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International Review
of PHYSICS - Papers
Vol.
4. n. 2, pp. 52-60
Abstract
-
The evolution of a stably stratified turbulence
submitted to a vertical shear is investigated using second order
modelling. For its great success during the last two decades, the second
order model of Sarkar Spezial Gatski (1990), is retained for kinematic
field and has been coupled with three different models of the scalar
field respectively. The obtained results have shown, in comparison to
the results of direct numerical simulation of Jacobitz that the model of
Sarkar, Spezial and Gatski is of a big contribution on predicting
asymptotic equilibrium states for non dimensionless parameters.
Copyright © 2010 Praise Worthy Prize S.r.l. -
All rights reserved
Keywords:
Stratified Turbulence, Second Order Models, Asymptotic Equilibrium
States.
Vol.
4. n. 2, pp. 61-68
Abstract
-
The unsteady flow of an incompressible viscous dusty fluid with uniform
distribution of dust particles in porous medium between two parallel
plates when one of which is impulsively brought to rest is discussed.
The flow is due to the influence of time dependent pressure gradient.
The flow analysis is carried out using differential geometry techniques
and by using Laplace transform technique the problem is solved. The
effect of porosity on the components of velocity of both fluid and dust
particles are studied with the aid of graphs. Further the skin friction
is obtained at the boundaries.
Copyright © 2010 Praise Worthy Prize S.r.l. -
All rights reserved
Keywords:
Frenet Frame Field System, Laminar Flow, Dusty Gas, Impulsive
Motion, Time Dependent Pressure Gradient, Porous Media.
Vol.
4. n. 2, pp. 69-75
Abstract
-
Electronics is subjected to variations in temperature about the hundred
Celsius degrees. The semiconductors being very sensitive to the
temperature variations, it becomes paramount of importance to include
and understand the phenomena that the variations in the temperature
involve. The operating temperature of components and consequently of
circuits has a direct influence on their static characteristics thus
leading to their ageing. It is also important to notice that the
evolution of microelectronics causes the reduction of devices sizes.
This reduction although useful for the integration of new systems and
their speed performances presents the disadvantage of being harmful for
their performances in consumption. This is due to the leakage currents
which are increasingly significant and which unfortunately increase with
the increasing of temperature. Consequently, it becomes essential, to
take into account not only the electric aspects which cannot any more
only be considered, but also the thermal aspects in the design of MOS
circuits. The studies run up at the present time against the ignorance
of the temperature like interactive variable in the models suggested in
the libraries of the suppliers of analogical CAD. We propose in this
work to highlight temperature variation effects on the performances of
last generation MOS transistors such as the BSIM4 MOS model, and
consequently of the performances of the CMOS circuits.
Copyright © 2010 Praise Worthy Prize S.r.l. -
All rights reserved
Keywords:
BSIM4 (Berkeley Short-channel IGFET Model) in50nm Technology,
Electric Behaviour, Leakage Currents, Temperature Effect, Thermal
Behaviour.
 Predicting
Air Temperature in a Natural Ventilated Greenhouse with Tomato Crop
by K. Lekouch, M. El
Jazouli, L. Bouirden
Vol.
4. n. 2, pp. 76-82
Abstract -
Greenhouse climate and ventilation rate are essential for improving
environmental management and control efficiencies. The aim of the
present study is the experimental investigation of the numerous climatic
variables, as well as theirs interactions which affect the air
temperature in natural ventilation. On this purpose, two types of models
are described and used to predict the internal greenhouse environment.
This study focuses on the dynamical behaviors of the inside air
temperature. Physical models based on balance energy and neural networks
models have been covered. These models are described as functions of the
outside climate, the rate of natural ventilation is deduced and the
shelter ventilation performances are discussed and compared with those
of other structures already studied in the same area. The data used to
compute the simulation models were acquired in a canareen type
greenhouse with real tomato culture using a sampling time interval of 15
minutes. The greenhouse is automated with several sensors that are
connected to an acquisition and control system based on a personal
computer. The results obtained by these two models are compared with the
experimental results and show a satisfactory correlation.
Copyright © 2010 Praise Worthy Prize S.r.l. -
All rights reserved
Keywords:
Greenhouse; Natural Ventilation; Balance Energy; Artificial Neural
Networks.
Direct
Numerical Simulation of Regular and Fractal-Grid Turbulence Using the Immersed
Boundary Method and Fully Conservative Higher-Order Finite-Difference Schemes
by Hiroki Suzuki, Kouji
Nagata, Yasuhiko Sakai, Toshiyuki Hayase
Vol.
4. n. 2, pp. 83-90
Abstract - A
high-accuracy direct numerical simulation (DNS) code is constructed to
simulate grid-generated turbulence with scalar transfer based on the
fully conservative higher-order finite-difference schemes and the
higher-order compact scheme in the staggered mesh arrangement.
Turbulence-generating grids are reproduced by using the immersed
boundary method with direct forcing in the Navier-Stokes equations. The
numerical code is applied to the DNS of the turbulent field with scalar
transfer downstream of regular and fractal grids. The turbulence and
scalar fields downstream of the grids and streamwise variations of the
intensities, dissipation, and timescales are presented in this paper.
Copyright © 2010 Praise Worthy Prize S.r.l. -
All rights reserved
Keywords:
Compact Scheme, Direct Numerical Simulation, Finite-Difference Method,
Grid-Generated Turbulence, Immersed Boundary Method, Scalar Transfer.
Vol.
4. n. 2, pp. 91-94
Abstract
-
Piezoresistive pressure sensors based on Silicon have a large thermal
drift because of their high sensitivity to temperature (ten times more
sensitive to temperature than metals). So the study of the thermal
behavior of these sensors is essential to define the parameters that
cause the drift of the output characteristics. In this study, we adopted
two different hole mobility models to determine how the temperature
affect the sensor’s gauges values. We calculated the thermal
coefficients for both mobility models and we compared them with
experimental results. Finally, we calculated the effect of temperature
and doping concentration on the output characteristics of the sensor.
This study allows us to predict the sensor behavior against temperature
and to minimize this effect by optimizing the doping concentration.
Copyright © 2010 Praise Worthy Prize S.r.l. -
All rights reserved
Keywords:
Carriers Mobility, Offset Voltage, Piezoresistivity, Pressure,
Sensor, Silicon.
Vol.
4. n. 2, pp. 95-99
Abstract
-
Electron impact excitation and de-excitation rate coefficients have been
evaluated for 48 excited atomic states for Cu II ion at different plasma
temperatures kTe and the corresponding electron densities Ne resulting
from our experimental measurements. These coefficients have been
determined at different incident electron excitation temperatures in the
range between (1.07 and 2.29) eV. The population densities have been
also calculated at different values of kTe and the corresponding
electron densities in the range between (0.95 and 3.1) × 1016 cm-3. The
calculations have been performed by using the coupled rate simultaneous
equations in which the monopole and the quadrupole transitions have been
introduced in the calculations in addition to the dipole transitions.
Copyright © 2010 Praise Worthy Prize S.r.l. -
All rights reserved
Keywords:
Rate Coefficients, Population Densities.
Abstract
-
Collimator dimension and interaction probability of
radiation play important roles on Compton scattered radiation counts. In
this study the effect of collimator on FWHM (full-width at half-Maximum)
is verified theoretically and experimentally. At the first, the geometry
is defined by Monte Carlo simulation. Two 137Cs gamma apart sources and
a 2"×2" NaI(Tl) detector are used to obtain experimental results.
Theoretical results show, the FWHM is function of geometrical
arrangement and collimator dimension. The experimental results depict
optimum thickness of lead that used as collimator is 5cm. the diameter
bore (circular section parallel holed) is obtained 3mm for 2"× 2" NaI(Tl)
detector. It is understood that conical hole collimator can improve FWHM
under specific conditions.
Copyright © 2010 Praise Worthy Prize S.r.l. -
All rights reserved
Keywords:
Monte Carlo, Collimator, NaI(Tl) detector, Scintillator, FWHM,
Gamma.
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