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任务正激活与任务负激活的工作机制是认知功能实现的基本要素.这一拮抗关系的失衡或者受损可能会引发一系列严重的退行性神经疾病,然而到目前为止,尚不清楚这种拮抗现象的神经机制.该文基于默认模式网络与任务正网络在突触层面上相互抑制的假设,并结合多种刺激条件下的工作记忆模型,进行了计算机数值模拟.研究结果表明: 1) 任务正网络与任务负网络之间在神经活动上呈现出拮抗关系; 2) 伴随着工作记忆刺激方向数目的增加,任务负网络神经活动的衰减程度会随之增大; 3) 当工作记忆相关的脑区其神经活动增加时,任务负网络的神经活动减少; 4) 并且随着工作记忆任务难度的增加,任务负网络的神经活动会迅速衰减.这些计算结果都与神经科学实验数据是匹配的.由于任务负激活是默认模式网络的主要特征,因此默认模式网络与任务正网络在突触层面上的相互抑制是这两种不同性质网络之间形成拮抗关系的根本原因. 相似文献
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采用分子动力学方法模拟了纳米管道内水分子的流动行为. 考察了压强差、 管道直径和管道长度对通量的影响, 验证了流体在直径为2~2.8 nm管道中的流动行为符合Hagen-Poiseuille(HP)方程. 研究发现, 末端效应具有长度依赖性, 对于较短的管道其末端效应更为显著. 为了深入了解真实非均匀管道的流动行为, 使用直径不同的2种管道以不同的连接顺序组合成4种非均匀管道模型, 最终得到了不同的流量. 提出了二元管道模型, 对非均匀管道内的流动行为进行了初步探讨. 相似文献
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微波辐照2,6-二(2′-咪唑啉-2′-基)吡啶的合成及其与DNA的相互作用 总被引:1,自引:0,他引:1
在微波辐射和无催化剂条件下,由吡啶-2,6-二甲酸与乙二胺反应合成了2,6-二(2′-咪唑啉-2′-基)吡啶,并用红外光谱、质谱、核磁共振、熔点分析测试技术对化合物的组成和结构进行了分析与表征。考察了反应溶剂、反应物比及微波辐射功率。结果表明,不同溶剂对反应产物和副产物的比例有明显影响,最佳溶剂为乙二醇,最佳反应条件为:原料摩尔比1:2.7,微波功率450W,辐射时间65min,温度130℃,总收率71.2%。通过紫外吸收光谱和黏度测定了其与DNA的相互作用,测得键合常数Kb=(9.60±0.05)×104L/mol,较常见的键合常数小。推测化合物与DNA可能是以氢键作用与DNA沟面结合。 相似文献
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Modulated supersonic molecular beam (SMB) injection is introduced to study transport features of non-local transport phenomenon on HL-2A. Repetitive non-local effect induced by modulated SMBI allows Fourier trans-formation of the temperature perturbation, yielding detailed investigation of the pulse propagation. Fourier analysis provides evidence for existence of internal transport barriers. Meanwhile, experimental progress of nonlocal effect was made in the HL-2A Tokamak in 200Z The core electron temperature Te rise increases from 18% to more than 40% and the duration of the Te rise could be prolonged by changing the conditions of SMB injection. 相似文献
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Direct transition of potential of water droplets to electric energy using aligned single-walled carbon nanotubes 下载免费PDF全文
In this paper, we report that an electromotive force (EMF)
can be induced in a rope of aligned single-walled carbon nanotubes
(SWNTs) when water droplets fall on this rope. The magnitude of this
EMF depends sensitively on the slant angle of the SWNTs. Most
interestingly, both the magnitude and the direction of the induced
EFM can be modulated by applying a current to the SWNTs. The
concepts of electrical slip and no-slip are proposed and can be
quantitatively described by ``electrical slip resistance'. This
kind of generator does not need any magnet, rotor, {etc} and shows
quite a different operating mechanism and design compared with a
conventional large scale hydroelectric power generator. 相似文献
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First Principles Study on NaxLi1-xFePO4 As Cathode Material for Rechargeable Lithium Batteries 总被引:2,自引:0,他引:2 下载免费PDF全文
The electronic structure and ionic dynamic properties of pure and Na doped (Li site) LiFePO4 have been investigated by first-principles calculations. The band gap of the Na doped material is much narrow than that of the undoped one, indicating of better electronic conductive properties. First-principles based molecular dynamic simulations have been performed to examine the migration energy barriers for the Li ion diffusion. The results shown that the energy barriers for Li diffusion decreased a little along the one-dimensional diffusion pathway, indicating that the ionic conductive property is also improved, as compared with the high valance doping (such as CF) cases. 相似文献
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含铜/镍金属酶的成熟需要一系列的铜/镍金属伴侣蛋白,这些铜/镍金属伴侣蛋白分别参与铜或者镍的转运,对维持细胞体内铜/镍金属平衡至关重要,同时金属酶完成金属催化活性中心的组装也依赖于这类伴侣蛋白。近年来关于铜/镍金属蛋白的研究取得可喜的进展,这些研究为进一步认识体内铜/镍平衡体系提供了重要依据。本文首先简要地介绍铜的摄取和细胞内平衡体系,接着着重介绍三个重要的铜转运蛋白Atox1、Cox17和CCS关于结构和功能的进展,以及这些铜转运蛋白和药物相互作用的机理。然后详细介绍在氢化酶和脲酶成熟路径中参与了镍的摄取、调节、转运和存储,维持细胞内镍金属平衡的镍伴侣蛋白,并介绍了脲酶、氢化酶这两条成熟路径之间的联系。 相似文献