Mössbauer spectral studies of di- and triorganotin(IV) histidinylleucinates

Some new di- and triorganotin(IV) derivatives of the formulae, R₂SnL, where R =Me, Ph, and n-Oct, and L is the dianion of histidinylleucine (H₂L abbreviated as H₂(His-Leu)) and R′₃ SnHL, where R^′?= Me and Ph, HL = monoanion of histidinylleucine, have been synthesized. The bonding and coordination behaviour in these derivatives are discussed on the basis of FT-IR and ¹¹⁹Sn Mössbauer spectroscopic studies. The ¹¹⁹Sn Mössbauer studies, together with the IR data suggest that the ligand in R₂Sn(His-Leu) acts as dianionic tridentate coordinating through C(O)O^???, –NH₂ at axial positions and N_peptide at equatorial position while in case of R′₃Sn(HHis ? Leu) the ligand acts as a monoanionic bidentate coordinating through C(O)O^??? and –NH₂ giving a distorted trigonal–bipyramidal environment around tin.     

Interaction of loosely bound radioactive 7Be and stable 7Li with 9Be

Quasielastic scattering angular distributions have been measured for the ⁷Be + ⁹Be system at E _lab = 17 , 19 and 21MeV in the angular range $ \theta_{{cm}}^{}$ = 24^° - 57^° . An optical model (OM) analysis of these data has been carried out in order to extract optical potential parameters and reaction cross-sections. One-proton stripping cross-sections were also measured for this system at E _lab = 19 and 21MeV. These transfer angular-distribution data were compared with the finite-range distorted-wave Born approximation (FRDWBA) calculations. For the ⁷Li + ⁹Be system quasielastic scattering angular distributions were measured and emitted light charged particles were detected at E _lab = 15.75 , 24.00 and 30.00MeV in the angular range $ \theta_{{cm}}^{}$ = 7^° - 70^° . Fusion cross-sections were obtained by reproducing the measured $ \alpha$ -evaporation spectra from the compound nucleus at backward angles with the statistical model calculations. The ratios of the experimental fusion cross-sections to the total reaction cross-sections (obtained from OM analysis) were found to be small. This result suggests that the break-up process has a strong influence on the fusion process leading to a reduction in the fusion cross-section.     

Why does the open-circuit voltage in a micro-crystalline silicon PIN solar cell decrease with increasing crystalline volume fraction?

In hydrogenated micro-crystalline silicon (μc-Si:H) thin film solar cells, the open-circuit voltage (V_OC) shows a decline when the crystalline volume fraction (F_c) of the intrinsic μc-Si:H layer increases from 60% to over 90%. In this article we have simulated the experimental characteristics of solar cells, having intrinsic layers of different degrees of crystallinity to understand the reasons why. In order to model all aspects of the characteristics, we had to assume (a) wider band tails, (b) a higher mid-gap defect density and (c) a lower band gap for the more crystallized material. Modeling reveals that all three factors lower the field in the volume of the device and hence V_OC, due to higher photo-generated hole-trapping close to the P/I interface. The third factor brings the quasi-Fermi levels closer to the band-edges, resulting in higher free and trapped carrier densities throughout the device, with the trapped hole population particularly high at the P/I interface. We further show that V_OC is higher in a crystalline silicon PN cell, in spite of a sharply reduced band gap, because the lower effective density of states at the band-edges and sharply reduced band gap defect density overcome the effect of the smaller band gap.     

Shock wave driven out by a piston in a mixture of a non-ideal gas and small solid particles under the influence of the gravitation field with monochromatic radiation

Similarity solutions for a spherical shock wave in a mixture of small solid particles of micro size and a non-ideal gas are discussed under the influence of the gravitational field with monochromatic radiation. The solid particles are uniformly distributed in the mixture, and the shock wave is assumed to be driven by a piston. It is assumed that the equilibrium flow-conditions are maintained and the moving piston continuously supplies the variable energy input. Due to the central mass ($\overline{m}$) at the origin (Roche model), the medium is considered to be under the influence of the gravitational field. In comparison to the attraction of the central mass at the origin, the gravitational effect of the mixture itself is neglected. The density of the undisturbed medium is assumed to be constant in order to obtain the self-similar solutions. The effect of the parameter of non-idealness of the gas $\overline{b}$, the mass concentration of solid particles in the mixture μ_p, the ratio of the density of solid particles to the initial density of the gas G_a and the gravitational parameter G₀ are obtained. It is shown that due to an increase in the gravitational parameter the compressibility of the medium at any point in the flow field behind the shock front decrease and the flow variables velocity, pressure, radiation flux and shock strength are increased. Also, an increase in the ratio of the density of solid particles to the initial density of the gas G_a and the gravitational parameter G₀ has the same effect on the shock strength and the reverse effect on the compressibility. The non-idealness of the gas causes a decrease in the shock strength and widens the disturbed region between the piston and the shock.     

Tunable dielectric and conductivity properties of two 4-n alkoxy benzoic acid

We have presented dielectric and conductivity studies of two liquid crystal (LC) compounds- p-octyloxybenzoic acid (8OBA) and p-decyloxybenzoic acid (10OBA). Dielectric permittivity study of those compounds gives the evidence of space charge polarization and ionic conductance in the samples. Dielectric permittivity is found to be the highest for 8OBA than 10OBA. Both compounds found to exhibit positive dielectric anisotropy. Splay elastic constant as a function of temperature has also been investigated. Frequency and temperature dependent electrical conductivity of these two LC compounds have been studied in detail. Activation energy has been estimated from both dc and ac conduction process.     

Synthesis of 2-Arylpyrimido[4,5-b]porphyrins via Cyclization Reaction with Ammonia

A facile synthetic strategy for the synthesis of a new series of β,β’-fused 2-arylpyrimido[4,5-b]porphyrins has been developed by using condensation cyclization reaction with ammonia. 2-Aroylamino-3-formylporphyrins were synthesized from 2-aroylaminoporphyrins under Vilsmeier–Haack reaction conditions, which were then efficiently converted to the corresponding 2-arylpyrimido[4,5-b]-5,10,15,20-tetrakis(4-chlorophenyl)-porphyrins via a condensation cyclization reaction. The nickel(II), copper(II), free-base and zinc(II) analogues of 2-arylpyrimido[4,5-b]porphyrins were successfully synthesized in 65–72 % yields and structurally characterized on the basis of spectral data analysis. On photophysical evaluation, 2-arylpyrimido[4,5-b]porphyrins demonstrated a 12–19 nm bathochromic shift in their electronic absorption spectra and up to 10 nm red shift in their emission spectra as compared to the simple meso-(tetrakis(4-chlorophenyl))porphyrins due to the extended π-conjugation.     

Study of Scaling Exponents of the Surface Evolved in 2 + 1 Dimension through Competitive Growth between Random Deposition and that with Surface Relaxation

Rough surface develops through computer simulation by competition between growth mechanism random deposition (RD) with a probability of occurrence p and growth mechanism random deposition with surface relaxation (RDSR) with a probability of occurrence 1 − p, on L × L square plane for system size L to record the statistical average of time variation of surface roughness W(L, t) and average height H(t) for the model for specific values of L and p. Other than the pure RD model, the entire evolution may be divided into three regions separated by two specific cross-over times t_x and t_sat. The value of interface width at saturation W_sat depends on both L and p. The first growth exponent β₁ increases exponentially with an increase in p and does not depend on L. The values of the second growth exponent β₂, roughness exponent α, dynamic exponent z( = α/β₂ ), and α + z are 0.0234 ± 0.0008, 0.0506 ± 0.0065, 2.1577 ± 0.0073, and 2.2083 ± 0.0138 respectively and they show no dependence on L and p values. Value of the first cross-over time t_x increases exponentially with an increase in p and does not depend on L. Value of the second cross-over time t_sat increases with an increase in both p and L values. The average growth velocity is unity for the model and is independent of both L and p. For the model, the growth velocity is unity and the fractional porosity is zero. The scaling exponents show some deviation from the relevant universality classes and depend on competitive growth probability for this model. No finite-size effect is present in the model.