5,014 research outputs found
Suppressed Andreev Reflection at the Normal-Metal / Heavy-Fermion Superconductor CeCoIn Interface
Dynamic conductance spectra are taken from Au/CeCoIn point contacts in
the Sharvin limit along the (001) and (110) directions. Our conductance
spectra, reproducibly obtained over wide ranges of temperature, constitute the
cleanest data sets ever reported for HFSs. A signature for the emerging
heavy-fermion liquid is evidenced by the development of the asymmetry in the
background in the normal state. Below , an enhancement of the sub-gap
conductance arising from Andreev reflection is observed, with the magnitude of
13.3 % and 11.8 % for the (001) and the (110) point contacts,
respectively, an order of magnitude smaller than those observed in conventional
superconductors but consistent with those in other HFSs. Our zero-bias
conductance data for the (001) point contacts are best fit with the extended
BTK model using the d-wave order parameter. The fit to the full conductance
curve of the (001) point contact indicates the strong coupling nature
(). However, our observed suppression of both the
Andreev reflection signal and the energy gap indicates the failure of existing
models. We provide possible directions for theoretical formulations of the
electronic transport across an N/HFS interface. Several qualitative features
observed in the (110) point contacts provide the first clear spectroscopic
evidence for the symmetry.Comment: 13 pages, 7 figures, LaTeX, paper invited and submitted to SPIE
Conference on Strongly Correlated Electron Materials: Physics and
Nanoengineering, in San Diego, California, July 31 - August 4, 200
Vortex dynamics
Vortex flows of interest to aerodynamicists cover a wide range of scales from a fraction of an inch in boundary layer flows to many feet in wake flows. In many applications these flows are poorly understood and, due to their complexity, present a challenge both analytically and experimentally. Four topics representing the spectrum of experimental and analytical vortex research are presented
Investigation of spherical tearing mode
The purpose of this research was to better understand tearing and reconnection in genuinely three-dimensional configurations. We have identified an equilibrium model that should contain the required features. Three papers have been written and a fourth is in preparation. They are listed in the bibliography
The MASSIVE Survey - VIII. Stellar Velocity Dispersion Profiles and Environmental Dependence of Early-Type Galaxies
We measure the radial profiles of the stellar velocity dispersions,
, for 90 early-type galaxies (ETGs) in the MASSIVE survey, a
volume-limited integral-field spectroscopic (IFS) galaxy survey targeting all
northern-sky ETGs with absolute -band magnitude mag, or
stellar mass , within 108 Mpc. Our wide-field
107" 107" IFS data cover radii as large as 40 kpc, for which we
quantify separately the inner (2 kpc) and outer (20 kpc) logarithmic slopes
and of . While
is mostly negative, of the 56 galaxies with sufficient
radial coverage to determine we find 36% to have rising
outer dispersion profiles, 30% to be flat within the uncertainties, and 34% to
be falling. The fraction of galaxies with rising outer profiles increases with
and in denser galaxy environment, with 10 of the 11 most massive galaxies
in our sample having flat or rising dispersion profiles. The strongest
environmental correlations are with local density and halo mass, but a weaker
correlation with large-scale density also exists. The average is similar for brightest group galaxies, satellites, and isolated
galaxies in our sample. We find a clear positive correlation between the
gradients of the outer dispersion profile and the gradients of the velocity
kurtosis . Altogether, our kinematic results suggest that the increasing
fraction of rising dispersion profiles in the most massive ETGs are caused (at
least in part) by variations in the total mass profiles rather than in the
velocity anisotropy alone.Comment: Accepted/in press, MNRA
The MASSIVE Survey - VII. The Relationship of Angular Momentum, Stellar Mass and Environment of Early-Type Galaxies
We analyse the environmental properties of 370 local early-type galaxies
(ETGs) in the MASSIVE and ATLAS3D surveys, two complementary volume-limited
integral-field spectroscopic (IFS) galaxy surveys spanning absolute -band
magnitude , or stellar mass . We find these galaxies to reside in a diverse range of
environments measured by four methods: group membership (whether a galaxy is a
brightest group/cluster galaxy, satellite, or isolated), halo mass, large-scale
mass density (measured over a few Mpc), and local mass density (measured within
the th neighbour). The spatially resolved IFS stellar kinematics provide
robust measurements of the spin parameter and enable us to examine
the relationship among , , and galaxy environment. We find a
strong correlation between and , where the average
decreases from to below 0.1 with increasing mass, and the fraction
of slow rotators increases from % to 90%. We show for
the first time that at fixed , there are almost no trends between galaxy
spin and environment; the apparent kinematic morphology-density relation for
ETGs is therefore primarily driven by and is accounted for by the joint
correlations between and spin, and between and environment. A
possible exception is that the increased at high local density
is slightly more than expected based only on these joint correlations. Our
results suggest that the physical processes responsible for building up the
present-day stellar masses of massive galaxies are also very efficient at
reducing their spin, in any environment.Comment: Accepted to MNRA
The MASSIVE Survey XIII -- Spatially Resolved Stellar Kinematics in the Central 1 kpc of 20 Massive Elliptical Galaxies with the GMOS-North Integral-Field Spectrograph
We use observations from the GEMINI-N/GMOS integral-field spectrograph (IFS)
to obtain spatially resolved stellar kinematics of the central kpc of
20 early-type galaxies (ETGs) with stellar masses greater than in the MASSIVE survey. Together with observations from the wide-field
Mitchell IFS at McDonald Observatory in our earlier work, we obtain
unprecedentedly detailed kinematic maps of local massive ETGs, covering a scale
of kpc. The high () signal-to-noise of the GMOS spectra
enable us to obtain two-dimensional maps of the line-of-sight velocity,
velocity dispersion , as well as the skewness and kurtosis
of the stellar velocity distributions. All but one galaxy in the sample have
profiles that increase towards the center, whereas the slope of
at one effective radius () can be of either sign. The is
generally positive, with 14 of the 20 galaxies having positive within the
GMOS aperture and 18 having positive within . The positive
and rising towards small radii are indicative of a central black
hole and velocity anisotropy. We demonstrate the constraining power of the data
on the mass distributions in ETGs by applying Jeans anisotropic modeling (JAM)
to NGC~1453, the most regular fast rotator in the sample. Despite the
limitations of JAM, we obtain a clear minimum in black hole mass,
stellar mass-to-light ratio, velocity anisotropy parameters, and the circular
velocity of the dark matter halo.Comment: Accepted to Ap
Recommended from our members
Young Adults, Social Networks, and Addiction Recovery: Post Treatment Changes in Social Ties and Their Role as a Mediator of 12-Step Participation
Background: Social factors play a key role in addiction recovery. Research with adults indicates individuals with substance use disorder (SUD) benefit from mutual-help organizations (MHOs), such as Alcoholics Anonymous, via their ability to facilitate adaptive network changes. Given the lower prevalence of sobriety-conducive, and sobriety-supportive, social contexts in the general population during the life-stage of young adulthood, however, 12-step MHOs may play an even more crucial recovery-supportive social role for young adults, but have not been investigated. Greater knowledge could enhance understanding of recovery-related change and inform young adults’ continuing care recommendations. Methods: Emerging adults (N = 302; 18–24 yrs; 26% female; 95% White) enrolled in a study of residential treatment effectiveness were assessed at intake, 1, 3, 6, and 12 months on 12-step attendance, peer network variables (“high [relapse] risk” and “low [relapse] risk” friends), and treatment outcomes (Percent Days Abstinent; Percent Days Heavy Drinking). Hierarchical linear models tested for change in social risk over time and lagged mediational analyses tested whether 12-step attendance conferred recovery benefits via change in social risk. Results: High-risk friends were common at treatment entry, but decreased during follow-up; low-risk friends increased. Contrary to predictions, while substantial recovery-supportive friend network changes were observed, this was unrelated to 12-step participation and, thus, not found to mediate its positive influence on outcome. Conclusions: Young adult 12-step participation confers recovery benefit; yet, while encouraging social network change, 12-step MHOs may be less able to provide social network change directly for young adults, perhaps because similar-aged peers are less common in MHOs. Findings highlight the importance of both social networks and 12-step MHOs and raise further questions as to how young adults benefit from 12-step MHOs
The MASSIVE Survey - X. Misalignment between Kinematic and Photometric Axes and Intrinsic Shapes of Massive Early-Type Galaxies
We use spatially resolved two-dimensional stellar velocity maps over a
field of view to investigate the kinematic features of 90
early-type galaxies above stellar mass in the MASSIVE
survey. We measure the misalignment angle between the kinematic and
photometric axes and identify local features such as velocity twists and
kinematically distinct components. We find 46% of the sample to be well aligned
(), 33% misaligned, and 21% without detectable rotation
(non-rotators). Only 24% of the sample are fast rotators, the majority of which
(91%) are aligned, whereas 57% of the slow rotators are misaligned with a
nearly flat distribution of from to . 11
galaxies have and thus exhibit minor-axis ("prolate")
rotation in which the rotation is preferentially around the photometric major
axis. Kinematic misalignments occur more frequently for lower galaxy spin or
denser galaxy environments. Using the observed misalignment and ellipticity
distributions, we infer the intrinsic shape distribution of our sample and find
that MASSIVE slow rotators are consistent with being mildly triaxial, with mean
axis ratios of and . In terms of local kinematic features,
51% of the sample exhibit kinematic twists of larger than , and 2
galaxies have kinematically distinct components. The frequency of misalignment
and the broad distribution of reported here suggest that the most
massive early-type galaxies are mildly triaxial, and that formation processes
resulting in kinematically misaligned slow rotators such as gas-poor mergers
occur frequently in this mass range.Comment: Accepted to MNRA
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