甲醇在γ-Al2O3,CeO2及其负载Pd催化剂上吸附和分解的原位红外光谱研究

利用原位傅里叶变换红外光谱 (FTIR)技术对甲醇在γ Al2 O3,CeO2 以及Pd/Al2 O3,Pd/CeO2 催化剂上的吸附和分解行为进行了研究。综合考虑了载体和活性组分的作用 ,分析了甲醇在不同载体负载Pd催化剂上可能的分解途径。在Pd/CeO2 催化剂上 ,活性组分和载体对甲醇分解的过程表现出了一种协同效应。     

Beam emittance investigation in high brightness injector using different driver laser profiles

Beam emittance plays an important role in any accelerator, and it is a main parameter to judge the performance of an accelerator. Emittance optimization is an indispensable part in conditioning and operation of the facility. For a laser-driven high brightness injector, different time structure of the laser pulse has different effects on transverse emittance. In order to compare Gaussian and flat-top laser pulse, systematic simulations of 500 pC have been done. From the simulation results, one can see that flat-top pulse laser will yield smaller minimal transverse beam size and transverse beam emittance than Gaussian pulse laser.     

2.0μm附近模拟呼吸气体中~(13)CO_2/~(12)CO_2同位素丰度的高精度实时在线测量

采用可调谐二极管激光吸收光谱技术,结合一新型多通池搭建了一套模拟呼吸气体中CO_2同位素丰度的测量装置.气体的压强、温度和流速被很好地控制且均能保持长期的稳定性;采用三次多项式拟合光谱基线,对光谱进行归一化,很好地消除了功率变化对测量结果的影响;利用移窗-回归技术消除频率漂移对同位素丰度测量的影响.实验结果表明:移窗-回归法的引入不仅延长了系统的稳定时间,还提高了系统的测量精度;小波去噪的应用获得了比多光谱平均法高2倍的信噪比;系统的稳定时间为100 s;Kalman滤波后系统测量精度为0.067‰.     

Microstructure and wear resistance of laser clad cobalt-based alloy multi-layer coatings

Multi-layer Co-based alloy (HMSP 2537) were deposited on Ni-based superalloy plate with a TJ-TL-T5000 type CO₂ laser. Sections of such coatings were examined to reveal their microstructure and phase composition using optical microscope, scanning electron microscope (SEM), and X-ray diffractometer (XRD). The hardness and wear resistance of the coatings were tested. The results showed that the prime phase (γ-Co dendrite) and other phases, such as CrNi, Co₇W₆, and Cr₂₃C₆ existed in the coatings. Dendrite or cellular microstructures were observed perpendicular to the interface, and coarsening microstructures were obtained as more layers deposited. Dendrite paralleling to laser scan speed was also found near the top surface of the last layer. Fine microstructures of γ-Co dendrite and lamellar eutectic in inter-dendritic regions strengthened the coatings. Microhardness and wear resistance of the coatings were much higher than that of substrate but slightly decreased with layers increased.     

数控高精度PWM调制特种电源

介绍了两种斯特林制冷机数控驱动源,分析了单极性驱动方式与双极性驱动方式对红外探测芯片产生的干扰情况,并根据与系统的联试比较了两种数控驱动源的优缺点.说明了数字滤波技术、PID控制算法及V/F转换电路在提高温控精度和减少电源对探测芯片干扰中的优势.     

Structure and magnetostriction of Tb0.4Nd0.6(Fe0.8Co0.2) x alloys

Structural, magnetic and magnetostrictive properties of Tb_0.4Nd_0.6(Fe_0.8Co_0.2) _x (1.50 ≤ x ≤ 1.90) alloys have been investigated by means of X-ray diffraction (XRD), a vibrating sample magnetometer and a standard strain technique. XRD analysis shows the presence of single Laves phase with a cubic MgCu₂-type structure for the high Nd content alloy around the composition of x = 1.80, which tends to be formed by curing at relatively low annealing temperature. The easy direction of magnetization at room temperature is observed toward <111> axis, accompanied by a rhombohedral distortion with a large spontaneous magnetostriction λ₁₁₁. An optimized effect on the linear anisotropic magnetostriction, 360 ppm at 3 kOe, was observed for the high Nd content Tb_0.4Nd_0.6(Fe_0.8Co_0.2)_1.80 alloy, which can be attributed to its single Laves phase, the large λ₁₁₁ (~1,520 ppm) of the MgCu₂-type (Tb,Nd)(Fe,Co)₂ phase and the good soft magnetic behaviors.     

Hybrid phononic crystal plates for lowering and widening acoustic band gaps

We propose hybrid phononic-crystal plates which are composed of periodic stepped pillars and periodic holes to lower and widen acoustic band gaps. The acoustic waves scattered simultaneously by the pillars and holes in a relevant frequency range can generate low and wide acoustic forbidden bands. We introduce an alternative double-sided arrangement of the periodic stepped pillars for an enlarged pillars’ head diameter in the hybrid structure and optimize the hole diameter to further lower and widen the acoustic band gaps. The lowering and widening effects are simultaneously achieved by reducing the frequencies of locally resonant pillar modes and prohibiting suitable frequency bands of propagating plate modes.     

Single-beam and enhanced two-beam second-harmonic generation from silicon nanocrystals by use of spatially inhomogeneous femtosecond pulses

Optical second-harmonic generation (SHG) is used as a noninvasive probe of the interfaces of Si nanocrystals (NCs) embedded uniformly in an SiO2 matrix. Measurements of the generated SH mode verify that the second-harmonic polarization has a nonlocal dipole form proportional to (E x Delta inverted) E that depends on inhomogeneities in the incident field E, as proposed in recent models based on a locally noncentrosymmetric dipolar response averaged over the spherical NC interfaces. A two-beam SHG geometry is found to enhance this polarization greatly compared to single-beam SHG, yielding strong signals useful for scanning, spectroscopy, and real-time monitoring. This configuration provides a general strategy for enhancing the second-order nonlinear response of centrosymmetric samples, as demonstrated here for both Si nanocomposites and their glass substrates.     

Dual-color operation of a femtosecond optical parametric oscillator exhibiting stable relative carrier-envelope phase-slip frequencies

A femtosecond optical parametric oscillator is demonstrated that can operate in a regime where two signal pulses with well-separated center wavelengths are simultaneously resonant. Measurements show that the oscillator output contains a stable modulation at a frequency corresponding to the difference in the carrier-envelope phase-slip frequencies of the co-resonant pulses. The physical origin of this internal beat signal is attributed to second-order mixing effects, and its frequency is shown to be consistent with theory.     

Theoretical study of diluted Co/Cu alloys

This study employs the self-consistent Green's function method to study the magnetic properties of diluted _CoxCu1-x${\mathrm{Co}}_x{\mathrm{Cu}}_{1-x}$ alloys from a consideration of their spin dynamics characteristics. The numerical results show that in dilute cobalt concentrations (i.e. x?0.4$x?0.4$), the critical temperatures vary linearly with x for different itinerant carrier concentration conditions. Interestingly, the carrier concentration does not affect the degree of dependency of the temperature on the cobalt concentration when the carrier concentration is less than the atomic number concentration of the alloy.