Around-the-clock observations of the Q0957+561A,B gravitationally lensed quasar. II. Results for the second observing season

We report on an observing campaign in 2001 March to monitor the brightness of the later arriving Q0957+561B image in order to compare with the previously published brightness observations of the (first-arriving) A image. The 12 participating observatories provided 3543 image frames, which we have analyzed for brightness fluctuations. From our classical methods for time-delay determination, we find a 417.09 ± 0.07 day time delay, which should be free of effects due to incomplete sampling. During the campaign period, the quasar brightness was relatively constant and only small fluctuations were found; we compare the structure function for the new data with structure function estimates for the 1995-1996 epoch and show that the structure function during our observing interval is unusually depressed. We also examine the data for any evidence of correlated fluctuations at zero lag. We discuss the limits of our ability to measure the cosmological time delay if the quasar's emitting surface is time resolved, as seems likely

Comparison of CCD astrolabe multi-site solar diameter observations

Astronomy and Astrophysics, v. 427, n. 2, p. 717-723, 2004. http://dx.doi.org/10.1051/0004-6361:20041334International audienc

On Centralizing and Strong Commutativity Preserving Maps of Semiprime Rings

We study some properties of centralizing and strong commutativity preserving maps of semiprime rings.Anhui Provincial Natural Science Foundation [1408085QA08]; Key University Science Research Project of Anhui Province [KJ2014A183]; Training Program of Chuzhou University of China [2014PY06]The first author is supported by the Anhui Provincial Natural Science Foundation (1408085QA08) and the Key University Science Research Project of Anhui Province (KJ2014A183), and also by the Training Program of Chuzhou University (2014PY06) of China

Intermediate-term variations in solar radius during solar cycle 23

International audienceIn this study, we look for the mid-term variations in the daily average data of solar radius measurements made at the Solar Astrolabe Station of TUBITAK National Observatory (TUG) during solar cycle 23 for a time interval from 2000 February 26 to 2006 November 15. Due to the weather conditions and seasonal effect dependent on the latitude, the data series has the temporal gaps. For spectral analysis of the data series, thus, we use the Date Compensated Discrete Fourier Transform (DCDFT) and the CLEANest algorithm, which are powerful methods for irregularly spaced data. The CLEANest spectra of the solar radius data exhibit several significant mid-term periodicities at 393.2, 338.9, 206.5, 195.2, 172.3 and 125.4 days which are consistent with periods detected in several solar time series by several authors during different solar cycles. The knowledge relating to the origin of solar radius variations is not yet present. To see whether these variations will repeat in next cycles and to understand how the amplitudes of such variations change with different phases of the solar cycles, we need more systematic efforts and the long-term homogeneous data. Since most of the periodicities detected in the present study are frequently seen in solar activity indicators, it is thought that the physical mechanisms driving the periodicities of solar activity may also be effective in solar radius variations