6,962 research outputs found
Investigation of spray dispersion and particulate formation in diesel fuel flames
An experimental study of electrostatical atomized and dispersed diesel fuel jets was conducted at various back pressures to 40 atm. A new electrostatic injection technique was utilized to generate continuous, stable fuel sprays at charge densities of 1.5 to 2.0 C/m3 of fluid at one atm, and about 1.0 C/m3 at 40 atm. Flowrates were varied from 0.5 to 2.5 ml/s and electric potentials to -18 kV. Visual observations showed that significant enhanced dispersion of charged fuel jets occurred at high back pressures compared to aerodynamic breakup and dispersion. The average drop size was about the same as the spray triode orifice diameter, and was between the Kelly theory and the Rayleigh limit. The ignition tests, done only at one atm, indicated stable combustion of the electrostatically dispersed fuel jets
Implementation of a local principal curves algorithm for neutrino interaction reconstruction in a liquid argon volume
A local principal curve algorithm has been implemented in three dimensions
for automated track and shower reconstruction of neutrino interactions in a
liquid argon time projection chamber. We present details of the algorithm and
characterise its performance on simulated data sets.Comment: 14 pages, 17 figures; typing correction to Eq 5, the definition of
the local covariance matri
Disturbance Observer
Disturbance observer is an inner-loop output-feedback controller whose role
is to reject external disturbances and to make the outer-loop baseline
controller robust against plant's uncertainties. Therefore, the closed-loop
system with the DOB approximates the nominal closed-loop by the baseline
controller and the nominal plant model with no disturbances. This article
presents how the disturbance observer works under what conditions, and how one
can design a disturbance observer to guarantee robust stability and to recover
the nominal performance not only in the steady-state but also for the transient
response under large uncertainty and disturbance
High p_T Triggered Delta-eta,Delta-phi Correlations over a Broad Range in Delta-eta
The first measurement of pseudorapidity (Delta-eta) and azimuthal angle
(Delta-phi) correlations between high transverse momentum charged hadrons (p_T
> 2.5 GeV/c) and all associated particles is presented at both short- (small
Delta-eta) and long-range (large Delta-eta) over a continuous pseudorapidity
acceptance (-4<Delta-eta<2). In these proceedings, the various near- and
away-side features of the correlation structure are discussed as a function of
centrality in Au+Au collisions measured by PHOBOS at sqrt(s_NN)=200 GeV. In
particular, this measurement allows a much more complete determination of the
longitudinal extent of the ridge structure, first observed by the STAR
collaboration over a limited eta range. In central collisions the ridge
persists to at least Delta-eta=4, diminishing in magnitude as collisions become
more peripheral until it disappears around Npart=80.Comment: 5 pages, 2 figures, presented at the 20th International Conference on
Ultra-Relativistic Nucleus-Nucleus Collisions, "Quark Matter 2008", Jaipur,
India, February 4-10, 2008. Full author list included and typo corrected in
equation
Pseudorapidity dependence of parton energy loss in relativistic heavy ion collisions
We analyze the recent data from the BRAHMS Collaboration on the
pseudorapidity dependence of nuclear modification factors in Au+Au collisions
at = 200 GeV by using the full three dimensional hydrodynamic
simulations for the density effects on parton energy loss. We first compute the
transverse spectra at and 2.2, and next take a ratio
, where is a nuclear
modification factor. It is shown that hydrodynamic components account for
at low and that quenched pQCD components lead
at high which are consistent with the data.
Strong suppression at is compatible with the parton energy loss in
the final state.Comment: 5 pages, 4 figures; one figure adde
Three-Axis Fiber-Optic Body Force Sensor for Flexible Manipulators
This paper proposes a force/torque sensor structure that can be easily integrated into a flexible manipulator structure. The sensor's ring-like structure with its hollow inner section provides ample space for auxiliary components, such as cables and tubes, to be passed through and, hence, is very suitable for integration with tendon-driven and fluid-actuated manipulators. The sensor structure can also accommodate the wiring for a distributed sensor system as well as for diagnostic instruments that may be incorporated in the manipulator. Employing a sensing approach based on optical fibers as done here allows for the creation of sensors that are free of electrical currents at the point of sensing and immune to magnetic fields. These sensors are inherently safe when used in the close vicinity of humans and their measuring performance is not impaired when they are operated in or nearby machines, such as magnetic resonance imaging scanners. This type of sensor concept is particularly suitable for inclusion in instruments and robotic tools for minimally invasive surgery. This paper summarizes the design, integration challenges, and calibration of the proposed optical three-axis force sensor. The experimental results confirm the effectiveness of our optical sensing approach and show that after calibrating its stiffness matrix, force and momentum components can be determined accurately
Fast-Neutron Activation of Long-Lived Isotopes in Enriched Ge
We measured the production of \nuc{57}{Co}, \nuc{54}{Mn}, \nuc{68}{Ge},
\nuc{65}{Zn}, and \nuc{60}{Co} in a sample of Ge enriched in isotope 76 due to
high-energy neutron interactions. These isotopes, especially \nuc{68}{Ge}, are
critical in understanding background in Ge detectors used for double-beta decay
experiments. They are produced by cosmogenic-neutron interactions in the
detectors while they reside on the Earth's surface. These production rates were
measured at neutron energies of a few hundred MeV. We compared the measured
production to that predicted by cross-section calculations based on CEM03.02.
The cross section calculations over-predict our measurements by approximately a
factor of three depending on isotope. We then use the measured cosmic-ray
neutron flux, our measurements, and the CEM03.02 cross sections to predict the
cosmogenic production rate of these isotopes. The uncertainty in extrapolating
the cross section model to higher energies dominates the total uncertainty in
the cosmogenic production rate.Comment: Revised after feedback and further work on extrapolating cross
sections to higher energies in order to estimate cosmic production rates.
Also a numerical error was found and fixed in the estimate of the Co-57
production rat
What's Interesting About Strangeness Production? - An Overview of Recent Results
In this paper I highlight a few selected topics on strange particle
production in heavy-ion collisions. By studying the yield and spectra of
strange particles we hope to gain understanding of the conditions reached in,
and the ensuing dynamics of, the systems produced when ultra-relativistic
heavy-ions are collided.Comment: 17 Pages, 18 figures, Hot Quarks 2004 Proceeding
Critical Susceptibility Exponent Measured from Fe/W(110) Bilayers
The critical phase transition in ferromagnetic ultrathin Fe/W(110) films has
been studied using the magnetic ac susceptibility. A statistically objective,
unconstrained fitting of the susceptibility is used to extract values for the
critical exponent (gamma), the critical temperature Tc, the critical amplitude
(chi_o) and the range of temperature that exhibits power-law behaviour. A
fitting algorithm was used to simultaneously minimize the statistical variance
of a power law fit to individual experimental measurements of chi(T). This
avoids systematic errors and generates objective fitting results. An ensemble
of 25 measurements on many different films are analyzed. Those which permit an
extended fitting range in reduced temperature lower than approximately .00475
give an average value gamma=1.76+-0.01. Bilayer films give a weighted average
value of gamma = 1.75+-0.02. These results are in agreement with the
-dimensional Ising exponent gamma= 7/4. Measurements that do not exhibit
power-law scaling as close to Tc (especially films of thickness 1.75ML) show a
value of gamma higher than the Ising value. Several possibilities are
considered to account for this behaviour.Comment: -Submitted to Phys. Rev. B -Revtex4 Format -6 postscript figure
An open extensible tool environment for Event-B
Abstract. We consider modelling indispensable for the development of complex systems. Modelling must be carried out in a formal notation to reason and make meaningful conjectures about a model. But formal modelling of complex systems is a difficult task. Even when theorem provers improve further and get more powerful, modelling will remain difficult. The reason for this that modelling is an exploratory activity that requires ingenuity in order to arrive at a meaningful model. We are aware that automated theorem provers can discharge most of the onerous trivial proof obligations that appear when modelling systems. In this article we present a modelling tool that seamlessly integrates modelling and proving similar to what is offered today in modern integrated development environments for programming. The tool is extensible and configurable so that it can be adapted more easily to different application domains and development methods.
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