324 research outputs found
Deconvolution with Shapelets
We seek to find a shapelet-based scheme for deconvolving galaxy images from
the PSF which leads to unbiased shear measurements. Based on the analytic
formulation of convolution in shapelet space, we construct a procedure to
recover the unconvolved shapelet coefficients under the assumption that the PSF
is perfectly known. Using specific simulations, we test this approach and
compare it to other published approaches. We show that convolution in shapelet
space leads to a shapelet model of order
with and being the maximum orders of the intrinsic
galaxy and the PSF models, respectively. Deconvolution is hence a
transformation which maps a certain number of convolved coefficients onto a
generally smaller number of deconvolved coefficients. By inferring the latter
number from data, we construct the maximum-likelihood solution for this
transformation and obtain unbiased shear estimates with a remarkable amount of
noise reduction compared to established approaches. This finding is
particularly valid for complicated PSF models and low images, which
renders our approach suitable for typical weak-lensing conditions.Comment: 9 pages, 9 figures, submitted to A&
Recommended from our members
Comparisons of IASI-A and AATSR measurements of top-of-atmosphere radiance over an extended period
This study examines the trustworthiness of the Advanced Along-Track Scanning Radiometer (AATSR) and the Infrared Atmospheric Sounding Interferometer (IASI-A), as on-orbit reference instruments that are useful in re-calibrating the Advanced Very High Resolution Radiometer (AVHRR) series (Mittaz and Harris, 2011). To do this, a 39-month period (1 January 2008 to 31 March 2011) of AATSR and IASI-A inter-comparisons of top-of-atmosphere (TOA) radiance measurements is examined. Our inter-comparison reveals features of the AATSR and IASI-A bias with respect to scan angle, scene temperature, time and orbital maneuvers, and gives insight into their trustworthiness as an in-orbit reference instruments.
The first feature that our study reveals is that the AATSR (nadir view) and IASI-A are both stable (have no perceptible trends in the period of study). The second feature is that IASI-A is perhaps more accurate ( ∼  0.05 K) than its stated accuracy (0.5 K). In fact the AATSR and IASI-A bias is close to the AATSR pre-launch bias (plus a small offset of +0.07 K) implying that IASI-A can get close to pre-launch levels of accuracy. Third, a very small scan angular dependence of AATSR and IASI-A bias indicates that the IASI-A response vs. scan angle algorithm is robust, while the instrument is in orbit.
Inter-comparisons of AATSR with IASI-A further reveal the impact of orbital maneuvers of the ENVISAT, the platform carrying AATSR, done in October 2011 and not anticipated previously. Our study reveals that this maneuver introduced a temperature-dependent bias in the AATSR measurements for low temperatures (< 240 K) in the period following this maneuver (Cocevar et al., 2011). Our study also shows that the known AATSR 12 µm channel offset is in fact temperature dependent, grows up to 0.4 K, varies seasonally and is correlated with instrument temperature and cannot be corrected by shifting the spectral response function (SRF) of AATSR.
We also present a set of recommendations to help identify the parameters under which these instruments can provide the most trustworthy observations for the AVHRR re-calibration
A new analysis of the WASP-3 system: no evidence for an additional companion
In this work we investigate the problem concerning the presence of additional
bodies gravitationally bounded with the WASP-3 system. We present eight new
transits of this planet and analyse all the photometric and radial velocity
data published so far. We did not observe significant periodicities in the
Fourier spectrum of the observed minus calculated (O-C) transit timing and
radial velocity diagrams (the highest peak having false-alarm probabilities of
56 per cent and 31 per cent, respectively) or long-term trends. Combining all
the available information, we conclude that the radial velocity and transit
timing techniques exclude, at 99 per cent confidence limit, any perturber more
massive than M \gtrsim 100 M_Earth with periods up to 10 times the period of
the inner planet. We also investigate the possible presence of an exomoon on
this system and determined that considering the scatter of the O-C transit
timing residuals a coplanar exomoon would likely produce detectable transits.
This hypothesis is however apparently ruled out by observations conducted by
other researchers. In case the orbit of the moon is not coplanar the accuracy
of our transit timing and transit duration measurements prevents any
significant statement. Interestingly, on the basis of our reanalysis of SOPHIE
data we noted that WASP-3 passed from a less active (log R'_hk=-4.95) to a more
active (log R'_hk=-4.8) state during the 3 yr monitoring period spanned by the
observations. Despite no clear spot crossing has been reported for this system,
this analysis claims for a more intensive monitoring of the activity level of
this star in order to understand its impact on photometric and radial velocity
measurements.Comment: MNRAS accepted (14/08/2012
IGG-antibody seroprevalence of West Nile Virus among blood donors in Nairobi and Nakuru regional blood transfusion testing centers in Kenya
Background: West Nile Virus (WNV) is an arbovirus transmitted by infected mosquitoes which cause most of its incidence (CDC, 2015). It is transmitted by the culex mosquito which is prevalent in Kenya.Objective: To determine and compare the sero prevalence of WNV among blood donors in Nairobi and Nakuru Regional blood transfusion testing centers in Kenya.Study design: A cross-sectional studySetting: It was carried out in two Regional Blood Transfusion Centers (RBTCs) which are based in Nairobi and Nakuru. These two centers are associated with possible low and high prevalence respectively.Subject: A total of 180 blood samples were randomly selected over a period of one month. These blood samples were tested for WNV IgG using ELISA. Results: Majority of the donors were below 35 years of age and were predominantly male. WNV IgG prevalence was 15% in blood donors (95% CI 10-20.5%). Prevalence of cross infection of TTI and WNV was 8.3% (95% CI 4.4- 12.2%). The prevalence of WVN IgG was highest in the 19-35 years’ age group (16.5%) and females (21.6%) though the results were not statistically significant. There was no difference in the IgG positivity between the different centers.Conclusion: Infection with WNV should be of public health concern because about a fifth of those infected with WNV develop illness. About 10% of those who develop neurological symptoms succumb to the disease
The importance of the merging activity for the kinetic polarization of the Sunyaev-Zel'dovich signal from galaxy clusters
The polarization sensitivity of the upcoming millimetric observatories will
open new possibilities for studying the properties of galaxy clusters and for
using them as powerful cosmological probes. For this reason it is necessary to
investigate in detail the characteristics of the polarization signals produced
by their highly ionized intra-cluster medium (ICM). This work is focussed on
the polarization effect induced by the ICM bulk motions, the so-called kpSZ
signal, which has an amplitude proportional to the optical depth and to the
square of the tangential velocity. In particular we study how this polarization
signal is affected by the internal dynamics of galaxy clusters and what is its
dependence on the physical modelling adopted to describe the baryonic
component. This is done by producing realistic kpSZ maps starting from the
outputs of two different sets of high-resolution hydrodynamical N-body
simulations. The first set (17 objects) follows only non-radiative
hydrodynamics, while for each of 9 objects of the second set we implement four
different kinds of physical processes. Our results shows that the kpSZ signal
turns out to be a very sensitive probe of the dynamical status of galaxy
clusters. We find that major merger events can amplify the signal up to one
order of magnitude with respect to relaxed clusters, reaching amplitude up to
about 100 nuK. This result implies that the internal ICM dynamics must be taken
into account when evaluating this signal because simplicistic models, based on
spherical rigid bodies, may provide wrong estimates. Finally we find that the
dependence on the physical modelling of the baryonic component is relevant only
in the very inner regions of clusters.Comment: 13 pages, 7 figures, submitted to A&
Reproducibility of Statistical Tests Based on Randomised Response Data
Reproducibility of experimental conclusions is an important topic in various fields, including social studies. The lack of reproducibility in research results not only limits scientific progress, but also wastes time, resources, and undermines society’s confidence in scientific findings. This paper focuses on the statistical reproducibility of hypothesis test outcomes based on data collected using randomised response techniques (RRT). Nonparametric predictive inference (NPI) is used to quantify reproducibility, which is well-suited to treat reproducibility as a prediction problem. NPI relies on few model assumptions and provides lower and upper bounds for reproducibility probabilities. This paper concludes that less variability in the reported responses of RRT methods leads to higher reproducibility of statistical hypothesis tests based on RRT data with the same degree of privacy
Smoothed Bootstrap Methods for Hypothesis Testing
This paper demonstrates the application of smoothed bootstrap methods and Efron’s methods for hypothesis testing on real-valued data, right-censored data and bivariate data. The tests include quartile hypothesis tests, two sample medians and Pearson and Kendall correlation tests. Simulation studies indicate that the smoothed bootstrap methods outperform Efron’s methods in most scenarios, particularly for small datasets. The smoothed bootstrap methods provide smaller discrepancies between the actual and nominal error rates, which makes them more reliable for testing hypotheses
Predictive inference for system reliability after common-cause component failures
Abstract This paper presents nonparametric predictive inference for system reliability following common-cause failures of components. It is assumed that a single failure event may lead to simultaneous failure of multiple components. Data consist of frequencies of such events involving particular numbers of components. These data are used to predict the number of components that will fail at the next failure event. The effect of failure of one or more components on the system reliability is taken into account through the system's survival signature. The predictive performance of the approach, in which uncertainty is quantified using lower and upper probabilities, is analysed with the use of ROC curves. While this approach is presented for a basic scenario of a system consisting of only a single type of components and without consideration of failure behaviour over time, it provides many opportunities for more general modelling and inference, these are briefly discussed together with the related research challenges
SHELS: Testing Weak Lensing Maps with Redshift Surveys
Weak lensing surveys are emerging as an important tool for the construction
of "mass selected" clusters of galaxies. We evaluate both the efficiency and
completeness of a weak lensing selection by combining a dense, complete
redshift survey, the Smithsonian Hectospec Lensing Survey (SHELS), with a weak
lensing map from the Deep Lens Survey (DLS). SHELS includes 11,692 redshifts
for galaxies with R < 20.6 in the four square degree DLS field; the survey is a
solid basis for identifying massive clusters of galaxies with redshift z <
0.55. The range of sensitivity of the redshift survey is similar to the range
for the DLS convergence map. Only four the twelve convergence peaks with
signal-to-noise > 3.5 correspond to clusters of galaxies with M > 1.7 x 10^14
solar masses. Four of the eight massive clusters in SHELS are detected in the
weak lensing map yielding a completeness of roughly 50%. We examine the seven
known extended cluster x-ray sources in the DLS field: three can be detected in
the weak lensing map, three should not be detected without boosting from
superposed large-scale structure, and one is mysteriously undetected even
though its optical properties suggest that it should produce a detectable
lensing signal. Taken together, these results underscore the need for more
extensive comparisons among different methods of massive cluster
identification.Comment: 34 pages, 16 figures, ApJ accepte
- …