X-ray diffraction by thermotropic main-chain polymers with side groups. II. semiflexible polyesters

Semiflexible thermotropic aromatic polyesters with lateral groups were aligned magnetically and mechanically in monodomains after separation into high-molecular-weight (polymer) and low-molecular-weight (oligomer) fractions. Based on the x-ray intensity distributions recorded for a series of seven different substituents in the arylsulfonyl substituted group, a novel smectic structure was determined for H, F, Cl, OCH₃, and CH₃ in the para position while a normal nematic alignment prevailed when it contained Br or NO₂.     

HPLC in the investigation of taxonomic problems. Classification of poplar genotypes

Summary The RP-HPLC technique has been applied to the analysis of the flavonoid content of leaf extracts from various genotypes ofPopulus nigra andPopulus deltoides and from several of their hybrids. Two elution procedures different either as regards gradient program or the type of organic modifier used were checked to optimize the reliability of the results obtained. Before making any identification, the chromatographic profiles proved so typical of each species as to allow of their use as fingerprints in this type of taxonomic problem. Individual identifications were carried out by spiking real samples with known amounts of standard substances. The presence of flavonoid compounds previously identified was confirmed and a few new identifications were proposed.     

Synthesis and antimicrobial evaluation of novel 3-(arylideneamino)-3a,8a-dihydroxy-1,3,3a,8a-tetrahydroindeno[1,2-d]imidazole-2,8-diones and their 2-thioxo analogues

The preparation of some novel 3-(arylideneamino)-3a,8a-dihydroxy-1,3,3a,8a-tetrahydroindeno[1,2-d]imidazole-2,8-diones 8(i–xiv) and 3-(arylideneamino)-3a,8a-dihydroxy-2-thioxo-1,3,3a,8a-tetrahydroindeno[1,2-d]imidazol-8(2H)-ones 9(i–xiv) have been reported through one-pot catalyst-free reaction of aldehydes, semicarbazide hydrochloride/thiosemicarbazide with ninhydrin. All the synthesized compounds have been screened for antimicrobial activity and some of them were observed to possess broad spectrum antibacterial potential as well as significant antagonistic potential against fungal pathogens.     

Synthesis and studies on photochromic properties of vanadium doped TiO2 nanoparticles

Pure and (0.5–3 at%) vanadium doped TiO₂ nanoparticles have been synthesized by wet chemical method. The as synthesized materials have been characterized by using XRD, atomic force microscope (AFM), Raman, EPR and UV–vis spectroscopy techniques. From XRD studies, both pure as well as vanadium doped TiO₂ have been found to show pure anatase phase. The value of lattice constant c is smaller in doped TiO₂ as compared to undoped and has been found to decrease with increase in vanadium concentration. AFM studies show formation of spherical particles with particle size ～23 nm in all the samples. Photochromic behavior of these materials has been studied by making their films in alkyd resin. Vanadium doped TiO₂ films show reversible change in color from beige-yellow to brownish violet on exposure to UV light. The mechanism of coloration and bleaching process has been discussed.     

Soft biometrics in conjunction with optics based biohashing

Biometric systems are gaining importance because of increased reliability for authentication and identification. A biometric recognition technique has been proposed earlier, in which biohashing code has been generated by using a joint transform correlator. The main drawback of the base biohashing method is the low performance of the technique when an “impostor” steals the pseudo-random numbers of the genuine and tries to authenticate as genuine. In the proposed technique, soft biometrics of the same person has been used to improve the discrimination between the genuine and the impostor populations. The soft biometrics are those characteristics that provide some information about the individual, but lack the distinctiveness and permanence to sufficiently differentiate between any two individuals. In the enrolment process, biohash code of the target face images has been integrated with the different soft biometrics of the same person. The obtained code has been stored for verification. In the verification process, biohash code of the face image to be verified is again diffused with the soft biometric of the person. The obtained code is matched with the stored code of the target. The receiving operating characteristic (ROC) curve and the equal error rate (EER) have been used to evaluate the performance of the technique. A detailed study has been carried out to find out the optimum values of the weighting factor for the diffusion process.     

Spin-polarized electron–electron quantum bilayers: Finite width effect

We study the effect of finite width on the ground-state of a spin-polarized electron–electron quantum bilayers (EEBL) system at temperature T=0. Correlations among carriers are treated beyond the static mean-field theories by using the quantum or dynamical version of Singwi, Tosi, Land and Sjölander (qSTLS) theory. Numerical results are presented for the pair-correlation function, the ground-state energy, the static density susceptibility, and the static local-field correction factor as a function of density parameter r_sl and interlayer spacing d. Interestingly, we find that the inclusion of finite width lowered the critical density, for the onset of Wigner crystal (WC) ground-state, as compared to the similar recent study of spin-polarized EEBL system without finite width effect. Further, spin-polarization effect is seen to introduce a marked change in the ground-state energy of the EEBL system as compared to the results of unpolarized EEBL system with finite width. Results of ground-state energies are also compared with the recent diffusion Monte Carlo (DMC) and variational Monte Carlo (VMC) simulation studies of spin-polarized EEBL system with zero width.     

The low frequency behaviour in high frequency capacitance–voltage characteristics due to contribution of band-to-band tunnelling and generation–recombination in Hg0.75Cd0.25Te MIS capacitors

Hg_1−xCd_xTe Metal–Insulator–Semiconductor (MIS) capacitors were studied both experimentally and theoretically to investigate the capacitance contributions due to band-to-band (btb) tunnelling and generation–recombination (gr) of carriers to inversion layer capacitance. A good fit to the data has been obtained by including the btb contributions rather than gr contributions.     

Bose-einstein correlations in the target fragmentation region in 200A GeV16O+nucleus collisions

Correlations between positive pions are investigated in the target fragmentation region of 200A GeV¹⁶O+nucleus collisions. The pions are measured with the Plastic Ball detector in the WA80 experiment at the CERN SPS. The target mass dependence of the radii and the correlation strength extracted by interferometry is studied. A new approach to the fit of the correlation function is introduced. The correlation strength and both invariant and transverse radii increase with decreasing target mass. The transverse radius for¹⁶O+C reactions appears to be much larger than the geometrical radius of the nuclei involved. For the Au target only a small fraction of the measured pions contributes to the apparent correlation. Hints for a much larger second component in¹⁶O+Au reactions are observed. Rescattering phenomena may provide a clue to understand these phenomena.     

A Convenient and Facile Synthesis of Isoxazolyl‐chromeno[4,3,2‐de]pyrimido[4,5‐h][1,6]napthyridinones

The ceric ammonium nitrate‐catalyzed synthesis of (E)‐5‐amino‐N‐(3‐methyl‐5‐styrylisoxazol‐4‐yl)‐2‐arylchromeno[4,3,2‐de][1,6]napthyridin‐4‐carboxamides 5 was simply achieved upon the one‐pot four‐component reaction of isoxazolyl cyanoacetamide 1 with malononitrile 2 , 2‐hydroxy acetophenone 3 , and aromatic aldehydes 4 in ethanol. Compounds 5 on heating with acetic anhydride underwent tandem N‐acetylation and cyclocondensation involving intramolecular cyclization to afford the title compounds (E)‐11‐methyl‐12‐(3‐methyl‐5‐styrylisoxazol‐4‐yl)‐2‐arylchromeno[4,3,2‐de][1,6]napthyridin‐13(12H)‐ones 6 in good yields. The chemical structures have been confirmed by analytical and spectral analyses.