68,235 research outputs found
Universal long-wavelength nonlinear optical response of noble gases
We demonstrate numerically that the long-wavelength nonlinear dipole moment
and ionization rate versus electric field strength for different noble
gases can be scaled onto each other, revealing universal functions that
characterize the form of the nonlinear response. We elucidate the physical
origin of the universality by using a metastable state analysis of the
light-atom interaction in combination with a scaling analysis. Our results also
provide a powerful new means of characterizing the nonlinear response in the
mid-infrared and long-wave infrared for optical filamentation studies.Comment: 8 pages, 6 figure
Antibunching in an optomechanical oscillator
We theoretically analyze antibunching of the phonon field in an
optomechanical oscillator employ- ing the membrane-in-the-middle geometry. More
specifically, a single-mode mechanical oscillator is quadratically coupled to a
single-mode cavity field in the regime in which the cavity dissipation is a
dominant source of damping, and adiabatic elimination of the cavity field leads
to an effective cubic nonlinearity for the mechanics. We show analytically in
the weak coupling regime that the mechan- ics displays a chaotic phonon field
for small optomechanical cooperativity, whereas an antibunched single-phonon
field appears for large optomechanical cooperativity. This opens the door to
control of the second-order correlation function of a mechanical oscillator in
the weak coupling regime
Static and Dynamic Properties of Trapped Fermionic Tonks-Girardeau Gases
We investigate some exact static and dynamic properties of one-dimensional
fermionic Tonks-Girardeau gases in tight de Broglie waveguides with attractive
p-wave interactions induced by a Feshbach resonance. A closed form solution for
the one-body density matrix for harmonic trapping is analyzed in terms of its
natural orbitals, with the surprising result that for odd, but not for even,
numbers of fermions the maximally occupied natural orbital coincides with the
ground harmonic oscillator orbital and has the maximally allowed fermionic
occupancy of unity. The exact dynamics of the trapped gas following turnoff of
the p-wave interactions are explored.Comment: 4 pages, 2 figures, submitted to PR
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A Rank Approach to Equity Forecast Construction
The purpose of this paper is to present a rank based approach to cross-sectionallinear factor modelling. The emphasis is on approximating factor exposures in aconsistent manner in order to facilitate the merging of subjective information(from professional investors) with objective information (from accounting dataand/or state of the art quantitative models) in a statistically rigorous way withoutneeding to impose the unrealistic simplifying assumptions typical of more standardtime series models. We deal with the problems of identifying country and sectorreturns by an innovative hierarchical factor structure. This is all discussed fromthe perspective that investment models are not immutable but rather need to bedesigned with characteristics that are fit for their purpose; for example, returningaggregate county and sector forecasts that are consistent by construction
Control of unstable steady states by time-delayed feedback methods
We show that time-delayed feedback methods, which have successfully been used
to control unstable periodic ortbits, provide a tool to stabilize unstable
steady states. We present an analytical investigation of the feedback scheme
using the Lambert function and discuss effects of both a low-pass filter
included in the control loop and non-zero latency times associated with the
generation and injection of the feedback signal.Comment: 8 pages, 11 figure
Circulating Subbeam Systems and the Physics of Pulsar Emission
The purpose of this paper is to suggest how detailed single-pulse
observations of ``slow'' radio pulsars may be utilized to construct an
empirical model for their emission. It links the observational synthesis
developed in a series of papers by Rankin starting in the 1980s to the more
recent empirical feedback model of Wright (2003a) by regarding the entire
pulsar magnetosphere as a non-steady, non-linear interactive system with a
natural built-in delay. It is argued that the enhanced role of the outer gap in
such a system indicates an evolutionary link to younger pulsars, in which this
region is thought to be highly active, and that pulsar magnetospheres should no
longer be seen as being ``driven'' by events on the neutron star's polar cap,
but as having more in common with planetary magnetospheres and auroral
phenomena.Comment: 15 pages, 3 figure
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