Study of beam divergence and thrust vector eccentricity characteristics of the Hall thruster based on dual Faraday probe array planes and its applications

The accurate knowledge of the thrust vector eccentricity and beam divergence characteristics of Hall thrusters are of significant engineering value for the beneficial integration and successful application of Hall thrusters on spacecraft.For the characteristics of the plume bipolar diffusion due to the annular discharge channel of the Hall thruster,a Gaussian-fitted method for thrust vector deviation angle and beam divergence of Hall thrusters based on dual Faraday probe array planes was proposed in respect of the Hall thruster beam characteristics.The results show that the ratios of the deviation between the maximum and minimum values of the beam divergence angle and the thrust vector eccentricity angle using a Gaussian fit to the optimized Faraday probe dual plane to the mean value are 1.4%and 11.5%,respectively.The optimized thrust vector eccentricity angle obtained has been substantially improved,by approximately 20%.The beam divergence angle calculated using a Gaussian fitting to the optimized Faraday probe dual plane is approximately identical to the non-optimized one.The beam divergence and thrust vector eccentricity angles for different anode mass flow rates were obtained by averaging the beam divergence and thrust vector eccentricity angles calculated by the dual-plane,Gaussian-fitted ion current density method for different cross-sections.The study not only allows for an immediate and effective tool for determining the design of thrust vector adjustment mechanisms of spacecraft with different power Hall thrusters but also for characterizing the 3D spatial distribution of the Hall thruster plume.

Improved Double-Probe Technique for Spatially Resolved Diagnosis of Dual-Frequency Capacitive Plasmas

The conventional double-probe technique was improved with a combination of selfpowering and radio-frequency（RF） choking.RF perturbations in dual-frequency capacitively coupled discharge were effectively eliminated,as judged by the disappearance of self-bias on the probes.The improved technique was tested by spatially resolved measurements of the electron temperature and ion density in both the axial and radial directions of a dual-frequency capacitive plasma.The measured data in the axial direction were compared with simulation results,and they were excellently consistent with each other.The measured radial distributions of the ion density and electron temperature were influenced significantly by the lower frequency（LF） power.It was shown that superposition of the lower frequency to the higher frequency（HF） power shifted the maximum ion density from the radial center to the edge region,while the trend for the electron temperature profile was the opposite.The changing feature of the ion density distribution is qualitatively consistent with that of the optical emission intensity reported.

早期香蕉枯萎病Foc4双探针核酸纸基检测传感器研制

为实现对早期香蕉枯萎病4号生理小种(fusarium oxysporum f.sp.cubense 4, Foc4)的准确检测,该研究提出一种基于胶体金的双探针纸基传感器。该传感器将2种不同粒径的胶体金分别与检测探针和信号增强探针结合,利用DNA探针代替抗原和抗体,形成双探针体系,通过增加信号增强探针降低检测限。基于目标序列与双探针体系的碱基互补配对形成“金标探针-目标序列-T线探针”复合物并在传感器的测试区被捕获,10 min内形成肉眼可见的目标产物,通过分析测试条带得到光强度峰面积并代入标准曲线中,实现Foc4定量检测。试验结果表明,双探针纸基传感器的检测限达到0.001 nmol/L,是传统纸基传感器的100倍,提高了检测灵敏度;在0.001~1 000.000 nmol/L范围内,Foc4浓度与测试线光强度峰面积呈线性关系;使用高浓度非互补探针进行试验干扰,发现非互补序列对检测效果基本无影响,表明该传感器具有较好的特异性;香蕉叶片Foc4检测的平均回收率为77.6%~102.3%,相对标准偏差为7.4%~7.7%。与传统形态学观察等检测方法相比,该研究提出的双探针核酸纸基检测传感器可以及时、快速、准确地判断早期Foc4的存在,具有良好的推广性和实际应用价值。

双针热脉冲测定冻土热特性的数值模拟方法

使用双针热脉冲(dual probe heat pulse, DPHP)测定冻土热特性时施加热脉冲后会导致加热探针周围的冰融化,使用目前常用的仅考虑热传导(忽略融化相变、冰水两相分界面)的解析解处理DPHP温度数据,会导致在-5℃至0℃温度范围内无法准确测量热导率(λ)和比热(C_(v))。为了能够准确测定冻土的λ和C_v,有必要考虑DPHP加热过程中引起的冰融化的相变潜热。该研究基于COMSOL仿真软件模拟了考虑相变潜热、相变区间以及移动冰水界面的DPHP测量过程,采用随温度非线性变化的真实冻土热特性进行模拟,并与真实冻土的DPHP测量数据对比。结果表明:1)COMSOL仿真在不考虑相变条件下与无限线性热源模型结果完全吻合(R^(2)=0.998 9);2)当土壤初始温度低于-5℃时,考虑相变发生的COMSOL仿真能够准确模拟试验结果,表现出较高的相关性(R^(2)> 0.93),在-1~0℃的土壤初始温度范围内,无限线性热源模型的结果与试验测量显著偏离(R^(2) <0.001 3);3)在不同土壤初始温度下,相变温度为-1.5~-0.5℃的仿真结果与试验数据具有较高的相关性(R^(2)> 0.7)。该研究结果检验了有限元仿真用于真实冻土DPHP研究的可行性,可为准确预测冻土热特性的研究提供方法。

基于Eu^(3+)-生物质碳量子点探针的比率型荧光传感体系检测盐酸四环素

该文以橙皮为原料制备的碳量子点(CDs)与铕离子(Eu^(3+))构建双发射比率型荧光探针(Eu^(3+)-CDs)并用于抗生素盐酸四环素的检测。在370 nm激发波长下,Eu^(3+)-CDs荧光探针在425 nm处出现较强的蓝色荧光峰,在617 nm处出现较弱的红色荧光峰。随着盐酸四环素浓度的逐渐增大,Eu3+与盐酸四环素螯合形成的配合物增多,在425 nm处的CDs荧光(I_(F425))逐渐减弱,而617 nm处铕配合物的荧光(I_(F617))逐渐增强,可基于荧光强度比I_(F617)/I_(F425)的变化对盐酸四环素进行测定。考察了Eu^(3+)的浓度、pH值和反应时间对探针荧光强度的影响。在最佳条件下,该双发射比率型荧光探针对盐酸四环素具有特异性识别能力,荧光强度比(I_(F617)/I_(F425))与盐酸四环素浓度在10~100µmol/L范围内存在良好的线性关系,相关系数r^(2)=0.9926,检出限为5.09µmol/L。该方法成功用于猪肉中盐酸四环素含量的检测,加标回收率为102%~110%,相对标准偏差为0.20%~2.4%,具有较好的实用性。

Plasma Uniformity in a Dual Frequency Capacitively Coupled Plasma Reactor Measured by Optical Emission Spectroscopy

Local measurement of plasma radial uniformity was performed in a dual frequency capacitively coupled argon plasma （DF-CCP） reactor using an optical probe. The optical probe collects the light emission from a small separate volume in plasma, thus enabling to diagnose the plasma uniformity for different experimental parameters. Both the gas pressure and the low- frequency （LF） power have apparent effects on the radial uniformity of argon plasma. With the increase in either pressure or LF power, the emission profiles changed from a bell-shaped to a double-peak distribution. The influence of a fused-silica ring around the electrodes on the plasma uniformity was also studied using the optical probe. Possible reasons that result in nonuniform plasmas in our experiments are discussed.

Investigation of Capacitively Coupled Argon Plasma Driven by Dual-Frequency with Different Frequency Configurations

Low pressure argon dual-frequency （DF） capacitively coupled plasma （CCP） is generated by using different frequency configurations, such as 13.56/2, 27/2, 41/2, and 60/2 MHz. Characteristics of the plasma are investigated by using a floating double electrical probe and optical emission spectroscopy （OES）. It is shown that in the DF-CCPs, the electron temperature Te decreases with the increase in exciting frequency, while the onset of 2 MHz induces a sudden increase in Te and the electron density increases basically with the increase in low frequency （LF） power. The intensity of 750.4 nm emission line increases with the LF power in the case of 13.56/2 MHz, while different tendencies of line intensity with the LF power appear for other configurations. The reason for this is also discussed.

Abnormal Enhancement of N_2^+ Emission Induced by Lower Frequency in N_2 Dual-Frequency Capacitively Coupled Plasmas

Nitrogen dual-frequency capacitively coupled plasmas （DF-CCPs） with different fre- quency configurations, i.e., 60/2 MHz and 60/13.56 MHz, are investigated by means of opticM emission spectroscopy （OES） and a floating double probe. The excited nitrogen molecule ion N＋（B） is monitored by measuring the emission intensity of the （0,0） bandhead of the first neg- ative system （FNS） at 391.44 nm. It is shown that in the discharge with 60/13.56 MHz, the N＋ emission intensity decreases with the increase in pressure. In the discharge with 60/2 MHz, however, an abnormal enhancement of N＋ emission at higher pressure is observed when a higher power of 2 MHz is added. Variation in the ion density shows a similar dependence on the gas pressure. This indicates that in the discharge with 60/2 MHz there is a mode transition from the alpha to gamma type when a higher power of 2 MHz is added at high pressures. Combining the measurements using OES and double probe, the influence of low frequency on the discharge is investigated and the excitation route of the N＋（B） state in the discharge of 60/2 MHz is also discussed.

Plasma diagnosis of tetrahedral amorphous carbon films by filtered cathodic vacuum arc deposition

Filtered cathodic vacuum arc(FCVA)deposition is regarded as an important technique for the synthesis of tetrahedral amorphous carbon(ta-C)films due to its high ionization rate,high deposition rate and effective filtration of macroparticles.Probing the plasma characteristics of arc discharge contributes to understanding the deposition mechanism of ta-C films on a microscopic level.This work focuses on the plasma diagnosis of an FCVA discharge using a Langmuir dualprobe system with a discrete Fourier transform smoothing method.During the ta-C film deposition,the arc current of graphite cathodes and deposition pressure vary from 30 to 90 A and from 0.3 to 0.9 Pa,respectively.The plasma density increases with arc current but decreases with pressure.The carbon plasma density generated by the arc discharge is around the order of10^(10)cm^(-3).The electron temperature varies in the range of 2-3.5 eV.As the number of cathodic arc sources and the current of the focused magnetic coil increase,the plasma density increases.The ratio of the intensity of the D-Raman peak and G-Raman peak(I_(D)/I_(G))of the ta-C films increases with increasing plasma density,resulting in a decrease in film hardness.It is indicated that the mechanical properties of ta-C films depend not only on the ion energy but also on the carbon plasma density.

Experimental Characterization of Dual-Frequency Capacitively Coupled Plasma with Inductive Enhancement in Argon

The dual-frequency capacitively coupled plasma （DF-CCP） with inductive enhancement system is a newly designed plasma reactor. Different from the conventional inductively coupled plasma （ICP） reactors, now a radio frequency （rf） power is connected to an antenna placed outside the chamber with a one-turn bare coil placed between two electrodes in DF-CCP. This paper gives a detailed description of its structure of discharges in this apparatus were made via a Moreover, investigations on some characteristics Langmuir probe.

Application of dual color fluorescence in situ hybridiza tion (D-FISH) to the diagnosis of a 49, XXXXY chromo somal abnormality

To study the technique of D-FISH and its application in the diagnosis of a 49, XXXXY chromosomal abnormality. Methods: Biotin-labeled alpha satellite X chromosome DNA (pBamX7) probe and digoxi-genin-labeled Y chromosome long arm terminal repetitive sequence (pY3.4) probe in situ hybridized with pre-treated slides of peripheral blood chromosome and interphase nucleus. After washing, the slides were treated with avidin-FITC, rhodamine-FITC and anti-avidin, amplified with an additional layer and counter-stained with DAPI in an antifade solution. The hy bridization signals and chromosomal or interphase nucleus settings were observed respectively with WIB, WIG and WU filters under fluorescent microscope (Olympus AX-70) and the number of metaphase chromosome and interphase nucleus in the peripheral blood was counted. Results: The biotin-labeled pBamX7 probe showed 4 green hybridization signal and the digoxigenin-labeled pY3.4 probe showed 1 red hybridization signal. The chromosome or cytoplasm counter-stained with DAPI showed blue. The positive rate of X chromosome hybridization signal for the 350 metaphase chromosomes and interphase nucleus was 91.43 % and 92. 57 %, respectively, while that of the Y chromosome hybridization signal was 99.5 % and 99.8 %, respectively. Conclusion: D-FISH is a valuable technique in diagnosing 49, XXXXY chromosomal abnormality and other sex chromosomal abnormalities. [Reprod Contracep (in Chinese) 2002; 22: 287]

炭疽杆菌双毒力因子荧光PCR检测方法的建立及应用

由炭疽杆菌(Bacillus anthracis)引起的炭疽(anthrax)是严重危害人类和家畜健康的重大传染病。为了提高出入境口岸对不明粉未快件样品的查验效率,防范通过包裹夹带生化武器,本研究使用TaqMan探针技术,建立了针对炭疽杆菌两种毒力质粒pOX1和pOX2的双重荧光PCR检测方法,并对该方法的特异性、灵敏性和稳定性进行了试验。结果显示:本研究建立的炭疽杆菌双重荧光PCR检测方法具有较强的特异性,只特异性检出炭疽杆菌pOX1和pOX2,而与金黄色葡萄球菌等19种对照病原菌均无交叉反应;灵敏度与单重荧光PCR方法相近,最低检测限可达10 copies/μL;稳定性好,反应体系低温保存2、4、6、8个月后,检测阳性质粒的Ct值和峰值相差不大。应用该方法检测600份猪牛羊组织样本,均未检出炭疽杆菌阳性核酸。本研究建立的双重荧光PCR检测方法为炭疽杆菌的快速检测提供了技术支撑。

基于双功能纳米探针的免疫层析技术在食品安全检测中的应用

免疫层析技术在基层食品安全监测中发挥着举足轻重的作用。探针材料是决定免疫层析试纸条检测性能的关键。大量研究表明,基于功能集成化策略的双功能纳米材料作为探针可极大地提升免疫层析方法的性能。基于双信号探针的免疫层析方法、基于磁性光学纳米探针的免疫层析方法和基于探针催化信号放大的多级比色免疫层析方法因优异的分析性能和巨大的应用潜力而备受关注。该文详细阐述了这三类免疫层析技术的原理、发展现状及其在食品安全检测方面的应用,并讨论了该领域的发展趋势和面临的主要挑战。

双路偏振结构的激光多普勒测速系统

为了消除光束倾角带来的不确定性,本文建立了一种双路偏振式激光多普勒测速系统。该系统使用双光束双探头结构来探测物体的运动信息。首先,通过转动实验精确获得双光束间的夹角大小,对于任意光束倾角,本文采用双探头装置收集运动物体表面的散射光束,结合双路偏振式光路结构,得到两路干涉信号的多普勒频移。然后,创新性采用了细化分帧算法对两路干涉信号进行实时解调,通过两路速度分量的合成得到物体真实速度。实验结果表明:速度在10 mm/min~1500 mm/min范围内,测量值与理论值之间的平均误差可以达到1%~5%。在非平稳运动过程中,通过细化分帧算法修正后的v-t图像RMSE均值为1.19 mm/min。该系统结构满足速度测量的稳定可靠、精度高、抗干扰能力强等要求。

量子点修饰Ln-ZIF杂化材料的构筑及其对单宁酸的荧光检测

采用一步水热法制备了一种具有新型褶皱球结构的镧系金属Eu3+掺杂的金属有机骨架材料Eu/ZIF-67,并进一步通过配位键合的方式将ZnO量子点负载到Eu/ZIF-67的表面,形成了一种类沸石咪唑酯骨架的双发射荧光杂化材料Eu/ZIF-67@ZnO QDs。通过对材料的结构、形貌以及荧光传感性能表征分析,发现该荧光材料具有ZnO量子点和镧系红光铕离子的双重荧光发射。此外,进一步探究了Eu/ZIF-67@ZnO QDs对单宁酸的荧光传感性能。结果表明,单宁酸能够有效猝灭Eu/ZIF-67@ZnO QDs在ZnO QDs处的特征荧光发射,检出限为0.029 9μmol/L。同时,Eu/ZIF-67@ZnO QDs对单宁酸的荧光响应具有抗干扰能力,可作为一种经济高效的荧光传感器来特异性识别单宁酸。

一种带外部锁场通道的小型化核磁共振射频探头设计

温度漂移是影响桌面式核磁共振波谱仪测量精度的一个重要因素,在探头中添加锁场线圈实现场频联锁是抑制温度漂移的常用手段.本文基于实验室紧凑型Halbach磁体,设计了一套带有外部锁场功能的双通道探头.针对目标区域,使用COMSOL仿真对比了螺线管线圈、鞍形线圈和亥姆霍兹线圈的磁场均匀性、信噪比和品质因数,发现螺线管线圈具有最佳综合性能.进一步针对螺线管线圈结构,对线圈直径、高度、匝数、匝间距以及漆包线半径进行了仿真优化,得到漆包线半径为0.4 mm、线圈直径和高度为8.2 mm、匝间距为1.6 mm、匝数为5是最优螺线管尺寸.基于仿真结果,制作了探头实物,并配合外围电路进行测试.结果表明,两个线圈通道之间串扰较小,信号检测通道信噪比达到50以上,锁场通道信噪比达到20以上.锁场实验结果表明,添加锁场后整体系统的频率漂移约为0.2 ppm/h(1 ppm=10^(-6)),验证了此探头设计可用于基于紧凑型Halbach磁体的磁共振设备.

基于磁性纳米颗粒伏马菌素B双探针竞争ELISA检测方法的建立

建立一种基于磁性纳米颗粒能同时检测样品中伏马菌素B_(1)(fumonisin B_(1),FB_(1))、FB_(2)和FB_(3)总量的双探针竞争酶联免疫吸附实验(enzyme linked immunosorbent assay,ELISA)检测方法。采用通过活化酯法制备磁性纳米颗粒-FB_(1)捕获探针,利用改良过碘酸钠法合成McAb-HRP探针,对检测步骤进行优化,确定最佳反应条件。所建立检测方法对FB_(1)和FBs的检测范围分别为0.07~1.98 ng/mL和0.10~9.86 ng/mL。在玉米样品中加标回收率范围为86.2%~105.1%。所建立方法检测结果与液相色谱-串联质谱检测结果的相关系数(R^(2))为0.9966。双探针竞争ELISA检测法检测速度快、准确性高、重复性好,为玉米中伏FBs的快速筛选提供了新方法。

双探头H-ADCP在线流量监测系统在西江黄金水道流量监测的应用初探——以梧州水文站为例

梧州水文站上游约2000 m是干流浔江与支流桂江交汇处,下游170 m为云龙大桥,水流形态复杂,实现流量在线监测是一大难题。尝试基于回波强度判断H-ADCP单元流速的有效性,通过建立双探头H-ADCP不同单元流速组合计算的指标流量与断面流量模型及水量计算分析来研究双探头H-ADCP在线流量监测系统在西江黄金水道梧州水文站河段的适用性。结果表明,水位在3.29~22.31 m,指标流量在3270~39500 m^(3)/s时双探头H-ADCP在线流量监测系统可在梧州水文站应用。

一种新型黏度和硫化氢荧光探针的制备及应用

黏度是一个重要的微环境参数,同时硫化氢(H_(2)S)也是一种重要的气体分子,这两者都会参与和影响许多生理和病理过程.因此,对细胞内黏度和H_(2)S浓度变化的检测具有实际意义.设计合成了荧光探针Mito-ANP,实现了同时检测体系内黏度和H_(2)S.当体系的黏度增加时,探针Mito-ANP的旋转被禁止,从而释放出红色的荧光.而加入H_(2)S后,探针Mito-ANP的双键与H_(2)S发生亲核加成反应释放出绿色荧光.探针Mito-ANP与硫化氢(H_(2)S)和黏度呈良好的线性关系,并且对H_(2)S具有专一的选择性.此外,探针Mito-ANP还能成功地用于神经细胞中硫化氢和黏度变化的荧光成像.

基于双荧光中心碳量子点的比率型荧光探针快速检测乐果

环境和农产品中乐果的残留,对人体和生态环境都造成了巨大的威胁。急需构建一种高效、简便及廉价的检测方法用于乐果的快速检测。通过对木糖和碳酸氢铵进行简单的水热处理,成功制备了掺杂氮型碳量子点(N-CQDs)。N-CQDs的激发光谱表明,其在238和330 nm处各有一个荧光中心,它们的荧光发射中心均位于402 nm左右。随着乐果的不断加入,238 nm激发的发射光谱能在1 min内被有效猝灭,而330 nm激发的发射光谱荧光变化不明显,基于此构建了比率型荧光探针用于乐果的快速检测。在最佳反应条件下,比率型荧光探针对乐果的检测范围为2~100和100~180 ng·mL^(-1),检出限为0.67 ng·mL^(-1)。常见的离子和农药对乐果的干扰不大,表明该比率型荧光探针无需特异性酶的标记即可对乐果显示出良好的选择性。该方法用于实际火龙果样品中乐果的检测,并与国家标准规定的气相色谱-质谱法(GC-MS)比较。所建立的方法在实际火龙果样品检测中回收率在92.55%~102.24%之间,其相对标准偏差(RSD)小于3.62%(n=3)。而国标规定的GC-MS法的回收率在84.22%~100.64%之间,RSD在2.95%~10.95%(n=3)之间。结果表明,与GC-MS法相比,所建立的比率型荧光探针显示出更高的准确度与精密度,实验结果令人满意。