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Nanoscale displacement of the image of an atomic source of radiation

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Chinese Optics Letters 2009年第2期7卷 149-151页

作者： Henk f. Arnoldus Department of Physics and Astronomy Mississippi State University

Light emitted by an atomic source of radiation appears to travel along a straight line （ray） from the location of the source to the observer in the far field. However, when the energy flow pattern of the radiation is resolved with an accuracy better than an optical wavelength, it turns out that the field lines are usually curved. We consider electric dipole radiation, a prime example of which is the radiation emitted by an atom during an electronic transition, and we show that the field lines of energy flow are in general curves. Near the location of the dipole, the field lines exhibit a vortex structure, and in the far field they approach a straight line. The spatial extension of the vortex in the optical near field is of nanoscale dimension. Due to the rotation of the field lines near the source, the asymptotic limit of a field line is not exactly in the radially outward direction and as a consequence, the image in the far field is slightly shifted. This sub-wavelength displacement of the image of the source should be amenable to experimental observation with contemporary nanoscale-precision techniques.

关键词： Atoms Electric dipole moments flow patterns Nanotechnology Vortex flow

On the Indeterminacy in Hardness of Shape Memory Alloys

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Journal of Materials Science & Technology 2004年第6期20卷 700-702页

作者： f.T.Cheng DeDartment of Applied Phvsics

The present communication addresses an interesting problem related to the indeterminacy in hardness of superelastic NiTi reported by Xu et al. The origin of the indeterminacy is attributed to the inadequacy of the conventional Vickers hardness testing measurement which does not record elastic deformation, and thus the indeterminacy may be removed with suitable techniques. Concepts of hardness in relation to deformation are clarified. Recommendations for measuring the hardness of NiTi and other elastic-plastic materials are suggested, together with comments on the advantages and disadvantages of each of these methods.

关键词： Hardness Elastic-plastic materials Elastic recovery Vickers microhardness test NiTi SMA

SPHERICAL MEANS, DISTRIBUTIONS AND CONVOLUTION OPERATORS IN CLIffORD ANALYSIS

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Chinese Annals of Mathematics,Series B 2003年第2期24卷 133-146页

作者： f.BRACKX R.DELANGHE f.SOMMEN Department of Mathematical Analysis Ghent UniversityB-9000 GentBelgium.Department of Mathematical AnalysisGhent UniversityB-9000 GentBelgium.Department of Mathematical AnalysisGhent UniversityB-9000 GentBelgium.

New higher dimensional distributions are introduced in the framework of Clifford *** complete the picture already established in previous work, offering unity and structuralclarity. Amongst them are the building block... 详细信息

关键词： Spherical means Distributions Convolution operators Clifford analysis

Cognition and the brain of brood parasitic cowbirds

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Integrative Zoology 2019年第2期14卷 145-157页

作者： David f.SHERRY Mélanie f.GUIGUENO Department of Psychology Western University LondonOntario Department of Natural Resource Sciences McGill UniversityMontrealQuebecCanada

Cowbirds are brood *** lay their eggs in the nests of other species,which then incubate the cowbird eggs and raise the young *** and returning to heterospecific nests presents cowbirds with several cognitive *** some species,such as brown-headed cowbirds(Molothrus ater),females but not males search for and remember the locations of potential host *** describe recent research on sex differences in cognition and the hippocampus associated with this sex difference in search for host *** brown-headed cowbirds perform better than males on some,but not all,tests of spatial memory and females show a pattern of adult hippocampal neurogenesis not found in males or in closely related non-parasitic *** of the apparent specialization of the hippocampus,brown-headed cowbirds may be a good model in which to examine spatial information processing in the avian hippocampus and we also describe recent research on the spatial response properties of brown-headed cowbird hippocampal neurons.

关键词： adult neurogenesis brood parasites cowbirds hippocampus sex differences spatial memory

flow-field Analysis of Anti-Kidney Vortex film Cooling

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Journal of Thermal Science 2012年第1期21卷 66-76页

作者： Lars Grf Leonhard Kleiser Institute of fluid Dynamics

film cooling is an important measure to enable an increase of the inlet temperature of a gas turbine and, thereby, to improve its overall efficiency. The coolant is ejected through spanwise rows of holes in the blades or endwalls to build up a film shielding the material. The holes often are inclined in the downstream direction and give rise to a kidney vortex. This is a counter-rotating vortex pair, with an upward flow direction between the two vortices, which tends to lift off the surface and to locally feed hot air towards the blade outside the pair. Reversing the rotational sense of the vortices reverses these two drawbacks into advantages. In the considered case, an anti-kidney vortex is generated using two subsequent rows of holes both inclined downstream and yawed spanwise with alternating angles. In a previous study, we performed large-eddy simulations (which focused on the fully turbulent boundary layer) of this anti-kidney vortex film-cooling and compared them to a corresponding physical experiment. The present work analyzes the simulated flow field in detail, beginning in the plenum (inside the blade or endwall) through the holes up to the mixture with the hot boundary layer. To identify the vortical structures found in the mean flow and in the instantaneous flow, we mostly use the λ 2 criterion and the line integral convolution (LIC) technique indicating sectional streamlines. The flow regions (coolant plenum, holes, and boundary layer) are studied subsequently and linked to each other. To track the anti-kidney vortex throughout the boundary layer, we propose two criteria which are based on vorticity and on LIC results. This enables us to associate the jet vortices with the cooling effectiveness at the wall, which is the key feature of film cooling.

关键词： film cooling anti-kidney vortex vortex identification trajectory tracking large-eddy simulation LES compound angle double row kidney vortex jet in cross-flow.

Elastic, thermodynamic, electronic, and optical properties of recently discovered superconducting transition metal boride NbRuB:An ab-initio investigation

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Chinese Physics B 2017年第10期26卷 339-347页

作者： f Parvin S H Naqib Department of Physics University of Rajshahi

The elastic, thermodynamic, electronic, and optical properties of recently discovered and potentially technologically important transition metal boride NbRuB, are investigated using the density functional formalism. Both generalized gradient approximation （GGA） and local density approximation （LDA） are used for optimizing the geometry and for estimating various elastic moduli and constants. The optical properties of NbRuB are studied for the first time with different photon polarizations. The frequency （energy） dependence of various optical constants complement quite well the essential features of the electronic band structure calculations. Debye temperature of NbRuB is estimated from the thermodynamical study. All these theoretical estimates are compared with published results, where available, and discussed in detail. Both electronic band structure and optical conductivity reveal robust metallic characteristics. The NbRuB possesses significant elastic anisotropy. Electronic features, on the other hand, are almost isotropic in nature. The effects of electronic band structure and Debye temperature on the emergence of superconductivity are also analyzed.

关键词： hard materials ternary borides DfT calculations electronic band structure optical properties superconductivity

Surface morphology and impurity distribution of electron beam recrystallized silicon films on low cost substrates for solar cell absorber

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Rare Metals 2006年第Z1期25卷 195-200页

作者： GROMBALL f MüLLER J Department of Mikrosystemtechnik Technische Universitt Hamburg-Harburg Hamburg 21073 Germany

A line shaped electron beam recrystallised polycrystalline silicon film on the low cost substrate was investigated for the use of the solar cell absorber. The applied EB energy density strongly influences the surface morphology of the film system. Lower EB energy density results in droplet morphology and the rougher SiO2 capping layer due to the low fluidity. With the energy increasing, the capping layer becomes smooth and continuous and less and small pinholes form in the silicon film. Tungstendisilicide (WSi2) is formed at the interface tungsten/silicon but also at the grain boundaries of the silicon. Because of the fast melting and cooling of the silicon film, the eutectic of silicon and tungstendisilicide mainly forms at the grain boundary of the primary silicon dendrites. The SEM-EDX analysis shows that there are no chlorine and hydrogen in the area surrounding a pinhole after recrystallization because of outgassing during the solidification.

关键词： polycrystalline silicon film solar cell recrystallization energy surface morphology outgassing

Impact of wastewater reuse on cobalt status in Egyptian environment

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Journal of Environmental Sciences 2003年第3期15卷 388-395页

作者： M.f. Abdel-Sabour Soil and Water Research Department Nuclear Research Center Atomic Energy Authority

Cobalt is used in the manufacture of alloys, catalysts in the petroleum industry, catalytic converters, and paint pigments. Thus the potential for Co releases into the environment is highly increased. Use of waste sludges and sewage effluent to fertilize and irrigate soils has also increased soil Co concentrations. Total cobalt contents of alluvial delta soil of Egypt show considerable variation ranging from 13.1 to 64.7 ppm. The impact of either wastewater irrigation or industrial activities on soil total Co was obvious due to accumulation of organic matter and solid waste in the surface soil samples. food crops and vegetables should not be grown on soil highly contaminated by Co. It is noteworthy that the delayed neutron activation analysis(DNAA) technique could be used successfully for total Co determination due to its high sensitivity. It is quit clearly that dust samples of Cairo City contains higher Co level, as compared to Suez Canal Region(Ismailia, Port Said and El-Suez cities). The high values in Cairo City may be due to the existence of industries around the city and the intensive traffic. To minimize Co environmental hazards, waste effluents should be treated on site. Thus, levels of potentially toxic Co needs to be continuously monitored and should be removed during several treatment processes before the disposal of these wastes.

关键词： cobalt environment Egypt

Influence of Processing Parameters on the Strength of Air Brazed Alumina Joints Using Aluminium Interlayer

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Journal of Materials Science & Technology 2011年第7期27卷 641-646页

作者： A. Ibrahim f. Hasan Department of Metallurgical and Materials Engineering University of Engineering and TechnologyLahore Pakistan

Alumina specimens were joined together with thin aluminium interlayer at 750 and 900°C under different applied pressures and holding time in air. flexural strength of the joints was then measured using a standard four-point bend test method. Characterization of the interface was carried out to correlate the increase in flexural strength with the applied pressure, holding temperature and time. The study showed that the strength of joint is affected by all three parameters, i.e., processing temperature, holding time as well as applied pressure.

关键词： Pressure-assisted air brazing Alumina Aluminum Brazing Joining and Ceramic