Device topological thermal management of β-Ga_2O_3 Schottky barrier diodes

The ultra-wide bandgap semiconductor β gallium oxide(β-Ga_2 O_3) gives promise to low conduction loss and high power for electronic devices. However, due to the natural poor thermal conductivity of β-Ga_2 O_3, their power devices suffer from serious self-heating effect. To overcome this problem, we emphasize on the effect of device structure on peak temperature in β-Ga_2 O_3 Schottky barrier diodes(SBDs) using TCAD simulation and experiment. The SBD topologies including crystal orientation of β-Ga_2 O_3, work function of Schottky metal, anode area, and thickness, were simulated in TCAD, showing that the thickness of β-Ga_2 O_3 plays a key role in reducing the peak temperature of diodes. Hence, we fabricated β-Ga_2 O_3 SBDs with three different thickness epitaxial layers and five different thickness substrates. The surface temperature of the diodes was measured using an infrared thermal imaging camera. The experimental results are consistent with the simulation results. Thus, our results provide a new thermal management strategy for high power β-Ga_2 O_3 diode.     

High-responsivity solar-blind photodetector based on MOCVD-grown Si-doped β-Ga_2O_3 thin film

Si-doped β-Ga_2O_3 films are fabricated through metal-organic chemical vapor deposition(MOCVD). Solar-blind ultraviolet(UV) photodetector(PD) based on the films is fabricated by standard photolithography, and the photodetection properties are investigated. The results show that the photocurrent increases to 11.2 m A under 200 μW·cm-2254 nm illumination and ±20 V bias, leading to photo-responsivity as high as 788 A·W~(-1). The Si-doped β-Ga_2O_3-based PD is promised to perform solar-blind photodetection with high performance.     

Time-resolved radial uniformity of pulse-modulated inductively coupled O_2/Ar plasmas

Time-resolved radial uniformity of pulse-modulated inductively coupled O_2/Ar plasma has been investigated by means of a Langmuir probe as well as an optical probe in this paper. The radial uniformity of plasma has been discussed through analyzing the nonuniformity factor β(calculated by the measured n_e, lower β means higher plasma radial uniformity). The results show that during the active-glow period, the radial distribution of ne exhibits an almost flat profile at the beginning phase, but it converts into a parabola-like profile during the steady state. The consequent evolution for β is that when the power is turned on, it declines to a minimum at first, and then it increases to a maximum, after that, it decays until it keeps constant. This phenomenon can be explained by the fact that the ionization gradually becomes stronger at the plasma center and meanwhile the rebuilt electric field(plasma potential and ambipolar potential) will confine the electrons at the plasma center as well. Besides, the mean electron energy( ε_(on)) at the pulse beginning decreases with the increasing duty cycle. This will postpone the plasma ignition after the power is turned on. This phenomenon has been verified by the emission intensity of Ar(λ = 750.4 nm). During the after-glow period, it is interesting to find that the electrons have a large depletion rate at the plasma center. Consequently, ne forms a hollow distribution in the radial direction at the late stage of after-glow. Therefore, β exhibits a maximum at the same time. This can be attributed to the formation of negative oxygen ion(O~-) at the plasma center when the power has been turned off.     

Ab initio investigation of photoinduced non-thermal phase transition in β-cristobalite

Using the linear-response method, we investigate the phonon properties of β-cristobalite crystal under electronic excitation effect. We find that the transverse-acoustic phonon frequency becomes imaginary as the electron temperature is increased, which means that the lattice of β-cristobalite becomes unstable under intense laser irradiation. In addition, for the optic phonon mode, the LO(H)–TO(H) splitting disappears when the electronic temperature reaches a certain value,corresponding to the whole transverse-acoustic phonon branches becoming negative. It means that the electronic excitation destroys the macroscopic electric field of β-cristobalite. Based on the calculated phonon band structures, some thermodynamic properties are calculated as a function of temperature at different electronic temperatures. These investigations provide evidence that non-thermal melting takes place during a femtosecond pulse laser interaction with β-cristobalite.     

Z箍缩内爆产生的电磁脉冲辐射

讨论了Z箍缩内爆产生的低频电磁脉冲的辐射特性. Z箍缩驱动金属丝阵或固体套筒高速内爆,部分磁能通过与负载的运动耦合而向外辐射. 理论结果表明,电磁脉冲辐射功率由电流和内爆轨迹共同决定. 在中国工程物理研究院流体物理研究所的初级实验平台上开展了负载电流为7 MA,10%–90%上升时间65 ns的丝阵Z箍缩实验,根据实验测得的电流和内爆轨迹得到了电磁脉冲的辐射功率和频谱. 电磁脉冲峰值功率约为1 GW,能量约为0.5 J,能量转换效率约为10^-7;峰值频率位于20–70 MHz,具有较宽的辐射频谱. 电磁脉冲辐射参数远小于软X射线辐射参数（峰值功率为50 TW,能量为0.5 MJ）. 在弱相对论条件下,电磁脉冲辐射功率近似地正比于电流的6次方,随电流急剧增大. 软X射线辐射是丝阵Z箍缩过程中的主要能量转换形式,本文的研究结论表明,在更高的驱动电流下,电磁脉冲辐射将提供另一种重要的能量转换途径,势必会对诊断设备造成严重影响;此外,这类强电磁脉冲在其他领域也具有潜在的应用价值. 关键词： Z箍缩 内爆 电磁脉冲     

1H NMR研究β-环糊精与环氧氯丙烷共聚物的反应机理和分子链结构

β-环糊精(cyclodcxtrin)与环氧氯丙烷(Epichlorohydrin)一个系列的共聚物获得,¹H NMR以D₂O或DMSO-d₆为溶剂的测定,其谱峰被归属.共聚合反应机理为以羟基和环氧基为活性中心的亲核取代.当环氧氯丙烷:β-环糊精=n ≤ 3时,聚合物分子链呈现以β-环糊精母体为中心的线状或低枝化状链结构;当n ≥ 5时,分子链出现交联网络结构.n越大(n ≤ 12),分子量越急剧增加,其交联度也越大.     

Temperature and current sensitivity extraction of optical superconducting transition-edge sensors based on a two-fluid model

Optical superconducting transition-edge sensor(TES) has been widely used in quantum information, biological imaging, and fluorescence microscopy owing to its high quantum efficiency, low dark count, and photon number resolving capability. The temperature sensitivity(α_I) and current sensitivity(β_I) are important parameters for optical TESs, which are generally extracted from the complex impedance. Here we present a method to extract α_I and β_I based on a twofluid model and compare the calculated current–voltage curves, pulse response, and theoretical energy resolution with the measured ones. This method shows qualitative agreement that is suitable for further optimization of optical TESs.     

电磁辐射诱发神经元放电节律转迁的动力学行为研究

本文首先根据能量转换理论建立了电磁辐射影响下神经元电流变量模型, 然后结合Hodgkin-Huxley(HH)神经元模型研究了电磁辐射对单个神经元以及耦合神经元放电行为的影响. 结果表明, 随着电磁辐射强度的增大, 神经元放电率逐渐减小, 最后达到一个比较稳定的值. 神经元原有的周期型放电由于辐射强度的增大而逐步过渡到簇放电状态, 并借助动态分岔理论解释了这种放电模式的转换. 同时证明了磁辐射对单个神经元放电的影响可以通过神经元间的耦合传递到临近其他神经元中.     

Dynamical response of a neuron–astrocyte coupling system under electromagnetic induction and external stimulation

Previous studies have observed that electromagnetic induction can seriously affect the electrophysiological activity of the nervous system. Considering the role of astrocytes in regulating neural firing, we studied a simple neuron–astrocyte coupled system under electromagnetic induction in response to different types of external stimulation. Both the duration and intensity of the external stimulus can induce different modes of electrical activity in this system, and thus the neuronal firing patterns can be subtly controlled. When the external stimulation ceases, the neuron will continue to fire for a long time and then reset to its resting state. In this study, "delay" is defined as the delayed time from the firing state to the resting state, and it is highly sensitive to changes in the duration or intensity of the external stimulus. Meanwhile, the self-similarity embodied in the aforementioned sensitivity can be quantified by fractal dimension. Moreover, a hysteresis loop of calcium activity in the astrocyte is observed in the specific interval of the external stimulus when the stimulus duration is extended to infinity, since astrocytic calcium or neuron electrical activity in the resting state or during periodic oscillation depends on the initial state. Finally, the regulating effect of electromagnetic induction in this system is considered. It is clarified that the occurrence of "delay" depends purely on the existence of electromagnetic induction. This model can reveal the dynamic characteristics of the neuron–astrocyte coupling system with magnetic induction under external stimulation. These results can provide some insights into the effects of electromagnetic induction and stimulation on neuronal activity.     

场耦合忆阻神经网络的电活动

神经元之间除了突触耦合，还存在磁通耦合.因此在传统的神经元模型中引入磁通量，并研究场耦合下神经网络的放电活动具有实际意义.建立一个含场耦合的Hodgkin-Huxley忆阻神经网络，引入神经元节点之间的距离权重，用磁通量描述时变电磁场，采用磁控忆阻器实现膜电位和磁通量之间的耦合.探讨距离权重和系统大小对神经网络放电活动的影响.研究发现，随着权重增大，神经网络放电活动增强，且系统规模越大，诱导神经元兴奋性的权重阈值越大，系统大小不影响神经网络活性随距离权重变化的规律.在不同的权重值下，神经网络活性随系统大小变化的规律明显不同.研究表明，距离权重和系统大小对含场耦合的忆阻神经网络放电活动有重要影响，其中距离权重起主导作用.     

Cyclotron-resonance maser driven by magnetic compression of rarefied plasma

Conditions are found at which adiabatic magnetic compression of plasma confined in a mirror magnetic trap is accompanied by the accumulation of significant energy in a hot anisotropic electron tail with the subsequent release of this energy as a pulse of coherent electromagnetic radiation. The possibilities of creating THz radiation sources up to the GW power level are discussed.     

精确提取一维互易有限周期性结构色散特性的宏元胞法

提出了一种可精确提取一维互易有限周期性结构色散特性的宏元胞法. 将多个周期性元胞组合构成单个“宏元胞”, 以严格考量元胞间的互耦效应, 通过Bloch分析分别计算出正向激励和反向激励时Bloch 波的本征传输因子ξ^N和1/ξ^N, 对ξ^N取复对数操作即可解出一维有限周期性结构的衰减常数α, 而复对数函数的多值性使得相移常数β存在多整数分支的选择问题. 通过与解卷绕法获得的β近似值相比较,选择出合理的整数分支, 可精确计算出β. 与传统的本征模式法、解卷绕法及单元胞法相比,宏元胞法对元胞间的耦合强度不作要求, 计算更加精确快速, 可作为刻画一维互易有限周期性结构色散和Bloch阻抗特性的有力工具. 关键词： 宏元胞法 Bloch分析 色散特性     

二氢沉香呋喃倍半萜的2D NMR研究

利用¹H-¹³C相关(¹H-¹³C COSY)谱对1β-乙酰氧基-2β(α-甲基丁酰氧基)-6α-羟基-8β,9α-二苯甲酰氧基-β-二氢沉香呋喃(A),和1β-乙酰氧基-2β(α-甲基丁酰氧基)-6α-羟基-8β(β-呋喃甲酰氧基)-9α-苯甲酰氧基-β-二氢沉香呋喃(B)的¹³C NMR谱化学位移进行了全指定,利用¹H-¹H远程相关(¹H-¹H COSYLR)谱确定了化合物A和B中6-Ha和7-He,8-He和9-He的弱偶合,以及7-He和9-He的弱W型远程偶合.     

Stochastic resonance and synchronization behaviors of excitatory-inhibitory small-world network subjected to electromagnetic induction

The phenomenon of stochastic resonance and synchronization on some complex neuronal networks have been investigated extensively.These studies are of great significance for us to understand the weak signal detection and information transmission in neural systems.Moreover,the complex electrical activities of a cell can induce time-varying electromagnetic fields,of which the internal fluctuation can change collective electrical activities of neuronal networks.However,in the past there have been a few corresponding research papers on the influence of the electromagnetic induction among neurons on the collective dynamics of the complex system.Therefore,modeling each node by imposing electromagnetic radiation on the networks and investigating stochastic resonance in a hybrid network can extend the interest of the work to the understanding of these network dynamics.In this paper,we construct a small-world network consisting of excitatory neurons and inhibitory neurons,in which the effect of electromagnetic induction that is considered by using magnetic flow and the modulation of magnetic flow on membrane potential is described by using memristor coupling.According to our proposed network model,we investigate the effect of induced electric field generated by magnetic stimulation on the transition of bursting phase synchronization of neuronal system under electromagnetic radiation.It is shown that the intensity and frequency of the electric field can induce the transition of the network bursting phase synchronization.Moreover,we also analyze the effect of magnetic flow on the detection of weak signals and stochastic resonance by introducing a subthreshold pacemaker into a single cell of the network and we find that there is an optimal electromagnetic radiation intensity,where the phenomenon of stochastic resonance occurs and the degree of response to the weak signal is maximized.Simulation results show that the extension of the subthreshold pacemaker in the network also depends greatly on coupling strength.The presented results may have important implications for the theoretical study of magnetic stimulation technology,thus promoting further development of transcranial magnetic stimulation(TMS) as an effective means of treating certain neurological diseases.     

蛋白质二硫键异构酶与α-突触核蛋白的相互作用及对其聚集的影响

α-突触核蛋白（α-synuclein,αsyn）的错误折叠和聚集是帕金森症的疾病特征.分子伴侣蛋白质二硫键异构酶（PDI）可在体外结合αsyn的N端并抑制其聚集,但PDI的识别机制至今仍不明确.我们通过液体核磁共振（NMR）实验,发现人源PDI b'xa'可结合αsyn的N端区域.此外,硫黄素T（ThT）荧光实验结果表明PDI b'xa'会显著抑制αsyn的聚集.我们进一步利用NMR滴定实验确定了PDI主要通过b'结构域的疏水空腔结合αsyn.最后,我们以此构建了PDI结合αsyn的对接模型,并提出了PDI抑制αsyn聚集的作用机理.这一工作为理解PDI抑制αsyn聚集提供了实验依据.     

用2D NMR研究一对差向异构体的化学结构

从刺南蛇藤中首次分离到一对差向异构体,用NMK方法(¹H NMR,¹³C NMR,DEPT,¹H-¹H COSY,¹³C-¹H COSY,NOESY,HMBC)并结合其它结构信息,确定其化学结构为;1α,6β,8α,13-四乙酰氧基-9α-苯甲酰氧基-β-二氢沉香呋喃(1)和1α,6β,8α,13-四乙酰氧基-9β-苯甲酰基-β-二氢沉香呋喃(2).其中1为新化合物,命名为Celastrine。     

Lateral β-Ga2O3 Schottky barrier diode fabricated on (-201) single crystal substrate and its temperature-dependent current-voltage characteristics

Lateral β-Ga₂O₃ Schottky barrier diodes (SBDs) each are fabricated on an unintentionally doped (-201) n-type β-Ga₂O₃ single crystal substrate by designing L-shaped electrodes. By introducing sidewall electrodes on both sides of the conductive channel, the SBD demonstrates a high current density of 223 mA/mm and low specific on-resistance of 4.7 mΩ ·cm². Temperature-dependent performance is studied and the Schottky barrier height is extracted to be in a range between 1.3 eV and 1.35 eV at temperatures ranging from 20 ℃ to 150 ℃. These results suggest that the lateral β-Ga₂O₃ SBD has a tremendous potential for future power electronic applications.     

电离辐射对小鼠肾脏影响的代谢组学研究

电离辐射对生物体影响是目前生物医学领域研究的热点之一.本文利用基于核磁共振氢谱（¹H NMR）的代谢组学技术研究来自暴露于不同的电离辐射的C57BL/6J小鼠的肾脏的水溶性萃取物,并试图寻找电离辐射对小鼠肾脏影响的特异性生物标志物.分析结果表明,辐射组可与相应的对照组明显区分.在所发现的75个代谢物中,有6种代谢物的浓度发生显著性变化,分别为2-氨基丁酸、3-羟基丁酸、高丝氨酸、1,3-丙二胺、β-丙氨酸和抗坏血酸.这些代谢物可能成为高剂量电离辐射对生物体肾脏代谢影响的标志物.     

Generation of 1.5-kW, 1-THz coherent radiation from a gyrotron with a pulsed magnetic field

To cover a so-called terahertz gap in available sources of coherent electromagnetic radiation, the gyrotron with a pulsed solenoid producing up to a 40 T magnetic field has been designed, manufactured, and tested. At a 38.5 T magnetic field, the gyrotron generated coherent radiation at 1.022 THz frequency in 50 musec pulses. The microwave power and energy per pulse were about 1.5 kW and 75 mJ, respectively. Details of the gyrotron design, manufacturing, operation and measurements of output radiation are given.     

High-pressure elastic anisotropy and superconductivity of hafnium:A first-principles calculation

The elastic anisotropy and superconductivity upon hydrostatic compression of α, ω, and β Hf are investigated using first-principle methods. The results of elastic anisotropies show that they increase with increasing pressure for α andω phases, while decrease upon compression for β phase. The calculated superconducting transition temperatures are in excellent agreement with experiments. Electron–phonon coupling constants(λ) are increasing with pressure for α and ωphases, while decreasing for β phase. For β phase, the large values of λ are mainly due to the obvious TA1 soft mode.Under further compression, the TA1 soft vibrational mode will disappear gradually.