高岭石质密封传压介质金刚石合成扩大试验研究

以高岭石替代叶蜡石为主要原料制作密封传压介质并进行了金刚石合成扩大试验.分别以试块密度、腔体直径和热处理工艺为因素进行了条件试验.根据平均单产量、粗粒级含量、高强度颗粒含量、锤耗以及合成稳定性对实验结果进行表征.结果表明:φ40 mm腔体与φ42mm腔体使用效果较好,而φ44mm腔体合成稳定性相对较差.通过三段升温,最高温度320℃的低温长时热处理工艺,φ44mm腔体密封传压介质稳定性明显增加.采用以上最优条件,φ44mm腔体高岭石质密封传压介质的使用效果为:平均单产120 ct,≥130 N晶粒所占比例为40;,≥50/60晶粒比例为80;,锤耗小于1.2 kg/1×104 ct,合成稳定性较好.通过以上结果得出结论:高岭石质密封传压介质合成金刚石的效果与叶蜡石质密封传压介质相当,试验中采用的高岭石适合制作金刚石合成用密封传压介质.     

应用于光抽运铯原子钟的小型稳频激光器（英文）

设计了一种应用于光抽运铯原子钟的稳频激光器,用小型化的饱和吸收装置对激光进行稳频,用于产生饱和吸收谱的泵浦光的偏振方向与检测光的偏振方向相互垂直,通过调节激光的偏振方向增大铯原子的跃迁几率.相对于一般简化的饱和吸收装置,小型化的饱和吸收装置产生的用于锁频的参考信号的幅度更大.当激光频率被锁定在铯原子的6S_(1/2),F=4→6P_(3/2),F=5能级跃迁线上时,对激光器的稳定度进行了测量,百秒稳定度为1.88×10~(-11).该稳频激光器的体积较小,有利于光抽运铯原子钟的小型化和工程化应用.     

MXene Ti_3C_2T_x saturable absorber for pulsed laser at 1.3 μm

The excellent optical properties of MXene provide new opportunities for short-pulse lasers. A diode-pumped passively Q-switched laser at 1.3 μm wavelength with MXene Ti_3C_2T_x as saturable absorber was achieved for the first time. The stable passively Q-switched laser has 454 ns pulse width and 162 kHz repetition rate at 4.5 W incident pumped power. The experimental results show that the MXene Ti_3C_2T_x saturable absorber can be used as an optical modulator to generate short pulse lasers in a solid-state laser field.     

Dynamical effects of switching a super-critical well potential on pair creation from a vacuum

The dynamical effects on electron-positron pair creation from a vacuum caused by the switching processes of a supercritical well potential are investigated in detail. The results show that only when the switching on and switching off time both increase will the final pair yield converge to the integer of embedded bound states nearly exponentially. But a single adiabatic switching on or switching off cannot lead to an integer pair yield. If the potential is turned on abruptly, associated with the discrete and embedded bound states, there is multi-frequency oscillation around the pair number's saturation. The slowly switching on can suppress the amplitude of this oscillation and reduce the final pair yield. The switching off can also reduce the final pair number in the same order of magnitude. The evolution of a single-pair number shows a robust long range correlation between particle and antiparticle. For an adiabatic switching case, the single-pair dominates the early pair creation, their upper limit value is equal to the integer, and these single-pairs will totally disentangle during the switching off.     

Tunable Nd,La:SrF_2 laser and passively Q-switched operation based on gold nanobipyramids saturable absorber

A novel Nd, La:SrF_2 disordered crystal is prepared, and its continuous-wave wavelength tuning operation is performed for the first time. Employing a surface plasmon resonance(SPR) based gold nanobipyramids(G-NBPs) saturable absorber,we obtain a compact diode-pumped passively Q-switched Nd, La:SrF_2 laser. The stable Q-switched pulse operates with the shortest pulse duration of 1.15 μs and the maximum repetition rate of 41 k Hz. The corresponding single pulse energy is 2.24 μJ. The results indicate that G-NBPs could be a promising saturable absorber applied to the diode-pumped solid state lasers(DPSSLs).     

Structural modification in swift heavy ion irradiated muscovite mica

Two-layer monoclinic(2 M) muscovite mica sheets with a thickness of 12 μm are irradiated with Sn ions at room temperature with electronic energy loss( dE/dx)_e of 14.7 keV/nm. The ion fluence is varied between 1×10~(11) and1×10~(13) ions/cm~2. Structural transition in irradiated mica is investigated by x-ray diffraction(XRD). The main diffraction peaks shift to the high angles, and the inter-planar distance decreases due to swift heavy ion(SHI) irradiation. Dehydration takes place in mica during SHI irradiation and mica with one-layer monoclinic(1 M) structure is thought to be generated in 2 M mica after SHI irradiation. In addition, micro stress and damage cross section in irradiated mica are analyzed according to XRD data. High resolution transmission electron microscopy(HRTEM) is used on the irradiated mica to obtain the detailed information about the latent tracks and structural modifications directly. The latent track in mica presents an amorphous zone surrounded by strain contrast shell, which is associated with the residual stress in irradiated mica.     

Modulation depth of series SQUIDs modified by Josephson junction area

The superconducting quantum interference device(SQUID) amplifier is widely used in the field of weak signal detection for its low input impedance, low noise, and low power consumption. In this paper, the SQUIDs with identical junctions and the series SQUIDs with different junctions were successfully fabricated. The Nb/Al-AlO_x/Nb trilayer and input Nb coils were prepared by asputtering equipment. The SQUID devices were prepared by a sputtering and the lift-off method.Investigations by AFM, OM and SEM revealed the morphology and roughness of the Nb films and Nb/Al-AlO_x/Nb trilayer.In addition, the current–voltage characteristics of the SQUID devices with identical junction and different junction areas were measured at 2.5 K in the He~3 refrigerator. The results show that the SQUID modulation depth is obviously affected by the junction area. The modulation depth obviously increases with the increase of the junction area in a certain range. It is found that the series SQUID with identical junction area has a transimpedance gain of 58 ? approximately.     

基于模糊PID的UEGO传感器控制方法研究

宽域废气氧(Universal Exhaust Gas Oxygen,简称UEGO)传感器具有较宽的空燃比测量范围,广泛地应用于稀燃发动机空燃比控制系统。UEGO传感器需要配套控制器才能正常工作,通过控制传感器的温度和泵电流,实现空燃比的测量。然而,UEGO传感器温度具有非线性,泵电流参数存在摄动,给其控制带来了困难。为了缩短冷启动时间,采用斜坡加热与模糊PI相结合的分段温度控制策略,以克服温度的非线性和冷启动的加热限制;采用基于OE模型的系统辨识法,建立不同工况下的泵电流模型,据此采用模糊PID的控制方法提高泵电流的控制精度与响应速度,克服泵电流参数不确定性的影响,从而提高传感器的动态性能。在空气环境和混合气配气平台上进行实验,结果表明：UEGO传感器冷启动时间少于20s,温度控制精度较高,泵电流调节时间为191ms,动态响应速度快、抗干扰能力强。     

强上转换发光的LiLu_(1-x)Yb_xF_4∶Tm@LiGdF_4核壳纳米晶的制备

利用高温热分解法制备了LiLuF_4∶Yb,Tm@LiGdF_4核壳纳米晶。在980nm激光激发下,与未包覆的样品相比,LiLuF_4∶Yb,Tm@LiGdF_4核壳纳米晶的发光增强了15倍左右,这主要是因为通过惰性壳层的包覆可以有效抑制表面猝灭效应。另外,随着核中Yb~(3+)离子的摩尔分数从20%增加到100%,上转换发光强度逐渐增大,最大增加了12.4倍左右。这主要是由于增加Yb~(3+)离子的浓度可以增加纳米粒子对激发光的吸收和提高Yb~(3+)到Tm~(3+)的能量传递速率。所制备的LiYbF_4∶2%Tm@LiGdF_4核壳纳米晶的发光效率高达4%。     

超热电子在稠密等离子体中输运的混合粒子模拟方法

相对论激光等离子体相互作用以及所产生的带电粒子束在高密度等离子体中的输运行为非常重要.该物理问题的数值模拟研究仍面临技术挑战.本文介绍一种粒子/流体混合模拟方法.该方法中超热电子采用动力学方法描述,背景冷的稠密等离子体采用简化的流体方程描述,适合于超热电子密度远小于背景电子密度,超热电子能量远大于背景电子温度.我们的三维并行混合模拟程序HEETS的模拟结果表明：背景材料的电离和电阻率模型至关重要,将严重影响高能电子输运过程的模拟.