839 research outputs found
A Reservoir of Ionized Gas in the Galactic Halo to Sustain Star Formation in the Milky Way
Without a source of new gas, our Galaxy would exhaust its supply of gas
through the formation of stars. Ionized gas clouds observed at high velocity
may be a reservoir of such gas, but their distances are key for placing them in
the Galactic halo and unraveling their role. We have used the Hubble Space
Telescope to blindly search for ionized high-velocity clouds (iHVCs) in the
foreground of Galactic stars. We show that iHVCs with 90 < |v_LSR| < 170 km/s
are within one Galactic radius of the sun and have enough mass to maintain star
formation, while iHVCs with |v_LSR|>170 km/s are at larger distances. These may
be the next wave of infalling material.Comment: This paper is part of a set of three papers on circumgalactic gas
observed with COS and STIS on HST, to be published in Science, together with
related papers by Tripp et al. and Tumlinson et al., in the November 18, 2011
edition. This version has not undergone final copyediting. Please see Science
online for the final printed versio
Unveiling GRB hard X-ray afterglow emission with Simbol-X
Despite the enormous progress occurred in the last 10 years, the Gamma-Ray
Bursts (GRB) phenomenon is still far to be fully understood. One of the most
important open issues that have still to be settled is the afterglow emission
above 10 keV, which is almost completely unexplored. This is due to the lack of
sensitive enough detectors operating in this energy band. The only detection,
by the BeppoSAX/PDS instrument (15-200 keV), of hard X-ray emission from a GRB
(the very bright GRB 990123), combined with optical and radio observations,
seriously challenged the standard scenario in which the dominant mechanism is
synchrotron radiation produced in the shock of a ultra-relativistic fireball
with the ISM, showing the need of a substantial revision of present models. In
this respect, thanks to its unprecedented sensitivity in the 10-80 keV energy
band, Simbol-X, through follow-up observations of bright GRBs detected and
localized by GRB dedicated experiments that will fly in the >2010 time frame,
will provide an important breakthrough in the GRB field.Comment: 4 pages, 2 figures. Paper presented at "Simbol-X: the hard X-ray
universe in focus", held in Bologna, Italy, on 14-16 May 2007. To be
published in Memorie della Societa' Astronomica Italian
Early Detection of Wild Rocket Tracheofusariosis Using Hyperspectral Image-Based Machine Learning
Fusarium oxysporum f. sp. raphani is responsible for wilting wild rocket (Diplotaxis tenuifolia L. [D.C.]). A machine learning model based on hyperspectral data was constructed to monitor disease progression. Thus, pathogenesis after artificial inoculation was monitored over a 15-day period by symptom assessment, qPCR pathogen quantification, and hyperspectral imaging. The host colonization by a pathogen evolved accordingly with symptoms as confirmed by qPCR. Spectral data showed differences as early as 5-day post infection and 12 hypespectral vegetation indices were selected to follow disease development. The hyperspectral dataset was used to feed the XGBoost machine learning algorithm with the aim of developing a model that discriminates between healthy and infected plants during the time. The multiple cross-prediction strategy of the pixel-level models was able to detect hyperspectral disease profiles with an average accuracy of 0.8. For healthy pixel detection, the mean Precision value was 0.78, the Recall was 0.88, and the F1 Score was 0.82. For infected pixel detection, the average evaluation metrics were Precision: 0.73, Recall: 0.57, and F1 Score: 0.63. Machine learning paves the way for automatic early detection of infected plants, even a few days after infection
Super-solar N/C in the NLS1 Galaxy Markarian 1044
Narrow-Line Seyfert 1s (NLS1s) are known to have extreme values of a number
of properties compared to Active Galactic Nuclei (AGN) as a class. In
particular, previous emission-line studies have suggested that NLS1s are
unusually metal rich compared to broad-line AGN of comparable luminosity. We
present low- and medium-resolution spectroscopic observations of the NLS1
Markarian 1044 with the Hubble Space Telescope Imaging Spectrometer (STIS). We
identify two blueshifted intrinsic absorption systems at -1145 and -295 km/s
relative to the systemic velocity of the galaxy. Using a simple photoionization
model of the absorbing gas, we find that the strongest and best-measured of the
absorption systems has N/C approximately 6.96 times the solar value. We also
report on the discovery of three new Ly-alpha forest lines with neutral
Hydrogen column density log greater than 12.77 in the log. This number is
consistent with the 2.6 expected in the path length to the source redshift of
Mrk 1044.Comment: Submitted to ApJ. 21 pages including 4 figures & 5 table
Neurological complications of sickle cell disease in Africa: protocol for a systematic review
INTRODUCTION: Sickle cell disease (SCD) is highly prevalent in Africa. Considered as a public health problem, it is associated with high morbidity and mortality. Neurological complications of SCD can cause significant disability with important socioeconomic and psychological impact on the patients and their families, and can even lead to death if not properly managed. There are important knowledge gaps regarding the burden of neurological complications of SCD in African populations. We propose to conduct the first systematic review to summarise the epidemiological data available on neurological complications of SCD in Africa. METHODS AND ANALYSIS: We will search PubMed, MEDLINE, EMBASE and the African Index Medicus from 1 January 1950 to 31 May 2016 for studies of neurological complications of SCD in Africa. After study selection, full-text paper acquisition, data extraction and synthesis, we will assess all studies for quality, risk of bias and heterogeneity. Appropriate methods of meta-analysis will be used to pool prevalence estimates from studies with similar features, globally and in major subgroups. This protocol complies with the 2015 Preferred Reporting Items for Systematic reviews and Meta-Analysis protocols (PRISMA-P) guidelines. ETHICS AND DISSEMINATION: The proposed study will use published data. Therefore, there is no requirement for ethical approval. This review is expected to provide relevant data to help quantify the burden of neurological complications of SCD in African populations, inform policymakers and identify further research topics. The final report of the systematic review will be published in a peer-reviewed journal and presented at conferences. REVIEW REGISTRATION NUMBER: CRD42016039574
The Equilibrium Photoionized Absorber in 3C351
We present two ROSAT PSPC observations of the radio-loud, lobe-dominated
quasar 3C 351, which shows an `ionized absorber' in its X-ray spectrum. The
factor 1.7 change in flux in the 2~years between the observations allows
a test of models for this ionized absorber.
The absorption feature at ~0.7 keV (quasar frame) is present in both spectra
but with a lower optical depth when the source intensity - and hence the
ionizing flux at the absorber - is higher, in accordance with a simple,
single-zone, equilibrium photoionization model. Detailed modeling confirms this
agrement quantitatively. The maximum response time of 2 years allows us to
limit the gas density: n_e > 2 x 10^4 cm^{-3}; and the distance of the ionized
gas from the central source R < 19 pc. This produces a strong test for a
photoionized absorber in 3C~351: a factor 2 flux change in ~1 week in this
source must show non-equilibrium effects in the ionized absorber.Comment: 10 pages, 3 figures, accepted by Ap
- …