234 research outputs found
Incidence of WISE -selected obscured AGNs in major mergers and interactions from the SDSS
We use the Wide-field Infrared Survey Explorer (WISE) and the Sloan Digital Sky Survey (SDSS) to confirm a connection between dust-obscured active galactic nuclei (AGNs) and galaxy merging. Using a new, volume-limited (z ≤ 0.08) catalogue of visually selected major mergers and galaxy–galaxy interactions from the SDSS, with stellar masses above 2 × 1010 M⊙, we find that major mergers (interactions) are 5–17 (3–5) times more likely to have red [3.4] − [4.6] colours associated with dust-obscured or ‘dusty’ AGNs, compared to non-merging galaxies with similar masses. Using published fibre spectral diagnostics, we map the [3.4] − [4.6] versus [4.6] − [12] colours of different emission-line galaxies and find that one-quarter of Seyferts have colours indicative of a dusty AGN. We find that AGNs are five times more likely to be obscured when hosted by a merging galaxy, half of AGNs hosted by a merger are dusty, and we find no enhanced frequency of optical AGNs in merging over non-merging galaxies. We conclude that undetected AGNs missed at shorter wavelengths are at the heart of the ongoing AGN-merger connection debate. The vast majority of mergers hosting dusty AGNs are star forming and located at the centres of Mhalo < 1013 M⊙ groups. Assuming plausibly short-duration dusty-AGN phases, we speculate that a large fraction of gas-rich mergers experience a brief obscured AGN phase, in agreement with the strong connection between central star formation and black hole growth seen in merger simulations
Incidence of WISE -selected obscured AGNs in major mergers and interactions from the SDSS
We use the Wide-field Infrared Survey Explorer (WISE) and the Sloan Digital Sky Survey (SDSS) to confirm a connection between dust-obscured active galactic nuclei (AGNs) and galaxy merging. Using a new, volume-limited (z ≤ 0.08) catalogue of visually selected major mergers and galaxy–galaxy interactions from the SDSS, with stellar masses above 2 × 1010 M⊙, we find that major mergers (interactions) are 5–17 (3–5) times more likely to have red [3.4] − [4.6] colours associated with dust-obscured or ‘dusty’ AGNs, compared to non-merging galaxies with similar masses. Using published fibre spectral diagnostics, we map the [3.4] − [4.6] versus [4.6] − [12] colours of different emission-line galaxies and find that one-quarter of Seyferts have colours indicative of a dusty AGN. We find that AGNs are five times more likely to be obscured when hosted by a merging galaxy, half of AGNs hosted by a merger are dusty, and we find no enhanced frequency of optical AGNs in merging over non-merging galaxies. We conclude that undetected AGNs missed at shorter wavelengths are at the heart of the ongoing AGN-merger connection debate. The vast majority of mergers hosting dusty AGNs are star forming and located at the centres of Mhalo < 1013 M⊙ groups. Assuming plausibly short-duration dusty-AGN phases, we speculate that a large fraction of gas-rich mergers experience a brief obscured AGN phase, in agreement with the strong connection between central star formation and black hole growth seen in merger simulations
A path integral approach to the dynamics of a random chain with rigid constraints
In this work the dynamics of a freely jointed random chain which fluctuates
at constant temperature in some viscous medium is studied. The chain is
regarded as a system of small particles which perform a brownian motion and are
subjected to rigid constraints which forbid the breaking of the chain. For
simplicity, all interactions among the particles have been switched off and the
number of dimensions has been limited to two. The problem of describing the
fluctuations of the chain in the limit in which it becomes a continuous system
is solved using a path integral approach, in which the constraints are imposed
with the insertion in the path integral of suitable Dirac delta functions. It
is shown that the probability distribution of the possible conformations in
which the fluctuating chain can be found during its evolution in time coincides
with the partition function of a field theory which is a generalization of the
nonlinear sigma model in two dimensions. Both the probability distribution and
the generating functional of the correlation functions of the positions of the
beads are computed explicitly in a semiclassical approximation for a
ring-shaped chain.Comment: 36 pages, 2 figures, LaTeX + REVTeX4 + graphicx, minor changes in the
text, reference adde
Two Derivations of the Master Equation of Quantum Brownian Motion
Central to many discussion of decoherence is a master equation for the
reduced density matrix of a massive particle experiencing scattering from its
surrounding environment, such as that of Joos and Zeh. Such master equations
enjoy a close relationship with spontaneous localization models, like the GRW
model. This aim of this paper is to present two derivations of the master
equation. The first derivation is a pedagogical model designed to illustrate
the origins of the master equation as simply as possible, focusing on physical
principles and without the complications of S-matrix theory. This derivation
may serve as a useful tutorial example for students attempting to learn this
subject area. The second is the opposite: a very general derivation using
non-relativistic many body field theory. It reduces to the equation of the type
given by Joos and Zeh in the one-particle sector, but correcting certain
numerical factors which have recently become significant in connection with
experimental tests of decoherence. This master equation also emphasizes the
role of local number density as the ``preferred basis'' for decoherence in this
model.Comment: 19 pages, RevTe
Rate of parity violation from measure concentration
We present a geometric argument determining the kinematic (phase-space)
factor contributing to the relative rate at which degrees of freedom of one
chirality come to dominate over degrees of freedom of opposite chirality, in
models with parity violation. We rely on the measure concentration of a subset
of a Euclidean cube which is controlled by an isoperimetric inequality. We
provide an interpretation of this result in terms of ideas of Statistical
Mechanics.Comment: 10 pages, no figure
Quantum Physics and Human Language
Human languages employ constructions that tacitly assume specific properties
of the limited range of phenomena they evolved to describe. These assumed
properties are true features of that limited context, but may not be general or
precise properties of all the physical situations allowed by fundamental
physics. In brief, human languages contain `excess baggage' that must be
qualified, discarded, or otherwise reformed to give a clear account in the
context of fundamental physics of even the everyday phenomena that the
languages evolved to describe. The surest route to clarity is to express the
constructions of human languages in the language of fundamental physical
theory, not the other way around. These ideas are illustrated by an analysis of
the verb `to happen' and the word `reality' in special relativity and the
modern quantum mechanics of closed systems.Comment: Contribution to the festschrift for G.C. Ghirardi on his 70th
Birthday, minor correction
Replication-Coupled DNA-Protein Crosslink Repair by SPRTN and the Proteasome in <i>Xenopus</i> Egg Extracts
Renormalization Group Theory for Global Asymptotic Analysis
We show with several examples that renormalization group (RG) theory can be
used to understand singular and reductive perturbation methods in a unified
fashion. Amplitude equations describing slow motion dynamics in nonequilibrium
phenomena are RG equations. The renormalized perturbation approach may be
simpler to use than other approaches, because it does not require the use of
asymptotic matching, and yields practically superior approximations.Comment: 13 pages, plain tex + uiucmac.tex (available from babbage.sissa.it),
one PostScript figure appended at end. Or (easier) get compressed postscript
file by anon ftp from gijoe.mrl.uiuc.edu (128.174.119.153), file
/pub/rg_sing_prl.ps.
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Accurate and sensitive quantification of protein-DNA binding affinity
Transcription factors (TFs) control gene expression by binding to genomic DNA in a sequence-specific manner. Mutations in TF binding sites are increasingly found to be associated with human disease, yet we currently lack robust methods to predict these sites. Here, we developed a versatile maximum likelihood framework named No Read Left Behind (NRLB) that infers a biophysical model of protein-DNA recognition across the full affinity range from a library of in vitro selected DNA binding sites. NRLB predicts human Max homodimer binding in near-perfect agreement with existing low-throughput measurements. It can capture the specificity of the p53 tetramer and distinguish multiple binding modes within a single sample. Additionally, we confirm that newly identified low-affinity enhancer binding sites are functional in vivo, and that their contribution to gene expression matches their predicted affinity. Our results establish a powerful paradigm for identifying protein binding sites and interpreting gene regulatory sequences in eukaryotic genomes
The Renormalization Group and Singular Perturbations: Multiple-Scales, Boundary Layers and Reductive Perturbation Theory
Perturbative renormalization group theory is developed as a unified tool for
global asymptotic analysis. With numerous examples, we illustrate its
application to ordinary differential equation problems involving multiple
scales, boundary layers with technically difficult asymptotic matching, and WKB
analysis. In contrast to conventional methods, the renormalization group
approach requires neither {\it ad hoc\/} assumptions about the structure of
perturbation series nor the use of asymptotic matching. Our renormalization
group approach provides approximate solutions which are practically superior to
those obtained conventionally, although the latter can be reproduced, if
desired, by appropriate expansion of the renormalization group approximant. We
show that the renormalization group equation may be interpreted as an amplitude
equation, and from this point of view develop reductive perturbation theory for
partial differential equations describing spatially-extended systems near
bifurcation points, deriving both amplitude equations and the center manifold.Comment: 44 pages, 2 Postscript figures, macro \uiucmac.tex available at macro
archives or at ftp://gijoe.mrl.uiuc.edu/pu
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