Isgur - Wise Functions for Confined Light Quarks in a Colour Electric Potential

We explore the influence on the Isgur-Wise function of the colour electric potential between heavy and light quarks in mesons. It is shown that in bag models, its inclusion tends to restore light quark flavour symmetry relative to the MIT bag predictions, and that relative to this model it flattens the Isgur-Wise function. Results compare very well with observations.Comment: 9 pages, 1 figure (available upon request), Latex, TPJU - 4/9

Relativistic Flux Tube Model Calculation of the Isgur-Wise Function

The Relativistic Flux Tube model is used to calculate of the Isgur-Wise functions describing the exclusive semileptonic decays of $\bar{B}$ and $\bar{B}_{s}$ mesons. The light quark mass dependence is investigated and the predicted universal function agrees well with the results of lattice simulations, and with the experimental data. Recent experimental measurements of the \bar{B}\ra D^{*}l\bar{\nu}_{l} decay distribution yield the CKM element $V_{bc}=0.035\pm 0.001$. The IW function slope and second derivative at the zero recoil point are predicted to be $\xi'(1) = -0.93\pm 0.04$ and $\xi''(1)= 1.7\pm 0.1$ for a range of light quark massses. The importance of including higher derivatives in analyses of experiment is emphasized.Comment: Latex (uses epsf macro), 14 pages of text, 6 postscript figures included. MAD/PH/85

A Review on Solar Wind Modeling: Kinetic and Fluid Aspects

The paper reviews the main advantages and limitations of the kinetic exospheric and fluid models of the solar wind (SW). The general theoretical background is outlined: the Boltzmann and Fokker-Planck equations, the Liouville and Vlasov equations, the plasma transport equations derived from an "equation of change". The paper provides a brief history of the solar wind modeling. It discusses the hydrostatic model imagined by Chapman, the first supersonic hydrodynamic models published by Parker and the first generation subsonic kinetic model proposed by Chamberlain. It is shown that a correct estimation of the electric field, as in the second generation kinetic exospheric models developed by Lemaire and Scherer, provides a supersonic expansion of the corona, reconciling the hydrodynamic and the kinetic approach. The modern developments are also reviewed emphasizing the characteristics of several generations of kinetic exospheric and multi-fluid models. The third generation kinetic exospheric models consider kappa velocity distribution function (VDF) instead of a Maxwellian at the exobase and in addition they treat a non-monotonic variation of the electric potential with the radial distance; the fourth generation exospheric models include Coulomb collisions based on the Fokker-Planck collision term. Multi-fluid models of the solar wind provide a coarse grained description of the system and reproduce with success the spatio-temporal variation of SW macroscopic properties (density, bulk velocity). The main categories of multi-fluid SW models are reviewed: the 5-moment, or Euler, models, originally proposed by Parker to describe the supersonic SW expansion; the 8-moment and 16-moment fluid models, the gyrotropic approach with improved collision terms as well as the gyrotropic models based on observed VDFs. The outstanding problem of collisions, including the long range Coulomb encounters, is also discussed, both in the kinetic and multi-fluid context. Although for decades the two approaches have been seen as opposed, in this paper we emphasize their complementarity. The review of the kinetic and fluid models of the solar wind contributes also to a better evaluation of the open questions still existent in SW modeling and suggests possible future developments

DVB-T passive radar dual polarization measurements in the presence of strong direct signal interference

A dual-polarization passive bistatic radar is used to evaluate the potential benefit of cross-polarized measurements for the suppression of strong direct signal interference in the DVB-T band. The linear array antenna consists of 10 bowtie elements, 5 of which measuring horizontal and 5 vertical polarization. Two small GPS-equipped aircraft were used as targets, flying prescribed patterns. Two antenna locations were used, one in which the broadcasting transmitter was only 20° from the antenna boresight, causing strong direct signal interference, and one in which the antenna was partially shielded from the transmitter. In both polarization channels, reconstruction of the reference signal and reciprocal filtering was used to suppress interference. GPS data from the aircraft was used to find the bistatic range, Doppler, and azimuth location, and the signal to interference pluss noise ratio (SINR) at this location was measured. In addition, the azimuth inferred from GPS was compared with the direction derived from the radar measurements. We find no advantage using cross polarization, even in the case with strong direct signal interference: On average there is no significant difference between co-And crosspolarized SINR, and the co-polarized channel is slightly better predicting the correct azimuth

Simulations supporting the design of a measurement model of an unmanned aerial vehicle with low radar signature

The objective of the NATO/STO/SET-252 Task Group is to design and manufacture a validation model of a representative target in terms of geometrical complexity and the use of materials for the reduction of main scattering mechanisms. Computational Electromagnetics (CEM) is a crucial engineering tool in the overall design process and used to identify the scattering centers, to assess the effect of coatings or distortions like surface roughness, and finally to ascertain the radar signature of the model. Cross-comparisons of computational results are performed using different formulations and methods. With regards to the future growing number of autonomous and unmanned vehicles and services, the results are not only military relevant but also valuable for civil air traffic control and air surveillance