Al-Azhar University, Faculty of Science (Boys)
Al-Azhar Bulletin of Science
1110-2535
2636-3305
26
Issue 2-B
2015
12
01
STRUCTURAL AND OPTICAL PROPERTIES OF CD1-XZNXS ALLOY QUANTUM DOTS
1
16
EN
A. A.
ABD EL-RAHMAN
Faculty of Science, Al-Azhar University, Girl’s Branch National Institute of Laser Enhanced Science (NILES), Cairo University
F. I.
MANDOUH
Faculty of Science, Al-Azhar University, Girl’s Branch National Institute of Laser Enhanced Science (NILES), Cairo University.
M. B.
MOHAMMED
Faculty of Science, Al-Azhar University, Girl’s Branch National Institute of Laser Enhanced Science (NILES), Cairo University.
GH.
ADEL
Faculty of Science, Al-Azhar University, Girl’s Branch National Institute of Laser Enhanced Science (NILES), Cairo University.
E. A.
MAHMOUD
Faculty of Science, Al-Azhar University, Girl’s Branch National Institute of Laser Enhanced Science (NILES), Cairo University.
10.21608/absb.2015.22607
Cd1-xZnxS (0≤x≤1) alloy quantum dots (QDs) were synthesized via coprecipitation method using cetyltrimethyl ammonium bromide (CTAB) as a capping material. Elemental composition of the investigated samples was determined by the energy dispersive x-ray spectroscopy (EDX). X-ray powder diffraction (XRD) and high resolution transmission electron microscope (HRTEM) were used to characterize the crystalline structure, particle size and morphology. XRD analysis indicated that the as synthesized nanomaterials, except for ZnS, have a mixture of cubical and hexagonal phases. The percentage of the hexagonal phase was very small. ZnS nanocrystal has a cubical structure. The particle size and the lattice constant decreased with the increase of Zn content. HRTEM data showed the presence of QDs and confirmed the XRD results. Ultraviolet-visible (UV-vis) absorption spectroscopy was employed to study the optical properties. Absorption band edges showed blue-shift systematically with the increase of Zn content. The results are interpreted in terms of the quantum-size confinement effect. Measurements of XRD and UV-vis absorption spectra under different annealing temperatures up to 400°C were performed. The annealed compositions showed mixture of cubical and hexagonal crystal structure. Tendency for phase transformation, from cubic to hexagonal upon annealing were observed. The degree of tendency for phase transformation increased with the decrease of Zn content and the increase of the annealing temperature. Particle sizes were increased with increasing the annealing temperature. UV- vis absorption spectra exhibited red-shift systematically with the increase of the annealing temperature. The values of the optical band gap energies decreased with increasing annealing temperature.<br /><br />
QD,Structural Characterizations,UV-vis spectra,Thermal annealing
https://absb.journals.ekb.eg/article_22607.html
https://absb.journals.ekb.eg/article_22607_f68b360f05adb326fb02241e3638dc84.pdf
Al-Azhar University, Faculty of Science (Boys)
Al-Azhar Bulletin of Science
1110-2535
2636-3305
26
Issue 2-B
2015
12
01
VISIBILITY INTERVALS BETWEEN TWO SATELLITES ORBITS UNDER J2-GRAVITY AND DRAG FORCE
1
10
EN
AHMED
W.N.
Departments of 1Applied Mathematics, Physics Division, National Research Centre.
AWAD
M.E.
Astronomy, Faculty of science, Cairo University.
HASSAN
I.A.
Astronomy and Meteorology, Faculty of science, Al-Azhar University.
AMMAR
M.K.
Mathematic, Faculty of science, Helwan University.
AMIN
M. R.
Departments of 1Applied Mathematics, Physics Division, National Research Centre.
10.21608/absb.2015.22634
The research introduces a general analytical and computational technique for satellite-to-satellite visibility. The effect of earth’s oblateness and drag force were taken into account.The Visibility function in terms of the orbital elements of the two satellites and the time were derived. The rise and set periods of the satellites are determined through the sign of the visibility function. Numerical examples were worked for some satellites.
Visibility function – line of site-,rise and set times-Earth oblateness- Drag force
https://absb.journals.ekb.eg/article_22634.html
https://absb.journals.ekb.eg/article_22634_4463665cd7a6df39c936db12996bcfaf.pdf
Al-Azhar University, Faculty of Science (Boys)
Al-Azhar Bulletin of Science
1110-2535
2636-3305
26
Issue 2-B
2015
12
01
MODELING TRIVARIATE CORRELATED BINARY DATA
1
13
EN
AHMED MOHAMED
MOHAMED EL-SAYED
Department of High Institute for Specific Studies Management Information Systems Nazlet Al-Batran, Giza, Egypt.
10.21608/absb.2015.22635
This paper provides the estimation and the test procedures for the measures of association in the correlated binary data associated with covariates. The generalized linear model (GLM) using the serial dependence and the developed alternative quadratic exponential form (AQEF) procedures are employed for the trivariate binary correlated outcome variables. The log-odds ratios, as measures of association, are estimated and the appropriate tests are suggested. For comparison between the two procedures, we used the simulation study and an application to an ecology problem which involves the estimation of the measures of association and their tests. The over-dispersion criteria is investigated for these procedures. Finally, the deviance and scaled deviance are used as tests for the goodness of fit of the model to determine the best procedure.
Trivariate Bernoulli Distribution,Markov model,Generalized linear model,Deviance,Likelihood ratio test,Maximum likelihood estimators,Alternative quadratic exponential form
https://absb.journals.ekb.eg/article_22635.html
https://absb.journals.ekb.eg/article_22635_3c4f132f7100d32e2eac69a61c7e87b3.pdf