98,551 research outputs found
Fitting Precision Electroweak Data with Exotic Heavy Quarks
The 1999 precision electroweak data from LEP and SLC persist in showing some
slight discrepancies from the assumed standard model, mostly regarding and
quarks. We show how their mixing with exotic heavy quarks could result in a
more consistent fit of all the data, including two unconventional
interpretations of the top quark.Comment: 7 pages, no figure, 2 typos corrected, 1 reference update
A computational method for viscous incompressible flows
An implicit, finite-difference procedure for numerically solving viscous incompressible flows is presented. The pressure-field solution is based on the pseudocompressibility method in which a time-derivative pressure term is introduced into the mass-conservation equation to form a set of hyperbolic equations. The pressure-wave propagation and the spreading of the viscous effect is investigated using simple test problems. Computed results for external and internal flows are presented to verify the present method which has proved to be very robust in simulating incompressible flows
Selected highlights from the study of mesons
We provide a brief review of recent progress in the study of mesons using
QCD's Dyson-Schwinger equations. Along the way we touch on aspects of
confinement and dynamical chiral symmetry breaking but in the main focus upon:
exact results for pseudoscalar mesons, including aspects of the eta-eta'
problem; a realisation that the so-called vacuum condensates are actually an
intrinsic, localised property of hadrons; an essentially nonperturbative
procedure for constructing a symmetry-preserving Bethe-Salpeter kernel, which
has enabled a demonstration that dressed-quarks possess momentum-dependent
anomalous chromo- and electromagnetic moments that are large at infrared
momenta, and resolution of a longstanding problem in understanding the
mass-splitting between rho- and a1-mesons such that they are now readily seen
to be parity partners in the meson spectrum; features of electromagnetic form
factors connected with charged and neutral pions; and computation and
explanation of valence-quark distribution functions in pseudoscalar mesons. We
argue that in solving QCD, a constructive feedback between theory and extant
and forthcoming experiments will enable constraints to be placed on the
infrared behaviour of QCD's beta-function, the nonperturbative quantity at the
core of hadron physics.Comment: 28 pages, 15 figures, 2 tables. Version to appear in the Chinese
Journal of Physic
Phased array antenna beamforming using optical processor
The feasibility of optical processor based beamforming for microwave array antennas is investigated. The primary focus is on systems utilizing the 20/30 GHz communications band and a transmit configuration exclusively to serve this band. A mathematical model is developed for computation of candidate design configurations. The model is capable of determination of the necessary design parameters required for spatial aspects of the microwave 'footprint' (beam) formation. Computed example beams transmitted from geosynchronous orbit are presented to demonstrate network capabilities. The effect of the processor on the output microwave signal to noise quality at the antenna interface is also considered
Flavor SU(4) breaking between effective couplings
Using a framework in which all elements are constrained by Dyson-Schwinger
equation studies in QCD, and therefore incorporates a consistent, direct and
simultaneous description of light- and heavy-quarks and the states they
constitute, we analyze the accuracy of SU(4)-flavor symmetry relations between
{\pi}{\rho}{\pi}, K{\rho}K and D{\rho}D couplings. Such relations are widely
used in phenomenological analyses of the interactions between matter and
charmed mesons. We find that whilst SU(3)-flavor symmetry is accurate to 20%,
SU(4) relations underestimate the D{\rho}D coupling by a factor of five.Comment: 5 pages, two figure
Remote sensing of precipitable water over the oceans from Nimbus-7 microwave measurements
Global maps of precipitable water over derived from scanning multichannel microwave radiometer (SMMR) data reveal salient features associated with ocean currents and the large scale general circulation in the atmosphere. Nimbus-7 SMMR brightness temperature measurements in the 21 and 18 GHz channels are used to sense the precipitable water in the atmospheric over oceans. The difference in the brightness temperature (T sub 21 -T sub 18), both in the horizontal and vertical polarization, is found to be essentially a function of the precipitable water in the atmosphere. An equation, based on the physical consideration of the radiative transfer in the microwave region, is developed to relate the precipitable water to (T sub 21 - T sub 18). It shows that the signal (T sub 21- T sub 18) does not suffer severely from the noise introduced by variations in the sea surface temperature, surface winds, and liquid water content in non rain clouds. The rms deviation between the estimated precipitable water from SMMR data and that given by the closely coincident ship radiosondes is about 0.25 g/ sq c
The effect of barriers on wave propagation phenomena: With application for aircraft noise shielding
The frequency spectrum was divided into high and low frequency regimes and two separate methods were developed and applied to account for physical factors associated with flight conditions. For long wave propagation, the acoustic filed due to a point source near a solid obstacle was treated in terms of an inner region which where the fluid motion is essentially incompressible, and an outer region which is a linear acoustic field generated by hydrodynamic disturbances in the inner region. This method was applied to a case of a finite slotted plate modelled to represent a wing extended flap for both stationary and moving media. Ray acoustics, the Kirchhoff integral formulation, and the stationary phase approximation were combined to study short wave length propagation in many limiting cases as well as in the case of a semi-infinite plate in a uniform flow velocity with a point source above the plate and embedded in a different flow velocity to simulate an engine exhaust jet stream surrounding the source
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