66,041 research outputs found
Near field and far field scattering of surface plasmon polaritons by one-dimensional surface defects
A rigorous formulation for the scattering of surface plasmon polaritons (SPP)
from a one-dimensional surface defect of any shape that yields the
electromagnetic field in the vacuum half-space above the vacuum-metal interface
is developed by the use of an impedance boundary condition. The electric and
magnetic near fields, the angular distribution of the far-field radiation into
vacuum due to SPP-photon coupling, and the SPP reflection and transmission
coefficients are calculated by numerically solving the k-space integral
equation upon which the formulation is based. In particular, we consider
Gaussian-shaped defects and study the dependence of the above mentioned
physical quantities on their 1/e half-width a and height h. SPP reflection is
significant for narrow defects; maximum reflection (plasmon mirrors) is
achieved for a~lambda/10. For increasing defect widths, protuberances and
indentations behave differently. The former give rise to a monotonic increase
of radiation at the expense of SPP transmission for increasing defect
half-width. Indentations exhibit a significant increase of radiation (decrease
of SPP transmission) for half-widths of the order of or smaller than the
wavelength, but tend to total SPP transmission in an oscillatory manner upon
further increasing the half-width. Light-emitters might thus be associated with
either wide indentations, or protuberances with widths that are of the order of
or smaller than the wavelength.Comment: REVTeX 3.1, 10 pages with 9 EPS figures (epsf macro
Quantifying Non-circular Streaming Motions in Disc Galaxies
High-quality velocity maps of galaxies frequently exhibit signatures of
non-circular streaming motions. We here apply the software tool, "velfit"
recently proposed by Spekkens & Sellwood, to five representative galaxies from
the THINGS sample. We describe the strengths and weaknesses of the tool, and
show that it is both more powerful and yields results that are more easily
interpreted than the commonly used procedure. We demonstrate that it can
estimate the magnitudes of forced non-circular motions over a broad range of
bar strengths from a strongly barred galaxy, through cases of mild bar-like
distortions to placing bounds on the shapes of halos in galaxies having
extended rotation curves. We identify mild oval distortions in the inner parts
of two dwarf galaxies, NGC 2976 and NGC 7793, and show that the true strength
of the non-axisymmetric gas flow in the strongly barred galaxy NGC 2903 is
revealed more clearly in our fit to an optical Halpha map than to the neutral
hydrogen data. The method can also yield a direct estimate of the ellipticity
of a slowly-rotating potential distortion in the flat part of a rotation curve,
and we use our results to place tight bounds on the possible ellipticity of the
outer halos of NGC 3198 and NGC 2403.Comment: 12 pages, 8 color figures, to appear in MNRAS. Version 2 of the
software can be downloaded from
http://www.physics.rutgers.edu/~spekkens/velfit
Hypernuclear Physics at PANDA
Hypernuclear research will be one of the main topics addressed by the PANDA
experiment at the planned Facility for Anti-proton and Ion Research FAIR at
Darmstadt, Germany. A copious production of Xi-hyperons at a dedicated internal
target in the stored anti-proton beam is expected, which will enable the
high-precision gamma-spectroscopy of double strange systems for the first time.
In addition to the general purpose PANDA setup, the hypernuclear experiments
require an active secondary target of silicon layers and absorber material as
well as high purity germanium (HPGe) crystals as gamma-detectors. The design of
the setup and the development of these detectors is progressing: a first HPGe
crystal with a new electromechanical cooling system was prepared and the
properties of a silicon strip detector as a prototype to be used in the
secondary target were studied. Simultaneously to the hardware projects,
detailed Monte Carlo simulations were performed to predict the yield of
particle stable hypernuclei. With the help of the Monte Carlo a procedure for
Lambda-Lambda-hypernuclei identification by the detection and correlation of
the weak decay pions was developed.Comment: prepared for the International Conference on Exotic Atoms and Related
Topics (EXA2011), Vienna, Sept. 5-9, 201
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