2,661 research outputs found
On the Estimation of Euler Equations in the Presence of a Potential Regime Shift
The concept of a peso problem is formalized in terms of a linear Euler equation and a nonlinear marginal model describing the dynamics of the exogenous driving process. It is shown that, using a threshold autoregressive model as a marginal model, it is possible to produce time-varying peso premia. A Monte Carlo method and a method based on the numerical solution of integral equations are considered as tools for computing conditional future expectations in the marginal model. A Monte Carlo study illustrates the poor performance of the generalized method of moment (GMM) estimator in small and even relatively large samples. The poor performance is particularly acute in the presence of a peso problem but is also serious in the simple linear case.peso problem; Euler equations; GMM; threshold autoregressive models
Perpendicular bladeâvortex-interaction over an oscillating airfoil in light dynamic stall
An experimental and numerical study was performed to investigate the effects of perpendicular blade vortex interactions on the aerodynamic performance of an oscillating airfoil. The selected test cases studied the aerodynamic interaction of a stream-wise vortex impacting on a NACA 23012 airfoil oscillating in light dynamic stall regime, representing a typical condition of the retreating blade of a helicopter in forward flight. The analysis of particle image velocimetry surveys and time-accurate simulation results enabled to point out the different effects due to the blade pitching motion on the interacting flow field. Thus, numerical results enabled to achieve a detailed insight about the aerodynamic loads acting on the oscillating airfoil in the interacting cases. In particular, the comparison with the clean airfoil case shows that a severe loss of performance is produced by the interaction of the vortex during the airfoil downstroke motion, as the vortex impact triggers the local stall of the blade section
Improved Smoothing Algorithms for Lattice Gauge Theory
The relative smoothing rates of various gauge field smoothing algorithms are
investigated on -improved \suthree Yang--Mills gauge field
configurations. In particular, an -improved version of APE
smearing is motivated by considerations of smeared link projection and cooling.
The extent to which the established benefits of improved cooling carry over to
improved smearing is critically examined. We consider representative gauge
field configurations generated with an -improved gauge field
action on \1 lattices at and \2 lattices at
having lattice spacings of 0.165(2) fm and 0.077(1) fm respectively. While the
merits of improved algorithms are clearly displayed for the coarse lattice
spacing, the fine lattice results put the various algorithms on a more equal
footing and allow a quantitative calibration of the smoothing rates for the
various algorithms. We find the relative rate of variation in the action may be
succinctly described in terms of simple calibration formulae which accurately
describe the relative smoothness of the gauge field configurations at a
microscopic level
Light-Quark FLIC Fermion Simulations of the Exotic Meson
We investigate the mass of the exotic meson, created with hybrid
interpolating fields. Access to light quark masses approaching 25 MeV is
facilitated by the use of the Fat-Link Irrelevant Clover (FLIC) fermion action,
and large () lattices. Our results indicate that the
exotic exhibits significant curvature close to the chiral limit, and yield a
mass in agreement with the candidate and exclusive of
the .Comment: 6 pages, 1 table, 2 figures, talk given at Lattice '05. Removed
unccessary figure
The electric dipole moment of the nucleon from simulations at imaginary vacuum angle theta
We compute the electric dipole moment of proton and neutron from lattice QCD
simulations with N_f=2 flavors of dynamical quarks at imaginary vacuum angle
theta. The calculation proceeds via the CP odd form factor F_3. A novel feature
of our calculation is that we use partially twisted boundary conditions to
extract F_3 at zero momentum transfer. As a byproduct, we test the QCD vacuum
at nonvanishing theta.Comment: 22 pages, 10 figure
Experimental Investigation of the Rotor-Wing Aerodynamic Interaction in a Tiltwing Aircraft in Hover
The hovering performance and the lifting capability of tiltrotor aircraft are strongly affected by the aerodynamic interaction between wing and rotors. The tiltwing concept represents a promising technology to increase the hover performance by reducing the wing-rotor interference. The present work describes an experimental activity carried out on a 1/4 scaled tiltwing aircraft half-model to achieve a detailed insight about the main issues characterising the aerodynamic interaction between wing and rotor in hover. The results of the experimental campaign, including both force measurements and Particle Image Velocimetry surveys, enabled to evaluate both the aircraft performance for different configurations of the tilting wing and to achieve a detailed insight about the flow physics of the rotor wake in the interaction with the wing. The test activity provided a comprehensive experimental database that was obtained over a not confidential aircraft configuration
Experimenting Rotorcraft Flight in Complex Environmental Conditions Using the Wind Tunnel: Helicopter Ship Landing Case
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