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CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
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Alberti G Brunet E Dionigi C Juanes O de La Mata MJ Rodríguez-Ubis JC Vivani R 《Angewandte Chemie (International ed. in English)》1999,38(22):3351-3353
The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space. 相似文献
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The relationship between the mode content and the fractional Fourier and fractional Hankel transforms of a function is established. It is shown that the Laguerre-Gauss spectrum of a rotationally symmetric wave front can be determined from the wave front's fractional Hankel transforms taken at the optical axis. 相似文献
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J. A. Van Oijen R. J. M. Bastiaans G. R. A. Groot L. P. H. De Goey 《Flow, Turbulence and Combustion》2005,75(1-4):67-84
Direct numerical simulation is a very powerful tool to evaluate the validity of new models and theories for turbulent combustion.
In this paper, direct numerical simulations of spherically expanding premixed turbulent flames in the thin reaction zone regime
and in the broken reaction zone regime are performed. The flamelet-generated manifold method is used in order to deal with
detailed reaction kinetics. The computational results are analyzed by using an extended flame stretch theory. It is investigated
whether this theory is able to describe the influence of flame stretch and curvature on the local burning velocity of the
flame. It is found that if the full profiles of flame stretch and curvature through the flame front are included in the theory,
the local mass burning rate is well predicted. The influence of several approximations, which are used in other existing theories,
is studied. When flame stretch is assumed constant through the flame front or when curvature of the flame front is neglected,
the theory fails to predict the local mass burning rate. The influence of using a reduced chemistry model is investigated
by comparing flamelet simulations with reduced and detailed chemistry. 相似文献
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Xi Jiang K. H. Luo L. P. H. de Goey R. J. M. Bastiaans J. A. van Oijen 《Flow, Turbulence and Combustion》2011,86(1):63-88
The effects of swirl and downstream wall confinement on an annular nonpremixed flame were investigated using direct numerical
simulation (DNS). Fully three-dimensional parallel DNS was performed employing high-order numerical methods and high-fidelity
boundary conditions to solve governing equations for variable-density flow and finite-rate Arrhenius chemistry. Three swirl
numbers have been examined: 0 (without swirl), 0.4 and 0.8, while the effects of downstream wall confinement have been examined
for swirl numbers 0 and 0.4. Results have been presented in terms of instantaneous and time-averaged flow quantities, which
have also been analysed using energy spectra and proper orthogonal decomposition (POD). Effects of swirl on the fluid dynamic
behaviour of the annular nonpremixed flame were found to be significant. The fluid dynamic behaviour of the flame is greatly
affected by the interaction between the geometrical recirculation zone (GRZ) near the jet nozzle exit due to the annular configuration,
the central recirculation zone (CRZ) associated with swirl, the unsteady vortical structures in the jet column due to the
shear instability, and the downstream wall confinement. Depending on the degree of swirl, the GRZ near the burner mouth and
the CRZ may co-exist or one zone may be overwhelmed by another. At a moderate swirl number, the co-existence leads to a flame
with strong reaction attached to the burner mouth; while at a high swirl number, the CRZ dominates over the GRZ. The precessing
vortex core was observed to exist in the swirling flow fields. The Nusselt number distribution of the annular impinging flames
differs from that of round impinging jets. The POD analysis revealed that wall effects on the flow field are mainly associated
with the higher mode numbers. 相似文献
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It is shown that a lossless first-order optical system whose real symplectic ray transformation matrix can be diagonalized and has only real eigenvalues, is similar to a separable hyperbolic expander in the sense that the respective ray transformation matrices are related by means of a similarity transformation. Moreover, it is shown how eigenfunctions of such a system can be determined, based on the fact that simple powers are eigenfunctions of a separable magnifier. As an example, a set of eigenfunctions of a hyperbolic expander is determined and the resemblance between these functions and the well-known Hermite-Gauss modes is exploited. 相似文献
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