109 research outputs found
Mesure des activités de l'uranium ( 238U, 234U) et du rapport isotopique 234U/238U dans des échantillons d’eau naturelle au Maroc à l'aide de la spectrométrie alpha
Measurement of the activities of uranium (238U, 234U) and of Isotopic ratio 234U 238U in natural water samples in Morocco using spectrometry alphaIn this work, specific activities of     234U and 238U and isotopic activity ratios have been measured for 68 natural water samples collected from 5 principal sources of water in Morocco: Wells (18 samples), springs (17 hot spring water samples and 7 cold spring water samples), rivers (13 samples), lakes (5 samples) and tap water (8 samples). These samples have been collected in Moroccan regions characterized by various geology, different socio-economical activities. The obtained results have allow us to establish general tendencies of measured parameters repartition in sources of the analysed waters. This tendency is clear for hot springs where activities of uranium are relatively low and 234&U/238&U activities ratios are important. This is due to temperature and oxydoreduction conditions of waters that are favourable in particularly to 234U solubility. The results so-obtained are comparable to those habitually found in natural waters in different regions of world and show that there is no radioactive pollution in these water
Activités de l’uranium et du radium dans des échantillons d’eau naturelle au Sahara marocain
Measure of uranium and radium activities in some natural watersamples from Moroccan SaharaThe preliminary results of  238U, 234U, 226Ra, 228Ra and 228Th activities and of 234U/238U,228Ra/226Ra, 228Th/228Ra and 226Ra/238U activity ratios obtained for 8 wells, 5 drillings, 2 springs and 3 tap water samples collected in Laayoune and Es-Smara regions in the Moroccan Sahara are given in this work. The analyzed natural water samples have been collected from sources situated in a desert region rich in phosphates. Except for the one water drilling sample no used by population, the calculation of equivalent doses to the maximal activities for each isotope show that all measured activities are inferior to the maximum contaminant levels recommended by the International Commission of Radioprotection and they don't present any risk for population health. The obtained results are comparable to those already found in other regions in Morocco or in the world
Doped and non-doped organic light-emitting diodes based on a yellow carbazole emitter into a blue-emitting matrix
A new carbazole derivative with a 3,3'-bicarbazyl core 6,6'-substituted by dicyanovinylene groups (6,6'-bis(1-(2,2'-dicyano)vinyl)-N,N'-dioctyl-3,3'-bicarbazyl; named (OcCz2CN)2, was synthesized by carbonyl-methylene Knovenagel condensation, characterized and used as a component of multilayer organic light-emitting diodes (OLEDs). Due to its -donor-acceptor type structure, (OcCz2CN)2 was found to emit a yellow light at max=590 nm (with the CIE coordinates x=0.51; y = 0.47) and was used either as a dopant or as an ultra-thin layer in a blue-emitting matrix of 4,4'-bis(2,2'-diphenylvinyl)-1,1'-biphenyl (DPVBi). DPVBi (OcCz2CN)2-doped structure exhibited, at doping ratio of 1.5 weight %, a yellowish-green light with the CIE coordinates (x = 0.31; y = 0.51), an electroluminescence efficiency EL=1.3 cd/A, an external quantum efficiency ext= 0.4 % and a luminance L= 127 cd/m2 (at 10 mA/cm2) whereas for non-doped devices utilizing the carbazolic fluorophore as a thin neat layer, a warm white with CIE coordinates (x = 0.40; y= 0.43), EL= 2.0 cd/A, ext= 0.7 %, L = 197 cd/m2 (at 10 mA/cm2) and a color rendering index (CRI) of 74, were obtained. Electroluminescence performances of both the doped and non-doped devices were compared with those obtained with 5,6,11,12-tetraphenylnaphtacene (rubrene) taken as a reference of highly efficient yellow emitter
Diffusion of triplet excitons in an operational Organic Light Emitting Diode
Measurements of the diffusion length L for triplet excitons in small
molecular-weight organic semiconductors are commonly carried out using a
technique in which a phosphorescent-doped probe layer is set in the vicinity of
a supposed exciton generation zone. However, analyses commonly used to retrieve
ignore microcavity effects that may induce a strong modulation of the
emitted light as the position of the exciton probe is shifted. The present
paper investigates in detail how this technique may be improved to obtain more
accurate results for L. The example of 4,4'-bis(carbazol-9-yl)1,1'-biphenyl
(CBP) is taken, for which a triplet diffusion length of L=16 +/- 4 nm (at 3
mA/cm2) is inferred from experiments. The influence of triplet-triplet
annihilation, responsible for an apparent decrease of L at high current
densities, is theoretically investigated, as well as the 'invasiveness' of the
thin probe layer on the exciton distribution. The interplay of microcavity
effects and direct recombinations is demonstrated experimentally with the
archetypal trilayer structure
[N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)]-4,4'-diaminobiphenyl (NPB)/CBP/
2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (named bathocuproine, BCP). It is
shown that in this device holes do cross the NPB/CBP junction, without the
assistance of electrons and despite the high energetic barrier imposed by the
shift between the HOMO levels. The use of the variable-thickness doped layer
technique in this case is then discussed. Finally, some guidelines are given
for improving the measure of the diffusion length of triplet excitons in
operational OLEDs, applicable to virtually any small molecular-weight material.Comment: Accepted for publication in Physical Review
Speaker adaptation for speech recognition systems. Multiple linear regression and multilayer perceptrons
Interspeaker variability is a major source of errors in automatic speech
recognition . This paper describes a series of experiments, conducted at
TELECOM Paris by the « Pattern Recognition and Speech Processing »
Group, for controlling some aspects of this variability, thus allowing for
the adaptation of speech recognition systems to new users .
The firsi experiments are based on a linear data analysis technique
multiple linear regression (MLR) .
The second set uses multilayer perceptrons, and yields slightly better
results, because non linear phenomena are taken into account. The average improvement of recognition scores is 16 % with the second
approach, versus 15 % with the first one .
Those techniques can also be used for the adaptation of recognizers to new
acoustical environments and recording conditions .La variabilité interlocuteur est une source majeure d'erreurs en reconnaissance
automatique de la parole (RAP) . Cet article décrit une série
d'expériences, menées par l'Équipe « Reconnaissance des Formes et
Traitement de la Parole » de TÉLÉCOM Paris, dans le but de contrôler
certains aspects de cette variabilité, et permettre ainsi une adaptation au
locuteur des systèmes actuels de reconnaissance de parole .
Les premières expĂ©riences utilisent une technique linĂ©aire empruntĂ©e Ă
l'analyse des données, la régression linéaire multiple .
Les secondes font appel aux perceptrons multicouches, et fournissent des
résultats légèrement meilleurs, grâce à la prise en compte de phénomènes
non linéaires . L'amélioration des taux de reconnaissance obtenue est, en moyenne, de
16 % pour les secondes, contre 15 % pour les premières .
Ces techniques peuvent également être utilisées pour l'adaptation des
reconnaisseurs Ă de nouveaux environnements acoustiques ou conditions
de prise de son
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