620 research outputs found
Field-based effects of allelopathy in invaded tallgrass prairie
Allelopathic phytochemicals have been linked to invasion success, but their role in the invasion process remains unclear. Toxicity effects demonstrated with lab bioassays may be neutralized in soils, and their role in population expansion can be intertwined with nonallelopathic processes that also influence dispersal and establishment. Here, we use greenhouse experiments to test the soil-based impacts of invasive fine fescue (Festuca rubra L.) on recruitment in tallgrass prairie. Fescue roots release the growth inhibitor m-tyrosine. Using root washes and fescue-conditioned soils to mimic field potency, we determined allelopathic impacts on recruitment, including intraspecific limitation. We also tested whether nonallelopathic factors (propagule pressure, disturbance, and fertility) influence invasion into constructed fescue and prairie mesocosms, and whether root washes inhibit arbuscular mycorrhizal (AM) fungi. We observed significant negative effects of fescue soils and root washes on germination and seedling survival, including on fescue itself. Mesocosm invasion, however, was determined more by nonallelopathic mechanisms (propagule pressure and rapid growth). In prairie mesocosms, fescue invasion was higher than its own understory, with no effects of disturbance or fertility. Tallgrass species had difficulty establishing in all environments, regardless of propagule pressure. Impacts on AM fungal hyphal length and spore production were insignificant. Our results suggest that nonallelopathic traits may be sufficient to explain fescue invasion, with allelopathy likely emerging as a final "coup de grâce" for recruiting native grasses once dominance has been attained. Allelopathic species, including fine fescue, may thus not necessarily be invasive unless nonallelopathic traits facilitate establishment prior to the accumulation of soil-based toxins
Presentation of B-cell lymphoma in childhood and adolescence: a systematic review and meta-analysis
Background: The diagnosis of B-cell lymphoma, one of the commonest cancers seen in childhood and adolescence, is challenging. There is a crucial need to identify and delineate the prevalence of associated symptoms in order to improve early diagnosis. Aims: To identify clinical presentations associated with childhood and adolescent B-cell lymphomas and estimate symptom prevalence. Methods: A systematic review of observational studies and meta-analysis of proportions was carried out. Medline and EMBASE were systematically searched, with no language restrictions, from inception to 1st August 2022. Observational studies with at least 10 participants, exploring clinical presentations of any childhood and adolescent lymphoma, were selected. Proportions from each study were inputted to determine the weighted average (pooled) proportion, through random-effects meta-analysis. Results: Studies reported on symptoms, signs and presentation sites at diagnosis of 12,207 children and adolescents up to the age of 20. Hodgkin’s lymphoma most frequently presented with adenopathy in the head-and-neck region (79% [95% CI 58%-91%]), whilst non-Hodgkin’s lymphoma presented abdominally (55% [95% CI 43%-68%]). Symptoms associated with lymphoma included cervical lymphadenopathy (48% [95% CI 20%-77%]), peripheral lymphadenopathy (51% [95% CI 37%-66%]), B-symptoms (40% [95% CI 34%-44%]), fever (43% [95% CI 34%-54%]), abdominal mass (46% [95% CI 29%-64%]), weight loss (53% [95% CI 39%-66%]), head-and-neck mass (21% [95% CI 6%-47%]), organomegaly (29% [95% CI 23%-37%]), night sweats (19% [95% CI 10%-32%]), abdominal pain (28% [95% CI 15%-47%]), bone pain (17% [95% CI 10%-28%]) and abnormal neurology (11% [95% CI 3%-28%]). Conclusion: This systematic review and meta-analysis of proportions provides insight into the heterogeneous clinical presentations of B-cell lymphoma in childhood and adolescence and provides estimates of symptom prevalence. This information is likely to increase public and clinical awareness of lymphoma presentations and aid earlier diagnosis. This review further highlights the lack of studies exploring childhood and adolescent lymphoma presentations in primary care, where patients are likely to present at the earliest stages of their disease
Rotational modulation of X-ray emission in Orion Nebula young stars
We investigate the spatial distribution of X-ray emitting plasma in a sample
of young Orion Nebula Cluster stars by modulation of their X-ray light-curves
due to stellar rotation. The study, part of the Chandra Orion Ultradeep Project
(COUP), is made possible by the exceptional length of the observation: 10 days
of ACIS integration during a time span of 13 days, yielding a total of 1616
detected sources in the 17x17 arcmin field of view. We here focus on a
subsample of 233 X-ray-bright stars with known rotational periods. We search
for X-ray modulation using the Lomb Normalized Periodogram method.
X-ray modulation related to the rotation period is detected in at least 23
stars with periods between 2 and 12 days and relative amplitudes ranging from
20% to 70%. In 16 cases, the X-ray modulation period is similar to the stellar
rotation period while in seven cases it is about half that value, possibly due
to the presence of X-ray emitting structures at opposite stellar longitudes.
These results constitute the largest sample of low mass stars in which X-ray
rotational modulation has been observed. The detection of rotational modulation
indicates that the X-ray emitting regions are distributed inhomogeneneously in
longitude and do not extend to distances significantly larger than the stellar
radius. Modulation is observed in stars with saturated activity levels
(L_X/L_bol ~ 10^(-3)) showing that saturation is not due to the filling of the
stellar surface with X-ray emitting regions.Comment: 41 pages, 15 figures, ApJS in press. Figure 15 (34 panels) is an
on-line only figure and is not included. A pdf file which includes figure 15
as well as full resolution versions of figure 10 and 11 is available at:
http://www.astropa.unipa.it/~ettoref/COUP_RotMod.pd
High-amplitude, long-term X-ray variability in the solar-type star HD 81809: the beginning of an X-ray activity cycle?
We present the initial results from our XMM program aimed at searching for
X-ray activity cycles in solar-type stars. HD 81809 is a G2-type star (somewhat
more evolved than the Sun, and with a less massive companion) with a pronounced
8.2 yr chromospheric cycle, as evident from from the Mt. Wilson program data.
We present here the results from the initial 2.5 years of XMM observations,
showing that large amplitude (a factor of approx. 10) modulation is present in
the X-ray luminosity, with a clearly defined maximum in mid 2002 and a steady
decrease since then. The maximum of the chromospheric cycle took place in 2001;
if the observed X-ray variability is the initial part of an X-ray cycle, this
could imply a phase shift between chromospheric and coronal activity, although
the current descent into chromospheric cycle minimum is well reflected into the
star's X-ray luminosity. The observations presented here provide clear evidence
for the presence of large amplitude X-ray variability coherent with the
activity cycle in the chromosphere in a star other than the Sun.Comment: Accepted for publication in A&
ROSAT HRI Observations of the Crab Pulsar: An Improved Temperature upper limit for PSR 0531+21
ROSAT HRI observations have been used to determine an upper limit of the Crab
pulsar surface temperature from the off-pulse count rate. For a neutron star
mass of 1.4 \Mo and a radius of 10 km as well as the standard distance and
interstellar column density, the redshifted temperature upper limit is\/
K . This is the lowest temperature
upper limit obtained for the Crab pulsar so far. Slightly different values for
are computed for the various neutron star models available in the
literature, reflecting the difference in the equation of state.Comment: 5 pages, uuencoded postscript, to be published in the Proceedings of
the NATO Advanced Study Insitute on "Lives of the Neutron Stars", ed. A.
Alpar, U. Kiziloglu and J. van Paradijs ( Kluwer, Dordrecht, 1995 )
Chandra Orion Ultradeep Project: Observations and Source Lists
We present a description of the data reduction methods and the derived
catalog of more than 1600 X-ray point sources from the exceptionally deep
January 2003 Chandra X-ray Observatory observation of the Orion Nebula Cluster
and embedded populations around OMC-1. The observation was obtained with
Chandra's Advanced CCD Imaging Spectrometer (ACIS) and has been nicknamed the
Chandra Orion Ultradeep Project (COUP). With an 838 ks exposure made over a
continuous period of 13.2 days, the COUP observation provides the most uniform
and comprehensive dataset on the X-ray emission of normal stars ever obtained
in the history of X-ray astronomy.Comment: 52 pages, 11 figures, 12 tables. Accepted for publication in ApJS,
special issue dedicated to Chandra Orion Ultradeep Project. A version with
high quality figures can be found at
http://www.astro.psu.edu/users/gkosta/COUP_Methodology.pd
Clinical characteristics of pertussis-associated cough in adults and children: a diagnostic systematic review and meta-analysis
Background: Pertussis (whooping cough) is a highly infective cause of cough that causes significant morbidity and mortality. Existing case definitions include paroxysmal cough, whooping and post-tussive vomiting but diagnosis can be difficult. We determined the diagnostic accuracy of clinical characteristics of pertussis-associated cough. Methods: We systematically searched CINAHL, Embase, Medline and SCI-EXPANDED/CPCI-S up to June 2016. Eligible studies compared clinical characteristics in those positive and negative for Bordetella pertussis infection, confirmed by laboratory investigations. Two authors independently completed screening, data extraction and quality and bias assessments. For each characteristic RevMan was used to produce descriptive forest plots. We used the bivariate meta-analysis method to generate pooled estimates of sensitivity and specificity. Results: Of 1969 identified papers, 53 were included. Forty-one clinical characteristics were assessed for diagnostic accuracy. In adult patients, paroxysmal cough and absence of fever had a high sensitivity (93.2%, CI 83.2-97.4 and 81.8%, CI 72.2-88.7 respectively) and low specificity (20.6%, CI 14.7-28.1 and 18.8%, CI 8.1-37.9 respectively), whereas post-tussive vomiting and whooping had low sensitivity (32.5%, CI 24.5-41.6 and 29.8%, CI 8.0-45.2 respectively) and high specificity (77.7%, CI 73.1-81.7 and 79.5%, CI 69.4-86.9 respectively). Post-tussive vomiting in children is moderately sensitive (60.0%, CI 40.3-77.0) and specific 66.0%, CI 52.5-77.3). Conclusions: In adult patients the presence of whooping or post-tussive vomiting should rule in a possible diagnosis of pertussis, whereas the lack of a paroxysmal cough or the presence of fever should rule it out. In children, post-tussive vomiting is much less helpful as a clinical diagnostic test
The conspicuous absence of X-ray emission from carbon-enriched Wolf-Rayet stars
The carbon-rich WC5 star WR 114 was not detected during a 15.9 ksec XMM-Newton observation, implying an upper limit to the X- ray luminosity of L-X less than or similar to 2.5 x 10(30) erg s(-1) and to the X-ray to bolometric luminosity ratio of L- X/L(bo)l less than or similar to 4 x 10(-9). This confirms indications from earlier less sensitive measurements that there has been no convincing X-ray detection of any single WC star. This lack of detections is reinforced by XMM-Newton and Chandra observations of WC stars. Thus the conclusion has to be drawn that the stars with radiatively-driven stellar winds of this particular class are insignificant X-ray sources. We attribute this to photoelectronic absorption by the stellar wind. The high opacity of the metal-rich and dense winds from WC stars puts the radius of optical depth unity at hundreds or thousands of stellar radii for much of the X-ray band. We believe that the essential absence of hot plasma so far out in the wind exacerbated by the large distances and correspondingly high ISM column densities makes the WC stars too faint to be detectable with current technology. The result also applies to many WC stars in binary systems, of which only about 20% are identified X-ray sources, presumably due to colliding winds
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