29,300 research outputs found
Magnetization-controlled spin transport in DyAs/GaAs layers
Electrical transport properties of DyAs epitaxial layers grown on GaAs have
been investigated at various temperatures and magnetic fields up to 12T. The
measured longitudinal resistances show two distinct peaks at fields around 0.2
and 2.5T which are believed to be related to the strong spin-disorder
scattering occurring at the phase transition boundaries induced by external
magnetic field. An empirical magnetic phase diagram is deduced from the
temperature dependent experiment, and the anisotropic transport properties are
also presented for various magnetic field directions with respect to the
current flow.Comment: 3 pages with 3 figure
The X-ray light curve of Gamma-ray bursts: clues to the central engine
We present the analysis of a large sample of gamma-ray burst (GRB) X-ray
light curves in the rest frame to characterise their intrinsic properties in
the context of different theoretical scenarios. We determine the morphology,
time scales, and energetics of 64 long GRBs observed by \emph{Swift}/XRT
\emph{without} flaring activity. We furthermore provide a one-to-one comparison
to the properties of GRBs \emph{with} X-ray flares. We find that the steep
decay morphology and its connection with X-ray flares favour a scenario in
which a central engine origin. We show that this scenario can also account for
the shallow decay phase, provided that the GRB progenitor star has a
self-similar structure with a constant envelope-to-core mass ratio . However, difficulties arise for very long duration
( s) shallow phases. Alternatively, a spinning-down magnetar
whose emitted power refreshes the forward shock can quantitatively account for
the shallow decay properties. In particular we demonstrate that this model can
account for the plateau luminosity vs. end time anticorrelation.Comment: 12 pages, 8 figures, accepted for publication in A&
Torus Models of the Outer Disc of the Milky Way using LAMOST Survey Data
With a sample of 48,161 K giant stars selected from the LAMOST DR 2
catalogue, we construct torus models in a large volume extending, for the first
time, from the solar vicinity to a Galactocentric distance of kpc,
reaching the outskirts of the Galactic disc. We show that the kinematics of the
K giant stars match conventional models, e.g. as created by Binney in 2012, in
the Solar vicinity. However such two-disc models fail if they are extended to
the outer regions, even if an additional disc component is utilised. If we
loosen constraints in the Sun's vicinity, we find that an effective thick disc
model could explain the anti-centre of the MW. The LAMOST data imply that the
sizes of the Galactic discs are much larger, and that the outer disc is much
thicker, than previously thought, or alternatively that the outer structure is
not a conventional disc at all. However, the velocity dispersion
of the kinematically thick disc in the best-fitting model is about 80 km
s and has a scale parameter for an exponential distribution
function of kpc. Such a height is strongly rejected by
current measurements in the solar neighbourhood, and thus a model beyond
quasi-thermal, two or three thin or thick discs is required.Comment: 11 pages, 7 figures and 3 tables, Accepted for publication in MNRA
Mercury deposition in southern New Hampshire, 2006–2009
The atmospheric deposition of mercury (Hg) occurs via several mechanisms including wet, dry, and occult processes. In an effort to understand the atmospheric cycling and seasonal depositional characteristics of Hg, event-based wet deposition samples and reactive gaseous Hg (RGM) measurements were collected for approximately 3 years at Thompson Farm (TF), a near-coastal rural site in Durham, NH, part of the University of New Hampshire AIRMAP Observing Network. Total aqueous mercury exhibited seasonal patterns in Hg wet deposition at TF. The lowest Hg wet deposition was measured in the winter with an average total seasonal deposition of 1.56 μg m−2compared to the summer average of 4.71 μg m−2. Inter-annual differences in total wet deposition are generally linked with precipitation volume, with the greatest deposition occurring in the wettest year. Relationships between surface level RGM and Hg wet deposition were also investigated based on continuous RGM measurements at TF from November 2006 to September 2009. No correlations were observed between RGM mixing ratios and Hg wet deposition, however the ineffective scavenging of RGM during winter precipitation events was evidenced by the less frequent depletion of RGM below the detection level. Seasonal dry deposition of reactive gaseous Hg (RGM) was estimated using an order-of-magnitude approach. RGM mixing ratios and dry deposition estimates were greatest during the winter and spring. The seasonal ratios of Hg wet deposition to RGM dry deposition vary by up to a factor of 80
Applying mesh conformation on shape analysis with missing data
A mesh conformation approach that makes use of deformable generic meshes has been applied to establishing correspondences between 3D shapes with missing data. Given a group of shapes with correspondences, we can build up a statistical shape model by applying principal component analysis (PCA). The conformation at first globally maps the generic mesh to the 3D shape based on manually located corresponding landmarks, and then locally deforms the generic mesh to clone the 3D shape. The local deformation is constrained by minimizing the energy of an elastic model. An algorithm was also embedded in the conformation process to fill missing surface data of the shapes. Using synthetic data, we demonstrate that the conformation preserves the configuration of the generic mesh and hence it helps to establish good correspondences for shape analysis. Case studies of the principal component analysis of shapes were presented to illustrate the successes and advantages of our approach
SDSS-IV MaNGA: The intrinsic shape of slow rotator early-type galaxies
By inverting the distributions of galaxies' apparent ellipticities and
misalignment angles (measured around the projected half-light radius ) between their photometric and kinematic axes, we study the intrinsic shape
distribution of 189 slow rotator early-type galaxies with stellar masses
, extracted from a
sample of about 2200 galaxies with integral-field stellar kinematics from the
DR14 of the SDSS-IV MaNGA IFU survey. Thanks to the large sample of slow
rotators, Graham+18 showed that there is clear structure in the misalignment
angle distribution, with two peaks at both and
misalignment (characteristic of oblate and prolate rotation respectively). Here
we invert the observed distribution from Graham+18. The large sample allows us
to go beyond the known fact that slow rotators are weakly triaxial and to place
useful constraints on their intrinsic triaxiality distribution (around ) for the first time. The shape inversion is generally non-unique. However,
we find that, for a wide set of model assumptions, the observed distribution
clearly requires a dominant triaxial-oblate population. For some of our models,
the data suggest a hint for a minor triaxial-prolate population, but a dominant
prolate population is ruled out.Comment: Accepted for publication in ApJL, 10 pages, 4 figures, 1 tabl
Neutrino afterglow from Gamma-Ray Bursts: ~10^{18} eV
We show that a significant fraction of the energy of a gamma-ray burst(GRB)
is probably converted to a burst of 10^{17}-10^{19} eV neutrinos and multiple
GeV gammas that follow the GRB by > 10 s . If, as previously suggested, GRB's
accelerate protons to ~10^{20} eV, then both the neutrinos and the gammas may
be detectable.Comment: Accepted ApJ; added sentence re: sterile neutrinos; related material
at http://www.sns.ias.edu/~jn
SiS in the circumstellar envelope of IRC +10126: maser and quasi-thermal emission
We present new Effelsberg-100 m, ATCA, and VLA observations of rotational SiS
transitions in the circumstellar envelope (CSE) of IRC +10216. Thanks to the
high angular resolution achieved by the ATCA observations, we unambiguously
confirm that the molecule's J=1-0 transition exhibits maser action in this CSE,
as first suggested more than thirty years ago. The maser emission's radial
velocity peaking at a local standard of rest velocity of -39.8620.065 km/s
indicates that it arises from an almost fully accelerated shell. Monitoring
observations show time variability of the SiS (1-0) maser. The two lowest-
SiS quasi-thermal emission lines trace a much more extended emitting region
than previous high-J SiS observations. Their distributions show that the SiS
quasi-thermal emission consists of two components: one is very compact
(radius<1.5", corresponding to <3 cm), and the other extends
out to a radius >11". An incomplete shell-like structure is found in the
north-east, which is indicative of existing SiS shells. Clumpy structures are
also revealed in this CSE. The gain of the SiS (1-0) maser (optical depths of
about -5 at the blue-shifted side and, assuming inversion throughout the entire
line's velocity range, about -2 at the red-shifted side) suggests that it is
unsaturated. The SiS (1-0) maser can be explained in terms of ro-vibrational
excitation caused by infrared pumping, and we propose that infrared continuum
emission is the main pumping source.Comment: Accepted for publication in ApJ. A high-resolution version can be
found at https://gongyan2444.github.io/pdf/cw-leo-sis.pdf 3D movies of SiS
cubes can be found at https://gongyan2444.github.io/movie/sis10-3d.avi and
https://gongyan2444.github.io/movie/sis21-3d.av
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