A geometrical instability for ultra-light fields during inflation?

Westudythebehaviourofisocurvatureperturbationsinnon-linearsigmamodels which naturally emerge in supergravity and string inflationary scenarios. We focus on the case of negatively curved field manifolds which can potentially lead to a geometrical destabilisation of isocurvature modes. We find however that heavy fields are stable when their effective mass is computed on the attractor background solution. On the other hand, we show that ultra-light fields can potentially suffer from a geometrical instability when the background trajectory is a geodesic in field space. In this case a full understanding of the system is likely to require the use of non-perturbative methods.Comment: Matches published version, 5 pages, 2 figure

Photoelectrocatalytic Performances of Nanostructured/Decorated TiO 2

The behaviour of TiO2 based electrodes was investigated during the photoelectrocatalytic water splitting process. TiO2 nanotubes and compact oxide structures were obtained by electrochemical oxidation of Ti foils. A subsequent hydrothermal process carried out at both the nanotubular and compact oxide structures allowed decorating the structure by TiO2 nanoparticles. The synthesized TiO2 samples worked as photoanodes both in a bulk three electrode cell and in a thin gap cell. The results from measurements of the photocurrent and from electrochemical impedance spectroscopy were used to highlight a combined effect of the wavelength of the incident light and the kind of cell configuration, on the global performance of the systems. The results indicate that the decoration process does not result only in a simple increase of the specific surface, but it also determines a different concentration of the bulk and superficial sites in the electrode. The different response of the sites at different wavelengths, along with the accessibility of the electrolyte to the porous structure are evocated to justify the experimental behaviour observed

Impact Force of a Geomorphic Dam-Break Wave against an Obstacle: Effects of Sediment Inertia

The evaluation of the impact force on structures due to a flood wave is of utmost importance for estimating physical damage and designing adequate countermeasures. The present study investigates, using 2D shallow-water approximation, the morphodynamics and forces caused by a dam-break wave against a rigid obstacle in the presence of an erodible bed. A widely used coupled equilibrium model, based on the two-dimensional Saint–Venant hydrodynamic equations combined with the sediment continuity Exner equation (SVEM), is compared with a more complex two-phase model (TPM). Considering an experimental set-up presented in the literature with a single rigid obstacle in a channel, two series of tests were performed, assuming sand or light sediments on the bottom. The former test is representative of a typical laboratory experiment, and the latter may be scaled up to a field case. For each test, two different particle diameters were considered. Independently from the particle size, it was found that in the sand tests, SVEM performs similarly to TPM. In the case of light sediment, larger differences are observed, and the SVEM predicts a higher force of about 26% for both considered diameters. The analysis of the flow fields and the morphodynamics shows these differences can be essentially ascribed to the role of inertia of the solid particles

Applicability of Diffusive model for mud-flows: An unsteady analysis

applied to the analysis of debris- and mud- flow dynamics. For this reason, the study of their applicability conditions represents an important concern. The present work investigates on the applicability conditions of the Diffusive Wave Model (DWM) for the prediction of mud-flows of shear-thinning fluid represented by a power-law rheology. The study has been carried out through the numerical solution of the DWM and the Full Wave Model (FWM) in unsteady conditions with hydrographs of different durations assigned at the channel inlet. The analysis has considered different rheological indexes, several values of the Froude (F) and of the Kinematic Wave (K) numbers. Predictions of DWM and FDM have been compared considering the mean value of dimensionless errors on maximum flow depth,ε∗h, and maximum discharge ε∗q. Positive (negative) error leads to an overestimation (underestimation) of the maximum flow depth and flow discharge in the prediction of the DWM. In the present analysis the DWM is considered safely applicable in case of underestimation, i.e. for positive values of ε∗h and ε∗q. Negative errors are acceptable if their absolute value is smaller than 5%. For all the investigated values of the governing parameters, the performance of the DWM has been found to strongly depend on the value of the rheological index, worsening as the fluid rheology becomes more shear-thinning. Regardless of the hydrograph duration, and for fixed power-law exponent (n) and F values, results indicate the existence of limiting values of the kinematic wave numberKh and Kq above which the DWM is applicable in terms of maximum depth and discharge, respectively. For K values smaller than Kh and Kq, the DWM applicability depends also on the hydrograph duration. In these conditions and for several values of the (F, n) pair, the threshold values of the hydrograph duration necessary for DWM applicability have been identified. The presented applicability criteria represent a useful guideline for the practical application of the DWM in assessing the hazard of a mud flood

analysis of photocurrent and capacitance of tio2 nanotube polyaniline hybrid composites synthesized through electroreduction of an aryldiazonium salt

TiO2 nanotube–polyaniline hybrid composites were synthesized using an aminophenyl under-layer electrochemically grafted on TiO2 obtaining improvements in photocurrent and capacitance

Adipose Tissue-Liver Cross Talk in the Control of Whole-Body Metabolism: Implications in Nonalcoholic Fatty Liver Disease.

Adipose tissue and the liver play significant roles in the regulation of whole-body energy homeostasis, but they have not evolved to cope with the continuous, chronic, nutrient surplus seen in obesity. In this review, we detail how prolonged metabolic stress leads to adipose tissue dysfunction, inflammation, and adipokine release that results in increased lipid flux to the liver. Overall, the upshot of hepatic fat accumulation alongside an insulin-resistant state is that hepatic lipid enzymatic pathways are modulated and overwhelmed, resulting in the selective buildup of toxic lipid species, which worsens the pro-inflammatory and pro-fibrotic shift observed in nonalcoholic steatohepatitis

Trasporto di metalli verso i laghi del sistema Flumendosa Campidano in conseguenza dell'erosione dei suoli

Weathering of mine tailings represents an important metal source in Sardinia. The accumulation of mobilized metals onto soil in the mineralized areas and the subsequent erosional transport of soil towards the freshwater reservoirs endangers the quality of drinking water. The here described study on the Flumendosa-Campidano system shows the prescence and spatial distribution of metals in the system and underlines the necessity to control the more mobile and dangerous metals, as for exampIe cadmium

Investigation on the Adsorption and Photooxidation of Glycerol at TiO2 Nanotubular Arrays

A study is presented on the adsorption of glycerol at TiO2as well as on its oxidative process during the contemporary water Photoelectro-splitting for hydrogen production. A deepening in the understanding on the working mechanism of the TiO2nanotubular photoanodes and on the interactions between glycerol and these structures has been gained through photocurrent tests, voltammetric scans, and EIS analysis. A range of wavelength of the incident radiation is investigated from 340 to 400 nm at which the effect of glycerol on the photocurrent is measured. Quantitative analysis of the EIS results is performed by the equivalent circuit approach

two dimensional two phase depth integrated model for transients over mobile bed

AbstractFast geomorphic transients may involve complex scenarios of sediment transport, occurring near the bottom as bed load (i.e., saltating, sliding, and rolling) or as suspended load in the upper portion of the flow. The two sediment transport modalities may even coexist or alternate each other during the same event, especially when the shear stress varies considerably. Modeling these processes is therefore a challenging task, for which the usual representation of the flow as a mixture may result in being unsatisfactory. In the present paper, a new two-phase depth-averaged model is presented that accounts for variable sediment concentration in both bed and suspended loads. Distinct phase velocities are considered for bed load, whereas the slip velocity between the two phases is neglected in the suspended load. It is shown that the resulting two-phase model is hyperbolic, and the analytical expression of the eigenvalues is provided. The entrainment/deposition of sediment between the bottom and the bed ..

Genetic diversity of <i>NRAMP1</i> 3'-UTR microsatellite in cattle breeds reared in Sardinia

The aim of this study was to compare the allele frequency of 3'-UTR NRAMP1 (Natural Resistance-Associated Macrophage Protein) microsatellite between local and specialized dairy cattle breeds reared in Sardinia, Italy. Blood samples were collected and DNA was extracted from 97 Sarda, 55 Italian Brown and 36 Italian Friesian cattle and analysed by means of PCR and PCR-SSCP. On the whole, three alleles were found, GT13, GT14, and GT15. GT13 showed the highest frequency in all the breeds: 0.874 in the Sarda, 0.973 in the Italian Brown and 1 in the Italian Friesian. For the Sarda, both GT14 and GT15 showed a frequency of 0.063, while for the Italian Brown 0.018 and 0.009, respectively. Homozygous GT13/GT13 was the unique genotype for the Italian Friesian and the most representative for the Italian Brown (0.964) and Sarda (0.823). The other genotypes for the Sarda were: GT14/GT14 (0.042), GT13/GT14 (0.010), GT13/GT15 (0.094) and GT14/GT15 (0.031); as regards the Italian Brown, both GT14/GT14 and GT13/GT15 showed a genotypic frequency of 0.018. The observed heterozygosity was lower than the expected value both for the Sarda and the Italian Brown. Sarda showed a higher genetic variability than Italian Brown and Italian Friesian