25,937 research outputs found
A multiwavelength survey of interacting galaxies
Galaxy-galaxy collisions are known to produce drastic changes in morphology and, in many cases, enhance the level of star formation activity in galaxies. In order to better quantify the effects that interactions have on the star formation characteristics of galaxies the authors undertook a multiwavelength survey of a large sample of interacting disk-type galaxies. The sample is optically-selected, the inclusion of systems having been based upon the presence of unusual morphological features--such as tidal tails, plumes, rings, warped disks--suggestive of tidal interaction. The sample is composed of about 115 systems, most of which are spiral-spiral pairs, with a few spiral-elliptical pairs and a few merging systems (see Bushouse 1986 for more details of the sample selection). This sample has now been studied in the optical, infrared, and radio regimes, including optical spectra and H alpha images, near-infrared photometry and imaging, far-infrared photometry, H I 21 cm emission-line measurements, Very Large Array (VLA) 20 cm maps, and CO emission-line measurements. This paper presents an overview and comparison of the results of the optical, infrared and CO surveys. With these data the authors can compare the far-infrared and CO properties of the galaxies with the classic optical and radio indicators of star formation activity and thereby determine what, if any, relationships exist between star formation activity and the far-infrared and CO properties of the galaxies
A balanced homodyne detector for high-rate Gaussian-modulated coherent-state quantum key distribution
We discuss excess noise contributions of a practical balanced homodyne
detector in Gaussian-modulated coherent-state (GMCS) quantum key distribution
(QKD). We point out the key generated from the original realistic model of GMCS
QKD may not be secure. In our refined realistic model, we take into account
excess noise due to the finite bandwidth of the homodyne detector and the
fluctuation of the local oscillator. A high speed balanced homodyne detector
suitable for GMCS QKD in the telecommunication wavelength region is built and
experimentally tested. The 3dB bandwidth of the balanced homodyne detector is
found to be 104MHz and its electronic noise level is 13dB below the shot noise
at a local oscillator level of 8.5*10^8 photon per pulse. The secure key rate
of a GMCS QKD experiment with this homodyne detector is expected to reach
Mbits/s over a few kilometers.Comment: 22 pages, 11 figure
Mid-Infrared Images of Luminous Infrared Galaxies in a Merging Sequence
We report mid-infrared observations of several luminous infrared galaxies
(LIGs) carried out with the Infrared Space Observatory. Our sample was chosen
to represent different phases of a merger sequence of galaxy-galaxy interaction
with special emphasis on early/intermediate stages of merging. The mid-infrared
emission of these LIGs shows extended structures for the early and intermediate
mergers, indicating that most of the mid-infrared luminosities are not from a
central active galactic nucleus (AGN). Both the infrared hardness (indicated by
the IRAS 12, 25, and 60 \micron flux density ratios) and the peak-to-total
flux density ratios of these LIGs increase as projected separation of these
interacting galaxies become smaller, consistent with increasing star formation
activities that are concentrated to a smaller area as the merging process
advances. These observations provide among the first observational constraint
of largely theoretically based scenarios.Comment: 10 pages, 3 figures, please refer to ApJ Letters for the final
versio
Heisenberg-picture approach to the exact quantum motion of a time-dependent forced harmonic oscillator
In the Heisenberg picture, the generalized invariant and exact quantum
motions are found for a time-dependent forced harmonic oscillator. We find the
eigenstate and the coherent state of the invariant and show that the
dispersions of these quantum states do not depend on the external force. Our
formalism is applied to several interesting cases.Comment: 15 pages, two eps files, to appear in Phys. Rev. A 53 (6) (1996
Circumnuclear Structures in Megamaser Host Galaxies
Using HST, we identify circumnuclear (- pc scale) structures in
nine new HO megamaser host galaxies to understand the flow of matter from
kpc-scale galactic structures down to the supermassive black holes (SMBHs) at
galactic centers. We double the sample analyzed in a similar way by Greene et
al. (2013) and consider the properties of the combined sample of 18 sources. We
find that disk-like structure is virtually ubiquitous when we can resolve
pc scales, in support of the notion that non-axisymmetries on these
scales are a necessary condition for SMBH fueling. We perform an analysis of
the orientation of our identified nuclear regions and compare it with the
orientation of megamaser disks and the kpc-scale disks of the hosts. We find
marginal evidence that the disk-like nuclear structures show increasing
misalignment from the kpc-scale host galaxy disk as the scale of the structure
decreases. In turn, we find that the orientation of both the pc scale
nuclear structures and their host galaxy large-scale disks is consistent with
random with respect to the orientation of their respective megamaser disks.Comment: 24 pages, 16 figures, 4 tables; Resubmitted to ApJ after referee's
comment
Quantum key distribution with "dual detectors"
To improve the performance of a quantum key distribution (QKD) system, high
speed, low dark count single photon detectors (or low noise homodyne detectors)
are required. However, in practice, a fast detector is usually noisy. Here, we
propose a "dual detectors" method to improve the performance of a practical QKD
system with realistic detectors: the legitimate receiver randomly uses either a
fast (but noisy) detector or a quiet (but slow) detector to measure the
incoming quantum signals. The measurement results from the quiet detector can
be used to bound eavesdropper's information, while the measurement results from
the fast detector are used to generate secure key. We apply this idea to
various QKD protocols. Simulation results demonstrate significant improvements
in both BB84 protocol with ideal single photon source and Gaussian-modulated
coherent states (GMCS) protocol; while for decoy-state BB84 protocol with weak
coherent source, the improvement is moderate. We also discuss various practical
issues in implementing the "dual detectors" scheme.Comment: 22 pages, 9 figure
- …