5,483 research outputs found
Technical Note: Adjoint formulation of the TOMCAT atmospheric transport scheme in the Eulerian backtracking framework (RETRO-TOM)
A new methodology for the formulation of an adjoint to the transport component
of the chemistry transport model TOMCAT is described and
implemented in a new model, RETRO-TOM. The Eulerian backtracking method
is used, allowing the
forward advection scheme (Prather's second-order moments) to be
efficiently exploited in the backward adjoint calculations.
Prather's scheme is shown to be time symmetric,
suggesting the possibility of high accuracy. To attain this accuracy,
however, it is necessary to make a careful treatment of the "density
inconsistency" problem inherent to offline transport models. The
results are verified using a series of test experiments. These
demonstrate the high accuracy of RETRO-TOM when compared with direct
forward sensitivity calculations, at least for problems in which flux limiters in the
advection scheme are not required. RETRO-TOM therefore combines the
flexibility and stability of a "finite difference of adjoint" formulation with the
accuracy of an "adjoint of finite difference" formulation
Measuring the to Ratio in a High Statistics Atmospheric Neutrino Experiment
By exploiting differences in muon lifetimes it is possible to distinguish
from charged current interactions in underground
neutrino detectors. Such observations would be a useful tool in understanding
the source of the atmospheric neutrino anomaly.Comment: 6 pages no figure
Burst dynamics during drainage displacements in porous media: Simulations and experiments
We investigate the burst dynamics during drainage going from low to high
injection rate at various fluid viscosities. The bursts are identified as
pressure drops in the pressure signal across the system. We find that the
statistical distribution of pressure drops scales according to other systems
exhibiting self-organized criticality. The pressure signal was calculated by a
network model that properly simulates drainage displacements. We compare our
results with corresponding experiments.Comment: 7 pages, 4 figures. Submitted to Europhys. Let
LoCuSS: The steady decline and slow quenching of star formation in cluster galaxies over the last four billion years
We present an analysis of the levels and evolution of star formation activity
in a representative sample of 30 massive galaxy clusters at 0.15<z<0.30 from
the Local Cluster Substructure Survey (LoCuSS), combining wide-field Spitzer
24um data with extensive spectroscopy of cluster members. The specific-SFRs of
massive (M>10^10 M_sun) star-forming cluster galaxies within r200 are found to
be systematically 28% lower than their counterparts in the field at fixed
stellar mass and redshift, a difference significant at the 8.7-sigma level.
This is the unambiguous signature of star formation in most (and possibly all)
massive star-forming galaxies being slowly quenched upon accretion into massive
clusters, their SFRs declining exponentially on quenching time-scales in the
range 0.7-2.0 Gyr. We measure the mid-infrared Butcher-Oemler effect over the
redshift range 0.0-0.4, finding rapid evolution in the fraction (f_SF) of
massive (M_K3M_sun/yr, of the
form f_SF (1+z)^7.6. We dissect the origins of the Butcher-Oemler effect,
revealing it to be due to the combination of a ~3x decline in the mean
specific-SFRs of star-forming cluster galaxies since z~0.3 with a ~1.5x
decrease in number density. Two-thirds of this reduction in the specific-SFRs
of star-forming cluster galaxies is due to the steady cosmic decline in the
specific-SFRs among those field galaxies accreted into the clusters. The
remaining one-third reflects an accelerated decline in the star formation
activity of galaxies within clusters. The slow quenching of star-formation in
cluster galaxies is consistent with a gradual shut down of star formation in
infalling spiral galaxies as they interact with the intra-cluster medium via
ram-pressure stripping or starvation mechanisms. We find no evidence for the
build-up of cluster S0 bulges via major nuclear star-burst episodes.Comment: 24 pages, 12 figures. Accepted for publication in Ap
X-point collapse and saturation in the nonlinear tearing mode reconnection
We study the nonlinear evolution of the resistive tearing mode in slab
geometry in two dimensions. We show that, in the strongly driven regime (large
Delta'), a collapse of the X-point occurs once the island width exceeds a
certain critical value ~1/Delta'. A current sheet is formed and the
reconnection is exponential in time with a growth rate ~eta^1/2, where eta is
the resistivity. If the aspect ratio of the current sheet is sufficiently
large, the sheet can itself become tearing-mode unstable, giving rise to
secondary islands, which then coalesce with the original island. The saturated
state depends on the value of Delta'. For small Delta', the saturation
amplitude is ~Delta' and quantitatively agrees with the theoretical prediction.
If Delta' is large enough for the X-point collapse to have occured, the
saturation amplitude increases noticeably and becomes independent of Delta'.Comment: revtex4, 4 pages, 18 figure
Viscous stabilization of 2D drainage displacements with trapping
We investigate the stabilization mechanisms due to viscous forces in the
invasion front during drainage displacement in two-dimensional porous media
using a network simulator. We find that in horizontal displacement the
capillary pressure difference between two different points along the front
varies almost linearly as function of height separation in the direction of the
displacement. The numerical result supports arguments taking into account the
loopless displacement pattern where nonwetting fluid flow in separate strands
(paths). As a consequence, we show that existing theories developed for viscous
stabilization, are not compatible with drainage when loopless strands dominate
the displacement process.Comment: The manuscript has been substantially revised. Accepted in Phys. Rev.
Let
Jet Deflection via Cross winds: Laboratory Astrophysical Studies
We present new data from High Energy Density (HED) laboratory experiments
designed to explore the interaction of a heavy hypersonic radiative jet with a
cross wind. The jets are generated with the MAGPIE pulsed power machine where
converging conical plasma flows are produced from a cylindrically symmetric
array of inclined wires. Radiative hypersonic jets emerge from the convergence
point. The cross wind is generated by ablation of a plastic foil via
soft-X-rays from the plasma convergence region. Our experiments show that the
jets are deflected by the action of the cross wind with the angle of deflection
dependent on the proximity of the foil. Shocks within the jet beam are apparent
in the data. Analysis of the data shows that the interaction of the jet and
cross wind is collisional and therefore in the hydro-dynamic regime. MHD plasma
code simulations of the experiments are able to recover the deflection
behaviour seen in the experiments. We consider the astrophysical relevance of
these experiments applying published models of jet deflection developed for AGN
and YSOs. Fitting the observed jet deflections to quadratic trajectories
predicted by these models allows us to recover a set of plasma parameters
consistent with the data. We also present results of 3-D numerical simulations
of jet deflection using a new astrophysical Adaptive Mesh Refinement code.
These simulations show highly structured shocks occurring within the beam
similar to what was observed in the experimentsComment: Submitted to ApJ. For a version with figures go to
http://web.pas.rochester.edu/~afrank/labastro/CW/Jet-Wind-Frank.pd
Interaction of JLP with Plk1 recruits FoxK1 to interact and form a ternary complex
JLP (JNK associated Leucine zipper protein) is a scaffolding protein, which has been shown to interact
with and activate JNK/p38MAPK pathway. Its interaction with various signaling proteins is associated
with coordinated regulation of cellular process such as endocytosis, motility, neurite outgrowth, cell
proliferation and apoptosis. Here we identified a mitotic Serine/Threonine kinase, Polo like kinase 1
(Plk1), as a novel interaction partner of JLP through a mass spectrometry based approach. We show that the N-terminal domain of JLP interacts with the polo-box domain (PBD) of Plk1 in a phosphorylation-dependent
manner. Our results indicate that, JLP is phospho-primed on Thr 351 residue on its Nterminus,
which is recognized by the PBD of Plk1 leading to phosphorylation of JLP at additional sites.
Moreover, treatment of cells with the Plk1 inhibitor, BI2536 affects the interaction demonstrating the
importance of Plk1 kinase activity in this process. Since JLP is a scaffolding protein that recruits proteins
to mediate specific cell signaling events, we hypothesized that the interaction of JLP with Plk1 might
result in the recruitment of other proteins to this complex. To test this hypothesis, we carried out SILAC
labeling of proteins in mitotic cells in the presence or absence of BI2536. Through mass-spectrometry
we identified the transcription factor, FoxK1 as a Plk1-dependent JLP-interacting protein. Furthermore,
we show that JLP, Plk1 and FoxK1 form a ternary complex, which occurs only during mitosis. Knockdown
of Plk1 and not JLP, affected the interaction between JLP and FoxK1 indicating that the formation of the
ternary complex is dependent on Plk1. FoxK1 has been previously characterized as a transcriptional
repressor of cyclin dependent kinase inhibitor, p21/WAF1. We observed that knockdown of JLP in U2OS
cells results in increased protein levels of FoxK1 and a reduction of p21 expression. Moreover,
immunofluorescence studies in asynchronous cells showed that FoxK1 is excluded from the nucleus
during mitosis. Based on our observations, we propose that formation of the ternary complex between
JLP, Plk1 and FoxK1 regulates the stability and/or localization of FoxK1
The drivers of AGN activity in galaxy clusters: AGN fraction as a function of mass and environment
We present an analysis of optical spectroscopically identified active galactic nuclei (AGN) down to a cluster magnitude of M * + 1 in a sample of six self-similar Sloan Digital Sky Survey galaxy clusters at z ~ 0.07. These clusters are specifically selected to lack significant substructure at bright limits in their central regions so that we are largely able to eliminate the local action of merging clusters on the frequency of AGN. We demonstrate that the AGN fraction increases significantly from the cluster centre to 1.5R virial , but tails off at larger radii. If only comparing the cluster core region to regions at ~2R virial , no significant variation would be found. We compute the AGN fraction by mass and show that massive galaxies (log(stellarmass) > 10.7) are host to a systematically higher fraction of AGN than lower mass galaxies at all radii from the cluster centre. We attribute this deficit of AGN in the cluster centre to the changing mix of galaxy types with radius. We use the WHAN diagnostic to separate weak AGN from 'retired' galaxies in which the main ionization mechanism comes from old stellar populations. These retired AGN are found at all radii, while the mass effect is much more pronounced: we find that massive galaxies are more likely to be in the retired class. Further, we show that our AGN have no special position inside galaxy clusters - they are neither preferentially located in the infall regions nor situated at local maxima of galaxy density as measured with ∑ 5 . However, we find that the most powerful AGN (with [O III] equivalent widths < -10 Å) reside at significant velocity offsets in the cluster, and this brings our analysis into agreement with previous work on X-ray-selected AGN. Our results suggest that if interactions with other galaxies are responsible for triggering AGN activity, the time lag between trigger and AGN enhancement must be sufficiently long to obfuscate the encounter site and wipe out the local galaxy density signal. © 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society
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