3,835 research outputs found
Evaluation of ERTS-1 image sensor spatial resolution in photographic form
There are no author-identified significant results in this report
Learning near-optimal policies with Bellman-residual minimization based fitted policy iteration and a single sample path
We consider the problem of finding a near-optimal policy in continuous space, discounted Markovian Decision Problems given the trajectory of some behaviour policy. We study the policy iteration algorithm where in successive iterations the action-value functions of the intermediate policies are obtained by picking a function from some fixed function set (chosen by the user) that minimizes an unbiased finite-sample approximation to a novel loss function that upper-bounds the unmodified Bellman-residual criterion. The main result is a finite-sample, high-probability bound on the performance of the resulting policy that depends on the mixing rate of the trajectory, the capacity of the function set as measured by a novel capacity concept that we call the VC-crossing dimension, the approximation power of the function set and the discounted-average concentrability of the future-state distribution. To the best of our knowledge this is the first theoretical reinforcement learning result for off-policy control learning over continuous state-spaces using a single trajectory
Regularized fitted Q-iteration: application to planning
We consider planning in a Markovian decision problem, i.e., the problem of finding a good policy given access to a generative model of the environment. We propose to use fitted Q-iteration with penalized (or regularized) least-squares regression as the regression subroutine to address the problem of controlling model-complexity. The algorithm is presented in detail for the case when the function space is a reproducing kernel Hilbert space underlying a user-chosen kernel function. We derive bounds on the quality of the solution and argue that data-dependent penalties can lead to almost optimal performance. A simple example is used to illustrate the benefits of using a penalized procedure
Photon Production from a Quark--Gluon Plasma
In-medium interactions of a particle in a hot plasma are considered in the
framework of thermal field theory. The formalism to calculate gauge invariant
rates for photon and dilepton production from the medium is given. In the
application to a QED plasma, astrophysical consequences are pointed out. The
photon production rate from strongly interacting quarks in the quark--gluon
plasma, which might be formed in ultrarelativistic heavy ion collisions, is
calculated in the previously unaccessible regime of photon energies of the
order of the plasma temperature. For temperatures below the chiral phase
transition, an effective field theory incorporating dynamical chiral symmetry
breaking is employed, and perturbative QCD at higher temperatures. A smooth
transition between both regions is obtained. The relevance to the soft photon
problem and to high energy heavy ion experiments is discussed.Comment: Paper in ReVTeX. Figures and complete paper available via anonymous
ftp, ftp://tpri6c.gsi.de/pub/phenning/hq95ga
Deterministic control of magnetic vortex wall chirality by electric field
Concepts for information storage and logical processing based on magnetic domain walls have great potential for implementation in future information and communications technologies. To date, the need to apply power hungry magnetic fields or heat dissipating spin polarized currents to manipulate magnetic domain walls has limited the development of such technologies. The possibility of controlling magnetic domain walls using voltages offers an energy efficient route to overcome these limitations. Here we show that a voltage-induced uniaxial strain induces reversible deterministic switching of the chirality of a magnetic vortex wall. We discuss how this functionality will be applicable to schemes for information storage and logical processing, making a significant step towards the practical implementation of magnetic domain walls in energy efficient computing
Measurement of Dijet Angular Distributions at CDF
We have used 106 pb^-1 of data collected in proton-antiproton collisions at
sqrt(s)=1.8 TeV by the Collider Detector at Fermilab to measure jet angular
distributions in events with two jets in the final state. The angular
distributions agree with next to leading order (NLO) predictions of Quantum
Chromodynamics (QCD) in all dijet invariant mass regions. The data exclude at
95% confidence level (CL) a model of quark substructure in which only up and
down quarks are composite and the contact interaction scale is Lambda_ud(+) <
1.6 TeV or Lambda_ud(-) < 1.4 TeV. For a model in which all quarks are
composite the excluded regions are Lambda(+) < 1.8 TeV and Lambda(-) < 1. 6
TeV.Comment: 16 pages, 2 figures, 2 tables, LaTex, using epsf.sty. Submitted to
Physical Review Letters on September 17, 1996. Postscript file of full paper
available at http://www-cdf.fnal.gov/physics/pub96/cdf3773_dijet_angle_prl.p
Observation of Hadronic W Decays in t-tbar Events with the Collider Detector at Fermilab
We observe hadronic W decays in t-tbar -> W (-> l nu) + >= 4 jet events using
a 109 pb-1 data sample of p-pbar collisions at sqrt{s} = 1.8 TeV collected with
the Collider Detector at Fermilab (CDF). A peak in the dijet invariant mass
distribution is obtained that is consistent with W decay and inconsistent with
the background prediction by 3.3 standard deviations. From this peak we measure
the W mass to be 77.2 +- 4.6 (stat+syst) GeV/c^2. This result demonstrates the
presence of two W bosons in t-tbar candidates in the W (-> l nu) + >= 4 jet
channel.Comment: 20 pages, 4 figures, submitted to PR
Search for charged Higgs decays of the top quark using hadronic tau decays
We present the result of a search for charged Higgs decays of the top quark,
produced in collisions at 1.8 TeV. When the charged
Higgs is heavy and decays to a tau lepton, which subsequently decays
hadronically, the resulting events have a unique signature: large missing
transverse energy and the low-charged-multiplicity tau. Data collected in the
period 1992-1993 at the Collider Detector at Fermilab, corresponding to
18.70.7~pb, exclude new regions of combined top quark and charged
Higgs mass, in extensions to the standard model with two Higgs doublets.Comment: uuencoded, gzipped tar file of LaTeX and 6 Postscript figures; 11 pp;
submitted to Phys. Rev.
Inclusive jet cross section in collisions at TeV
The inclusive jet differential cross section has been measured for jet
transverse energies, , from 15 to 440 GeV, in the pseudorapidity region
0.10.7. The results are based on 19.5 pb of data
collected by the CDF collaboration at the Fermilab Tevatron collider. The data
are compared with QCD predictions for various sets of parton distribution
functions. The cross section for jets with GeV is significantly
higher than current predictions based on O() perturbative QCD
calculations. Various possible explanations for the high- excess are
discussed.Comment: 8 pages with 2 eps uu-encoded figures Submitted to Physical Review
Letter
Measurement of the lepton charge asymmetry in W-boson decays produced in p-pbar collisions
We describe a measurement of the charge asymmetry of leptons from W boson
decays in the rapidity range 0 enu, munu events from
110+/-7 pb^{-1}of data collected by the CDF detector during 1992-95. The
asymmetry data constrain the ratio of d and u quark momentum distributions in
the proton over the x range of 0.006 to 0.34 at Q2 \approx M_W^2. The asymmetry
predictions that use parton distribution functions obtained from previously
published CDF data in the central rapidity region (0.0<|y_l|<1.1) do not agree
with the new data in the large rapidity region (|y_l|>1.1).Comment: 13 pages, 3 tables, 1 figur
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