一种基于谱线幅值归零的加窗插值FFT谐波检测方法

提出了一种基于谱线幅值归零的加窗插值FFT谐波检测方法用于分析复杂电网信号中的各次谐波.该检测方法将每一次在离散频谱中找到的最大谱线及其左右两侧的数根谱线幅值归零,直到各次谐波分析完毕.通过仿真实验分析了在基波频率稳定时对模拟信号的测量精度,研究了基波频率波动对谐波分析的影响.通过对EAST实验数据的分析,验证了该谐波...     

基于Franz-Keldysh效应的倏逝波锗硅电吸收调制器设计

本文设计了一种基于Franz-Keldysh (FK) 效应的GeSi电吸收调制器. 调制器集成了脊形硅单模波导. 光由脊形硅波导以倏逝波形式耦合进锗硅吸收层. 在硅基锗二极管FK效应实验测试的基础上, 有源区调制层锗硅中的硅组分设计为1.19%, 从而使得器件工作在C (1528–1560 nm) 波段. 模拟结果显示该调制器的3 dB带宽可达64 GHz, 消光比为8.8 dB, 而插损仅为2.7 dB. 关键词： 锗硅 调制器 电光集成     

Oriented O(3P2), Ne(3P2), and He(3S1) atoms emerging from a bent magnetic guide

We describe our observation of strongly oriented total electronic angular momentum J in O(³P₂), Ne(³P₂), and He(³S₁) atoms emerging from a bent magnetic multipole guide, as measured by resonant multiphoton ionisation. This was contrary to our expectation because no additional (uniform) magnetic fields were applied to orient the atoms behind the exit of the guide. Two- and three-photon ionisation techniques were employed to determine the degree of J polarisation, from which we infer that atoms become oriented as a result of a combination of weak fringe fields, possible stray fields, and the fact that molecular beam packets do not oscillate around the geometric center of the bent multipole guide. We conclude that similar effects may exist in other, related experiments and that a detailed characterisation of the degree of orientation is required prior to any study of chemical dynamics or spectroscopy. This paper should serve as a warning for anybody using similar devices not to assume isotropic angular momentum distributions of atoms and molecules emerging from a magnetic guide or a decelerator, particularly when it is bent; whenever possible, the possibility for a J anisotropy should be experimentally checked.     

强流ECR离子源引出系统研究

为了提高强流ECR 离子源的引出束流品质,分别设计了1# 和2# 引出系统,利用束流引出模拟软件PBGUNS 对1# 和2# 引出系统进行了质子束流引出与传输的模拟计算,结合实际测得的发射度数据分析引出系统,发现2# 引出系统比1# 引出系统引出束流品质高。对ECR 离子源引出系统的电势等位线分布等参数引起的球差进行了简单数学推导及MATLAB 绘图,并结合1# 和2# 引出系统束流相图模拟结果证明了球差会使引出束流品质有效发射度增长,通过适当加大电极孔径可改善束流聚焦情况,得到了束流光学聚焦较好的束流引出系统设计。To improve the quality of extracted ion beam from a high current ECR ion source, 1# and 2# extraction systems were designed and tested. The PBGUNS code was used to simulate the 1# and 2# extraction systems of proton ion beam. The emittance measurement results with the two different extraction systems were compared and analyzed with the simulation, the conclusion that more high quality beam extracted from 2# system than 1# system was got. The formula derivation of ECR ion source extraction system spherical aberration and MATLAB drawing was done by the analyzing on the distribution of extraction field equipotentials, effective emittance increasing caused by spherical berration was proved by 1# and 2# extraction systems beam phase space simulation result, beam focusing would be improved if electrode hole size increasing appropriately and a general concept on good optics focusing of ion beam extraction system was proposed finally.     

Formation of hydrophobic coating on PMMA surface using unipolar nanosecond-pulse DBD in atmospheric air

Dielectric barrier discharge (DBD) can modify the material surface and result in complicated physical and chemical reactions to improve the surface hydrophilicity, which is proved to be an effective method for surface modification. Compared with the traditional ac-excitation DBD, the DBD using unipolar pulses can avoid local overheat of microdischarges and can improve discharge efficiency under some conditions. In this paper, DBD excited by repetitive unipolar nanosecond generator was used to improve the hydrophobicity of Plexiglass (PMMA) surface by means of the interaction between air plasma and silicone oil. The output voltage had a rise time of 40 ns and a full width at half maximum of about 70 ns. The surface hydrophobicity of the PMMA, before and after the surface modification, was evaluated via the contact angle measurement under different experimental conditions. The values of the contact angle shown in this paper were the average of eight measured values, and the standard deviations were also calculated. The surface energy including polar and dispersion components was calculated using the measured average contact angles of distilled water and polyethyleneglycol. The results showed that, as the increase of the discharge voltage, the contact angle increased but the surface energy decreased. With the increase of treatment time, the water contact angle of the modified surface increased at the beginning, and it would reach to a maximum at 7.5 min treatment, and then decreased. The effect of pulse frequency on the modification results was different at various treatment times. In addition, the possible physical and chemical reaction among the DBD plasma, silicone oil and the PMMA surface was discussed.     

Calculation on the CO2 influences on the structure,stability of (MgO)m (m = 1–6) clusters

ABSTRACT

The concentration of carbon dioxide (CO₂) has a significant influence on the morphology of thermal decomposition products of magnesite. So, structures, stabilities and adsorption mechanisms of (MgO)_m (m?=?1–6) clusters by one or two CO₂ molecules were calculated by the GGA-PW91 method. The results show that the stability of the considered clusters is (MgO)_m(CO₂)₂ clusters > (MgO)_m(CO₂) clusters > (MgO)_m clusters by the average binding energy. Certain low-lying isomers of (MgO)_m(CO₂) and (MgO)_m(CO₂)₂ clusters which have an isolated O atom are deviating from the cluster center which possess higher kinetic activity. (MgO)_m clusters prefer to adsorb a CO₂ molecule, while (MgO)₃(CO₂) clusters prefer to adsorb a CO₂ molecule rather than the neighbors. Magnesite is difficult to transit to (MgCO₃)₂ clusters at room temperature. However, magnesite will spontaneously transit to (MgO)₂ clusters and further transit to MgO crystal which need to adsorb more energy at 700?K.     

The High Energy X-ray telescope (HE) onboard the Insight-HXMT astronomy satellite

The Insight-Hard X-ray Modulation Telescope(Insight-HXMT) is a broadband X-ray and γ-ray(1-3000 ke V) astronomy satellite. One of its three main telescopes is the High Energy X-ray telescope(HE). The main detector plane of HE comprises 18 Na I(Tl)/Cs I(Na) phoswich detectors, where Na I(Tl) is used as the primary detector to measure ~ 20-250 ke V photons incident from the field of view(FOV) defined by collimators, and Cs I(Na) is used as the active shielding detector to Na I(Tl) by pulse shape discrimination. Additionally, Cs I(Na) is used as an omnidirectional γ-ray monitor. The HE collimators have a diverse FOV,i.e. 1.1°×5.7°(15 units), 5.7°×5.7°(2 units), and blocked(1 unit). Therefore, the combined FOV of HE is approximately5.7°×5.7°. Each HE detector has a diameter of 190 mm resulting in a total geometrical area of approximately 5100 cm2, and the energy resolution is ~15% at 60 ke V. For each recorded X-ray event by HE, the timing accuracy is less than 10 μs and the deadtime is less than 10 μs. HE is used for observing spectra and temporal variability of X-ray sources in the 20-250 ke V band either by pointing observations for known sources or scanning observations to unveil new sources. Additionally, HE is used for monitoring the γ-ray burst in 0.2-3 Me V band. This paper not only presents the design and performance of HE instruments but also reports results of the on-ground calibration experiments.     

激光束散角复合控制技术

为了降低部分相干光光学系统设计的复杂度及成本,增加部分相干光应用的便捷性,提出了一种液晶空间光调制器的激光相干度及束散角复合控制方法。首先介绍了对激光光束进行相干度和束散角复合控制的基本理论和方法;然后分别设置了相干度和束散角检测实验,检测了本方法所调制激光光束的相干度和束散角的准确性。实验结果表明,采用液晶空间光调制器生成相干度为0.9 mm、束散角为7.5 mrad,以及相干度为1.5 mm、束散角为3.8 mrad的部分相干光束,其相干度与理论值相比误差在5%以内,其相干度均方根误差分别为0.027386和0.031314,峰谷值分别为0.084 658和0.089 103;其束散角与理论值相比误差在5%以内,其束散角均方根误差分别为0.022 478和0.023 186,峰谷值分别为0.081 201和0.092 130。可见,该方法可以实现高精度的相干度及束散角复合控制。     

物理演示实验教学在高素质新型军事人才培养中的作用

培养高素质新型军事人才是国防科技大学的核心任务之一.物理演示实验以直观、形象地演示物理现象为课程特色,可有效提高学员对物理规律、物理本质的直观认识和深刻理解,并引起学员的深入思考,在教学实践中可促进学员科学素质、综合能力和创新能力的提高.