12,271 research outputs found
Measurement of temperature profiles in hot gases and flames
Computer program was written for calculation of molecular radiative transfer from hot gases. Shape of temperature profile was approximated in terms of simple geometric forms so profile could be characterized in terms of few parameters. Parameters were adjusted in calculations using appropriate radiative-transfer expression until best fit was obtained with observed spectra
Factorization of correlations in two-dimensional percolation on the plane and torus
Recently, Delfino and Viti have examined the factorization of the three-point
density correlation function P_3 at the percolation point in terms of the
two-point density correlation functions P_2. According to conformal invariance,
this factorization is exact on the infinite plane, such that the ratio R(z_1,
z_2, z_3) = P_3(z_1, z_2, z_3) [P_2(z_1, z_2) P_2(z_1, z_3) P_2(z_2,
z_3)]^{1/2} is not only universal but also a constant, independent of the z_i,
and in fact an operator product expansion (OPE) coefficient. Delfino and Viti
analytically calculate its value (1.022013...) for percolation, in agreement
with the numerical value 1.022 found previously in a study of R on the
conformally equivalent cylinder. In this paper we confirm the factorization on
the plane numerically using periodic lattices (tori) of very large size, which
locally approximate a plane. We also investigate the general behavior of R on
the torus, and find a minimum value of R approx. 1.0132 when the three points
are maximally separated. In addition, we present a simplified expression for R
on the plane as a function of the SLE parameter kappa.Comment: Small corrections (final version). In press, J. Phys.
Measurement of temperature profiles in hot gases by emission-absorption spectroscopy Final report
Measurement of spectral radiances and absorptances in hot gase
In-Plane Magnetolumnescence of Modulation-Doped GaAs/AlGaAs Coupled Double Quantum Wells
In-plane magnetic field photoluminescence spectra from a series of
GaAs/AlGaAs coupled double quantum wells show distinctive doublet structures
related to the symmetric and antisymmetric states. The magnetic field behavior
of the upper transition from the antisymmetric state strongly depends on sample
mobility. In lower mobility samples, the transition energy shows an -type kink with fields (namely a maximum followed by a minimum), whereas
higher mobility samples have a linear dependence. The former is due to a
homogeneous broadening of electron and hole states and the results are in good
agreement with theoretical calculations.Comment: 3 pages, 4 figures, submitted to Appl. Phys. Let
Modern and ancient hiatuses in the pelagic caps of Pacific guyots and seamounts and internal tides
Incidences of non-deposition or erosion at the modern seabed and hiatuses within the pelagic caps of guyots and seamounts are evaluated along with paleo-temperature and
physiographic information to speculate on the character of Late Cenozoic internal tidal waves in the upper Pacific Ocean. Drill core and seismic reflection data are used to
classify sediment at the drill sites as having been either accumulating or eroding/nondepositing in the recent geological past. When those classified sites are compared against predictions of a numerical model of the modern internal tidal wave field (Simmons, 2008), the sites accumulating particles over the past few million years are found to lie away from beams of the modeled internal tide, while those that have not been accumulating are in internal tide beams. Given the correspondence to the modern internal wave field, we examine whether internal tides can explain ancient hiatuses at the drill sites. For example, Late Cenozoic pelagic caps on guyots among the Marshall Islands contain two hiatuses of broadly similar age, but the dates of the first pelagic sediments deposited following each hiatus do not correlate between guyots, suggesting that they originate not from ocean chemical changes but from physical processes, such as erosion by internal tidal waves. We investigate how changing conditions such as ocean
temperature and basin physiography may have affected internal tides through the Cenozoic. Allowing for subsequent rotation or uplift by plate tectonics, ancient
submarine ridges among the Solomon, Bonin and Marianas Island chains may have been responsible for some sediment hiatuses at these distant guyot sites
Axigluons cannot explain the observed top quark forward-backward asymmetry
We study an SU(3)^2 axigluon model introduced by Frampton, Shu, and Wang to
explain the recent Fermilab Tevatron observation of a significant positive
enhancement in the top quark forward-backward asymmetry relative to standard
model predictions. First, we demonstrate that data on neutral B_d-meson mixing
excludes the region of model parameter space where the top asymmetry is
predicted to be the largest. Keeping the gauge couplings below the critical
value that would lead to fermion condensation imposes further limits at large
axigluon mass, while precision electroweak constraints on the model are
relatively mild. Furthermore, by considering an extension to an SU(3)^3 color
group, we demonstrate that embedding the model in an extra-dimensional
framework can only dilute the axigluon effect on the forward-backward
asymmetry. We conclude that axigluon models are unlikely to be the source of
the observed top quark asymmetry.Comment: 12 pages, 7 eps figures included. Minor changes to conform with
published versio
Single top or bottom production associated with a scalar in \gamma p collision as a probe of topcolor-assisted technicolor
In the framework of the topcolor-assisted technicolor (TC2) models, we study
the productions of a single top or bottom quark associated with a scalar in
\gamma-p collision, which proceed via the subprocesses c\gamma -> t\pi_t^0,
c\gamma -> t h_t^0 and c\gamma -> b\pi^+_t mediated by the anomalous top or
bottom coupling tc\pi_t^0, tch_t^0 and bc\pi_t^+. These productions, while
extremely suppressed in the Standard Model, are found to be significantly
enhanced in the large part of the TC2 parameter space, especially the
production via c\gamma -> b\pi^+ can have a cross section of 100 fb, which may
be accessible and allow for a test of the TC2 models.Comment: 13 pages, 4 figures, comments and references adde
Spin-dependent transport in molecular tunnel junctions
We present measurements of magnetic tunnel junctions made using a
self-assembled-monolayer molecular barrier. Ni/octanethiol/Ni samples were
fabricated in a nanopore geometry. The devices exhibit significant changes in
resistance as the angle between the magnetic moments in the two electrodes is
varied, demonstrating that low-energy electrons can traverse the molecular
barrier while maintaining spin coherence. An analysis of the voltage and
temperature dependence of the data suggests that the spin-coherent transport
signals can be degraded by localized states in the molecular barriers.Comment: 4 pages, 5 color figure
Coulomb Driven New Bound States at the Integer Quantum Hall States in GaAs/Al(0.3)Ga(0.7)As Single Heterojunctions
Coulomb driven, magneto-optically induced electron and hole bound states from
a series of heavily doped GaAs/Al(0.3)Ga(0.7)As single heterojunctions (SHJ)
are revealed in high magnetic fields. At low magnetic fields (nu > 2), the
photoluminescence spectra display Shubnikov de-Haas type oscillations
associated with the empty second subband transition. In the regime of the
Landau filling factor nu < 1 and 1 < nu <2, we found strong bound states due to
Mott type localizations. Since a SHJ has an open valence band structure, these
bound states are a unique property of the dynamic movement of the valence holes
in strong magnetic fields
- …