BBO，LBO，KDP晶体光参量啁啾脉冲放大特性的比较研究

 对BBO，LBO，KDP晶体I类非共线匹配下的光参量啁啾脉冲放大的相位匹配、参量范围、增益特性等进行了理论分析，重点对BBO和LBO的光参量啁啾脉冲放大特性进行了比较。结果表明对于以光参量啁啾脉冲放大系统代替800nm中心波长的Ti:sappire再生放大系统，用BBO晶体可获得更宽的增益带宽，而对1 053nm中心波长的种子光用LBO晶体更好。     

Quinone transfer radical polymerization (QTRP) of styrene: Catalysis by different metal complexes

Styrene has been polymerized by a Quinone Transfer Radical Polymerization (QTRP) based on the redox reaction of an ortho‐quinone and a metal catalyst. Several metal acetylacetonates have been tested in this work. The radical polymerization of styrene is largely controlled when phenanthrenequinone (PhQ) is used with catalytic amounts of Co(acac)₂, Ni(acac)₂, Mn(acac)_{2 or 3}, and Al(acac)₃. As a rule, in the presence of all these metallic complexes, the polystyrene molar mass increases with the monomer conversion, and polydispersity (M_w/M_n) is in the 1.3–1.6 range (at least until 40% monomer conversion). Styrene polymerization has also been resumed by polystyrene chains prepared by QTRP. In the specific case of manganese acetylacetonates, an amine or phosphine ligand has to be added for the control to be effective. Finally, two mechanistic hypotheses have been proposed, depending on whether the oxidation state of the metal can be easily changed or not. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2723‐2733, 2005     

Quantum chemical and conventional TST calculations of rate constants for the OH + alkane reaction

Reactions of OH with methane, ethane, propane, i-butane, and n-butane have been modeled using ab initio (MP2) and hybrid DFT (BHandHLYP) methods, and the 6-311G(d,p) basis set. Furthermore, single-point calculations at the CCSD(T) level were carried out at the optimized geometries. The rate constants have been calculated using the conventional transition-state theory (CTST). Arrhenius equations are proposed in the temperature range of 250–650 K. Hindered Internal Rotation partition functions calculations were explicitly carried out and included in the total partition functions. These corrections showed to be relevant in the determination of the pre-exponential parameters, although not so important as in the NO₃ + alkane reactions [G. Bravo-Pérez, J.R. Alvarez-Idaboy, A. Cruz-Torres, M.E. Ruíz, J. Phys. Chem. A 106 (2002) 4645]. The explicit participation of the tunnel effect has been taken into account. The calculated rate coefficients provide a very good agreement with the experimental data. The best agreement for the overall alkane + OH reactions seemed to occur when the BHandHLYP geometries and partition functions are used. For propane and i-butane, in addition to the respective secondary and tertiary H-abstraction channels, the primary one has been considered. These pathways are confirmed to be significant in spite of the large differences in activation energies between primary and secondary or primary and tertiary channels, respectively of propane and i-butane reactions and should not be disregarded.     

Investigation of nanoparticle generation during femtosecond laser ablation of metals

The production of nanoparticles via femtosecond laser ablation of gold and copper is investigated experimentally involving measurements of the ablated mass, plasma diagnostics, and analysis of the nanoparticle size distribution. The targets were irradiated under vacuum with a spot of uniform energy distribution. Only a few laser pulses were applied to each irradiation site to make sure that the plume expansion dynamics were not altered by the depth of the laser-produced crater. Under these conditions, the size distribution of nanoparticles does not exhibit a maximum and the particle abundance monotonously decreases with size. Furthermore, the results indicate that two populations of nanoparticles exist within the plume: small clusters that are more abundant in the fast frontal plume component and larger particles that are located mostly at the back. It is shown that the ablation efficiency is strongly related to the presence of nanoparticles in the plume.     

Finite modular congruence lattices

We consider the variety of modular lattices generated by all finite lattices obtained by gluing together some M₃’s. We prove that every finite lattice in this variety is the congruence lattice of a suitable finite algebra (in fact, of an operator group). Received February 26, 2004; accepted in final form December 16, 2004.     

Covering space for monotonic homotopy of trajectories of control systems

This paper considers monotonic (or causal) homotopy between trajectories of control systems. The main result is the construction of an analogue of the simply connected covering space. The constructed covering Γ(Σ,x) has the structure of a manifold and satisfies the property that two trajectories are monotonic homotopic if and only if the end points of their liftings coincide.     

Complexation Study and Spectrofluorimetric Determination of Pipemidic Acid with γ-Cyclodextrin

The fluorimetric characteristics of pipemidic acid (PIPE) have been investigated. It has been proven that the fluorescence emission band of pipemidic acid at 439 nm is significantly intensified in the presence of γ-cyclodextrin. The inclusional complexation between the antibacterial pipemidic acid and γ-cyclodextrin (γ-CD) has been studied. A 1:1 stoichiometry of the complex was established and its association constant was calculated by a nonlinear regression method, monitoring the changes in the fluorescence signal of pipemidic acid in the presence of γ-CD. According to the results obtained, a spectrofluorimetric method for the determination of PIPE has been proposed. The best limits of detection and quantification were obtained in presence of γ-CD, in acidic media. The dynamic range of the method was comprised between 0.18 and 1.40 μg/ml.     

Bounded turning and quasiconformal maps

We considern-dimensional quasiconformal maps of an arbitrary domain onto a domain with specific properties and prove various results related to the Hayman-Wu theorem.