355nm Nd∶YAG激光在H_2中的高效一级斯托克斯转换

对脉冲Nd∶YAG激光(355 nm)在H2和H2∶He-Ar混合气体中的受激拉曼散射(SRS)进行了研究。在0.5 MPa的氢气中,同时测量到从二级反斯托克斯到三级斯托克斯的多波长输出,其总转化效率达88%;而高压下只剩下一级和二级斯托克斯输出,其中二级斯托克斯最大能量转化效率达44%(对应量子效率为63%)。由于高级斯托克斯的竞争,纯氢气中一级斯托克斯的最大能量转换效率不超过43%。通过向3 MPa氢气中掺入2 MPaAr气后,很好地抑制了二级斯托克斯的产生,从而获得了能量转换效率高达71%(对应量子效率为83%)的一级斯托克斯输出。对四波混频和级联受激拉曼散射在氢气多级斯托克斯产生中的作用以及惰性气体对它们的影响进行了讨论。     

2-fold and 3-fold mixing: why 3-dot-type counterexamples are impossible in one dimension

V.A. Rohlin asked in 1949 whether 2-fold mixing implies 3-fold mixing for a stationary process (ξ_i )_i2ℤ, and the question remains open today. In 1978, F. Ledrappier exhibited a counterexample to the 2-fold mixing implies 3-fold mixing problem, the socalled 3-dot system, but in the context of stationary random fields indexed by ℤ². In this work, we first present an attempt to adapt Ledrappier's construction to the onedimensional case, which finally leads to a stationary process which is 2-fold but not 3-fold mixing conditionally to the σ-algebra generated by some factor process. Then, using arguments coming from the theory of joinings, we will give some strong obstacles proving that Ledrappier's counterexample can not be fully adapted to one-dimensional stationary processes.     

Investigations of low- and high-spin states of <Superscript>132</Superscript>La

The fusion evaporation reaction ¹²²Sn(¹⁴N, 4n)¹³²La was used to populate the high-spin states of ¹³²La at the beam energy of 60 MeV. A new band consisting of mostly E2 transitions has been discovered. This band has the interesting links to the ground state 2^- and the isomeric state 6^-. A new transition of energy 351 keV connecting the low-spin states of the positive-parity band based on the πh _11/2 ⊗ νh _11/2 particle configuration, has been found. This has played a very important role in resolving the existing ambiguities and inconsistencies in the spin assignment of the band head. Received: 12 August 2002 / Accepted: 18 March 2003 / Published online: 7 May 2003     

Photorefractive Four-Wave Mixing Switches Utilizing Pockels Effect -Longitudinal and Lateral Switches-

We carried out detailed calculations for photorefractive wave-mixing switches based on one of three crystals with high electro-optic coefficients, namely, BaTiO₃, Strontium Barium Niobate (SBN (0.75)), and Potasium Sodium Strontium Barium Niobate (KNSBN). A comparison of results for the three crystals shows that a 0_-cut BaTiO³ crystal is suitable for a longitudinal switch and requires a voltage of about 80 for a 2-mm-thick crystal to induce sufficient phase mismatch. The electrodes must be transparent for the incident and diffracted beams. A 45_-cut SBN (0.75) crystal, however, is suitable for a lateral switch and requires a voltage of about 150 for a 1-mm-wide crystal. The electrodes do not need to be transparent.     

A Supergene Differentiation Model for Orebearing Granitic Magma

According to the features of geophysics, experimental petrology, granite geology and geochemistry, the differentiations of ore-bearing granitic magmas are discussed. It is put forward that only the supergene differentiations of ore-bearing granitic magma might exist, instead of the hypogene one of the magma. Based on it, a supergene differentiation model for the ore-bearlng granitic magma is presented.     

Neutron emission under particular nonequilibrium conditions from Pd and Ti electrolytically charged with deuterium

Summary We report on neutron emission in palladium and titanium electrolitically charged with deuterium. The detection of neutrons is observed after thermal treatment of the electrode. In the hypothesis that neutrons came from cold fusion processes, we estimate a fusion rate as high as 1.3·10⁻²¹ fusions/deuteron pair/second.     

Extension of a combined analytical/numerical initial value problem solver for unsteady periodic flow

Here we describe analytical and numerical modifications that extend the Differential Reduced Ejector/ mixer Analysis (DREA), a combined analytical/numerical, multiple species ejector/mixing code developed for preliminary design applications, to apply to periodic unsteady flow. An unsteady periodic flow modelling capability opens a range of pertinent simulation problems including pulse detonation engines (PDE), internal combustion engine ICE applications, mixing enhancement and more fundamental fluid dynamic unsteadiness, e.g. fan instability/vortex shedding problems. Although mapping between steady and periodic forms for a scalar equation is a classical problem in applied mathematics, we will show that extension to systems of equations and, moreover, problems with complex initial conditions are more challenging. Additionally, the inherent large gradient initial condition singularities that are characteristic of mixing flows and that have greatly influenced the DREA code formulation, place considerable limitations on the use of numerical solution methods. Fortunately, using the combined analytical–numerical form of the DREA formulation, a successful formulation is developed and described. Comparison of this method with experimental measurements for jet flows with excitation shows reasonable agreement with the simulation. Other flow fields are presented to demonstrate the capabilities of the model. As such, we demonstrate that unsteady periodic effects can be included within the simple, efficient, coarse grid DREA implementation that has been the original intent of the DREA development effort, namely, to provide a viable tool where more complex and expensive models are inappropriate. Copyright © 2002 John Wiley & Sons, Ltd.     

偶氮苯衍生物三阶非线性的四波混频研究

用皮秒Ｎｄ：ＹＡＧ激光器的倍频光（５３２ｎｍ）对具有离域π－共轭电子云结构的偶氮苯类样品材料作简并四波混频补给，测得三阶非线性电极化率ｘ＾（３）和它们的时间响应分别为１０＾－９ｅｓｕ和２０ｐｓ，并对影响ｘ＾（３）的瞬时光栅作用和ｘ＾（３）的响应时间人了讨论。     

离子束引起的在Al／Cr双层薄膜界面处的原子混合

用600keV的Kr~ 离子轰击Al/Cr双层薄膜样品进行界面原子反应及相互混合的研究。实验样品是在单晶硅上蒸镀约500nm厚的铝膜,相继再蒸上所需厚度的铬膜而制成的。轰击剂量为2.0×10~(15)-2.5×10~(16)Kr~ /cm~2。用2.0MeVa粒子对轰击前后的样品进行了卢瑟福背散射(RBS)分析,发现界面处有明显的原子混合存在;当轰击剂量≥1.0×10~(16)Kr~ /cm~2时,RBS谱出现有明显的坪台,经拟合计算和x射线衍射(XRD)测量证实确有化合物Al_(13)Cr_2存在;还分别得到了原子混合量及混合效率与轰击剂量的关系;最后对界面处的原子混合机制进行了讨论。