A cosmological concordance model with dynamical vacuum term

We demonstrate that creation of dark-matter particles at a constant rate implies the existence of a cosmological term that decays linearly with the Hubble rate. We discuss the cosmological model that arises in this context and test it against observations of the first acoustic peak in the cosmic microwave background (CMB) anisotropy spectrum, the Hubble diagram for supernovas of type Ia (SNIa), the distance scale of baryonic acoustic oscillations (BAO) and the distribution of large scale structures (LSS). We show that a good concordance is obtained, albeit with a higher value of the present matter abundance than in the \Lambda CDM model. We also comment on general features of the CMB anisotropy spectrum and on the cosmic coincidence problem.Comment: Revised version. Accepted for publication in Physics Letters

Charging Effects and Quantum Crossover in Granular Superconductors

The effects of the charging energy in the superconducting transition of granular materials or Josephson junction arrays is investigated using a pseudospin one model. Within a mean-field renormalization-group approach, we obtain the phase diagram as a function of temperature and charging energy. In contrast to early treatments, we find no sign of a reentrant transition in agreement with more recent studies. A crossover line is identified in the non-superconducting side of the phase diagram and along which we expect to observe anomalies in the transport and thermodynamic properties. We also study a charge ordering phase, which can appear for large nearest neighbor Coulomb interaction, and show that it leads to first-order transitions at low temperatures. We argue that, in the presence of charge ordering, a non monotonic behavior with decreasing temperature is possible with a maximum in the resistance just before entering the superconducting phase.Comment: 15 pages plus 4 fig. appended, Revtex, INPE/LAS-00

Magneto-transport and magnetic susceptibility of SmFeAsO1-xFx (x = 0.0 and 0.20)

Bulk polycrystalline samples, SmFeAsO and the iso-structural superconducting SmFeAsO0.80F0.20 are explored through resistivity with temperature under magnetic field {\rho}(T, H), AC and DC magnetization (M-T), and Specific heat (Cp) measurements. The Resistivity measurement shows superconductivity for x = 0.20 sample with Tc(onset) ~ 51.7K. The upper critical field, [Hc2(0)] is estimated ~3770kOe by Ginzburg-Landau (GL) theory. Broadening of superconducting transition in magneto transport is studied through thermally activated flux flow in applied field up to 130 kOe. The flux flow activation energy (U/kB) is estimated ~1215K for 1kOe field. Magnetic measurements exhibited bulk superconductivity with lower critical field (Hc1) of ~1.2kOe at 2K. In normal state, the paramagnetic nature of compound confirms no trace of magnetic impurity which orders ferromagnetically. AC susceptibility measurements have been carried out for SmFeAsO0.80F0.20 sample at various amplitude and frequencies of applied AC drive field. The inter-granular critical current density (Jc) is estimated. Specific heat [Cp(T)] measurement showed an anomaly at around 140K due to the SDW ordering of Fe, followed by another peak at 5K corresponding to the antiferromagnetic (AFM) ordering of Sm+3 ions in SmFeAsO compound. Interestingly the change in entropy (marked by the Cp transition height) at 5K for Sm+3 AFM ordering is heavily reduced in case of superconducting SmFeAsO0.80F0.20 sample.Comment: 18 pages text + Figs: comments/suggestions welcome ([email protected]

Water requirements and single and dual crop coefficients of sugarcane grown in a tropical region, Brazil

A field experiment was conducted throughout 2009/2010 in a sugarcane field of a commercial distillery located on the coastal area of Paraiba state, Brazil. The objectives were to determine sugarcane water requirements and to test the single and dual crop coefficients by comparing the calculated values of ET with measured ones. Crop evapotranspiration was determined by field water balance, reference evapotranspiration (ETo) by the Penman-Monteith approach, while single and dual crop coefficients were computed through the standard FAO-56 methodology. The experi- mental area was cultivated with irrigation ap-plied weekly by a centre pivot system in addition to rainfall and the irrigation scheduling was based on 100% ETo. Three statistical tests, mean bias difference (MBD), normalized root mean square difference (NRMSD) and regression analysis, were used to evaluate the performance of single and dual crop coefficients. Results showed that there was a notable symmetry between ET meas- ured and ET calculated by Kc dual. The ET val- ues, calculated from Kc single, underestimated those obtained from soil water balance meas- urements by 36%

Evidence of stochastic resonance in the mating behavior of Nezara viridula (L.)

We investigate the role of the noise in the mating behavior between individuals of Nezara viridula (L.), by analyzing the temporal and spectral features of the non-pulsed type female calling song emitted by single individuals. We have measured the threshold level for the signal detection, by performing experiments with the calling signal at different intensities and analyzing the insect response by directionality tests performed on a group of male individuals. By using a sub-threshold signal and an acoustic Gaussian noise source, we have investigated the insect response for different levels of noise, finding behavioral activation for suitable noise intensities. In particular, the percentage of insects which react to the sub-threshold signal, shows a non-monotonic behavior, characterized by the presence of a maximum, for increasing levels of the noise intensity. This constructive interplay between external noise and calling signal is the signature of the non-dynamical stochastic resonance phenomenon. Finally, we describe the behavioral activation statistics by a soft threshold model which shows stochastic resonance. We find that the maximum of the ensemble average of the input-output cross-correlation occurs at a value of the noise intensity very close to that for which the behavioral response has a maximum.Comment: 6 pages, 4 figures, to appear in EPJ B (2008

Bianchi Type-I Cosmological Models with Variable G and 4\Lambda$-Terms in General Relativity

Einstein's field equations with variable gravitational and cosmological ``constant'' are considered in presence of perfect fluid for Bianchi type-I spacetime. Consequences of the four cases of the phenomenological decay of $\Lambda$ have been discussed which are consistent with observations. The physical significance of the cosmological models have also been discussed.Comment: 12 pages, no figur

Holographic \Lambda(t)CDM model in a non-flat universe

The holographic $\Lambda(t)$CDM model in a non-flat universe is studied in this paper. In this model, to keep the form of the stress-energy of the vacuum required by general covariance, the holographic vacuum is enforced to exchange energy with dark matter. It is demonstrated that for the holographic model the best choice for the IR cutoff of the effective quantum field theory is the event horizon size of the universe. We derive the evolution equations of the holographic $\Lambda(t)$CDM model in a non-flat universe. We constrain the model by using the current observational data, including the 557 Union2 type Ia supernovae data, the cosmic microwave background anisotropy data from the 7-yr WMAP, and the baryon acoustic oscillation data from the SDSS. Our fit results show that the holographic $\Lambda(t)$CDM model tends to favor a spatially closed universe (the best-fit value of $\Omega_{k0}$ is -0.042), and the 95% confidence level range for the spatial curvature is $-0.101<\Omega_{k0}<0.040$. We show that the interaction between the holographic vacuum and dark matter induces an energy flow of which the direction is first from vacuum to dark matter and then from dark matter to vacuum. Thus, the holographic $\Lambda(t)$CDM model is just a time-varying vacuum energy scenario in which the interaction between vacuum and dark matter changes sign during the expansion of the universe.Comment: 8 pages, 4 figures. version for publication in EPJC. arXiv admin note: text overlap with arXiv:1112.235

Echinoderms from Todos os Santos Bay and Aratu Bay (Bahia, Brazil)

Neste trabalho são registrados os equinodermos (exceto Holothuroidea) obtidos durante a execução do projeto "Marine Environmental Evaluation of the Todos os Santos Bay-MAREMBA" em julho/agosto de 1996 e durante o projeto "Geoecologia das comunidades bentônicas infralitorais da Baía de Todos os Santos (BTS), BA, Brasil: diversidade biótica e sedimentológica", (1997). Um total de 33 espécies pertencentes a 15 famílias foram registradas e re-descritas. A distribuição de Ophiactis brasiliensis Manso, 1988 e Amphiodia trychna H.L. Clark, 1918 é estendida para a região nordeste do Brasil. A classe Ophiuroidea foi dominante nas amostragens em termos de abundância e freqüência de ocorrência, em particular as espécies Amphiodia atra Stimpson, 1852, Amphipholis subtilis (Ljungman, 1867), Ophiactislymani Ljungman, 1871 e Ophiostigma isocanthum (Say, 1825). O asteróide Oreaster reticulatus (Linnaeus, 1758) é considerado vulnerável à exploração humana e foi escasso durante as coletas. Outras espécies encontradas na BTS, tais como os asteroides Luidia clathrata (Say, 1825) e L. senegalensis (Lamarck, 1816) e o equinóide Eucidaristribuloides (Lamarck, 1816) figuram na lista nacional de espécies de invertebrados aquáticos ameaçados de extinção._______________________________________________________________________________ ABSTRACT: We present the results of the studies on biodiversity of Echinodermata (except Holothuroidea) from the Projects "Marine Environmental Evaluation of the Todos os Santos Bay - MAREMBA" (July/August 1996) and "Geoecology of the Benthic Infralitoral Communities of Todos os Santos Bay (BTS), Bahia, Brazil" (1997). A total of 33 species from 15 families were registered and re-described. The distribution of Ophiactis brasiliensis Manso, 1988 and Amphiodia trychna H.L. Clark, 1918 is extended to northwestern Brazil. The class Ophiuroidea was dominant in samples in terms of abundance and frequency of occurrence, in particular Amphiodia atra Stimpson, 1852, Amphipholis subtilis (Ljungman, 1867), Ophiactislymani Ljungman, 1871and Ophiostigma isocanthum (Say, 1825). The asteroid Oreaster reticulatus (Linnaeus, 1758) is considered vulnerable to human exploration and was scarce during the surveys. Other species found at BTS, such the asteroids Luidia clathrata (Say, 1825) and L. senegalensis (Lamarck, 1816) and the echinoid Eucidaristribuloides (Lamarck, 1816)are included in the national list of threatened invertebrate species