We estimate the two-photon exchange contribution to elastic electron-proton scattering at large momentum transfer by using a quark-parton representation of virtual Compton scattering. We thus can relate the two-photon exchange amplitude to the generalized parton distributions which also enter in other wide angle scattering processes. We find that the interference of one-and two-photon exchange contribution is able to substantially resolve the difference between electric form factor measurements from Rosenbluth and polarization transfer experiments. Two-photon exchange has additional consequences which could be experimentally observed, including nonzero polarization effects and a positron-proton/electron-proton scattering asymmetry. The predicted Rosenbluth plot is no longer precisely linear; it acquires a measurable curvature, particularly at large laboratory angle.

The trend to use administrative health care databases as research material is increasing but not well explored.

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We study the ground state phase diagram of the hard-core extended boson Hubbard model on the square lattice with both nearest-(nn) and next-nearest-neighbor (nnn) hopping and repulsion, using Gutzwiller mean field theory and quantum Monte Carlo simulations. We observe the formation of supersolid states with checkerboard, striped, and quarter-filled crystal structures, when the system is doped away from commensurate fillings. In the striped supersolid phase, a strong anisotropy in the superfluid density is obtained from the simulations; however, the transverse component remains finite, indicating a true two-dimensional superflow. We find that upon doping, the striped supersolid transitions directly into the supersolid with quarter-filled crystal structure, via a first-order stripe melting transition.

Tumor hypoxia, present in many human cancers, can lead to resistance to radiation and chemotherapy, is associated with a more aggressive tumor phenotype and is an independent prognostic factor of clinical outcome. It is therefore important to identify and localize tumor hypoxia in cancer patients. In the current study, serial microPET imaging was used to evaluate iodine-124-labeled iodo-azomycin-galactoside ((124)I-IAZG) (4.2-day physical half-life) as a hypoxia imaging agent in 17 MCa breast tumors and six FSaII fibrosarcomas implanted in mice. For comparison, another promising hypoxic-cell PET radiotracer, fluorine-18-labeled fluoro-misonidazole ((18)F-FMISO), was also imaged in the same tumor-bearing animals. Twelve animals were also imaged with (18)F-labeled fluoro-deoxyglucose ((18)F-FDG). In addition, histological examination was performed, and direct measurement of tumor oxygenation status carried out with the Oxylite probe system. Two size groups were used, relatively well-oxygenated tumors in the range of 80-180 mg were designated as small, and those >300 mg and highly hypoxic, as large. Based on the data from 11 MCa and six FSaII tumors, both (124)I-IAZG and (18)F-FMISO images showed high tracer uptake in the large tumors. In (18)F-FMISO images at 1, 3-4, and 6-8 h post-injection (p.i.), there was considerable whole-body background activity. In contrast, (124)I-IAZG imaging was optimal when performed at 24-48 h p.i., when the whole-body background had dissipated considerably. As a result, the (124)I-IAZG images at 24-48 h p.i. had higher tumor to whole-body activity contrast than the (18)F-FMISO images at 3-6 h p.i. Region-of-interest analysis was performed as a function of time p.i. and indicated a tumor uptake of 5-10% (of total-body activity) for FMISO at 3-6 h p.i., and of ~17% for IAZG at 48 h p.i. This was corroborated by biodistribution data in that the tumor-to-normal tissue (T/N, normal tissues of blood, heart, lung, liver, spleen, kidney, intestine, and muscle) activity ratios of IAZG at 24 h p.i. was 1.5-2 times higher than those of FMISO at 3 h p.i., with the exception of stomach. Statistical analysis indicated that these differences in T/N ratios were significant. The small tumors were visualized in the (18)F-FDG images, but not in the (124)I-IAZG or (18)F-FMISO images. This was perhaps due to the combined effect of a smaller tumor volume and a lower hypoxic fraction. Oxylite probe measurement indicated a lesser proportion of regions with pO(2)<2.5 mmHg in the small tumors (e.g., pO(2) was <2.5 mmHg in 28% and 67% of the data in small and large FSaII tumors, respectively), and the biodistribution data showed lower uptake of the tracers in the small tumors than in the large tumors. In the first study of its kind, using serial microPET imaging in conjunction with biodistribution analysis and direct probe measurements of local pO(2) to evaluate tumor hypoxia markers, we have provided data showing the potential of (124)I-IAZG for hypoxia imaging.

SCI patients with disability are at a higher risk of stroke, especially the ischemic type. Strategies to prevent stroke are therefore suggested for them.

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