908 research outputs found
Influence of jet exit conditions on the passive scaler field of an axisymmetric free jet
The influence of initial flow conditions on the passive scalar field of a turbulent free jet issuing from the round nozzle is investigated in this paper by a review of the literature and a detailed experimental study. Two sets of distinctly different initial conditions are generated using two nozzle types: a smooth contraction and a long straight pipe. The present measurements of the passive scalar (temperature) field were conducted in a slightly heated air jet from each nozzle at a Reynolds number of 16 000 using identical experimental facilities and a single measurement technique. Significant differences between the flows from the two nozzles are revealed throughout the measured flow region which covers the axial range from 0 to 70 jet exit diameters. The study suggests that the differences observed in the statistics of the scalar field may be related to differences in the underlying turbulence structure of the jet in the near field. The present findings support the analytical result of George (1989) that the entire flow is influenced by the initial conditions, resulting in a variety of self-similar states in the far field.J. Mi, D. S. Nobes and G. J. Natha
Precision lattice QCD calculations and predictions of fundamental physics in heavy quark systems
I describe the recent success in performing accurate calculations of the
effects of the strong force on particles containing bottom and charm quarks.
Since quarks are never seen in isolation, and so cannot be studied directly,
numerical simulations are key to understanding the properties of these
particles and extracting information about the quarks. The results have direct
impact on the worldwide experimental programme that is aiming to determine the
parameters of the Standard Model of particle physics precisely and thereby
uncover or constrain the possibilities for physics beyond the Standard Model.
The numerical simulation of the strong force is a huge computational task and
the recent success is the result of international collaboration in developing
techniques that are fast enough to do the calculations on powerful
supercomputers.Comment: Invited talk at SCIDAC 2006, Denver, June 2006. 15 page
Topographic Evolution in the Atomic Scale Growth and Erosion Continuum
This review gives a detailed survey of the range of fascinating surface features which develop under growth or erosion conditions under the combined influence of thermal and more energetic atomic particle fluxes. Collisionally induced atomic ejection and migration, and thermally and radiation induced atom and defect diffusion processes are outlined and their relevance to topographic initiation and evolution explored. A range of experimental observations of surface feature elaboration is discussed from net growth to net erosion conditions and models for their explanation are considered. It is concluded that while much data have been accumulated, much of these have been in so diverse experimental conditions that precise modelling in atomic terms is difficult and generalisations are treacherous. A clear need for structured, extensive studies exists with very precise parameter definition and control
Recent results from lattice calculations
Recent results from lattice QCD calculations relevant to particle physics
phenomenology are reviewed. They include the calculations of strong coupling
constant, quark masses, kaon matrix elements, and D and B meson matrix
elements. Special emphasis is on the recent progress in the simulations
including dynamical quarks.Comment: 13 pages, 8 figures, plenary talk at the 32nd International
Conference on High-Energy Physics (ICHEP 2004), August 16-22, 2004, Beijing,
Chin
Design and Fabrication of a 1 m Model of the 70 mm Bore Twin Aperture Superconducting Quadrupole for the LHC Insertions
For reasons of geometrical acceptance, 70 mm bore twin aperture quadrupoles are required in the LHC insertions. For an operating gradient of 160 T/m at 4.5 K, a design based on a four layer coil wound from two graded 8.2 mm NbTi conductors has been developed. Three 1 m single aperture quadrupoles of this design have been built and successfully tested. Thereafter, the magnets have been disassembled and the coils re-collared using self-supporting collars. In this paper, we describe the design features of the twin aperture quadrupole, and report on the initial collaring tests and procedures for collaring and final assembly of the 1 m magnet
Perturbative expansions from Monte Carlo simulations at weak coupling: Wilson loops and the static-quark self-energy
Perturbative coefficients for Wilson loops and the static-quark self-energy
are extracted from Monte Carlo simulations at weak coupling. The lattice
volumes and couplings are chosen to ensure that the lattice momenta are all
perturbative. Twisted boundary conditions are used to eliminate the effects of
lattice zero modes and to suppress nonperturbative finite-volume effects due to
Z(3) phases. Simulations of the Wilson gluon action are done with both periodic
and twisted boundary conditions, and over a wide range of lattice volumes (from
to ) and couplings (from to ).
A high precision comparison is made between the simulation data and results
from finite-volume lattice perturbation theory. The Monte Carlo results are
shown to be in excellent agreement with perturbation theory through second
order. New results for third-order coefficients for a number of Wilson loops
and the static-quark self-energy are reported.Comment: 36 pages, 15 figures, REVTEX documen
Branching ratios of Bc Meson Decaying to Pseudoscalar and Axial-Vector Mesons
We study Cabibbo-Kobayashi-Maskawa (CKM) favored weak decays of Bc mesons in
the Isgur-Scora-Grinstein-Wise (ISGW) quark model. We present a detailed
analysis of the Bc meson decaying to a pseudoscalar meson (P) and an
axial-vector meson (A). We also give the form factors involving transition in
the ISGW II framework and consequently, predict the branching ratios of decays.Comment: 19 pages,7 table
Accurate Determinations of from Realistic Lattice QCD
We obtain a new value for the QCD coupling constant by combining lattice QCD
simulations with experimental data for hadron masses. Our lattice analysis is
the first to: 1) include vacuum polarization effects from all three light-quark
flavors (using MILC configurations); 2) include third-order terms in
perturbation theory; 3) systematically estimate fourth and higher-order terms;
4) use an unambiguous lattice spacing; and 5) use an \order(a^2)-accurate QCD
action. We use 28~different (but related) short-distance quantities to obtain
.Comment: 4 pages, 2 figures, 1 table. The revised version differs from the
original because we now use 4-loop beta functions (rather than 3-loop). This
shifts the answer a little (mostly from the evolution from the lattice scale
to M_z -- lattice results aren't very different) and reduces the error
slightl
Similarities and differences between the E5 oncoproteins of bovine papillomaviruses type 1 and type 4: Cytoskeleton, motility and invasiveness in E5-transformed bovine and mouse cells
Bovine papillomaviruses (BPVs) are oncogenic viruses. In cattle, BPV-1/2 is associated with urinary bladder cancer and BPV-4 with upper GI tract cancer. BPV E5 is a small hydrophobic protein localised in the endoplasmic reticulum (ER) and Golgi apparatus (GA). E5 is the major transforming protein of BPVs, capable of inducing cell transformation in cultured mouse fibroblasts and, in cooperation with E7, in primary bovine cells. E5-induced cell transformation is accompanied by activation of several cellular protein kinases, including growth factor receptors, and alkalinisation of endosomes and GA. We have reported that BPV E5 causes swelling and fragmentation of the GA and extensive vacuolisation of the cytoplasm. We now show that E5 from both BPV-1 and BPV-4 disturbs the actin cytoskeleton and focal adhesions in transformed bovine cells, where these morphological and behavioural characteristics are accompanied by hyperphosphorylation of the cellular phosphotyrosine kinase c-src. Both BPV-1 and BPV-4 E5 increase the motility of transformed mouse cells, but only BPV-1 E5 causes transformed mouse cells to penetrate a matrigel matrix. BPV-1 transformed mouse cells, but not BPV-4 transformed mouse cells, have hyperhpsphorylated c-src
Quarkonium mass splittings in three-flavor lattice QCD
We report on calculations of the charmonium and bottomonium spectrum in
lattice QCD. We use ensembles of gauge fields with three flavors of sea quarks,
simulated with the asqtad improved action for staggered fermions. For the heavy
quarks we employ the Fermilab interpretation of the clover action for Wilson
fermions. These calculations provide a test of lattice QCD, including the
theory of discretization errors for heavy quarks. We provide, therefore, a
careful discussion of the results in light of the heavy-quark effective
Lagrangian. By and large, we find that the computed results are in agreement
with experiment, once parametric and discretization errors are taken into
account.Comment: 21 pages, 17 figure
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