3,301 research outputs found
The influence of microlensing on the shape of the AGN Fe K-alpha line
We study the influence of gravitational microlensing on the AGN Fe K-alpha
line confirming that unexpected enhancements recently detected in the iron line
of some AGNs can be produced by this effect. We use a ray tracing method to
study the influence of microlensing in the emission coming from a compact
accretion disc considering both geometries, Schwarzschild and Kerr.
Thanks to the small dimensions of the region producing the AGN Fe K-alpha
line, the Einstein Ring Radii associated to even very small compact objects
have size comparable to the accretion disc hence producing noticeable changes
in the line profiles. Asymmetrical enhancements contributing differently to the
peaks or to the core of the line are produced by a microlens, off-centered with
respect to the accretion disc.
In the standard configuration of microlensing by a compact object in an
intervening galaxy, we found that the effects on the iron line are two orders
of magnitude larger than those expected in the optical or UV emission lines. In
particular, microlensing can satisfactorily explain the excess in the iron line
emission found very recently in two gravitational lens systems, H 1413+117 and
MG J0414+0534.
Exploring other physical {scenario} for microlensing, we found that compact
objects (of the order of one Solar mass) which belong to {the bulge or the
halo} of the host galaxy can also produce significant changes in the Fe
K line profile of an AGN. However, the optical depth estimated for
this type of microlensing is {very small, , even in a favorable
case.Comment: Astron. Astrophys. accepte
Bipolar-Driven Large Magnetoresistance in Silicon
Large linear magnetoresistance (MR) in electron-injected p-type silicon at
very low magnetic field is observed experimentally at room temperature. The
large linear MR is induced in electron-dominated space-charge transport regime,
where the magnetic field modulation of electron-to-hole density ratio controls
the MR, as indicated by the magnetic field dependence of Hall coefficient in
the silicon device. Contrary to the space-charge-induced MR effect in unipolar
silicon device, where the large linear MR is inhomogeneity-induced, our results
provide a different insight into the mechanism of large linear MR in
non-magnetic semiconductors that is not based on the inhomogeneity model. This
approach enables homogeneous semiconductors to exhibit large linear MR at low
magnetic fields that until now has only been appearing in semiconductors with
strong inhomogeneities.Comment: 23 pages, 4 figures (main text), 6 figures (supplemental material
Papillary muscle traction in mitral valve prolapse: Quantitation by two-dimensional echocardiography
Previous angiographic observations in patients with mitral valve prolapse have suggested that superior leaflet displacement results in abnormal superior tension on the papillary muscle tips that causes their superior traction or displacement. It has further been postulated that such tension can potentially affect the mechanical and electrophysiologic function of the left ventricle. The purpose of this study was to confirm and quantitate this phenomenon noninvasively by using two-dimensional echocardiography to determine whether superior displacement of the papillary muscle tips occurs and its relation to the degree of mitral leaflet displacement.Directed echocardiographic examination of the papillary muscles and mitral anulus was carried out in a series of patients with classic mitral valve prolapse and results were compared with those in a group of normal control subjects. Distance from the anulus to the papillary muscle tip was measured both in early and at peak ventricular systole. In normal subjects, this distance did not change significantly through systole, whereas in the patient group it decreased, corresponding to a superior displacement of the papillary muscle tips toward the anulus in systole (8.5 ± 2.6 vs. 0.8 ± 0.7 mm; p < 0.0001). This superior papillary muscle motion paralleled the superior displacement of the leaflets in individual patients (y = l.0x + 0.8; r = 0.93) and followed a similar time course. The systolic motion of the mitral anulus toward the apex, assessed with respect to a fixed external reference, was not significantly different in the patients and control groups (14.3 ± 4 vs. 15.5 ± 4.4 mm; p = 0.4) and therefore could not explain the superior papillary muscle tip motion relative to the anulus in the patients with mitral valve prolapse.These results demonstrate that normal mechanisms maintain a relatively constant distance between the papillary muscle tips and the mitral anulus during systole. In classic mitral valve prolapse, superior leaflet displacement is paralleled by superior displacement of the papillary muscles that is consistent with superiorly directed forces causing their traction. Two-dimensional echocardiography can therefore be used to measure these relations and test hypotheses as to their clinical correlates in patients with mitral valve prolapse
Type Ia Supernova cosmology combining data from the mission and the Vera C. Rubin Observatory
The mission will provide first-of-its-kind coverage in the
near-infrared over deep (three fields, 10-20 square degrees each) and
wide (10000 square degrees) fields. While the survey is not designed to
discover transients, the deep fields will have repeated observations over a
two-week span, followed by a gap of roughly six months. In this analysis, we
explore how useful the deep field observations will be for measuring properties
of Type Ia supernovae (SNe Ia). Using simulations that include 's
planned depth, area and cadence in the deep fields, we calculate that more than
3700 SNe between will have at least five detections around
peak with signal-to-noise ratio larger than 3. While on their own,
light curves are not good enough to directly constrain distances, when combined
with LSST deep field observations, we find that uncertainties on SN distances
are reduced by 20-30% for . Furthermore, we
predict how well additional mock data can be used to constrain a key
systematic in SN Ia studies - the size of the luminosity 'step' found between
SNe hosted in high mass () and low mass () galaxies. This measurement has unique information in the rest-frame
NIR. We predict that if the step is caused by dust, we will be able to measure
its reduction in the NIR compared to optical at the 4 level. We
highlight that the LSST and observing strategies used in this work are
still provisional and some level of joint processing is required. Still, these
first results are promising, and assuming begins observations well
before the Nancy Roman Space Telescope (Roman), we expect this dataset to be
extremely helpful for preparation for Roman itself
Differences Between Hole and Electron Doping of a Two-Leg CuO Ladder
Here we report results of a density-matrix-renormalization-group (DMRG)
calculation of the charge, spin, and pairing properties of a two-leg CuO
Hubbard ladder. The outer oxygen atoms as well as the rung and leg oxygen atoms
are included along with near-neighbor and oxygen-hopping matrix elements. This
system allows us to study the effects of hole and electron doping on a system
which is a charge transfer insulator at a filling of one hole per Cu and
exhibits power law, d-wave-like pairing correlations when doped. In particular,
we focus on the differences between doping with holes or electrons.Comment: REVTEX 4, 10 pages, 13 figure
A Topcolor Jungle Gym
We discuss an alternative to the topcolor seesaw mechanism. In our scheme,
all the light quarks carry topcolor, and there are many composite SU(2)
doublets. This makes it possible to get the observed top quark mass and
observed breaking in a way that is quite different from the
classic seesaw mechanism. We discuss a model of this kind that arises naturally
in the context of dynamically broken topcolor. There are many composite scalars
in a theory of this kind. This has important effects on the Pagels-Stokar
relation and the Higgs mass. We find GeV, lighter than in
typical topcolor models. We also show that the electroweak singlet quarks in
such a model can be lighter than the corresponding quarks in a seesaw model.Comment: 23 pages, LaTeX, uses epsf and psfi
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