A. B. Ahmed  R. K. Gartia 《physica status solidi (a)》1985,89(1):231-235

Fractional glow technique (FGT) is satisfactorily applied in analysing the rather broad thermo luminescence (TL) curve observed in a plagioclase feldspar. Monochromatic TL recorded through various filters reveals that the broad composite curve consists of at least four peaks appearing in the region of 80 to 100, 130 to 160, 200 to 230, and 250 to 280 °C. FGT analysis in the temperature range of 40 to 250 °C shows the existence of three discrete traps with thermal activation energies around 0.78, 1.16, and 1.42 eV. While the 0.78 and 1.16 eV traps can be assigned to the first and the second TL peaks respectively, the 1.42 eV trap can be attributed to the third and fourth TL peaks. The peak occuring in the region of 250 to 280 °C (fourth peak) is further analysed by the peak shape method and various heating rates method. The values of activation energies obtained by these methods are found to be (1.43 ± 0.03) and (1.46 ± 0.05) eV, respectively. These results justify the assignment of the 1.42 eV trap to the fourth pèak.  相似文献   

    

Saleh A. Ahmed  Ziad Moussa  Shaya Y. Al‐Raqa  Saleh N. Alamry 《Journal of Physical Organic Chemistry》2009,22(6):593-606

Multi‐addressable photophysical properties of new synthesized photochromic materials based on photochromic dihydroindolizine system (DHI) covalently linked to N‐acyl‐11 aminoundecanoic acid (AUDA) or to its sodium salt or to its ester, through an amidic or urethane linkage have been studied. The DHI skeleton in these compounds is substituted in both the fluorene part (region A) or in the heterocyclic base (region B) with the gelling moieties. These molecules have been designed to respond to their environment. Interestingly, they are shown to act as efficient gelators for polar organic fluids, water and obviously they exhibit a thermosensitive answer as low molecular mass organogelators. In these fluids, the aggregative properties are totally suppressed upon conversion to neutral carboxylic species. The gels of these carboxylate sodium salts are shown to be markedly affected by light irradiation. Supramolecular gelating assemblies can be disrupted by the photoinduced ring opening of the DHI subunit, so that the macroscopic flowing property is recovered. Upon a further thermal treatment, the system is reversibly converted back to the supramolecular network. Controlled gelation could be achieved using temperature, light, or acidity as external stimuli. These new synthesized photochromic gels with their multi‐addressable properties will find their applications as super photoresponsive materials. Developing and tuning of the photophysical properties of the synthesized compounds by the amide and urethane substituents in the 4‐position of the fluorene and pyridazine regions have been achieved. The absorption maxima (λ_max) and the half‐lives (t_1/2) of the colored betaines were detected in all cases using UV/VIS spectrophotometric measurements. Irradiation of DHI 12‐20 in CH₂Cl₂ or in acetonitrile solutions at ambient temperature with polychromatic light leads to the formation of red to red‐violet colored betaines 12 ′ ‐20 ′. The kinetics of the bleaching process of betaines 12 ′ ‐20 ′ to DHIs 12‐20 were found to take place in the second range (96‐218 s) and fit well the first order thermal back reaction. Some of these DHIs showed a photostability higher than that of the standard one. These interesting photophysical properties will help this family of compounds to find useful applications. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

    

Paolo Fornasini  Sameh I. Ahmed  Andrea Sanson  Marco Vaccari 《physica status solidi b》2008,245(11):2497-2503

Extended X‐ray absorption fine structure (EXAFS) can give information on the local dynamical behavior of crystals, opening new perspectives for understanding the origin of negative thermal expansion (NTE). In this paper, after a short review on the effects of thermal disorder in EXAFS spectra and on the relation between EXAFS and Bragg diffraction, some recent results on crystals with the zincblende and cuprite structures are presented and critically compared. The tension effect giving rise to NTE can be correlated to the anisotropy of the mean square relative displacements measured by EXAFS. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

Ibtesam O. Radi  Mudar A. Abdulsattar  Ahmed M. Abdul‐Lettif 《physica status solidi b》2007,244(4):1304-1317

A self‐consistent LUC (large unit cell) formalism on the basis of semiempirical INDO (intermediate neglect of differential overlap) Hamiltonians has been used to study the electronic properties of diamond and to investigate the pressure dependence of these properties. The calculated properties are in good agreement with the experiments except the conduction‐band width. The increase of pressure on diamond is predicted to cause the following effects; an increase of the valence and conduction‐band widths with a decrease of the direct bandgap, an increase of the electronic occupation probability for the p‐orbital with a decrease of this probability for the s‐orbital, and a decrease of the X‐ray scattering factor. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

    

Mohamed El-Gamel  John R. Cannon  Ahmed I. Zayed. 《Mathematics of Computation》2004,73(247):1325-1343

There are few techniques available to numerically solve sixth-order boundary-value problems with two-point boundary conditions. In this paper we show that the Sinc-Galerkin method is a very effective tool in numerically solving such problems. The method is then tested on examples with homogeneous and nonhomogeneous boundary conditions and a comparison with the modified decomposition method is made. It is shown that the Sinc-Galerkin method yields better results.

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Ahmed Mohammed 《Proceedings of the American Mathematical Society》2007,135(1):141-149

Given a positive and an increasing nonlinearity that satisfies an appropriate growth condition at infinity, we provide a condition on for which the Monge-Ampère equation admits a solution with infinite boundary value on a strictly convex domain . Sufficient conditions for the nonexistence of such solutions will also be given.

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Ahmed I. Zayed 《Proceedings of the American Mathematical Society》2007,135(7):2193-2203

Many systems of orthogonal polynomials and functions are bases of a variety of function spaces, such as the Hermite and Laguerre functions which are orthogonal bases of and and the Jacobi polynomials which are an orthogonal basis of a weighted The associated Legendre functions, and more generally, the spheroidal wave functions are also an orthogonal basis of

The prolate spheroidal wave functions, which are a special case of the spheroidal wave functions, possess a very surprising and unique property. They are an orthogonal basis of both and a subspace of known as the Paley-Wiener space of bandlimited functions. They also satisfy a discrete orthogonality relation. No other system of classical orthogonal functions is known to possess this strange property. This raises the question of whether there are other systems possessing this property.

The aim of the article is to answer this question in the affirmative by providing an algorithm to generate such systems and then demonstrating the algorithm by a new example.

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MOUSTAFA Nagy Emam  EISSA Elham Ahmed 《色谱》2007,25(6):871-875

 The Flory-Huggins interaction parameter (χ∞1,2) and solubility parameter (δ2) and its hydrogen bonding sensing component (δh) were determined using inverse gas chromatography (IGC). These parameters were successfully used in the probes of chemical changes that occur during the oxidation of naphthenic and paraffinic base oils in a GC column. Changes in χ∞1,2 values reflect the different types of intermolecular interactions (dispersive, polar, hydrogen bonding) of the given lubricating base oil during oxidation. The obtained results showed that δh component of solubility parameter is the most important parameter for probing the oxidative-chemical changes during the oxidation of given lubricating oils.  相似文献   

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Mukhtar Ahmed Rana  Shahid Manzoor 《中国物理快报》2008,25(9):3208-3211

Total fragmentation cross section for the reaction 158A Pb ions ＋ Cu target is measured using the most sensitive track detector CR-39. Measured values are compared with calculations. Exposures of target-detector stack with 158A P5 projectiles are made at CERN-SPS beam facility. Results of calibration of CR-39 detector in a charge region （63 ≤ Z ≤ 83） are also reported, which can be used for high energy particle identification using CR-39 and in determination of partial charge changing cross sections. The charge resolution δz achieved by this technique is about 0.2e. A systematic dependence of total fragmentation cross section on target properties is revealed and the corresponding results are presented.  相似文献   

    

Ahmed Mohammed 《Proceedings of the American Mathematical Society》2001,129(9):2617-2621