Global Oscillation Network Group data reveal that the internal structure of the sun can be well represented by a calibrated standard model. However, immediately beneath the convection zone and at the edge of the energy-generating core, the sound-speed variation is somewhat smoother in the sun than it is in the model. This could be a consequence of chemical inhomogeneity that is too severe in the model, perhaps owing to inaccurate modeling of gravitational settling or to neglected macroscopic motion that may be present in the sun. Accurate knowledge of the sun's structure enables inferences to be made about the physics that controls the sun; for example, through the opacity, the equation of state, or wave motion. Those inferences can then be used elsewhere in astrophysics. 相似文献
Wide-angle seismic data along the Mantle Electromagnetic and Tomography (MELT) arrays show that the thickness of 0.5- to 1. 5-million-year-old crust of the Nazca Plate is not resolvably different from that of the Pacific Plate, despite an asymmetry in depth and gravity across this portion of the East Pacific Rise. Crustal thickness on similarly aged crust on the Nazca plate near a magmatically robust part of the East Pacific Rise at 17 degrees15'S is slightly thinner (5.1 to 5.7 kilometers) than at the 15 degrees55'S overlapping spreading center (5.8 to 6.3 kilometers). This small north-south off-axis crustal thickness difference may reflect along-axis temporal variations in magma supply, whereas the across-axis asymmetry in depth and gravity must be caused by density variations in the underlying mantle. 相似文献
Atmospheric general circulation models used for climate simulation and weather forecasting require the fluxes of radiation, heat, water vapor, and momentum across the land-atmosphere interface to be specified. These fluxes are calculated by submodels called land surface parameterizations. Over the last 20 years, these parameterizations have evolved from simple, unrealistic schemes into credible representations of the global soil-vegetation-atmosphere transfer system as advances in plant physiological and hydrological research, advances in satellite data interpretation, and the results of large-scale field experiments have been exploited. Some modern schemes incorporate biogeochemical and ecological knowledge and, when coupled with advanced climate and ocean models, will be capable of modeling the biological and physical responses of the Earth system to global change, for example, increasing atmospheric carbon dioxide. 相似文献
It was suggested that the cryodamage to oocytes' DNA has been responsible for the compromised developmental competence of cryopreserved oocytes. Vitrification of bovine oocytes affected not only cellular components, but also nuclear material. A significant rate of DNA fragmentation was found in bovine frozen or vitrified oocytes analysed by Comet assay regardless of cryopreservation method. Our method of vitrification using droplet system after gentle pre-equilibration treatment is one of the most effective cryopreservation methods employed for bovine oocytes so far, making it possible to develop 30% blastocyst stage embryos. In this study, the extent of DNA damage in bovine oocytes vitrified using three vitrification methods (droplet system, Open Pulled Straw and traditional vitrification in 0.25 ml insemination straws) was compared using Comet assay. Vitrification in droplet system and Open Pull Straws vitrification did not result in detectable cryoinjuries of DNA of bovine oocytes. On the contrary, DNA fragmentation was found in four of 26 oocytes vitrified in 0.25 ml straws (15.4%, p ≤ 0.05 in comparison with the other vitrification methods). 相似文献
Toxigenic strains of Pasteurella multocida were readily differentiated from non-toxigenic strains by an agarose overlay method using bovine turbinate cells or bovine lung cells. Cells which were young and densely confluent were best suited to this assay. The incubation period required to distinguish toxigenic strains was dependent on the confluence of the monolayers, which was affected by the seeding rate, cell passage level and growth time prior to overlay. The agarose overlay method correctly identified 11 of 11 reference strains of Pasteurella multocida, and visible cytotoxic changes were present in the monolayers after 48 to 65 h. Outbreaks of the enzootic form of atrophic rhinitis in 2 New South Wales piggeries were associated with the isolation of toxigenic type D strains of P. multocida. 相似文献
The effect of fasting on spawning performance, maternal, and egg nutrient composition, and on embryo/larval development was monitored in gilthead seabream (Sparus aurata). Two broodstocks were fasted during two consecutive years, for a period of 43 and 54 days within the spawning season, in a preliminary (year 1, 5-year-old breeders) and the main study (year 2, 6-year-old breeders), respectively. Mean daily fecundity showed a declining trend during fasting in the main study only, while fertilization success was high in both years and it was not affected by fasting, as was hatching and 5-day larval survival. There was a loss of 23.5% of maternal body mass due to fasting, and a reduction in gonadosomatic and hepatosomatic indexes, as well as crude protein in maternal muscle and gonads, but not in the liver. After fasting, muscle Σω-6 PUFA and C18:3ω-3 were reduced while C20:4ω-6, 20:5ω-3/20:4ω-6, and C22:6ω-3/20:4ω-6 increased; in the liver, significant reductions were observed in C16:0, C18:3 ω-3, 20:5ω-3/C22:6ω-3 and increases in C18:0, C20:5ω-3, Σω-6 PUFA, and 20:5ω-3/20:4ω-6; in gonads, C15:0, ΣMUFA, 20:5ω-3/C22:6ω-3, 20:5ω-3/20:4ω-6 were increased, while C18:1ω-9 and C20:5ω-3 decreased. Contrary to maternal tissues, the energy density and proximate composition of the eggs did not change due to fasting. The study suggests that fasting of gilthead seabream breeders for 6–8 weeks during the spawning period does not affect spawning performance, egg proximate composition, or embryo and early larval development since maternal nutrient reserves are mobilized to maintain optimal egg nutrient composition.