2,624 research outputs found
Studies on the uptake of benzanthrone by rat skin and its efflux through serum
The uptake of benzanthrone by rat skin showed saturation kinetics and was dependent upon the weight of skin and time, temperature and pH of the incubation medium. Heating of segments above 50°C caused significant lowering of the uptake. The uptake was irreversibly inhibited by HgCl2 and not by sodium arsenate, KCN, NaF, p-chloromercuribenzoate, N-ethyl-maleimide, cycloheximide, iodoacetic acid and 2,4-dinitrophenol suggesting that the uptake was not energy-dependent. Lipid micelles of the skin accounted for a part of the binding. Most of the benzanthrone taken up by the skin was effluxed through serum proteins
Catching butterflies in the sky: Extended catalog of winged or X-shaped radio sources from the latest FIRST data release
We present a catalog of 290 "winged" or X-shaped radio galaxies (XRGs)
extracted from the latest (2014 December 17) data release of the "Very Large
Array Faint Images of the Radio Sky at Twenty centimeter." We have combined
these radio images with their counterparts in the TIFR GMRT sky survey at 150
MHz, in an attempt to identify any low surface brightness radio emission
present in these sources. This has enabled us to assemble a sample of 106
"strong" XRG candidates and 184 "probable" XRG candidates whose XRG designation
needs to be verified by further observations. The present sample of 290 XRG
candidates is almost twice as large as the number of XRGs currently known.
Twenty-five of our 290 XRG candidates (9 "strong" and 16 "probable") are
identified as quasars. Double-peaked narrow emission lines are seen in the
optical spectra of three of the XRG candidates (two "strong" and one
"probable"). Nearly 90% of the sample is located in the FR II domain of the
Owen-Ledlow diagram. A few of the strong XRG candidates have a rather flat
radio spectrum (spectral index alpha flatter than -0.3) between 150 MHz and 1.4
GHz, or between 1.4 and 5 GHz. Since this is not expected for lobe-dominated
extragalactic radio sources (like nearly all known XRGs), these sources are
particularly suited for follow-up radio imaging and near-simultaneous
measurement of the radio spectrum.Comment: 22 pages, 9 figures, 3 tables, accepted for publication in ApJ
Early detection of earthquake magnitude based on stacked ensemble model
A new machine learning model, named, EEWPEnsembleStack has been developed for predicting the magnitude of the earthquake from a few seconds of recorded ground motion after the arrival of the P phase. The testing and training dataset consists of 2360 and 591 strong-motion records from central Japan recorded by the Kyoshin Network. Eight parameters that are well correlated with the magnitude have been used for training and testing of the model. Feature ablation study using several models shows that a minimum mean absolute error of 0.42 has been obtained for the case when the model has been trained by using all parameters rather than by a single parameter. The model ablation study indicates that among all individually trained single models, the minimum error has been obtained for a Decision Tree regression model. However, the error is minimized when all machine learning models have been together utilized in the EEWPEnsembleStack model for the training purposes. The EEWPEnsembleStack model has been used to predict a 6.3 magnitude earthquake by using its 21 records from various stations that lie within 50 to 150 km epicentral distance. The predicted magnitude from the developed model using weighted magnitude prediction is obtained as 6.4, which is close to the actual magnitude. The comparison of the predicted magnitude of this earthquake from the developed model with that predicted by using popular τc and Pd methods clearly indicates the suitability of the developed machine learning model over other conventional models. © 202
Intra-night optical variability of core dominated radio quasars: the role of optical polarization
Context. Rapid variations in optical flux are seen in many quasars and all blazars. The amount of variability in different classes of active galactic nuclei has been studied extensively but many questions remain unanswered. Aims. We present the results of a long-term programme to investigate the intra-night optical variability (INOV) of powerful flat spectrum radio core-dominated quasars (CDQs), with a focus on probing the relationship of INOV to the degree of optical polarization. Methods. We observed a sample of 16 bright CDQs showing strong broad optical emission lines and consisting of both high and low optical polarization quasars (HPCDQs and LPCDQs). In this first systematic study of its kind, we employed the 104-cm Sampurnanand telescope, the 201-cm Himalayan Chandra telescope and the 200-cm IUCAA-Girawali Observatory telescope, to carry out R-band monitoring on a total of 47 nights. Using the CCD as an N-star photometer to densely monitor each quasar for a minimum duration of about 4 h per night, INOV exceeding ~1–2 per cent could be reliably detected. Combining these INOV data with those taken from the literature, after ensuring conformity with the basic selection criteria we adopted for the 16 CDQs monitored by us, we were able to increase the sample size to 21 CDQs (12 LPCDQs and 9 HPCDQs) monitored on a total of 73 nights. Results. As the existence of a prominent flat-spectrum radio core signifies that strong relativistic beaming is present in all these CDQs, the definitions of the two sets differ primarily in fractional optical polarization, with the LPCDQs showing a very low median Pop ≃ 0.4 per cent. Our study yields an INOV duty cycle (DC) of ~28 per cent for the LPCDQs and ~68 percent for HPCDQs. If only strong INOV with fractional amplitude above 3 per cent is considered, the corresponding DCs are ~7 per cent and ~40 per cent, respectively. Conclusions. From this strong contrast between the two classes of luminous, relativistically beamed quasars, it is apparent that relativistic beaming is normally not a sufficient condition for strong INOV and a high optical polarization is the other necessary condition. Moreover, the correlation is found to persist for many years after the polarization measurements were made. Some possible implications of this result are pointed out, particularly in the context of the recently detected rapid γ-ray variability of blazars
Probing spectral properties of radio-quiet quasars searched for optical microvariability-II
In the context of AGN unification scheme rapid variability properties play an
important role in understanding any intrinsic differences between sources in
different classes. In this respect any clue based on spectral properties will
be very useful toward understanding the mechanisms responsible for the origin
of rapid small scale optical variations, or microvariability. Here we have
added spectra of 46 radio-quiet quasars (RQQSOs) and Seyfert 1 galaxies to
those of our previous sample of 37 such objects, all of which had been
previously searched for microvariability. We took new optical spectra of 33
objects and obtained 13 others from the literature. Their \hbeta and \mgii
emission lines were carefully fit to determine line widths (FWHM) as well as
equivalent widths (EW) due to the broad emission line components. The line
widths were used to estimate black hole masses and Eddington ratios, .
Both EW and FWHM are anticorrelated with . Nearly all trends were in
agreement with our previous work, although the tendency for sources exhibiting
microvariability to be of lower luminosity was not confirmed. Most importantly,
this whole sample of EW distributions provides no evidence for the hypothesis
that a weak jet component in the radio quiet AGNs is responsible for their
microvariability.Comment: 15 pages, 9 figures, 6 tables, Accepted in MNRAS main journa
Optical polarimetry of the blazar CGRaBS~ J0211+1051 from MIRO
We report the detection of high polarization in the first detailed optical
linear polarization measurements on the BL Lac object CGRaBS J0211+1051, which
flared in -rays on 2011 January 23 as reported by Fermi. The
observations were made during 2011 January 30 - February 3 using
photo-polarimeter mounted at the 1.2m telescope of Mt Abu InfraRed
Observatory(MIRO). The CGRaBS J0211+1051 was detected to have degree of polarization (DP) with steady position angle (PA) at
43 on 2011 January 30. During Jan 31 and Feb 1, while polarization
shows some variation, position angle remains steady for the night. Several
olarization flashes occurred during February 2 and 3 resulting in changes in
the DP by more than 4% at short time scales ( 17 to 45 mins). A mild
increase in the linear polarization with frequency is noticed during the nights
of February 2 & 3. The source exhibited significant inter-night variations in
the degree of polarization (changed by about 2 to 9%) and position angle
(changed by 2 to 22) during the five nights of observations. The
intra-night activity shown by the source appears to be related to turbulence in
the relativistic jet. Sudden change in the PA accompanied by a rise in the DP
could be indicative of the fresh injection of electrons in the jet. The
detection of high and variable degree of polarization categorizes the source as
low energy peaked blazar.Comment: 14-pages including 3-figure
Optical microvariability properties of BALQSOs
We present optical light curves of 19 radio quiet (RQ) broad absorption line
(BAL) QSOs and study their rapid variability characteristics. Systematic CCD
observations, aided by a careful data analysis procedure, have allowed us to
clearly detect any such microvariability exceeding 0.01--0.02 mag. Our
observations cover a total of 13 nights (~72 hours) with each quasar monitored
for about 4 hours on a given night. Our sample size is a factor of three larger
than the number of radio-quiet BALQSOs previously searched for
microvariability. We introduce a scaled F-test statistic for evaluating the
presence of optical microvariability and demonstrate why it is generally
preferable to the statistics usually employed for this purpose. Considering
only unambiguous detections of microvariability we find that ~11 per cent of
radio-quiet BALQSOs (two out of 19 sources) show microvariability for an
individual observation length of about 4 hr. This new duty cycle of 11 per cent
is similar to the usual low microvariability fraction of normal RQQSOs with
observation lengths similar to those of ours. This result provides support for
models where radio-quiet BALQSO do not appear to be a special case of the
RQQSOs in terms of their microvariability properties.Comment: 13 pages, 3 figures, 3 tables, accepted for publication in MNRAS main
journa
Rapid optical variability of TeV blazars
In this first systematic attempt to characterise the intranight optical
variability (INOV) of TeV detected blazars, we have monitored a well defined
set of 9 TeV blazars on total 26 nights during 2004-2010. In this R (or V)-band
monitoring programme only one blazar was monitored per night for a minimum
duration of 4 hours. Using the CCD, an INOV detection threshold of ~ 1-2 % was
achieved in the densely sampled DLCs. We have further expanded the sample by
including another 13 TeV blazars from literature. This enlarged sample of 22
TeV blazars, monitored on a total of 116 nights (including 55 nights newly
reported here), has enabled us to arrive at the first estimate of the INOV duty
cycle of TeV detected blazars. Applying the C-test, the INOV DC is found to be
59 %, which decreases to 47 % if only INOV fractional amplitudes above 3 % are
considered. These observations also permit, for the first time, a comparison of
the INOV characteristics of the two major subclasses of TeV detected BL Lacs,
namely LBLs and HBLs, for which we find the INOV DCs to be ~ 63 % and ~ 38 %,
respectively. This demonstrates that the INOV differential between LBLs and
HBLs persists even when only their TeV detected subsets are considered. Despite
dense sampling, the intranight light curves of the 22 TeV blazars have not
revealed even a single feature on time scale substantially shorter than 1 hour,
even though the inner jets of TeV blazars are believed to have exceptionally
large bulk Lorentz factors (and correspondingly stronger time compression). An
intriguing feature, clearly detected in the light curve of the HBL J1555+1111,
is a 4 per cent `dip' on a 1 hour timescale. This unique feature could have
arisen from absorption in a dusty gas cloud, occulting a superluminally moving
optical knot in the parsec scale jet of this relatively luminous BL Lacs
object.Comment: 39 pages, 3 figures, accepted for publication in MNRA
- …