Modeling X-ray emission from stellar coronae

By extrapolating from observationally derived surface magnetograms of low-mass stars we construct models of their coronal magnetic fields and compare the 3D field geometry with axial multipoles. AB Dor, which has a radiative core, has a very complex field, whereas V374 Peg, which is completely convective, has a simple dipolar field. We calculate global X-ray emission measures assuming that the plasma trapped along the coronal loops is in hydrostatic equilibrium and compare the differences between assuming isothermal coronae, or by considering a loop temperature profiles. Our preliminary results suggest that the non-isothermal model works well for the complex field of AB Dor, but not for the simple field of V374 Peg.Comment: 4 pages, proceedings of Cool Stars 15, St Andrews, July 2008, to be published in the Conference Proceedings Series of the American Institute of Physic

1999 Fine Art Graduation Exhibition Catalogue

Graduation Exhibition 1999 Fine Art ProgramFanshawe College London Regional Art & Historical Museum April 14 to May 16, 1999 Guest Speaker: Arlene KennedyDirector, McIntosh GalleryUWO London, Ontariohttps://first.fanshawec.ca/famd_design_fineart_gradcatalogues/1028/thumbnail.jp

Next-Generation Technology and Electoral Democracy: Understanding the Changing Environment

Democracies around the world are facing growing threats to their electoral systems in the digital age. Foreign interference in the form of dis- and misinformation has already influenced the results of democratic elections and altered the course of history. This special report, the result of a research project conducted in partnership with the Konrad-Adenauer-Stiftung (KAS) Canada, examines these cyberthreats from a Canadian and German perspective. Both Canada and Germany share common goals centred around protecting human rights, democracy and the rule of law, and international peace and security. Using case studies from experts in fields such as computer science, law and public policy, the special report offers recommendations to guide policy makers and stakeholders on how to protect elections from next-generation technologies and the threats they pose to democracy

X-Ray flares in Orion Young Stars. II. Flares, Magnetospheres, and Protoplanetary Disks

We study the properties of powerful X-ray flares from 161 pre-main sequence (PMS) stars observed with the Chandra X-ray Observatory in the Orion Nebula region. Relationships between flare properties, protoplanetary disks and accretion are examined in detail to test models of star-disk interactions at the inner edge of the accretion disks. Previous studies had found no differences in flaring between diskfree and accreting systems other than a small overall diminution of X-ray luminosity in accreting systems. The most important finding is that X-ray coronal extents in fast-rotating diskfree stars can significantly exceed the Keplerian corotation radius, whereas X-ray loop sizes in disky and accreting systems do not exceed the corotation radius. This is consistent with models of star-disk magnetic interaction where the inner disk truncates and confines the PMS stellar magnetosphere. We also find two differences between flares in accreting and diskfree PMS stars. First, a subclass of super-hot flares with peak plasma temperatures exceeding 100 MK are preferentially present in accreting systems. Second, we tentatively find that accreting stars produce flares with shorter durations. Both results may be consequences of the distortion and destabilization of the stellar magnetosphere by the interacting disk. Finally, we find no evidence that any flare types, even slow-rise flat-top flares are produced in star-disk magnetic loops. All are consistent with enhanced solar long-duration events with both footprints anchored in the stellar surface.Comment: Accepted for publication in ApJ (07/17/08); 46 pages, 14 figures, 2 table

X-ray flares in Orion young stars. I. Flare characteristics

Pre-main sequence (PMS) stars are known to produce powerful X-ray flares which resemble magnetic reconnection solar flares scaled by factors up to 10^4. However, numerous puzzles are present including the structure of X-ray emitting coronae and magnetospheres, effects of protoplanetary disks, and effects of stellar rotation. To investigate these issues in detail, we examine 216 of the brightest flares from 161 PMS stars observed in the Chandra Orion Ultradeep Project (COUP). These constitute the largest homogeneous dataset of PMS, or indeed stellar flares at any stellar age, ever acquired. Our effort is based on a new flare spectral analysis technique that avoids nonlinear parametric modeling. It can be applied to much weaker flares and is more sensitive than standard methods. We provide a catalog with >30 derived flare properties and an electronic atlas for this unique collection of stellar X-ray flares. The current study (Paper I) examines the flare morphologies, and provides general comparison of COUP flare characteristics with those of other active X-ray stars and the Sun. Paper II will concentrate on relationships between flare behavior, protoplanetary disks, and other stellar properties. Several results are obtained. First, the COUP flares studied here are among the most powerful, longest, and hottest stellar X-ray flares ever studied. Second, no significant statistical differences in peak flare luminosity or temperature distributions are found among different morphological flare classes, suggesting a common underlying mechanism for all flares. Third, comparison with the general solar-scaling laws indicates that COUP flares may not fit adequately proposed power-temperature and duration-temperature solar-stellar fits. Fourth, COUP super-hot flares are found to be brighter but shorter than ... ABRIDGEDComment: Accepted for publication in ApJ (07/11/08); 63 pages, 16 figures, 4 table

Trends in reasons for emergency calls during the COVID-19 crisis in the department of Gironde, France using artificial neural network for natural language classification

Abstract Objectives During periods such as the COVID-19 crisis, there is a need for responsive public health surveillance indicators in order to monitor both the epidemic growth and potential public health consequences of preventative measures such as lockdown. We assessed whether the automatic classification of the content of calls to emergency medical communication centers could provide relevant and responsive indicators. Methods We retrieved all 796,209 free-text call reports from the emergency medical communication center of the Gironde department, France, between 2018 and 2020. We trained a natural language processing neural network model with a mixed unsupervised/supervised method to classify all reasons for calls in 2020. Validation and parameter adjustment were performed using a sample of 39,907 manually-coded free-text reports. Results The number of daily calls for flu-like symptoms began to increase from February 21, 2020 and reached an unprecedented level by February 28, 2020 and peaked on March 14, 2020, 3 days before lockdown. It was strongly correlated with daily emergency room admissions, with a delay of 14 days. Calls for chest pain and stress and anxiety, peaked 12 days later. Calls for malaises with loss of consciousness, non-voluntary injuries and alcohol intoxications sharply decreased, starting one month before lockdown. No noticeable trends in relation to lockdown was found for other groups of reasons including gastroenteritis and abdominal pain, stroke, suicide and self-harm, pregnancy and delivery problems. Discussion The first wave of the COVID-19 crisis came along with increased levels of stress and anxiety but no increase in alcohol intoxication and violence. As expected, call related to road traffic crashes sharply decreased. The sharp decrease in the number of calls for malaise was more surprising. Conclusion The content of calls to emergency medical communication centers is an efficient epidemiological surveillance data source that provides insights into the societal upheavals induced by a health crisis. The use of an automatic classification system using artificial intelligence makes it possible to free itself from the context that could influence a human coder, especially in a crisis situation. The COVID-19 crisis and/or lockdown induced deep modifications in the population health profile.Surveillance épidémiologique de la période pandémique covid-19 par classification automatique en temps réel des notes cliniques des centres d'appels d'urgence du 15 à l'aide de réseaux de neurones artificiels de type Transformer

Serine/Threonine Kinase 17A is a Novel Candidate for Therapeutic Targeting in Glioblastoma

STK17A is a relatively uncharacterized member of the death-associated protein family of serine/threonine kinases which have previously been associated with cell death and apoptosis. Our prior work established that STK17A is a novel p53 target gene that is induced by a variety of DNA damaging agents in a p53-dependent manner. In this study we have uncovered an additional, unanticipated role for STK17A as a candidate promoter of cell proliferation and survival in glioblastoma (GBM). Unexpectedly, it was found that STK17A is highly overexpressed in a grade-dependent manner in gliomas compared to normal brain and other cancer cell types with the highest level of expression in GBM. Knockdown of STK17A in GBM cells results in a dramatic alteration in cell shape that is associated with decreased proliferation, clonogenicity, migration, invasion and anchorage independent colony formation. STK17A knockdown also sensitizes GBM cells to genotoxic stress. STK17A overexpression is associated with a significant survival disadvantage among patients with glioma which is independent of age, molecular phenotype, IDH1 mutation, PTEN loss, and alterations in the p53 pathway and partially independent of grade. In summary, we demonstrate that STK17A provides a proliferative and survival advantage to GBM cells and is a potential target to be exploited therapeutically in patients with glioma

Predicting drowning from sea and weather forecasts: development and validation of a model on surf beaches of southwestern France

OBJECTIVE: To predict the coast-wide risk of drowning along the surf beaches of Gironde, southwestern France. METHODS: Data on rescues and drownings were collected from the Medical Emergency Center of Gironde (SAMU 33). Seasonality, holidays, weekends, weather and metocean conditions were considered potentially predictive. Logistic regression models were fitted with data from 2011 to 2013 and used to predict 2015-2017 events employing weather and ocean forecasts. RESULTS: Air temperature, wave parameters, seasonality and holidays were associated with drownings. Prospective validation was performed on 617 days, covering 232 events (rescues and drownings) reported on 104 different days. The area under the curve (AUC) of the daily risk prediction model (combined with 3-day forecasts) was 0.82 (95% CI 0.79 to 0.86). The AUC of the 3-hour step model was 0.85 (95% CI 0.81 to 0.88). CONCLUSIONS: Drowning events along the Gironde surf coast can be anticipated up to 3 days in advance. Preventative messages and rescue preparations could be increased as the forecast risk increased, especially during the off-peak season, when the number of available rescuers is low

X-rays in the Orion Nebula Cluster: Constraints on the origins of magnetic activity in pre-main sequence stars

A recent Chandra/ACIS observation of the Orion Nebula Cluster detected 1075 sources (Feigelson et al. 2002), providing a uniquely large and well-defined sample to study the dependence of magnetic activity on bulk properties for stars descending the Hayashi tracks. The following results are obtained: (1) X-ray luminosities L_t in the 0.5-8 keV band are strongly correlated with bolometric luminosity with = -3.8 for stars with masses 0.7<M<2 Mo, an order of magnitude below the main sequence saturation level; (2) the X-ray emission drops rapidly below this level in some or all stars with 2<M<3 Mo; (3) the presence or absence of infrared circumstellar disks has no apparent relation to X-ray levels; and (4) X-ray luminosities exhibit a slight rise as rotational periods increase from 0.4 to 20 days. This last finding stands in dramatic contrast to the strong anticorrelation between X-rays and period seen in main sequence stars. The absence of a strong X-ray/rotation relationship in PMS stars, and particularly the high X-ray values seen in some very slowly rotating stars, is a clear indication that the mechanisms of magnetic field generation differ from those operating in main sequence stars. The most promising possibility is a turbulent dynamo distributed throughout the deep convection zone, but other models such as alpha-Omega dynamo with `supersaturation' or relic core fields are not immediately excluded. The drop in magnetic activity in intermediate-mass stars may reflect the presence of a significant radiative core. The evidence does not support X-ray production in large-scale star-disk magnetic fields.Comment: 51 pages, 8 figures. To appear in the Astrophysical Journa