5,691 research outputs found

    The use of RAPD markers to detect genetic patterns in Aleurodicus dispersus (Hemiptera : Aleyrodidae) populations from the Canary Islands

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    Aleurodicus dispersus Russell (Hemiptera: Aleyrodidae), a highly polyphagous species, has since the 90’s been an important pest of ornamentals and tropical crops in the Canary Islands. In this study the RAPD-PCR technique was used to study the genetic structure of this whitefly in this archipelago. A total of 68 different bands were scored in seven populations using six primers for amplification. No differences in RAPD patterns were found among populations from different islands of the Canaries. These findings indicate a very high genetic similarity among populations and low level of genetic variability and support a single colonization event by few A. dispersus whiteflies and recent dispersion throughout the archipelago

    The role of magnetic islands in modifying long range temporal correlations of density fluctuations and local heat transport

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    This work explores the relation between magnetic islands, long range temporal correlations and heat transport. A low order rational surface (t = 3/2) was purposely scanned outward through an electron cyclotron resonance heated (ECRH) plasma in the TJ-II stellarator. Density turbulence and the poloidal flow velocity were characterized using a two channel Doppler reflectometer. Simultaneously, the ECRH power was modulated to characterize heat transport, using measurements from a 12 channel electron cyclotron emission diagnostic. A systematic variation of the poloidal velocity was found to be associated with the t = 3/2 rational surface. Near the rational surface, the Hurst exponent, quantifying the nature of long-range correlations, was reduced below 0.5 (indicating subdiffusion), while at radii smaller than that of the rational surface, it was found to be significantly enhanced (superdiffusion). In the latter region, heat transport was enhanced as well, thus establishing a link between density fluctuations and anomalous heat transport. The observed variation of the Hurst exponent was consistent with a magnetohydrodynamic turbulence simulation

    Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV

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    A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7 TeV is presented. The data were collected at the LHC, with the CMS detector, and correspond to an integrated luminosity of 4.6 inverse femtobarns. No significant excess is observed above the background expectation, and upper limits are set on the Higgs boson production cross section. The presence of the standard model Higgs boson with a mass in the 270-440 GeV range is excluded at 95% confidence level.Comment: Submitted to JHE

    Measurement of the ppbar to ttbar production cross section at sqrt(s)=1.96 TeV in the fully hadronic decay channel

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    A measurement of the top quark pair production cross section in proton anti-proton collisions at an interaction energy of sqrt(s)=1.96 TeV is presented. This analysis uses 405 pb-1 of data collected with the D0 detector at the Fermilab Tevatron Collider. Fully hadronic ttbar decays with final states of six or more jets are separated from the multijet background using secondary vertex tagging and a neural network. The ttbar cross section is measured as sigma(ttbar)=4.5 -1.9 +2.0 (stat) -1.1 +1.4 (syst) +/- 0.3 (lumi) pb for a top quark mass of m(t) = 175 GeV/c^2.Comment: 10 pages, 10 figures, submitted to Phys. Rev.

    Combined search for the quarks of a sequential fourth generation