5,857 research outputs found
Lagrangian Formalism in Perturbed Nonlinear Klein-Gordon Equations
We develop an alternative approach to study the effect of the generic
perturbation (in addition to explicitly considering the loss term) in the
nonlinear Klein-Gordon equations. By a change of the variables that cancel the
dissipation term we are able to write the Lagrangian density and then,
calculate the Lagrangian as a function of collective variables. We use the
Lagrangian formalism together with the Rice {\it Ansatz} to derive the
equations of motion of the collective coordinates (CCs) for the perturbed
sine-Gordon (sG) and systems. For the collective coordinates,
regardless of the {\it Ansatz} used, we show that, for the nonlinear
Klein-Gordon equations, this approach is equivalent to the {\it Generalized
Traveling Wave Ansatz} ({\it GTWA})Comment: 9 page
AuNx stabilization with interstitial nitrogen atoms: A Density Functional Theory Study
Researchers have been studying 4d and 5d Series Transition Metal Nitrides lately as a result of the experimental production of AuN, PtN, CuN. In this paper, we used the Density Functional Theory (DFT) implementing a pseudopotential plane-wave method to study the incorporation of nitrogen atoms in the face-centered cube (fcc) lattice of gold (Au). First, we took the fcc structure of gold, and gradually located the nitrogen atoms in tetrahedral (TH) and octahedral (OH) interstitial sites. AuN stabilized in: 2OH (30%), 4OH and 4TH (50%), 4OH - 2TH (close to the wurtzite structure) and 6TH (60%). This leads us to think that AuN behaves like a Transition Metal Nitride since the nitrogen atoms look for tetrahedral sites. © Published under licence by IOP Publishing Ltd
ac driven sine-Gordon solitons: dynamics and stability
The ac driven sine-Gordon equation is studied analytically and numerically,
with the aim of providing a full description of how soliton solutions behave.
To date, there is much controversy about when ac driven dc motion is possible.
Our work shows that kink solitons exhibit dc or oscillatory motion depending on
the relation between their initial velocity and the force parameters. Such
motion is proven to be impossible in the presence of damping terms. For
breathers, the force amplitude range for which they exist when dissipation is
absent is found. All the analytical results are compared with numerical
simulations, which in addition exhibit no dc motion at all for breathers, and
an excellent agreement is found. In the conclusion, the generality of our
results and connections to others systems for which a similar phenomenology may
arise are discussed.Comment: 10 pages, latex, PostScript figures included with epsfig, to appear
in European Physical Journal B, see GISC homepage at
http://valbuena.fis.ucm.es/ for related wor
Non-sinusoidal current and current reversals in a gating ratchet
In this work, the ratchet dynamics of Brownian particles driven by an
external sinusoidal (harmonic) force is investigated. The gating ratchet effect
is observed when another harmonic is used to modulate the spatially symmetric
potential in which the particles move. For small amplitudes of the harmonics,
it is shown that the current (average velocity) of particles exhibits a
sinusoidal shape as a function of a precise combination of the phases of both
harmonics. By increasing the amplitudes of the harmonics beyond the small-limit
regime, departures from the sinusoidal behavior are observed and current
reversals can also be induced. These current reversals persist even for the
overdamped dynamics of the particles.Comment: 11 pages, 9 figure
Exact stationary solutions of the parametrically driven and damped nonlinear Dirac equation
Two exact stationary soliton solutions are found in the parametrically driven and damped nonlinear Dirac equation. The parametric force
considered is a complex ac force. The solutions appear when their frequencies are locked to half the frequency of the parametric force, and
their phases satisfy certain conditions depending on the force amplitude and on the damping coe cient. Explicit expressions for the charge,
the energy, and the momentum of these solutions are provided. Their stability is studied via a variational method using an ansatz with only
two collective coordinates. Numerical simulations con rm that one of the solutions is stable, while the other is an unstable saddle point.
Consequently, the stabilization of damped Dirac solitons can be achieved via time-periodic parametric excitations.Junta de Andalucía and Ministerio de Economía y Competitividad of Spain FIS2017-89349-PMinisterio de Ciencia, Innovación y Universidades of Spain PGC2018-093998-BI0
Obtaining Au thin films in atmosphere of reactive nitrogen through magnetron sputtering
4d and 5d series of the transition metals are used to the obtaining nitrides metallic, due to the synthesis of PtN, AgN and AuN in the last years. Different nitrides are obtained in the Plasma Assisted Physics Vapour Deposition system, due to its ionization energy which is necessary for their formation. In this paper a Magnetron Sputtering system was used to obtain Au thin films on Si wafers in Nitrogen atmosphere. The substrate temperature was varied between 500 to 950°C. The samples obtained at high temperatures (>500°C) show Au, Si and N elements, as it is corroborated in the narrow spectrum obtained for X-Ray Photoelectron Spectroscopy; besides the competition of orientation crystallographic texture between (111) and (311) directions was present in the X-Ray Diffraction analysis to the sample heated at 950°C
Reply to Comment on "Existence of Internal Modes of sine-Gordon Kinks"
In this reply to the comment by C. R. Willis, we show, by quoting his own
statements, that the simulations reported in his original work with Boesch
[Phys. Rev. B 42, 2290 (1990)] were done for kinks with nonzero initial
velocity, in contrast to what Willis claims in his comment. We further show
that his alleged proof, which assumes among other approximations that kinks are
initially at rest, is not rigorous but an approximation. Moreover, there are
other serious misconceptions which we discuss in our reply. As a consequence,
our result that quasimodes do not exist in the sG equation [Phys. Rev. E 62,
R60 (2000)] remains true.Comment: Reply to a comment by C. R. Willis on Phys. Rev. E 62, R60 (2000), to
appear in Physical Review
Speed-of-light pulses in the massless nonlinear Dirac equation with a potential
We consider the massless nonlinear Dirac (NLD) equation in dimension
with scalar-scalar self-interaction in the
presence of three external electromagnetic potentials , a potential
barrier, a constant potential, and a potential well. By solving numerically the
NLD equation, we find that, for all three cases, after a short transit time,
the initial pulse breaks into two pulses which are solutions of the massless
linear Dirac equation traveling in opposite directions with the speed of light.
During this splitting the charge and the energy are conserved, whereas the
momentum is conserved when the solutions possess specific symmetries. For the
case of the constant potential, we derive exact analytical solutions of the
massless NLD equation that are also solutions of the massless linearized Dirac
equation.Comment: 11 pages, 7 figure
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