The Hermann tortoise (Testudo hermanni boettgeri Mojsisovics, 1889) is present in Romania at its range limit. The main range is located in the Southwestern part of the country, in a sub-optimal sub-Mediterranean climate. Testudo hermanni boettgeri is also found in the Southeastern part of the country, the population there being insignificant to be included in our study. The range from Southwestern part of Romania has a surface of similar to 4420 sq km, from which only similar to 672 sq km is favorable to the tortoise. From the range extension point of view, the Hermann tortoise is a subspecies with a restrictive habitat, and the population is strongly declining-a tendency that most likely will continue in the future. This decline is accentuated by the habitat loss. The main threats for the Hermann tortoise are due to housing and urban area encroachment, tourism and recreation areas, annual and perennial non-timber crops, mining and quarrying, energy production and mining, recreational activities, increase in fire frequency/intensity, droughts, temperature extremes, climate change and severe weather. The threatened status established according to IUCN criteria for the regional level under uncertainty have led to framing the species in the endangered EN Blab(i,ii,iii,v) category.
The Benchmark of the Rance beams has been organised in order to evaluate the capabilities of various modelling tools, to predict the residual load carrying capacity of corroded beams. The Rance beams have been corroded in a marine environment for nearly 40 years. Different types of prestressed beams, made of different types of cement, have been subjected to four points bending monotonous and cyclic tests as well as direct traction tests. The tests have been carried on up to failure, in order to evaluate the residual carrying capacity of the beams. Different teams have participated to the blind prediction of the tests results. In this framework, the CEA/DM2S/LM2S team has performed bidimensionnal modellings which are described in details in this paper. The various constitutive elements of the beams are represented: for concrete, the isotropic Mazars' damage model is used, in a non local version, for prestressing and passive steels, an elasto-plastic strain hardening model is adopted. The corrosion effects, taken into account for the longitudinal rebars, are derived on one hand from the measurements performed on the beams after the tests, and on the other hand from the literature. They consist mainly in a reduction of the rebars cross-section, as well as in their ductility. In principle, the properties of the bond between steel and rebars are also modified by the corrosion. Here, because of the unavailability of specific data on the smooth rebars of the Rance beams, the bond has been modelled by means of specific joint finite elements. The load carrying capacity has been calculated for the monotonous as well as the cyclic tests. Moreover, a sensitivity analysis has been performed, by considering variants where either the rebars are sane, or they have only reduced sections, with their original ductility. The results are compared to the experimental database, and discussed.
We present a new nonlinear solid-state technique for temporal femtosecond pulses cleaning. The contrast reaches 10 -10 for millijoule input pulse. Efficiency is demonstrated at 800 nm and 1 μm. The method is reliable enough to solve the contrast issue for Petawatt class lasers.
Results of experimental investigation and numerical modeling of high strain rate behavior of aluminium alloys AMg-6 and D-16 are presented. Using Split Hopkinson Pressure Bar (SHPB) parameters of Johnson-Cook's model and other models from LS-DYNA library were determined in strain rate range 10(2)-10(4) s(-1). For verification of the models a comparison of the results of numerical modeling and model experiments was carried out. Modificated Taylor's test and modification of SHPB test for high-speed penetration were carried out as model experiments.
The paper presents the range and possibilities of using expert systems at diagnostic measurements of insulation systems of power appliances taken by the acoustic emission (AE) method. Multi -parametric descriptors characterizing the AE signals, which can be used in the knowledge base as criteria making the identification of basic partial discharge forms (PDs) possible, have been characterized in detail. The tables show descriptors describing the AE signals registered in time, frequency, time-frequency domains and statistical data. Moreover, computational tools that can be used in the process of conclusion drawing were suggested and the range of the research work done by the authors of the paper aiming at creating a computerized expert system was presented.
The morphology of the (111) surface of gold induced by ion sputtering has been investigated in the temperature range between 190 and 400 K using thermal energy He atom scattering with a beam energy around 3meV. After sputtering at grazing incidence (about 75°) along the azimuthal direction and at crystal temperature in a range 160-260 K, a well defined ripple structure with ridges oriented along the incoming ion beam direction has been observed. In fact the diffraction pattern in the same direction shows a sharp specular peak while in the 90° direction the pattern shows a specular peak with two satellites around 0.03 A -1 . The evolution with time of this structure has been followed at different crystal temperatures T c in the range 300-400K to gain information on ripple stability and on the diffusion processes contributing to ripple decay. Preliminary results show that up to 350 K the diffraction pattern does not show appreciable changes at least for 24 hours. Instead for T c ≥ 370K the intensity of satellite peaks decreases with a rate which depends on temperature. At 400K the satellite peaks disappear within 1 hour while at 370K they survive at least for 6 hours.
Interaction of sub-nanosecond intense laser pulses with foams containing fine and large pores has been studied experimentally. Laser penetration and energy transport in the foam material are measured via streaked side-on x-ray slit images. Shock wave transition through the foam is detected via streaked optical self-emission from foil attached on the foam rear side. The shock transition time increases with the pore size, foam density, and also with the contents of high Z additions in plastic foams. Foil acceleration is observed via 3-frame interferometry. Comparison of experimental results with numerical simulations and an analytical model is underway.
The temperature resistance of chemically bonded phases on commercial silica gel. LiChrosorb RP 2, RP 8, RP 18 and unmodified Si 60 were tested at different temperatures by photoacoustic FT-IR spectroscopy. The surface characteristics and possible degradation of hydrocarbon phase at higher temperatures were investigated by means of FT-IR/PAS technique. For a series of investigated samples heated up to 423K, the FT-IR/PAS spectra are similar to those for initial silica samples. The most characteristic band for alkyl modified silica gel, i.e., RP 2, RP 8, and RP 18 was observed between 3200 cm-1 to 2800 cm-1 corresponding to various hydrocarbon species. The bands at 3745 cm-1, 3650 cm-1, and 3430 cm-1 observed in the photoacoustic FT-IR spectra may be ascribed to isolated silanol groups (Si-OH), geminal groups (si-(OH) 2 ) and hydrogen-bonded Si-OH groups, respectively. For all samples the intensity of the broad band in the region 3800 cm-1 to 3200 cm-1 decreases with the increasing temperature. The additional peak at 3745 cm-1 for chemically bonded long hydrocarbon chain, i.e., C18 and C8 after thermal treatment at 573 K is observed.
OMEGA EP is a new high-energy petawatt laser system under construction at the University of Rochester's Laboratory for Laser Energetics. This paper describes our designs for two diagnostics critical to OMEGA EP's mission. The focal-spot diagnostic (FSD) is responsible for characterizing the focal spot of OMEGA EP's off-axis parabolic mirror at full energy. The ultrafast temporal diagnostic (UTD) is responsible for characterizing pulse shapes of full-energy target shots ranging in width from <1 to 100 ps as well as setting the desired pulse width before the shot. These diagnostics will enable, for the first time, complete spatial and temporal characterization of the focus of a high-energy petawatt laser at full energy.
Negative ion beams have been proposed as drivers for inertial confinement fusion (ICF), as high-velocity neutral projectiles produced by photodetachment may efficiently impact and heat up a hydrogen pellet target. Charge-changing cross sections are henceforth needed to estimate the beam attenuation in the residual gases. In this work we analyse cross section measurements for the several electron-loss collision channels of fluorine anions impinging on argon (10-50 keV/u energy range) and producing charge states from Ar + to Ar 4+ . Cross sections for projectile destruction associated to target ionization rise steeply with velocity, displaying a clear energy threshold. This threshold is characteristic of a collision process involving direct interaction between a projectile electron and a target electron.
We examine enhanced hard x-ray emission (20 - 200 keV) from plasmas produced on nanoparticles coated optically polished copper surface under different prepulse conditions. We observe that enhancement reduces with increasing prepulse intensity. The dynamics of the process is seen to be in the ps regime. We attribute this to preplasma formation on nanoparticles and subsequent modification/destruction of the nanostructure layer before the arrival of the main pulse. It is suggested that high-contrast ultrashort pulses are essential for nanoparticles to function as yield enhancers.
At present, the mass balance of the Antarctic Ice Sheet (AIS) and its contribution to global sea level change are poorly known. Current methods to determine AIS mass balance as well as the inherent uncertainties are discussed. Special emphasis is placed on the increasingly important role of regional atmospheric climate models, which can reduce the uncertainties in surface accumulation, the correction for the firn layer depth and density in ice thickness calculations and moreover help in interpreting surface elevation changes in terms of accumulation and firn density variability. Some recent advances in these fields of research are presented.
As the need for fuel efficient automobiles increases, car designers are investigating light-weight materials for automotive bodies that will reduce the overall automobile weight. Aluminium alloy tube is a desirable material to use in automotive bodies due to its light weight. However, aluminium suffers from lower formability than steel and its energy absorption ability in a crash event after a forming operation is largely unknown. As part of a larger study on the relationship between crashworthiness and forming processes, constitutive models for 3mm AA5754 aluminium tube were developed. A nominal strain rate of 100/s is often used to characterize overall automobile crash events, whereas strain rates on the order of 1000/s can occur locally. Therefore, tests were performed at quasi-static rates using an Instron test fixture and at strain rates of 500/s to 1500/s using a tensile split Hopkinson bar. High rate testing was then conducted at rates of 500/s, 1000/s and 1500/s at 21°C, 150°C and 300°C. The generated data was then used to determine the constitutive parameters for the Johnson-Cook and Zerilli-Armstrong material models.
Les molecules enantiomeres presentent des activites optiques opposees, mais des rotations Faraday egales. Nous demontrons, par une mesure differentielle, que les stereoisomeres meso, qui, par compensation interne, n'ont pas d'activite optique, presentent au contraire des effets Faraday differents de leurs stereoisomeres chiraux. Ce resultat, obtenu sur l'acide tartrique, est en accord avec les valeurs theoriques issues d'un modele d'interaction dipolaire.
Les processus dynamiques se produisant lors de transitions de phase ultra-rapide peuvent etre deduits a partir de mesures de diffraction ou d'absorption de rayonnement X. Les lasers femtosecondes ont recemment ete utilises pour etudier la dynamiques de la matiere au moyen d'une pompe optique et d'une sonde X: du rayonnement X K alpha produit par interaction laser plasma. Nous presentons nos plus recents resultats concernant le developpement d'un syteme de spectroscopie d'absorption du rayonnement X (XAS) basee sur une source laser-plasma large bande dans la gamme 1-5 nm permettant d'atteindre une resolution temporelle femtoseconde. Le systeme est concu pour sonder les dynamiques electroniques ayant lieu durant la transion de phase semiconducteur-metal du dyoxide de vanadium (V02) lorsque celle-ci est initiee par une impulsion laser femtoseconde. Dans la presente experience, un spectre large bande proche du seuil L du vanadium (511 eV) et du seuil K de l'oxygene (525 eV) du V02 a ete genere et mesure avec un haut rapport signal sur bruit (100), une grande resolution spectrale (AE/E = 4.2 x 10 -3 ), et une resolution temporelle de 1,2 ps.
A hydrodynamic code is used to simulate plane strain tension experiments: extension of sheets and expansion of cylinders. The material is characterized by an elastic-plastic constitutive law. The stress state in the structure is first approximately uniform, but numerical fluctuations proper to the hydrodynamic code grow and give birth to a non homogeneous deformation state. The last step shows the concentration of plastic deformation in necks, prior to rupture. Simulations show very clearly that the wavelength of instabilities and the instant of their appearance depends on some physical values: traction speed, aspect ratio, parameters of the constitutive law. Simulations of plane strain expansion of rings are compared to experimental results of expansion of cylinders. Several fragments are created and their size is similar, which validates partly the simulations.
We study temporal evolution of interfaces in two-dimensional Rayleigh-Taylor and incompressible Richtmyer-Meshkov instabilities numerically. An interface is treated as a vortex sheet and the vortex method is used in order to describe motion of the vortex sheet. Successive profiles of an interface and the temporal evolution of the strength of a vortex sheet are presented and, especially, the evolution of the strength of a vortex core at which the strength of a sheet takes its maximum value is discussed. Motion of vortex cores are investigated for different Atwood numbers and it is shown that loci of vortex cores in lower Atwood numbers are chaotic, while loci in higher Atwood numbers are monotonous for both Rayleigh-Taylor and Richtmyer-Meshkov instabilities.
We present here our numerical model of K-α emission from ultrashort pulse laser irradiated foil targets for the experimental conditions [1]. In our simulations, we use initial plasma density profile calculated by hydrodynamic code for the ASE prepulse target interaction. This profile contains a long subcritical part and we show how this subcritical part may influences fast electron generation and K-α emission from the target.
The French Laser Mega Joule (LMJ) target area is currently designed to achieve ignition and significant fusion gain in the laboratory. Design studies for target equipments are well advanced, target chamber and target area frame (concrete) is even started. A detailed overview of the target area equipments is presented: target chamber, frame, diagnostic inserter manipulator, final optic assembly, dual diagnostic and laser reference, non cryogenic target positioner. Recent technical and architectural choices are detailed including safety transfers and alignment processes (target, laser and diagnostic). All these target equipments allow to optimize shot chronogram, from target metrology to the shot, including calibration process.
Nous présentons des résultats récents concernant des premières investigations de microscopie interférentielle par laser X-UV d'endommagement optique.Le laser X-UV utilisé est un laser collisionnel en régime quasi-stationnaire émettant à 21.2 nm, développé au Prague Asterix Laser System (PALS, Prague, République Tchèque).Des échantillons de silice fondue de haute qualité, avec ou sans rayure, étaient irradiées en face avant par un laser bleu, correspondant au 3 ème harmonique du laser à iode du PALS (1.315 m), servant également à réaliser le laser X-UV à 21.2 nm.Celui-ci était utilisé, 5 ns après l'irradiation pour réaliser une imagerie microscopique et interférentielle de la face arrière de l'échantillon.Les résultats font apparaître des déformations locales transitoires.Des premières analyses mettent en évidence une probable variation de la rugosité de la surface.Cette démonstration expérimentale encourageante ouvre la voie à de futures investigations, notamment sur notre prochaine installation laser : LASERIX.
