3,663 research outputs found
Frequency-Domain Stochastic Modeling of Stationary Bivariate or Complex-Valued Signals
There are three equivalent ways of representing two jointly observed
real-valued signals: as a bivariate vector signal, as a single complex-valued
signal, or as two analytic signals known as the rotary components. Each
representation has unique advantages depending on the system of interest and
the application goals. In this paper we provide a joint framework for all three
representations in the context of frequency-domain stochastic modeling. This
framework allows us to extend many established statistical procedures for
bivariate vector time series to complex-valued and rotary representations.
These include procedures for parametrically modeling signal coherence,
estimating model parameters using the Whittle likelihood, performing
semi-parametric modeling, and choosing between classes of nested models using
model choice. We also provide a new method of testing for impropriety in
complex-valued signals, which tests for noncircular or anisotropic second-order
statistical structure when the signal is represented in the complex plane.
Finally, we demonstrate the usefulness of our methodology in capturing the
anisotropic structure of signals observed from fluid dynamic simulations of
turbulence.Comment: To appear in IEEE Transactions on Signal Processin
Space-based geoengineering: challenges and requirements
The prospect of engineering the Earth's climate (geoengineering) raises a multitude of issues associated with climatology, engineering on macroscopic scales, and indeed the ethics of such ventures. Depending on personal views, such large-scale engineering is either an obvious necessity for the deep future, or yet another example of human conceit. In this article a simple climate model will be used to estimate requirements for engineering the Earth's climate, principally using space-based geoengineering. Active cooling of the climate to mitigate anthropogenic climate change due to a doubling of the carbon dioxide concentration in the Earth's atmosphere is considered. This representative scenario will allow the scale of the engineering challenge to be determined. It will be argued that simple occulting discs at the interior Lagrange point may represent a less complex solution than concepts for highly engineered refracting discs proposed recently. While engineering on macroscopic scales can appear formidable, emerging capabilities may allow such ventures to be seriously considered in the long term. This article is not an exhaustive review of geoengineering, but aims to provide a foretaste of the future opportunities, challenges, and requirements for space-based geoengineering ventures
A Power Variance Test for Nonstationarity in Complex-Valued Signals
We propose a novel algorithm for testing the hypothesis of nonstationarity in
complex-valued signals. The implementation uses both the bootstrap and the Fast
Fourier Transform such that the algorithm can be efficiently implemented in
O(NlogN) time, where N is the length of the observed signal. The test procedure
examines the second-order structure and contrasts the observed power variance -
i.e. the variability of the instantaneous variance over time - with the
expected characteristics of stationary signals generated via the bootstrap
method. Our algorithmic procedure is capable of learning different types of
nonstationarity, such as jumps or strong sinusoidal components. We illustrate
the utility of our test and algorithm through application to turbulent flow
data from fluid dynamics
Autologous Chondrocyte Implantation: Scaffold-Based Solutions
Autologous chondrocyte implantation is a surgical technique utilized for repair of articular cartilage defects. The originally described technique for autologous chondrocyte implantation involves applying a liquid suspension of the cultured chondrocytes to a cartilage defect and sealing the defect with a periosteum or collagen patch. Scaffolds for housing chondrocytes were introduced to allow for increased ease of delivery and application, to avoid leakage of chondrocytes out of the defect, and to allow for an implant that more closely mimics the non-uniform tissue architecture of healthy articular cartilage. In this chapter we describe the design, clinical outcomes, and commercial availability of various scaffolds reported in the clinical literature for autologous chondrocyte implantation
Evolution of pulmonary inflammation and nutritional status in infants and young children with cystic fibrosis
Introduction Improved nutrition is the major proven
benefit of newborn screening programmes for cystic
fibrosis (CF) and is associated with better clinical
outcomes. It was hypothesised that early pulmonary
inflammation and infection in infants with CF is
associated with worse nutrition.
Methods Weight, height and pulmonary inflammation
and infection in bronchoalveolar lavage (BAL) were
assessed shortly after diagnosis in infants with CF and
again at 1, 2 and 3 years of age. Body mass index (BMI)
was expressed as z-scores. Inflammatory cells and
cytokines (interleukin 1b (IL-1b), IL-6, IL-8 and tumour
necrosis factor a (TNFa)), free neutrophil elastase
activity and myeloperoxidase were measured in BAL.
Mixed effects modelling was used to assess longitudinal
associations between pulmonary inflammation,
pulmonary infection (Staphylococcus aureus and
Pseudomonas aeruginosa) and BMI z-score after
adjusting for potential confounding factors.
Results Forty-two infants were studied (16 (38%) male;
39 (93%) pancreatic insufficient); 36 were diagnosed by
newborn screening (at median age 4 weeks) and six by
early clinical diagnosis (meconium ileus). Thirty-one
(74%) received antistaphylococcal antibiotics. More than
two-thirds were asymptomatic at each assessment.
Mean BMI z-scores wer
Theoretical and Experimental Investigation of Heat Conduction in Air, Including Effects of Oxygen Dissociation
Solutions are presented for the conduction of beat through a semi-infinite gas medium having a uniform initial temperature and a constant boundary temperature. The coefficients of thermal conductivity and diffusivity are treated as variables, and the solutions are extended to the case of air at temperatures where oxygen dissociation occurs. These solutions are used together with shock-tube measurements to evaluate the integral of thermal conductivity for air as a function of temperature
Estimating the Economic Value of Australian Stock Herding Dogs
This study aimed to estimate the value of the typical Australian herding dog in terms of predicted return on investment. This required an assessment of the costs associated with owning herding dogs and estimation of the work they typically perform. Data on a total of 4,027 dogs were acquired through The Farm Dog Survey which gathered information from 812 herding dog owners around Australia. The median cost involved in owning a herding dog was estimated to be a total of AU40,000. So, herding dogs typically provided their owners with a 5.2-fold return on investment. When respondents were asked to nominate the maximal, one-off, veterinary expenditure they would consider to remedy an illness or injury for an especially valued dog, the median response was AU$1,001–2,000 which is not concordant with the dogs’ calculated median lifetime value. The current findings equip working dog owners with useful information to make financially appropriate expenditure decisions related to their working dogs. This is expected to increase farm profitability and improve welfare for farm dogs
Valuable Behavioural Phenotypes in Australian Farm Dogs
This report presents findings regarding the ways to optimise the performance of livestock working dogs in Australia. The methods available to optimise dog performance include both environmental and genetic factors. The objectives of this study were to identify objective measures of desirable behavioural phenotypes in Australian livestock working dogs and explore genetic parameters of these \u27quality of working life\u27 traits within the Kelpie breed. The document reports on genotyping that reveals gene-behaviour associations and describes heritability estimates that underpin a database for potential estimated breeding value (EBV) calculations
Valuable Behavioural Phenotypes in Australian Farm Dogs
This report presents findings regarding the ways to optimise the performance of livestock working dogs in Australia. The methods available to optimise dog performance include both environmental and genetic factors. The objectives of this study were to identify objective measures of desirable behavioural phenotypes in Australian livestock working dogs and explore genetic parameters of these \u27quality of working life\u27 traits within the Kelpie breed. The document reports on genotyping that reveals gene-behaviour associations and describes heritability estimates that underpin a database for potential estimated breeding value (EBV) calculations
Estimating the Economic Value of Australian Stock Herding Dogs
This study aimed to estimate the value of the typical Australian herding dog in terms of predicted return on investment. This required an assessment of the costs associated with owning herding dogs and estimation of the work they typically perform. Data on a total of 4,027 dogs were acquired through The Farm Dog Survey which gathered information from 812 herding dog owners around Australia. The median cost involved in owning a herding dog was estimated to be a total of AU40,000. So, herding dogs typically provided their owners with a 5.2-fold return on investment. When respondents were asked to nominate the maximal, one-off, veterinary expenditure they would consider to remedy an illness or injury for an especially valued dog, the median response was AU$1,001–2,000 which is not concordant with the dogs’ calculated median lifetime value. The current findings equip working dog owners with useful information to make financially appropriate expenditure decisions related to their working dogs. This is expected to increase farm profitability and improve welfare for farm dogs
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