AFM study of morphological development during the melt-crystallization of poly(ethylene oxide)

The atomic force microscope (AFM) has been used to investigate morphological development during the crystallization of poly(ethylene oxide) (PEO) from the melt. PEOs with molecular weights of 1 × 10⁵ and 7 × 10⁶ were used. Height and amplitude images were recorded, using the tapping mode. For both polymers, the mode of spherulite development varied with the velocity of the growth front. For slow growth velocities, the growth of the crystallites was linear, with growth initially occurring by single lamellae, later developing into growth arms by screw dislocation spawning of crystallites. At intermediate growth velocities, stacks of lamellae develop rapidly. The splaying apart of adjacent crystals and growth arms is abundant. The operation of growth spirals was observed directly in this growth velocity range. The crystals formed by the giant screw dislocations diverge immediately from the original growth direction, providing a source of interlamellar splaying. At low and intermediate velocities, the front propagates by the advance of primary growth arms, with the regions between the arms filled in by arms growing behind the primary front. At the highest velocity observed here, the formation of lamellar bundles and immediate splaying results in recognizable spherulites developing at the earliest stages of crystallization. The change from linear growth to splaying and nonlinear growth are qualitatively explained in terms of driving force, elastic resistance and the presence of compositional and/or elastic fields in the melt. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2311–2325, 1998     

环己烯和2-甲基戊烯-1在几种Y型分子筛上的吸附量热研究

用SETARAM热流式量热计测定了环己烯和2-甲基戊烯-1于室温下在NaY、CaY、R_EY和HY等几种分子筛上的微分吸附热。我们又用Benson基团加合法计算得到了生成仲碳离子和叔碳离子时的吸附热。根据实验测得的于不同吸附量时环己烯和2-甲基戊烯-1的吸附热之差值, 对它们在上述几种Y型分子筛上的吸附机理进行了讨论。     

Difference schemes for a general parabolic problem with interface

Stability and convergence of finite difference schemes approximating a general parabolic partial differential equation with interface are examined. Convergence rate estimates compatible with the smoothness of the input data are obtained. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sulfur heterocycles. I. Use of 4,4-dimethyl-1,3-oxathiolane-3,3-dioxide as a carbonyl anion equivalent

The title heterocycle is used as a carbonyl anion equivalent in the preparation of aldehydes and α-silyl ketones; the key step is the thermal demasking of the heterocycle by loss of isobutylene and sulfur dioxide.     

Preparation and characterization of transparent conducting ZnS:Al films

Al-doped ZnS films were deposited using close-spaced evaporation of the powders synthesized by chemical precipitation method. The films were prepared for different Al concentrations in the range 0–10 at.% on glass substrates kept at 300 °C. The effect of Al-doping on ZnS composition, microstructure and optoelectronic properties of as-grown ZnS layers was determined using appropriate techniques. The films were polycrystalline and showed (111) preferred orientation for all the doping concentrations in spite of an additional phase of Al₂S₃ observed at higher dopant levels. The surface morphological studies indicated that the Al incorporation had a considerable effect on the surface roughness of the films. The optical measurements indicated that the optical energy band gap decreased slightly with the increase of dopant concentration without affecting the optical transmittance characteristics significantly. The electrical analysis indicated that the resistivity of the layers changed significantly with the doping concentration in the layers. The change of photoluminescence behaviour of the as-grown ZnS:Al films with dopant concentration was also studied.     

Two positivity preserving flux limited,second‐order numerical methods for a haptotaxis model

Two numerical methods for a one‐dimensional haptotaxis model, which exploit the use of van Leer flux limiter, are developed and analyzed. Sufficient conditions time step size and flux limiting are given for such formulation to ensure the non‐negativity of the discrete solution and second‐order accuracy in space. Another advantage is that we avoid solving large nonlinear systems of algebraic equations. The discrete preservation of total conservation of cell density, concentration, and logarithmic density is also verified for the numerical solution. Numerical results concerning accuracy, convergence rate, positivity, and conservation properties are presented and discussed. Similar approach could be applied efficiently in the corresponding two‐ and three‐dimensional problems. © 2012 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2013     

The Immersed Interface Method for a Nonlinear Chemical Diffusion Equation with Local Sites of Reactions

A diffusion equation with nonlinear localized chemical reactions is considered in this paper. As a result of the reactions, although the equation is parabolic, the derivatives of the solution are discontinuous across the interfaces (local sites of reactions). A second-order accurate immersed interface method is constructed for the diffusion equation involving interfaces. The new method is more accurate than the standard approach and it does not require the interfaces to be grid points. Several experiments that confirm second-order accuracy are presented. The efficiency of the proposed algorithm is also demonstrated for solving blow up problems. The proposed technique could be extended for construction of efficient numerical algorithms on uniform grids for the present equations with moving interfaces [9] but more analysis is required.     

Terahertz Transmission Spectroscopy of Nonpolar Materials and Relationship with Composition and Properties

Terahertz time-domain spectroscopy is used to study properties of non-polar materials. Terahertz absorption spectra and refractive indices are measured in a number of glasses, lubricating oils, and types of paper. The results are correlated with material properties.     

Experimental evidence of highly energy relaxed products in the 35 MeV/u84Kr+197Au reaction

The Q_β-values of⁹⁹Rb,^99,100Sr and¹⁰⁰Y have been measured for the first time at the mass separator OSTIS of the ILL; for⁹⁹Y,^99,100Zr and¹⁰⁰Nb, the results of earlier experiments were confirmed with reduced experimental errors. The two-neutron binding energies derived from the experimental Q_β-values clearly indicate that the nuclei¹⁰⁰Sr and¹⁰⁰Y are strongly deformed.