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.     

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.     

CO and H(3)(+) in the protoplanetary disk around the star HD141569

Massive planets have now been found orbiting about 80 stars. A long outstanding question critical to theories of planet formation has been the timescale on which gas-giant planets form; in particular, stars more massive than the Sun may blow away the surrounding gas associated with their formation more quickly than it can be accumulated by the protoplanetary cores. Evidence for a protoplanet around a Herbig AeBe star (such stars are 2 3 times more massive than the Sun) would constrain the timescale of planet formation. Here we report the detection of CO and H(3)(+) emission from the 5-10-million-year-old Herbig AeBe star HD141569. We interpret the CO data as indicating that the inner disk surrounding the star is past the early phase of accretion and planetesimal formation, and that most of the gas has been cleared out to a distance of more than 17 astronomical units. CO effectively destroys H(3)(+) (ref. 2), so their presence in the same source is surprising. Moreover, H(3)(+) line emission has previously been detected only from the atmospheres of the giant planets in the Solar System. The H(3)(+) and CO may therefore be distributed in the disk at different circumstellar distances, or, alternatively, H(3)(+) may be located in the extended envelope of a protoplanet.     

Water vapour in the atmosphere of a transiting extrasolar planet

Water is predicted to be among the most abundant (if not the most abundant) molecular species after hydrogen in the atmospheres of close-in extrasolar giant planets ('hot Jupiters'). Several attempts have been made to detect water on such planets, but have either failed to find compelling evidence for it or led to claims that should be taken with caution. Here we report an analysis of recent observations of the hot Jupiter HD 189733b (ref. 6) taken during the transit, when the planet passed in front of its parent star. We find that absorption by water vapour is the most likely cause of the wavelength-dependent variations in the effective radius of the planet at the infrared wavelengths 3.6 mum, 5.8 mum (both ref. 7) and 8 mum (ref. 8). The larger effective radius observed at visible wavelengths may arise from either stellar variability or the presence of clouds/hazes. We explain the report of a non-detection of water on HD 189733b (ref. 4) as being a consequence of the nearly isothermal vertical profile of the planet's atmosphere.     

The building blocks of planets within the 'terrestrial' region of protoplanetary disks

Our Solar System was formed from a cloud of gas and dust. Most of the dust mass is contained in amorphous silicates, yet crystalline silicates are abundant throughout the Solar System, reflecting the thermal and chemical alteration of solids during planet formation. (Even primitive bodies such as comets contain crystalline silicates.) Little is known about the evolution of the dust that forms Earth-like planets. Here we report spatially resolved detections and compositional analyses of these building blocks in the innermost two astronomical units of three proto-planetary disks. We find the dust in these regions to be highly crystallized, more so than any other dust observed in young stars until now. In addition, the outer region of one star has equal amounts of pyroxene and olivine, whereas the inner regions are dominated by olivine. The spectral shape of the inner-disk spectra shows surprising similarity with Solar System comets. Radial-mixing models naturally explain this resemblance as well as the gradient in chemical composition. Our observations imply that silicates crystallize before any terrestrial planets are formed, consistent with the composition of meteorites in the Solar System.     

Deficiency of molecular hydrogen in the disk of beta Pictoris

Molecular hydrogen (H2) is by far the most abundant material from which stars, protoplanetary disks and giant planets form, but it is difficult to detect directly. Infrared emission lines from H2 have recently been reported towards beta Pictoris, a star harbouring a young planetary system. This star is surrounded by a dusty 'debris disk' that is continuously replenished either by collisions between asteroidal objects or by evaporation of ices on Chiron-like objects. A gaseous disk has also been inferred from absorption lines in the stellar spectrum. Here we present the far-ultraviolet spectrum of beta Pictoris, in which H2 absorption lines are not seen. This allows us to set a very low upper limit on the column density of H2: N(H2) 6 x 10-4. As CO would be destroyed under ambient conditions in about 200 years (refs 9, 11), our result demonstrates that the CO in the disk arises from evaporation of planetesimals.     

Identification of iron sulphide grains in protoplanetary disks

Sulphur is depleted in cold dense molecular clouds with embedded young stellar objects, indicating that most of it probably resides in solid grains. Iron sulphide grains are the main sulphur species in cometary dust particles, but there has been no direct evidence for FeS in astronomical sources, which poses a considerable problem, because sulphur is a cosmically abundant element. Here we report laboratory infrared spectra of FeS grains from primitive meteorites, as well as from pyrrhotite ([Fe, Ni](1-x)S) grains in interplanetary dust, which show a broad FeS feature centred at approximately 23.5 micrometres. A similar broad feature is seen in the infrared spectra of young stellar objects, implying that FeS grains are an important but previously unrecognized component of circumstellar dust. The feature had previously been attributed to FeO. The observed astronomical line strengths are generally consistent with the depletion of sulphur from the gas phase, and with the average Galactic sulphur/silicon abundance ratio. We conclude that the missing sulphur has been found.     

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.     

圆盘反应器成膜性能的实验研究

在直径为0.48m圆盘反应器内研究了物料黏度、液位、圆盘转速等因素对反应器功率、最小成膜转速、持液量以及膜厚的影响规律。结果表明:最小成膜转速随黏度的增加而降低,随液位的降低而升高;持液量随黏度和转速增加而增大,黏度较低时增加的趋势低于黏度较高时;无因次混合时间随着线速度的增加先减小后增加;同时得到了功率准数以及膜厚的关联式。     

圆盘反应器内流动和成膜性能的数值模拟

采用流体体积函数法(VOF)对卧式旋转圆盘反应器的流动和成膜特性进行了数值模拟,并考察了圆盘转速和反应器内液位高度对液膜厚度及分布的影响规律。研究结果表明,VOF方法能够较好的模拟圆盘反应器内液膜的流动和成膜特性,反应器内液相流场、成膜过程、液膜厚度及分布的模拟数据与实验结果吻合良好;液膜厚度随圆盘转速增加而增大,液位高度的变化对其影响不大;圆盘成膜具有最低转速和最低液位;同时模拟得到了圆盘表面液膜的分布规律。     

准噶尔盆地腹部地区原油单体烃碳、氢同位素组成

选择准噶尔盆地腹部3个凹陷和隆起区不同储层中13个原油样品,进行了全油碳同位素组成分析,应用GC-MS,GC-IRMS和GC-TC-IRMS技术先后开展饱和烃生物标记化合物、正构烷烃单体碳、氢同位素组成分析.首先通过全油碳同位素组成和生物标记化合物参数将侏罗系原油和二叠系原油明显区分开,进一步通过饱和烃单体碳同位素分析将准噶尔盆地不同储层原油划分为两种类型及它们的过渡型:以侏罗系与二叠系乌尔禾组为代表的陆相淡水型和以石炭系与二叠系风城组为代表的咸水湖相型及两者的混合型,并对油藏在破坏和后期充注再成藏的过程中混合原油的单体碳同位素组成变化做了讨论.原油单体氢同位素组成对不同水环境和古纬度反应敏感,其明显的分馏效应在石炭系、二叠系和侏罗系原油中有很好的表现,据此可以对不同时期古环境进行很好的区分.     

圆盘近尾迹中低频不稳定特性研究

利用大涡模拟(LES)和热线实验测量手段,采用小波分析及FFT方法对Re=104的圆盘近尾迹中的特征频率进行了捕捉,着重对低频不稳定性进行了研究.LES和热线实验结果表明,圆盘近尾迹中除对应于剪切层Kelvin-Helmholtz不稳定的高频率StKH≈1.6和大尺度涡旋脱落频率StV≈0.14外,还存在两个低频率:StL1≈0.02和StL2≈0.03.进一步对导致低频不稳定性的物理机制进行了分析,发现低频率StL1≈0.02与涡旋脱落周向旋转有关,而低频率StL2≈0.03与回流区的伸缩运动有关.本研究合理解释了目前钝体绕流低频数值分散的原因.     

一次暴雨过程局地水汽和热力动力条件的综合观测分析

应用多种非常规探测资料对2010年7月18日和19日大理发生的暴雨天气过程进行了分析,结果表明:GPS探测的大气可降水量对降水的发生具有较好的指示意义,大气可降水量的急剧增(减)过程,预示着降水即将出现(消亡);辐射和湍流通量在暴雨发生前,存在明显变化;风廓线雷达的水平风和垂直风在暴雨过程中有很好的指示意义.     

幂律流体在旋转盘上的流动与传热数值分析

针对非牛顿幂律流体在无限大旋转圆盘上层流边界层内三维流动与传热问题,在普朗特数为常数的条件下,利用广义Karman相似变换,将连续方程、动量方程及能量方程形成的偏微分方程组化成常微分方程组,再采用多重打靶法数值求解非线性两点边值问题.分别针对剪薄型流体、牛顿流体和剪厚型流体,得到不同幂律指标下的速度和温度分布及不同普朗特数下温度场的结果.结果表明径向速度分量的峰值随幂律指标的增大而增大,轴向速度受边界层厚度的影响较突出,盘表面的传热随幂律指标和普朗特数都呈现递增趋势.最后将本文流场结果与Andersson等在不考虑传热情况下的结果进行比较表明吻合性较好.     

用Disk Manager2000管理和维护大容量硬盘

详细介绍了利用 Disk Manager2000对新硬盘进行安装及安装中盘符交错的问题。安装后如何对硬盘进行维护、分区等。其中介绍了重新分区、正确定位光驱盘符、不同盘之间的文件拷贝,以及怎样创建 For Dos 的启动盘。同时介绍了硬盘检测工具 Run SmartedFender 使用方法。