Synthesis of 4-alkoxy-Δ3-pyrrolin-2-ones and tetramic acids

Acetoacetic ester is converted into 4-alkoxy-Δ³-pyrrolin-2-ones which can be hydrolyzed to give tetramic acids.     

Higher order symmetrizer and application to an unusual transport equation

We study a class of stationary transport equation with nonlocal low-order tems We obtain the existence and uniqueness of a solution in sobolev spaces     

求解复杂湍流的非线性涡黏性系数模型和代数应力模型

非线性涡黏性系数模型和代数应力模型联系了线性涡黏性系数湍流模型和完整的微分 雷诺应力模型.随着它们受到日益关注,其形式也越来越多样化.本篇综述的目的是对这些模 型加以总结并比较它们之间的共同点及不同之处,指出它们与完整微分雷诺应力模型之间的 关系,以及相对于线性涡黏性系数模型而言它们在预报流场上所具有的优势.     

Isotropic-nematic phase transition of single-walled carbon nanotubes in strong acids

We present the first quantitative assessment of the maximum amount of nanotubes that can exist in the isotropic phase () of single-walled carbon nanotubes (SWNTs) in Br?nsted-Lowry acids. We employ a centrifugation technique in conjunction with UV-vis-nIR spectroscopy to quantify , which is also the critical concentration of the isotropic-nematic transition of SWNTs in strong acids. Centrifugation of biphasic dispersions of SWNTs, that is, acid dispersions consisting of an isotropic phase in equilibrium with an ordered nematic liquid crystalline phase, results in a clear phase separation, where the isotropic phase is supernatant. Dilution of the isotropic phase with a known amount of acid followed by UV-vis-nIR absorbance measurements yields , that is, the maximum concentration of SWNTs that can exist in the isotropic phase in a given acid for a given SWNTs' length distribution. At low SWNT concentration (below 200 ppm) in superacids, light absorbance in the range from 400 to 1400 nm scales linearly with concentration. This Beer's law behavior yields calibration curves for measuring SWNTs' concentration in acids. We find that the critical concentration of the isotropic-nematic transition increases with acid strength in accordance with the previously proposed sidewall protonation mechanism for dispersing SWNTs in acids.     

Simultaneous forward- and backward-hemisphere elastic-light-scattering patterns of respirable-size aerosols

Two-dimensional angular optical scattering (TAOS) patterns of aerosols are measured simultaneously from the forward hemisphere 15 degrees < theta < 90 degrees as well as the backward hemisphere 90 degrees < theta < 165 degrees (detecting 63% of the 4pi sr of scattered light) by using an ellipsoidal reflector and an intensified CCD detector. TAOS patterns were obtained from polystyrene-latex spheres (individuals and aggregates) and from single Bacillus subtilis spores. These information-rich patterns, measured with a single laser pulse for individual particles on the fly, suggest that forward-TAOS and backward-TAOS measurements may be used for rapid classification of single aerosol particles.     

Static dielectric constants and molecular dipole distributions of liquid water and ice-Ih investigated by the PAW-PBE exchange-correlation functional

The static dielectric constants, ε(s), of ice-Ih and liquid water were calculated using density functional theory with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional and the projector-augmented-wave (PAW) approach. Proton disordered ice configurations and uncorrelated liquid configurations were sampled with the electrostatic switching method using force fields specially designed to facilitate the ab initio free energy perturbation calculations. Our results indicate that PAW-PBE underestimates the ε(s) of both ice-Ih and liquid water but predicts the ratio of ice and water ε(s) in good agreement with experimental measurements. PAW-PBE gives average water dipole moments of 2.50 D in ice-Ih and 2.48 D in the liquid. Our results show that the fixed-charge water models developed by adaptive force matching can reproduce the PAW-PBE dipole moments with an error of approximately 5%. The ice and liquid models created in this work have polarizabilities of 1.32 ?(3) and 1.30 ?(3), respectively, along the HOH bisector direction.     

Dynamics of photon-induced degradation and fluorescence in riboflavin microparticles

An unexpected blue-fluorescence band (around 420 nm) from both micrometer-sized dried particles and aqueous droplets of riboflavin [7,8-dimethyl-10-(D-1^′-ribityl)-isoalloxazine] is observed when the microparticles are irradiated with a pulsed UV (355- or 351-nm) laser. The intensity of the band increases quadratically with input laser energy density (fluence) and is attributable to a one-photon-excited fluorescence of lumichrome (7,8-dimethyl-alloxazine) that is produced by photo-degradation of riboflavin. The well-known greenish-yellow fluorescence band (at 560 nm for dried particles and 535 nm for aqueous droplets) from riboflavin increases sublinearly with UV-laser fluence. With a laser input fluence above 5 J/cm² the riboflavin fluorescence decays earlier and the lumichrome fluorescence reaches a maximum later than the peak of the input laser pulse. The temporal dynamics of the 420- and 535-nm fluorescence peaks are consistent with a rate-equation simulation of photon-induced conversion of riboflavin to lumichrome and the subsequent fluorescence of lumichrome. Received: 28 September 2000 / Revised version: 11 December 2000 / Published online: 21 February 2001     

Single-shot fluorescence spectra of individual micrometer-sized bioaerosols illuminated by a 351- or a 266-nm ultraviolet laser

Reproducible fluorescence spectra of individual 2- to 5-microm -diameter biological aerosol particles excited with a single shot from a Q -switched laser (266 or 351 nm) have been obtained with highly improved signal-to-noise ratios. Critical to the advance are crossed diode-laser trigger beams, which precisely define the sample volume, and a reflecting objective, which minimizes chromatic aberration and has a large N.A. for collecting fluorescence. Several allergens (red oak, meadow oat pollen, paper mulberry pollen, and puffball spores) have different fluorescence spectra. Bacillus subtilis fluorescence spectrum deteriorates at high 266-nm incident intensity. Dry riboflavin particles illuminated with a 351-nm light exhibit a new 420-nm fluorescence peak that grows nonlinearly with laser pulse energy.