Phase diagram of a two-component Fermi gas with resonant interactions

The pairing of fermions lies at the heart of superconductivity and superfluidity. The stability of these pairs determines the robustness of the superfluid state, and the quest for superconductors with high critical temperature equates to a search for systems with strong pairing mechanisms. Ultracold atomic Fermi gases present a highly controllable model system for studying strongly interacting fermions. Tunable interactions (through Feshbach collisional resonances) and the control of population or mass imbalance among the spin components provide unique opportunities to investigate the stability of pairing-and possibly to search for exotic forms of superfluidity. A major controversy has surrounded the stability of superfluidity against an imbalance between the two spin components when the fermions interact resonantly (that is, at unitarity). Here we present the phase diagram of a spin-polarized Fermi gas of (6)Li atoms at unitarity, experimentally mapping out the superfluid phases versus temperature and density imbalance. Using tomographic techniques, we reveal spatial discontinuities in the spin polarization; this is the signature of a first-order superfluid-to-normal phase transition, and disappears at a tricritical point where the nature of the phase transition changes from first-order to second-order. At zero temperature, there is a quantum phase transition from a fully paired superfluid to a partially polarized normal gas. These observations and the implementation of an in situ ideal gas thermometer provide quantitative tests of theoretical calculations on the stability of resonant superfluidity.     

Origin of ferromagnetic exchange interactions in a fullerene-organic compound

Organic ferromagnets, which exhibit exchange interactions between unpaired electrons in pi-orbitals, are rare, and the origin of ferromagnetism in these compounds has so far remained unexplained. Tetrakis(dimethylamino)ethylene-fullerene[60] (TDAE-C60) shows a transition to a ferromagnetic state with fully saturated s = 1/2 molecular spins at the relatively high Curie temperature (for organic materials) of 16 K (ref. 4). It has been suggested that the orientations of the C60 molecules may be important for ferromagnetism in this material, but in the absence of structural data at low temperatures there has been little progress towards understanding these microscopic interactions. Here we report the results of a comparative structural study of two different magnetic forms of TDAE-C60 crystals at low temperatures, correlating the structural properties--in particular, the intermolecular orientations--with the magnetic properties. We find that both ferromagnetism and spin-glass-like ordering are possible in this material, and depend on the orientational state of C60 molecules. This resolves the apparent contradictions posed by different macroscopic measurements, and opens the way to a microscopic understanding of pi-electron ferromagnetic exchange interactions in organic materials.     

Origin of the obliquities of the giant planets in mutual interactions in the early Solar System

The origin of the spin-axis orientations (obliquities) of the giant planets is a fundamental issue because if the obliquities resulted from tangential collisions with primordial Earth-sized protoplanets, then they are related to the masses of the largest planetesimals out of which the planets form. A problem with this mechanism, however, is that the orbital planes of regular satellites would probably be uncorrelated with the obliquities, contrary to observations. Alternatively, they could have come from an external twist that affected the orientation of the Solar System plane; but in this model, the outer planets must have formed too rapidly, before the event that produced the twist. Moreover, the model cannot be quantitatively tested. Here I show that the present obliquities of the giant planets were probably achieved when Jupiter and Saturn crossed the 1:2 orbital resonance during a specific migration process: different migration scenarios cannot account for the large observed obliquities. The existence of the regular satellites of the giant planets does not represent a problem in this model because, although they formed soon after the planetary formation, they can follow the slow evolution of the equatorial plane it produces.     

Volatile content of lunar volcanic glasses and the presence of water in the Moon's interior

The Moon is generally thought to have formed and evolved through a single or a series of catastrophic heating events, during which most of the highly volatile elements were lost. Hydrogen, being the lightest element, is believed to have been completely lost during this period. Here we make use of considerable advances in secondary ion mass spectrometry to obtain improved limits on the indigenous volatile (CO(2), H(2)O, F, S and Cl) contents of the most primitive basalts in the Moon-the lunar volcanic glasses. Although the pre-eruptive water content of the lunar volcanic glasses cannot be precisely constrained, numerical modelling of diffusive degassing of the very-low-Ti glasses provides a best estimate of 745 p.p.m. water, with a minimum of 260 p.p.m. at the 95 per cent confidence level. Our results indicate that, contrary to prevailing ideas, the bulk Moon might not be entirely depleted in highly volatile elements, including water. Thus, the presence of water must be considered in models constraining the Moon's formation and its thermal and chemical evolution.     

从古文字看算盘的起源

一般认为,算盘来源于算筹,但其产生于何时,迄今尚无定论.考诸古文字的玄、算、筭的形、音、义,都与贝串、玉贯有关,佐之以文献、考古和民俗材料的证据,认为:筹算和珠算,在产生上虽一先一后,但并非一个系统,珠算来源于币贯算,可能与筹算并行了好长时间.算盘直接来源于具有计数和计算双重功能的贝串、玉贯、钱贯,至迟产生于西周时期.     

土星盘面倾角的变化研究

根据地球、土星的平轨道根素和土星轴的指向,提出了一种计算土星盘面与地球观测者视线夹角的几何方法。计算表明土星的下一个秋分日为2025年5月22日,在2025年3月23日,地球将穿越土星盘面（土星侧对地球,盘面倾角为0°）。2017年10月16日（±1日）,土星盘的倾角达到最大,数值为26．99°。15年后的2032年5月11日（±1日）,土星盘的另一侧达到最大倾角,数值为-26．96°。土星轨道面相对于黄道面的倾角对计算结果的影响不超过±0．32°。     

试析“人日”的起源与礼俗

“人日”起源于人们对人自身的重视、对幸福美好生活的追求,人日具有节日饮食、节日装饰、登高赋诗与出游踏青、拜神及驱鬼除秽等多项礼俗内容。     

产β-内酰胺酶抑制剂菌株的筛选

本文先从不同环境来源的微生物中筛选出抗青霉素菌株作为试验菌，再从当地不同环境土要中分离了40种放线菌，7种细菌作为筛,了终找到了两株产β－内酰胺酶抑制剂的菌株，但活力不是很好，可作为出发菌株，用基因工程或诱变育种进一步变异达到高产效果。     

The development of a protoplanetary disk from its natal envelope

Class 0 protostars, the youngest type of young stellar objects, show many signs of rapid development from their initial, spheroidal configurations, and therefore are studied intensively for details of the formation of protoplanetary disks within protostellar envelopes. At millimetre wavelengths, kinematic signatures of collapse have been observed in several such protostars, through observations of molecular lines that probe their outer envelopes. It has been suggested that one or more components of the proto-multiple system NGC 1333-IRAS 4 (refs 1, 2) may display signs of an embedded region that is warmer and denser than the bulk of the envelope. Here we report observations that reveal details of the core on Solar System dimensions. We detect in NGC 1333-IRAS 4B a rich emission spectrum of H2O, at wavelengths 20-37 microm, which indicates an origin in extremely dense, warm gas. We can model the emission as infall from a protostellar envelope onto the surface of a deeply embedded, dense disk, and therefore see the development of a protoplanetary disk. This is the only example of mid-infrared water emission from a sample of 30 class 0 objects, perhaps arising from a favourable orientation; alternatively, this may be an early and short-lived stage in the evolution of a protoplanetary disk.     

Reflected light from sand grains in the terrestrial zone of a protoplanetary disk

In the standard model of terrestrial planet formation, the first step in the process is for interstellar dust to coagulate within a protoplanetary disk surrounding a young star, forming large grains that settle towards the disk plane. Interstellar grains of typical size approximately 0.1 microm are expected to grow to millimetre- (sand), centimetre- (pebble) or even metre-sized (boulder) objects rather quickly. Unfortunately, such evolved disks are hard to observe because the ratio of surface area to volume of their constituents is small. We readily detect dust around young objects known as 'classical' T Tauri stars, but there is little or no evidence of it in the slightly more evolved 'weak-line' systems. Here we report observations of a 3-Myr-old star, which show that grains have grown to about millimetre size or larger in the terrestrial zone (within approximately 3 au) of this star. The fortuitous geometry of the KH 15D binary star system allows us to infer that, when both stars are occulted by the surrounding disk, it appears as a nearly edge-on ring illuminated by one of the central binary components. This work complements the study of terrestrial zones of younger disks that have been recently resolved by interferometry.     

从形式之源流发展谈艺术的本质

在艺术史上,"形式"对于艺术的作用及与艺术本质的关系历来成为美学家争论的焦点,本文梳理美学史上有代表性的形式学说,从中吸取合理因素,获取对于艺术本质的认识,即艺术是情感的对象化形式.本文试从三方面进行分析:一、强调价值作用的形式阐明了某种审美理想;二、取得自主地位的形式表达某种审美情感;三、作为艺术本质的形式揭示了形式感的本质作用.于是审美理想,审美情感形式感是艺术构成的本质要素.艺术即形式是饱含了审美情感与表达某种审美理想,又传达出某种形式感的形式,形式感是它的生命线.还需明确的是本文所谈之形式与具体实存之形状无关,实指逻辑意义上之形式,哲学层面上之形式.     

开放型大尺度磁场对黑洞吸积盘过渡区能量的提取

在黑洞磁层理论的基础上,利用改进的等效电路方法推导出黑洞吸积盘过渡区的喷流功率的表达式(简称TL功率),并进一步比较TL与BZ、DL功率的相对重要性,结果表明:对于低自转黑洞,TL功率比BZ、DL功率明显占优势.此外,利用该文提出的模型获得的TL功率能很好地拟合两个3CRFRI射电星系的强喷流功率.     

成语来源的历史递减性原因试探

统计显示，成语的来源呈现一种时代越久远，数量越繁荣的特点。本文从成语的来源、成语自身的语言特点、成语形成的历时性以及成语在发展过程中各阶段为其提供的不同语料等方面进行了细致的分析，试图对这一现象做出一个比较全面合理的解释。     

试论二言诗至九言诗之源头

诗歌是中国古代文学瑰宝的重要组成部分,各种诗都有着各自的起源,而且相互之间又有不可分割的联系。     

基于磁盘动态镜像的技术实现

在网络系统中利用磁盘的静态镜像无法满足服务器系统数据及时更新的需求.提出了在Windows 2000 Server环境下,利用镜像功能对服务器的系统及其数据实现动态备份的方法,取得预期的效果.该方案投资少,易实现.     

Thermal history of Mars inferred from orbital geochemistry of volcanic provinces

Reconstruction of the geological history of Mars has been the focus of considerable attention over the past four decades, with important discoveries being made about variations in surface conditions. However, despite a significant increase in the amount of data related to the morphology, mineralogy and chemistry of the martian surface, there is no clear global picture of how magmatism has evolved over time and how these changes relate to the internal workings and thermal evolution of the planet. Here we present geochemical data derived from the Gamma Ray Spectrometer on board NASA's Mars Odyssey spacecraft, focusing on twelve major volcanic provinces of variable age. Our analysis reveals clear trends in composition that are found to be consistent with varying degrees of melting of the martian mantle. There is evidence for thickening of the lithosphere (17-25?km?Gyr(-1)) associated with a decrease in mantle potential temperature over time (30-40?K?Gyr(-1)). Our inferred thermal history of Mars, unlike that of the Earth, is consistent with simple models of mantle convection.     

Origin of the algae

Eukaryotic algae are traditionally separated into three broad divisions: the rhodophytes, the chromophytes and the chlorophytes. The evolutionary relationships between these groups, their links with other eukaryotes and with other photosynthetic groups, such as euglenophytes and cryptophytes, have been the subject of much debate and speculation. Here we analyse partial sequences of the large (28S) cytoplasmic ribosomal RNA from ten new species of protists belonging to various groups of unicellular algae. By combining them with the homologous sequences from 14 other unicellular and multicellular eukaryotes, we show that rhodophytes, chromophytes and chlorophytes emerge as three distinct groups late among eukaryotes, that is, close to the metazoa-metaphytes radiation. This implies a relatively late occurrence of eukaryotic photosynthetic symbiosis. We also provide details of intra- and inter-phyla relationships.