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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.
New defects were revealed in PECVD SiOxNyHz thin layers upon VUV-illuminations with a deuterium (De) lamp. The ESR signal measured after a 8-hour illumination reached a saturated amplitude one or two decades higher than the dark ESR signal. The dark ESR signal level was recovered after a 3-hour anneal at 380°C. In addition to the silicon dangling bonds already identified in the dark ESR, the bridging nitrogen dangling bonds and over-coordinated nitrogen were identified after VUV-radiations. The relative densities of the various kinds of defect are given as a function of the O/O+N oxynitride composition.
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.
We report on the performance of the digital baseband feedback circuit developed to readout and process signals from arrays of transition edge sensors for SPICA-SAFARI in frequency domain multiplexing (FDM). The standard procedure to readout the SQUID current amplifiers is to use a feedback loop (flux-locked loop: FLL). However the achievable FFL bandwidth is limited by the cable transport delay td, which makes standard feedback inconvenient. A much better approach is to use baseband feedback. We have developed a model of the electronic readout chain for SPICA-SAFARI instrument by using an Anlog-digital co-simulation based on Simulink-System Generator environment.
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.
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.
Ablation depths of stainless steel targets irradiated by 80-fs
laser pulses at a flux F ≤ 40 J/cm2
(intensity ≤ 5 × 1014 W/cm2)
in the presence of air at atmospheric pressure are experimentally
measured. These values are lower than the theoretical predictions
for metal targets in vacuum. Results are analyzed on the basis of
the role of the ambient gas and of crater formation on the behavior
of the ablated material.
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.
1 GHz very high frequency acoustical imaging displays a micronic resolution. Owing to its nature of
sub-surface imaging, it is well adapted to the characterization of porosity. Used as a means for
quantitative measurements through acoustic signature processing, it provides sufficiently localized
information to characterize the elastic properties proper to each component of a SiC/SiC minicomposite,
the fiber and the matrix.
The acoustic near field method consists in studying the alteration of the resonance
curve of a horn whose tip, the probe, is immersed in the sample. The operating
mode in a medium in which strong variations of the rheological properties take
place, is modelled for two horn shapes, one with a conical probe, the second one
with a stepped cylindrical probe. The experimental curves obtained during the
cement setting prove the validity of the simulations. The sensitivity of the horn to a
given step of the setting is achieved by adjusting the probe shape.
The alterations of the resonance frequency of the vibrating tip of an acoustic sensor detect
the density and the viscosity of liquids. The employed acoustic near-field sensor has
several resonance frequencies which correspond to its different parts. We determined that
the resonance of the body of the acoustic sensor is sensitive to the rheological
characteristics of viscoelastic media. We carried out experiments with bitumens and we
modified the acoustic load on the sensor in two ways: the immersion depth of the tip and
the temperature of the bitumen specimens. Theoretical and experimental results are
The characteristics of the various modes of acoustic waves (velocity, attenuation,
efficiency) radiated towards the focused sensor of an acoustic microscope are
related to the acoustic properties of the coupling fluid. The aqueous solutions of
electrolytes are suitable as coupling fluids because their acoustic properties can
be adjusted owing to the choice of the nature and of the concentration of the
dissolved ions. By adjusting the properties of the couplant, the performances of the
sensors of the acoustic microscopes can be extended. The image contrasts and the
accuracy of measurements of the acoustic waves velocity are improved, the radiation
of the chosen modes are enhanced and very high frequencies can be used.
In order to allow non-destructive characterizations by acoustic microscopy, the
materials presenting in their properties a gradient perpendicular to the surface are
modelled. The method consists in regarding the material as built of a succession of
homogeneous layers numerous enough for the acoustic parameters to vary
quasi-continuously. The gradient in Young modulus existing in the material is related
to a gradient in acoustic properties measurable by acoustic microscopy. The role of
the shape of the gradient profile is taken into account in the study of the
convergence of the velocity of the surface mode VS. The dispersion of the
velocity VSversusd/λ (d is the depth of the gradient area
and λ is the wavelength) is studied as a function of the gradient profile. The
shape of the curves shows that the best sensitivity to the profile is obtained for
An experiment has been performed with the LULI
Multi-TeraWatt Laser. The acceleration of electrons injected
in a plasma wave generated by the laser wakefield mechanism
has been observed with a maximum energy gain of 1.5 MeV.
It has been shown that the electrons deflected during the
interaction, could scatter on the walls of the experimental
chamber, and fake a high-energy signal. A special effort
has been given in the electron detection to separate the
accelerated electrons signal from the background noise.The
experimental results agree with theoretical predictions
and numerical simulations when 3D effects on the electron
beam are taken into account.
This study explains processes for the characterization by acoustic
microscopy of materials presenting, along a thickness d close to the surface, a
gradient in elastic properties in direction perpendicular to the surface. The method,
modelling the non-homogeneous area by a finite number of layers of the same thickness,
is sensitive to the factor fd (f is the working frequency) and to the nature
of the gradient profile. The study of the dispersion of the Rayleigh velocity as a
function of frequency shows that the shape of the curve Maynly depends on the gradient
profile and on the structure (surface material and bulk material). When the numerical
derivative of the dispersion curves presents inflexion points, they can be linked to
the depth and to the nature of the profile. Modelling of the materials displaying a
gradient shows that, in some cases, the plot of the curvature of the dispersion curves
as a function of frequency is a useful means of characterization.
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.
The nonlinear evolution of electrostatic plasma waves excited by mode conversion is studied in an inhomogeneous, collisionless, unmagnetized plasma. Experiments in the microwave range (f = 3.5 GHz), performed in a plasma (ne ≃ 1011 cm−3) created in a multipolar discharge, show that the electrostatic plasma-wave evolution exhibits a transition from a nonlinear steady-state regime toward chaos, occurring when the pump field or the gradient length is increased. The Zakharov equations, which model the plasmawave evolution coupled with low-density perturbation, are solved numerically with parameters close to those of the experiment; this simulation allows a characterization of the two regimes.
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