12,989 research outputs found
Non-perturbative renormalization of moments of parton distribution functions
We compute non-perturbatively the evolution of the twist-2 operators
corresponding to the average momentum of non-singlet quark densities. The
calculation is based on a finite-size technique, using the Schr\"odinger
Functional, in quenched QCD. We find that a careful choice of the boundary
conditions, is essential, for such operators, to render possible the
computation. As a by-product we apply the non-perturbatively computed
renormalization constants to available data of bare matrix elements between
nucleon states.Comment: Lattice2003(Matrix); 3 pages, 3 figures. Talk by A.
Scaling test of quenched Wilson twisted mass QCD at maximal twist
We present the results of an extended scaling test of quenched Wilson twisted
mass QCD. We fix the twist angle by using two definitions of the critical mass,
the first obtained by requiring the vanishing of the pseudoscalar meson mass
m_PS for standard Wilson fermions and the second by requiring restoration of
parity at non-zero value of the twisted mass mu and subsequently extrapolating
to mu=0. Depending on the choice of the critical mass we simulate at values of
beta in [5.7,6.45], for a range of pseudoscalar meson masses 250 MeV < m_PS < 1
GeV and we perform the continuum limit for the pseudoscalar meson decay
constant f_PS and various hadron masses (vector meson m_V, baryon octet m_oct
and baryon decuplet m_dec) at fixed value of r_0 m_PS. For both definitions of
the critical mass, lattice artifacts are consistent with O(a) improvement.
However, with the second definition, large O(a^2) discretization errors present
at small quark mass with the first definition are strongly suppressed. The
results in the continuum limit are in very good agreement with those from the
Alpha and CP-PACS Collaborations.Comment: 6 pages, Talk presented at Lattice 2005, Dublin, 25-30 July 200
Field-reversed bubble in deep plasma channels for high quality electron acceleration
We study hollow plasma channels with smooth boundaries for laser-driven
electron acceleration in the bubble regime. Contrary to the uniform plasma
case, the laser forms no optical shock and no etching at the front. This
increases the effective bubble phase velocity and energy gain. The longitudinal
field has a plateau that allows for mono-energetic acceleration. We observe as
low as 10^{-3} r.m.s. relative witness beam energy uncertainty in each
cross-section and 0.3% total energy spread. By varying plasma density profile
inside a deep channel, the bubble fields can be adjusted to balance the laser
depletion and dephasing lengths. Bubble scaling laws for the deep channel are
derived. Ultra-short pancake-like laser pulses lead to the highest energies of
accelerated electrons per Joule of laser pulse energy
Bond Strength Tests Between Silicon Wafers and Duran Tubes (Fusion Bonded Fluidic Interconnects)
The fusion bond strength of glass tubes with standard silicon wafers is presented. Experiments with plain silicon wafers and those coated with silicon oxide and silicon nitride are presented. Results obtained are discussed in terms of homogeneity and strength of fusion bond. High pressure testing shows that the bond strength is large enough for most applications of fluidic interconnects. The bond strength for 525 /spl mu/m thick silicon with glass tubes having outer diameter of 6 mm and with wall thickness 2 mm, is more than 60 bars after annealing at a temperature of 800/spl deg/C
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