393,494 research outputs found
Augmented Homotopical Algebraic Geometry
We develop the framework for augmented homotopical algebraic geometry. This
is an extension of homotopical algebraic geometry, which itself is a
homotopification of classical algebraic geometry. To do so, we define the
notion of augmentation categories, which are a special class of generalised
Reedy categories. For an augmentation category, we prove the existence of a
closed Quillen model structure on the presheaf category which is compatible
with the Kan-Quillen model structure on simplicial sets. Moreover, we use the
concept of augmented hypercovers to define a local model structure on the
category of augmented presheaves. We prove that crossed simplicial groups, and
the planar rooted tree category are examples of augmentation categories.
Finally, we introduce a method for generating new examples from old via a
categorical pushout construction.Comment: 36 pages, comments welcom
Ultraviolet/X-ray variability and the extended X-ray emission of the radio-loud broad absorption line quasar PG 1004+130
We present the results of recent Chandra, XMM-Newton, and Hubble Space
Telescope observations of the radio-loud (RL), broad absorption line (BAL)
quasar PG 1004+130. We compare our new observations to archival X-ray and UV
data, creating the most comprehensive, high signal-to-noise, multi-epoch,
spectral monitoring campaign of a RL BAL quasar to date. We probe for
variability of the X-ray absorption, the UV BAL, and the X-ray jet, on
month-year timescales. The X-ray absorber has a low column density of
cm when it is assumed to be fully
covering the X-ray emitting region, and its properties do not vary
significantly between the 4 observations. This suggests the observed absorption
is not related to the typical "shielding gas" commonly invoked in BAL quasar
models, but is likely due to material further from the central black hole. In
contrast, the CIV BAL shows strong variability. The equivalent width (EW) in
2014 is EW=11.240.56 \AA, showing a fractional increase of =1.160.11 from the 2003 observation, 3183 days earlier
in the rest-frame. This places PG 1004+130 among the most highly variable BAL
quasars. By combining Chandra observations we create an exposure 2.5 times
deeper than studied previously, with which to investigate the nature of the
X-ray jet and extended diffuse X-ray emission. An X-ray knot, likely with a
synchrotron origin, is detected in the radio jet ~8 arcsec (30 kpc) from the
central X-ray source with a spatial extent of ~4 arcsec (15 kpc). No similar
X-ray counterpart to the counterjet is detected. Asymmetric, non-thermal
diffuse X-ray emission, likely due to inverse Compton scattering of Cosmic
Microwave Background photons, is also detected.Comment: 15 pages, 7 figures, 3 tables. Accepted for publication in Ap
Atmospheric Circulation of Brown Dwarfs and Jupiter and Saturn-like Planets: Zonal Jets, Long-term Variability, and QBO-type Oscillations
Brown dwarfs and directly imaged giant planets exhibit significant evidence
for active atmospheric circulation, which induces a large-scale patchiness in
the cloud structure that evolves significantly over time, as evidenced by
infrared light curves and Doppler maps. These observations raise critical
questions about the fundamental nature of the circulation, its time
variability, and the overall relationship to the circulation on Jupiter and
Saturn. Jupiter and Saturn themselves exhibit numerous robust zonal (east-west)
jet streams at the cloud level; moreover, both planets exhibit long-term
stratospheric oscillations involving perturbations of zonal wind and
temperature that propagate downward over time on timescales of ~4 years
(Jupiter) and ~15 years (Saturn). These oscillations, dubbed the Quasi
Quadrennial Oscillation (QQO) for Jupiter and the Semi-Annual Oscillation (SAO)
on Saturn, are thought to be analogous to the Quasi-Biennial Oscillation (QBO)
on Earth, which is driven by upward propagation of equatorial waves from the
troposphere. To investigate these issues, we here present global,
three-dimensional, high-resolution numerical simulations of the flow in the
stratified atmosphere--overlying the convective interior--of brown dwarfs and
Jupiter-like planets. The effect of interior convection is parameterized by
inducing small-scale, randomly varying perturbations in the
radiative-convective boundary at the base of the model. In the simulations, the
convective perturbations generate atmospheric waves and turbulence that
interact with the rotation to produce numerous zonal jets. Moreover, the
equatorial stratosphere exhibits stacked eastward and westward jets that
migrate downward over time, exactly as occurs in the terrestrial QBO, Jovian
QQO, and Saturnian SAO. This is the first demonstration of a QBO-like
phenomenon in 3D numerical simulations of a giant planet.Comment: 27 pages, 15 figures, in press at ApJ; this is the revised (accepted)
version, which includes a major new section providing detailed analysis of
the types of wave modes present in the model, and characterizing the
wave-mean-flow interactions by which they generate the QBO-like oscillation
Flux surface shaping effects on tokamak edge turbulence and flows
Shaping of magnetic flux surfaces is found to have a strong impact on
turbulence and transport in tokamak edge plasmas. A series of axisymmetric
equilibria with varying elongation and triangularity, and a divertor
configuration are implemented into a computational gyrofluid turbulence model.
The mechanisms of shaping effects on turbulence and flows are identified.
Transport is mainly reduced by local magnetic shearing and an enhancement of
zonal shear flows induced by elongation and X-point shaping.Comment: 10 pages, 11 figures. Submitted to Physics of Plasma
Effective Field Theory for Top Quark Physics
Physics beyond the standard model can affect top-quark physics indirectly. We
describe the effective field theory approach to describing such physics, and
contrast it with the vertex-function approach that has been pursued previously.
We argue that the effective field theory approach has many fundamental
advantages and is also simpler.Comment: 7 pages, 5 figures. To appear in the Proceedings of the International
Workshop on Top Quark Physics (top2010), Bruges, Belgium, May 31 - June 4,
201
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