166 research outputs found
Intranight variability of 3C 454.3 during its 2010 November outburst
Context. 3C 454.3 is a very active flat spectrum radio quasar (blazar) that
has undergone a recent outburst in all observed bands, including the optical.
Aims. In this work we explore the short-term optical variability of 3C 454.3
during its outburst by searching for time delays between different optical
bands. Finding one would be important for understanding the evolution of the
spectrum of the relativistic electrons, which generate the synchrotron jet
emission.
Methods. We performed photometric monitoring of the object by repeating
exposures in different optical bands (BVRI). Occasionally, different telescopes
were used to monitor the object in the same band to verify the reliability of
the smallest variations we observed.
Results. Except on one occasion, where we found indications of a lag of the
blue wavelengths behind the red ones, the results are inconclusive for most of
the other cases. There were either no structures in the light curves to be able
to search for patterns, or else different approaches led to different
conclusions.Comment: 4 pages, 4 figures. Accepted for publication in A&
Nature of Intra-night Optical Variability of BL Lacertae
We present the results of extensive multi-band intra-night optical monitoring
of BL Lacertae during 2010--2012. BL Lacertae was very active in this period
and showed intense variability in almost all wavelengths. We extensively
observed it for a total for 38 nights; on 26 of them observations were done
quasi-simultaneously in B, V, R and I bands (totaling 113 light curves), with
an average sampling interval of around 8 minutes. BL Lacertae showed
significant variations on hour-like timescales in a total of 19 nights in
different optical bands. We did not find any evidence for periodicities or
characteristic variability time-scales in the light curves.
The intranight variability amplitude is generally greater at higher
frequencies and decreases as the source flux increases.
We found spectral variations in BL Lacertae in the sense that the optical
spectrum becomes flatter as the flux increases but in several flaring states
deviates from the linear trend suggesting different jet components contributing
to the emission at different times.Comment: 12 Pages, 5 figures, 3 Tables, Accepted for Publication in MNRA
Fifty years of spellchecking
A short history of spellchecking from the late 1950s to the present day, describing its development through dictionary lookup, affix stripping, correction, confusion sets, and edit distance to the use of gigantic databases
The nature of the intra-night optical variability in blazars
In this paper we present results of a short-term optical monitoring of 13
blazars. The objects were monitored mostly in the R-band for a total of ~ 160
hours between 2006 and 2011. We study the nature of the short-term variations
and show that most of them could be described as slow, smooth, and (almost)
linear changes of up to ~ 0.1 mag/hour, but many objects show no short-term
variations at all. In fact, we found only ~ 2 per cent chance to observe
variability of more than 0.1 mag/hour for the sample we observed. Hints for
quasi-periodic oscillations at very low amplitude levels are also found for
some objects. We briefly discuss some of the possible mechanisms to generate
the intra-night variability and the quasi-periodic oscillations.Comment: 10 pages, 13 figures, 1 table, Accepted for Publication in MNRA
UBVRI observations of the flickering of RS Ophiuchi at Quiescence
We report observations of the flickering variability of the recurrent nova RS
Oph at quiescence on the basis of simultaneous observations in 5 bands (UBVRI).
RS Oph has flickering source with (U-B)_0=-0.62 \pm 0.07, (B-V)_0=0.15 \pm
0.10, (V-R)_0=0.25 \pm 0.05. We find for the flickering source a temperature
T_fl = 9500 \pm 500 K, and luminosity L_fl = 50 - 150 L_sun (using a distance
of d=1.6kpc). We also find that on a (U-B) vs (B-V) diagram the flickering of
the symbiotic stars differs from that of the cataclysmic variables. The
possible source of the flickering is discussed. The data are available upon
request from the authors and on the web
www.astro.bas.bg/~rz/RSOph.UBVRI.2010.MNRAS.tar.gz.Comment: 7 pages, MNRAS (accepted
Duality for Exotic Bialgebras
In the classification of Hietarinta, three triangular
-matrices lead, via the FRT formalism, to matrix bialgebras which are not
deformations of the trivial one. In this paper, we find the bialgebras which
are in duality with these three exotic matrix bialgebras. We note that the
duality of FRT is not sufficient for the construction of the bialgebras
in duality. We find also the quantum planes corresponding to these bialgebras
both by the Wess-Zumino R-matrix method and by Manin's method.Comment: 25 pages, LaTeX2e, using packages: cite, amsfonts, amsmath, subeq
Skeletal Muscle–Derived Cell Implantation for the Treatment of Fecal Incontinence: A Randomized, Placebo-Controlled Study
Background and Aims: Fecal incontinence (FI) improvement following injection of autologous skeletal muscle–derived cells has been previously suggested. This study aimed to test the efficacy and safety of said cells through a multicenter, placebo-controlled study, to determine an appropriate cell dose, and to delineate the target patient population that can most benefit from cell therapy. Methods: Patients experiencing FI for at least 6 months were randomized to receive a cell-free medium or low or high dose of cells. All patients received pelvic floor electrical stimulation before and after treatment. Incontinence episode frequency (IEF), FI quality of life, FI burden assessed on a visual analog scale, Wexner score, and parameters reflecting anorectal physiological function were all assessed for up to 12 months. Results: Cell therapy improved IEF, FI quality of life, and FI burden, reaching a preset level of statistical significance in IEF change compared with the control treatment. Post hoc exploratory analyses indicated that patients with limited FI duration and high IEF at baseline are most responsive to cells. Effects prevailed or increased in the high cell count group from 6 to 12 months but plateaued or diminished in the low cell count and control groups. Most physiological parameters remained unaltered. No unexpected adverse events were observed. Conclusions: Injection of a high dose of autologous skeletal muscle–derived cells followed by electrical stimulation significantly improved FI, particularly in patients with limited FI duration and high IEF at baseline, and could become a valuable tool for treatment of FI, subject to confirmatory phase 3 trial(s). (ClinicalTrialRegister.eu; EudraCT Number: 2010-021463-32)
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