7,113 research outputs found
Observation of the rare decay B+ -> K+π0π0 and measurement of the quasi-two-body contributions B+ -> K*(892)+π0, B+ -> f0(980)K+, and B+ -> χc0K+
We report an analysis of charmless hadronic decays of charged B mesons to the final state K(+) pi(0)pi(0), using a data sample of (470.9 +/- 2.8) x 10(6) B (B) over bar events collected with the BABAR detector at the Y(4S) resonance. We observe an excess of signal events, with a significance above 10 standard deviations including systematic uncertainties, and measure the branching fraction and CP asymmetry to be B(B(+) -> K(+) pi(0)pi(0)) = (16.2 +/- 1.2 +/- 1.5) x 10(-6) and A(CP)(B(+) -> K(+) pi(0)pi(0)) = -0.06 +/- 0.06 +/- 0.04, where the uncertainties are statistical and systematic, respectively. Additionally, we study the contributions of the B(+) -> K*(892)(+) pi(0), B(+) -> f(0)(980)K(+), and B(+) -> chi(c0)K(+) quasi-two-body decays. We report the world's best measurements of the branching fraction and CP asymmetry of the B(+) -> K(+) pi(0)pi(0) and B(+) -> K(+)(892)(+) pi(0) channels
Acoustic tests of duct-burning turbofan jet noise simulation
The results of a static acoustic and aerodynamic performance, model-scale test program on coannular unsuppressed and multielement fan suppressed nozzle configurations are summarized. The results of the static acoustic tests show a very beneficial interaction effect. When the measured noise levels were compared with the predicted noise levels of two independent but equivalent conical nozzle flow streams, noise reductions for the unsuppressed coannular nozzles were of the order of 10 PNdB; high levels of suppression (8 PNdB) were still maintained even when only a small amount of core stream flow was used. The multielement fan suppressed coannular nozzle tests showed 15 PNdB noise reductions and up to 18 PNdB noise reductions when a treated ejector was added. The static aerodynamic performance tests showed that the unsuppressed coannular plug nozzles obtained gross thrust coefficients of 0.972, with 1.2 to 1.7 percent lower levels for the multielement fan-suppressed coannular flow nozzles. For the first time anywhere, laser velocimeter velocity profile measurements were made on these types of nozzle configurations and with supersonic heated flow conditions. Measurements showed that a very rapid decay in the mean velocity occurs for the nozzle tested
Acoustic tests of duct-burning turbofan jet noise simulation: Comprehensive data report. Volume 2: Model design and aerodynamic test results
The selection procedure is described which was used to arrive at the configurations tested, and the performance characteristics of the test nozzles are given
A Dynamical Mass Constraint for Pre-Main-Sequence Evolutionary Tracks: The Binary NTT 045251+3016
We present an astrometric/spectroscopic orbital solution for the
pre-main-sequence binary NTT 045251+3016. Our measurements for the primary and
secondary masses are 1.45 +/- 0.19 M_sun and 0.81 +/- 0.09 M_sun, respectively,
and 145 +/- 8 pc for the distance of the system, consistent with prior
estimates for the Taurus-Auriga star-forming region. The evolutionary tracks of
D'Antona & Mazzitelli (1997), Baraffe et al. (1998), and Palla & Stahler (1999)
are tested against these dynamical mass measurements. Due to the intrinsic
color/T_eff variation within the K5 spectral class, each pre-main-sequence
model provides a mass range for the primary. The theoretical mass range derived
from the Baraffe et al. (1998) tracks that use a mixing length parameter
alpha=1.0 is closest to our measured primary mass, deviating between 1.3 and
1.6 sigma. The set of Baraffe et al. (1998) tracks that use alpha=1.9 deviate
between 1.6 and 2.1 sigma from our measured primary mass. The mass range given
by the Palla & Stahler (1999) tracks for the primary star deviate between 1.6
and 2.9 sigma. The D'Antona & Mazzitelli (1997) tracks give a mass range that
deviates by at least 3.0 sigma from our derived primary mass, strongly
suggesting that these tracks are inconsistent with our observation.
Observations of the secondary are less constraining than those of the primary,
but the deviations between the dynamical mass of the secondary and the mass
inferred for the secondary from the various pre-main-sequence tracks mirror the
deviations of the primary star. All of the pre-main-sequence tracks are
consistent with coevality of the components of NTT 045251+3016.Comment: 27 pages, 6 figures, 5 tables -- accepted by A
Observational Tests and Predictive Stellar Evolution II: Non-standard Models
We examine contributions of second order physical processes to results of
stellar evolution calculations amenable to direct observational testing. In the
first paper in the series (Young et al. 2001) we established baseline results
using only physics which are common to modern stellar evolution codes. In the
current paper we establish how much of the discrepancy between observations and
baseline models is due to particular elements of new physics. We then consider
the impact of the observational uncertainties on the maximum predictive
accuracy achievable by a stellar evolution code. The sun is an optimal case
because of the precise and abundant observations and the relative simplicity of
the underlying stellar physics. The Standard Model is capable of matching the
structure of the sun as determined by helioseismology and gross surface
observables to better than a percent. Given an initial mass and surface
composition within the observational errors, and no additional constraints for
which the models can be optimized, it is not possible to predict the sun's
current state to better than ~7%. Convectively induced mixing in radiative
regions, seen in multidimensional hydrodynamic simulations, dramatically
improves the predictions for radii, luminosity, and apsidal motions of
eclipsing binaries while simultaneously maintaining consistency with observed
light element depletion and turnoff ages in young clusters (Young et al. 2003).
Systematic errors in core size for models of massive binaries disappear with
more complete mixing physics, and acceptable fits are achieved for all of the
binaries without calibration of free parameters. The lack of accurate abundance
determinations for binaries is now the main obstacle to improving stellar
models using this type of test.Comment: 33 pages, 8 figures, accepted for publication in the Astrophysical
Journa
A comparative study of different integrate-and-fire neurons: spontaneous activity, dynamical response, and stimulus-induced correlation
Stochastic integrate-and-fire (IF) neuron models have found widespread
applications in computational neuroscience. Here we present results on the
white-noise-driven perfect, leaky, and quadratic IF models, focusing on the
spectral statistics (power spectra, cross spectra, and coherence functions) in
different dynamical regimes (noise-induced and tonic firing regimes with low or
moderate noise). We make the models comparable by tuning parameters such that
the mean value and the coefficient of variation of the interspike interval
match for all of them. We find that, under these conditions, the power spectrum
under white-noise stimulation is often very similar while the response
characteristics, described by the cross spectrum between a fraction of the
input noise and the output spike train, can differ drastically. We also
investigate how the spike trains of two neurons of the same kind (e.g. two
leaky IF neurons) correlate if they share a common noise input. We show that,
depending on the dynamical regime, either two quadratic IF models or two leaky
IFs are more strongly correlated. Our results suggest that, when choosing among
simple IF models for network simulations, the details of the model have a
strong effect on correlation and regularity of the output.Comment: 12 page
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