3,568 research outputs found
Evidence for the Galactic X-ray Bulge II
A mosaic of 5 \ros~PSPC pointed observations in the Galactic plane
() reveals X-ray shadows in the keV band cast by
distant molecular clouds. The observed on-cloud and off-cloud X-ray fluxes
indicate that % and % of the diffuse X-ray background in this
direction in the \tq~keV and 1.5 keV bands, respectively, originates behind the
molecular gas which is located at 3 kpc from the Sun. The implication of
the derived background X-ray flux beyond the absorbing molecular cloud is
consistent with, and lends further support to recent observations of a Galactic
X-ray bulge.Comment: 19 pages, 5 figures, 2 table
A Correlation between the Emission Intensity of Self-Assembled Germanium Islands and the Quality Factor of Silicon Photonic Crystal Nanocavities
We present a comparative micro-photoluminescence study of the emission
intensity of self-assembled germanium islands coupled to the resonator mode of
two-dimensional silicon photonic crystal defect nanocavities. The emission
intensity is investigated for cavity modes of L3 and Hexapole cavities with
different cavity quality factors. For each of these cavities many nominally
identical samples are probed to obtain reliable statistics. As the quality
factor increases we observe a clear decrease in the average mode emission
intensity recorded under comparable optical pumping conditions. This clear
experimentally observed trend is compared with simulations based on a
dissipative master equation approach that describes a cavity weakly coupled to
an ensemble of emitters. We obtain evidence that reabsorption of photons
emitted into the cavity mode is responsible for the observed trend. In
combination with the observation of cavity linewidth broadening in power
dependent measurements, we conclude that free carrier absorption is the
limiting effect for the cavity mediated light enhancement under conditions of
strong pumping.Comment: 8 pages, 5 figure
The Robinson-Trautman Type III Prolongation Structure Contains K
The minimal prolongation structure for the Robinson-Trautman equations of
Petrov type III is shown to always include the infinite-dimensional,
contragredient algebra, K, which is of infinite growth. Knowledge of
faithful representations of this algebra would allow the determination of
B\"acklund transformations to evolve new solutions.Comment: 20 pages, plain TeX, no figures, submitted to Commun. Math. Phy
Shape control of QDs studied by cross-sectional scanning tunneling microscopy
In this cross-sectional scanning tunneling microscopy study we investigated
various techniques to control the shape of self-assembled quantum dots (QDs)
and wetting layers (WLs). The result shows that application of an indium flush
during the growth of strained InGaAs/GaAs QD layers results in flattened QDs
and a reduced WL. The height of the QDs and WLs could be controlled by varying
the thickness of the first capping layer. Concerning the technique of antimony
capping we show that the surfactant properties of Sb result in the preservation
of the shape of strained InAs/InP QDs during overgrowth. This could be achieved
by both a growth interrupt under Sb flux and capping with a thin GaAsSb layer
prior to overgrowth of the uncapped QDs. The technique of droplet epitaxy was
investigated by a structural analysis of strain free GaAs/AlGaAs QDs. We show
that the QDs have a Gaussian shape, that the WL is less than 1 bilayer thick,
and that minor intermixing of Al with the QDs takes place.Comment: 7 pages, 10 figure
Shape control of QDs studied by cross-sectional scanning tunneling microscopy
In this cross-sectional scanning tunneling microscopy study we investigated
various techniques to control the shape of self-assembled quantum dots (QDs)
and wetting layers (WLs). The result shows that application of an indium flush
during the growth of strained InGaAs/GaAs QD layers results in flattened QDs
and a reduced WL. The height of the QDs and WLs could be controlled by varying
the thickness of the first capping layer. Concerning the technique of antimony
capping we show that the surfactant properties of Sb result in the preservation
of the shape of strained InAs/InP QDs during overgrowth. This could be achieved
by both a growth interrupt under Sb flux and capping with a thin GaAsSb layer
prior to overgrowth of the uncapped QDs. The technique of droplet epitaxy was
investigated by a structural analysis of strain free GaAs/AlGaAs QDs. We show
that the QDs have a Gaussian shape, that the WL is less than 1 bilayer thick,
and that minor intermixing of Al with the QDs takes place.Comment: 7 pages, 10 figure
Solutions of the sDiff(2)Toda equation with SU(2) Symmetry
We present the general solution to the Plebanski equation for an H-space that
admits Killing vectors for an entire SU(2) of symmetries, which is therefore
also the general solution of the sDiff(2)Toda equation that allows these
symmetries. Desiring these solutions as a bridge toward the future for yet more
general solutions of the sDiff(2)Toda equation, we generalize the earlier work
of Olivier, on the Atiyah-Hitchin metric, and re-formulate work of Babich and
Korotkin, and Tod, on the Bianchi IX approach to a metric with an SU(2) of
symmetries. We also give careful delineations of the conformal transformations
required to ensure that a metric of Bianchi IX type has zero Ricci tensor, so
that it is a self-dual, vacuum solution of the complex-valued version of
Einstein's equations, as appropriate for the original Plebanski equation.Comment: 27 page
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