Direct equivalence between quantum phase transition phenomena in radiation-matter and magnetic systems: scaling of entanglement

We show that the quantum phase transition arising in a standard radiation-matter model (Dicke model) belongs to the same universality class as the infinitely-coordinated, transverse field XY model. The effective qubit-qubit exchange interaction is shown to be proportional to the square of the qubit-radiation coupling. A universal finite-size scaling is derived for the corresponding two-qubit entanglement (concurrence) and a size-consistent effective Hamiltonian is proposed for the qubit subsystem.Comment: 4 pages, 3 figures. Minor changes. Published versio

Vanishing Cosmological Constant in Modified Gauss-Bonnet Gravity with Conformal Anomaly

We consider dark energy cosmology in a de Sitter universe filled with quantum conformal matter. Our model represents a Gauss-Bonnet model of gravity with contributions from quantum effects. To the General Relativity action an arbitrary function of the GB invariant, f(G), is added, and taking into account quantum effects from matter the cosmological constant is studied. For the considered model the conditions for a vanishing cosmological constant are considered. Creation of a de Sitter universe by quantum effects in a GB modified gravity is discussed.Comment: 8 pages latex, 1 figure. To appear in Int. J. Mod. Phys.

Probing ferroelectricity in highly conducting materials through their elastic response: persistence of ferroelectricity in metallic BaTiO3-d

The question whether ferroelectricity (FE) may coexist with a metallic or highly conducting state, or rather it must be suppressed by the screening from the free charges, is the focus of a rapidly increasing number of theoretical studies and is finally receiving positive experimental responses. The issue is closely related to the thermoelectric and multiferroic (also magnetic) applications of FE materials, where the electrical conductivity is required or spurious. In these circumstances, the traditional methods for probing ferroelectricity are hampered or made totally ineffective by the free charges, which screen the polar response to an external electric field. This fact may explain why more than 40 years passed between the first proposals of FE metals and the present experimental and theoretical activity. The measurement of the elastic moduli, Young's modulus in the present case, versus temperature is an effective method for studying the influence of doping on a FE transition because the elastic properties are unaffected by electrical conductivity. In this manner, it is shown that the FE transitions of BaTiO3-d are not suppressed by electron doping through O vacancies; only the onset temperatures are depressed, but the magnitudes of the softenings, and hence of the piezoelectric activity, are initially even increased

EVN observations of 6.7-GHz methanol maser polarization in massive star-forming regions II. First statistical results

Magnetic fields have only recently been included in theoretical simulations of high-mass star formation. The simulations show that magnetic fields play an important role in the formation and dynamics of molecular outflows. Masers, in particular 6.7-GHz CH3OH masers, are the best probes of the magnetic field morphologies around massive young stellar objects on the smallest scales of 10-100 AU. This paper focuses on 4 massive young stellar objects, IRAS06058+2138-NIRS1, IRAS22272+6358A, S255-IR, and S231, which complement our previous 2012 sample (the first EVN group). From all these sources, molecular outflows have been detected in the past. Seven of the European VLBI Network antennas were used to measure the linear polarization and Zeeman-splitting of the 6.7-GHz CH3OH masers in the star-forming regions in this second EVN group. We detected a total of 128 CH3OH masing cloudlets. Fractional linear polarization (0.8%-11.3%) was detected towards 18% of the CH3OH masers in our sample. The linear polarization vectors are well ordered in all the massive young stellar objects. We measured significant Zeeman-splitting in IRAS06058+2138-NIRS1 (DVz=3.8+/-0.6 m/s) and S255-IR (DVz=3.2+/-0.7 m/s). By considering the 20 massive young stellar objects towards which the morphology of magnetic fields was determined by observing 6.7-GHz CH3OH masers in both hemispheres, we find no evident correlation between the linear distributions of CH3OH masers and the outflows or the linear polarization vectors. On the other hand, we present first statistical evidence that the magnetic field (on scales 10-100 AU) is primarily oriented along the large-scale outflow direction. Moreover, we empirically find that the linear polarization fraction of unsaturated CH3OH masers is P_l<4.5%.Comment: 13 pages, 8 figures, 7 tables, accepted by Astronomy & Astrophysic

Description of Silvinichthys pedernalensis n. sp. (Teleostei, Siluriformes) from the Andean Cordillera of southern South America

Descripción de Silvinichthys pedernalensis sp. n. (Teleostei, Siluriformes) de la cordillera de los Andes en la parte meridional de Sudamérica Se describe una nueva especie, Silvinichthys pedernalensis, en un arroyo andino de la provincia de San Juan, en Argentina, a partir del patrón de coloración y caracteres merísticos, morfométricos y osteológicos. S. pedernalensis difiere notablemente de todos los demás miembros conocidos del género Silvinichthys debido a la combinación de los siguientes rasgos: ausencia de cintura y aleta pélvica, hueso supraorbital ancho, 14–18 odontoides interoperculares, 6–8 odontoides operculares, 7 radios ramificados de la aleta pectoral, 11 radios de la aleta dorsal, 7 pterigióforos de la aleta dorsal, 6 radios branquióstegos, 14 radios dorsales procurrentes de la aleta caudal y 15 ventrales, 16 costillas, 39 vértebras, pigmentación marmórea oscura de la cabeza y el cuerpo, altura de la cabeza (9,9–12,2% de la longitud estándar [LE]), ancho interorbital (28,3–36,1% de la longitud de la cabeza [LC]), longitud de la barbilla nasal (27,3–39,0% LE), longitud de la barbilla maxilar (39,5–61,7% LE), longitud de la barbilla submaxilar (24,7–41,9% LE), longitud del hocico (40,6–44,4% LC), altura del cuerpo (10,1–12,6% LE), ancho de la aleta anal (10,2–11,7% LE) y longitud del pedúnculo caudal (19,3–21,5% LE).Descripción de Silvinichthys pedernalensis sp. n. (Teleostei, Siluriformes) de la cordillera de los Andes en la parte meridional de Sudamérica Se describe una nueva especie, Silvinichthys pedernalensis, en un arroyo andino de la provincia de San Juan, en Argentina, a partir del patrón de coloración y caracteres merísticos, morfométricos y osteológicos. S. pedernalensis difiere notablemente de todos los demás miembros conocidos del género Silvinichthys debido a la combinación de los siguientes rasgos: ausencia de cintura y aleta pélvica, hueso supraorbital ancho, 14–18 odontoides interoperculares, 6–8 odontoides operculares, 7 radios ramificados de la aleta pectoral, 11 radios de la aleta dorsal, 7 pterigióforos de la aleta dorsal, 6 radios branquióstegos, 14 radios dorsales procurrentes de la aleta caudal y 15 ventrales, 16 costillas, 39 vértebras, pigmentación marmórea oscura de la cabeza y el cuerpo, altura de la cabeza (9,9–12,2% de la longitud estándar [LE]), ancho interorbital (28,3–36,1% de la longitud de la cabeza [LC]), longitud de la barbilla nasal (27,3–39,0% LE), longitud de la barbilla maxilar (39,5–61,7% LE), longitud de la barbilla submaxilar (24,7–41,9% LE), longitud del hocico (40,6–44,4% LC), altura del cuerpo (10,1–12,6% LE), ancho de la aleta anal (10,2–11,7% LE) y longitud del pedúnculo caudal (19,3–21,5% LE).Silvinichthys pedernalensis, a new species, is described from an Andean stream in Provincia San Juan, Argentina, based on its coloration pattern, and its meristic, morphometric and osteological characters. S. pedernalensis differs markedly from all other known members of the genus Silvinichthys as a result of the combination of the absence of pelvic girdle and fin, the wide supraorbital bone, the number of interopercle odontodes 14–18, the number of opercular odontodes 6–8, the branched pectoral–fin rays 7, the dorsal–fin rays 11, the number of dorsal pterygiophore 7, the branchiostegal rays 6, the dorsal procurrent caudal–fin rays 14 and ventral 15, the ribs 16, the vertebrae 39, the dark marmorated pigmentation on the body and head, the head depth 9.9–12.2% SL, the interorbital wide 28.3–36.1% HL, the nasal barbel length 27.3–39.0% SL, the maxillary barbel length 39.5–61.7% SL, the submaxillary barbel length 24.7–41.9% SL, the snout length 40.6–44.4% HL, the body depth 10.1–12.6% SL, the anal base fin 10.2–11.7% SL, and the caudal peduncle length 19.3–21.5% SL

Ultrafast non-linear optical signal from a single quantum dot: exciton and biexciton effects

We present results on both the intensity and phase-dynamics of the transient non-linear optical response of a single quantum dot (SQD). The time evolution of the Four Wave Mixing (FWM) signal on a subpicosecond time scale is dominated by biexciton effects. In particular, for the cross-polarized excitation case a biexciton bound state is found. In this latter case, mean-field results are shown to give a poor description of the non-linear optical signal at small times. By properly treating exciton-exciton effects in a SQD, coherent oscillations in the FWM signal are clearly demonstrated. These oscillations, with a period corresponding to the inverse of the biexciton binding energy, are correlated with the phase dynamics of the system's polarization giving clear signatures of non-Markovian effects in the ultrafast regime.Comment: 10 pages, 3 figure

Interplay between excitation kinetics and reaction-center dynamics in purple bacteria

Photosynthesis is arguably the fundamental process of Life, since it enables energy from the Sun to enter the food-chain on Earth. It is a remarkable non-equilibrium process in which photons are converted to many-body excitations which traverse a complex biomolecular membrane, getting captured and fueling chemical reactions within a reaction-center in order to produce nutrients. The precise nature of these dynamical processes -- which lie at the interface between quantum and classical behaviour, and involve both noise and coordination -- are still being explored. Here we focus on a striking recent empirical finding concerning an illumination-driven transition in the biomolecular membrane architecture of {\it Rsp. Photometricum} purple bacteria. Using stochastic realisations to describe a hopping rate model for excitation transfer, we show numerically and analytically that this surprising shift in preferred architectures can be traced to the interplay between the excitation kinetics and the reaction center dynamics. The net effect is that the bacteria profit from efficient metabolism at low illumination intensities while using dissipation to avoid an oversupply of energy at high illumination intensities.Comment: 21 pages, 13 figures, accepted for publication in New Journal of Physic

Analytic results for NN particles with 1/r21/r^2 interaction in two dimensions and an external magnetic field

The $2N$-dimensional quantum problem of $N$ particles (e.g. electrons) with interaction $\beta/r^2$ in a two-dimensional parabolic potential $\omega_0$ (e.g. quantum dot) and magnetic field $B$, reduces exactly to solving a $(2N-4)$-dimensional problem which is independent of $B$ and $\omega_0$. An exact, infinite set of relative mode excitations are obtained for any $N$. The $N=3$ problem reduces to that of a ficticious particle in a two-dimensional, non-linear potential of strength $\beta$, subject to a ficticious magnetic field $B_{\rm fic}\propto J$, the relative angular momentum.Comment: To appear in Physical Review Letters (in press). RevTeX file. Two figures available from [email protected] or [email protected]

The female body experience as parte of the identity construction process in "Dreaming in cubano", by Cristina García

Soñar en cubano es una novela cubano-estadounidense escrita por Cristina García (1993) que narra la historia matriarcal de tres generaciones de mujeres durante el período de la Revolución castrista. Pasiones, enfermedades, síntomas y traumas aparecen y desaparecen periódicamente en los cuerpos de los personajes femeninos, y sugieren un discurso alternativo que opera a través de una variedad de registros y códigos corporales. El objetivo de este trabajo es revelar cómo el trauma colectivo experimentado por los personajes femeninos de la novela refleja el desorden de las circunstancias socio-políticas en que se desarrolla, forjando la experiencia y memoria corporales de los personajes frente a la condición poscolonial. Este trabajo concluye que la experiencia corporal femenina cumple un rol central en el proceso de reconstrucción identitaria en el contexto de la diáspora cubana, evidenciando el cuerpo femenino como sitio potencial de resistencia y contienda frente al discurso eurocéntrico y patriarcal.Soñar en cubano is a Cuban-American novel by Cristina García (1993) that tells the matriarchal history of three generations of women during the period of the Cuban Revolution. Passions, diseases, symptoms and traumas appear and disappear periodically in the bodies of female characters, and suggest an alternative discourse that operates through a variety of corporeal codes and registers. The objective of this work is to reveal how the collective trauma experienced by the female characters of the novel reflects the disorder of the socio-political circumstances of the context, forging the body memory and experience of the characters in the postcolonial condition. This work concludes that female body experience plays a central role in the process of identity reconstruction in the context of the Cuban diaspora, revealing the female body as a potential site of resistance and contention against the patriarchal, Eurocentric discourse.Fil: Quiroga, Lucía B.. Universidad Nacional de San Lui