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101.
Universal behavior of entrainment due to coherent structures in turbulent shear flow 总被引:1,自引:0,他引:1
Govindarajan R 《Physical review letters》2002,88(13):134503
A solution is suggested for a persistent mystery in the physics of turbulent flows: cumulus clouds rise to towering heights, practically without entraining the ambient medium, while apparently similar turbulent jets quickly lose their identity through entrainment and mixing. Dynamical system computations on a model vortical flow show that entrainment due to coherent structures depends sensitively on relative speeds of fluid parcels. Local heating, for example, can alter drastically the sizes of Kolmogorov-Arnol'd-Moser tori and chaotic mixing regions. The entrainment rate and, hence, the lifetime of a turbulent shear flow show a universal, nonmonotone dependence on the heating. 相似文献
102.
The transmitted photon spectra of133Ba,22Na,137Cs,54Mn and60Co point sources are measured through different thicknesses of water, concrete and sand. The multiple-scatter peaks observed
in these materials at 60, 90 and 100 keV energies respectively are found to be independent of incident photon energy and thickness
of the medium. 相似文献
103.
S. M. Marathe P. S. Murty M. Sreenivasa Rao K. V. Subba Rao 《Fresenius' Journal of Analytical Chemistry》1982,311(5):507-510
Summary A method has been described for the determination of twelve trace elements (Pb, Sn, Cr, Co, Ni, V, Y, La, Zr, Cu, Zn, Sc) in different types of rocks using optical emission Spectroscopy (OES). The method employs a single set of synthetic standards for analysing any type of rock, basic, acidic or intermediate. When an external element, such as osmium, has been added to serve as internal standard, the analytical data showed poor precision. A new method of internal standardization has, therefore, been attempted. In this, a line due to silicon whose intensity is influenced by two adjacent Fe lines, has been used as the internal standard. Such an approach gave better presision (expressed in terms of coefficient of variation). Six international rock standards have been analysed and the data obtained have been compared with that previously reported.
Bestimmung von Spurenelementen in Gesteinen durch optische Emissions-Spektroskopie: Ein neues Verfahren zur inneren Eichung
Zusammenfassung Zwölf Spurenelemente (Pb, Sn, Cr, Co, Ni, V, Y, La, Zr, Cu, Zn, Sc) werden in verschiedenen Gesteinstypen bestimmt. Basische, saure und intermediäre Gesteine können mit einem einzigen Satz synthetischen Standards analysiert werden. Bei Benutzung eines externen Elements (Os) zur Eichung wurden schlechte Ergebnisse erhalten. Bei dem neuen Verfahren wird eine bessere Reproduzierbarkeit (ausgedrückt als Variationskoeffizient) durch Verwendung einer Siliciumlinie, die durch benachbarte Eisenlinien beeinflußt wird, erzielt. Sechs internationale Standardgesteinsproben wurden nach diesem Verfahren untersucht und die Ergebnisse mit früher erhaltenen verglichen.相似文献
104.
105.
Oseen’ approximations are used to study the slow motion of a viscous, incompressible, electrically conducting fluid past a
circular cylinder in the presence of a uniform aligned magnetic field. Using series truncation method, the analytical solutions
for the first three terms in the Fourier sine series expansion of the stream function are obtained. Numerical values of the
tangential drag for different values of magnetic interaction parameter and viscous Reynolds number are calculated. 相似文献
106.
107.
Experiments have been carried out to determine heat transfer rates from a continuously moving belt to an air jet impinging normally. The parameters that were varied included the jet velocity (4 < VN < 40 m/s), the jet width (4.8 < B < 19 mm), the nozzle-to-plate distance (3 < H/2B < 11) and the belt speed (0. 15 < VB < 5. 5 m/s). An infrared thermometer was used for the measurement of temperature of the moving belt. The average heat transfer coefficients increase with belt speed steeply initially to a maximum value and then remain almost constant for all higher belt speeds. The maximum heat transfer coefficients are about 1.5 to 2.0 times higher than those predicted for the stationary surface. The present data on continuously surface in still air and in impinging jet flow are well compared with the data on rotating cylinders reported in the literature.
Nomenclature A Heat transfer area - B Width of the nozzle - D Diameter of the cylinder or equivalent diameter of the flat surface (D=L/) - k Thermal conductivity - Gr Grashof number - h Heat transfer coefficient - H Height of the nozzle from the surface - i Number of nozzles - L Heat transfer length of a flat surface - NuD Nusselt number hD/k - ReDB Belt Reynoldsnumber, DVB/ - ReDN Nozzle Reynolds number, DVN/ - ReSN Nozzle Reynolds number, SVN/ - S Hydraulic diameter of the nozzle, 2B - VB Belt velocity or circumferential velocity of a cylinder - VN Nozzle celocity - Kinematic viscosity 相似文献
Wärmeübergang zwischen einem senkrecht auftreffenden Strahl und einer bewegten Oberfläche
Zusammenfassung Experimentell bestimmte Wärmeübergangskoeffizienten für Düsengeschwindigkeiten zwischen 4 m/s und 40 m/s, sowie Düsenbreiten zwischen 4,8 mm und 19 mm lagen bei Bandgeschwindigkeiten zwischen 0, 15 m/s bis 5, 5 m/s ca. 50 % bis 100 % höher als bei unbewegtem Band. Die gemessenen Daten bei bewegtem wie bei unbewegtem Band schließen gut an bekannte Werte aus der Literatur an.
Nomenclature A Heat transfer area - B Width of the nozzle - D Diameter of the cylinder or equivalent diameter of the flat surface (D=L/) - k Thermal conductivity - Gr Grashof number - h Heat transfer coefficient - H Height of the nozzle from the surface - i Number of nozzles - L Heat transfer length of a flat surface - NuD Nusselt number hD/k - ReDB Belt Reynoldsnumber, DVB/ - ReDN Nozzle Reynolds number, DVN/ - ReSN Nozzle Reynolds number, SVN/ - S Hydraulic diameter of the nozzle, 2B - VB Belt velocity or circumferential velocity of a cylinder - VN Nozzle celocity - Kinematic viscosity 相似文献
108.
[reaction: see text] Syntheses of two novel omuralide derivatives are described. 相似文献
109.
Krishnaveni NS Surendra K Reddy MA Nageswar YV Rao KR 《The Journal of organic chemistry》2003,68(5):2018-2019
Aromatic acetals have been deprotected to the corresponding aldehydes under biomimetic conditions for the first time using beta-cyclodextrin in water under neutral conditions, thereby overcoming many of the drawbacks associated with earlier methodologies. This method, apart from being simple with regard to recycling of the catalyst, also has the potential for industrial applications. 相似文献
110.
C.V. Subba Reddy Z.R. Deng Q.Y. Zhu Y. Dai J. Zhou W. Chen S.-I. Mho 《Applied Physics A: Materials Science & Processing》2007,89(4):995-999
Molybdenum trioxide (MoO3) and PPyxMoO3 (x=0.5 and 1) nanobelts were obtained by the simple hydrothermal process from MoO3 sol. The morphology and structure of the samples were characterized using X-ray diffractometry (XRD), Fourier transformation
infrared spectroscopy (FTIR), Raman spectra, SEM and AFM. The results show that the H atoms in polypyrrole are H-bonded with
the O atoms in the Mo=O bonds of MoO3 nanobelts. Using the electrolyte, we fabricated electrochemical cells with a configuration of Li/(LiPF6+EC+DMC)/(MoO3+acetyleneblack+PTFE) and studied discharge profiles.
PACS 81.07.BC; 81.05.Je; 82.47.Aa; 82.45.Fk; 82.45.Gj 相似文献