524 research outputs found
Historic Light Curve and Long-term Optical Variation of BL Lacertae 2200+420
In this paper, historical optical(UBVRI) data and newly observed data from
the Yunnan Observatory of China(about100 years) are presented for BL Lacertae.
Maximum variations in UBVRI: 5.12, 5.31, 4.73, 2.59, and 2.54 and color indices
of U-B = -0.11 +/- 0.20, B-V= 1.0 +/- 0.11, V-R= 0.73 +/- 0.19, V-I= 1.42 +/-
0.25, R-I= 0.82 +/- 0.11, and B-I= 2.44 +/- 0.29 have been obtained from the
literature; The Jurkevich method is used to investigate the existence of
periods in the B band light curve, and a long-term period of 14 years is found.
The 0.6 and 0.88 year periods reported by Webb et al.(1988) are confirmed. In
addition, a close relation between B-I and B is found, suggesting that the
spectra flattens when the source brightens.Comment: 21 pages, 6 figures, 2 table, aasms4.sty, to be published in ApJ,
Vol. 507, 199
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
Observation of Berry's Phase in a Solid State Qubit
In quantum information science, the phase of a wavefunction plays an
important role in encoding information. While most experiments in this field
rely on dynamic effects to manipulate this information, an alternative approach
is to use geometric phase, which has been argued to have potential fault
tolerance. We demonstrate the controlled accumulation of a geometric phase,
Berry's phase, in a superconducting qubit, manipulating the qubit geometrically
using microwave radiation, and observing the accumulated phase in an
interference experiment. We find excellent agreement with Berry's predictions,
and also observe a geometry dependent contribution to dephasing.Comment: 5 pages, 4 figures, version with high resolution figures available at
http://qudev.ethz.ch/content/science/PubsPapers.htm
Imidotungsten(VI) complexes with chelating amino and imino phenolates
The reaction of WOCl(4) with 2,4-di-tert-butyl-6-((isopropylamino)methyl)phenol followed by the reaction with phenyl isocyanate leads to the formation of imidotungsten(VI) complex [W(NPh)Cl(3)(OC(6)H(3)(CH(2)NH-i-Pr)-2-t-Bu(2)-4,6)] 4 with a chelating aminophenolate ligand. When the same procedure was applied using aminophenols with bulkier substituents in the amino group, the final product was an unexpected Schiff-base complex [W(NPh)Cl(3)(OC(6)H(3)(CH = NPh)-2-t-Bu(2)-4,6)] 5, where the ligand is derived from 2,4-di-tert-butyl-6-((phenylimino)methyl)phenol. Complex 5 is also formed in the thermal degradation of 4. On the whole, 5 appears to be formed by a disproportionation of intermediate compounds, which are analogous to complex 4. The solid-state structures of 4 and 5 have been determined by X-ray crystallography whereas the solution structures were studied by (1)H and (13)C NMR
Tunable resonators for quantum circuits
We have designed, fabricated and measured high-Q coplanar
waveguide microwave resonators whose resonance frequency is made tunable with
magnetic field by inserting a DC-SQUID array (including 1 or 7 SQUIDs) inside.
Their tunability range is 30% of the zero field frequency. Their quality factor
reaches up to 3. We present a model based on thermal fluctuations
that accounts for the dependance of the quality factor with magnetic field.Comment: subm. to JLTP (Proc. of LTD12 conference
Broadband Spectral Analysis of PKS 0528+134: A Report on Six Years of EGRET Observations
The multiwavelength spectra of PKS 0528+134 during six years of observations
by EGRET have been analyzed using synchrotron self-Compton (SSC) and external
radiation Compton (ERC) models. We find that a two-component model, in which
the target photons are produced externally to the gamma-ray emitting region,
but also including an SSC component, is required to suitably reproduce the
spectral energy distributions of the source. Our analysis indicates that there
is a trend in the observed properties of PKS 0528+134, as the source goes from
a gamma-ray low state to a flaring state. We observe that during the higher
gamma-ray states, the bulk Lorentz factor of the jet increases and the ERC
component dominates the high-energy emission. Our model calculations indicate
the trend that the energies of the electrons giving rise to the synchrotron
peak decreases, and the power-ratio of the gamma-ray and low energy spectral
components increases, as the source goes from a low to a high gamma-ray state.Comment: 36 pages, 13 figures, final version accepted for publication in ApJ;
includes minor modification
Application of <sup>14</sup>C analyses to source apportionment of carbonaceous PM<sub>2.5</sub> in the UK
Determination of the radiocarbon (<sup>14</sup>C) content of airborne particulate matter yields insight into the proportion of the carbonaceous material derived from fossil and contemporary carbon sources. Daily samples of PM<sub>2.5</sub> were collected by high-volume sampler at an urban background site in Birmingham, UK, and the fraction of <sup>14</sup>C in both the total carbon, and in the organic and elemental carbon fractions, determined by two-stage combustion to CO<sub>2</sub>, graphitisation and quantification by accelerator mass spectrometry. OC and EC content was also determined by Sunset Analyzer. The mean fraction contemporary TC in the PM<sub>2.5</sub> samples was 0.50 (range 0.27–0.66, n = 26). There was no seasonality to the data, but there was a positive trend between fraction contemporary TC and magnitude of SOC/TC ratio and for the high values of these two parameters to be associated with air-mass back trajectories arriving in Birmingham from over land. Using a five-compartment mass balance model on fraction contemporary carbon in OC and EC, the following average source apportionment for the TC in these PM<sub>2.5</sub> samples was derived: 27% fossil EC; 20% fossil OC; 2% biomass EC; 10% biomass OC; and 41% biogenic OC. The latter category will comprise, in addition to BVOC-derived SOC, other non-combustion contemporary carbon sources such as biological particles, vegetative detritus, humic material and tyre wear. The proportion of total PM<sub>2.5</sub> at this location estimated to derive from BVOC-derived secondary organic aerosol was 9–29%. The findings from this work are consistent with those from elsewhere in Europe and support the conclusion of a significant and ubiquitous contribution from non-fossil biogenic sources to the carbon in terrestrial aerosol
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
TEMPO2, a new pulsar timing package. III: Gravitational wave simulation
Analysis of pulsar timing data-sets may provide the first direct detection of
gravitational waves. This paper, the third in a series describing the
mathematical framework implemented into the tempo2 pulsar timing package,
reports on using tempo2 to simulate the timing residuals induced by
gravitational waves. The tempo2 simulations can be used to provide upper bounds
on the amplitude of an isotropic, stochastic, gravitational wave background in
our Galaxy and to determine the sensitivity of a given pulsar timing experiment
to individual, supermassive, binary black hole systems.Comment: Accepted by MNRA
A kinematic study of the compact jet in quasar B3 1633+382
We present a study of the motion of compact jet components in quasar B3
1633+382. Through analyzing 14 epochs of VLBI observations of three components
(B1, B2, and B3) at 22 GHz, we find two different possibilities of component
classification. Thus two corresponding kinematical models can be adopted to
explain the evolutionary track of components. One is a linear motion, while
another is a helical model. Future observations are needed to provide new
kinematical constraints for the motion of these components in this source.Comment: 7 pages, 3 figures; Accepted for publication in A&
- …