Distribution and Abundance of Brant (Branta Bernicla) on the Central Arctic Coastal Plain of Alaska

The distribution and abundance of brant (Branta bernicla) were surveyed on the central Arctic Coastal Plain of Alaska between 1989 and 1992. Numbers of nests ranged between 319 and 517 in 43 to 67 locations. More than 70% of the nesting locations consisted of >=5 nests; only one or two locations had >=100 nests in any year. Brant attempted to nest every year at primary sites, but less frequently at secondary and solitary nest sites. Estimated numbers of nesting brant averaged 800 birds (range=630-1064); failed and nonbreeding brant ranged between 293 and 740 birds. During brood-rearing, approximately 900 to 3200 brant (26% to 48% goslings) used coastal habitats within the study area. Some coastal habitats were used annually; others were used only intermittently. Inland lakes were used by only a few brant each year. The earliest comparable data from the mid-1970s suggest that the population of brant in the study area has remained fairly stable. Factors affecting distribution of brant within the study area included environmental conditions, such as snowmelt and persistent ice, and predators. Indirect effects of oil development on brant distribution may include temporarily altered hydrologic regimes and elevated predator populations.Entre 1989 et 1992, on a établi un relevé de la distribution et de l'abondance de la bernache cravant (Branta bernicla) dans la partie centrale de la plaine côtière de l'Arctique en Alaska. Le nombre de nids allait de 319 à 517 dans 43 à 67 sites. Plus de 70 p. cent des sites de nidification comportaient <= 5 nids; seuls un ou deux sites abritaient >= 100 nids au cours d'une année. La bernache essayait chaque année d'établir son nid sur un site primaire, mais moins fréquemment sur un site secondaire ou solitaire. Le nombre estimé de bernaches qui nichaient était d'en moyenne 800 oiseaux (gamme: de 630 à 1064); le nombre de bernaches dont les oeufs n'éclosaient pas et de celles qui ne se reproduisaient pas allait de 293 à 740. Au cours de l'élevage de la couvée, environ 900 à 3200 bernaches (de 26 à 48 p. cent d'oisons) utilisaient les habitats côtiers situés dans la zone d'étude. Certains habitats côtiers étaient utilisés sur une base annuelle; d'autres de façon intermittente. Chaque année, les lacs intérieurs étaient utilisés par seulement quelques bernaches. Les données comparables les plus anciennes datant du milieu des années 1970 suggèrent que la population de bernaches constituant le sujet de l'étude est restée relativement stable. Parmi les facteurs qui influençaient la distribution de la bernache dans le périmètre de l'étude, on comptait les conditions environnementales comme la fonte nivale et la glace pérenne, ainsi que les prédateurs. Les répercussions indirectes de l'exploitation pétrolière sur la distribution de la bernache peuvent inclure des changements temporaires dans le régime des eaux et une augmentation de la population de prédateurs

A method for creating larger clay samples with permeability anisotropy for geotechnical centrifuge modelling

Long-term ground movements associated with geotechnical constructions are predominantly caused by the dissipation of excess pore-water pressures and are governed by the permeabilities of both the soil and the geotechnical structure. Natural soil has inherent anisotropy due to the layering and structure as a result of the natural deposition process. A significant factor that influences the rate of consolidation and seepage in natural soils is that the horizontal permeability can be orders of magnitude larger than the vertical permeability. This is often considered in numerical modelling during geotechnical design however, due to the lack of reliable field measurements available, validating these numerical models can be difficult. Geotechnical centrifuge techniques have successfully been used to investigate responses to complex construction events but are, generally, models created from reconstituted soil. This results in models with well-defined but homogeneous properties. There is a fundamental difference between centrifuge models and natural soil deposits. As a result, centrifuge models are better suited to simulating the short-term response of the soil to a construction event. The work presented outlines a procedure for creating large clay models suitable for geotechnical centrifuge testing with a sedimented structure. These models have anisotropy of the horizontal and vertical permeability allowing for more representative soil behaviour (in terms of dissipation of pore-water pressures) which can be used to investigate the long-term movements resulting from geotechnical construction events

Tests of varied sample preparation methods for centrifuge modelling

Centrifuge modelling is an established technique capable of investigating the ground’s response to complex geotechnical events. Centrifuge models are often created from reconstituted soil, with well-defined boundary conditions and known soil parameters. Clay soil models may be prepared by mixing clay powder with distilled water to form a slurry. This slurry is placed within a soil container and subjected to a vertical stress (usually in a consolidation press or consolidated inflight). This creates an isotropic model but there is a fundamental difference between this soil model and naturally occurring soil deposits. The structure and fabric present within a naturally occurring clay is not reproduced by this preparation process. It is well-established that structure and fabric in naturally deposited soils are as significant in their effect on soil behaviour as, for instance, the stress history. Inherent structure and fabric within clay soils creates anisotropy which can vary with depth, this is particularly apparent when considering the permeability. Creating a soil model for centrifuge modelling with representative permeability anisotropy would allow for a better representation of consolidation driven events and the ability to observe long-term behaviour of complex geotechnical events. Currently, there are limited methods of doing so, leading to a considerable gap in knowledge associated with the behaviour of layered ground. This paper describes the development of the equipment and experimental procedure for quantifying the structure developed by different sample preparation techniques for centrifuge modelling

Composition measurement of epitaxial Sc<inf>x</inf>Ga<inf>1-x</inf>N films

Four different methods for measuring the compositions of epitaxial ScxGa1-xN films were assessed and compared to determine which was the most reliable and accurate. The compositions of epitaxial ScxGa1-xN films with 0 ≤ x ≤ 0.26 were measured directly using Rutherford backscattering (RBS) and x-ray photoelectron spectroscopy (XPS), and indirectly using c lattice parameter measurements from x-ray diffraction and c/a ratio measurements from electron diffraction patterns. RBS measurements were taken as a standard reference. XPS was found to underestimate the Sc content, whereas c lattice parameter and c/a ratio were not reliable for composition determination due to the unknown degree of strain relaxation in the film. However, the Sc flux used during growth was found to relate linearly with x and could be used to estimate the Sc content

Resonant transmission through an open quantum dot

We have measured the low-temperature transport properties of a quantum dot formed in a one-dimensional channel. In zero magnetic field this device shows quantized ballistic conductance plateaus with resonant tunneling peaks in each transition region between plateaus. Studies of this structure as a function of applied perpendicular magnetic field and source-drain bias indicate that resonant structure deriving from tightly bound states is split by Coulomb charging at zero magnetic field.Comment: To be published in Phys. Rev. B (1997). 8 LaTex pages with 5 figure

Half-metallicity and Slater-Pauling behavior in the ferromagnetic Heusler alloys

Introductory chapter for the book "Halfmetallic Alloys - Fundamentals and Applications" to be published in the series Springer Lecture Notes on Physics, P. H. Dederichs and I. Galanakis (eds). It contains a review of the theoretical work on the half-metallic Heusler alloys.Comment: Introductory chapter for the book "Halfmetallic Alloys - Fundamentals and Applications" to be published in the series Springer Lecture Notes on Physics, P. H. Dederichs and I. Galanakis (eds

Late Ebola virus relapse causing meningoencephalitis: a case report

Background: There are thousands of survivors of the 2014 Ebola outbreak in west Africa. Ebola virus can persist in survivors for months in immune-privileged sites; however, viral relapse causing life-threatening and potentially transmissible disease has not been described. We report a case of late relapse in a patient who had been treated for severe Ebola virus disease with high viral load (peak cycle threshold value 13·2). Methods: A 39-year-old female nurse from Scotland, who had assisted the humanitarian effort in Sierra Leone, had received intensive supportive treatment and experimental antiviral therapies, and had been discharged with undetectable Ebola virus RNA in peripheral blood. The patient was readmitted to hospital 9 months after discharge with symptoms of acute meningitis, and was found to have Ebola virus in cerebrospinal fluid (CSF). She was treated with supportive therapy and experimental antiviral drug GS-5734 (Gilead Sciences, San Francisco, Foster City, CA, USA). We monitored Ebola virus RNA in CSF and plasma, and sequenced the viral genome using an unbiased metagenomic approach. Findings: On admission, reverse transcriptase PCR identified Ebola virus RNA at a higher level in CSF (cycle threshold value 23·7) than plasma (31·3); infectious virus was only recovered from CSF. The patient developed progressive meningoencephalitis with cranial neuropathies and radiculopathy. Clinical recovery was associated with addition of high-dose corticosteroids during GS-5734 treatment. CSF Ebola virus RNA slowly declined and was undetectable following 14 days of treatment with GS-5734. Sequencing of plasma and CSF viral genome revealed only two non-coding changes compared with the original infecting virus. Interpretation: Our report shows that previously unanticipated, late, severe relapses of Ebola virus can occur, in this case in the CNS. This finding fundamentally redefines what is known about the natural history of Ebola virus infection. Vigilance should be maintained in the thousands of Ebola survivors for cases of relapsed infection. The potential for these cases to initiate new transmission chains is a serious public health concern

Observation of exclusive DVCS in polarized electron beam asymmetry measurements

We report the first results of the beam spin asymmetry measured in the reaction e + p -> e + p + gamma at a beam energy of 4.25 GeV. A large asymmetry with a sin(phi) modulation is observed, as predicted for the interference term of Deeply Virtual Compton Scattering and the Bethe-Heitler process. The amplitude of this modulation is alpha = 0.202 +/- 0.028. In leading-order and leading-twist pQCD, the alpha is directly proportional to the imaginary part of the DVCS amplitude.Comment: 6 pages, 5 figure

Complete measurement of three-body photodisintegration of 3He for photon energies between 0.35 and 1.55 GeV

The three-body photodisintegration of 3He has been measured with the CLAS detector at Jefferson Lab, using tagged photons of energies between 0.35 GeV and 1.55 GeV. The large acceptance of the spectrometer allowed us for the first time to cover a wide momentum and angular range for the two outgoing protons. Three kinematic regions dominated by either two- or three-body contributions have been distinguished and analyzed. The measured cross sections have been compared with results of a theoretical model, which, in certain kinematic ranges, have been found to be in reasonable agreement with the data.Comment: 22 pages, 25 eps figures, 2 tables, submitted to PRC. Modifications: removed 2 figures, improvements on others, a few minor modifications to the tex

eta-prime photoproduction on the proton for photon energies from 1.527 to 2.227 GeV

Differential cross sections for the reaction gamma p -> eta-prime p have been measured with the CLAS spectrometer and a tagged photon beam with energies from 1.527 to 2.227 GeV. The results reported here possess much greater accuracy than previous measurements. Analyses of these data indicate for the first time the coupling of the etaprime N channel to both the S_11(1535) and P_11(1710) resonances, known to couple strongly to the eta N channel in photoproduction on the proton, and the importance of j=3/2 resonances in the process.Comment: 6 pages, 3 figure