Big Bang Nucleosynthesis and the Density of Baryons in the Universe

Now that extragalactic deuterium observations are being made, Big Bang Nucleosynthesis (BBN) is on the verge of undergoing a transformation. Previously, the emphasis was on demonstrating the concordance of the Big Bang Nucleosynthesis model with the abundances of the light isotopes extrapolated back to their primordial values using stellar and Galactic evolution theories. Once the primordial deuterium abundance is converged upon, the nature of the field will shift to using the much more precise primordial D/H to constrain the more flexible stellar and Galactic evolution models (although the question of potential systematic error in 4He abundance determinations remains open). The remarkable success of the theory to date in establishing the concordance has led to the very robust conclusion of BBN regarding the baryon density. The BBN constraints on the cosmological baryon density are reviewed and demonstrate that the bulk of the baryons are dark and also that the bulk of the matter in the universe is non-baryonic. Comparison of baryonic density arguments from Lyman- clouds, x-ray gas in clusters, and the microwave anisotropy are made and shown to be consistent with the BBN value.     

Big Bang Theory and Primordial Nuclei

A summary of the discussions of Working Group 1 (Rees, Reeves, Schramm, Steigman, Tammann, and TPW) on Big Bang Theory as it relates to primordial nuclei and their galactic evolution.     

The Big Bang — Implosion and explosion

This review paper first gives a resumé of the standard model of cosmology, the hot Big Bang model of the Universe, high-lighting its successes and failings. This is followed by a brief exposition of some of the concepts in elementary particle physics which are basic to understanding modern cosmology. Thereafter a brief account of the inflationary models of the Universe is given which is followed by a critique of these models. Next, a viable explanation of the origin of the Big Bang is given within the framework of the singularity free model of the Universe proposed recently by the author. A critique of this model is also given. Finally, the cosmological implications of the data from theCosmic Background Explorer (COBE) is briefly discussed.     

Nucleosynthesis in Supernovae

We present the status and open problems of nucleosynthesis in supernova explosions of both types, responsible for the production of the intermediate mass, Fe-group and heavier elements (with the exception of the main s-process). Constraints from observations can be provided through individual supernovae (SNe) or their remnants (e.g. via spectra and gamma-rays of decaying unstable isotopes) and through surface abundances of stars which witness the composition of the interstellar gas at their formation. With a changing fraction of elements heavier than He in these stars (known as metallicity) the evolution of the nucleosynthesis in galaxies over time can be determined. A complementary way, related to gamma-rays from radioactive decays, is the observation of positrons released in \(\beta^{+}\)-decays, as e.g. from \(^{26}\mbox{Al}\), \(^{44}\mbox{Ti}\), \(^{56,57}\mbox{Ni}\) and possibly further isotopes of their decay chains (in competition with the production of \(e^{+}e^{-}\) pairs in acceleration shocks from SN remnants, pulsars, magnetars or even of particle physics origin). We discuss (a) the role of the core-collapse supernova explosion mechanism for the composition of intermediate mass, Fe-group (and heavier?) ejecta, (b) the transition from neutron stars to black holes as the final result of the collapse of massive stars, and the relation of the latter to supernovae, faint supernovae, and gamma-ray bursts/hypernovae, (c) Type Ia supernovae and their nucleosynthesis (e.g. addressing the \(^{55}\mbox{Mn}\) puzzle), plus (d) further constraints from galactic evolution, \(\gamma\)-ray and positron observations. This is complemented by the role of rare magneto-rotational supernovae (related to magnetars) in comparison with the nucleosynthesis of compact binary mergers, especially with respect to forming the heaviest r-process elements in galactic evolution.     

Nucleosynthesis from non-thermal particles

The long-standing problem of nucleosynthesis from non-thermal charged particles is reviewed with emphasis on some novel points. Recent theoretical results predict very efficient acceleration of nuclei (up to GeV range) by violent systems with energy release in the form of multiple shock waves —OB associations and coronae of AGNs and black holes candidates in galactic accretion disks. A detection of gamma-line emission from the Orion complex by theCOMPTEL telescope on board ofGRO could confirm theoretical predictions. Production of lithium by non-thermal particles in Orion-like objects is discussed. The mechanism can be responsible for the observed variations of abundance of isotopes.     

Nucleosynthesis in massive stars

We discuss three aspects of the nucleosynthesis in massive and intermediate-mass stars during their early evolutionary phases. These are related to the CNO abundances in giant or supergiant stars, to the²⁶Al yield from massive stars via stellar wind, and to the production of the s-process nuclei in massive stars.     

C. J. Hogan,The Little Book of the Big Bang: A Cosmic Primer

Space Science Reviews -     

粉尘爆炸与爆炸危险度评价

分析了粉尘爆炸的分类、条件、特性、因素、爆炸极限和最小点火能,重点介绍了粉尘爆炸的机理。在此基础上,采用Fuzzy评价的方法,建立了发生粉尘爆炸的危险度评价模型。     

Stars and Stellar Systems at z > 5: Implications for Structure Formation and Nucleosynthesis

Enough UV radiation was generated before z = 5 to have ionized the intergalactic medium. If this comes from stars (probably aggregated in systems of subgalactic scale), one straightforwardly calculates that the associated nucleosynthesis would be sufficient to produce a universal abundance of order 1 percent of solar. The first pre-galaxies may eventually be detectable by their direct UV emission, with characteristic spectral features at Lyman alpha; high-z supernovae may also be detectable. Other probes of the IGM beyond z = 5, and of the epochs of reheating and reionization, are discussed, along with possible links between the diffusion of pregalactic metals and the origin of magnetic fields.     

GAMECO的发展计划

广州飞机维修工程有限公司(GAME-CO)由于现有场地的限制约束了其业务迅速发展，现已着手实施一项雄心勃勃的扩展计划，正投资1亿多美元在广州新的白云机场建造包括一座足以处理A380的新的大型设施。从6月中开始，建造一座专门用于褪漆及喷漆的机库，计划2002年完成，2003年初开始投入使用。GAMECO新的设施完成后，将是亚洲少数具有用于极大型飞机维修设施的公司之一。香港飞机工程公司（HAECO）已有一座适用于A380的6120m2的机库，新加坡航空公司的工程分公司（SIAEC）正在建设两座新的足以适用于空客公司的超大型运输机的机库。…     

自动化的重要进展

介绍飞机制造商在用自动化改进效率、加速生产以及减少工伤方面取得的进展. 现代飞机制造的特点是要求采用一系列独特的制造技术,其中有激光器、遥控器、定位技术甚至卫星定位技术等,均是在现代工厂中应用的技术.虽然机器人在航空制造中用的仍然不多,但其他-些技术使操作人员的操作变得更加容易,在保持工作岗位安全的同时,效率更高.     

小巨人制造大未来——访宁夏小巨人机床有限公司总经理孙文靖

小巨人公司不仅仅制造数控机床,我们更希望在中国传播数控机床的制造技术和使用技术,传播全新的数字化制造理念,这是我们的使命。今后小巨人公司将继续以网络化为基础,信息化为手段,智能化为目标的思想为指导进一步提高公司的智能化水平,为中国制造业贡献力量。     

雲行天地间 诞生于山野的刺绣华服

在云南永仁县崇山峻岭深处,有一个偏僻的彝族小山村——直苴。每年农历正月十五,当地村民都会自发组织盛大的"彝族赛装节",纵情歌舞、赛装比美、跳脚狂欢、通宵达旦,表达对美好生活的不懈追求与无限向往。这一习俗传承了1300多年,被誉为中国乃至世界最古老的"原生态乡村T台秀"。     

各国大型主战无人机研究进展

无人机在情报、侦察、监视等方面有着传统应用,但随着无人机的发展,承担打击任务将是无人机的必然职能,各军事强国也都围绕这一职能进行着多方面的研究。本文分析目前各国大型主战无人机的发展,讨论无人主战飞机的发展趋势。     

波音737MAX不断刷新波音订单纪录

2011年12月13日,美国西南航空宣布订购150架波音737MAX,成为这一换发机型的启动用户,美西南航同时还订购了58架新一代波音737,这笔订单目录价值近190亿美元,在数量和价值两方面均刷新了波音民机订单纪录。2011年11月17日,波音与印尼狮     

五方角力 大支线喷气客机市场竞争加剧

2007年，70～90座级的大支线喷气飞机市场竞争，从以前庞巴迪和巴西航空工业公司的对台戏已经演化为一场五方的角力之战。2008年这场竞争将会如何？     

小型燃气涡轮发动机技术的大提升

霍尼韦尔宇航公司计划于今年第1季度完成美国陆军小型重油发动机(SHFF)项目的技术验证机的整机初始试车.     

GE力推以结果为导向的大数据分析

GE航空集团用18个月的时间将发动机机队诊断数据顺利迁移至新的Predix数据平台。该平台试图通过以结果为导向的大数据分析,实现对发动机机队的性能预测。     

老龄飞机的维修文件问题

保证老龄商务飞机的适航不仅仅需要认真的维护,一份完善的书面记录同样是非常重要的。     

一种测定大值的风速计

简单叙述了研制1种大风速值简易精密测量仪器原理和方法，并对测量误差进行了估算。