Higher-order Kerr terms allow ionization-free filamentation in gases

We show that higher-order nonlinear indices ($n_4$, $n_6$, $n_8$, $n_{10}$) provide the main defocusing contribution to self-channeling of ultrashort laser pulses in air and Argon at 800 nm, in contrast with the previously accepted mechanism of filamentation where plasma was considered as the dominant defocusing process. Their consideration allows to reproduce experimentally observed intensities and plasma densities in self-guided filaments.Comment: 11 pages, 6 figures (11 panels

Spectral dependence of purely-Kerr driven filamentation in air and argon

Based on numerical simulations, we show that higher-order nonlinear indices (up to $n_8$ and $n_{10}$, respectively) of air and argon have a dominant contribution to both focusing and defocusing in the self-guiding of ultrashort laser pulses over most of the spectrum. Plasma generation and filamentation are therefore decoupled. As a consequence, ultraviolet wavelength may not be the optimal wavelengths for applications requiring to maximize ionization.Comment: 14 pages, 4 figures (14 panels

Development of Magnetohydrodynamic Modes During Sawteeth in Tokamak Plasmas

A dynamical analysis applied to a reduced resistive magnetohydrodynamics model is shown to explain the chronology of the nonlinear destabilization of modes observed in tokamak sawteeth. A special emphasis is put on the nonlinear self-consistent perturbation of the axisymmetric m = n = 0 mode that manifests through the q-profile evolution. For the very low fusion-relevant resistivity values, the q-profile is shown to remain almost unchanged on the early nonlinear timescale within the central tokamak region, which supports a partial reconnection scenario. Within the resistive region, indications for a local flattening or even a local reversed-shear of the q-profile are given. The impact of this ingredient in the occurrence of the sawtooth crash is discussed.Fil: Firpo, Marie C.. Ecole Polytechnique; Francia. Centre National de la Recherche Scientifique; FranciaFil: Ettoumi, W.. Ecole Polytechnique; Francia. Centre National de la Recherche Scientifique; FranciaFil: Farengo, R.. Comision Nacional de Energia Atomica. Gerencia del Area de Investigaciones y Aplicaciones no Nucleares. Gerencia de Fisica (CAB); Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Ferrari, Hugo Emilio. Comision Nacional de Energia Atomica. Gerencia del Area de Investigaciones y Aplicaciones no Nucleares. Gerencia de Fisica (CAB); Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Garcia Martinez, Pablo Luis. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Lifschitz, A. F.. Ecole Polytechnique; Francia. Centre National de la Recherche Scientifique; Franci

On negative higher-order Kerr effect and filamentation

As a contribution to the ongoing controversy about the role of higher-order Kerr effect (HOKE) in laser filamentation, we first provide thorough details about the protocol that has been employed to infer the HOKE indices from the experiment. Next, we discuss potential sources of artifact in the experimental measurements of these terms and show that neither the value of the observed birefringence, nor its inversion, nor the intensity at which it is observed, appear to be flawed. Furthermore, we argue that, independently on our values, the principle of including HOKE is straightforward. Due to the different temporal and spectral dynamics, the respective efficiency of defocusing by the plasma and by the HOKE is expected to depend substantially on both incident wavelength and pulse duration. The discussion should therefore focus on defining the conditions where each filamentation regime dominates.Comment: 22 pages, 11 figures. Submitted to Laser physics as proceedings of the Laser Physics 2010 conferenc

Genomic diversity and relationship of Bacillus thuringiensis and Bacillus cereus by multi-REP-PCR fingerprinting

The genomic diversity and relationship among 56 Bacillus thuringiensis and Bacillus cereus type strains were investigated by multi-REP-PCR fingerprinting consisting of three PCR reactions targeting the enterobacterial ERIC1 and ERIC2 and the streptococcal BOXA1R consensus sequences. A total of 113 polymorphic bands were generated in the REP-PCR profiles that allowed tracing of a single dendrogram with three major groups. Bacillus cereus strains clustered together in the A and B groups. Most of the B. thuringiensis strains clustered in group C, which included groups of serovars with a within-group similarity higher than 40% as follows: darmstadiensis, israelensis, and morrisoni; aizawai, kenyae, pakistani, and thompsoni; canadensis, entomocidus, galleriae, kurstaki, and tolworthi; alesti, dendrolimus, and kurstaki; and finitimus, sotto, and thuringiensis. Multi-REP-PCR fingerprinting clustered B. thuringiensis serovars in agreement with previously developed multilocus sequence typing schemes, indicating that it represents a rapid shortcut for addressing the genetic relationship of unknown strains with the major known serovars

Screening of nickel tolerant bacteria and assessing for genes encoding for nickel resistance

Nickel and various heavy metals are known for their toxic effects on human health and the environment. A number of conventional technologies (such as ion exchange, chemical precipitation, chemical oxidation) have been developed for metal removal and detoxification from wastewater. However, these processes have been shown to be expensive and inefficient. For these reasons, biological process has been considered as an attractive alternative to physico-chemical methods leading to the clean up of metal-contaminated environments. Heavy metals resistant microorganisms involved in this biological process are able to uptake both soluble and particulate forms of metals either through bioaccumulation (living cells) and biosorption (dead cells). In our study, a collection of 90 bacterial strains assigned to diverse species of Bacillus, Proteobacteria and Actinobacteria, was screened for multi-heavy metals resistance and accumulation capability. Taking in account the affinity of exopolysaccharide for metals binding, our collection has been also screened for exopolysaccharide production. Moreover the active nickel removal ability was investigated by ICP-MS and the amplification of specific metal-resistance genes nccA, cnr3 and nrbE encoding for nickel-cobalt-cadmium resistance, was performed. Our results revealed that strains affiliated to Actinobacteria and Proteobacteria were able to resist to high nickel concentrations ranged from 0.5 to 1 mM. One strain identified as Microbacterium foliorum was found to have the highest tolerance to Ni2+ (2 mM). A weak nickel accumulation has been detected in selected bacteria. Preliminary results showed that there was no implication of microbial exopolysaccharide production in nickel accumulation. Further experiments are currently in progress in order to improve the efficiency of nickel removal process

Gammaproteobacteria occurrence and microdiversity in Tyrrhenian Sea sediments as revealed by cultivation-dependent and -independent approaches

Bacterial diversity in Tyrrhenian Sea sediments was assessed using cultivation-dependent and independent approaches. Samples collected from the different sediment layers (up to 30 cm) relative to four seamount and non-seamount stations, at depths from 3425 to 3580 m, were subjected to DNA extraction and 165 rRNA amplification targeting the V3 region. Denaturing gradient gel electrophoresis (DGGE) showed several heterogeneous profiles and 27 single bands were excised and sequenced. Sequence analysis revealed the presence of Firmicutes, Actinobacteria and Chloroflexi in 26% of the DGGE bands and a predominance of sequences affiliated to cultivable and uncultivable clones of Gammaproteobacteria (55%). To corroborate these findings, cultivation attempts were performed that allowed the isolation of 87 strains assigned to the proteobacterial classes. Identification was achieved by means of automated ribosomal intergenic spacer analysis (ARISA) and by 165 rDNA sequencing. The isolates were related to the gamma, alpha and beta subclasses of Proteobacteria with respective percentages of 77, 17 and 6%. The most predominant Gammaproteobacteria isolates, assigned to the Psychrobacter marin-cola and P. submarinus clade (n = 53) and to Halomonas aquamarina (n = 14), showed a huge intraspecific diversity with 29 distinct ARISA haplotypes. The detection by both approaches of these psychrophilic and moderately halophilic species and their extensive microdiversity indicated their predominance in Tyrrhenian Sea sediments where they constituted the indigenous microflora

Nickel and copper biosorption by EPS producing Ensifer adhaerens strain As3-5a

Anthropogenic and industrial activities are responsible for environment contamination through the release of toxic heavy metals. Recent studies have reported that microbial biofilms producing extracellular polymeric substances (EPS) contribute significantly to heavy metals removal due to the capacity of EPS to bind and sequester heavy metals from industrial effluents. In the present work, an EPS producing bacterial strain, affiliated to Ensifer adhaerens, was characterized and used in biosorption experiments, in order to implement Nickel and Copper removal process from electroplating wastewaters. Ensifer adhaerens was grown in Luria Broth (LB) medium in a 5L bioreactor. At defined sampling times (24, 48 and 72 hours), cultural broths were deposited onto cellulose acetate membranes. Nickel (50 mg/L) and Copper (200 mg/L), provided as distilled water solutions as well as electroplating wastewaters, were passed through the biomass-activated filters. Abiotic systems were also prepared in order to monitor abiotic losses of heavy metals. Nickel and Copper analysis were conducted by inductively coupled plasma mass spectroscopy (ICP-MS). Twenty four hours-grown biomass removed from water solutions 6.12 mg/L of Nickel and 132.17 mg/L of Copper, separately. When both present in bimetallic water solution, the two metals were removed more efficiently: Ni 25.15 mg/L and Cu 174.03 mg/L. When electroplating wastewater was passed through the biomass-activated filter the removal of Nickel was 17.56 mg/L in the absence of Copper, and of 22.48 mg/L of Nickel and 204 mg/L of Copper in the presence of a bi-metallic wastewater. When the biomass was grown in EPS not inducing conditions, heavy metal removal was not observed, suggesting their role in the process. The high biosorption potential of Ensifer adhaerens strain As3-5a in single and bi-metal systems indicates that the EPS producing strain may be exploited as eco-friendly and low-cost biotechnology for the clean-up of industrial effluents from nickel and copper

Diversity and phylogeny of culturable spore-forming Bacilli isolated from marine sediments

Members of the genus Bacillus and related genera are ubiquitous in nature. However, Bacillus species isolated from marine sediments have attracted less interest respect to their terrestrial relatives. Here, we report the phylogenetic diversity of a collection of 96 Bacilli, isolated from 17 distinct stations of 5 oceanographic campaigns. The diversity was analysed by phenotypic and molecular approaches based on the amplified rDNA restriction analysis (ARDRA), amplification of the internal transcribed spacers (ITS-PCR) and on 16S rRNA sequencing. Intraspecific polymorphism was efficiently detected by biochemical analysis and ARDRA while results of ITS-PCR were in agreement with 16S rRNA sequencing. The identification results assigned 68% of the isolates to the species B. subtilis, B. licheniformis, B. pumilus and B. cereus. Phylogenetic analysis allowed the separation of 9 isolates in a clade that may represent a group of obligate marine Bacillus since they clustered with B. firmus, B. foraminis and marine isolates with metal oxidation and bioaccumulation capabilities. The remaining isolates showed a close affiliation to the genera Virgibacillus, Gracilibacillus and Paenibacillus. The widespread of Bacilli and their high diversity level observed in this work point out the need of more extensive studies to understand their distribution and ecology in deep-sea environments