1,340 research outputs found
Near-IR Spectropolarimetry of NGC 1088
Get PDFOriginal paper can be found at: http://www.astrosociety.org/pubs/cs/035-069.html--Copyright Astronomical Society of the PacificThe current unified model of Seyfert galaxies, as proposed by Antonucci and Miller (1985), has most, if not all, Seyfert 2 galaxies hosting a Seyfert 1 type nucleus in their cores. The broad lines from the type 1 nucleus can be scattered and be seen in the polarized flux spectrum, provided the geometry is correct. Whether the mechanism is electron or dust scattering has been a question of some debate. Since dust would normally have a low scattering efficiency in the infrared, near-IR spectropolarimetry should help in determing the nature of the scatterers. To this end we present the first near-IR spectropolarimetry of NGC 1068 a "Seyfert 2" galaxy in which polarized broad lines have been observed at optical wavelengths
Multilateral inversion of A_r, C_r and D_r basic hypergeometric series
Full text linkIn [Electron. J. Combin. 10 (2003), #R10], the author presented a new basic
hypergeometric matrix inverse with applications to bilateral basic
hypergeometric series. This matrix inversion result was directly extracted from
an instance of Bailey's very-well-poised 6-psi-6 summation theorem, and
involves two infinite matrices which are not lower-triangular. The present
paper features three different multivariable generalizations of the above
result. These are extracted from Gustafson's A_r and C_r extensions and of the
author's recent A_r extension of Bailey's 6-psi-6 summation formula. By
combining these new multidimensional matrix inverses with A_r and D_r
extensions of Jackson's 8-phi-7 summation theorem three balanced
very-well-poised 8-psi-8 summation theorems associated with the root systems
A_r and C_r are derived.Comment: 24 page
Effects of incubation time and filtration method on Kd of indigenous selenium and iodine in temperate soils
Get PDFIn this study, the effects of incubation time and the method of soil solution extraction and filtration on the empirical distribution coefficient (Kd) obtained by de-sorbing indigenous selenium (Se) and iodine (I) from arable and woodland soils under temperate conditions were investigated.
Incubation time had a significant soil- and element- dependent effect on the Kd values, which tended to decrease with the incubation time. Generally, a four-week period was sufficient for the desorption Kd value to stabilise. Concurrent solubilisation of soil organic matter (OM) and release of organically-bound Se and I was probably responsible for the observed decrease in Kd with time. This contrasts with the conventional view of OM as a sink for Se and I in soils. Selenium and I Kd values were not significantly affected by the method of soil solution extraction and filtration.
The results suggest that incubation time is a key criterion when selecting Se and I Kd values from the literature for risk assessments. Values derived from desorption of indigenous soil Se and I might be most appropriate for long-term assessments since they reflect the quasi-equilibrium state of their partitioning in soils
Modelling the future of the Hawaiian honeycreeper : an ecological and epidemiological problem
Get PDFThe Hawaiian honeycreeper (Drepanididae) faces the threat of extinction; this is believed to be due primarily to predation from alien animals, endemic avian malaria (Plasmodium relictum) and climate change. A deterministic SI modelling approach is developed, incorporating these three factors and a metapopulation approach in conjunction with a quasi-equilibrium assumption to simplify the vector populations. This enables the qualitative study of the behaviour of the system. Numerical results suggest that although (partial) resistance to avian malaria may be advantageous for individual birds, allowing them to survive infection, this allows them to become carriers of infection and hence greatly increases the spread of this disease. Predation obviously reduces the life-expectancy of honeycreepers, but in turn this reduces the spread of infection from resistant carriers; therefore the population-level impact of predation is reduced. Various control strategies proposed in the literature are also considered and it is shown that predation control could either help or hinter, depending upon resistance of the honeycreeper species. Captive propagation or habitat restoration may be the best feasible solution to the loss of both heterogeneity within the population and the loss of the species as a whole
The use of DNA markers in the pre-clinical diagnosis of familial adenomatous polyposis in families in South Africa
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Determining the fate of selenium in wheat biofortification: an isotopically labelled field trial study
Get PDFAims
The principal aim of this research was to quantify retention of a single, realistic Se biofortification application (10 g ha-1) in contrasting soils over two growing seasons utilizing an enriched stable Se isotope (77Se) to discriminate between applied Se and native soil Se.
Methods
Isotopically enriched 77Se (Na2SeO4) was applied (10 g ha-1) to four replicate plots (2 m x 2 m) of winter wheat, on three contrasting soils on the University of Nottingham farm (UK), at early stem extension in May 2012. Labelled 77Se was assayed in soil and crop fractions by ICP-MS.
Results
Topsoil retained a proportion of applied Se at harvest (c. 15 – 31 %) with only minor retention in subsoil (2-4 %), although losses were 37 – 43 %. Further analysis of topsoil 77Se, the following spring, and at second harvest, suggested that labelled Se retained in soil was25 fixed and uptake by a following crop was negligible.
Conclusions
Prolonged biofortification leads to accumulation of Se in soil but the retained Se has very low bioavailability and mobility. The time required to double the soil Se content would be about 500 years. However, reincorporation of cereal straw could provide a residual source of Se for a following crop, depending on timing and management
Resonant Absorption as Mode Conversion?
Full text linkResonant absorption and mode conversion are both extensively studied
mechanisms for wave "absorption" in solar magnetohydrodynamics (MHD). But are
they really distinct? We re-examine a well-known simple resonant absorption
model in a cold MHD plasma that places the resonance inside an evanescent
region. The normal mode solutions display the standard singular resonant
features. However, these same normal modes may be used to construct a ray
bundle which very clearly undergoes mode conversion to an Alfv\'en wave with no
singularities. We therefore conclude that resonant absorption and mode
conversion are in fact the same thing, at least for this model problem. The
prime distinguishing characteristic that determines which of the two
descriptions is most natural in a given circumstance is whether the converted
wave can provide a net escape of energy from the conversion/absorption region
of physical space. If it cannot, it is forced to run away in wavenumber space
instead, thereby generating the arbitrarily small scales in situ that we
recognize as fundamental to resonant absorption and phase mixing. On the other
hand, if the converted wave takes net energy way, singularities do not develop,
though phase mixing may still develop with distance as the wave recedes.Comment: 23 pages, 8 figures, 2 tables; accepted by Solar Phys (July 9 2010
Qualitative to quantitative: linked trajectory of method triangulation in a study on HIV/AIDS in Goa, India
Full text linkIodine soil dynamics and methods of measurement: a review
Get PDFIodine is an essential micronutrient for human health: insufficient intake can have multiple effects on development and growth, affecting approximately 1.9 billion people worldwide. Previous reviews have focussed on iodine analysis in environmental and biological samples, however, no such review exists for the determination of iodine fractionation and speciation in soils. This article reviews the geodynamics of both stable 127I and the long-lived isotope 129I (t1/2 ¼ 15.7 million years), alongside the analytical methods for determining iodine concentrations in soils, including consideration of sample preparation. The ability to measure total iodine concentration in soils has developed significantly from rudimentary spectrophotometric analysis methods to inductively coupled plasma mass spectrometry (ICP-MS). Analysis with ICP-MS has been reported as the best method for determining iodine concentrations in a range of environmental samples and soils due to developments in extraction procedures and sensitivity, with extremely good detection limits typically <mg L_1. The ability of ICP-MS to measure iodine and its capabilities to couple on-line separation tools has the significance to develop the understanding of iodine geodynamics. In addition, nuclear-related analysis and recent synchrotron light source analysis are discussed
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