1,363 research outputs found
An XMM-Newton Survey of the Soft X-ray Background. II. An All-Sky Catalog of Diffuse O VII and O VIII Emission Intensities
We present an all-sky catalog of diffuse O VII and O VIII line intensities,
extracted from archival XMM observations. The O VII and O VIII intensities are
typically ~2-11 and <~3 ph/cm^2/s/sr (LU), respectively, although much brighter
intensities were also recorded. Our data set includes 217 directions observed
multiple times by XMM. The time variation of the intensities from such
directions may be used to constrain SWCX models. The O VII and O VIII
intensities typically vary by <~5 and <~2 LU between repeat observations,
although several intensity enhancements of >10 LU were observed. We compared
our measurements with SWCX models. The heliospheric SWCX intensity is expected
to vary with ecliptic latitude and solar cycle. We found that the observed
oxygen intensities generally decrease from solar maximum to solar minimum, both
at high ecliptic latitudes (as expected) and at low ecliptic latitudes (not as
expected). The geocoronal SWCX intensity is expected to depend on the solar
wind proton flux and on the sightline's path through the magnetosheath. The
intensity variations seen in directions that have been observed multiple times
are in poor agreement with the predictions of a geocoronal SWCX model. The
oxygen lines account for ~40-50% of the 3/4 keV X-ray background that is not
due to unresolved AGN, in good agreement with a previous measurement. However,
this fraction is not easily explained by a combination of SWCX emission and
emission from hot plasma in the halo. The line intensities tend to increase
with longitude toward the inner Galaxy, possibly due to an increase in the
supernova rate in that direction or the presence of a halo of accreted material
centered on the Galactic Center. The variation of intensity with Galactic
latitude differs in different octants of the sky, and cannot be explained by a
single simple plane-parallel or constant-intensity halo model. (Abridged)Comment: Accepted for publication in the Astrophysical Journal Supplement
Series. 29 pages (main body of paper) plus 85 pages (full versions of Tables
1, 2, and 4 - these tables will be published as machine-readable tables in
the journal, and appear in abbreviated form in the main body of the paper).
12 figures. v2: Minor corrections, conclusions unaltere
The Origin of the Hot Gas in the Galactic Halo: Confronting Models with XMM-Newton Observations
We compare the predictions of three physical models for the origin of the hot
halo gas with the observed halo X-ray emission, derived from 26 high-latitude
XMM-Newton observations of the soft X-ray background between l=120\degr and
l=240\degr. These observations were chosen from a much larger set of
observations as they are expected to be the least contaminated by solar wind
charge exchange emission. We characterize the halo emission in the XMM-Newton
band with a single-temperature plasma model. We find that the observed halo
temperature is fairly constant across the sky (~1.8e6-2.3e6 K), whereas the
halo emission measure varies by an order of magnitude (~0.0005-0.006 cm^-6 pc).
When we compare our observations with the model predictions, we find that most
of the hot gas observed with XMM-Newton does not reside in isolated extraplanar
supernova remnants -- this model predicts emission an order of magnitude too
faint. A model of a supernova-driven interstellar medium, including the flow of
hot gas from the disk into the halo in a galactic fountain, gives good
agreement with the observed 0.4-2.0 keV surface brightness. This model
overpredicts the halo X-ray temperature by a factor of ~2, but there are a
several possible explanations for this discrepancy. We therefore conclude that
a major (possibly dominant) contributor to the halo X-ray emission observed
with XMM-Newton is a fountain of hot gas driven into the halo by disk
supernovae. However, we cannot rule out the possibility that the extended hot
halo of accreted material predicted by disk galaxy formation models also
contributes to the emission.Comment: 20 pages, 14 figures. New version accepted for publication in ApJ.
Changes include new section discussing systematic errors (Section 3.2),
improved method for characterizing our model spectra (4.2.2), changes to
discussion of other observations (5.1). Note that we can no longer rule out
possibility that extended hot halo of accreted material contributes to
observed halo emission (see 5.2.1
Design and performance testing of quantitative real time PCR assays for influenza A and B viral load measurement
Background: The antiviral effect of anti-influenza drugs such as zanamivir may be demonstrated in patients as an increased rate of decline in viral load over a time course of treatment as compared with placebo. Historically this was measured using plaque assays, or Culture Enhanced Enzyme Linked Immunosorbent Assay (CE-ELISA). Objectives: to develop and characterise real time quantitative PCR (qPCR) assays to measure influenza A and B viral load in clinical samples, that offer improvements over existing methods, in particular virus infectivity assays. Study design: The dynamic range and robustness were established for the real time qPCR assays along with stability of the assay components. Cross validation of the real time PCR assays with CE-ELISA was performed by parallel testing of both serial dilutions of three different subtypes of cultured virus and a panel of influenza positive throat swab specimens. Results: the assays were specific for influenza A and B and the dynamic ranges were at least seven logs. The assay variability was within acceptable limits but increased towards the lower limit of quantification, which was 3.33 log10 viral cDNA copies/ml of virus transport medium (ten viral RNA copies/PCR). The components of the assay were robust enough to withstand extended storage and several freeze–thawcycles. For the real time PCR assays the limit of quantification was equivalent to the virus infectivity cut off, which equates to a 93-fold increase in sensitivity. Conclusion: Well characterised real time PCR assays offer significant improvements over the existing methods for measuring the viral load of strains of influenza A and B in clinical specimens
The Duration of Spontaneous Active and Pushing Phases of Labour among 75,243 US women when intervention is minimal: A prospective, observational cohort study
Background Friedman\u27s curve, despite acknowledged limitations, has greatly influenced labour management. Interventions to hasten birth are now ubiquitous, challenging the contemporary study of normal labour. Our primary purpose was to characterise normal active labour and pushing durations in a large, contemporary sample experiencing minimal intervention, stratified by parity, age, and body mass index (BMI). Methods This is a secondary analysis of the national, validated Midwives Alliance of North America 4·0 (MANA Stats) data registry (n = 75,243), prospectively collected between Jan 1, 2012 and Dec 31, 2018 to describe labour and birth in home and birth center settings where common obstetric interventions [i.e., oxytocin, planned cesarean] are not available. The MANA Stats cohort includes pregnant people who intended birth in these settings and prospectively collects labour and birth processes and outcomes regardless of where birth or postpartum care ultimately occurs. Survival curves were calculated to estimate labour duration percentiles (e.g. 10th, 50th, 90th, and others of interest), by parity and sub-stratified by age and BMI. Findings Compared to multiparous women (n = 32,882), nulliparous women (n = 15,331) had significantly longer active labour [e.g., median 7.5 vs. 3.3 h; 95th percentile 34.8 vs. 12.0 h] and significantly longer pushing phase [e.g., median 1.1 vs. 0.2 h; 95th percentile 5.5 vs. 1.1 h]. Among nulliparous women, maternal age \u3e35 was associated with longer active first stage of labour and longer pushing phase, and BMI \u3e30 kg/m² was associated with a longer active first stage of labour but a shorter pushing phase. Patterns among multiparous women were different, with those \u3e35 years of age experiencing a slightly more rapid active labour and no difference in pushing duration, and those with BMI \u3e30 kg/m² experiencing a slightly longer active labour but, similarly, no difference in pushing duration. Interpretation Nulliparous women had significantly longer active first stage and pushing phase durations than multiparous women, with further variation noted by age and by BMI. Contemporary US women with low-risk pregnancies who intended birth in settings absent common obstetric interventions and in spontaneous labour with a live, vertex, term, singleton, non-anomalous fetus experienced labour durations that were often longer than prior characterizations, particularly among nulliparous women. Results overcome prior and current sampling limitations to refine understanding of normal labour durations and time thresholds signaling ‘labour dystocia’
Modeling the X-rays Resulting from High Velocity Clouds
With the goal of understanding why X-rays have been reported near some high
velocity clouds, we perform detailed 3 dimensional hydrodynamic and
magnetohydrodynamic simulations of clouds interacting with environmental gas
like that in the Galaxy's thick disk/halo or the Magellanic Stream. We examine
2 scenarios. In the first, clouds travel fast enough to shock-heat warm
environmental gas. In this scenario, the X-ray productivity depends strongly on
the speed of the cloud and the radiative cooling rate. In order to shock-heat
environmental gas to temperatures of > or = 10^6 K, cloud speeds of > or = 300
km/s are required. If cooling is quenched, then the shock-heated ambient gas is
X-ray emissive, producing bright X-rays in the 1/4 keV band and some X-rays in
the 3/4 keV band due to O VII and other ions. If, in contrast, the radiative
cooling rate is similar to that of collisional ionizational equilibrium plasma
with solar abundances, then the shocked gas is only mildly bright and for only
about 1 Myr. The predicted count rates for the non-radiative case are bright
enough to explain the count rate observed with XMM-Newton toward a Magellanic
Stream cloud and some enhancement in the ROSAT 1/4 keV count rate toward
Complex C, while the predicted count rates for the fully radiative case are
not. In the second scenario, the clouds travel through and mix with hot ambient
gas. The mixed zone can contain hot gas, but the hot portion of the mixed gas
is not as bright as those from the shock-heating scenario.Comment: 15 pages, 9 figures, 1 table. Accepted for publication in the
Astrophysical Journa
Hot Gas in the Galactic Thick Disk and Halo Near the Draco Cloud
This paper examines the ultraviolet and X-ray photons generated by hot gas in
the Galactic thick disk or halo in the Draco region of the northern hemisphere.
Our analysis uses the intensities from four ions, C IV, O VI, O VII, and O
VIII, sampling temperatures of ~100,000 to ~3,000,000 K. We measured the O VI,
O VII and O VIII intensities from FUSE and XMM-Newton data and subtracted off
the local contributions in order to deduce the thick disk/halo contributions.
These were supplemented with published C IV intensity and O VI column density
measurements. Our estimate of the thermal pressure in the O VI-rich thick
disk/halo gas, p_{th}/k = 6500^{+2500}_{-2600} K cm^{-3}, suggests that the
thick disk/halo is more highly pressurized than would be expected from
theoretical analyses. The ratios of C IV to O VI to O VII to O VIII,
intensities were compared with those predicted by theoretical models. Gas which
was heated to 3,000,000 K then allowed to cool radiatively cannot produce
enough C IV or O VI-generated photons per O VII or O VIII-generated photon.
Producing enough C IV and O VI emission requires heating additional gas to
100,000 < T < 1,000,000 K. However, shock heating, which provides heating
across this temperature range, overproduces O VI relative to the others.
Obtaining the observed mix may require a combination of several processes,
including some amount of shock heating, heat conduction, and mixing, as well as
radiative cooling of very hot gas.Comment: 10 pages, 2 figures. Accepted for publication in the Astrophysical
Journa
Autologous haematopoietic stem cell transplantation for refractory stiff-person syndrome: the UK experience
Stiff Person Syndrome (SPS) is a rare immune-mediated disabling neurological disorder characterised by muscle spasms and high GAD antibodies. There are only a few case reports of autologous haematopoietic stem cell transplantation (auto-HSCT) as a treatment for SPS.
Objective
To describe the UK experience of treating refractory SPS with auto-HSCT.
Methods
Between 2015 and 2019, 10 patients with SPS were referred to our institution for consideration of auto-HSCT. Eight patients were deemed suitable for autograft and four were treated. Of the treated patients, three had classical SPS and one had the progressive encephalomyelitis with rigidity and myoclonus variant. All patients were significantly disabled and had failed conventional immunosuppressive therapy. Patients were mobilised with Cyclophosphamide (Cy) 2 g/m2 + G-CSF and conditioned with Cy 200 mg/kg + ATG followed by auto-HSCT.
Results
Despite their significantly reduced performance status, all patients tolerated the procedure with no unexpected toxicities. Following autograft, all patients improved symptomatically and stopped all forms of immunosuppressive therapies. Two patients were able to ambulate independently from being wheelchair dependent. One patient’s walking distance improved from 300 meters to 5 miles and one patient’s ambulation improved from being confined to a wheelchair to be able to walk with a frame. Two patients became seronegative for anti-GAD antibodies and normalised their neurophysiological abnormalities.
Conclusions
Auto-HSCT is an intensive but well tolerated and effective treatment option for patients with SPS refractory to conventional immunotherapy. Further work is warranted to optimise patient selection and establish the efficacy, long-term safety, and cost-effectiveness of this treatment
Narrow Components within the Fe Kalpha Profile of NGC 3516: Evidence for the Importance of General Relativistic Effects?
We present results from a simultaneous Chandra HETG and XMM-Newton
observation of NGC 3516. We find evidence for several narrow components of Fe
Kalpha along with a broad line. We consider the possibility that the lines
arise in an blob of material ejected from the nucleus with velocity ~0.25c. We
also consider an origin in a neutral accretion disk, suffering enhanced
illumination at 35 and 175 gravitational radii, perhaps due to magnetic
reconnection. The presence of these narrow features indicates there is no
Comptonizing region along the line-of-sight to the nucleus. This in turn is
compelling support for the hypothesis that broad Fe Kalpha components are, in
general, produced by strong gravity.Comment: 12 pages, 3 color figures. LaTeX with postscript figures. Resubmitted
June 7 2002, to Astrophysical Journal Letter
Sustaining entrepreneurial business: a complexity perspective on processes that produce emergent practice
This article examines the management practices in an entrepreneurial small firm which sustain the business. Using a longitudinal qualitative case study, four general processes are identified (experimentation, reflexivity, organising and sensing), that together provide a mechanism to sustain the enterprise. The analysis draws on concepts from entrepreneurship and complexity science. We suggest that an entrepreneur’s awareness of the role of these parallel processes will facilitate their approaches to sustaining and developing enterprises. We also suggest that these processes operate in parallel at multiple levels, including the self, the business and inter-firm networks. This finding contributes to a general theory of entrepreneurship. A number of areas for further research are discussed arising from this result
Evidence for an X-ray Emitting Galactic Bulge: Shadows Cast by Distant Molecular Gas
A mosaic of 7 ROSAT PSPC pointed observations in the direction of (l,b ~ 10,0
deg) reveals deep X-ray shadows in the 0.5-2.0 keV band cast by dense molecular
gas. The comparison between the observed on-cloud and off-cloud X-ray fluxes
indicates that ~43% of the diffuse X-ray background in this direction in both
the 3/4 keV and 1.5 keV bands originates behind the molecular gas, which is
located at 2-4 kpc from the Sun. Given the short mean free path of X-rays in
the 3/4 keV band in the Galactic plane (~1 kpc assuming an average space
density of 1 cm^-3), this large percentage of the observed flux which
originates beyond the molecular gas most likely indicates a strong enhancement
in the distribution of X-ray emitting gas in the Galactic center region,
possibly associated with a Galactic X-ray bulge.Comment: 16 pages LaTex, 2 figures. Accepted for the publication in
Astrophysical Journal, Letter
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