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In this work, we present from first principles a direct numerical simulation (DNS) of a fully turbulent channel flow of a dilute polymer solution. The polymer chains are modeled as finitely extensible and elastic dumbbells. The simulation algorithm is based on a semi-implicit, time-splitting technique which uses spectral approximations in the spatial coordinates. The computations are carried out on a CRAY T3D parallel computer. The simulations are carried out under fully turbulent conditions albeit, due to computational constraints, not at as high Reynolds number as that usually encountered in polymer-induced drag reduction experiments. In order to compensate for the lower Reynolds number, we simulate more elastic fluids than the ones encountered in drag reduction experiments resulting in Weissenberg numbers (a dimensionless number characterizing the flow elasticity) of similar magnitude. The simulations show that the polymer induces several changes in the turbulent flow characteristics, all of them consistent with available experimental results. In particular, we have observed, associated with drag reduction, a decrease in the streamwise vorticity fluctuations and an increase in the average spacing between the streamwise streaks of low speed fluid within the buffer layer. These findings suggest a partial inhibition of turbulence generating events within the buffer layer by the macromolecules after the onset of drag reduction. This inhibition is further shown to be associated with an enhanced effective viscosity attributed to the extensional thickening properties of polymer solutions, as proposed in the past by Metzner, Lumley and other investigators. Using the simulation results obtained for different sets of parameter values which modify the relaxational and extensional properties of the model, we propose a set of criteria for the onset of drag reduction.

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We measure the time dependence of the ratio of decay rates for the rare decay D{0}-->K{+}pi{-} to the Cabibbo-favored decay D{0}-->K{-}pi;{+}. A signal of 12.7x10;{3} D{0}-->K{+}pi{-} decays was obtained using the Collider Detector at Fermilab II detector at the Fermilab Tevatron with an integrated luminosity of 1.5 fb;{-1}. We measure the D0-D[over ]{0} mixing parameters (R_{D},y{'},x{'2}), and find that the data are inconsistent with the no-mixing hypothesis with a probability equivalent to 3.8 Gaussian standard deviations.

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A strong signal for double parton (DP) scattering is observed in a 16 pb(-1) sample of <(p)over bar p> --> gamma/pi(0) + 3 jets + X data from the CDF experiment at the Fermilab Tevatron. In DP events, two separate hard scatterings take place in a single <(p)over bar p> collision. We isolate a large sample of data (similar to 14 000 events) of which 53% are found to be DP. The process-independent parameter of double parton scattering, sigma(eff), is obtained without reference to theoretical calculations by comparing observed DP events to events with hard scatterings in separate <(p)over bar p> collisions. The result sigma(eff) = (14.5 +/- 1.7(-2.3)(+1.7)) mb represents a significant improvement over previous measurements, and is used to constrain simple models of parton spatial density. The Feynman x dependence of sigma(eff) is investigated and none is apparent. Further, no evidence is found for kinematic correlations between the two scatterings in DP events

We report the first measurements of inclusive W and Z boson cross sections times the corresponding leptonic branching ratios for pp collisions at √ s = 1.96 TeV based on the decays of the W and Z bosons into electrons and muons. The data were recorded with the CDF II detector at the Fermilab 4Tevatron and correspond to an integrated luminosity of 72.0 ± 4.3 pb −1 . We test e-µ lepton universality in W decays by measuring the ratio of the W → µν to W → eν cross sections and determine a value of 0.991 ± 0.004(stat.) ± 0.011(syst.) for the ratio of W −ℓ−ν couplings (gµ/ge). Since there is no sign of non-universality, we combine our cross section measurements in the different lepton decay modes and obtain σW ×Br(pp → W → ℓν) = 2.749 ± 0.010(stat.) ± 0.053(syst.) ± 0.165(lum.) nb and σ γ * /Z × Br(pp → γ * /Z → ℓℓ) = 254.9 ± 3.3(stat.) ± 4.6(syst.) ± 15.2(lum.) pb for dilepton pairs in the mass range between 66 GeV/c 2 and 116 GeV/c 2 . We compute the ratio R of the W → ℓν to Z → ℓℓ cross sections taking all correlations among channels into account and obtain R = 10.84 ± 0.15(stat.) ± 0.14(syst.) including a correction for the virtual photon exchange component in our measured γ * /Z → ℓℓ cross section. Based on the measured value of R, we extract values for the W leptonic branching ratio, Br(W → ℓν) = 0.1082 ± 0.0022; the total width of the W boson, Γ(W ) = 2092 ± 42 MeV; and the ratio of W and Z boson total widths, Γ(W )/Γ(Z) = 0.838 ± 0.017. In addition, we use our extracted value of Γ(W ) whose value depends on various electroweak parameters and certain CKM matrix elements to constrain the Vcs CKM matrix element, |Vcs| = 0.976± 0.030.