42,866 research outputs found
The radiation properties of an accretion disk with a non-zero torque on its inner edge
The structure of the inner edge of the accretion disk around a black hole can
be altered, if the matter inside the marginally stable orbit is magnetically
connected to the disk. In this case, a non-zero torque is exerted on its inner
edge, and the accretion efficiency can be much higher than that in
the standard accretion disk model. We explore the radiation properties of an
accretion disk at its sonic point around a black hole with a time-steady torque
exerted on the inner edge of the disk. The local structure of the accretion
flow at the sonic point is investigated in the frame of general relativity. It
is found that the accretion flow will be optically thin at its sonic point for
most cases, if the additional accretion efficiency caused by
the torque is as high as 10 %. The results imply that the variable torque
may trigger transitions of the flow between different accretion types.Comment: 6 pages, to appear in PASJ, Vol. 55, No. 1 (February 25, 2003
Profiles of thermal line emission from advection dominated accretion flows
Recently, Narayan & Raymond (1999) proposed that the thermal emission lines
from the hot plasma in advection dominated accretion flows (ADAFs) are
potentially observable with the next generation of X-ray observatories, with
which the physical properties of some X-ray sources can be probed. In ADAFs,
the temperature of the ion is so high that the thermal broadening of the line
is important. We calculate the profiles of thermal line emission from ADAFs, in
which both the thermal and Doppler broadening have been considered. It is found
that the double-peaked profiles are present for high inclination angles between
the axis of disk and the line of sight. The double-peaked profiles are smeared
in low inclination cases, and completely disappear while the inclination angle
is less than , where the thermal and turbulent broadening dominated
on the line profiles. We also note that the thermal line profile is affected by
the location of the transition radius of ADAF. The self-similar
height-integrated disk structure and the emissivity with power-law dependence
of radius are adopted in our calculations. The results obtained in this work
can be used as a diagnosis on the future X-ray observations of the thermal
lines. Some important physical quantities of ADAFs could be inferred from
future thermal line observations.Comment: 7 page
Coherent Perfect Absorbers: Time-reversed Lasers
We show that an arbitrary body or aggregate can be made perfectly absorbing
at discrete frequencies if a precise amount of dissipation is added under
specific conditions of coherent monochromatic illumination. This effect arises
from the interaction of optical absorption and wave interference, and
corresponds to moving a zero of the elastic S-matrix onto the real wavevector
axis. It is thus the time-reversed process of lasing at threshold. The effect
is demonstrated in a simple Si slab geometry illuminated in the 500-900 nm
range. Coherent perfect absorbers are novel linear optical elements, absorptive
interferometers, which may be useful for controlled optical energy transfer.Comment: 4 pages, 4 figure
Noise Properties of Coherent Perfect Absorbers and Critically-coupled Resonators
The performance of a coherent perfect absorber (time-reversed laser) is
limited by quantum and thermal noise. At zero temperature, the quantum shot
noise dominates the signal for frequencies close to the resonance frequency,
and both vanish exactly at the resonance frequency. We compute the sensitivity
of the absorbing cavity as a background-free detector, limited by finite signal
or detector bandwidth.Comment: 6 pages, 3 figure
Long-Range Plasmon Assisted Energy Transfer Between Fluorescent Emitters
We demonstrate plasmon assisted energy transfer between fluorophores located
at distances up to m on the top of a thin silver film. Thanks to the
strong confinement and large propagation length of surface plasmon polaritons,
the range of the energy transfer is almost two orders of magnitude larger than
the values reported in the literature so far. The parameters driving the energy
transfer range are thoroughly characterized and are in very good agreement with
theoretically expected values.Comment: 5 pages, 4 figures, accepted for publication in Physical Review
Letter
Analysis of the Early-time Optical Spectra of SN 2011fe in M101
The nearby Type Ia supernova (SN Ia) SN 2011fe in M101 (cz = 241 km s^(–1)) provides a unique opportunity to study the early evolution of a "normal" SN Ia, its compositional structure, and its elusive progenitor system. We present 18 high signal-to-noise spectra of SN 2011fe during its first month beginning 1.2 days post-explosion and with an average cadence of 1.8 days. This gives a clear picture of how various line-forming species are distributed within the outer layers of the ejecta, including that of unburned material (C+O). We follow the evolution of C II absorption features until they diminish near maximum light, showing overlapping regions of burned and unburned material between ejection velocities of 10,000 and 16,000 km s^(–1). This supports the notion that incomplete burning, in addition to progenitor scenarios, is a relevant source of spectroscopic diversity among SNe Ia. The observed evolution of the highly Doppler-shifted O I λ7774 absorption features detected within 5 days post-explosion indicates the presence of O I with expansion velocities from 11,500 to 21,000 km s^(–1). The fact that some O I is present above C II suggests that SN 2011fe may have had an appreciable amount of unburned oxygen within the outer layers of the ejecta
Competing Ground States in Triple-layered Sr4Ru3O10: Verging on Itinerant Ferromagnetism with Critical Fluctuations
Sr4Ru3O10 is characterized by a sharp metamagnetic transition and
ferromagnetic behavior occurring within the basal plane and along the c-axis,
respectively. Resistivity at magnetic field, B, exhibits low-frequency quantum
oscillations when B||c-axis and large magnetoresistivity accompanied by
critical fluctuations driven by the metamagnetism when B^c-axis. The complex
behavior evidenced in resistivity, magnetization and specific heat presented is
not characteristic of any obvious ground states, and points to an exotic state
that shows a delicate balance between fluctuations and order.Comment: 18 pages, 4 figure
The Performance of CRTNT Fluorescence Light Detector for Sub-EeV Cosmic Ray Observation
Cosmic Ray Tau Neutrino Telescopes (CRTNT) using for sub-EeV cosmic ray
measurement is discussed. Performances of a stereoscope configuration with a
tower of those telescopes plus two side-triggers are studied. This is done by
using a detailed detector simulation driven by Corsika. Detector aperture as a
function of shower energy above 10^17 eV is calculated. Event rate of about 20k
per year for the second knee measurement is estimated. Event rate for cross
calibration with detectors working on higher energy range is also estimated.
Different configurations of the detectors are tried for optimization.Comment: 5 pages, 4 figures, submitted to HEP & N
Polarization correlated photons from a positively charged quantum dot
Polarized cross-correlation spectroscopy on a quantum dot charged with a
single hole shows the sequential emission of photons with common circular
polarization. This effect is visible without magnetic field, but becomes more
pronounced as the field along the quantization axis is increased. We interpret
the data in terms of electron dephasing in the X+ state caused by the
Overhauser field of nuclei in the dot. We predict the correlation timescale can
be increased by accelerating the emission rate with cavity-QED
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