21,644 research outputs found
An algebraic interpretation of the Wheeler-DeWitt equation
We make a direct connection between the construction of three dimensional
topological state sums from tensor categories and three dimensional quantum
gravity by noting that the discrete version of the Wheeler-DeWitt equation is
exactly the pentagon for the associator of the tensor category, the
Biedenharn-Elliott identity. A crucial role is played by an asymptotic formula
relating 6j-symbols to rotation matrices given by Edmonds.Comment: 10 pages, amstex, uses epsf.tex. New version has improved
presentatio
AS-204/LM-1 launch vehicle operational flight trajectory
Apollo Saturn-204/LM-1 launch vehicle operational flight trajector
Improving Performance of Iterative Methods by Lossy Checkponting
Iterative methods are commonly used approaches to solve large, sparse linear
systems, which are fundamental operations for many modern scientific
simulations. When the large-scale iterative methods are running with a large
number of ranks in parallel, they have to checkpoint the dynamic variables
periodically in case of unavoidable fail-stop errors, requiring fast I/O
systems and large storage space. To this end, significantly reducing the
checkpointing overhead is critical to improving the overall performance of
iterative methods. Our contribution is fourfold. (1) We propose a novel lossy
checkpointing scheme that can significantly improve the checkpointing
performance of iterative methods by leveraging lossy compressors. (2) We
formulate a lossy checkpointing performance model and derive theoretically an
upper bound for the extra number of iterations caused by the distortion of data
in lossy checkpoints, in order to guarantee the performance improvement under
the lossy checkpointing scheme. (3) We analyze the impact of lossy
checkpointing (i.e., extra number of iterations caused by lossy checkpointing
files) for multiple types of iterative methods. (4)We evaluate the lossy
checkpointing scheme with optimal checkpointing intervals on a high-performance
computing environment with 2,048 cores, using a well-known scientific
computation package PETSc and a state-of-the-art checkpoint/restart toolkit.
Experiments show that our optimized lossy checkpointing scheme can
significantly reduce the fault tolerance overhead for iterative methods by
23%~70% compared with traditional checkpointing and 20%~58% compared with
lossless-compressed checkpointing, in the presence of system failures.Comment: 14 pages, 10 figures, HPDC'1
Does Resource Commercialization Induce Local Conservation? A Cautionary Tale From Southwestern Morocco
Ecotourism, bioprospecting and non-timber product marketing have been promoted recently as market-based instruments for environment protection, but without sound understanding of the resulting net conservation effects. We present evidence on the local conservation effects of recent argan oil commercialization in Morocco, which seems a promising case study in conservation through resource commercialization. Our empirical analysis shows, however, that resource commercialization is not creating strong net conservation incentives because assumptions implicit in the prevailing logic prove incorrect in this case. Generally, the experience of southwestern Morocco provides a cautionary tale about the assumed efficacy of conservation strategies founded on resource commercialization.Resource /Energy Economics and Policy,
Asymptotics of 4d spin foam models
We study the asymptotic properties of four-simplex amplitudes for various
four-dimensional spin foam models. We investigate the semi-classical limit of
the Ooguri, Euclidean and Lorentzian EPRL models using coherent states for the
boundary data. For some classes of geometrical boundary data, the asymptotic
formulae are given, in all three cases, by simple functions of the Regge action
for the four-simplex geometry.Comment: 10 pages, Proceedings for the 2nd Corfu summer school and workshop on
quantum gravity and quantum geometry, talk given by Winston J. Fairbair
Spectra and binding energy predictions of chiral interactions for 7Li
Using the no-core shell model approach, we report on the first results for
7Li based on the next-to-next-to-leading order chiral nuclear interaction.
Both, two-nucleon and three-nucleon interactions are taken into account. We
show that the p-shell nuclei are sensitive to the subleading parts of the
chiral interactions including three-nucleon forces. Though chiral interactions
are soft, we do not observe overbinding for this p-shell nucleus and find a
realistic description for the binding energy, excitation spectrum and radius.Comment: 12 pages, 12 figure
Effective interactions for light nuclei: an effective (field theory) approach
One of the central open problems in nuclear physics is the construction of
effective interactions suitable for many-body calculations. We discuss a
recently developed approach to this problem, where one starts with an effective
field theory containing only fermion fields and formulated directly in a
no-core shell-model space. We present applications to light nuclei and to
systems of a few atoms in a harmonic-oscillator trap. Future applications and
extensions, as well as challenges, are also considered
A compact micro-wave synthesizer for transportable cold-atom interferometers
We present the realization of a compact micro-wave frequency synthesizer for
an atom interferometer based on stimulated Raman transitions, applied to
transportable inertial sensing. Our set-up is intended to address the hyperfine
transitions of Rubidium 87 atoms at 6.8 GHz. The prototype is evaluated both in
the time and the frequency domain by comparison with state-of-the-art frequency
references developed at LNE-SYRTE. In free-running mode, it features a residual
phase noise level of -65 dBrad$^2.Hz^{-1} at 10-Hz offset frequency and a white
phase noise level in the order of -120 dBrad^2.Hz^{-1} for Fourier frequencies
above 10 kHz. The phase noise effect on the sensitivity of the atomic
interferometer is evaluated for diverse values of cycling time, interrogation
time and Raman pulse duration. To our knowledge, the resulting contribution is
well below the sensitivity of any demonstrated cold atom inertial sensors based
on stimulated Raman transitions. The drastic improvement in terms of size,
simplicity and power consumption paves the way towards field and mobile
operations.Comment: accepted for publication in Review of Scientific Instruments, 6
pages, 4 figure
Effective Theory for Trapped Few-Fermion Systems
We apply the general principles of effective field theories to the
construction of effective interactions suitable for few- and many-body
calculations in a no-core shell model framework. We calculate the spectrum of
systems with three and four two-component fermions in a harmonic trap. In the
unitary limit, we find that three-particle results are within 10% of known
semi-analytical values even in small model spaces. The method is very general,
and can be readily extended to other regimes, more particles, different species
(e.g., protons and neutrons in nuclear physics), or more-component fermions (as
well as bosons). As an illustration, we present calculations of the
lowest-energy three-fermion states away from the unitary limit and find a
possible inversion of parity in the ground state in the limit of trap size
large compared to the scattering length. Furthermore, we investigate the lowest
positive-parity states for four fermions, although we are limited by the
dimensions we can currently handle in this case.Comment: 8 pages, 5 figure
BAYES' ESTIMATES OF THE DOUBLE HURDLE MODEL IN THE PRESENCE OF FIXED COSTS
We present a model of market adoption (participation) where the presence of non-negligible fixed costs leads to non-zero censoring of the traditional double-hurdle regression. Fixed costs arise due to household resources that must be devoted a priori to the decision to participate in the market. These costs-usually a cost of time-motivate two-step decision-making and focus attentions on the minimum-efficient scale of operations (the minimum amount of milk sales) at which market entry becomes viable. This focus, in turn, motivates a non-zero-censored Tobit regression estimated through routine application of Markov chain Monte Carlo Methods.market participation, fixed costs, double-hurdle model, censored regression., Financial Economics, O1, O11, C34, O13, Q16, D1,
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