20,910 research outputs found
Directions in propulsion control
The research needs in the area of propulsion control as driven by trends in advanced aircraft are considered. Ongoing propulsion control research at NASA Lewis is discussed. Special emphasis is made on research to improve control system reliability through the use of analytical redundancy to accommodate failed control sensors. In conclusion, a discussion of new research thrusts in the area of supersonic STOVL integrated control and intelligent system control is presented
Directions in propulsion control
Discussed here is research at NASA Lewis in the area of propulsion controls as driven by trends in advanced aircraft. The objective of the Lewis program is to develop the technology for advanced reliable propulsion control systems and to integrate the propulsion control with the flight control for optimal full-system control
Scaling of Power Corrections for Angularities from Dressed Gluon Exponentiation
We study power corrections to a recently introduced family of event shapes,
the class of angularities, within the formalism of dressed gluon exponentiation
(DGE). We find that the universal scaling rule for the leading power
corrections deduced from resummation also holds when taking renormalon
enhancements into account. The scaling is due to boost invariance of eikonal
dynamics in the two-jet limit, which we recover in the context of DGE.
Furthermore, dressed gluon exponentiation provides an ansatz for non-leading
power corrections that violate the scaling. These non-leading corrections are
further suppressed by non-integer powers of the hard scale.Comment: 24 page
Symbolic reduction of block diagrams using FORMAC
Two computer programs - one written in FORMAC to generate the desired symbolic expressions, the other in FORTRAN 4 to numerically evaluate the expressions are announced. The FORTRAN program accepts the symbolic punched output from the FORMAC program in either unexpanded or expanded form. It numerically evaluates the expressions
B -> X_d gamma and constraints on new physics
We combine recent progress in measuring the branching ratio of the decay
B->X_d gamma$ with the discovery that hadronic uncertainties in the CP-averaged
branching ratio drop out to a large extent. Implications of these improvements
on the size of possible new physics effects are investigated. We find the
updated SM prediction for the CP-averaged branching ratio to be Br[B->X_d
gamma]^SM_E_gamma>1.6 GeV = 1.54^+0.26-0.31*10^-5, which should be compared
with the experimental value of Br[B->X_d gamma]^exp_E_gamma>1.6GeV =
(1.41+-0.57) 10^-5. After performing a model independent analysis, we consider
different new physics models: the MSSM with generic sources of flavor
violation, the two Higgs doublet model of type III and a model with
right-handed charged currents. It is found that the constraints on the SUSY
parameters delta^d_13 have improved and that the absolute value of the
right-handed quark mixing matrix element |V^R_td| must be smaller than
1.5*10^-4.Comment: 5 pages, 3 figures, experimental value for b->d+gamma corrected,
version accepted for publication in PR
Real-time growth rate for general stochastic SIR epidemics on unclustered networks
Networks have become an important tool for infectious disease epidemiology.
Most previous theoretical studies of transmission network models have either
considered simple Markovian dynamics at the individual level, or have focused
on the invasion threshold and final outcome of the epidemic. Here, we provide a
general theory for early real-time behaviour of epidemics on large
configuration model networks (i.e. static and locally unclustered), in
particular focusing on the computation of the Malthusian parameter that
describes the early exponential epidemic growth. Analytical, numerical and
Monte-Carlo methods under a wide variety of Markovian and non-Markovian
assumptions about the infectivity profile are presented. Numerous examples
provide explicit quantification of the impact of the network structure on the
temporal dynamics of the spread of infection and provide a benchmark for
validating results of large scale simulations.Comment: 45 pages, 8 figures, submitted to Mathematical Biosciences on
29/11/2014; Version 2: resubmitted on 15/04/2015; accepted on 17/04/2015.
Changes: better explanations in introduction; restructured section 3.3 (3.3.3
added); section 6.3.1 added; more precise terminology; typos correcte
The impact of tidal errors on the determination of the Lense-Thirring effect from satellite laser ranging
The general relativistic Lense-Thirring effect can be detected by means of a
suitable combination of orbital residuals of the laser-ranged LAGEOS and LAGEOS
II satellites. While this observable is not affected by the orbital
perturbation induced by the zonal Earth solid and ocean tides, it is sensitive
to those generated by the tesseral and sectorial tides. The assessment of their
influence on the measurement of the parameter mu, with which the
gravitomagnetic effect is accounted for, is the goal of this paper. After
simulating the combined residual curve by calculating accurately the
mismodeling of the more effective tidal perturbations, it has been found that,
while the solid tides affect the recovery of mu at a level always well below
1%, for the ocean tides and the other long-period signals Delta mu depends
strongly on the observational period and the noise level: Delta mu(tides)
amounts to almost 2% after 7 years. The aliasing effect of K1 l=3 p=1 tide and
SRP(4241) solar radiation pressure harmonic, with periods longer than 4 years,
on the perigee of LAGEOS II yield to a maximum systematic uncertainty on
\m_{LT} of less than 4% over different observational periods. The zonal
18.6-year tide does not affect the combined residuals.Comment: 24 pages, 4 tables, 6 figures, submitted to Int. Journal of Mod.
Phys. D. Changes in auctorship, references and conten
Energy-state formulation of lumped volume dynamic equations with application to a simplified free piston Stirling engine
Lumped volume dynamic equations are derived using an energy state formulation. This technique requires that kinetic and potential energy state functions be written for the physical system being investigated. To account for losses in the system, a Rayleigh dissipation function is formed. Using these functions, a Lagrangian is formed and using Lagrange's equation, the equations of motion for the system are derived. The results of the application of this technique to a lumped volume are used to derive a model for the free piston Stirling engine. The model was simplified and programmed on an analog computer. Results are given comparing the model response with experimental data
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