2,478 research outputs found
Cosmic Superstring Scattering in Backgrounds
We generalize the calculation of cosmic superstring reconnection probability
to non-trivial backgrounds. This is done by modeling cosmic strings as wound
tachyon modes in the 0B theory, and the spacetime effective action is then used
to couple this to background fields. Simple examples are given including
trivial and warped compactifications. Generalization to strings is
discussed.Comment: 12 pages, 2 figures; v2: references adde
Use of cumulative mortality data in patients with acute myocardial infarction for early detection of variation in clinical practice: observational study
OBJECTIVES: Use of cumulative mortality adjusted for
case mix in patients with acute myocardial infarction
for early detection of variation in clinical practice.
DESIGN: Observational study.
SETTING: 20 hospitals across the former Yorkshire
region.
PARTICIPANTS: All 2153 consecutive patients with
confirmed acute myocardial infarction identified
during three months.
MAIN OUTCOME MEASURES: Variable lifeadjusted
displays showing cumulative differences between
observed and expected mortality of patients; expected
mortality calculated from risk model based on
admission characteristics of age, heart rate, and
systolic blood pressure.
RESULTS: The performance of two individual hospitals
over three months was examined as an example. One,
the smallest district hospital in the region, had a series
of 30 consecutive patients but had five more deaths
than predicted. The variable lifeadjusted display
showed minimal variation from that predicted for the
first 15 patients followed by a run of unexpectedly
high mortality. The second example was the main
tertiary referral centre for the region, which admitted
188 consecutive patients. The display showed a period
of apparently poor performance followed by
substantial improvement, where the plot rose steadily
from a cumulative net lives saved of - 4 to 7. These
variations in patient outcome are unlikely to have
been revealed during conventional audit practice.
CONCLUSIONS: Variable lifeadjusted display has been
integrated into surgical care as a graphical display of
riskadjusted survival for individual surgeons or centres.
In combination with a simple risk model, it may have a
role in monitoring performance and outcome in
patients with acute myocardial infarction
Multilateral inversion of A_r, C_r and D_r basic hypergeometric series
In [Electron. J. Combin. 10 (2003), #R10], the author presented a new basic
hypergeometric matrix inverse with applications to bilateral basic
hypergeometric series. This matrix inversion result was directly extracted from
an instance of Bailey's very-well-poised 6-psi-6 summation theorem, and
involves two infinite matrices which are not lower-triangular. The present
paper features three different multivariable generalizations of the above
result. These are extracted from Gustafson's A_r and C_r extensions and of the
author's recent A_r extension of Bailey's 6-psi-6 summation formula. By
combining these new multidimensional matrix inverses with A_r and D_r
extensions of Jackson's 8-phi-7 summation theorem three balanced
very-well-poised 8-psi-8 summation theorems associated with the root systems
A_r and C_r are derived.Comment: 24 page
Variational Monte Carlo Calculations of H and He with a relativistic Hamiltonian - II
In relativistic Hamiltonians the two-nucleon interaction is expressed as a
sum of , the interaction in the rest frame,
and the ``boost interaction'' which depends upon the
total momentum and vanishes in the rest frame. The
can be regarded as a sum of four terms: , ,
and ; the first three originate from the
relativistic energy-momentum relation, Lorentz contraction and Thomas
precession, while the last is purely quantum. The contributions of and have been previously calculated with the
variational Monte Carlo method for H and He. In this brief note we
report the results of similar calculations for the contributions of and . These are found to be rather small.Comment: 7 pages, P-94-09-07
Gravitational Wave Bursts from Cosmic Superstring Reconnections
We compute the gravitational waveform produced by cosmic superstring
reconnections. This is done by first constructing the superstring reconnection
trajectory, which closely resembles that of classical, instantaneous
reconnection but with the singularities smoothed out due to the string path
integral. We then evaluate the graviton vertex operator in this background to
obtain the burst amplitude. The result is compared to the detection threshold
for current and future gravitational wave detectors, finding that neither
bursts nor the stochastic background would be detectable by Advanced LIGO. This
disappointing but anticipated conclusion holds even for the most optimistic
values of the reconnection probability and loop sizes.Comment: 26 pages, 6 figures; v2: references added and typos correcte
Acceleration and Classical Electromagnetic Radiation
Classical radiation from an accelerated charge is reviewed along with the
reciprocal topic of accelerated observers detecting radiation from a static
charge. This review commemerates Bahram Mashhoon's 60th birthday.Comment: To appear in Gen. Rel. Gra
Coin Tossing as a Billiard Problem
We demonstrate that the free motion of any two-dimensional rigid body
colliding elastically with two parallel, flat walls is equivalent to a billiard
system. Using this equivalence, we analyze the integrable and chaotic
properties of this new class of billiards. This provides a demonstration that
coin tossing, the prototypical example of an independent random process, is a
completely chaotic (Bernoulli) problem. The related question of which billiard
geometries can be represented as rigid body systems is examined.Comment: 16 pages, LaTe
Quantum Algorithms for Learning and Testing Juntas
In this article we develop quantum algorithms for learning and testing
juntas, i.e. Boolean functions which depend only on an unknown set of k out of
n input variables. Our aim is to develop efficient algorithms:
- whose sample complexity has no dependence on n, the dimension of the domain
the Boolean functions are defined over;
- with no access to any classical or quantum membership ("black-box")
queries. Instead, our algorithms use only classical examples generated
uniformly at random and fixed quantum superpositions of such classical
examples;
- which require only a few quantum examples but possibly many classical
random examples (which are considered quite "cheap" relative to quantum
examples).
Our quantum algorithms are based on a subroutine FS which enables sampling
according to the Fourier spectrum of f; the FS subroutine was used in earlier
work of Bshouty and Jackson on quantum learning. Our results are as follows:
- We give an algorithm for testing k-juntas to accuracy that uses
quantum examples. This improves on the number of examples used
by the best known classical algorithm.
- We establish the following lower bound: any FS-based k-junta testing
algorithm requires queries.
- We give an algorithm for learning -juntas to accuracy that
uses quantum examples and
random examples. We show that this learning algorithms is close to optimal by
giving a related lower bound.Comment: 15 pages, 1 figure. Uses synttree package. To appear in Quantum
Information Processin
Searching for Signatures of Cosmic Superstrings in the CMB
Because cosmic superstrings generically form junctions and gauge theoretic
strings typically do not, junctions may provide a signature to distinguish
between cosmic superstrings and gauge theoretic cosmic strings. In cosmic
microwave background anisotropy maps, cosmic strings lead to distinctive line
discontinuities. String junctions lead to junctions in these line
discontinuities. In turn, edge detection algorithms such as the Canny algorithm
can be used to search for signatures of strings in anisotropy maps. We apply
the Canny algorithm to simulated maps which contain the effects of cosmic
strings with and without string junctions. The Canny algorithm produces edge
maps. To distinguish between edge maps from string simulations with and without
junctions, we examine the density distribution of edges and pixels crossed by
edges. We find that in string simulations without Gaussian noise (such as
produced by the dominant inflationary fluctuations) our analysis of the output
data from the Canny algorithm can clearly distinguish between simulations with
and without string junctions. In the presence of Gaussian noise at the level
expected from the current bounds on the contribution of cosmic strings to the
total power spectrum of density fluctuations, the distinction between models
with and without junctions is more difficult. However, by carefully analyzing
the data the models can still be differentiated.Comment: 15 page
Operator-Algebraic Approach to the Yrast Spectrum of Weakly Interacting Trapped Bosons
We present an operator-algebraic approach to deriving the low-lying
quasi-degenerate spectrum of weakly interacting trapped N bosons with total
angular momentum \hbar L for the case of small L/N, demonstrating that the
lowest-lying excitation spectrum is given by 27 g n_3(n_3-1)/34, where g is the
strength of the repulsive contact interaction and n_3 the number of excited
octupole quanta. Our method provides constraints for these quasi-degenerate
many-body states and gives higher excitation energies that depend linearly on
N.Comment: 7 pages, one figur
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