5,158 research outputs found
Enhancing the Performance of Integrated Optical Sensor by Slow-light: Theoretical Study on Ring-Resonator Based Structures
In this work, the performance of three kinds of integrated optical ring-resonator based slow-light structures for sensing applications is theoretically studied using the transfer matrix method and the complex transmission coefficient approach. Enhancement of sensing performance due to the slowlight phenomenon is quantitatively formulated. The modeling results show that using realistic structure parameters, a refractive index detection limit of one order better than the state of the art Mach-Zehnder interferometer sensing structure is possible by the inclusion of such a slow-light structure. The role of ring(s) attenuation constant in limiting the usable light slowness and the achievable sensor resolution is also discussed. For a sufficiently small ring attenuation constant, the optimal sensing performance of a single resonator circuit can be better than that of multiple resonator circuits, while offering less fabrication complexities, cleaner spectra, shorter device length, and higher figure of merit
First detection of galaxy-galaxy-galaxy lensing in RCS. A new tool for studying the matter environment of galaxy pairs
The weak gravitational lensing effect, small coherent distortions of galaxy
images by means of a gravitational tidal field, can be used to study the
relation between the matter and galaxy distribution. In this context, weak
lensing has so far only been used for considering a second-order correlation
function that relates the matter density and galaxy number density as a
function of separation. We implement two new, third-order correlation functions
that have recently been suggested in the literature, and apply them to the
Red-Sequence Cluster Survey. We demonstrate that it is possible, even with
already existing data, to make significant measurements of third-order lensing
correlations. We develop an optimised computer code for the correlation
functions. To test its reliability a set of tests are performed. The
correlation functions are transformed to aperture statistics, which allow easy
tests for remaining systematics in the data. In order to further verify the
robustness of our measurement, the signal is shown to vanish when randomising
the source ellipticities. Finally, the lensing signal is compared to crude
predictions based on the halo-model. On angular scales between roughly 1 arcmin
and 11 arcmin a significant third-order correlation between two lens positions
and one source ellipticity is found. We discuss this correlation function as a
novel tool to study the average matter environment of pairs of galaxies.
Correlating two source ellipticities and one lens position yields a less
significant but nevertheless detectable signal on a scale of 4 arcmin. Both
signals lie roughly within the range expected by theory which supports their
cosmological origin.[ABRIDGED]Comment: 15 pages, 12 figures, accepted by A&A; minor change
Ultra-sharp soliton switching in a directional coupler
By a numerical investigation it is shown that a directional coupler, described by two linearly coupled non-linear Schro¨dinger equations, can be used to construct a soliton switch with an extremely narrow transition region
Propagating Residual Biases in Cosmic Shear Power Spectra
In this paper we derive a full expression for the propagation of
multiplicative and additive shape measurement biases into the cosmic shear
power spectrum. In doing so we identify several new terms that are associated
with selection effects, as well as cross-correlation terms between the
multiplicative and additive biases and the shear field. The computation of the
resulting bias in the shear power spectrum scales as the fifth power of the
maximum multipole considered. Consequently the calculation is unfeasible for
large l-modes, and the only tractable way to assess the full impact of shape
measurement biases on cosmic shear power spectrum is through forward modelling
of the effects. To linear order in bias parameters the shear power spectrum is
only affected by the mean of the multiplicative bias field over a survey and
the cross correlation between the additive bias field and the shear field. If
the mean multiplicative bias is zero then second order convolutive terms are
expected to be orders of magnitude smaller.Comment: 10 pages, accepted to the Open Journal of Astrophysic
Subtidal water level variation controlled by river flow and tides
Subtidal water level dynamics in the Berau river, East Kalimantan, Indonesia, feature a pronounced fortnightly variation. The daily mean water levels at a station about 60 km from the sea are 0.2–0.6 m higher during spring tide than during neap tide. To explain the underlying mechanisms, a local subtidal momentum balance is set up from field data, using continuous discharge estimates inferred from measurements taken with a horizontal acoustic Doppler current profiler. It is demonstrated that terms accounting for friction and variation in the water surface gradient are dominant in the subtidal momentum balance. To further investigate the sources of subtidal water level variation, a generic method of analysis is proposed to decompose the subtidal friction term into contributions caused by river flow, by interaction between tidal motions and river flow, and by the tidal motions alone. At the station under study, mainly the river-tide interaction term is responsible for generating fortnightly variation of the subtidal water level. The contribution from interaction between diurnal, semidiurnal, and quarterdiurnal tides to subtidal friction is significantly smaller. Provided that the reduction of tidal velocity amplitudes with increasing discharges can be predicted from a regression model, the results presented herein can be used to predict changes in subtidal water levels as a result of increased river discharges
Opportunity for development or necessary nuisance? The case for viewing working with interpreters as a bonus in therapeutic work
This paper explores the central role a language interpreter can play in the process of the therapeutic relationship. Although others have described the changes to the therapeutic dyad that the presence of a third party (an interpreter) brings, little attention has been paid to the advantages and additional opportunities of this altered therapeutic situation. This paper details these gains and further argues that clinicians who are willing to gain experience of working with interpreters will find that benefits accrue at the micro and macro levels: at the micro level, through enhancement of their work with individual non English speaking clients, and at the macro level through learning about different cultural perspectives, idioms of distress and the role of language in the therapeutic endeavour. This is in addition to developing skills to fulfil legal and professional requirements relating to equity of service provision. Some ideas are offered to explain the negative slant than runs throughout the literature in this area and tends to colour the overall discussion of therapeutic work with interpreters and, before the final section, makes some specific suggestions which may help maximise the gains possible in such work while reducing difficulties
Intrinsic galaxy shapes and alignments II: Modelling the intrinsic alignment contamination of weak lensing surveys
Intrinsic galaxy alignments constitute the major astrophysical systematic of
forthcoming weak gravitational lensing surveys but also yield unique insights
into galaxy formation and evolution. We build analytic models for the
distribution of galaxy shapes based on halo properties extracted from the
Millennium Simulation, differentiating between early- and late-type galaxies as
well as central galaxies and satellites. The resulting ellipticity correlations
are investigated for their physical properties and compared to a suite of
current observations. The best-faring model is then used to predict the
intrinsic alignment contamination of planned weak lensing surveys. We find that
late-type galaxy models generally have weak intrinsic ellipticity correlations,
marginally increasing towards smaller galaxy separation and higher redshift.
The signal for early-type models at fixed halo mass strongly increases by three
orders of magnitude over two decades in galaxy separation, and by one order of
magnitude from z=0 to z=2. The intrinsic alignment strength also depends
strongly on halo mass, but not on galaxy luminosity at fixed mass, or galaxy
number density in the environment. We identify models that are in good
agreement with all observational data, except that all models over-predict
alignments of faint early-type galaxies. The best model yields an intrinsic
alignment contamination of a Euclid-like survey between 0.5-10% at z>0.6 and on
angular scales larger than a few arcminutes. Cutting 20% of red foreground
galaxies using observer-frame colours can suppress this contamination by up to
a factor of two.Comment: 23 pages, 14 figures; minor changes to match version published in
MNRA
Optical response of highly granular YBaCuO films prepared by non-vacuum aerosol deposition
Highly granular YBaCuO films on SrTiO3 substrates with Tc,o~90K and Jc > 104 A/cm2 were prepared by non-vacuum aerosol deposition. The optical response for these films was investigated on a 10 × 10 μm2 microbridge. Besides a bolometric response around the transition temperature, a sharp response peak was observed at low temperature and high bias current using a He-Ne laser (0.63 μm wavelength) illumination. This response was caused by a junction behaviour due to the presence of many boundary-type weak links in our microbridge
Joint Analysis of Cluster Observations: II. Chandra/XMM-Newton X-ray and Weak Lensing Scaling Relations for a Sample of 50 Rich Clusters of Galaxies
We present a study of multiwavelength X-ray and weak lensing scaling
relations for a sample of 50 clusters of galaxies. Our analysis combines
Chandra and XMM-Newton data using an energy-dependent cross-calibration. After
considering a number of scaling relations, we find that gas mass is the most
robust estimator of weak lensing mass, yielding 15 +/- 6% intrinsic scatter at
r500 (the pseudo-pressure YX has a consistent scatter of 22%+/-5%). The scatter
does not change when measured within a fixed physical radius of 1 Mpc. Clusters
with small BCG to X-ray peak offsets constitute a very regular population whose
members have the same gas mass fractions and whose even smaller <10% deviations
from regularity can be ascribed to line of sight geometrical effects alone.
Cool-core clusters, while a somewhat different population, also show the same
(<10%) scatter in the gas mass-lensing mass relation. There is a good
correlation and a hint of bimodality in the plane defined by BCG offset and
central entropy (or central cooling time). The pseudo-pressure YX does not
discriminate between the more relaxed and less relaxed populations, making it
perhaps the more even-handed mass proxy for surveys. Overall, hydrostatic
masses underestimate weak lensing masses by 10% on the average at r500; but
cool-core clusters are consistent with no bias, while non-cool-core clusters
have a large and constant 15-20% bias between r2500 and r500, in agreement with
N-body simulations incorporating unthermalized gas. For non-cool-core clusters,
the bias correlates well with BCG ellipticity. We also examine centroid shift
variance and and power ratios to quantify substructure; these quantities do not
correlate with residuals in the scaling relations. Individual clusters have for
the most part forgotten the source of their departures from self-similarity.Comment: Corrects an error in the X-ray luminosities (erratum
submitted)---none of the other results are affected. Go to
http://sfstar.sfsu.edu/jaco for an electronic fitter and updated quick data
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