An Optimal Dimensionality Sampling Scheme on the Sphere for Antipodal Signals In Diffusion Magnetic Resonance Imaging

We propose a sampling scheme on the sphere and develop a corresponding spherical harmonic transform (SHT) for the accurate reconstruction of the diffusion signal in diffusion magnetic resonance imaging (dMRI). By exploiting the antipodal symmetry, we design a sampling scheme that requires the optimal number of samples on the sphere, equal to the degrees of freedom required to represent the antipodally symmetric band-limited diffusion signal in the spectral (spherical harmonic) domain. Compared with existing sampling schemes on the sphere that allow for the accurate reconstruction of the diffusion signal, the proposed sampling scheme reduces the number of samples required by a factor of two or more. We analyse the numerical accuracy of the proposed SHT and show through experiments that the proposed sampling allows for the accurate and rotationally invariant computation of the SHT to near machine precision accuracy.Comment: Will be published in the proceedings of the International Conference Acoustics, Speech and Signal Processing 2015 (ICASSP'2015

An Optimal Dimensionality Multi-shell Sampling Scheme with Accurate and Efficient Transforms for Diffusion MRI

This paper proposes a multi-shell sampling scheme and corresponding transforms for the accurate reconstruction of the diffusion signal in diffusion MRI by expansion in the spherical polar Fourier (SPF) basis. The sampling scheme uses an optimal number of samples, equal to the degrees of freedom of the band-limited diffusion signal in the SPF domain, and allows for computationally efficient reconstruction. We use synthetic data sets to demonstrate that the proposed scheme allows for greater reconstruction accuracy of the diffusion signal than the multi-shell sampling schemes obtained using the generalised electrostatic energy minimisation (gEEM) method used in the Human Connectome Project. We also demonstrate that the proposed sampling scheme allows for increased angular discrimination and improved rotational invariance of reconstruction accuracy than the gEEM schemes.Comment: 4 pages, 4 figures presented at ISBI 201

Dynamics of scalar dissipation in isotropic turbulence: a numerical and modelling study

The physical mechanisms underlying the dynamics of the dissipation of passive scalar fluctuations with a uniform mean gradient in stationary isotropic turbulence are studied using data from direct numerical simulations (DNS), at grid resolutions up to 5123. The ensemble-averaged Taylor-scale Reynolds number is up to about 240 and the Schmidt number is from ⅛ to 1. Special attention is given to statistics conditioned upon the energy dissipation rate because of their important role in the Lagrangian spectral relaxation (LSR) model of turbulent mixing. In general, the dominant physical processes are those of nonlinear amplification by strain rate fluctuations, and destruction by molecular diffusivity. Scalar dissipation tends to form elongated structures in space, with only a limited overlap with zones of intense energy dissipation. Scalar gradient fluctuations are preferentially aligned with the direction of most compressive strain rate, especially in regions of high energy dissipation. Both the nature of this alignment and the timescale of the resulting scalar gradient amplification appear to be nearly universal in regard to Reynolds and Schmidt numbers. Most of the terms appearing in the budget equation for conditional scalar dissipation show neutral behaviour at low energy dissipation but increased magnitudes at high energy dissipation. Although homogeneity requires that transport terms have a zero unconditional average, conditional molecular transport is found to be significant, especially at lower Reynolds or Schmidt numbers within the simulation data range. The physical insights obtained from DNS are used for a priori testing and development of the LSR model. In particular, based on the DNS data, improved functional forms are introduced for several model coefficients which were previously taken as constants. Similar improvements including new closure schemes for specific terms are also achieved for the modelling of conditional scalar variance

FEASIBILITY OF AN OKLAHOMA FRESH GREENS AND COWPEAS PACKING COOPERATIVE

Oklahoma's green producers are not benefiting from a growing fresh market. In order to seize the opportunities offered by the growing fresh market for leafy greens, investment in packing facilities have been evaluated. To make use of these facilities during summer months, the addition of a cowpea shelling enterprise is considered. A business plan for a new generation cooperative is estimated using an updated version of "The Packing Simulation Model" (PACKSIM) The business associates PACKSIM with @RISK®, to incorporate risks in the financial analysis.Agribusiness,

Associated primes of graded components of local cohomology modules

The i-th local cohomology module of a finitely generated graded module M over a standard positively graded commutative Noetherian ring R with respect to the irrelevant ideal R+, is itself graded; all its graded components are finitely generated modules over R-0, the component of R of degree 0. It is known that the n-th component H-R+(i) (M)(n) of this local cohomology module H-R+(i) (M) is zero for all nmuch greater than0. This paper is concerned with the asymptotic behaviour of Ass(R0)(H-R+(i) (M)(n)) as n--> -infinity. The smallest i for which such study is interesting is the finiteness dimension f of M relative to R+, defined as the least integer j for which H-R+(j) (M) is not finitely generated. Brodmann and Hellus have shown that AssR(0)(H-R+(f) (M)(n)) is constant for all nmuch less than0 ( that is in their terminology AssR(0)(H-R+(f) (M)(n)) is asymptotically stable for n--> -infinity). The first main aim of this paper is to identify the ultimate constant value ( under the mild assumption that R is a homomorphic image of a regular ring) : our answer is precisely the set of contractions to R-0 of certain relevant primes of R whose existence is confirmed by Grothendieck's Finiteness Theorem for local cohomology. Brodmann and Hellus raised various questions about such asymptotic behaviour when i>f. They noted that Singh's study of a particular example ( in which f=2) shows that AssR(0)(H-R+(3) (R)(n)) need not be asymptotically stable for n--> -infinity. The second main aim of this paper is to determine, for Singh's example, AssR(0)(H-R+(3) (R)(n)) quite precisely for every integer n and, thereby answer one of the questions raised by Brodmann and Hellus

Establishing the comparative durability of African mahogany (Khaya senegalensis) in weather exposed above-ground applications

This study was established to evaluate the natural durability of ten- and twenty-year-old plantation-grown Khaya senegalensis (African mahogany) above ground. Whilst mature African mahogany heartwood is expected to last five to 15 years in ground, Australian natural durability standards and specifications do not currently provide information on the durability performance of African mahogany when used above ground. A ground proximity field test was installed at DAFF’s South Johnstone Research Facility in north Queensland and modified ground proximity tests were also installed in a fungal cellar at DAFF’s Salisbury Research Facility near Brisbane. Whilst the plantation African mahogany tested appears more durable than pine, it is not yet possible to determine if its’ durability is consistent with expectations for durability class 3 or durability class 2 timbers above ground. Minimal decay of test specimens had occurred after 12 months and more time is required before reliable conclusions can be drawn. Data gathered, however, are vital for any future durability modelling for plantation African mahogany, to calculate the lag for decay initiation and rates of decay

Alternative and horticulture crop education and marketing pilot project

How do farmers embark on a new type of production system, such as for vegetable and horticultural crops? This project helped a group of southern Iowa farmers organize infrastructure and find markets for these crops outside the usual farmers markets

Asymmetric Arbitage and Normal Backwardation

This paper provides a theoretical explanation for the existence of backwardation on the futures markets, based on Routhakker's work dealing with asymmetry of arbitrage on such markets. The central assumption of the paper is that cash and futures prices tend to be more highly correlated at low than at high cash prices. This assumption reflects the asymmetry in arbitrage opportunities in futures markets; in particular, at the maturity date of a futures contract, the futures price cannot exceed the cash price of any grade-location combination deliverable under the futures contract. The main result of the paper is a proposition that asserts that with identical long and short hedgers, with the same wheat commitments on both sides of the market, and with utility functions exhibiting constant or decreasing absolute risk aversion, if the probability density function over cash and futures prices is sufficiently concentrated at low cash prices, then the resulting market equilibrium will exhibit backwardation, that is, the current future price is a downward biased estimator of the future futures price as well as being a downward biased estimator of the future cash price