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41.
A ray model is developed and validated for prediction of the insertion loss of hard parallel noise barriers placed in an urban environment either in front of a row of tall buildings or in a street canyon. The model is based on the theory of geometrical acoustics for sound diffraction at the edge of a barrier and multiple reflections by the ground, barrier and fa?ade surfaces. It is crucial to include the diffraction and multiple reflection effects in the ray model as they play important roles in determining the overall sound pressure levels for receivers located between the fa?ade and the near-side barrier. Comparisons of the ray model with a wave-based boundary element formulation show reasonably good agreement over a broad frequency range. Results of scale model experimental studies are also presented. It is demonstrated that the ray model agrees tolerably well with the scale model experimental data. 相似文献
42.
Effects of shell composition,dosage and alkali type on the morphology of polymer hollow microspheres
Polymer hollow microspheres were prepared by performing alkali treatment on the multilayer core/shell polymer latex particles containing carboxyl groups. Effects of the shell composition and dosage as well as alkali type on the morphology of the microspheres were investigated. Results showed that in comparison with acrylonitrile(AN) and methacrylic acid(MAA), using butyl acrylate(BA) as the shell co-monomer decreased the glass transition temperature(T_g) of shell effectively and was beneficial to the formation of uniform and big hollow structure. Along with the increase of the shell dosage, the alkali-treated microspheres sequentially presented porous and hollow morphology, and the size of microspheres increased, while the hollow diameter increased first and then decreased, and the maximum hollow ratio reached 39.5%. Furthermore, the multilayer core/shell microspheres had better tolerance to NH_3·H_2O than to NaOH. When the molar ratio of alkali to methacrylic acid(MR_(alkali/acid)) for Na OH ranged from 1.15 to 1.30 or MRalkali/acid for NH_3·H_2O ranged from 1.30 to 2.00, the regular polymer hollow microspheres could be obtained. 相似文献
43.
Knyazev E. V. Bolotov V. V. Ivlev K. E. Povoroznyuk S. N. Kan V. E. Sokolov D. V. 《Physics of the Solid State》2019,61(3):433-439
Physics of the Solid State - The morphology, structure, and electrophysical characteristics of multiwall carbon nanotubes (MWCNTs), as affected by defects induced by ion bombardment, are studied... 相似文献
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Irregular Bi2WO6 nanolaminars have been successfully synthesized via a rapid sonochemical approach using bismuth nitrate and tungstic acid as precursors in an aqueous solution. The characteristics of them were investigated in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption, pore value, PL spectroscopy and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). These irregular nanolaminars are of geometric shapes of orthorhombic Bi2WO6 with their basal plane being (0 0 1). They possess high crystallinity, lager surface area and pore value, which means fewer traps and stronger photocatalytic activity. The growth mechanism of such special nanolaminar was related to the sonochemical synthesis route, which played a key role in the formation of Bi2WO6 nanolaminar. Simultaneously, it was found that the formation of Bi2WO6 nanolaminar is a time dependent process. The Bi2WO6 nanolaminar has higher photocatalytic activity than bulk Bi2WO6 nanoparticle obtained by refluxing method for rhodamine B (Rh.B) degradation under visible light irradiation (λ > 400 nm). 相似文献
47.
YongHuaLI HalBinKAN BingJunYU 《数学学报(英文版)》2004,20(3):569-576
In this paper, a special kind of partial algebras called projective partial groupoids is defined.It is proved that the inverse image of all projections of a fundamental weak regular ^*-semigroup under the homomorphism induced by the maximum idempotent-separating congruence of a weak regular ^*-semigroup has a projective partial groupoid structure. Moreover, a weak regular ^*-product which connects a fundamental weak regular ^*-semigroup with corresponding projective partial groupoid is defined and characterized. It is finally proved that every weak regular ^*-product is in fact a weak regular ^*-semigroup and any weak regular ^*-semigroup is constructed in this way. 相似文献
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以Ar气为工作介质 ,研究了激光强度、工作介质密度对高次谐波辐射的影响 .结果表明 ,足够高的激光强度和气体密度是获得更大强度更高次谐波的基本条件 .观察到可分辨的最高谐波次数为第81次(相应的波长为969nm) ,不可分辨的谐波辐射不低于第91次 (相应的波长为863nm) ,这是目前世界上从Ar气中观察到的最高级次(最短波长)的谐波辐射 .理论分析表明 ,更高次谐波是从Ar+产生的 .以Ne气为工作介质 ,通过观察Ne+的特征谱线 ,研究了气体电离产生的自由电子对高次谐波辐射的破坏作用 .目前 ,以Ne气为工作介质观察到的可分辨的最高次谐波为第107次(相应波长为7.33nm) .而观察到的不可分辨的谐波辐射不低于第131次谐波(相应波长短于5.99nm) . 相似文献
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A linear coloring of a graph G is a proper vertex coloring such that the graph induced by the vertices of any two color classes is the union of vertex-disjoint paths.The linear chromatic number lc(G) o... 相似文献