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91.
An ultracryostat and multidecameter were used to determine the temperature dependence of the dielectric constant ?′ and dielectric loss ?″ over a wide range of frequencies of single crystals and polycrystalline samples of (NH4)2SO4 in the region of the low temperature phase transition. A sharp increase was observed in the values of ?′ and ?″ at about ?50°C. In addition, a dielectric dispersion was detected and found to be more pronounced in the high temperature phase. This dispersion was attributed to piezoelectric resonance. The observed sudden increase in the values of the dielectric constant and dielectric loss below ? 50°C was attributed to the ferroelectric nature of the low temperature phase of (NH4)2SO4.A DTA thermogram showed a sharp peak at ? 50°C which indicated that the phase transition is one of first order type. A TMA thermogram showed that this transformation was associated with a rapid increase in the expansion coefficient. Such an increase in the lattice parameter might be attributed to the enhanced rotation of electric dipoles associated with the distorted NH4+ and SO42? ions. The distortion of both the ammonium and sulfate ions in addition to their expected orientational motion are suggested to be responsible for the ferroelectric behaviour of ammonium sulfate below ?50°C.A transition to a metastable hexagonal state at about ?40°C is thought to occur, and this transformation is found to be irreversible. 相似文献
92.
This work elucidates the photoconductivity (PC) of thallium monosulfide single crystals. Results are obtained in the 77–300
K temperature range, 1500–4500 V lx excitation intensity, 6–18 V applied voltage, and in the 640–1500 nm wavelength range.
Both the ac-photoconductivity (ac-PC) and the spectral distribution of the photocurrent are studied in different values of
light intensity, applied voltage and temperature. Dependencies of carrier lifetime on light intensity, applied voltage and
temperature are also investigated as a result of the ac-PC measurements. The temperature dependence of the energy gap width
was described by studying the dc-photoconductivity (dc-PC).
相似文献
93.
A study on laminar motion of a viscous incompressible fluid between two parallel eccentric cylinders
The flow of incompressible viscous fluid between two eccentric cylinders under the action of a difference between the pressures imposed at the ends of the cylinders is analyzed. Using bipolar coordinates, the resulting boundary value problem is solved analytically, and the average flux velocity is calculated for various values of the geometric parameters of the problem. 相似文献
94.
Tea bags including fruits of Ammi visnaga L. are used in Egypt as remedy for the treatment of kidney stones. Our study focuses on developing simple and rapid method utilising HPLC for quantitative estimation of khellol glucoside (KG), khellin (KH) and visnagin (VS) simultaneously. Their concentrations were determined in A. visnaga L. fruits at different developmental stages and in pharmaceutical formulations together with following up them during shelf life. Separation was accomplished using HPLC. Perfect resolution between KG, KH and VS was possible through using a mobile phase consisting of water:methanol:tetrahydrofuran (50:45:5, v/v/v). Peaks were detected at 245 nm. The suggested method for the determination of KG, KH and VS was successful in determining the analytes of interest without any interference of other compounds and matrix. All validation parameters were satisfactory and the procedure was relatively easy and fast as extracts are evaluated without previous steps of purification. 相似文献
95.
Husseiny MI El-Aziz MA Badr Y Mahmoud MA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,67(3-4):1003-1006
Pseudomonas aeruginosa were used for extra-cellular biosynthesis of gold nanoparticles (Au NPs). Consequently, Au NPs were formed due to reduction of gold ion by bacterial cell supernatant of P. aeruginosa ATCC 90271, P. aeruginosa (2) and P. aeruginosa (1). The UV-vis and fluorescence spectra of the bacterial as well as chemical prepared Au NPs were recorded. Transmission electron microscopy (TEM) micrograph showed the formation of well-dispersed gold nanoparticles in the range of 15-30 nm. The process of reduction being extra-cellular and may lead to the development of an easy bioprocess for synthesis of Au NPs. 相似文献
96.
The European Physical Journal E - Three recently observed facts of the translocation of actual hexameric and nonstructural (NS) helicases are related to the various physical quantities and are in... 相似文献
97.
Single phase MnPS3 powder was prepared by solid state reaction between Mn, S and P carried out at 650 °C in evacuated silica tube. The structure, morphology and sorption characteristics of the prepared solid were investigated. The results revealed that the obtained MnPS3 compound was capable of adsorbing 3.5 wt% hydrogen at −193 °C and a pressure of 30 bar. Little amount of hydrogen (0.07 wt%) was adsorbed at room temperature. The hydrogen adsorption/desorption cycles at various temperatures did not result in irreversible chemical structural changes of the MnPS3 compound, but the microstructure after hydrogen cycling diminished and became finer. 相似文献
98.
Hamdan A.S. Al-Shamiri Maram T.H. Abou Kana I.M. Azzouz Y.A. Badr 《Optics & Laser Technology》2009,41(4):415-418
The field of laser dyes-active solid polymer materials is a promising field and quite competitive with liquid dye lasers. This paper investigates some photo-physical parameters of pyromethene (PM-567, PM-597) and Rhodamine B dyes incorporated into glycidyl methacrylate (GMA) promising polymeric host matrix. These parameters are: absorption and emission cross-sections, fluorescence lifetime and quantum yield, in addition to FT-Raman spectra as an indication for binding the dye molecules with the backbones of GMA polymeric chain. 相似文献
99.
Benboubker Mohamed Badr Hjiaj Hassan OUARO Stanislas 《Journal of Applied Analysis & Computation》2014,4(3):245-270
In this work, we give an existence result of entropy solutions for nonlinear anisotropic elliptic equation of the type $$- \mbox{div} \big( a(x,u,\nabla u)\big)+ g(x,u,\nabla u) + |u|^{p_{0}(x)-2}u = f-\mbox{div} \phi(u),\quad \mbox{ in } \Omega,$$ where $-\mbox{div}\big(a(x,u,\nabla u)\big)$ is a Leray-Lions operator, $\phi \in C^{0}(I\!\!R,I\!\!R^{N})$. The function $g(x,u,\nabla u)$ is a nonlinear lower order term with natural growth with respect to $|\nabla u|$, satisfying the sign condition and the datum $f$ belongs to $L^1(\Omega)$. 相似文献
100.
Let (??,??) be an infinite graph endowed with a reversible Markov kernel p and let P be the corresponding operator. We also consider the associated discrete gradient ?. We assume that ?? is doubling, a uniform lower bound for p(x,y) when p(x,y)>0, and gaussian upper estimates for the iterates of p. Under these conditions (and in some cases assuming further some Poincaré inequality) we study the comparability of (I?P)1/2 f and ?f in Lebesgue spaces with Muckenhoupt weights. Also, we establish weighted norm inequalities for a Littlewood?CPaley?CStein square function, its formal adjoint, and commutators of the Riesz transform with bounded mean oscillation functions. 相似文献