2,491 research outputs found
Improved interpolating fields for hadrons at non-vanishing momentum
We demonstrate that a reduction in the noise-to-signal ratio may be obtained
for hadrons at non-zero momenta whilst maintaining a good overlap with the
ground state through a generalisation of Gaussian/Wuppertal smearing. The use
of an anisotropic smearing wavefunction is motivated by the physical picture of
a boosted hadron.Comment: 7 pages, 6 figures, poster presented at the 30th International
Symposium on Lattice Field Theory (Lattice 2012), Cairns, Australia, June
24-29, 201
Nanoscale austenite reversion through partitioning, segregation, and kinetic freezing: Example of a ductile 2 GPa Fe-Cr-C steel
Austenite reversion during tempering of a Fe-13.6Cr-0.44C (wt.%) martensite
results in an ultrahigh strength ferritic stainless steel with excellent
ductility. The austenite reversion mechanism is coupled to the kinetic freezing
of carbon during low-temperature partitioning at the interfaces between
martensite and retained austenite and to carbon segregation at
martensite-martensite grain boundaries. An advantage of austenite reversion is
its scalability, i.e., changing tempering time and temperature tailors the
desired strength-ductility profiles (e.g. tempering at 400{\deg}C for 1 min.
produces a 2 GPa ultimate tensile strength (UTS) and 14% elongation while 30
min. at 400{\deg}C results in a UTS of ~ 1.75 GPa with an elongation of 23%).
The austenite reversion process, carbide precipitation, and carbon segregation
have been characterized by XRD, EBSD, TEM, and atom probe tomography (APT) in
order to develop the structure-property relationships that control the
material's strength and ductility.Comment: in press Acta Materialia 201
The Shape of Covariantly Smeared Sources in Lattice QCD
Covariantly smeared sources are commonly used in lattice QCD to enhance the
projection onto the ground state. Here we investigate the dependence of their
shape on the gauge field background and find that the presence of localized
concentrations of magnetic field can lead to strong distortions which reduce
the smearing radii achievable by iterative smearing prescriptions. In
particular, as , iterative procedures like Jacobi smearing require
increasingly large iteration counts in order to reach physically-sized smearing
radii 0.5 fm, and the resulting sources are strongly distorted. To
bypass this issue, we propose a covariant smearing procedure (``free-form
smearing'') that allows us to create arbitrarily shaped sources, including in
particular Gaussians of arbitrary radius.Comment: 1+15 pages, 7 figures (24 pdf images
Characterization of new hybrid pixel module concepts for the ATLAS Insertable B-Layer upgrade
The ATLAS Insertable B-Layer (IBL) collaboration plans to insert a fourth
pixel layer inside the present Pixel Detector to recover from eventual failures
in the current pixel system, especially the b-layer. Additionally the IBL will
ensure excellent tracking, vertexing and b-tagging performance during the LHC
phase I and add robustness in tracking with high luminosity pile-up. The
expected peak luminosity for IBL is 2 to 3centerdot1034 cm-2s-1 and IBL is
designed for an integrated luminosity of 700 fb-1. This corresponds to an
expected fluence of 5centerdot1015 1 MeV neqcm-2 and a total ionizing dose of
250 MRad. In order to cope with these requirements, two new module concepts are
under investigation, both based on a new front end IC, called FE-I4. This IC
was designed as readout chip for future ATLAS Pixel Detectors and its first
application will be the IBL. The planar pixel sensor (PPS) based module concept
benefits from its well understood design, which is kept as similar as possible
to the design of the current ATLAS Pixel Detector sensor. The second approach
of the new three dimensional (3D) silicon sensor technology benefits from the
shorter charge carrier drift distance to the electrodes, which completely
penetrate the sensor bulk. Prototype modules of both sensor concepts have been
build and tested in laboratory and test beam environment before and after
irradiation. Both concepts show very high performance even after irradiation to
5centerdot1015 1 MeV neqcm-2 and meet the IBL specifications in terms of hit
efficiency being larger than 97%. Lowest operational threshold studies have
been effected and prove independent of the used sensor concept the excellent
performance of FE-I4 based module concepts in terms of noise hit occupancy at
low thresholds.Comment: Part of 9th International Conference on Position Sensitive Detectors
(PSD9
Nucleon axial form factors from two-flavour Lattice QCD
We present preliminary results on the axial form factor and the
induced pseudoscalar form factor of the nucleon. A systematic
analysis of the excited-state contributions to form factors is performed on the
CLS ensemble `N6' with and lattice spacing . The relevant three-point functions were computed with
source-sink separations ranging from to $t_s \sim \
1.4 \ \text{fm}$. We observe that the form factors suffer from non-trivial
excited-state contributions at the source-sink separations available to us. It
is noted that naive plateau fits underestimate the excited-state contributions
and that the method of summed operator insertions correctly accounts for these
effects.Comment: 7 pages, 12 figures; talk presented at Lattice 2014 -- 32nd
International Symposium on Lattice Field Theory, 23-28 June, 2014, Columbia
University New York, N
Mechanical properties of three-dimensional interconnected alumina/steel metal matrix composites
Three-dimensional interconnected alumina/steel metal matrix composites (MMCs) were produced by pressureless Ti-activated melt infiltration method using three types of Al2O3 powder with different sizes and shapes. By partial sintering during infiltration an interpenetrating ceramic network was realised. The effect of the ceramic particle size and shape on the resulting ceramic network, volume % fraction and the MMC properties is presented. The MMCs were characterised for mechanical properties at room temperature and elevated temperature. An increase in flexural strength and Young's modulus with decreasing particle size has been observed. In addition, the effect of the volume of ceramic content and the surface finish of the MMCs on the wear behaviour is show
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