Donna M. Pierce

Damping of the dipole vortex.

When a circular electric dipole moment, rotating in the x-y plane, is embedded in a material with relative permittivity ε(r) and relative permeability μ(r), the field lines of energy flow of the emitted radiation are dramatically influenced by the surrounding material. For emission in free space, the field lines swirl around the z axis and lie on a cone. The direction of rotation of the field lines around the z axis is the same as the direction of rotation of the dipole moment. We found that when the real part of ε(r) is negative, the rotation of the field lines changes direction, and hence the energy counter-rotates the dipole moment. When there is damping in the material, due to an imaginary part of ε(r), the cone turns into a funnel, and the density of the field lines diminishes near the location of the source. In addition, all radiation is emitted along the z axis and the x-y plane, whereas for emission in free space, the radiation is emitted in all directions. It is also shown that the displacement of the dipole image in the far field depends on the material parameters and that the shift can be much larger than the shift of the image in free space.

Redistribution of energy flow in a material due to damping

The field lines of energy flow of the radiation emitted by a linear dipole in free space are straight lines, running radially outward from the source. When the dipole is embedded in a medium, the field lines are curves when the imaginary part of the relative permittivity is finite. It is shown that due to the damping in the material all radiation is emitted in directions perpendicular to the dipole axis, whereas for a dipole in free space the radiation is emitted in all directions except along the dipole axis. It is also shown that some field lines in the near field form semiloops. Energy flowing along these semiloops is absorbed by the material and does not contribute to the radiative power in the far field.

THE SPATIAL DISTRIBUTION OF C2, C3, AND NH IN COMET 2P/ENCKE

We examine the spatial distribution of C{sub 2}, C{sub 3}, and NH radicals in the coma of comet Encke in order to understand their abundances and distributions in the coma. The observations were obtained from 2003 October 22-24, using the 2.7 m telescope at McDonald Observatory. Building on our original study of CN and OH, we have used our modified version of the vectorial model, which treats the coma as one large cone, in order to reproduce Enckes highly aspherical and asymmetric coma. Our results suggest that NH can be explained by the photodissociation of NH{sub 2}, assuming that NH{sub 2} is produced rapidly from NH{sub 3} in the innermost coma. Our modeling of C{sub 2} and C{sub 3} suggests a multi-generational photodissociation process may be required for their production. Using the results of our previous study, we also obtain abundance ratios with respect to OH and CN. Overall, we find that Encke exhibits typical carbon-chain abundances, and the results are consistent with other studies of comet Encke.

Inspire: Linking graduate students with K12 teachers to address remote sensing educational needs

The INSPIRE program links graduate students with middle school and high school teachers and students to simultaneously address the need to inspire future students in remote sensing fields as well as providing professional development opportunities for graduate students currently in those disciplines. The INSPIRE program involves each year 10 graduate students (a cumulative total thus far of 50), 5 public school teachers, and approximately 300 middle school and 300 high school students in three school districts with a majority of low-socio economic students, a demographic underrepresented in the remote sensing field in the U.S. The program has resulted in more than 400 formal lesson plans for teachers of grades 7 through 12. To date, the INSPIRE lesson plans have been accessed and downloaded more than 1000 times, resulting in widespread dissemination of the materials and far reaching impact on future generations of students entering the remote sensing field. This paper provides an overview of the program activities, impacted populations, and impact assessment and evaluation.

Vortices in Electric Dipole Radiation

In the geometrical optics limit of light propagation, light travels from a source to an observer along straight lines, known as optical rays. On the other hand, the energy in an electromagnetic field flows along the field lines of the Poynting vector. It can be shown (Born & Wolf, 1980) that in the geometrical optics limit, where variations in the radiation field on the scale of a wavelength are neglected, the optical rays coincide with the field lines of the Poynting vector, and both are straight lines. In nanophotonics and near-field optics, where sub-wavelength resolution of the energy transport is of interest, the optical rays lose their significance. Energy flows along the field lines of the Poynting vector, and these field lines are in general curves. When sub-wavelength resolution is required, we need the exact solution of Maxwell’s equations. In order to study the fundamental aspects of energy propagation, we consider the simplest and most important source of radiation, which is the electric dipole. When a small object, like an atom, molecule or nanoparticle, is placed in an external electromagnetic field (usually a laser beam), oscillating with angular frequency  , a current will be induced in the particle, and this gives the particle an electric dipole moment of the form