mri workers are occupationally exposed to static and time-varying gradient magnetic fields.  while the 24-hour time-averaged exposure to static magnetic fields is about a few mt, the maximum static field strength can be as high as 500 mt during patient set up. over the past several years, our lab has performed extensive experiments on the health effects of exposure of animal models and humans t...

The role of magnetic fields in gamma-ray burst (GRB) flows remains controversial. The study of the early afterglow phases and, in particular, of the reverse shock dynamics and associated emission offers a promising probe of the magnetization of the ejecta. In this paper, we derive the conditions for the existence of a reverse shock in arbitrarily magnetized ejecta that decelerate and interact w...

the electrical conductivity of the earth is its physical parameter, which can be studied in global scales. the investigations of the earth's electrical conductivity are based on geomagnetic field variations. time variations of the geomagnetic field consist of long-term and short-term (transient) variations. external sources induce electric currents into the earth. the induced electric curr...

NATO needs better methods of measuring and predicting human performance, as well as novel methods of training soldiers that might enhance performance. New breakthroughs with magnetic resonance imaging (MRI) show promise in both areas. Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, i...

A thermal radiative component is likely to accompany the first stages of the prompt emission of gamma-ray bursts (GRBs) and X-ray flashes. We analyse the effect of such a component on the observable spectrum, assuming that the observable effects are due to a dissipation process occurring below or near the thermal photosphere. For comparable energy densities in the thermal and leptonic component...

Long-term deprivation of visual input for several days or weeks leads to marked changes in the excitability and function of the occipital cortex. The time course of these changes is poorly understood. In this study, we addressed the question whether a short period of light deprivation (minutes to a few hours) can elicit such changes in humans. Noninvasive transcranial magnetic stimulation (TMS)...

Previous analysis of the magnetic spectrum of Mars showed only a crustal source field [1]. The observational spectrum was fairly well fitted by the spectrum expected from random dipolar sources scattered on a spherical shell about 46 ± 10 km below Mars’ 3389.5 km mean radius. This de-correlation depth overestimates the typical depth of extended magnetized structures, and so was judged closer to...

HETE-2 has provided strong evidence that the properties of X-Ray Flashes (XRFs) and GRBs form a continuum, and therefore that these two types of bursts are the same phenomenon. We show that both the structured jet and the uniform jet models can explain the observed properties of GRBs reasonably well. However, if one tries to account for the properties of both XRFs and GRBs in a unified picture,...