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We present a series of shock-wave measurements on aluminum based on the use of a simultaneous Photon Doppler Velocimetry (PDV) and triature velocity interferometer system for any reflector. Our dual setup can accurately measure shock velocities, especially in the low-speed range (−1) and fast dynamics (−1 in velocity and few ns FWHM in time. The advantages of such coupled velocimetry measurements are discussed, as well as new opportunities in dynamic materials science and applications.

International audience; The paper presents an investigation on water drop breakup in the ‘catastrophic’ mode at Weber numbers above 105. Experimental data have been obtained on a detonation shock tube operated at a Mach number between 4.2 and 4.6. Displacement and deformation of the mist cloud generated around the droplet were observed with a shadowgraph system, and Schlieren imagery was used to visualise the bow and wake shocks around the droplet. We observe that all measured quantities scale with the initial drop diameter. In order to analyse the experimental results and relate these observables to the breakup process, numerical hydrodynamic simulations have been performed. Once validated by direct comparison with our experimental observations, the simulation results are used to see “through” the mist and infer the droplet evolution with dimensionless time T. According to our results, the breakup mechanism can be divided into 3 steps. First (T < 1), most of the liquid mass remains in one main drop, whose shape flattens due to the hydrodynamic forces; then (1 < T < 2) fragmentation begins along the outer rim of the liquid drop and splits the corresponding mass into two parts; the first spreads out radially in small fragments while the remains finally (2 < T < 3.5) take the shape of a filament aligned with the flow. Our results are consistent with a complete breakup time Tb = 5.5.

International audience; We present the results of an experimental campaign conducted on the LULI2000 laser facility. Semi-infinite targets of a commercial grade of porous graphite were submitted to high-power laser irradiation inorder to generate craters. A 15 ns pulse duration was used along with a focal spot diameter of 900 μm to deliver energies up to 750 J. Numerical simulations of these shots have been performed following a specificmethodology which can be divided in three steps. Firstly, the mechanical loading induced by the laser iscalibrated by simulating the same shot on a thin aluminum target of which free surface velocity is measured byPDV and line-VISAR. Secondly, the same shot is performed on a thin graphite target to validate the materialmodel of graphite. Thirdly, the craterization shot on semi-infinite target is simulated. Numerical results arecompared to experimental measurements of craters obtained using an interferometric profilometer.

For many years, spall fracture of shock-loaded materials has been one of the most widely studied phenomena in shock physics, for both fundamental and technological motivations. Laser driven shocks provide a means to investigate this process over ranges of extremely high strain rates and short durations, and they allow recovering spalled samples more easily than plate impact or explosive loading techniques. In this paper, we present laser shock experiments on gold and aluminium in cryogenic conditions (relevant in the context of inertial confinement fusion), and on iron at high temperatures up to about 1000 K. Time-resolved measurements of the free surface velocity are used to determine the evolution of the spall strength with sample temperature. They are complemented by post-test observations of the recovered targets, which reveal clear changes in fracture surface morphology in the spall craters. In the case of iron, possible influences of pressure-induced phase transformations prior to tensile loading are discussed on the basis of hydrodynamic simulations.

International audience; Although shock-induced fracture and fragmentation of materials at low temperatures are issues of considerable interest for many applications, such as the protection from hypervelocity impacts in outer space or the ongoing development of high energy laser facilities aiming at inertial confinement fusion, little data can be found on the subject yet. In this paper, laser driven shock experiments are performed on gold and aluminum samples at both ambient and cryogenic (down to about 30 K) temperatures. Complementary techniques including transverse optical shadowgraphy, time-resolved velocity measurements, and post-recovery analyses are combined to assess the effects of target temperature upon the processes of microjetting, spallation, and dynamic punching, which are expected to govern fragments generation and ejection. The results indicate that cryogenic temperature tends to reduce the resistance to tensile and shear stresses, promotes brittle fracture, and leads to slightly higher fragments ejection velocities.

International audience; Scab is an important disease in pear orchards caused by an ascomycetous fungus, Venturia pirina. Young leaves, stems and fruits at all stages of their development are susceptible. Breeding has been undertaken to obtain new hybrids with a good level of resistance to V. pirina. In this context, a better understanding of the host-parasite relationship is necessary. A microscopic study of susceptibility and resistance symptoms on leaves and stems was undertaken on a susceptible cultivar ('Angelys') and a resistant cultivar ('Navara'). Cultivars were grafted onto the rootstock 'Kirchensaller', grown in greenhouse conditions and inoculated with a mixture of local strains of V. pirina. The samples were prepared for confocal micoscopy, scanning electron microscopy and histological studies. On 'Angelys' and 'Navara', the early stages of host-parasite relationships observed by confocal microscopy are similar. A subcuticular primary stroma develops slowly on the susceptible host, 'Angelys'. Often hyphae of the fungus progress deeply between epidermal cells in leaves and stems. The leaf and stem tissue cells show no important changes. Sporulation occurs on leaves 12 to 14 days and on stems 18 to 21 days after inoculation. On the resistant host 'Navara', conidia germinate and form an appressorium, but only a reduced primary subcuticular stroma is observed on the leaf. The cultivar 'Navara's' resistance reaction is of the hypersensitive type. Microscopic analysis shows collapse and necrosis of the epidermal cells; the underlying parenchyma cells undergo important changes. The susceptibility and the resistance symptoms observed on pear leaves with V. pirina are very similar to the symptoms observed with Venturia inaqualis on apple trees but severe symptoms are observed on pear stems with destruction of superficial tissues and deep changes in the cortical parenchyma. The symptom of resistance on stems appears later and is very different from those observed on leaves.

International audience; Dynamic fragmentation of shock-loaded metals is an issue of considerable importance for both basic science and a variety of technological applications, such as inertial confinement fusion, which involves high energy laser irradiation of thin metallic shells. In this context, we present an experimental and numerical study of debris ejection in laser shock-loaded metallic targets (aluminum, gold, and iron) where fragmentation is mainly governed by spall fracture occurring upon tensile loading due to wave interactions inside the sample. Experimental results consist of time-resolved velocity measurements, transverse optical shadowgraphy of ejected debris, and postshock observations of targets and fragments recovered within a transparent gel of low density. They are compared to numerical computations performed with a hydrodynamic code. A correct overall consistency is obtained.

International audience

Possible relationships between the timing of eyespot symptom appearance, the development of Oculimacula yallundae and the responses of infected wheat plants were investigated. By comparing, for 45 days after inoculation (d.a.i.), eyespot- and mock-inoculated coleoptiles and leaf sheaths of a wheat line carrying the Pch1 partial resistance gene, this study showed that cell death, used as a criterion for symptom appearance, occurred on the first leaf sheath around 30 d.a.i. Monitoring of O. yallundae development by optical and scanning electron microscopy revealed that the fungus colonized the coleoptile within 30 d.a.i. It then attacked the first leaf sheath and underwent morphological and growth modifications. For 30 d.a.i., infected plants responded by local accumulations of H(2)O(2) and callose in coleoptile epidermal cells and by up-regulation of pathogenesis-related (PR) genes. From 30 d.a.i., natural browning occurred in the first leaf sheath epidermis and the expression level of PR genes, determined by quantitative PCR, significantly increased in infected plants. These results show that the wheat/O. yallundae interaction is characterized by two distinct phases: the asymptomatic phase and the symptomatic phase. The possibility that O. yallundae should be considered hemibiotrophic rather than necrotrophic is discussed.

Mandevilla sanderi is a plant of tropical origin of great horticultural interest because of its abundant flowering and its persistent foliage. Vegetative propagation requires the removal of leafy branches on the mother plant to produce cuttings. This loss of biomass must be compensated for by the growth of new branches thanks to the mobilization of reserves within the plant. Lack of knowledge about the physiology of this species therefore makes it necessary to characterize its different organs both at the level of their anatomic organization as well as at the level of their ability to store starch. After histological characterization of the different organs (leaves, stems, and roots), starch reserves were localized by histochemical analysis and quantified by biochemical analysis. Starch grains are mainly found in the parenchymatous cortex, the parenchymatous pith and xylem parenchyma cells, in tuberous roots and stems, and in the palisade and spongy mesophyll of leaves. In 22-week-old plants, the greatest quantity of starch is found in the leaves, whereas the tuberous roots have the highest concentration. The histological description of the different organs of Mandevilla sanderi and the localization of starch reserves allow us to assess the potential role of the different organs in plant growth and development. In the particular case of mother plant management, it is hoped that this knowledge will make it possible to optimize conditions for removing leafy branches.

2 vol.; Pear breeding for Scab and Psylla resistance. Xth International Symposium on Pear Growing

2 Vol.; Behaviour studies of new strains of [i]Venturia pirina[/i] isolated from "conference" cultivar on a range of pear cultivars. Xth International Symposium on Pear Growing

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Pathogenicity of virulent [i]Venturia inaequalis[/i] on four apple clones ([i]Malus sp[/i].). Eucarpia Symposium on Fruit Breeding and Genetics

The ν 6 , ν 17 , and ν 21 fundamental bands of dimethyl ether have been assigned and rotationally analyzed. The spectra used were recorded at 0.005 cm −1 spectral resolution with a Fourier-transform spectrometer coupled to a supersonic molecular beam leading to a rotational temperature of about 70 K. The ν 6 and ν 21 bands do not seem to be perturbed and the analysis of the rotational structure leads to band centers located at 933.906 6(9) and 1 103.951(1) cm −1 , respectively, and to accurate rotational and centrifugal distortion constants. For the ν 17 band at 2817.385(2) cm −1 , only the P and R branches could be assigned.

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The intensities and foreign gas broadening coefficients of 57 selected lines of the ν 4 band of NH 3 have been measured in the region of 1550 cm -1 using a high resolution Brucker Fourier transform spectrometer. The line intensities were obtained by using the methods of absorbance at the line center and by fitting Voigt profiles to the measured shapes of the lines. The latter method also provides the collisional widths of the lines. In addition, collision cross relaxation coefficients of O 2 and air foreign gases were measured for 9 doublets of NH 3 in the ν 4 band. The J and K quantum numbers dependencies of pressure-broadening coefficients and line intensities are discussed. The observed air broadening and cross relaxation coefficients were found to be in reasonable quantitative agreement with the concentration-weighted average of the N 2 and O 2 broadening coefficients. The comparison of our present and previous results obtained for the NH 3 –H 2 , NH 3 –air, NH 3 –N 2 and NH 3 –CO 2 collisions shows an increase of the pressure broadening and cross relaxation coefficients with quadrupole moment of the foreign gas. The analysis of the line intensities was based on the third-order theory of line strengths and yields effective transition moments, vibrational band strengths and correction parameters of the symmetric and antisymmetric partial bands of the fundamental ν 4 band.

A new theoretical approach of the unsteady detonation in condensed explosives was developped. The first experimental results presented in this paper confirm that the evolution of the front can be described by the propagation of front-waves, as predicted by the model. It seems, also, that the speed of these waves is a decreasing function of detonation velocity and doesn't depend on the confinement of the explosive.

Resistance overcome by a new race of pathogen is today one of the greatest preoccupations of breeders. The resistance of Vm gene was overcome and the Vf gene was also broken down under certain conditions. The resistance of Vm gene, present in a Malus micromalus clone, was overcome by race 5 of Venturia inaequalis; this gene constitutes outstanding material for studying host-parasite interactions. Consecutive inoculation of resistant and susceptible hybrids with race 1 and 5 of Venturia inaequalis enables rigorous histological and cytological studies. When the resistance is overcome, susceptible and resistant symptoms coexist. At symptom expression, the conidiogenesis is restricted in comparison to the susceptible control. Host reactions are limited to the upper epidermis with abundant subcuticular stroma and very deep erosion of epidermal walls. Epidermal cells collapse irregularly and wall or organelle modifications vary from one cell to another. The resistance’s mechanisms still operate. It is possible to envisage that Venturia inaequalis has acquired sites compatible with those of the receiving host.

In this paper we report experimental and theoretical results on total inelastic cross-sections for NH3 molecules colliding with H2 at room temperature. The use of time resolved infrared-infrared double resonance allows one to follow the population relaxation for different energy levels of NH3. A CO2 pulsed pump laser tuned to a line in the v 2 band of NH3 induces a transient transfer of population and the return to equilibrium is probed with a c.w. diode laser turned to lines in the v 4 band of NH3. The time evolution of the probe absorption for different pressures of the two gases is then related to the inelastic cross-sections of the states involved. The so-determined cross-sections for the (j = 5, k = 4, e = +1) and (j = 1, k = 1, e = -1) states of NH3 are respectively 27 A2 and 31 A2. We have also calculated inelastic cross-sections using a semi-classical model and an ab initio potential energy surface for different values of (j, k, e) (i.e. j = 1, 2, 3, k = 1, 2, 3 and e = ±1) and of j 2 (total angul...

Scab is one of the most harmful diseases of the apple tree; the causal agent is an ascomycete fungus Venturia inaequalis (Cke.) Wint. The majority of cultivars used is susceptible. Among the different sources of resistance which are available, the resistance coded for by the Vm gene, present in a Malus micromalus clone, constitutes outstanding material for studying host-parasite interactions. The clone 9AR2T196 and its seedlings Vm/vm are resistant to race 1, the common race of V. inaequalis but susceptible to the race 5. Consecutive inoculation of plants in the glasshouse with race 1 and 5 on the same host or on seedlings with the same genetic background allows rigorous comparative histological and cytological studies.

The different symptoms of resistance coded by the VF gene were studied on glasshouse-grown apple seedlings after inoculation with a conidial suspension of Venturia inaequalis. Scanning-electron microscopy and histological observations defined precisely three different classes of symptoms. Class 1 corresponds to a hypersensitive reaction. Class 2 is characterized by considerable tissue modifications but no sporulation whatsoever occurs; this reaction defines resistant hybrids. In class 3 the fungus remains active and can sometimes sporulate abundantly; this class was divided into two subgroups, one comprising all the hybrids of weak resistance, the other the hybrids of weak susceptibility.

International audience; La perception est dotée d'une double nature: elle donne à connaître le monde et engage une relation de (dé)plaisir avec des apparences. Cette étude pluridisciplinaire entend éclairer les interactions qui, à la charnière du cognitif et de l'esthétique, se déploient dans l'expérience perceptive.

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