14,681 research outputs found
A function space model for canonical systems
Recently, a generalization to the Pontryagin space setting of the notion of canonical (Hamiltonian) systems which involves a finite number of inner singularities has been given. The spectral theory of indefinite canonical systems was investigated with help of an operator model. This model consists of a Pontryagin space boundary triple and was constructed in an abstract way. Moreover, the construction of this operator model involves a procedure of splitting-and-pasting which is technical but at the present stage of development in general inevitable. In this paper we provide an isomorphic form of this operator model which acts in a finite-dimensional extension of a function space naturally associated with the given indefinite canonical system. We give explicit formulae for the model operator and the boundary relation. Moreover, we show that under certain asymptotic hypotheses the procedure of splitting-and-pasting can be avoided by employing a limiting process. We restrict attention to the case of one singularity. This is the core of the theory, and by making this restriction we can significantly reduce the technical effort without losing sight of the essential ideas
Impulsive solar X-ray bursts. 4: Polarization, directivity and spectrum of the reflected and total bremsstrahlung radiation from a beam of electrons directed toward the photosphere
A Monte Carlo method is described for evaluation of the spectrum, directivity and polarization of X-rays diffusely reflected from stellar photospheres. the accuracy of the technique is evaluated through comparison with analytic results. Using the characteristics of the incident X-rays of the model for solar X-ray flares, the spectrum, directivity and polarization of the reflected and the total X-ray fluxes are evaluated. The results are compared with observations
Impulsive solar X-ray bursts. 3: Polarization and directivity of bremsstrahlung radiation from a beam of electrons directed toward the photosphere
The spectrum, directivity and state of polarization is presented of the bremsstrahlung radiation expected from a beam of high energy electrons spiraling along radial magnetic field lines toward the photosphere. The results are used for calculation of the characteristics of the reflected plus direct flux
Automobile Prices, Gasoline Prices, and Consumer Demand for Fuel Economy
The relationship between gasoline prices and the demand for vehicle fuel efficiency is important for environmental policy but poorly understood in the academic literature. We provide empirical evidence that automobile manufacturers price as if consumers respond to gasoline prices. We derive a reduced-form regression equation from theoretical micro-foundations and estimate the equation with nearly 300,000 vehicle-week-region observations over the period 2003-2006. We find that vehicle prices generally decline in the gasoline price. The decline is larger for inefficient vehicles, and the prices of particularly efficient vehicles actually rise. Structural estimation that ignores these effects underestimates consumer preferences for fuel efficiency.Automobiles, Gasoline, Consumer Preference, Demand, Fuel Efficiency
Search for Stable Magnetohydrodynamic Equilibria in Barotropic Stars
It is now believed that magnetohydrodynamic equilibria can exist in stably
stratified stars due to the seminal works of Braithwaite & Spruit (2004) and
Braithwaite & Nordlund (2006). What is still not known is whether
magnetohydrodynamic equilibria can exist in a barotropic star, in which stable
stratification is not present. It has been conjectured by Reisenegger (2009)
that there will likely not exist any magnetohydrodynamical equilibria in
barotropic stars. We aim to test this claim by presenting preliminary MHD
simulations of barotropic stars using the three dimensional stagger code of
Nordlund & Galsgaard (1995).Comment: 4 pages, 2 figures, to appear in the proceedings of IAUS 302:
"Magnetic Fields Throughout Stellar Evolution
Localized induction equation and pseudospherical surfaces
We describe a close connection between the localized induction equation
hierarchy of integrable evolution equations on space curves, and surfaces of
constant negative Gauss curvature.Comment: 21 pages, AMSTeX file. To appear in Journal of Physics A:
Mathematical and Genera
Dendritic side-branching with anisotropic viscous fingering
We studied dendritic side-branching mechanism in the experiment of
anisotropic viscous fingering. We measured the time dependence of growth speed
of side-branch and the envelop of side-branches. We found that the speed of
side-branch gets to be faster than one of the stem and the growth exponent of
the speed changes at a certain time. The envelope of side-branches is
represented as Y ~ X^1.47.Comment: 8 pages, 8 figures, to submited in J. Crystal Growt
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