13,285 research outputs found
Phonon engineering with superlattices: generalized nanomechanical potentials
Earlier implementations to simulate coherent wave propagation in
one-dimensional potentials using acoustic phonons with gigahertz-terahertz
frequencies were based on coupled nanoacoustic resonators. Here, we generalize
the concept of adiabatic tuning of periodic superlattices for the
implementation of effective one-dimensional potentials giving access to cases
that cannot be realized by previously reported phonon engineering approaches,
in particular the acoustic simulation of electrons and holes in a quantum well
or a double well potential. In addition, the resulting structures are much more
compact and hence experimentally feasible. We demonstrate that potential
landscapes can be tailored with great versatility in these multilayered
devices, apply this general method to the cases of parabolic, Morse and
double-well potentials and study the resulting stationary phonon modes. The
phonon cavities and potentials presented in this work could be probed by
all-optical techniques like pump-probe coherent phonon generation and Brillouin
scattering
Canonical Quantization of SU(3) Skyrme Model in a General Representation
A complete canonical quantization of the SU(3) Skyrme model performed in the
collective coordinate formalism in general irreducible representations. In the
case of SU(3) the model differs qualitatively in different representations. The
Wess-Zumino-Witten term vanishes in all self-adjoint representations in the
collective coordinate method for separation of space and time variables. The
canonical quantization generates representation dependent quantum mass
corrections, which can stabilize the soliton solution. The standard symmetry
breaking mass term, which in general leads to representation mixing,
degenerates to the SU(2) form in all self-adjoint representations.Comment: 24 RevTex4 pages, no figure
Effect of a Weak Electromagnetic Field on Particle Acceleration by a Rotating Black Hole
We study high energy charged particle collisions near the horizon in an
electromagnetic field around a rotating black hole and reveal the condition of
the fine-tuning to obtain arbitrarily large center-of-mass (CM) energy. We
demonstrate that the CM energy can be arbitrarily large as the uniformly
magnetized rotating black hole arbitrarily approaches maximal rotation under
the situation that a charged particle plunges from the innermost stable
circular orbit (ISCO) and collides with another particle near the horizon.
Recently, Frolov [Phys. Rev. D 85, 024020 (2012)] proposed that the CM energy
can be arbitrarily high if the magnetic field is arbitrarily strong, when a
particle collides with a charged particle orbiting the ISCO with finite energy
near the horizon of a uniformly magnetized Schwarzschild black hole. We show
that the charged particle orbiting the ISCO around a spinning black hole needs
arbitrarily high energy in the strong field limit. This suggests that Frolov's
process is unstable against the black hole spin. Nevertheless, we see that
magnetic fields may substantially promote the capability of rotating black
holes as particle accelerators in astrophysical situations.Comment: 22 pages, 4 figure
Acceleration of colliding shells around a black hole: Validity of the test particle approximation in the Banados-Silk-West process
Recently, Banados, Silk and West (BSW) showed that the total energy of two
colliding test particles has no upper limit in their center of mass frame in
the neighborhood of an extreme Kerr black hole, even if these particles were at
rest at infinity in the infinite past. We call this mechanism the BSW mechanism
or BSW process. The large energy of such particles would generate strong
gravity, although this has not been taken into account in the BSW analysis. A
similar mechanism is seen in the collision of two spherical test shells in the
neighborhood of an extreme Reissner-Nordstr\"om black hole. In this paper, in
order to draw some implications concerning the effects of gravity generated by
colliding particles in the BSW process, we study a collision of two spherical
dust shells, since their gravity can be exactly treated. We show that the
energy of two colliding shells in the center of mass frame observable from
infinity has an upper limit due to their own gravity. Our result suggests that
an upper limit also exists for the total energy of colliding particles in the
center of mass frame in the observable domain in the BSW process due the
gravity of the particles.Comment: 19 pages, 2 figures, title change
Observation of an optical non-Fermi-liquid behavior in the heavy fermion state of YbRhSi
We report far-infrared optical properties of YbRhSi for photon
energies down to 2 meV and temperatures 0.4 -- 300 K. In the coherent heavy
quasiparticle state, a linear dependence of the low-energy scattering rate on
both temperature and photon energy was found. We relate this distinct dynamical
behavior different from that of Fermi liquid materials to the non-Fermi liquid
nature of YbRhSi which is due to its close vicinity to an
antiferromagnetic quantum critical point.Comment: 5 pages, 4 figures. submitte
Electronic inhomogeneity in EuO: Possibility of magnetic polaron states
We have observed the spatial inhomogeneity of the electronic structure of a
single-crystalline electron-doped EuO thin film with ferromagnetic ordering by
employing infrared magneto-optical imaging with synchrotron radiation. The
uniform paramagnetic electronic structure changes to a uniform ferromagnetic
structure via an inhomogeneous state with decreasing temperature and increasing
magnetic field slightly above the ordering temperature. One possibility of the
origin of the inhomogeneity is the appearance of magnetic polaron states.Comment: 4 pages, 3 figure
Contour methods for long-range Ising models: weakening nearest-neighbor interactions and adding decaying fields
We consider ferromagnetic long-range Ising models which display phase
transitions. They are long-range one-dimensional Ising ferromagnets, in which
the interaction is given by with , in particular, .
For this class of models one way in which one can prove the phase transition is
via a kind of Peierls contour argument, using the adaptation of the
Fr\"ohlich-Spencer contours for , proposed by Cassandro,
Ferrari, Merola and Presutti. As proved by Fr\"ohlich and Spencer for
and conjectured by Cassandro et al for the region they could treat,
for , although in the
literature dealing with contour methods for these models it is generally
assumed that , we can show that this condition can be removed in the
contour analysis. In addition, combining our theorem with a recent result of
Littin and Picco we prove the persistence of the contour proof of the phase
transition for any . Moreover, we show that when we add a
magnetic field decaying to zero, given by and
where , the
transition still persists.Comment: 13 page
Some tests on the control of weeds in the arable land with 2,4-D. VI. On the weed control in the sweet potato and soybean fields.
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