1,034 research outputs found
Flight Tests of Various Tail Modifications on the Brewster XSBA-1 Airplane II : Measurements of Flying Qualities with Tail Configuration Number Two
Several tail modifications of the Brewster XSBA-1 scout-bomber were investigated and results compared. Modifications consisted of variation of the chord of the elevator and rudder while the total area of the surfaces is kept constant and variations of the total area of the vertical tail surface. Configuration number 2 reduced trim changes by 50 percent and reduced average elevator control force gradient from 30 to 27 pounds/g. Stick travel required to stall in maneuver was 4.6 inches
Signature of small rings in the Raman spectra of normal and compressed amorphous silica: A combined classical and ab initio study
We calculate the parallel (VV) and perpendicular (VH) polarized Raman spectra
of amorphous silica. Model SiO2 glasses, uncompressed and compressed, were
generated by a combination of classical and ab initio molecular-dynamics
simulations and their dynamical matrices were computed within the framework of
the density functional theory. The Raman scattering intensities were determined
using the bond-polarizability model and a good agreement with experimental
spectra was found. We confirm that the modes associated to the fourfold and
threefold rings produce most of the Raman intensity of the D1 and D2 peaks,
respectively, in the VV Raman spectra. Modifications of the Raman spectra upon
compression are found to be in agreement with experimental data. We show that
the modes associated to the fourfold rings still exist upon compression but do
not produce a strong Raman intensity, whereas the ones associated to the
threefold rings do. This result strongly suggests that the area under the D1
and D2 peaks is not directly proportional to the concentration of small rings
in amorphous SiO2.Comment: 21 pages, 8 figures. Phys. Rev. B, in pres
Urinary peptides as a novel source of T Cell allergen epitopes
Mouse allergy in both laboratory workers and in inner-city children is associated with allergic rhinitis and asthma, posing a serious public health concern. Urine is a major source of mouse allergens, as mice spray urine onto their surroundings, where the proteins dry up and become airborne on dust particles. Here, we tested whether oligopeptides that are abundant in mouse urine may contribute to mouse allergic T cell response. Over 1,300 distinct oligopeptides were detected by mass spectrometry analysis of the low molecular weight filtrate fraction of mouse urine (LoMo). Posttranslationally modified peptides were common, accounting for almost half of total peptides. A pool consisting of 225 unique oligopeptides of 13 residues or more in size identified within was tested for its capacity to elicit T cell reactivity in mouse allergic donors. Following 14-day in vitro stimulation of PBMCs, we detected responses in about 95% of donors tested, directed against 116 distinct peptides, predominantly associated with Th2 cytokines (IL-5). Peptides from non-urine related proteins such as epidermal growth factor, collagen, and Beta-globin accounted for the highest response (15.9, 9.1, and 8.1% of the total response, respectively). Peptides derived from major urinary proteins (MUPs), kidney androgen-regulated protein (KAP), and uromodulin were the main T cell targets from kidney or urine related sources. Further ex vivo analysis of enrichment of 4-1BB expressing cells demonstrated that LoMo pool-specific T cell reactivity can be detected directly ex vivo in mouse allergic but not in non-allergic donors. Further cytometric analysis of responding cells revealed a bone fide memory T cell phenotype and confirmed their Th2 polarization. Overall, these data suggest that mouse urine-derived oligopeptides are a novel target for mouse allergy-associated T cell responses, which may contribute to immunopathological mechanisms in mouse allergy
Long-distance quantum communication with "polarization" maximally entangled states
We propose a scheme for long-distance quantum communication where the
elementary entanglement is generated through two-photon interference and
quantum swapping is performed through one-photon interference. Local
"polarization" maximally entangled states of atomic ensembles are generated by
absorbing a single photon from on-demand single-photon sources. This scheme is
robust against phase fluctuations in the quantum channels, moreover speeds up
long-distance high-fidelity entanglement generation rate.Comment: 5 pages 5 figure
Reflection and Ducting of Gravity Waves Inside the Sun
Internal gravity waves excited by overshoot at the bottom of the convection
zone can be influenced by rotation and by the strong toroidal magnetic field
that is likely to be present in the solar tachocline. Using a simple Cartesian
model, we show how waves with a vertical component of propagation can be
reflected when traveling through a layer containing a horizontal magnetic field
with a strength that varies with depth. This interaction can prevent a portion
of the downward-traveling wave energy flux from reaching the deep solar
interior. If a highly reflecting magnetized layer is located some distance
below the convection zone base, a duct or wave guide can be set up, wherein
vertical propagation is restricted by successive reflections at the upper and
lower boundaries. The presence of both upward- and downward-traveling
disturbances inside the duct leads to the existence of a set of horizontally
propagating modes that have significantly enhanced amplitudes. We point out
that the helical structure of these waves makes them capable of generating an
alpha-effect, and briefly consider the possibility that propagation in a shear
of sufficient strength could lead to instability, the result of wave growth due
to over-reflection.Comment: 23 pages, 5 figures. Accepted for publication in Solar Physic
Energy landscape, two-level systems and entropy barriers in Lennard-Jones clusters
We develop an efficient numerical algorithm for the identification of a large
number of saddle points of the potential energy function of Lennard- Jones
clusters. Knowledge of the saddle points allows us to find many thousand
adjacent minima of clusters containing up to 80 argon atoms and to locate many
pairs of minima with the right characteristics to form two-level systems (TLS).
The true TLS are singled out by calculating the ground-state tunneling
splitting. The entropic contribution to all barriers is evaluated and
discussed.Comment: 4 pages, RevTex, 2 PostScript figure
Inhibiting decoherence via ancilla processes
General conditions are derived for preventing the decoherence of a single
two-state quantum system (qubit) in a thermal bath. The employed auxiliary
systems required for this purpose are merely assumed to be weak for the general
condition while various examples such as extra qubits and extra classical
fields are studied for applications in quantum information processing. The
general condition is confirmed with well known approaches towards inhibiting
decoherence. A novel approach for decoherence-free quantum memories and quantum
operations is presented by placing the qubit into the center of a sphere with
extra qubits on its surface.Comment: pages 8, Revtex
Structural and doping effects in the half-metallic double perovskite CrWO
he structural, transport, magnetic and optical properties of the double
perovskite CrWO with have been studied. By
varying the alkaline earth ion on the site, the influence of steric effects
on the Curie temperature and the saturation magnetization has been
determined. A maximum K was found for SrCrWO having an almost
undistorted perovskite structure with a tolerance factor . For
CaCrWO and BaCrWO structural changes result in a strong
reduction of . Our study strongly suggests that for the double perovskites
in general an optimum is achieved only for , that is, for an
undistorted perovskite structure. Electron doping in SrCrWO by a
partial substitution of Sr by La was found to reduce both
and the saturation magnetization . The reduction of could be
attributed both to band structure effects and the Cr/W antisites induced by
doping. Band structure calculations for SrCrWO predict an energy gap in
the spin-up band, but a finite density of states for the spin-down band. The
predictions of the band structure calculation are consistent with our optical
measurements. Our experimental results support the presence of a kinetic energy
driven mechanism in CrWO, where ferromagnetism is stabilized by a
hybridization of states of the nonmagnetic W-site positioned in between the
high spin Cr-sites.Comment: 14 pages, 10 figure
Is cosmology consistent?
We perform a detailed analysis of the latest CMB measurements (including
BOOMERaNG, DASI, Maxima and CBI), both alone and jointly with other
cosmological data sets involving, e.g., galaxy clustering and the Lyman Alpha
Forest. We first address the question of whether the CMB data are internally
consistent once calibration and beam uncertainties are taken into account,
performing a series of statistical tests. With a few minor caveats, our answer
is yes, and we compress all data into a single set of 24 bandpowers with
associated covariance matrix and window functions. We then compute joint
constraints on the 11 parameters of the ``standard'' adiabatic inflationary
cosmological model. Out best fit model passes a series of physical consistency
checks and agrees with essentially all currently available cosmological data.
In addition to sharp constraints on the cosmic matter budget in good agreement
with those of the BOOMERaNG, DASI and Maxima teams, we obtain a heaviest
neutrino mass range 0.04-4.2 eV and the sharpest constraints to date on gravity
waves which (together with preference for a slight red-tilt) favors
``small-field'' inflation models.Comment: Replaced to match accepted PRD version. 14 pages, 12 figs. Tiny
changes due to smaller DASI & Maxima calibration errors. Expanded neutrino
and tensor discussion, added refs, typos fixed. Combined CMB data, window and
covariance matrix at http://www.hep.upenn.edu/~max/consistent.html or from
[email protected]
The Planetary Nebula Luminosity Function at the Dawn of Gaia
The [O III] 5007 Planetary Nebula Luminosity Function (PNLF) is an excellent
extragalactic standard candle. In theory, the PNLF method should not work at
all, since the luminosities of the brightest planetary nebulae (PNe) should be
highly sensitive to the age of their host stellar population. Yet the method
appears robust, as it consistently produces < 10% distances to galaxies of all
Hubble types, from the earliest ellipticals to the latest-type spirals and
irregulars. It is therefore uniquely suited for cross-checking the results of
other techniques and finding small offsets between the Population I and
Population II distance ladders. We review the calibration of the method and
show that the zero points provided by Cepheids and the Tip of the Red Giant
Branch are in excellent agreement. We then compare the results of the PNLF with
those from Surface Brightness Fluctuation measurements, and show that, although
both techniques agree in a relative sense, the latter method yields distances
that are ~15% larger than those from the PNLF. We trace this discrepancy back
to the calibration galaxies and argue that, due to a small systematic error
associated with internal reddening, the true distance scale likely falls
between the extremes of the two methods. We also demonstrate how PNLF
measurements in the early-type galaxies that have hosted Type Ia supernovae can
help calibrate the SN Ia maximum magnitude-rate of decline relation. Finally,
we discuss how the results from space missions such as Kepler and Gaia can help
our understanding of the PNLF phenomenon and improve our knowledge of the
physics of local planetary nebulae.Comment: 12 pages, invited review at the conference "The Fundamental Cosmic
Distance Scale: State of the Art and Gaia Perspective", to appear in
Astrophysics and Space Scienc
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