4,006 research outputs found
A Multi-Wavelength Study of the Western Lobe of W50 Powered by the Galactic Microquasar SS 433
W50 remains the only supernova remnant (SNR) confirmed to harbor a
microquasar: the powerful enigmatic source SS 433. Our past study of this
fascinating SNR revealed two X-ray lobes distorting the radio shell as well as
non-thermal X-rays at the site of interaction between the SS 433 eastern jet
and the eastern lobe of W50. In this paper we present the results of a 75 ksec
CHANDRA ACIS-I observation of the peak of W50-west targeted to 1) determine the
nature of the X-ray emission and 2) correlate the X-ray emission with that in
the radio and infrared domains. We have confirmed that at the site of
interaction between the western jet of SS 433 and dense interstellar gas the
X-ray emission is non-thermal in nature. The helical pattern observed in radio
is also seen with CHANDRA. No correlation was found between the infrared and
X-ray emission.Comment: A refereed publication, submitted Sept. 30, 2004, accepted Jan. 12,
2005, to appear in Advances in Space Research. 7 pages, including 4 figures
(3 color) & 1 table (the resolution of most figures has been reduced for
astro-ph submission only). A gzipped postscript or pdf version of the paper
with high-resolution images can be downloaded from:
http://aurora.physics.umanitoba.ca/~moldowan/Astro-Ph
Convergence rates of the DPG method with reduced test space degree
This paper presents a duality theorem of the Aubin-Nitsche type for
discontinuous Petrov Galerkin (DPG) methods. This explains the numerically
observed higher convergence rates in weaker norms. Considering the specific
example of the mild-weak (or primal) DPG method for the Laplace equation, two
further results are obtained. First, the DPG method continues to be solvable
even when the test space degree is reduced, provided it is odd. Second, a
non-conforming method of analysis is developed to explain the numerically
observed convergence rates for a test space of reduced degree
Thermal stress analysis for a wood composite blade
Heat conduction throughout the blade and the distribution of thermal stresses caused by the temperature distribution were determined for a laminated wood wind turbine blade in both the horizontal and vertical positions. Results show that blade cracking is not due to thermal stresses induced by insulation. A method and practical example of thermal stress analysis for an engineering body of orthotropic materials is presented
Thermal-stress analysis for wood composite blade
The thermal-stress induced by solar insolation on a wood composite blade of a Mod-OA wind turbine was investigated. The temperature distribution throughout the blade (a heat conduction problem) was analyzed and the thermal-stress distribution of the blades caused by the temperature distribution (a thermal-stress analysis problem) was then determined. The computer programs used for both problems are included along with output examples
Thermal-stress analysis for a wood composite blade
A thermal-stress analysis of a wind turbine blade made of wood composite material is reported. First, the governing partial differential equation on heat conduction is derived, then, a finite element procedure using variational approach is developed for the solution of the governing equation. Thus, the temperature distribution throughout the blade is determined. Next, based on the temperature distribution, a finite element procedure using potential energy approach is applied to determine the thermal-stress distribution. A set of results is obtained through the use of a computer, which is considered to be satisfactory. All computer programs are contained in the report
Design of sliding mode controller for chaotic Josephson-junction
It is known that a shunted nonlinear resistive-capacitive-inductance Josephson-junction (RCLSJ) model has a chaotic attractor. This attractor is created as a result of Hopf bifurcation that occurs when a certain direct current (DC) applied to one of the junction terminals. This chaotic attractor prevents the system from reaching the phase-locked state and hence degrade the performance of the junction. This paper aims at controlling and taming this chaotic attractor induced in this model and pulling the system to the phase-locked state. To achieve this task, a sliding mode controller is proposed. The design procedures involve two steps. In the first one, we construct a suitable sliding surface so that the dynamic of the system follows the sliding manifolds in order to meet design specifications. Secondly, a control law is created to force the chaotic attractor to slide on the sliding surface and hence stabilizes system trajectory. The RCLSJ model under consideration is simulated with and without the designed controller. Results demonstrate the validity of the designed controller in taming the induced chaos and stabilizing the system under investigation
Chaos and Bifurcation Control Using Nonlinear Recursive Controller
Chaos and bifurcation control is achieved by nonlinear controller that is able to mitigate the characteristics of a class of nonlinear systems that are experiencing such phenomenon. In this paper, a backstepping nonlinear recursive controller is presented. Comparison has been made between it and a Pole Placement controller. The study shows the effectiveness of the proposed control under various operating conditions
Kikuchi ultrafast nanodiffraction in four-dimensional electron microscopy
Coherent atomic motions in materials can be revealed using time-resolved X-ray and electron Bragg diffraction. Because of the size
of the beam used, typically on the micron scale, the detection of
nanoscale propagating waves in extended structures hitherto has not
been reported. For elastic waves of complex motions, Bragg intensities
contain all polarizations and they are not straightforward to
disentangle. Here, we introduce Kikuchi diffraction dynamics, using
convergent-beam geometry in an ultrafast electron microscope, to
selectively probe propagating transverse elastic waves with nanoscale
resolution. It is shown that Kikuchi band shifts, which are sensitive
only to the tilting of atomic planes, reveal the resonance
oscillations, unit cell angular amplitudes, and the polarization
directions. For silicon, the observed wave packet temporal envelope (resonance frequency of 33 GHz), the out-of-phase temporal behavior of
Kikuchi's edges, and the magnitude of angular amplitude (0.3 mrad) and
polarization [011] elucidate the nature of the motion:
one that preserves the mass density (i.e., no compression or expansion)
but leads to sliding of planes in the antisymmetric shear eigenmode of
the elastic waveguide. As such, the method of Kikuchi diffraction
dynamics, which is unique to electron imaging, can be used to
characterize the atomic motions of propagating waves and their
interactions with interfaces, defects, and grain boundaries at the
nanoscale
Controlling Chaos and Bifurcation of Subsynchronous Resonance in Power System
Linear and nonlinear state feedback controllers are proposed to control the bifurcation of a new phenomenon in power system, this phenomenon of electro-mechanical interaction between the series resonant circuits and torsional mechanical frequencies of the turbine generator sections, which known as Subsynchronous Resonance (SSR). The first system of the IEEE second benchmark model is considered. The dynamics of the two axes damper windings, Automatic Voltage Regulator (AVR) and Power System Stabilizer (PSS) are included. The linear controller gives better initial disturbance response than that of the nonlinear, but in a small narrow region of compensation factors. The nonlinear controller not only can be easily implemented, but also it stabilizes the operating point for all values of the bifurcation parameter
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