1,080 research outputs found
Valve recession: From experiment to predictive model
Increasing demands on engine performance and cost reductions have meant that advances made in materials and production technology are often outpaced This frequently results in wear problems occurring with engine components. Few models exist for predicting wear, and consequently each wear problem has to be investigated, the cause isolated and remedial action taken. The objective of this work was to carry out experimental studies to investigate valve and seat insert wear mechanisms and use the test results to develop a recession prediction tool to assess the potential for valve recession and solve problems that occur more quickly. Experimental apparatus has been developed that is capable of providing a valid simulation of the wear of diesel automotive inlet valves and seats. Test methodologies developed have isolated the effects of impact and sliding. A semi-empirical wear model for predicting valve recession has been developed based on data gathered during the bench testing. A software program, RECESS, was developed to run the model. Model predictions are compared with engine dynamometer tests and bench tests. The model can be used to give a quantitative prediction of the valve recession to be expected with a particular material pair or a qualitative assessment of how parameters need to be altered in order to reduce recession. The valve recession model can be integrated into an industrial environment in order to help reduce costs and timescales involved in solving valve/seat wear problems
Genuine collective flow from Lee-Yang zeroes
We propose to use the theory of phase transitions of Lee and Yang as a
practical tool to analyze long-range correlations in a finite-size system. We
apply it to the analysis of anisotropic flow in nucleus-nucleus collisions, and
show that this method is more reliable than any other used so far.Comment: 5 pages, 3 eps figures, RevTeX. v2: overall presentation modifie
Subject-specific, multiscale simulation of electrophysiology: a software pipeline for image-based models and application examples
Many simulation studies in biomedicine are based on a similar sequence of processing steps, starting from images and running through geometric model generation, assignment of tissue properties, numerical simulation and visualization of the resultsâa process known as image-based geometric modelling and simulation. We present an overview of software systems for implementing such a sequence both within highly integrated problem-solving environments and in the form of loosely integrated pipelines. Loose integration in this case indicates that individual programs function largely independently but communicate through files of a common format and support simple scripting, so as to automate multiple executions wherever possible. We then describe three specific applications of such pipelines to translational biomedical research in electrophysiology
Crystal structure of Cu-Sn-In alloys around the {\eta} phase field studied by neutron diffraction
The study of the Cu-Sn-In ternary system has become of great importance in
recent years, due to new environmental regulations forcing to eliminate the use
of Pb in bonding technologies for electronic devices. A key relevant issue
concerns the intermetallic phases which grow in the bonding zone and are
determining in their quality and performance. In this work, we focus in the
{\eta}-phase (Cu2In or Cu6Sn5) that exists in both end binaries and as a
ternary phase. We present a neutron diffraction study of the constitution and
crystallography of a series of alloys around the 60 at.% Cu composition, and
with In contents ranging from 0 to 25 at.%, quenched from 300\degreeC. The
alloys were characterized by scanning electron microscopy, probe microanalysis
and high-resolution neutron diffraction. The Rietveld refinement of neutron
diffraction data allowed to improve the currently available model for site
occupancies in the hexagonal {\eta}-phase in the binary Cu-Sn as well as in
ternary alloys. For the first time, structural data is reported in the ternary
Cu-Sn-In {\eta}-phase as a function of composition, information that is of
fundamental technological importance as well as valuable input data for ongoing
modelisations of the ternary phase diagram.Comment: 8 pages, 10 figure
Analysis of anisotropic flow with Lee-Yang zeroes
We present a new method to extract anisotropic flow in heavy ion collisions
from the genuine correlation among a large number of particles. Anisotropic
flow is obtained from the zeroes in the complex plane of a generating function
of azimuthal correlations, in close analogy with the theory of phase
transitions by Lee and Yang. Flow is first estimated globally, i.e., averaged
over the phase space covered by the detector, and then differentially, as a
function of transverse momentum and rapidity for identified particles. The
corresponding estimates are less biased by nonflow correlations than with any
other method. The practical implementation of the method is rather
straightforward. Furthermore, it automatically takes into account most
corrections due to azimuthal anisotropies in the detector acceptance. The main
limitation of the method is statistical errors, which can be significantly
larger than with the ``standard'' method of flow analysis if the flow and/or
the event multiplicities are too small. In practice, we expect this to be the
most accurate method to analyze directed and elliptic flow in fixed-target
heavy-ion collisions between 100 MeV and 10 GeV per nucleon (at the Darmstadt
SIS synchrotron and the Brookhaven Alternating Gradient Synchrotron), and
elliptic flow at ultrarelativistic energies (at the Brookhaven Relativistic
Heavy Ion Collider, and the forthcoming Large Hadron Collider at CERN).Comment: 32 pages, 7 eps figures, RevTe
FERMION ZERO MODES AND BLACK-HOLE HYPERMULTIPLETS WITH RIGID SUPERSYMMETRY
The gravitini zero modes riding on top of the extreme Reissner-Nordstrom
black-hole solution of N=2 supergravity are shown to be normalizable. The
gravitini and dilatini zero modes of axion-dilaton extreme black-hole solutions
of N=4 supergravity are also given and found to have finite norms. These norms
are duality invariant. The finiteness and positivity of the norms in both cases
are found to be correlated with the Witten-Israel-Nester construction; however,
we have replaced the Witten condition by the pure-spin-3/2 constraint on the
gravitini. We compare our calculation of the norms with the calculations which
provide the moduli space metric for extreme black holes.
The action of the N=2 hypermultiplet with an off-shell central charge
describes the solitons of N=2 supergravity. This action, in the
Majumdar-Papapetrou multi-black-hole background, is shown to be N=2 rigidly
supersymmetric.Comment: 18 pages, LaTe
Lepton flavor violation decays in the topcolor-assisted technicolor model and the littlest Higgs model with parity
The new particles predicted by the topcolor-assisted technicolor ()
model and the littlest Higgs model with T-parity (called model) can
induce the lepton flavor violation () couplings at tree level or one loop
level, which might generate large contributions to some processes. Taking
into account the constraints of the experimental data on the relevant free
parameters, we calculate the branching ratios of the decay processes
with = , and
in the context of these two kinds of new physics models. We find
that the model and the model can indeed produce significant
contributions to some of these decay processes.Comment: 24 pages, 7 figure
Observation of exclusive DVCS in polarized electron beam asymmetry measurements
We report the first results of the beam spin asymmetry measured in the
reaction e + p -> e + p + gamma at a beam energy of 4.25 GeV. A large asymmetry
with a sin(phi) modulation is observed, as predicted for the interference term
of Deeply Virtual Compton Scattering and the Bethe-Heitler process. The
amplitude of this modulation is alpha = 0.202 +/- 0.028. In leading-order and
leading-twist pQCD, the alpha is directly proportional to the imaginary part of
the DVCS amplitude.Comment: 6 pages, 5 figure
Electron Scattering From High-Momentum Neutrons in Deuterium
We report results from an experiment measuring the semi-inclusive reaction
where the proton is moving at a large angle relative to the
momentum transfer. If we assume that the proton was a spectator to the reaction
taking place on the neutron in deuterium, the initial state of that neutron can
be inferred. This method, known as spectator tagging, can be used to study
electron scattering from high-momentum (off-shell) neutrons in deuterium. The
data were taken with a 5.765 GeV electron beam on a deuterium target in
Jefferson Laboratory's Hall B, using the CLAS detector. A reduced cross section
was extracted for different values of final-state missing mass ,
backward proton momentum and momentum transfer . The data
are compared to a simple PWIA spectator model. A strong enhancement in the data
observed at transverse kinematics is not reproduced by the PWIA model. This
enhancement can likely be associated with the contribution of final state
interactions (FSI) that were not incorporated into the model. A ``bound neutron
structure function'' was extracted as a function of and
the scaling variable at extreme backward kinematics, where effects of
FSI appear to be smaller. For MeV/c, where the neutron is far
off-shell, the model overestimates the value of in the region of
between 0.25 and 0.6. A modification of the bound neutron structure
function is one of possible effects that can cause the observed deviation.Comment: 33 pages RevTeX, 9 figures, to be submitted to Phys. Rev. C. Fixed 1
Referenc
Complete measurement of three-body photodisintegration of 3He for photon energies between 0.35 and 1.55 GeV
The three-body photodisintegration of 3He has been measured with the CLAS
detector at Jefferson Lab, using tagged photons of energies between 0.35 GeV
and 1.55 GeV. The large acceptance of the spectrometer allowed us for the first
time to cover a wide momentum and angular range for the two outgoing protons.
Three kinematic regions dominated by either two- or three-body contributions
have been distinguished and analyzed. The measured cross sections have been
compared with results of a theoretical model, which, in certain kinematic
ranges, have been found to be in reasonable agreement with the data.Comment: 22 pages, 25 eps figures, 2 tables, submitted to PRC. Modifications:
removed 2 figures, improvements on others, a few minor modifications to the
tex
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