arXiv subjects

D. Simic

Publications and source records attributed to D. Simic.

5 recordsLinked to original sources

arXiv2010

Applying MVC and PAC patterns in mobile applications

Additional requirements are set for mobile applications in relation to applications for desktop computers. These requirements primarily concern the support to different platforms on which such applications are performed, as well as the requirement for providing more modalities of input/output interaction. These requirements have influence on the user interface and therefore it is needed to consider the usability of MVC (Model-View-Controller) and PAC (Presentation-Abstraction-Control) design patterns for the separation of the user interface tasks from the business logic, specifically in mobile applications. One of the questions is making certain choices of design patterns for certain classes of mobile applications. When using these patterns the possibilities of user interface automatic transformation should be kept in mind. Although the MVC design pattern is widely used in mobile applications, it is not universal, especially in cases where there are requirements for heterogeneous multi-modal input-output interactions.

cs.SE↗

arXiv2002

IP Pegasi: Investigation of the accretion disk structure. Searching evidences for spiral shocks in the quiescent accretion disk

We present the results of spectral investigations of the cataclysmic variable IP Peg in quiescence. Optical spectra obtained on the 6-m telescope at the Special Astrophysical Observatory (Russia), and on the 3.5-m telescope at the German-Spanish Astronomical Center (Calar Alto, Spain), have been analysed by means of Doppler tomography and Phase Modelling Technique. From this analysis we conclude that the quiescent accretion disk of IP Peg has a complex structure. There are also explicit indications of spiral shocks. The Doppler maps and the variations of the peak separation of the emission lines confirm this interpretation. We have detected that all the emission lines show a rather considerable asymmetry of their wings varying with time. The wing asymmetry shows quasi-periodic modulations with a period much shorter than the orbital one. This indicates the presence of an emission source in the binary rotating asynchronously with the binary system. We also have found that the brightness of the bright spot changes considerably during one orbital period. The spot becomes brightest at an inferior conjunction, whereas it is almost invisible when it is located on the distant half of the accretion disk. Probably, this phenomenon is due to an anisotropic radiation of the bright spot and an eclipse of the bright spot by the outer edge of the accretion disk.

astro-ph↗

arXiv2001

Detection of spiral structure of the quiescent accretion disk of IP Pegasi

We present the results of the spectral investigations of IP Peg in quiescence. Optical spectra obtained on 6-m telescope at the Special Astrophysical Observatory (Russia), and on the 3.5-m telescope at the German-Spanish Astronomical Center (Calar Alto, Spain), have been analysed by means of Doppler tomography and phase modeling technique. This analysis has allowed us to make conclusions, that the quiescent accretion disk of IP Peg has a complicated structure. Equally with the bright spot originated in the region of interaction between the stream and the disk's particles, there are also explicit indications of the spiral shocks. We also have found that the brightness of the bright spot considerably oscillates during orbital period. The spot becomes brightest at an inferior conjunction. On the contrary, the spot is almost not visible when it is located on a distant half of the accretion disk. Apparently, it is connected to an eclipse of the bright spot by an outer edge of the accretion disk.

astro-ph↗

arXiv2000

The Northern ROSAT All-Sky (NORAS) Galaxy Cluster Survey I: X-ray Properties of Clusters Detected as Extended X-ray Sources

In the construction of an X-ray selected sample of galaxy clusters for cosmological studies, we have assembled a sample of 495 X-ray sources found to show extended X-ray emission in the first processing of the ROSAT All-Sky Survey. The sample covers the celestial region with declination $δ\ge 0°$ and galactic latitude $|b_{II}| \ge 20°$ and comprises sources with a count rate $\ge 0.06$ counts s$^{-1}$ and a source extent likelihood of 7. In an optical follow-up identification program we find 378 (76%) of these sources to be clusters of galaxies. ...

astro-ph↗

arXiv1998

Detailed optical studies of the galactic supersoft X-ray source QR And (RXJ0019.8+2156)

We present high-speed long term photometric observations from 1992 to 1996 (UBVRI), as well as recently obtained (1997) spectrophotometric and high resolution spectroscopic studies of the bright galactic supersoft X-ray source RXJ0019.8+2156. Our photometry reveals a highly variable object. The shortest observed quasi-periodic variations are humps with a period of approx 1.8h. The timings of the main minimum are not exactly regular and occur on average around phase phi=0.0. With our new data set we calculated an update of the orbital period. Our simultaneous spectroscopic and spectrophotometric studies from 1997 give an even more detailed insight: blue and red shifted satellite lines at HeII 4686 and at the strong Balmer lines, which are interpreted as high velocity outflows, can clearly be detected. We also present for the first time an analysis of this supersoft source by means of Doppler tomography. The lines of HeII (4542,4686), H_a and H_b show no emission from an accretion disk. These emission lines originate in regions within the binary system with very low velocities. The spatial origin of the emitting material is not quite clear and will be investigated in a follow-up paper.

astro-ph↗