7,620 research outputs found
Absorption in dipole-lattice models of dielectrics
We develop a classical microscopic model of a dielectric. The model features
nonlinear interaction terms between polarizable dipoles and lattice vibrations.
The lattice vibrations are found to act as a pseudo-reservoir, giving broadband
absorption of electromagnetic radiation without the addition of damping terms
in the dynamics. The effective permittivity is calculated using a perturbative
iteration method and is found to have the form associated with real
dielectrics. Spatial dispersion is naturally included in the model and we also
calculate the wavevector dependence of the permittivity.Comment: 13 pages, 9 figures; references added to section
Puncture discharges in surface dielectrics as contaminant sources in spacecraft environments
Spacecraft in geosynchronous orbits are known to become charged to large negative potentials during the local midnight region of the satellite orbit. Such discharges have been studied by the electron beam irradiation of dielectric samples in a vacuum environment. In addition to static measurements and photographic examination of the puncture discharges in Teflon samples, the transient characteristics of the electrical discharges are determined from oscillographs of voltage and current and by charged particle measurements employing a biased Faraday cup and a retarding potential analyzer. Using these latter techniques, studies of angular and energy distributions of charged particles have indicated an initial burst of high energy electrons (5 x 10 to the 13th power per discharge at energies greater than 300 eV) followed by a less intense burst of lower energy negative particles. Positive ions are emitted from the discharge site in an initial high velocity burst followed by a lower velocity burst tentatively identified as carbon
Optimal traps in graphene
We transform the two-dimensional Dirac-Weyl equation, which governs the
charge carriers in graphene, into a non-linear first-order differential
equation for scattering phase shift, using the so-called variable phase method.
This allows us to utilize the Levinson Theorem to find zero-energy bound states
created electrostatically in realistic structures. These confined states are
formed at critical potential strengths, which leads to us posit the use of
`optimal traps' to combat the chiral tunneling found in graphene, which could
be explored experimentally with an artificial network of point charges held
above the graphene layer. We also discuss scattering on these states and find
the zero angular momentum states create a dominant peak in scattering
cross-section as energy tends towards the Dirac point energy, suggesting a
dominant contribution to resistivity.Comment: 11 pages, 5 figure
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