Spin Alignment of Heavy Meson Revisited

Using heavy quark effective theory a factorized form for inclusive production rate of a heavy meson can be obtained, in which the nonperturbative effect related to the heavy meson can be characterized by matrix elements defined in the heavy quark effective theory. Using this factorization, predictions for the full spin density matrix of a spin-1 and spin-2 meson can be obtained and they are characterized only by one coefficient representing the nonperturbative effect. Predictions for spin-1 heavy meson are compared with experiment performed at $e^+e^-$ colliders in the energy range from $\sqrt{s}=10.5$GeV to $\sqrt{s}=91$GeV, a complete agreement is found for $D^*$- and $B^*$-meson. There are distinct differences from the existing approach and they are discussed.Comment: 6 pages, Talk given at 3rd Circum-Pan-Pacific Symposium on "High Energy Spin Physics", Beijing, China, 8-13, 200

Turbulent transport in hydromagnetic flows

The predictive power of mean-field theory is emphasized by comparing theory with simulations under controlled conditions. The recently developed test-field method is used to extract turbulent transport coefficients both in kinematic as well as nonlinear and quasi-kinematic cases. A striking example of the quasi-kinematic method is provided by magnetic buoyancy-driven flows that produce an alpha effect and turbulent diffusion.Comment: 17 pages, 6 figures, topical issue of Physica Scripta on turbulent mixing and beyon

Mean magnetic field generation in sheared rotators

A generalized mean magnetic field induction equation for differential rotators is derived, including a compressibility, and the anisotropy induced on the turbulent quantities from the mean magnetic field itself and a mean velocity shear. Derivations of the mean field equations often do not emphasize that there must be anisotropy and inhomogeneity in the turbulence for mean field growth. The anisotropy from shear is the source of a term involving the product of the mean velocity gradient and the cross-helicity correlation of the isotropic parts of the fluctuating velocity and magnetic field, \lb{\bfv}\cdot{\bfb}\rb^{(0)}. The full mean field equations are derived to linear order in mean fields, but it is also shown that the cross-helicity term survives to all orders in the velocity shear. This cross-helicity term can obviate the need for a pre-existing seed mean magnetic field for mean field growth: though a fluctuating seed field is necessary for a non-vanishing cross-helicity, the term can produce linear (in time) mean field growth of the toroidal field from zero mean field. After one vertical diffusion time, the cross-helicity term becomes sub-dominant and dynamo exponential amplification/sustenance of the mean field can subsequently ensue. The cross-helicity term should produce odd symmetry in the mean magnetic field, in contrast to the usually favored even modes of the dynamo amplification in sheared discs. This may be important for the observed mean field geometries of spiral galaxies. The strength of the mean seed field provided by the cross- helicity depends linearly on the magnitude of the cross-helicity.Comment: 15 pages, LaTeX, matches version accepted to ApJ, minor revision

Inertial range scaling in numerical turbulence with hyperviscosity

Numerical turbulence with hyperviscosity is studied and compared with direct simulations using ordinary viscosity and data from wind tunnel experiments. It is shown that the inertial range scaling is similar in all three cases. Furthermore, the bottleneck effect is approximately equally broad (about one order of magnitude) in these cases and only its height is increased in the hyperviscous case--presumably as a consequence of the steeper decent of the spectrum in the hyperviscous subrange. The mean normalized dissipation rate is found to be in agreement with both wind tunnel experiments and direct simulations. The structure function exponents agree with the She-Leveque model. Decaying turbulence with hyperviscosity still gives the usual t^{-1.25} decay law for the kinetic energy, and also the bottleneck effect is still present and about equally strong.Comment: Final version (7 pages

The bacillary and macrophage response to hypoxia in tuberculosis and the consequences for T cell antigen recognition

M. tuberculosis is a facultative anaerobe and its characteristic pathological hallmark, the granuloma, exhibits hypoxia in humans and in most experimental models. Thus the host and bacillary adaptation to hypoxia is of central importance in understanding pathogenesis and thereby to derive new drug treatments and vaccines

Magnetohydrodynamic turbulence in warped accretion discs

Warped, precessing accretion discs appear in a range of astrophysical systems, for instance the X-ray binary Her X-1 and in the active nucleus of NGC4258. In a warped accretion disc there are horizontal pressure gradients that drive an epicyclic motion. We have studied the interaction of this epicyclic motion with the magnetohydrodynamic turbulence in numerical simulations. We find that the turbulent stress acting on the epicyclic motion is comparable in size to the stress that drives the accretion, however an important ingredient in the damping of the epicyclic motion is its parametric decay into inertial waves.Comment: to appear in the proceedings of the 20th Texas Symposium on Relativistic Astrophysics, J. C. Wheeler & H. Martel (eds.

The response of a turbulent accretion disc to an imposed epicyclic shearing motion

We excite an epicyclic motion, whose amplitude depends on the vertical position, $z$, in a simulation of a turbulent accretion disc. An epicyclic motion of this kind may be caused by a warping of the disc. By studying how the epicyclic motion decays we can obtain information about the interaction between the warp and the disc turbulence. A high amplitude epicyclic motion decays first by exciting inertial waves through a parametric instability, but its subsequent exponential damping may be reproduced by a turbulent viscosity. We estimate the effective viscosity parameter, $\alpha_{\rm v}$, pertaining to such a vertical shear. We also gain new information on the properties of the disc turbulence in general, and measure the usual viscosity parameter, $\alpha_{\rm h}$, pertaining to a horizontal (Keplerian) shear. We find that, as is often assumed in theoretical studies, $\alpha_{\rm v}$ is approximately equal to $\alpha_{\rm h}$ and both are much less than unity, for the field strengths achieved in our local box calculations of turbulence. In view of the smallness ($\sim 0.01$) of $\alpha_{\rm v}$ and $\alpha_{\rm h}$ we conclude that for $\beta = p_{\rm gas}/p_{\rm mag} \sim 10$ the timescale for diffusion or damping of a warp is much shorter than the usual viscous timescale. Finally, we review the astrophysical implications.Comment: 12 pages, 18 figures, MNRAS accepte