31,117 research outputs found
Intrinsic adaptive mesh techniques
An alternating direction adaptive grid movement code was developed and a thesis adaptive angular meshes was directed. The alternating direction code was also established on the NASA Langley computer system and is available for use there. In essence, grid points are moved on an abstract surface above physical space by means of alternating coordinate directions. The abstract surface is formed with the salient solution properties if they can be extracted by a priori physical reasoning; or otherwise, in the absence of such reasoning, by the use of error estimates in some chosen norm. Upon formulation, all important driving properties for adaptive purposes are consolidated into one object - the abstract surface. At a basic level, a uniform distribution of surface points is equivalent to gradient resolution. This arises from a projection back down into physical space. At a higher level, a more accurate view of the abstract surface is obtained when changes in surface direction are also resolved. The appropriate measure for direction changes is normal curvature. It is defined as the rate of change of surface tangent planes as a surface coordinate curve is transversed in uniform increments of arc length
Computer model of catalytic combustion/Stirling engine heater head
The basic Acurex HET code was modified to analyze specific problems for Stirling engine heater head applications. Specifically, the code can model: an adiabatic catalytic monolith reactor, an externally cooled catalytic cylindrical reactor/flat plate reactor, a coannular tube radiatively cooled reactor, and a monolithic reactor radiating to upstream and downstream heat exchangers
S-wave quantum entanglement in a harmonic trap
We analyze the quantum entanglement between two interacting atoms trapped in
a spherical harmonic potential. At ultra-cold temperature, ground state
entanglement is generated by the dominated s-wave interaction. Based on a
regularized pseudo-potential Hamiltonian, we examine the quantum entanglement
by performing the Schmidt decomposition of low-energy eigenfunctions. We
indicate how the atoms are paired and quantify the entanglement as a function
of a modified s-wave scattering length inside the trap.Comment: 10 pages, 5 figures, to be apear in PR
Theoretical studies on tone noise from a ducted fan rotor
The method of computing radiated noise from a ducted rotor due to inflow distortion and turbulence are examined. Analytical investigations include an appropriate description of sources, the cut-off conditions imposed on the modal propagation of the pressure waves in the annular duct, and reflections at the upstream end of the duct. Far field sound pressure levels at blade passing frequency due to acoustic radiation from a small scale low speed fan are computed. Theoretical predictions are in reasonable agreement with experimental measurements
Loss of purity by wave packet scattering at low energies
We study the quantum entanglement produced by a head-on collision between two
gaussian wave packets in three-dimensional space. By deriving the two-particle
wave function modified by s-wave scattering amplitudes, we obtain an
approximate analytic expression of the purity of an individual particle. The
loss of purity provides an indicator of the degree of entanglement. In the case
the wave packets are narrow in momentum space, we show that the loss of purity
is solely controlled by the ratio of the scattering cross section to the
transverse area of the wave packets.Comment: 7 pages, 1 figur
Improving Effective Surgical Delivery in Humanitarian Disasters: Lessons from Haiti
Kathryn Chu and colleagues describe the experiences of Médecins sans Frontières after the 2010 Haiti earthquake, and discuss how to improve delivery of surgery in humanitarian disasters
Effect of Hydrostatic Pressure on the Superconductivity in NaxCoO2.yH2O
The effect of hydrostatic pressure on the superconducting transition
temperature of Na{0.35}CoO{2}.yH{2}O was investigated by ac susceptibility
measurements up to 1.6 GPa. The pressure coefficient of T{c} is negative and
the dependence T{c}(p) is nonlinear over the pressure range investigated. The
magnitude of the average dlnT{c}/dp=-0.07 GPa^{-1} is comparable to the
pressure coefficient of electron-doped high-T{c} copper oxide superconductors
with a similar value of T{c}. Our results provide support to the assumption of
two-dimensional superconductivity in Na{0.35}CoO{2}.yH{2}O, which is similar to
the cuprate systems, and suggest that intercalation of larger molecules may
lead to an enhancement of T{c}.Comment: Revised Manuscrip
Traffic and Navigation Support through an Automobile Heads Up Display (A-HUD)
The automobile industry has produced many cars with new features over the past decade. Taking advantage of advances in technology, cars today have fuel-efficient hybrid engines, proximately sensors, windshield wipers that can detect rain, built-in multimedia entertainment, and all-wheel drive systems that adjust power in real-time. However, the interaction between the driver and the car has not changed significantly. The information being delivered – both in quantity and method – from the car to the driver has not seen the same improvements as there has been “under the hood.” This is a position paper that proposes immersing the driver inside an additional layer of traffic and navigation data, and presenting that data to the driver by embedding display systems into the automobile windows and mirrors. We have developed the initial concepts and ideas for this type of virtual display. Through gaze tracking the digital information is superimposed and registered with real world entities such as street signs and traffic intersections
Physical Structure of Small Wolf-Rayet Ring Nebulae
We have selected the seven most well-defined WR ring nebulae in the LMC (Br
2, Br 10, Br 13, Br 40a, Br 48, Br 52, and Br 100) to study their physical
nature and evolutionary stages. New CCD imaging and echelle observations have
been obtained for five of these nebulae; previous photographic imaging and
echelle observations are available for the remaining two nebulae. Using the
nebular dynamics and abundances, we find that the Br 13 nebula is a
circumstellar bubble, and that the Br 2 nebula may represent a circumstellar
bubble merging with a fossil main-sequence interstellar bubble. The nebulae
around Br 10, Br 52, and Br 100 all show influence of the ambient interstellar
medium. Their regular expansion patterns suggest that they still contain
significant amounts of circumstellar material. Their nebular abundances would
be extremely interesting, as their central stars are WC5 and WN3-4 stars whose
nebular abundances have not been derived previously. Intriguing and tantalizing
implications are obtained from comparisons of the LMC WR ring nebulae with ring
nebulae around Galactic WR stars, Galactic LBVs, LMC LBVs, and LMC BSGs;
however, these implications may be limited by small-number statistics. A SNR
candidate close to Br 2 is diagnosed by its large expansion velocity and
nonthermal radio emission. There is no indication that Br 2's ring nebula
interacts dynamically with this SNR candidate.Comment: 20 pages, Latex (aaspp4.sty), 2 figures, accepted by the Astronomical
Journal (March 99 issue
Cosmological Constraints on Radion Evolution in the Universal Extra Dimension Model
The constraints on the radion evolution in the Universal Extra Dimension
(UED) model from Cosmic Microwave Background (CMB) and Type Ia supernovae (SNe
Ia) data are studied. In the UED model, where both the gravity and standard
model fields can propagate in the extra dimensions, the evolution of the extra
dimensional volume, the radion, induces variation of fundamental constants. We
discuss the effects of variation of the relevant constants in the context of
UED for CMB power spectrum and SNe Ia data. We then use the three-year WMAP
data to constrain the radion evolution at z \sim 1100, and the 2 \sigma
constraint on \dot{\rho} / \rho_0 (\rho is a function of the radion, to be
defined in the text) is [ -8.8, 6.6] \times 10 ^{-13} yr^-1. The SNe Ia gold
sample yields a constraint on \dot{\rho} / \rho_0, for redshift between 0 and
1, to be [-4.7, 14] \times 10^{-13} yr^-1. Furthermore, the constraints from
SNe Ia can be interpreted as bounds on the evolution QCD scale parameter,
\dot{\Lambda}_{QCD} / \Lambda_{QCD, 0}, [-1.4, 2.8] \times 10^{-11} yr^-1,
without reference to the UED model.Comment: 8 pages, 3 figures, comments added, to appear in Phys. Rev.
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