论管状电阻网络的阻值

利用周期性条件严格地计算了管状电阻网络的电阻问题,得到了管状网络中任意两点间阻值与管状网络周期的函数关系式.同时借助三维图,形象地分析了周期性条件对管状电阻网络阻值的影响,并指出无限大平面和无限长梯状电阻网络是无限长管状电阻网络的特例.     

规则联接的多边形电阻网络的等效电阻研究

规则联接的多边形电阻网络可以简化为两部分相同的电阻网络的并联,将其中一部分变换为梯形电阻网络,针对奇数边形和偶数边形对应的梯形网络不同,经过相应的变换得到了规则联接的多边形电阻网络的表达式,这一结论也适用于规则联接的多边形电容网络.     

Mechanism of resistance distribution properties in oxide-based resistance switching nanodevice

Although oxide-based resistive switching memory (OxRAM) is one of the strong next-generation high-capacity memory candidates, it has an unresolved problem that the higher the resistance levels, the larger the cycle-to-cycle resistance variabilities to be operated in multi-resistance level mode. In this paper, we develop a simple theory from the operating principles of OxRAMs that excellently matches with experiments both qualitatively and quantitatively. From the theory, we can finally understand the fundamental capabilities of multi-resistance level operation of OxRAMs, and how to improve the switching properties within that.     

用电阻定义式求特殊电容器直流电阻

在电子线路工程及其教学过程中,都需要对电容器的直流电阻进行计算.然而,对一些特殊形状的电容器的直流电阻计算,普遍采用的电流密度法是比较麻烦的.本文根据电阻定义式,结合电阻的串联和并联的简洁关系,简单明了地对球冠形电容器、柱冠形电容器和正多棱柱形电容器等的直流电阻进行了计算,并给出相应的定量表达式.     

低温下固体接触热阻与接触电阻的实验研究

在低温工程中,两个接触固体之间存在着接触热阻与接触电阻,将对低温实验中热量及电流的传输产生显著的影响,是进行低温下物性研究的关键。自行研制了一套可同步实现固体接触热阻和接触电阻的测量装置,该系统具有较高的精度,可实现外界力、温度等对接触热阻的测量,同时具备接触电阻的实时测量功能。在此基础上,开展了外界压力、温度、电流对接触热阻和接触电阻的实验研究。实验结果显示:随着压力的增大,接触热阻与接触电阻随之减小;低温下,随着温度的增大接触热阻与接触电阻增大,接触电阻增大的速率要比接触热阻快。温度平衡时,20mA范围内的电流变化对接触电阻的影响显著,对接触热阻影响非常小。当界面温度达到室温后,首次观测到接触热阻和接触电阻会随着温度的增大而减小。     

对比式液体电阻演示器

现行教材中关于电阻大小与导体的材料、长度、横截面积、温度有关的实验只是用固态(金属)材料做实验得出结论,对于液体是否也符合该规律, 教材未做详尽说明. 为此,利用注射器等材料制作了对比式液体电阻演示器, 该演示装置可探究柱状液体的电阻与液体成分、长度、横截面积、温度的关系.     

Low-temperature resistance of DNA-templated nanowires

We present low-temperature measurements of the electrical conductivity of metallic nanowires assembled on single DNA molecules by chemical deposition of a thin continuous palladium film. The investigated nanowires exhibit ohmic transport behaviour at room temperature. At low temperature we observe an increase of resistance with decreasing temperature that follows a logarithmic dependence. This behaviour can be described with quantum effects in a disordered metallic film. Received: 4 October 2001 / Accepted: 12 December 2001 / Published online: 20 March 2002     

Anisotropy of domain wall resistance

The resistive effect of domain walls in FePd films with perpendicular anisotropy was studied experimentally as a function of field and temperature. The films were grown directly on MgO substrates, which induces an unusual virgin magnetic configuration composed of 60 nm wide parallel stripe domains. This allowed us to carry out the first measurements of the anisotropy of domain wall resistivity in the two configurations of current perpendicular and parallel to the walls. At 18 K, we find 8.2% and 1.3% for the domain wall magnetoresistance normalized to the wall width (8 nm) in these two respective configurations. These values are consistent with the predictions of Levy and Zhang.     

Peltier-effect-induced correction to ohmic resistance

The standard ohmic measurements by means of two extra leads contain an additional thermal correction to resistance. The current results in heating (cooling) at the first (second) sample contact because of the Peltier effect. The contact temperatures are different. The measured voltage is the sum of the ohmic voltage swing and the Peltier-effect-induced thermoelectromotive force that is linear in the current. As a result, the thermal correction to the resistance measured exists as I→0. The correction could be comparable with the ohmic resistance. Above some critical frequency depending on thermal inertial effects, the thermal correction disappears.     

Impurity resistance in ferromagnetic metals

We studied the electrical resistivity of the ferromagnetic metal due to nonmagnetic impurities by considering the different densities of states at the Fermi surface and the different screened potentials for ± spin electrons. Contrary to Nieminen's result which shows that the electrical resistivity decreases when the magnetization increases, we find that the electric resistivity increases monotonically with increasing magnetization. We also do not find the resistivity minimum predicted by Kim and Schwartz.     

Contactless method of resistance measurement

A contactless method to measure the resistance is suggested that allows one to calculate the distribution of the resistance over the sample with a step of 0.1 mm in the resistance range 10⁷−10¹³ Ω (polyethylene, silicon dioxide, and other high-resistivity materials). In the course of measurement, the sample must be on a nonconductive substrate. The system is charged (or discharged) with a needlelike electrizer, and a charge (or discharge) current pulse is detected. The amplitude of the pulse grows with conductivity of the sample and therefore can be used to measure its resistance. Using this method, one can quickly determine, e.g., the photoconductivity of the material and temperature dependence of the resistivity or estimate how, say, the air humidity or a nearby radioactive source influences the conductivity. With the resistance of the sample known, one can find, for example, the humidity of the environment, illuminance, or radioactive radiation intensity.     

Contact resistance of quantum tubes

We consider the conductance of a quantum tube connected to a metallic contact. The number of angular momentum states that the tube can support depends on the strength of the radial confinement. We calculate the transmission coefficients which yield the conductance via the Landauer formula, and discuss the relation of our results to armchair carbon nanotubes embedded in a metal. For Al and Au contacts and tubes with a realistic radial confinement we find that the transmission can be close to unity corresponding to a contact resistance close to h / 2 e²per band at the Fermi level in the carbon nanotube.     

用空气阻力系数测定仪研究运动物体所受空气阻力的成因与定量分析

通过构建一个小型风洞,在对几种典型形状物体的风阻研究基础上,从能量转化的角度,提出了一套对空气阻力系数的理论模型,并通过实验分别对4种不同形状的物体进行了定量验证,实验结果与理论推导能较好地吻合.提出的空气阻力理论也应该可适用于液体的情况.     

多端口石墨烯系统中的非局域电阻

非局域测量方法由于其能够间接探测某些难以直接俘获的非平庸物理机理,近年来已逐渐成为凝聚态物理的研究热点之一.最近的实验在H形多端口石墨烯样品中发现了巨大的非局域电阻信号.在排除了经典欧姆、边缘态等可能的输运形式后,人们倾向于认为这类非局域电阻是由多端石墨烯系统中存在的自旋霍尔效益或谷霍尔效应所导致.借助于非平衡格林函数输运计算,目前的理论可以在同样的多端石墨烯体系中得到部分与实验符合较好的数值模拟结果.针对实验中发现的某些难以理解的、甚至与经典理论相矛盾的非局域电阻性质,例如非局域电阻相比局域电阻在偏离电中性点时的迅速衰减、出现在能隙中的非局域电阻峰值等,目前的理论研究取得了一定的进展,但对这些奇异现象的理解仍存在较大的争议.本综述详细回顾了多端口石墨烯体系中非局域电阻的相关实验,并针对性地介绍与之配套的理论进展及对未来研究的展望.     

Role of coherence in resistance quantization

The quantization of resistances in the quantum Hall effect and ballistic transport through quantum point contacts is compared with the quantization of the charge relaxation resistance of a coherent mesoscopic capacitor. While the former two require the existence of a perfectly transmitting channel, the charge relaxation resistance remains quantized for arbitrary backscattering. The quantum Hall effect and the quantum point contact require only local phase coherence. In contrast quantization of the charge relaxation resistance requires global phase coherence.     

晶体管基区电阻rbb的测试

同学们对高中教材关于“波的干涉”的理解总存在着一些偏差，现分析如下。     

测试接地电阻实验的设计

利用模拟实验测试了形状规则和不规则接地体的接地电阻。