First Study of Weak (EC+β+) Decay Branch for the Neutron-Deficient Isotoep 209Fr

²⁰⁹Fr has been produced by irradiation of ¹⁹⁷Au with ¹⁶O from SFC accelarator uia the fusion-evaporation 4n channel.The(EC+β⁺)decay of ²⁰⁹Fr has been studied by a He-jet tape transport system.The decay scheme is proposed for the first time based on γ-t,X-γ-t,γ-γ-t coincidece and γ-γ delay coincidence measurements,which takes account of 20 observed γ ray.Five members of low-lying states in ²⁰⁹Rn can be explained by the multi-plet [(²¹⁰Rn2⁺)(νf_5/2)^－1].The branching ratio for(EC+β⁺) decay of ²⁰⁹Fr has been estimated experimentaly to be(3.0±1.5)%.     

ΔI=2 Energy Staggering in Superdeformed Bands in 149Gd(b1) and 153Dy(b1)

The particle-rotor model is applied to describe the odd A superdeformed nuclear states in A～150 mass region. The calculated ΔI=2 Staggering in superdeformed bands in ¹⁴⁹Gd(bl) and ¹⁵³Dy(bl) is compared with the observed data for the first time.     

Quantum interference in carbon-nanotube electron resonators

A new mechanism is proposed to explain the slow conductance fluctuations in the conductance-gate voltage plot observed in the nanotube electron resonators. It is found that the slow conductance fluctuation is an intrinsic quantum interference phenomenon and exists in all metallic nanotube resonators except zigzag ones. Analytical expressions for both slow and rapid oscillation periods of the conductance fluctuations have been derived, which are well consistent with the existing experiments. It is predicted that the ratio of the slow oscillation period to the rapid one is independent of the gate-voltage efficiency, and determined only by the nanotube length used in experiments.     

Efficiency Enhancement of Coaxial-Cavity Electron Cyclotron Resonance Maser by Tapering Guide Magnetic Field

A coaxial-cavity cyclotron resonance maser (CRM) oscillator with tapered guide magnetic field is proposed. It is shown that the transmission quality can be improved by tapering the guide magnetic field. Simulation indicates that the efficiency of a millimeter-wave gyrotron oscillator may be reached up to 38.7% by optimizing the tapered magnetic field.     

Einstein relation in chemically doped organic semiconductors

Based on the assumption of Gaussian energy distributions of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), analytical expressions of generalized Einstein relation in chemically doped organic semiconductor are developed, by approximation of Coulomb traps with a rectangle potential well. Numerical calculations show that traditional Einstein relations do not hold for chemically doped organic semiconductors. Similar to physical doping, the dependence of diffusion coefficient to mobility D/μ ratio on the carrier concentration has a maximum. An essential difference between chemical doping and physical doping is that, the D/μ ratio in chemically doped organic semiconductors depends not only on carrier concentration and doping concentration, but also on the applied electric field. PACS 71.20.Rv; 72.90.+y; 73.50.-h     

栅耦合型静电泄放保护结构设计

提出了一种新型栅耦合型静电泄放(ESD)保护器件——压焊块电容栅耦合型保护管.该结构不仅解决了原有栅耦合型结构对特定ESD冲击不能及时响应的问题，而且节省了版图面积，提高了ESD失效电压.0.5 μm标准互补型金属氧化物半导体工艺流片测试结果表明，该结构人体模型ESD失效电压超过8 kV.给出了栅耦合型ESD保护结构中ESD检测结构的设计方法，能够精确计算检测结构中电容和电阻的取值. 关键词： 静电泄放 栅耦合 金属氧化物半导体场效应管 压焊块电容     

Preparation, electrical and gas-sensing properties of perovskite-type La1−xMgxFeO3 semiconductor materials

The La_1−xMg_xFeO₃ powder was prepared by sol-gel method using citric acid. The compounds crystallized were perovskite phase with orthorhombic structure. The Mg-doping restrains the growth of the grain size. The conductivity and gas sensing of La_1−xMg_x FeO₃-based sensors were investigated. We found the La_0.92Mg_0.08 FeO₃-based sensors have the best response and selectivity to ethanol gas. Great differences on the conductance-temperature curves of La_0.92Mg_0.08 FeO₃-based sensors between in ethanol gas and air or other gas such as H₂, CO and CH₄ were also found. The conductance in ethanol gas decreased with temperature from 130 to 240 °C. But in air and other gas such as H₂, CO and CH₄ the conductance increases all the time. It indicates that at 240 °C the conductance difference between air and ethanol was the biggest and the response reach the maximum.     

改进的同步迭代算法在光声血管成像中的应用

光声成像结合了光学成像和声学成像的优点，是一种高分辨率，高对比度的无损伤医学成像技术.一种改进的同步迭代算法应用于光声图像重建.仿真和模拟结果表明，与传统的代数迭代算法相比，在90°，135°，180°的有限场光声成像中，此算法对测量误差的校正和迭代次数的收敛上具有较大的优势，图像重建的速度和成像质量都有了明显的提高.实验中，一种圆形扫描结构的光声成像装置，用于180°的有限场扫描，利用改进的同步迭代算法，重建出了高对比度和高分辨率（60μm）的鸡胚胎光声血管图像.实验证明，这种算法的应用，大幅度减少了数据采集时间，为光声成像技术运用于实时监测血流灌注和肿瘤光动力治疗的血管损伤效应提供了潜在的应用价值. 关键词： 光声成像 有限角度 代数迭代算法 光声血管成像     

Quantitative analysis of asymmetrical cortical activity in motor areas during sequential finger movement

Brain asymmetry is a phenomenon well known for handedness and has been studied in motor cortices. However, few quantitative studies on asymmetrical cortical activity in motor areas have been conducted. In this study, we systematically investigated asymmetrical cortical activity in motor areas during sequential finger movement by quantitatively analyzing functional magnetic resonance imaging (fMRI) blood oxygenation level-dependent (BOLD) responses. The norm of BOLD signal percentage of change was introduced to quantitatively measure the BOLD signal intensity change difference between the left and right motor areas. The results of the data collected from six subjects show that the norm of BOLD signal percentage of change in the right motor area is higher than that in the left motor area for two-hand movement (P=.0059) and single-hand movement (P=.0279) with right-handedness. These results from fMRI show the asymmetry of motor areas and may suggest that the left hemisphere motor area comes into being as an adaptation system that needs few neuron cells only to finish any movement task for right-handedness. The activation intensity in the left motor area is reduced with normal right finger movement. The activation intensity in the right motor area is obviously higher than that in the left motor area.     

Co掺杂对YBa2 Cu3 O7-δ电阻率与塞贝克系数的影响

用固态反应法制备了YBa2Cu3-xCoxO7-δ(x=0.0,0.1,0.2,0.5)样品,研究了Co掺杂对YBa2Cu3O7-δ高温区的电阻率和塞贝克系数的影响。随着Co含量的增加,样品的电阻率和塞贝克系数逐渐增大,从金属性导电转变为p型半导体导电。x=0.2和0.5样品的电导活化能在500K处发生突变,高温区的活化能大于低温区的活化能。通过塞贝克系数与温度的关系,计算出x=0.2和0.5样品的费米能级分别为0.02和0.12 eV。当温度高于650-700K时,氧脱附显著影响样品的电输运性质,导致电阻率和塞贝克系数随温度增加而增大。