Effect of Electron Beam Irradiation on the Kinetics of Non-isothermal Crystallization of Nylon 66

The non-isothermal crystallization kinetics was studied by differential scanning calorimetric analysis on nylon 66 and e-beam irradiated nylon 66 at different cooling rates. The Modified Avrami equation, the Ozawa equation and the Combined Avrami-Ozawa equation were applied to study the kinetics of non-isothermal crystallization of nylon 66. The crystallization behavior of pristine nylon 66 polymer was compared with that of e-beam irradiated nylon 66 and observed that the kinetics of non-isothermal crystallization of nylon66 was affected largely upon e-beam irradiation. E-beam irradiation not only decreased the crystallization temperature of nylon 66, but influenced the mechanism of nucleation and crystal growth and reduced the overall crystallization rate of nylon 66 also. The crystallization activation energy calculated by the Kissinger method for irradiated nylon 66 was lower than that of pristine nylon 66.     

The Fitting of Luminescence Rises and Decays

This review presents a number of mathematical expressions which the experimental scientist may find useful to fit to time-dependent luminescence intensity (and concentration) data for both decay and rise situations. Some of these expressions have been drawn from literature sources and are presented here in a unified form. In compiling these expressions, a number of gaps were found in the literature, and, in this review, new expressions have been derived to fill some of these gaps. The final section of the review summarizes both the existing and the new kinetic expressions and provides an explanation of how to use them. Some of the subtleties and pitfalls of using kinetic data fitting to determine reaction mechanisms are also discussed.     

Investigation of surface plasma resonances in small sodium clusters

Photoabsorption cross sections of small neutral sodium clusters are measured at wavelengths from 452 to 604 nm. We find that surface plasma oscillations of the valence electrons dominate the photoabsorption spectra. The experimental results are consistent with predictions based on an extended Clemenger-Nilsson model, general sum rules, and the experimental static electric polarizabilities. For Na₈ a single broad resonance is observed, the peak wavelength is in excellent agreement with the model. The data for Na₉ and Na₁₀ support the prediction of double resonances.     

COMPARISON OF UV ACTION SPECTRA FOR LETHALITY AND MUTATION IN Salmonella typhimurium USING A BROAD BAND SOURCE AND MONOCHROMATIC RADIATIONS

Abstract— The UV-B region (280–320 nm) is thought to be primarily responsible for the mutagenic, lethal, and carcinogenic effects of solar radiation. We have conducted UV-B action spectroscopy for mutagenesis and survival of Ames' Salmonella typhimurium strain TA98 ( uvrB , pKM101) using both monochromatic radiation from a dye laser and broader bandwidth radiation emitted from FS-20 sunlamps. A series of optical filters having different transmission cut-offs together with the sunlamp source provided bandwidths having successively less short wavelength components from which a "broad band" action spectrum was deduced. The two sets of action spectra differed both qualitatively and quantitatively: in comparison to the monochromatic action spectra, the "broad band" spectra showed up to a 200-fold reduced efficiency for both mutation induction and lethality by UV-B wavelengths. These results suggest a large protective effect of the background UV-A and/or visible radiations which were present during the broad spectrum irradiations and which are also present in solar radiation. Additional experiments show that to the extent tested this protective effect is not due to photo-reactivation or irradiance (dose rate) effects     

Control of low-speed turbulent separated flow using jet vortex generators

A parametric study has been performed with jet vortex generators to determine their effectiveness in controlling flow separation associated with low-speed turbulent flow over a two-dimensional rearward-facing ramp. Results indicate that flow-separation control can be accomplished, with the level of control achieved being a function of jet speed, jet orientation (with respect to the free-stream direction), and jet location (distance from the separation region in the free-stream direction). Compared to slot blowing, jet vortex generators can provide an equivalent level of flow control over a larger spanwise region (for constant jet flow area and speed).Nomenclature C _p pressure coefficient, 2(P-P_)/V ² - C _Q total flow coefficient, Q/ v - D ₀ jet orifice diameter - Q total volumetric flow rate - R Reynolds number based on momentum thickness - u fluctuating velocity component in the free-stream (x) direction - V free-stream flow speed - VR ratio of jet speed to free-stream flow speed - x coordinate along the wall in the free-stream direction - jet inclination angle (angle between the jet axis and the wall) - jet azimuthal angle (angle between the jet axis and the free-stream direction in a horizontal plane) - boundary-layer thickness - momentum thickness - lateral distance between jet orifices A version of this paper was presented at the 12th Symposium on Turbulence, University of Missouri-Rolla, 24–26 Sept. 1990     

Single-step synthesis of D3h-symmetric bicyclooxacalixarenes

Bicyclooxacalixarenes are obtained in up to 95% yield by condensation of phloroglucinol with electron-poor meta-dihalogenated benzenes or pyridines. Single-crystal X-ray analysis reveals that these compounds adopt highly symmetrical, all-1,3-alternate cage-like structures. [structure: see text]     

Stability and convergence of the spectral Lagrange-Galerkin method for mixed periodic/non-periodic convection-dominated diffusion problems

We present a convergence analysis of the spectral Lagrange-Galerkinmethod for mixed periodic/non-periodic convection-diffusionproblems. The scheme is unconditionally stable, independentof the diffusion coefficient, even in the case when numericalquadrature is used. The theoretical predictions are illustratedby a series of numerical experiments. For the periodic case,our results present a significant improvement on those givenby Süli & Ware (1991) SIAM J. Numer.Anal.28, 423-445).