Detection of pristine gas two billion years after the Big Bang

In the current cosmological model, only the three lightest elements were created in the first few minutes after the Big Bang; all other elements were produced later in stars. To date, however, heavy elements have been observed in all astrophysical environments. We report the detection of two gas clouds with no discernible elements heavier than hydrogen. These systems exhibit the lowest heavy-element abundance in the early universe, and thus are potential fuel for the most metal-poor halo stars. The detection of deuterium in one system at the level predicted by primordial nucleosynthesis provides a direct confirmation of the standard cosmological model. The composition of these clouds further implies that the transport of heavy elements from galaxies to their surroundings is highly inhomogeneous.     

论情景喜剧《生活大爆炸》汉语字幕组对言语幽默的处理

美国情景喜剧《生活大爆炸》是一部美国国内家喻户晓的幽默力作,尤其在青少年观众群体中受到了热烈的追捧。近年来,随着他在世界范围的热播,在各国观众中也都得到了热烈反响。作为一部情景喜剧,言语和情景幽默是该剧主要表现形式和表现手段,而他在我国能得以广泛传播并且反响热烈,这与汉语字幕组对其言语幽默的成功翻译是分不开的。     

Deep mixing of 3He: reconciling Big Bang and stellar nucleosynthesis

Low-mass stars, approximately 1 to 2 solar masses, near the Main Sequence are efficient at producing the helium isotope 3He, which they mix into the convective envelope on the giant branch and should distribute into the Galaxy by way of envelope loss. This process is so efficient that it is difficult to reconcile the low observed cosmic abundance of 3He with the predictions of both stellar and Big Bang nucleosynthesis. Here we find, by modeling a red giant with a fully three-dimensional hydrodynamic code and a full nucleosynthetic network, that mixing arises in the supposedly stable and radiative zone between the hydrogen-burning shell and the base of the convective envelope. This mixing is due to Rayleigh-Taylor instability within a zone just above the hydrogen-burning shell, where a nuclear reaction lowers the mean molecular weight slightly. Thus, we are able to remove the threat that 3He production in low-mass stars poses to the Big Bang nucleosynthesis of 3He.     

Comment on "Deep mixing of 3He: reconciling Big Bang and stellar nucleosynthesis"

Eggleton et al. (Reports, 8 December 2006, p. 1580) reported on a deep-mixing mechanism in low-mass stars caused by a Rayleigh-Taylor instability that destroys all of the helium isotope 3He produced during the star's lifetime. Observations of 3He in planetary nebulae, however, indicate that some stars produce prodigious amounts of 3He. This is inconsistent with the claim that all low-mass stars should destroy 3He.     

“大树进城”刍议

对近年来的“大树进城”之弊进行了剖析;并提出了相关建议。     

大数据在图书馆的应用研究与探讨

大数据作为一项新兴的信息技术,对图书馆的数据存贮、数据分析计算能力是一次检验,并会对传统图书馆业务产生不小的冲击。对于图书馆本身可以通过重视用户数据与信息、利用数据分析工具提高自身服务的创新应对考验与挑战。笔者对中美图书馆大数据应用现状做了对比,分析并阐述了大数据给图书馆带来的机会与影响,并对大数据在图书馆中的应用提出了建议。