The evolution of comets in the Oort cloud and Kuiper belt

Comets are remnants from the time when the outer planets formed, approximately 4-4.5 billion years ago. They have been in storage since then in the Oort cloud and Kuiper belt-distant regions that are so cold and sparsely populated that it was long thought that comets approaching the Sun were pristine samples from the time of Solar System formation. It is now recognized, however, that a variety of subtle but important evolutionary mechanisms operate on comets during their long storage, so they can no longer be regarded as wholly pristine.     

Rapid evolution of the most luminous galaxies during the first 900 million years

The first 900 million years (Myr) to redshift z approximately 6 (the first seven per cent of the age of the Universe) remains largely unexplored for the formation of galaxies. Large samples of galaxies have been found at z approximately 6 (refs 1-4) but detections at earlier times are uncertain and unreliable. It is not at all clear how galaxies built up from the first stars when the Universe was about 300 Myr old (z approximately 12-15) to z approximately 6, just 600 Myr later. Here we report the results of a search for galaxies at z approximately 7-8, about 700 Myr after the Big Bang, using the deepest near-infrared and optical images ever taken. Under conservative selection criteria we find only one candidate galaxy at z approximately 7-8, where ten would be expected if there were no evolution in the galaxy population between z approximately 7-8 and z approximately 6. Using less conservative criteria, there are four candidates, where 17 would be expected with no evolution. This demonstrates that very luminous galaxies are quite rare 700 Myr after the Big Bang. The simplest explanation is that the Universe is just too young to have built up many luminous galaxies at z approximately 7-8 by the hierarchical merging of small galaxies.     

Changing role of even-skipped during the evolution of insect pattern formation.

The development of Drosophila is typical of the so-called long germband mode of insect development, in which the pattern of segments is established by the end of the blastoderm stage. Short germband insects, such as the grasshopper Schistocerca americana, by contrast, generate all or most of their metameric pattern after the blastoderm stage by the sequential addition of segments during caudal elongation. This difference is discernible at the molecular level in the pattern of initiation of the segment polarity gene engrailed, and the homeotic gene abdominal-A (ref. 5). For example, in both types of insects, engrailed is expressed by the highly conserved germband stage in a pattern of regularly spaced stripes, one stripe per segment. In Drosophila, the complete pattern is visible by the end of the blastoderm stage, although engrailed appears initially in alternate segments in a pair-rule pattern that reflects its known control by pair-rule genes such as even-skipped. In contrast, in the grasshopper, the engrailed stripes appear one at a time after the blastoderm stage as the embryo elongates. To address the molecular basis for this difference, we have cloned the grasshopper homologue of the Drosophila pair-rule gene even-skipped and show that it does not serve a pair-rule function in early development, although it does have a similar function in both insects during neurogenesis later in development.     

层状云微物理结构演变特征的个例研究

在人工增雨作业的同时,利用机载粒子测量系统对一次降水云系的探测资料进行了深入分析,给出了云和降水的宏微观结构演变特性,研究表明：（１）层状云中的中小尺度降水云区,是造成地面降水分布不均匀的物理原因;（２）云滴浓度与平均直径之间呈负相关关系;（３）支滴谱的垂直分布是典型的３种类型;（４）层状云微结构在水平方向上的起伏较大,存在４种不同类型。     

Rapid evolution of male reproductive genes in the descent of man

A diverse body of morphological and genetic evidence has suggested that traits pertaining to male reproduction may have evolved much more rapidly than other types of character. Recently, DNA sequence comparisons have also shown a very high level of divergence in male reproductive proteins between closely related Drosophila species, among marine invertebrates and between mouse and rat. Here we show that rapid evolution of male reproductive genes is observable in primates and is quite notable in the lineages to human and chimpanzee. Nevertheless, rapid evolution by itself is not necessarily an indication of positive darwinian selection; relaxation of negative selection is often equally compatible with the DNA sequence data. By taking three statistical approaches, we show that positive darwinian selection is often the driving force behind this rapid evolution. These results open up opportunities to test the hypothesis that sexual selection plays some role in the molecular evolution of higher primates.     

Rapid evolution of reproductive barriers driven by sexual conflict

A growing amount of experimental data indicates extremely rapid evolution of traits and proteins related to fertilization in many diverging taxa. These data come from studies of sperm or pollen competition between closely related species, and from molecular studies of fertilization proteins. The positive selection for evolutionary novelty that appears to be acting on fertilization systems seems paradoxical because successful reproduction requires the close matching of female and male traits. It has been suggested that perpetual coevolution between the sexes can result from sexual conflict in mating. Sexual conflict occurs when characteristics that enhance the reproductive success of one sex reduce the fitness of the other sex. Numerous examples of sexual conflict resulting from sensory exploitation, polyspermy and the cost of mating have been discussed in detail. The potential for coevolution due to such conflict has been evaluated experimentally. Here I develop a simple mathematical model describing coevolutionary dynamics of male and female traits involved in reproduction. The model shows that continual change in such traits at a constant speed is expected whenever females (or eggs) experience fitness loss from having too many compatible males (or sperms). The plausibility of runaway coevolution increases with increasing population size. Rapid evolution of reproductive barriers driven by sexual conflict may explain increased speciation rates after colonization of new habitats ('adaptive radiation') and high species richness in resource-rich environments.     

渤南凹陷构造演化与超压形成及演化过程的关系分析

盆地的构造演化通过构造活动、沉积体系控制了异常压力的发育,同时异常压力的存在对后期形成的断层有影响.本文通过双元孔隙度演化函数建模对渤南凹陷的古压力进行了恢复,研究表明,渤南凹陷的异常压力主要在裂陷期末开始发育,在坳陷期达到最大.同时由于异常压力的存在引起了流体压裂,对南部缓坡带盆倾断层的形成具有诱导作用.     

可变的广义Chaplygin气体的演化及其结构形成

在Friedmann理论框架下,将可变的广义Chaplygin气体（VGCG）作为一种暗能量模型,研究了与其相关的宇宙学量的演化规律.在此基础上,通过导出相关的物理量（诸如：物质的密度反差,增长变量和增长因子）所满足的运动方程,并对其求数值解,我们不仅给出了它们的演化图,深入探讨了相应的演化规律,而且还与ΛCDM模型做比较,讨论了此暗能量模型对宇宙结构形成的影响.研究结果表明,当今宇宙是从过去的减速膨胀演化为现在乃至将来的加速膨胀,并且在近阶段可以模拟ΛCDM模型的演化,它与目前的天文观测符合得较好.     

百色盆地古近系那读组和百岗组层序地层划分与沉积演化

野外剖面显示百色盆地古近系那读组内部、那读组与百岗组之间存在不整合面。综合分析地震、测井等资料,将盆地古近系那读组和百岗组划分为1个二级层序,3个三级层序。那读组那三段构成三级层序的层序Ⅰ,那读组那二和那一段构成三级层序的层序Ⅱ,百岗组构成三级层序的层序Ⅲ。层序Ⅰ和层序Ⅱ是盆地断陷期的沉积,具有相似的充填特征,层序Ⅲ是盆地坳陷期的沉积。层序Ⅱ既发育厚度大、分布范围广的深湖亚相泥岩,又发育河流相、三角洲相和扇三角洲相砂岩,是盆地内主要的生储盖组合发育层序。盆地北部层序Ⅱ,Ⅲ发育的扇三角洲是盆地有利储集岩。各层序低水位体系域发育长轴分布的河流相和三角洲相砂岩,这些砂岩是盆地隐蔽性圈闭勘探的有利储层。     

百色盆地古近系那读组和百岗组层序地层划分与沉积演化

野外剖面显示百色盆地古近系那读组内部、那读组与百岗组之间存在不整合面。综合分析地震、测井等资料,将盆地古近系那读组和百岗组划分为1个二级层序,3个三级层序。那读组那三段构成三级层序的层序Ⅰ,那渎组那二和那一段构成三级层序的层序Ⅱ,百岗组构成三级层序的层序Ⅲ。层序Ⅰ和层序Ⅱ是盆地断陷期的沉积,具有相似的充填特征,层序Ⅲ是盆地坳陷期的沉积。层序Ⅱ既发育厚度大、分布范围广的深湖亚相泥岩,又发育河流相、三角洲相和扇三角洲相砂岩,是盆地内主要的生储盖组合发育层序。盆地北部层序Ⅱ,Ⅲ发育的扇三角洲是盆地有利储集岩。各层序低水位体系域发育长轴分布的河流相和三角洲相砂岩,这些砂岩是盆地隐蔽性圈闭勘探的有利储层。     

Rapid kinetics of second messenger formation in olfactory transduction

Olfactory transduction is thought to be mediated by a membrane-bound receptor protein initiating a multistep reaction cascade which ultimately leads to a depolarizing generator current. There is considerable evidence for the involvement of adenylate cyclase in vertebrate olfactory transduction, and some data indicate that phospholipase C may have a central role in insect olfaction. However, one must show that odorants not only stimulate enzyme activity but also induce changes in concentrations of relevant second messengers. One important criterion for a candidate second messenger of chemo-electrical transduction is that its formation must precede the onset of the odorant-induced membrane permeability changes which proceed on a subsecond time-scale. Here we report an odorant-induced, transient accumulation of cyclic AMP in isolated olfactory cilia from rats, and the generation of inositol trisphosphate in antennal preparations from insects, both of which show subsecond time courses that are sufficiently rapid to mediate the odorant-regulated permeability of olfactory receptor cells.     

Determining the ages of comets from the fraction of crystalline dust

The timescale for the accretion of bodies in the disk surrounding a young star depends upon a number of assumptions, but there are few observational constraints. In our own Solar System, measurements of meteoritic components can provide information about the inner regions of the nebula, but not the outer parts. Observations of the evolution of more massive protostellar systems (Herbig Ae/Be stars) imply that significant changes occur in the physical properties of their dust with time. The simplest explanation is that thermal annealing of the original, amorphous grains in the hot inner nebula slowly increases the fractional abundance of crystalline material over time. Crystalline dust is then transported outward, where it is incorporated into comets that serve as a long-term reservoir for dust disks, such as that surrounding Beta Pictoris. Here we show that when applied to our own Solar System, this process can explain observed variations in both the volatile and dusty components of comets, while also providing a natural indicator of a comet's mean formation age. Studies of comets with different dust contents can therefore be used to investigate the timescales of the early Solar System.     

Simulations of the formation, evolution and clustering of galaxies and quasars

The cold dark matter model has become the leading theoretical picture for the formation of structure in the Universe. This model, together with the theory of cosmic inflation, makes a clear prediction for the initial conditions for structure formation and predicts that structures grow hierarchically through gravitational instability. Testing this model requires that the precise measurements delivered by galaxy surveys can be compared to robust and equally precise theoretical calculations. Here we present a simulation of the growth of dark matter structure using 2,160(3) particles, following them from redshift z = 127 to the present in a cube-shaped region 2.230 billion lightyears on a side. In postprocessing, we also follow the formation and evolution of the galaxies and quasars. We show that baryon-induced features in the initial conditions of the Universe are reflected in distorted form in the low-redshift galaxy distribution, an effect that can be used to constrain the nature of dark energy with future generations of observational surveys of galaxies.     

青藏高原盆地系统演化与高原形成时间

青藏高原在以时间为坐标的隆升过程中,高原的范围、高度都是呈阶段性递增的.随着青藏高原的构造隆升,在高原的内部和外围发育了众多的沉积盆地,在这些沉积盆地中详细地记录了青藏高原的隆升过程.高原北部盆地的演化显示出向北递进增长的特征,以南北挤压为动力背景的北部前陆盆地演化代表了盆地对高原周缘造山带的响应关系:金沙江缝合带、昆仑山、祁连山的新生代逆冲抬升的时间分别为53 Ma、46 Ma和29.5 Ma.对高原南北盆地-造山带的构造演化对比发现:祁连山和高喜马拉雅的逆冲时间相同,说明青藏高原在渐新世基本定型.     

A collisional family of icy objects in the Kuiper belt

The small bodies in the Solar System are thought to have been highly affected by collisions and erosion. In the asteroid belt, direct evidence of the effects of large collisions can be seen in the existence of separate families of asteroids--a family consists of many asteroids with similar orbits and, frequently, similar surface properties, with each family being the remnant of a single catastrophic impact. In the region beyond Neptune, in contrast, no collisionally created families have hitherto been found. The third largest known Kuiper belt object, 2003 EL61, however, is thought to have experienced a giant impact that created its multiple satellite system, stripped away much of an overlying ice mantle, and left it with a rapid rotation. Here we report the discovery of a family of Kuiper belt objects with surface properties and orbits that are nearly identical to those of 2003 EL61. This family appears to be fragments of the ejected ice mantle of 2003 EL61.     

英吉苏凹陷天然气藏成岩演化模式及成藏机理

在对英吉苏凹陷基本地质条件、次生孔隙的形成、成岩序列分析及成岩演化阶段划分的基础上,建立了英吉苏凹陷天然气藏的成岩演化模式,研究了英吉苏凹陷天然气的成藏机理,建立了成藏模式.结果表明:英吉苏凹陷具备了形成大中型气藏的地质条件和成藏要素.研究结论对塔里木盆地气藏分布规律的研究以及寻找新的油气资源提供必要的依据.     

Laboratory models of the thermal evolution of the mantle during rollback subduction

The subduction of oceanic lithosphere plays a key role in plate tectonics, the thermal evolution of the mantle and recycling processes between Earth's interior and surface. Information on mantle flow, thermal conditions and chemical transport in subduction zones come from the geochemistry of arc volcanoes, seismic images and geodynamic models. The majority of this work considers subduction as a two-dimensional process, assuming limited variability in the direction parallel to the trench. In contrast, observationally based models increasingly appeal to three-dimensional flow associated with trench migration and the sinking of oceanic plates with a translational component of motion (rollback). Here we report results from laboratory experiments that reveal fundamental differences in three-dimensional mantle circulation and temperature structure in response to subduction with and without a rollback component. Without rollback motion, flow in the mantle wedge is sluggish, there is no mass flux around the plate and plate edges heat up faster than plate centres. In contrast, during rollback subduction flow is driven around and beneath the sinking plate, velocities increase within the mantle wedge and are focused towards the centre of the plate, and the surface of the plate heats more along the centreline.     

博格达山隆升对北三台地区构造形成与演化的控制作用

对博格达山前北三台地区大量二、三维地震剖面进行了分析与解释 ,并建立了该区的构造格架。北三台凸起是研究区的主体 ,构造特征可概括为一核、二坡、三鼻、四断和多条环形地层尖灭线。发育的断裂多为区域性的 ,由于受造山带隆升的影响 ,断裂的长期活动控制了地层的沉积及岩相的展布。对地震剖面和古地质图的分析表明 ,北三台地区的构造形成与演化受博格达造山带隆升产生的压陷挠曲作用控制。依据造山带隆升过程 ,将研究区的构造演化分为造山期压陷挠曲盆地发育阶段、弱挤压挠曲性质的陆内坳陷发育阶段、陆内坳陷压陷盆地发育阶段和再生前陆盆地发育阶段。其中海西运动晚期和燕山运动中期 (Ⅱ幕 )对研究区的构造格局起了定型作用     

Distant metastasis occurs late during the genetic evolution of pancreatic cancer

Metastasis, the dissemination and growth of neoplastic cells in an organ distinct from that in which they originated, is the most common cause of death in cancer patients. This is particularly true for pancreatic cancers, where most patients are diagnosed with metastatic disease and few show a sustained response to chemotherapy or radiation therapy. Whether the dismal prognosis of patients with pancreatic cancer compared to patients with other types of cancer is a result of late diagnosis or early dissemination of disease to distant organs is not known. Here we rely on data generated by sequencing the genomes of seven pancreatic cancer metastases to evaluate the clonal relationships among primary and metastatic cancers. We find that clonal populations that give rise to distant metastases are represented within the primary carcinoma, but these clones are genetically evolved from the original parental, non-metastatic clone. Thus, genetic heterogeneity of metastases reflects that within the primary carcinoma. A quantitative analysis of the timing of the genetic evolution of pancreatic cancer was performed, indicating at least a decade between the occurrence of the initiating mutation and the birth of the parental, non-metastatic founder cell. At least five more years are required for the acquisition of metastatic ability and patients die an average of two years thereafter. These data provide novel insights into the genetic features underlying pancreatic cancer progression and define a broad time window of opportunity for early detection to prevent deaths from metastatic disease.