613 research outputs found
Unusual Stokes V profiles during flaring activity of a delta sunspot
We analyze a set of full Stokes profile observations of the flaring active
region NOAA 10808 recorded with the Vector-Spectromagnetograph (VSM) of the
SOLIS facility. We aim to quantify transient and permanent changes in the
magnetic field and velocity field. The results are put in context with MDI
magnetograms and reconstructed RHESSI X-ray images. We find signs of
restructuring of the photospheric magnetic field during the flare close to the
polarity inversion line (PIL) at the flaring site. At two locations in the
umbra we encounter strong fields (approx. 3 kG), as inferred from the Stokes I
profiles which, however, exhibit a low polarization signal. During the flare we
observe in addition asymmetric Stokes V profiles at one of these sites. The
asymmetric Stokes V profiles appear co-spatial and co-temporal with a strong
apparent polarity reversal observed in MDI-magnetograms and a chromospheric
hard X-ray source. The two-component atmosphere fits of the asymmetric Stokes
profiles result in line-of-sight velocity differences in the range of approx.
12km/s to 14 km/s between the two components in the photosphere. Another
possibility is that local atmospheric heating is causing the observed
asymmetric Stokes V profile shape. In either case our analysis shows that a
very localized patch of approx. 5 arcsec in the photospheric umbra, co-spatial
with a flare footpoint, exhibits a sub-resolution fine structure.Comment: 13 pages, 10 figures, 1 tabl
phot1 inhibition of ABCB19 primes lateral auxin fluxes in the shoot apex required for phototropism
It is well accepted that lateral redistribution of the phytohormone auxin underlies the bending of plant organs towards light. In monocots, photoreception occurs at the shoot tip above the region of differential growth. Despite more than a century of research, it is still unresolved how light regulates auxin distribution and where this occurs in dicots. Here, we establish a system in Arabidopsis thaliana to study hypocotyl phototropism in the absence of developmental events associated with seedling photomorphogenesis. We show that auxin redistribution to the epidermal sites of action occurs at and above the hypocotyl apex, not at the elongation zone. Within this region, we identify the auxin efflux transporter ATP-BINDING CASSETTE B19 (ABCB19) as a substrate target for the photoreceptor kinase PHOTOTROPIN 1 (phot1). Heterologous expression and physiological analyses indicate that phosphorylation of ABCB19 by phot1 inhibits its efflux activity, thereby increasing auxin levels in and above the hypocotyl apex to halt vertical growth and prime lateral fluxes that are subsequently channeled to the elongation zone by PIN-FORMED 3 (PIN3). Together, these results provide new insights into the roles of ABCB19 and PIN3 in establishing phototropic curvatures and demonstrate that the proximity of light perception and differential phototropic growth is conserved in angiosperm
AGN Jet-induced Feedback in Galaxies. II. Galaxy colours from a multicloud simulation
We study the feedback from an AGN on stellar formation within its host
galaxy, mainly using one high resolution numerical simulation of the jet
propagation within the interstellar medium of an early-type galaxy. In
particular, we show that in a realistic simulation where the jet propagates
into a two-phase ISM, star formation can initially be slightly enhanced and
then, on timescales of few million years, rapidly quenched, as a consequence
both of the high temperatures attained and of the reduction of cloud mass
(mainly due to Kelvin-Helmholtz instabilities). We then introduce a model of
(prevalently) {\em negative} AGN feedback, where an exponentially declining
star formation is quenched, on a very short time scale, at a time t_AGN, due to
AGN feedback. Using the Bruzual & Charlot (2003) population synthesis model and
our star formation history, we predict galaxy colours from this model and match
them to a sample of nearby early-type galaxies showing signs of recent episodes
of star formation (Kaviraj et al. 2007). We find that the quantity t_gal -
t_AGN, where t_gal is the galaxy age, is an excellent indicator of the presence
of feedback processes, and peaks significantly around t_gal - t_AGN \approx
0.85 Gyr for our sample, consistent with feedback from recent energy injection
by AGNs in relatively bright (M_{B} \lsim -19) and massive nearby early-type
galaxies. Galaxies that have experienced this recent feedback show an
enhancement of 3 magnitudes in NUV(GALEX)-g, with respect to the unperturbed,
no-feedback evolution. Hence they can be easily identified in large combined
near UV-optical surveys.Comment: 18 pages, 16 figures, accepted for publication on MNRAS. This version
includes revisions after the referee's repor
Identification of Direct Target Engagement Biomarkers for Kinase-Targeted Therapeutics
Pharmacodynamic (PD) biomarkers are an increasingly valuable tool for decision-making and prioritization of lead compounds during preclinical and clinical studies as they link drug-target inhibition in cells with biological activity. They are of particular importance for novel, first-in-class mechanisms, where the ability of a targeted therapeutic to impact disease outcome is often unknown. By definition, proximal PD biomarkers aim to measure the interaction of a drug with its biological target. For kinase drug discovery, protein substrate phosphorylation sites represent candidate PD biomarkers. However, substrate phosphorylation is often controlled by input from multiple converging pathways complicating assessment of how potently a small molecule drug hits its target based on substrate phoshorylation measurements alone. Here, we report the use of quantitative, differential mass-spectrometry to identify and monitor novel drug-regulated phosphorylation sites on target kinases. Autophosphorylation sites constitute clinically validated biomarkers for select protein tyrosine kinase inhibitors. The present study extends this principle to phosphorylation sites in serine/threonine kinases looking beyond the T-loop autophosphorylation site. Specifically, for the 3′-phosphoinositide-dependent protein kinase 1 (PDK1), two phospho-residues p-PDK1Ser410 and p-PDK1Thr513 are modulated by small-molecule PDK1 inhibitors, and their degree of dephosphorylation correlates with inhibitor potency. We note that classical, ATP-competitive PDK1 inhibitors do not modulate PDK1 T-loop phosphorylation (p-PDK1Ser241), highlighting the value of an unbiased approach to identify drug target-regulated phosphorylation sites as these are complementary to pathway PD biomarkers. Finally, we extend our analysis to another protein Ser/Thr kinase, highlighting a broader utility of our approach for identification of kinase drug-target engagement biomarkers
New-physics contributions to the forward-backward asymmetry in B -> K* mu+ mu-
We study the forward-backward asymmetry (AFB) and the differential branching
ratio (DBR) in B -> K* mu+ mu- in the presence of new physics (NP) with
different Lorentz structures. We consider NP contributions from vector-axial
vector (VA), scalar-pseudoscalar (SP), and tensor (T) operators, as well as
their combinations. We calculate the effects of these new Lorentz structures in
the low-q^2 and high-q^2 regions, and explain their features through analytic
approximations. We find two mechanisms that can give a significant deviation
from the standard-model predictions, in the direction indicated by the recent
measurement of AFB by the Belle experiment. They involve the addition of the
following NP operators: (i) VA, or (ii) a combination of SP and T (slightly
better than T alone). These two mechanisms can be distinguished through
measurements of DBR in B -> K* mu+ mu- and AFB in B -> K mu+ mu-.Comment: 33 pages, revtex, 9 figures. Paper originally submitted with the
wrong figures. This is corrected in the replacement. An incorrect factor of 2
found in a formula. This is corrected and figures modified. Conclusions
unchanged. Typos correcte
Restoration of factorization for low hadron hadroproduction
We discuss the applicability of the factorization theorem to low-
hadron production in hadron-hadron collision in a simple toy model, which
involves only scalar particles and gluons. It has been shown that the
factorization for high- hadron hadroproduction is broken by soft gluons in
the Glauber region, which are exchanged among a transverse-momentum-dependent
(TMD) parton density and other subprocesses of the collision. We explain that
the contour of a loop momentum can be deformed away from the Glauber region at
low , so the above residual infrared divergence is factorized by means of
the standard eikonal approximation. The factorization is then restored in
the sense that a TMD parton density maintains its universality. Because the
resultant Glauber factor is independent of hadron flavors, experimental
constraints on its behavior are possible. The factorization can also be
restored for the transverse single-spin asymmetry in hadron-hadron collision at
low in a similar way, with the residual infrared divergence being
factorized into the same Glauber factor.Comment: 12 pages, 2 figures, version to appear in EPJ
Environmental Effects on Evolution of Cluster Galaxies in a LCDM Universe
We investigate environmental effects on evolution of bright cluster galaxies
in a dominated cold dark matter universe using a combination of
dissipationless N-body simulations and a semi-analytic galaxy formation model.
The N-body simulations enable us to calculate orbits of galaxies in simulated
clusters. Therefore we can incorporate stripping of cold gas from galactic
disks by ram pressure from intracluster medium into our model. In this paper we
study how ram pressure stripping (RPS) and small starburst induced by a minor
merger affect colors, star formation rates, and morphologies of cluster
galaxies. We find that the RPS is not important for colors and SFRs of galaxies
in the cluster core if star formation time-scale is properly chosen, because
the star formation is sufficiently suppressed by consumption of the cold gas in
the disks. Then observed color and SFR gradients can be reproduced without the
RPS. The small starburst triggered by a minor merger hardly affects the SFRs
and colors of the galaxies as well. We also examine whether these two processes
can resolve the known problem that the major merger-driven bulge formation
scenario predict too few galaxies of intermediate bulge-to-total luminosity
ratio (B/T) in clusters. When the minor burst is taken into account, the
intermediate B/T population is increased and the observed morphology gradients
in clusters are successfully reproduced. When the minor burst is considered,
the RPS also plays an important role in formation of the intermediate B/T
galaxies. We present redshift evolution of morphological fractions predicted by
our models. The predicted number ratios of the intermediate B/T galaxies to the
bulge-dominated galaxies show nearly flat or slightly increasing trends with
increasing redshift.Comment: 12 pages, 9 figures, accepted for publication in ApJ (v587 n2 April
20, 2003
New Physics in Bs -> J/psi phi: a General Analysis
Recently, the CDF and D0 collaborations measured indirect CP violation in Bs
-> J/psi phi and found a hint of a signal. If taken at face value, this can be
interpreted as a nonzero phase of Bs-Bsbar mixing (beta_s), in disagreement
with the standard model, which predicts that beta_s ~= 0. In this paper, we
argue that this analysis may be incomplete. In particular, there can be new
physics (NP) in the bbar -> sbar c cbar decay. If so, the value of beta_s is
different than for the case in which NP is assumed to be present only in the
mixing. We have examined several models of NP and found that, indeed, there can
be significant contributions to the decay. These effects are consistent with
measurements in B -> J/psi K* and Bd -> J/psi Ks. Due to the NP in the decay,
polarization-dependent indirect CP asymmetries and triple-product asymmetries
are predicted in Bs -> J/psi phi.Comment: 28 pages, JHEP, no figures. Considerable changes made. Abstract and
main text of paper modified to alter presentation. Appendix added. References
added. Conclusions unchanged
Increasing the simulation performance of large-scale evacuations using parallel computing techniques based on domain decomposition
Evacuation simulation has the potential to be used as part of a decision support system during large-scale incidents to provide advice to incident commanders. To be viable in these applications, it is essential that the simulation can run many times faster than real time. Parallel processing is a method of reducing run times for very large computational simulations by distributing the workload amongst a number of processors. This paper presents the development of a parallel version of the rule based evacuation simulation software buildingEXODUS using domain decomposition. Four Case Studies (CS) were tested using a cluster, consisting of 10 Intel Core 2 Duo (dual core) 3.16 GHz CPUs. CS-1 involved an idealised large geometry, with 20 exits, intended to illustrate the peak computational speed up performance of the parallel implementation, the population consisted of 100,000 agents; the peak computational speedup (PCS) was 14.6 and the peak real-time speedup (PRTS) was 4.0. CS-2 was a long area with a single exit area with a population of 100,000 agents; the PCS was 13.2 and the PRTS was 17.2. CS-3 was a 50 storey high rise building with a population of 8000/16,000 agents; the PCS was 2.48/4.49 and the PRTS was 17.9/12.9. CS-4 is a large realistic urban area with 60,000/120,000 agents; the PCS was 5.3/6.89 and the PRTS was 5.31/3.0. This type of computational performance opens evacuation simulation to a range of new innovative application areas such as real-time incident support, dynamic signage in smart buildings and virtual training environments
The composition of the protosolar disk and the formation conditions for comets
Conditions in the protosolar nebula have left their mark in the composition
of cometary volatiles, thought to be some of the most pristine material in the
solar system. Cometary compositions represent the end point of processing that
began in the parent molecular cloud core and continued through the collapse of
that core to form the protosun and the solar nebula, and finally during the
evolution of the solar nebula itself as the cometary bodies were accreting.
Disentangling the effects of the various epochs on the final composition of a
comet is complicated. But comets are not the only source of information about
the solar nebula. Protostellar disks around young stars similar to the protosun
provide a way of investigating the evolution of disks similar to the solar
nebula while they are in the process of evolving to form their own solar
systems. In this way we can learn about the physical and chemical conditions
under which comets formed, and about the types of dynamical processing that
shaped the solar system we see today.
This paper summarizes some recent contributions to our understanding of both
cometary volatiles and the composition, structure and evolution of protostellar
disks.Comment: To appear in Space Science Reviews. The final publication is
available at Springer via http://dx.doi.org/10.1007/s11214-015-0167-
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