1,106 research outputs found
Thermoelectric relations in the conformal limit in Dirac and Weyl semimetals
In the Fermi liquid description of metals, electrical and thermoelectric
transport coefficients are linked by robust relations which can be challenged
by strong interactions or when the electron liquid enters a different regime.
These relations have been very powerful in the characterisation of novel
materials. We show that Dirac and Weyl semimetals at zero doping and zero
temperature (the conformal limit) have a very singular behavior due to a
quantum anomaly. Away from this point, a Mott relation can be established
Self-organization of ultrasound in viscous fluids
We report the theoretical and experimental demonstration of pattern formation
in acoustics. The system is an acoustic resonator containing a viscous fluid.
When the system is driven by an external periodic force, the ultrasonic field
inside the cavity experiences different pattern-forming instabilities leading
to the emergence of periodic structures. The system is also shown to possess
bistable regimes, in which localized states of the ultrasonic field develop.
The thermal nonlinearity in the viscous fluid, together with the
far-from-equilibrium conditions, are is the responsible of the observed
effects
Bistable and dynamic states of parametrically excited ultrasound in a fluid-filled cavity
In this paper we have considered the problem of parametric sound generation
in an acoustic resonator flled with a fluid, taking explicitely into account
the influence of the nonlinearly generated second harmonic. A simple model is
presented, and its stationary solutions obtained. The main feature of these
solutions is the appearance of bistable states of the fundamental field
resulting from the coupling to the second harmonic. An experimental setup was
designed to check the predictions of the theory. The results are consistent
with the predicted values for the mode amplitudes and parametric thresholds. At
higher driving values a self-modulation of the amplitudes is observed. We
identify this phenomenon with a secondary instability previously reported in
the frame of the theoretical model.Comment: 5 figures. Submitted to JAS
Nondiffractive sonic crystals
We predict theoretically the nondiffractive propagation of sonic waves in
periodic acoustic media (sonic crystals), by expansion into a set of plane
waves (Bloch mode expansion), and by finite difference time domain calculations
of finite beams. We also give analytical evaluations of the parameters for
nondiffractive propagation, as well as the minimum size of the nondiffractively
propagating acoustic beams.Comment: 7 figures, submitted to J. Acoust. Soc. A
Heterologous expression of AtNPR1 gene in olive for increasing fungal tolerance
The NPR1 gene encodes a key component of SAR signaling mediated by salicylic acid (SA). After a pathogen infection, the accumulation of SA releases NPR1 monomers in the cytosol that are translocated to the nucleus, activating the expression of pathogenesis-related (PR) genes. Overexpression of NPR1 has conferred resistance to fungal, viral and bacterial pathogens in several plant species. The aim of this research was to generate transgenic olive plants expressing the gene AtNPR1 from Arabidopsis thaliana to obtain material resistant to fungal pathogens. Three transgenic lines expressing AtNPR1 gene under the control of the constitutive promoter CaMV35S were obtained following the protocol of Torreblanca et al. (2010), using an embryogenic line derived from a seed of cv. Picual. Level of AtNPR1 expression in transgenic calli varied greatly among the different lines, being higher in the line NPR1-780. The elicitation of embryogenic calli in liquid medium with AS did not increase endochitinase activity, a PR protein. However, jasmonic acid induced a transient increase in chitinase activity after 24 h of treatment in all the lines, being the increment higher in transgenic NPR1 than in control. After maturation and germination of transgenic somatic embryos, plants were micropropagated and acclimated to ex vitro conditions. The expression of AtNPR1 did not alter the growth of transgenic plants neither in vitro nor in the greenhouse. Experiments are in progress to determine the resistance of transgenic AtNPR1 plants to V. dalihae and R. necatrix.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech.
Research projects: Plan Nacional AGL2014-52518-C2-1-R; AGL2017-83368-C2-1-R and Junta de Andalucía P11-AGR799
Theory of quantum fluctuations of optical dissipative structures and its application to the squeezing properties of bright cavity solitons
We present a method for the study of quantum fluctuations of dissipative
structures forming in nonlinear optical cavities, which we illustrate in the
case of a degenerate, type I optical parametric oscillator. The method consists
in (i) taking into account explicitly, through a collective variable
description, the drift of the dissipative structure caused by the quantum
noise, and (ii) expanding the remaining -internal- fluctuations in the
biorthonormal basis associated to the linear operator governing the evolution
of fluctuations in the linearized Langevin equations. We obtain general
expressions for the squeezing and intensity fluctuations spectra. Then we
theoretically study the squeezing properties of a special dissipative
structure, namely, the bright cavity soliton. After reviewing our previous
result that in the linear approximation there is a perfectly squeezed mode
irrespectively of the values of the system parameters, we consider squeezing at
the bifurcation points, and the squeezing detection with a plane--wave local
oscillator field, taking also into account the effect of the detector size on
the level of detectable squeezing.Comment: 10 figure
Modelo de elementos finitos de la columna lumbar
En este trabajo se describe un modelo de Elementos Finitos de la columna lumbar
humana. El objetivo buscado es la utilización del mismo como herramienta de investigación
aplicada a la cirugía ortopédica de columna lumbar. Para conseguir este objetivo se ha
elaborado un modelo no lineal y paramétrico de la columna lumbar completa, el cual puede
modificarse con facilidad tanto en su geometría como en sus características mecánicas de
modo que puedan reflejarse tanto distintas alteraciones segmentarias como diversas técnicas
de fijación. También se expone la contrastación del modelo, realizada a partir de resultados
experimentales recogidos de la literatura sobre el tema.Peer Reviewe
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