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.     

An early extrasolar planetary system revealed by planetesimal belts in beta Pictoris

beta Pictoris (beta Pic) is a main-sequence star with an edge-on dust disk that might represent a state of the early Solar System. The dust does not seem to be a remnant from the original protoplanetary disk, but rather is thought to have been generated from large bodies like planetesimals and/or comets. The history and composition of the parent bodies can therefore be revealed by determining the spatial distribution, grain size, composition and crystallinity of the dust through high-resolution mid-infrared observations. Here we report that the sub-micrometre amorphous silicate grains around beta Pic have peaks in their distribution around 6, 16 and 30 au (1 au is the Sun-Earth distance), whereas the crystalline and micrometre-sized amorphous silicate grains are concentrated in the disk centre. As sub-micrometre grains are blown quickly out from the system by radiation pressure from the central star, the peaks indicate the locations of ongoing dust replenishment, which originates from ring-like distributions of planetesimals or 'planetesimal belts'.     

Stabilization of the disk around beta Pictoris by extremely carbon-rich gas

The edge-on disk surrounding the nearby young star beta Pictoris is the archetype of 'debris disks', which are composed of dust and gas produced by collisions between--and evaporation of--planetesimals, analogues of Solar System comets and asteroids. These disks may provide insight into the formation and early evolution of terrestrial planets. Previous work on beta Pic concluded that the disk gas has roughly solar abundances of elements, but this poses a problem because such gas should rapidly be blown away from the star, contrary to observations showing a stable gas disk in keplerian rotation. Here we report the detection of singly and doubly ionized carbon (C II, C III) and neutral atomic oxygen (O I) gas in the beta Pic disk. Carbon is extremely overabundant relative to every other measured element. This appears to solve the problem of the stable gas disk, because the carbon overabundance should keep the gas disk in keplerian rotation. The overabundance may indicate that the gas is produced from material more carbon-rich than expected of Solar System analogues.     

Inhibin beta in central neural pathways involved in the control of oxytocin secretion

Inhibin (I) a gonadal hormone glycoprotein which suppresses follicle-stimulating hormone (FSH) secretion from the anterior pituitary, is a heterodimer consisting of an alpha subunit and one of two distinct beta subunits. S1 nuclease analysis has revealed that RNAs encoding all three subunits (alpha, beta A and beta B) are expressed in rat brain. We report here on the localization, and a potential function, of inhibin beta in the rat brain. A cell group centred in the nucleus of the solitary tract (NTS), a major recipient of visceral sensory information, was stained immunohistochemically with antisera against synthetic fragments of I beta, but not I alpha. The distribution of I beta-stained fibres is consistent with known NTS projections, and includes a prominent projection to oxytocinergic aspects of the magnocellular neurosecretory system.     

A role for ghrelin in the central regulation of feeding

Ghrelin is an acylated peptide that stimulates the release of growth hormone from the pituitary. Ghrelin-producing neurons are located in the hypothalamus, whereas ghrelin receptors are expressed in various regions of the brain, which is indicative of central-and as yet undefined-physiological functions. Here we show that ghrelin is involved in the hypothalamic regulation of energy homeostasis. Intracerebroventricular injections of ghrelin strongly stimulated feeding in rats and increased body weight gain. Ghrelin also increased feeding in rats that are genetically deficient in growth hormone. Anti-ghrelin immunoglobulin G robustly suppressed feeding. After intracerebroventricular ghrelin administration, Fos protein, a marker of neuronal activation, was found in regions of primary importance in the regulation of feeding, including neuropeptide Y6 (NPY) neurons and agouti-related protein (AGRP) neurons. Antibodies and antagonists of NPY and AGRP abolished ghrelin-induced feeding. Ghrelin augmented NPY gene expression and blocked leptin-induced feeding reduction, implying that there is a competitive interaction between ghrelin and leptin in feeding regulation. We conclude that ghrelin is a physiological mediator of feeding, and probably has a function in growth regulation by stimulating feeding and release of growth hormone.     

Localization and the possible role of plasminogen activators and inhibitors in early stages of placentation

The distribution of mRNAs of tissue type (t) and urokinase type (u) plasminogen activator (PA) plus their corresponding inhibitors, type-1 (PAI-1) and type-2 (PAI-2) have been studied in the tissues of human first and second trimester placentae by in situ hybridization. The results show that: (ⅰ) All the molecules, tPA, uPA, PAI-1 and PAI-2, were identified in the blood vessels, the majority of extravillous trophoblastic cells of the decidual layer between Rohr’s and Nitabuch’s stria and in the trophoblast cells lining the chorionic plate, basal plate, intercotyledonary septae and cytotrophoblast cells of the chorionic villous tree. (ⅱ) No expression of such probes was observed in the basal and chorionic plate, glandular cells of the decidua, the septal tissues or the villous core mesenchyme. The co-distribution of the molecules observed suggests that the co-ordinated expression of the activators and inhibitors in various cells of the placental tissue may play a role in angiogenesis related to conversion of spiral arteries into utero-placental arteries and establishment of a chorio-decidual blood flow during early stages of placentation.     

A central role for JNK in obesity and insulin resistance

Obesity is closely associated with insulin resistance and establishes the leading risk factor for type 2 diabetes mellitus, yet the molecular mechanisms of this association are poorly understood. The c-Jun amino-terminal kinases (JNKs) can interfere with insulin action in cultured cells and are activated by inflammatory cytokines and free fatty acids, molecules that have been implicated in the development of type 2 diabetes. Here we show that JNK activity is abnormally elevated in obesity. Furthermore, an absence of JNK1 results in decreased adiposity, significantly improved insulin sensitivity and enhanced insulin receptor signalling capacity in two different models of mouse obesity. Thus, JNK is a crucial mediator of obesity and insulin resistance and a potential target for therapeutics.     

A physiological role for GABAB receptors in the central nervous system

The role of GABA in synaptic transmission in the mammalian central nervous system is more firmly established than for any other neurotransmitter. With virtually every neuron studied, the synaptic action of GABA is mediated by bicuculline-sensitive GABAA receptors which selectively increase chloride conductance. However, it has been shown that GABA has a presynaptic inhibitory action on transmitter release that is insensiive to bicuculline and is selectively mimicked by baclofen. The receptors involved in this action are referred to as GABAB receptors, to distinguish them from the classic bicuculline-sensitive GABAA receptors. In hippocampal pyramidal cells an additional postsynaptic action of GABA and baclofen has been reported that is also insensitive to GABAA antagonists, and may be mediated by GABAB receptors on the postsynaptic neuron. This action of GABA and baclofen involves an increase in potassium conductance. Synaptic activation of pathways converging on hippocampal pyramidal cells results in a slow inhibitory postsynaptic potential which involves an increase in potassium conductance, and it has been suggested that GABAB receptors might be responsible for this synaptic potential. However, to establish convincingly that GABAB receptors are physiologically important in the central nervous system, a selective GABAB antagonist is required. Here we provide this missing evidence. Using the hippocampal slice preparation, we now report that the phosphonic acid derivative of baclofen, phaclofen, is a remarkably selective antagonist of both the postsynaptic action of baclofen and the bicuculline-resistant action of GABA, and that it selectively abolishes the slow inhibitory postsynaptic potential in pyramidal cells.     

框架在导航型课件开发中的核心作用

利用Authorware编写结构复杂的综合程序时，要做到所编写的程序结构简洁明了、易读性强、便于多人同时开发和以后的修改，离不开框架（含导航图标）的灵活使用．系统变量和系统函数是Authorware的高级应用，而框架则是编写Authorware程序的一个核心和支架，程序的各功能模块通过支架从而便于组织和控制。尤其是在课件开发中框架的作用和地位对编程是很重要的．     

高能不等核碰撞中的参与者数和二元核子核子碰撞数

采用核核碰撞的Glauber模型,给出了高能d核与Au核在不同对心碰撞中的参与者数与二元核子核子碰撞数,所得结果与RHIC PHOBOS合作组给出的结果相吻合.     

坚持创新核心地位，建设世界科技强国

 推动高质量发展、实现人民高品质生活、构建新发展格局、顺利开启全面建设社会主义现代化国家新征程对加快建设世界科技强国提出了更为迫切的需求。面对新发展阶段科技创新和创新发展的新形势与新任务,必须坚持创新在现代化建设全局中的核心地位,坚持自立自强、全面创新、系统治理、开放融合原则,增强科技创新系统供给、支撑、引领能力,提升科技自立自强水平,进而强化科技自立自强对国家发展的战略支撑。     

The possible pivotal role of the eastward dust transport from Central Asia in the global temperature decrease

It is generally considered that the occurrence of glacial-interglacial gyrations can be explained with the Milankovitch theory. However, the solutions of some problems in the theory are currently not derived yet. After researching the eastward dust transport from Central Asia, we have found that there is a positive feedback mechanism between the eastward dust transport and the global temperature decrease. This magnifies the effect of solar radiation change in the high-latitude Hemisphere, and results in area of the Northern the occurrence of the global glacial epoch. The positive feedback mechanism starts with the reduction of solar radiation in the high-latitude area of the Northern Hemisphere. Subsequently, the global temperature decreases and global glacial epoch occurs, in which the pivotal fac- tor is the eastward dust transport from Central Asia. With the theory of the positive feedback mechanism, some problems in the Milankovitch theory can be solved well.