Sorting and transmission electron microscopy analysis of single or double wall carbon nanotubes

On the basis of the recent progress on the sorting of carbon nanotubes’ structure with respect to their diameter or number of walls, we investigate by transmission electron microscopy the sorting efficiency, with a comparison with optical absorption spectroscopy measurements. We study density gradient ultracentrifugation sorted single walled or double walled carbon nanotubes, showing obviously the ability to separate carbon nanotubes of different diameters or/and number of walls. This microscopic approach affords accurate information about the sorted samples such as the real mean diameter, the relative concentration of double walled carbon nanotubes over single walled carbon nanotubes, standard deviation, and the real diameter distribution of carbon nanotubes, even beyond any possible accurate analysis from optical absorption spectroscopy. Therefore, we demonstrate that the diameter analysis of the sorted samples by TEM can indeed afford some information about the relevant optical properties of carbon nanotubes

Stopping of energetic sulfur and bromine ions in dense hydrogen plasma

The concepts of communicative space, media sphere and public sphere are sometimes used like synonyms one of the other. However, according to us, they are three different concepts: public sphere and media sphere are two distinct spaces symbolic systems which, both, are anchored in communicative spac

Stark broadening of B IV lines for astrophysical and laboratory plasma research

Stark broadening parameters for 36 multiplets of B IV have been calculated using the semi-classical perturbation formalism. Obtained results have been used to investigate the regularities within spectral series and temperature dependence.Comment: 8 pages, 6 figures, 1 table, in press in Advances in Space Researc

Pi-stacking functionalization through micelles swelling: Application to the synthesis of single wall carbon nanotube/porphyrin complexes for energy transfer

We report on a new, orginal and efficient method for "pi-stacking" functionalization of single wall carbon nanotubes. This method is applied to the synthesis of a high-yield light-harvesting system combining single wall carbon nanotubes and porphyrin molecules. We developed a micelle swelling technique that leads to controlled and stable complexes presenting an efficient energy transfer. We demonstrate the key role of the organic solvent in the functionalization mechanism. By swelling the micelles, the solvent helps the non water soluble porphyrins to reach the micelle core and allows a strong enhancement of the interaction between porphyrins and nanotubes. This technique opens new avenues for the functionalization of carbon nanostructures.Comment: 6 pages, 5 figure

Ion stopping in dense plasma target for high energy density physics

The basic physics of nonrelativistic and electromagnetic ion stopping in hot and ionized plasma targets is thoroughly updated. Corresponding projectile-target interactions involve enhanced projectile ionization and coupling with target free electrons leading to significantly larger energy losses in hot targets when contrasted to their cold homologues. Standard stoppping formalism is framed around the most economical extrapolation of high velocity stopping in cold matter. Further elaborations pay attention to target electron coupling and nonlinearities due to enhanced projectile charge state, as well. Scaling rules are then used to optimize the enhanced stopping of MeV/amu ions in plasmas with electron linear densities nel ~ 10 18 -10 20 cm -2 . The synchronous firing of dense and strongly ionized plasmas with the time structure of bunched and energetic multicharged ion beam then allow to probe, for the first time, the long searched enhanced plasma stopping and projectile charge at target exit. Laser ablated plasmas (SPQR1) and dense linear plasma columns (SPQR2) show up as targets of choice in providing accurate and on line measurements of plasma parameters. Corresponding stopping results are of a central significance in asserting the validity of intense ion beam scenarios for driving thermonuclear pellets. Other applications of note feature thorium induced fission, novel ion sources and specific material processing through low energy ion beams. Last but not least, the given ion beam-plasma target interaction physics is likely to pave a way to the production and diagnostics of warm dense matter (WDM)

Model atmospheres of chemically peculiar stars: Self-consistent empirical stratified model of HD24712

High-resolution spectra of some chemically peculiar stars clearly demonstrate the presence of strong abundance gradients in their atmospheres. However, these inhomogeneities are usually ignored in the standard scheme of model atmosphere calculations, braking the consistency between model structure and spectroscopically derived abundance pattern. In this paper we present first empirical self-consistent stellar atmosphere model of roAp star HD24712, with stratification of chemical elements included, and which is derived directly from the observed profiles of spectral lines without time-consuming simulations of physical mechanisms responsible for these anomalies. We used the LLmodels stellar model atmosphere code and DDAFIT minimization tool for analysis of chemical elements stratification and construction of self-consistent atmospheric model. Empirical determination of Pr and Nd stratification in the atmosphere of HD24712 is based on NLTE line formation for Prii/iii and Ndii/iii with the use of the DETAIL code. Based on iterative procedure of stratification analysis and subsequent re-calculation of model atmosphere structure we constructed a self-consistent model of HD24712, i.e. the model which temperature-pressure structure is consistent with results of stratification analysis. It is shown that stratification of chemical elements leads to the considerable changes in model structure as to compare with non-stratified homogeneous case. We find that accumulation of REE elements allows for the inverse temperature gradient to be present in upper atmosphere of the star with the maximum temperature increase of about 600K.Comment: Comments: Accepted by A&A, 16 pages, 10 figures, 3 table

INVESTIGATION OF THE TRANSMISSION AND STOPPING OF LIGHT IONS PASSING THROUGH A PLASMA TARGET

Transmission and energy losses of 2 MeV/u Carbon and Sulphur beams passing through a plasma target, have been extensively investigated. A hydrogen plasma ignited by an electrical discharge was coupled to the Orsay Tandem beam accelerator. Fluctuations in beam transmission have been observed and attributed to a magnetic focusing effect generated during the plasma evolution. Energy loss measurements were performed on the basis of time of flight techniques and indicate an enhanced stopping power of the plasma relative to its cold matter equivalent

Chemical stratification in the atmosphere of Ap star HD 133792. Regularized solution of the vertical inversion problem

High spectral resolution studies of cool Ap stars reveal conspicuous anomalies of the shape and strength of many absorption lines. This is a signature of large atmospheric chemical gradients produced by the selective radiative levitation and gravitational settling of chemical species. Here we present a new approach to mapping the vertical chemical structures in stellar atmospheres. We have developed a regularized chemical inversion procedure that uses all information available in high-resolution stellar spectra. The new technique for the first time allowed us to recover chemical profiles without making a priori assumptions about the shape of chemical distributions. We have derived average abundances and applied the vertical inversion procedure to the high-resolution VLT UVES spectra of the weakly magnetic, cool Ap star HD 133792. Our analysis yielded improved estimates of the atmospheric parameters of HD 133792. We show that this star has negligible vsini and the mean magnetic field modulus =1.1+/-0.1 kG. We have derived average abundances for 43 ions and obtained vertical distributions of Ca, Si, Mg, Fe, Cr, and Sr. All these elements except Mg show high overabundance in the deep layers and solar or sub-solar composition in the upper atmosphere of HD 133792. In contrast, the Mg abundance increases with height. We find that transition from the metal-enhanced to metal-depleted zones typically occurs in a rather narrow range of depths in the atmosphere of HD 133792. Based on the derived photospheric abundances, we conclude that HD 133792 belongs to the rare group of evolved cool Ap stars, which possesses very large Fe-peak enhancement, but lacks a prominent overabundance of the rare-earth elements.Comment: Accepted by A&A; 12 pages, 9 figure

Impact of ribosomal operon copy number on genome stability in Escherichia coli

Le nombre total d'opérons d'ARN ribosomique (ARNr) par génomes bactériens est supérieur aux exigences permettant d'obtenir des taux de croissance maximaux. Nous supposons qu'un tel excès d'opérons d'ARNr par génome est nécessaire pour faire face à certaines perturbations environnementales. En effet, chez Escherichia coli (E. coli), la diminution du nombre d'opérons d'ARNr par génome entraîne une augmentation du temps nécessaire pour le redémarrage de la croissance à la sortie de la phase stationnaire. Cette diminution du nombre d'ARNr a également pour effet d'augmenter le temps de redémarrage suite à des stress nutritionnels. L'hypothèse qui a été émise et que le temps nécessaire permettant d'atteindre une capacité de traduction maximale dans les cellules ayant un nombre décroissant d'ARNr était augmenté. Pour tester cette hypothèse, nous avons étudié chez E. coli l'impact du nombre variable d'opérons d'ARNr dans le génome sur la croissance, le taux de mortalité, la réplication de l'ADN et la stabilité du génome. Nous avons montré que la durée de la phase de latence des souches ayant un nombre réduit d'opérons d'ARNr était principalement due à des taux de mortalité très élevés et non à une augmentation du temps requis pour obtenir une capacité de traduction maximum. Au cours de la phase de latence, les cellules avec un nombre diminué d'opérons d'ARNr ont initié la réplication de l'ADN de manière identique aux cellules ayant tous leurs opérons d'ARNr. Cependant, dans les cellules avec un nombre diminué d'opérons d'ARNr, nous avons observé : une perturbation de l'élongation de la réplication de l'ADN, une augmentation de la quantité de cassures des brins d'ADN, une production de ROS, l'induction de la réponse SOS, et une augmentation de la mutagenèse. Enfin, nous avons de déterminé que la survie de ces cellules nécessitait un mécanisme de recombinaison homologue. Nous avons montré que la cause principale des effets délétères observés lors de la réduction du nombre d'opérons d'ARNr est provoquée par le blocage de la machinerie de réplication de l'ADN par des R-loops sur les loci des opérons d'ARNr restants. De plus, après utilisation de traitements détruisant les ribosomes, nous avons montré que dans une souche possédant toutes les copies d'opérons d'ARNr, que la durée de la phase de redémarrage post stress est également affectée par des conflits de réplication-transcription et la présence de R-loops. Notre étude montre que la multiplicité des opérons d'ARNr est nécessaire pour faire face à des perturbations environnementales nécessitant une augmentation rapide de la capacité de traduction. Ce nombre d'opérons d'ARNr garantit que les opérons d'ARNr ne sont pas saturés individuellement par les ARN polymérases. Cette multiplicité du nombre d'opérons d'ARNr peut être considéré comme le gardien de la stabilité génomique.The full number of ribosomal RNA (rRNA) operons per bacterial genomes exceeds requirements for the maximal growth rates. Instead, it is believed that such excess is necessary for coping with environmental perturbations. Indeed, decreasing rRNA operons multiplicity per Escherichia coli genome results in increasing time required for growth restart upon exit from stationary phase, as well as after nutritional upshifts and stresses. This was attributed to a longer time required to reach full translational capacity for cells with decreasing number of rRNA operons. To test this hypothesis, we examined an impact of the different number of rRNA operons per E. coli genome on growth. We showed that the apparent long lag phase upon exit from stationary phase of strains having reduced number of rRNA operons was primarily due to very high mortality rates and not due to time required for the synthesis of enough of the cellular components necessary for growth. During lag growth phase, cells with reduced number of rRNA operons initiated DNA replication like cells having full number of rRNA operons. However, they had severely affected DNA replication elongation, increased quantity of DNA strand breaks, ROS production, SOS induction, mutagenesis, and their survival required homologous recombination machinery. We showed that the primary cause of these deleterious consequences of the reduction of rRNA operon copy number was blockage of the DNA replication machinery by R-loops at the sites of the over-transcribed remaining rRNA operons. We showed that the length of recovery phase after ribosome-destroying treatments is also affected by transcription-translation conflicts and R-loops even in cells having full number of rRNA operons. Taken together our study shows that full number of rRNA copies is necessary for coping with a variety of environmental perturbations primarily because it assures that individual rRNA operons are not saturated by RNAP, which can be considered as the genome stability insurance

Caractérisation d'une source de rayonnement extrême-ultraviolet (EUV) par décharge capillaire (mise en évidence du seuil d'ablation des parois)

Ce travail concerne l'étude et la caractérisation d'une source de rayonnement Extrême Ultraviolet (EUV) pouvant répondre à diverses applications scientifiques et industrielles en particulier celles liées à la nouvelle génération de la lithographie EUV. Cette source pulsée nommée CAPELLA consiste en une décharge dans un capillaire en alumine où circule un gaz. Ce type de décharge produit un plasma chaud, dense et fortement ionisé émettant dans l'EUV. Les échanges thermiques entre le plasma et la paroi peuvent être suffisamment importants pour que la paroi se trouve ablatée. L'utilisation d'un modèle thermique qui détermine l'évolution temporelle de la température de la paroi permet de calculer le seuil d'ablation. Des mesures spectroscopiques du plasma dans plusieurs plages spectrales ont confirmé la présence de ce seuil pour une densité d'énergie injectée de 350 J.cm-3. Les résultats des mesures spectroscopiques ont été comparés aux résultats issus du modèle.ORLEANS-BU Sciences (452342104) / SudocSudocFranceF