Visual processing in the leech central nervous system

In animals with complex visual systems spatial contrast is enhanced by mutual inhibition between retinal neurones monitoring different fields. By analogy, if animals like leeches and some caterpillars, that have several simple (non-image-forming) eyes aimed in different directions, are capable of rudimentary form detection, one might predict mutual antagonism between eyes monitoring different fields. In support of this prediction, I report here a paired interneurone in the central nervous system (CNS) of the leech which is stimulated by eyes on one side of the animal and inhibited by eyes on the other. There are striking parallels between these neurones and other integrating neurones, in particular those processing bilateral auditory input in crickets, suggesting that the visual system of the leech may be representative of a general class of sensory processing systems.     

Peripheral nerve injury triggers central sprouting of myelinated afferents.

The central terminals of primary afferent neurons are topographically highly ordered in the spinal cord. Peripheral receptor sensitivity is reflected by dorsal horn laminar location: low-threshold mechanoreceptors terminate in laminae III and IV (refs 2, 3) and high-threshold nociceptors in laminae I, II and V (refs 4,5). Unmyelinated C fibres, most of which are nociceptors, terminate predominantly in lamina II (refs 5, 7). There is therefore an anatomical framework for the transfer of specific inputs to localized subsets of dorsal horn neurons. This specificity must contribute to the relationship between a low-intensity stimulus and an innocuous sensation and a noxious stimulus and pain. We now show that after peripheral nerve injury the central terminals of axotomized myelinated afferents, including the large A beta fibres, sprout into lamina II. This structural reorganization in the adult central nervous system may contribute to the development of the pain mediated by A-fibres that can follow nerve lesions in humans.     

Functional neurogenesis in the adult hippocampus

There is extensive evidence indicating that new neurons are generated in the dentate gyrus of the adult mammalian hippocampus, a region of the brain that is important for learning and memory. However, it is not known whether these new neurons become functional, as the methods used to study adult neurogenesis are limited to fixed tissue. We use here a retroviral vector expressing green fluorescent protein that only labels dividing cells, and that can be visualized in live hippocampal slices. We report that newly generated cells in the adult mouse hippocampus have neuronal morphology and can display passive membrane properties, action potentials and functional synaptic inputs similar to those found in mature dentate granule cells. Our findings demonstrate that newly generated cells mature into functional neurons in the adult mammalian brain.     

Relaxin affects the central control of oxytocin release

In several species the myometrium is quiescent shortly before parturition. At this time high titres of relaxin are present in the plasma and there is evidence that the hormone has a direct inhibitory action on the uterine muscle. Relaxin could also contribute to uterine quiescence by inhibiting oxytocin release. To determine whether relaxin has a central action on the release of oxytocin, we have studied the effect of intravenous injections of porcine relaxin on milk ejection in the anaesthetized lactating rat. We report that reflex milk ejection was suppressed by relaxin in a dose-dependent manner, the onset of inhibition being rapid and lasting from 10 to 60 min. After the period of inhibition the normal temporal pattern of reflex milk ejection was resumed. Mammary sensitivity to exogenous or endogenous oxytocin was reduced by relaxin but not sufficiently to explain the effects observed. Furthermore, relaxin (1 microgram per rat) injected into the cerebral ventricles profoundly disturbed the pattern of reflex milk ejection without affecting the response of the mammary gland to oxytocin. These results suggest a novel role for relaxin within the central nervous system. The site in the brain at which the effects of relaxin are exerted remains unknown.     

中央空调冷却塔机组噪声的治理

中央空调集中制冷系统是目前住宅小区普遍采用的空调系统,但是系统冷却塔的噪声是一个严重的污染源。文章在对某小区中央空调冷却塔的噪声特性测试与分析的基础上,提出了具有针对性的控制措施,通过实际治理工作,使冷却塔的辐射噪声降低了10 dB以上,原来被污染的区域达到了2类区标准。     

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.     

基于集中控制的Web Cache体系结构

在Web Cache体系结构中引入基于集中策略的控制层, 利用控制层监控各个Cache的工作状况, 对其存储空间和工作负载进行全局、 有效地控制, 以达到Cache中的存储结构合理化和工作负载平衡. 在控制层中实现负载平衡算法解决Cache 瓶颈问题, 基于Pull机制的预取算法和TTL与生存系数相结合的淘汰算法提高命中率和系统 效率. 通过引入这些算法, 使控制层对整个Web Cache层进行有效控制, 从而提高系统的命中率, 极大地缩短请求响应时间.     

Induction of neurogenesis in the neocortex of adult mice

Neurogenesis normally only occurs in limited areas of the adult mammalian brain--the hippocampus, olfactory bulb and epithelium, and at low levels in some regions of macaque cortex. Here we show that endogenous neural precursors can be induced in situ to differentiate into mature neurons, in regions of adult mammalian neocortex that do not normally undergo any neurogenesis. This differentiation occurs in a layer- and region-specific manner, and the neurons can re-form appropriate corticothalamic connections. We induced synchronous apoptotic degeneration of corticothalamic neurons in layer VI of anterior cortex of adult mice and examined the fates of dividing cells within cortex, using markers for DNA replication (5-bromodeoxyuridine; BrdU) and progressive neuronal differentiation. Newly made, BrdU-positive cells expressed NeuN, a mature neuronal marker, in regions of cortex undergoing targeted neuronal death and survived for at least 28 weeks. Subsets of BrdU+ precursors expressed Doublecortin, a protein found exclusively in migrating neurons, and Hu, an early neuronal marker. Retrograde labelling from thalamus demonstrated that BrdU+ neurons can form long-distance corticothalamic connections. Our results indicate that neuronal replacement therapies for neurodegenerative disease and CNS injury may be possible through manipulation of endogenous neural precursors in situ.     

中央空调噪声分析及控制研究 3

中央空调机组的噪声源主要来自于气动、机械和电磁等3个方面因素,并以此提出了中央空调机组噪声控制方法;从3个方面系统地分析和论述了噪声控制措施:选择包括高阻尼减振垫、叶片数量多的轴流风叶等性能良好的动力部件,利用金属网罩等特殊结构的隔音减振结构设计,采用合理的安装工艺并利用消声装置等机组合理的安装和配置等;实践表明,此方法较好地控制了中央空调的运行噪声.     

中央空调系统变流量控制方式探讨

分析了现有中央空调系统存在的问题.对中央空调系统的三种变流量控制方式压差控制、温差控制、负荷控制进行分析.结合一个工程实例,说明土壤源热泵空调系统采用温差变流量控制时的运行特性.     

Positional determination of supernumerary blast cell death in the leech embryo

Segmented animals are divided into a longitudinal array of developmentally homologous subunits known as metameres. The embryonic origin of the segmental body plan has been studied in a variety of organisms, with particular emphasis on the mechanisms underlying the delineation of the individual metameres and their secondary diversification. I have examined the embryonic events which determine the total number of segments in the glossiphoniid leech Helobdella triserialis. The germinal band of the leech consists of chains of segmental founder cells, called blast cells, and is normally reduced to 32 segments by the degeneration of supernumerary blast cells located at its caudal end. By using a novel technique for selective cell ablation, the segmental register of the four ectodermal cell lines can be altered so that lineally identifiable blast cells take part in the formation of ectopic segments. I show here that the survival or death of ectodermal blast cells is determined by position independent of their cell lineage identities, implying that the final number of segments is imposed on the ectoderm by interactions with the other embryonic tissues.     

中央空调变流量控制的原理

对中央空调的工作原理和结构进行了阐述,得出了频率变速法与传统变速方法相比的优点:软启动实现可启动电流对电网的减缓冲击,使调速的范围变大,平滑调速可以调节,与直流调速相似程度。     

变频控制技术在中央空调水系统中的应用

随着人民生活水平的提高,现代建筑中中央空调系统的使用率越来越高。在传统的中空调水系统中采用定速泵,进入空调主机的循环水为定流量,能耗较大。随着变频器技术的发展,变频控制技术已经广泛的应用于中央空调水系统中。根据空调水系统工作原理、水泵变频调速原理及变频器、变频调速技术工作原理确定水系统中采用的变频调速控制方案。控制方案分为空调主机进行优化设计方案和冷冻水泵、冷却水泵的变频控制方案。采用变频泵控制流量可以大大减少能耗。根据不同的设计需要,中央空调水系统中采用的3种变频泵控制系统,分别是二次泵系统、一次泵变流量系统、变频泵与工频泵并联系统。