Glass‐transition and gas‐transport characteristics of polymer nanocomposites based on crosslinked poly(ethylene oxide)

The glass‐transition and gas‐transport properties of rubbery polymer nanocomposites based on crosslinked poly(ethylene oxide) and metal oxide nanoparticles were studied. Nanocomposite samples were prepared by the UV photopolymerization of poly(ethylene glycol) diacrylate (n ～ 14) in the presence of magnesium oxide or silica nanoparticles. The thermomechanical properties of the composites were investigated with dynamic mechanical and dielectric spectroscopy methods. The inclusion of nanoparticles in the crosslinked poly(ethylene glycol) diacrylate network led to a systematic increase in rubbery modulus and a modest positive offset (～6°C) in the measured glass‐transition temperature for both systems. Bulk density measurements indicated only minimal void volume fraction in the composites, and CO₂ and light gas permeability decreased with particle loading; for example, the CO₂ infinite dilution permeability at 35°C decreased from 106 barrer in the unfilled polymer to 55 barrer in a nanocomposite containing 30 wt % magnesium oxide nanoparticles. The inclusion of toluene diluent in the prepolymerization mixtures produced a limited enhancement in sample permeability, but the sizeable increases in gas transport with particle loading reported for certain other rubbery nanocomposite systems were not realized in the crosslinked poly(ethylene glycol) diacrylate composites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Compact high-resolution spaceborne echelle grating spectrometer with acousto-optical tunable filter based order sorting for the infrared domain from 2.2 to 4.3 microm

A new compact spaceborne high-resolution spectrometer developed for the European Space Agency's Venus Express spacecraft is described. It operates in the IR wavelength range of 2.2 to 4.3 microm and measures absorption spectra of minor constituents in the Venusian atmosphere. It uses a novel echelle grating with a groove density of 4 lines/mm in a Littrow configuration in combination with an IR acousto-optic tunable filter for order sorting and an actively cooled HgCdTe focal plane array of 256 by 320 pixels. It is designed to obtain an instrument line profile of 0.2 cm(-1). First results on optical and spectral properties are reported.     

PEG-based hydrogel membrane coatings

As a first step towards preparing fouling-resistant coatings for water purification membranes, three series of copolymer hydrogel networks were synthesized using poly(ethylene glycol) diacrylate (PEGDA) as the crosslinker and acrylic acid (AA), 2-hydroxyethyl acrylate (HEA), or poly(ethylene glycol) acrylate (PEGA) as comonomers. Copolymers containing varying amounts of PEGDA with each of these comonomers were prepared. Glass transition temperatures obeyed the Fox equation. Crosslink density strongly influenced water uptake and water permeability for materials of constant chemical composition. For example, the volume fraction of water sorbed by a 100 mol% PEGDA hydrogel was 0.61. However, introducing comonomers into the network reduced hydrogel crosslink density, and in hydrogels having the same ethylene oxide content, water sorption increased as crosslink density decreased. The highest water volume fraction observed was 0.72, obtained in a copolymer containing 80 mol% PEGA and 20 mol% PEGDA. Water permeability increased systematically with increasing water sorption, and water permeability coefficients ranged from 10 to 26 L μm/(m² h bar). NaCl partition coefficients ranged from 0.36 to 0.53 (g NaCl/cm³ hydrogel)/(g NaCl/cm³ solution). NaCl diffusion coefficients varied little with polymer composition; in this regard, diffusion coefficient values ranged from 4.3 × 10⁻⁶ to 7.4 × 10⁻⁶ cm²/s. Based on contact angle measurements using n-decane in water, oil exhibited a low affinity for the surfaces of these polymers, suggesting that coatings prepared from such materials might improve the fouling resistance of membranes towards oily wastewater.     

CD、DVD信号源对AV及Hi-Fi系统的重要性

很多消费者舍得花一万元以上买放大器或音箱、或者买万多元的投影机,但投资在信号源的部分却只有三两千元。本人三十年来认识的发烧人很多,圈中一致认为对信号源的投资是要重视的对象,否则AV及Hi-Fi系统的投资会失误,投影机也不能有理想的发挥。我们发烧界的Hi-Fi理论认为越是接近音源投资越大,这个理论是发烧公认的。所以近日我把所有常见的蓝光DVD机进行测试后,最后我会把个人认为可以有理想效果的3台蓝光DVD机留在AV房占为己有。     

Noble-gas hydrides: new chemistry at low temperatures

Noble-gas chemistry has been undergoing a renaissance in recent years, due in large part to noble-gas hydrides, HNgY, where Ng = noble-gas atom and Y = electronegative fragment. These molecules are exceptional because of their relatively weak bonding and large dipole moments, which lead to strongly enhanced effects of the environment, complexation, and reactions. In this Account, we discuss the matrix-isolation synthesis of noble-gas hydrides, their spectroscopic and structural properties, and their stabilities.This family of species was discovered in 1995 and now has 23 members that are prepared in noble-gas matrices (HXeBr, HKrCl, HXeH, HXeOH, HXeO, etc.). The preparations of the first neutral argon molecule, HArF, and halogen-free organic noble-gas molecules (HXeCCH, HXeCC, HKrCCH, etc.) are important highlights of the field. These molecules are formed by the neutral H + Ng + Y channel. The first addition reaction involving HNgY molecules was HXeCC + Xe + H --> HXeCCXeH, and this led to the first hydride with two noble-gas atoms (recently extended by HXeOXeH). The experimental synthesis of HNgY molecules starts with production of H and Y fragments in solid noble gas via the UV photolysis of suitable precursors. The HNgY molecules mainly form upon thermal mobilization of the fragments.One of the unusual properties of these molecules is the hindered rotation of some HNgY molecules in solid matrices; this has been theoretically modeled. HNgY molecules also have unusual solvation effects, and the H-Xe stretching mode shifts to higher frequencies (up to about 150 cm-1) upon interaction with other species.The noble hydrides have a new bonding motif: HNgY molecules can be represented in the form (H-Ng)+Y-, where (H-Ng)+ is mainly covalent, whereas the interaction between (HNg)+ and Y- is predominantly ionic. The HNgY molecules are highly metastable species representing high-energy materials. The decomposition process HNgY --> Ng + HY is always strongly exoergic; however, the decomposition is prevented by high barriers, for instance, about 2 eV for HXeCCH. The other decomposition channel HNgY --> H + Ng + Y is endothermic for all prepared molecules.Areas that appear promising for further study include the extension of argon chemistry, preparation of new bonds with noble-gas atoms (such as Xe-Si bond), and studies of radon compounds. The calculations suggest the existence of related polymers, aggregates, and even HNgY crystals, and their experimental preparation is a major challenge. Another interesting task, still in its early stages, is the preparation of HNgY molecules in the gas phase.     

Inverse heat conduction problems in three-dimensional anisotropic functionally graded solids

A meshless method based on the local Petrov–Galerkin approach is applied to inverse transient heat conduction problems in three-dimensional solids with continuously inhomogeneous and anisotropic material properties. The Heaviside step function is used as a test function in the local weak form, leading to the derivation of local integral equations. Nodal points are randomly distributed in the domain analyzed, and each node is surrounded by a spherical subdomain in which a local integral equation is applied. A meshless approximation based on the moving least-squares method is employed in the implementation. After performing spatial integrations, we obtain a system of ordinary differential equations for certain nodal unknowns. A backward finite-difference method is used for the approximation of the diffusive term in the heat conduction equation. A truncated singular-value decomposition is used to solve the ill-conditioned linear system of algebraic equations at each time step. The effectiveness of the meshless local Petrov–Galerkin (MLPG) method for this inverse problem is demonstrated by numerical examples.     

Single,twin and triple buried heating pipes: on potential savings in heat losses and costs

In order to make district heating systems competitive in areas with single family houses or in other areas with low heat demands it is necessary to reduce the heat losses from the pipes. In recent years the twin pipe has become popular in the Nordic countries. In the article we describe how the heat loss and the heat loss coefficients can be calculated. We introduce the triple pipe with three media pipes (two supply pipes and one return pipe). The temperature dependency and the ageing of polyurethane insulation are briefly discussed. A comparison is made for different 80 mm distribution pipes and for different service pipes with respect to heat losses and to resources, i.e. materials needed for the casing and polyurethane insulation and the gravel in the excavations. For the distribution pipe we found that an egg‐shaped twin pipe can reduce the heat loss by 37% and the investments by 12% compared with a pair of single pipes. For the service pipes we found that the triple pipe reduces the heat loss by 45% compared with a common pair of single pipes and by 24% compared with circular twin pipes. The reduction in investment index is 21%. The article also addresses the question of the heat exchange between the two media pipes in a twin pipe. Copyright © 2005 John Wiley & Sons, Ltd.     

Hybrid particle swarm optimization with wavelet mutation and its industrial applications.

A new hybrid particle swarm optimization (PSO) that incorporates a wavelet-theory-based mutation operation is proposed. It applies the wavelet theory to enhance the PSO in exploring the solution space more effectively for a better solution. A suite of benchmark test functions and three industrial applications (solving the load flow problems, modeling the development of fluid dispensing for electronic packaging, and designing a neural-network-based controller) are employed to evaluate the performance and the applicability of the proposed method. Experimental results empirically show that the proposed method significantly outperforms the existing methods in terms of convergence speed, solution quality, and solution stability.