Improving the boundary efficiency of a compact finite difference scheme through optimising its composite template

This paper presents efforts to improve the boundary efficiency and accuracy of a compact finite difference scheme, based on its composite template. Unlike precursory attempts the current methodology is unique in its quantification of dispersion and dissipation errors, which are only evaluated after the matrix system of equations has been rearranged for the derivative. This results in a more accurate prediction of the boundary performance, since the analysis is directly based on how the derivative is represented in simulations. A genetic algorithm acts as a comprehensive method for the optimisation of the boundary coefficients, incorporating an eigenvalue constraint for the linear stability of the matrix system of equations. The performance of the optimised composite template is tested on one-dimensional linear wave convection and two-dimensional inviscid vortex convection problems, with uniform and curvilinear grids. In all cases, it yields substantial accuracy and efficiency improvements while maintaining stable solutions and fourth-order accuracy

Quantam wave turbulence

The nonlinear quantum kinetic equation for the interaction of sound waves is solved via analytic and numerical techniques. In the classical regime energy cascades to higher frequency (ω) according to the steady-state power law ω-3/2. In the quantum limit, the system prefers a reverse cascade of energy which follows the power law ω-6. Above a critical flux, a new type of spectrum appears which is neither self-similar nor close to equilibrium. This state of nonlinear quantum wave turbulence represents a flow of energy directly from the classical source to the quantum degrees of freedom

Airfoil noise reductions through leading edge serrations

This paper provides an experimental investigation into the use of leading edge (LE) serrations as a means of reducing the broadband noise generated due to the interaction between the aerofoil's LE and impinging turbulence. Experiments are performed on a flat plate in an open jet wind tunnel. Grids are used to generate isotropic homogeneous turbulence. The leading edge serrations are in the form of sinusoidal profiles of wavelengths, λ, and amplitudes, 2h. The frequency and amplitude characteristics are studied in detail in order to understand the effect of LE serrations on noise reduction characteristics and are compared with straight edge baseline flat plates. Noise reductions are found to be insignificant at low frequencies but significant in the mid frequency range (500 Hz-8 kHz) for all the cases studied. The flat plate results are also compared to the noise reductions obtained on a serrated NACA-65 aerofoil with the same serration profile. Noise reductions are found to be significantly higher for the flat plates with a maximum noise reduction of around 9 dB compared with about 7 dB for the aerofoil. In general, it is observed that the sound power reduction level (ΔPWL) is sensitive to the amplitude, 2h of the LE serrations but less sensitive to the serration wavelength, λ. Thus, this paper sufficiently demonstrates that the LE amplitude acts as a key parameter for enhancing the noise reduction levels in flat plates and aerofoils

Gauge covariance and the fermion-photon vertex in three- and four- dimensional, massless quantum electrodynamics

In the quenched approximation, the gauge covariance properties of three vertex Ans\"{a}tze in the Schwinger-Dyson equation for the fermion self energy are analysed in three- and four- dimensional quantum electrodynamics. Based on the Cornwall-Jackiw-Tomboulis effective action, it is inferred that the spectral representation used for the vertex in the gauge technique cannot support dynamical chiral symmetry breaking. A criterion for establishing whether a given Ansatz can confer gauge covariance upon the Schwinger-Dyson equation is presented and the Curtis and Pennington Ansatz is shown to satisfy this constraint. We obtain an analytic solution of the Schwinger-Dyson equation for quenched, massless three-dimensional quantum electrodynamics for arbitrary values of the gauge parameter in the absence of dynamical chiral symmetry breaking.Comment: 17 pages, PHY-7143-TH-93, REVTE

Window on Higgs Boson: Fourth Generation b′b^\prime Decays Revisited

Direct and indirect searches of the Higgs boson suggest that 113 GeV $\lesssim m_H \lesssim$ 170 GeV is likely. With the LEP era over and the Tevatron Run II search via $p\bar p \to WH+X$ arduous, we revisit a case where $WH$ or $ZH +$ jets could arise via strong $b^\prime\bar b^\prime$ pair production. In contrast to 10 years ago, the tight electroweak constraint on $t^\prime$--$b^\prime$ (hence $t^\prime$--$t$) splitting reduces FCNC $b^\prime\to bZ$, $bH$ rates, making $b^\prime\to cW$ naturally competitive. Such a "cocktail solution" is precisely the mix that could evade the CDF search for $b^\prime\to bZ$, and the $b^\prime$ may well be lurking below the top. In light of the Higgs program, this two-in-one strategy should be pursued.Comment: 4 pages, RevTex, 4 eps figures, One more figure, version to be published in Phys. Rev.

First-trimester maternal vitamin D status and risk for gestational diabetes (GDM) a nested case-control study

BACKGROUND: Vitamin D deficiency may contribute to impaired glucose metabolism. There are sparse data regarding vitamin D and the development of gestational diabetes (GDM). The objective of this study was to assess if first-trimester vitamin D deficiency is more prevalent in women later diagnosed with GDM compared with women with uncomplicated pregnancies. METHODS: We conducted a nested case-control study of pregnant women who had previously given blood for routine genetic multiple marker screening and subsequently delivered at a tertiary hospital between November 2004 and July 2009. From an overall cohort of 4225 women, 60 cases of GDM were matched by race/ethnicity with 120 women delivering at term (≥37 weeks) with uncomplicated pregnancies. Banked maternal serum was used to measure maternal 25-hydroxyvitamin D [25(OH)D]. RESULTS: The prevalence of first-trimester maternal vitamin D deficiency (defined as 25(OH)D < 50 nmol/L) was comparable among women with GDM compared with controls (5/60 vs 8/120, p = 0.90). The median 25(OH)D level for all subjects was 89 nmol/L (interquartile range, 73-106 nmol/L). Seventy three percent (117/160) of the cohort had 25(OH)D levels ≥75 nmol/L. CONCLUSIONS: In a cohort of pregnant women with mostly sufficient levels of serum 25(OH)D, vitamin D deficiency was not associated with GDM. Further studies are warranted with larger cohorts, especially in populations with lower levels of vitamin D

FLI1 (Friend leukemia virus integration 1)

Review on FLI1 (Friend leukemia virus integration 1), with data on DNA, on the protein encoded, and where the gene is implicated