Symmetry Aspects in Nonrelativistic Multi-Scalar Field Models and Application to a Coupled Two-Species Dilute Bose Gas

We discuss unusual aspects of symmetry that can happen due to entropic effects in the context of multi-scalar field theories at finite temperature. We present their consequences, in special, for the case of nonrelativistic models of hard core spheres. We show that for nonrelativistic models phenomena like inverse symmetry breaking and symmetry non-restoration cannot take place, but a reentrant phase at high temperatures is shown to be possible for some region of parameters. We then develop a model of interest in studies of Bose-Einstein condensation in dilute atomic gases and discuss about its phase transition patterns. In this application to a Bose-Einstein condensation model, however, no reentrant phases are found.Comment: 8 pages, 1 eps figure, IOP style. Based on a talk given by R. O. Ramos at the QFEXT05 workshop, Barcelona, Spain, September 5-9, 2005. One reference was update

Recording from two neurons: second order stimulus reconstruction from spike trains and population coding

We study the reconstruction of visual stimuli from spike trains, recording simultaneously from the two H1 neurons located in the lobula plate of the fly Chrysomya megacephala. The fly views two types of stimuli, corresponding to rotational and translational displacements. If the reconstructed stimulus is to be represented by a Volterra series and correlations between spikes are to be taken into account, first order expansions are insufficient and we have to go to second order, at least. In this case higher order correlation functions have to be manipulated, whose size may become prohibitively large. We therefore develop a Gaussian-like representation for fourth order correlation functions, which works exceedingly well in the case of the fly. The reconstructions using this Gaussian-like representation are very similar to the reconstructions using the experimental correlation functions. The overall contribution to rotational stimulus reconstruction of the second order kernels - measured by a chi-squared averaged over the whole experiment - is only about 8% of the first order contribution. Yet if we introduce an instant-dependent chi-square to measure the contribution of second order kernels at special events, we observe an up to 100% improvement. As may be expected, for translational stimuli the reconstructions are rather poor. The Gaussian-like representation could be a valuable aid in population coding with large number of neurons

In vitro propagation of Cordia verbenaceae L. (Boraginaceae).

Clonal propagation by tissue culture is useful to regenerate large populations of plants with similar characteristics. There are no previous reports of micropropagation of Cordia verbenacea. In this study, in vitro techniques were applied multiply this important Brazilian medicinal plant. Apical and nodal segments were cultured on Murashige and Skoog solid (0,6%) medium (MS) supplemented with 0.1, 1.0, 5.0 and 10.0 µM kinetin and 0.01µM naphthaleneacetic acid (NAA). Segments apical yielded more propagules than nodal segments. The number and length of propagules increased with in kinetin levels at 5 µM kinetin, decrease with more concentration. The treatment containing 5 µM kinetin and 0.01µM NAA yielded 2.7 propagules per explant. Propagules rooted on MS medium without growth regulators. Finally, 90-95% of the micropropagated plants survived when transferred to greenhouse conditions

Evidence for entanglement at high temperatures in an engineered molecular magnet

The molecular compound [Fe$_{2}$($\mu_{2}$-oxo)(C$_{3}$H$_{4}$N$_{2}$)$_{6}$(C$_{2}$O$_{4}$)$_{2}$] was designed and synthesized for the first time and its structure was determined using single-crystal X-ray diffraction. The magnetic susceptibility of this compound was measured from 2 to 300 K. The analysis of the susceptibility data using protocols developed for other spin singlet ground-state systems indicates that the quantum entanglement would remain at temperatures up to 732 K, significantly above the highest entanglement temperature reported to date. The large gap between the ground state and the first-excited state (282 K) suggests that the spin system may be somewhat immune to decohering mechanisms. Our measurements strongly suggest that molecular magnets are promising candidate platforms for quantum information processing

Experimental Determination of Thermal Entanglement in Spin Clusters using Magnetic Susceptibility Measurements

The present work reports an experimental observation of thermal entanglement in a clusterized spin chain formed in the compound Na$_2$Cu$_5$Si$_4$O$_{14}$. The presence of entanglement was investigated through two measured quantities, an Entanglement Witness and the Entanglement of Formation, both derived from the magnetic susceptibility. It was found that pairwise entanglement exists below $\sim 200$ K. Tripartite entanglement was also observed below $\sim 240$ K. A theoretical study of entanglement evolution as a function of applied field and temperature is also presented.Comment: Submited to Phys. Rev.

Patrones de comportamiento y alimentación del mono aullador Alouatta belzebul en zonas de selva talada y sin talar del este de la Amazonia

This work compared the activity patterns and diet of a group of Alouatta belzebul in areas of logged and unlogged forest in eastern Amazonia. An instantaneous scan sampling procedure was used for the behavioral study (9.3 ± 1.9 complete observation days/month) from February to November 2000. Fruit availability was estimated monthly. Activity budgets were not significantly different between sites. Rest was the predominant activity in both sites (53.6 % and 48.7 %, respectively). Average daily path length was 683.5 ± 215.1 m (n = 93), and the home range was 17.8 ha, including 7 ha in unlogged forest and 10.8 ha in the logged forest. Neither fruit availability nor diet varied significantly between sites. The diet was predominantly folivorous (43.4 % and 46.6 % in unlogged and logged forest, respectively) and frugivorous (43.9 % and 42.8 %). The spatial use by the group was positively related to fruit sources. This study documented the ability of a ranging group of A. belzebul to survive in a habitat influenced by reduced impact logging without dramatically influencing its activity patterns and diet.En este trabajo se comparan los patrones de comportamiento y alimentación de un grupo de Alouatta belzebul en zonas de selva deforestada y sin deforestar del este de la Amazonia. Para el estudio del comportamiento se utilizó un muestreo de barrido temporal instantáneo (observación completa durante 9,3 ± 1,9 meses/días) entre los meses de febrero y noviembre de 2000. La disponibilidad de fruta se calculó mensualmente. Las actividades realizadas no fueron significativamente diferentes en ninguna de las dos ubicaciones. El descanso fue la actividad predominante en ambas, 53,6 % y 48.7 % respectivamente. La media de la longitud de los recorridos diarios era de 683,5 ± 215,1 m (n = 93) y el área de acción era de de 17,8 hectáreas, incluyendo 7 hectáreas de selva sin talar y 10,8 hectáreas de bosques talados. Ni la disponibilidad de fruta ni la dieta variaron significativamente entre las zonas. La dieta era eminentemente folívora (43,4 % y 46,6 % en las zonas de selva sin talar y deforestada, respectivamente) y frugívora (43,9 % y 42,8 %). El uso que el grupo hacía del espacio estaba relacionado de manera positiva con las fuentes de suministro de frutas. En este estudio se ha documentado la habilidad de un grupo de A. belzebul en libertad para sobrevivir en un hábitat afectado por una tala de impacto reducido sin que ello afectase dramáticamente a sus patrones de comportamiento y alimentación