Activity-dependent homeostatic specification of transmitter expression in embryonic neurons

Neurotransmitters are essential for interneuronal signalling, and the specification of appropriate transmitters in differentiating neurons has been related to intrinsic neuronal identity and to extrinsic signalling proteins. Here we show that altering the distinct patterns of Ca2+ spike activity spontaneously generated by different classes of embryonic spinal neurons in vivo changes the transmitter that neurons express without affecting the expression of markers of cell identity. Regulation seems to be homeostatic: suppression of activity leads to an increased number of neurons expressing excitatory transmitters and a decreased number of neurons expressing inhibitory transmitters; the reverse occurs when activity is enhanced. The imposition of specific spike frequencies in vitro does not affect labels of cell identity but again specifies the expression of transmitters that are inappropriate for the markers they express, during an early critical period. The results identify a new role of patterned activity in development of the central nervous system.     

模糊综合评判与AHP的联系

模糊综合评判是一种对对象进行综合分类的方法，能解决传统观点看来无法进行数量分析的问题。层次分析法（AHP）可以对非定量事物作定量分析，对人们的主观判断作客观描述。本文给出了AHP中内部独立的递阶层次结构合成排序的概率解释，讨论了模糊综合评判与AHP的联系。     

微波对陶瓷材料的作用

研究了微波对陶瓷材料的作用,综合了Ｍａｘｗｅｌ电磁理论及介质理论,从理论上分析了微波与物质相互作用的机理。指出了介质吸收微波源于介质对微波的电导损耗和极化损耗,高温下,电导损耗将占主要地位。即使在介质吸收为零的情况下,由于介质的反射,微波也不能百分之百穿过介质。利用微波加热物质,物质的损耗有一定的限制,对于２．４５ＧＨｚ的微波,物质电导率应在１０－４～１Ω－１ｃｍ－１之间。对微波场中非均匀固体的行为进行了简单的分析和预测。     

CH4／CO2催化重整制取合成气

采用微型固定床反应装置,评价了现有工业上７种催化剂。考察了３７７１的焙烧温度、焙烧时间、还原温度、不 及反应温度对ＣＨ４／ＣＯ２催化重整反应性能的影响。使用该催化剂合成气的收率最高。     

基于高相关指标综合排名方法的研究

文章用主成分分析、加权平均、平均秩对一个实例的综合排名进行研究和比较,给出在高相关指标情行下,平均秩法在综合排名中具有一定的可行性和有效性.     

粉煤灰全尾砂胶结充填料

实验选取了Ⅰ级和Ⅱ级两种粉煤灰,以石灰和脱硫石膏为激发剂制备的胶凝材料完全取代传统的胶结剂水泥,以胶砂比为1∶4,水胶比为1∶1左右制备的粉煤灰全尾砂充填料在45±1℃下养护3 d,强度可达5.432 MPa,在20±1℃下养护28 d强度可达3～7 MPa,满足一般矿山对充填料的要求.根据料浆质量分数和坍落度关系曲线,得到了该材料制备成的可泵送膏体质量分数范围为80.5%～83.0%.通过X射线衍射和扫描电镜分析,胶凝材料的水化产物主要为凝胶类物质、钙矾石和方解石.     

Crowding induces live cell extrusion to maintain homeostatic cell numbers in epithelia

For an epithelium to provide a protective barrier, it must maintain homeostatic cell numbers by matching the number of dividing cells with the number of dying cells. Although compensatory cell division can be triggered by dying cells, it is unknown how cell death might relieve overcrowding due to proliferation. When we trigger apoptosis in epithelia, dying cells are extruded to preserve a functional barrier. Extrusion occurs by cells destined to die signalling to surrounding epithelial cells to contract an actomyosin ring that squeezes the dying cell out. However, it is not clear what drives cell death during normal homeostasis. Here we show in human, canine and zebrafish cells that overcrowding due to proliferation and migration induces extrusion of live cells to control epithelial cell numbers. Extrusion of live cells occurs at sites where the highest crowding occurs in vivo and can be induced by experimentally overcrowding monolayers in vitro. Like apoptotic cell extrusion, live cell extrusion resulting from overcrowding also requires sphingosine 1-phosphate signalling and Rho-kinase-dependent myosin contraction, but is distinguished by signalling through stretch-activated channels. Moreover, disruption of a stretch-activated channel, Piezo1, in zebrafish prevents extrusion and leads to the formation of epithelial cell masses. Our findings reveal that during homeostatic turnover, growth and division of epithelial cells on a confined substratum cause overcrowding that leads to their extrusion and consequent death owing to the loss of survival factors. These results suggest that live cell extrusion could be a tumour-suppressive mechanism that prevents the accumulation of excess epithelial cells.     

Charge self-regulation upon changing the oxidation state of transition metals in insulators

Transition-metal atoms embedded in an ionic or semiconducting crystal can exist in various oxidation states that have distinct signatures in X-ray photoemission spectroscopy and 'ionic radii' which vary with the oxidation state of the atom. These oxidation states are often tacitly associated with a physical ionization of the transition-metal atoms--that is, a literal transfer of charge to or from the atoms. Physical models have been founded on this charge-transfer paradigm, but first-principles quantum mechanical calculations show only negligible changes in the local transition-metal charge as the oxidation state is altered. Here we explain this peculiar tendency of transition-metal atoms to maintain a constant local charge under external perturbations in terms of an inherent, homeostasis-like negative feedback. We show that signatures of oxidation states and multivalence--such as X-ray photoemission core-level shifts, ionic radii and variations in local magnetization--that have often been interpreted as literal charge transfer are instead a consequence of the negative-feedback charge regulation.     

自主学习在地理课堂教学中的有效应用

自主学习能使学习者形成好的学习习惯 ,改变学习态度 .在学习中发现客观世界和地理知识之间的必然联系 ,充分表达自己的观点 ,积极地获得知识和技能 ,从而提高学习者观察、思维、推理及解决问题的能力 .     

烯胺酮类化合物的合成方法

烯胺酮是目前应用较为广泛的有机合成中间体,根据成键形式的不同对其合成方法进行了综述.     

专家综合评判方法

作者提出了两种通过专家评议、确定评议对象优劣的综合评判方法,即等级评判法和比较评判法,并从理论上证明了所得结果至少是多目标问题的有效解。     

生物柴油的合成技术

综述了生物柴油生产的原料、催化剂、合成方法和生产工艺等相关研究进展.目前生物柴油工业化生产主要采用的均相酸、碱催化酯交换反应,很多都是在常压、低温下进行,其优点是反应转化率高,但是废催化剂会带来环境问题;非均相催化剂和酶催化剂则是目前研究的热点,固体碱、固定化酶等催化剂可以很容易实现与反应产物的分离;高温高压技术、超临界技术等也被用于酯交换反应过程.综合分析了国内外生物柴油的发展现状,提出生物柴油是一种极具发展前景的清洁燃料以及我国发展生物柴油的几点建议.     

Synthetic Absorbable Surgical Sutures

This paper reviewed all types of the polymer - based synthetic absorbable surgical sutures that have been commercially produced. The chemical component, biological and mechanical properties, and using effect of these sutures were discussed. The recent development and the possible coming research orientation in these areas were also presented.