71,174 research outputs found
Instability of ion kinetic waves in a weakly ionized plasma
The fundamental higher-order Landau plasma modes are known to be generally
heavily damped. We show that these modes for the ion component in a weakly
ionized plasma can be substantially modified by ion-neutral collisions and a dc
electric field driving ion flow so that some of them can become unstable. This
instability is expected to naturally occur in presheaths of gas discharges at
sufficiently small pressures and thus affect sheaths and discharge structures.Comment: Published in Phys. Rev. E, see
http://link.aps.org/doi/10.1103/PhysRevE.85.02641
Microscopic and Macroscopic Stress with Gravitational and Rotational Forces
Many recent papers have questioned Irving and Kirkwood's atomistic expression
for stress. In Irving and Kirkwood's approach both interatomic forces and
atomic velocities contribute to stress. It is the velocity-dependent part that
has been disputed. To help clarify this situation we investigate [1] a fluid in
a gravitational field and [2] a steadily rotating solid. For both problems we
choose conditions where the two stress contributions, potential and kinetic,
are significant. The analytic force-balance solutions of both these problems
agree very well with a smooth-particle interpretation of the atomistic
Irving-Kirkwood stress tensor.Comment: Fifteen pages with seven figures, revised according to referees'
suggestions at Physical Review E. See also Liu and Qiu's arXiv contribution
0810.080
Rigorous elimination of fast stochastic variables from the linear noise approximation using projection operators
The linear noise approximation (LNA) offers a simple means by which one can
study intrinsic noise in monostable biochemical networks. Using simple physical
arguments, we have recently introduced the slow-scale LNA (ssLNA) which is a
reduced version of the LNA under conditions of timescale separation. In this
paper, we present the first rigorous derivation of the ssLNA using the
projection operator technique and show that the ssLNA follows uniquely from the
standard LNA under the same conditions of timescale separation as those
required for the deterministic quasi-steady state approximation. We also show
that the large molecule number limit of several common stochastic model
reduction techniques under timescale separation conditions constitutes a
special case of the ssLNA.Comment: 10 pages, 1 figure, submitted to Physical Review E; see also BMC
Systems Biology 6, 39 (2012
Enhanced stability of layered phases in parallel hard-spherocylinders due to the addition of hard spheres
There is increasing evidence that entropy can induce microphase separation in
binary fluid mixtures interacting through hard particle potentials. One such
phase consists of alternating two dimensional liquid-like layers of rods and
spheres. We study the transition from a uniform miscible state to this ordered
state using computer simulations and compare results to experiments and theory.
We conclude that (1) there is stable entropy driven microphase separation in
mixtures of parallel rods and spheres, (2) adding spheres smaller then the rod
length decreases the total volume fraction needed for the formation of a
layered phase, therefore small spheres effectively stabilize the layered phase;
the opposite is true for large spheres and (3) the degree of this stabilization
increases with increasing rod length.Comment: 11 pages, 9 figures. Submitted to Phys. Rev. E. See related website
http://www.elsie.brandeis.ed
Charge Transport Scalings in Turbulent Electroconvection
We describe a local-power law scaling theory for the mean dimensionless
electric current in turbulent electroconvection. The experimental system
consists of a weakly conducting, submicron thick liquid crystal film supported
in the annulus between concentric circular electrodes. It is driven into
electroconvection by an applied voltage between its inner and outer edges. At
sufficiently large voltage differences, the flow is unsteady and electric
charge is turbulently transported between the electrodes. Our theoretical
development, which closely parallels the Grossmann-Lohse model for turbulent
thermal convection, predicts the local-power law . and are dimensionless
numbers that are similar to the Rayleigh and Prandtl numbers of thermal
convection, respectively. The dimensionless function , which is
specified by the model, describes the dependence of on the aspect ratio
. We find that measurements of are consistent with the theoretical
model.Comment: 12 pages, 7 figures, Submitted to Phys. Rev. E. See also
http://www.physics.utoronto.ca/nonlinea
Sedimentation and subsidence history of the Lomonosov Ridge
During the first scientific ocean drilling expedition to the Arctic Ocean (Arctic Coring Expedition [ACEX]; Integrated Ocean Drilling Program Expedition 302), four sites were drilled and cored atop the central part of the Lomonosov Ridge in the Arctic Ocean at ~88°N, 140°E (see Fig. F18 in the "Sites M0001–M0004" chapter). The ridge was rifted from the Eurasian continental margin at ~57 Ma (Fig. F1) (Jokat et al., 1992, 1995). Since the rifting event and the concurrent tilting and erosion of this sliver of the outer continental margin, the Lomonosov Ridge subsided while hemipelagic and pelagic sediments were deposited above the angular rifting unconformity (see Fig. F7A in the "Sites M0001–M0004" chapter).The sections recovered from the four sites drilled during Expedition 302 can be correlated using their seismic signature, physical properties (porosity, magnetic susceptibility, resistivity, and P-wave velocity), chemostratigraphy (ammonia content of pore waters), lithostratigraphy, and biostratigraphy. The lithostratigraphy of the composite section combined with biostratigraphy provides an insight into the complex history of deposition, erosion, and preservation of the biogenic fraction. Eventually, the ridge subsided to its present water depth as it drifted from the Eurasian margin. In this chapter, we compare a simple model of subsidence history with the sedimentary record recovered from atop the ridge
Autocatalytic plume pinch-off
A localized source of buoyancy flux in a non-reactive fluid medium creates a
plume. The flux can be provided by either heat, a compositional difference
between the fluid comprising the plume and its surroundings, or a combination
of both. For autocatalytic plumes produced by the iodate-arsenous acid
reaction, however, buoyancy is produced along the entire reacting interface
between the plume and its surroundings. Buoyancy production at the moving
interface drives fluid motion, which in turn generates flow that advects the
reaction front. As a consequence of this interplay between fluid flow and
chemical reaction, autocatalytic plumes exhibit a rich dynamics during their
ascent through the reactant medium. One of the more interesting dynamical
features is the production of an accelerating vortical plume head that in
certain cases pinches-off and detaches from the upwelling conduit. After
pinch-off, a new plume head forms in the conduit below, and this can lead to
multiple generations of plume heads for a single plume initiation. We
investigated the pinch-off process using both experimentation and simulation.
Experiments were performed using various concentrations of glycerol, in which
it was found that repeated pinch-off occurs exclusively in a specific
concentration range. Autocatalytic plume simulations revealed that pinch-off is
triggered by the appearance of accelerating flow in the plume conduit.Comment: 10 figures. Accepted for publication in Phys Rev E. See also
http://www.physics.utoronto.ca/nonlinear/papers_chemwave.htm
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