2,909 research outputs found
Can a charged ring levitate a neutral, polarizable object? Can Earnshaw's Theorem be extended to such objects?
Stable electrostatic levitation and trapping of a neutral, polarizable object
by a charged ring is shown to be theoretically impossible. Earnshaw's Theorem
precludes the existence of such a stable, neutral particle trap.Comment: 11 pages, 1 figur
Mie scattering by a charged dielectric particle
We study for a dielectric particle the effect of surplus electrons on the
anomalous scattering of light arising from the transverse optical phonon
resonance in the particle's dielectric constant. Excess electrons affect the
polarizability of the particle by their phonon-limited conductivity, either in
a surface layer (for negative electron affinity) or the conduction band (for
positive electron affinity). We demonstrate that surplus electrons shift an
extinction resonance in the infrared. This offers an optical way to measure the
charge of the particle and thus to use it in a plasma as a minimally invasive
electric probe.Comment: 5 pages, 5 figures, accepted manuscrip
Multiphysics simulation of corona discharge induced ionic wind
Ionic wind devices or electrostatic fluid accelerators are becoming of
increasing interest as tools for thermal management, in particular for
semiconductor devices. In this work, we present a numerical model for
predicting the performance of such devices, whose main benefit is the ability
to accurately predict the amount of charge injected at the corona electrode.
Our multiphysics numerical model consists of a highly nonlinear strongly
coupled set of PDEs including the Navier-Stokes equations for fluid flow,
Poisson's equation for electrostatic potential, charge continuity and heat
transfer equations. To solve this system we employ a staggered solution
algorithm that generalizes Gummel's algorithm for charge transport in
semiconductors. Predictions of our simulations are validated by comparison with
experimental measurements and are shown to closely match. Finally, our
simulation tool is used to estimate the effectiveness of the design of an
electrohydrodynamic cooling apparatus for power electronics applications.Comment: 24 pages, 17 figure
Testing the neutrality of matter by acoustic means in a spherical resonator
New measurements to test the neutrality of matter by acoustic means are
reported. The apparatus is based on a spherical capacitor filled with gaseous
SF excited by an oscillating electric field. The apparatus has been
calibrated measuring the electric polarizability. Assuming charge conservation
in the decay of the neutron, the experiment gives a limit of
for the electron-proton charge
difference, the same limit holding for the charge of the neutron. Previous
measurements are critically reviewed and found incorrect: the present result is
the best limit obtained with this technique
Classical and quantum three-dimensional integrable systems with axial symmetry
We study the most general form of a three dimensional classical integrable
system with axial symmetry and invariant under the axis reflection. We assume
that the three constants of motion are the Hamiltonian, , with the standard
form of a kinetic part plus a potential dependent on the position only, the
-component of the angular momentum, , and a Hamiltonian-like constant,
, for which the kinetic part is quadratic in the momenta. We find
the explicit form of these potentials compatible with complete integrability.
The classical equations of motion, written in terms of two arbitrary potential
functions, is separated in oblate spheroidal coordinates. The quantization of
such systems leads to a set of two differential equations that can be presented
in the form of spheroidal wave equations.Comment: 17 pages, 3 figure
The role of angular momentum in the construction of electromagnetic multipolar fields
Multipolar solutions of Maxwell's equations are used in many practical
applications and are essential for the understanding of light-matter
interactions at the fundamental level. Unlike the set of plane wave solutions
of electromagnetic fields, the multipolar solutions do not share a standard
derivation or notation. As a result, expressions originating from different
derivations can be difficult to compare. Some of the derivations of the
multipolar solutions do not explicitly show their relation to the angular
momentum operators, thus hiding important properties of these solutions. In
this article, the relation between two of the most common derivations of this
set of solutions is explicitly shown and their relation to the angular momentum
operators is exposed.Comment: 13 pages, 2 figure
Ultrafocused electromagnetic field pulses with a hollow cylindrical waveguide
We theoretically show that a dipole externally driven by a pulse with a lower-bounded temporal width, and placed inside a cylindrical hollow waveguide, can generate a train of arbitrarily short and focused electromagnetic pulses. The waveguide encloses vacuum with perfect electric conducting walls. A dipole driven by a single short pulse, which is properly engineered to exploit the linear spectral filtering of the cylindrical hollow waveguide, excites longitudinal waveguide modes that are coherently refocused at some particular instances of time, thereby producing arbitrarily short and focused electromagnetic pulses. We numerically show that such ultrafocused pulses persist outside the cylindrical waveguide at distances comparable to its radius
Transient Heavy Element Absorption Systems in Novae: Episodic Mass Ejection from the Secondary Star
A high-resolution spectroscopic survey of postoutburst novae reveals
short-lived heavy element absorption systems in a majority of novae near
maximum light, having expansion velocities of 400-1000 km/s and velocity
dispersions between 35-350 km/s. A majority of systems are accelerated
outwardly, and they all progressively weaken and disappear over timescales of
weeks. A few of the systems having narrow, deeper absorption reveal a rich
spectrum of singly ionized Sc, Ti, V, Cr, Fe, Sr, Y, Zr, and Ba lines. Analysis
of the richest such system, in Nova LMC 2005, shows the excitation temperature
to be 104 K and elements lighter than Fe to have abundance enhancements over
solar values by up to an order of magnitude. The gas causing the absorption
systems must be circumbinary and its origin is most likely mass ejection from
the secondary star. The absorbing gas pre-exists the outburst and may represent
episodic mass transfer events from the secondary star that initiate the nova
outburst(s). If SNe Ia originate in single degenerate binaries, such absorption
systems could be detectable before maximum lightComment: 19 pages, 6 figures, accepted for publication in the Astrophysical
Journa
Optically Levitating Dielectrics in the Quantum Regime: Theory and Protocols
We provide a general quantum theory to describe the coupling of light with
the motion of a dielectric object inside a high finesse optical cavity. In
particular, we derive the total Hamiltonian of the system as well as a master
equation describing the state of the center of mass mode of the dielectric and
the cavity field mode. In addition, a quantum theory of elasticity is used in
order to study the coupling of the center of mass motion with internal
vibrational excitations of the dielectric. This general theory is applied to
the recent proposal of using an optically levitating nanodielectric as a cavity
optomechanical system [Romero-Isart et al. NJP 12, 033015 (2010), Chang et al.
PNAS 107, 1005 (2010)]. On this basis, we also design a light-mechanics
interface to prepare non-Gaussian states of the mechanical motion, such as
quantum superpositions of Fock states. Finally, we introduce a direct
mechanical tomography scheme to probe these genuine quantum states by time of
flight experiments.Comment: 27 pages, revtex 2 columns, 8 figure
Making electromagnetic wavelets
Electromagnetic wavelets are constructed using scalar wavelets as
superpotentials, together with an appropriate polarization. It is shown that
oblate spheroidal antennas, which are ideal for their production and reception,
can be made by deforming and merging two branch cuts. This determines a unique
field on the interior of the spheroid which gives the boundary conditions for
the surface charge-current density necessary to radiate the wavelets. These
sources are computed, including the impulse response of the antenna.Comment: 29 pages, 4 figures; minor corrections and addition
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