Diode-pumped 671 nm laser frequency doubled by CPM LBO

A design of diode-pumped high-efficiency Nd:YVO₄/LBO red laser is reported. Using critical phase-matching (CPM) LBO, 671 nm red laser was obtained from 1342 nm light by intracavity frequency doubling. With an incident pump laser of 800 mW, using type-I and type-II CPM LBO, 97 and 52 mWTEM₀₀ mode red laser outputs were obtained, with optical-to-optical conversion efficiencies of up to 12.1% and 6.5%, respectively.     

Studies on antiatherosclerotic agents. Synthesis of 5-substituted derivatives of 7-ethoxycarbonyl-6,8-dimethyl-1(2H)-phthalazinone.off.

Several 5-substituted derivatives of 7-ethoxycarbonyl-6,8-dimethyl-1(2H)- phthalazinone were prepared by means of nitration, reductive amination, and diazonium decomposition. The substituents introduced included NO2, NH2, F, Cl, CN. Among the derivatives, the fluorine compound was obtained only in poor yield because intramolecular cyclization occurred predominantly.     

Purification and some properties of squalene-2,3-epoxide: lanosterol cyclase from rat liver

Squalene-2,3-epoxide: lanosterol cyclase was purified from rat liver in five steps as a soluble and homogeneous protein. The purified enzyme showed a single band on SDS-polyacrylamide gel electrophoresis with a molecular weight of 75 kD. In its native state it behaved as a homo-dimer. The isoelectric point of 5.5 and the apparent Km value for (3S)-squalene-epoxide of 55 microM were estimated for the cyclase.     

多边形棒状透镜出端辐射均匀性的研究

研究了用多角形棒状透镜产生高均匀性正方形和圆形照明的最佳结构参量.结果表明,对于正方形棒状透镜,输出端的照明均匀性随透镜的长度振荡变化,在某些特定长度达到极小值.对于圆形照明面积,比较了从三角到八角的六种多边形.利用三角形积分透镜可以获得最佳的照明均匀性,但光能利用率相对较低,六角形积分透镜可同时获得较高的照明均匀性和光能利用率.     

赝能隙导致的YBa2(Cu1-xMx)3O7-δ(M=Co,Zn)薄膜的输运性质异常

报道了两类典型元素替代的超导Y123相体系-YBa2(Cu1-xCox)3O7-δ(x=0.01,0.02)和YBa2(Cu1-yZny)3O7-δ(y=0.005,0.010)薄膜的电阻率-温度特性(ρ(T))和Hall效应(RH (T)).研究表明,Co掺杂的Y123相体系十分类似于氧欠掺杂的情况,对Co掺杂的薄膜样品,由电阻率-温度特性定义的赝能隙打开的温度T*分别为193和225K.而Zn掺杂的样品没有观察到赝能隙打开对电阻率-温度特性的影响.由Hall效应的测量和Hall角(cotθH)定义了另一个特征温度T 0,介于Tc与T*之间,这一特征温度与核磁共振(NMR)给出的赝能隙打开温度相近,说明可能源于电子自旋自由度上的能隙打开.在室温到Tc范围内,电阻率-温度特性和Hall效应分别定义了两类不同的转变温度(T*和T 0),可能分别源于电子电荷和自旋通道上的赝能隙的打开,预示着电荷和自旋自由度分别进入某种基态.     

Efficient computation of natural convection in a concentric annulus between an outer square cylinder and an inner circular cylinder

In this work, the natural convection in a concentric annulus between a cold outer square cylinder and a heated inner circular cylinder is simulated using the differential quadrature (DQ) method. The vorticity‐stream function formulation is used as the governing equation, and the coordinate transformation technique is introduced in the DQ computation. It is shown in this paper that the outer square boundary can be approximated by a super elliptic function. As a result, the coordinate transformation from the physical domain to the computational domain is set up by an analytical expression, and all the geometrical parameters can be computed exactly. Numerical results for Rayleigh numbers range from 104 to 106 and aspect ratios between 1.67 and 5.0 are presented, which are in a good agreement with available data in the literature. It is found that both the aspect ratio and the Rayleigh number are critical to the patterns of flow and thermal fields. The present study suggests that a critical aspect ratio may exist at high Rayleigh number to distinguish the flow and thermal patterns. Copyright © 2002 John Wiley & Sons, Ltd.     

二项式光场与级联三能级原子的量子纠缠

利用量子熵理论，研究了二项式光场与级联三能级原子的量子纠缠，讨论了光场与原子的初始参量对其量子纠缠性质的影响.结果表明，利用二项式光场的特性，可以揭示从相干态到数态之间的所有态光场与三能级原子相互作用时的量子纠缠性质.选择适当的系统参数可以制备稳定的光场-原子qutrit纠缠态. 关键词： 二项式光场 级联三能级原子 光场熵 量子纠缠     

On the Whitham Equations for the Defocusing Nonlinear Schrodinger Equation with Step Initial Data

The behavior of solutions of the finite-genus Whitham equations for the weak dispersion limit of the defocusing nonlinear Schrodinger equation is investigated analytically and numerically for piecewise-constant initial data. In particular, the dynamics of constant-amplitude initial conditions with one or more frequency jumps (i.e., piecewise linear phase) are considered. It is shown analytically and numerically that, for finite times, regions of arbitrarily high genus can be produced; asymptotically with time, however, the solution can be divided into expanding regions which are either of genus-zero, genus-one, or genus-two type, their precise arrangement depending on the specifics of the initial datum given. This behavior should be compared to that of the Korteweg-de Vries equation, where the solution is divided into regions which are either genus-zero or genus-one asymptotically. Finally, the potential application of these results to the generation of short optical pulses is discussed: The method proposed takes advantage of nonlinear compression via appropriate frequency modulation, and allows control of both the pulse amplitude and its width, as well as the distance along the fiber at which the pulse is produced     

Distributed feedback multipeak laser emission in Rhodamine 6G doped organic-inorganic hybrids

Organic-inorganic hybrid materials were prepared from an ureasil precursor (ureapropyltriethoxysilane designated as UPTES) and acrylic acid modified zirconium (IV) n-propoxide. Thin films containing rhodamine 6G (Rh6G) were prepared by spin-coating on glass substrates with different Zr:Si molar ratios (Zr:Si = 75:25, 50:50 and 25:75). Refractive index, thickness, number of propagating modes and attenuation coefficient were measured at 543.5, 632.8 and 1550 nm wavelengths by the prism coupling technique. Distributed feedback (DFB) laser effect was observed and studied as a function of films thickness and refractive index.