133 research outputs found
Dielectric Resonator Method for Measuring the Electrical Conductivity of Carbon Nanotubes from Microwave to Millimeter Frequencies
We describe a dielectric resonator-based measurement method for determining the electrical conductivity of carbon nanotubes at microwave to millimeter frequencies.
This measurement method is not limited by the metal conductor contact resistances or impedance mismatch commonly encountered in the measurement of single nanotubes.
The measurement of carbon nanotubes yielded conductivities of approximately 0.08×107 S/m
Boundary Effects on the Determination of Metamaterial Parameters from Normal Incidence Reflection and Transmission Measurements
A method is described for the determination of the effective electromagnetic
parameters of a metamaterial based only on external measurements or
simulations, taking boundary effects at the interfaces between a conventional
material and metamaterial into account. Plane-wave reflection and transmission
coefficients at the interfaces are regarded as additional unknowns to be
determined, rather than explicitly dependent on the material parameters. Our
technique is thus analogous to the line-reflect-line (LRL) calibration method
in microwave measurements. The refractive index can be determined from
S-parameters for two samples of different thickness. The effective wave
impedance requires the additional assumption that generalized sheet transition
conditions (GSTCs) account for the boundary effects. Expressions for the bulk
permittivity and permeability then follow easily. Our method is validated by
comparison with the results using the Nicolson-Ross-Weir (NRW) for determining
properties of an ordinary material measured in a coaxial line. Utilizing
S-parameters obtained from 3-D full wave simulations, we test the method on
magnetodielectric metamaterials. We compare the results from our method and the
conventional one that does not consider boundary effects. Moreover, it is shown
that results from our method are consistent under changes in reference plane
location, whereas the results from other methods are not.Comment: 16 pages, 16 figures. Submitted to IEEE Transactions on Antennas and
Propagatio
Electrical Material Property Measurements using a Free-Field, Ultra-Wideband System [Dielectric Measurements]
We present nondestructive measurements of material properties using TEM horn antennas and an ultra-wideband measurement system. Time-domain gating and genetic algorithms are used to process the data and extract the dielectric properties of the material under test
Dynamics of Barred Galaxies
Some 30% of disc galaxies have a pronounced central bar feature in the disc
plane and many more have weaker features of a similar kind. Kinematic data
indicate that the bar constitutes a major non-axisymmetric component of the
mass distribution and that the bar pattern tumbles rapidly about the axis
normal to the disc plane. The observed motions are consistent with material
within the bar streaming along highly elongated orbits aligned with the
rotating major axis. A barred galaxy may also contain a spheroidal bulge at its
centre, spirals in the outer disc and, less commonly, other features such as a
ring or lens. Mild asymmetries in both the light and kinematics are quite
common. We review the main problems presented by these complicated dynamical
systems and summarize the effort so far made towards their solution,
emphasizing results which appear secure. (Truncated)Comment: This old review appeared in 1993. Plain tex with macro file. 82 pages
18 figures. A pdf version with figures at full resolution (3.24MB) is
available at http://www.physics.rutgers.edu/~sellwood/bar_review.pd
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