A common explosion mechanism for type Ia supernovae

Type Ia supernovae, the thermonuclear explosions of white dwarf stars composed of carbon and oxygen, were instrumental as distance indicators in establishing the acceleration of the universe's expansion. However, the physics of the explosion are debated. Here we report a systematic spectral analysis of a large sample of well-observed type Ia supernovae. Mapping the velocity distribution of the main products of nuclear burning, we constrain theoretical scenarios. We find that all supernovae have low-velocity cores of stable iron-group elements. Outside this core, nickel-56 dominates the supernova ejecta. The outer extent of the iron-group material depends on the amount of nickel-56 and coincides with the inner extent of silicon, the principal product of incomplete burning. The outer extent of the bulk of silicon is similar in all supernovae, having an expansion velocity of approximately 11,000 kilometers per second and corresponding to a mass of slightly over one solar mass. This indicates that all the supernovae considered here burned similar masses and suggests that their progenitors had the same mass. Synthetic light-curve parameters and three-dimensional explosion simulations support this interpretation. A single explosion scenario, possibly a delayed detonation, may thus explain most type Ia supernovae.     

Detection of circumstellar material in a normal type Ia supernova

Type Ia supernovae are important cosmological distance indicators. Each of these bright supernovae supposedly results from the thermonuclear explosion of a white dwarf star that, after accreting material from a companion star, exceeds some mass limit, but the true nature of the progenitor star system remains controversial. Here we report the spectroscopic detection of circumstellar material in a normal type Ia supernova explosion. The expansion velocities, densities, and dimensions of the circumstellar envelope indicate that this material was ejected from the progenitor system. In particular, the relatively low expansion velocities suggest that the white dwarf was accreting material from a companion star that was in the red-giant phase at the time of the explosion.     

胆酸钠对山羊鼻腔相关扁桃体黏膜上皮吸收灭活病毒的影响

为研究胆酸钠促进山羊鼻腔相关扁桃体黏膜上皮吸收禽流感灭活病毒的形态学机制,经鼻腔接种胆酸钠和禽流感灭活病毒后,用组织学光镜和电镜制片技术研究山羊咽扁桃体和咽鼓管扁桃体上皮结构的变化以及灭活病毒的吸收情况。结果表明:单独应用灭活病毒后扁桃体黏膜上皮结构完整;而应用胆酸钠或胆酸钠配合灭活病毒后扁桃体中可观察到较多脱离黏膜上皮的细胞,脱落的细胞大部分是上皮细胞和淋巴细胞,上皮细胞间间隙增大,紧密连接被打开。应用胆酸钠配合灭活病毒后可观察到部分细胞内含有病毒的囊泡。鼻腔接种后第3天,应用胆酸钠的扁桃体黏膜上皮结构基本恢复,几乎没有观察到脱离上皮的细胞。结论:胆酸钠通过打开山羊鼻腔相关扁桃体黏膜上皮细胞之间的紧密连接来促进灭活病毒的吸收;虽然胆酸钠可引起部分上皮脱落,但这种副作用是短暂的并是可修复的。     

原子吸收光谱法测定小麦品种子粒中钾钠钙镁的含量

采用火焰原子吸收光谱法,测定了6种不同类型的冬小麦品种子粒中钾、钠、钙、镁宏量元素的含量。结果表明：钾、钠、钙、镁元素的相对标准偏差(RSD)分别小于0．77％、7．01％、3．82％、1．63％;并以小麦粉标准样品(GBW08503)进行比较测定。标准样品的测定值与标准值基本一致。该方法简便、快速、准确。