415 research outputs found
The N-strikes-out algorithm: A steady-state algorithm for coevolution
We introduce the N-strikes-out algorithm, a simple steady-state genetic algorithm for competitive coevolution. The algorithm can be summarised as follows: Run competitions between randomly chosen individuals, keep track of the number of defeats for each individual, and remove any individual which has been defeated N times. Naive application of the algorithm in 2-population problems leads to severe disengagement. We find that disengagement can be eliminated (for all tasks involving real-valued continuous scores) by determining 'victories' and 'defeats' between fellow members of the same species, using competitions against a single member of the opposing species as a point of comparison. We apply our algorithm to the "box-grabbing" problem for artificial 3D creatures introduced by Sims. We compare our algorithm with Sims' original Last Elite Opponent algorithm, and describe (and explain) different results obtained with two different implementations differing mainly by the harshness of their selection regimes
A simple method for the determination of lipid composition of human bile
The Entero-Test, a device for easy sampling of gastrointestinal contents, including bile, has been used for determination of biliary lipid composition. The device consists of a weighted gelatin capsule containing 140 cm of a highly absorbent nylon line. The capsule is swallowed while one end of the string is taped to the face. After 3.5 h, when the line has reached the duodenum, gallbladder contraction is stimulated by intramuscular administration of ceruletide. The line is pulled out, and the last 15 cm are eluted four times in methanol. Total bile acids (by 3 alpha-hydroxysteroid-dehydrogenase assay), individual bile acids (by high performance liquid chromatography), phospholipids (by assay of lipid-soluble phosphorus), and cholesterol (by gas-liquid chromatography) are determined in the eluate. Tests in vitro demonstrated no preferential binding and a good recovery of biliary lipids from the thread. Similar values of biliary cholesterol saturation were obtained by means of duodenal intubation and of the Entero-Test in a series of 12 subjects (r = 0.952). In 5 subjects, individual bile acids were also measured and were found to be similar with both techniques (r = 0.948). When the test was repeated over 3 days in a series of 7 subjects, biliary cholesterol saturation was found to be remarkably reproducible (CV = 7.6%). Thus, the Entero-Test is a convenient technique for the determination of biliary lipid composition, which can be particularly useful in longitudinal studies
Precise measurement of the top quark mass in the dilepton channel at D0
We measure the top quark mass (mt) in ppbar collisions at a center of mass
energy of 1.96 TeV using dilepton ttbar->W+bW-bbar->l+nubl-nubarbbar events,
where l denotes an electron, a muon, or a tau that decays leptonically. The
data correspond to an integrated luminosity of 5.4 fb-1 collected with the D0
detector at the Fermilab Tevatron Collider. We obtain mt = 174.0 +- 1.8(stat)
+- 2.4(syst) GeV, which is in agreement with the current world average mt =
173.3 +- 1.1 GeV. This is currently the most precise measurement of mt in the
dilepton channel.Comment: 7 pages, 4 figure
A search for charged massive long-lived particles
We report on a search for charged massive long-lived particles (CMLLPs),
based on 5.2 fb of integrated luminosity collected with the D0 detector
at the Fermilab Tevatron collider. We search for events in which one
or more particles are reconstructed as muons but have speed and ionization
energy loss inconsistent with muons produced in beam collisions.
CMLLPs are predicted in several theories of physics beyond the standard model.
We exclude pair-produced long-lived gaugino-like charginos below 267 GeV and
higgsino-like charginos below 217 GeV at 95% C.L., as well as long-lived scalar
top quarks with mass below 285 GeV.Comment: submitted to Phys. Rev. Letter
Journal Staff
We present the first measurements of the differential cross section d sigma/dp(T)(gamma) for the production of an isolated photon in association with at least two b-quark jets. The measurements consider photons with rapidities vertical bar y(gamma)vertical bar < 1.0 and transverse momenta 30 < p(T)(gamma) < 200 GeV. The b-quark jets are required to have p(T)(jet) > 15 GeVand vertical bar y(jet)vertical bar < 1.5. The ratio of differential production cross sections for gamma + 2 b-jets to gamma + b-jet as a function of p(T)(gamma) is also presented. The results are based on the proton-antiproton collision data at root s = 1.96 TeV collected with the D0 detector at the Fermilab Tevatron Collider. The measured cross sections and their ratios are compared to the next- to- leading order perturbative QCD calculations as well as predictions based on the k(T)- factorization approach and those from the sherpa and pythia Monte Carlo event generators
Measurement of the top quark pair production cross section in the lepton+jets channel in proton-antiproton collisions at =1.96 TeV
We present a measurement of the inclusive top quark pair production cross
section in \ppbar collisions at (\sqrt{s}=1.96) TeV utilizing data
corresponding to an integrated luminosity of \lumi\ collected with the D0
detector at the Fermilab Tevatron Collider. We consider final states containing
one high- isolated electron or muon and at least two jets, and we
perform three analyses: one exploiting specific kinematic features of \ttbar
events, the second using -jet identification, and the third using both
techniques to separate \ttbar\ signal from background. In the third case, we
determine simultaneously the cross section and the ratio of the
production rates of +heavy flavor jets and +light flavor jets, which
reduces the impact of the systematic uncertainties related to the background
estimation. Assuming a top quark mass of 172.5 GeV, we obtain
pb. This result agrees with
predictions of the standard model.Comment: 19 pages, 6 figures, submitted to Phys. Rev.
Direct measurement of the mass difference between top and antitop quarks
We present a direct measurement of the mass difference between top and
antitop quarks (dm) in lepton+jets top-antitop final states using the "matrix
element" method. The purity of the lepton+jets sample is enhanced for
top-antitop events by identifying at least one of the jet as originating from a
b quark. The analyzed data correspond to 3.6 fb-1 of proton-antiproton
collisions at 1.96 TeV acquired by D0 in Run II of the Fermilab Tevatron
Collider. The combination of the e+jets and mu+jets channels yields dm = 0.8
+/- 1.8 (stat) +/- 0.5 (syst) GeV, which is in agreement with the standard
model expectation of no mass difference.Comment: submitted to Phys. Rev.
Measurement of the semileptonic charge asymmetry in B0 meson mixing with the D0 detector
We present a measurement of the semileptonic mixing asymmetry for B0 mesons,
a^d_{sl}, using two independent decay channels: B0 -> mu+D-X, with D- ->
K+pi-pi-; and B0 -> mu+D*-X, with D*- -> antiD0 pi-, antiD0 -> K+pi- (and
charge conjugate processes). We use a data sample corresponding to 10.4 fb^{-1}
of ppbar collisions at sqrt(s) = 1.96 TeV, collected with the D0 experiment at
the Fermilab Tevatron collider. We extract the charge asymmetries in these two
channels as a function of the visible proper decay length (VPDL) of the B0
meson, correct for detector-related asymmetries using data-driven methods, and
account for dilution from charge-symmetric processes using Monte Carlo
simulation. The final measurement combines four signal VPDL regions for each
channel, yielding a^d_{sl} = [0.68 \pm 0.45 \text{(stat.)} \pm 0.14
\text{(syst.)}]%. This is the single most precise measurement of this
parameter, with uncertainties smaller than the current world average of B
factory measurements.Comment: Version includes minor textual changes following peer review by
journal, most notably the updating of Ref. [21] to reflect the most recent
publicatio
Measurement of spin correlation in ttbar production using dilepton final states
We measure the correlation between the spin of the top quark and the spin of
the anti-top quark in (ttbar -> W+ W- b bbar -> l+ nu b l- nubar bbar) final
states produced in ppbar collisions at a center of mass energy sqrt(s)=1.96
TeV, where l is an electron or muon. The data correspond to an integrated
luminosity of 5.4 fb-1 and were collected with the D0 detector at the Fermilab
Tevatron collider. The correlation is extracted from the angles of the two
leptons in the t and tbar rest frames, yielding a correlation strength C=
0.10^{+0.45}_{-0.45}, in agreement with the NLO QCD prediction within two
standard deviations, but also in agreement with the no correlation hypothesis.Comment: 10 pages, 3 figures, submitted to PL
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