869 research outputs found
Spectral properties of microwave graphs with local absorption
The influence of absorption on the spectra of microwave graphs has been
studied experimentally. The microwave networks were made up of coaxial cables
and T junctions. First, absorption was introduced by attaching a 50 Ohm load to
an additional vertex for graphs with and without time-reversal symmetry. The
resulting level-spacing distributions were compared with a generalization of
the Wigner surmise in the presence of open channels proposed recently by Poli
et al. [Phys. Rev. Lett. 108, 174101 (2012)]. Good agreement was found using an
effective coupling parameter. Second, absorption was introduced along one
individual bond via a variable microwave attenuator, and the influence of
absorption on the length spectrum was studied. The peak heights in the length
spectra corresponding to orbits avoiding the absorber were found to be
independent of the attenuation, whereas, the heights of the peaks belonging to
orbits passing the absorber once or twice showed the expected decrease with
increasing attenuation.Comment: 7 pages, 7 figure
Diffuse optics for glaciology
Optical probing of glaciers has the potential for tremendous impact on
environmental science. However, glacier ice is turbid, which prohibits the use
of most established optical measurements for determining a glacier's interior
structure. Here, we propose a method for determining the depth, scattering and
absorption length based upon diffuse propagation of short optical pulses. Our
model allows us to extract several characteristics of the glacier. Performing
Monte Carlo simulations implementing Mie scattering and mixed boundary
conditions, we show that the proposed approach should be feasible with current
technology. The results suggest that optical properties and geometry of the
glacier can be extracted from realistic measurements, which could be
implemented with low cost and small footprint
Liquid hydridosilane precursor prepared from cyclopentasilane via sonication at low temperatures without the action of light
AbstractWe report on a liquid hydridosilane precursor ink prepared via the ultrasonically induced ring-opening polymerisation of cyclopentasilane (Si5H10) without irradiation by ultraviolet light. The sonication is carried out in N2 atmosphere at temperatures between 20 and 75°C. We use size exclusion chromatography (SEC) to show polymer growth and estimate molecular mass with increasing sonication time. In combination with UV–vis transmission measurements, further SEC analysis is used to compare solutions subjected to either purely thermal or ultrasonic treatment at the same process temperature and for the same duration. Our findings provide strong evidence showing that the initiation of the polymerisation is sonocatalytic in nature and not thermic due to the macroscopic temperature of the solution. The liquid precursor is used to produce homogeneous hydrogenated amorphous silicon (a-Si:H) thin films via spin coating and pyrolytic conversion. The optoelectronic properties of the films are subsequently improved by hydrogen radical treatment. Fourier transform infrared spectroscopy (FTIR) is used to determine a compact film morphology and electrical conductivity measurements show that the layers attain a light-to-dark photosensitivity ratio of 2×103 making them suitable for application in optoelectronic devices
The Mass Distributions of Starless and Protostellar Cores in Gould Belt Clouds
Using data from the SCUBA Legacy Catalogue (850 um) and Spitzer Space
Telescope (3.6 - 70 um), we explore dense cores in the Ophiuchus, Taurus,
Perseus, Serpens, and Orion molecular clouds. We develop a new method to
discriminate submillimeter cores found by SCUBA as starless or protostellar,
using point source photometry from Spitzer wide field surveys. First, we
identify infrared sources with red colors associated with embedded young
stellar objects (YSOs). Second, we compare the positions of these
YSO-candidates to our submillimeter cores. With these identifications, we
construct new, self-consistent starless and protostellar core mass functions
(CMFs) for the five clouds. We find best fit slopes to the high-mass end of the
CMFs of -1.26 +/- 0.20, -1.22 +/- 0.06, -0.95 +/- 0.20, and -1.67 +/- 0.72 for
Ophiuchus, Taurus, Perseus, and Orion, respectively. Broadly, these slopes are
each consistent with the -1.35 power-law slope of the Salpeter IMF at higher
masses, but suggest some differences. We examine a variety of trends between
these CMF shapes and their parent cloud properties, potentially finding a
correlation between the high-mass slope and core temperature. We also find a
trend between core mass and effective size, but we are very limited by
sensitivity. We make similar comparisons between core mass and size with visual
extinction (for A_V >= 3) and find no obvious trends. We also predict the
numbers and mass distributions of cores that future surveys with SCUBA-2 may
detect in each of these clouds.Comment: 56 pages, 18 figures, fixed typo in Eq 1, results in paper remain
unchange
Phase separation in star polymer-colloid mixtures
We examine the demixing transition in star polymer-colloid mixtures for star
arm numbers f=2,6,16,32 and different star-colloid size ratios. Theoretically,
we solve the thermodynamically self-consistent Rogers-Young integral equations
for binary mixtures using three effective pair potentials obtained from direct
molecular computer simulations. The numerical results show a spinodal
instability. The demixing binodals are approximately calculated, and found to
be consistent with experimental observations.Comment: 4 pages, 4 figures, submitted to PR
Interferometric imaging using shared quantum entanglement
Quantum entanglement-based imaging promises significantly increased
resolution by extending the spatial separation of optical collection apertures
used in very-long-baseline interferometry for astronomy and geodesy. We report
a table-top entanglement-based interferometric imaging technique that utilizes
two entangled field modes serving as a phase reference between two apertures.
The spatial distribution of a simulated thermal light source is determined by
interfering light collected at each aperture with one of the entangled fields
and performing joint measurements. This experiment demonstrates the ability of
entanglement to implement interferometric imaging
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