5,797 research outputs found
Multi-frequency imaging of perfectly conducting cracks via boundary measurements
Imaging of perfectly conducting crack(s) in a 2-D homogeneous medium using
boundary data is studied. Based on the singular structure of the Multi-Static
Response (MSR) matrix whose elements are normalized by an adequate test
function at several frequencies, an imaging functional is introduced and
analyzed. A non-iterative imaging procedure is proposed. Numerical experiments
from noisy synthetic data show that acceptable images of single and multiple
cracks are obtained.Comment: 4 pages, 3 figure
The relationship between radio power at 22 and 43 GHz and black hole properties of AGN in elliptical galaxies
We investigate the relationship between radio power and properties related to
active galactic nuclei (AGNs). Radio power at 1.4 or 5 GHz, which has been used
in many studies, can be affected by synchrotron self-absorption and free-free
absorption in a dense region. On the other hand, these absorption effects get
smaller at higher frequencies. Thus, we performed simultaneous observations at
22 and 43 GHz using the Korean VLBI Network (KVN) radio telescope based on a
sample of 305 AGN candidates residing in elliptical galaxies from the overlap
between the Sloan Digital Sky Survey (SDSS) Data Release 7 and Faint Images of
the Radio Sky at Twenty-Centimeters (FIRST). About 37% and 22% of the galaxies
are detected at 22 and 43 GHz, respectively. Assuming no flux variability
between the FIRST and KVN observation, spectral indices were derived from FIRST
and KVN data and we found that over 70% of the detected galaxies have flat or
inverted spectra, implying the presence of optically thick compact regions near
the centres of the galaxies. Core radio power does not show a clear dependence
on black hole mass at either low (1.4 GHz) or high (22 and 43 GHz) frequencies.
However, we found that the luminosity of the [OIII] 5007 emission line
and the Eddington ratio correlate with radio power more closely at high
frequencies than at low frequencies. This suggests that radio observation at
high frequencies can be an appropriate tool for unveiling the innermost region.
In addition, the luminosity of the [OIII] 5007 emission line and the
Eddington ratio can be used as a tracer of AGN activity. Our study suggests a
causal connection between high frequency radio power and optical properties of
AGNs.Comment: 14 pages, 13 figures, 5 tables, Accepted for publication in A&
Marangoni Effects on the Bubble Dynamics in a Pressure Driven Flow
The motion of air bubbles and water drops in a Hele-Shaw cell filled with a silicone oil has been studied experimentally and theoretically. By adding a predetermined amount of a surfactant to the water drops we attempted to investigate the surfactant influence systematically. While the motion of air bubbles was in reasonable agreement with the predictions of Taylor and Saffman, water drops behaved quite differently in that the translational velocities were smaller by an order of magnitude and their shapes were very unusual as observed previously by Kopf-Sill and Homsy. Assuming that the surrounding fluid wets the solid wall and the bubble (or the drop) surface is rigid due to the surfactant influence, we have estimated the translational velocity of an elliptic bubble. The calculated velocities were in good agreement with the observations indicating that the surfactant influence could retard the bubble motion significantly. The present study also indicates that the unusual bubble shapes are also due to the surfactant influence
Modular assembly of a protein nanotriangle using orthogonally interacting coiled coils
Synthetic protein assemblies that adopt programmed shapes would support many applications in nanotechnology. We used a rational design approach that exploits the modularity of orthogonally interacting coiled coils to create a self-assembled protein nanotriangle. Coiled coils have frequently been used to construct nanoassemblies and materials, but rarely with successful prior specification of the resulting structure. We designed a heterotrimer from three pairs of heterodimeric coiled coils that mediate specific interactions while avoiding undesired crosstalk. Non-associating pairs of coiled-coil units were strategically fused to generate three chains that were predicted to preferentially form the heterotrimer, and a rational annealing proc ess led to the desired oligomer. Extensive biophysical characterization and modeling support the formation of a molecular triangle, which is a shape distinct from naturally occurring supramolecular nanostructures. Our approach can be extended to design more complex nanostructures using additional coiled-coil modules, other protein parts, or templated surfaces
Quasiparticle spectrum of the hybrid s+g-wave superconductors YNi_2B_2C and LuNi_2B_2C
Recent experiments on single crystals of YNiBC have revealed the
presence of point nodes in the superconducting energy gap Delta(k} at k =
(1,0,0), (0,1,0), (-1,0,0), and (0,-1,0). In this paper we investigate the
effects of impurity scattering on the quasiparticle spectrum in the vortex
state of s+g-wave superconductors, which is found to be strongly modified in
the presence of disorder. In particular, a gap in the quasiparticle energy
spectrum is found to open even for infinitesimal impurity scattering, giving
rise to exponentially activated thermodynamic response functions, such as the
specific heat, the spin susceptibility, the superfluid density, and the nuclear
spin lattice relaxation. Predictions derived from this study can be verified by
measurements of the angular dependent magnetospecific heat and the
magnetothermal conductivity.Comment: 8 pages, RevTex, 4 figure
Anisotropy of in-plane magnetization due to nodal gap structure in the vortex state
We examine the interplay between anisotropy of the in-plane magnetization and
the nodal gap structure on the basis of the approximate analytic solution in
the quasiclassical formalism. We show that a four-fold oscillation appears in
the magnetization, and its amplitude changes sign at an intermediate field. The
high-field oscillation originates from the anisotropy of the upper critical
field, while the low-field behavior can be understood by the thermally
activated quasiparticles near nodes depending on the applied field angles. The
temperature dependence of the magnetization also shows a similar sign change.
The anisotropy of the magnetization offers a possible measurement to identify
the gap structure directly for a wide class of type II superconductors.Comment: 4 pages, 4 figure
Synchronization of Chaotic Oscillators due to Common Delay Time Modulation
We have found a synchronization behavior between two identical chaotic
systems^M when their delay times are modulated by a common irregular signal. ^M
This phenomenon is demonstrated both in two identical chaotic maps whose
delay times are driven by a common^M chaotic or random signal and in two
identical chaotic oscillators whose delay times are driven by^M a signal of
another chaotic oscillator. We analyze the phenomenon by using^M the Lyapunov
exponents and discuss it in relation with generalized synchronization.^MComment: 5 pages, 4 figures (to be published in PRE
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