10,032 research outputs found
Off-Shell Electromagnetic Form Fators of the Nucleon in Chiral Perturbation Theory
We study the electromagnetic form factors of a nucleon in next-to-leading
order chiral perturbation theory (CPT) in the case where one of the nucleons is
off its mass shell. We calculate the leading nonanalytic contributions to
relevant measures for the off-shell dependence in the limited kinematical range
allowed.Comment: 3 pages LaTeX with worldsci.sty (available by mailing
[email protected] and typing "get worldsci.sty" in the subject line),
invited talk given at the International Symposium on Medium Energy Physics,
Beijing, August 199
On the unsteady behavior of turbulence models
Periodically forced turbulence is used as a test case to evaluate the
predictions of two-equation and multiple-scale turbulence models in unsteady
flows. The limitations of the two-equation model are shown to originate in the
basic assumption of spectral equilibrium. A multiple-scale model based on a
picture of stepwise energy cascade overcomes some of these limitations, but the
absence of nonlocal interactions proves to lead to poor predictions of the time
variation of the dissipation rate. A new multiple-scale model that includes
nonlocal interactions is proposed and shown to reproduce the main features of
the frequency response correctly
Extreme Lagrangian acceleration in confined turbulent flow
A Lagrangian study of two-dimensional turbulence for two different
geometries, a periodic and a confined circular geometry, is presented to
investigate the influence of solid boundaries on the Lagrangian dynamics. It is
found that the Lagrangian acceleration is even more intermittent in the
confined domain than in the periodic domain. The flatness of the Lagrangian
acceleration as a function of the radius shows that the influence of the wall
on the Lagrangian dynamics becomes negligible in the center of the domain and
it also reveals that the wall is responsible for the increased intermittency.
The transition in the Lagrangian statistics between this region, not directly
influenced by the walls, and a critical radius which defines a Lagrangian
boundary layer, is shown to be very sharp with a sudden increase of the
acceleration flatness from about 5 to about 20
Sclera solar diameter observations
Focus is given to possible variations in solar luminosity and accurate methods of monitoring it. Aside from direct bolometry, one methodology for this type of research makes use of measurements of the solar diameter and limb darkening function as indirect indicators of the solar luminosity. This approach was reviewed
Wave-Optics Analysis of Pupil Imaging
Pupil imaging performance is analyzed from the perspective of physical optics. A multi-plane diffraction model is constructed by propagating the scalar electromagnetic field, surface by surface, along the optical path comprising the pupil imaging optical system. Modeling results are compared with pupil images collected in the laboratory. The experimental setup, although generic for pupil imaging systems in general, has application to the James Webb Space Telescope (JWST) optical system characterization where the pupil images are used as a constraint to the wavefront sensing and control process. Practical design considerations follow from the diffraction modeling which are discussed in the context of the JWST Observatory
Decay of scalar variance in isotropic turbulence in a bounded domain
The decay of scalar variance in isotropic turbulence in a bounded domain is
investigated. Extending the study of Touil, Bertoglio and Shao (2002; Journal
of Turbulence, 03, 49) to the case of a passive scalar, the effect of the
finite size of the domain on the lengthscales of turbulent eddies and scalar
structures is studied by truncating the infrared range of the wavenumber
spectra. Analytical arguments based on a simple model for the spectral
distributions show that the decay exponent for the variance of scalar
fluctuations is proportional to the ratio of the Kolmogorov constant to the
Corrsin-Obukhov constant. This result is verified by closure calculations in
which the Corrsin-Obukhov constant is artificially varied. Large-eddy
simulations provide support to the results and give an estimation of the value
of the decay exponent and of the scalar to velocity time scale ratio
Inertial range scaling of the scalar flux spectrum in two-dimensional turbulence
Two-dimensional statistically stationary isotropic turbulence with an imposed
uniform scalar gradient is investigated. Dimensional arguments are presented to
predict the inertial range scaling of the turbulent scalar flux spectrum in
both the inverse cascade range and the enstrophy cascade range for small and
unity Schmidt numbers. The scaling predictions are checked by direct numerical
simulations and good agreement is observed
Broilers with Taste - Sustainable chicken takes flight
Engelse versie van de brochure 'Pluimvee met smaak : duurzame kip krijgt vleugels', die laat zien waar kansen liggen voor de Nederlandse pluimveesector om te verduurzamen. Twee uiteenlopende concepten, de Som der Delen en de Windstreek, geven ieder op eigen wijze invulling aan duurzaamheid op het primaire bedrijf. Ze bevatten belangrijke elementen voor verduurzaming, die als geheel of in onderdelen, nu of later, in de praktijk gebracht kunnen worden. Duurzaamheid kent immers niet één, maar vele vormen, afhankelijk van de ondernemers, de markt en de omgeving
Octet Baryon Magnetic Moments in the Chiral Quark Model with Configuration Mixing
The Coleman-Glashow sum-rule for magnetic moments is always fulfilled in the
chiral quark model, independently of SU(3) symmetry breaking. This is due to
the structure of the wave functions, coming from the non-relativistic quark
model. Experimentally, the Coleman-Glashow sum-rule is violated by about ten
standard deviations. To overcome this problem, two models of wave functions
with configuration mixing are studied. One of these models violates the
Coleman-Glashow sum-rule to the right degree and also reproduces the octet
baryon magnetic moments rather accurately.Comment: 22 pages, RevTe
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