Hybrid Parallel Linear System Solvers

This paper presents a new approach to the solution of nonsymmetric linear systems that uses hybrid techniques based on both direct and iterative methods. An implicitly preconditioned modified system is obtained by applying projections onto block rows of the original system. Our technique provides the flexibility of using either direct or iterative methods for the solution of the preconditioned system. The resulting algorithms are robust, and can be implemented with high efficiency on a variety of parallel architectures. The algorithms are used to solve linear systems arising from the discretization of convection-diffusion equations as well as those systems that arise from the simulation of particulate flows. Experiments are presented to illustrate the robustness and parallel efficiency of these methods.     

Coherent oscillations of holes in GaAs0.86P0.14/Al0.7Ga0.3As surface quantum well

We show that in a GaAs_0.86P_0.14/Al_0.7Ga_0.3As near-surface quantum well, there is coherent oscillation of holes observed in time-resolved reflectivity signal when the top barrier of the quantum well is sufficiently thin. The quantum well states interact with the surface states under the influence of the surface electric field. The time period of the observed oscillation is 120±10 fs.     

Curing Kinetics and Thermal Stability of Diglycidyl Ether of Bisphenol‐A Using Mixtures of Heterocyclic Derivatives of Stannanes and 4,4′‐Diaminodiphenylsulfone

Curing kinetics of diglycidyl ether of bisphenol-A (DGEBA) in the presence of varying molar ratios of derivatives of stannanes to 4,4'-diaminodiphenylsulfone (DDS) was investigated by the dynamic differential scanning calorimetry. The derivatives were synthesized by reacting 1 mole of biguanide (B) with 1 mole of phenylethyltindihydride (PETH) or phenylmethyltindihydride (PMTH) or phenylbutyltindihydride (PBTH) and designated as BPETH or BPMTH or BPBTH respectively. These derivatives were characterized by elemental analysis and spectroscopic techniques such as IR, ¹H NMR, ¹³C NMR and ¹¹⁹Sn NMR. The mixtures of these derivatives to DDS at ratios of 0∶1, 0.25∶0.75, 0.5∶0.5, 0.75∶0.25 and 1∶0 were used to investigate the curing behaviour of DGEBA. The multiple heating rate method (5, 10, and 15 and 20 ℃•min^－1) was used to study the curing kinetics of epoxy resins. The thermal stability of the isothermally cured resins was also evaluated using dynamic thermogravimetry in a nitrogen atmosphere.     

钙钛矿结构荧光材料MZrO3:Eu3+,A (M=Ca2+, Ba2+; A=Li+, Na+, K+)的制备及其发光性质

Calcium and barium zirconate powders based upon CaZrO₃:Eu³⁺,A and BaZrO₃:Eu³⁺,A (A=Li⁺, Na⁺, K⁺) were prepared by combustion synthesis method and heating to ~1000℃ to improve crystallinity.The structure and morphology of materials were examined by X-ray diffraction (XRD) and scanningelectron microscopy (SEM). XRD results showed that CaZrO₃:Eu³⁺,A and BaZrO₃:Eu³⁺,A (A=Li⁺, Na⁺, K⁺) perovskites possessed orthorhombic and cubic structures, respectively. The morphologies of all powderswere very similar consisting of small, coagulated, cubical particles with narrow size distributions andsmooth and regular surfaces. The characteristic luminescences of Eu³⁺ ions in CaZrO₃:Eu³⁺,A (A=Li⁺, Na⁺, K⁺) lattices were present with strong emissions at 614 and 625 nm for ⁵D₀→⁷F₂ transitions with other weakeremissions observed at 575, 592, 655, and 701 nm corresponding to ⁵D₀→⁷F_n transitions (where n=0, 1, 3, 4 respectively). In BaZrO₃:Eu³⁺ both the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions at 595 and 613 nm were strong.Photoluminescence intensities of CaZrO₃:Eu³⁺ samples were higher than those of BaZrO₃:Eu³⁺ lattices. Thisremarkable increase of photoluminescence intensity (corresponding to ⁵D₀→⁷F_n transitions) was observedin CaZrO₃:Eu³⁺ and BaZrO₃:Eu³⁺ if co-doped with Li⁺ ions. An additional broad band composed of manypeaks between 440 to 575 nm was observed in BaZrO₃:Eu³⁺,,A samples. The intensity of this band wasgreatest in Li⁺ co-doped samples and lowest for K⁺ doped samples.     

ZnO/eosin-Y混合薄膜的生长机理和形态

Thin hybrid films of ZnO/eosin-Y were prepared by electrodeposition at-0.8 and-0.9 V in aqueous and non-aqueous baths at temperatures ranging from 40 to 90 ℃ with dye concentrations of 100 and 400 μmol·L-1.The films were characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM),energy-dispersive X-ray analysis (EDX),and absorption spectroscopy.The films prepared in a non-aqueous bath were non-porous and did not adsorb dye molecules on their surface.However,the films grown in aqueous media were porous in nature and adsorbed dye during the deposition of ZnO.Preferential growth of the film along the (002) face was observed,and the highest crystallinity was achieved when the film was deposited at 60 ℃.The maximum absorption was achieved for the films grown at 60 to 70 ℃,a deposition potential of-0.9 V,and a dye concentration of 100 μmol·L-1.     

硫酸存在时N-溴代苯二甲酰亚胺对甘露糖的胶束催化氧化

The kinetics of micellar-catalyzed oxidation of mannose by N-bromophthalimide was studied in the presence of sulfuric acid at 313 K. The orders of reaction with respect to [mannose], [oxidant], and [H+] were found to be fractional, first, and negative fractional order, respectively. Anionic micelles of sodiumdodecyl sulfate showed a partial inhibitory effect, while cationic micelles of cetyltrimethylammonium bromide increased the reaction rate with the same kinetic behavior. The reaction was catalyzed by cationic micelles, because of favorable electrostatic/thermodynamic/hydrophobic/hydrogen bonding between reactants and cationic micelles. Their catalytic roles are best explained by Berezin’s model. A variation of [phthalimide] showed that the rate of reaction decreased with increasing [phthalimide]. It was observed that, an increase of [mercuric acetate] had no effect on reaction velocity. The influence of salts on the reaction rate was also studied. The rate constant (kW ), binding constants (KS+KO), and corresponding activation parameters (Ea, ⊿H#, ⊿S#, and ⊿G#) were determined. A detailed mechanism with associated reaction kinetics is presented and discussed.     

镍铁氰化物纳米粒子的合成及其多相催化无溶剂条件下苯甲醇氧化的潜能(英文)

Nickel hexacyanoferrate nanoparticles were synthesized and characterized using elemental analysis, thermal analysis, infrared spectroscopy, and X-ray diffraction. A FE-SEM image of the nickel hexacyanoferrate showed that it consists of nearly spherical particles with sizes ranging from 30 to 70 nm. The synthesized material was found to be a heterogeneous catalyst useful for the solvent-free oxidation of benzyl alcohol with H2O2 as an oxidant. A 36% conversion of benzyl alcohol to benzaldehyde was achieved under optimized reaction conditions using specific parameters such as the amount of catalyst, the temperature, the benzyl alcohol to H2O2 molar ratio, and the reaction time.     

Temporal dynamics of high repetition rate pulsed single longitudinal mode dye laser

Theoretical and experimental studies of temporal dynamics of grazing incidence grating (GIG) cavity, single-mode dye laser pumped by high repetition rate copper vapour laser (CVL) are presented. Spectral chirp of the dye laser as they evolve in the cavity due to transient phase dynamics of the amplifier gain medium is studied. Effect of grating efficiency, focal spot size, pump power and other cavity parameters on the temporal behaviour of narrow band dye laser such as build-up time, pulse shape and pulse width is studied using the four level dye laser rate equation and photon evolution equation. These results are compared with experimental observations of GIG single-mode dye laser cavity. The effect of pulse stretching of CVL pump pulse on the temporal dynamics of the dye laser is studied.     

Mixing and phase separation in molecular fluid mixtures

The equation of state for a hard convex body (HCB) fluid mixture, which is based on the scaled particle theory, is utilized to derive the Helmholtz free energy, F, and the concentration fluctuations, S.,(O), to investigate the thermodynamic stability of athermal and not athermal molecular fluid mixtures. The role of the size and the non-sphericity geometrical factor of the molecule on the stability of the mixture is critically examined. The energetics of long-range attractive forces for not athermal mixtures have been introduced through the double Yukawa potential in conjunction with a realistic distribution function. The formalism allows one to investigate the properties of molecular mixtures under induced conditions of extreme temperature and pressure. The results suggest that geometrical factors coupled with energetics play a dominant role in phase separation.     

Performance of Dispersion-Compensated Optical Transmission Systems Based on Different Electrical Drivers

In this article, the simulation results have been presented for dispersive optical communication with different electrical drivers. The length of single-mode fiber has been put in a run that is compensated by dispersion-compensated fiber. The results have been presented and it is observed that of all the electrical drivers, the NRZ rectangular is best suited for dispersive optical communication systems. For this electrical driver, the parameters like BER remain constant and low. For other drivers, the BER decreases more for RZ super-Gaussian. Similarly, the Q factor increases with runs for all types of drivers except for NRZ rectangular, for which it decreases. For all the drivers, it is clear that as the runs are varied, the eye opening penalty increases, that is, there is less eye opening as the length of single-mode fiber is increased. It is also seen that the dispersion-compensated fiber compensates for the dispersion very effectively irrespective of the type of driver. Of the two formats, return to zero (RZ) and non-return to zero (NRZ), the earlier has more eye-opening penalty as the distortion is more and is clearly visible in all the rectangular, super-Gaussian, and raised cosine RZ formats. Of the three RZ formats, it is observed that RZ rectangular has the least eye-opening penalty. The non-return to zero format has less distortion and, of the two rectangular and raised cosine, the NRZ rectangular has less eye-opening penalty.