358 research outputs found
Symmetry characterization of eigenstates in opal-based photonic crystals
The complete symmetry characterization of eigenstates in bare opal systems is
obtained by means of group theory. This symmetry assignment has allowed us to
identify several bands that cannot couple with an incident external plane wave.
Our prediction is supported by layer-KKR calculations, which are also
performed: the coupling coefficients between bulk modes and externally excited
field tend to zero when symmetry properties mismatch.Comment: 7 pages, 5 figures, submitted to Physical Review
Exotic radiation from a photonic crystal excited by an ultra-relativistic electron beam
We report the observation of an exotic radiation (unconventional
Smith-Purcell radiation) from a one-dimensional photonic crystal. The physical
origin of the exotic radiation is direct excitation of the photonic bands by an
ultra-relativistic electron beam. The spectrum of the exotic radiation follows
photonic bands of a certain parity, in striking contrast to the conventional
Smith-Purcell radiation, which shows solely a linear dispersion. Key
ingredients for the observation are the facts that the electron beam is in an
ultra-relativistic region and that the photonic crystal is finite. The origin
of the radiation was identified by comparison of experimental and theoretical
results.Comment: 4 pages, 5 figure
Path-decomposition expansion and edge effects in a confined magnetized free-electron gas
Path-integral methods can be used to derive a `path-decomposition expansion'
for the temperature Green function of a magnetized free-electron gas confined
by a hard wall. With the help of this expansion the asymptotic behaviour of the
profiles for the excess particle density and the electric current density far
from the edge is determined for arbitrary values of the magnetic field
strength. The asymptotics are found to depend sensitively on the degree of
degeneracy. For a non-degenerate electron gas the asymptotic profiles are
essentially Gaussian (albeit modulated by a Bessel function), on a length scale
that is a function of the magnetic field strength and the temperature. For a
completely degenerate electron gas the asymptotic behaviour is again
proportional to a Gaussian, with a scale that is the magnetic length in this
case. The prefactors are polynomial and logarithmic functions of the distance
from the wall, that depend on the number of filled Landau levels . As a
consequence, the Gaussian asymptotic decay sets in at distances that are large
compared to the magnetic length multiplied by .Comment: 16 pages, 2 figures, submitted to J. Phys. A: Math. Gen; corrected
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Development of Prototype Low-cost and High-strength Fault Current Interrupting Arcing Horns for 77 kV Overhead Transmission Lines
Fault Current Interrupting Arcing Horns (FCIAH) are newly designed arcing horns installed on transmis-sion line towers as a countermeasure against lightning damage that greatly contribute to reducing power interruption by interrupting fault current independently within an AC cycle. This paper describes the de-velopment of two new prototype FCIAH for further cost reduction and strength enhancement, using computational fluid dynamics and short-circuit tests
PRELIMINARY STUDY ON LIMNOLOGICAL FEATURES OF LAKES AND RIVERS IN THE PEAT SWAMP AREA OF CENTRAL KALIMANTAN
Water quality, zoobenthos and epiphytic invertebrates were surveyed for waters in the peat swamp area of Central Kalimantan, Indonesia, during 22-25 February 1998. Water temperature was stratified markedly at depths of 0-1.5 m in Lekes Sabuah and Sembuluh. In Lake Sabuah, euphotic depth was as low as 0.76 m due to light attenuation by high concentration of dissolved organic matter as well as phytoplankton in the surface layer of water. Oxygen depletion was observed at bottom layers of Lake Sabuah and of northern inlet bay of Lake Sembuluh, where only a small number of zoobenthos (Oligochaeta) were collected. Water temperature was not stratified in the Kumai and Sekonyer Rivers. Dissolved oxygen concentration was low throughout the water column in the Sekonyer River. In the present lakes and rivers, biological production seemed to take place at depths of 0-1.5 m from water surface.Article信州大学理学部附属諏訪臨湖実験所報告 12: 81-88(2000)departmental bulletin pape
Photonic Band Gaps of Three-Dimensional Face-Centered Cubic Lattices
We show that the photonic analogue of the Korringa-Kohn-Rostocker method is a
viable alternative to the plane-wave method to analyze the spectrum of
electromagnetic waves in a three-dimensional periodic dielectric lattice.
Firstly, in the case of an fcc lattice of homogeneous dielectric spheres, we
reproduce the main features of the spectrum obtained by the plane wave method,
namely that for a sufficiently high dielectric contrast a full gap opens in the
spectrum between the eights and ninth bands if the dielectric constant
of spheres is lower than the dielectric constant of
the background medium. If , no gap is found in the
spectrum. The maximal value of the relative band-gap width approaches 14% in
the close-packed case and decreases monotonically as the filling fraction
decreases. The lowest dielectric contrast for which a
full gap opens in the spectrum is determined to be 8.13. Eventually, in the
case of an fcc lattice of coated spheres, we demonstrate that a suitable
coating can enhance gap widths by as much as 50%.Comment: 19 pages, 6 figs., plain latex - a section on coated spheres, two
figures, and a few references adde
Comparison of flow angle variations of E-region echo characteristics at VHF and HF
In this study, characteristics of the auroral E-region echoes at two significantly different radar frequencies of 12 and 50 MHz are compared. Considered observations were performed at the Syowa Antarctic station in March of 1997 using two HF and one VHF radars at various angles with respect to the magnetic L shells. The diurnal variation of echo occurrence was found to be similar at two frequencies and consistent with previous studies. On the other hand, variation of echo occurrence with L-shell angle φ was shown to be significantly different at two frequencies. 50-MHz echoes were detected preferentially along the L shell (dominating direction of the electrojet flow) while 12-MHz echoes were detected in a broad range of azimuths with the maximum in echo occurrence at φ=40-50°. By plotting the Doppler velocity versus L-shell angle, we demonstrate that 12-MHz echoes can be divided into two populations, the high- and low-velocity echoes. The high-velocity echoes were observed mostly along the L shells while the low-velocity echoes were observed at all directions. We also show that the echo populations exhibit different variation of the Doppler velocity with the L-shell angle. We argue that while the 50-MHz echoes are related to the Farley-Buneman and gradient drift plasma instabilities, the 12-MHz echoes can have additional sources, such as the thermo-diffusion instability and/or neutral wind-related plasma instabilities
Electron spin resonance in high-field critical phase of gapped spin chains
Motivated by recent experiments on Ni(C_{2}H_{8}N_{2})_{2}Ni(CN)_{4}
(commonly known as NENC), we study the electron spin resonance in the critical
high-field phase of the antiferromagnetic S=1 chain with strong planar
anisotropy and show that the ESR spectra exhibit several peculiarities in the
critical phase. Possible relevance of those results for other gapped spin
systems is discussed.Comment: 8 revtex pages, 1 eps figure include
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