72 research outputs found
Three-dimensional numerical simulation of 1GeV/Nucleon U92+ impact against atomic hydrogen
The impact of 1GeV/Nucleon U92+ projectiles against atomic hydrogen is
studied by direct numerical resolution of the time-dependent wave equation for
the atomic electron on a three-dimensional Cartesian lattice. We employ the
fully relativistic expressions to describe the electromagnetic fields created
by the incident ion. The wave equation for the atom interacting with the
projectile is carefully derived from the time-dependent Dirac equation in order
to retain all the relevant terms.Comment: 12 pages and 7 figures included in the tex
Spatial Modulation of linear and quadratic susceptibilities in Lithium Niobate crystals by using femtosecond laser pulses
In this work we present the spatial control of the linear susceptibility (χ1) in Lithium Niobate crystals by means of infrared (800 nm) femtosecond interaction. Diffraction gratings have been performed on the surface (relief) and inside (phase) of these samples by femtosecond laser writing. Also we have performed a spatial control of the quadratic susceptibility (χ 2 ) by direct writing of a pattern of ferroelectric domains on the surface of z cut substrates by using the second harmonic femtosecond pulses (400 nm). Finally, efficient photonic devices for second harmonic generation via quasi phase matching could be obtained following the experimental procedure presented in this work
Breakdown of stabilization of atoms interacting with intense, high-frequency laser pulses
Published versio
Comparative study of ornamental granite cleaning using femtosecond and nanosecond pulsed lasers
Granite has been widely used as a structural and ornamental element in public works and buildings. In damp climates it is almost permanently humid and its exterior surfaces are consequently biologically colonized and blackened We describe a comparative analysis of the performance of two different laser sources in removing biological crusts from granite surfaces: nanosecond Nd:YVO4 laser (355 nm) and femtosecond Ti:Sapphire laser at its fundamental wavelength (790 nm) and second harmonic (395 nm). The granite surface was analyzed using scanning electron microscopy, attenuated total reflection – Fourier transform infrared spectroscopy and profilometry, in order to assess the degree of cleaning and to characterize possible morphological and chemical changes caused by the laser sources.This work is supported by the CTM2010-19584, FIS2009-09522 and CSD2007-00013 research projects (Ministerio de Ciencia y Tecnología, Spanish Government) and by SA086A12-2 project (Junta de Castilla y León, Spain). FTIR, profilometry and SEM analyses were conducted at the University of Vigo's research centre (CACTI)
Transferring orbital and spin angular momenta of light to atoms
Light beams carrying orbital angular momentum, such as Laguerre-Gaussian
beams, give rise to the violation of the standard dipolar selection rules
during the interaction with matter yielding, in general, an exchange of angular
momentum larger than hbar per absorbed photon. By means of ab initio 3D
numerical simulations, we investigate in detail the interaction of a hydrogen
atom with intense Gaussian and Laguerre-Gaussian light pulses. We analyze the
dependence of the angular momentum exchange with the polarization, the orbital
angular momentum, and the carrier-envelope phase of light, as well as with the
relative position between the atom and the light vortex. In addition, a
quantum-trajectory approach based on the de Broglie-Bohm formulation of quantum
mechanics is used to gain physical insight into the absorption of angular
momentum by the hydrogen atom
A spectroscopy approach to the study of virus infection in the endophytic fungus Epichloë festucae
<p>Abstract</p> <p>Background</p> <p>In this work we propose a rapid method based on visible and near-infrared (Vis-NIR) spectroscopy to determine the occurrence of double-stranded RNA (dsRNA) viruses in <it>Epichloë festucae </it>strains isolated from <it>Festuca rubra </it>plants. In addition, we examined the incidence of infections by <it>E. festucae </it>in populations of <it>F. rubra </it>collected in natural grasslands of Western Spain.</p> <p>Methods</p> <p>Vis-NIR spectra (400-2498 nm) from 124 virus-infected and virus-free <it>E. festucae </it>isolates were recorded directly from ground and freeze-dried mycelium. To estimate how well the spectra for uninfected and infected fungal samples could be differentiated, we used partial least-squares discriminant analysis (PLS1-DA) and several data pre-treatments to develop calibration models.</p> <p>Results</p> <p>Applying the best regression model, obtained with two sampling years and using standard normal variate (SNV) combined with first derivative transformation to a new validating data set (42 samples), we obtained a correct classification for 75% of the uninfected isolates and up to 86% of the infected isolates.</p> <p>Conclusions</p> <p>The results obtained suggest that Vis-NIR spectroscopy is a promising technology for detection of viral infections in fungal samples when an alternative faster approach is desirable. It provides a tool adequately exact and more time- and cost-saving than the conventional reference analysis.</p
A Genetic Screen Reveals Arabidopsis Stomatal and/or Apoplastic Defenses against Pseudomonas syringae pv. tomato DC3000
Bacterial infection of plants often begins with colonization of the plant surface, followed by entry into the plant through wounds and natural openings (such as stomata), multiplication in the intercellular space (apoplast) of the infected tissues, and dissemination of bacteria to other plants. Historically, most studies assess bacterial infection based on final outcomes of disease and/or pathogen growth using whole infected tissues; few studies have genetically distinguished the contribution of different host cell types in response to an infection. The phytotoxin coronatine (COR) is produced by several pathovars of Pseudomonas syringae. COR-deficient mutants of P. s. tomato (Pst) DC3000 are severely compromised in virulence, especially when inoculated onto the plant surface. We report here a genetic screen to identify Arabidopsis mutants that could rescue the virulence of COR-deficient mutant bacteria. Among the susceptible to coronatine-deficient Pst DC3000 (scord) mutants were two that were defective in stomatal closure response, two that were defective in apoplast defense, and four that were defective in both stomatal and apoplast defense. Isolation of these three classes of mutants suggests that stomatal and apoplastic defenses are integrated in plants, but are genetically separable, and that COR is important for Pst DC3000 to overcome both stomatal guard cell- and apoplastic mesophyll cell-based defenses. Of the six mutants defective in bacterium-triggered stomatal closure, three are defective in salicylic acid (SA)-induced stomatal closure, but exhibit normal stomatal closure in response to abscisic acid (ABA), and scord7 is compromised in both SA- and ABA-induced stomatal closure. We have cloned SCORD3, which is required for salicylic acid (SA) biosynthesis, and SCORD5, which encodes an ATP-binding cassette (ABC) protein, AtGCN20/AtABCF3, predicted to be involved in stress-associated protein translation control. Identification of SCORD5 begins to implicate an important role of stress-associated protein translation in stomatal guard cell signaling in response to microbe-associated molecular patterns and bacterial infection
A Genomic Approach for the Identification and Classification of Genes Involved in Cell Wall Formation and its Regulation in Saccharomyces Cerevisiae
Using a hierarchical approach, 620 non-essential single-gene yeast deletants generated by
EUROFAN I were systematically screened for cell-wall-related phenotypes. By analyzing
for altered sensitivity to the presence of Calcofluor white or SDS in the growth medium,
altered sensitivity to sonication, or abnormal morphology, 145 (23%) mutants showing at
least one cell wall-related phenotype were selected. These were screened further to identify
genes potentially involved in either the biosynthesis, remodeling or coupling of cell wall
macromolecules or genes involved in the overall regulation of cell wall construction and to
eliminate those genes with a more general, pleiotropic effect. Ninety percent of the mutants
selected from the primary tests showed additional cell wall-related phenotypes. When
extrapolated to the entire yeast genome, these data indicate that over 1200 genes may
directly or indirectly affect cell wall formation and its regulation. Twenty-one mutants with
altered levels of β1,3-glucan synthase activity and five Calcofluor white-resistant mutants
with altered levels of chitin synthase activities were found, indicating that the
corresponding genes affect β1,3-glucan or chitin synthesis. By selecting for increased
levels of specific cell wall components in the growth medium, we identified 13 genes that
are possibly implicated in different steps of cell wall assembly. Furthermore, 14 mutants
showed a constitutive activation of the cell wall integrity pathway, suggesting that they
participate in the modulation of the pathway either directly acting as signaling components
or by triggering the Slt2-dependent compensatory mechanism. In conclusion, our screening
approach represents a comprehensive functional analysis on a genomic scale of gene
products involved in various aspects of fungal cell wall formation
Thermal and Optical Characterization of Undoped and Neodymium-Doped Y3ScAl4O12 Ceramics
Y3–3xNd3xSc1Al4O12 (x = 0, 0.01, and 0.02) ceramics were fabricated by sintering at high temperature under vacuum. Unit cell parameter refinement and chemical analysis have been performed. The morphological characterization shows micrograins with no visible defects. The thermal analysis of these ceramics is presented, by measuring the specific heat in the temperature range from 300 to 500 K. Their values at room temperature are in the range 0.81–0.90 J g1–K–1. The thermal conductivity has been determined by two methods: by the experimental measurement of the thermal diffusivity by the photopyroelectric method, and by spectroscopy, evaluating the thermal load. The thermal conductivities are in the range 9.7–6.5 W K–1 m–1 in the temperature interval from 300 to 500 K. The thermooptic coefficients were measured at 632 nm by the dark mode method using a prism coupler, and the obtained values are in the range 12.8–13.3 × 10–6 K–1. The nonlinear refractive index values at 795 nm have been evaluated to calibrate the nonlinear optical response of these materials.This work is supported by the Spanish Government under projects MAT2011-29255-C02-01-02, MAT2013-47395-C4-4-R, and the Catalan Government under project 2014SGR1358. It was also funded by the European Commission under the Seventh Framework Programme, project Cleanspace, FP7-SPACE-2010-1-GA No. 263044
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