1,125 research outputs found
Estimate of Bottom and Surface Stress During a Spring-Neap Tide Cycle by Dynamical Assimilation of Tide Gauge Observatons in the Chesapeake Bay
Dynamical assimilation of surface elevation from tide gauges is investigated to estimate the bottom drag coefficient and surface stress as a first step in improving modeled tidal and wind-driven circulation in the Chesapeake Bay. A two-dimensional shallow water model and an adjoint variational method with a limited memory quasi-Newton optimization algorithm are used to achieve this goal. Assimilation of tide gauge observations from 10 permanent stations in the Bay and use of a two-dimensional model adequately estimate the bottom drag coefficient, wind stress, and surface elevation at the Bay mouth. Subsequent use of these estimates in the circulation model considerably improves the modeled surface elevation in the entire Bay. Assimilation of predicted tidal elevations yields a drag coefficient, defined in the hydraulic way, varying between 2.5 x 10(-4) and 3.1 x 10(-3) The bottom drag coefficient displays a periodicity corresponding to the spring-neap tide cycle with a maximum value during neap tide and a minimum value during spring tide. From assimilation of actual tide gauge observations, it is found that the fortnightly modulation is altered during frontal passage. Furthermore, the response of the sea surface to the wind forcing is found to be more important in the lower Bay than in the upper Bay, where the barometric pressure effect seems to be more important
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A potential implicit particle method for high-dimensional systems
This paper presents a particle method designed for high-dimensional state estimation. Instead of weighing random forecasts by their distance to given observations, the method samples an ensemble of particles around an optimal solution based on the observations (i.e., it is implicit). It differs from other implicit methods because it includes the state at the previous assimilation time as part of the optimal solution (i.e., it is a lag-1 smoother). This is accomplished through the use of a mixture model for the background distribution of the previous state. In a high-dimensional, linear, Gaussian example, the mixture-based implicit particle smoother does not collapse. Furthermore, using only a small number of particles, the implicit approach is able to detect transitions in two nonlinear, multi-dimensional generalizations of a double-well. Adding a step that trains the sampled distribution to the target distribution prevents collapse during the transitions, which are strongly nonlinear events. To produce similar estimates, other approaches require many more particles
Development and operational experience of magnetic horn system for T2K experiment
A magnetic horn system to be operated at a pulsed current of 320 kA and to
survive high-power proton beam operation at 750 kW was developed for the T2K
experiment. The first set of T2K magnetic horns was operated for over 12
million pulses during the four years of operation from 2010 to 2013, under a
maximum beam power of 230 kW, and protons were exposed to
the production target. No significant damage was observed throughout this
period. This successful operation of the T2K magnetic horns led to the
discovery of the oscillation phenomenon in 2013 by
the T2K experiment. In this paper, details of the design, construction, and
operation experience of the T2K magnetic horns are described.Comment: 22 pages, 40 figures, also submitted to Nuclear Instrument and
Methods in Physics Research,
ArgoNeuT and the Neutrino-Argon Charged Current Quasi-Elastic Cross Section
ArgoNeuT, a Liquid Argon Time Projection Chamber in the NuMI beamline at
Fermilab, has recently collected thousands of neutrino and anti-neutrino events
between 0.1 and 10 GeV. The experiment will, among other things, measure the
cross section of the neutrino and anti-neutrino Charged Current Quasi-Elastic
interaction and analyze the vertex activity associated with such events. These
topics are discussed along with ArgoNeuT's automated reconstruction software,
currently capable of fully reconstructing the muon and finding the event vertex
in neutrino interactions.Comment: 6 pages, 4 figures, presented at the International Nuclear Physics
Conference, Vancouver, Canada, July 4-9, 2010, to be published in Journal of
Physics: Conference Series (JPCS
Scanning the Topological Sectors of the QCD Vacuum with Hybrid Monte Carlo
We address a long standing issue and determine the decorrelation efficiency
of the Hybrid Monte Carlo algorithm (HMC), for full QCD with Wilson fermions,
with respect to vacuum topology. On the basis of five state-of-the art QCD
vacuum field ensembles (with 3000 to 5000 trajectories each and
m_pi/m_rho-ratios in the regime >0.56, for two sea quark flavours) we are able
to establish, for the first time, that HMC provides sufficient tunneling
between the different topological sectors of QCD. This will have an important
bearing on the prospect to determine, by lattice techniques, the topological
susceptibility of the vacuum, and topology sensitive quantities like the spin
content of the proton, or the eta' mass.Comment: 5 pages, 4 eps-figure
Renaissance of the ~1 TeV Fixed-Target Program
This document describes the physics potential of a new fixed-target program
based on a ~1 TeV proton source. Two proton sources are potentially available
in the future: the existing Tevatron at Fermilab, which can provide 800 GeV
protons for fixed-target physics, and a possible upgrade to the SPS at CERN,
called SPS+, which would produce 1 TeV protons on target. In this paper we use
an example Tevatron fixed-target program to illustrate the high discovery
potential possible in the charm and neutrino sectors. We highlight examples
which are either unique to the program or difficult to accomplish at other
venues.Comment: 31 pages, 11 figure
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