[1] Using recently published electron phase space densities (PSD) as a function of L* (L* is approximately the radial distance in Earth radii at the equator) and time, energization and loss in the Earth's outer electron radiation belt were studied quantitatively and numerically using a radial diffusion model that included finite electron lifetimes and an internal source parameterized as a function of geomagnetic indices. We used PSD data at fixed values of the first and second adiabatic invariants, corresponding to electrons mirroring near the Earth's equator with an energy of $2.7 MeV at L* = 4. Model results for the second half of 2002 reproduced the average variations of the radiation belt electron PSD between L* = 2.5 and L* = 6 but with overprediction and underprediction at different times, implying that the same set of parameters cannot be applied to all storms. A detailed analysis of four individual storms showed that while electrons in three storms could be well simulated by energization from either radial diffusion only or internal heating only, incorporating both yielded the best results. For the other storm, an additional source of electrons was required to account for the enhanced PSD. The model results indicated that each storm is best simulated when a combination of radial diffusion and internal heating is used. Different storms required different magnitudes of radial diffusion and internal heating, and the relative contributions of these two acceleration mechanisms varied from storm to storm. A comparison of the results from different runs for the four storms and an analysis of the radial diffusion coefficients further suggest that internal heating contributes more to the enhancement of 2.7 MeV electrons at L* = 4 than radial diffusion.
A generic class of metamaterials is introduced and is shown to exhibit frequency dependent double negative effective properties. We develop a rigorous method for calculating the frequency intervals where either double negative or double positive effective properties appear and show how these intervals imply the existence of propagating Bloch waves inside sub-wavelength structures. The branches of the dispersion relation associated with Bloch modes are shown to be explicitly determined by the Dirichlet spectrum of the high dielectric phase and the generalized electrostatic spectra of the complement.
Active magnetic resonance (MR) tracking for gynecologic brachytherapy was made possible by attaching the micro radiofrequency coils to the brachytherapy applicator. The rectangular planar micro coil was fabricated using flexible printed circuits with dimensions of 8mm×1.5mm. A 5-Fr (1.6mm) tungsten brachytherapy stylet was custom-machined to incorporate the micro coils. The finite element analysis and the phantom tissue studies show that the proposed device enables in situ, real-time guidance of access routes to the target anatomy safely and accurately. The setup was tested in a Siemens 3T MR scanner. The micro coils can be localized rapidly (up to 40 Hz) and precisely (resolution: 0.6×0.6×0.6mm3) using an MR-tracking sequence.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.