3,429 research outputs found
Magnetoroton scattering by phonons in the fractional quantum Hall regime
Motivated by recent phonon spectroscopy experiments in the fractional quantum
Hall regime we consider processes in which thermally excited magnetoroton
excitations are scattered by low energy phonons. We show that such scattering
processes can never give rise to dissociation of magnetorotons into unbound
charged quasiparticles as had been proposed previously. In addition we show
that scattering of magnetorotons to longer wavelengths by phonon absorption is
possible because of the shape of the magnetoroton dispersion curve and it is
shown that there is a characteristic cross-over temperature above which the
rate of energy transfer to the electron gas changes from an exponential
(activated) to a power law dependence on the effective phonon temperature.Comment: LaTex document, 3 eps figures. submitted to Phys Rev
Astrometric Discovery of GJ 164B
We discovered a low-mass companion to the M-dwarf GJ 164 with the CCD-based
imaging system of the Stellar Planet Survey (STEPS) astrometric program. The
existence of GJ 164B was confirmed with Hubble Space Telescope NICMOS imaging
observations. A high-dispersion spectral observation in V sets a lower limit of
delta m> 2.2 mag between the two components of the system. Based upon our
parallax value of 0.082 +/- 0.008, we derive the following orbital parameters:
P = 2.04 +/- 0.03 y, a = 1.03 +/- 0.03 AU, and Mtotal = 0.265 +/- 0.020 MSun.
The component masses are MA = 0.170 +/- 0.015 MSun and MB = 0.095 +/- 0.015
MSun. Based on its mass, colors, and spectral properties, GJ 164B has spectral
type M6-8 V.Comment: pdf file 14 pages with 6 fig
Comments on "The long-period Galactic Cepheid RS Puppis. I. A geometric distance from its light echoes"
The luminous Galactic Cepheid RS Puppis is unique in being surrounded by a
dust nebula illuminated by the variable light of the Cepheid. In a recent paper
in this journal, Kervella et al. (2008) report a very precise geometric
distance to RS Pup, based on measured phase lags of the light variations of
individual knots in the reflection nebula. In this commentary, we examine the
validity of the distance measurement, as well as the reality of the spatial
structure of the nebula determined by Feast (2008) based upon the phase lags of
the knots. {Kervella et al. assumed that the illuminated dust knots lie, on
average, in the plane of the sky (otherwise it is not possible to derive a
geometric distance from direct imaging of light echoes). We consider the
biasing introduced by the high efficiency of forward scattering. We conclude
that most of the knots are in fact likely to lie in front of the plane of the
sky, thus invalidating the Kervella et al. result. We also show that the flat
equatorial disk structure determined by Feast is unlikely; instead, the
morphology of the nebula is more probably bipolar, with a significant tilt of
its axis with respect to the plane of the sky. Although the Kervella et al.
distance result is invalidated, we show that high-resolution polarimetric
imaging has the potential to yield a valid geometric distance to this important
Cepheid.Comment: 10 pages, 5 figures, 1 table; accepted by Astronomy & Astrophysic
Detectability of dissipative motion in quantum vacuum via superradiance
We propose an experiment for generating and detecting vacuum-induced
dissipative motion. A high frequency mechanical resonator driven in resonance
is expected to dissipate energy in quantum vacuum via photon emission. The
photons are stored in a high quality electromagnetic cavity and detected
through their interaction with ultracold alkali-metal atoms prepared in an
inverted population of hyperfine states. Superradiant amplification of the
generated photons results in a detectable radio-frequency signal temporally
distinguishable from the expected background.Comment: 4 pages, 2 figure
Oscillations in Quantum Entanglement During Rescattering
We study the time evolution of quantum entanglement between an electron and
its parent ion during the rescattering due to a strong few-cycle laser pulse.
Based on a simple one-dimensional model, we compute the Neumann entropy during
the process for several values of the carrier-envelope phase. The local maxima
of the oscillations in the Neumann entropy coincide with the zero crossings of
the electric field of the laser pulse. We employ the Wigner function to
qualitatively explain the quantum dynamics of rescattering in the phase space.Comment: 2 page
Overall Memory Impairment Identification with Mathematical Modeling of the CVLT-II Learning Curve in Multiple Sclerosis
The CVLT-II provides standardized scores for each of the List A five learning trials, so that the clinician can compare the patient's raw trials 1–5 scores with standardized ones. However, frequently, a patient's raw scores fluctuate making a proper interpretation difficult. The CVLT-II does not offer any other methods for classifying a patient's learning and memory status on the background of the learning curve. The main objective of this research is to illustrate that discriminant analysis provides an accurate assessment of the learning curve, if suitable predictor variables are selected. Normal controls were ninety-eight healthy volunteers (78 females and 20 males). A group of MS patients included 365 patients (266 females and 99 males) with clinically defined multiple sclerosis. We show that the best predictor variables are coefficients B3 and B4 of our mathematical model B3 ∗ exp(−B2 ∗ (X − 1)) + B4 ∗ (1 − exp(−B2 ∗ (X − 1))) because discriminant functions, calculated separately for B3 and B4, allow nearly 100% correct classification. These predictors allow identification of separate impairment of readiness to learn or ability to learn, or both
Collective states in highly symmetric atomic configurations, and single-photon traps
Abbreviated Abstract: We study correlated states in a circular and
linear-chain configuration of identical two-level atoms containing the energy
of a single quasi-resonant photon in the form of a collective excitation, where
the collective behaviour is mediated by exchange of transverse photons between
the atoms. For a circular configuration of atoms the effective Hamiltonian on
the radiationless subspace of the system can be diagonalized analytically. In
this case, the radiationless energy eigenstates carry a quantum
number which is analogous to the angular momentum quantum
number , carried by particles propagating in a central potential,
such as a hydrogen-like system. Just as the hydrogen s-states are the only
electronic wave functions which can occupy the central region of the Coulomb
potential, the quasi-particle corresponding to a collective excitation of the
circular atomic sample can occupy the central atom only for vanishing
quantum number . For large numbers of atoms in a maximally
subradiant state, a critical interatomic distance of emerges both
in the linear-chain and the circular configuration of atoms. The spontaneous
decay rate of the linear configuration exhibits a jump-like "critical"
behaviour for next-neighbour distances close to a half-wavelength. Furthermore,
both the linear-chain and the circular configuration exhibit exponential photon
trapping once the next-neighbour distance becomes less than a half-wavelength,
with the suppression of spontaneous decay being particularly pronounced in the
circular system. In this way, circular configurations containing sufficiently
many atoms may be natural candidates for {\it single-photon traps}.Comment: Invited contribution to "Xth International Conference on Quantum
Optics ICQO 2004" in Minsk, Belarus. To be published in Optics and
Spectroscop
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