The evolution of flame surface area and rate of CH layer extinction are measured during the interaction of a two-phase counterflow diffusion flame with fuel-side vortices of varying size and strength. Planar laser-induced fluorescence (PLIF) of CH is used to mark the flame front and particle-image velocimetry (PIV) is used to measure the strain rate field at various phases of the interaction process. Vortices of similar initial circulation but differing in size showed widely disparate peak strain rates and CH decay rates because of varying levels of flame-induced vortex dissipation. Vortex size is also found to have a significant effect on flame surface area evolution during and after extinction, with the presence of droplets playing a significant role in the latter. Implications of these results for the fundamental understanding of vortex–flame interactions are discussed. 相似文献
Convex underestimators of nonconvex functions, frequently used in deterministic global optimization algorithms, strongly influence their rate of convergence and computational efficiency. A good convex underestimator is as tight as possible and introduces a minimal number of new variables and constraints. Multilinear monomials over a coordinate aligned hyper-rectangular domain are known to have polyhedral convex envelopes which may be represented by a finite number of facet inducing inequalities. This paper describes explicit expressions defining the facets of the convex and concave envelopes of trilinear monomials over a box domain with bounds of opposite signs for at least one variable. It is shown that the previously used approximations based on the recursive use of the bilinear construction rarely yield the convex envelope itself. 相似文献
The half-lives of the first excited levels in odd-neutron nuclei103Mo and105Mo have been measured. From these data, values of the deformation parameter of?=0.31±0.05 and 0.29±0.06 for103Mo and105Mo, respectively, have been deduced assuming prolate spheroidal shapes. The present results in combination with previously determined properties of the ground-state bands of these nuclei are used to determineμ, the magnitude of the coefficient of the 12 term, in the Nilsson Hamiltonian, for the new region of deformation atA~-100. 相似文献
We propose to use new orthonormal wavelet packet bases, more efficient than the Fourier basis, to compress two-dimensional turbulent flows. We define the “best basis” of wavelet packets as the one which, for a given enstrophy density, condenses the L2 norm into a minimum number of non-negligible wavelet packet coefficients. Coefficients below a threshold are discarded, reducing the number of degrees of freedom. We then compare the predictability of the original flow evolution with several such reductions, varying the number of retained coefficients, either from a Fourier basis, or from the best-basis of wavelet packets. We show that for a compression ratio of 1/2, we still have a deterministic predictability using the wavelet packet best-basis, while it is lost when using the Fourier basis. Likewise, for compression ratios of 1/20 and 1/200 we still have statistical predictability using the wavelet packet best-basis, while it is lost when using the Fourier basis. In fact, the significant wavelet packet coefficients in the best-basis appear to correspond to coherent structures. The weak coefficients correspond to vorticity filaments, which are only passively advected by the coherent structures. In conclusion, the wavelet packet best-basis seems to distinguish the low-dimensional dynamically active part of the flow from the high-dimensional passive components. It gives us some hope of drastically reducing the number of degrees of freedom necessary to the computation of two-dimensional turbulent flows. 相似文献
A Structural Variant to the NaErCl4/α-NiWO4 Type for Ternary Rare-Earth Halides NaMCl4: Synthesis and Crystal Structure of NaLuCl4 Single crystals of NaLuCl4 (orthorhombic, Pbcn (Nr. 60), Z = 4, a = 618.6(1) pm, b = 1 592.2(2) pm, c = 657.0(1) pm) were grown for the first time from the binary components using the Bridgman technique. The crystal structure may be derived from a hexagonally closest packing of Cl? spheres with one half of all octahedral sites occupied by the cations Na+ and Lu3+, respectively. The close relation of the structure to that of NaErCl4 (α-NiWO4) is discussed. NaScCl4 was found to be isotypic to NaLuCl4. 相似文献
The photolysis of CH3ReO(O2)2·H2O in methylene chloride yields, like the thermolysis, molecular oxygen in the triplet spin state. The quantum yield QPh of photolysis shows a remarkable dependence the wavelength, increasing from 0.12 at 365 nm to 1.0 at 248 nm. One single excited state is responsible for this behaviour. The wavelength-dependent quantum yield profile corresponds in a first approximation to the ratio between the LMCT-band and the total absorption spectrum was made on a mathematical basis using symmetrical Gauss curves. This is the first time that a fluorescence and phosphorescence emission of an alkyl transition-metal complex of d0-configuration has been detected, thus allowing for the determination of both the S1 and the T1-energy levels. The quantum yield of the fluorescence (QF) is below 10−3; that of the phosphorescence is below 0.04.
Zusammenfassung
Die Photolyse von CH3ReO(O2)2·H2O in Methylenchlorid führt ebenso wie die Thermolyse dieses Komplexes zur Abspaltung von molekularem Sauerstoff im Triplettgrundzustand. Die Photolyse-Quantenausbeute QPh zeigt eine bemerkenswerte Abhängigkeit von der eingerstrahlten Wellenlänge und steigt von 0.12 bei 365 nm bis zu 1.0 bei 248 nm an. Hierfür kann hauptsächlich ein einziger angeregter Zustand verantwortich gemacht werden. Der Kurvenverlauf der wellenlängenabhängigen Quantenausbeute entspricht in guter Näherung dem Verhältnis der LMCT-Bande zum Gesamtabsorptionsspektrum. Die Zerlegung des Absorptionsspektrums in die einzelnen Banden erfolgte durch rechnerische Kurvenanalyse in symmetrische Gauss-Kurven. Erstmals konnte die Fluoreszenz- und die Phosphoreszenz-emission eines alkylhaltigen d0-Übergangsmetall-Komplexes detektiert werden und somit sowohl die S1-als auch die T1-Energielage bestimmt werden. Die Quantenausbeute der Fluoreszenz QF ist kleiner als 10−4, die Phosphoreszenzquantenausbeute beträgt weniger als 0.04. 相似文献
We have studied the reactione+e–e+e– using data taken by the CELLO detector at 35 GeV centre of mass energy with an integrated luminosity of 86 pb–1. The differential cross section is found to agree with the Standard Model and is used to set limits on possible deviations from the pointlike structure of the electron. The lower limits obtained for the compositeness scale range from 0.8 to 6.0 TeV (95% C.L.), depending on the structure of the current. 相似文献