17,581 research outputs found
Multiobjective analysis for the design and control of an electromagnetic valve actuator
The electromagnetic valve actuator can deliver much improved fuel efficiency and reduced emissions in spark ignition (SI) engines owing to the potential for variable valve timing when compared with cam-operated, or conventional, variable valve strategies. The possibility exists to reduce pumping losses by throttle-free operation, along with closed-valve engine braking. However, further development is required to make the technology suitable for accept- ance into the mass production market. This paper investigates the application of multiobjective optimization techniques to the conflicting objective functions inherent in the operation of such a device. The techniques are utilized to derive the optimal force–displacement characteristic for the solenoid actuator, along with its controllability and dynamic/steady state performance
Low-momentum interactions in three- and four-nucleon scattering
Low momentum two-nucleon interactions obtained with the renormalization group
method and the similarity renormalization group method are used to study the
cutoff dependence of low energy 3N and 4N scattering observables. The residual
cutoff dependence arises from omitted short-ranged 3N (and higher) forces that
are induced by the renormalization group transformations, and may help to
estimate the sensitivity of various 3N and 4N scattering observables to
short-ranged many-body forces.Comment: 5 pages, 8 figures, to be published in Phys. Rev.
A global simulation for laser driven MeV electrons in -diameter fast ignition targets
The results from 2.5-dimensional Particle-in-Cell simulations for the
interaction of a picosecond-long ignition laser pulse with a plasma pellet of
50- diameter and 40 critical density are presented. The high density
pellet is surrounded by an underdense corona and is isolated by a vacuum region
from the simulation box boundary. The laser pulse is shown to filament and
create density channels on the laser-plasma interface. The density channels
increase the laser absorption efficiency and help generate an energetic
electron distribution with a large angular spread. The combined distribution of
the forward-going energetic electrons and the induced return electrons is
marginally unstable to the current filament instability. The ions play an
important role in neutralizing the space charges induced by the the temperature
disparity between different electron groups. No global coalescing of the
current filaments resulted from the instability is observed, consistent with
the observed large angular spread of the energetic electrons.Comment: 9 pages, 6 figures, to appear in Physics of Plasmas (May 2006
Photodisintegration of the triton with realistic potentials
The process is treated by means of three-body integral
equations employing in their kernel the W-Matrix representation of the
subsystem amplitudes. As compared to the plane wave (Born) approximation the
full solution of the integral equations, which takes into account the final
state interaction, shows at low energies a 24% enhancement. The calculations
are based on the semirealistic Malfliet-Tjon and the realistic Paris and Bonn B
potentials. For comparison with earlier calculations we also present results
for the Yamaguchi potential. In the low-energy region a remarkable potential
dependence is observed, which vanishes at higher energies.Comment: 16 pages REVTeX, 8 postscript figures included, uses epsfig.st
Benchmark calculation for proton-deuteron elastic scattering observables including Coulomb
Two independent calculations of proton-deuteron elastic scattering
observables including Coulomb repulsion between the two protons are compared in
the proton lab energy region between 3 MeV and 65 MeV. The hadron dynamics is
based on the purely nucleonic charge-dependent AV18 potential. Calculations are
done both in coordinate space and momentum space. The coordinate-space
calculations are based on a variational solution of the three-body
Schr\"odinger equation using a correlated hyperspherical expansion for the wave
function. The momentum-space calculations proceed via the solution of the
Alt-Grassberger-Sandhas equation using the screened Coulomb potential and the
renormalization approach. Both methods agree within 1% on all observables,
showing the reliability of both numerical techniques in that energy domain. At
energies below three-body breakup threshold the coordinate-space method remains
favored whereas at energies higher than 65 MeV the momentum-space approach
seems to be more efficient.Comment: Submitted to Phys. Rev.
Microstructural changes of 'rocha' pear following storage under controlled atmosphere
This research effort was aimed at evaluating the influence of storage (for 4 mo at 2°C), under various controlled atmospheres (viz. 1.9 kPa O2 + 4.9 kPa CO2, 1.9 kPa O2 + 0.5 kPa CO2 and 1.9 kPa O2 + 0 kPa CO2), on the microstructure of ′Rocha′ pear. Toward this goal, the morphology of cellular disassembly, as well as the quantity of granules and intercellular space using scanning electron microscopy (SEM), were tentatively correlated with sensory and instrumental firmness, by 1, 6 and 8 d of exposure to air, at room temperature, after storage. A specific methodology, based on panel evaluation of SEM images, was developed and statistically validated. The degree of cellular disassembly increased throughout exposure time to air at room temperature. Pears stored under 1.9 kPa O2 + 0.5 kPa CO2 yielded a degree of cellular disassembly similar to that of the control
Ion acceleration from laser-driven electrostatic shocks
Multi-dimensional particle-in-cell simulations are used to study the
generation of electrostatic shocks in plasma and the reflection of background
ions to produce high-quality and high-energy ion beams. Electrostatic shocks
are driven by the interaction of two plasmas with different density and/or
relative drift velocity. The energy and number of ions reflected by the shock
increase with increasing density ratio and relative drift velocity between the
two interacting plasmas. It is shown that the interaction of intense lasers
with tailored near-critical density plasmas allows for the efficient heating of
the plasma electrons and steepening of the plasma profile at the critical
density interface, leading to the generation of high-velocity shock structures
and high-energy ion beams. Our results indicate that high-quality 200 MeV
shock-accelerated ion beams required for medical applications may be obtained
with current laser systems.Comment: 33 pages, 12 figures, accepted for publication in Physics of Plasma
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