虚拟参考咨询服务的评价方法与指标体系

阐述了虚拟参考咨询评价的必要性,对虚拟参考咨询服务评价的方法与指标体系进行了探讨,旨在提高虚拟参考咨询服务水平。     

分子云自引力坍缩的质量判据及自转平衡

运用维里定理对分子云中各种形式的能量进行了分析。经估算导出,在一定条件下分子云自转是平衡自引力坍缩的重要因素。给出了由观测确定云自转的方法,进而分析、比较了NGC2023、L134等分子云的观测结果。对Hopper-Disney云的自转平衡作用进行了估算,得到与恒星计数法趋于一致的、较合理的恒星生成率。     

84个IRAS源中的水脉泽探测

用乌鲁木齐站25 m望远镜上新安装的谱线测量系统, 对84个包括年轻星及OH/IR星候选体的IRAS源进行了水脉泽搜寻. 在4个恒星形成区及1个晚期恒星包层中测到新水脉泽. 新的脉泽成分在两个已知脉泽源中测到. 在另一个6年前已熄灭的源中, 在不同速度上测到强的脉泽, 表明水脉泽在该源中的新爆发.     

新兴技术及其对美国的含义

在人类的技术和人类社会有组织的活动之间总是有一种相互的作用。在某些情况下,存在着一种吸引力,即来自社会的对新技术的需要;在其他情况下,存在着一种推动力,即由新技术进入社会开创新局面。今天,在美国和世界范围内,两者兼有。我们确实能看到社会力量和价值的变化,它们正在加强技术,反过来新技术也加强了社会的力量。     

Different time courses of learning-related activity in the prefrontal cortex and striatum

To navigate our complex world, our brains have evolved a sophisticated ability to quickly learn arbitrary rules such as 'stop at red'. Studies in monkeys using a laboratory test of this capacity--conditional association learning--have revealed that frontal lobe structures (including the prefrontal cortex) as well as subcortical nuclei of the basal ganglia are involved in such learning. Neural correlates of associative learning have been observed in both brain regions, but whether or not these regions have unique functions is unclear, as they have typically been studied separately using different tasks. Here we show that during associative learning in monkeys, neural activity in these areas changes at different rates: the striatum (an input structure of the basal ganglia) showed rapid, almost bistable, changes compared with a slower trend in the prefrontal cortex that was more in accordance with slow improvements in behavioural performance. Also, pre-saccadic activity began progressively earlier in the striatum but not in the prefrontal cortex as learning took place. These results support the hypothesis that rewarded associations are first identified by the basal ganglia, the output of which 'trains' slower learning mechanisms in the frontal cortex.     

场效应晶体管的非线性与交扰调制

本文对场效应晶体管工作在低频和高频时的交扰调制在理论和实验两方面进行了研究。研究表明目前的大信号模型对于预示场效应晶体管的交扰调制都是不适宜的。本文指出,交扰调制的特性能够通过场效应晶样管所测得的低频特性,用冪级数近似表示法精确地预示出来。典型的场效应晶体管的交扰调制当频率约为100兆赫以下时,实质上是与频率无关的。本文提出了场效应晶体管的大信号模型,以便在非常高的频率工作时预示交扰调制及其有关现象。基于这一模型的交扰计算机预示与实验测量的结果完全一致。     

A filament of dark matter between two clusters of galaxies

It is a firm prediction of the concordance cold-dark-matter cosmological model that galaxy clusters occur at the intersection of large-scale structure filaments. The thread-like structure of this 'cosmic web' has been traced by galaxy redshift surveys for decades. More recently, the warm–hot intergalactic medium (a sparse plasma with temperatures of 10(5) kelvin to 10(7) kelvin) residing in low-redshift filaments has been observed in emission and absorption. However, a reliable direct detection of the underlying dark-matter skeleton, which should contain more than half of all matter, has remained elusive, because earlier candidates for such detections were either falsified or suffered from low signal-to-noise ratios and unphysical misalignments of dark and luminous matter. Here we report the detection of a dark-matter filament connecting the two main components of the Abell 222/223 supercluster system from its weak gravitational lensing signal, both in a non-parametric mass reconstruction and in parametric model fits. This filament is coincident with an overdensity of galaxies and diffuse, soft-X-ray emission, and contributes a mass comparable to that of an additional galaxy cluster to the total mass of the supercluster. By combining this result with X-ray observations, we can place an upper limit of 0.09 on the hot gas fraction (the mass of X-ray-emitting gas divided by the total mass) in the filament.     

Restoration of grasp following paralysis through brain-controlled stimulation of muscles

Patients with spinal cord injury lack the connections between brain and spinal cord circuits that are essential for voluntary movement. Clinical systems that achieve muscle contraction through functional electrical stimulation (FES) have proven to be effective in allowing patients with tetraplegia to regain control of hand movements and to achieve a greater measure of independence in daily activities. In existing clinical systems, the patient uses residual proximal limb movements to trigger pre-programmed stimulation that causes the paralysed muscles to contract, allowing use of one or two basic grasps. Instead, we have developed an FES system in primates that is controlled by recordings made from microelectrodes permanently implanted in the brain. We simulated some of the effects of the paralysis caused by C5 or C6 spinal cord injury by injecting rhesus monkeys with a local anaesthetic to block the median and ulnar nerves at the elbow. Then, using recordings from approximately 100 neurons in the motor cortex, we predicted the intended activity of several of the paralysed muscles, and used these predictions to control the intensity of stimulation of the same muscles. This process essentially bypassed the spinal cord, restoring to the monkeys voluntary control of their paralysed muscles. This achievement is a major advance towards similar restoration of hand function in human patients through brain-controlled FES. We anticipate that in human patients, this neuroprosthesis would allow much more flexible and dexterous use of the hand than is possible with existing FES systems.     

金牛座、蛇夫座中分子云的热性质和年轻星体的演化状态

运用CO分子谱线及红外天文卫星资料,求出了金牛座、蛇夫座核心2个恒星形成区的气体运动温度T_k和尘埃温度T_d,验证了尘埃加热分子云的基本条件;着重探讨了用T_d参量比较年轻星体演化状态的方法,得出蛇夫座核心区恒星比金牛座恒星年轻的初步结论。