Specification and morphogenesis of astrocytes

Astrocytes are the most abundant cell type in the mammalian brain. Interest in astrocyte function has increased dramatically in recent years because of their newly discovered roles in synapse formation, maturation, efficacy, and plasticity. However, our understanding of astrocyte development has lagged behind that of other brain cell types. We do not know the molecular mechanism by which astrocytes are specified, how they grow to assume their complex morphologies, and how they interact with and sculpt developing neuronal circuits. Recent work has provided a basic understanding of how intrinsic and extrinsic mechanisms govern the production of astrocytes from precursor cells and the generation of astrocyte diversity. Moreover, new studies of astrocyte morphology have revealed that mature astrocytes are extraordinarily complex, interact with many thousands of synapses, and tile with other astrocytes to occupy unique spatial domains in the brain. A major challenge for the field is to understand how astrocytes talk to each other, and to neurons, during development to establish appropriate astrocytic and neuronal network architectures.     

Protein translocation across biological membranes

Subcellular compartments have unique protein compositions, yet protein synthesis only occurs in the cytosol and in mitochondria and chloroplasts. How do proteins get where they need to go? The first steps are targeting to an organelle and efficient translocation across its limiting membrane. Given that most transport systems are exquisitely substrate specific, how are diverse protein sequences recognized for translocation? Are they translocated as linear polypeptide chains or after folding? During translocation, how are diverse amino acyl side chains accommodated? What are the proteins and the lipid environment that catalyze transport and couple it to energy? How is translocation coordinated with protein synthesis and folding, and how are partially translocated transmembrane proteins released into the lipid bilayer? We review here the marked progress of the past 35 years and salient questions for future work. Subcellular compartments have unique protein compositions, yet protein synthesis only occurs in the cytosol and in mitochondria and chloroplasts. How do proteins get where they need to go? The first steps are targeting to an organelle and efficient translocation across its limiting membrane. Given that most transport systems are exquisitely substrate specific, how are diverse protein sequences recognized for translocation? Are they translocated as linear polypeptide chains or after folding? During translocation, how are diverse amino acyl side chains accommodated? What are the proteins and the lipid environment that catalyze transport and couple it to energy? How is translocation coordinated with protein synthesis and folding, and how are partially translocated transmembrane proteins released into the lipid bilayer? We review here the marked progress of the past 35 years and salient questions for future work.     

Neuroscience. Early insult rewires pain circuits

On page 628, neuroscientists report that painful stimuli delivered to rats shortly after birth permanently rewire the spinal cord circuits that respond to pain. Not only do the circuits contain more axons, but the axons extend to more areas of the spinal cord than they normally would. The results should help convince skeptics of the importance of managing pain in human infants.     

做好党的创新理论传播者——试论高校思想政治课教师的责任观

高校思想政治课教师能否适应时代发展的要求,准确把握思想政治课教育工作的责任和使命,做好党的创新理论传播者,是高校思想政治课教师义不容辞的政治责任和崇高使命。高校思想政治课教师要自觉增强自身的政治责任意识,具备坚实的专业基础和复合型知识结构,经历角色的定位转换,才能自觉做好党的创新理论传播者。     

Neuroscience. Video game images persist despite amnesia

On page 350, researchers report the results of new work in which they used the computer game Tetris--which involves using spatial reasoning to slot falling blocks strategically into place--to study how the brain reviews what it has learned. The researchers found that people who have just learned to play Tetris have vivid images of the game pieces floating before their eyes as they fall asleep, a phenomenon the researchers say is critical for building memories. Much more surprisingly, the team also found that the images appear to people with amnesia who have played the game--even though they have no recollection of having done so.     

Josephson tunnel-junction electrode materials

Josephson superconducting devices of the tunnel-junction type have exciting potential for use in building ultrahigh-speed computers. We consider the properties of superconducting metals that are needed for such devices that would be used in integrated computer circuits operated at a temperature near absolute zero. Recent advances in lead-alloy thin-film materials are described that have led to substantial improvements in lead-alloy Josephson device reliability. The properties of a Pb(0.84)In(0.12)Au(0.04) alloy, of Nb, and of Nb(3)Sn are discussed as examples of three different groups of materials that are of interest. Investigations of lead-alloy and niobium devices have progressed to the point that it is evident that they have good potential for fabricating integrated circuits containing large numbers of devices.     

Reprogramming control of an allosteric signaling switch through modular recombination

Many eukaryotic signaling proteins are composed of simple modular binding domains, yet they can display sophisticated behaviors such as allosteric gating and multi-input signal integration, properties essential for complex cellular circuits. To understand how such behavior can emerge from combinations of simple domains, we engineered variants of the actin regulatory protein N-WASP (neuronal Wiskott-Aldrich syndrome protein) in which the "output" domain of N-WASP was recombined with heterologous autoinhibitory "input" domains. Synthetic switch proteins were created with diverse gating behaviors in response to nonphysiological inputs. Thus, this type of modular framework can facilitate the evolution or engineering of cellular signaling circuits.     

Scaling up digital circuit computation with DNA strand displacement cascades

To construct sophisticated biochemical circuits from scratch, one needs to understand how simple the building blocks can be and how robustly such circuits can scale up. Using a simple DNA reaction mechanism based on a reversible strand displacement process, we experimentally demonstrated several digital logic circuits, culminating in a four-bit square-root circuit that comprises 130 DNA strands. These multilayer circuits include thresholding and catalysis within every logical operation to perform digital signal restoration, which enables fast and reliable function in large circuits with roughly constant switching time and linear signal propagation delays. The design naturally incorporates other crucial elements for large-scale circuitry, such as general debugging tools, parallel circuit preparation, and an abstraction hierarchy supported by an automated circuit compiler.     

PHYSIOLOGY OF THE AMINO ACIDS

We have followed the amino acids from their entrance into the alimentary tract in the form of food proteins through the successive steps of digestion, absorption into the blood stream and passage from the blood stream into the tissues, where they are concentrated by some unknown mechanism to many times their concentration in the blood plasma. We have seen something of the way in which certain of the amino acids can be transformed into one another in the body or synthesized from ammonia and keto acids. However, we have had to admit that our bodies can form in such ways only about half of the different amino acids that are required, and that the other half must be made for us by plants, bacteria or other organisms which have greater synthetic powers than we. And finally we have seen something of the manifold fates of the amino acids after they have entered our tissues; how they may be destroyed and their nitrogenous parts turned into urea in the liver before it is possible to put them to their more specialized uses, how their carbon fractions can be used to form glucose, how they may sacrifice themselves to protect us from toxic products, how they can serve as source material for certain vitamins, hormones and other compounds with physiological functions still to be identified, and how finally those amino acids which are not deflected to these various fates may enter into the proteins of the tissues and become for a time parts of our living structures.     

叠加定理在非线性电阻电路中的应用

针对叠加定理只能用于线性电路的观点,从叠加定理的数学基础出发,通过应用替代定理等效变换非线性电路,创造性地提出了叠加定理在非线性电阻电路中应用的方法,给出了求解的基本步骤。举例说明,作为求解非线性电阻电路的中间步骤,叠加法是一种有效实用的方法。     

How animals move: an integrative view

Recent advances in integrative studies of locomotion have revealed several general principles. Energy storage and exchange mechanisms discovered in walking and running bipeds apply to multilegged locomotion and even to flying and swimming. Nonpropulsive lateral forces can be sizable, but they may benefit stability, maneuverability, or other criteria that become apparent in natural environments. Locomotor control systems combine rapid mechanical preflexes with multimodal sensory feedback and feedforward commands. Muscles have a surprising variety of functions in locomotion, serving as motors, brakes, springs, and struts. Integrative approaches reveal not only how each component within a locomotor system operates but how they function as a collective whole.     

MOS VLSI电流型模拟电子神经网络

本文提出了采用ＭＯＳ晶体管的电流型模拟电子神经网络的新实现。该电路结构非常简单，且具有ＭＯＳ ＶＬＳＩ的优点，新的神经元电路的神经态既可以是全电流型又可以是电压型。     

叠加定理在非线性电阻电路中的应用

针对叠加定理只能用于线性电路的观点,从叠加定理的数学基础出发,通过应用替代定理等效变换非线性电路,创造性地提出了叠加定理在非线性电阻电路中应用的方法,给出了求解的基本步骤。举例说明,作为求解非线性电阻电路的中间步骤,叠加法是一种有效实用的方法。     

社会主义新农村必须加强乡镇图书馆建设

指出乡镇图书馆目前所处"空壳"的原因和窘境,反映出当前农村乡镇图书馆服务现状,探讨"十一五"期间我国社会主义新农村建设必须加强乡镇图书馆业务建设这一课题,重,最闸述了乡镇图书馆在"十一五"期间的作用和工作方法,努力推进乡镇图书馆事业建设的实践.     

Evolutionary biology. Twinned genes live life in the fast lane

On page 1151, researchers describe new insights into how genes arise and fuel evolution. By trolling through sequence data for nine very distinct organisms, they have uncovered evidence that genes are copied far more frequently--and the duplicates are lost from the genome far faster--than researchers had thought. What's more, the work suggests that some duplicate genes play a key role in the evolution of new traits and in speciation.     

基于神经元晶体管和忆阻器的 Hopfield 神经网络及其在联想记忆中的应用

随着人工智能的高速发展,越来越多的神经元模型相继被提出,现有的神经元电路主要由普通晶体管、运算放大器等高功耗器件构成,存在结构复杂、集成度不高、兼容性差、功耗高、阈值调节难度高的缺点.针对以上不足,首次提出了一种全新的神经元结构,该结构仅由神经元晶体管、忆阻器和普通电阻构成,相比传统神经元电路,不包含复杂的差分运算电路以及电流与电压信号的转换电路,电路结构简单,同时具有良好的电路兼容性,可用于大规模集成.该结构利用神经元晶体管的加权求和特性以及阈值可控功能来模拟神经元信息传导过程,同时利用阈值忆阻器的阈值特性和阻值连续变化能力来设定和更新突触权值,使得该新型神经元结构不仅能实现传统神经元电路功能的同时,还具有能耗低、阈值动态可控、权值可编程的优点,不仅极大地简化了网络结构,还能加强网络性能.其次,还提出了基于这种新型神经元结构的忆阻离散Hopfield神经网络,该忆阻神经网络有助于促进人工神经形态系统的硬件实现,使神经网络系统能耗降低,集成度极大地提高,将这种网络运用在联想记忆和彩色数字图像恢复中,进一步说明了基于全新神经元结构的忆阻离散hopfield神经网络的实用性以及有效性.     

Molecular biology. Cancer fighter's modus operandi revealed

Researchers have deciphered how a promising cancer drug acts like a smart bomb, homing in on only a very narrow range of its potential targets in the cell. The compound, known as STI-571, has shown remarkable success in early clinical trials on patients with chronic myelogenous leukemia. Now, in work reported on page 1938, scientists reveal just how the compound works--information that could aid in the design of similar cancer therapies.     

Episodic-like memory in rats: is it based on when or how long ago?

Recent experiments with rats suggest that they show episodic-like or what-where-when memory for a preferred food found on a radial maze. Although memory for when a salient event occurred suggests that rats can mentally travel in time to a moment in the past, an alternative possibility is that they remember how long ago the food was found. Three groups of rats were tested for memory of previously encountered food. The different groups could use only the cues of when, how long ago, or when + how long ago. Only the cue of how long ago food was encountered was used successfully. These results suggest that episodic-like memory in rats is qualitatively different from human episodic memory.     

实验技术人员教学工作评价方案研究与实践

实验技术人员的教学工作评价分为工作数量评价和工作质量评价。工作数量以他们承担的实验教学工作任务来评价,工作质量由其所在的实验室和学院分别对他们的教学工作进行评价。评价体现了实验技术人员不同的劳动价值。评价结果与教学工作津贴挂钩。工作数量评价结果可为实验技术人员的定编提供依据。