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.     

ASTROPHYSICS: Astronomers Spot Their First Carbon Bomb

Carbon on the surface of an ultradense star detonated in a 3-hour thermonuclear explosion, according to a report at a meeting here last week of the American Astronomical Society's High Energy Astrophysics Division. If confirmed, the burst would be the first known cosmic explosion fueled solely by carbon rather than hydrogen or helium and could verify or revise models of carbon combustion.     

PTF 11kx: a type Ia supernova with a symbiotic nova progenitor

There is a consensus that type Ia supernovae (SNe Ia) arise from the thermonuclear explosion of white dwarf stars that accrete matter from a binary companion. However, direct observation of SN Ia progenitors is lacking, and the precise nature of the binary companion remains uncertain. A temporal series of high-resolution optical spectra of the SN Ia PTF 11kx reveals a complex circumstellar environment that provides an unprecedentedly detailed view of the progenitor system. Multiple shells of circumstellar material are detected, and the SN ejecta are seen to interact with circumstellar material starting 59 days after the explosion. These features are best described by a symbiotic nova progenitor, similar to RS Ophiuchi.     

Circumstellar material in type Ia supernovae via sodium absorption features

Type Ia supernovae are key tools for measuring distances on a cosmic scale. They are generally thought to be the thermonuclear explosion of an accreting white dwarf in a close binary system. The nature of the mass donor is still uncertain. In the single-degenerate model it is a main-sequence star or an evolved star, whereas in the double-degenerate model it is another white dwarf. We show that the velocity structure of absorbing material along the line of sight to 35 type Ia supernovae tends to be blueshifted. These structures are likely signatures of gas outflows from the supernova progenitor systems. Thus, many type Ia supernovae in nearby spiral galaxies may originate in single-degenerate systems.     

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.     

Waves and turbulence in a tokamak fusion plasma

The tokamak is a prototype fusion device in which a toroidal Magnetic field is used to confine a hot plasma. Coherent waves, excited near the plasma edge, can be used to transport energy into the plasma in order to heat it to the temperatures required for thermonuclear fusion. In addition, tokamak plasmas are known to exhibit high levels of turbulent density fluctuations, which can transport particles and energy out of the plasma. Recently, experiments have been conducted to elucidate the nature of both the coherent waves and the turbulence. The experiments provide insight into a broad range of interesting linear and nonlinear plasma phenomena and into many of the processes that determine such practical things as plasma heating and confinement.     

用CONE法研究ULDM的阻燃特性

采用硼、氮-磷、硅和卤素系4种组分复合的无机阻燃剂制备难燃超轻质木纤维发泡材料(ULDM),通过锥形量热仪(CONE)法对超轻质木纤维发泡材料独特的燃烧热解特点、燃烧过程的热释放及阻燃剂各组分协效作用进行研究。结果表明,超轻质木纤维发泡材料的燃烧热解有不同于其他木质材料的爆燃现象,放热集中且迅速,瞬间放热量高。经无机复合阻燃处理后的超轻质木纤维发泡材料有焰燃烧时间低于30 s,在火场高温中能够维持阴燃状态,燃烧热解进程缓和,放热平稳。证明了复合阻燃剂各组分可充分产生协效阻燃作用,硼系能迅速形成玻璃态隔离层,氮-磷系能促进脱水成炭,硅系能有效增强纤维和炭层热稳定性,卤素系能极大降低有效燃烧热。     

基于分形理论的汽油机富氧燃烧模型

阐述了湍流的分形特征,应用分形理论计算了湍流燃烧速度和质量燃烧率,分析了富氧燃烧时未燃混合气密度的计算方法。借助VB语言编制计算程序,进行了计算与实验对比分析。探讨了将分形理论应用到发动机富氧燃烧模型中的可行性。     

石油储罐防火防爆常见问题的分析

随着国内石油储罐类型和设计构造的不断改进,容量趋于大型化,相应安全技术条件不断完善,但在实际生产过程中, 还存在着许多影响油罐安全运行的问题。从加速 油罐防火防爆问题出发,对生产实践中遇到的一些实际问题进行分析,并提出了预防油罐发生火灾爆炸事故的具体措施。     

Fallout Dosages at Washington,D.C

It has been assumed that the fission product conglomerate emits one gamma ray per beta particle throughout its lifetime. The fallout velocities are not accurately known, and in some cases the detonation and response times have been approximated. For these reasons, the dosages reported in this paper can be accurate in order of magnitude only. With these reservations, an infinity dose of 0.2 roentgen or less due to all explosions between January 1951 and May 1955 is reported for Washington, D.C. Therefore, it is probable that the total fallout from all weapons tests that have so far been conducted will produce only a fraction of the lifetime dosage due to natural radioactivity and cosmic radiation (6). Most of the dosage comes from the Nevada tests, and only a small part from the Pacific thermonuclear tests (7). Fission products contained in that part of the cloud of a thermonuclear explosion which extends above the level of precipitation is found to contribute only very slightly to the dosage at great distances. No analysis was carried out for air activity data taken at other locations, but their qualitative similarity to those taken in Washington suggests that infinity doses in most other locations in the northern hemisphere will not be greatly different. Present results are in essential agreement with two other measurements that have been reported. Eisenbud and Harley (8) have measured fallout deposited on gummed papers (9) at various locations in the United States and have found an average dose of 0.001 roentgen per year. Stewart, Crooks, and Fisher (10) have measured the activity of air, rainwater, and ground deposits in England and report an infinity dose of 0.055 roentgen. This somewhat lower figure may result from their greater distance from Nevada, which appears to be the source of most of the fallout in the United States. The authors wish to thank Dr. H. Friedman and Dr. L. B. Lockhart for their continued support and for many helpful discussions.     

Visualization of turbulent flame fronts with planar laser-induced fluorescence

This report concerns the quantitative time-resolved visualization of reaction zones in laminar, transitional, and turbulent nonpremixed flames. Two-dimensional OH molecular concentrations were measured with planar laser-induced fluorescence excited by a sheet of light (formed from a single tunable ultraviolet laser pulse) and detected with a two-dimensional, image-intensified photodiode array camera. From the resulting data details of instantaneous flame front structures (including positions, shapes, and widths) were obtained.     

液化石油气储罐安全泄放与冷却水系统

储存易燃易爆液化石油气的储罐，必须设置安全泄放系统，同时加设冷却水系统，以防止火灾情况下发生爆炸事故。安全泄放与冷却水系统是二者互相联系的安全措施。液化石油气储罐应设置弹簧封闭全启式安全阀。把国家劳动部《压力容器安全技术监察规程》中安全阀计算公式与《建筑设计防火规范》中的有关内容联系起来，提出了液化石油气储罐安全阀的简化计算公式。对安全阀泄放管的设置提出了以下要求：由于安全阀排放时喷嘴处气速极大，     

液化石油气火灾爆炸事故类型分析

对液化石油气储运过程中的各种爆炸类型及成因进行了探讨，运用事故树方法分析了引起火灾爆炸的概率和原因。指出在液化石油气爆炸事故类型中，泄漏型火灾爆炸发生的概率最大，也最危险。提出了液化石油气火灾爆炸事故的预防措施。     

胶合板用新型有机阻燃剂的研究

分析探讨新型有机阻燃剂处理胶合板的阻燃机理、应用工艺、产品性能 .研究结果表明 :该阻燃剂对胶合板的阻燃性能良好、阻燃效果显著 ,用普通胶合板生产线生产阻燃胶合板是可行的 ,产品的各项性能指标达到了相关标准的要求     

油库爆炸危险性分析

从物理性爆炸和化学性爆炸两个方面分析了油库火灾爆炸的危险，提出了预防油库火灾爆炸事故发生的技术措施和管理措施，可为油库安全运营提供参考。     

含泥岩夹层盐穴储气库的爆炸动力响应数值模拟

为了探讨含泥岩夹层盐穴储气库在可燃气体爆炸作用下的稳定性,利用有限差分软件FLAC^3D,建立盐穴储气库的数值模型,分析爆炸载荷作用下含泥岩夹层盐穴储气库的动态响应,包括储气库围岩的应力状态变化、地震动幅值及稳定性等。结果表明:在可燃气体爆炸载荷作用下,泥岩夹层与盐岩中应力变化基本一致,不存在明显的薄弱部位;人工拟合爆炸波对洞室围岩的冲击作用比三角形爆炸波作用强;可燃气体爆炸作用对洞室围岩破坏的影响有限,随洞室深度的增大迅速衰减;深埋盐穴储气库比浅埋洞室抵抗爆炸作用的能力更强,有利于储气库洞室的稳定性。     

液化石油气蒸气爆炸过程研究进展

液化石油气蒸气爆炸是其储运过程中较易发生且危害极大的一种热力过程。探讨了液化石油气沸腾液体膨胀蒸气爆炸和沸腾液体压缩气泡爆炸的发生机理,介绍了国内外对储罐破裂前的热力响应过程和储罐破裂后的压力瞬变过程两个阶段的研究进展和取得的成果,并提出了若干尚待进一步研究的领域。     

Energy research: accelerator builders eager to aid fusion work

Useful fusion energy may be generated by means of heavy ion accelerator driven implosions if the contraints dictated by the physics and economics of thermonuclear targets and reactors can be satisfied.     

Protostellar feedback halts the growth of the first stars in the universe

The first stars fundamentally transformed the early universe by emitting the first light and by producing the first heavy elements. These effects were predetermined by the mass distribution of the first stars, which is thought to have been fixed by a complex interplay of gas accretion and protostellar radiation. We performed radiation-hydrodynamics simulations that followed the growth of a primordial protostar through to the early stages as a star with thermonuclear burning. The circumstellar accretion disk was evaporated by ultraviolet radiation from the star when its mass was 43 times that of the Sun. Such massive primordial stars, in contrast to the often-postulated extremely massive stars, may help explain the fact that there are no signatures of the pair-instability supernovae in abundance patterns of metal-poor stars in our galaxy.     

阻燃剂对刨花板热裂解产物的影响

为了研究阻燃剂的加入对刨花板热裂解产物的影响,通过对阻燃剂刨花板的热裂解产物进行GC-MS分析,并对比普通刨花板的数据,研究两者燃烧产物的差异。结果表明:阻燃剂的添加,能有效减少裂解产物的数量;阻燃剂主要与木质素结合,达到阻燃效果;该研究中添加无机阻燃剂的刨花板裂解产物的数量和类别均少于添加有机阻燃剂的刨花板。