Gas phase hydrogen permeation in alpha titanium and carbon steels

Commercially pure titanium and heats of Armco ingot iron and steels containing from 0.008-1.23 w/oC were annealed or normalized and machined into hollow cylinders. Coefficients of diffusion for alpha-Ti and alpha-Fe were determined by the lag-time technique. Steady state permeation experiments yield first power pressure dependence for alpha-Ti and Sievert's law square root dependence for Armco iron and carbon steels. As in the case of diffusion, permeation data confirm that alpha-titanium is subject to at least partial phase boundary reaction control while the steels are purely diffusion controlled. The permeation rate in steels also decreases as the carbon content increases. As a consequence of Sievert's law, the computed hydrogen solubility decreases as the carbon content increases. This decreases in explained in terms of hydrogen trapping at carbide interfaces. Oxidizing and nitriding the surfaces of alpha-titanium membranes result in a decrease in the permeation rate for such treatment on the gas inlet surfaces but resulted in a slight increase in the rate for such treatment on the gas outlet surfaces. This is explained in terms of a discontinuous TiH2 layer

Phylogenomic and comparative genomic studies robustly demarcate two distinct clades of Pseudomonas aeruginosa strains: proposal to transfer the strains from an outlier clade to a novel species Pseudomonas paraeruginosa sp. nov

The strains of Pseudomonas aeruginosa exhibit considerable differences in their genotypic and pathogenic properties. To clarify their evolutionary/taxonomic relationships, comprehensive phylogenomic and comparative genomic studies were conducted on the genome sequences of 212 P. aeruginosa strains covering their genetic diversity. In a phylogenomic tree based on 118 conserved proteins, the analysed strains formed two distinct clades. One of these clades, Clade- 1, encompassing >70 % of the strains including the type strain DSM 50071T, represents the species P. aeruginosa sensu stricto. Clade- 2, referred to in earlier work as the outlier group, with NCTC 13628T as its type strain, constitutes a novel species level lineage. The average nucleotide identity, average amino acid identity and digital DNA–DNA hybridization values between the strains from Clade- 1 and Clade- 2 are in the range of 93.4–93.7, 95.1–95.3 and 52–53 %, respectively. The 16S rRNA gene of P. aeruginosa DSM 50071T also shows 98.3 % similarity to that of NCTC13628T. These values are lower than the suggested cut- off values for species distinction, indicating that the Clade- 2 strains (NCTC 13628T) constitute a new species. We also report the identification of 12 conserved signature indels in different proteins and 24 conserved signature proteins that are exclusively found in either Clade- 1 or Clade- 2, providing a reliable means for distinguishing these clades. Additionally, in contrast to swimming motility, twitching motility is only present in Clade- 1 strains. Based on earlier work, the strains from these two clades also differ in their pathogenic mechanisms (presence/absence of Type III secretion system), production of biosurfactants, phenazines and siderophores, and several other genomic characteristics. Based on the evidence from different studies, we propose that the Clade- 2 strains constitute a novel species for which the name Pseudomonas paraeruginosa is proposed. The type strain is NCTC 13628T (=PA7T=ATCC 9027T). The description of Pseudomonas aeruginosa is also emended to include information for different molecular markers specific for this species

Reduction of leukocyte microvascular adherence and preservation of blood-brain barrier function by superoxide-lowering therapies in a piglet model of neonatal asphyxia

Background: Asphyxia is the most common cause of brain damage in newborns. Substantial evidence indicates that leukocyte recruitment in the cerebral vasculature during asphyxia contributes to this damage. We tested the hypothesis that superoxide radical (O2⋅_) promotes an acute post-asphyxial inflammatory response and blood-brain barrier (BBB) breakdown. We investigated the effects of removing O2⋅_ by superoxide dismutase (SOD) or C3, the cell-permeable SOD mimetic, in protecting against asphyxia-related leukocyte recruitment. We also tested the hypothesis that xanthine oxidase activity is one source of this radical.Methods: Anesthetized piglets were tracheostomized, ventilated, and equipped with closed cranial windows for the assessment of post-asphyxial rhodamine 6G-labeled leukocyte-endothelial adherence and microvascular permeability to sodium fluorescein in cortical venules. Asphyxia was induced by discontinuing ventilation. SOD and C3 were administered by cortical superfusion. The xanthine oxidase inhibitor oxypurinol was administered intravenously.Results: Leukocyte-venular adherence significantly increased during the initial 2 h of post-asphyxial reperfusion. BBB permeability was also elevated relative to non-asphyxial controls. Inhibition of O2⋅_ production by oxypurinol, or elimination of O2⋅_ by SOD or C3, significantly reduced rhodamine 6G-labeled leukocyte-endothelial adherence and improved BBB integrity, as measured by sodium fluorescein leak from cerebral microvessels.Conclusion: Using three different strategies to either prevent formation or enhance elimination of O2⋅_ during the post-asphyxial period, we saw both reduced leukocyte adherence and preserved BBB function with treatment. These findings suggest that agents which lower O2⋅_ in brain may be attractive new therapeutic interventions for the protection of the neonatal brain following asphyxia

EMRI corrections to the angular velocity and redshift factor of a mass in circular orbit about a Kerr black hole

This is the first of two papers on computing the self-force in a radiation gauge for a particle moving in circular, equatorial orbit about a Kerr black hole. In the EMRI (extreme-mass-ratio inspiral) framework, with mode-sum renormalization, we compute the renormalized value of the quantity $h_{\alpha\beta}u^\alpha u^\beta$, gauge-invariant under gauge transformations generated by a helically symmetric gauge vector; and we find the related order $\frak{m}$ correction to the particle's angular velocity at fixed renormalized redshift (and to its redshift at fixed angular velocity). The radiative part of the perturbed metric is constructed from the Hertz potential which is extracted from the Weyl scalar by an algebraic inversion\cite{sf2}. We then write the spin-weighted spheroidal harmonics as a sum over spin-weighted spherical harmonics and use mode-sum renormalization to find the renormalization coefficients by matching a series in $L=\ell+1/2$ to the large-$L$ behavior of the expression for $H := \frac12 h_{\alpha\beta}u^\alpha u^\beta$. The non-radiative parts of the perturbed metric associated with changes in mass and angular momentum are calculated in the Kerr gauge

Scaling and Formulary cross sections for ion-atom impact ionization

The values of ion-atom ionization cross sections are frequently needed for many applications that utilize the propagation of fast ions through matter. When experimental data and theoretical calculations are not available, approximate formulas are frequently used. This paper briefly summarizes the most important theoretical results and approaches to cross section calculations in order to place the discussion in historical perspective and offer a concise introduction to the topic. Based on experimental data and theoretical predictions, a new fit for ionization cross sections is proposed. The range of validity and accuracy of several frequently used approximations (classical trajectory, the Born approximation, and so forth) are discussed using, as examples, the ionization cross sections of hydrogen and helium atoms by various fully stripped ions.Comment: 46 pages, 8 figure

Direct measure of the exciton formation in quantum wells from time resolved interband luminescence

We present the results of a detailed time resolved luminescence study carried out on a very high quality InGaAs quantum well sample where the contributions at the energy of the exciton and at the band edge can be clearly separated. We perform this experiment with a spectral resolution and a sensitivity of the set-up allowing to keep the observation of these two separate contributions over a broad range of times and densities. This allows us to directly evidence the exciton formation time, which depends on the density as expected from theory. We also evidence the dominant contribution of a minority of excitons to the luminescence signal, and the absence of thermodynamical equilibrium at low densities

Anisotropic weakly localized transport in nitrogen-doped ultrananocrystalline diamond films

We establish the dominant effect of anisotropic weak localization (WL) in three dimensions associated with a propagative Fermi surface, on the conductivity correction in heavily nitrogen doped ultrananocrystalline diamond (UNCD) films based on magneto-resistance studies at low temperatures. Also, low temperature electrical conductivity can show weakly localized transport in 3D combined with the effect of electron-electron interactions in these materials, which is remarkably different from the conductivity in 2DWL or strong localization regime. The corresponding dephasing time of electronic wavefunctions in these systems described as ~ T^-p with p < 1, follows a relatively weak temperature dependence compared to the generally expected nature for bulk dirty metals having $p \geq 1$. The temperature dependence of Hall (electron) mobility together with an enhanced electron density has been used to interpret the unusual magneto-transport features and show delocalized electronic transport in these n-type UNCD films, which can be described as low-dimensional superlattice structures.Comment: 27 pages, 6 figures, To be published in Physical Review