Search results for "waves"
showing 10 items of 1766 documents
High-Resolution Radio Observations of Supernova SN1986J
2003
We present high-resolution observations of the supernova SN1986J in the galaxy NGC891 at the frequency of 5 GHz, more than 15 years after its explosion. The image shows a highly distorted shell of radio emission, suggesting that the shock front has been strongly deformed. The brightness distribution within the shell is also highly asymmetric, and we propose that such asymmetry could be due to the collision of the supernova ejecta with an anisotropic, clumpy medium. The average speed of the shell has decreased from about 7400 km s−1 in 1988.74 down to ~ 6300 km s−1 in 1999.14, pointing to a mild deceleration in the expansion of SN 1986J. Assuming a standard density profile for the progenitor…
A Brightening Coronal Loop Observed byTRACE. II. Loop Modeling and Constraints on Heating
2000
This is the second of two papers dedicated to the brightening of a coronal loop observed by the Transition Region and Coronal Explorer (TRACE) on 1998 June 26; it aims at hydrodynamic modeling of the brightening. Since the loop geometry is practically unchanged during the brightening, the evolution of the plasma confined in the loop is described with a one-dimensional hydrodynamic time-dependent numerical model, and from the results the emission along the loop in the TRACE 171 A band is synthesized. The information from Paper I is used to derive the geometry and the initial configuration of the loop as well as for comparison with the results of the model. The modeling is focused to determin…
Jet stability and the generation of superluminal and stationary components
2001
We present a numerical simulation of the response of an expanding relativistic jet to the ejection of a superluminal component. The simulation has been performed with a relativistic time-dependent hydrodynamical code from which simulated radio maps are computed by integrating the transfer equations for synchrotron radiation. The interaction of the superluminal component with the underlying jet results in the formation of multiple conical shocks behind the main perturbation. These trailing components can be easily distinguished because they appear to be released from the primary superluminal component, instead of being ejected from the core. Their oblique nature should also result in distinc…
Messungen der Himmelsstrahlung und deren Polarisationsgrad während der Sonnenfinsternis am 15.2.1961 in Viareggio (Italien)
1961
On the occasion of the total solar eclipse in Viareggio (Italy) measurements of intensity of sky radiation and polarization have been carried out at 90 degrees vertical distance from the sun. UV-, green- and red-filters have been used. The results showed a diminution of the intensity during the eclipse of about 3 powers of ten. The sky brightness in the point 90 degrees distant during the total eclipse was similar to the brightness when sun is 7 degrees below the horizon. About one minute before the total eclipse the degree of polarization diminuished to zero. — Furthermore photos of nearly the total sky were made using two cameras with wide angle lenses.
Rigidity and Dynamics of Random Spring Networks
1996
The static and dynamic elastic properties of two-dimensional random networks composed of Hookean springs are analyzed. These networks are proved to be nonrigid with respect to small deformations, and the floppy mode ratio is calculated exactly. The vibrational spectrum is shown to consist only of zero-frequency and localized modes. The exponential decay of the amplitude and velocity of the transient wave front are shown to be exactly described by a quasi-one-dimensional model of noninteracting paths of propagation.
Ising and Bloch walls of phase domains in two-dimensional parametric wave mixing
2004
Oscillators driven by a degenerate wave mixing process are bistable in the phase of the generated radiation. In systems with a large Fresnel number, domains of opposite phase form therefore spontaneously. A simple model predicts a real field in which phase domains are separated by Ising-type walls. In this paper we show experimentally (using complex field reconstruction from measurements) and theoretically (by an extended model) that the optical field can be real as well as complex valued and that complex field fronts are related to the front curvature.
Universal description of pattern formation in optical oscillators under bichromatic injection
2018
We study pattern formation in a complex Swift–Hohenberg equation with phase-sensitive (parametric) gain. Such an equation serves as a universal order parameter equation describing the onset of spontaneous oscillations in extended systems submitted to a bichromatic injection when the instability is toward long (transverse) wavelengths. Applications include two-level lasers and photorefractive oscillators. Under such an injection, the original continuous phase symmetry of the system is replaced by a discrete one and phase bistability emerges. This leads to the spontaneous formation of phase-locked spatial structures, such as phase domains and dark-ring (phase) cavity solitons. The stability o…
Scattering and Localization of Classical Waves Along a Wave Guide with Disorder and Dissipation
1993
The problem of localization of classical waves has recently attracted consider-able attention.1,2 Classical waves have, of course, been the subject of extensive research already in the last century, as emphasized by Landauer in his historical sketch.3 A variety of interesting phenomena is associated with classical waves like seismic waves, tidal waves, acoustic as well as optical waves. A major topic is the transport of energy or information by these waves. The current interest in classical waves is stimulated by the development of microelectronics with its very small structures, in particular very thin wires (as connections between the components of integrated circuits) which may (or may n…
Pattern formation through phase bistability in oscillatory systems with space-modulated forcing.
2010
We propose a novel forcing technique of spatially extended self-oscillatory systems able to excite phase bistability and the dissipative structures associated with it. The forcing is time periodic at a frequency close to the oscillators' frequency and is spatially modulated. The effects of this type of forcing are demonstrated analytically and numerically in a directly driven complex Ginzburg-Landau equation. Both spatially periodic and spatially random drives prove to be effective.
Polarization and modal attractors in conservative counterpropagating four-wave interaction
2005
An experimental and theoretical study of the resonant four-wave interaction scheme in the counterpropagating configuration reveals the existence of a novel attraction process in Hamiltonian systems. We show analytically that it is the specificity of the boundary conditions inherent in the counterpropagating configuration that makes attraction dynamics possible in spite of the reversible nature of the four-wave interaction. In the context of optics, this novel dynamical feature could be the basic mechanism of a universal polarizer performing total polarization conversion of unpolarized light with, in principle, 100% efficiency.