18,891 research outputs found
Wittgenstein on Personal Time
The most grandiose of the many philosophical
problems of time is whether it is real or not. An example of
a metaphysical argument to the effect that time is unreal is
that of the idealist F.H. Bradley. In setting forth his case
he made a distinction between 1) time as space-like and 2)
time "as presented,â€? the "now.â€
Bayesian Grammar Induction for Language Modeling
We describe a corpus-based induction algorithm for probabilistic context-free
grammars. The algorithm employs a greedy heuristic search within a Bayesian
framework, and a post-pass using the Inside-Outside algorithm. We compare the
performance of our algorithm to n-gram models and the Inside-Outside algorithm
in three language modeling tasks. In two of the tasks, the training data is
generated by a probabilistic context-free grammar and in both tasks our
algorithm outperforms the other techniques. The third task involves
naturally-occurring data, and in this task our algorithm does not perform as
well as n-gram models but vastly outperforms the Inside-Outside algorithm.Comment: 8 pages, LaTeX, uses aclap.st
Evaluation of scheduling techniques for payload activity planning
Two tasks related to payload activity planning and scheduling were performed. The first task involved making a comparison of space mission activity scheduling problems with production scheduling problems. The second task consisted of a statistical analysis of the output of runs of the Experiment Scheduling Program (ESP). Details of the work which was performed on these two tasks are presented
Dynamics of satellites, asteroids, and rings
Work is reported on: (1) the shapes and the internal structures of satellites; (2) the tidal heating of Miranda; (3) the dynamics of arc-like rings; and (4) the structure of the zodiacal cloud that was revealed by the Infrared Astronomy Satellite. Significant progress was made in determining the shape and internal structure of Mimas and in understanding the dynamical evolution of Miranda's orbit
Note on recent measurements of the \psi(1S)\to\ga \eta_C(1S) and \psi(2S)\to\ga \eta_C(1S) branching ratios
Recently published measurements of the branching ratios {\cal
B}(\psi(1S)\to\ga \eta_C(1S)) and {\cal B}(\psi(2S)\to\ga \eta_C(1S)) by the
CLEO collaboration are examined in the context of a potential model that
includes both relativistic and one-loop QCD corrections to the quark-antiquark
interaction. The prediction for the width \Gamma(\psi(1S)\to\ga \eta_C(1S))
is in excellent agreement with the new data but the prediction for
\Gamma(\psi(2S)\to\ga \eta_C(1S)) is too small. In an effort to understand
this discrepancy, we derive an upper bound on \Gamma(\psi(2S)\to\ga
\eta_C(1S)) and point out its experimental value saturates this bound.Comment: Corrected typos, addeded referenc
Recent developments in the modeling of heavy quarkonia
We examine the spectra and radiative decays of the cc-bar and bb-bar systems
using a model which incorporates the complete one-loop spin-dependent
perturbative QCD short distance potential, a linear confining term including
(spin-dependent) relativistic corrections to order v^2/c^2, and a fully
relativistic treatment of the kinetic energy. We compare the predictions of
this model to experiments, including states and decays recently measured at
Belle, BaBar, CLEO and CDF.Comment: 3 pages, contribution to PANIC05, Santa Fe, NM October 200
Light-Front Holography and AdS/QCD Correspondence
Light-Front Holography is a remarkable consequence of the correspondence
between string theory in AdS space and conformal field theories in
physical-space time. It allows string modes in the AdS fifth
dimension to be precisely mapped to the light-front wavefunctions of hadrons in
terms of a specific light-front impact variable which measures the
separation of the quark and gluonic constituents within the hadron. This
mapping was originally obtained by matching the exact expression for
electromagnetic current matrix elements in AdS space with the corresponding
exact expression for the current matrix element using light-front theory in
physical space-time. More recently we have shown that one obtains the identical
holographic mapping using matrix elements of the energy-momentum tensor, thus
providing an important consistency test and verification of holographic mapping
from AdS to physical observables defined on the light-front. The resulting
light-front Schrodinger equations predicted from AdS/QCD give a good
representation of the observed meson and baryon spectra and give excellent
phenomenological predictions for amplitudes such as electromagnetic form
factors and decay constants.Comment: 14 pages. Presented at QCD Down Under II, Auckland, New Zealand,
January 17-19, 200
Applications of AdS/QCD and Light-Front Holography to Baryon Physics
The correspondence between theories in anti-de Sitter space and field
theories in physical space-time leads to an analytic, semiclassical model for
strongly-coupled QCD which has scale invariance at short distances and color
confinement at large distances. These equations, for both mesons and baryons,
give a very good representation of the observed hadronic spectrum, including a
zero mass pion. Light-front holography allows hadronic amplitudes in the AdS
fifth dimension to be mapped to frame-independent light-front wavefunctions of
hadrons in physical space-time, thus providing a relativistic description of
hadrons at the amplitude level. The meson and baryon wavefunctions derived from
light-front holography and AdS/QCD also have remarkable phenomenological
features, including predictions for the electromagnetic form factors and decay
constants. The approach can be systematically improved using light-front
Hamiltonian methods. Some novel features of QCD for baryon physics are also
discussed.Comment: Presented by SJB at the International Conference on the Structure of
Baryons, BARYONS'10, December 7-11, 2010, Osaka, Japa
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