2,386 research outputs found
Nonlinear normal modes, modal interactions and isolated resonance curves
The objective of the present study is to explore the connection between the
nonlinear normal modes of an undamped and unforced nonlinear system and the
isolated resonance curves that may appear in the damped response of the forced
system. To this end, an energy balancing technique is used to predict the
amplitude of the harmonic forcing that is necessary to excite a specific
nonlinear normal mode. A cantilever beam with a nonlinear spring at its tip
serves to illustrate the developments. The practical implications of isolated
resonance curves are also discussed by computing the beam response to sine
sweep excitations of increasing amplitudes.Comment: Journal pape
Gilbert damping of high anisotropy Co/Pt multilayers
Using broadband ferromagnetic resonance, we measure the damping parameter of
[Co(5 \r{A})/Pt(3 \r{A})] multilayers whose growth was optimized to
maximize the perpendicular anisotropy. Structural characterizations indicate
abrupt interfaces essentially free of intermixing despite the miscible
character of Co and Pt. Gilbert damping parameters as low as 0.021 can be
obtained despite a magneto-crystalline anisotropy as large as
. The inhomogeneous broadening accounts for part of the
ferromagnetic resonance linewidth, indicating some structural disorder leading
to a equivalent 20 mT of inhomogenity of the effective field. The unexpectedly
relatively low damping factor indicates that the presence of the Pt heavy metal
within the multilayer may not be detrimental to the damping provided that
intermixing is avoided at the Co/Pt interfaces
Clockwise Stellar Disk and the Dark Mass in the Galactic Center
Two disks of young stars have recently been discovered in the Galactic
Center. The disks are rotating in the gravitational field of the central black
hole at radii r=0.1-0.3 pc and thus open a new opportunity to measure the
central mass. We find that the observed motion of stars in the clockwise disk
implies M=4.3+/-0.5 million solar masses for the fiducial distance to the
Galactic Center R_0=8 kpc and derive the scaling of M with R_0. As a tool for
our estimate we use orbital roulette, a recently developed method. The method
reconstructs the three-dimensional orbits of the disk stars and checks the
randomness of their orbital phases. We also estimate the three-dimensional
positions and orbital eccentricities of the clockwise-disk stars.Comment: Comments: 16 pages, 5 figures, ApJ, in pres
Quantum phase transition of dynamical resistance in a mesoscopic capacitor
We study theoretically dynamic response of a mesoscopic capacitor, which
consists of a quantum dot connected to an electron reservoir via a point
contact and capacitively coupled to a gate voltage. A quantum Hall edge state
with a filling factor nu is realized in a strong magnetic field applied
perpendicular to the two-dimensional electron gas. We discuss a noise-driven
quantum phase transition of the transport property of the edge state by taking
into account an ohmic bath connected to the gate voltage. Without the noise,
the charge relaxation for nu>1/2 is universally quantized at R_q=h/(2e^2),
while for nu<1/2, the system undergoes the Kosterlitz-Thouless transtion, which
drastically changes the nature of the dynamical resistance. The phase
transition is facilitated by the noisy gate voltage, and we see that it can
occur even for an integer quantum Hall edge at nu=1. When the dissipation by
the noise is sufficiently small, the quantized value of R_q is shifted by the
bath impedance.Comment: 5 pages, 2 figures, proceeding of the 19th International Conference
on the Application of High Magnetic Fields in Semiconductor Physics and
Nanotechnology (HMF-19
A transmission problem across a fractal self-similar interface
We consider a transmission problem in which the interior domain has
infinitely ramified structures. Transmission between the interior and exterior
domains occurs only at the fractal component of the interface between the
interior and exterior domains. We also consider the sequence of the
transmission problems in which the interior domain is obtained by stopping the
self-similar construction after a finite number of steps; the transmission
condition is then posed on a prefractal approximation of the fractal interface.
We prove the convergence in the sense of Mosco of the energy forms associated
with these problems to the energy form of the limit problem. In particular,
this implies the convergence of the solutions of the approximated problems to
the solution of the problem with fractal interface. The proof relies in
particular on an extension property. Emphasis is put on the geometry of the
ramified domain. The convergence result is obtained when the fractal interface
has no self-contact, and in a particular geometry with self-contacts, for which
an extension result is proved
Active hard-spheres in infinitely many dimensions
Few equilibrium --even less so nonequilibrium-- statistical-mechanical models
with continuous degrees of freedom can be solved exactly. Classical
hard-spheres in infinitely many space dimensions are a notable exception. We
show that even without resorting to a Boltzmann distribution, dimensionality is
a powerful organizing device to explore the stationary properties of active
hard-spheres evolving far from equilibrium. In infinite dimensions, we compute
exactly the stationary state properties that govern and characterize the
collective behavior of active hard-spheres: the structure factor and the
equation of state for the pressure. In turn, this allows us to account for
motility-induced phase-separation. Finally, we determine the crowding density
at which the effective propulsion of a particle vanishes.Comment: Main text : 6 pages, 2 figures. Supplemental material : 7 pages, 2
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