2,596 research outputs found
Investigation of nose bluntness and angle of attack effects on slender bodies in viscous hypersonic flows
Hypersonic flows over cones and straight biconic configurations are calculated for a wide range of free stream conditions in which the gas behind the shock is treated as perfect. Effect of angle of attack and nose bluntness on these slender cones in air is studied extensively. The numerical procedures are based on the solution of complete Navier-Stokes equations at the nose section and parabolized Navier-Stokes equations further downstream. The flow field variables and surface quantities show significant differences when the angle of attack and nose bluntness are varied. The complete flow field is thoroughly analyzed with respect to velocity, temperature, pressure, and entropy profiles. The post shock flow field is studied in detail from the contour plots of Mach number, density, pressure, and temperature. The effect of nose bluntness for slender cones persists as far as 200 nose radii downstream
Glueball Spin
The spin of a glueball is usually taken as coming from the spin (and possibly
the orbital angular momentum) of its constituent gluons. In light of the
difficulties in accounting for the spin of the proton from its constituent
quarks, the spin of glueballs is reexamined. The starting point is the
fundamental QCD field angular momentum operator written in terms of the
chromoelectric and chromomagnetic fields. First, we look at the restrictions
placed on the structure of glueballs from the requirement that the QCD field
angular momentum operator should satisfy the standard commutation
relationships. This can be compared to the electromagnetic charge/monopole
system, where the quantization of the field angular momentum places
restrictions (i.e. the Dirac condition) on the system. Second, we look at the
expectation value of this operator under some simplifying assumptions.Comment: 11 pages, 0 figures; added references and some discussio
CMB Lensing Power Spectrum Biases from Galaxies and Clusters using High-angular Resolution Temperature Maps
The lensing power spectrum from cosmic microwave background (CMB) temperature
maps will be measured with unprecedented precision with upcoming experiments,
including upgrades to ACT and SPT. Achieving significant improvements in
cosmological parameter constraints, such as percent level errors on sigma_8 and
an uncertainty on the total neutrino mass of approximately 50 meV, requires
percent level measurements of the CMB lensing power. This necessitates tight
control of systematic biases. We study several types of biases to the
temperature-based lensing reconstruction signal from foreground sources such as
radio and infrared galaxies and the thermal Sunyaev-Zel'dovich effect from
galaxy clusters. These foregrounds bias the CMB lensing signal due to their
non-Gaussian nature. Using simulations as well as some analytical models we
find that these sources can substantially impact the measured signal if left
untreated. However, these biases can be brought to the percent level if one
masks galaxies with fluxes at 150 GHz above 1 mJy and galaxy clusters with
masses above M_vir = 10^14 M_sun. To achieve such percent level bias, we find
that only modes up to a maximum multipole of l_max ~ 2500 should be included in
the lensing reconstruction. We also discuss ways to minimize additional bias
induced by such aggressive foreground masking by, for example, exploring a
two-step masking and in-painting algorithm.Comment: 14 pages, 14 figures, to be submitted to Ap
Pitting in Aluminum Thin Films Supersaturation and Effects of Dichromate Ions
The growth of pits in 209 nm thick Al films in chloride solutions with and without dichromate ions was examined using image analysis of the growing pits to determine pit current density. In pure chloride solutions, the pit current density decreased at high potentials after reaching a maximum value, and then was almost independent of applied potential. A hysteresis in the pit current density-potential behavior was observed during downward stepping of the potential from high values. This is a result of a combination of supersaturation of the pit electrolyte followed by salt film formation, and changes in mass transport from hydrogen bubbles that increase convection and lift the remnant passive film away from the dissolving surface. In solutions containing dichromate ions, the corrosion and repassivation potentials shifted in the noble direction, and rather large metastable pits formed at the open circuit. A large concentration of dichromate ions was needed to inhibit pit growth. In dichromate solutions, subsequent pit growth at higher potentials often initiated at the edge of the open-circuit pits. The rate of pit growth was lower for these pits because the remnant passive film layer was not easily lifted up at these sites, and thus created a barrier for mass transport away from the dissolving pit edge.This work was supported by Major H. DeLong at the United States Air Force Office of Scientific Research under contract F49620-96-0042
Energy Spectra and Energy Correlations in the Decay
It is shown that in the sequential decay , the energy distribution of the final state particles provides
a simple and powerful test of the vertex. For a standard Higgs boson, the
energy spectrum of any final fermion, in the rest frame of , is predicted to
be , with
and . By contrast, the spectrum for a
pseudoscalar Higgs is . There are
characteristic energy correlations between and and between
and . These considerations are applied to the ``gold--plated''
reaction , including possible effects of
CP--violation in the coupling. Our formalism also yields the energy
spectra and correlations of leptons in the decay .Comment: 14 pages + 4 figure
T-odd correlations in charged Kl4 decays
We analyse the sensitivity to physics beyond the SM of T-odd correlations in
decays, which do not involve the lepton polarization. We show that
a combined analysis of and decays can lead to new
constraints about CP violation in charged-current interactions,
complementary to those obtained from the transverse muon polarization in
and of comparable accuracy.Comment: 6 pages (LaTeX
Effects of Chromate and Chromate Conversion Coatings on Corrosion of Aluminum Alloy 2024-T3
Various effects of chromate conversion coatings (CCCs) and chromate in solution on the corrosion of AA2024-T3 and pure Al are studied in this work. Raman spectroscopy was used to investigate the nature of chromate in CCCs through a comparison with the spectra of known standards and artificial Cr(III)/Cr(VI) mixed oxides. Chromate was shown to be released from CCCs and to migrate to and protect a nearby, uncoated area in the artificial scratch cell. However, experiments investigating the effect of chromate in solution on anodic dissolution kinetics under potentiostatic control indicated that large chromate concentrations were needed to have an effect.This work was supported by Major H. DeLong at the United States Air Force Office of Scientific Research under contracts F49620-96-1-0479 and F49620-96-0042
Azimuthal Correlation in Lepton-Hadron Scattering via Charged Weak-Current Processes
We consider the azimuthal correlation of the final-state particles in charged
weak-current processes. This correlation provides a test of perturbative
quantum chromodynamics. The azimuthal asymmetry is large in the semi-inclusive
processes in which we identify a final-state hadron, say, a charged pion
compared to that in the inclusive processes in which we do not identify
final-state particles and use only the calorimetric information. In
semi-inclusive processes the azimuthal asymmetry is more conspicuous when the
incident lepton is an antineutrino or a positron than when the incident lepton
is a neutrino or an electron. We analyze all the possible charged weak-current
processes and study the quantitative aspects of each process. We also compare
this result to the ep scattering with a photon exchange.Comment: 25 pages, 2 Postscript figures, uses RevTeX, fixes.st
On the observability of the neutrino charge radius
It is shown that the probe-independent charge radius of the neutrino is a
physical observable; as such, it may be extracted from experiment, at least in
principle. This is accomplished by expressing a set of experimental
neutrino-electron cross-sections in terms of the finite charge radius and two
additional gauge- and renormalization-group-invariant quantities, corresponding
to the electroweak effective charge and mixing angle.Comment: 10 pages, 1 figure; a typo in Eq.1 corrected, some comments adde
- …