Correlation between the Soret coefficient and the static structure factor in a polymer blend

Mutual mass diffusion and thermal diffusion has been investigated in poly(dimethylsiloxane)/ poly(ethylmethylsiloxane) (PDMS/PEMS) polymer blends of equal weight fractions. Molar masses ranged from below 1 to over 20 kg/mol. Both the mutual mass (D) and the thermal diffusion (D_T) coefficient contain a thermally activated factor with an activation temperature of 1415 K. The molar mass dependence of D_T is due to an end-group effect of the local friction coefficient. The thermal diffusion coefficient in the limit of long chains and infinite temperature is D_T^0, = - 1.69×10^-7cm²(sK)^-1. The Soret coefficient S_T of blends far enough away from a critical point is proportional to the static structure factor S(q = 0).     

Morphologies and optical properties of poly(2,5-diethoxyphenylene) nanofibril arrays

An anodic aluminum oxide (AAO) membrane can be used as a template for the synthesis of nanostructures. In this paper, we have fabricated poly(2,5-diethoxyphenylene) (EtO-PPP) nanofibril arrays by oxidative coupling polymerization of 1,4-diethoxybenzene (DEB) within the pores of an AAO template. The detailed molecular structure of the polymer nanofibrils was characterized by using the infrared spectrum and the ¹H-NMR spectrum. We have used transmission electron microscopy, scanning electron microscopy, and atomic force microscopy to confirm the morphologies and images of the template and the fabricated nanometer scale of poly(2,5-diethoxyphenylene)nanofibril arrays. The experimental results demonstrate that the pores of the AAO membrane are regular and uniform, and parallel to each other. Furthermore, the EtO-PPP chains in the narrowest template-synthesized fibrils were oriented parallel to the pore axes of the AAO membrane, and perpendicular to the surface of the aluminum substrate. The polymer chain orientation is partially responsible for the enhanced conductivity. The ultraviolet absorption maximum shows that the polymer contains a better extended π-conjugation system along the poly(p-phenylene) backbone, which results in a longer-wavelength shift of the absorption band. The photoluminescence (PL) spectrum of nanofibril arrays exhibits a 5-nm blue shift of the emission in comparison with the unordered molecules. Received: 3 January 2002 / Accepted: 7 January 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-931/891-1100, E-mail: lihl@lzu.edu.cn     

A novel electron scattering apparatus combining a laser photoelectron source and a triply differentially pumped supersonic beam target: characterization and results for the resonance

A novel electron scattering apparatus for high resolution studies of angle-differential elastic and inelastic electron scattering from atoms and molecules in the gas phase is described and its performance characterized. It combines a laser photoelectron source, a triply differentially pumped collimated supersonic beam target (half angle 0.015 rad, background to beam density ratio < 0.01), and several electron multipliers for simultaneous detection of elastically scattered electrons and metastable atoms (or molecules) due to inelastic scattering. In detailed test measurements of the yield for the production of metastable He^*(2³S₁) atoms around its threshold, the dependence of the overall energy width on various experimental parameters has been investigated. So far a resolution down to 7 meV (FWHM) has been obtained. Under such conditions we have investigated the profile of the He^- (1 s 2 s ^{2 2} S _1/2 ) resonance at the scattering angles 22 ^° , 45 ^° , and 90 ^° . From a consistent fit of the measured profiles by resonant scattering theory we determine a new value for the resonance energy ( E _r = 19.365(1) eV) and an accurate resonance width ( Γ = 11.2(5) meV). These results are consistent with the previously recommended values. Received 23 July 2002 Published online 29 October 2002 RID="a" ID="a"e-mail: hotop@physik.uni-kl.de RID="b" ID="b"Permanent address: Department of Physics and Astronomy, Drake University, Des Moines, IA 50311, USA.     

Electron Transport in Ga-Rich InxGa1-xN Alloys

Resistivity and Hall effect measurements on n-type undoped Ga-rich InxGa1-xN （0.06 ≤ x ≤ 0.135） alloys grown by metal-organic vapour phase epitaxy （MOVPE） technique are carried out as a function of temperature （15-350 K）. Within the experimental error, the electron concentration in Inx Ga1-x N alloys is independent of temperature while the resistivity decreases as the temperature increases. Therefore, Inx Ga1-xN （0.06 ≤ x ≤0.135） alloys are considered in the metallic phase near the Mort transition. It has been shown that the temperaturedependent metallic conductivity can be well explained by the Mort model that takes into account electron-electron interactions and weak localization effects.     

Flow prolongation of some tangent valued forms

We study the prolongation of semibasic projectable tangent valued k-forms on fibered manifolds with respect to a bundle functor F on local isomorphisms that is based on the flow prolongation of vector fields and uses an auxiliary linear r-th order connection on the base manifold, where r is the base order of F. We find a general condition under which the Frölicher-Nijenhuis bracket is preserved. Special attention is paid to the curvature of connections. The first order jet functor and the tangent functor are discussed in detail. Next we clarify how this prolongation procedure can be extended to arbitrary projectable tangent valued k-forms in the case F is a fiber product preserving bundle functor on the category of fibered manifolds with m-dimensional bases and local diffeomorphisms as base maps.     

Measurements of residual stress in semi-insulating GaAs by Cr-related luminescence lines

We have measured systematically the Cr-related zero-phonon lines in the 0.839 eV region in a series of plastically-bent semi-insulating GaAs:Cr with compressive or tensile stress along various bending axes. As a result, it has been found that the residual stress in semi-insulating GaAs:Cr wafers can be sensitively characterized from a splitting and energy shift of the 0.839 eV Cr-related luminescence lines in the low-temperature photoluminescence spectra. Furthermore, we have applied this method to the characterization of the interface stress of OMVPE-grown ZnSe/GaAs:Cr heterostructure and found that anomalous stress exists at the ZnSe/GaAs interface, which is inconsistent with stress predicted by the lattice mismatch of the heterojunctions.     

Statistical features of traffic flow on urban freeways

Urban freeways play an important role in urban traffic networks. Compared with highway traffic, urban freeway traffic has different characteristics, such as denser on- and off-ramps, more complex road conditions, and lower velocity limits. Until now, however, there has been no comprehensive analysis of urban traffic flow. In this paper, through an analysis of the density dependence of velocity distribution, we investigate the fundamental velocity-density relationships of urban freeways, compare them with those of highway traffic, and explain them using existing traffic flow theories.     

Bulk and near-surface annealing behavior of the 0.8 eV luminescence in semi-insulating gallium arsenide

An annealing study of the 0.8 eV photoluminescence band in LEC GaAs has been performed, using a combination of 10 min annealing steps over a temperature range of 800–1100° C and one hour furnace annealing steps at 500–700° C. Results show that the defect responsible for the luminescence is stable in bulk material under all annealing conditions that have been investigated. In combination with earlier results, this demonstrates a stability of the defect to temperatures in excess of 900° C and indicates a parallel with the annealing behavior of the 0.67 eV band in semi-insulating GaAs. The observed annealing behavior is very different in the near-surface region, indicating an important role of As out-diffusion.     

Retrieving the complex degree of spatial coherence of electron beams

The possibility to characterize the coherence properties of an electron source is presented. The method, based on the determination of centered-reduced moments of the beam spot, allows the evaluation of both amplitude and phase of the complex degree of spatial coherence. The experimental results are in agreement with a different approach based on the Fourier analysis and with calculations according to the Van Cittert—Zernike theorem.     

Synthesis and biological activity of novel N-substituted 4-amino-6,7,8-trimethoxyquinazoline compounds

A series of N-substituted 4-amino-6,7,8-trimethoxyquinazoline derivatives has been synthesized from 4-chloro-6,7,8-trimethoxyquinazoline and aryl (or benzyl) amines using 2-propanol as a solvent. The starting material 4-chloro-6,7,8-trimethoxyquinazoline has been synthesized from natural gallic acid by a novel route. Their structures have been verified by elemental analysis and IR, ¹H, and ¹³C NMR spectroscopy. The title compounds have been evaluated for their in vitro antiproliferative activities against some cancer cells by the MTT method. Unfortunately, most of the compounds tested have exhibited a weaker anticancer activity than the reference standard drug PD153035. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, 1521–1531, September, 2007.