23,396 research outputs found
Surface response of spherical core-shell structured nanoparticle by optically induced elastic oscillations of soft shell against hard core
The optically induced oscillatory response of a spherical two-component,
shell-core structured, nanoparticle by nodeless elastic vibrations of soft
peripheral shell against hard and dynamically immobile inner core is
considered. The eigenfrequencies of the even-parity, spheroidal and odd-parity
torsional vibrational modes trapped in the finite-depth shell are obtained
which are of practical interest for modal specification of individual
resonances in spectra of resonant scattering of long wavelength electromagnetic
waves by ultrafine particles.Comment: Surface Review and Letters (World Scientific) Year: 2009 Vol: 16
Issue: 1 (February 2009) Page: 5 - 1
Disturbance Rejection in Multi-DOF Local Magnetic Actuation for Robotic Abdominal Surgery
The potential of multi-degrees-of-freedom (DOFs) local magnetic actuation (LMA) has been established in recent years for dexterous minimally invasive surgical manipulations. Nonetheless, having multiple magnetic based units, one for each DOF, within a close vicinity to each other leads to magnetic field interaction among the magnetic sources, hence, resulting in a disturbance to a given LMA unit. It is further realized that the disturbance is a result of actuation effort by the neighboring magnetic sources forming the LMA units, and that the actuation command to all LMA units is a known information to the controller. Therefore, partial information of the disturbance is known and can be exploited in a disturbance rejection strategy. In this letter, this disturbance is modeled and used to augment a simplified model of the systems dynamics of the LMA-based surgical manipulators. The internal model principle (IMP) strategy is selected in which an observer is designed to estimate the disturbance to be rejected. Numerical simulation as well as experimental validation were performed to validate the efficacy of the IMP. The results serve to remove a significant technical hurdle in bringing the new emerging technique of LMA into practical reality for abdominal surgeries
Post-Newtonian Models of Binary Neutron Stars
Using an energy variational method, we calculate quasi-equilibrium
configurations of binary neutron stars modeled as compressible triaxial
ellipsoids obeying a polytropic equation of state. Our energy functional
includes terms both for the internal hydrodynamics of the stars and for the
external orbital motion. We add the leading post-Newtonian (PN) corrections to
the internal and gravitational energies of the stars, and adopt hybrid orbital
terms which are fully relativistic in the test-mass limit and always accurate
to PN order. The total energy functional is varied to find quasi-equilibrium
sequences for both corotating and irrotational binaries in circular orbits. We
examine how the orbital frequency at the innermost stable circular orbit
depends on the polytropic index n and the compactness parameter GM/Rc^2. We
find that, for a given GM/Rc^2, the innermost stable circular orbit along an
irrotational sequence is about 17% larger than the innermost secularly stable
circular orbit along the corotating sequence when n=0.5, and 20% larger when
n=1. We also examine the dependence of the maximum neutron star mass on the
orbital frequency and find that, if PN tidal effects can be neglected, the
maximum equilibrium mass increases as the orbital separation decreases.Comment: 53 pages, LaTex, 9 figures as 10 postscript files, accepted by Phys.
Rev. D, replaced version contains updated reference
Unified theory for Goos-H\"{a}nchen and Imbert-Fedorov effects
A unified theory is advanced to describe both the lateral Goos-H\"{a}nchen
(GH) effect and the transverse Imbert-Fedorov (IF) effect, through representing
the vector angular spectrum of a 3-dimensional light beam in terms of a 2-form
angular spectrum consisting of its 2 orthogonal polarized components. From this
theory, the quantization characteristics of the GH and IF displacements are
obtained, and the Artmann formula for the GH displacement is derived. It is
found that the eigenstates of the GH displacement are the 2 orthogonal linear
polarizations in this 2-form representation, and the eigenstates of the IF
displacement are the 2 orthogonal circular polarizations. The theoretical
predictions are found to be in agreement with recent experimental results.Comment: 15 pages, 3 figure
Transferring orbital and spin angular momenta of light to atoms
Light beams carrying orbital angular momentum, such as Laguerre-Gaussian
beams, give rise to the violation of the standard dipolar selection rules
during the interaction with matter yielding, in general, an exchange of angular
momentum larger than hbar per absorbed photon. By means of ab initio 3D
numerical simulations, we investigate in detail the interaction of a hydrogen
atom with intense Gaussian and Laguerre-Gaussian light pulses. We analyze the
dependence of the angular momentum exchange with the polarization, the orbital
angular momentum, and the carrier-envelope phase of light, as well as with the
relative position between the atom and the light vortex. In addition, a
quantum-trajectory approach based on the de Broglie-Bohm formulation of quantum
mechanics is used to gain physical insight into the absorption of angular
momentum by the hydrogen atom
Universality class of the restricted solid-on-solid model with hopping
We study the restricted solid-on-solid (RSOS) model with finite hopping
distance , using both analytical and numerical methods. Analytically, we
use the hard-core bosonic field theory developed by the authors [Phys. Rev. E
{\bf 62}, 7642 (2000)] and derive the Villain-Lai-Das Sarma (VLD) equation for
the case which corresponds to the conserved RSOS (CRSOS) model
and the Kardar-Parisi-Zhang (KPZ) equation for all finite values of .
Consequently, we find that the CRSOS model belongs to the VLD universality
class and the RSOS models with any finite hopping distance belong to the KPZ
universality class. There is no phase transition at a certain finite hopping
distance contrary to the previous result. We confirm the analytic results using
the Monte Carlo simulations for several values of the finite hopping distance.Comment: 13 pages, 3 figure
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