198 research outputs found
Redshift Weights for Baryon Acoustic Oscillations : Application to Mock Galaxy Catalogs
Large redshift surveys capable of measuring the Baryon Acoustic Oscillation
(BAO) signal have proven to be an effective way of measuring the
distance-redshift relation in cosmology. Building off the work in Zhu et al.
(2015), we develop a technique to directly constrain the distance-redshift
relation from BAO measurements without splitting the sample into redshift bins.
We parametrize the distance-redshift relation, relative to a fiducial model, as
a quadratic expansion. We measure its coefficients and reconstruct the
distance-redshift relation from the expansion. We apply the redshift weighting
technique in Zhu et al. (2015) to the clustering of galaxies from 1000 QuickPM
(QPM) mock simulations after reconstruction and achieve a 0.75% measurement of
the angular diameter distance at and the same precision for
Hubble parameter H at . These QPM mock catalogs are designed to mimic
the clustering and noise level of the Baryon Oscillation Spectroscopic Survey
(BOSS) Data Release 12 (DR12). We compress the correlation functions in the
redshift direction onto a set of weighted correlation functions. These
estimators give unbiased and measurements at all redshifts within the
range of the combined sample. We demonstrate the effectiveness of redshift
weighting in improving the distance and Hubble parameter estimates. Instead of
measuring at a single 'effective' redshift as in traditional analyses, we
report our and measurements at all redshifts. The measured fractional
error of ranges from 1.53% at to 0.75% at . The
fractional error of ranges from 0.75% at to 2.45% at .
Our measurements are consistent with a Fisher forecast to within 10% to 20%
depending on the pivot redshift. We further show the results are robust against
the choice of fiducial cosmologies, galaxy bias models, and RSD streaming
parameters.Comment: 13 pages, 8 figures, submitted to MNRA
NOMA-enhanced computation over multi-access channels
Massive numbers of nodes will be connected in future wireless networks. This brings great difficulty to collect a large amount of data. Instead of collecting the data individually, computation over multi-access channels (CoMAC) provides an intelligent solution by computing a desired function over the air based on the signal-superposition property of wireless channels. To improve the spectrum efficiency in conventional CoMAC, we propose the use of non-orthogonal multiple access (NOMA) for functions in CoMAC. The desired functions are decomposed into several sub-functions, and multiple sub-functions are selected to be superposed over each resource block (RB). The corresponding achievable rate is derived based on sub-function superposition, which prevents a vanishing computation rate for large numbers of nodes. We further study the limiting case when the number of nodes goes to infinity. An exact expression of the rate is derived that provides a lower bound on the computation rate. Compared with existing CoMAC, the NOMA-based CoMAC not only achieves a higher computation rate but also provides an improved non-vanishing rate. Furthermore, the diversity order of the computation rate is derived, which shows that the system performance is dominated by the node with the worst channel gain among these sub-functions in each RB
Optimal Redshift Weighting For Redshift Space Distortions
The low statistical errors on cosmological parameters promised by future
galaxy surveys will only be realised with the development of new, fast,
analysis methods that reduce potential systematic problems to low levels. We
present an efficient method for measuring the evolution of the growth of
structure using Redshift Space Distortions (RSD), that removes the need to make
measurements in redshift shells. We provide sets of galaxy-weights that cover a
wide range in redshift, but are optimised to provide differential information
about cosmological evolution. These are derived to optimally measure the
coefficients of a parameterisation of the redshift-dependent matter density,
which provides a framework to measure deviations from the concordance
CDM cosmology, allowing for deviations in both geometric and/or
growth. We test the robustness of the weights by comparing with alternative
schemes and investigate the impact of galaxy bias. We extend the results to
measure the combined anisotropic Baryon Acoustic Oscillation (BAO) and RSD
signals.Comment: 10 pages, 5 figures, submitted to MNRA
Passivity-Based Co-Design of Active Damping and Voltage Controller for Converter-Based Grid Emulator
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