Orientation-dependent phase equilibria in in1−xGaxAs: A model including surface energies

Orientation-dependent growth phenomena have been observed for liquid-phase epitaxial In_1?xGa_xAs and other ternary and quaternary III–V semiconductors. The data cannot be explained by existing regular solution phase equilibria models. In this study we have used the quasi-regular solution formulation to derive a model which also considers equilibrium between the growing surface and the bulk solid under it. Orientation-dependent parameters characterizing the growing surface in the (100) and (111) directions have been included. The model is demonstrated for growth of In_1?xGa_xAs at 650 and 621°C. Excellent agreement is obtained with data for growth of the ternary on (lll)B InP substrates, whereas some adjustment of the parameters are necessary to obtain similar agreement in case of growth on (100)-oriented substrates.     

Electron energy states and miniband parameters in a class of non-uniform quantum well and superlattice structures

A simple method to compute the carrier energy states, miniband parameters and dispersion characteristics for single and multiple quantum well and superlattice structures is presented. The method utilizes the continuity of the envelope function across the heterojunctions according to the boundary conditions that both the wavefunction ψ and the particle current density $\text{ψ′}\text{m}{}^{\mathrm{★}}$ be continuous at each interface. The nonuniform potential distribution encountered in doped or compositionally graded materials is approximated by piecewise constant potential functions. In addition to being conceptually simple, the method is readily adopted to fairly complex structures where other more sophisticated methods such as LCAO, reduced Hamiltonian and tight binding theories may become unfeasible or unmanageable. It is shown that for an arbitrary stepped potential variation, the eigenvalues (or the energy states) of quantum wells or a finite number of coupled quantum wells can be found by utilizing a transverse resonance method which is readily implemented on a digital computer for the computation of these eigenvalues. For the case of periodic superlattices, the miniband parameters and the dispersion characteristics are computed from a suitably defined transmission matrix associated with a unit cell of the superlattice which may itself consist of multiple layers. Typical results for the computed parameters for several wells and simple, biperiodic, binary and polytype superlattices consisting of various Al_xGa_1?xAs and In_xGa_1?xAs alloys are presented.     

A brief and convergent synthetic route to defucogilvocarcin M chromophore: the formal synthesis of WS-5995 A and C

[reaction: see text] Densely substituted styryl sulfone 20 is shown to undergo double annulation with phthalide 21 to give, in one-pot operation and in excellent yield, the benzonaphthopyranone scaffold 22 of gilvocarcins.     

Regiospecific synthesis of isopestacin, a naturally occurring isobenzofuranone antioxidant

A DBU promoted aldol cyclocondensation of hydroxyisobenzofuranone 15 with cyclohexane-1,3-dione, followed by aromatization has resulted in the first short synthesis of isopestacin (1).     

Effect of phenols and carboxylic acids on photochromism of 1-alkyl-2-(arylazo)imidazoles

Light irradiated trans-to-cis isomerization of 1-alkyl-2-(arylazo)imidazole in the presence of phenol, catechol, benzoic acid and salicylic acid (called co-factors) has been studied in this work. The rate of trans→cis photoisomerization is decreased in the presence of co-factor in the medium and is dependent on the concentration of active quotient about photochrome. The decrease in rate follows catechol>benzoic acid>phenol>salicylic acid. This trend is due to the effects of dissociation ability of –O–H/–COOH, intermolecular association of the molecules etc. The reverse change, cis-to-trans, is very slow in light irradiation and has been carried out by a thermal process in the dark. The quantum yield of isomerization follows the same sequence of effects of co-factors.     

Trichosanthes dioica root possesses stimulant laxative activity in mice

Trichosanthes dioica Roxb. (Cucurbitaceae), named 'pointed gourd' in English, is a dioecious climber grown in India. This study was aimed at evaluating the laxative activity of the aqueous extract of T. dioica root (TDA) in Swiss albino mice. The laxative activity of TDA (100 and 200?mg?kg(-1) body weight per os) was evaluated by assessing the excretory bowel activities in naive (non-constipated) and in drug (loperamide)-induced constipation in mice. Further, the gastrointestinal transit was measured in both naive and in constipated mice. Castor oil (0.5?mL/mouse per os) was used as the reference. TDA significantly and dose-dependently increased all the excretory bowel activities and gastrointestinal transit in both naive and constipated mice. TDA at 200?mg?kg(-1) body weight was found to be the most active, causing diarrhoea in mice. Thus, T. dioica root demonstrated stimulant laxative activity in Swiss mice, validating its traditional usage in India.     

Effects of heat treatment on evolution of microstructure of boron free and boron containing biomedical Ti-13Zr-13Nb alloys

In the present study, the effects of heat treatment on the microstructure of Ti-13Zr-13Nb (TZN) and Ti-13Zr-13Nb-0.5B (TZNB) alloys have been investigated. Depending on the heat treatment conditions, the microstructure of the heat treated TZN alloy consisted mainly of elongated and/or equiaxed α, β or martensite. Slow cooling (furnace or air cooling) from the solution treatment temperature produced α and β phases in the microstructure. Rapid cooling (water quenching) resulted in martensite and retained β when the solution treatment temperature was above or close to β transus. However, martensite was not formed after water quenching from a solution treatment temperature which was below β transus due to partitioning effect of the alloying elements. Increasing the cooling rate from the furnace cooling to the air cooling led to finer microstructure. Aging of water quenched samples transformed the martensite, if present, into α and β, and the morphology of α phase changed from elongated to equiaxed and enhanced the growth of α. The microstructure of all the TZNB samples consisted of dispersed precipitated particles of TiB in the matrix. The majority of the boride particles showed an acicular (needle like) morphology. The other phases present in the TZNB alloy were similar to those in the similarly heat treated TZN alloy. Moreover, a growth of α phase was observed in the microstructure of TZNB alloy when compared with that of TZN alloy.