2,722 research outputs found
A Suzaku, NuSTAR, and XMM-Newton view on variable absorption and relativistic reflection in NGC 4151
We disentangle X-ray disk reflection from complex line-of-sight absorption in
the nearby Seyfert NGC 4151, using a suite of Suzaku, NuSTAR, and XMM-Newton
observations. Extending upon earlier published work, we pursue a physically
motivated model using the latest angle-resolved version of the lamp-post
geometry reflection model relxillCp_lp together with a Comptonization
continuum. We use the long-look simultaneous Suzaku/NuSTAR observation to
develop a baseline model wherein we model reflected emission as a combination
of lamp-post components at the heights of 1.2 and 15.0 gravitational radii. We
argue for a vertically extended corona as opposed to two compact and distinct
primary sources. We find two neutral absorbers (one full-covering and one
partial-covering), an ionized absorber (), and a highly-ionized
ultra-fast outflow, which have all been reported previously. All analyzed
spectra are well described by this baseline model. The bulk of the spectral
variability between 1 keV and 6 keV can be accounted for by changes in the
column density of both neutral absorbers, which appear to be degenerate and
inversely correlated with the variable hard continuum component flux. We track
variability in absorption on both short (2 d) and long (1 yr) timescales;
the observed evolution is either consistent with changes in the absorber
structure (clumpy absorber at distances ranging from the broad line region
(BLR) to the inner torus or a dusty radiatively driven wind) or a geometrically
stable neutral absorber that becomes increasingly ionized at a rising flux
level. The soft X-rays below 1 keV are dominated by photoionized emission from
extended gas that may act as a warm mirror for the nuclear radiation.Comment: 21 pages, 19 figures, 8 tables, accepted for publication by A&
The Transition State in a Noisy Environment
Transition State Theory overestimates reaction rates in solution because
conventional dividing surfaces between reagents and products are crossed many
times by the same reactive trajectory. We describe a recipe for constructing a
time-dependent dividing surface free of such recrossings in the presence of
noise. The no-recrossing limit of Transition State Theory thus becomes
generally available for the description of reactions in a fluctuating
environment
Stochastic Transition States: Reaction Geometry amidst Noise
Classical transition state theory (TST) is the cornerstone of reaction rate
theory. It postulates a partition of phase space into reactant and product
regions, which are separated by a dividing surface that reactive trajectories
must cross. In order not to overestimate the reaction rate, the dynamics must
be free of recrossings of the dividing surface. This no-recrossing rule is
difficult (and sometimes impossible) to enforce, however, when a chemical
reaction takes place in a fluctuating environment such as a liquid.
High-accuracy approximations to the rate are well known when the solvent forces
are treated using stochastic representations, though again, exact no-recrossing
surfaces have not been available. To generalize the exact limit of TST to
reactive systems driven by noise, we introduce a time-dependent dividing
surface that is stochastically moving in phase space such that it is crossed
once and only once by each transition path
Action-derived molecular dynamics in the study of rare events
We present a practical method to generate classical trajectories with fixed
initial and final boundary conditions. Our method is based on the minimization
of a suitably defined discretized action. The method finds its most natural
application in the study of rare events. Its capabilities are illustrated by
non-trivial examples. The algorithm lends itself to straightforward
parallelization, and when combined with molecular dynamics (MD) it promises to
offer a powerful tool for the study of chemical reactions.Comment: 7 Pages, 4 Figures (3 in color), submitted to Phys. Rev. Let
Accountability, Strategy, and International Non-Governmental Organizations
Increased prominence and greater influence expose international non-governmental development and environmental organizations (INGOs) to increased demands for accountability from a wide variety of stakeholdersdonors, beneficiaries, staffs, and partners among others. This paper focuses on developing the concept of INGO accountability, first as an abstract concept and then as a strategic idea with very different implications for different INGO strategies. We examine those implications for INGOs that emphasize service delivery, capacity-building, and policy influence. We propose that INGOs committed to service delivery may owe more accountability to donors and service regulators; capacity-building INGOs may be particularly obligated to clients whose capacities are being enhanced; and policy influence INGOs may be especially accountable to political constituencies and to influence targets. INGOs that are expanding their activities to include new initiatives may need to reorganize their accountability systems to implement their strategies effectively. This publication is Hauser Center Working Paper No. 7. The Hauser Center Working Paper Series was launched during the summer of 2000. The Series enables the Hauser Center to share with a broad audience important works-in-progress written by Hauser Center scholars and researchers
Photoproduction of Positive Mesons from Hydrogen: Results
The center-of-mass differential cross section for photoproduction of positive pions from hydrogen has been measured by the methods described in the two previous abstracts, in the angular range 40° to 150°, for photons from 220 to 475 Mev. (Photon energies refer to the Laboratory System.) Results obtained by the two methods are in essential agreement. At 90°, dσ/dω has a maximum of 2.7 X 10^(-29) cm^2/sterad near 280 Mev and falls by a factor 5 at 450 Mev. The maximum in the excitation curve is even more pronounced at larger angles, but less pronounced at smaller ones. At 40° (c.m.) the peak occurs near 350 Mev and at 450 Mev the cross section has decreased only to 0.7 the, peak value. Angular distributions in the center-of-mass system show a marked assymetry about 90°, which changes character from low energy to high. Below 325 Mev, there ii a backward maximum, whereas above 375 Mev, there is a forward maximum. The total cross section reaches a maximum near 290 Mev and decreases by about a factor 3 at 450 Mev. The results below 300 Mev agree with the data already reported from Berkeley and Cornell
Deep breathing couples CSF and venous flow dynamics
Venous system pathologies have increasingly been linked to clinically relevant disorders of CSF circulation whereas the exact coupling mechanisms still remain unknown. In this work, flow dynamics of both systems were studied using real-time phase-contrast flow MRI in 16 healthy subjects during normal and forced breathing. Flow evaluations in the aqueduct, at cervical level C3 and lumbar level L3 for both the CSF and venous fluid systems reveal temporal modulations by forced respiration. During normal breathing cardiac-related flow modulations prevailed, while forced breathing shifted the dominant frequency of both CSF and venous flow spectra towards the respiratory component and prompted a correlation between CSF and venous flow in the large vessels. The average of flow magnitude of CSF was increased during forced breathing at all spinal and intracranial positions. Venous flow in the large vessels of the upper body decreased and in the lower body increased during forced breathing. Deep respiration couples interdependent venous and brain fluid flow—most likely mediated by intrathoracic and intraabdominal pressure changes. Further insights into the driving forces of CSF and venous circulation and their correlation will facilitate our understanding how the venous system links to intracranial pressure regulation and of related forms of hydrocephalus
On two-dimensional Bessel functions
The general properties of two-dimensional generalized Bessel functions are
discussed. Various asymptotic approximations are derived and applied to analyze
the basic structure of the two-dimensional Bessel functions as well as their
nodal lines.Comment: 25 pages, 17 figure
NuSTAR and Suzaku X-ray Spectroscopy of NGC 4151: Evidence for Reflection from the Inner Accretion Disk
We present X-ray timing and spectral analyses of simultaneous 150 ks Nuclear
Spectroscopic Telescope Array (NuSTAR) and Suzaku X-ray observations of the
Seyfert 1.5 galaxy NGC 4151. We disentangle the continuum emission, absorption,
and reflection properties of the active galactic nucleus (AGN) by applying
inner accretion disk reflection and absorption-dominated models. With a
time-averaged spectral analysis, we find strong evidence for relativistic
reflection from the inner accretion disk. We find that relativistic emission
arises from a highly ionized inner accretion disk with a steep emissivity
profile, which suggests an intense, compact illuminating source. We find a
preliminary, near-maximal black hole spin a>0.9 accounting for statistical and
systematic modeling errors. We find a relatively moderate reflection fraction
with respect to predictions for the lamp post geometry, in which the
illuminating corona is modeled as a point source. Through a time-resolved
spectral analysis, we find that modest coronal and inner disk reflection flux
variation drives the spectral variability during the observations. We discuss
various physical scenarios for the inner disk reflection model, and we find
that a compact corona is consistent with the observed features.Comment: 20 pages, 12 figures, accepted for publication in Ap
EFFECTS OF WINDOW ANGLING, FEEDER PLACEMENT, AND SCAVENGERS ON AVIAN MORTALITY AT PLATE GLASS
- …