435 research outputs found
R-modes in the ocean of a magnetic neutron star
We study the dynamics of r-modes in the ocean of a magnetic neutron star. We
modeled the star's ocean with a spherical rotating thin shell and assumed that
the magnetic field symmetry axis is not aligned to the shell's spin axis. In
the magnetohydrodynamic approximation, we calculate the frequency of
r-modes in the shell of an incompressible fluid. Different r-modes with
and are coupled by the {\it inclined} magnetic field. Kinematical
secular effects for the motion of a fluid element in the shell undergoing
r-mode are studied. The magnetic corrected drift velocity of a given
fluid element undergoing the r-mode oscillations is obtained. The
magnetic field increases the magnitude of the fluid drift produced by the
r-mode drift velocity, the high- modes in the ocean fluid will damp
faster than the low- ones.Comment: 24 pages, 5 figures, to appear in ApJ, v574 n2 August 1, 2002 issu
Emerging Synergisms Between Drugs and Physiologically-Patterned Weak Magnetic Fields: Implications for Neuropharmacology and the Human Population in the Twenty-First Century
Synergisms between pharmacological agents and endogenous neurotransmitters are familiar and frequent. The present review describes the experimental evidence for interactions between neuropharmacological compounds and the classes of weak magnetic fields that might be encountered in our daily environments. Whereas drugs mediate their effects through specific spatial (molecular) structures, magnetic fields mediate their effects through specific temporal patterns. Very weak (microT range) physiologically-patterned magnetic fields synergistically interact with drugs to strongly potentiate effects that have classically involved opiate, cholinergic, dopaminergic, serotonergic, and nitric oxide pathways. The combinations of the appropriately patterned magnetic fields and specific drugs can evoke changes that are several times larger than those evoked by the drugs alone. These novel synergisms provide a challenge for a future within an electromagnetic, technological world. They may also reveal fundamental, common physical mechanisms by which magnetic fields and chemical reactions affect the organism from the level of fundamental particles to the entire living system
General Relativistic Rossby-Haurwitz waves of a slowly and differentially rotating fluid shell
We show that, at first order in the angular velocity, the general
relativistic description of Rossby-Haurwitz waves (the analogues of r-waves on
a thin shell) can be obtained from the corresponding Newtonian one after a
coordinate transformation. As an application, we show that the results recently
obtained by Rezzolla and Yoshida (2001) in the analysis of Newtonian
Rossby-Haurwitz waves of a slowly and differentially rotating, fluid shell
apply also in General Relativity, at first order in the angular velocity.Comment: 4 pages. Comment to Class. Quantum Grav. 18(2001)L8
Statistics and Characteristics of Spatio-Temporally Rare Intense Events in Complex Ginzburg-Landau Models
We study the statistics and characteristics of rare intense events in two
types of two dimensional Complex Ginzburg-Landau (CGL) equation based models.
Our numerical simulations show finite amplitude collapse-like solutions which
approach the infinite amplitude solutions of the nonlinear Schr\"{o}dinger
(NLS) equation in an appropriate parameter regime. We also determine the
probability distribution function (PDF) of the amplitude of the CGL solutions,
which is found to be approximately described by a stretched exponential
distribution, , where . This
non-Gaussian PDF is explained by the nonlinear characteristics of individual
bursts combined with the statistics of bursts. Our results suggest a general
picture in which an incoherent background of weakly interacting waves,
occasionally, `by chance', initiates intense, coherent, self-reinforcing,
highly nonlinear events.Comment: 7 pages, 9 figure
Effect of heat transfer on compressible boundary layer flow over a circular cylinder
The effect of heat transfer on the steady laminar compressible boundary layer flow past a horizontal circular cylinder has been studied. The resulting coupled nonlinear partial differential equations have been solved numerically using a very efficient finite-difference scheme. Specific results are given for the boundary layer separation parameter and the skin friction and heat transfer coefficients.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41701/1/707_2005_Article_BF01177230.pd
Rossby-Haurwitz waves of a slowly and differentially rotating fluid shell
Recent studies have raised doubts about the occurrence of r modes in
Newtonian stars with a large degree of differential rotation. To assess the
validity of this conjecture we have solved the eigenvalue problem for
Rossby-Haurwitz waves (the analogues of r waves on a thin-shell) in the
presence of differential rotation. The results obtained indicate that the
eigenvalue problem is never singular and that, at least for the case of a
thin-shell, the analogues of r modes can be found for arbitrarily large degrees
of differential rotation. This work clarifies the puzzling results obtained in
calculations of differentially rotating axi-symmetric Newtonian stars.Comment: 8pages, 3figures. Submitted to CQ
Non-Oberbeck-Boussinesq effects in turbulent thermal convection in ethane close to the critical point
As shown in earlier work (Ahlers et al., J. Fluid Mech. 569, p.409 (2006)),
non-Oberbeck Boussinesq (NOB) corrections to the center temperature in
turbulent Rayleigh-Benard convection in water and also in glycerol are governed
by the temperature dependences of the kinematic viscosity and the thermal
diffusion coefficient. If the working fluid is ethane close to the critical
point the origin of non-Oberbeck-Boussinesq corrections is very different, as
will be shown in the present paper. Namely, the main origin of NOB corrections
then lies in the strong temperature dependence of the isobaric thermal
expansion coefficient \beta(T). More precisely, it is the nonlinear
T-dependence of the density \rho(T) in the buoyancy force which causes another
type of NOB effect. We demonstrate that through a combination of experimental,
numerical, and theoretical work, the latter in the framework of the extended
Prandtl-Blasius boundary layer theory developed in Ahlers et al., J. Fluid
Mech. 569, p.409 (2006). The latter comes to its limits, if the temperature
dependence of the thermal expension coefficient \beta(T) is significant.Comment: 18 pages, 15 figures, 3 table
Spatial and spatio-temporal patterns in a cell-haptotaxis model
We investigate a cell-haptotaxis model for the generation of spatial and spatio-temporal patterns in one dimension. We analyse the steady state problem for specific boundary conditions and show the existence of spatially hetero-geneous steady states. A linear analysis shows that stability is lost through a Hopf bifurcation. We carry out a nonlinear multi-time scale perturbation procedure to study the evolution of the resulting spatio-temporal patterns. We also analyse the model in a parameter domain wherein it exhibits a singular dispersion relation
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