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We present the results of Raman measurements performed on AlxGa1−xN layers grown by MBE and MOCVD. The films were deposited on (0001) c-sapphire substrates, and the aluminum content covered the whole composition range for x from 0 (GaN) to 1 (AlN). It is shown that the energies of both A1(TO) and A1(LO) phonon modes smoothly increase with increasing x, indicating a one-mode behavior. The E2 phonon mode, however, presents a different behavior. Its energy increases very slowly with aluminum content and, for x≈0.4, a new phonon mode shows up which is shifted to higher energies by 50 cm−1. This new line leads to the E2 AlN mode for increasing aluminum content. The linewidths and intensities of these modes strongly depend on composition. These results are compared with recent theoretical calculations. Finally, the Raman selection rules in the MBE and MOCVD samples are compared and conclusions about the quality of the layers are drawn.
LOFT (Large Observatory For X-ray Timing) is one of the four candidate missions currently
under assessment study for the M3 mission in ESAs Cosmic Vision program to be launched in
2024. LOFT will carry two instruments with prime sensitivity in the 2–30 keV range: a 10
m2 class large area detector (LAD) with a <1° collimated field of view
and a wide field monitor (WFM) instrument. The WFM is based on the coded mask principle,
and 5 camera units will provide coverage of more than 1/3 of the sky. The prime goal of
the WFM is to detect transient sources to be observed by the LAD. With its wide field of
view and good energy resolution of <500 eV, the WFM will be an excellent instrument
for detecting and studying GRBs and X-ray flashes. The WFM will be able to detect
~150 gamma ray bursts per year, and a burst alert system will enable the
distribution of ~100 GRB positions per year with a ~1 arcmin location
accuracy within 30 s of the burst.
For the considered scheme of the external electron bunch injection in front of a laser pulse, the influence of the nonlinear driving laser pulse dynamics and electron bunch self-action to the processes of electron bunch compression and acceleration in the laser wakefield is analyzed. Self-consistent modelling results confirm that the nonlinear laser pulse dynamics limits the bunch compression due to variations of the phase velocity of the wake. A growth of the injected bunch charge leads to some extent to an increase of the trapped and accelerated bunch charge and to decrease of the trapped bunch radius and emittance due to increased self-focusing bunch. The three-dimensional theoretical model is elaborated and used to describe the propagation of laser pulses in dielectric capillary waveguides under imperfect coupling and focusing conditions with broken cylindrical symmetry. The role of cone entrances to the cylindrical part of a capillary is analyzed, and it is demonstrated that matching cones can considerably increase the transmission of laser pulses through the capillary, but cannot mitigate the requirements on the precision of the laser pulse focusing into a capillary. In order to avoid a speckle structure and strong transverse gradients of the fields, which can prevent the process of regular electron bunch acceleration, one has to ensure a small laser angle of incidence into the capillary not exceeding 1 mrad.
The World Heritage Site of Wanar in Senegal features 21 stone circles, remarkable not least because they were erected in the twelfth and thirteenth century AD, when Islam ruled the Indian Ocean and Europe was in its Middle Ages. The state of preservation has benefited the exemplary investigation currently carried out by a French-Senegalese team, which we are pleased to report here. The site began as a burial ground to which monumental stones were added, perhaps echoing the form of original funerary houses. Found in a neighbouring field were scoops left from the cutting out of the cylindrical monoliths from surface rock. While the origins of Wanar lie in a period of state formation, the monuments are shown to have had a long ritual use. The investigation not only provides a new context for one of the most important sites in West Africa but the precise determination of the sequence and techniques used at Wanar offers key pointers for the understanding of megalithic structures everywhere.
In the PECVD SixNyHzOw the hydrogen is principally incorporated as N-H bonds. For O/(O+N) below 0.4, the %H is constant at 25%; from 0.4 to 1, it decreases to 4%. We show that a chemical ordered model is likely to describe the hydrogen incorporation in the amorphous network while a random bond model fails.
Fly ash from power stations is used as concrete additive to improve strength and durability. Surprisingly, studies of ashes of identical mineralogical composition from two different places have reported different results in terms of the rheological properties of the fresh material. The viscosity of the pastes made from these different fly ashes seems to be linked to the proportion of spherical and smooth-shaped grains found in them. A quantitative image analysis was carried out to characterize the shape of the grains of these two ashes from different geographical origins. The main result proves that the higher the glassy particle content of the fly ash, the more the hydraulic matrix is fluid.
We have studied the magnetic properties of very thin PdFe films grown by molecular beam epitaxy. The behavior expected for a 2D Heisenberg system - that is a variation of the susceptibility as exp(B/T) and a logarithmic dependence of the magnetization on the applied field - is observed in a certain range of temperature and field. This is in agreement with recent results of Webb et al .
Raman scattering and photoluminescence (PL) spectroscopy with sub-bandgap excitation has been applied to explore tracing of common impurities (in particular of oxygen) in AlN. Bulk AlN crystals grown by the high temperature sublimation method were studied. PL bands have been observed at around 375 nm and at 560–660 nm and have been attributed to oxygen and to nitrogen vacancy/aluminium excess defects, respectively. The 375 nm UV PL band was found to shift with oxygen concentration. Micro-Raman spectra of the bulk AlN samples were measured in different polarisations. Besides normal Raman modes of AlN the presence of additional vibrational modes was detected. The modes were discussed and tentatively attributed to oxygen and silicon local vibrational modes (LVMs) in AlN.
Background and objective: Inhalation induction with sevoflurane provides acceptable conditions for tracheal intubation. Opioids significantly decrease the alveolar concentration needed to achieve tracheal intubation. The purpose of this study was to determine the target concentration of remifentanil providing excellent conditions for tracheal intubation with sevoflurane at 1 minimum alveolar concentration without muscle relaxant. Methods: Twenty-four consecutive patients, aged 18–50 yr, ASA I or II, were studied. Induction of anaesthesia was performed with sevoflurane at age-adjusted minimum alveolar concentration. Remifentanil was simultaneously administered using target-controlled infusion with the Minto model. Target plasma concentration of remifentanil was selected for each patient according to an up-and-down method. Results: The mean target concentration of remifentanil for successful tracheal intubation was 3.3 ng mL−1 (95% confidence interval: 2.6–3.9 ng mL−1). Arterial pressure, heart rate and bispectral index did not increase after tracheal intubation in the group of patients with successful intubation. Conclusions: Remifentanil at 3.3 ng mL−1 together with sevoflurane at 1 minimum alveolar concentration provides excellent conditions for tracheal intubation in 50% of patients.
Background and objective: The target effect-site concentration of propofol to insert a laryngeal mask airway was recently reported as almost 5 μg mL−1. The present study aimed to determine the target effect-site concentration with target-controlled infusion of propofol to place classical larnygeal mask airway or current laryngeal tube in adult patients. Methods: We included 40 patients scheduled for short gynaecological and radiological procedures under general anaesthesia in a randomized, double-blind manner using the Dixon's up-and-down statistical method. Monitoring included standard cardiorespiratory monitors, and bispectral index monitoring was used for all patients. Anaesthesia was conducted with a target-controlled infusion system: Diprifusor™. The initial target plasma concentration of propofol was 5 μg mL−1, and was changed stepwise by 0.5 μg mL−1 increments according to Dixon's up-and-down method. Criteria for acceptable insertion were: Muzi's score ≤2, and mean arterial blood pressure, heart rate or bispectral index variation <20% the baseline values.Results: Target effect-site concentration of propofol required to insert laryngeal tube was 6.3 ± 0.3 μg mL−1 with Dixon method and ED50 was 6.1 μg mL−1 (5.9–6.4) with logistic regression method. In the case of larnygeal mask airway they were 7.3 ± 0.2 μg mL−1 (Dixon method) and 7.3 μg mL−1 (7.1–7.5; with logistic regression) respectively (P < 0.05). ED95 (logistic regression) was 6.8 μg mL−1 (5.9–7.6) for laryngeal tube and 7.7 μg mL−1 (7.3–8.0) for larnygeal mask airway (P < 0.05). Haemodynamic incidents were 55% in the larnygeal mask airway group vs. 30% in the laryngeal tube group (P < 0.05). Conclusions: The target effect-site concentration of propofol for insertion of laryngeal tube was lower than for larnygeal mask airway (P < 0.05), with a consequent reduction of the propofol induced haemodynamic side-effects.
Background and objective: The purpose of this prospective randomized study was to assess the value of pressure support ventilation during inhalational induction with sevoflurane in adult patients. Methods: Thirty-five adult patients, ASA I–II and scheduled for ear nose throat surgery were studied. Vital capacity induction with 8% sevoflurane in 8 L min−1 oxygen was performed. Pressure support ventilation was used in Group 1 with pressure set at 15 cmH2O. In Group 2, patients breathed spontaneously. After 2 min, sevoflurane was set to 3% and remifentanil 1 μg kg−1 was injected over 2 min followed by an infusion of 0.1μg kg−1 min−1. Two minutes after the end of the bolus, intubation was performed. Bispectral index, oxygen saturation, respiratory rate, end-tidal carbon dioxide, expired tidal volume and expired sevoflurane concentration were recorded every minute. Results: Eighteen patients were included in Group 1 and 17 in Group 2. Saturation, respiratory rate and end-tidal carbon dioxide were similar in the two groups. Expired tidal volume was significantly higher and bispectral index values significantly lower in Group 1. Intubating conditions were better in Group 1. Conclusions: Pressure support ventilation provides both better ventilation and deeper level of anaesthesia during inhalation induction with sevoflurane.
We give on overview of recent advances in collisionally pumped optical
field-ionization soft X-ray lasers developed at LOA. Saturated
amplification has been achieved on the 5d-5p transition in Xe8+
at 41.8 nm, and on the 4d-4p transition in Kr8+ at 32.8 nm. We
demonstrate a significant increase of the energy output from the
Xe8+ laser driven within two types of wave-guide. Finally, we
present results of a pioneering work aimed to set up and characterize the
first true soft X-ray laser chain.
Torsional Couette flow between a rotating disk and a stationary wall is studied experimentally. The surface of the disk is either rigid or covered with a compliant coating. The influence of wall compliance on characteristic flow instabilities and on the laminar–turbulent flow transition is investigated. Data obtained from analysing flow visualizations are discussed. It is found that wall compliance favours two of the three characteristic wave patterns associated with the transition process and broadens the parameter regime in which these patterns are observed. The results for the effects of wall compliance on the third pattern are inconclusive. However, the experiments indicate that the third pattern is not a primary constituent of the laminar–turbulent transition process of torsional Couette flow.
A conical resonator using the acoustic near-field technique has been designed and developed.
This resonator design is sensitive to the density and viscosity of liquids, as well as to the
modification, without discontinuity, of the rheological properties of viscoelastic media. The
experimental measurements agree with the results expected from the modelling of the resonator.
L'étude de la signature acoustique permet de mesurer les vitesses de propagation des
ondes acoustiques longitudinale et transverse dans les matériaux massifs, vitesses à partir
desquelles on détermine leurs propriétés mécaniques. Pour des matériaux en couche mince, ces
vitesses ne sont plus mesurées directement Mays calculées à partir des vitesses accessibles
expérimentalement : celles des modes de Lamb généralisés. Ces modes ont des vitesses
dispersives et leur mesure dépend du liquide servant de couplant, dans lequel la couche est
immergée. Dans cette étude, les liquides de couplage (méthanol, eau et solutions aqueuses de
iodure de potassium KIaq. 6 M et d'hydroxyde de potassium KOHaq. 12 M) sont choisis en fonction
de leurs paramètres acoustiques. La modélisation de la signature acoustique permet de prévoir
leur influence respective, comment ils vont favoriser la détection des modes rapides et, d'une
façon générale, augmenter la précision sur la mesure de la vitesse de tous les modes accessibles.
Les études expérimentales confirment que la caractérisation de chaque mode peut être optimisée
par le choix d'une part de la fréquence et d'autre part du liquide de couplage en fonction de sa
vitesse, sa densité et son atténuation.
Amorphous silicon carbide films (a–SixC1−x :H) deposited by the argon- or helium-diluted PECVD technique were studied as a function of their composition. Microstructural investigations were mainly achieved by means of FTIR and XPS techniques. Nuclear techniques were used to obtain precise information on the film hydrogen content. The Si–H IR-absorption band was deconvoluted in different monohydride and dihydride silicon environments. The existence of SiH2 bonds in the Si-rich composition was evidenced. From the analysis of the C–H and Si–H absorption bands it is shown that hydrogen atoms are preferentially bonded to carbon atoms. The deconvolution of the Si2p core level peak suggests that above a composition of x ∊ 0.5, the noncarburized (Si, Si, H) local environment contribution increases to the detriment of the hydrocarburized (Si, C, H) environments. From the evolution of the C1s peak, it can be deduced that there is a change in the carbon atom bonding states when the film composition is varied. These results are correlated and discussed in terms of the local bonding environments and their evolution with film composition.
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