4,372 research outputs found
Systematic Errors in Cosmic Microwave Background Interferometry
Cosmic microwave background (CMB) polarization observations will require
superb control of systematic errors in order to achieve their full scientific
potential, particularly in the case of attempts to detect the B modes that may
provide a window on inflation. Interferometry may be a promising way to achieve
these goals. This paper presents a formalism for characterizing the effects of
a variety of systematic errors on interferometric CMB polarization
observations, with particular emphasis on estimates of the B-mode power
spectrum. The most severe errors are those that couple the temperature
anisotropy signal to polarization; such errors include cross-talk within
detectors, misalignment of polarizers, and cross-polarization. In a B mode
experiment, the next most serious category of errors are those that mix E and B
modes, such as gain fluctuations, pointing errors, and beam shape errors. The
paper also indicates which sources of error may cause circular polarization
(e.g., from foregrounds) to contaminate the cosmologically interesting linear
polarization channels, and conversely whether monitoring of the circular
polarization channels may yield useful information about the errors themselves.
For all the sources of error considered, estimates of the level of control that
will be required for both E and B mode experiments are provided. Both
experiments that interfere linear polarizations and those that interfere
circular polarizations are considered. The fact that circular experiments
simultaneously measure both linear polarization Stokes parameters in each
baseline mitigates some sources of error.Comment: 19 pages, 9 figures, submitted to Phys. Rev.
Mosaicking with cosmic microwave background interferometers
Measurements of cosmic microwave background (CMB) anisotropies by
interferometers offer several advantages over single-dish observations. The
formalism for analyzing interferometer CMB data is well developed in the
flat-sky approximation, valid for small fields of view. As the area of sky is
increased to obtain finer spectral resolution, this approximation needs to be
relaxed. We extend the formalism for CMB interferometry, including both
temperature and polarization, to mosaics of observations covering arbitrarily
large areas of the sky, with each individual pointing lying within the flat-sky
approximation. We present a method for computing the correlation between
visibilities with arbitrary pointing centers and baselines and illustrate the
effects of sky curvature on the l-space resolution that can be obtained from a
mosaic.Comment: 9 pages; submitted to Ap
A deep Chandra observation of the poor cluster AWM4 - II. The role of the radio jets in enriching the intra-cluster medium
We use a Chandra observation of the poor cluster AWM4 to map the temperature
and abundance of the intra-cluster medium, so as to examine the influence of
the central radio galaxy on its environment. While the cluster core is
generally enriched to near-solar abundances, we find evidence of super-solar
abundances correlated with the radio jets, extending ~35 kpc from the core of
the central dominant galaxy NGC 6051 along its minor axis. We conclude that the
enriched gas has been transported out of the central galaxy through the action
of the radio source. We estimate the excess mass of iron in the entrained gas
to be ~1.4x10^6 Msol, and find that this can be produced in the core of NGC
6051 within the timescale of the AGN outburst. The energy required to transport
this gas to its current location is ~4.5x10^57 erg, a significant fraction of
the estimated total mechanical energy output of the AGN, though this estimate
is dependent on the degree of enrichment of the uplifted gas. The larger
near-solar abundance region is also compatible with enrichment by metals mixed
outward from NGC 6051 over a much longer timescale.Comment: Accepted for publication in MNRAS, 11 pages, 6 figure
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Identification and quantification of major faba bean seed proteins
Faba bean (Vicia faba L.) holds great importance for human and animal nutrition for its high protein content. However, better understanding of its seed protein composition is required in order to develop cultivars that meet market demands for plant proteins with specific quality attributes. In this study, we screened 35 diverse Vicia faba genotypes by employing the one-dimensional sodium dodecyl sulfate–polyacrylamide gel electrophoresis (1D SDS-PAGE) method, and 35 major protein bands obtained from three genotypes with contrasting seed protein profiles were further analyzed by mass spectrometry (MS). Twenty-five of these protein bands (MW range: ∼ 9–107 kDa) had significant (p ≤ 0.05) matches to polypeptides in protein databases. MS analysis showed that most of the analyzed protein bands contained more than one protein type and, in total, over 100 proteins were identified. These included major seed storage proteins such as legumin, vicilin, and convicilin, as well as other protein classes like lipoxygenase, heat shock proteins, sucrose-binding proteins, albumin, and defensin. Furthermore, seed protein extracts were separated by size-exclusion high-performance liquid chromatography (SE-HPLC), and percentages of the major protein classes were determined. On average, legumin and vicilin/convicilin accounted for 50 and 27% of the total protein extract, respectively. However, the proportions of these proteins varied considerably among genotypes, with the ratio of legumin:vicilin/convicilin ranging from 1:1 to 1:3. In addition, there was a significant (p < 0.01) negative correlation between the contents of these major fractions (r = −0.83). This study significantly extends the number of identified Vicia faba seed proteins and reveals new qualitative and quantitative variation in seed protein composition, filling a significant gap in the literature. Moreover, the germplasm and screening methods presented here are expected to contribute in selecting varieties with improved protein content and quality
A microfabricated sensor for thin dielectric layers
We describe a sensor for the measurement of thin dielectric layers capable of
operation in a variety of environments. The sensor is obtained by
microfabricating a capacitor with interleaved aluminum fingers, exposed to the
dielectric to be measured. In particular, the device can measure thin layers of
solid frozen from a liquid or gaseous medium. Sensitivity to single atomic
layers is achievable in many configurations and, by utilizing fast, high
sensitivity capacitance read out in a feedback system onto environmental
parameters, coatings of few layers can be dynamically maintained. We discuss
the design, read out and calibration of several versions of the device
optimized in different ways. We specifically dwell on the case in which
atomically thin solid xenon layers are grown and stabilized, in cryogenic
conditions, from a liquid xenon bath
Strategic misrepresentation in online dating: The effects of gender, self-monitoring, and personality traits
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Unsettling sustainability: the poetics of discomfort
peerreview_statement: The publishing and review policy for this title is described in its Aims & Scope. aims_and_scope_url: http://www.tandfonline.com/action/journalInformation?show=aimsScope&journalCode=rgrl2
Ion energy distribution measurements in rf and pulsed dc plasma discharges
A commercial retarding field analyzer is used to measure the time-averaged ion energy distributions of impacting ions at the powered electrode in a 13.56 MHz driven, capacitively coupled, parallel plate discharge operated at low pressure. The study is carried out in argon discharges at 10 mTorr where the sheaths are assumed to be collisionless. The analyzer is mounted flush with the powered electrode surface where the impacting ion and electron energy distributions are measured for a range of discharge powers. A circuit model of the discharge, in combination with analytical solutions for the ion energy distribution in radio-frequency sheaths, is used to calculate other important plasma parameters from the measured energy distributions. Radio-frequency compensated Langmuir probe measurements provide a comparison with the retarding field analyzer data. The time-resolved capability of the retarding field analyzer is also demonstrated in a separate pulsed dc magnetron reactor. The analyzer is mounted on the floating substrate holder and ion energy distributions of the impinging ions on a growing film, with 100 ns time resolution, are measured through a pulse period of applied magnetron power, which are crucial for the control of the microstructure and properties of the deposited films
Creativity and Autonomy in Swarm Intelligence Systems
This work introduces two swarm intelligence algorithms -- one mimicking the behaviour of one species of ants (\emph{Leptothorax acervorum}) foraging (a `Stochastic Diffusion Search', SDS) and the other algorithm mimicking the behaviour of birds flocking (a `Particle Swarm Optimiser', PSO) -- and outlines a novel integration strategy exploiting the local search properties of the PSO with global SDS behaviour. The resulting hybrid algorithm is used to sketch novel drawings of an input image, exploliting an artistic tension between the local behaviour of the `birds flocking' - as they seek to follow the input sketch - and the global behaviour of the `ants foraging' - as they seek to encourage the flock to explore novel regions of the canvas. The paper concludes by exploring the putative `creativity' of this hybrid swarm system in the philosophical light of the `rhizome' and Deleuze's well known `Orchid and Wasp' metaphor
Observational Strategies of CMB Temperature and Polarization Interferometry Experiments
We have simulated the interferometric observation of the Cosmic Microwave
Background (CMB) temperature and polarization fluctuations. We have constructed
data pipelines from the time-ordered raw visibility samples to the CMB power
spectra which utilize the methods of data compression, maximum likelihood
analysis, and optimal subspace filtering. They are customized for three
observational strategies, such as the single pointing, the mosaicking, and the
drift-scanning. For each strategy, derived are the optimal strategy parameters
that yield band power estimates with minimum uncertainty. The results are
general and can be applied to any close-packed array on a single platform such
as the CBI and the forthcoming AMiBA experiments. We have also studied the
effect of rotation of the array platform on the band power correlation by
simulating the CBI single pointing observation. It is found that the band power
anti-correlations can be reduced by rotating the platform and thus densely
sampling the visibility plane. This enables us to increase the resolution of
the power spectrum in the l-space down to the limit of the sampling theorem
(Delta l = 226 = pi / theta), which is narrower by a factor of about sqrt{2}
than the resolution limit (Delta l = 300) used in the recent CBI single
pointing observation. The validity of this idea is demonstrated for a
two-element interferometer that samples visibilities uniformly in the
uv-annulus. From the fact that the visibilities are the Fourier modes of the
CMB field convolved with the beam, a fast unbiased estimator (FUE) of the CMB
power spectra is developed and tested. It is shown that the FUE gives results
very close to those from the quadratic estimator method without requiring large
computer resources even though uncertainties in the results increase.Comment: 33 pages, 6 figures, Accepted version for publication in
Astrophysical Journa
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