Asymmetric I-V characteristics and magnetoresistance in magnetic point contacts

We present a theoretical study of the transport properties of magnetic point contacts under bias. Our calculations are based on the Keldish's non-equilibrium Green's function formalism combined with a self-consistent empirical tight-binding Hamiltonian, which describes both strong ferromagnetism and charging effects. We demonstrate that large magnetoresistance solely due to electronic effects can be found when a sharp domain wall forms inside a magnetic atomic-scale point contact. Moreover we show that the symmetry of the $I$-$V$ characteristic depends on the position of the domain wall in the constriction. In particular diode-like curves can arise when the domain wall is placed off-center within the point contact, although the whole structure does not present any structural asymmetry.Comment: 7 figures, submitted to PR

Can the transformation time in phase change optical recording be improved by using femtosecond laser pulses?

CLEO/EUROPE ; EQEC European Quantum Electronics Conference, Munich ICm, Germany, 22-27 June, 2003N

Slow interfacial reamorphization of Ge films melted by ps laser pulses

Melting and rapid solidification is induced in 50-nm-thick amorphous Ge films on glass substrates by single laser pulses at 583 nm with a duration of 10 ps. The solidification process is followed by means of reflectivity measurements with ns time resolution both at the air/film (front) and the substrate/film (back) interfaces. Due to interference effects between the light reflected at the film-substrate and film-liquid interfaces, the back side reflectivity measurements turn out to be very sensitive to the melt depth induced by the laser pulse and their comparison to optical simulations enables the determination of the solidification dynamics. For low fluences, only a thin layer of the film is melted and solidification occurs interfacially leading to reamorphization of the molten material. The results provide a critical interface velocity for amorphization of ∼4 m/s, much slower than the one that has widely been reported for elementary semiconductors. For high fluences, the molten layer depth approaches the film thickness and the results are consistent with a bulk solidification process. In this case, recalescence effects upon solid phase nucleation become important and lead to the formation of crystallites distributed throughout the whole resolidified volume. © 1998 American Institute of Physics.Jan Siegel acknowledges the funding of the European Community through a grant (ERB40001GT954352) within the Training and Mobility of Researchers Program. This work has been partially supported by CICYT (Spain) under project TIC93-0125.Peer Reviewe

Natural origin products as a source of new antiviral molecules

Motivation: Human adenovirus (HAdV) is a DNA virus that can cause a wide range of diseases, including respiratory and gastrointestinal infections, or conjunctivitis, that in immunocompetent individuals are ausually mild and self-limited. However, in immunosuppresed people and especially in pediatric units, HAdV infections present high morbidity and mortality. Currently there is no specific treatment approved against HAdV. The aim of this work was to characterize the anti-HAdV activity of 18 compounds that were previously selected after high-troughput screening (HTP) of a library of 1340 compounds, coming from our collaboration with the European initiative COSTACTION CM 1407Methods: We had evaluated the anti-HAdV activity of the compounds performing in vitro assays: plaque assays to calculate the IC50 value, citotoxicity assays to calculate the CC50 value, yield reduction assays and qPCR in real time to evaluate the inhibitory effect, and nucleocitoplasm assays to evaluate their mechanism of action.Results: It has been proven that 2 compounds, BBN75 and GSAED772E-1S2R have a safe selectivity index, a great inhibitory effect and they may act in steps subsequent to the arrival of the viral genome at the nucleus of the host cell.Conclusions: The results indicates that BBN75 and GSAED772E-1S2R are promising anti-HAdV drugs to be evaluated at in vivo assays

Pressure-induced transient structural change of liquid germanium induced by high-energy picosecond laser pulses

The temporal evolution of the reflectivity of germanium at 514 nm upon irradiation with single high-energy picosecond laser pulses has been measured using a streak camera. It is found that, for a well-defined high fluence range, the reflectivity of the laser-induced molten phase attains a value of 0.85, considerably above the value reported for liquid Ge in thermal equilibrium (0.75). This behavior is consistent with a strong densification of the liquid phase remaining after the explosive vaporization of a thin surface layer. Within the specified fluence interval, this anomalously high reflectivity state is independent of the fluence and lasts tens of nanoseconds. Both characteristics point to the presence of a pressure-induced transient structural change in liquid germanium. © 2005 American Institute of Physics.Peer Reviewe

Nanocrystal size dependence of the third-order nonlinear optical response of Cu:Al2O3 thin films

3 pages, 3 figures.Metal nanocomposite thin films formed by Cu nanocrystals embedded in an amorphous Al2O3 host have been synthesized by pulsed laser deposition. The mean nanocrystal diameter d was varied in the range 3.0 ± 0.6 to 6 ± 1 nm. The linear and nonlinear optical properties of the films were studied in the vicinity of the surface plasmon resonance and the size dependence of the third-order nonlinear optical susceptibility of the metal nanocrystals has been determined. The observed dependence (1/d3) indicates that in the studied diameter interval, the nonlinear response is due to quantum confinement effects in which the major contribution is associated with electronic intraband transitions.This work has been partially supported by CICYT (Spain) under TIC 96-0467 project and by the EU under BRPR-CT98-0616 project. We acknowledge Dr. I. Vickridge (University of Paris VI et VII, France) for his assistance with RBS techniques.Peer reviewe

In situ studies of the crystallization kinetics in Sb-Ge films

The crystallization process in SbxGe1-x alloy films has been observed during in situ annealing in a transmission electron microscope. Results are presented for two films with x=0.89 (89 at. % Sb) and x=0.71 (71 at. % Sb), which lie on either side of the eutectic composition (x=0.85). In the former films radial crystals are observed to grow rapidly from discrete nuclei, whereas in the latter films the crystallization process occurs through a near-planar front. In addition, quantitative data obtained from these experiments show that the Sb0.89Ge0.11 films have a higher activation energy for crystal growth and a lower temperature for the nucleation of crystals. Significant differences are observed between the crystallization processes for the two films studied, with the Sb0.89Ge0.11 film showing better potential for development as an ultrafast optical phase-change storage medium. © 1995 American Institute of Physics.This work has been partially supported by CICYT under the TIC93-0125 project. We are grateful to The British Council/Spanish Joint Research Program for traveling fi- nances, the Glasstone Benefaction (AKPL), Professor R. J. Brook for provision of laboratory facilities, and the Materials Modelling Laboratory at Oxford for computing facilities. Dr. Neil Long is thanked for operation of the FEG STEM and production of the composition map shown in Fig. 6.Peer Reviewe

IL-17A and Streptococcus pneumoniae respiratory infection: Prospects for the development of new immunotherapies

Nasopharyngeal colonization by Streptococcus pneumoniae constitutes a pre-requisite for development of pneumonia and invasive pneumococcal diseases. Colonization is typically asymptomatic and is resolved due to a dynamic and complex interplay between microbiota, host immune system and environmental factors. Working with a murine model of pneumococcal nasopharyngeal colonization, we have shown that IL-17A is a key cytokine in this process, since Il17a-/- mice were persistently colonized for up to 6 months whereas wild type mice cleared colonization in 10 days. We are currently trying to elucidate the downstream mechanisms that may account for the phenotype showed in Il17a-/- mice, including the production of specific antibodies, as well as the recruitment of innate cells and the expression of immune mediators in WT and Il17a-/- mice. On the other hand, we have studied the role of IL-17A in the development of protective immunity against acute pneumococcal pneumonia. Previously, we showed that prior sublethal infection resulted in solid protection against invasive pneumonia which is associated with over expression of IL-17A together with the presence of Th17 cells in the lungs. However, Il17a-/- mice showed same level of protection than WT, demonstrating that IL-17A by itself is not essential for protective immunity. Interestingly Il17a-/- mice showed overexpression of other IL-17 related genes suggesting a complex network where compensatory effects may be occurring. Finally, we have developed and tested alternative immunotherapies against pneumococcal pneumonia, and have evaluated the role of IL17A in the protection afforded. Overall, we believe that deciphering the molecular basis of protective immunity will result in the development of new cost-effective immunotherapies against pneumococcal pneumonia

Optically active Er–Yb doped glass films prepared by pulsed laser deposition

3 pages, 2 figures.Active rare-earth Er3 + –Yb3 + co-doped phosphate glass films are produced in a single step by pulsed laser deposition. The films are multimode waveguides and exhibit the highest refractive index, optical density and 1.54 µm photoluminescence intensity and lifetime when deposited at low oxygen pressure (Pox4 (menor o igual) 10–5 Torr). The density of the films obtained under these conditions is higher than that of the target material as a consequence of the high kinetic energy of the species generated during ablation. Luminescent emission can be excited by optical pumping the Er3 + ions either directly or through cross-relaxation of the Yb3 + . Post-deposition annealing allows us to improve the luminescence performance.This work has been partially supported by CICYT (Spain) under Project No. TIC96-0467. One of the authors (J.M.B.) acknowledges financial support from the Spanish Ministry of Education.Peer reviewe