Conduction velocity variations minimize conduction time differences among retinal ganglion cell axons

The visual system is able to accurately represent the spatiotemporal relations among the elements of a changing visual scene as the image moves across the retinal surface. This precise spatiotemporal mapping occurs despite great variability in retinal position and conduction velocity even among retinal ganglion cells of the same physiological class-a variability that would seem to reduce the precision with which spatiotemporal information can be transmitted to central visual areas. There was a strong negative relation between the intraretinal and extraretinal conduction time for axons of individual ganglion cells of the X-cell class. The effect of this relation was to produce a nearly constant total transmission time between the soma of a retinal X cell and its central target site. Thus, the variation in the conduction velocities of retinal ganglion cell axons may ensure that, regardless of the constraints imposed by retinal topography, a precise spatiotemporal central representation of the retinal image is maintained.     

Release of coordinated behavior in crayfish by single central neurons

By stimulating and recording from the same interneuron at two separate points, we have shown that coordinated output to the postural abdominal muscles of crayfish can be produced by electrical stimulation of a single cell. Several central neurons can individually initiate one type of movement(for example, flexion),each producing a unique abdominal geometry.     

Restoration of LDL receptor activity in mutant cells by intercellular junctional communication

Exchange of small molecules between cells through intercellular junctions is a widespread phenomenon implicated in many physiological and developmental processes. This type of intercellular communication can restore the activity of low-density lipoprotein (LDL) receptors in mammalian cells that are deficient in the enzyme UDP-Gal/UDP-GalNAc 4-epimerase. Pure cultures of the 4-epimerase mutant are unable to synthesize normal carbohydrate chains on LDL receptors and many other glycoproteins and therefore do not express LDL receptor activity. When these cells are cocultivated with cells expressing normal 4-epimerase activity, the structure and function of LDL receptors are restored to normal by the transfer of this enzyme's products through intercellular junctions. The formation of functional junctions does not require normal glycosylation of membrane proteins. Because many convenient assays and selections for LDL receptor activity are available, this mutant can provide a powerful new tool for biochemical and genetic studies of intercellular junctional communication.     

长江三角洲白山羊群体间的基因流

用淀粉凝胶电泳法检测长江三角洲白山羊不同地理群体12个结构基因座位上的变异,探讨了群体间的基因流动情况.结果表明,群体间的遗传分化水平很低,群体间基因流平均为23.620 8,并且群体间的遗传距离与地理位置的相距远近存在线性相关性.较大的基因流是长江三角洲白山羊不同地理群体间遗传分化水平很低的主要原因.     

基于“快出慢进”的城区出入干道的信号协调控制

通过采取"快出慢进"交通协调控制优化策略,主线车流早、晚高峰时段的总停车次数比现有的单点信号控制方案分别下降了40%和47%;主线车流由西往东方向的早、晚高峰时段的平均行程车速比现有的单点信号控制方案分别提高了52%和76%,由东往西方向的早、晚高峰时段的平均行程车速比现有的单点信号控制方案分别提高了105%和163%.表明"快出慢进"的交通管理策略能满足交通管理需求,提高主线车流的运行效率.     

低密度刨花板的常规热压传热

采用常规热压方式对刨花板坯进行热压、制造低密度刨花板,测定并记录了热压过程中板坯中心层的温度,根据实验数据分析了热压温度、板坯含水率、板材厚度及板材密度与低密度刨花板中心层升温速度的关系,得出了低密度刨花板常规热压传热的基本规律。     

黄淮平原区玉米秸秆机械化直接还田与配套技术规程

1范围本标准规定了黄淮平原区,玉米收获、秸秆切碎还田、土壤机械耕作、小麦播种作业质量要求、机具配备、操作规程、检测方法,以及小麦田间管理措施和要求。     

Blood Flow Rates by Nuclear Magnetic Resonance Measurements

Blood flow rates may be determined by nuclear magnetic resonance relaxation time measurements. A set of experiments carried out on the flow of blood in mice tails has demonstrated the feasibility of the scheme. Two simple measurement methods are described, and the pertinent equations are given. In addition, some procedures for using nuclear magnetic resonance and electron paramagnetic resonance for tracing the flow of specific materials in the body are outlined.     

两相流水沙分离鳃流场的PIV测试及分析

利用粒子图像测速技术,测试了两种工况下垂向异重流式水沙分离鳃中水沙两相流的速度场,给出了分离鳃内泥沙运动的流速矢量分布图、流速云图及三维流场分布图.对测试结果的分析表明,分离鳃内部形成了泥沙沿鳃片上表面向下运动,清水沿鳃片下表面向上运动的垂向异重流现象,加速了泥沙的下沉.此分析结果与实际观察现象及理论分析一致,进一步探明了分离鳃的水沙分离机理.     

垂直流-表面流复合人工湿地系统对污水的净化效果研究

[目的]研究垂直流-表面流复合人工湿地系统对污水的净化效果。[方法]采用表面流湿地与垂直流湿地组合成的复合人工湿地系统对污水进行处理,研究该系统在水力停留时间分别为48、24、12、6 h时对污水的净化效果。[结果]垂直流湿地对COD、BOD的去除率达52%以上,复合湿地系统对有机物的去除率随水力停留时间的增加而有所增加,对COD、BOD的去除率分别为62%~70%、60%~82%。表面流湿地在N的去除上起比较重要的作用,复合湿地系统对TN、NH4+-N的去除率分别为23.5%~46.4%、42.85%~80.38%。垂直流湿地对TP的去除效果明显好于表面流湿地,在不同配水条件下,复合湿地系统对TP的去除率达47.84~73.56%。[结论]垂直流-表面流复合人工湿地系统对污水的净化效果较好。     

一种自适应的无线传感器网络流量控制机制

随着科技的发展和社会的进步,无线传感器网络在人们生活中的应用越来越广泛。然而,随着传感器网络负荷的增加,拥塞将会导致网络性能的大幅下降。采用基于自适应的无线传感器网络流量控制机制,通过对拥塞节点的虚拟代价进行计算和判断,并实时地将虚拟代价发送到发送节点,然后对发送节点进行流量控制,将能在很大程度上改善网络性能,提高网络服务质量。     

Motor control by sensory cortex

Classical studies of mammalian movement control define a prominent role for the primary motor cortex. Investigating the mouse whisker system, we found an additional and equally direct pathway for cortical motor control driven by the primary somatosensory cortex. Whereas activity in primary motor cortex directly evokes exploratory whisker protraction, primary somatosensory cortex directly drives whisker retraction, providing a rapid negative feedback signal for sensorimotor integration. Motor control by sensory cortex suggests the need to reevaluate the functional organization of cortical maps.     

Quality control by DNA repair

Faithful maintenance of the genome is crucial to the individual and to species. DNA damage arises from both endogenous sources such as water and oxygen and exogenous sources such as sunlight and tobacco smoke. In human cells, base alterations are generally removed by excision repair pathways that counteract the mutagenic effects of DNA lesions. This serves to maintain the integrity of the genetic information, although not all of the pathways are absolutely error-free. In some cases, DNA damage is not repaired but is instead bypassed by specialized DNA polymerases.     

金属离子界面反应对粘粒水流迁移强度的影响

土壤颗粒随水迁移常引发水土流失、农田面源污染等一系列环境问题的发生,且雨滴打击等外部作用被普遍认为是降水引发土粒迁移的主导作用,但土粒迁移的内在作用机制仍不十分清楚.本研究从一个新的角度探讨离子界面反应产生的粘粒间的内在作用力对粘粒水迁移的影响.为了能够准确计算粘粒间的作用力强度,以纯的蒙脱石粘土团聚体为材料,用Na~+和K~+两种一价阳离子来表征界面反应特征的差异.结果表明:1)Na~+体系中粘土颗粒迁移强度远远大于同浓度下的K~+体系;2)K~+体系下的电场强度远低于同浓度下的Na~+体系,相应地,Na~+体系中粘粒间静电排斥力远强于K~+体系;3)蒙脱石团聚体内部的静电场强度越强,颗粒间的静电排斥压越高,粘粒水迁移强度就越大.研究发现,团聚体中的电场强度主要通过颗粒间的静电排斥力影响粘粒水迁移,但在低电解质浓度下,这个电场还可能通过对水合斥力的影响来影响粘粒的水流迁移强度.本研究提出了在流水运动的外力作用下,引发粘粒迁移的内因驱动力:粘土团聚体中静电场产生的静电效应.由于本研究只考虑了流水的作用而没有考虑雨滴撞击力作用,所以本文并未否定雨滴击打对土壤迁移的重要作用.     

微波消解电感耦合等离子体发射光谱法测定空气和废气颗粒物中的铬、铜、镍

用微波消解法对空气滤膜和废气滤筒进行前处理,通过电感耦合等离子体发射光谱法测定了铬、铜、镍的浓度,并对测定结果进行了分析。结果表明,对空气样品中铬、铜、镍分析时微波消解法的检出限分别为0.006μg/m3、0.003μg/m3、0.04μg/m3,精密度分别为1.5%、3.2%、3.5%,加标回收率分别为104%、105%、103%。对废气样品中铬、铜、镍分析时,微波消解法的检出限分别为2.0μg/m3、0.8μg/m3、1.0μg/m3,精密度分别为3.5%、4.4%、4.3%,加标回收率分别为104%、107%、106%。同时对有证滤膜进行了测定,结果均合格。微波消解法测定的铬、铜、镍含量有较好的检出限、精密度和准确度,与电热板消解法不存在显著性差异,均适用于空气和废气颗粒物中的铬、铜、镍的测定。     

Q Sepharose FF分离藻红蛋白的工艺研究

[目的]建立Q Sepharose FF分离藻红蛋白的工艺方法并验证其放大可行性。[方法]通过对洗脱条件、上样体积以及洗脱流速的优化,确定最佳分离工艺条件;在确定的工艺条件下,将上样体积与柱体积等比例放大。[结果]Q Sepharose FF分离藻红蛋白的最佳工艺条件为:将30 ml坛紫菜提取液加载到8 ml Q Sepharose FF柱上,以1 ml/min的流速使用添加0-0.10-0.35-1.00 mol/L NaCl的NaH2PO4-Na2HPO4缓冲溶液(pH 6.0)分步洗脱,收集0.35 mol/L NaCl溶液洗脱时的色谱峰。在此条件下R-藻红蛋白的回收率和纯度系数(A565/A280)分别为44.3和1.15。按照该工艺,将75 ml藻红蛋白提取液加载到20 ml Q Sepharose FF柱上进行分离,发现分离效果没有发生明显变化。[结论]使用Q Sepharose FF介质能够分离坛紫菜提取液中的藻红蛋白且该工艺易于放大。     

Q Sepharose FF分离藻红蛋白的工艺研究(英文)

[目的]建立Q Sepharose FF分离藻红蛋白的工艺方法并验证其放大可行性。[方法]通过对洗脱条件、上样体积以及洗脱流速的优化,确定最佳分离工艺条件;在确定的工艺条件下,将上样体积与柱体积等比例放大。[结果]Q Sepharose FF分离藻红蛋白的最佳工艺条件为:将30ml坛紫菜提取液加载到8ml Q Sepharose FF柱上,以1ml/min的流速使用添加0-0.10-0.35-1.00mol/LNaCl的NaH2PO4-Na2HPO4缓冲溶液(pH6.0)分步洗脱,收集0.35mol/LNaCl溶液洗脱时的色谱峰。在些条件下,R-藻红蛋白的回收率和纯度系数(A565/A280)分别为44.3和1.15。按照该工艺,将75ml藻红蛋白提取液加载到20ml Q Sepharose FF柱上进行分离,发现分离效果没有发生明显变化。[结论]使用Q Sepharose FF介质能够分离坛紫菜提取液中的藻红蛋白且该工艺易于放大。     

间隔流动分析法测定阴离子表面活性剂研究

利用荷兰SKALAR公司的SAN++的间隔流动分析仪检测水中的阴离子表面活性剂的含量。将该方法与国标方法《亚甲蓝分光光度法》(GB/T7494—1987)进行比对试验,F检验与t检验结果表明,间隔流动分析法与国标方法(亚甲蓝分光光度法)无显著差异。     

流动注射比色法测定饲料中的亚硝酸盐

采用流动注射分析法测定饲料中的亚硝酸盐。线性范围为20~1 000 μg/L,相关系数r＝0.999 9;检出限为2.68 μg/L;用50 μg/L亚硝酸钠标准溶液连续测定7次,其相对标准偏差为2.60%;实际样品的加标回收率为82.8%~106.8%。本方法操作简便、灵敏度较高、线性范围宽、精密度高,适用于饲料中亚硝酸盐的测定。