Injection of photoelectrons into dense argon gas

The injection of photoelectrons in a gaseous or liquid sample is a widespread technique to produce a cold plasma in a weakly--ionized system in order to study the transport properties of electrons in a dense gas or liquid. We report here the experimental results of photoelectron injection into dense argon gas at the temperatureT=142.6 K as a function of the externally applied electric field and gas density. We show that the experimental data can be interpreted in terms of the so called Young-Bradbury model only if multiple scattering effects due to the dense environment are taken into account when computing the scattering properties and the energetics of the electrons.Comment: 18 pages, 10 figures, figure nr. 10 has been redrawn, to be submitted to Plasma Sources Science and Technolog

Current-induced magnetic superstructures in exchange-spring devices

We investigate the potential to use a magneto-thermo-electric instability that may be induced in a mesoscopic magnetic multi-layer (F/f/F) to create and control magnetic superstructures. In the studied multilayer two strongly ferromagnetic layers (F) are coupled through a weakly ferromagnetic spacer (f) by an "exchange spring" with a temperature dependent "spring constant" that can be varied by Joule heating caused by an electrical dc current. We show that in the current-in-plane (CIP) configuration a distribution of the magnetization, which is homogeneous in the direction of the current flow, is unstable in the presence of an external magnetic field if the length L of the sample in this direction exceeds some critical value Lc ~ 10 \mu m. This spatial instability results in the spontaneous formation of a moving domain of magnetization directions, the length of which can be controlled by the bias voltage in the limit L >> Lc. Furthermore, we show that in such a situation the current-voltage characteristics has a plateau with hysteresis loops at its ends and demonstrate that if biased in the plateau region the studied device functions as an exponentially precise current stabilizer.Comment: 8 pages, 6 figure

Identification of sortase A (SrtA) substrates in Streptococcus uberis: evidence for an additional hexapeptide (LPXXXD) sorting motif

Sortase (a transamidase) has been shown to be responsible for the covalent attachment of proteins to the bacterial cell wall. Anchoring is effected on secreted proteins containing a specific cell wall motif toward their C-terminus; that for sortase A (SrtA) in Gram-positive bacteria often incorporates the sequence LPXTG. Such surface proteins are often characterized as virulence determinants and play important roles during the establishment and persistence of infection. Intramammary infection with Streptococcus uberis is a common cause of bovine mastitis, which impacts on animal health and welfare and the economics of milk production. Comparison of stringently produced cell wall fractions from S. uberis and an isogenic mutant strain lacking SrtA permitted identification of 9 proteins likely to be covalently anchored at the cell surface. Analysis of these sequences implied the presence of two anchoring motifs for S. uberis, the classical LPXTG motif and an additional LPXXXD motif

Mobility of non thermal electrons and ions in very high density and purified nitrogen corona discharge

WOS:000471052300021International audienceThe mobility of nonthermal electrons and ions have been determined in very high and purified nitrogen corona discharge. Corona discharge was generated by plasma generator system with point-to-plane electrodes geometry configuration. Charateristic I-V has been done by using stabilized DC high voltage generator high up to 20 kV. Graph current of saturation corona unipolar for variation voltage and the distance between electrodes is curved with the semi-parabolic equation. We used I-V characteristic to determine charge patricles mobilities. In this research high purified and slighly purified nitrogen gas. For negative corona, we found that the mobility of charged particles is greater than negative ions and smaller than thermal electron mobility. Particles engaging and moving in the corona with high purification the gas are nonthermal electrons, positive ions for positive corona. From the current-voltage characteristic, we can conclude that the regime of our discharge in very pure gases (N2) corresponds to the current regime limited by space charge. By analogy with what has been observed in a "discharge tube" this regime is similar to an abnormal glow discharge regime. We have seen previously that the variation with the density of the ionic mobility is in good agreement with the direct measurements by the time of flight metho

Mobility of non thermal electrons and ions in very high density and purified nitrogen corona discharge

WOS:00047105230002