7,728 research outputs found
Preliminary characterization of a one-axis acoustic system
The acoustic fields and levitation forces produced along the axis of a single-axis resonance system were measured. The system consisted of a St. Clair generator and a planar reflector. The levitation force was measured for bodies of various sizes and geometries (i.e., spheres, cylinders, and discs). The force was found to be roughly proportional to the volume of the body until the characteristic body radius reaches approximately 2/k (k = wave number). The acoustic pressures along the axis were modeled using Huygens principle and a method of imaging to approximate multiple reflections. The modeled pressures were found to be in reasonable agreement with those measured with a calibrated microphone
Method and apparatus for shaping and enhancing acoustical levitation forces
A method and apparatus for enhancing and shaping acoustical levitation forces in a single-axis acoustic resonance system wherein specially shaped drivers and reflectors are utilized to enhance to levitation force and better contain fluid substance by means of field shaping is described
AUTOMATIC SUBGROUPING OF MULTITRACK AUDIO
Subgrouping is a mixing technique where the outputs of a subset of audio tracks in a multitrack are summed to a single audio bus. This is done so that the mix engineer can apply signal processing to an entire subgroup, speed up the mix work flow and manipu-late a number of audio tracks at once. In this work, we investigate which audio features from a set of 159 can be used to automati-cally subgroup multitrack audio. We determine a subset of audio features from the original 159 audio features to use for automatic subgrouping, by performing feature selection using a Random For-est classifier on a dataset of 54 individual multitracks. We show that by using agglomerative clustering on 5 test multitracks, the entire set of audio features incorrectly clusters 35.08 % of the audio tracks, while the subset of audio features incorrectly clusters only 7.89 % of the audio tracks. Furthermore, we also show that using the entire set of audio features, ten incorrect subgroups are created. However, when using the subset of audio features, only five incor-rect subgroups are created. This indicates that our reduced set of audio features provides a significant increase in classification ac-curacy for the creation of subgroups automatically. 1
Fermionic functional renormalization group for first-order phase transitions: a mean-field model
First-order phase transitions in many-fermion systems are not detected in the
susceptibility analysis of common renormalization-group (RG) approaches. Here
we introduce a counterterm technique within the functional
renormalization-group (fRG) formalism which allows access to all stable and
metastable configurations. It becomes possible to study symmetry-broken states
which occur through first-order transitions as well as hysteresis phenomena.
For continuous transitions, the standard results are reproduced. As an example,
we study discrete-symmetry breaking in a mean-field model for a commensurate
charge-density wave. An additional benefit of the approach is that away from
the critical temperature for the breaking of discrete symmetries large
interactions can be avoided at all RG scales.Comment: 17 pages, 8 figures. v2 corrects typos, adds references and a
discussion of the literatur
Antiferromagnetically coupled CoFeB/Ru/CoFeB trilayers
This work reports on the magnetic interlayer coupling between two amorphous
CoFeB layers, separated by a thin Ru spacer. We observe an antiferromagnetic
coupling which oscillates as a function of the Ru thickness x, with the second
antiferromagnetic maximum found for x=1.0 to 1.1 nm. We have studied the
switching of a CoFeB/Ru/CoFeB trilayer for a Ru thickness of 1.1 nm and found
that the coercivity depends on the net magnetic moment, i.e. the thickness
difference of the two CoFeB layers. The antiferromagnetic coupling is almost
independent on the annealing temperatures up to 300 degree C while an annealing
at 350 degree C reduces the coupling and increases the coercivity, indicating
the onset of crystallization. Used as a soft electrode in a magnetic tunnel
junction, a high tunneling magnetoresistance of about 50%, a well defined
plateau and a rectangular switching behavior is achieved.Comment: 3 pages, 3 figure
Relativistic photoelectron spectra in the ionization of atoms by elliptically polarized light
Relativistic tunnel ionization of atoms by intense, elliptically polarized
light is considered. The relativistic version of the Landau-Dykhne formula is
employed. The general analytical expression is obtained for the relativistic
photoelectron spectra. The most probable angle of electron emission, the
angular distribution near this angle, the position of the maximum and the width
of the energy spectrum are calculated. In the weak field limit we obtain the
familiar non-relativistic results. For the case of circular polarization our
analytical results are in agreement with recent derivations of Krainov [V.P.
Krainov, J. Phys. B, {\bf 32}, 1607 (1999)].Comment: 8 pages, 2 figures, accepted for publication in Journal of Physics
Relativistic electronic dressing in laser-assisted ionization of atomic hydrogen by electron impact
Within the framework of the coplanar binary geometry where it is justified to
use plane wave solutions for the study of the reaction and in the
presence of a circularly polarized laser field, we introduce as a first step
the DVRPWBA1 (Dirac-Volkov Plane Wave Born Approximation1) where we take into
account only the relativistic dressing of the incident and scattered electrons.
Then, we introduce the DVRPWBA2 (Dirac-Volkov Plane Wave Born Approximation2)
where we take totally into account the relativistic dressing of the incident,
scattered and ejected electrons. We then compare the corresponding triple
differential cross sections for laser-assisted ionization of atomic hydrogen by
electron impact both for the non relativistic and the relativistic regime.Comment: 18 pages, Latex, 7 figure
Relativistic semiclassical approach in strong-field nonlinear photoionization
Nonlinear relativistic ionization phenomena induced by a strong laser
radiation with elliptically polarization are considered. The starting point is
the classical relativistic action for a free electron moving in the
electromagnetic field created by a strong laser beam. The application of the
relativistic action to the classical barrier-suppression ionization is briefly
discussed. Further the relativistic version of the Landau-Dykhne formula is
employed to consider the semiclassical sub-barrier ionization. Simple
analytical expressions have been found for: (i) the rates of the strong-field
nonlinear ionization including relativistic initial and final state effects;
(ii) the most probable value of the components of the photoelectron final state
momentum; (iii) the most probable direction of photoelectron emission and (iv)
the distribution of the photoelectron momentum near its maximum value.Comment: 13 pages, 3 figures, to be published in Phys. Rev.
Formation of an Icosahedral Structure during the Freezing of Gold Nanoclusters: Surface-Induced Mechanism
The freezing behavior of gold nanoclusters was studied by employing molecular
dynamics simulations based on a semi-empirical embedded-atom method.
Investigations of the gold nanoclusters revealed that, just after freezing,
ordered nano-surfaces with a fivefold symmetry were formed with interior atoms
remaining in the disordered state. Further lowering of temperatures induced
nano-crystallization of the interior atoms that proceeded from the surface
towards the core region, finally leading to an icosahedral structure. These
dynamic processes explain why the icosahedral cluster structure is dominantly
formed in spite of its energetic metastability.Comment: 9 pages, 4 figures(including 14 eps-files
Non-dipole recollision-gated double ionization and observable effects
Using a three-dimensional semiclassical model, we study double ionization for
strongly-driven He fully accounting for magnetic field effects. For linearly
and slightly elliptically polarized laser fields, we show that recollisions and
the magnetic field combined act as a gate. This gate favors more transverse -
with respect to the electric field - initial momenta of the tunneling electron
that are opposite to the propagation direction of the laser field. In the
absence of non-dipole effects, the transverse initial momentum is symmetric
with respect to zero. We find that this asymmetry in the transverse initial
momentum gives rise to an asymmetry in a double ionization observable. Finally,
we show that this asymmetry in the transverse initial momentum of the tunneling
electron accounts for a recently-reported unexpectedly large average sum of the
electron momenta parallel to the propagation direction of the laser field.Comment: Amended the focus of the paper and discussion. 9 pages, 7 figure
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