3,533 research outputs found
Effects of simplifying assumptions on optimal trajectory estimation for a high-performance aircraft
When analyzing the performance of an aircraft, certain simplifying assumptions, which decrease the complexity of the problem, can often be made. The degree of accuracy required in the solution may determine the extent to which these simplifying assumptions are incorporated. A complex model may yield more accurate results if it describes the real situation more thoroughly. However, a complex model usually involves more computation time, makes the analysis more difficult, and often requires more information to do the analysis. Therefore, to choose the simplifying assumptions intelligently, it is important to know what effects the assumptions may have on the calculated performance of a vehicle. Several simplifying assumptions are examined, the effects of simplified models to those of the more complex ones are compared, and conclusions are drawn about the impact of these assumptions on flight envelope generation and optimal trajectory calculation. Models which affect an aircraft are analyzed, but the implications of simplifying the model of the aircraft itself are not studied. The examples are atmospheric models, gravitational models, different models for equations of motion, and constraint conditions
A Uniform Description of the States Recently Observed at B-factories
The newly found states Y(4260), Y(4361), Y(4664) and Z(4430) stir broad
interest in the study of spectroscopy in a typical charmonium scale. The
Y(4260) which was observed earlier has been interpreted as hybrid, molecular
state, and baryonium, etc. In this note we show for the first time that these
new structures, which are hard to be interpreted as charmonium states, can be
systematically embedded into an extended baryonium picture. According to this
assignment, the so far known characters of these states are understandable.
And, in the same framework, we make some predictions for experimenters to
measure in the future.Comment: 6 pages in Latex. to appear in J.Phys.
Precision Flavour Physics with and
We show that a combined analysis of and
allows for new physics tests practically free of form factor uncertainties.
Residual theory errors are at the level of several percent. Our study
underlines the excellent motivation for measuring these modes at a Super
Flavour Factory.Comment: 26 pages, 2 figure
Partial waves of baryon-antibaryon in three-body B meson decay
The conspicuous threshold enhancement has been observed in the
baryon-antibaryon subchannels of many three-body B decay modes. By examining
the partial waves of baryon-antibaryon, we first show for B- -->pp-bar K- that
the pK- angular correlation rules out dominance of a single pp-bar partial wave
for the enhancement, for instance, the resonance hypothesis or the strong
final-state interaction in a single channel. The measured pK- angular
correlation turns out to be opposite to the naive expectation of the
short-distance picture. We study the origin of this reversed angular
correlation in the context of the pp-bar partial waves and argue that NN-bar
bound states may be the cause of this sign reversal. Dependence of the angular
correlation on the pp-bar invariant mass is very important to probe the
underlying problem from the experimental side.Comment: 16 pages, 9 figures, the version for journal publicatio
How Resonances can synchronise with Thresholds
The mechanism by which a threshold may capture a resonance is examined. It
involves a threshold cusp interfering constructively with either or both (i) a
resonance produced via confinement, (ii) attractive t- and u-channel exchanges.
The fo(980), X(3872) and Z(4430) are studied in detail. The fo(980) provides a
valuable model of the locking mechanism. The X(3872) is too narrow to be fitted
by a cusp, and requires either a resonance or virtual state. The Z(4430) can be
fitted as a resonance but also can be fitted successfully by a cusp with no
nearby resonant pole.Comment: 19 pages, 6 figures. Replaces 0709.125
A NASA/RAE cooperation in the development of a real-time knowledge-based autopilot
As part of a US/UK cooperative aeronautical research program, a joint activity between the NASA Dryden Flight Research Facility and the Royal Aerospace Establishment on knowledge-based systems was established. This joint activity is concerned with tools and techniques for the implementation and validation of real-time knowledge-based systems. The proposed next stage of this research is described, in which some of the problems of implementing and validating a knowledge-based autopilot for a generic high-performance aircraft are investigated
Quenched lattice calculation of semileptonic heavy-light meson form factors
We calculate, in the continuum limit of quenched lattice QCD, the matrix
elements of the heavy-heavy vector current between heavy-light pseudoscalar
meson states. We present the form factors for different values of the initial
and final meson masses at finite momentum transfer. In particular, we calculate
the non-perturbative correction to the differential decay rate of the process B
--> D l nu including the case of a non-vanishing lepton mass.Comment: 16 pages, 10 figures, version accepted for publication on JHE
Spitzer 24-micron Time-Series Observations of the Eclipsing M-dwarf Binary GU Bootis
We present a set of {\it Spitzer} 24m MIPS time series observations of
the M-dwarf eclipsing binary star GU Bo\"otis. Our data cover three secondary
eclipses of the system: two consecutive events and an additional eclipse six
weeks later. The study's main purpose is the long wavelength (and thus limb
darkening-independent) characterization of GU Boo's light curve, allowing for
independent verification of the results of previous optical studies. Our
results confirm previously obtained system parameters. We further compare GU
Boo's measured 24m flux density to the value predicted by spectral fitting
and find no evidence for circumstellar dust. In addition to GU Boo, we
characterize (and show examples of) light curves of other objects in the field
of view. Analysis of these light curves serves to characterize the photometric
stability and repeatability of {\it Spitzer's} MIPS 24\micron array over short
(days) and long (weeks) timescales at flux densities between approximately
300--2,000Jy. We find that the light curve root mean square about the
median level falls into the 1--4% range for flux densities higher than 1mJy.
Finally, we comment on the fluctuations of the 24\micron background on short
and long timescales.Comment: ApJ accepted. 10 pages, 12 figure
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