as test compounds in the HPLC separation provides additional support for the influence of acetonitrile on pi-pi interactions between analyte molecules and a phenyl stationary phase. This study suggests that methanol be used as the preferred organic modifier with phenyl columns to achieve selectivity based upon pi-pi interactions.     

Synthesis of the C-linked disaccharide alpha-D-Man-(1-->4)-D-Man employing a SmI(2)-mediated C-glycosylation step: en route to cyclic C-oligosaccharides

Investigations are reported on the assembly of the C-linked disaccharide alpha-D-Man-(1-->4)-D-Man, representing the first steps in our projected synthesis of a cyclic C-oligomer containing repeating units of this C-dimer. The key step in this synthesis uses a SmI(2)-mediated coupling of 2,3,4,6-tetra-O-benzyl-alpha-D-mannopyranosyl 2'-pyridyl sulfone with a C4-formyl branched mannopyranoside unit, affording the C-disaccharide derivative with complete stereocontrol at the two new stereogenic centers. Subsequently, a modified tin hydride based deoxygenation produced the target carbohydrate analogue. The synthesis of the C4-formyl monosaccharide makes use of a stereoselective radical-based allylation followed by double bond migration and ozonolysis.