排序方式: 共有18条查询结果,搜索用时 15 毫秒
1.
Cabrera JA Bieler CR Olbricht BC van der Veer WE Janda KC 《The Journal of chemical physics》2005,123(5):054311
Time- and frequency-resolved pump-probe measurements on NeBr2 have been performed to better characterize its fragmentation dynamics on the B electronic state for vibrational levels in the energy region of the transition from direct vibrational predissociation to intramolecular vibrational relaxation dynamics. Above nu'=20 of the Br2 stretching mode, it was observed that the dependence of lifetime on the vibrational quantum number deviates from the energy-gap law by leveling off in the range of 10 psE transitions of the complex. These transitions are shifted 20 cm(-1) to lower energy from the free Br2 resonances, indicating an E state Ne-Br2 bond energy of 82 cm(-1). Measurements of NeBr2 vibrational predissociation via the delta nu=-2 channel were also performed for nu'=27, 28, and 29. The closing of the delta nu=-1 channel leads to an increase in the lifetimes of these vibrational levels. A new Nd:yttrium aluminum garnet pumped dual optical parametric oscillator/optical parametric amplifier system is described that allows us to conveniently record time-delayed pump-probe spectra with 2-cm(-1) spectral resolution and 15-ps time resolution. 相似文献
2.
Recent experiments suggest that the Ising pyrochlore magnets Ho2Ti2O7 and Dy2Ti2O7 display qualitative properties of the nearest-neighbor "spin ice" model. We discuss the dipolar energy scale present in both these materials and discuss how spin-ice behavior can occur despite the presence of long-range dipolar interactions. We present results of numerical simulations and a mean field analysis of Ising pyrochlore systems. Based on our quantitative theory, we suggest that the spin-ice behavior in these systems is due to long-range dipolar interactions, and that the nearest-neighbor exchange in Dy2Ti2O7 is antiferromagnetic. 相似文献
3.
F. Flemming C. Olbricht B. Wegner A. Sadiki J. Janicka F. Bake U. Michel B. Lehmann I. Röhle 《Flow, Turbulence and Combustion》2005,75(1-4):3-27
In order to evaluate the direct and indirect contributions to the total combustion noise emission, a combustion chamber consisting
of a swirl burner and an exit nozzle of Laval-shape, representing a gas turbine combustor, is investigated by means of experiments
and large eddy simulation. Focused on the isothermal flow case first and encouraged by a good overall agreement between the
LES and the experimental data for the flow field, a first characterisation of the flow with respect to noise sources is performed.
To analyse acoustic properties of the flow, time and length scales are evaluated inside the combustor. Furthermore, the evidence
for the existence of a precessing vortex core (PVC), typical for configurations with swirl, is revealed. Finally, the effect
of the PVC on the flow inside the Laval nozzle is discussed. 相似文献
4.
The dynamics of fluid systems which consist of a suspended material in a Newtonian continuous phase is investigated theoretically. Criteria are derived to predict conditions under which the strength of a flow, i.e. a measure of the form and magnitude of the velocity gradient tensor, is sufficient to induce significant deformation and/or orientation of the fluid microstructure, that is, the elements which collectively comprise the suspended phase. The development relies upon the choice of a model to describe the microstructure, and the form of the criteria reflects this choice. Once the choice is made, however, the detailed material properties of a particular fluid system enter only as parameters in the resulting equations, and thus, the results encompass a large class of systems, including particulate suspensions and macromolecular solutions. Two microstructure models are investigated here. When the microstructure is characterized by a vector, the flow strengths of all linear flows are displayed in a single figure from which the strength of a particular flow can be evaluated directly. A comparison is then made for selected flows between these results and those for the case where an irreducible second order tensor is employed to describe the microstructure. A significant difference between the two models derives from the fact that the “volume” of the microstructure must be conserved in the second-order tensor case. The criteria are finally used to predict the degree of macromolecular stretching in a model turbulent flow and the breakup of immiscible liquid drops in simple shear flow. A comparison between the flow strength predictions and experimental data yields good qualitative agreement in the latter case. 相似文献
5.
We obtain exact cosmological solutions of a higher derivative theory described by the Lagrangian L=R+2αR
2 in the presence of interacting scalar field. The interacting scalar field potential required for a known evolution of the
FRW universe in the framework of the theory is obtained using a technique different from the usual approach to solve the Einstein
field equations. We follow here a technique to determine potential similar to that used by Ellis and Madsen in Einstein gravity.
Some new and interesting potentials are noted in the presence of R
2 term in the Einstein action for the known behaviours of the universe. These potentials in general do not obey the slow rollover
approximation. 相似文献
6.
We compare the orbital angular momentum of the ‘quark’ in the scalar diquark model as well as that of the electron in QED (to order α) obtained from the Jaffe–Manohar decomposition to that obtained from the Ji relation. We estimate the importance of the vector potential in the definition of orbital angular momentum. 相似文献
7.
C. Olbricht F. Hahn A. Sadiki J. Janicka 《International Journal of Heat and Fluid Flow》2007,28(6):1215-1226
This contribution introduces a hybrid LES-Monte-Carlo method for a coupled solution of the flow and the multi-dimensional scalar joint pdf in two complex mixing devices. For this purpose an Eulerian Monte-Carlo method is used. First, a complex mixing device (jet-in-crossflow, JIC) is presented in which the stochastic convergence and the coherency between the scalar field solution obtained via finite-volume methods and that from the stochastic solution of the pdf for the hybrid method are evaluated. Results are compared to experimental data. Secondly, an extensive investigation of the micromixing on the basis of assumed shape and transported SGS-pdfs in a configuration with practical relevance is carried out. This consists of a mixing chamber with two opposite rows of jets penetrating a crossflow (multi-jet-in-crossflow, MJIC). Some numerical results are compared to available experimental data and to RANS based results. It turns out that the hybrid LES-Monte-Carlo method could achieve a detailed analysis of the mixing at the subgrid level. 相似文献
8.
9.
In this paper we discuss the properties of amorphous hydrogenated silicon and germanium films prepared by homogeneous chemical vapor deposition. Emphasis is placed upon the important differences between HOMOCVD and plasma-deposited films. Experiments and calculations are presented which illustrate the most important reactor dynamical parameters. 相似文献
10.
The response of a dumbbell model for dilute polymer solutions is examined for periodic sequences of homogeneous flows chosen to approximate the unsteady kinematics appropriate for flow through porous media. The evolution of particle shape depends on the kinematic history of the flow and on microrheological properties of the dumbbell such as a variable friction factor and a nonlinear spring. The effect of vorticity on macromolecular stretching is found to differ qualitatively from results for steady flows, and entrance effects that persist over timescales much larger than the intrinsic macromolecular relaxation time are observed. 相似文献