Three discoveries of γ Cas analogues from dedicated XMM–Newton observations of Be stars

ABSTRACT In the last years, a peculiarity of some Be stars – their association with unusually hard and intense X-ray emission – was shown to extend beyond a mere few cases. In this paper, we continue our search for new cases by performing a limited survey of 18 Be stars using XMM–Newton. The targets were selected either on the basis of a previous X-ray detection (exosat,rosat, XMM-slew survey) without spectral information available or because of the presence of a peculiar spectral variability. Only two targets remain undetected in the new observations and three other stars display only faint and soft X-rays. Short-term and/or long-term variations were found in one third of the sample. The spectral characterization of the X-ray brightest 13 stars of the sample led to the discovery of three new γ Cas (HD 44458, HD 45995, and V558 Lyr), bringing the total to 25 known cases, and another γ Cas candidate (HD 120678), bringing the total to two.

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Let there be more variability in two γ Cas stars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa617 ◽

2020 ◽

Vol 494 (1) ◽

pp. 958-974 ◽

Cited By ~ 2

Author(s):

Yaël Nazé ◽

Andrzej Pigulski ◽

Gregor Rauw ◽

Myron A Smith

Keyword(s):

Spectroscopic Analysis ◽

Activity Levels ◽

Be Stars ◽

Spectral Variability ◽

Short Term ◽

Photometric Variability ◽

High Frequencies ◽

Low Amplitude ◽

High Degree

ABSTRACT We investigate the short-term optical variability of two γ Cas analogues, πAqr and BZ Cru, thanks to intensive ground-based spectroscopic and space-borne photometric monitorings. For both stars, low-amplitude (mmag) coherent photometric variability is detected. The associated signals display long-term amplitude variations, as in other Be stars. However, these signals appear at high frequencies, especially in πAqr, indicating p modes with a high degree l, a quite unusual feature amongst Be stars. While BZ Cru presents only low-level spectral variability, without clear periodicity, this is not the case of πAqr. In this star, the dominant photometric frequencies, near ∼12 d−1, are confirmed spectroscopically in separate monitorings taken during very different disc activity levels; the spectroscopic analysis suggests a probable tesseral nature for the mode.

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Digital x-ray mapping of nanometer-size supported bimetallic catalysts

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100104716 ◽

1988 ◽

Vol 46 ◽

pp. 530-531

Author(s):

L. T. Germinario

Keyword(s):

Background Radiation ◽

Metal Cluster ◽

Single Element ◽

Beam Diameter ◽

X Rays ◽

X Ray ◽

Major Interest ◽

Induced Changes

Understanding the role of metal cluster composition in determining catalytic selectivity and activity is of major interest in heterogeneous catalysis. The electron microscope is well established as a powerful tool for ultrastructural and compositional characterization of support and catalyst. Because the spatial resolution of x-ray microanalysis is defined by the smallest beam diameter into which the required number of electrons can be focused, the dedicated STEM with FEG is the instrument of choice. The main sources of errors in energy dispersive x-ray analysis (EDS) are: (1) beam-induced changes in specimen composition, (2) specimen drift, (3) instrumental factors which produce background radiation, and (4) basic statistical limitations which result in the detection of a finite number of x-ray photons. Digital beam techniques have been described for supported single-element metal clusters with spatial resolutions of about 10 nm. However, the detection of spurious characteristic x-rays away from catalyst particles produced images requiring several image processing steps.

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Non-destructive characterization of additively manufactured components with x-ray computed tomography for part qualification: A study with laboratory and synchrotron x-rays

Materials Characterization ◽

10.1016/j.matchar.2021.110894 ◽

2021 ◽

Vol 173 ◽

pp. 110894

Author(s):

Ercan Cakmak ◽

Philip Bingham ◽

Ross W. Cunningham ◽

Anthony D. Rollett ◽

Xianghui Xiao ◽

...

Keyword(s):

Computed Tomography ◽

X Rays ◽

X Ray ◽

X Ray Computed ◽

Non Destructive ◽

Non Destructive Characterization

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Integration of Dental Implants in Conjunction with EDTA-Conditioned Dentin Grafts: An Experimental Study

Dentistry Journal ◽

10.3390/dj9060063 ◽

2021 ◽

Vol 9 (6) ◽

pp. 63

Author(s):

Payam Farzad ◽

Ted Lundgren ◽

Adel Al-Asfour ◽

Lars Andersson ◽

Christer Dahlin

Keyword(s):

Direct Contact ◽

Mineral Content ◽

X Rays ◽

X Ray ◽

Dentin Surface ◽

Significant Difference ◽

C And N ◽

Micro Implants ◽

Demineralized Dentin

This study was undertaken to investigate the integration of titanium micro-implants installed in conjunction with previously dentin-grafted areas and to study the morphological appearance, mineral content, and healing pattern of xenogenic EDTA-conditioned dentin blocks and granules grafted to cavities in the tibial bone of rabbits. Demineralized and non-demineralized dentin blocks and granules from human premolars were implanted into cavities prepared on the lateral aspects of the tibias of rabbits. After a healing period of six months, micro-implants were installed at each surgical site. Histological examinations were carried out after 24 weeks. Characterization of the EDTA-conditioned dentin blocks was performed by means of light microscopy, dental X-rays, scanning electron microscopy, and energy dispersive X-ray analysis (EDX). No implants were found to be integrated in direct contact with the dentin particles or blocks. On the EDTA-conditioned dentin surface, the organic marker elements C and N dominated, as revealed by EDX. The hydroxyapatite constituents Ca and P were almost absent on the dentin surface. No statistically significant difference was observed between the EDTA-conditioned and non-demineralized dentin, as revealed by BIC and BA. The bone-inductive capacity of the dentin material seemed limited, although demineralization by means of EDTA indicated higher BIC and BA values in conjunction with the installed implants in the area. A 12 h EDTA treatment did not fully decalcify the grafts, as revealed by X-ray analysis.

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Classification of Fresh Fractures of the Lunate

Journal of Hand Surgery (European Volume) ◽

10.1016/0266-7681_88_90180-5 ◽

1988 ◽

Vol 13 (4) ◽

pp. 458-462

Author(s):

H. TEISEN ◽

J. HJARBAEK

Keyword(s):

Vascular Anatomy ◽

X Rays ◽

Lunate Bone ◽

X Ray

The X-rays of 17 patients with fresh fractures of the lunate bone have been reviewed. The fractures were classified according to their radiological appearances and according to the vascular anatomy of the lunate. A long term X-ray follow-up examination was performed.

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(M,β)-Stability of Positive Linear Systems

Mathematical Problems in Engineering ◽

10.1155/2016/9605464 ◽

2016 ◽

Vol 2016 ◽

pp. 1-11 ◽

Cited By ~ 3

Author(s):

Octavian Pastravanu ◽

Mihaela-Hanako Matcovschi

Keyword(s):

Linear System ◽

Linear Systems ◽

Transient Behavior ◽

Short Term ◽

Time Dynamics ◽

The Right ◽

Long Term Behavior ◽

Stability Concept

The main purpose of this work is to show that the Perron-Frobenius eigenstructure of a positive linear system is involved not only in the characterization of long-term behavior (for which well-known results are available) but also in the characterization of short-term or transient behavior. We address the analysis of the short-term behavior by the help of the “(M,β)-stability” concept introduced in literature for general classes of dynamics. Our paper exploits this concept relative to Hölder vectorp-norms,1≤p≤∞, adequately weighted by scaling operators, focusing on positive linear systems. Given an asymptotically stable positive linear system, for each1≤p≤∞, we prove the existence of a scaling operator (built from the right and left Perron-Frobenius eigenvectors, with concrete expressions depending onp) that ensures the best possible values for the parametersMandβ, corresponding to an “ideal” short-term (transient) behavior. We provide results that cover both discrete- and continuous-time dynamics. Our analysis also captures the differences between the cases where the system dynamics is defined by matrices irreducible and reducible, respectively. The theoretical developments are applied to the practical study of the short-term behavior for two positive linear systems already discussed in literature by other authors.

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A survey of short-term and long-term stability of tube parameters in a mammography unit

Nuclear Technology and Radiation Protection ◽

10.2298/ntrp1404321p ◽

2014 ◽

Vol 29 (4) ◽

pp. 321-325

Author(s):

Jovica Praskalo ◽

Jasna Davidovic ◽

Biljana Kocic ◽

Monika Zivkovic ◽

Svetlana Pejovic

Keyword(s):

Screening Program ◽

Short Term ◽

X Ray ◽

Term Stability ◽

Long Term Stability ◽

Mammography Screening Program ◽

The Republic ◽

Set Up ◽

The Given

In order to set up a successful mammography screening program in the Republic of Srpska, a Siemens Mammomat 1000 X-ray machine was selected for analysis as the said mammography system is widely used in clinical practice. The variations in tube parameters (specific air kerma, high-voltage accuracy and reproducibility, linearity between exposure and dose exposure time) were monitored over a five-year period, from 2008 to 2012. In addition, due to observed daily fluctuations for chosen parameters, a series of measurements were performed three times a day within a single-month period (mainly October 2012). The goal of such an experimental set up is to assess short-term and long-term stability of tube parameters in the given mammography unit and to make a comparison between them. The present paper shows how an early detection of significant parameter fluctuations can help eliminate irregularities and optimize the performance of mammography systems.

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