Direct Inversion in Complex Geometries

Progress on the POFFIS high frequency flow imaging method is described. Both theoretical and experimental advances have occurred during the current year. Some success was achieved at imaging an off-axis trailer hitch flaw. However, the issue of variable speed was not completely resolved and research on this issue will continue

Progress on a Mathematical Inversion Technique for Non-Destructive Evaluation

Last year, computer output was presented for synthetic pulse-echo data which was processed according to a mathematical imaging technique. This technique was based on the physical optics farfield inverse scattering (acronym, POFFIS) formalism for scattering by volume defects. This year, a number of theoretical advances have been made in the POFFIS formalism, with attendant revisions in the computer algorithm. Firstly, a revised POFFIS formalism was developed in which the surface of the scatterer is directly related to the scattering data. In this formalism, aperture limited scattering data yields an image of a corresponding aperture of the scattering surface of the defect. Secondly, this formalism will also yield an image of the scatterina surface of a crack. Thirdly, for true amplitude data, the impedance or reflection coefficient may be read directly from the computer output. Related to this last result was the elimination of an image fading phenomenon at certain critical angles. Fourthly, the computer algorithm, which was originally designed to process data for a spherically symmetric trailer hitch , was modified (and tested) to process data when the range to the center of the coordinate system was different at each observation angle. Fifthly, the algorithm was modified (and tested) to process data when the average propagation speed varied with anqle. Implementation on a real data set is discussed

Nondestructive Detection of Voids by a High Frequency Technique

A direct solution of the ultrasonic inverse scattering problem, known by the acronym POFFIS, which stands for Physical Optics Far Field lnverse Scattering, has been developed. This technique has been used to reconstruct the shape and size of both simulated and real void flaws in materials

The production and persistence of ΣRONO2 in the Mexico City plume

Alkyl and multifunctional nitrates (RONO2, ΣANs) have been observed to be a significant fraction of NOy in a number of different chemical regimes. Their formation is an important free radical chain termination step ending production of ozone and possibly affecting formation of secondary organic aerosol. ΣANs also represent a potentially large, unmeasured contribution to OH reactivity and are a major pathway for the removal of nitrogen oxides from the atmosphere. Numerous studies have investigated the role of nitrate formation from biogenic compounds and in the remote atmosphere. Less attention has been paid to the role ΣANs may play in the complex mixtures of hydrocarbons typical of urban settings. Measurements of total alkyl and multifunctional nitrates, NO2, total peroxy nitrates (ΣPNs), HNO3 and a representative suite of hydrocarbons were obtained from the NASA DC-8 aircraft during spring of 2006 in and around Mexico City and the Gulf of Mexico. ΣANs were observed to be 10–20% of NOy in the Mexico City plume and to increase in importance with increased photochemical age. We describe three conclusions: (1) Correlations of ΣANs with odd-oxygen (Ox) indicate a stronger role for ΣANs in the photochemistry of Mexico City than is expected based on currently accepted photochemical mechanisms, (2) ΣAN formation suppresses peak ozone production rates by as much as 40% in the near-field of Mexico City and (3) ΣANs play a significant role in the export of NOy from Mexico City to the Gulf Region

The Selective Downregulation of Class I Major Histocompatibility Complex Proteins by HIV-1 Protects HIV-Infected Cells from NK Cells

AbstractTo avoid detection by CTL, HIV encodes mechanisms for removal of class I MHC proteins from the surface of infected cells. However, class I downregulation potentially exposes the virus-infected cell to attack by NK cells. Human lymphoid cells are protected from NK cell cytotoxicity primarily by HLA-C and HLA-E. We present evidence that HIV-1 selectively downregulates HLA-A and HLA-B but does not significantly affect HLA-C or HLA-E. We then identify the residues in HLA-C and HLA-E that protect them from HIV downregulation. This selective downregulation allows HIV-infected cells to avoid NK cell–mediated lysis and may represent for HIV a balance between escape from CTL and maintenance of protection from NK cells. These results suggest that subpopulations of CTL and NK cells may be uniquely suited for combating HIV

Infrared alignment of SUSY flavor structures

The various experimental bounds on flavor-changing interactions severely restrict the low-energy flavor structures of soft supersymmetry breaking parameters. In this work, we show that with a particular assumption of Yukawa couplings, the fermion mass and sfermion soft mass matrices are simultaneously diagonalized by common mixing matrices and we then obtain an alignment solution for the flavor problems. The required condition is generated by renormalization group evolutions and achieved at low-energy scale independently of high-energy structures of couplings. In this case, the diagonal entries of the soft scalar mass matrices are determined by gaugino and Higgs soft masses. We also discuss possible realizations of this scenario and the characteristic sparticle spectrum in the models.Comment: 18 pages, 1 figur

Generalized messengers of supersymmetry breaking and the sparticle mass spectrum

We investigate the sparticle spectrum in models of gauge-mediated supersymmetry breaking. In these models, supersymmetry is spontaneously broken at an energy scale only a few orders of magnitude above the electroweak scale. The breakdown of supersymmetry is communicated to the standard model particles and their superpartners by "messenger" fields through their ordinary gauge interactions. We study the effects of a messenger sector in which the supersymmetry-violating F-term contributions to messenger scalar masses are comparable to the supersymmetry-preserving ones. We also argue that it is not particularly natural to restrict attention to models in which the messenger fields lie in complete SU(5) GUT multiplets, and we identify a much larger class of viable models. Remarkably, however, we find that the superpartner mass parameters in these models are still subject to many significant contraints.Comment: 24 pages, LaTeX, uses epsf.sty, 4 figures. Assumptions clarified, numerical bounds tweaked, typos correcte