An Estimate for the Problem of Illumination of the Boundary of a Convex Body in E3

Let A be a convex body in Euclidean space E3. We denote by H(A) the smallest number of homothetic 'reduced copies of A by which it is possible to cover the whole of A. The conjecture of Hadwiger is H(A) 8. We prove that H(A) 16.     

闭壳层原子相关效应的多体理论计算：Ne原子基态相关能

对coupled-pair many-electron theory(CPMET)展开中的非线性四体效应采取了近似处理,用角动量图技术和两体函数方法得到了适用于一般闭壳层原子的径向微分方程。然后以X_a模型作为零级近似,通过迭代求解成功地计算了Ne原子基态的任意阶相相关能,从而说明至少对于闭壳层原子体系而言,用X_a模型作零级近似同样可以进行成功的多体理论计算。     

归一化偏差本体反射特征的研究

使图像获得不受光照和几何条件影响的颜色特性描述是实现颜色恒常性的关系，利用双色反射模型和有限维线性模型，提取归一化偏差体反射特征。被实验证明是实现颜色恒常性的一个重要途径，本文详细阐述了归一化偏差本体反射特征的特性，其计算方法，应用的前提条件，以及应用限制，并在实际图像处理中，考虑到了这些影响的因素。     

让世界跳跃的人--马克思*普朗克

回顾了普朗克在物理学上的贡献和对爱因斯坦的帮助，挖掘了他的物理思想，得到对他公正的认识．     

Schlieren measurement of turbulent structure in a diffusion flame

The regular and random mixing structures in a turbulent diffusion flame were investigated using the quantitative, dynamic crossed-beam schlieren method. Evidence was found close to the nozzle relating to the vortexlike structure of eddies surrounding the central fuel jet flow. The observations also make possible resolution of turbulent intensity, scales, convection, and spectra within the diffusion flame without the use of seeding or intrusion of measuring probes. It is found that length scales and other turbulence parameters in the diffusion flame progressively revert to values similar to those expected and observed in scalar passive mixing as the combustion reaction intensity reduces with axial distance from the nozzle system.     

Thermal aqueous liquid chromatography—the TALC technique

Thermal Aqueous Liquid Chromatography (TALC) using pure water as a mobile phase should be a very attractive technique promoting the use of liquid chromatography in routine analysis, either in the laboratory or in future on-line process control. This simple form of chromatography, the selectivity of which depends on the fixed phase only, would allow the use of flame ionization as an almost universal, low-cost detector in liquid chromatography. The potential of the TALC technique is illustrated by selected examples.     

Beam-injection flame furnace AAS: comparison of different nozzle types for beam generation and application of sub-critical liquid carbon dioxide as carrier and gas pressure pump

In beam injection flame furnace AAS (BIFF-AAS) the sample is introduced as a free-flying high-speed liquid beam into an AAS flame-heated nickel tube, resulting in a considerable improvement in the power of detection. For optimization of beam generation different nozzle types (smooth jet nozzles, turbulent working nozzles) have been compared at different pressures. It was found that the type of the nozzle hardly influences the analytical signal. However, the flow rates resulting from the different inner diameters of the nozzles and the applied pressures led to drastic changes in the analytical signal. For these investigations a recently developed 0.6 MPa (84 psig) diaphragm pump system was used. Furthermore, for the first time ever sub-critical liquid carbon dioxide has been used simultaneously as a liquid gas-pressure pump, as carrier in a flow-injection system (FIA), and for the beam generation. Transport of the carrier takes place as a result of the head pressure (6 MPa) of the liquid CO₂ in the gas cylinder. For volatile elements (e.g. Cd, Hg, Pb, and Tl) detection limits between 0.2 µg L^–1 (Cd) and 28 µg L^–1 (Hg) were found, the standard deviation was from 0.6% to 3.2% depending on the element, concentration, and sample volume used. The use of liquid CO₂ as a carrier in FIA systems opens up new possibilities for online sample pretreatment and trace preconcentration.     

Flow Structure of Lifted Swirling Jet Flames

Swirling combustion is widely applied in various applications such as gas turbines, utility boilersor waste incinerators. This article contributes to the ongoing research by providing experimentaldata that are gathered in the mixing zone of a lifted swirling premixed natural gas flame. Theobjective of this paper is fivefold: (1) to introduce the lifted swirling flame featuring lowNO _x emissions (2) to provide experimental data such as major species distributions, temperature and streamlines of the flow pattern, (3) to report on velocity bias in probability density function (PDF) distributions and to present PDF sequences of velocities in medium scale swirling flows, (4) to make an assessment on the local small-scale turbulence that is present in the swirling mixinglayer and (5) to provide new experimental data for model verification and development.The PDFs are corrected in order to compensate for the velocity bias phenomenon, which is typicalfor randomly sampled LDA data. Sequences of axial PDF data are presented and measurement locationsof interest are selected to look at the PDF characteristics of the internal and externalrecirculation zones, the mixing layer and the onset of the reacting flow into detail. The mixinglayer PDFs covered a wide velocity range and revealed bimodality; even the concept ofmulti-modality is suggested and explored. Analysis showed that a sum of two Gaussian distributionscan accurately envelop the experimental PDFs. The reason for this broadband turbulence behavior isto be found in combination of precessing and flapping motion of the flow structures, and also incombustion generated instabilities of the lifted flame. As a result, the flame brush is wide (largescale motion) and the mixing (small-scale turbulence) flattens any high temperatures in thecombustion process.The multi-scale turbulence concept is subsequently used to make anassessment of the local turbulence characteristics in the mixing layer.The idea is that the PDFs capture both contributions of the flow-inherent fine grain turbulence (u _l ) which is superposed on slowlarge scale fluctuating structures. It is this u _l that will be of interest in continued research on the classification of the lifted flame into acombustion regime diagram (e.g. Borghi diagram). Finally, the bimodalitycharacter in reacting flows and the prediction of large-scale structuresmay be a challenge for LES researchers.     

钝体后湍流预混燃烧的PDF模拟

本文采用PDF方法对矩形燃烧室内钝体后的湍流预混火焰进行了数值模拟。脉动速度-频率-标量联合的PDF输运方程用Monte Carlo方法求解,质量、动量和能量的平均值由基于无结构网格的有限体积法求解,压力通过状态方程获得。PDF方程中所需的平均密度、平均速度和压力由有限体积法提供,并将用Monte Carlo方法求出的雷诺应力、化学反应源项和比热比传递给有限体积法。本文对丙烷和空气燃烧的不同简化化学反应机理进行了研究,并与实验结果进行比较,获得满意的结果。     

Emulsion Combustion and Flame Spray Synthesis of Zinc Oxide/Silica Particles

Two flame spray methods, emulsion combustion method (ECM) and flame spray pyrolysis (FSP), were compared for synthesis of pure and mixed SiO₂ and ZnO nanoparticles. The effect of silicon precursor was investigated using liquid hexamethyldisiloxane (HMDSO) or SiO₂ sol, while for ZnO zinc acetate (ZA) was used. Gas phase reaction took place when using HMDSO as Si precursor, forming nanoparticles, whereas the SiO₂ sol used as Si source was not evaporated in the flame, creating large aggregates of the sol particles (e.g. 1 m). The FSP of ZA produced ZnO homogeneous nanoparticles. Lower flame temperatures in ECM than in FSP resulted in mixed gas and liquid phase reaction, forming ZnO particles with inhomogeneous sizes. The FSP of HMDSO and ZA led to intimate gas-phase mixing of Zn and Si, suppressing each other's particle growth, forming nanoparticles of 19 nm in BET-equivalent average primary particle diameter. Nucleation of ZnO and SiO₂ occurred independently by ECM of HMDSO and ZA as well as by FSP of the SiO₂ sol and ZA, creating a ZnO and SiO₂ mixture. The reaction of ZnO with SiO₂ was likely to be enhanced by ECM of the SiO₂ sol and ZA where both Zn and Si species were not evaporated completely, resulting in ZnO, -willemite and Zn_1.7SiO₄ mixed phase.