Singular diffusion and criticality in a confined sandpile

We investigate the behavior of a two-state sandpile model subjected to a confining potential in one and two dimensions. From the microdynamical description of this simple model with its intrinsic exclusion mechanism, it is possible to derive a continuum nonlinear diffusion equation that displays singularities in both the diffusion and drift terms. The stationary-state solutions of this equation, which maximizes the Fermi-Dirac entropy, are in perfect agreement with the spatial profiles of time-averaged occupancy obtained from model numerical simulations in one as well as in two dimensions. Surprisingly, our results also show that, regardless of dimensionality, the presence of a confining potential can lead to the emergence of typical attributes of critical behavior in the two-state sandpile model, namely, a power-law tail in the distribution of avalanche sizes.Comment: 5 pages, 5 figure

Cosmographic constraints on a class of Palatini f(R) gravity

Modified gravity, known as $f(R)$ gravity, has presently been applied to Cosmology as a realistic alternative to dark energy. For this kind of gravity the expansion of the Universe may accelerate while containing only baryonic and cold dark matter. The aim of the present investigation is to place cosmographic constraints on the class of theories of the form $f(R)=R - \alpha/R^n$ within the Palatini approach. Although extensively discussed in recent literature and confronted with several observational data sets, cosmological tests are indeed inconclusive about the true signal of $n$ in this class of theories. This is particularly important to define which kind of corrections (infra-red or high-energy) to general relativity this class of theory indeed represent. We shed some light on this question by examining the evolution of the deceleration parameter $q(z)$ for these theories. We find that for a large range of $\alpha$, models based on $f(R) = R - \alpha/R^{n}$ gravity in the Palatini approach can only have positive values for $n$, placing thus a broad restriction on this class of gravity.Comment: 4 pages, 2 figures, Latex, Submitte

Neutrinoless double beta decay with and without Majoron-like boson emission in a 3-3-1 model

We consider the contributions to the neutrinoless double beta decays in a $SU(3)_L\otimes U(1)_N$ electroweak model. We show that for a range of the parameters in the model there are diagrams involving vector-vector-scalar and trilinear scalar couplings which can be potentially as contributing as the light massive Majorana neutrino exchange one. We use these contributions to obtain constraints upon some mass scales of the model, like the masses of the new charged vector and scalar bosons. We also consider briefly the decay in which besides the two electrons a Majoron-like boson is emitted.Comment: Revtex, 10 pages and 8 eps figures. Extended version to be published in Physical Review

Fast chemical treatments for ligno-cellulosic yeast carriers’ production from brewers´ spent grains

Caustic (NaOH) and acid-caustic (HCl + NaOH) treatments have both been previously proposed to prepare ligno-cellulosic yeast carriers from Brewers´ Spent Grains (BSG) [1]. However, these treatments are time consuming (more than 24 h). Base-treated carriers are more hydrophobic if compared to acid-base treated, enhancing adhesion in one hand, but more floatable and easily washed out from the reactor in the other hand [2]. Thus, a balance between hydrophilic (cellulose) and hydrophobic (lignin) composition in carriers obtained from BSG must be idealized. The aim of this study was to idealize a fast and simple treatment on ligno-cellulosic substrate from BSG. Two types of BSG have been used in this work: dried BSG settle as pellets for animal nutrition and fresh BSG, directly from the beer industry. Both pelleted and fresh BSG were subjected to a series of proposed chemical treatments, as well as to treatments suggested in the literature [1] (Table 1 summarizes the conditions used). Carriers were assessed for cellulose content through high performance liquid chromatography (HPLC) (Varian, Metacarb 67H Column 300 x 6.5 mm). Briefly, approximately 0.5 g of each dried carrier was digested with sulfuric acid. The digested material was settled in glass flasks with water, autoclaved and filtered. Then, the solids were held separately for lignin content determination, while the liquid was settled in vials for sugars assessment