Analyse multielementaire instrumentale des phosphates marocains par photoactivation nucleaire

Photonuclear activation and high resolution gamma-ray spectrometry have been used to determine non-destructively the concentrations of 25 trace elements in Maroccan phosphate rock. The activation was simultaneously performed for phosphate samples and multielement standards in the bremsstrahlung beam of a linear electron accelerator at 18 and 30 MeV maximum energies. Gamma-ray spectra were recorded with a 79 cm³ Ge(Li) detector and a programmable analyzer IN 96. A detailed study of interferences was carried out. Limits of detection between 0.5 and 125 μg·g^?1 were obtained.     

White light emission from nano-fibrous ZnO thin films/porous silicon nanocomposite

Nanocomposites composed of nano-fibrous ZnO thin films and porous silicon (PS) were prepared and examined by atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy, and photoluminescence (PL) to investigate their structural and optical properties. PS, consisting of irregular and random nanosized-pores, was prepared by electrochemical anodization. The nano-fibrous ZnO thin films were grown on PS by the sol-gel spin-coating method. The texture coefficient (TC _(hkl)) of the nano-fibrous ZnO thin films was calculated to determine the preferred orientation. The nano-fibrous ZnO thin films were grown with a c-axis preferred orientation. The residual stress in the films was reduced in the case of PS. The observed broad PL emission peak from 460 to 598 nm was attributed to coupled emission from ZnO to PS. The results show that white light luminescence with blue, green, and red emission peaks having highly uniform intensities can be obtained from the nanocomposite via a relatively simple and low-cost sol-gel spin-coating method.     

Optimum design of InGaP/GaAs dual-junction solar cells with different tunnel diodes

We design the InGaP/GaAs dual-junction (DJ) solar cells by optimizing short-circuit current matching between top and bottom cells using the Silvaco ATLAS. The relatively thicker base layer of top cell exhibits a larger short-circuit current density (J _sc) while the thicker base layer of bottom cell allows for a smaller J _sc. The matched J _sc of 10.61±0.05 and 13.25±0.06 mA/cm ² under AM1.5G and AM0 illuminations, respectively, are obtained, leading to the increased conversion efficiency. The base thicknesses of top InGaP cells are optimized at 0.8 and 0.65 μm for AM1.5G and AM0 illuminations, respectively, and the base thicknesses of bottom GaAs cells are optimized at 2 μm. For the optimized solar cell structure, the maximum J _sc = 10.66 mA/cm ² (13.31 mA/cm ²), V _oc =  2.34 V (2.35 V), and fill factor =  87.84% (88.1%) are obtained under AM1.5G (AM0) illumination, exhibiting a maximum conversion efficiency of 25.78% (23.96%). The effect of tunnel diode structure, i.e, GaAs/GaAs, AlGaAs/AlGaAs, and InGaP/InGaP, on the characteristics of solar cells is investigated. The photogeneration rate in the DJ solar cell structure is also obtained by incident light of different wavelengths.     

Growth morphology of zinc tris(thiourea) sulphate crystals

The growth morphology of crystals of zinc tris(thiourea) sulphate (ZTS) is investigated experimentally, and computed using the Hartman-Perdok approach. Attachment energies of the observed habit faces are calculated for determining their relative morphological importance. A computer code is developed for carrying out these calculations. A special procedure is adopted for computing the cohesive energy of a slice of the structure parallel to any rational crystallographic plane. For estimating the cohesive energies, formal charges on the experimentally determined atomic positions in the molecules of ZTS are calculated by ab initio molecular-orbital computations, with wave functions obtained by the Hartree-Fock procedure. Fairly good agreement with the observed crystal morphology is obtained for a model of growth mechanism in which ZTS is assumed to exist in solution sa szinc tris(thiourea) ions and sulphate ions.     

Fractional Linear Multistep Methods for Abel-Volterra Integral Equations of the First Kind

Fractional powers of linear multistep methods are suggestedfor the numerical solution of weakly singular Volterra integralequations of the first kind. The proposed methods are convergentof the order of the underlying multistep method. The stabilityproperties are directly related to those of the multistep method.     

The Grunsky Norm and Some Coefficient Estimates for Bounded Functions

We estimate the growth order in n of the Taylor coefficientsof bounded univalent functions in the unit disk. Our estimatedepends on the norm of the Grunsky operator. In particular,we improve the known results for coefficients of quasiconformallyextendible univalent functions. 1991 Mathematics Subject Classification30C50, 30C75, 30C55.     

Experimental search for B = 2, T= 0 states in the d + d → d + X reaction

A search for isoscalar dibaryonic resonances by means of missing-mass spectra in the d + d → d + X reaction has been attempted using deuteron beams of T = 2.29,2.00 and 1.65 GeV. The results do not show any evidence for a narrow peak with a limit of $\text{30 nb}\text{GeV}{}^2$ for a 15 MeV width or a broad enhancement which could be unambiguously attributed to a dibaryonic resonance.     

Investigation of the quantitative properties of the quadrupole orthogonal acceleration time-of-flight mass spectrometer with electrospray ionisation using 3,4-methylenedioxymethamphetamine

This paper describes the investigation of the potential of a quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOF) equipped with an atmospheric pressure ionisation interface for quantitative measurements of small molecules separated by reversed phase liquid chromatography. To this end, the detection limits and linear dynamic range in particular were studied in an LC/MS/MS experiment using 3,4-methylenedioxymethamphetamine standards and 3,4-methylenedioxyethylamphetamine for internal standardisation. In a second phase, the experiment was repeated with real biological extracts (whole blood, serum, and vitreous humour). A calibration for 3,4-methylenedioxymethamphetamine and its metabolite 3,4-methylenedioxyamphetamine was prepared in each of these matrices again using 3,4-methylenedioxyethylamphetamine as internal standard. The resulting quantitative data were compared with those obtained by liquid chromatography with fluorescence detection for the same extracts. The Q-TOF results revealed excellent sensitivity and a linear dynamic range of nearly four decades (2-10 000 pg on-column, r(2) = 0.9998, 1/x weighting). Furthermore, all the calibration curves prepared in biological material were superimposable, LC/MS/MS and LC-fluorescence, and the quantitative results for actual samples compared very favourably. It was concluded that the Q-TOF achieves a linear dynamic range for quantitative LC/MS/MS work exceeding that of fluorescence detection and at much better absolute sensitivity. Copyright 1999 John Wiley & Sons, Ltd.     

Optical fiber-coupled InGaAs-based terahertz time-domain spectroscopy system

The successful demonstration of an optical fiber-coupled terahertz time-domain spectroscopy (THz-TDS) system is described in this study. The terahertz output power of the emitter with two optical band rejection filters was 132 nW, which is an improvement of 70% over the output power without any filters. This improvement is due to the suppression of an optical modulated signal that is reverse-generated when an alternating current bias exceeding a certain threshold is applied to the emitter. Under the optimal alignment conditions, the terahertz detector in a fiber-coupled THz-TDS system clearly measured water vapor dips in the free space.