1,217 research outputs found
Experimental characterization of an uniaxial angle cut whispering gallery mode resonator
The usual configuration of uniaxial whispering gallery mode resonators is a
disk shaped geometry where the optic axis points along the symmetry axis, a so
called z-cut resonator. Recently x-cut resonators, where the optic axis lies in
the equatorial plane, became of interest as they enable extremely broadband
second harmonic generation. In this paper we report on the properties of a more
generalized system, the so called angle-cut resonator, where the optic axis
exhibits an arbitrary angle against the symmetry axis. We show experimentally
that the modal structure and quality factors are similar to common resonators
but that the polarization properties differ quite significantly: due to the
asymmetry the polarization depends on the equatorial position and is, in
general, elliptical
Radio spectral properties and the magnetic field of the SNR S147
(Abridged) S147 is a large faint shell-type supernova remnant (SNR). Its
remarkable spectral break at cm-wavelengths is an important physical property
to characterize the SNR evolution. However, the spectral break is based on
radio observations with limited precision. We made new radio continuum and
polarization observations of S147 at 11cm and at 6cm with the Effelsberg 100-m
telescope and the Urumqi 25-m telescope, respectively. These new data were
combined with published lower frequency data from the Effelsberg 100-m
telescope and very high frequency data from WMAP to investigate the spectral
turnover and polarization properties of S147. S147 consists of numerous
filaments embedded in diffuse emission. We found that the integrated flux
densities of S147 are 34.8+/-4.0 Jy at 11cm and 15.4+/-3.0Jy at 6cm. These new
measurements confirm the known spectral turnover at ~1.5GHz, which can be
entirely attributed to the diffuse emission component. The spectral index above
the turnover is -1.35+/-0.20. The filamentary emission component has a constant
spectral index over the entire wavelength range up to 40.7GHz of -0.35+/-0.15.
The weak polarized emission of S147 is at the same level as the ambient diffuse
Galactic polarization. The rotation measure of the eastern filamentary shell is
about -70 rad/m2. The filamentary and diffuse emission components of S147 have
different physical properties, which make S147 outstanding among shell type
SNRs.The weak polarization of S147 at 11cm and at 6cm can be attributed to a
section of the S147 shell showing a tangential magnetic field direction.Comment: 11 pages, 17 figures, accepted for publication in Astronomy &
Astrophysics, the resolution of some figures have been reduced. For high
resolution version, see
ftp://ftp.mpifr-bonn.mpg.de/outgoing/p098wre/xiao-etal.pdf,revised following
the language edito
Radio properties of the low surface brightness SNR G65.2+5.7
Many physical properties of this SNR such as spectrum and polarization can
only be investigated by radio observations. The 11 cm and 6\
cm continuum and polarization observations of SNR G65.2+5.7 were made with the
Effelsberg 100-m and the Urumqi 25-m telescopes, respectively, to investigate
the integrated spectrum, the spectral index distribution, and the magnetic
field properties. 21 cm archival data from the Effelsberg 100-m
telescope have been also used. The integrated flux densities of G65.2+5.7 at
cm and cm are Jy and 16.81.8 Jy,
respectively. The power-law spectrum () is well fitted by
from 83 MHz to 4.8 GHz. Spatial spectral variations are
small. Along the northern shell strong depolarizion is observed at both
wavelengths. The southern filamentary shell of SNR G65.2+5.7 is polarized up to
54% at cm. There is significant depolarization at cm
and confusion with diffuse polarized Galactic emission. Using equipartition
principle, we estimated the magnetic field strength for the southern
filamentary shell about 20 G (filling factor 1) to 50 G (filling
factor 0.1). A faint HI shell may be associated with the SNR. Despite its
unusual strong X-ray and optical emission and its very low surface brightness,
the radio properties of SNR G65.2+5.7 are found to be typical for evolved shell
type SNRs. SNR G65.2+5.7 may be expanding in a preblown cavity as indicated by
a deficit of HI gas and a possible HI-shell.Comment: 11pages,13figures,accepted by A&A, revised following the language
editor. For high resolution version, please go to
ftp://ftp.mpifr-bonn.mpg.de/outgoing/p098wre/xiao-etal-g65.pd
Assessing numbers and faces: a prerequisite for improving access to lymphatic filariasis morbidity care
Concerted efforts to eliminate lymphatic filariasis worldwide have registered success; multiple rounds of mass drug administration have led to the interruption of transmission in many previously endemic areas. However, the management of patients with established clinical disease (e.g., lymphoedema, hydrocoele and acute dermatolymphangioadenitis) has not been addressed sufficiently. Two recent studies from Malawi underscore the need for accurate epidemiological and clinical data, and comprehensive morbidity assessments across various domains of daily life. Addressing these issues will guide the implementation of programmes to improve access to treatment and disability prevention for affected individuals in Malawi and beyon
Derivation of a Matrix-valued Boltzmann Equation for the Hubbard Model
For the spin-1/2 Fermi-Hubbard model we derive the kinetic equation valid for weak interactions by using time-dependent perturbation expansion up to second order. In recent theoretical and numerical studies the kinetic equation has been merely stated without further details. In this contribution we provide the required background material.Peer reviewe
Naturally-phasematched second harmonic generation in a whispering gallery mode resonator
We demonstrate for the first time natural phase matching for optical
frequency doubling in a high-Q whispering gallery mode resonator made of
Lithium Niobate. A conversion efficiency of 9% is achieved at 30 micro Watt
in-coupled continuous wave pump power. The observed saturation pump power of
3.2 mW is almost two orders of magnitude lower than the state-of-the-art. This
suggests an application of our frequency doubler as a source of non-classical
light requiring only a low-power pump, which easily can be quantum noise
limited. Our theoretical analysis of the three-wave mixing in a whispering
gallery mode resonator provides the relative conversion efficiencies for
frequency doubling in various modes
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