scholarly journals Photospheric Activity in Selected Be Stars: λ Eri and γ Cas

1994 ◽  
Vol 162 ◽  
pp. 241-253
Author(s):  
Myron A. Smith
Keyword(s):  
X Rays ◽  
Be Stars ◽  
Process Thought ◽  
Almost All

Recent observations of rapid variations in optical He I lines, X-rays, and FUV wavelengths in the prototypical classical Be stars λ Eri and star γ Cas hint that the violent processes occur on the surfaces of these stars almost all the time. We suggest that of these phenomena show greater similarities with magnetic flaring than any other process thought to occur on stars.

scholarly journals Effect of Compact Objects Near Be Stars

1987 ◽  
Vol 92 ◽  
pp. 516-518
Author(s):  
Krishna M.V. Apparao ◽  
S.P. Tarafdar
Keyword(s):  
Black Holes ◽  
Neutron Star ◽  
Rotation Period ◽  
Compact Object ◽  
Compact Objects ◽  
X Rays ◽  
Be Stars ◽  
Eccentric Orbit ◽  
X Ray ◽  
Be Star

Several Be stars are identified with bright X-ray sources. (Rappaport and Van den Heuvel, 1982). The bright X-ray emission and observed periodicities indicate the existence of compact objects (white dwarfs, neutron stars or black holes) near the Be stars. A prime example is the brightest X-ray source A0538-66 in LMC, which contains a neutron star with a rotation period of 59 ms. Apparao (1985) explained the X-ray emission, which occurs in periodic flares, by considering an inclined eccentric orbit for the neutron star around the assumed Be-star. The neutron star when it enters a gas ring (around the Be-star) accreting matter giving out X-rays.The X-ray emission from the compact objects, when the gas ring from the Be-star envelopes the objects, has interesting consequences. The X-ray emission produces an ionized region (compact object Stromgren sphere or COSS) in the gas surrounding the compact object (CO).

scholarly journals Massive star mass-loss revealed by X-ray observations of young supernovae

2018 ◽  
Vol 14 (S346) ◽  
pp. 83-87
Author(s):  
Vikram V. Dwarkadas
Keyword(s):  
Mass Loss ◽  
Massive Stars ◽  
Ambient Medium ◽  
Mass Loss Rate ◽  
Stellar Mass ◽  
X Rays ◽  
X Ray ◽  
The Common ◽  
Almost All ◽  
Loss Rates

AbstractMassive stars lose a considerable amount of mass during their lifetime. When the star explodes as a supernova (SN), the resulting shock wave expands in the medium created by the stellar mass-loss. Thermal X-ray emission from the SN depends on the square of the density of the ambient medium, which in turn depends on the mass-loss rate (and velocity) of the progenitor wind. The emission can therefore be used to probe the stellar mass-loss in the decades or centuries before the star’s death.We have aggregated together data available in the literature, or analysed by us, to compute the X-ray lightcurves of almost all young supernovae detectable in X-rays. We use this database to explore the mass-loss rates of massive stars that collapse to form supernovae. Mass-loss rates are lowest for the common Type IIP supernovae, but increase by several orders of magnitude for the highest luminosity X-ray SNe.

scholarly journals Photometric characteristics of the Be stars: almost twenty years of UBV monitoring at the Hvar observatory

1994 ◽  
Vol 162 ◽  
pp. 301-302
Author(s):  
K. Pavlovski ◽  
H. Božić ◽  
Ž. Ružić ◽  
P. Harmanec ◽  
J. Horn ◽  
...  
Keyword(s):  
Be Stars ◽  
Photoelectric Photometry ◽  
Ample Evidence ◽  
Large Group ◽  
Almost All ◽  
By Products

Since their discovery (by Father Secchi in 1866) until the end of sixties, Be stars were not a subject of any systematic studies of their possible light and colour variations. Already at that time, the astronomical literature contained ample evidence showing that a number of Be stars were light variables. However, almost all such findings resulted as by-products of studies of different or wider groups of objects. Feinstein (1968) was probably the first who pointed out explicitly that many Be stars are light variables. A pioneering study which was aimed at the detection of light variations of a large group of Be stars by means of differential photoelectric photometry was carried out by Haupt & Schroll (1974).

X-Ray Absorption Spectroscopy Applied to Metal Accumulation

2009 ◽  
Vol 71-73 ◽  
pp. 613-616
Author(s):  
Regina Pinto de Carvalho ◽  
G.C. Silva ◽  
M. Sylvia S. Dantas ◽  
I.F. Vasconcelos ◽  
Virgínia S.T. Ciminelli
Keyword(s):  
Physical State ◽  
Unique Feature ◽  
Metal Accumulation ◽  
X Rays ◽  
Absorption Probability ◽  
X Ray ◽  
Analytical Technique ◽  
Absorption Phenomenon ◽  
Almost All ◽  
X Ray Absorption

X-Rays Absorption Fine Structure Spectroscopy (XAFS) is an analytical technique that can be used as a probe to characterize almost all elements, even if they appear in diluted or non-crystalline systems. This is due to the fact that the absorption probability of X-rays has a unique feature for each element, and is modulated by the chemical and physical state of that element, as well as by its neighborhood. This paper presents a brief description of the X-rays absorption phenomenon and the analytical technique involving this phenomenon, as well as the application of XAFS in biosorption studies. For more details on XAFS theory, refer to [1].

scholarly journals Analyse Du Rebut Des Cliches Radiographiques Dans Le Service De Radiologie Et Imagerie Médicale Du Chu Campus De Lomé Au Togo

2017 ◽  
Vol 13 (33) ◽  
pp. 244
Author(s):  
P. Gbande ◽  
L. Sonhaye ◽  
K. Adambounou ◽  
K. Lambon ◽  
B. N’timon ◽  
...  
Keyword(s):  
Medical Imaging ◽  
Prospective Study ◽  
Lower Limb ◽  
University Hospital ◽  
X Rays ◽  
Financial Loss ◽  
X Ray ◽  
Chest X Ray ◽  
Almost All

Purpose: To analyze the waste factors of rejected X-rays films. Methodology: Descriptive and analytical prospective study from 1 January to 30 June 2017 carried out in the department of radiology and medical imaging of the Campus University Hospital of Lomé in Togo. Results: 4912 patients had received 5630 radiographic incidences, including 3288 (58.4%) on the analogy and 2342 (41.5%) on the digital. The reject rate was 12.5%. The vast majority of the X-rays films, 682 (96.9%) were rejected by the radiographers themselves just after development. The resumption frequency ranged from one repeat (550 X-rays films, or 78%) to 4 repeats (8 X-rays films, or 1%). Almost all of the rejected films, 702 (99.7%) came from the analogical room. Chest X-ray was the incidence with more rejection in 33.9% followed by pelvic and lower limb incidences in 21% of cases. More than 2/3 of the rejected films, 473 (67.2%), came from the students' act. The causes of the rejection were mainly centering (25.5%), underexposure (20.17%) and overexposure (12.93). The financial loss caused by the scrap of X-rays films amounted to about 418800F CFA or 638.5 €. Conclusion: Strengthening communication between radiographers and radiologists is necessary to avoid unnecessary repeats of patient’s radiographs.

scholarly journals Study of nuclear properties with muonic atoms

2020 ◽  
Vol 135 (10) ◽  
Author(s):  
A. Knecht ◽  
A. Skawran ◽  
S. M. Vogiatzi
Keyword(s):  
Nuclear Charge Radius ◽  
X Rays ◽  
Gas Cell ◽  
Capture Process ◽  
Muonic Atoms ◽  
Hydrogen Deuterium ◽  
Almost All ◽  
Deuterium Gas ◽  
Radioactive Atoms ◽  
Pressure Hydrogen

AbstractMuons are a fascinating probe to study nuclear properties. Muonic atoms can easily be formed by stopping negative muons inside a material. The muon is subsequently captured by the nucleus and, due to its much higher mass compared to the electron, orbits the nucleus at very small distances. During this atomic capture process, the muon emits characteristic X-rays during its cascade down to the ground state. The energies of these X-rays reveal the muonic energy level scheme, from which properties like the nuclear charge radius or its quadrupole moment can be extracted. While almost all stable elements have been examined using muons, probing highly radioactive atoms has so far not been possible. The muX experiment has developed a technique based on transfer reaction inside a high-pressure hydrogen/deuterium gas cell to examine targets available only in microgram quantities.

scholarly journals Be Star Surveys in Open Clusters with Balmer-line Photometry

2000 ◽  
Vol 175 ◽  
pp. 63-66
Author(s):  
Gemma Capilla ◽  
Juan Fabregat ◽  
Deborah Baines
Keyword(s):  
Emission Line ◽  
Main Sequence ◽  
Open Clusters ◽  
Balmer Line ◽  
Be Stars ◽  
Late Type ◽  
Efficient Tool ◽  
Be Star ◽  
Almost All ◽  
Evolutionary Interpretation

AbstractWe present CCD Hα and Hβ photometry of young open clusters. We show that the comparison of the α and β photometric indices provides an efficient tool for identifying emission line stars. We report on the discovery of several new Be stars.The preliminary results of our survey are the following: i. the younger clusters (age < 10 Myr) are almost lacking of Be stars, ii. clusters in the age interval 10–30 Myr are rich in Be stars. Almost all of them are of spectral types earlier than B5, while late-type Be stars are scarce. These results point towards an evolutionary interpretation of the Be phenomenon, in the sense that Be stars are close to the end of their main sequence lifetime.

scholarly journals ROENTGEN RAY INTOXICATION

1922 ◽  
Vol 35 (2) ◽  
pp. 187-202 ◽  
Author(s):  
S. L. Warren ◽  
G. H. Whipple
Keyword(s):  
Small Intestine ◽  
Clinical Evidence ◽  
Clinical Work ◽  
X Rays ◽  
Fatal Intoxication ◽  
Unit Dose ◽  
Slight Rise ◽  
Almost All ◽  
Proper Consideration ◽  
Urinary Nitrogen

Roentgen radiation of the thorax (abdomen shielded) in dogs, even with large doses (up to 512 milliampere minutes), gives no clinical evidence of intoxication. There may be a transient leucopenia and a slight rise in urinary nitrogen. Roentgen radiation of the abdomen (thorax shielded) in dogs, with a dose of 350 milliampere minutes, will almost certainly cause a fatal intoxication. Smaller doses may be survived but usually with signs of gastrointestinal intoxication. This lethal intoxication due to abdominal radiation presents a remarkably uniform clinical and anatomical picture. There is a latent period of 24 to 36 hours, during which the dog is perfectly normal clinically. The 2nd day usually shows the beginning of diarrhea and perhaps some vomitus. The 3rd and 4th days show progressive intoxication with increasing vomiting and bloody diarrhea until the dog becomes stuporous. Death is almost always on the 4th day. Anatomically the only lesions of significance are to be found in the small intestine. The epithelium of the crypts and villi shows more or less complete necrosis, and this condition may involve almost all of the small intestine. The epithelium may vanish completely except for a few cells here and there which have escaped and are often found in mitosis, probably an effort at repair and regeneration. We are forced to the conclusion that this remarkable injury of the epithelium of the small intestine is responsible for the various abnormal reactions and final lethal intoxication which follow a unit dose of Roentgen radiation over the abdomen of a normal dog. This sensitiveness of the intestinal epithelium to x-rays is not appreciated and should be given proper consideration in clinical work.

scholarly journals Possible Contributions of Supernova Remnants to the Soft X-ray Diffuse Background (0.1 - 1 keV)

1983 ◽  
Vol 101 ◽  
pp. 361-365
Author(s):  
W. T. Sanders ◽  
D. N. Burrows ◽  
D. McCammon ◽  
W. L. Kraushaar
Keyword(s):  
Supernova Remnants ◽  
Large Scale ◽  
Supernova Remnant ◽  
Galactic Halo ◽  
Galactic Plane ◽  
X Rays ◽  
X Ray ◽  
Band Emission ◽  
Diffuse Background ◽  
Almost All

Almost all of the B band (0.10–0.19 keV) and C band (0.15–0.28 keV) X-rays probably originate in a hot region surrounding the Sun, which Cox and Anderson have modeled as a supernova remnant. This same region may account for a significant fraction of the M band (0.5–1 keV) X-rays if the nonequilibrium models of Cox and Anderson are applicable. A population of distant SNR similar to the local region, with center-to-center spacing of about 300 pc, could provide enough galactic M band emission to fill in the dip in the count rate in the galactic plane that would otherwise be present due to absorption of both the extra-galactic power law flux and any large-scale-height stellar (or galactic halo) emission.

Deep Neural Network-Based Screening Model for COVID-19-Infected Patients Using Chest X-Ray Images

2020 ◽  
pp. 2151004 ◽  
Author(s):  
Dilbag Singh ◽  
Vijay Kumar ◽  
Vaishali Yadav ◽  
Manjit Kaur
Keyword(s):  
Neural Network ◽  
Performance Metrics ◽  
Automated Analysis ◽  
X Rays ◽  
X Ray ◽  
Screening Model ◽  
X Ray Imaging ◽  
Adaptive Differential Evolution ◽  
Chest X Ray ◽  
Almost All

There are limited coronavirus disease 2019 (COVID-19) testing kits, therefore, development of other diagnosis approaches is desirable. The doctors generally utilize chest X-rays and Computed Tomography (CT) scans to diagnose pneumonia, lung inflammation, abscesses, and/or enlarged lymph nodes. Since COVID-19 attacks the epithelial cells that line our respiratory tract, therefore, X-ray images are utilized in this paper, to classify the patients with infected (COVID-19 [Formula: see text]ve) and uninfected (COVID-19 [Formula: see text]ve) lungs. Almost all hospitals have X-ray imaging machines, therefore, the chest X-ray images can be used to test for COVID-19 without utilizing any kind of dedicated test kits. However, the chest X-ray-based COVID-19 classification requires a radiology expert and significant time, which is precious when COVID-19 infection is increasing at a rapid rate. Therefore, the development of an automated analysis approach is desirable to save the medical professionals’ valuable time. In this paper, a deep convolutional neural network (CNN) approach is designed and implemented. Besides, the hyper-parameters of CNN are tuned using Multi-objective Adaptive Differential Evolution (MADE). Extensive experiments are performed by considering the benchmark COVID-19 dataset. Comparative analysis reveals that the proposed technique outperforms the competitive machine learning models in terms of various performance metrics.

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