Optička i električna svojstva neozračenog i rendgenskim zračenjem ozračenog PMABB

Studies of the optical and electrical (ferroelectric, electrical conductivity) properties of non- and X-ray-irradiated pentakis undecabromodibismuthate (PMABB) orthorhombic crystals were made. The crystal is anisotropic, weakly positively birefringent and optically biaxial with the optical angle 2V = 72◦ 150. The temperature dependence of linear birefringence ∆(∆nc) in the temperature range from 295 K to 320 K shows an anomaly at the phase-transition temperature Tc = 312 K, in agreement with the published result. The spontaneous polarization Ps seems slightly large in comparison with those of other ferroelectrics, owing to the strengthened packing along the polar axis. The results show that the microscopic mechanism driving the phase transition has the same influence on the spontaneous birefringence δs(∆nc) and on Ps in the compound. Effects of irradiation on the refractive indices and their dispersions as well as on the optical anisotropy and optical birefingence are studied. The coercive field Ec and the bias field Eb build up during the irradiation, while Ps shows no change with the enhanced doses until the threshold irradiation (D0 = 4 × 104 rad) is reached, then it begins to decay in a fairly rapid manner. The results are discussed in terms of the conventional double-minimum potential energy used for the description of the ferroelectric mechanism. Measurements of the electrical conductivity σ in the same temperature range show an anomaly at Tc due to the generation of protonic carriers as a result of rotational motion of cations. The maximum σ-value at the threshold irradiation D0 is observed and the variation of σ in the vicinity of D0 was studied.Proučavala su se optička i električna svojstva ortorombnih kristala pentakis undecabromodibismuthata (PMABB) prije ozračivanja i ozračenih s nekoliko doza rendgenskog zračenja. Kristali PMABB su anizotropni, malo pozitivno dvolomni i optički dvoosni s optičkim kutom 2V = 72◦ 150 . Spontana polarizacija Ps je relativno velika zbog snažnijeg slaganja vodikovim vezanjem duž polarne c-osi. Mikroskopski mehanizmi koji uzrokuju fazni prijelaz jednako utječu na Ps i na spontani dvolom δs(∆nc). Ps se ne mijenja za doze ispod kritične, DD0 smanjuje se naglo. Ishodi mjerenja se raspravljaju na osnovi dvostrukog minimuma potencijala koji se rabi za opis feroelektričnog mehanizma. Koercitivno polje Ec i polarizacijsko polje Eb rastu s ozračivanjem zbog promjena unutarnjih polja. Električna vodljivost σ pokazuje anomaliju na kritičnoj temperaturi Tc zbog stvaranja protonskih nositelja koji su posljedica zakretanja kationa. Pri DD0 smanjuje zbog djelovanja klopki

Shapiro and parametric resonances in coupled Josephson junctions

The effect of microwave irradiation on the phase dynamics of intrinsic Josephson junctions in high temperature superconductors is investigated. We compare the current-voltage characteristics for a stack of coupled Josephson junctions under external irradiation calculated in the framework of CCJJ and CCJJ+DC models.Comment: 4 pages, Manuscript for Dubna-Nano 2012, submitted for Journal of Physics:Conference Serie

Low Incidence of Androgen Receptor Mutation Among Egyptian Children with Androgen Resistance

Introduction: In Egypt, disorders of sex development (DSD) constitute a significant entity among the birth defect list. Previous studies have reported that end organ androgen unresponsiveness, i.e. Androgen resistance, was the most prevalent underlying mechanism among Egyptian 46,XY DSD cases. Based on cytogenetic and hormonal diagnostic criteria as well as few sporadic case reports, it was proposed that androgen receptor (AR) defects [i.e. Androgen insensitivity syndrome (AIS), OMIM#300068] might constitute a major etiology within this category. However, this has never been systematically ascertained through an AR molecular diagnostic approach. Aim of the Work: The current study aimed to assess the role of AR mutations as an underlying etiology among a sample of Egyptian 46,XY DSD pediatric patients presenting with androgen end organ unresponsiveness. Patients and Method: In the current study, 21 children [ag