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Static deformation of an irregular initially stressed medium محمود محمد سليم صالح

"Static deformation of an irregular initially stressed medium," Appl.

          Math. Comput., Amsterdam, Netherlands, (2007) Vol. 188 (2) 1274-1284.

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Effect of irregularity on Static deformation of elastic half-space محمود محمد سليم صالح

In the present paper, the problem of two-dimensional static deformation of an isotropic
elastic half-space of irregular thickness has been studied using the eigenvalue approach,
following a Fourier transform. The irregularity is expressed by a rectangular shape. As
an application, the normal line-load acting inside an irregular isotropic half-space has
been considered. Further, the results for the displacements have been derived in the
closed form. To examine the effect of irregularity, variations of the displacements with
horizontal distance have been shown graphically for different values of irregularity size,
and they are compared with those for the medium with uniform shape. It is found that
irregularity affects the deformation significantly.

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Reflection of Plane Waves at Free Surface of an Initially Stressed Dissipative Medium محمود محمد سليم صالح

The paper discuses the effect of initial stresses on the reflection coefficients of plane
waves in a dissipative medium. Basic governing equations are formulated in context of Biot's
incremental deformation theory. These governing equations are solved analytically to obtain the
dimensional phase velocities of plane waves propagating in plane of symmetry. Closed-form
expressions for the reflection coefficients of P and SV waves incident at the free surface of an initially
stressed dissipative medium are obtained. Numerical computations, using these expressions, are carried
out for a particular model. Computations made with the results predicted in presence and absence of the
initial stresses and the results have been shown graphically. The study shows that the presence of
compressive initial stresses increases the velocity of longitudinal wave (P-wave) but diminishes that of
transverse wave (SV-wave). Also the numerical results presented indicate that initial stresses might
effect the reflection coefficients in a dissipative medium significantly.

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Effects of initial compression stress on wave propagation in carbon nanotubes محمود محمد سليم صالح

An analytical method to investigate wave propagation in single- and double- walled carbon
nanotubes under initial compression stress is presented. The nanotube structures are treated within the
multilayer thin shell approximation with the elastic properties taken to be those of the graphene sheet. The
governing equations are derived based on Fl¨ugge equations of motion. Frequency equations of wave propagation
in single and double wall carbon nanotubes are described through the effects of initial compression
stress and van der Waals force. To show the effects of Initial compression stress on the wave propagation
in nanotubes, the symmetrical mode can be analyzed based on the present elastic continuum model. It is
shown that the wave speed are sensitive to the compression stress especially for the lower frequencies.

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Statistical investigation of prevalence of smoking among rural primary and secondary school students in Aflaj area, Kingdom of Saudi Arabia محمود محمد سليم صالح

Objective A school survey was conducted in twelve preparatory and secondary
schools in Aflaj governorate , Kingdom of Saudi Arabia in the academic year 2005-
2006 in order to assess the students’ knowledge, attitudes and practice toward
smoking. Methods An anonymous self-administered questionnaire was used. A total
of 1696 students were interviewed. Results The response rate was 100%. The
prevalence of ever tried cigarette was 10% (154 students) with a median age of
initiation at 17 years of age. About 4%(63 students) from the smoker's students have
stopped smoking. This study examined how perceptions of student smoking in the
school environment and the actual smoking rate among senior students at a school are
related to smoking onset. Multilevel Logistic Regression analysis was used to
examine correlates of ever smoking in the sample. The influence of family members,
teachers and neighbors on smoking status was studied. Fathers’, mothers’ and
brothers’ smoking was found not to be significantly related to students smoking
status. On studying the effect of having a smoker teacher or neighbor on students
smoking, having a smoker neighbor increases the risk of student one and half time
(OR=1.63, 95%CI=1-2.4) while students having a teacher smoking have almost one
the risk of smoking than the others students (OR= 1.2, 95% CI=0.8-1). Conclusions
This investigation show most of students (83%) thought that smoking has health,
economic and social harmful. Also, 84% of students thought that there is a relation
between smoking and drugs and fire as well.. The religious factor play...

Torsional vibration of carbon nanotubes under initial compression stress محمود محمد سليم صالح

This study examines torsional vibration of Single-walled carbon nanotubes (SWCNTs) subjected to initial compression
stresses. The nanotube structures are treated within the multilayer thin shell approximation with the
elastic properties taken to be those of the graphene sheet. Simplified Fl¨ugge shell equations of motion are proposed
as the governing equations of vibration for the carbon nanotubes. A new equation of motion and phase
velocity of torsional waves propagating in carbon nanotubes (CNTs) subjected to initial compression stresses
have been derived. The study reveals that the initial stresses present in the tube has a notable effect on the
propagation of torsional waves. The results has been discussed and shown graphically. This investigation is
very significant for potential application and design of nanoelectronics and nanodevices.

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Vibrational analysis of pre-stressed carbon nanotubes” Journal of Actaphysica محمود محمد سليم صالح

In this paper an analytical method to investigate vibrational analysis of double-walled carbon nanotubes
under initial compression stress. Simplified Flügge shell equations of motion are proposed as the governing
equations of vibration for the carbon nanotubes. The nanotube structures are treated within the multilayer thin
shell approximation with the elastic properties taken to be those of the graphene sheet. Vibration frequency
equations in double wall carbon nanotubes are described through the effects of initial compression stresses. We
investigate the influence of initial compression stress on the vibrational characteristics of carbon nanotubes based
on the proposed theoretical approach. In this study, we consider the double-walled nanotubes with an inner
diameter of 2.2 nm and an outer diameter of 3.0 nm. The theoretical investigation may give a useful reference for
potential application and design of nanoelectronics and nanodevices

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Dispersion of dilatation wave propagation in single-wall carbon nanotubes using nonlocal scale effects محمود محمد سليم صالح

Nonlocal continuum mechanics allows
one to account for the small length scale effect that
becomes significant when dealing with micro- or
nano-structures. This paper investigates a model of
wave propagation in single-wall carbon nanotubes
(SWCNTs) with small scale effects are studied. The
equation of motion of the dilatation wave is obtained
using the nonlocal elastic theory. We show that a
dispersive wave equation is obtained from a nonlocal
elastic constitutive law, based on a mixture of a local
and a nonlocal strain. The SWCNTs structures are
treated within the multilayer thin shell approximation
with the elastic properties taken to be those of the
graphene sheet. The SWCNT was the (40,0) zigzag
tube with an effective diameter of 3.13 nm. Non-
linear frequency equations of wave propagation in
SWCNTs are described through the effect of small
scale. The phase velocity and the group velocity are
derived, respectively. The nonlinear dispersion rela-
tion is analyzed with different wave numbers versus
scale coefficient. It can be observed from the results
that the dispersion properties of the dilatation wave
are induced by the small scale effects, which will
disappear in local continuous models. The dispersion
degree can be strengthened by increasing the scale
coefficient and the wave number. Furthermore, the
characteristics for the group velocity of the dilatation
wave in carbon nanotubes can also be tuned by these
factors.

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Topological Variable Precision Rough Set Model عبدالفتاح عبدالله عزام

Topological generalization of rough sets (RS) and variable precision rough set model (VP-model) are applied together to get a new approach for basic RS concepts. Some examples are given. Properties of the suggested approximations are obtained and a comparison between the new concepts and some similar approximation are given.

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Topological Application on VP-Model عبدالفتاح عبدالله عزام

Using a nonstandard method for classification of objects, a topological structure is constructed and used to get new types of approximations.  Basic concepts of topological variable precision rough set model are applied to information systems to get reductions and decision rules. We give a detailed explanation for case study in the process of chemical data analysis.

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