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The filamentation and collapse of Langmuir waves in a weak magnetic field are analysed in two particular cases of low-frequency acoustic perturbations: (i) adiabatic perturbations which correspond to subsonic collapse, and (ii) nonadiabatic perturbations which correspond to supersonic collapse. Here the existence of Langmuir filaments and Langmuir collapse in a weak magnetic field are due to nonlinear interaction of high-frequency Langmuir waves (which make small angle with the external magnetic field) with low-frequency acoustic perturbations along the magnetic field.
Waist circumference (WC) is a measure of central adiposity related to elevated risk factor levels in children and adolescents. The aim of the present study was to describe WC percentiles in 7- to 10-year-old Brazilian children and to compare frequencies of obesity and overweight as defined by BMI and frequencies of excess and at risk of abdominal adiposity as defined by WC to the corresponding age and sex data from British references. A representative sample of 2919 schoolchildren of the city of Florianopolis (southern Brazil) was examined. Smoothed WC percentiles were derived using the least mean square method. Frequencies of overweight and obesity and of excess and at risk of abdominal adiposity were assessed using the 91st and 98th centiles of the British references as cut-off points. WC increased with age in both boys and girls, with higher values for boys at every age and percentile level. Nutritional status categories of children assessed by the 91st and 98th British BMI and WC centiles showed moderate agreement (weighted κ = 0·58). Overweight was more frequent in Brazilian than British children: 15·1 % of girls and 20·1 % of boys were above the 91st percentile of the 1990 BMI for age British references. About one-quarter (22·0 % of girls and 26·9 % of boys) exceeded the 91st percentile of WC British references. The present data could be used to compare WC in children in other populations and may serve as a baseline for future studies of temporal trends in WC in Brazil.
We present preliminary results of a photometric multisite campaign on the $\delta$ Scuti-type Pre–Main-Sequence star IP Per. Nine telescopes have been involved in the observations, with a total of about 173 hour of observations over around 40 nights. Our current data permitted us to confirm the multiperiodic nature of this star and to determine at least 9 pulsational frequencies. A preliminary nonradial theoretical analysis seems to show that the star pulsates in a mixture of $l=0, 1, 2$ modes.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html
Hf-family compounds have been widely studied as high k gate dielectric materials, they can be elaborated in a wide range of deposition techniques but ALD and MOCVD are the most advanced. In this contribution, the deposition of pure HfO2 is performed by Atomic Vapour Deposition, which is a sort of pulsed-mode MOCVD. The precursor, diluted into a solvent, is pulsed through specific injectors (TriJet®), micro-droplets are vaporised and distributed to the substrate through a showerhead. ATR-FTIR and Hg-probe measurements have been extensively used to evaluate the materials. The advantage of this specific MOCVD system is that it allows working within a wide range of liquid injection frequencies. Thus, we have been able to show that the frequency of injection has a huge impact on the structural and electrical properties of the material. It has been evidence that working at low frequencies is crucial in order to get good electrical behaviour. Higher temperature deposition shows also a clear benefit. An EOT of 1.15 nm with 6.10−2 A/cm2 at |Vfb| + 1 V, that is to say about 3 orders of magnitude below what is obtained with SiO2 has been obtained on capacitors with TiN gate. This is a very good achievement fore pure HfO2 deposited by MOCVD.
This work has been made in the frame of MEDEA + T207 European project with the help of Air Liquide and Epichem.
We have studied the strain state, film and surface morphology of SiGe virtual substrates (Ge concentrations in-between 20% and 55%) grown by reduced pressure – chemical vapor deposition. The macroscopic degree of strain relaxation of those virtual substrates is equal to 97.2 ± 1.5%. The misfit dislocations generated to relax the lattice mismatch between Si and SiGe are mostly confined inside the graded layer. Indeed, the threading dislocations density obtained for Ge concentrations of 20% and 26% is indeed typically of the order of 7.5 ± 2.5 105 cm−2. Low surface root mean square roughness have been obtained, with values in-between 2 and 5 nm. In order to check the electronic quality of our layers, we have grown a MODFET-like heterostructure, with a buried tensile-strained Si channel 8 nm thick embedded inside SiGe 26%. We have obtained a well-behaved 2-dimensional electron gas in the Si channel, with electron sheet densities and mobilities at 1.45K of 5.4×1011 cm−2 and 212 000 cm2 V−1 s−1, respectively.
Ge-based photodetectors operating in the telecommunication wavelength range (1.3-1.6 μm) of silica fibers are highly desirable for the development of optical interconnections on SOI substrates. We have therefore investigated the structural and optical properties of Ge thick films grown directly onto Si(001) substrates using a production-compatible Reduced Pressure Chemical Vapor Deposition system. The thick Ge layers grown using a low-temperature / high temperature approach are in a definite tensile-strain configuration, with a threading dislocation density for as-grown layers of the order of 3×107 cm−2. The surface of those Ge thick layers is rather smooth, especially when considering the large lattice mismatch in-between Ge and Si. The root mean square roughness is indeed of the order of 2 nm only for as-grown layers. The layers produced are of high optical quality. An absorption coefficient α ≈10000 cm−1 @ 1.3μm (4500 cm−1 @ 1.55μm) has been found at room temperature for our Ge thick layers. A 30 meV bandgap shrinkage with respect to bulk Ge (0.77 eV ≎ 0.80 eV) is observed as well in those tensilestrained Ge epilayers.
Ice cores and snow pits of the cryosphere contain particles that detail the history of past atmospheric air compositions. Some of these particles result from combustion processes and have undergone long-range transport to arrive in the Arctic. Recent research has focused on the separation of particulate matter from ice and snow, as well as the subsequent analysis of the separated particles for 14C with accelerator mass spectrometry (AMS) and for individual particle compositions with laser microprobe mass analysis (LAMMA). The very low particulate concentrations in Arctic samples make these measurements a challenge. The first task is to separate the particles from the ice core. Two major options exist to accomplish this separation. One option is to melt the ice and then filter the meltwater. A second option is to sublimate the ice core directly, depositing the particles onto a surface. This work demonstrates that greater control is obtained through sublimation. A suite of analytical methods has been used for the measurement of the carbon in snow and ice. Total carbon was analyzed with a carbon/nitrogen/hydrogen (CHN) analyzer. AMS was used for the determination of carbon isotopes. Since source identification of the carbonaceous particles is of primary importance here, the use of LAMMA was incorporated to link individual particle molecular-structural patterns to the same group of particles that were measured by the other techniques. Prior to this study, neither AMS nor LAMMA had been applied to particles contained in snow. This paper discusses the development and limitations of the methodology required to make these measurements.