Dielectric relaxation and predominance of NSPT and OLPT conduction processes in Ba0.9Sr0.1TiO3

We investigate the relaxation and conduction mechanism of Ba0.90Sr0.10TiO3 (BST) ceramic, synthesized by the solid state reaction method. The dielectric and relaxation properties are analyzed in the temperature range of 380-450{\deg}C with alternative current in the frequency range of 20Hz-1MHz. Variation of dielectric constant, \epsilon', with temperature shows a normal ferroelectric transition at Tc=95{\deg}C with a weak degree of diffuseness. The modified Cole-Cole equation is used to describe all contributions to the relaxation mechanism. The frequency exponent m({\omega},T) deduced from experimental data of the dielectric loss ({\epsilon}") as m({\omega}, T)=($\partial$ ln {\epsilon}"/$\partial$ ln {\omega}) shows a temperature and frequency dependence. Two conduction process are observed: non-overlapping small-polaron tunneling (NSPT) at low frequencies and overlapping large polaron tunneling (OLPT) at high frequencies. The analysis of Nyquist plots reveals also the presence of two contributions, who which the activation energies have been calculated

Comparaison des activités des isotopes de l'uranium et du radium dans quelques échantillons d'eau de puits et de sources thermales au Maroc

Les activités des isotopes de l'uranium et du radium (234U,238U,226Ra,228Ra) ainsi que les rapports d'activité (234U/238U,226Ra/238U,228 Ra/226Ra) ont été mesurés, pour la première fois au Maroc, dans 15 échantillons d'eau de puits et 12 échantillons d'eau de sources thermales. Les résultats obtenus montrent que, contrairement aux eaux de puits, les eaux des sources thermales présentent des activités de238U relativement faibles et des activités de226Ra et des rapports234U/238U élevés. Les activités de l'uranium et du radium mesurées sont comparables à celles que l'on trouve habituellement dans d'autres régions non polluées du monde, elles sont inférieures aux limites maximales admissibles ce qui ne pose aucun risque pour la santé publique au Maroc.Activities and activity ratios of uranium and radium isotopes (234U,238U,226Ra,228Ra,234U/238U,226Ra/238U,228Ra/226Ra) have been determined, for the first time in Morocco, for 15 well water samples and 12 spring water samples. The obtained results show that, unlike well waters, the thermal spring waters present relatively low 238U activities and elevated226Ra activities and 234U/238U activity ratios. Uranium and radium activities are similar to those published for other non polluting regions of the world, they are inferior to the Maximum Contaminant Levels and don't present any risk for public health in Morocco

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

Mesure de l'uranium dans un ensemble d'échantillons de formations naturelles au Maroc : implications environnementales

Measure of uranium in some samples of natural deposits in Morocco: environmental implications. In this work, we report the measurement results of uranium content in some natural formation samples in Morocco. The such results are used in several studies concerning the Earth sciences and the Environment such as geochronology, archaeology, geophysical and geophysical studies and prospecting of radioactive pollution. The analyses were carried out on some of natural deposits samples such as the corals, the fossil shells molluscs, the phosphates, the travertines, the lichens and of the impure carbonate deposits. Measurements were realized by spectrometry alpha for fossil shell molluscs, corals, travertines and impure carbonates, by Gamma spectrometry using a well detector with scintillation NaI for phosphates and by neutron activation for lichens. Isotopic 234U/238U ratio was also measured and discussed

Assessment of Computed Tomography Dose Index (CTDI) During CT Pelvimetry Using Monte Carlo Simulation

A pelvimetry examination is sometimes prescribed to a pregnant woman at the end of her pregnancy in order to assess the dimensions of her pelvis prior to childbirth. This examination has long been performed by using X-ray, but is now increasingly being replaced by CT-scan The objective of this study is to assess the radiation doses received during a practical CT pelvimetry examination performed using a Hitashi Supria 16-slice CT scanner. The radiation doses were estimated using Monte Carlo (MC)-based simulation with GATE code to model the 16-slice CT scanner machine. The GATE code operates using GEANT4 libraries. A polyymethyl metacrylate (PMMA) acrylic phantom of 32 cm diameter was modeled to represent the patient's body. X-ray energy spectrum generated using the SRS-78 spectrum processor was used for simulation. The simulation was executed with the same exposure parameters as the practical CT pelvimetry examination with dose parameters of 1 mGy, 0.9 mGy, and 36.6 mGy.cm, respectively, for the weighted CT dose index (CTDIw), the volume CT dose index (CTDIvol), and dose-length product (DLP). The MC simulation results provide dose parameters of 1.16 mGy, 1.07 mGy, and 43.6 mGy.cm, respectively, for the CTDIw, CTDIvol, and DLP. The differences between the simulation and the practical examination were 16 %, 18 %, and 18 %, respectively. These differences are considered in a quite good agreement. The results were also consistent with other similar studies. This work proves that the Monte Carlo simulation with the GATE code is usable to assess the patient doses during a CT pelvimetry examination

Technique de datation des échantillons riches en uranium par les séries de l'uranium en utilisant la spectrométrie gamma à basse énergie

Dating technique of samples rich in uranium by the series of the uranium by using the gamma spectrometry with low energyIn this work, a dating technique by the series of the uranium using the gamma spectrometry with Flow energy

Impact des gisements des phosphates sur la radioactivité dans les échantillons d’eau naturelle et d’air au Marocag

Impact of the phosphate layers on the radioactivity in the natural water samples and air in MoroccoIn this work, we present the results of radioactivity measurements in some samples of phosphate deposits and in samples in interaction with these  phosphate deposits such air and water. In phosphate samples, we have determined with gamma spectrometry using a well NaI(Tl) detector, concentrations of uranium in some samples of unrefined Moroccan phosphates. In air, we have measured, with nuclear solid track detector LR 115 type II,the volumic activity of 222Rn in some dwellings situated in phosphate areas. In water, we have measured activities of uranium and radium radio-isotopes (234U, 238U) with alpha spectrometry and those of radium ( 226Ra, 228Ra) with gamma spectrometry using a 220 cm3 low-background well type gamma ray detector in the aboratoire Souterrain de Modane (LSM-Centre National de la Recherche Scientifique (CNRS/CEA, France).The obtained results in Moroccan  phosphate samples and in samples in interaction with them are comparable to those habitually obtained in the same samples in the world and these activity do not present any risk for public health. Some harmful effects in the longterm could be avoided by simple precautions such ventilation of dwellings and localities of mining treatment

Novel Clustering Method Based on K-Medoids and Mobility Metric

The structure and constraint of MANETS influence negatively the performance of QoS, moreover the main routing protocols proposed generally operate in flat routing. Hence, this structure gives the bad results of QoS when the network becomes larger and denser. To solve this problem we use one of the most popular methods named clustering. The present paper comes within the frameworks of research to improve the QoS in MANETs. In this paper we propose a new algorithm of clustering based on the new mobility metric and K-Medoid to distribute the nodes into several clusters. Intuitively our algorithm can give good results in terms of stability of the cluster, and can also extend life time of cluster head

Enhancenig OLSR routing protocol using K-means clustering in MANETs

The design of robust routing protocol schemes for MANETs is quite complex, due to the characteristics and structural constraints of this network. A numerous variety of protocol schemes have been proposed in literature. Most of them are based on traditional method of routing, which doesn’t guarantee basic levels of Qos, when the network becomes larger, denser and dynamic. To solve this problem we use one of the most popular methods named clustering. In this work we try to improve the Qos in MANETs. We propose an algorithm of clustering based in the new mobility metric and K-Means method to distribute the nodes into several clusters; it is implemented to standard OLSR protocol giving birth a new protocol named OLSR Kmeans-SDE. The simulations showed that the results obtained by OLSR Kmeans-SDE exceed those obtained by standard OLSR Kmeans and OLSR Kmed+ in terms of, traffic Control, delay and packet delivery ratio

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