Reciprocating Probe Measurements of L-H Transition in LHCD H-Mode on EAST

As the power available in the initial phase of the ITER operation will be limited, accessing the high confinement mode （H-mode） with low heating power will be a critical issue. In the recent experiment on EAST, the H-mode was obtained for the first time with lower hybrid current drive （LHCD） wave only. Reciprocating Langmuir probe measurements at the outer midplane showed that the electron density ne and electron tempel：ature Te in the scrape-off layer （SOL） were significantly reduced in the ELM-free phase, resulting in the increase of lower-hybrid wave （LHW） reflection. It was found that the power loss Ploss was comparable during the L-H transition, by comparing the adjacent L-mode and H-mode discharge. The Da emission, Te and ne decreased rapidly in the time scale of about 1 ms, and the radial electric field Er turned positive in this process near the last closed flux surface. Multiple L-H-L transitions were observed during a single shot when the applied LHW power was marginal to the threshold. The floating potential （Vf） had negative spikes corresponding with the Da signal, and Er oscillation evolved into several intermittent negative spikes just before the L-H transition. In some shots, dithering was observed just before the L-H transition.

Magnetic Phase Transition in Two-Dimensional CrBr_(3) Probed by a Quantum Sensor

Recently,magnetism in two-dimensional(2 D)van der Waals(vd W)materials has attracted wide interests.It is anticipated that these materials will stimulate discovery of new physical phenomena and novel applications.The capability to quantitatively measure the magnetism of 2 D magnetic vd W materials is essential to understand these materials.Here we report on quantitative measurements of ferromagnetic-to-paramagnetic phase transition of an atomically thin(down to 11 nm)vd W magnet,namely Cr Br_(3),with a Curie point of 37.5 K.This experiment demonstrates that surface magnetism can be quantitatively investigated,which is useful for a wide variety of potential applications.

Transit time ultrasound perivascular flow probe technology is superior to MR imaging on hepatic blood flow measurement in a porcine model

Background: The hepatic hemodynamics is an essential parameter in surgical planning as well as in various disease processes. The transit time ultrasound(TTUS) perivascular flow probe technology is widely used in clinical practice to evaluate the hepatic inflow, yet invasive. The phase-contrast-MRI(PC-MRI) is not invasive and potentially applicable in assessing the hepatic blood flow. In the present study, we compared the hepatic inflow rates using the PC-MRI and the TTUS probe, and evaluated their predictive value of post-hepatectomy adverse events. Methods: Eighteen large white pigs were anaesthetized for PC-MRI and approximately 75% hepatic resection was performed under a unified protocol. The blood flow was measured in the hepatic artery(Qha), the portal vein(Qpv), and the aorta above the celiac trunk(Qca) using PC-MRI, and was compared to the TTUS probe. The Bland-Altman method was conducted and a partial least squares regression(PLS) model was implemented. Results: The mean Qpv measured in PC-MRI was 0.55 ± 0.12 L/min, and in the TTUS probe was 0.74 ± 0.17 L/min. Qca was 1.40 ± 0.47 L/min in the PC-MRI and 2.00 ± 0.60 L/min in the TTUS probe. Qha was 0.17 ± 0.10 L/min in the PC-MRI, and 0.13 ± 0.06 L/min in the TTUS probe. The Bland-Altman method revealed that the estimated bias of Qca in the PC-MRI was 32%(95% CI:-49% to 15%); Qha 17%(95% CI:-15% to 51%); and Qpv 40%(95% CI:-62% to 18%). The TTUS probe had a higher weight in predicting adverse outcomes after 75% resection compared to the PC-MRI( β= 0.35 and 0.43 vs β = 0.22 and 0.07, for tissue changes and premature death, respectively). Conclusions: There is a tendency of the PC-MRI to underestimate the flow measured by the TTUS probes. The TTUS probe measures are more predictive of relevant post-hepatectomy outcomes.

Spatial variation behaviors of argon inductively coupled plasma during discharge mode transition

A Langmuir probe and an ICCD are employed to study the discharge mode transition in Ar inductively coupled plasma. Electron density and plasma emission intensity are measured during the E （capacitive discharge） to H （inductive discharge） mode transitions at different pressures. It is found that plasma exists with a low electron density and a weak emission intensity in the E mode, while it has a high electron density and a strong emission intensity in the H mode. Meanwhile, the plasma emission intensity spatial （2D an asymmetric profile in the E mode. Moreover, the at high pressure, but increase almost continuously at image） profile is symmetrical in the H mode, but the 2D image is electron density and emission intensity jump up discontinuously the E to H mode transition under low pressure.

Investigation of E-H mode transition in magnetic-pole-enhanced inductively coupled neon-argon mixture plasma

In this paper,E-H mode transition in magnetic-pole-enhanced inductively coupled neon-argon mixture plasma is investigated in terms of fundamental plasma parameters as a function of argon fraction(0%-100%),operating pressure(1 Pa,5 Pa,10 Pa and 50 Pa),and radio frequency(RF)power(5-100 W).An RF compensated Langmuir probe and optical emission spectroscopy are used for the diagnostics of the plasma under study.Owing to the lower ionization potential and higher collision cross-section of argon,when its fraction in the discharge is increased,the mode transition occurs at lower RF power;i.e.for 0%argon and1 Pa pressure,the threshold power of the E-H mode transition is 65 W,which reduces to 20 W when the argon fraction is increased.The electron density increases with the argon fraction at afixed pressure,whereas the temperature decreases with the argon fraction.The relaxation length of the low-energy electrons increases,and decreases for high-energy electrons with argon fraction,due to the Ramseur effect.However,the relaxation length of both groups of electrons decreases with pressure due to reduction in the mean free path.The electron energy probability function(EEPF)profiles are non-Maxwellian in E-mode,attributable to the nonlocal electron kinetics in this mode;however,they evolve to Maxwellian distribution when the discharge transforms to H-mode due to lower electron temperature and higher electron density in H-mode.The tail of the measured EEPFs is found to deplete in both E-and H-modes when the argon fraction in the discharge is increased,because argon has a much lower excitation potential(11.5 eV)than neon(16.6 eV).

The Spin Transition and Susceptibility of NMR Samples in a Time Dependent Longitudinal Field

To construct pulsed high magnet, with rapid adjustments to large changes in the field strength, it is a mandatory acces-sory to development a special NMR probes to provide a precise real-time map of the magnetic field. In order to do so, it is necessary to understand the variations of the spin transition and susceptibility of NMR samples in a time dependent longitudinal field. This work analyzes the effect on the spin transition by a time dependent longitudinal field. For a 1/2 spin system, we have derived a simple formula for the prediction of the probabilities of occupation of the 1/2 and ?1/2 states in a non-static field. We also calculate the magnetic susceptibility of the water and give an analysis of the effect on the magnetic susceptibility in a time dependent longitudinal field and RF frequency.

Axial profiles of argon helicon plasma by optical emission spectroscope and Langmuir probe

We present the axial profiles of argon helicon plasma measured by a local optical emission spectroscope(OES) and Langmuir RF-compensated probe. The results show that the emission intensity of the argon atom lines(750 nm, 811 nm) is proportional to the plasma density determined by the Langmuir probe. The axial profile of helicon plasma depends on the discharge mode which changes with the RF power. Excited by helical antenna, the axial distribution of plasma density is similar to that of the external magnetic field in the capacitive coupled mode(E-mode). As the discharge mode changes into the inductively coupled mode(H-mode), the axial distribution of plasma density in the downstream can still be similar to that of the external magnetic field, but becomes more uniform in the upstream. When the discharge entered wave coupled mode(W-mode), the plasma becomes nearly uniform along the axis, showing a completely different profile from the magnetic field. The W-mode is expected to be a mixed pattern of helicon(H) and Trivelpiece-Gould(TG) waves.

A First Principles Simulation Framework for the Interactions between a Si(001) Surface and a Scanning Probe

By means of total energy calculations within the framework of the local density approximation (LDA), the interactions between a silicon Si(001) surface and a scanning probe are investigated. The tip of the probe, comprising 4 Si atoms scans along the dimer lines above an asymmetric p(2 × 1) surface, at a distance where the chemical interaction between tip-surface is dominant and responsible for image resolution. At that distance, the tip causes the dimer to toggle when it scans above the lower atom of a dimer. The toggled dimers create an alternating pattern, where the immediately adjacent neighbours of a toggled dimer remain unchanged. After the tip has fully scanned across the p(2 × 1) surface, causes the dimers to arrange in a p(2 × 2) reconstruction, reproducing the images obtained in scanning probe experiments. Our modelling methodology includes simulations that reveal the energy input required to overcome the barrier to the onset of dimer toggling. The results show that the energy input to overcome this barrier is lower for the p(2 × 1) surface than that for the p(2 × 2) or c(4 × 2) surfaces.

Scientists Innovate On-site in situ High-Pressure Ultrafast Pump-Probe Spectroscopy Instrument

Time-resolved ultrafast spectroscopy has been widely employed in condensed matter physics(and other sciences)due to its unique advantages,such as ultrahigh temporal resolution,capability of detecting excited-states above the Fermi surface,and generation of coherent boson excitations.It has been extensively used to investigate various condensed matter physics,including high-temperature superconductivity,complex phase transition.

太赫兹功率放大单片封装技术研究

本文对太赫兹功率放大单片封装技术进行研究,主要包括波导-微带垂直过渡和模块内的模式谐振抑制技术.不同于常规的矩形探针平面过渡,本文提出了一种基于分叉探针的垂直过渡结构,适用于多层电路排布的系统/模块封装,并在WR-4波导频段(170~260 GHz)进行了背靠背结构的实验验证,在整个波导频带内,回波损耗优于16 dB,单个过渡的插入损耗约0.42 dB,这包括了波导模块接触不良造成的额外的损耗.为进一步降低过渡损耗,提出了一种开口谐振环结构,用来抑制不良接触导致的电磁泄漏,使过渡损耗降低为原来的一半.此外,为避免功率放大模块内部发生模式谐振,提出将电磁带隙结构设置在平面传输线的上腔来抑制高次模的激励、传输和谐振.应用上述技术对工作于210~230 GHz的功率放大单片进行封装及测试.在210 GHz,小信号增益达到最大值20.75 dB,单端封装损耗约0.8 dB;在217 GHz达到最大输出功率15.6 dBm,与芯片手册数据吻合较好.

MoS_(2)/MoTe_(2)垂直异质结的电荷传输及其调制

二维材料异质结器件具有纳米级厚度及范德瓦耳斯接触表面,因而表现出独特的光电特性.本文构建了栅压可调的MoS_(2)/MoTe_(2)垂直异质结器件,利用开尔文探针力显微镜(KPFM)技术结合电输运测量,揭示了MoS_(2)/MoTe_(2)异质结分别在黑暗和532 nm激光照射条件下的电荷输运行为,发现随着栅压的变化异质结表现出从n-n^(+)结到p-n结的反双极性特征.系统地解释了MoS_(2)/MoTe_(2)异质结的电荷输运机制,包括n-n^(+)结和p-n结在正偏和反偏下条件下的电荷输运过程、随栅压变化而发生的转变的结区行为、接触势垒对电荷输运的影响、n-n^(+)结和p-n结具有不同整流特征的原因、偏压对带间隧穿的重要作用及光生载流子对电学输运行为的影响等.本文所使用的方法可推广到其他二维异质结体系,为提高二维半导体器件性能及其应用提供了重要的参考和借鉴.

MoS_(2)和MoTe_(2)同质结和异质结中的表面电势排列

过渡金属硫族化合物(TMD)薄层仅改变几何形状(如层厚)就可调节带隙、电子亲和势和费米能级,使器件设计更灵活。但因缺乏费米能级排列信息,TMD同质/异质结器件常因未知的能带弯曲而偏离预期。利用扫描开尔文探针显微镜(SKPM)表征了TMD同质/异质结,结果显示,Mo S_(2)和Mo Te_(2)同质结的费米能级随层厚增加向本征费米能级移动(背景掺杂浓度降低),而Mo Te_(2)/Mo S_(2)异质结中探测到宽耗尽区和强光响应,同时给出表面污染(分子尺度)对单层TMD表面电势的影响。上述发现将在器件设计中帮助精准堆叠范德华(vdW)层。

Highly lipophilic coumarin fluorophore with excimer-monomer transition property for lipid droplet imaging

Lipid droplet(LD) fluorescent imaging plays an important role in the detection of lipid-related diseases.Due to their poor photostability and low hydrophobicity of currently available LD imaging fluorophores,LD imaging is limited by its short imaging period and low imaging contrast. Herein, we reasonably designed a highly lipophilic compound Cou-Flu with excellent photostability and excimer-monomer transition property. It exhibited weak excimer emission in cytoplasm, but strong monomer emission in LDs,enabling high contrast LD imaging and LD movement tracing in cells. Zebrafish imaging study demonstrated that Cou-Flu was also suitable for in vivo LD detection with excellent sensitivity. We anticipate that Cou-Flu could be widely applied to understand LD-related intracellular activities and even LD-related diseases in the future.

测量爆燃到爆震转捩距离的离子探针技术研究

为了测量爆震管中从爆燃到爆震转捩距离,研制了一套基于对比电路的离子探针系统。通过该系统测量爆震管中火焰传播速度的轴向分布,确定了爆燃到爆震的转捩距离。系统结构简单,造价低廉,可用于高温环境下测量。运用该系统测量的乙炔与氧气混合气从爆燃到爆震转捩的距离,其结果与采用高频响的压力传感器系统的测量结果一致。

湍动流化床过渡段固含率分布特征的实验及数值模拟

在湍动流化床中,过渡段对于包括甲醇制烯烃在内的气固催化快反应有着重要的作用。采用PV6D反射型光纤探针对内径95mm的湍动流化床内过渡段的固含率分布和脉动参数进行了测量,分别考察了表观气速和静床高的影响,并采用修正的基于颗粒动力学的三段曳力双流体模型进行模拟。实验表明,湍动流化床过渡段中固含率的轴向分布呈现S型和指数型两种类型,固含率轴向与径向分布都在过渡段内出现最大梯度,表明过渡段中固体浓度分布比稀相段和密相段更不均匀。表观气速和静床高的变化将导致S型和指数型分布的相互转变,并且对过渡段底部与壁面附近的固体高浓度区影响最为显著。局部固含率脉动概率密度分布表明,在静床高较小时,随着气速的增大,床层下部气含率最大值位置将从中心区移动至环隙区,呈现气含率的双峰型分布。本文提出的修正三段曳力模型考虑了颗粒团聚的影响,对过渡段中分布板影响区之外的固含率分布均能较好地模拟。

四种典型炸药燃烧转爆轰试验研究

为了对常用组分构成的炸药燃烧转爆轰(DDT)过程进行预估,采用熔铸工艺制备了P1(40%TNT/60%RDX)、P2(40%DNTF/40%HMX/10%TATB/5%Al/5%添加剂)、P3(25%DNTF/40%AP/30%Al/5%添加剂)3种混合炸药,采用浇注工艺制备了P4(30%RDX/30%AP/30%Al/10%添加剂)炸药,用同轴电离探针测试技术对4种炸药进行了DDT试验,从DDT管的破碎状态、DDT过程中波阵面传播速度及爆轰转变距离分析了DDT响应特征。结果表明,炸药P1、P2、P3发生了DDT,爆轰转变距离范围分别为750~825mm、375~450mm、675~750mm,炸药P4未发生DDT;炸药P2的DDT管破裂最剧烈,炸药P3次之,炸药P1最小,表明DDT管的破碎程度与炸药的爆压正相关;炸药配方中含有热分解温度接近的组分,使热分解放热量快速叠加,促使燃烧状态失稳,提高燃烧向爆轰的转变;浇注成型工艺由于存在惰性添加剂对炸药组分的隔离包覆和吸热作用,降低了炸药由燃烧向爆轰转变的可能性。

Ka波段波导-微带转接器的设计

本文分析了Ka波段波导-微带探针转接微波特性,利用全波分析软件对它进行了仿真分析,设计了Ka波段波导-微带转接器,实验测试与仿真设计结果十分相近:在26.5～40GHz内插入损耗0.75～1.27dB,回波损耗-38～-23dB,该波导-微带转接器在整个频段内性能良好,符合工程应用的要求。

DNTF基炸药燃烧转爆轰影响因素实验研究

为了研究二硝基呋咱基氧化呋咱(DNTF)基混合炸药燃烧到爆轰转变(DDT)过程的有效调控技术,采用同轴电离探针测量技术研究了点火药量、DDT管壁厚约束、成型方式等对DNTF基混合炸药DDT性能的影响,从DDT管破裂状态、DDT过程不同位置处波阵面速度、诱导爆轰距离等变化对实验结果进行了分析。结果表明,DDT管壁厚约束对DNTF基混合炸药DDT的诱导爆轰距离没有明显影响,都在375 mm左右,但壁厚减小会使爆燃阶段持续时间增加,达到爆轰的初始速度减小到5515 m·s^(-1);点火药量增加对DNTF基混合炸药DDT反应剧烈性没有明显影响,但会减小初始燃烧持续时间和诱导爆轰距离;压制成型试样DDT的初始燃烧持续时间、爆燃持续时间及诱导爆轰距离均大于熔铸成型试样,但反应剧烈性没有差别。

基于车载数据的城市道路交叉口自适应控制研究

在总结现有交叉口交通控制弊端的基础上,通过对控制目标和任务的分析,基于车路协同系统的全时空车载数据,以单车道的车队和多车道的车队簇为控制对象,利用车头时距和间距研究车队和车队簇的形成和动态变化规律,建立了基于车载数据的交叉口自适应控制模型,同时在相位切换逻辑中考虑了两难区.最后基于二次开发的仿真平台,对研究成果进行了测试和验证,相关的案例分析表明,模型应用对于交叉口平峰和低峰情况下的运行效率和安全性有显著改善.

钻杆漏磁检测探头的设计

钻杆经常在加厚过渡区与杆体交界处发生穿刺或断裂失效,利用有限元分析软件模拟仿真,通过电磁场数值计算,对钻杆漏磁检测探头进行了磁路分析、结构优化及量化设计。给出了钻杆漏磁检测探头总体结构设计。提出并探讨了探头芯最佳检测姿态及其必要性。设计出了探头芯多个浮动自由度的实现方案。阐述了减少检测盲区的途径及检测探头的模块化设计。实验测试表明:该漏磁检测探头具有检测盲区小、探头芯柔性化、模块化的特征和良好的试用效果。