Measurement of 129Xe frequency shift due to Cs–129Xe collisions

Enhancement factor K0, which characterizes NMR and EPR frequency shifts for Cs-129Xe, is measured for the first time. The enhancement factor r-o was measured to be （702±41） at 80 ℃ and （653±20） at 90 ℃, using the NMR frequency shift, detected by atomic magnetometer at a low magnetic field of 100 nT. This result is useful for predicting the EPR frequency shifts for Cs and the NMR frequency shifts for 129Xe in spin-exchange cells.     

两层耦合可激发介质中螺旋波转变为平面波

采用Br-Eiswirth模型研究了两层耦合可激发介质中螺旋波的动力学,两层介质通过网络连接,即在每一层介质上,每一列选一个可激发单元作为中心点,在一层介质上同一列的可激发单元只与另一层介质上对应的中心点及其8个邻居有耦合.数值模拟结果表明:通过这种局部耦合,在适当小的耦合强度下两耦合螺旋波可实现同步,增大耦合强度会导致螺旋波漫游和漂移,造成螺旋波不同步,观察到螺旋波与静息态、低频平面波和不规则斑图共存现象.在适当强的耦合强度下,还观察到两螺旋波转变成同步的平面波消失现象.对产生这些现象的物理机理做了讨论.     

1.2 kW C波段固态高效率GaN微波源研制

针对传统大功率Si,GaAs固态微波源效率低和高温度性能差的不足,采用导热系数优良的宽禁带GaN单元功放模块集成、低损耗同轴波导径向空间功率合成方法,研制出一种1.2 kW全固态C波段高效率宽禁带GaN微波源。实验结果表明：该方法实现了大功率固态微波源高效率及连续长时间高温风冷散热运行,系统安全可靠。单路功放模块集成6位移相器,移相精度5.6,增益35 dB,输出功率大于31 W。系统连续波输出功率1.2 kW ,总效率30%,谐波抑制-54.8 dBc;杂散-63.69 dBc,相位噪声-94.03 dBc/Hz@1kHz。     

Snap-through piezoelectric energy harvesting

Snap-through mechanism is employed to harvest electricity from random vibration through piezoelectricity. The random excitation is assumed to be Gaussian white noise. The snap-through piezoelectric energy harvester possesses the bistability. For small-amplitude vibration in a potential well, the Ito stochastic differential equation of the electromechanical coupling system is derived from the Taylor approximation at a stable equilibrium point. The method of the moment differential equations is applied to determine the statistical moments of the displacement response and the output voltage. The effects of the system parameters on the output voltage and the output power are examined. The approximate analytical outcomes are qualitatively and quantitatively supported by the numerical simulations. For large-amplitude interwell motion, the effects of the parameters on the output voltage and the output power are numerically investigated. Nonlinearity produced by the snap-through improves energy harvesting so that the snap-through piezoelectric energy harvester can outperform the linear energy harvester in the similar size under Gaussian white noise excitations.     

Effect of boric acid on structure,morphology and luminescent properties of divalent europium doped calcium aluminate phosphors

Blue phosphors Ca_1 − xAl₂O₄: xEu²⁺ were prepared by high temperature solid-state method. Their structure, morphology and luminescent properties were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and fluorescence spectroscopy. The effect of different amounts of fluxing agent H₃BO₃ on structure, morphology and luminescent properties of blue phosphors Ca_1 − xAl₂O₄: xEu²⁺ luminous intensity caused by different amount of H₃BO₃ was also investigated. The amount of H₃BO₃ doped Ca_1 − xAl₂O₄: xEu²⁺ in optimal luminous intensity had been determined. The results showed that both the excitation and emission spectra of samples were all broad bands, and that the peak of emission spectra was near 442 nm, which was corresponding to the 4f⁶5d → 4f⁷ transition of Eu²⁺ illuminating blue light. Ca_1 − xAl₂O₄: xEu²⁺ (x = 3.5 mol%) could be gained with good morphology and the best luminous intensity when H₃BO₃ mass ratio was 0.5 wt%.     

Assessing the relationship between the inter-rod coupling and the efficiency of piezocomposite high-intensity focused ultrasound transducers

The electroacoustic conversion efficiency of the ultrasonic transducer is a critical performance index for high-power applications. The material properties, volume fraction (VF) and aspect ratio (AR) are typically regarded as the design parameters of the piezocomposite transducer. We hypothesized that the spacing between piezoelectric rods was also a dominant factor. Therefore, the inter-rod coupling effects on the efficiency of 1–3 piezocomposite ultrasonic transducers were investigated in this study. The efficiencies of six flat and three curved 1.0 MHz PZT4 epoxy composite transducers with different geometric parameters were measured. Finite element transient analyses of the inter-rod electrical-mechanical coupling in the composites were carried out to explain the measured results. The experimental results showed that for 0.47 AR, the 79% VF transducers had lower efficiency than the 64% VF and 53% VF transducers. For 0.19 AR, the efficiency of the 59% VF transducer was not greater than the efficiency of the 39% VF transducer. Numerical analyses demonstrated that the positive peak voltage induced by the coupling of the side rods was more than twice the level induced by the coupling of the diagonal rods for any spacing. The diagonal coupling voltage peak did not change for spacings larger than 0.2 mm. Moreover, for spacings of 0.05 and 0.1 mm, the inter-rod coupling caused 24% and 20% waveform shifts of the driving voltage, respectively, while the 0.2 mm spacing coupling caused a 14% reduction in the amplitude of the driving voltage. As a result, the asymmetry of the driving voltage degraded the efficiency of the composite transducers and became more severe when the spacing was decreased. We concluded that the efficiency loss induced by inter-rod coupling as a function of spacing should be considered when designing piezocomposite transducers.     

Magnetic properties of two-dimensional charged spin-1 Bose gases

Within the mean-field theory, we investigate the magnetic properties of a charged spin-1 Bose gas in two dimensions. In this system the diamagnetism competes with paramagnetism, where the Landé factor g   is introduced to describe the strength of the paramagnetic effect. The system presents a crossover from diamagnetism to paramagnetism with the increasing of the Landé factor. _gc$g_c$ denotes the critical value of the Landé factor. We get the same value of _gc$g_c$ both in the low temperature and strong magnetic field limit. Our results also show that in very weak magnetic field no condensation happens in the two-dimensional charged spin-1 Bose gas.     

Experimental validation of domain-level gradient-based and hierarchical PCE-based routing and control in heterogeneous optical networks

A domain-level gradient-based routing （DLR） algorithm for heterogeneous optical networks with syn- chronous digital hierarchy and optical transport network domains is proposed and experimentally vali- dated. This algorithm classifies domains into groups with incremental levels on the basis of domain-level partitioning, and guides paths level by level along a gradient on the basis of interdomain routing tree evolution. The proposed algorithm is implemented in the hierarchical path computation element-based control architecture for connection provisioning. Testbeds with commercial and emulated nodes are es- tablished to verify the feasibility and performance of the algorithm. Experimental and emulation results show that DLR effectively performs in terms of network blocking probability, real time characteristics, and scalability.     

探究轻质塑料桶在尖端附近的旋转现象

基于轻质塑料桶在尖端放电时旋转方向的不一致现象提出问题,利用酒精灯火焰来显示带电粒子的流动方向,并探究在接地尖端附近粒子运动的异常现象。实验发现,接地端也存在放电现象。     

Highly efficient single longitudinal mode-pulsed green laser

A novel design for a highly efficient 1-kHz single-frequency green laser is proposed.An efficient singlefrequency laser pulse output at 532-nm wavelength may be obtained by combining the injection seeding with intracavity frequency doubling in a compact U-shaped cavity formed by two plano dichroic mirrors in an end-pumping arrangement.The laser is capable of producing green pulses with a total energy of 6.3 mJ at a pulse repetition rate of 1 kHz.The pulse width is about 10 ns and the optical-optical efficiency from the 808-nm pump source to the 532-nm green output is around 12.7%.