Coherent Flaw Reflectivity Estimation in Nonstationary Noise

This paper presents a model for RF broadband ultrasonic A-scans obtained from materials composed of microstructures, in which isolated flaws or impurities may exist. The model incorporates both the RF phase and magnitude differences between the microstructure and coherent flaw echo spectra. An adaptive implementation of the maximum-likelihood estimator (MLE) is presented for estimating A-scan amplitudes associated with coherent scatterers embedded in grain echoes. The adaptive implementation is motivated by the nonstationary behavior of the back-scattered energy received over the duration of the A-scan [1]. This nonstationarity results from the frequency dependent absorption, scattering, and diffraction that occurs as the pulse propagates through the materia

Axial anomaly and magnetism of nuclear and quark matter

We consider the response of the QCD ground state at finite baryon density to a strong magnetic field B. We point out the dominant role played by the coupling of neutral Goldstone bosons, such as pi^0, to the magnetic field via the axial triangle anomaly. We show that, in vacuum, above a value of B ~ m_pi^2/e, a metastable object appears - the pi^0 domain wall. Because of the axial anomaly, the wall carries a baryon number surface density proportional to B. As a result, for B ~ 10^{19} G a stack of parallel pi^0 domain walls is energetically more favorable than nuclear matter at the same density. Similarly, at higher densities, somewhat weaker magnetic fields of order B ~ 10^{17}-10^{18} G transform the color-superconducting ground state of QCD into new phases containing stacks of axial isoscalar (eta or eta') domain walls. We also show that a quark-matter state known as ``Goldstone current state,'' in which a gradient of a Goldstone field is spontaneously generated, is ferromagnetic due to the axial anomaly. We estimate the size of the fields created by such a state in a typical neutron star to be of order 10^{14}-10^{15} G.Comment: 18 pages, v2: added a discussion of the energy cost of neutralizing the domain wall charg

Health system constraints to optimal coverage of the prevention of mother-to-child HIV transmission programme in South Africa: lessons from the implementation of the national pilot programme

Background: It is three years since the government of South Africa began implementing a PMTCT programme. Over this period of time attempts have been made to scale up this programme across all provinces under routine health service conditions. Objectives: To report on the uptake and performance of South Africa\'s national pilot programme for preventing mother to child HIV transmission (PMTCT) and to identify health system constraints to optimal coverage. Methods: Routine programme data were collected from antenatal records and delivery registers at the pilot sites and interviews were conducted with health workers on site and with provincial programme managers. Results: Routine PMTCT programme data were collected from all 18 pilot sites for the period January to December 2002. During this period, of 84406 women attending the sites for first antenatal visits, 47267 (56%) agreed to an HIV test. 14340 (30%) of the women tested were HIV positive and of these 7853 (55%) were dispensed nevirapine. 7950 (99%) of infants born to women identified as being HIV positive received nevirapine syrup. 58% (4196/7237) of HIV positive women expressed an intention to exclusively formula feed, and 42% (3041/7237) intended to exclusively breastfeed. 1907 infants were due for 12 month HIV testing between January and December 2002, of these 949 (50%) infants were tested. Conclusions: Programme effectiveness was limited by the low rate of HIV test acceptance, poor delivery of nevirapine to mothers and inability to track mother-infant pairs postnatally for 12-month HIV testing of infants. Infant feeding intentions of mothers suggest inadequate counselling and possible negative effects of the provision of free formula milk. The poor perfor- mance of the main components of this programme will seriously reduce its operational effectiveness. There is a need for greater integration of VCT within antenatal care, a review of the current policy of providing free formula milk and an alternative model for mother-infant follow up. African Health Sciences Vol. 5 (3) 2005: pp. 213-21

High-pressure study on the superconducting pyrochlore oxide Cd2Re2O7

Superconducting and structural phase transitions in a pyrochlore oxide Cd2Re2O7 are studied under high pressure by x-ray diffraction and electrical resistivity measurements. A rich P-T phase diagram is obtained, which contains at least two phases with the ideal and slightly distorted pyrochlore structures. It is found that the transition between them is suppressed with increasing pressure and finally disappears at a critical pressure Pc = 3.5 GPa. Remarkable enhancements in the residual resistivity as well as the coefficient A of the AT 2 term in the resistivity are found around the critical pressure. Superconductivity is detected only for the phase with the structural distortion. It is suggested that the charge fluctuations of Re ions play a crucial role in determining the electronic properties of Cd2Re2O7.Comment: 5 pages, 5 figures, submitted to J. Phys. Soc. Jp

Intrafeather and Intraindividual Variation in the Stable-Hydrogen Isotope (δD) Content of Raptor Feathers

Stable-hydrogen isotope ratios (deuterium:protium; δD) in feathers enable researchers to evaluate patterns of avian movement and to estimate the source areas of migratory birds. However, variation in feather δD remains inadequately described, thus confounding inferences of avian movement and origin. We assessed variation within a feather and among feathers within and between tracts in three species of immature raptors. Within contour feathers, measurements of δD increased from a distal section to an adjacent, proximal section; the magnitude of δD increase varied with raptor species. Furthermore, contour and flight feathers differed systematically in their δD content. Two explanations for intrafeather and intraindividual variation warrant further investigation: (1) hydrogen isotope fractionation associated with feather growth rate, and (2) the incorporation of temporal variation in environmental δD into growing feathers. We consider these explanations for raptors and passerines, which seemingly differ in the incorporation of deuterium into feathers. Additionally, corresponding sections of multiple contour feathers exhibited better measurement repeatability than multiple sections within a contour feather; the variability of multiple δD measurements within a feather tract (geometric SD: ±3.5%) suggests that biological effects on the repeatability of δD measurements from concurrently grown feather material are difficult to distinguish from analytical effects. In most cases, intrafeather and intraindividual variation can be minimized by informed sample selection decisions, but both sources of variation must be considered when stable-hydrogen isotopes are used to infer the geographic origins of migrants, ascertain migratory connectivity, and facilitate avian conservation decisions

Zero-temperature generalized phase diagram of the 4d transition metals under pressure

We use an accurate implementation of density functional theory (DFT) to calculate the zero-temperature generalized phase diagram of the 4$d$ series of transition metals from Y to Pd as a function of pressure $P$ and atomic number $Z$. The implementation used is full-potential linearized augmented plane waves (FP-LAPW), and we employ the exchange-correlation functional recently developed by Wu and Cohen. For each element, we obtain the ground-state energy for several crystal structures over a range of volumes, the energy being converged with respect to all technical parameters to within $\sim 1$ meV/atom. The calculated transition pressures for all the elements and all transitions we have found are compared with experiment wherever possible, and we discuss the origin of the significant discrepancies. Agreement with experiment for the zero-temperature equation of state is generally excellent. The generalized phase diagram of the 4$d$ series shows that the major boundaries slope towards lower $Z$ with increasing $P$ for the early elements, as expected from the pressure induced transfer of electrons from $sp$ states to $d$ states, but are almost independent of $P$ for the later elements. Our results for Mo indicate a transition from bcc to fcc, rather than the bcc-hcp transition expected from $sp$-$d$ transfer.Comment: 28 pages and 10 figures. Submitted to Phys. Rev.

Management of the South Coast Purse Seine Fishery

This paper has presented a strategy for moving the management of the small pelagics fishery off the south coast to management of the whole fishery, which facilitates a more biologically sound and economically stable fishery

Mott-Superfluid transition in bosonic ladders

We show that in a commensurate bosonic ladder, a quantum phase transition occurs between a Mott insulator and a superfluid when interchain hopping increases. We analyse the properties of such a transition as well as the physical properties of the two phases. We discuss the physical consequences for experimental systems such as Josephson Junction arrays.Comment: 4 pages, 2 figures, revtex

Loop Current Eddy Formation and Baroclinic Instability

The formation of three Loop Current Eddies, Ekman, Franklin, and Hadal, during the period April 2009 through November 2011 was observed by an array of moored current meters and bottom mounted pressure equipped inverted echo sounders. The array design, areal extent nominally 89° W to 85° W, 25° N to 27° N with 30–50 km mesoscale resolution, permits quantitative mapping of the regional circulation at all depths. During Loop Current Eddy detachment and formation events, a marked increase in deep eddy kinetic energy occurs coincident with the growth of a large-scale meander along the northern and eastern parts of the Loop Current. Deep eddies develop in a pattern where the deep fields were offset and leading upper meanders consistent with developing baroclinic instability. The interaction between the upper and deep fields is quantified by evaluating the mean eddy potential energy budget. Largest down-gradient heat fluxes are found along the eastern side of the Loop Current. Where strong, the horizontal down-gradient eddy heat flux (baroclinic conversion rate) nearly balances the vertical down-gradient eddy heat flux indicating that eddies extract available potential energy from the mean field and convert eddy potential energy to eddy kinetic energy