1,306 research outputs found
Studies of hot B subdwarfs. Part 2: Energy distributions of three bright sdB/sdOB stars in the 950-5500 angstrom range
Voyager ultraviolet spectrometer observations of the subdwarf B or OB stars HD 205805, UV 1758+36 and Feige 66 are presented. All three objects display the H I Layman series in absorption. These observations are combined with low dispersion IUE spectrophotometry and with Stroemgren photometry to construct virtually complete energy distributions, which extend over the range 950-5500 angstroms. Effective temperatures based on model atmosphere calculations for high gravity, hydrogen rich stars are determined. Our analyses yield T Sub e 28,200 + or - 1300 K for HD 205805, T sub e 31, 800 + or - 1100 K for UV 1758+36, and T sub e 35,700 + or - 1500 K for Feige 66. The importance of far ultraviolet observations below L sub alpha in reducing the uncertainties associated with the interstellar extinction and the degradation of the IUE sensitivity is emphasized
Beyond the iron group: heavy metals in hot subdwarfs
We report the discovery of strong photospheric resonance lines of Ga III, Ge
IV, Sn IV and Pb IV in the UV spectra of more than two dozen sdB and sdOB stars
at temperatures ranging from 22000 K to 40000 K. Lines of other heavy elements
are also detected, however in these cases more atomic data are needed. Based on
these discoveries, we present a hypothesis to explain the apparent lack of
silicon in sdB stars hotter than ~32000 K. The existence of triply ionised Ge,
Sn, and Pb suggests that rather than silicon sinking deep into the photosphere,
it is removed from the star in a fractionated stellar wind. This hypothesis
provides a challenge to diffusion models of sdB stars.Comment: 5 pages, 3 figures, to appear in A&A Letter
Abundance studies of sdB stars using UV echelle HST/STIS spectroscopy
Aims: We test the hypothesis that the pulsations in sdB stars are correlated
with the surface abundances of iron-group elements. Any correlation might
explain why, when given two spectroscopically similar stars, one will pulsate
while the other will not. Methods: We have obtained high-resolution ultraviolet
spectra two pulsating and three non-pulsating sdB stars using the Space
Telescope Imaging Spectrograph onboard the Hubble Space Telescope. We
determined abundances for 25 elements including the iron group and even heavier
elements such as tin and lead using LTE curve-of-growth and spectrum synthesis
techniques. Results: We find no clear correlation between pulsations and metal
abundances, and we comment on the resulting implications, including whether it
is possible to determine the difference between a pulsating and a non-pulsating
sdB spectroscopically. In addition to the main goal of our observations, we
have also investigated the effect of supersolar metallicity on fundamental
parameter determination, possible trends with iron abundance, and the
hypothesis that weak winds may be selectively removing elements from the
stellar envelopes. These effects provide challenges to stellar atmosphere
modelling and diffusion models for sdB stars.Comment: 14 pages, 12 figures, accepted for publication in A&
Monitoring the Earthquake Activity in an Area with Shale Gas Potential in Southeastern New Brunswick, Canada
MRI-based classification of IDH mutation and 1p/19q codeletion status of gliomas using a 2.5D hybrid multi-task convolutional neural network
Isocitrate dehydrogenase (IDH) mutation and 1p/19q codeletion status are
important prognostic markers for glioma. Currently, they are determined using
invasive procedures. Our goal was to develop artificial intelligence-based
methods to non-invasively determine these molecular alterations from MRI. For
this purpose, pre-operative MRI scans of 2648 patients with gliomas (grade
II-IV) were collected from Washington University School of Medicine (WUSM; n =
835) and publicly available datasets viz. Brain Tumor Segmentation (BraTS; n =
378), LGG 1p/19q (n = 159), Ivy Glioblastoma Atlas Project (Ivy GAP; n = 41),
The Cancer Genome Atlas (TCGA; n = 461), and the Erasmus Glioma Database (EGD;
n = 774). A 2.5D hybrid convolutional neural network was proposed to
simultaneously localize the tumor and classify its molecular status by
leveraging imaging features from MR scans and prior knowledge features from
clinical records and tumor location. The models were tested on one internal
(TCGA) and two external (WUSM and EGD) test sets. For IDH, the best-performing
model achieved areas under the receiver operating characteristic (AUROC) of
0.925, 0.874, 0.933 and areas under the precision-recall curves (AUPRC) of
0.899, 0.702, 0.853 on the internal, WUSM, and EGD test sets, respectively. For
1p/19q, the best model achieved AUROCs of 0.782, 0.754, 0.842, and AUPRCs of
0.588, 0.713, 0.782, on those three data-splits, respectively. The high
accuracy of the model on unseen data showcases its generalization capabilities
and suggests its potential to perform a 'virtual biopsy' for tailoring
treatment planning and overall clinical management of gliomas
WRAPPING SURFACES TO CONTROL MOMENT ARM LENGTHS DURING A SQUAT TASK
Simulation of high flexion tasks such as squatting is hindered through invalid moment length estimation when using generic musculoskeletal (MSK) models. The purpose of this study was to examine the effect of wrapping surface (WS) at the knee and hip joints on the muscle moment arms calculated using a MSK model during squatting tasks. A generic full body model was modified by (1) increasing knee and hip flexion range of motion (ROM), (2) adjusting translation and size parameters of two WS, and (3) implementing three additional WS. Muscle moment-arm lengths were calculated in OpenSim using motion capture data. The WS prevent muscles to cross into the bones, and the moment arm length of several hip extensors reach a plateau after 85Âș of hip flexion. The use of the modified MSK that includes additional WS is suited for the analysis of high flexion tasks
Backward masked fearful faces enhance contralateral occipital cortical activity for visual targets within the spotlight of attention
Spatial attention has been argued to be adaptive by enhancing the processing of visual stimuli within the âspotlight of attentionâ. We previously reported that crude threat cues (backward masked fearful faces) facilitate spatial attention through a network of brain regions consisting of the amygdala, anterior cingulate and contralateral visual cortex. However, results from previous functional magnetic resonance imaging (fMRI) dot-probe studies have been inconclusive regarding a fearful face-elicited contralateral modulation of visual targets. Here, we tested the hypothesis that the capture of spatial attention by crude threat cues would facilitate processing of subsequently presented visual stimuli within the masked fearful face-elicited âspotlight of attentionâ in the contralateral visual cortex. Participants performed a backward masked fearful face dot-probe task while brain activity was measured with fMRI. Masked fearful face left visual field trials enhanced activity for spatially congruent targets in the right superior occipital gyrus, fusiform gyrus and lateral occipital complex, while masked fearful face right visual field trials enhanced activity in the left middle occipital gyrus. These data indicate that crude threat elicited spatial attention enhances the processing of subsequent visual stimuli in contralateral occipital cortex, which may occur by lowering neural activation thresholds in this retinotopic location
A 10-hour period revealed in optical spectra of the highly variable WN8 Wolf-Rayet star WR 123
Aims. What is the origin of the large-amplitude variability in Wolf-Rayet WN8
stars in general and WR123 in particular? A dedicated spectroscopic campaign
targets the ten-hour period previously found in the high-precision photometric
data obtained by the MOST satellite. Methods. In June-August 2003 we obtained a
series of high signal-to-noise, mid-resolution spectra from several sites in
the {\lambda}{\lambda} 4000 - 6940 A^{\circ} domain. We also followed the star
with occasional broadband (Johnson V) photometry. The acquired spectroscopy
allowed a detailed study of spectral variability on timescales from \sim 5
minutes to months. Results. We find that all observed spectral lines of a given
chemical element tend to show similar variations and that there is a good
correlation between the lines of different elements, without any significant
time delays, save the strong absorption components of the Hei lines, which tend
to vary differently from the emission parts. We find a single sustained
periodicity, P \sim 9.8 h, which is likely related to the relatively stable
pulsations found in MOST photometry obtained one year later. In addition,
seemingly stochastic, large-amplitude variations are also seen in all spectral
lines on timescales of several hours to several days.Comment: 6 pages, 4 figures, 2 tables, data available on-line, accepted in A&A
Research Note
Canadaâs Earthquakes: âThe Good, the Bad, and the Uglyâ
Much of Canada is âearthquake countryâ. Tiny earthquakes (that can only be recorded by seismographs) happen every day. On average, earthquakes large enough to be felt occur every week in Canada, damaging earthquakes are years to decades apart, and some of the worldâs largest earthquakes are typically separated by intervals of centuries. In this article, we provide details on the most significant earthquakes that have been recorded in, or near, Canada, including where and when they occurred, how they were felt, and the effects of those earthquakes. We also provide a brief review of how earthquakes are monitored across Canada and some recent earthquake hazard research. It is the results of this monitoring and research, which provide knowledge on earthquake hazard, that are incorporated into the National Building Code of Canada. This, in turn, will contribute to reduced property losses from future earthquakes across Canada.
SOMMAIRE
Un bonne partie du Canada est un âpays de sĂ©ismesâ. De petits sĂ©ismes (que seuls les sĂ©ismographes peuvent enregistrer) sây produisent quotidiennement. En moyenne, un sĂ©isme assez fort pour quâon le ressente sây produit Ă intervalle dâune semaine; assez fort pour causer des dommages sây produit Ă intervalle de quelques annĂ©es Ă quelques dĂ©cennies; alors que lâintervalle de rĂ©currence des plus grands sĂ©ismes est de lâordre des siĂšcles. Dans le prĂ©sent article on trouvera des dĂ©tails sur les plus importants sĂ©ismes sâĂ©tant produits sur ou Ă proximitĂ© du territoire canadien, incluant le lieu et le moment, leurs manifestations et leurs rĂ©percussions. On y dĂ©crit sommairement les moyens de dĂ©tection dĂ©ployĂ©s sur le territoire canadien ainsi que quelques-unes des recherches rĂ©centes sur les risques sismiques. Ce sont les rĂ©sultats des efforts de surveillance et des recherches sur les tremblements de terre qui ont Ă©tĂ© intĂ©grĂ©s dans le Code national du bĂątiment du Canada. Et cela aidera Ă amoindrir les rĂ©percussions des sĂ©ismes Ă venir sur la propriĂ©tĂ©
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