736 research outputs found
GASLESS COMBUSTION FRONTS WITH HEAT LOSS
For a model of gasless combustion with heat loss, we use geometric s
ingular
perturbation theory to show existence of traveling combustion fr
onts. We show that the
fronts are nonlinearly stable in an appropriate sense if an Evans fun
ction criterion, which
can be verified numerically, is satisfied. For a solid reactant and exot
hermicity parameter
that is not too large, we verify numerically that the criterion is satisfi
ed
Critical velocity of a mobile impurity in one-dimensional quantum liquids
We study the notion of superfluid critical velocity in one spatial dimension.
It is shown that for heavy impurities with mass exceeding a critical mass
, the dispersion develops periodic metastable branches resulting
in dramatic changes of dynamics in the presence of an external driving force.
In contrast to smooth Bloch Oscillations for , a heavy impurity
climbs metastable branches until it reaches a branch termination point or
undergoes a random tunneling event, both leading to an abrupt change in
velocity and an energy loss. This is predicted to lead to a non-analytic
dependence of the impurity drift velocity on small forces.Comment: 5 pages, 2 figures; New version with Supplemental Material (3 pages,
6 figures); Accepted to PR
Global shallow water magnetohydrodynamic waves in the solar tachocline
We derive analytical solutions and dispersion relations of global magnetic
Poincar\'e (magneto-gravity) and magnetic Rossby waves in the approximation of
shallow water magnetohydrodynamics. The solutions are obtained in a rotating
spherical coordinate system for strongly and weakly stable stratification
separately in the presence of toroidal magnetic field. In both cases magnetic
Rossby waves split into fast and slow magnetic Rossby modes. In the case of
strongly stable stratification (valid in the radiative part of the tachocline)
all waves are slightly affected by the layer thickness and the toroidal
magnetic field, while in the case of weakly stable stratification (valid in the
upper overshoot layer of the tachocline) magnetic Poincar\'e and fast magnetic
Rossby waves are found to be concentrated near the solar equator, leading to
equatorially trapped waves. However, slow magnetic Rossby waves tend to
concentrate near the poles, leading to polar trapped waves. The frequencies of
all waves are smaller in the upper weakly stable stratification region than in
the lower strongly stable stratification one
Computer mapping of LANDSAT data for environmental applications
The author has identified the following significant results. Land cover overlays and maps produced from LANDSAT are providing information on existing land use and resources throughout the 208 study area. The overlays are being used to delineate drainage areas of a predominant land cover type. Information on cover type is also being combined with other pertinent data to develop estimates of sediment and nutrients flows from the drainage area. The LANDSAT inventory of present land cover together with population projects is providing a basis for developing maps of anticipated land use patterns required to evaluate impact on water quality which may result from these patterns. Overlays of forest types were useful for defining wildlife habitat and vegetational resources in the region. LANDSAT data and computer assisted interpretation was found to be a rapid cost effective procedure for inventorying land cover on a regional basis. The entire 208 inventory which include acquisition of ground truth, LANDSAT tapes, computer processing, and production of overlays and coded tapes was completed within a period of 2 months at a cost of about 0.6 cents per acre, a significant improvement in time and cost over conventional photointerpretation and mapping techniques
Neutral Plasma Oscillations at Zero Temperature
We use cold plasma theory to calculate the response of an ultracold neutral
plasma to an applied rf field. The free oscillation of the system has a
continuous spectrum and an associated damped quasimode. We show that this
quasimode dominates the driven response. We use this model to simulate plasma
oscillations in an expanding ultracold neutral plasma, providing insights into
the assumptions used to interpret experimental data [Phys. Rev. Lett. 85, 318
(2000)].Comment: 4.3 pages, including 3 figure
Inviscid dynamical structures near Couette flow
Consider inviscid fluids in a channel {-1<y<1}. For the Couette flow
v_0=(y,0), the vertical velocity of solutions to the linearized Euler equation
at v_0 decays in time. At the nonlinear level, such inviscid damping has not
been proved. First, we show that in any (vorticity) H^{s}(s<(3/2)) neighborhood
of Couette flow, there exist non-parallel steady flows with arbitrary minimal
horizontal period. This implies that nonlinear inviscid damping is not true in
any (vorticity) H^{s}(s<(3/2)) neighborhood of Couette flow and for any
horizontal period. Indeed, the long time behavior in such neighborhoods are
very rich, including nontrivial steady flows, stable and unstable manifolds of
nearby unstable shears. Second, in the (vorticity) H^{s}(s>(3/2)) neighborhood
of Couette, we show that there exist no non-parallel steadily travelling flows
v(x-ct,y), and no unstable shears. This suggests that the long time dynamics in
H^{s}(s>(3/2)) neighborhoods of Couette might be much simpler. Such contrasting
dynamics in H^{s} spaces with the critical power s=(3/2) is a truly nonlinear
phenomena, since the linear inviscid damping near Couette is true for any
initial vorticity in L^2
New vector-scalar contributions to neutrinoless double beta decay and constraints on R-parity violation
We show that in minimal supersymmetric standard model (MSSM) with R-parity
breaking as well as in the left-right symmetric model, there are new observable
contributions to neutrinoless double beta decay arising from hitherto
overlooked diagrams involving the exchange of one W boson and one scalar boson.
In particular, in the case of MSSM, the present experimental bounds on
neutrinoless double beta decay lifetime improves the limits on certain R-parity
violating couplings by about two orders of magnitude. It is shown that similar
diagrams also lead to enhanced rates for conversion in
nuclei, which are in the range accessible to ongoing experiments.Comment: Latex file; 9 pages; 3 figures available on reques
BVRIJK light curves and radial velocity curves for selected Magellanic Cloud Cepheids
We present high precision and well sampled BVRIJK light curves and radial
velocity curves for a sample of five Cepheids in the SMC. In addition we
present radial velocity curves for three Cepheids in the LMC. The low
metallicity (Fe/H ~ -0.7) SMC stars have been selected for use in a
Baade-Wesselink type analysis to constrain the metallicity effect on the
Cepheid Period-Luminosity relation. The stars have periods of around 15 days so
they are similar to the Cepheids observed by the Extragalactic Distance Scale
Key Project on the Hubble Space Telescope. We show that the stars are
representative of the SMC Cepheid population at that period and thus will
provide a good sample for the proposed analysis. The actual Baade-Wesselink
analysis are presented in a companion paper.Comment: Accepted for publication in A&A, 23 pages, 10 figures, data tables
will be made available electronically from the CD
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