Critical behavior in lattice models with two symmetric absorbing state

We analyze nonequilibrium lattice models with up-down symmetry and two absorbing states by mean-field approximations and numerical simulations in two and three dimensions. The phase diagram displays three phases: paramagnetic, ferromagnetic and absorbing. The transition line between the first two phases belongs to the Ising universality class and between the last two, to the direct percolation universality class. The two lines meet at the point describing the voter model and the size $\ell$ of the ferromagnetic phase vanishes with the distance $\varepsilon$ to the voter point as $\ell\sim\varepsilon$, with possible logarithm corrections in two dimensions

Has a Higgs-flavon with a 750750 GeV mass been detected at the LHC13?

Higgs-flavon fields appear as a part of the Froggatt-Nielsen (FN) mechanism, which attempts to explain the hierarchy of Yukawa couplings. We explore the possibility that the 750 GeV diphoton resonance recently reported at the LHC13, could be identified with a low-scale Higgs-flavon field $H_F$ and find the region of the parameter space consistent with CMS and ATLAS data. It is found that the extra vector-like fermions of the ultraviolet completion of the FN mechanism are necessary in order to reproduce the observed signal. We consider a standard model (SM) extension that contains two Higgs doublets (a standard one and an inert one) and one complex FN singlet. The inert doublet includes a stable neutral boson, which provides a viable dark matter candidate, while the mixing of the standard doublet and the FN singlet induces flavor violation in the Higgs sector at the tree-level. Constraints on the parameters of the model are derived from the LHC Higgs data, which include the search for the lepton flavor violating decay of the SM Higgs boson $h\to \bar{\mu}\tau$. It is also found that in some region of the parameter space the model may give rise to a large branching ratio for the $H_F \to hh$ decay, of the order of 0.1, which could be searched for at the LHC.Comment: 18 pages, 7 Figures, includes updated files to match published versio

Kinetic Ising System in an Oscillating External Field: Stochastic Resonance and Residence-Time Distributions

Experimental, analytical, and numerical results suggest that the mechanism by which a uniaxial single-domain ferromagnet switches after sudden field reversal depends on the field magnitude and the system size. Here we report new results on how these distinct decay mechanisms influence hysteresis in a two-dimensional nearest-neighbor kinetic Ising model. We present theoretical predictions supported by numerical simulations for the frequency dependence of the probability distributions for the hysteresis-loop area and the period-averaged magnetization, and for the residence-time distributions. The latter suggest evidence of stochastic resonance for small systems in moderately weak oscillating fields.Comment: Includes updated results for Fig.2 and minor text revisions to the abstract and text for clarit

New methods to reconstruct XmaxX_{\rm max} and the energy of gamma-ray air showers with high accuracy in large wide-field observatories

Novel methods to reconstruct the slant depth of the maximum of the longitudinal profile (\Xmax) of high-energy showers initiated by gamma-rays as well as their energy ($E_0$) are presented. The methods were developed for gamma rays with energies ranging from a few hundred GeV to $\sim 10$ TeV. An estimator of \Xmax is obtained, event-by-event, from its correlation with the distribution of the arrival time of the particles at the ground, or the signal at the ground for lower energies. An estimator of $E_0$ is obtained, event-by-event, using a parametrization that has as inputs the total measured energy at the ground, the amount of energy contained in a region near to the shower core and the estimated \Xmax. Resolutions about $40 \, (20)\,{\rm g/cm^2}$ and about $30 \, (20)\%$ for, respectively, \Xmax and $E_0$ at $1 \, (10) \ \rm{TeV}$ energies are obtained, considering vertical showers. The obtained results are auspicious and can lead to the opening of new physics avenues for large wide field-of-view gamma-ray observatories. The dependence of the resolutions with experimental conditions is discussed.Comment: 11 pages; 15 figures, to appear in EPJ

Mean-field analysis of the majority-vote model broken-ergodicity steady state

We study analytically a variant of the one-dimensional majority-vote model in which the individual retains its opinion in case there is a tie among the neighbors' opinions. The individuals are fixed in the sites of a ring of size $L$ and can interact with their nearest neighbors only. The interesting feature of this model is that it exhibits an infinity of spatially heterogeneous absorbing configurations for $L \to \infty$ whose statistical properties we probe analytically using a mean-field framework based on the decomposition of the $L$-site joint probability distribution into the $n$-contiguous-site joint distributions, the so-called $n$-site approximation. To describe the broken-ergodicity steady state of the model we solve analytically the mean-field dynamic equations for arbitrary time $t$ in the cases n=3 and 4. The asymptotic limit $t \to \infty$ reveals the mapping between the statistical properties of the random initial configurations and those of the final absorbing configurations. For the pair approximation ($n=2$) we derive that mapping using a trick that avoids solving the full dynamics. Most remarkably, we find that the predictions of the 4-site approximation reduce to those of the 3-site in the case of expectations involving three contiguous sites. In addition, those expectations fit the Monte Carlo data perfectly and so we conjecture that they are in fact the exact expectations for the one-dimensional majority-vote model

População de afídeos de cereais de inverno em Coxilha/RS, dados de 2013-2014.

Orientador: Douglas Lau

População de parasitoides de afídeos de cereais de inverno em Coxilha/RS, dados de 2013-2014.

Orientador: Douglas Lau

IMUNOTERAPIA COM VENENO DE HIMENÓPTEROS: A EXPERIÊNCIA DE UMA CONSULTA

Resumo: Na Europa a prevalência de alergia ao veneno de himenópteros estima-se em 20%. As reacções sistémicas graves são indicação para imunoterapia específica com veneno de himenópteros após confirmação de atopia. Esta é eficaz em 91-100% dos casos de alergia ao veneno de vespa e 77-80% dos casos de alergia ao veneno de abelha. Apresentamos quatro casos clínicos de doentes com reacções sistémicas ao veneno de himenópteros que efectuaram imunoterapia. Três crianças apresentavam alergia ao veneno de abelha e uma ao veneno de vespa. Tinham IgE específica para o veneno de himenópteros, classes IV a VI. A duração da imunoterapia variou entre quatro e sete anos, com diminuição da classe de IgE específica em todos os doentes no final do tratamento. Três crianças tiveram contacto com o alergénio, durante ou após terminarem a imunoterapia, e nenhuma delas desencadeou uma reacção sistémica. A duração da imunoterapia continua a ser controversa. A ausência de reacção após contacto com o alergénio é sugestiva de sucesso do tratamento

Bio-Hydrogen production from glycerol by a strain of Enrerobacter aerogenes

In this work, H2 production by a strain of Enterobacter aerogenes using as substrate pure glycerol and glycerol-containing biodiesel wastes was compared. The effect of physico-chemical parameters such as temperature, initial substrate and biomass concentrations on the bio-hydrogen production efficiency was investigated. The influence of the simultaneous removal of gases produced was also evaluated The results obtained showed that a decrease of the process temperature of 37 to 30 ºC leads to both, an increase of the bio-hydrogen production rate and a decrease of the equilibrium time of the process. Furthermore, it was also observed that using 10 g/dm3 of pure glycerol or biodiesel wastes containing the same concentration of glycerol as substrate lead to very similar bio-hydrogen production yields (2.5dm3 H2/dm3 fermentation medium). This proves that the performance of the strain of E. aerogenes used was not influenced by the presence of other components than glycerol in biodiesel residues, at least for the biodiesel wastes concentration studied. Simultaneous removal of gaseous phase (mainly H2 and CO2), with its production, shows to be very efficient leading to an increase of the value of the H2/CO2 volumetric ratio, in the headspace, from 2 to 8, which is very promising regarding costs involved in the technologies for purification of H2 produced