Browsing Mathematics, Statistics & Physics by Publication Date

Now showing items 1-20 of 742

    • Absolute evaluation of ferrous and ferric concentration in Ca amphibole 

      Bahgat, A. A.; Fayek, M. K. ( WILEY-VCH Verlag , 1982 , Article)
      Studies are made of M?sshauer absorption of 57Fe in a Ca-amphibole schist sample at room and liquid nitrogen temperatures. The absolute concentration and the recoilless fraction for ferrous and ferric cations are determined ...

    • Mössbauer study of ZnxNi5/3−xFe1Sb1/3O4 spinel ferrite 

      El Nimr, M.K.; Saleh, H.A.; Fayek, M. K. ( Springer Verlag , 1985 , Article)
      The antimony substituted nickel ferrite ZnxNi5/3–xFe1Sb1/3O4 with different values ofx are prepared, checked by x-ray and studied with57Fe Mössbauer spectroscopy over a wide temperature range. Characteristic spectra of ...

    • Mössbauer effect study of Li21+Me4+Fe63+O122−spinels 

      Saleh, H.A.; El Nimr, M.K.; Nada, N.; Fayek, M. K. ( Baltzer Science Publishers, Baarn/Kluwer Academic Publishers , 1986 , Article)
      Mossbauer effect spectra are obtained for the cubic ferrites Li2 Me Fe6 O12 (where Me4+ is one of the tetravalent elements Ge, Si and Ti) at 78K up to their magnetic transition temperatures. In a rather large temperature ...

    • On the Valence State of Iron in Sr0.52+Ca0.52+Fe0.54+ Me0.54+O32− 

      Fayek, M. K.; Elnimr, M. K.; El Hamalawy, A.; Sekina, M. A. ( WILEY-VCH Verlag GmbH & Co. , 1989 , Article)
      Powder samples of Sr0.5Ca0.5Fe0.5Me0.5O3 (Me = Co, Zr or Mn) and Sr0.3La0.7FeO3 are investigated by X-ray diffraction and Mossbauer effect spectroscopy. Analysis of the completely ordered spectra suggested three kinds ...

    • The Influence of Cation Substitution on the Magnetic Behaviour of Magnesium Ferrite 

      Fayek, M.; Elnimr, M.; Nada, N.; Saleh, H.; Eid, Y. ( WILEY-VCH Verlag GmbH & Co. , 1989 , Article)
      New polycrystalline specimens of the ferrites Mg1.5Fe1Si0.5O4, Mg1.5Fe1Ge0.5O4, Mg1.5Fe1Ti0.5O4 and Mg1.66Fe1Sb0.33O4 have been prepared and studied by nuclear gamma ray resonance technique, over a wide temperature range. ...

    • On Transformations and Perturbations of Orthogonal r-Frames 

      Sherif, N. ( WILEY-VCH Verlag GmbH & Co. , 1993 , Article)
      A decomposition of Cn into a finite direct sum of orthogonal subspaces can be conveniently represented by its orthogonal projector frame, which is the collection of the corresponding orthogonal projectors. Two such ...

    • Effect of gamma radiation on the morphology and Thermophysical properties of the pollen wall of Phoenix dactylifera L. 

      El-Ghazaly, Gamal; Kassem, M.E. ( Qatar University , 1994 , Article)
      Pollen grains of Phoenix dactylifera were exposed to different doses of gamma radiation (250,500,1000 rad and 1 M rad). To access the effect of radiation on the external morphology of the pollen grains, they were examined ...

    • A 6th-order local approximation by a cubic curve 

      Rababah, A.; Ta'ani, A. A. ( Qatar University , 1997 , Article)
      We derive and present a MAPLE program for the construction of a parametric cubic polynomial curve which has sixth-order contract with a given smooth curve at a given point, thus providing a local sixth-order approximation ...

    • Radon concentration determination in some dwellings of Doha city of Qatar 

      Arafa, W.; El-Karadawi, E. ( Elsevier , 1997 , Article)
      Yearly average radon concentrations have not been reported yet in Qatar. Only few measurements on indoor radon concentrations have been conducted during the autumn season in 1992. To complete these measurements a determination ...

    • Positron annihilation lifetime study of pure and treated polyvinyl chloride 

      Al-Qaradawi, I. Y.; Abdel-Hady, E. E. ( scientific.net , 1997 , Article)
      Positron annihilation lifetime technique (PAL) has been applied to investigate the behavior of the free volume in pure and doped polyvinyl chloride (PVC) as a function of Pb concentration and temperature. It is noticed ...

    • Membrane solubilization in erythrocytes as a measure of radiation exposure to fast neutrons 

      Monem, A Soltan; Ali, Fadel M; Al-Thani, Noura J J.; Ali, Samira A ( IOP Publishing , 1999 , Article)
      Membrane solubilization and osmotic fragility of rat erythrocytes irradiated in vivo with fast neutron fluences ranging from 106 to 5 x 107 n cm-2 using a 252Cf source were measured instantaneously using a light scattering ...

    • Study on ferroelastic characteristics of gamma irradiated lithium potassium sulfate crystal 

      N.K, Madi; Kassem, M.E; El-Muraikhi, M; El-Khatib, A.M ( Elsevier , 1999 , Article)
      A detailed study of the optical absorption vs. γ-irradiation dose for lithium potassium sulfate crystal, LiKSO4 cut out perpendicular to x, y and z directions is presented. The optical density was measured within the ...

    • Thermalization times of positrons in molecular gases 

      Al-Qaradawi, Ilham; Charlton, Michael; Borozan, Ivan; Whitehead, Ralph (2000 , Article)
      The time that a particle takes to reach thermal equilibrium in gas is a gross measure of the efficiency with which such particle can exchange its kinetic energy with the medium. The time taken for positrons to reach thermal ...

    • Microstructure of heat-treated steel probed by positron annihilation 

      Al-Qaradawi, I. Y.; Abdel-Hady, E. E.; Megahed, H. (2001 , Conference)
      Positron annihilation lifetime technique has been applied to study the microstructure change in steel after heat treatment. For this purpose, the specimens are heat treated in various manners; normalizing, annealing, ...

    • Three-body effects in the annihilation of positrons on molecules 

      Charlton, Michael; Van der Werf, Dirk Peter; Al-Qaradawi, Ilham ( APS , 2002 , Article)
      The three body effects in the annihilation of positrons on molecules were discussed. The positron annihilation in ethylene gas at room temperature and at densities below one amagat, showed that the mean free positron ...

    • Tests of a diamond field-assisted positron moderator 

      Al-Qaradawi, I. Y.; Sellin, P. A.; Coleman, P. G. ( Elsevier , 2002 , Conference)
      Diagnostic studies have been performed on a 70 μm thick diamond film with a view to its development as a possible field-assisted moderator (FAM) for slow positron emission. The film was coated on one side with a 200 nm ...

    • Re-emission of slow positrons from tungsten at elevated temperatures 

      Al-Qaradawi, I. Y.; Coleman, P. G. ( Elsevier , 2002 , Conference)
      A series of measurements have been made on the dependence of the intensity and energy spectrum of slow positrons re-emitted from polycrystalline tungsten foil held at temperatures of up to 500 °C. Irrespective of target ...

    • Positron annihilation studies of the effect of gamma irradiation dose in polymers 

      Al-Qaradawi, I. Y.; Britton, D. T.; Abdel-Hady, E. E.; Abdulmalik, D. A.; Al-Shobaki, M. A.; ... more authors ( Elsevier Ltd , 2003 , Conference)
      Positron annihilation lifetime (PAL) technique has been applied to study the effect of gamma irradiation dose on the structure of low-density polyethylene and polystyrene. The positron annihilation lifetime measurements ...

    • Electron irradiated low-density polyethylene studied by positron annihilation lifetime spectroscopy 

      Al-Qaradawi, I. Y. ( Elsevier Ltd , 2003 , Conference)
      A study of the degree and rate of cross-linking of low-density polyethylene (LDPE) as a result of irradiation by high-energy electron beam has been performed using positron annihilation lifetime (PAL) technique. The PAL ...

    • Temperature and electric field effects on the dielectric dispersion of modified polyvinyl chloride 

      M.E., Bassiouni; Al-Shamy, F.; Madi, N.K.; Kassem, M.E. ( Elsevier , 2003 , Article)
      The effect of electric field on the dielectric dispersion of modified polyvinyl chloride (PVC) has been investigated. The applied direct current (DC) field strength was ranging from 0 to 104 V cm−1. The complex permitivity ...