Properties of holographic dark energy at the Hubble length

We consider holographic cosmological models of dark energy in which the infrared cutoff is set by the Hubble's radius. We show that any interacting dark energy model, regardless of its detailed form, can be recast as a non interacting model in which the holographic parameter $c^{2}$ evolves slowly with time. Two specific cases are analyzed. We constrain the parameters of both models with observational data, and show that they can be told apart at the perturbative level.Comment: 4 pages, 6 figures. Contribution to the Proceedings ERE201

On the average Gamma-Ray Burst X-ray flaring activity

Gamma-ray burst X-ray flares are believed to mark the late time activity of the central engine. We compute the temporal evolution of the average flare luminosity $$ in the common rest frame energy band of 44 GRBs taken from the large \emph{Swift} 5-years data base. Our work highlights the importance of a proper consideration of the threshold of detection of flares against the contemporaneous continuous X-ray emission. In the time interval $30 \rm{s}\propto t^{-2.7\pm 0.1}$; this implies that the flare isotropic energy scaling is $E_{\rm{iso,flare}}\propto t^{-1.7}$. The decay of the continuum underlying the flare emission closely tracks the average flare luminosity evolution, with a typical flare to steep-decay luminosity ratio which is $L_{\rm{flare}}/L_{\rm{steep}}=4.7$: this suggests that flares and continuum emission are deeply related to one another. We infer on the progenitor properties considering different models. According to the hyper-accreting black hole scenario, the average flare luminosity scaling can be obtained in the case of rapid accretion ($t_{\rm{acc}}\ll t$) or when the last \sim 0.5 M_{\sun} of the original 14 M_{\sun} progenitor star are accreted. Alternatively, the steep $\propto t^{-2.7}$ behaviour could be triggered by a rapid outward expansion of an accretion shock in the material feeding a convective disk. If instead we assume the engine to be a rapidly spinning magnetar, then its rotational energy can be extracted to power a jet whose luminosity is likely to be between the monopole ($L\propto e^{-2t}$) and dipole ($L\propto t^{-2}$) cases. In both scenarios we suggest the variability, which is the main signature of the flaring activity, to be established as a consequence of different kinds of instabilities.Comment: MNRAS accepte

Exploring the movement dynamics of deception

Both the science and the everyday practice of detecting a lie rest on the same assumption: hidden cognitive states that the liar would like to remain hidden nevertheless influence observable behavior. This assumption has good evidence. The insights of professional interrogators, anecdotal evidence, and body language textbooks have all built up a sizeable catalog of non-verbal cues that have been claimed to distinguish deceptive and truthful behavior. Typically, these cues are discrete, individual behaviors—a hand touching a mouth, the rise of a brow—that distinguish lies from truths solely in terms of their frequency or duration. Research to date has failed to establish any of these non-verbal cues as a reliable marker of deception. Here we argue that perhaps this is because simple tallies of behavior can miss out on the rich but subtle organization of behavior as it unfolds over time. Research in cognitive science from a dynamical systems perspective has shown that behavior is structured across multiple timescales, with more or less regularity and structure. Using tools that are sensitive to these dynamics, we analyzed body motion data from an experiment that put participants in a realistic situation of choosing, or not, to lie to an experimenter. Our analyses indicate that when being deceptive, continuous fluctuations of movement in the upper face, and somewhat in the arms, are characterized by dynamical properties of less stability, but greater complexity. For the upper face, these distinctions are present despite no apparent differences in the overall amount of movement between deception and truth. We suggest that these unique dynamical signatures of motion are indicative of both the cognitive demands inherent to deception and the need to respond adaptively in a social context

Parabolic dunes in north-eastern Brazil

In this work we present measurements of vegetation cover over parabolic dunes with different degree of activation along the north-eastern Brazilian coast. We are able to extend the local values of the vegetation cover density to the whole dune by correlating measurements with the gray-scale levels of a high resolution satellite image of the dune field. The empirical vegetation distribution is finally used to validate the results of a recent continuous model of dune motion coupling sand erosion and vegetation growth.Comment: 18 pages, 14 figures, aubmitted to Geomorpholog

Nitrous oxide in fresh water systems: An estimate for the yield of atmospheric N2O associated with disposal of human waste

The N2O content of waters in the Potomac and Merrimack Rivers was measured on a number of occasions over the period April to July 1977. The concentrations of dissolved N2O exceeded those which would apply in equilibrium with air by factors ranging from about 46 in the Potomac to 1.2 in the Merrimack. Highest concentrations of dissolved N2O were associated with sewage discharges from the vicinity of Washington, D. C., and analysis indicates a relatively high yield, 1.3 to 11%, for prompt conversion of waste nitrogen to N2O. Measurements of dissolved N2O in fresh water ponds near Boston demonstrated that aquatic systems provide both strong sources and sinks for atmospheric N2O

Size segregation and convection

The size segregation of granular materials in a vibrating container is investigated using Molecular Dynamics. We find that the rising of larger particles is accompanied by the existence of convection cells even in the case of the lowest possible frequencies. The convection can, however, also be triggered by the larger particle itself. The possibility of rising through this mechanism strongly depends on the depth of the larger particle.Comment: 7 pages, 4 figure

Magnetic behaviour of PrPd2B2C

We have synthesized a new quaternary borocarbide PrPd$_{2}$B$_{2}$C and measured its magnetization, electrical resistivity and specific heat. The compound crystallizes in the LuNi$_{2}$B$_{2}$C-type tetragonal structure (space group {\it I4/mmm}). Above 100 K the magnetic susceptibility follows Curie-Weiss behavior with effective moment $\mu_{eff}$ = 3.60 $\mu_{B}$, which is very close to the value expected for Pr$^{3+}$ ions. We do not find evidence for magnetic or superconducting transition down to 0.5 K. Specific heat exhibits a broad Schottky type anomaly with a peak at 24 K, very likely related to crystal electric field (CEF) excitation. The magnetic properties suggest the presence of a singlet CEF ground state leading to a Van-Vleck paramagnetic ground state.Comment: 2 pages, 2 figure

Vibration-induced granular segregation: a phenomenon driven by three mechanisms

The segregation of large spheres in a granular bed under vertical vibrations is studied. In our experiments we systematically measure rise times as a function of density, diameter and depth; for two different sinusoidal excitations. The measurements reveal that: at low frequencies, inertia and convection are the only mechanisms behind segregation. Inertia (convection) dominates when the relative density is greater (less) than one. At high frequencies, where convection is suppressed, fluidization of the granular bed causes either buoyancy or sinkage and segregation occurs.Comment: 4 pages. 3 figures, revtex4, to appear in PRL (in press

Synthesis of Y1Ba2Cu3O(sub x) superconducting powders by intermediate phase reaction

One of the more striking problems for the synthesis of the Y1Ba2Cu3Ox compound is the high-temperature decomposition of the BaCO3. This compound is present as raw material or as an intermediate compound in chemical processes such as amorphous citrate, coprecipitation oxalate, sol-gel process, acetate pyrolisis, etc. This fact makes difficult the total formation reaction of the Y1Ba2Cu3Ox phase and leads to the presence of undesirable phases such as the BaCuO2 phase, the 'green phase', Y2BaCuO5 and others. Here, a new procedure to overcome this difficulty is studied. The barium cation is previously combined with yttrium and/or copper to form intermediate compounds which can react between them to give Y1Ba2Cu3Ox. BaY2O4 and BaCu2O3 react according to the equation BaY2O4+3BaCu2O3 yields 2Y1Ba2Cu3Ox. BaY2O4 is a stable compound of the Y2O3-BaO system; BaCu2O3 is an intimate mixture of BaCuO2 and uncombined CuO. The reaction kinetics of these phases have been established between 860 and 920 C. The phase evolution has been determined. The crystal structure of the Y1Ba2Cu3Ox obtained powder was studied. According to the results obtained from the kinetics study the Y1Ba2Cu3Ox the synthesis was performed at temperatures of 910 to 920 C for short treatment times (1 to 2 hours). Pure Y1Ba2Cu3Ox was prepared, which develops orthorombic type I structure despite of the cooling cycle. Superconducting transition took place at 91 K. The sintering behavior and the superconducting properties of sintered samples were studied. Density, microstructure and electrical conductivity were measured. Sintering densities higher than 95 percent D(sub th) were attained at temperatures below 940 C. Relatively fine grained microstructure was observed, and little or no-liquid phase was detected