3,673 research outputs found
The dark and luminous matter coupling in the formation of spheroids: an SPH investigation
No full textUsing N-body/hydrodynamical simulations which include prescriptions for star formation, feed-back and chemical evolution, we explore the interaction between baryons and dark matter (DM) at a galactic scale. The N-body simulations we performed using a Tree-SPH code that follows the evolution of individual DM halos inside which stars form from cooling gas, and evolve, delivering in the interstellar medium (LSM) mass, both metals and energy. We examine the formation and evolution of a giant and a dwarf elliptical galaxy of total masses 10(12)M. and 10(9)M., respectively. Starting from an initial density profile like the universal Navarro et al. (1996) profile in the inner region, baryons sink towards the center due to cooling energy losses. At the end of the collapse, the innermost part (similar or equal to 1/20 of the halo size) of the galaxy is baryon-dominated, whereas the outer regions are DM dominated. The star formation proceeds at a much faster speed in the giant galaxy where a spheroid of 8 x 10(10)M. is formed in 2 Gyr, with respect to the dwarf galaxy where the spheroid of 2 x 10(7)M. is formed in 4 Gyr. For the two objects the final distributions of stars are well fitted by a Hernquist profile with effective radii of r(e) = 30 kpc and 2.8 kpc, respectively. The dark-to-luminous transition radius r(IBD) occurs roughly at 1 r(e), as in real ellipticals. The DM halo density evolution is non-adiabatic and does not lead to a core radius
NBODY/SPH simulations of individual galaxies
No full textWe present preliminary results on galactic Dark Matter (DM), halo structure, and galaxy evolution. We show how during the first Gyr of the evolution of a 1010M⊙ dwarf elliptica feed-back from stars (SNæ~ and stellar winds) leads to an extended constant density isothermal core with radius of 0.15 the virial radius R200. We also present first results on galaxy merging as a possibile scenario to form ellipticals, studying in particular how the details of the merging evolution vary as a function of the mass ratio of the interacting galaxies
Effect of diet supplementation with Toyocerin (Bacillus cereus var. toyoi) on performance and health of growing rabbits
No full textTwo trials were performed to evaluate the effect of a dietary supplementation with Bacillus cereus var. toyoi on performance and health of growing rabbits. The studies were conducted in two
commercial farms using the same experimental diets. In the first trial, 216 rabbits were controlled from 35 d (weaning) until 70 d of age. In the second trial, 180 rabbits were controlled from 37 until 79 d of age. At weaning, rabbits were put into bicellular cages, divided into three groups and fed the experimental diets: diet C, diet T1 and diet T2 supplemented with 0, 200 ppm (2x105 spores/g diet) and 1000 ppm (1x106 spores/g diet) of Toyocerin® (concentration: 1x109 B. cereus var. toyoi spores/g), respectively. The diets did not contain antibiotics or growth promoters and presented similar chemical composition
(CP: 17.4% DM, NDF: 40.8% DM; ADL: 5.2% DM, starch: 16.5% DM). The differences in growth performance between the two trials depended mainly on the different final age of rabbits. Weight gain (42.0 vs 36.5 g/d) was lower and feed conversion (3.12 vs 3.96) higher in the second trial. Mortality (13.0% vs 21.7%) and morbidity (2.8% vs 25.0%) were significantly higher in the second trial. The probiotic supplementation (diet C vs diets T1+T2) significantly increased final live weight (2,517 vs 2,580 g; P=0.02) and daily weight gain (38.2 vs 39.8 g/d; P=0.01) and improved feed conversion (3.63 vs 3.50; P=0.01). Morbidity was significantly lower with supplemented diets (18.2 vs 10.3%; P=0.03), while mortality and sanitary risk were not affected by dietary treatment. No effect of probiotic inclusion rate (diet T1 vs diet T2) and no significant interaction between dietary treatment and trial were measured. In conclusion, the supplementation of Bacillus cereus var. toyoi improved growth performance and reduced morbidity of rabbits reared in farms with or without severe health problems. Increasing probiotic inclusion rate from 2x105 to 1x106 spores/g diet did not improve rabbit growth
performance and health
Relación fibra digestible/FAD y nivel de almidón en dietas de conejos en crecimiento
No full textTo evaluate the effect of digestible fibre (DF; hemicelluloses+pectins)/ADF ratio (1.0 and 1.3) and starch level (12, 15, and 18%) on health, digestive physiology, growth performance, and carcass traits, 246 rabbits weaned at 27 d were fed until slaughter (76 d) with six diets formulated according to a bifactorial arrangement (2 DF/ADF ratios by 3 starch levels). Increasing DF/ADF improved DM digestibility (P<0.01), but did not affect growth performance, caecal content characteristics and slaughter traits. Increasing starch level improved DM digestibility and feed efficiency (P<0.001), decreased linearly ileal mucosa villi height (P=0.04), without affecting growth performance, caecal fermentation and slaughter results. The increase of DF/ADF ratio tended to reduce mortality (25.0 vs 17.6%; P=0.11), whereas the raise of starch greatly increased mortality (6.9 to 43.1%; P<0.001) and sanitary risk (13.9 to 63.9%; P<0.001)
KINEMATICAL AND CHEMICAL VERTICAL STRUCTURE OF THE GALACTIC THICK DISK. II. A LACK OF DARK MATTER IN THE SOLAR NEIGHBORHOOD
No full textArtículo de publicación ISIWe estimated the dynamical surface mass density Sigma at the solar position between Z = 1.5 and 4 kpc from the Galactic plane, as inferred from the kinematics of thick disk stars. The formulation is exact within the limit of validity of a few basic assumptions. The resulting trend of Sigma(Z) matches the expectations of visible mass alone, and no dark component is required to account for the observations. We extrapolate a dark matter (DM) density in the solar neighborhood of 0 +/- 1mM(circle dot) pc(-3), and all the current models of a spherical DM halo are excluded at a confidence level higher than 4 sigma. A detailed analysis reveals that a small amount of DM is allowed in the volume under study by the change of some input parameter or hypothesis, but not enough to match the expectations of the models, except under an exotic combination of non-standard assumptions. Identical results are obtained when repeating the calculation with kinematical measurements available in the literature. We demonstrate that a DM halo would be detected by our method, and therefore the results have no straightforward interpretation. Only the presence of a highly prolate (flattening q > 2) DM halo can be reconciled with the observations, but this is highly unlikely in Lambda CDM models. The results challenge the current understanding of the spatial distribution and nature of the Galactic DM. In particular, our results may indicate that any direct DM detection experiment is doomed to fail if the local density of the target particles is negligible.Chilean Centro de Astrofisica FONDAP
15010003
Chilean Centro de Excelencia en Astrofisica y Tecnologias Afines (CATA)
GEMINI-CONICYT
32080008
COMITE MIXTO
Yale University/Universidad de Chile collaboration
US National Science Foundation
Yale University
Universidad Nacional de San Juan, Argentin
Digestible fibre to ADF ratio and protein concentration in diets for early-weaned rabbits
No full textTo evaluate the effects of three ratios of digestible fibre (DF = hemicelluloses and pectins) to ADF (1.1, 1.3 and 1.5) and two levels of crude protein (CP, 16% and 17%) on digestive efficiency, growth performance, health status, and meat quality, from early-weaning (26 d of age) to slaughter (74 d) 246 rabbits were given ad libitum access to six diets according to a 3x2 factorial arrangement. Increasing DF/ADF linearly increased DM, fibre fraction and energy (59.9 vs. 62.3 vs. 65.9%, P<0.01) digestibility and daily weight gain (42.4 vs. 43.2 vs. 45.2 g/d; P=0.02) and improved feed conversion (P<0.01), without affecting slaughter results, carcass and meat quality. Total caecal VFA concentration increased (51.3 vs. 66.9 and 66.0 mmol/l; P<0.01) as DF/ADF raised from 1.1 to 1.3 and 1.5. Increasing dietary protein improved DM and nutrient digestibility and feed conversion (P<0.01), as well as slaughter dressing percentage (61.2 vs 61.8%, P=0.03). Dietary protein concentration did not modify caecal content characteristics or carcass and meat quality. A higher mortality (P=0.05) was measured in rabbits fed diets at 1.1 DF/ADF (27.1%) in comparison with rabbits fed diets at 1.3 (14.3%) and 1.5 (17.1%). However, feeding the highest DF/ADF diets, mortality raised up to 23.9% with the 16% CP diet, while was only 11.4% with the 17% CP diet
Healthy Aging within an Image: Using Muscle Radiodensitometry and Lifestyle Factors to Predict Diabetes and Hypertension
No full textThe strong age dependency of many deleterious health outcomes likely reflects the cumulative effects from a variety of risk and protective factors that occur over one's life course. This notion has become increasingly explored in the etiology of chronic disease and associated comorbidities in aging. Our recent work has shown the robust classification of individuals at risk for cardiovascular pathophysiology using CT-based soft tissue radiodensity parameters obtained from nonlinear trimodal regression analysis (NTRA). Past and present lifestyle influences the incidence of comorbidities like hypertension (HTN), diabetes (DM) and cardiac diseases. 2,943 elderly subjects from the AGES-Reykjavik study were sorted into a three-level binary-tree structure defined by: 1) lifestyle factors (smoking and self-reported physical activity level), 2) comorbid HTN or DM, and 3) cardiac pathophysiology. NTRA parameters were extracted from mid-thigh CT cross-sections to quantify radiodensitometric changes in three tissue types: lean muscle, fat, and loose-connective tissue. Between-group differences were assessed at each binary-tree level, which were then used in tree-based machine learning (ML) models to classify subjects with DM or HTN. Classification scores for detecting HTN or DM based on lifestyle factors were excellent (AUCROC: 0.978 and 0.990, respectively). Finally, tissue importance analysis underlined the comparatively-high significance of connective tissue parameters in ML classification, while predictive models of DM onset from five-year longitudinal data gave a classification accuracy of 94.9%. Altogether, this work serves as an important milestone toward the construction of predictive tools for assessing the impact of lifestyle factors and healthy aging based on a single image
Digestible fiber to ADF ratio and starch level in diets for growing rabbits
No full textTo evaluate the effect of digestible fibre (DF, hemicelluloses+pectins)/ADF ratio (1.0 and 1.3) and starch level (12, 15, and 18%) on health status, digestive physiology, growth performance, and carcass traits, 246 rabbits weaned at 27 d were fed until slaughter (76 d) with six diets formulated according to a bifactorial arrangement (2 DF/ADF ratios by 3 starch levels). Increasing DF/ADF improved DM digestibility (P<0.01), but did not affect growth performance, caecal content characteristics and slaughter traits. Increasing starch level improved digestibility efficiency and conversion index (P<0.001), decreased ileal mucosa villi height (P=0.04), without affecting growth performance, caecal fermentation and slaughter results. The increase of DF/ADF ratio tended to reduce mortality (25.0 vs 17.6%; P=0.11), whereas the raise of starch greatly increased mortality (from 6.9 to 43.1%; P<0.001) and sanitary risk (from 13.9 to 63.9%; P<0.001)
Tree water relations and climatic variations at the alpine timberline: seasonal changes of sap flux and xylem water potential in Larix decidua Miller, Picea abies (L.) Karst. and Pinus cembra L
No full textTrees growing at the alpine timberline very seldom undergo severe water stress because of high precipitation during the vegetative period. Since trees are adapted to moist conditions, moderate water deficit may lead to a strong reduction in transpiration. Transpiration and xylem water potential were measured in two individuals each of Pinus cembra, Larix decidua and Picea abies growing at the timberline (2 080 m a.s.l.) in the north-eastern Italian Alps. From June to October 1996 predawn water potential was between -0.29 and -1.0 MPa with moderate differences among species. Throughout the growing period L. decidua showed a progressive decrease in the minimum water potential (from -0.45 to -1.93 MPa); in P. abies and P. cembra variations were more correlated to weather conditions with minima (-1.2 and -1.49 MPa, respectively) during a mild drought period. L. decidua showed the mean daily maximum sap flux density (about 3.3 dm 3 dm-2 h-1) while mean maximum values in P. abies and P. cembra were about 0.9 and 0.7, respectively. High daily fluctuations of sap flow were observed in relation to rapid variations in weather conditions, particularly in L. decidua. Regardless of species a very high stomatal sensitivity to vapour pressure deficit was recorded. The three species seem to have evolved different drought avoidance strategies. L. decidua maintained a relatively high transpiration even during moderate water deficit periods because of its high water uptake capacity. During the same drought period P. abies and P. cembra showed an evident reduction in sap flux, suggesting a water saving behaviour. These different responses should be taken into account when considering the effects of global change on timberline trees. (© Inra/Elsevier, Paris.)Relations hydriques des arbres et facteurs du climat à la limite forestière alpine : variations saisonnières du flux de sève et du potentiel hydrique chez Larix decidua Miller, Picea abies (L.) Karst. et Pinus cembra L. Les arbres situés à la limite forestière dans les Alpes sont rarement soumis à des contraintes hydriques sévères, car les précipitations durant la période de végétation sont élevées. Alors que ces arbres sont adaptés à des conditions de forte humidité, une contrainte hydrique modérée peut conduire à une forte réduction de leur transpiration. La transpiration et le potentiel hydrique ont été mesurés sur deux individus de chacune des espèces : Pinus cembra, Larix decidua et Picea abies dans la zone de la limite forestière (altitude 2 080 m), dans le nord-est des Alpes italiennes. De juin à octobre 1996, le potentiel hydrique de base a varié entre -0,29 et -1,0 MPa, avec peu de différences entre espèces. Au cours de la période de végétation, L. decidua a montré une diminution progressive de son potentiel hydrique minimum (passant de -0,45 Mpa à -1,93 Mpa). Chez P. abies et P. cembra, les variations de ce paramètre étaient plus fortement corrélées aux facteurs climatiques, les valeurs atteintes étant respectivement de -1,2 Mpa et de -1,49 Mpa pour ces deux espèces, lors d'une période de sécheresse modérée. Les valeurs les plus élevées de densité de flux de sève ont été observées chez L. decidua (environ 3,3 dm3 dm-2 h-1), contre 0,9 dm3 dm-2 h-1 chez P. abies et 0,7 dm 3 dm-2 h-1 chez P. cembra. Des fortes variations journalières de flux de sève ont été mises en évidence en relation avec les fluctuations rapides des conditions climatiques, notamment chez L. decidua. Une forte sensibilité des stomates au déficit de saturation de l'air a été observée pour chacune de ces espèces. Ces trois espèces semblent avoir développé différentes stratégies de réponse à la sécheresse : L. deciduca a maintenu un taux de transpiration relativement élevé, même lors d'une sécheresse, en relation avec une forte capacité d'extraction de l'eau dans le sol. Au cours de la même période de dessèchement, P. abies et P. cembra ont montré une nette réduction de leur flux de sève, ce qui indiquerait une stratégie d'évitement. Ces différentes réponses doivent être prises en compte lorsqu'on s'intéresse aux effets des changements climatiques dans cette zone de limite forestière. (© Inra/Elsevier, Paris.
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