Search results for "eclipse"

UML/OCL-based modeling of work-based access control policies for collaborative healthcare systems

2016

A work-based access control (WBAC) model is proposed by introducing the team role concept and modifying the user-role assignment model from a previous work. The main goals of WBAC are flexibility, easy manageability, security, as well as suitability to support cooperative work of dynamic teams in healthcare environments. One of the major challenges of WBAC regards authorization constraints in terms of organizational policies. In this article, we show how Unified Modeling Language (UML) and Object Constraints Language (OCL) are utilized to design and analyze the authorization constraints of WBAC in cooperative engagements with complex scenarios in the collaborative healthcare domain. We also…

Three X-ray Flares Near Primary Eclipse of the RS CVn Binary XY UMa

2016

We report on an archival X-ray observation of the eclipsing RS CVn binary XY UMa ($\rm P_{orb}\approx$ 0.48d). In two $\emph{Chandra}$ ACIS observations spanning 200 ks and almost five orbital periods, three flares occurred. We find no evidence for eclipses in the X-ray flux. The flares took place around times of primary eclipse, with one flare occurring shortly ($<0.125\rm P_{orb}$) after a primary eclipse, and the other two happening shortly ($<0.05\rm P_{orb}$) before a primary eclipse. Two flares occurred within roughly one orbital period ($\Delta \phi\approx1.024\rm P_{orb}$) of each other. We analyze the light curve and spectra of the system, and investigate coronal length scales both…

Messungen der Himmelsstrahlung und deren Polarisationsgrad während der Sonnenfinsternis am 15.2.1961 in Viareggio (Italien)

1961

On the occasion of the total solar eclipse in Viareggio (Italy) measurements of intensity of sky radiation and polarization have been carried out at 90 degrees vertical distance from the sun. UV-, green- and red-filters have been used. The results showed a diminution of the intensity during the eclipse of about 3 powers of ten. The sky brightness in the point 90 degrees distant during the total eclipse was similar to the brightness when sun is 7 degrees below the horizon. About one minute before the total eclipse the degree of polarization diminuished to zero. — Furthermore photos of nearly the total sky were made using two cameras with wide angle lenses.

New ephemeris of the ADC source 2A 1822-371: a stable orbital-period derivative over 30 years

2010

We report on a timing of the eclipse arrival times of the low mass X-ray binary and X-ray pulsar 2A 1822-371 performed using all available observations of the Proportional Counter Array on board the Rossi X-ray Timing Explorer, XMM-Newton pn, and Chandra. These observations span the years from 1996 to 2008. Combining these eclipse arrival time measurements with those already available covering the period from 1977 to 1996, we obtain an orbital solution valid for more than thirty years. The time delays calculated with respect to a constant orbital period model show a clear parabolic trend, implying that the orbital period in this source constantly increases with time at a rate $\dot P_orb = …

Accretion onto Neutron Stars: spectral and timing investigation of Low Mass X-ray Binaries

2021

Tool integration in Eclipse

2005

Extension of Electron Monte Carlo Dose Calculation in Eclipse to Siemens Linear Accelerators

2009

Initially, the implementation of the macro Monte Carlo (MC) method into Eclipse (Varian Medical Systems), named eMC, was carried out for Varian accelerators only. In this work eMC algorithm has been modified to allow also accurate dose calculations for electron beams for Siemens accelerators.

Spectral analysis of the low-mass X-ray pulsar 4U 1822-371: Reflection component in a high-inclination system

2021

Context. The X-ray source 4U 1822-371 is an eclipsing low-mass X-ray binary and X-ray pulsar, hosting a NS that shows periodic pulsations in the X-ray band with a period of 0.59 s. The inclination angle of the system is so high (80–85°) that in principle, it should be hard to observe both the direct thermal emission of the central object and the reflection component of the spectrum because they are hidden by the outer edge of the accretion disc. Despite the number of studies carried out on this source, many aspects such as the geometry of the system, its luminosity, and its spectral features are still debated. Aims. Assuming that the source accretes at the Eddington limit, the analysis perf…

Els viatges de la física: perseguint ombres, mesurant meridians

2013

A partir del segle XVII l’estudi acurat i resolució de diversos problemes de la física, principalment relacionats amb l’astronomia i la forma de la Terra, però no sols, ha passat per realitzar mesures a diferents llocs i, per tant, per l’organització de viatges científics amb aquests objectius específics. Presentarem alguns d’aquests problemes i les solucions adoptades a l’època.

Updated orbital ephemeris of the ADC source X 1822-371: a stable orbital expansion over 40 years

2019

The source X 1822-371 is an eclipsing compact binary system with a period close to 5.57 hr and an orbital period derivative $\dot{P}_{\rm orb}$ of 1.51(7)$\times 10^{-10}$ s s$^{-1}$. The very large value of $\dot{P}_{\rm orb}$ is compatible with a super-Eddington mass transfer rate from the companion star, as suggested by X-ray and optical data. The XMM-Newton observation taken in 2017 allows us to update the orbital ephemeris and verify whether the orbital period derivative has been stable over the last 40 yr. We added to the X-ray eclipse arrival times from 1977 to 2008 two new values obtained from the RXTE and XMM-Newton observations performed in 2011 and 2017, respectively. We estimate…