17,092 research outputs found
Meier (Robert J.), Otten (Charlotte M.), Abdel-Hameed (F.). — Evolutionary models and studies in human diversity.
No full textFerembach D. Meier (Robert J.), Otten (Charlotte M.), Abdel-Hameed (F.). — Evolutionary models and studies in human diversity.. In: Bulletins et Mémoires de la Société d'anthropologie de Paris, XIII° Série. Tome 5 fascicule 4, 1978. pp. 341-342
Joule heating in nanowires
No full textWe study the effect of Joule heating from electric currents flowing through ferromagnetic nanowires on the temperature of the nanowires and on the temperature of the substrate on which the nanowires are grown. The spatial current density distribution, the associated heat generation, and diffusion of heat is simulated within the nanowire and the substrate. We study several different nanowire and constriction geometries as well as different substrates: (thin) silicon nitride membranes, (thick) silicon wafers, and (thick) diamond wafers. The spatially resolved increase in temperature as a function of time is computed. For effectively three-dimensional substrates (where the substrate thickness greatly exceeds the nanowire length), we identify three different regimes of heat propagation through the substrate: regime (i), where the nanowire temperature increases approximately logarithmically as a function of time. In this regime, the nanowire temperature is well-described analytically by You et al. [APL89, 222513 (2006)]. We provide an analytical expression for the time tc that marks the upper applicability limit of the You model. After tc, the heat flow enters regime (ii), where the nanowire temperature stays constant while a hemispherical heat front carries the heat away from the wire and into the substrate. As the heat front reaches the boundary of the substrate, regime (iii) is entered where the nanowire and substrate temperature start to increase rapidly. For effectively two-dimensional substrates (where the nanowire length greatly exceeds the substrate thickness), there is only one regime in which the temperature increases logarithmically with time for large times. We provide an analytical expression, valid for all pulse durations, that allows one to accurately compute this temperature increase in the nanowire on thin substrate
Behavioural responses related to increasing core body temperature of grazing dairy cows experiencing moderate heat stress
No full textExposure to direct solar radiation, high ambient temperature, lack of wind movement, coupled with own metabolic heat production, makes grazing dairy cows vulnerable to heat stress. In pastures, it would be beneficial to monitor heat stress by observable changes in behaviour. We hypothesised that grazing dairy cows exhibit behavioural changes due to increasing heat load in temperate climate. Over two consecutive summers, 38 full-time grazing Holstein dairy cows were investigated in 12 experimental periods of up to 3 consecutive days where the cows were repeatedly exposed to various levels of moderate heat load determined by the comprehensive climate index (CCI). The CCI defines the ambient climate conditions, combining air temperature, relative humidity, solar radiation and wind speed. Vaginal temperature (VT) was automatically measured as an indicator of heat stress. In addition, as a less invasive method, we investigated if reticular temperature (RET) can be indicative of heat stress on pastures. Walking activity, lying-, feeding, and ruminating durations were recorded continuously with sensors. Respiration rate (RR), proximity to and competition at the water trough, social licking, self-licking, inter-individual distance, and fly intensity were directly observed. Data were analysed in the morning (0900–1100 h) and during the hottest time of day when cows were on pasture (1230–1430 h). The VT and RET showed similar patterns in relation to the CCI, suggesting that RET can be suitable for continuous monitoring of heat stress on pastures. In the morning, the cow’s VT and RET did not relevantly react to the CCI. During the period 1230–1430 h, the cow’s mean VT (mean vaginal temperature (VTMEAN); range: 37.7–40.3 °C) and mean RET (mean reticular temperature; range: 37.0–41.1 °C) were positively related to the mean CCI (mean comprehensive climate index) in this period (mean ± SD: 25.9 ± 5.71 °C). For cows with greater VTMEAN, an increased mean RR and decreased durations of walking, lying, feeding, and ruminating were found. These cows were also more likely to be in proximity to the water trough and to have small inter-individual distances. Changes in these traits seem to reflect behavioural adaptations to heat stress in a temperate climate and could be used to detect the heat stress in individual dairy cows on pastures
An extension of the maximum F ratio with unequal degrees of freedom
No full textA set of tables for the upper 5 and 1 percent critical points of the maximum F ratio test for homogeneity of variance is presented. These tables cover the situation where the set, k, of mean square estimates the variance can be divided into two groups of k��� and k���, such that k= k��� + k��� . That is, there are k independent mean square estimates of variance with v��� degrees of freedom and k��� independent mean square estimates of variance with v��� degrees of freedom. These tables are for k between 2 and 12, and the degrees of freedom are between 2 and 16 in increments of 2. A more exact approximation is also developed to include the cases where the degrees of freedom do not satisfy the assumptions used to develop the tables. This approximation uses the lower and upper degrees as well as k and the present tables; whereas, the previous approximation used to k, v (line over v) and tables of the critical points of the maximum F ratio test where all the degrees of freedom were equal. The approximation developed herein is shown to be 'better' that the previously used approximation when compared with the exact F (subscript max.) values for small k. An extension of the approximation is also presented. This discussion shows how the approximation can be generalized to develop approximations for other tests of homogeneity of variance. More specifically, the approximation is applied to Bartlett's M statistic. These approximations can be used to decrease computational labor involved in some of the tests for homogeneity of variance
John Malalas as a source for John of Antioch's Historia Chroniké. The evidence of the Excerpta Historica Constantiniana
No full textReview: Harmonised in vitro digestion and the Ussing chamber for investigating the effects of polyphenols on intestinal physiology in monogastrics and ruminants
No full textBecause of the relevant effects of plant-derived polyphenols (PPs) on monogastrics and ruminants’ nutrition, emissions and performance, an increasing number of in vivo and in vitro studies are being performed to better understand the mechanisms of action of polyphenols at both the ruminal and intestinal levels. The biological properties of these phenolic compounds strongly depend on their degradation, absorption and metabolism. The harmonised in vitro digestion method (INFOGEST) is one of the most reliable in vitro methods used to assess the bioaccessibility and or antioxidant activity of PP contained in different matrixes, as well as the interactions of PP and their degradation products with other feed ingredients. The effects of PP released from their matrix after in vitro digestion on different intestinal physiological parameters, such as epithelium integrity, can be further evaluated by the use of ex vivo models such as the Ussing chamber. This review aims to describe the combination of the INFOGEST method, coupled with the Ussing chamber as a valuable model for the digestion and subsequent effects and absorption of phenolic compounds in monogastrics and potentially in ruminants. The advances, challenges and limits of this approach are also discussed
Meteoritic and bedrock constraints on the glacial history of Frontier Mountain in northern Victoria Land, Antarctica
No full textin 2001, a small H4 chondrite, Frontier Mountain (FRO) 01149, was found on a glacially eroded surface near the top of Frontier Mountain, Antarctica, about 600 m above the present ice level. The metal and sulphides are almost completely oxidized due to terrestrial weathering. We used a chemical leaching procedure to remove weathering products, which contained atmospheric Be-10 and Cl-36 in a ratio similar to that found in Antarctic ice. The FRO 01149 meteorite has a terrestrial age of 3.0 +/- 0.3 Myr based on the concentrations of the cosmogenic radionuclides Be-10, Al-26 and Cl-36. This age implies that FRO 01149 is the oldest stony meteorite (fossil meteorites excluded) discovered on Earth. The noble gas cosmic ray exposure age of FRO 01149 is similar to 30 Myr. The meteorite thus belongs to the 33 Myr exposure age peak of H-chondrites. The bedrock surface on which FRO 01149 was found has wet-based glacial erosional features recording a former high-stand of the East Antarctic ice sheet. This ice sheet evidently overrode the highest peaks (> 2800 m a.s.l.) of the inland sector of the Transantarctic Mountains in northern Victoria Land. We argue that FRO 01149 was a local fall and that its survival on a glacially eroded bedrock surface constrains the age of the last overriding event to be older than similar to 3 Myr. The concentrations of in-situ produced cosmogenic Be-10, Al-26 and Ne-21 in a glacially eroded bedrock sample taken from near the summit of Frontier Mountain yield a surface exposure age of 4.4 Myr and indicate that the bedrock was covered by several meters of snow. The exposure age is also consistent with bedrock exposure ages of other summit plateaus in northern Victoria Land
Zeitreihenanalysen von Interaktionsprozessen bei der Bearbeitung komplexer Probleme in Expertengruppen
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