Alpha particle detector with planar double Schottky contacts directly fabricated on semi-insulating GaN:Fe template

Alpha particle radiation detectors with planar double Schottky contacts (DSC) are directly fabricated on 5-μm-thick epitaxial semi-insulating (SI) GaN:Fe film with resistivity higher than 1×10⁸Ω·cm. Under 10 V bias, the detector exhibits a low dark current of less than 5.0×10^-11 A at room-temperature, which increases at higher temperatures. Linear behavior in the semi-log reverse current-voltage plot suggests that Poole-Frenkel emission is the dominant carrier leakage mechanism at high bias. Distinct double-peak characteristics are observed in the energy spectrum of alpha particles regardless of bias voltage. The energy resolution of the SI-GaN based detector is determined to be ～ 8.6% at the deposited energy of 1.209 MeV with a charge collection efficiency of ～ 81.7%. At a higher temperature of 90 ℃, the measured full width at half maximum (FWHM) rises to 235 keV with no shift of energy peak position, which proves that the GaN detector has potential to work stably in high temperature environment. This study provides a possible route to fabricate the low cost GaN-based alpha particle detector with reasonable performance.     

亚微秒脉冲表面介质阻挡放电等离子体诱导连续漩涡的研究

使用粒子激光图像测速技术对亚微秒脉冲激励表面介质阻挡放电激励器连续产生诱导漩涡进行了实验研究, 给出了包含脉冲重复频率和漩涡频率的双频率激励模式的具体形式. 实验过程中出现了原发型与继发型两类示踪粒子空白区, 前者由放电释热的微爆炸作用造成, 使得诱导流动远离壁面, 能够减小壁面摩擦阻力的作用; 以暴露电极左侧继发型空白区被完全吹除作为重复启动激励的临界点. 为提高控制效果应采用尽可能高的脉冲重复频率, 漩涡时间内脉冲数量应大于10, 最大诱导速度随脉冲数量增大而增大, 但动量传递效率降低. 使用亚微秒脉冲激励具备释热、体积力两种作用机理. 关键词： 双频率亚微秒脉冲 表面介质阻挡放电 连续漩涡     

Towards a unified view of fluids

It has traditionally been believed that, unlike normal fluids whose structural properties are determined primarily by the intermolecular short-range repulsive interactions, the properties of polar and associating fluids are strongly affected by the long-range Coulombic interactions. In the course of investigations to determine the primary driving forces governing the behaviour of various (non-simple) fluids, and hence to gain a deeper understanding of the molecular mechanisms leading to the development of theoretically based simple models and theory, extensive and systematic computer simulations have been performed on typical quadrupolar (carbon dioxide), dipolar (acetone and acetonitrile), and associating (hydrogen fluoride, methanol, and water) fluids using the available realistic effective pair potentials and their variants involving forces of different ranges. In addition to the main structural characteristics (one- and two-dimensional site–site correlation functions, local g factors, and radial slices through the full pair correlation function), the dielectric constants and the thermodynamic properties (internal energy and pressure) of both the homogeneous liquid and supercritical fluid phases, and vapor–liquid equilibria have also been considered. Furthermore, in the case of water, the diffusion coefficient and viscosity have also been considered along with water at the interface. All the obtained results lead to the unambiguous conclusion that the structure, defined in terms of the complete set of site–site correlation functions, for both polar and associating pure fluids is governed by the same molecular mechanism as for normal fluids, i.e. by the short-range interactions (which, however, may be both repulsive and attractive), whereas the long-range part of the electrostatic forces, regardless of their strength, plays only a marginal role and may be treated as a perturbation only. The consequences of these findings for theory and applications are also discussed.     

Intermolecular multiple-quantum coherence NMR signals modulated by double distant dipolar fields

A modified CRAZED pulse sequence was applied to obtain the intermolecular multiple-quantum coherence NMR signals from double distant dipolar fields in highly polarized spin systems. Complete theoretical analyses were explicitly derived from the dipolar field treatment combined with product operator formalism. Two typical samples containing several different components were chosen for the experimental verifications. The computer simulations and experimental observations are consistent with the theoretical predictions. The results presented herein provide a convenient way to understand the combined effects of multiple distant dipolar fields from the different components in complicated chemical or biological solutions. When experimental conditions such as selective radio-frequency pulses are not optimal, it may be helpful to identify possible unexpected signals or artefacts of high-resolution NMR spectroscopy in inhomogeneous fields.     

Effect of Discharge Plasma Potential on Diffusion Plasma Parameters Controlled by a Mesh Grid in a Double Plasma Device

The plasma region under investigation is separated from the discharge region by a mesh grid. Plasma potential and electron number densities and electron temperatures under bi‐Maxwellian approximation for electron distribution function of the multi‐dipole argon plasma are measured. The cold electrons in the diffusion region are produced by local ionization. The hot electrons are the ionizing electrons behaving as Maxwellian. The electron trapping process in the discharge region is produced by potential well due to positive plasma potential with respect to the anode and by a repulsive grid. The dependence of ratios of the density of the hot to the cold electrons N_E (=N_eh/N_ec) and hot to cold electron temperature T(=T_eh/T_ec) in the diffusion region on the depth of the potential well has been investigated. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrogen bonds at silica–CO2 saturated water interface under geologic sequestration conditions

To investigate the effects of sequestration condition on hydrogen bonds between mineral and water, molecular dynamics simulations have been performed. The simulations were conducted at conditions related with geologic sequestration sites: pressure (3.1–32.6 MPa), temperature (318 and 383 K), salinity (0–3 M), salt (NaCl and CaCl₂) and silica surface models Q² (geminal), Q³ (isolated) and amorphous Q³. The hydrogen bonds were classified into four types: silica–silica, silica–dissolved CO₂, silica–water as donors and silica–water as acceptors. The mean numbers of hydrogen bonds for each type were analysed. The results show that: (1) silica surface silanol groups do not form H-bonds with dissolved CO₂ molecules in water (brine); (2) The mean number of hydrogen bonds between silanol groups follows the order: Q² > amorphous Q³ > Q³; (3) The mean number of hydrogen bonds between silanol and water molecules follows the order: Q³ > amorphous Q³ > Q².     

Hydrostatic pressure effect on the metal-insulator transition in LaO0.7Ca0.3Mn1−x(Fe/Ge)xO3 perovskites

Abstract

The temperature dependences of the resistivity of La_0.7Ca_0.3Mn_1?xFe_xO₃ and La_0.7Ca_0.3Mn_1?xFe_xO₃ (0 < × < 0.04) mixed crystals were studied under hydrostatic pressures up to 15kbar. The substitution of Fe for Mn results in an increase of the resistivity and a continuous decrease of the metal-insulator transition temperature T_mi while the substitution of Ge for Mn leads to a more complicated T_mi(x)-curve. In all cases T_mi shifts under pressure with a rate between 1.6 and 2.9K/kbar and a correlation between T_mi and its pressure derivative dT_mi/dP is observed which is in accordance with the general trend of dT_mi/dP versus T_mi as derived for other manganites and is discussed in terns of a competition between superexchange and double exchange.     

STABLE DOUBLE LR ALGORITHM AND ITS ERROR ANALYSIS

In this paper, the normative matrices and their double LR transformation with origin shifts are defined, and the essential relationship between the double LR transformation of a normative matrix and the QR transformation of the related symmetric tridiagonal matrix is proved. We obtain a stable double LR algorithm for double LR transformation of normative matrices and give the error analysis of our algorithm. The operation number of the stable double LR algorithm for normative matrices is only four sevenths of the rational QR algorithm for reed symmetric tridiagonal matrices.     

基于小波-双马尔可夫随机场的纹理分割

传统高斯金字塔马尔可夫随机场模型仅仅捕捉图像低频信息,纹理分割效果不太理想.根据纹理图像小波分解后各频带的统计性质和层次关系,优化频带选取,提出了一种变形小波结构,建立了融合这种结构上尺度内部和尺度之间关系的双马尔可夫随机场模型,引入了一种近似最大联合概率分割算法,并从理论上分析了该算法的合理性.实验表明,与基于高斯金字塔马尔可夫随机场模型的分割方法相比,该算法分割质量明显提高;并且,对模型中自由参数的选取进行比较,证实它们在给定区间上的选择具有鲁棒性.     

用硅双结型色敏器件测量色温

提出了一种用硅双结型色敏器件测量色温的方法．在合理的测控电路下，硅双结型色敏器件的电流对数比与实验灯泡的色温值呈良好的单值对应，经单片机处理后可以得到分段线性关系．通过对电流对数比与波长随线的数据拟合，结果表明，用硅双结型色敏器件测量色温，其测量温度可以到10^4K以上，精度可以达到10K．本文的方法与传统方法相比减少了工作量，降低了费用，具有通用性和实用价值．