排序方式： 共有19条查询结果，搜索用时 15 毫秒
1.
Sugerman BE Ercolano B Barlow MJ Tielens AG Clayton GC Zijlstra AA Meixner M Speck A Gledhill TM Panagia N Cohen M Gordon KD Meyer M Fabbri J Bowey JE Welch DL Regan MW Kennicutt RC 《Science (New York, N.Y.)》2006,313(5784):196-200
We present late-time optical and mid-infrared observations of the Type II supernova 2003gd in the galaxy NGC 628. Mid-infrared excesses consistent with cooling dust in the ejecta are observed 499 to 678 days after outburst and are accompanied by increasing optical extinction and growing asymmetries in the emission-line profiles. Radiative-transfer models show that up to 0.02 solar masses of dust has formed within the ejecta, beginning as early as 250 days after outburst. These observations show that dust formation in supernova ejecta can be efficient and that massive-star supernovae could have been major dust producers throughout the history of the universe. 相似文献
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In 45 primiparous sows, we examined endocrine, ovarian and reproductive responses to split-weaning or five injections per day of 800 ng GnRH from 18 to 21 days of lactation. There was no effect of treatment on absolute or changes in sow weight or backfat depth during lactation. Average piglet growth rates were similar among treatments except that piglets suckling split-weaned sows grew faster (p < 0.05) during days 18–21. On day 18, mean plasma LH concentrations and LH pulse frequency remained relatively stable in conventionally weaned sows but increased (p < 0.01) in response to split-weaning and GnRH. Prior to weaning on day 21, mean plasma LH concentrations remained elevated in GnRH-treated sows but had returned to control levels in split weaned sows. There was no treatment effect on preweaning LH pulse frequency noted on day 21. Weaning was associated with an increase in plasma LH concentrations in all the treatment groups. Mean plasma IGF-I remained relatively constant in conventionally weaned and GnRH sows, decreased in response to split weaning on day 18 (p < 0.02), but were elevated (p < 0.03) in split wean sows on day 21. On the day after weaning, split wean sows had more (p < 0.04) ovarian follicles ≥3 mm than conventionally weaned sows, with GnRH sows being intermediate. The wean-to-oestrus interval was reduced in split-wean sows compared with those conventionally weaned (p < 0.01), with GnRH sows being intermediate. There was no effect of treatment on ovulation rates, numbers of embryos, or embryonic survival rates. These data indicate that split-weaning of litters results in a more rapid return to oestrus after weaning and that this effect is associated with a transient acute increase in circulating gonadotrophins and earlier resumption of ovarian follicular development. 相似文献
3.
2,3-dimethyl-quinoxaline-1,4-dioxide and 2-methyl-quinoxaline-1,4-dioxide proved to be ergotropic in the feeding of a hydrocolloid ration as well as of a broiler fattening feed. They are at least equal to Nitrovin. The ergotropic effect of the hydrocolloid ration was higher than that of the conventional ration. For this reason methylated quinoxaline-1,4-dioxides are considered as belonging to the intestinal stabilisers. They increased nutrient and energy retention and decreased feed efficiency by approximately equal to 10%. Residues in the liver, the kidneys and the intestines could only be detected after 10 times the ergotropic amount. 相似文献
4.
Matsuura M Dwek E Meixner M Otsuka M Babler B Barlow MJ Roman-Duval J Engelbracht C Sandstrom K Lakićević M van Loon JT Sonneborn G Clayton GC Long KS Lundqvist P Nozawa T Gordon KD Hony S Panuzzo P Okumura K Misselt KA Montiel E Sauvage M 《Science (New York, N.Y.)》2011,333(6047):1258-1261
We report far-infrared and submillimeter observations of supernova 1987A, the star whose explosion was observed on 23 February 1987 in the Large Magellanic Cloud, a galaxy located 160,000 light years away. The observations reveal the presence of a population of cold dust grains radiating with a temperature of about 17 to 23 kelvin at a rate of about 220 times the luminosity of the Sun. The intensity and spectral energy distribution of the emission suggest a dust mass of about 0.4 to 0.7 times the mass of the Sun. The radiation must originate from the supernova ejecta and requires the efficient precipitation of all refractory material into dust. Our observations imply that supernovae can produce the large dust masses detected in young galaxies at very high redshifts. 相似文献
5.
Nico K Michiels Nils Anthes Nathan S Hart Jürgen Herler Alfred J Meixner Frank Schleifenbaum Gregor Schulte Ulrike E Siebeck Dennis Sprenger Matthias F Wucherer 《BMC ecology》2008,8(1):16
Background
At depths below 10 m, reefs are dominated by blue-green light because seawater selectively absorbs the longer, 'red' wavelengths beyond 600 nm from the downwelling sunlight. Consequently, the visual pigments of many reef fish are matched to shorter wavelengths, which are transmitted better by water. Combining the typically poor long-wavelength sensitivity of fish eyes with the presumed lack of ambient red light, red light is currently considered irrelevant for reef fish. However, previous studies ignore the fact that several marine organisms, including deep sea fish, produce their own red luminescence and are capable of seeing it. 相似文献6.
The mare provides a unique experimental model for studying follicle development in monovular species. Development of antral follicles in horses is characterized by the periodic growth of follicular waves which often involve the selection of a single dominant follicle. If properly stimulated, the dominant follicle will complete development and eventually ovulate a fertile oocyte. Regulation of follicular wave emergence and follicle selection involves an interplay between circulating gonadotropins and follicular factors that ensures that individual follicles are properly stimulated to grow (or to regress) at any given stage of follicular wave development. Periodic development of follicular waves continuously occurs during most of post-natal life in the mare and is influenced by factors such as stage of oestrous cycle, season, pregnancy, age, breed and individual so that different types of follicular waves (minor or major, ovulatory or anovulatory) and different levels of activity within waves may develop under different physiological conditions. Changes in gonadotropin levels and/or in the sensitivity of follicles to circulating gonadotropins seem to account largely for these physiological variations in follicle development. 相似文献
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Soil nitrite as a source of atmospheric HONO and OH radicals 总被引：4，自引：0，他引：4
Su H Cheng Y Oswald R Behrendt T Trebs I Meixner FX Andreae MO Cheng P Zhang Y Pöschl U 《Science (New York, N.Y.)》2011,333(6049):1616-1618
Hydroxyl radicals (OH) are a key species in atmospheric photochemistry. In the lower atmosphere, up to ~30% of the primary OH radical production is attributed to the photolysis of nitrous acid (HONO), and field observations suggest a large missing source of HONO. We show that soil nitrite can release HONO and explain the reported strength and diurnal variation of the missing source. Fertilized soils with low pH appear to be particularly strong sources of HONO and OH. Thus, agricultural activities and land-use changes may strongly influence the oxidizing capacity of the atmosphere. Because of the widespread occurrence of nitrite-producing microbes, the release of HONO from soil may also be important in natural environments, including forests and boreal regions. 相似文献
9.
Stephanie Venn-Watson Celeste Benham Frances M Gulland Cynthia R Smith Judy St Leger Pam Yochem Hendrik Nollens Uriel Blas-Machado Jeremiah Saliki Katie Colegrove James FX Wellehan Jr Rebecca Rivera 《Veterinary research》2012,43(1):85
Herpesviruses have been recognized in marine mammals, but their clinical relevance is not always easy to assess. A novel otarine herpesvirus-3 (OtHV3) was detected in a geriatric California sea lion (Zalophus californianus), and using a newly developed quantitative PCR assay paired with histology, OtHV3 was associated with esophageal ulcers and B cell lymphoblastic lymphoma in this animal. The prevalence and quantities of OtHV3 were then determined among buffy coats from 87 stranded and managed collection sea lions. Stranded sea lions had a higher prevalence of OtHV3 compared to managed collection sea lions (34.9% versus 12.5%; p = 0.04), and among the stranded sea lions, yearlings were most likely to be positive. Future epidemiological studies comparing the presence and viral loads of OtHV3 among a larger population of California sea lions with and without lymphoid neoplasia or esophageal ulcers would help elucidate the relevance of OtHV3-associated pathologies to these groups. 相似文献
10.
新《兽药管理条例》实施中的问题浅析 总被引：1，自引：0，他引：1
介绍了新<兽药管理条例>在目前兽药管理实践中存在的问题,如处方药与非处方药的认定,兽用原料药和药物饲料添加剂的认定,动物饲养中滥用人用药品,对兽药使用者的科学管理等;提出了解决这些问题的相关建议. 相似文献