1,198 research outputs found
Double-diffusive instabilities of a shear-generated magnetic layer
Previous theoretical work has speculated about the existence of
double-diffusive magnetic buoyancy instabilities of a dynamically evolving
horizontal magnetic layer generated by the interaction of forced vertically
sheared velocity and a background vertical magnetic field. Here we confirm
numerically that if the ratio of the magnetic to thermal diffusivities is
sufficiently low then such instabilities can indeed exist, even for high
Richardson number shear flows. Magnetic buoyancy may therefore occur via this
mechanism for parameters that are likely to be relevant to the solar
tachocline, where regular magnetic buoyancy instabilities are unlikely.Comment: Submitted to ApJ
Generation linewidth of an auto-oscillator with a nonlinear frequency shift: Spin-torque nano-oscillator
It is shown that the generation linewidth of an auto-oscillator with a
nonlinear frequency shift (i.e. an auto-oscillator in which frequency depends
on the oscillation amplitude) is substantially larger than the linewidth of a
conventional quasi-linear auto-oscillator due to the renormalization of the
phase noise caused by the nonlinearity of the oscillation frequency. The
developed theory, when applied to a spin-torque nano-contact auto-oscillator,
predicts a minimum of the generation linewidth when the nano-contact is
magnetized at a critical angle to its plane, corresponding to the minimum
nonlinear frequency shift, in good agreement with recent experiments.Comment: 4 pages, 2 figure
The Evolution of a Double Diffusive Magnetic Buoyancy Instability
Recently, Silvers, Vasil, Brummell, & Proctor (2009), using numerical
simulations, confirmed the existence of a double diffusive magnetic buoyancy
instability of a layer of horizontal magnetic field produced by the interaction
of a shear velocity field with a weak vertical field. Here, we demonstrate the
longer term nonlinear evolution of such an instability in the simulations. We
find that a quasi two-dimensional interchange instability rides (or "surfs") on
the growing shear-induced background downstream field gradients. The region of
activity expands since three-dimensional perturbations remain unstable in the
wake of this upward-moving activity front, and so the three-dimensional nature
becomes more noticeable with time.Comment: 9 pages; 3 figures; accepted to appear in IAU symposium 27
A nonlinear model for rotationally constrained convection with Ekman pumping
It is a well established result of linear theory that the influence of
differing mechanical boundary conditions, i.e., stress-free or no-slip, on the
primary instability in rotating convection becomes asymptotically small in the
limit of rapid rotation. This is accounted for by the diminishing impact of the
viscous stresses exerted within Ekman boundary layers and the associated
vertical momentum transport by Ekman pumping. By contrast, in the nonlinear
regime recent experiments and supporting simulations are now providing evidence
that the efficiency of heat transport remains strongly influenced by Ekman
pumping in the rapidly rotating limit. In this paper, a reduced model is
developed for the case of low Rossby number convection in a plane layer
geometry with no-slip upper and lower boundaries held at fixed temperatures. A
complete description of the dynamics requires the existence of three distinct
regions within the fluid layer: a geostrophically balanced interior where fluid
motions are predominately aligned with the axis of rotation, Ekman boundary
layers immediately adjacent to the bounding plates, and thermal wind layers
driven by Ekman pumping in between. The reduced model uses a classical Ekman
pumping parameterization to alleviate the need for spatially resolving the
Ekman boundary layers. Results are presented for both linear stability theory
and a special class of nonlinear solutions described by a single horizontal
spatial wavenumber. It is shown that Ekman pumping allows for significant
enhancement in the heat transport relative to that observed in simulations with
stress-free boundaries. Without the intermediate thermal wind layer the
nonlinear feedback from Ekman pumping would be able to generate a heat
transport that diverges to infinity. This layer arrests this blowup resulting
in finite heat transport at a significantly enhanced value.Comment: 38 pages, 14 figure
Study Of Oxidation Processes In Duck Meat With Application Of Rosemary And Grape Seed Extracts
The substantiation of the expedience of using antioxidants of a natural origin to decelerate oxidation processes in different meat products is an urgent direction of these studies. The prospective way of a solution of the problem of meat products oxidation spoilage is the use of vegetable extracts. The experimental studies of the effective use of the composition of rosemary and grape seed extracts in Peking duck forcemeat at the long storage were realized. Their influence on the dynamics of hydrolytic and peroxide oxidation of forcemeat lipids was studied. The analysis of oxidation secondary products accumulation was realized at the same time.The positive effect of the combined use of rosemary and grape seeds extracts on frozen Peking duck forcemeat was established, the optimal concentration of offered preparations was determined
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