Relaxation processes in harmonic glasses?

A relaxation process, with the associated phenomenology of sound attenuation and sound velocity dispersion, is found in a simulated harmonic Lennard-Jones glass. We propose to identify this process with the so called microscopic (or instantaneous) relaxation process observed in real glasses and supercooled liquids. A model based on the memory function approach accounts for the observation, and allows to relate to each others: 1) the characteristic time and strength of this process, 2) the low frequency limit of the dynamic structure factor of the glass, and 3) the high frequency sound attenuation coefficient, with its observed quadratic dependence on the momentum transfer.Comment: 11 pages, 3 figure

\u3cem\u3eTithonia diversifolia\u3c/em\u3e for Ruminant Nutrition

India and Brazil lead the world ranking of livestock enteric methane emissions (FAO 2006). According to FAO (2006), Brazil (9.6 Tg of CH4/year) is the highest emitter of methane from cattle, followed by India (8.6 Tg of CH4/year) and the USA (5.1 Tg of CH4/year). In livestock, methane (CH4) formed from enteric fermentation of carbohydrates is primarily responsible for the emissions in the sector. Regarding livestock methane emission, Delgado et al. (2012) evaluated 20 tree and shrub species using in vitro technique and demonstrated a reducing effect on the amount of methane when Tithonia diversifolia was compared with, for example, Cynodon nlemfuensis grass. Tithonia diversifolia belongs to the division - Sphermatophyta; class - Eudicotiledoneae; sub-class - Metaclamídeas; Order - Campanulate; Family - Asteraceae; Genre - Tithonia, and Species - Tithonia diversifolia (Hemsl.), Gray (Souza 2008). Tithonia diversifolia can be very useful in animal nutrition (Fig. 1) by increasing the protein content of animal diet at low cost (Murgueitio et al. 2010) as well as in the recovery of degraded soils for it grows in areas with low levels of fertility and has high ability to absorb phosphorus, even if it is unavailable to other forage species (Kwabiah et al. 2003). The objective of this study was to assess the nutritional qualities, including quantification of enteric methane generated during in vitro ruminal fermentation, of Tithonia diversifolia as an alternative forage for ruminant nutrition in the tropics

Land use in Brazilian continental wetland Ramsar sites

Wetlands are systems of high biological diversity, productivity, and high economic and social importance to mankind. Despite its importance, wetlands are very threatened by human activities. World-wide, wetlands receive international recognition since 1971 by the Ramsar Convention. Guidelines adopted by Brazil to include its wetlands into the Ramsar List require that Ramsar sites are legally protected. This work analyses the main environmental pressures in the inner and surrounding areas of the 19 Brazilian inland Ramsar sites. Results show that wetland habitats are relatively well conserved in the inner areas of the 19 Ramsar sites. The proportion of natural landscape between the surrounding areas of Ramsar sites varies broadly (between 20 % and 99 %). Low anthropic disturbance inside of Ramsar sites suggests that external human pressures have not affected yet core areas of Ramsar sites. Brazilian guidelines to establish Ramsar sites only in protected areas has been very effective in Brazil, despite the many environmental pressures of protected areas, such as invasion by exotic species, tenure, human occupation, exploitation of illegal resources, etc.Los humedales son sistemas de alta diversidad biológica, productividad y alta importancia económica y social para la humanidad. A pesar de su importancia, los humedales se encuentran muy amenazados por las actividades humanas. A nivel mundial, los humedales reciben reconocimiento internacional desde 1971 por la Convención de Ramsar. Las directrices adoptadas por Brasil para incluir sus humedales en la Lista Ramsar exigen que los sitios Ramsar estén legalmente protegidos. Este trabajo analiza las principales presiones ambientales en el interior y alrededores de los 19 sitios Ramsar del interior brasileño. Los resultados muestran que los hábitats de los humedales están relativamente bien conservados en las áreas internas de los 19 sitios Ramsar. La proporción de paisaje natural entre las áreas circundantes de los sitios Ramsar varía ampliamente (entre 20 % y 99 %). La baja perturbación antrópica dentro de los sitios Ramsar sugiere que las presiones humanas externas aún no han afectado las áreas centrales de los sitios Ramsar. Las directrices brasileñas para establecer sitios Ramsar solo en áreas protegidas han sido muy eficaces en Brasil, a pesar de las muchas presiones ambientales de las áreas protegidas, como la invasión de especies exóticas, la tenencia, la ocupación humana, la explotación de recursos ilegales, etc

Elastic constant dishomogeneity and Q2Q^2 dependence of the broadening of the dynamical structure factor in disordered systems

We propose an explanation for the quadratic dependence on the momentum $Q$, of the broadening of the acoustic excitation peak recently found in the study of the dynamic structure factor of many real and simulated glasses. We ascribe the observed $Q^2$ law to the spatial fluctuations of the local wavelength of the collective vibrational modes, in turn produced by the dishomegeneity of the inter-particle elastic constants. This explanation is analitically shown to hold for 1-dimensional disordered chains and satisfatorily numerically tested in both 1 and 3 dimensions.Comment: 4 pages, RevTeX, 5 postscript figure

Moisture Control, Inoculant and Particle Size in Tropical Grass Silages

Decreased fermentation and spoilage losses with improved aerobic stability during feed out can be accomplished by several strategies, such as wilting, addition of microbial additives and moisture absorbents. Particle size reduction may increase bulk density and improve the fermentation. The objective of this trial was to evaluate the effects of particle size, moisture content and a microbial additive on chemical-physical parameters and losses in silages made from Tanzania grass

Saddles in the energy landscape probed by supercooled liquids

We numerically investigate the supercooled dynamics of two simple model liquids exploiting the partition of the multi-dimension configuration space in basins of attraction of the stationary points (inherent saddles) of the potential energy surface. We find that the inherent saddles order and potential energy are well defined functions of the temperature T. Moreover, decreasing T, the saddle order vanishes at the same temperature (T_MCT) where the inverse diffusivity appears to diverge as a power law. This allows a topological interpretation of T_MCT: it marks the transition from a dynamics between basins of saddles (T>T_MCT) to a dynamics between basins of minima (T<T_MCT).Comment: 4 pages, 3 figures, to be published on PR

Correlation between the granulosa cell layer and active caspase-3 expression in ovarian follicles of Tropidurus hispidus and T. semitaeniatus (Squamata, Tropiduridae): immunohistochemical approach

The greatest threats to terrestrial reptiles are urban development and habitat modification. In this sense, a better understanding of folliculogenesis in these animals would be important to knowledge of reproductive biology. The aim of this study was to analyze the correlation between the thickness of the granulosa cell layer and the expression of the active caspase-3 protein in the previtellogenic and vitellogenic follicles of T. hispidus and T. semitaeniatus. Ovaries were used for histological (morphology and morphometry: thickness of granulosa layer) and immunohistochemical (active caspase-3 expression) analyses. The previtellogenic follicles of T. hispidus and T. semitaeniatus showed a thicker granulosa layer, with pyriform and small cells. The vitellogenic follicles had a monolayer of cuboid cells, and a thicker thecal layer. The thickness of the granulosa layer was significantly higher in the previtellogenic compared to the vitellogenic phase for both species. However, no differences were observed between the species. Active caspase-3 was observed in the pyriform and intermediate cells in previtellogenesis of T. hispidus and T. semitaeniatus. Nevertheless, no immunostaining was observed in the vitellogenic phase in both species. In conclusion, this study shows that the thickness of the granulosa cell layer is higher in the previtellogenic follicles compared to the vitellogenic follicles in the two Tropidurus species. Pyriform and intermediate cells from previtellogenic follicles show high expression of the protein, indicating that remodeling of the epithelium is associated with apoptosis. Finally, our results provide a scientific basis for assisted reproductive techniques and conservation actions to the reptiles in the future.Las mayores amenazas para los reptiles terrestres son el desarrollo urbano y la modificación del hábitat. En este sentido, una mejor comprensión de la foliculogénesis en estos animales sería importante para el conocimiento de la biología reproductiva. El objetivo de este estudio fue analizar la correlación entre el grosor de la capa de células de la granulosa y la expresión de la proteína caspase-3 activa en los folículos previtelogénicos y vitelogénicos de T. hispidus y T. semitaeniatus. Los ovarios se usaron para análisis histológicos (morfología y morfometría: grosor de la capa de la granulosa) e inmunohistoquímicos (expresión activa de caspase-3). Los folículos previtelogénicos de T. hispidus y T. semitaeniatus mostraron una capa de granulosa más gruesa, con células piriformes y pequeñas. Los folículos vitelogénicos tenían una monocapa de células cuboides y una capa tecal más gruesa. El grosor de la capa de granulosa fue significativamente mayor en la fase previtelogénica en comparación con la fase vitelogénica para ambas especies. Sin embargo, no se observaron diferencias entre las especies. Se observó caspase-3 activa en las células piriformes e intermedias en previtelogénesis de T. hispidus y T. semitaeniatus. Sin embargo, no se observó inmunotinción en la fase vitelogénica en ambas especies. En conclusión, este estudio muestra que el grosor de la capa de células de la granulosa es mayor en los folículos previtelogénicos en comparación con los folículos vitelogénicos en las dos especies de Tropidurus. Las células piriformes e intermedias de folículos previtelogénicos muestran una alta expresión de la proteína, lo que indica que la remodelación del epitelio está asociada con la apoptosis. Finalmente, nuestros resultados proporcionan una base científica para técnicas de reproducción asistida y acciones de conservación para los reptiles en el futuro.Asociación Herpetológica Argentin

Black hole thermodynamical entropy

As early as 1902, Gibbs pointed out that systems whose partition function diverges, e.g. gravitation, lie outside the validity of the Boltzmann-Gibbs (BG) theory. Consistently, since the pioneering Bekenstein-Hawking results, physically meaningful evidence (e.g., the holographic principle) has accumulated that the BG entropy $S_{BG}$ of a $(3+1)$ black hole is proportional to its area $L^2$ ($L$ being a characteristic linear length), and not to its volume $L^3$. Similarly it exists the \emph{area law}, so named because, for a wide class of strongly quantum-entangled $d$-dimensional systems, $S_{BG}$ is proportional to $\ln L$ if $d=1$, and to $L^{d-1}$ if $d>1$, instead of being proportional to $L^d$ ($d \ge 1$). These results violate the extensivity of the thermodynamical entropy of a $d$-dimensional system. This thermodynamical inconsistency disappears if we realize that the thermodynamical entropy of such nonstandard systems is \emph{not} to be identified with the BG {\it additive} entropy but with appropriately generalized {\it nonadditive} entropies. Indeed, the celebrated usefulness of the BG entropy is founded on hypothesis such as relatively weak probabilistic correlations (and their connections to ergodicity, which by no means can be assumed as a general rule of nature). Here we introduce a generalized entropy which, for the Schwarzschild black hole and the area law, can solve the thermodynamic puzzle.Comment: 7 pages, 2 figures. Accepted for publication in EPJ