排序方式: 共有4条查询结果,搜索用时 15 毫秒
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Castro-Tirado AJ Zapatero-Osorio MR Caon N Cairos LM Hjorth J Pedersen H Andersen MI Gorosabel J Bartolini C Guarnieri A Piccioni A Frontera F Masetti N Palazzi E Pian E Greiner J Hudec R Sagar R Pandey AK Mohan V Yadav RK Nilakshi Bjornsson G Jakobsson P Burud I et al 《Science (New York, N.Y.)》1999,283(5410):2069-2073
Broad-band (ultraviolet to near-infrared) observations of the intense gamma ray burst GRB 990123 started approximately 8.5 hours after the event and continued until 18 February 1999. When combined with other data, in particular from the Robotic Telescope and Transient Source Experiment (ROTSE) and the Hubble Space Telescope (HST), evidence emerges for a smoothly declining light curve, suggesting some color dependence that could be related to a cooling break passing the ultraviolet-optical band at about 1 day after the high-energy event. The steeper decline rate seen after 1.5 to 2 days may be evidence for a collimated jet pointing toward the observer. 相似文献
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Luciane Anita Savi Thiago Caon Ana Paula de Oliveira Andrea Michel Sobottka Wolfgang Werner Flvio Henrique Reginatto Eloir Paulo Schenkel Clia Regina Monte Barardi Cludia Maria Oliveira Simes 《Fitoterapia》2010,81(8):1142-1146
Flavonoids are dietary components and the most ubiquitous phenolic compounds found in nature, showing a range of pharmacological activities including antiviral action. This study describes the antiviral screening of 60 different flavones and flavonols against human rotavirus (Wa-1 strain) as well as their cytotoxicity in MA104 cells. Cytotoxicity was investigated by cell morphology assessment and antirotavirus activity by cytopathic effect inhibition. Results were expressed as CC50 and IC50, respectively, in order to calculate the selectivity index (SI = CC50/IC50) of each compound. Structure–activity relationships (SAR) were proposed based on antirotavirus activity. 相似文献
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Andersen MI Castro-Tirado AJ Hjorth J Moller P Pedersen H Caon N Cairos LM Korhonen H Osorio MR Perez E Frontera F 《Science (New York, N.Y.)》1999,283(5410):2075-2077
An optical spectrum of the afterglow from the unusually bright gamma-ray burst GRB 990123 obtained on 24.25 January 1999 universal time showed an absorption system at a redshift of z = 1.600. The absence of a hydrogen Lyman alpha forest sets an upper limit of z < 2.17, whereas ultraviolet photometry indicates an upper limit of z < 2.05. The probability of intersecting an absorption system as strong as the one observed along a random line of sight out to this z is at most a few percent, implying that GRB 990123 was probably at z = 1. 600. Currently favored cosmological parameters imply that an isotropic energy release equivalent to the rest mass of 1.8 neutron stars (4.5 x 10(54) erg) was emitted in gamma rays. Nonisotropic emission, such as intrinsic beaming, may resolve this energy problem. 相似文献
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Hjorth J Bjornsson G Andersen MI Caon N Cairos LM Castro-Tirado AJ Osorio MR Pedersen H Costa E 《Science (New York, N.Y.)》1999,283(5410):2073-2075
Polarization of the optical emission from GRB 990123 was measured on 24.17 January 1999 universal time with the Nordic Optical Telescope. An upper limit of 2.3% on the linear polarization was found. Accurate polarization measurements provide important clues to the blast wave geometry and magnetic field structure of gamma-ray bursts (GRBs). The lack of detectable polarization for GRB 990123 indicates that the optical afterglow was produced by a blast wave of unknown geometry with an insignificant coherent magnetic field or by a beamed outflow at high Lorentz factor seen at a small viewing angle. Such a collimated jet would help solve the problem of energy release in this exceptionally luminous cosmological burst. 相似文献
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