Optical Monitoring of BL Lacertae Object OJ 287: a 40-Day Period?

We present the results of our optical monitoring of the BL Lacertae object OJ 287 during the first half of 2005. The source did not show large-amplitude variations during this period and was in a relatively quiescent state. A possible period of 40 days was derived from its light curves in three BATC wavebands. A bluer-when-brighter chromatism was discovered, which is different from the extremely stable color during the outburst in 1994--96. The different color behaviors imply different variation mechanisms in the two states. We then re-visited the optical data on OJ 287 from the OJ-94 project and found as well a probable period of 40 days in its optical variability during the late-1994 outburst. The results suggest that two components contribute to the variability of OJ 287 during its outburst state. The first component is the normal {\sl blazar} variation. This component has an amplitude similar to that of the quiescent state and also may share a similar periodicity. The second component can be taken as a `low-frequency modulation' to the first component. It may be induced by the interaction of the assumed binary black holes in the center of this object. The 40-day period may be related to the helical structure of the magnetic field at the base of the jet, or to the orbital motion close to the central primary black hole.Comment: 31 pages, 8 figures, accepted by A

An Eccentric Circumbinary Accretion Disk and the Detection of Binary Massive Black Holes

We present a two-dimensional grid-based hydrodynamic simulation of a thin, viscous, locally-isothermal corotating disk orbiting an equal-mass Newtonian binary point mass on a fixed circular orbit. We study the structure of the disk after multiple viscous times. The binary maintains a central hole in the viscously-relaxed disk with radius equal to about twice the binary semimajor axis. Disk surface density within the hole is reduced by orders of magnitude relative to the density in the disk bulk. The inner truncation of the disk resembles the clearing of a gap in a protoplanetary disk. An initially circular disk becomes elliptical and then eccentric. Disturbances in the disk contain a component that is stationary in the rotating frame in which the binary is at rest; this component is a two-armed spiral density wave. We measure the distribution of the binary torque in the disk and find that the strongest positive torque is exerted inside the central low-density hole. We make connection with the linear theory of disk forcing at outer Lindblad resonances (OLRs) and find that the measured torque density distribution is consistent with forcing at the 3:2 (m=2) OLR, well within the central hole. We also measure the time dependence of the rate at which gas accretes across the hole and find quasi-periodic structure. We discuss implications for variability and detection of active galactic nuclei containing a binary massive black hole.Comment: 10 pages; replaced to match ApJ version; includes new physical interpretation of torque density (Sec. 4.1); large mpeg animation is available at http://www.tapir.caltech.edu/~milos/circBinaryEccDisk.mp

Potential inhibition of filamentous microorganisms in sludge bulking by static magnetic field

In activated sludge system, the performance of the process largely depends on the balance between filamentous and floc -forming microorganisms. When the normal balance of these biological communities is disturbed, filamentous microorganisms t end to proliferate, causing various problems to the treatment performances such as sludge bulking. Various approaches have been used to control the p roliferation of filamentous microorganisms. However, the approaches led to various drawbacks that eventually worsen the performances of treatment systems. Therefore, this study is aimed to investigate the potential approach using static magnetic field in inhibi ting filamentous microorganisms that presence in the sludge bulking. Magnetic field of intensity 88 mT was used. Its exposure on the filamentous microorganisms was investigated in terms of filaments' characteristics such as branching, shape and filaments' location. The analysis indicated that the magnetically exposed activated sludge showed less possibility presence of the filamentous microorganisms compared to unexposed activated sludge

Effect of temperature variations in anaerobic fluidized membrane bioreactor : membrane fouling and microbial community dynamics assessment

publishedVersionPeer reviewe

Simultaneous MITSuME gRI monitoring of S5 0716+714

We present results of our intra-night optical flux monitoring observations of S5 0716+714 done simultaneously in gRI filters. The observations were done using Multicolor Imaging Telescopes for Survey and Monstrous Explosions (MITSuME) instrument on the 50 cm telescope at the Okayama Astrophysical Observatory over 30 nights between 11 March 2008 and 8 May 2008. Of these 30 nights, 22 nights have continuous (without any break) observations with duration ranging from 1 to 6 hours and hence were considered for intra-night optical variability (INOV). In total we have 4888 datapoints which were simultaneous in gR and I filters. Of the 22 nights considered for INOV, the object showed flux variability on 19 nights with the amplitude of variability in the I-band ranging from ~4% to ~55%. The duty cycle for INOV was thus found to be 83%. No time lag between different bands was noticed on most of the nights, except for 3 nights where the variation in g was found to lead that of the I band by 0.3 to 1.5 hrs. On inter-night timescales, no lag was found between g and I bands. On inter-night timescales as well as intra-night timescales on most of the nights, the amplitude of variability was found to increase toward shorter wavelengths. The flux variations in the different bands were not achromatic, with the blazar tending to become bluer when brighter both on inter-night and intra-night timescales; and this might be attributed to the larger amplitude variation at shorter wavelengths. A clear periodic variation of 3.3 hrs was found on 1 April 2008 and a hint for another possible periodic variability of 4 hrs was found on 31 March 2008. During our 30 days of observations over a 2 month period the source has varied with an amplitude of variability as large as ~80%.Comment: 11 pages, 8 figures and 5 tables, Accepted in MNRA

Death within 8 years after childhood convulsive status epilepticus:a population-based study

The risk of long-term mortality and its predictors following convulsive status epilepticus in childhood are uncertain. We report mortality within 8 years after an episode of convulsive status epilepticus, and investigate its predictors from a paediatric, prospective, population-based study from north London, UK. In the current study, we followed-up a cohort previously ascertained during a surveillance study of convulsive status epilepticus in childhood. After determining the survival status of the cohort members, we defined cause of death as that listed on their death certificates. We estimated a standardized mortality ratio to compare mortality in our cohort with that expected in the reference population. Multivariable Cox regression analysis was used to investigate any association between the clinical and demographic factors at the time of status epilepticus and subsequent risk of death. The overall case fatality was 11% (95% confidence interval 7.5–16.2%); seven children died within 30 days of their episode of convulsive status epilepticus and 16 during follow-up. The overall mortality in our cohort was 46 times greater than expected in the reference population, and was predominantly due to higher mortality in children who had pre-existing clinically significant neurological impairments when they had their acute episode of convulsive status epilepticus. Children without prior neurological impairment who survived their acute episode of convulsive status epilepticus were not at a significantly increased risk of death during follow-up. There were no deaths in children following prolonged febrile convulsions and idiopathic convulsive status epilepticus. A quarter of deaths during follow-up were associated with intractable seizures/convulsive status epilepticus, and the rest died as a complication of their underlying medical condition. On regression analysis, presence of clinically significant neurological impairments prior to convulsive status epilepticus was the only independent risk factor for mortality. In conclusion, there is a high risk of death within 8 years following childhood convulsive status epilepticus but most deaths are not seizure related. Presence of pre-existing clinically significant neurological impairments at the time of convulsive status epilepticus is the main risk factor for mortality within 8 years after the acute episode. The attributable role of convulsive status epilepticus on mortality remains uncertain, but appears less than is generally perceived

Measuring gravitational waves from binary black hole coalescences: I. Signal to noise for inspiral, merger, and ringdown

We estimate the expected signal-to-noise ratios (SNRs) from the three phases (inspiral,merger,ringdown) of coalescing binary black holes (BBHs) for initial and advanced ground-based interferometers (LIGO/VIRGO) and for space-based interferometers (LISA). LIGO/VIRGO can do moderate SNR (a few tens), moderate accuracy studies of BBH coalescences in the mass range of a few to about 2000 solar masses; LISA can do high SNR (of order 10^4) high accuracy studies in the mass range of about 10^5 to 10^8 solar masses. BBHs might well be the first sources detected by LIGO/VIRGO: they are visible to much larger distances (up to 500 Mpc by initial interferometers) than coalescing neutron star binaries (heretofore regarded as the "bread and butter" workhorse source for LIGO/VIRGO, visible to about 30 Mpc by initial interferometers). Low-mass BBHs (up to 50 solar masses for initial LIGO interferometers; 100 for advanced; 10^6 for LISA) are best searched for via their well-understood inspiral waves; higher mass BBHs must be searched for via their poorly understood merger waves and/or their well-understood ringdown waves. A matched filtering search for massive BBHs based on ringdown waves should be capable of finding BBHs in the mass range of about 100 to 700 solar masses out to 200 Mpc (initial LIGO interferometers), and 200 to 3000 solar masses out to about z=1 (advanced interferometers). The required number of templates is of order 6000 or less. Searches based on merger waves could increase the number of detected massive BBHs by a factor of order 10 or more over those found from inspiral and ringdown waves, without detailed knowledge of the waveform shapes, using a "noise monitoring" search algorithm. A full set of merger templates from numerical relativity could further increase the number of detected BBHs by an additional factor of up to 4.Comment: 40 pages, Revtex, psfig.tex, seven figures, submitted to Phys Rev

Multiwavelength observations of Mkn 501 during the 1997 high state

During the observation period 1997, the nearby Blazar Mkn 501 showed extremely strong emission and high variability. We examine multiwavelength aspects of this event using radio, optical, soft and hard X-ray and TeV data. We concentrate on the medium-timescale variability of the broadband spectra, averaged over weekly intervals. We confirm the previously found correlation between soft and hard X-ray emission and the emission at TeV energies, while the source shows only minor variability at radio and optical wavelengths. The non-linear correlation between hard X-ray and TeV fluxes is consistent with a simple analytic estimate based on an SSC model in which Klein-Nishina effects are important for the highest-energy electrons in the jet, and flux variations are caused by variations of the electron density and/or the spectral index of the electron injection spectrum. The time-averaged spectra are fitted with a Synchrotron Self-Compton (SSC) dominated leptonic jet model, using the full Klein-Nishina cross section and following the self-consistent evolution of relativistic particles along the jet, accounting for gamma-gamma absorption and pair production within the source as well as due to the intergalactic infrared background radiation. The contribution from external inverse-Compton scattering is tightly constrained by the low maximum EGRET flux and found to be negligible at TeV energies. We find that high levels of the X-ray and TeV fluxes can be explained by a hardening of the energy spectra of electrons injected at the base of the jet, in remarkable contrast to the trend found for gamma-ray flares of the flat-spectrum radio quasar PKS 0528+134.Comment: accepted for publication in ApJ, 31 pages, 11 figure

The 72-Hour WEBT Microvariability Observation of Blazar S5 0716+714 in 2009

Context. The international whole earth blazar telescope (WEBT) consortium planned and carried out three days of intensive micro-variability observations of S5 0716+714 from February 22, 2009 to February 25, 2009. This object was chosen due to its bright apparent magnitude range, its high declination, and its very large duty cycle for micro-variations. Aims. We report here on the long continuous optical micro-variability light curve of 0716+714 obtained during the multi-site observing campaign during which the Blazar showed almost constant variability over a 0.5 magnitude range. The resulting light curve is presented here for the first time. Observations from participating observatories were corrected for instrumental differences and combined to construct the overall smoothed light curve. Methods. Thirty-six observatories in sixteen countries participated in this continuous monitoring program and twenty of them submitted data for compilation into a continuous light curve. The light curve was analyzed using several techniques including Fourier transform, Wavelet and noise analysis techniques. Those results led us to model the light curve by attributing the variations to a series of synchrotron pulses. Results. We have interpreted the observed microvariations in this extended light curve in terms of a new model consisting of individual stochastic pulses due to cells in a turbulent jet which are energized by a passing shock and cool by means of synchrotron emission. We obtained an excellent fit to the 72-hour light curve with the synchrotron pulse model