Modified Gravity at Astrophysical Scales

Using a perturbative approach we solve stellar structure equations for low-density (solar-type) stars whose interior is described with a polytropic equation of state in scenarios involving a subset of modified gravity theories. Rather than focusing on particular theories, we consider a model-independent approach in which deviations from General Relativity are effectively described by a single parameter $\xi$. We find that for length scales below those set by stellar General Relativistic radii the modifications introduced by modified gravity can affect the computed values of masses and radii. As a consequence, the stellar luminosity is also affected. We discuss possible further implications for higher density stars and observability of the effects before described.Comment: 12 pages, 7figures, matches published versio

Interpolation of families

We identify the intermédiate space of a complex interpolation family - in the sense of Coifman, Cwikel, Rochberg, Sagher and Weissof LP spaces with change of measure, for the complex interpolation method associated to an analytic functional

A generic persistence model for CLP systems (and two useful implementations)

This paper describes a model of persistence in (C)LP languages and two different and practically very useful ways to implement this model in current systems. The fundamental idea is that persistence is a characteristic of certain dynamic predicates (Le., those which encapsulate state). The main effect of declaring a predicate persistent is that the dynamic changes made to such predicates persist from one execution to the next one. After proposing a syntax for declaring persistent predicates, a simple, file-based implementation of the concept is presented and some examples shown. An additional implementation is presented which stores persistent predicates in an external datábase. The abstraction of the concept of persistence from its implementation allows developing applications which can store their persistent predicates alternatively in files or databases with only a few simple changes to a declaration stating the location and modality used for persistent storage. The paper presents the model, the implementation approach in both the cases of using files and relational databases, a number of optimizations of the process (using information obtained from static global analysis and goal clustering), and performance results from an implementation of these ideas

The role of noise and initial conditions in the asymptotic solution of a bounded confidence, continuous-opinion model

We study a model for continuous-opinion dynamics under bounded confidence. In particular, we analyze the importance of the initial distribution of opinions in determining the asymptotic configuration. Thus, we sketch the structure of attractors of the dynamical system, by means of the numerical computation of the time evolution of the agents density. We show that, for a given bound of confidence, a consensus can be encouraged or prevented by certain initial conditions. Furthermore, a noisy perturbation is added to the system with the purpose of modeling the free will of the agents. As a consequence, the importance of the initial condition is partially replaced by that of the statistical distribution of the noise. Nevertheless, we still find evidence of the influence of the initial state upon the final configuration for a short range of the bound of confidence parameter

Comparison of fermentation characteristics and bacterial diversity in the rumen of sheep and batch cultures of rumen microorganisms

The objective of the current study was to assess how closely batch cultures (BC) of rumen microorganisms can mimic the dietary differences in fermentation characteristics found in the rumen, and to analyse changes in bacterial diversity over the in vitro incubation period. Four ruminally and duodenally cannulated sheep were fed four diets having forage : concentrate ratios (FCR) of 70 : 30 or 30 : 70, with either alfalfa hay or grass hay as forage. Rumen fluid from each sheep was used to inoculate BC containing the same diet fed to the donor sheep, and the main rumen fermentation parameters were determined after 24 h of incubation. There were differences between BC and sheep in the magnitude of most measured parameters, but BC detected differences among diets due to forage type similar to those found in sheep. In contrast, BC did not reproduce the dietary differences due to FCR found in sheep for pH, degradability of neutral detergent fibre and total volatile fatty acid (VFA) concentrations. There were differences between systems in the magnitude of most determined parameters and BC showed higher pH values and NH3–N concentrations, but lower fibre degradability and VFA and lactate concentrations compared with sheep. There were significant relationships between in vivo and in vitro values for molar proportions of acetate, propionate and butyrate, and the acetate : propionate ratio. The automated ribosomal intergenic spacer analysis (ARISA) of 16S ribosomal deoxyribonucleic acid showed that FCR had no effect on bacterial diversity either in the sheep rumen fluid used as inoculum (IN) or in BC samples. In contrast, bacterial diversity was greater with alfalfa hay diets than those with grass hay in the IN, but was unaffected by forage type in the BC. Similarity index between the bacterial communities in the inocula and those in the BC ranged from 67·2 to 74·7%, and was unaffected by diet characteristics. Bacterial diversity was lower in BC than in the inocula with 14 peaks out of a total of 181 detected in the ARISA electropherograms never appearing in BC samples, which suggests that incubation conditions in the BC may have caused a selection of some bacterial strains. However, each BC sample showed the highest similarity index with its corresponding rumen IN, which highlights the importance of using rumen fluid from donors fed a diet similar to that being incubated in BC when conducting in vitro experiments

METHANOGENESIS IN RABBIT CAECUM AS AFFECTED BY THE FERMENTATION PATTERN: IN VITRO AND IN VIVO MEASUREMENTS

[EN] Methane formation and caecal fermentation patterns were studied in vivo and in vitro in 16 white New Zealand rabbits (70-80 d and 2.27 ± 0.064 kg) allocated to four diets formulated to have a similar neutral detergent fibre (33.8±0.53%) and protein (17.7±0.33%) content, with two different fibre sources (alfalfa hay, AH or sugar beet pulp, SP) and starch (wheat or maize). Animals received the diet for 16 to 20 days before methane production was measured in vivo in a respiratory chamber. Animals were subsequently slaughtered at approximately 9:00 and caecal contents were sampled and used as inoculum for in vitro incubations to determine gas and methane production. Volatile fatty acid (VFA) and purine base (PB) concentrations were determined from both caecal content and incubation medium after 6 h. Total VFA concentration in caecal content decreased (P<0.05) in rabbits fed AH-maize diet compared with rabbits fed AH-wheat and SP-maize diets (37.7 vs. 59.6 mM), with those fed SP-wheat showing an intermediate value (53.0 mM). Fermentation pattern was affected when maize was the source of starch compared to wheat, with lower acetate (0.72 vs. 0.79; P<0.01) and higher butyrate (0.19 vs. 0.14; P<0.001) molar proportions. Fermentation in vivo vs. in vitro showed some differences (molar proportions of acetate, 0.76 vs. 0.73, P<0.001, and propionate, 0.069 vs. 0.091, P<0.001, in vivo and in vitro, respectively), probably due to differences in pH (6.0 vs. 6.7 in vivo and in vitro; P<0.001). Only 2 out of 16 rabbits produced a substantial volume of methane in vivo (on average, 12.6 ml/BW0.75/d or 0.56 mmol/BW0.75/d), showing a high inter-individual variability that hindered comparison of treatment differences. In contrast, methane was detected in vitro in all cases and volumes were more homogenous, a higher formation (P<0.05) being observed with maize compared to wheat. A similar effect was shown in total gas production. The low methane production and H2 recovery suggest the importance of H2 disposal mechanisms other than methanogenesis, such as reductive acetogenesis. PB concentration in caecal content and the incubation medium, as an index of microbial concentration, was highest when SP was added with maize (P<0.05).For the realisation of this work, A. Belenguer and L. Abecia received grants from the Spanish Ministry of Education and Science and the Basque Government, respectively. This work was financed by the Diputación General de Aragón through project DGA PM095/2006.Belenguer, A.; Fondevila, M.; Balcells, J.; Abecia, L.; Lachica, M.; Carro, M. (2011). METHANOGENESIS IN RABBIT CAECUM AS AFFECTED BY THE FERMENTATION PATTERN: IN VITRO AND IN VIVO MEASUREMENTS. World Rabbit Science. 19(2):75-83. doi:10.4995/wrs.2011.826SWORD758319

Influence of processing method of rumen contents on microbial populations in the inoculum and in vitro fermentation of substrates of variable composition

The in vitro batch culture technique is being increasingly used to study rumen fermentation, but the results are affected by several factors, being the source of the inoculum one of the most relevant. This work was conducted to assess the effects of different processing methods of ruminal contents on microbial populations in the obtained fluid, and its influence on fermentation parameters when the fluid was used as inoculum for in vitro incubations. Rumen contents were obtained from four rumen-fistulated sheep fed a 2:1 alfalfa hay:concentrate diet and subjected to the following treatments: SQ: squeezed through four layers of cheesecloth; FL: SQ treatment and further filtration through a 100-μm nylon cloth; STO: blended for three min at 230 rev min−1 in a Stomacher® and further filtrations as in SQ. Microbial populations’ abundance and bacterial diversity in the ruminal fluids were analysed by quantitative PCR (qPCR) and automated ribosomal intergenic spacer analysis (ARISA), respectively. Three forages (alfalfa hay, grass hay and barley straw) were incubated in vitro, either alone or mixed with concentrate (1:1), using each of the ruminal fluids as inoculum. There were no differences between SQ and FL methods in any of the microbial populations analysed, but STO increased the relative abundance of Fibrobacter succinogenes and Ruminococcus albus (P 0.05) by the processing methods. There were no interactions (P > 0.05) between the processing method and the characteristics of the substrates for any of the fermentation parameters analysed. Compared with SQ, the STO method resulted in greater (P < 0.05) methane production and ammonia-N concentrations in 8 h incubations. After 24 h of incubation, the use of STO inoculum increased (P < 0.05) methane production and dry matter degradability compared with SQ, with no differences in the rest of the parameters. No differences between SQ and FL methods were detected in any parameter. The results show that stomaching the rumen contents prior to inoculation of in vitro cultures modified some microbial populations, but had only subtle effects on fermentation parameters

Habitability: CAMELOT 4

During 1988 to 1989 the NASA/USRA Advanced Design Program sponsored research and design efforts aimed at developing habitability criteria and at defining a habitability concept as a useful tool in understanding and evaluating dwellings for prolonged stays in extraterrestrial space. The Circulating Auto sufficient Mars-Earth Luxurious Orbital Transport (CAMELOT) was studied as a case in which the students would try to enhance the quality of life of the inhabitants by applying architectural design methodology. The study proposed 14 habitability criteria considered necessary to fulfill the defined habitability concept, which is that state of equilibrium that results from the interaction between components of the Individual Architecture Mission Complex, which allows a person to sustain physiological homeostatis, adequate performance, and acceptable social relationships. Architecture, design development, refinements and revisions to improve the quality of life, new insights on artificial gravity, form and constitution problems, and the final design concept are covered

Perspectivas y retos de los extractos vegetales como aditivos alimentarios en rumiantes

Algunas plantas producen y almacenan compuestos secundarios que ejercen actividades beneficiosas en el organismo humano y animal. En lo que se refiere a su uso en alimentación animal, constituyen una alternativa natural a los aditivos antibióticos promotores del crecimiento, cuyo uso en rumiantes se ha centrado fundamentalmente en sus efectos sobre la fermentación rumial