609 research outputs found
The FHD/ppsilon Epoch of Reionization Power Spectrum Pipeline
Epoch of Reionization data analysis requires unprecedented levels of accuracy
in radio interferometer pipelines. We have developed an imaging power spectrum
analysis to meet these requirements and generate robust 21 cm EoR measurements.
In this work, we build a signal path framework to mathematically describe each
step in the analysis, from data reduction in the FHD package to power spectrum
generation in the ppsilon package. In particular, we focus on the
distinguishing characteristics of FHD/ppsilon: highly accurate
spectral calibration, extensive data verification products, and end-to-end
error propagation. We present our key data analysis products in detail to
facilitate understanding of the prominent systematics in image-based power
spectrum analyses. As a verification to our analysis, we also highlight a
full-pipeline analysis simulation to demonstrate signal preservation and lack
of signal loss. This careful treatment ensures that the
FHD/ppsilon power spectrum pipeline can reduce radio
interferometric data to produce credible 21 cm EoR measurements.Comment: 21 pages, 10 figures, accepted by PAS
The association between retinal vein ophthalmodynamometric force change and optic disc excavation
Aim: Retinal vein ophthalmodynamometric force (ODF) is predictive of future optic disc excavation in glaucoma, but it is not known if variation in ODF affects prognosis. We aimed to assess whether a change in ODF provides additional prognostic information. Methods: 135 eyes of 75 patients with glaucoma or being glaucoma suspects had intraocular pressure (IOP), visual fields, stereo optic disc photography and ODF measured on an initial visit and a subsequent visit at mean 82 (SD 7.3) months later. Corneal thickness and blood pressure were recorded on the latter visit. When venous pulsation was spontaneous, the ODF was recorded as 0 g. Change in ODF was calculated. Flicker stereochronoscopy was used to determine the occurrence of optic disc excavation, which was modelled against the measured variables using multiple mixed effects logistic regression. Results: Change in ODF (p=0.046) was associated with increased excavation. Average IOP (p=0.66) and other variables were not associated. Odds ratio for increased optic disc excavation of 1.045 per gram ODF change (95% CI 1.001 to 1.090) was calculated. Conclusion: Change in retinal vein ODF may provide additional information to assist with glaucoma prognostication and implies a significant relationship between venous change and glaucoma patho-physiology
Construction of an environmentally sustainable development on a modified coastal sand mined and landfill site-Part 2. Re-establishing the natural ecosystems on the reconstructed beach dunes
Mimicking natural processes lead to progressive colonization and stabilization of the reconstructed beach dune ecosystem, as part of the ecologically sustainable development of Magenta Shores, on the central coast of New South Wales, Australia. The retained and enhanced incipient dune formed the first line of storm defence. Placement of fibrous Leptospermum windrows allowed wind blown sand to form crests and swales parallel to the beach. Burial of Spinifex seed head in the moist sand layer achieved primary colonization of the reconstructed dune and development of a soil fungal hyphae network prior to introduction of secondary colonizing species. Monitoring stakes were used as roosts by birds, promoting re-introduction of native plant species requiring germination by digestive tract stimulation. Bush regeneration reduced competition from weeds, allowing native vegetation cover to succeed. On-going weeding and monitoring are essential at Magenta Shores until bitou bush is controlled for the entire length of beach. The reconstructed dunes provide enhanced protection from sand movement and storm bite, for built assets, remnant significant vegetation and sensitive estuarine ecosystems. © 2010 by the authors
Computation of Equilibrium Distributions of Markov Traffic-Assignment Models
Markov traffic-assignment models explicitly represent the day-to-day evolving interaction between traffic congestion and drivers' information acquisition and choice processes. Such models can, in principle, be used to investigate traffic flows in stochastic equilibrium, yielding estimates of the equilibrium mean and covariance matrix of link or route traffic flows. However, in general these equilibrium moments cannot be written down in closed form. While Monte Carlo simulations of the assignment process may be used to produce “empirical” estimates, this approach can be extremely computationally expensive if reliable results (relatively free of Monte Carlo error) are to be obtained. In this paper an alternative method of computing the equilibrium distribution is proposed, applicable to the class of Markov models with linear exponential learning filters. Based on asymptotic results, this equilibrium distribution may be approximated by a Gaussian process, meaning that the problem reduces to determining the first two multivariate moments in equilibrium. The first of these moments, the mean flow vector, may be estimated by a conventional traffic-assignment model. The second, the flow covariance matrix, is estimated through various linear approximations, yielding an explicit expression. The proposed approximations are seen to operate well in a number of illustrative examples. The robustness of the approximations (in terms of network input data) is discussed, and shown to be connected with the “volatility” of the traffic assignment process
PI in the sky: The astronaut science advisor on SLS-2
The Astronaut Science Advisor (ASA, also known as Principal-Investigator-in-a-Box) is an advanced engineering effort to apply expert systems technology to experiment monitoring and control. Its goal is to increase the scientific value of information returned from experiments on manned space missions. The first in-space test of the system will be in conjunction with Professor Larry Young's (MIT) vestibulo-ocular 'Rotating Dome' experiment on the Spacelab Life Sciences 2 mission (STS-58) in the Fall of 1993. In a cost-saving effort, off-the-shelf equipment was employed wherever possible. Several modifications were necessary in order to make the system flight-worthy. The software consists of three interlocking modules. A real-time data acquisition system digitizes and stores all experiment data and then characterizes the signals in symbolic form; a rule-based expert system uses the symbolic signal characteristics to make decisions concerning the experiment; and a highly graphic user interface requiring a minimum of user intervention presents information to the astronaut operator. Much has been learned about the design of software and user interfaces for interactive computing in space. In addition, we gained a great deal of knowledge about building relatively inexpensive hardware and software for use in space. New technologies are being assessed to make the system a much more powerful ally in future scientific research in space and on the ground
A General Stochastic Process for Day-to-Day Dynamic Traffic Assignment: Formulation, Asymptotic Behaviour, and Stability Analysis
This paper presents a general modelling approach to day-to-day dynamic assignment to a congested network through discrete-time stochastic and deterministic process models including an explicit modelling of users’ habit as a part of route choice behaviour, through an exponential smoothing filter, and of their memory of network conditions on past days, through a moving average or an exponentially smoothing filter. An asymptotic analysis of the mean process is carried out to provide a better insight. Results of such analyses are also used for deriving conditions, about values of the system parameters, assuring that the mean process is dissipative and/or converges to some kind of attractor. Numerical small examples are also provided in order to illustrate the theoretical results obtained
A Stewardship Cost Perspective on the Governance of Delegation Relationships:The Case of Social Franchising
We explore how nonprofits can effectively govern delegation relationships. We extend stewardship theory by conceptualizing stewardship costs—costs in delegation relationships based on stewardship behavior. As stewards are theorized as other-regarding, self-actualizing, and intrinsically motivated, so far, literature almost exclusively points to the positive performance potential of stewardship behavior. Addressing this shortcoming, we develop propositions showing how stewardship selection costs rooted in the psychological characteristics of stewardship behavior and stewardship management costs rooted in situational factors of stewardship behavior occur during relationship formation and maintenance, and how they counteract the potential to increase performance. We identify and systematize opportunity costs of delayed growth, limited growth potential, and lost standardization gains, as well as increased selection and management costs. To demonstrate the theoretical potential and empirical relevance of our framework, we illustrate our arguments by referring to social franchising, a scaling strategy considered relevant for nonprofits as well as social enterprises
The Murchison Widefield Array Transients Survey (MWATS). A search for low frequency variability in a bright Southern hemisphere sample
We report on a search for low-frequency radio variability in 944 bright (>
4Jy at 154 MHz) unresolved, extragalactic radio sources monitored monthly for
several years with the Murchison Widefield Array. In the majority of sources we
find very low levels of variability with typical modulation indices < 5%. We
detect 15 candidate low frequency variables that show significant long term
variability (>2.8 years) with time-averaged modulation indices M = 3.1 - 7.1%.
With 7/15 of these variable sources having peaked spectral energy
distributions, and only 5.7% of the overall sample having peaked spectra, we
find an increase in the prevalence of variability in this spectral class. We
conclude that the variability seen in this survey is most probably a
consequence of refractive interstellar scintillation and that these objects
must have the majority of their flux density contained within angular diameters
less than 50 milli-arcsec (which we support with multi-wavelength data). At 154
MHz we demonstrate that interstellar scintillation time-scales become long
(~decades) and have low modulation indices, whilst synchrotron driven
variability can only produce dynamic changes on time-scales of hundreds of
years, with flux density changes less than one milli-jansky (without
relativistic boosting). From this work we infer that the low frequency
extra-galactic southern sky, as seen by SKA-Low, will be non-variable on
time-scales shorter than one year.Comment: 19 pages, 11 figure
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