We experimentally investigate the presence of anisotropy from the inertial to the dissipative scales in homogeneous turbulence. We employ an apparatus in which two facing arrays of randomly actuated air jets generate turbulence with negligible mean flow and shear, over a volume several times larger than the energy-containing eddy size. The Reynolds number based on the Taylor microscale is varie...

Kinetic equations modeling the behavior of the velocity probability density function sPDFd in homogeneous anisotropic decaying turbulence are hypothesized and their implications for return-to-isotropy are investigated. Anisotropic turbulent decay is a parametrically simple but theoretically complex turbulent flow that is dominated by nonlinear interactions. The physical implications of the Bhat...

The statistical expectation values of the temperature fluctuations of cosmic microwave background (CMB) are assumed to be preserved under rotations of the sky. We investigate the statistical isotropy of the CMB anisotropy maps recently measured by the Wilkinson Microwave Anisotropy Probe (WMAP) using bipolar spherical harmonic power spectrum proposed in Hajian & Souradeep 2003. The Bipolar Powe...

We consider reduced Witt rings of finite chain length. We show there is a bound, in terms of the chain length and maximal signature, on the dimension of anisotropic, totally indefinite forms. From this we get the ascending chain condition on principal ideals and hence factorization of forms into products of irreducible forms. 2000 Mathematics Subject Classification: 11E81, 12D15

It is pointed out that the cross section for the scattering of identical charged bosons is isotropic over a broad angular range around 90o when the Sommerfeld parameter has a critical value, which depends exclusively on the spin of the particle. A discussion of systems where this phenomenon can be observed is presented. The scattering of identical particles is a routine exercise in quantum mech...

The application of uniaxial pressure can induce elastic anisotropy in otherwise isotropic rocks. We consider models based on two very different rock classes, granites and weakly consolidated granular systems. We show (1) that these models share common underlying assumptions, (2) that they lead to similar qualitative behavior, and (3) that both provide a microscopic basis for elliptical anisotro...

We consider homogeneous non-Abelian vector fields with general potential terms in an expanding universe. We find a mechanical analogy with a system of N interacting particles (with N the dimension of the gauge group) moving in three dimensions under the action of a central potential. In the case of bounded and rapid evolution compared to the rate of expansion, we show by making use of a general...

We experimentally demonstrate a micromachined reconfigurable metamaterial with polarization independent characteristics for multiple resonances in terahertz spectral region. The metamaterial unit cell consists of eight out-of-plane deformable microcantilevers placed at each corner of an octagon ring. The octagon shaped unit cell geometry provides the desired rotational symmetry, while the out-o...

It is often assumed that primordial perturbations are statistically isotropic, which implies, among other properties, that their power spectrum is invariant under rotations. In this article, we test this assumption by placing bounds on deviations from rotational invariance of the primordial spectrum. Using five-year Wilkinson Microwave Anisotropy Probe cosmic microwave anisotropy maps, we set l...

From two calibrated perspective views of a scene we make a direct metric reconstruction. From assumptions of translational, rotational, and scale invariance of 3D space and camera models we deduce the priors needed for a Bayesian estimation. This means that the reconstruction is optimal in the sense of Bayesian estimation with assumptions of Gaussian uncorrelated image noise and no preferred po...