67,664 research outputs found
Semi-classical States for Non-self-adjoint Schrodinger Operators
We prove that the spectrum of certain non-self-adjoint Schrodinger operators
is unstable in the semi-classical limit. Similar results hold for a fixed
operator in the high energy limit. The method involves the construction of
approximate semi-classical modes of the operator by the JWKB method for
energies far from the spectrum
Triviality of the Peripheral Point Spectrum
If T_t=\rme^{Zt} is a positive one-parameter contraction semigroup acting
on where is a countable set and , then the
peripheral point spectrum of cannot contain any non-zero elements. The
same holds for Feller semigroups acting on if is locally compact
Formation Channels for Blue Straggler Stars
In this chapter we consider two formation channels for blue straggler stars:
1) the merger of two single stars via a collision, and 2) those produced via
mass transfer within a binary. We review how computer simulations show that
stellar collisions are likely to lead to relatively little mass loss and are
thus effective in producing a young population of more-massive stars. The
number of blue straggler stars produced by collisions will tend to increase
with cluster mass. We review how the current population of blue straggler stars
produced from primordial binaries decreases with increasing cluster mass. This
is because exchange encounters with third, single stars in the most massive
clusters tend to reduce the fraction of binaries containing a primary close to
the current turn-off mass. Rather, their primaries tend to be somewhat more
massive and have evolved off the main sequence, filling their Roche lobes in
the past, often converting their secondaries into blue straggler stars (but
more than 1 Gyr or so ago and thus they are no longer visible today as blue
straggler stars).Comment: Chapter 9, in Ecology of Blue Straggler Stars, H.M.J. Boffin, G.
Carraro & G. Beccari (Eds), Astrophysics and Space Science Library, Springe
Decomposing the Essential Spectrum
We use C*-algebra theory to provide a new method of decomposing the eseential
spectra of self-adjoint and non-self-adjoint Schrodinger operators in one or
more space dimensions
Spectral Properties of Random Non-self-adjoint Matrices and Operators
We describe some numerical experiments which determine the degree of spectral
instability of medium size randomly generated matrices which are far from
self-adjoint. The conclusion is that the eigenvalues are likely to be
intrinsically uncomputable for similar matrices of a larger size. We also
describe a stochastic family of bounded operators in infinite dimensions for
almost all of which the eigenvectors generate a dense linear subspace, but the
eigenvalues do not determine the spectrum. Our results imply that the spectrum
of the non-self-adjoint Anderson model changes suddenly as one passes to the
infinite volume limit.Comment: keywords: eigenvalues, spectral instability, matrices, computability,
pseudospectrum, Schroedinger operator, Anderson mode
Personal space : bring on the physics revolution
Some years ago a student submitted a practical assignment in which he wrote something along these lines: I collected the data on Sauchiehall Street on Friday afternoon. I asked any young-looking males (who didnt look too scary!) to fill in the questionnaire. It started to rain about four oclock so I went in Costa Coffee, and when I came out there werent so many people about, so I finished it off on Saturday morning. Colleagues felt this was inappropriate in a practical essay on a scientific subject. They objected to the use of the word I, which by definition made it a subjective account; and they suggested that a phrase such as Data were collected from a random sample of young males would have been more suitable. But I disagreed strongly, arguing that the student account was more informative, more scientific, more honest, and there was no attempt to hide behind scientific rhetoric. And obviously, the sample could not be called random
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