17,263 research outputs found
Harmonic coordinates in the string and membrane equations
In this note, we first show that the solutions to Cauchy problems for two
versions of relativistic string and membrane equations are diffeomorphic. Then
we investigate the coordinates transformation presented in Ref. [9] (see (2.20)
in Ref. [9]) which plays an important role in the study on the dynamics of the
motion of string in Minkowski space. This kind of transformed coordinates are
harmonic coordinates, and the nonlinear relativistic string equations can be
straightforwardly simplified into linear wave equations under this
transformation
Onset of unsteady horizontal convection in rectangle tank at
The horizontal convection within a rectangle tank is numerically simulated.
The flow is found to be unsteady at high Rayleigh numbers. There is a Hopf
bifurcation of from steady solutions to periodic solutions, and the
critical Rayleigh number is obtained as for the
middle plume forcing at , which is much larger than the formerly obtained
value. Besides, the unstable perturbations are always generated from the
central jet, which implies that the onset of instability is due to velocity
shear (shear instability) other than thermally dynamics (thermal instability).
Finally, Paparella and Young's [J. Fluid Mech. 466 (2002) 205] first hypotheses
about the destabilization of the flow is numerically proved, i.e. the middle
plume forcing can lead to a destabilization of the flow.Comment: 4pages, 6 figures, extension of Chin. Phys. Lett. 2008, 25(6), in
pres
NNLO QCD Corrections to t-channel Single Top-Quark Production and Decay
We present a fully differential next-to-next-to-leading order calculation of
t-channel single top-quark production and decay at the LHC under narrow-width
approximation and neglecting cross-talk between incoming protons. We focus on
the fiducial cross sections at 13 TeV, finding that the next-to-next-to-leading
order QCD corrections can reach the level of -6%. The scale variations are
reduced to the level of a percent. Our results can be used to improve
experimental acceptance estimates and the measurements of the single top-quark
production cross section and the top-quark electroweak couplings.Comment: 6 pages, 4 figures, version appear on PRD rapid communicatio
Ultrafast magnetic vortex core switching driven by topological inverse Faraday effect
We present a theoretical discovery of an unconventional mechanism of inverse
Faraday effect (IFE) which acts selectively on topological magnetic structures.
The effect, topological inverse Faraday effect (TIFE), is induced by spin
Berry's phase of the magnetic structure when a circularly polarized light is
applied. Thus a spin-orbit interaction is not necessary unlike in the
conventional IFE. We demonstrate by numerical simulation that TIFE realizes
ultrafast switching of a magnetic vortex within a switching time of 150 ps
without magnetic field.Comment: 11 pages, 4 figure
The dynamics of loop formation in a semiflexible polymer
The dynamics of loop formation by linear polymer chains has been a topic of
several theoretical/experimental studies. Formation of loops and their opening
are key processes in many important biological processes. Loop formation in
flexible chains has been extensively studied by many groups. However, in the
more realistic case of semiflexible polymers, not much results are available.
In a recent study (K. P. Santo and K. L. Sebastian, Phys. Rev. E, \textbf{73},
031293 (2006)), we investigated opening dynamics of semiflexible loops in the
short chain limit and presented results for opening rates as a function of the
length of the chain. We presented an approximate model for a semiflexible
polymer in the rod limit, based on a semiclassical expansion of the bending
energy of the chain. The model provided an easy way to describe the dynamics.
In this paper, using this model, we investigate the reverse process, i.e., the
loop formation dynamics of a semiflexible polymer chain by describing the
process as a diffusion-controlled reaction. We perform a detailed
multidimensional analysis of the problem and calculate closing times for a
semiflexible chain which leads to results that are physically expected. Such a
multidimensional analysis leading to these results does not seem to exist in
the literature so far.Comment: 37 pages 4 figure
Origin of adiabatic and non-adiabatic spin transfer torques in current-driven magnetic domain wall motion
A consistent theory to describe the correlated dynamics of quantum mechanical
itinerant spins and semiclassical local magnetization is given. We consider the
itinerant spins as quantum mechanical operators, whereas local moments are
considered within classical Lagrangian formalism. By appropriately treating
fluctuation space spanned by basis functions, including a zero-mode wave
function, we construct coupled equations of motion for the collective
coordinate of the center-of-mass motion and the localized zero-mode coordinate
perpendicular to the domain wall plane. By solving them, we demonstrate that
the correlated dynamics is understood through a hierarchy of two time scales:
Boltzmann relaxation time when a non-adiabatic part of the spin-transfer torque
appears, and Gilbert damping time when adiabatic part comes up.Comment: 4 pages, 2 figure
Dynamical control of two-level system's decay and long time freezing
We investigate with exact numerical calculation coherent control of a
two-level quantum system's decay by subjecting the two-level system to many
periodic ideal phase modulation pulses. For three spectrum intensities
(Gaussian, Lorentzian, and exponential), we find both suppression and
acceleration of the decay of the two-level system, depending on difference
between the spectrum peak position and the eigen frequency of the two-level
system. Most interestingly, the decay of the two-level system freezes after
many control pulses if the pulse delay is short. The decay freezing value is
half of the decay in the first pulse delay.Comment: 6 pages, 6 figures, published in Phys. Rev.
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