5,987 research outputs found
Kelu-1 is a Binary L Dwarf: First Brown Dwarf Science from Laser Guide Star Adaptive Optics
(Abridged) We present near-IR imaging of the nearby L dwarf Kelu-1 obtained
with the Keck sodium laser guide star adaptive optics (LGS AO) system as part
of a high angular resolution survey for substellar binaries. Kelu-1 was one of
the first free-floating L dwarfs identified, and the origin of its
overluminosity compared to other similar objects has been a long-standing
question. Our images clearly resolve Kelu-1 into a 0.29'' (5.4 AU) binary, and
a previous non-detection by HST demonstrates that the system is a true physical
pair. Binarity explains the properties of Kelu-1 that were previously noted to
be anomalous compared to other early-L dwarfs. We estimate spectral types of
L1.5-L3 and L3-L4.5 for the two components, giving model-derived masses of
0.05-0.07 Msun and 0.045-0.065 Msun for an estimated age of 0.3-0.8 Gyr. More
distant companions are not detected to a limit of 5-9 Mjup. The presence of
lithium absorption indicates that both components are substellar, but the
weakness of this feature relative to other L dwarfs can be explained if only
Kelu-1B is Li-bearing. Determining whether both or only one of the components
possesses lithium could constrain the age of Kelu-1 (and other Li-bearing L
binaries) with higher precision than is possible for most ultracool field
objects. These results are the first LGS AO observations of brown dwarfs and
demonstrate the potential of this new instrumental capability for substellar
astronomy.Comment: 24 pages, Astrophysical Journal, in press (Nov 20, 2005 issue). Note
that Figure 1 of the PDF version is degraded by arxiv.org, but the Postscript
version is fine. Version 2 includes very minor changes to match the published
versio
Understanding the Protected Nodes and Collapse of the Fermi Arcs in Underdoped Cuprate Superconductors
We show how recent angle resolved photoemission measurements addressing the
Fermi arcs in the cuprates reveal a very natural phenomenological description
of the complex superfluid phase. Importantly, this phenomenology is consistent
with a previously presented microscopic theory. By distinguishing the order
parameter and the excitation gap, we are able to demonstrate how the collapse
of the arcs below into well defined nodes is associated with the
\emph{smooth} emergence of superconducting coherence. Comparison of this theory
with experiment shows good semi-quantitative agreement.Comment: 4 pages, 4 figures, replaced with updated versio
On the spin--boson model with a sub--Ohmic bath
We study the spin--boson model with a sub--Ohmic bath using infinitesimal
unitary transformations. Contrary to some results reported in the literature we
find a zero temperature transition from an untrapped state for small coupling
to a trapped state for strong coupling. We obtain an explicit expression for
the renormalized level spacing as a function of the bare papameters of the
system. Furthermore we show that typical dynamical equilibrium correlation
functions exhibit an algebaric decay at zero temperature.Comment: 9 pages, 2 Postscript figure
Quantum Hydrodynamic Model for the enhanced moments of Inertia of molecules in Helium Nanodroplets: Application to SF
The increase in moment of inertia of SF in helium nanodroplets is
calculated using the quantum hydrodynamic approach. This required an extension
of the numerical solution to the hydrodynamic equation to three explicit
dimensions. Based upon an expansion of the density in terms of the lowest four
Octahedral spherical harmonics, the predicted increase in moment of inertia is
, compared to an experimentally determined value of , i.e., 55% of the observed value. The difference is likely in at
least part due to lack of convergence with respect to the angular expansion,
but at present we do not have access to the full densities from which a higher
order expansion can be determined. The present results contradict those of Kwon
et al., J. Chem. Phys. {\bf 113}, 6469 (2000), who predicted that the
hydrodynamic theory predicted less than 10% of the observed increase in moment
of inertia.Comment: 10 pages, including 1 figur
Doctor of Philosophy
dissertationNursing students are faced with stress on a regular basis, which can impact physical and psychological functioning. Despite the identification of stress, anxiety, poor performance, and risk for depression, few studies identify measures to manage stress in a student nurse population. The purpose of this study was to examine the effectiveness of a brief mindfulness breathing intervention to decrease stress and ultimately the risk for depression while increasing self-efficacy with clinical skills performance in a 1st-year student nurse population. Participants were recruited from an associate degree nursing program at a northwestern university. Data gathered included demographic information, depression scores, physiological measures (i.e., blood pressure and pulse), self-efficacy scores, and skills performance scores. The design was a two-group (experimental and no-treatment control) true experimental randomized control trial with the following four repeated measures: (a) pretest, (b) posttest, (c) 2-month follow-up test, and (d) 4-month follow-up test. Data collection took place from November 2009 to March 2010. The sample (N = 85) was predominantly female (87.1%, n = 74) and Caucasian (89.4%, n = 86). Fifty-six of the participants were married and 46% of the participants identified themselves as parents of children still living at home. Analyses of variance demonstrated a greater mean decrease for the intervention group than for the treatment-as-usual group following the mindfulness breathing intervention for depression, F(1,82) = 6.864, p = .010; systolic, F(1,81) = 6.557, p = .012; and diastolic, F(1,81) = 6.078, p = .016-measures indicating the intervention may be of benefit. Pulse did not reach statistical significance. Analyses of variance for mindfulness, self-efficacy, and skills performance did not reach significance. Correlations conducted on measures indicated that as depression decreased, systolic and diastolic measures also decreased. As mindfulness increased, self-efficacy increased, and as self-efficacy increased, skills performance also increased. These results suggest that mindfulness may be of benefit as a method to decrease the risk for depression while contributing to increased self-efficacy and skills performance in a student nurse population. Although not all measures achieved statistical significance, the findings are encouraging for increasing feelings of confidence, leading to a more rewarding educational experience in nursing student
Superfluidity in Three-species Mixture of Fermi Gases across Feshbach Resonances
In this letter a generalization of the BEC-BCS crossover theory to a
multicomponent superfluid is presented by studying a three-species mixture of
Fermi gas across two Feshbach resonances. At the BEC side of resonances, two
kinds of molecules are stable which gives rise to a two-component Bose
condensate. This two-component superfluid state can be experimentally
identified from the radio-frequency spectroscopy, density profile and short
noise measurements. As approaching the BCS side of resonances, the
superfluidity will break down at some point and yield a first-order quantum
phase transition to normal state, due to the mismatch of three Fermi surfaces.
Phase separation instability will occur around the critical regime.Comment: 4 pages, 3 figures, revised versio
Calculation of NMR Properties of Solitons in Superfluid 3He-A
Superfluid 3He-A has domain-wall-like structures, which are called solitons.
We calculate numerically the structure of a splay soliton. We study the effect
of solitons on the nuclear-magnetic-resonance spectrum by calculating the
frequency shifts and the amplitudes of the soliton peaks for both longitudinal
and transverse oscillations of magnetization. The effect of dissipation caused
by normal-superfluid conversion and spin diffusion is calculated. The
calculations are in good agreement with experiments, except a problem in the
transverse resonance frequency of the splay soliton or in magnetic-field
dependence of reduced resonance frequencies.Comment: 15 pages, 10 figures, updated to the published versio
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