4,124 research outputs found
Resistivity measurements of neutron-irradiated pure metals and Al-Zn alloys
Report presents resistivity measurements and their interpretation for neutron-irradiated pure metals and Al-Zn alloys. The influence of temperature, the role of point defects, and the aging behavior on resistivity are considered. The experimental procedures and results are discussed in detail
Polarization of light from warm clouds above an accretion disk: effects of strong-gravity near a black hole
We study polarization from scattering of light on a cloud in radial motion
along the symmetry axis of an accretion disk. Radiation drag from the disk and
gravitational attraction of the central black hole are taken into account, as
well as the effect of the cloud cooling in the radiation field. This provides
us with a self-consistent toy-model for predicted lightcurves, including the
linear polarization that arises from the scattering. Strong gravitational
lensing creates indirect images; these are formed by photons that originate
from the disk, get backscattered onto the photon circular orbit and eventually
redirected towards an observer. Under suitable geometrical conditions the
indirect photons may visibly influence the resulting magnitude of polarization
and light-curve profiles. Relevant targets are black holes in active galactic
nuclei and stellar-mass Galactic black-holes exhibiting episodic
accretion/ejection events.Comment: Accepted for publication in PASJ; 7 pages, 4 figure
Of NBOs and kHz QPOs: a low-frequency modulation in resonant oscillations of relativistic accretion disks
The origin of quasi periodic modulations of flux in the kilohertz range (kHz
QPOs), observed in low-mass X-ray binaries, is usually assumed to be physically
distinct from that of the ``normal branch oscillations'' (NBOs) in the
Z-sources. We show that a low-frequency modulation of the kHz QPOs is a natural
consequence of the non-linear relativistic resonance suggested previously to
explain the properties of the high-frequency twin peaks. The theoretical
results discussed here are reminiscent of the 6 Hz variations of frequency and
amplitude of the kHz QPOs reported by Yu, van der Klis and Jonker (2001).Comment: Accepted for publication in PASJ; 4 pages, 1 figur
Numerical variational methods applied to cylinder buckling
We review and compare different computational variational methods applied to
a system of fourth order equations that arises as a model of cylinder buckling.
We describe both the discretization and implementation, in particular how to
deal with a 1 dimensional null space. We show that we can construct many
different solutions from a complex energy surface. We examine numerically
convergence in the spatial discretization and in the domain size. Finally we
give a physical interpretation of some of the solutions found.Comment: 23 pages, 12 figures, 6 table
Novel Fiber Design for Wideband Conversion and Amplification in Multimode Fibers
We propose an operating principle to achieve broadband and highly tunable
mode conversion and amplification exploiting inter-modal four wave mixing in a
multimode fiber. A bandwidth of 30 nanometers is demonstrated by properly
designing a simple step-index silica fiber.Comment: Ecoc conference 201
Intermodal Four-Wave-Mixing and Parametric Amplification in km-long Fibers
We theoretically and numerically investigate intermodal four-wave-mixing in
km-long fibers, where random birefringence fluctuations are present along the
fiber length. We identify several distinct regimes that depend on the relative
magnitude between the length scale of the random fluctuations and the
beat-lengths of the interacting quasi-degenerate modes. In addition, we analyze
the impact of polarization mode-dispersion and we demonstrate that random
variations of the core radius, which are typically encountered during the
drawing stage of the fiber, can represent the major source of bandwidth
impairment. These results set a boundary on the limits of validity of the
classical Manakov model and may be useful for the design of multimode
parametric amplifiers and wavelength converters, as well as for the analysis of
nonlinear impairments in long-haul spatial division multiplexed transmission
- …