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In this paper, we present a model of the Brownian motor in a feedback controlled ratchet, in which the application of the flashing potential depends on the state of the particle to be controlled. We derive an analytical expression for the velocity induced by the feedback ratchet, which is a function of several parameters, including the ratio of the two switching temperatures and the asymmetry parameter of the potential field. The motor shows a current inversion when either parameter is varied. 相似文献
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A flashing ratchet model of a two-headed molecular motor in a two-dimensional potential is proposed to simulate the hand-over-hand motion of kinesins.Extensive Langevin simulations of the model are performed.We discuss the dependences of motion and efficiency on the model parameters,including the external force and the temperature.A good qualitative agreement with the expected behavior is observed. 相似文献
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4 MV静电加速器由高压系统、离子源及束流系统、控制系统和气体系统四部分组成。调试中出现了离子源不起弧、加速管破裂、控制系统失灵和输电带输电能力降低等技术问题,分析了出现这些问题的原因,然后分别采取了相应的措施加以解决:变换工作流程,在每次关机前先把引出电压降为零,开机时等离子源起弧后再把引出电压升到预定值;对过渡法兰进行车加工,重新封装;对高压端的控制设备采取屏蔽措施,在输入、输出端使用TVS二极管,对控制软件进行抗干扰设计;对绝缘气体进行循环干燥等。调试出了流强为100 μA、能量在3 MeV以上的稳定质子流。 相似文献
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为了使RF离子源具有良好的引出特性, 测试了吸极几何参数、振荡器板压、引出电压对离子源引出特性的影响, 对实验结果进行了分析. 在其他参数不变的情况下, 存在最佳的D/d; 增加D/d,有利于过聚焦的离子束恢复聚焦状态. b/D增大时, 聚焦度上升, 引出束流下降. B/d减小时,聚焦度增大; 当B/d小于4时, 聚焦度增加趋势变缓. 综合考虑聚焦度、引出束流和气压,D/d,b/D,B/d适宜的选择范围分别为1.6—2.1, 0.7—1.1, 4—7. 改变引出电压和振荡器功率对离子源性能的影响具有相反的方向, 两者都存在最佳工作点. 相似文献
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为了使RF离子源具有良好的引出特性,测试了吸极几何参数、振荡器板压和引出电压对离子源聚焦度的影响,对实验结果进行了分析。在其它参数不变的情况下,吸极的外径D与内径d之比存在最佳值,增加D/d,有利于过聚焦的离子束恢复聚焦状态。吸极的长度为L,石英套管比吸极长l。当l/D增大时,聚焦度上升,引出束流下降。L/d之比减小时,聚焦度增大。当L/d小于4时,聚焦度增加趋势变缓。综合考虑聚焦度、引出束流和气压,D/d,l/D,L/d适宜的选择范围分别为1.6~2.1,0.7~1.1,4~7。增加振荡器功率会使离子束呈弱聚焦,而增加引出电压会使离子束呈过聚焦。振荡器功率和引出电压都存在最佳值。 相似文献
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正电子湮没谱学技术是研究材料微观结构非常有效的一种核谱学分析方法, 主要用于获取材料内部微观结构的分布信息, 特别是微观缺陷结构及其特性等传统表征方法难以获取的微观结构信息. 近年来, 在慢正电子束流技术快速发展的基础上, 正电子湮没谱学技术在薄膜材料表面和界面微观结构的研究中得到了广泛应用. 特别是该技术对空位型缺陷的高灵敏表征能力, 使其在金属/合金材料表面微观缺陷的形成机理、缺陷结构特性及其演化行为等研究方面具有独特的优势. 针对材料内部微观缺陷的形成、演化机理以及缺陷特性的研究, 如缺陷的微观结构、化学环境、电子密度和动量分布等, 正电子湮没谱学测量方法和表征分析技术已经发展成熟. 而能量连续可调的低能正电子束流, 进一步实现了薄膜材料表面微观结构深度分布信息的实验表征. 本文综述了慢正电子束流技术应用研究的最新进展, 主要围绕北京慢正电子束流装置在金属/合金材料微观缺陷的研究中对微观缺陷特性的表征和表面微观缺陷演化行为的应用研究成果展开论述. 相似文献
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为适应光谱仪微型化、集成化的发展趋势,详细分析了MEMS微镜应用于微型长波近红外光谱仪的方法和涉及的主要问题,例如分光系统的设计、MEMS微镜的选择、探测器与前置放大电路的设计等。并将50Hz谐振频率、峰峰驱动电压为10V的MEMS微镜、高灵敏度的InGaAs单元探测器,结合立特罗式分光光路,设计和实现了900~2 055nm波段的微型长波近红外光谱仪样机,其中1 000~1 965nm谱段的光谱分辨率介于9.4~16nm之间。采用MEMS扫描微镜技术后,一方面简化了光谱仪中的复杂机械结构,使尺寸可以更小;另一方面实现了单探测器的长波近红外光谱仪,与阵列长波近红外探测器光谱仪相比,成本有所降低。作为应用实例,此样机成功对纯水以及乙醇-水溶液的长波近红外光谱进行了测量,实现了乙醇-水溶液的浓度预测分析,其中本样机测量的纯水长波近红外光谱与文献相符。 相似文献
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A flashing ratchet model of a two-headed molecular motor in a two-dimensional potential is proposed to simulate the hand-over-hand motion of kinesins. Extensive Langevin simulations of the model are performed. We discuss the dependences of motion and efficiency on the model parameters, including the external force and the temperature. A good qualitative agreement with the expected behavior is observed. 相似文献
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Effects of proton irradiation at different incident angles on InAlAs/InGaAs InP-based HEMTs 下载免费PDF全文
InP-based high electron mobility transistors(HEMTs) will be affected by protons from different directions in space radiation applications. The proton irradiation effects on InAlAs/InGaAs hetero-junction structures of InP-based HEMTs are studied at incident angles ranging from 0 to 89.9° by SRIM software. With the increase of proton incident angle, the change trend of induced vacancy defects in the InAlAs/InGaAs hetero-junction region is consistent with the vacancy energy loss trend of incident protons. Namely, they both have shown an initial increase, followed by a decrease after incident angle has reached 30°. Besides, the average range and ultimate stopping positions of incident protons shift gradually from buffer layer to hetero-junction region, and then go up to gate metal. Finally, the electrical characteristics of InP-based HEMTs are investigated after proton irradiation at different incident angles by Sentaurus-TCAD. The induced vacancy defects are considered self-consistently through solving Poisson's and current continuity equations. Consequently, the extrinsic transconductance, pinch-off voltage and channel current demonstrate the most serious degradation at the incident angle of 30?, which can be accounted for the most severe carrier sheet density reduction under this condition. 相似文献