6,414 research outputs found
Quark-Gluon Jet Differences at LEP
A new method to identify the gluon jet in 3-jet ``{\bf Y}'' decays of
is presented. The method is based on differences in particle multiplicity
between quark jets and gluon jets, and is more effective than tagging by
leptonic decay. An experimental test of the method and its application to a
study of the ``string effect'' are proposed. Various jet-finding schemes for
3-jet events are compared.Comment: 11 pages, LaTeX, 4 PostScript figures availble from the author
([email protected]), MSUTH-92-0
The prediction of extratropical storm tracks by the ECMWF and NCEP ensemble prediction systems
The prediction of extratropical cyclones by the European Centre for Medium Range Weather Forecasts (ECMWF) and the National Centers for Environmental Prediction (NCEP) Ensemble Prediction Systems (EPS) has been investigated using an objective feature tracking methodology to identify and track the cyclones along the forecast trajectories. Overall the results show that the ECMWF EPS has a slightly higher level of skill than the NCEP EPS in the northern hemisphere (NH). However in the southern hemisphere (SH), NCEP has higher predictive skill than ECMWF for the intensity of the cyclones. The results from both EPS indicate a higher level of predictive skill for the position of extratropical cyclones than their intensity and show that there is a larger spread in intensity than position. Further analysis shows that the predicted propagation speed of cyclones is generally too slow for the ECMWF EPS and show a slight bias for the intensity of the cyclones to be overpredicted. This is also true for the NCEP EPS in the SH. For the NCEP EPS in the NH the intensity of the cyclones is underpredicted. There is small bias in both the EPS for the cyclones to be displaced towards the poles. For each ensemble forecast of each cyclone, the predictive skill of the ensemble member that best predicts the cyclones position and intensity was computed. The results are very encouraging showing that the predictive skill of the best ensemble member is significantly higher than that of the control forecast in terms of both the position and intensity of the cyclones. The prediction of cyclones before they are identified as 850 hPa vorticity centers in the analysis cycle was also considered. It is shown that an indication of extratropical cyclones can be given by at least 1 ensemble member 7 days before they are identified in the analysis. Further analysis of the ECMWF EPS shows that the ensemble mean has a higher level of skill than the control forecast, particularly for the intensity of the cyclones, 2 from day 3 of the forecast. There is a higher level of skill in the NH than the SH and the spread in the SH is correspondingly larger. The difference between the ensemble mean and spread is very small for the position of the cyclones, but the spread of the ensemble is smaller than the ensemble mean error for the intensity of the cyclones in both hemispheres. Results also show that the ECMWF control forecast has ½ to 1 day more skill than the perturbed members, for both the position and intensity of the cyclones, throughout the forecast
Manifest Duality in Born-Infeld Theory
Born-Infeld theory is formulated using an infinite set of gauge fields, along
the lines of McClain, Wu and Yu. In this formulation electromagnetic duality is
generated by a fully local functional. The resulting consistency problems are
analyzed and the formulation is shown to be consistent.Comment: 15 pages, Late
VC-dimension of short Presburger formulas
We study VC-dimension of short formulas in Presburger Arithmetic, defined to
have a bounded number of variables, quantifiers and atoms. We give both lower
and upper bounds, which are tight up to a polynomial factor in the bit length
of the formula
Spectra of phase point operators in odd prime dimensions and the extended Clifford group
We analyse the role of the Extended Clifford group in classifying the spectra
of phase point operators within the framework laid out by Gibbons et al for
setting up Wigner distributions on discrete phase spaces based on finite
fields. To do so we regard the set of all the discrete phase spaces as a
symplectic vector space over the finite field. Auxiliary results include a
derivation of the conjugacy classes of .Comment: Latex, 19page
Dipolar particles in a double-trap confinement: Response to tilting the dipolar orientation
We analyze the microscopic few-body properties of dipolar particles confined
in two parallel quasi-one-dimensional harmonic traps. In particular, we show
that an adiabatic rotation of the dipole orientation about the trap axes can
drive an initially non-localized few-fermion state into a localized state with
strong inter-trap pairing. For an instant, non-adiabatic rotation, however,
localization is inhibited and a highly excited state is reached. This state may
be interpreted as the few-body analog of a super-Tonks-Girardeau state, known
from one-dimensional systems with contact interactions
A trick for passing degenerate points in Ashtekar formulation
We examine one of the advantages of Ashtekar's formulation of general
relativity: a tractability of degenerate points from the point of view of
following the dynamics of classical spacetime. Assuming that all dynamical
variables are finite, we conclude that an essential trick for such a continuous
evolution is in complexifying variables. In order to restrict the complex
region locally, we propose some `reality recovering' conditions on spacetime.
Using a degenerate solution derived by pull-back technique, and integrating the
dynamical equations numerically, we show that this idea works in an actual
dynamical problem. We also discuss some features of these applications.Comment: 9 pages by RevTeX or 16 pages by LaTeX, 3 eps figures and epsf-style
file are include
What do we mean by school entry age? Conceptual ambiguity and its implications: the example of Indonesia
The age pattern of school entry reflects a complex social and empirical reality that is inadequately captured by a single number. Recognising these complexities in national and international research and policy discourse raises important but neglected questions around the identification of vulnerable groups, the relative value of pre-primary and primary education, as well as the normative powers and responsibilities of governments vis-Ă -vis parents, and the international educational community vis-Ă -vis both. This is illustrated by the example of Indonesia, where the official age norm for primary school entry is widely disregarded in practice, with a majority of children starting school one or even two years earlier. Crucially, it is the compliant children entering at the statutory age who tend to be from more disadvantaged households, and enjoy no benefit in educational outcomes from their greater maturity
Finite-size effects in the dynamics of few bosons in a ring potential
We study the temporal evolution of a small number of ultra-cold bosonic
atoms confined in a ring potential. Assuming that initially the system is in a
solitary-wave solution of the corresponding mean-field problem, we identify
significant differences in the time evolution of the density distribution of
the atoms when it instead is evaluated with the many-body Schr\"odinger
equation. Three characteristic timescales are derived: the first is the period
of rotation of the wave around the ring, the second is associated with a
"decay" of the density variation, and the third is associated with periodic
"collapses" and "revivals" of the density variations, with a factor of separating each of them. The last two timescales tend to infinity in the
appropriate limit of large , in agreement with the mean-field approximation.
These findings are based on the assumption of the initial state being a
mean-field state. We confirm this behavior by comparison to the exact solutions
for a few-body system stirred by an external potential. We find that the exact
solutions of the driven system exhibit similar dynamical features.Comment: To appear in Journal of Physics
Information geometry of density matrices and state estimation
Given a pure state vector |x> and a density matrix rho, the function
p(x|rho)= defines a probability density on the space of pure states
parameterised by density matrices. The associated Fisher-Rao information
measure is used to define a unitary invariant Riemannian metric on the space of
density matrices. An alternative derivation of the metric, based on square-root
density matrices and trace norms, is provided. This is applied to the problem
of quantum-state estimation. In the simplest case of unitary parameter
estimation, new higher-order corrections to the uncertainty relations,
applicable to general mixed states, are derived.Comment: published versio
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