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M. Greiner

Publications and source records attributed to M. Greiner.

25 records · Page 2Linked to original sources
arXiv2003

Detection of spatial correlations in an ultracold gas of fermions

Spatial correlations are observed in an ultracold gas of fermionic atoms close to a Feshbach resonance. The correlations are detected by inducing spin-changing rf transitions between pairs of atoms. We observe the process in the strongly interacting regime for attractive as well as for repulsive atom-atom interactions and both in the regime of high and low quantum degeneracy. The observations are compared with a two-particle model that provides theoretical predictions for the measured rf transition rates.

cond-mat.soft↗
arXiv2003

On the effects of surrogacy of energy dissipation in determining the intermittency exponent in fully developed turbulence

The two-point correlation function of the energy dissipation, obtained from a one-point time record of an atmospheric boundary layer, reveals a rigorous power-law scaling with intermittency exponent mu=0.20 over almost the entire inertial range of scales. However, for the related integral moment, the power-law scaling is restricted to the upper part of the inertial range only. This observation is explained in terms of the operational surrogacy of the construction of energy dissipation, which influences the behaviour of the correlation function for small separation distances.

cond-mat.stat-mech↗
arXiv2001

Spatio-temporal log-stable process for the turbulent energy-cascade

We present a dynamical log-stable process for the spatio-temporal evolution of the energy-dissipation field in fully developed turbulence. The process is constructed from multifractal scaling relations required for two-point correlators of arbitrary order. n-point correlation functions are calculated analytically and interpreted in terms of generalised fusion rules and in terms of the random multiplicative cascade picture. Multiplier distributions are compared with experimental results.

cond-mat.stat-mech↗
arXiv2000

Cumulant ratios in fully developed turbulence

In the context of random multiplicative cascade processes, we derive analytical solutions for one- and two-point cumulants with restored translational invariance. On taking ratios of cumulants in ln epsilon, geometrical effects due to spatial averaging cancel out. These ratios can successfully distinguish between splitting functions while multifractal scaling exponents and multiplier distributions cannot.

hep-ph↗
arXiv1998

Fix-point Multiplier Distributions in Discrete Turbulent Cascade Models

One-point time-series measurements limit the observation of three-dimensional fully developed turbulence to one dimension. For one-dimensional models, like multiplicative branching processes, this implies that the energy flux from large to small scales is not conserved locally. This then renders the random weights used in the cascade curdling to be different from the multipliers obtained from a backward averaging procedure. The resulting multiplier distributions become solutions of a fix-point problem. With a further restoration of homogeneity, all observed correlations between multipliers in the energy dissipation field can be understood in terms of simple scale-invariant multiplicative branching processes.

chao-dyn↗
arXiv1997

Probing Hierarchical Clustering by Scale-Scale Correlations of Wavelet Coefficients

It is of fundamental importance to determine if and how hierarchical clustering is involved in large-scale structure formation of the universe. Hierarchical evolution is characterized by rules which specify how dark matter halos are formed by the merging of halos at smaller scales. We show that scale-scale correlations of the matter density field are direct and sensitive measures to quantify this merging tree. Such correlations are most conveniently determined from discrete wavelet transforms. Analyzing two samples of Ly-alpha forests of QSO's absorption spectra, we find significant scale-scale correlations whose dependence is typical for a branching process. Therefore, models which predict a "history" independent evolution are ruled out and the halos hosting the Ly-alpha clouds must have gone through a "history" dependent merging process during their formation.

astro-ph↗