526 research outputs found
Asymptotic Dynamics of High Dynamic Range Stratified Turbulence.
Direct numerical simulations of homogeneous sheared and stably stratified turbulence are considered to probe the asymptotic high dynamic range regime suggested by Gargett et al. J. Fluid Mech. 144, 231 (1984)10.1017/S0022112084001592 and Shih et al. J. Fluid Mech. 525, 193 (1999)10.1017/S0022112004002587. We consider statistically stationary configurations of the flow that span three decades in dynamic range defined by the separation between the Ozmidov length scale L_{O}=sqrt[Δ/N^{3}] and the Kolmogorov length scale L_{K}=(Îœ^{3}/Δ)^{1/4}, up to Re_{b}âĄ(L_{O}/L_{K})^{4/3}=Δ/(ÎœN^{2})âŒO(1000), where Δ is the mean turbulent kinetic energy dissipation rate, Îœ is the kinematic viscosity, and N is the buoyancy frequency. We isolate the effects of Re_{b}, particularly on irreversible mixing, from the effects of other flow parameters of stratified and sheared turbulence. Specifically, we evaluate the influence of dynamic range independent of initial conditions. We present evidence that the flow approaches an asymptotic state for Re_{b}âȘ300, characterized both by an asymptotic partitioning between the potential and kinetic energies and by the approach of components of the dissipation rate to their expected values under the assumption of isotropy. As Re_{b} increases above 100, there is a slight decrease in the turbulent flux coefficient Î=Ï/Δ, where Ï is the dissipation rate of buoyancy variance, but, for this flow, there is no evidence of the commonly suggested ÎâRe_{b}^{-1/2} dependence when 100â€Re_{b}â€1000.This work was funded by the U.S. Office of Naval Research via grant N00014-15-1-2248. High performance computing resources were provided through the U.S. Department of Defense High Performance Computing Modernization Program by the Army Engineer Research and Development Center, the Army Research Laboratory and the Navy DSRC under Frontier Project FP-CFD-FY14- 007. The research activity of C.P.C. is supported by EPSRC Programme Grant EP/K034529/1 entitled `Mathematical Underpinnings of Stratified Turbulence'
Robust identification of dynamically distinct regions in stratified turbulence
We present a new robust method for identifying three dynamically distinct regions in a stratified turbulent flow, which we characterise as quiescent flow, intermittent layers and turbulent patches. The method uses the cumulative filtered distribution function of the local density gradient to identify each region. We apply it to data from direct numerical simulations of homogeneous stratified turbulence, with unity Prandtl number, resolved on up to grid points. In addition to classifying regions consistently with contour plots of potential enstrophy, our method identifies quiescent regions as regions where \unicode[STIX]{x1D716}/\unicode[STIX]{x1D708}N^{2}\sim O(1), layers as regions where \unicode[STIX]{x1D716}/\unicode[STIX]{x1D708}N^{2}\sim O(10) and patches as regions where \unicode[STIX]{x1D716}/\unicode[STIX]{x1D708}N^{2}\sim O(100). Here, \unicode[STIX]{x1D716} is the dissipation rate of turbulence kinetic energy, \unicode[STIX]{x1D708} is the kinematic viscosity and is the (overall) buoyancy frequency. By far the highest local dissipation and mixing rates, and the majority of dissipation and mixing, occur in patch regions, even when patch regions occupy only 5Â % of the flow volume. We conjecture that treating stratified turbulence as an instantaneous assemblage of these different regions in varying proportions may explain some of the apparently highly scattered flow dynamics and statistics previously reported in the literature.The research activities of G.D.P. and S.dB.K. were funded by the US Office of Naval Research via grant N00014-15-1-2248. Additional support to G.D.P. and S.dB.K. was provided from the UK Engineering and Physical Sciences Research Council grant EP/K034529/1 entitled âMathematical Underpinnings of Stratified Turbulenceâ, which also funds the research activity of J.R.T. and C.P.C. H.S. gratefully acknowledges the award of a Crighton Fellowship at the Department of Applied Mathematics & Theoretical Physics, University of Cambridge. High-performance computing resources were provided through the US Department of Defense High Performance Computing Modernization Program by the Army Engineer Research and Development Center and the Army Research Laboratory under Frontier Project FP-CFD-FY14-007.This is the author accepted manuscript. The final version is available from Cambridge University Press via https://doi.org/10.1017/jfm.2016.61
Search for CP violation in D+âÏÏ+ and D+sâK0SÏ+ decays
A search for CP violation in D + â ÏÏ + decays is performed using data collected in 2011 by the LHCb experiment corresponding to an integrated luminosity of 1.0 fbâ1 at a centre of mass energy of 7 TeV. The CP -violating asymmetry is measured to be (â0.04 ± 0.14 ± 0.14)% for candidates with K â K + mass within 20 MeV/c 2 of the Ï meson mass. A search for a CP -violating asymmetry that varies across the Ï mass region of the D + â K â K + Ï + Dalitz plot is also performed, and no evidence for CP violation is found. In addition, the CP asymmetry in the D+sâK0SÏ+ decay is measured to be (0.61 ± 0.83 ± 0.14)%
Study of decays to the final state and evidence for the decay
A study of decays is performed for the first time
using data corresponding to an integrated luminosity of 3.0
collected by the LHCb experiment in collisions at centre-of-mass energies
of and TeV. Evidence for the decay
is reported with a significance of 4.0 standard deviations, resulting in the
measurement of
to
be .
Here denotes a branching fraction while and
are the production cross-sections for and mesons.
An indication of weak annihilation is found for the region
, with a significance of
2.4 standard deviations.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-022.html,
link to supplemental material inserted in the reference
Viral, bacterial, and fungal infections of the oral mucosa:Types, incidence, predisposing factors, diagnostic algorithms, and management
Updated measurements of exclusive J/Ï and Ï(2S) production cross-sections in pp collisions at âs = 7 TeV
The differential cross-section as a function of rapidity has been measured for the exclusive production of J/Ï and Ï(2S) mesons in protonâproton collisions at âs = 7 TeV, using data collected by the LHCb experiment, corresponding to an integrated luminosity of 930 pbâ1. The cross-sections times branching fractions to two muons having pseudorapidities between 2.0 and 4.5 are measured to be where the first uncertainty is statistical and the second is systematic. The measurements agree with next-to-leading order QCD predictions as well as with models that include saturation effects
Measurement of the Îb0, Îb-, and Ωb- Baryon Masses
Bottom baryons decaying to a J/Ï meson and a hyperon are reconstructed using 1.0ââfb-1 of data collected in 2011 with the LHCb detector. Significant Îb0âJ/ÏÎ, Îb-âJ/ÏÎ- and Ωb-âJ/ÏΩ- signals are observed and the corresponding masses are measured to be M(Îb0)=5619.53±0.13(stat.)±0.45(syst.)ââMeV/c2, M(Îb-)=5795.8±0.9(stat.)±0.4(syst.)ââMeV/c2, M(Ωb-)=6046.0±2.2(stat.)±0.5(syst.)ââMeV/c2, while the differences with respect to the Îb0 mass are M(Îb-)-M(Îb0)=176.2±0.9(stat.)±0.1(syst.)ââMeV/c2, M(Ωb-)-M(Îb0)=426.4±2.2(stat.)±0.4(syst.)ââMeV/c2. These are the most precise mass measurements of the Îb0, Îb- and Ωb- baryons to date. Averaging the above Îb0 mass measurement with that published by LHCb using 35ââpb-1 of data collected in 2010 yields M(Îb0)=5619.44±0.13(stat.)±0.38(syst.)ââMeV/c2
First Measurement of the Charge Asymmetry in Beauty-Quark Pair Production
The difference in the angular distributions between beauty quarks and antiquarks, referred to as the charge asymmetry, is measured for the first time in b (b) over bar pair production at a hadron collider. The data used correspond to an integrated luminosity of 1.0 fb(-1) collected at 7 TeV center-of-mass energy in proton-proton collisions with the LHCb detector. The measurement is performed in three regions of the invariant mass of the b (b) over bar system. The results obtained are A(C)(b (b) over bar) (40 10(5) GeV/c(2)) = 1.6 +/- 1.7 +/- 0.6%,where A(C)(b (b) over bar) is defined as the asymmetry in the difference in rapidity between jets formed from the beauty quark and antiquark, where in each case the first uncertainty is statistical and the second systematic. The beauty jets are required to satisfy 2 20 GeV, and have an opening angle in the transverse plane Delta phi > 2.6 rad. These measurements are consistent with the predictions of the standard model
Measurement of the B0s âJ/Ïη lifetime
Using a data set corresponding to an integrated luminosity of 3 fbâ1, collected by the LHCb experiment in pp collisions at centre-of-mass energies of 7 and 8 TeV, the effective lifetime in the Bs0âJ/Ïη decay mode, Ïeff, is measured to be
Ïeff=1.479±0.034 (stat)±0.011 (syst) ps. Assuming CP conservation, Ïeff corresponds to the lifetime of the light Bs0 mass eigenstate. This is the first measurement of the effective lifetime in this decay mode
Observation of B+c â D0K+ decays
Using proton-proton collision data corresponding to an integrated luminosity of 3.0 fbâ1, recorded by
the LHCb detector at center-of-mass energies of 7 and 8 TeV, the B+
c â D0K+ decay is observed with a
statistical significance of 5.1 standard deviations. By normalizing to B+ â DÂŻ 0Ï+ decays, a measurement of
the branching fraction multiplied by the production rates for B+
c relative to B+ mesons in the LHCb
acceptance is obtained, R
D
0
K
=
(
f
c
/
f
u
)
Ă
B
(
B
+
c
â
D
0
K
+
)
=
(
9.
3
+
2.8
â
2.5
±
0.6
)
Ă
10
â
7, where the first
uncertainty is statistical and the second is systematic. This decay is expected to proceed predominantly
through weak annihilation and penguin amplitudes, and is the first B+
c decay of this nature to be observed
- âŠ