Diastereo- and enantioselective conjugate addition of α-substituted nitroacetates to maleimides under base-free neutral phase-transfer conditions

Highly diastereo- and enantioselective conjugate addition of α-substituted nitroacetates to maleimides under base-free neutral phase-transfer conditions was developed for the synthesis of α,α-disubstituted α-amino acid derivatives.     

Catalytic asymmetric synthesis of 1,1-disubstituted tetrahydro-β-carbolines by phase-transfer catalyzed alkylations

Efficient catalytic asymmetric synthesis of 1,1-disubstituted tetrahydro-β-carbolines has been achieved via asymmetric alkylation of 1-cyanotetrahydro-β-carbolines using a binaphthyl-modified N-spiro-type chiral phase-transfer catalyst. This is a valuable example of hitherto difficult highly enantioselective alkylations at α-carbon of the cyano group under phase-transfer conditions.     

Cost‐efficient monitoring of continuous‐time stochastic processes based on discrete observations

Planning a cost‐efficient monitoring policy of stochastic processes arises from many industrial problems. We formulate a simple discrete‐time monitoring problem of continuous‐time stochastic processes with its applications to several industrial problems. A key in our model is a doubling trick of the variables, with which we can construct an algorithm to solve the problem. The cost‐efficient monitoring policy balancing between the observation cost and information loss is governed by an optimality equation of a fixed point type, which is solvable with an iterative algorithm based on the Feynman‐Kac formula. This is a new linkage between monitoring problems and mathematical sciences. We show regularity results of the optimization problem and present a numerical algorithm for its approximation. A problem having model ambiguity is presented as well. The presented model is applied to problems of environment, ecology, and energy, having qualitatively different target stochastic processes with each other.     

Self-pulsing dynamics of ytterbium-doped fiber laser with pump-bypassed cavity

In addition to efficient continuous wave laser action at 1.06 μm (⁴ F _3/2→⁴ I _11/2 transition), with a slope efficiency 30% and 30 mW pump power threshold, this work presents a throughout study of the spectroscopic, and thermo-optical properties of a 2.0 mol % Nd³⁺ doped fluoroindogallate glass. The characterization of the sample using the pump probe experimental technique indicated the presence of two broad excited state absorption bands from 0.94 to 1.05 μm (⁴ F _3/2→² D _3/2, ² G _9/2, ⁴ G _11/2, ² K _15/2) and from 1.16 to 1.42 μm (⁴ F _3/2→⁴ G _9/2, ⁴ G _7/2, ² K _13/2), found not to interfere with the stimulated emission at 1.06 μm, with a peak cross section value σ_SE = 2.55×10^-21 cm² and a full width at half maximum of 22 nm. Thermal lens measurements were performed to quantify the Auger upconversion parameter (γ=(1.26±0.09)×10^-16 cm³/s) and evaluate the thermal loading in the sample in comparison to other commercial glasses. PACS 181.05.Kf; 78.45.+h; 42.70.Hj     

Optimization of the laser performance in Nd3+:YAG ceramic microchip lasers

Based on the four-level system, a theoretical model of diode-laser end-pumped fundamental continuous-wave Nd³⁺:YAG ceramic microchip lasers is proposed. The fluorescence concentration quenching effect and the absorption efficiency of the host have been taken into account in the model. The theoretical results of the numerical calculations are in good agreement with those of experiments. The effects of the concentration of the Nd³⁺:YAG ceramic, the thickness of the Nd³⁺:YAG ceramic, and the transmission of the output coupler on the laser performance (threshold and output power) are addressed. The optimization of the concentration and the thickness for the Nd³⁺:YAG ceramic microchip laser is presented. This modeling is not only applicable to the Nd³⁺:YAG ceramic microchip laser but also to other four-level microchip lasers. PACS 42.55.-f; 42.55.Xi; 42.70.Hj; 02.60.Cb     

Vibration and buckling of cylinders with elliptical cross section

A study of the free vibration of finite cylinders with elliptical cross section under external pressure is presented. The bucklng pressure is obtained as a special case in the free vibration analysis. The elliptical cross section is considered to be composed of two circular arcs, and the equations of a circular cylindrical shell are applied. Numerical examples are presented to examine the effect of out-of-roundness on the natural frequencies and the buckling pressure.     

Isothermal cis-trans isomerization behavior of polyacetylene films

Isothermal cis-trans isomerization behavior was studied by differential scanning calorimetry for conventional Shirakawa polyacetylene (S-PA) film and highly stretchable polyacetylene (hs-x) films synthesized using catalysts aged at high temperature. The rate of isomerization is slower for S-PA than for hs-x. Kinetic results of isomerization are analyzed by a stretched exponential function with exponent n (0 < n < 1), which is different from the previously assumed single exponential function. An activation energy of 31 kcal/mol was obtained for all the samples. © 1995 John Wiley & Sons, Inc.     

The electronic properties of [CH(FeCl4)0.061]x

The temperature dependence of d.c. conductivity, thermopower and electron paramagnetic resonance (EPR) results on [CH(FeCl₄)_0.061]_x are reported. The d.c. conductivity and thermopower measurements indicate metallic charge transport along the polyacetylene chain interrupted by the interfibril contact resistances and also ‘dragged’ primarily by the dopant ions. The initial measurements of EPR show Dysonian lineshape with very broad linewidth (ΔH ≈ 600 G at room temperature). The temperature dependence of EPR absorption intensity implies that there exist localized magnetic moments. The observed g value (g ≈ 2.03) suggests the dopant anion is in a form of (FeCl₄)^-.     

Photoluminescence and luminescence excitation spectra in ZnSiP2

Summary Measurements of photoluminescence and luminescence excitation spectra of ZnSiP₂ have been performed at 4.2K and two results were obtained. One is the observation of a new sharp emission line at 1.980 eV, due to the bound exciton associated with the pseudodirect gap. The other is the observation of another new series of absorption lines in the luminescence excitation spectrum of an emission line, at 1.984 eV, in addition to those reported previously. These results indicate that in ZnSiP₂ radiative transitions occur at both the indirect and the pseudodirect gaps. Paper presented at the ?V International Conference on Ternary and Multinary Compound?, held in Cagliari, September 14–16, 1982.