非均匀分布纵向耦合束不稳定性的研究

利用Vlasov方程研究了非均匀分布情形下的纵向多束团不稳定性.当束团均匀分布时,由该方法所得到的结果与ZAP程序给出的结果一致;对于非均匀分布的情形,由该分析解得到的结果与模拟跟踪方法所得到的结果接近.     

金刚石对顶砧中触点位置误差对样品电阻率测量精度的影响

利用有限元分析方法,研究了金刚石对顶砧中电极与样品接触点位置变化对范德堡法测量样品电阻率精度的影响.结果表明:当电极中心与样品边缘的间距b≤d/9(d为样品直径)时能得到精确的电阻率测量结果;当电极位置远离样品边缘而逐渐接近样品中心时,其位置变化对电阻率测量精度的影响迅速增大;相同的电极位置变化对具有较大电阻率的半导体样品电阻率测量精度的影响更明显. 关键词： 电阻率 有限元方法 金刚石对顶砧     

基于PSD的微小位移测量研究

介绍了一种新型的纳米精度光学测量系统.该系统结合半导体位置探测器件(PositionSensitive Detection,PSD)及现代计算机技术,利用激光在两平面镜间多次反射,将测量镜的纳米量级被测物位移放大到PSD能够分辨出的微米量级的位移,从而利用相对低精度的手段完成高精度的测量.实验表明此系统能够对微小位移进行放大测量,测量精度达到11.5 nm.     

水和乙醇对纳米管结构聚苯胺电阻率的影响

研究了水和无水乙醇对萘磺酸掺杂的纳米管结构聚苯胺的电阻率-温度依赖关系的影响（测量温区为80—300K）.实验结果表明，水分子和乙醇分子的进入均使样品的电导率升高.利用电荷能量限制隧道模型结合纳米管粉末压片的结构特点，认为样品电阻主要来源于纳米管间接触电阻.水或乙醇分子在纳米管聚苯胺中通过与分子链的相互作用，增加了链间与链上非局域化载流子的数量，增大管间接触界面，降低了载流子的隧穿势垒，进而提高了导电能力.但水和乙醇对样品导电性质影响程度是不同的，主要是因为水分子和乙醇分子在结构和物理化学性质上的不同. 关键词： 聚苯胺 纳米管 电阻率     

直边界对电阻率测量的影响及修正

针对直线四探针法中直边界对硅片电阻率测量的影响开展了实验研究.结果表明,直边界会导致硅片电阻率测量结果偏大.依据实验数据,分析得到了存在单一直边界影响时的电阻率修正公式,并验证了该公式是有效、准确的.     

晶粒尺寸对薄膜电阻率温度系数的影响

报道了Ｐｄ薄膜电阻率温度系数（ＴＣＲ）随不同薄膜厚度和不同退火温度的变化．实验结果表明：薄膜ＴＣＲ值远小于体材料的值，且对晶粒尺寸有一定的依赖关系；薄膜晶粒尺寸越大，其ＴＣＲ值也越大。采用晶粒间界散射的二流体模型对此结果进行了讨论。 关键词：     

萘磺酸掺杂对纳米管结构聚苯胺低温电阻率的影响

通过研究用自组装法制备的萘磺酸掺杂的纳米管结构聚苯胺(苯胺与萘磺酸的摩尔比分别为1∶025,1∶05,1∶1,1∶2,1∶3)的电阻率温度依赖关系(测量温区为80—300K),仔细分析聚苯胺的结构形貌特征,提出了变程跳跃隧道穿透混合模型:认为在萘磺酸掺杂的纳米管结构聚苯胺样品中,跳跃和隧穿两种机制同时起作用,载流子沿纳米管传导是变程跳跃过程起主要作用,而载流子在纳米管之间的传导是隧穿过程起主要作用.实验结果表明,不同浓度的萘磺酸掺杂对样品的低温电阻率的影响很大,随着掺杂浓度增加,载流子传导所需克服的能垒C0迅速减小,当掺杂接近饱和时,C0不再减小.实验中还研究了不同形貌对电阻率的影响,结果表明样品中纳米管所占比例的增大有利于载流子传导 关键词： 聚苯胺 纳米管 低温电阻率     

多层溅射制备Wsix/Si薄膜的电阻率特性研究

利用多层溅射技术制备了ＷＳｉ_x／Ｓｉ薄膜，然后测量其平面电阻的退火行为，发现平面电阻在６００－７００℃之间退火后有陡降，这对应于非晶ＷＳｉ_x薄膜中Ｗ₅Ｓｉ₃四角相的形成。ｘ射线衍射和慢正电子湮没测量也证实了这一点。认为薄膜电阻率的突变反映了导电机制的变化，它和薄膜结构的变化有很好的对应关系。 关键词：     

位置探测器PSD应用于三维坐标测量的理论研究

提出了一种应用位置探测器 PSD进行三维坐标测量的新技术 ,介绍了由三套 PSD对空间发光点交汇成像而构成的三坐标测量系统。阐述了该系统的测量原理及测量精度分析。该系统具有结构简单、应用方便、自动化程度高、测量精度高、适用范围广等重要特点 ,可有效地应用于机械制造、机器人及汽车检测、航空及医学等测量领域     

一维PSD瞬态响应特性的有限差分方法研究

基于有限差分方法,提出了一种新的PSD RC网络传输线模型模拟算法.利用该算法,得到了一维PSD在不同光信号激励下,从开始响应到进入稳态后的各个阶段的精确数值解.揭示了PSD电极对不同照射点的起始响应时间的差异正相关于光入射点与PSD几何中心之间的距离.在高速瞬态探测时,PSD器件参数限制了激励光脉冲信号的频率,其最高调制速率为1/(3.75Tc).模拟计算结果证明了PSD稳态位置响应结果与入射光类型和时间无关.     

Performance studies on high pressure 1-D position sensitive neutron detectors

The powder diffractometer and Hi-Q diffractometer at Dhruva reactor make use of five identical 1-D position sensitive detectors (PSDs) to scan scattering angles in the range 3° to 140°. In order to improve the overall throughput of these spectrometers, it is planned to install a bank of 15 high-efficiency and high-resolution PSDs arranged in three layers with five PSDs in each layer. With each high pressure PSD (³He 10 bar + Kr 2 bar) showing the efficiency gain of 1.8 at 1.2 Å, detector bank is expected to show overall gain of 5.5 times the present detection efficiency and reduction in data collection time by equivalent factor. The 1-D PSDs are developed in batches of five, and are characterized so that all PSDs operate at uniform parameters such as position resolution, uniformity of efficiency and linearity of response. Position spectrum indicates the differential position resolution to be ～1 mm and integral position resolution to be 3–4 mm. Broadening of position spectrum at the extreme end of sensitive length of PSD is analysed using fine shift of the beam. Dependence of position resolution and dynamic range of output pulse on the input impedance of pre-amplifier is also presented.     

Influence of gadolinium on magnetization and DC resistivity of Ni-Zn nanoferrites

The study of gadolinium substitution in small amounts on the saturation magnetization and DC resistivity of nickel-zinc nanoferrite has led to the understanding of the degree of formation of a secondary orthoferrite GdFeO₃ phase, the generation of cationic and oxygen vacancies and the dilution of gadolinium in the lattice. The role of secondary phase in modifying the electromagnetic properties has been stressed by making further investigations on the Curie temperature and the activation energies.     

Modern trends in the development of position sensitive neutron detectors for condensed matter research

Different types of neutron scattering experiment for the study of condensed matter properties pose specific and often contradictory requirements for detector characteristics. There is no single type of detector which satisfies all the criteria. Therefore, compromise is inevitable and some of the characteristics are trade off in favour of others. Present report gives an overview of detector systems presently operating at the leading neutron scattering facilities as well as some development work around the globe.      

CFETR包层等效电阻率对等离子体垂直位移增长率的影响

基于CFETR工程设计,使用TOKSYS建立了CFETR极向场线圈、真空室壁和包层结构的等效二维模型.在三种平衡的等离子体位形下,分析了包层结构整体等效电阻率和极向不同位置的等效电阻率对等离子体垂直位移增长率的影响.结果表明,垂直位移增长率随着包层整体等效电阻率的增加近似线性增大;降低极向±60°附近的等效电阻率,能减...     

Electrical resistivity of dilute,interacting fermions

A first-principles calculation of the initial decay of a current-carrying state is used to infer the electrical resistivity ofinteracting fermions (electrons or holes). This approach is useful when it is impractical to apply the Kubo formalism.     

Influence of grain boundary state on electrical resistivity of ultrafine grained aluminium

An ultrafine grained (UFG) structure has been obtained in commercial purity Al by high-pressure torsion (HPT). Changes in microhardness and electrical resistivity of the UFG material after annealing at various temperatures within a range of 363–673 K have been investigated in correlation with the microstructure evolution. It has been shown that annealing at 363 K leads to substantial decrease in the electrical resistivity while keeping high microhardness level and approximately the same average grain size. The contributions from the various microstructural units (vacancies, dislocations, grain boundaries (GBs)) to the electrical resistivity were analysed. It was shown for the first time that a non-equilibrium state associated with strain-distorted grain boundary (GB) structure strongly affects electrical resistivity of UFG Al. The resistivity of non-equilibrium GBs in UFG structure formed by HPT was evaluated to be at least 50% higher than the resistivity of the thermally equilibrium GBs in a coarse-grained structure.     

Effect of pressure on the resistivity of spinel ferrite

The far-infrared spectra of six mixed ferrites (Cd_xCo_1−x+tTi_tFe_2−2tO₄; x=0.2, 0.00?t?0.25) in the range 200-1000 cm⁻¹ are reported. Two strong high-frequency bands ν₁ and ν₂ are observed. The first one ν₁ is assigned to the tetrahedral and the second ν₂ is assigned to the octahedral site. A small kink ν₃ around near ν₂ is observed and its intensity increases with divalent octahedral metal ion concentration. Seebeck coefficient measurements showed that the substitution of tetravalent ion Ti⁴⁺ does not change the polarity of the Seebeck coefficient from p- to n-type. The activation energy and the carrier mobility μ were also calculated. The effect of mechanical pressure on the dc resistivity was investigated.     

Magnetic brillouin zone effect on the resistivity of semimetallic-like fermi surface in USb

To probe the effect of the protein environment on the retinal chromophore of rhodopsin, we performed molecular dynamics simulations using combined quantum mechanics/molecular mechanics (QM/MM). The starting geometry of the protein is based on the 2.6Å X-ray structure of bovine rhodopsin of Okada et al. [T. Okada, et al. Proc. Natl. Acad. Sci. USA 99 5982 (2002)]. The wild-type chromophore of rhodopsin according to our calculations shows a highly twisted conformation around the central region, from C10 to C13, due to non-bonded interaction with the protein pocket. The absolute sense of twist of the C11–C12 and C12–C13 bonds is negative (?19 ± 9°) and positive (170 ± 8°), respectively. The 13-demethyl retinal chromophore, in which the methyl group at the C13 position is removed, is less distorted in this region. The C11–C12 bond is less twisted (?15 ± 10°) and the C12–C13 bond is planar (179 ± 9°) . The flattened geometry of this artificial chromophore is supported by spectroscopic evidence.     

Influence of imperfectly bonded micropolar elastic half-space with non-homogeneous viscoelastic layer on propagation behavior of shear wave

A mathematical model is developed in which the effect of imperfect bonding between the constituents of layer and half-space on the phase velocity and damped velocity of SH-wave is discussed. The model consists of a micropolar elastic half-space bonded imperfectly with a heterogeneous viscoelastic layer. The dispersion equation and damping equation of SH-wave propagation in the said model is obtained in the closed form analytically. The effects of imperfect bonding, internal friction, heterogeneity, micropolarity, and complex interface stiffness parameters highlighted through numerical computation and graphical demonstrations. Standard Love-wave equation and dispersion equation as well as damping equation for perfectly bonded micropolar half-space with heterogeneous viscoelastic layer is obtained as a special case of the problem. Through comparative study of homogeneity with heterogeneity in the layer; imperfect bonding of layer and half-space with their welded (perfect) contact; and presence of micropolarity in half-space with its absence in half-space are compared meticulously.     

空气中激光等离子体通道导电性能的研究

超强飞秒激光在大气中传输时，可以形成很长的等离子体通道.对通道电阻率和测量电极与等离子体通道间的接触电阻进行了测量，并对影响等离子体通道电阻率的主要因素进行了研究分析.提出减小等离子体通道电阻的方案. 关键词： 等离子体通道 电阻率 接触电阻