42,151 research outputs found
An LU implicity scheme for high speed inlet analysis
A numerical method is developed to analyze the inviscid flowfield of a high speed inlet by the solution of the Euler equations. The lower-upper implicit scheme in conjunction with adaptive dissipation proves to be an efficient and robust nonoscillatory shock capturing technique for high Mach number flows as well as for transonic flows
Sliding elastic lattice: an explanation of the motion of superconducting vortices
We introduce a system where an elastic lattice of particles is moved slowly
at a constant velocity under the influence of a local external potential,
construct a rigid-body model through simplification processes, and show that
the two systems produce similar results. Then, we apply our model to a
superconducting vortex system and produce path patterns similar to the ones
reported in [Lee et al., Phys. Rev. B 84, 060515 (2011)] suggesting that the
reasoning of the simplification processes in this paper can be a possible
explanation of the experimentally observed phenomenon.Comment: 5 pages, 3 figures, Submitted to Physical Review Letters; Reference
[17] Lee et al., Phys. Rev. B Accepted changed to Lee et al., Phys. Rev. B
84, 060515 (2011
Formation of recollimation shocks in jets of high-mass X-ray binaries
We study conditions for formation of recollimation shocks in jets interacting
with stellar winds in high-mass X-ray binaries. We show the existence of a
critical jet power, dependent on the wind rate and velocity and the jet
velocity, above which a recollimation shock is not formed. For jet powers below
critical, we derive the location of the shock. We show that surface shocks may
still exist above the critical power, but only occupy a small volume of the jet
and do not significantly alter the jet opening angle. We test these prediction
by 3-D numerical simulations, which confirm the existence and the value of the
critical power. We apply our results to Cyg X-1 and Cyg X-3.Comment: MNRAS, in pres
Initial Observations of Sunspot Oscillations Excited by Solar Flare
Observations of a large solar flare of December 13, 2006, using Solar Optical
Telescope (SOT) on Hinode spacecraft revealed high-frequency oscillations
excited by the flare in the sunspot chromosphere. These oscillations are
observed in the region of strong magnetic field of the sunspot umbra, and may
provide a new diagnostic tool for probing the structure of sunspots and
understanding physical processes in solar flares.Comment: 10 pages, 6 figures, ApJL in pres
Error estimates for interpolation of rough data using the scattered shifts of a radial basis function
The error between appropriately smooth functions and their radial basis
function interpolants, as the interpolation points fill out a bounded domain in
R^d, is a well studied artifact. In all of these cases, the analysis takes
place in a natural function space dictated by the choice of radial basis
function -- the native space. The native space contains functions possessing a
certain amount of smoothness. This paper establishes error estimates when the
function being interpolated is conspicuously rough.Comment: 12 page
Sustaining Economic Exploitation of Complex Ecosystems in Computational Models of Coupled Human-Natural Networks
Understanding ecological complexity has stymied scientists for decades. Recent elucidation of the famously coined "devious strategies for stability in enduring natural systems" has opened up a new field of computational analyses of complex ecological networks where the nonlinear dynamics of many interacting species can be more realistically mod-eled and understood. Here, we describe the first extension of this field to include coupled human-natural systems. This extension elucidates new strategies for sustaining extraction of biomass (e.g., fish, forests, fiber) from ecosystems that account for ecological complexity and can pursue multiple goals such as maximizing economic profit, employment and carbon sequestration by ecosystems. Our more realistic modeling of ecosystems helps explain why simpler "maxi-mum sustainable yield" bioeconomic models underpinning much natural resource extraction policy leads to less profit, biomass, and biodiversity than predicted by those simple models. Current research directions of this integrated natu-ral and social science include applying artificial intelligence, cloud computing, and multiplayer online games
Nonlinear Development of Streaming Instabilities In Strongly Magnetized Plasmas
The nonlinear development of streaming instabilities in the current layers
formed during magnetic reconnection with a guide field is explored. Theory and
3-D particle-in-cell simulations reveal two distinct phases. First, the
parallel Buneman instability grows and traps low velocity electrons. The
remaining electrons then drive two forms of turbulence: the parallel
electron-electron two-stream instability and the nearly-perpendicular lower
hybrid instability. The high velocity electrons resonate with the turbulence
and transfer momentum to the ions and low velocity electrons.Comment: Accepted by PR
Large Amplitude Dynamics of the Pairing Correlations in a Unitary Fermi Gas
A unitary Fermi gas has a surprisingly rich spectrum of large amplitude modes
of the pairing field alone, which defies a description within a formalism
involving only a reduced set of degrees of freedom, such as quantum
hydrodynamics or a Landau-Ginzburg-like description. These modes are very slow,
with oscillation frequencies well below the pairing gap, which makes their
damping through quasiparticle excitations quite ineffective. In atomic traps
these modes couple naturally with the density oscillations, and the
corresponding oscillations of the atomic cloud are an example of a new type of
collective mode in superfluid Fermi systems. They have lower frequencies than
the compressional collective hydrodynamic oscillations, have a non-spherical
momentum distribution, and could be excited by a quick time variation of the
scattering length.Comment: 4 pages, 3 figures, published version, updated figures and a number
of change
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