Chirality-Dependent Resistivity in Carbon Nanotubes

Abstract

The phonon-mediated resistivity is calculated for metallic carbon nanotubes based on a continuum model for electrons and phonons. In armchair nanotubes, only twisting modes contribute to the resistivity, while both stretching and breathing modes are important in zigzag nanotubes. The resistivity shows chirality dependence at low temperatures where breathing modes are not populated but becomes independent of the chirality at high temperatures.     

地层水矿化度对含水饱和度精度的影响分析

精确确定地层混合液电阻率和阿尔奇参数是剩余油饱和度评价的核心技术,但是在注水开发过程中地层混合液电阻率是动态变化的,同时当地层水矿化度变化较大时,胶结指数m和饱和度指数n随地层水矿化度的增大而增大,影响了由阿尔奇公式确定的含水饱和度的计算精度。提出首先采用变倍数物质平衡法得到地层混合液电阻率,再利用W-S模型和阿尔奇公式建立动态m、n值计算公式,在求准一系列地质参数的基础上再进行含水饱和度的计算。结果表明:采用变倍数物质平衡法能够得到精度较高的混合液电阻率;采用随地层水矿化度变化的m、n值能够显著提高含水饱和度的计算精度。     

降雨对棒板(棒棒)空气间隙交流放电特性的影响

针对近年来我国输电线路频繁出现风偏闪络事故,分析认为暴雨是造成输电线路风偏闪络的原因之一。通过模拟降雨试验研究降雨强度、雨水电阻率、环境温度对棒板(棒棒)空气间隙交流放电特性的影响。试验结果表明：降雨强度、雨水电阻率均使棒板(棒棒)空气间隙交流放电电压降低,其中降雨强度对棒板空气间隙交流放电电压的影响最明显;降雨强度I=2~14 mm/min时,棒板间隙距离d=0.4、0.6、0.7 m的交流放电电压最大降低幅度分别为6.73%、6.54%、6.02%,而棒棒间隙的最大降低幅度分别为2.66％、3.22%、3.07%;降雨强度对棒板交流放电电压影响大,对棒棒影响小;暴雨情况下环境温度的升高使棒板空气间隙交流放电电压升高,其最大变化幅度为7.03%。     

基于模糊C均值聚类的二维直流电阻率与射频大地电磁联合反演

为结合直流电阻率（direct current resistivity, DCR）与射频大地电磁（radio-magnetotelluric, RMT）法反演优势,开展了二维DCR与RMT数据联合反演研究。在经典最小结构模型正则化的基础上,采用平衡算子调节两个数据间的权重,引入模糊C均值（fuzzy C-means, FCM）聚类对电阻率模型进行约束,根据数据均方根误差自动调整FCM聚类项的权重,提高了联合反演效果。通过单独反演与联合反演结果的对比,分析了两种方法的反演能力,总结了联合反演的优势。模型试算表明,DCR与RMT数据联合反演得到的电阻率模型较单独反演更接近实际模型,FCM聚类约束的应用可进一步提高联合反演的效果。     

Effects of polarization and p-type GaN resistivity on the spectral response of InGaN/GaN multiple quantum well solar cells

Effects of polarization and p-type GaN resistivity on the spectral response of InGaN/GaN multiple quantum well(MQW) solar cells are investigated. It is found that due to the reduction of piezoelectric polarization and the enhancement of tunneling transport of photo-generated carriers in MQWs, the external quantum efficiency(EQE) of the solar cells increases in a low energy spectral range(λ 370 nm) when the barrier thickness value decreases from 15 nm to 7.5 nm. But the EQE decreases abruptly when the barrier thickness value decreases down to 3.75 nm. The reasons for these experimental results are analyzed. We are aware that the reduction of depletion width in MQW region, caused by the high resistivity of the p-type GaN layer may be the main reason for the abnormally low EQE value at long wavelengths(λ 370 nm).     

温度对纳米ZnO膜电学光学性质影响的研究

关键词：     

硅探测器的数字化脉冲形状甄别

介绍了利用硅探测器的脉冲形状甄别进行粒子鉴别的原理。详细叙述了基于数字化方法的脉冲形状甄别的实现。采样频率和位数是数字化方法的两个重要参数。对于硅探测器信号,采用100 MS/s,12 bit的Digitizer可以满足脉冲形状甄别法对时间分辨的要求。同时对该方法粒子鉴别的特征和能量阈值做了简要的分析和对比。粒子背面入射硅探测器的所得的阈值低于正面入射的情况。例如对于氖周围的同位素,背面入射情况的阈值约为100 MeV,为正面入射情况下鉴别阈值的二分之一,相当与ΔE-E方法中ΔE探测器厚度约为60 μm情况下的阈值。最后定性讨论了硅探测器的电阻率不均匀性和沟道效应对粒子鉴别性能的影响。In this paper Pulse Shape Discrimination(PSD) for silicon detector has been briefly introduced. The emerging digital method successfully applied to detector signal processing makes digital PSD method one of the most promising particle identification methods. Sampling frequency and the number of bits are two key parameters of digital method. For silicon detector signal, adopting 100 Ms/s, 12 bit Digitizer can satisfy the time resolution requirement of PSD method. The identification characteristic and energy threshold of this method have been discussed and compared with both front injection and rear injection cases. Energy threshold with rear injection usually is much lower than that with front injection. For example, around for Neon isotope energy threshold with rear injection is about 100 MeV which is only half of the threshold with front injection, also equivalent to thickness of about 60 μm silicon detector threshold in ΔE-E method. At the end the impact of silicon detector's resistivity nonuniformity and channel effect on the identification capacity of PSD method has been discussed in detail.     

Diffusion tensor magnetic resonance imaging of the normal breast

Purpose

The objective of this study was to evaluate diffusion anisotropy of the breast parenchyma and assess the range and repeatability of diffusion tensor imaging (DTI) parameters in normal breast tissue.

Materials and Methods

The study was approved by our institutional review board and included 12 healthy females (median age, 36 years). Diffusion tensor imaging was performed at 1.5 T using a diffusion-weighted echo planar imaging sequence. Diffusion tensor imaging parameters including tensor eigenvalues (λ₁, λ₂, λ₃), fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured for anterior, central and posterior breast regions.

Results

Mean normal breast DTI measures were λ₁=2.51×10⁻³ mm²/s, λ₂=1.89×10⁻³ mm²/s, λ₃=1.39×10⁻³ mm²/s, ADC=1.95±0.24×10⁻³ mm²/s and FA=0.29±0.05 for b=600 s/mm². Significant regional differences were observed for both FA and ADC (P<.05), with higher ADC in the central breast and higher FA in the posterior breast. Comparison of DTI values calculated using b=0, 600 s/mm² vs. b=0, 1000 s/mm², showed significant differences in ADC (P<.001), but not FA. Repeatability assessment produced within-subject coefficient of variations of 4.5% for ADC and 11.4% for FA measures.

Conclusion

This study demonstrates anisotropy of water diffusion in normal breast tissue and establishes a normative range of breast FA values. Attention to the influence of breast region and b value on breast DTI measurements may be important for clinical interpretation and standardization of techniques.     

活性炭/有机质复合相变材料的热-电性能

用活性炭(AC)作为支撑材料,石蜡(PW)、十六酸(PA)和硬脂酸(SA)作为相变主材,通过熔融共混法制备AC/PW、AC/PA和AC/SA复合相变材料,并考察了其热-电性能。结果表明,添加活性炭时有机质均不会泄漏;复合材料充-放热过程中温度场分布都比较均匀,热循环会使材料导热性能略有下降;此外,三种复合材料的电阻率均随压力增加而减小。     

在N—甲基吡咯烷酮中聚苯硫醚合成的宏观动力学

研究了无水硫化钠与对二氯苯（以Ｎ－甲基吡咯烷酮为溶剂）合成聚苯硫醚反应的宏观动力学，该反应是一个小分子缩合串联自缩聚的过程，通过测定不同反应聚合体系中氯化钠的徨成率和硫化内的转化率，建立了该反应的宏观动力学方程：１／（１－ＰＮａＣｌ＋ＰＮａ２ｓ）＝Ｃ０Ｋｔ＋１；并计算得到２２０、２５０℃的表观反应速率为４．５×１０＾－４和３．０×１０＾－３ｋｇ／（ｍｏｌ．ｓ），表观活化能为１３４ｋＪ／ｍｏｌ。