760 research outputs found
Proximity effect-assisted absorption of spin currents in superconductors
The injection of pure spin current into superconductors by the dynamics of a
ferromagnetic contact is studied theoretically. Taking into account suppression
of the order parameter at the interfaces (inverse proximity effect) and the
energy-dependence of spin-flip scattering, we determine the
temperature-dependent ferromagnetic resonance linewidth broadening. Our results
agree with recent experiments in Nb|permalloy bilayers [C. Bell et al.,
arXiv:cond-mat/0702461].Comment: 4 page
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
Long-term Variability Properties and Periodicity Analysis for Blazars
In this paper, the compiled long-term optical and infrared measurements of
some blazars are used to analyze the variation properties and the optical data
are used to search for periodicity evidence in the lightcurve by means of the
Jurkevich technique and the discrete correlation function (DCF) method.
Following periods are found: 4.52-year for 3C 66A; 1.56 and 2.95 years for AO
0235+164;
14.4, 18.6 years for PKS 0735+178; 17.85 and 24.7 years for PKS 0754+100;
5.53 and 11.75 for OJ 287. 4.45, and 6.89 years for PKS 1215; 9 and 14.84 years
for PKS 1219+285;
2.0, 13.5 and 22.5 for 3C273; 7.1 year for 3C279;
6.07 for PKS 1308+326; 3.0 and 16.5 years for PKS 1418+546;
2.0 and 9.35 years for PKS 1514-241; 18.18 for PKS 1807+698;
4.16 and 7.0 for 2155-304; 14 and 20 years for BL Lacertae. Some explanations
have been discussed.Comment: 10 pages, 2 table, no figure, a proceeding paper for Pacific Rim
Conference on Stellar Astrophysics, Aug. 1999, HongKong, Chin
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
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
Leisure-time physical activity and DNA methylation agea twin study
BackgroundEpigenetic clocks may increase our understanding on human aging and how genetic and environmental factors regulate an individual aging process. One of the most promising clocks is Horvath's DNA methylation (DNAm) age. Age acceleration, i.e., discrepancy between DNAm age and chronological age, tells us whether the person is biologically young or old compared to his/her chronological age. Several environmental and lifestyle factors have been shown to affect life span. We investigated genetic and environmental predictors of DNAm age in young and older monozygotic (MZ) and dizygotic (DZ) twins with a focus on leisure time physical activity.ResultsQuantitative genetic modeling revealed that the relative contribution of non-shared environmental factors was larger among older compared with younger twin pairs [47% (95% CI 35, 63) vs. 26% (95% CI: 19, 35), pPeer reviewe
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
- …