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Periodicals - LEBANESE SCIENCE JOURNAL VOL.1,
NO.2, 2000
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The effects of oxygen deficiency
on the structural, magnetic and electrical
properties in perovskite manganites
N. Abdelmoula, K. Guidara, E. Dhahri,
A. Cheikhrouhou and J. C. Joubert
The effects of oxygen deficiency on structural
magnetic and electrical properties of
La0.7Sr0.3MnO3-δ
∅δ where ∅ is a vacancy and 0 ≤
δ ≤ 0.15, has been investigated.
We present a new method of creating vacancies
in the oxygen sites achieved at atmospheric
pressure. X-ray diffraction patterns reveal
that these materials have a rhombohedral
structure for δ ≤ 0.075 and orthorhombic
when δ ≥ 0.1. The magnetization
and resistivity measurements as a function
of temperature show a ferromagnetic metallic
behavior for δ ≤ 0.075 at low
temperatures and paramagnetic semiconductor
above the Curie temperature TC.
The magnitude of the saturation magnetization
Ms and the ferromagnetic phase
are reduced with increasing δ. A
ferromagnetic insulating state below 115K
is observed for δ = 0.1 sample.
It seems to be due to an ordering of the
Mn3+ and Mn4+ species
on the manganese lattice.Back
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Simultaneous structural and magnetic transitions
in La0.6Sr0.4MnO3-δ
δ (0.0 ≤ δ ≤ 0.2)
A.Zouari
Non stoichiometric substituted lanthanum
manganite was prepared in the form of polycrystalline
products by solid state reaction method.
The structural characterisation was done
by X-ray diffraction. All samples crystallise
in a single phase, showing the characteristic
peaks of the perovskite. A structural phase
transition from the rhombohedral phase to
the orthorhombic phase was observed at the
rate δ = 0.127 corresponding to a concentration
in Mn3+ about of 85%. Magnetization measurements
gave ferromagnetic order for 0 ≤ δ ≤ 0.127
and antiferromagnetic order for 0.15 ≤ δ ≤ 0.20. The Curie temperature is very sensitive
to the presence of vacancies. The magnetic
interactions between the manganese ions
were calculated; this result confirmed the
obtained magnetic properties.Back
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Study of double stator induction machine
fed by two independent voltage source inverters
N. Moubayed, F. Meibody-Tabar, B.
Davat and I. Rasoanarivo
One simple and efficient way to apply a
power segmentation in AC machine PWM-VSI
set consists in realising multi-star windings
and supplying each one by its own three
phase PWM-VSI. This leads theoretically
to use modular inverters of lower power
(current or/and voltage) which allows higher
chopping frequency. With this power segmentation
method, it is possible to supply one or
more than one of star windings if for any
reason some of them cannot be supplied.
In this paper, one treats the example of
a Double Star Induction Machine (DSIM) supplied
by two PWM-VSI. The model of the machine
highlights the eventuality of appearance
of high amplitude current ripples if there
is a strong magnetic coupling between the
star windings. The conditions of safely
supplying of DSIM are given and are validated
by simulation and experimental results.
One presents, finally, the conception of
multi-star windings with weak magnetic coupling
in AC machines.Back
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Simplified approach for modeling base current
of bipolar transistors
H. Samet and N. Lakhoua
Analytic resolution of the transport equations
of minority carriers in a highly doped semiconductor
region can not be achieved in a rigorous
manner. Rinaldi (1993) has presented a general
analytic solution of the transport equations
of minority carriers in the emitter region
of a bipolar transistor in the form of a
multiple integral asymptotic series. Taking
this solution into consideration, the minority
hole saturation current of the emitter J0e
is studied as a function of the doping and
the width of the emitter region. The calculations
take into account the mobility µp,
the lifetime τp and the Band-Gap Narrowing
(BGN) of the minority carriers. An approach
to the problem based on average values of
the concentration N, the mobility µp
and the lifetime τp of the minority carriers
is also proposed in this paper. The saturation
current is then expressed in a classic form
as in the case of a uniform doping. This
approach allows considerable reduction in
computation time. On the other hand, and
in comparison with Rinaldi’s calculation,
the approach by the average values can be
considered as accurate (error ≈ 1%) in the
following conditions:
1) The emitter width W is less than or equal
to 1µm (W ≤ 1µm )
2) The recombination velocity at the emitter
surface is large (Sp = 107 cm/s),
3) The emitter surface doping is of the
order of 1019 cm-3. For such doping, this
approach can also be considered as sufficient
in the case of small recombination velocity
(Sp = 102 cm/s). Indeed, the error is inferior
to 10% when the emitter width is less than
0.7 µm.Back
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Four quadrant multiplier for analog VLSI
neural networks
H. Chible
In this paper a four quadrant analog multiplier
is presented. The multiplier can be used
for general purpose but it is suitable for
Analog VLSI implementation of artificial
neural networks because of its small silicon
area and its low power consumption. The
main feature of the multiplier is the high
value of the weight voltage [ 0:Vdd]. The
innovative idea in the multiplier proposed
is to obtain a linear function by substituting
quadratic function inside the square root
function.Back
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Localization and characterization of ultra
thin gate oxide breakdown regions
N. Akil, P. LeMinh, J. Holleman, V. E.
Houtsma, and P. H. Woerlee
Nano-scale diodes were formed after intentional
gate oxide breakdown of n+ –polysilicon/oxide/p+
–substrate MOS capacitors by Fowler-Nordheim
constant current injection. The nano-scale
diodes called diode-antifuses are created
by the formation of a small link through
the oxide between the n+ –poly and
the p+ –substrate with the properties
of a diode. In this paper we report a simple
method to localize the antifuse in terms
to characterize the broken down oxide area.
The method is based on the use of the blue-UV
light emission from hot carriers to expose
a deposited layer of photo resist on the
top of the structure. After developing the
exposed resist, a hole is observed in the
photo resist layer where the antifuse was
formed. This method can be applied on a
ULSI circuit under operation to fix the
regions of hot carriers and characterize
them easily, or to identify where output
power is lost by the circuit in terms to
improve its design.Back
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Stochastic iterative search heuristics
for mapping data to multicomputers
N. Mansour
An empirical comparison of a class of
five stochastic iterative search optimization-based
heuristics for mapping data to the processor-nodes
of a multicomputer is presented. In this
class, three well-known stochastic heuristics,
a new algorithm that we propose, and a
new implementation of a stochastic search
paradigm are included. The well-known
heuristics are: Simulated Annealing, Neural
Network, and Genetic Algorithm. The new
heuristic is derived from Physics and
is based on Simulated Tempering. The new
implementation is for a Tabu Search heuristic.
The empirical comparison of these five
heuristics involves their solution qualities
and performances. As a result of this
comparison, we recommend that:
(i) the Neural Network be used for fast
mapping of general applications,
(ii) the Genetic Algorithm be used for
applications that are mapped once and
are then repeatedly run with the same
mapping.Back
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Analyse numérique des conditions
d’émission sur un écoulement
de type jet circulaire en régime
laminaire
H. Ben Aissia, Y. Zaouali, S. El Golli
L’étude proposée est
relative à une résolution
numérique des équations
de Navier-Stockes régissant les
écoulements de type jet circulaire
et isotherme en régime laminaire.
Notre travail a été orienté
vers l’étude de l’influence
des conditions d’émission
du gaz à la section d’injection
sur les paramètres de l’écoulement
à partir de l’analyse des
résultats numériques concernant
la vitesse verticale. Le code de calcul
numérique que nous avons développé
utilise une méthode aux différences
finies à maillage décalé.
Les résultats obtenus ne concordent
avec ceux proposés dans la littérature
que dans la zone d’affinité.
Par ailleurs les conditions d’émission
sont ignorées dams la zone d’écoulement
établi. La validation expérimentale
du code de calcul numérique par
des mesures de la vitesse longitudinale
a été réalisée
au moyen d’un vélocimètre
laser à effet Doppler en diffusion
avant.Back
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Ostéopétrose: bases cellulaires
et moléculaires. Etude expérimentale
et étude clinique
A. Elkak, N.Balmain
L’ostéopétrose résulte
d’un défaut de la résorption
osseuse conséquence d’une
anomalie au niveau du développement
des ostéoclastes. Dans ce travail
nous décrirons à la fois
les différents aspects de l’ostéopétrose
et la biologie des ostéoclastes.
Une quantification par analyse d’image
a été faite pour évaluer
l’effet d’un facteur de croissance
le M-CSF sur la différenciation
des ostéoclastes chez un enfant
présentant une ostéopétrose.
L’analyse statistique est effectuée
avec le programme STAT 2005 (TITN Alcatel).
La longueur de contact des ostéoclastes
différenciés rapportée
à la longueur totale des travées
osseuses augmente d’une façon
significative après le traitement
par le M-CSF passant de 0.8 ± 1.04 avant
traitement à 29.30 ± 8.19 après
traitement suggérant d’un
effet positif à court terme par
le rHu M-CSF chez l’enfant ostéopétrotique.Back
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Aphids as pests and vectors of virus
diseases affecting agricultural crops
in Lebanon and Syria
A. S. Talhouk and K. M. Makkouk
Annual surveys to identify aphid species
which attack agricultural crops as well
as wild plant species in Lebanon and Syria
were conducted during the period 1969-1976.
Ninety four aphid species belonging to
four families (Lachnidae, Calliterpidae,
Thelaxidae, and Aphididae) were identified,
and permanent slide mounts were prepared.
The role of some of the identified aphids,
as potential vectors of plant virus diseases
of economic importance to agricultural
crops known to occur in Syria and Lebanon,
is highlighted.Back
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Nouvelles données sur Echinogammarus
berytensis Alouf. Essai de biogéographie
des amphipodes dulçaquicoles du
Liban
N. Alouf
L’Amphipode d’eau douce Echinogammarus
berytensis, espèce présumée
disparue, est redécouverte dans
une nouvelle station du Liban. La répartition
d’autres Amphipodes d’eau
douce appartenant aux genres Niphargus,
Gammarus et Echinogammarus et la paléogéographie
du site de Beyrouth sont étudiées.Back
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