1,139 research outputs found
Diffuse 0.5-1 keV X-Rays and Nuclear Gamma-Rays from Fast Particles in the Local Hot Bubble
We show that interactions of fast particles with the boundary shell of the
local hot bubble could make an important contribution to the 0.5-1 keV diffuse
X-ray background observed with ROSAT. The bulk of these nonthermal X-rays are
due to line emission from fast O ions of energies around 1 MeV/nucleon. This is
the typical energy per particle in the ejecta of the supernova which is thought
to have energized the bubble. We find that there is sufficient total energy in
the ejecta to produce X-rays of the required intensity, subject to the details
of the evolution of the fast particle population since the supernova explosion
(about 3 10 years ago based on the age of the Geminga pulsar). The
unequivocal signature of lines from deexcitations in fast ions is their large
width (~0.1 for O lines), which will clearly distinguishes them
from X-ray lines produced in a hot plasma. If a small fraction of the total
ejecta energy is converted into accelerated particle kinetic energy (>~30
MeV/nucleon), the gamma-ray line emission produced in the boundary shell of the
local hot bubble could account for the recently reported COMPTEL observations
of nuclear gamma-ray lines from a broad region towards the Galactic center.Comment: 13 pages, 4 figures, submitted to Ap
The large-scale bias of the hard X-ray background
Recent deep X-ray surveys combined with spectroscopic identification of the
sources have allowed the determination of the rest-frame 2-8 keV luminosity as
a function of redshift. In addition, an analysis of the HEAO1 A2 2-10 keV
full-sky map of the X-ray background (XRB) reveals clustering on the scale of
several degrees. Combining these two results in the context of the currently
favored Lambda-CDM cosmological model implies an average X-ray bias factor,
b_x, of b_x^2 = 1.12 +- 0.33, i.e., b_x = 1.06 +- 0.16. These error estimates
include only statistical error; the systematic error sources, while comparable,
appear to be sub-dominant. This result is in contrast to the large biases of
some previous estimates and is more in line with current estimates of the
optical bias of L* galaxies.Comment: 6 pages, 3 eps figures, accepted for ApJ, vol. 612, 10 September 200
Role and rationale for the use of milnacipran in the management of fibromyalgia
Fibromyalgia (FM) is a complex syndrome characterized by chronic widespread musculoskeletal pain which is often accompanied by multiple other symptoms, including fatigue, sleep disturbances, decreased physical functioning, and dyscognition. Due to these multiple symptoms, as well as high rates of comorbidity with other related disorders, patients with FM often report a reduced quality of life. Although the pathophysiology of FM is not completely understood, patients with FM experience pain differently from the general population, most likely due to dysfunctional pain processing in the central nervous system leading to both hyperalgesia and allodynia. In many patients with FM, this aberrant pain processing, or central sensitization, appears to involve decreased pain inhibition within the spinal tract, which is mediated by descending pathways that utilize serotonin, norepinephrine, and other neurotransmitters. The reduced serotonin and norepinephrine levels observed in patients with FM suggest that medications which increase the levels of these neurotransmitters, such as serotonin and norepinephrine reuptake inhibitors (SNRIs), may have clinically beneficial effects in FM and other chronic pain conditions. Milnacipran is an SNRI that has been approved for the management of FM. In clinical trials, treatment with milnacipran for up to 1 year has been found to improve the pain and other symptoms of FM. Because FM is characterized by multiple symptoms that all contribute to the decreased quality of life and ability to function, the milnacipran pivotal trials implemented responder analyses. These utilized a single composite endpoint to identify the proportion of patients who reported simultaneous and clinically significant improvements in pain, global disease status, and physical function. Other domains assessed during the milnacipran trials include fatigue, multidimensional functioning, mood, sleep quality, and patient-reported dyscognition. This review article provides information intended to help clinicians make informed decisions about the use of milnacipran in the clinical management of patients with FM. It draws primarily on results from 2 of the pivotal clinical trials that formed the basis of approval of milnacipran in the United States by the Food and Drug Administration
Designing Personalized Treatment: An Application to Anticoagulation Therapy
In this study, we develop an analytical framework for personalizing the anticoagulation therapy of patients who are taking warfarin. Consistent with medical practice, our treatment design consists of two stages: (i) the initiation stage, modeled using a partially-observable Markov decision process, during which the physician learns through systematic belief updates about the unobservable patient sensitivity to warfarin, and (ii) the maintenance stage, modeled using a Markov decision process, during which the physician relies on his formed belief about patient sensitivity to determine the stable, patient-specific, warfarin dose to prescribe. We develop an expression for belief updates in the POMDP, establish the optimality of the myopic policy for the MDP, and derive conditions for the existence and uniqueness of a myopically optimal dose. We validate our models using a real-life patient data set gathered at the Hematology Clinic of the Jewish General Hospital in Montreal. The proposed analytical framework and case study enable us to develop useful clinical insights, for example, concerning the length of the initiation period and the importance of correctly assessing patient sensitivity
A strongly changing accretion morphology during the outburst decay of the neutron star X-ray binary 4U 1608â52
It is commonly assumed that the properties and geometry of the accretion flow in transient low-mass X-ray binaries (LMXBs) significantly change when the X-ray luminosity decays below âŒ10â»ÂČ of the Eddington limit (L_(Edd)). However, there are few observational cases where the evolution of the accretion flow is tracked in a single X-ray binary over a wide dynamic range. In this work, we use NuSTAR and NICER observations obtained during the 2018 accretion outburst of the neutron star LMXB 4U 1608â52, to study changes in the reflection spectrum. We find that the broad FeâKα line and Compton hump, clearly seen during the peak of the outburst when the X-ray luminosity is âŒ10Âłâ· erg sâ»Âč (âŒ0.05 L_(Edd)), disappear during the decay of the outburst when the source luminosity drops to âŒ4.5 Ă 10Âłâ” erg sâ»Âč (âŒ0.002 L_(Edd)). We show that this non-detection of the reflection features cannot be explained by the lower signal-to-noise ratio at lower flux, but is instead caused by physical changes in the accretion flow. Simulating synthetic NuSTAR observations on a grid of inner disc radius, disc ionization, and reflection fraction, we find that the disappearance of the reflection features can be explained by either increased disc ionization (logâΟ âł 4.1) or a much decreased reflection fraction. A changing disc truncation alone, however, cannot account for the lack of reprocessed FeâKα emission. The required increase in ionization parameter could occur if the inner accretion flow evaporates from a thin disc into a geometrically thicker flow, such as the commonly assumed formation of a radiatively inefficient accretion flow at lower mass accretion rates
Durability of Therapeutic Response to Milnacipran Treatment for Fibromyalgia. Results of a Randomized, Double-Blind, Monotherapy 6-Month Extension Study
To evaluate the durability of improvement and long-term efficacy of milnacipran treatment in fibromyalgia, to assess efficacy in patients re-randomized from placebo to milnacipran, and to collect additional information on the tolerability and efficacy of long-term treatment with milnacipran.A total of 449 patients who successfully completed a 6-month lead-in study enrolled in this 6-month extension study (87.7% of eligible subjects). Patients initially receiving milnacipran 200âmg/day during the lead-in study were maintained at 200âmg/day (nâ=â209); patients initially assigned to placebo or milnacipran 100âmg/day were re-randomized (1:4) to either 100âmg/day (nâ=â48) or 200âmg/day (nâ=â192) of milnacipran for an additional 6 months of treatment. Efficacy assessments included visual analog scale pain ratings, Fibromyalgia Impact Questionnaire (FIQ) total score, and Patient Global Impression of Change (PGIC).Patients continuing on milnacipran demonstrated a sustained reduction in pain over the full 12-month period. Additional beneficial effects were also maintained, as indicated by the PGIC and FIQ. Patients initially assigned to either placebo or milnacipran 100âmg/day in the lead-in study and subsequently re-randomized to milnacipran 200âmg/day in the extension study experienced further improvements in their mean pain scores, FIQ total scores, and PGIC ratings at 1 year. Milnacipran treatment was generally well tolerated. The most commonly reported newly emergent adverse event was nausea.In addition to confirming that milnacipran safely and effectively improves the multiple symptoms of fibromyalgia, these data indicate that milnacipran provides 1-year durable efficacy in this patient population.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78636/1/j.1526-4637.2009.00755.x.pd
The X-ray surface brightness distribution from diffuse gas
We use simulations to predict the X-ray surface brightness distribution
arising from hot, cosmologically distributed diffuse gas. The distribution is
computed for two bands: 0.5-2 keV and 0.1-0.4 keV, using a
cosmological-constant dominated cosmology that fits many other observations. We
examine a number of numerical issues such as resolution, simulation volume and
pixel size and show that the predicted mean background is sensitive to
resolution such that higher resolution systematically increases the mean
predicted background. Although this means that we can compute only lower bounds
to the predicted level, these bounds are already quite restrictive. Since the
observed extra-galactic X-ray background is mostly accounted for by compact
sources, the amount of the observed background attributable to diffuse gas is
tightly constrained. We show that without physical processes in addition to
those included in the simulations (such as radiative cooling or
non-gravitational heating), both bands exceed observational limits. In order to
examine the effect of non-gravitational heating we explore a simple modeling of
energy injection and show that substantial amounts of heating are required
(i.e. 5 keV per particle when averaged over all baryons). Finally, we also
compute the distribution of surface brightness on the sky and show that it has
a well-resolved characteristic shape. This shape is substantially modified by
non-gravitational heating and can be used as a probe of such energy injection.Comment: 11 pages, 11 figures, submitted to Ap
De l'homme au chiffre. Réflexions sur l'observation démographique en Afrique
Ce manuel aborde de façon concrÚte les problÚmes posés par la collecte des données démographiques à partir de l'expérience des praticiens du domaine. La définition des concepts et les problÚmes linguistiques sont envisagés. Les phases de réalisation d'une opération sont examinées à travers l'organisation du travail sur le terrain, la cartographie, l'exploitation des données et l'archivage des documents. La derniÚre partie présente les méthodes de collecte particuliÚres à certains thÚmes (fécondité, mortalité, migrations, emploi et activité
A Persistent Disk Wind in GRS 1915+105 with NICER
The bright, erratic black hole X-ray binary GRS 1915+105 has long been a
target for studies of disk instabilities, radio/infrared jets, and accretion
disk winds, with implications that often apply to sources that do not exhibit
its exotic X-ray variability. With the launch of NICER, we have a new
opportunity to study the disk wind in GRS 1915+105 and its variability on short
and long timescales. Here we present our analysis of 39 NICER observations of
GRS 1915+105 collected during five months of the mission data validation and
verification phase, focusing on Fe XXV and Fe XXVI absorption. We report the
detection of strong Fe XXVI in 32 (>80%) of these observations, with another
four marginal detections; Fe XXV is less common, but both likely arise in the
well-known disk wind. We explore how the properties of this wind depends on
broad characteristics of the X-ray lightcurve: mean count rate, hardness ratio,
and fractional RMS variability. The trends with count rate and RMS are
consistent with an average wind column density that is fairly steady between
observations but varies rapidly with the source on timescales of seconds. The
line dependence on spectral hardness echoes known behavior of disk winds in
outbursts of Galactic black holes; these results clearly indicate that NICER is
a powerful tool for studying black hole winds.Comment: Accepted for publication in ApJL. Comments welcom
The 3-53 keV Spectrum of the Quasar 1508+5714: X-rays from z = 4.3
We present a high-quality X-ray spectrum in the 3--53 keV rest-frame band of
the radio-loud quasar 1508+5714, by far the brightest known X-ray source at z >
4. A simple power-law model with an absorption column density equal to the
Galactic value in the direction of the source provides an excellent and fully
adequate fit to the data; the measured power-law photon index Gamma = 1.42
(+0.13,-0.10). Upper limits to Fe K alpha line emission and Compton-reflection
components are derived. We offer evidence for both X-ray and radio variability
in this object and provide the first contemporaneous radio spectrum (alpha =
-0.25). The data are all consistent with a picture in which the emission from
this source is dominated by a relativistically beamed component in both the
X-ray and radio bands.Comment: 8 pages, TeX, 2 postscript figures; to appear in ApJ Letter
- âŠ