772 research outputs found
The design development and evaluation of an active control aircraft model wind tunnel facility.
Recent progress in the field of Active Controls Technology(ACT) has resulted in increased interest in dynamic wind tunnel testing for basic research. The present work reports the
findings of a three year research and development programme to build a dynamic wind tunnel testing facility. The task included the design and construction of a controllable
dynamically scaled aircraft model, a suspension system to give the model four degrees of freedom, and an electronic control unit to interface with the model for operating the
primary controls, for stability augmentation and for providing output signals for measurement purposes.
The dynamic characteristics of the model have been recorded for some simulated representative flight conditions and are compared with theoretical predictions and the expected characteristics derived from full size aircraft data. The use of various stability augmentation functions has also been investigated to assess the usefulness of the
electronic control unit as a means for providing stability augmentation. The results show the system to have considerable potential as an ACT Simulator. Modifications are suggested for further development of the facility to achieve a higher degree of accuracy and versatility
End of Life Care and Do Not Resuscitate Orders: How Much Does Age Influence Decision Making? A Systematic Review and Meta-analysis
With population aging, “do not resuscitate” (DNAR) decisions, pertaining to the appropriateness of attempting
resuscitation following a cardiac arrest, are becoming commoner. It is unclear from the literature whether using age
to make these decisions represents “ageism.” We undertook a systematic review of the literature using CINAHL,
Medline, and the Cochrane database to investigate the relationship between age and DNAR. All 10 studies fulfilling
our inclusion criteria found that “do not attempt resuscitation” orders were more prevalent in older patients; eight
demonstrated that this was independent of other mediating factors such as illness severity and likely outcome. In
studies comparing age groups, the adjusted odds of having a DNAR order were greater in patients aged 75 to 84
and ≥85 years (adjusted odds ratio [AOR] 1.70, 95% confidence interval [CI] = [1.25, 2.33] and 2.96, 95% CI = [2.34,
3.74], respectively), compared with those <65 years. In studies treating age as a continuous variable, there was no
significant increase in the use of DNAR with age (AOR 0.98, 95% CI = [0.84, 1.15]). In conclusion, age increases the
use of “do not resuscitate” orders, but more research is needed to determine whether this represents “ageism.
Gauges and Cosmological Backreaction
We present a formalism for spatial averaging in cosmology applicable to
general spacetimes and coordinates, and allowing the easy incorporation of a
wide variety of matter sources. We apply this formalism to a
Friedmann-LeMaitre-Robertson-Walker universe perturbed to second-order and
present the corrections to the background in an unfixed gauge. We then present
the corrections that arise in uniform curvature and conformal Newtonian gauges.Comment: 13 pages. Updated: reference added, typos corrected, exposition
clarified. Version 3: Replaced with version published by JCA
Calculation of magnetic anisotropy energy in SmCo5
SmCo5 is an important hard magnetic material, due to its large magnetic
anisotropy energy (MAE). We have studied the magnetic properties of SmCo5 using
density functional theory (DFT) calculations where the Sm f-bands, which are
difficult to include in DFT calculations, have been treated within the LDA+U
formalism. The large MAE comes mostly from the Sm f-shell anisotropy, stemming
from an interplay between the crystal field and the spin-orbit coupling. We
found that both are of similar strengths, unlike some other Sm compounds,
leading to a partial quenching of the orbital moment (f-states cannot be
described as either pure lattice harmonics or pure complex harmonics), an
optimal situation for enhanced MAE. A smaller portion of the MAE can be
associated with the Co-d band anisotropy, related to the peak in the density of
states at the Fermi energy. Our result for the MAE of SmCo5, 21.6 meV/f.u.,
agrees reasonably with the experimental value of 13-16 meV/f.u., and the
calculated magnetic moment (including the orbital component) of 9.4 mu_B agrees
with the experimental value of 8.9 mu_B.Comment: Submitted to Phys. Rev.
Effects of non-linearities on magnetic field generation
Magnetic fields are present on all scales in the Universe. While we
understand the processes which amplify the fields fairly well, we do not have a
"natural" mechanism to generate the small initial seed fields. By using fully
relativistic cosmological perturbation theory and going beyond the usual
confines of linear theory we show analytically how magnetic fields are
generated. This is the first analytical calculation of the magnetic field at
second order, using gauge-invariant cosmological perturbation theory, and
including all the source terms. To this end, we have rederived the full set of
governing equations independently. Our results suggest that magnetic fields of
the order of G can be generated (although this depends on the small
scale cut-off of the integral), which is largely in agreement with previous
results that relied upon numerical calculations. These fields are likely too
small to act as the primordial seed fields for dynamo mechanisms.Comment: 21 pages; v2: minor changes, added references; v3: version accepted
for publication in JCA
Search for Higgs bosons decaying to tautau pairs in ppbar collisions at sqrt(s) = 1.96 TeV
We present a search for the production of neutral Higgs bosons decaying into
tautau pairs in ppbar collisions at a center-of-mass energy of 1.96 TeV. The
data, corresponding to an integrated luminosity of 5.4 fb-1, were collected by
the D0 experiment at the Fermilab Tevatron Collider. We set upper limits at the
95% C.L. on the product of production cross section and branching ratio for a
scalar resonance decaying into tautau pairs, and we then interpret these limits
as limits on the production of Higgs bosons in the minimal supersymmetric
standard model (MSSM) and as constraints in the MSSM parameter space.Comment: 7 pages, 5 figures, submitted to PL
Measurement of the photon-jet production differential cross section in collisions at \sqrt{s}=1.96~\TeV
We present measurements of the differential cross section dsigma/dpT_gamma
for the inclusive production of a photon in association with a b-quark jet for
photons with rapidities |y_gamma|< 1.0 and 30<pT_gamma <300 GeV, as well as for
photons with 1.5<|y_gamma|< 2.5 and 30< pT_gamma <200 GeV, where pT_gamma is
the photon transverse momentum. The b-quark jets are required to have pT>15 GeV
and rapidity |y_jet| < 1.5. The results are based on data corresponding to an
integrated luminosity of 8.7 fb^-1, recorded with the D0 detector at the
Fermilab Tevatron Collider at sqrt(s)=1.96 TeV. The measured cross
sections are compared with next-to-leading order perturbative QCD calculations
using different sets of parton distribution functions as well as to predictions
based on the kT-factorization QCD approach, and those from the Sherpa and
Pythia Monte Carlo event generators.Comment: 10 pages, 9 figures, submitted to Phys. Lett.
Limits on anomalous trilinear gauge boson couplings from WW, WZ and Wgamma production in pp-bar collisions at sqrt{s}=1.96 TeV
We present final searches of the anomalous gammaWW and ZWW trilinear gauge
boson couplings from WW and WZ production using lepton plus dijet final states
and a combination with results from Wgamma, WW, and WZ production with leptonic
final states. The analyzed data correspond to up to 8.6/fb of integrated
luminosity collected by the D0 detector in pp-bar collisions at sqrt{s}=1.96
TeV. We set the most stringent limits at a hadron collider to date assuming two
different relations between the anomalous coupling parameters
Delta\kappa_\gamma, lambda, and Delta g_1^Z for a cutoff energy scale Lambda=2
TeV. The combined 68% C.L. limits are -0.057<Delta\kappa_\gamma<0.154,
-0.015<lambda<0.028, and -0.008<Delta g_1^Z<0.054 for the LEP parameterization,
and -0.007<Delta\kappa<0.081 and -0.017<lambda<0.028 for the equal couplings
parameterization. We also present the most stringent limits of the W boson
magnetic dipole and electric quadrupole moments.Comment: 10 pages, 5 figures, submitted to PL
Measurement of three-jet differential cross sections d sigma-3jet / d M-3jet in p anti-p collisions at sqrt(s)=1.96 TeV
We present the first measurement of the inclusive three-jet differential
cross section as a function of the invariant mass of the three jets with the
largest transverse momenta in an event in p anti-p collisions at sqrt(s) = 1.96
TeV. The measurement is made in different rapidity regions and for different
jet transverse momentum requirements and is based on a data set corresponding
to an integrated luminosity of 0.7 fb^{-1} collected with the D0 detector at
the Fermilab Tevatron Collider. The results are used to test the three-jet
matrix elements in perturbative QCD calculations at next-to-leading order in
the strong coupling constant. The data allow discrimination between
parametrizations of the parton distribution functions of the proton.Comment: 10 pages, 4 figures, 2 tables, submitted to Phys. Lett. B, corrected
chi2 values for NNPD
Search for pair production of the scalar top quark in muon+tau final states
We present a search for the pair production of scalar top quarks
(), the lightest supersymmetric partners of the top quarks, in
collisions at a center-of-mass energy of 1.96 TeV, using data
corresponding to an integrated luminosity of {7.3 } collected with the
\dzero experiment at the Fermilab Tevatron Collider. Each scalar top quark is
assumed to decay into a quark, a charged lepton, and a scalar neutrino
(). We investigate final states arising from and
. With no significant excess of events observed above the
background expected from the standard model, we set exclusion limits on this
production process in the (,) plane.Comment: Submitted to Phys. Lett.
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