1,381,532 research outputs found
Regularities with random interactions in energy centroids defined by group symmetries
Regular structures generated by random interactions in energy centroids
defined over irreducible representations (irreps) of some of the group
symmetries of the interacting boson models IBM, IBM, IBM- and
IBM- are studied by deriving trace propagations equations for the
centroids. It is found that, with random interactions, the lowest and highest
group irreps in general carry most of the probability for the corresponding
centroids to be lowest in energy. This generalizes the result known earlier,
via numerical diagonalization, for the more complicated fixed spin ()
centroids where simple trace propagation is not possible.Comment: 18 pages, 3 figure
Semiparametric posterior limits
We review the Bayesian theory of semiparametric inference following Bickel
and Kleijn (2012) and Kleijn and Knapik (2013). After an overview of efficiency
in parametric and semiparametric estimation problems, we consider the
Bernstein-von Mises theorem (see, e.g., Le Cam and Yang (1990)) and generalize
it to (LAN) regular and (LAE) irregular semiparametric estimation problems. We
formulate a version of the semiparametric Bernstein-von Mises theorem that does
not depend on least-favourable submodels, thus bypassing the most restrictive
condition in the presentation of Bickel and Kleijn (2012). The results are
applied to the (regular) estimation of the linear coefficient in partial linear
regression (with a Gaussian nuisance prior) and of the kernel bandwidth in a
model of normal location mixtures (with a Dirichlet nuisance prior), as well as
the (irregular) estimation of the boundary of the support of a monotone family
of densities (with a Gaussian nuisance prior).Comment: 47 pp., 1 figure, submitted for publication. arXiv admin note:
substantial text overlap with arXiv:1007.017
Global aspects of accelerating and rotating black hole space-times
The complete family of exact solutions representing accelerating and rotating
black holes with possible electromagnetic charges and a NUT parameter is known
in terms of a modified Plebanski-Demianski metric. This demonstrates the
singularity and horizon structure of the sources but not that the complete
space-time describes two causally separated black holes. To demonstrate this
property, the metric is first cast in the Weyl-Lewis-Papapetrou form. After
extending this up to the acceleration horizon, it is then transformed to the
boost-rotation-symmetric form in which the global properties of the solution
are manifest. The physical interpretation of these solutions is thus clarified.Comment: 15 pages, 1 figure. To appear in Class. Quantum Gra
Leonardo's rule, self-similarity and wind-induced stresses in trees
Examining botanical trees, Leonardo da Vinci noted that the total
cross-section of branches is conserved across branching nodes. In this Letter,
it is proposed that this rule is a consequence of the tree skeleton having a
self-similar structure and the branch diameters being adjusted to resist
wind-induced loads
Theory of polarization enhancement in epitaxial BaTiO/SrTiO superlattices
The spontaneous polarization of epitaxial BaTiO/SrTiO superlattices
is studied as a function of composition using first-principles density
functional theory within the local density approximation. With the in-plane
lattice parameter fixed to that of bulk SrTiO, the computed superlattice
polarization is enhanced above that of bulk BaTiO for superlattices with
BaTiO fraction larger than 40%. In contrast to their bulk paraelectric
character, the SrTiO layers are found to be {\it tetragonal and polar},
possessing nearly the same polarization as the BaTiO layers. General
electrostatic arguments elucidate the origin of the polarization in the
SrTiO layers, with important implications for other ferroelectric
nanostructures.Comment: 4 pages, 2 Figures, 1 Tabl
Observations of QSO J2233-606 in the Southern Hubble Deep Field
The Hubble Deep Field South (HDF-S) HST observations are expected to begin in
October 1998. We present a composite spectrum of the QSO in the HDF-S field
covering UV/optical/near IR wavelengths, obtained by combining data from the
ANU 2.3m Telescope with STIS on the HST. This intermediate resolution spectrum
covers the range 1600-10000A and allows us to derive some basic information on
the intervening absorption systems which will be important in planning future
higher resolution studies of this QSO.Comment: 9 pages and 2 figures, submitted to ApJ
Geometry and Topology of Escape I: Epistrophes
We consider a dynamical system given by an area-preserving map on a
two-dimensional phase plane and consider a one-dimensional line of initial
conditions within this plane. We record the number of iterates it takes a
trajectory to escape from a bounded region of the plane as a function along the
line of initial conditions, forming an ``escape-time plot''. For a chaotic
system, this plot is in general not a smooth function, but rather has many
singularities at which the escape time is infinite; these singularities form a
complicated fractal set. In this article we prove the existence of regular
repeated sequences, called ``epistrophes'', which occur at all levels of
resolution within the escape-time plot. (The word ``epistrophe'' comes from
rhetoric and means ``a repeated ending following a variable beginning''.) The
epistrophes give the escape-time plot a certain self-similarity, called
``epistrophic'' self-similarity, which need not imply either strict or
asymptotic self-similarity.Comment: 15 pages, 9 figures, to appear in Chaos, first of two paper
Extensions of C*-dynamical systems to systems with complete transfer operators
Starting from an arbitrary endomorphism of a unital C*-algebra
we construct a bigger C*-algebra and extend onto in such a way
that the extended endomorphism has a unital kernel and a hereditary
range, i.e. there exists a unique non-degenerate transfer operator for
, called the complete transfer operator. The pair is
universal with respect to a suitable notion of a covariant representation and
depends on a choice of an ideal in . The construction enables a natural
definition of the crossed product for arbitrary .Comment: Compressed and submitted version, 9 page
Soot formation and burnout in flames
The amount of soot formed when burning a benzene/hexane mixture in a turbulent combustor was examined. Soot concentration profiles in the same combustor for kerosene fuel are given. The chemistry of the formation of soot precursors, the nucleation, growth and subsequent burnout of soot particles, and the effect of mixing on the previous steps were considered
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