104 research outputs found
Excitation of the 3.071mm Hyperfine Line in Li-Like 57-Fe in Astrophysical Plasmas
As noted first by Sunyaev & Churazov (1984), the 3.071 mm hyperfine line from
might be observable in astrophysical plasmas. We assess the
atomic processes which might contribute to the excitation of this line. We
determine the intensity of the hyperfine line from an isothermal, coronal
plasma in collisional ionization equilibrium and for a coronal plasma cooling
isobarically due to its own radiation. Comparisons of the hyperfine line to
other lines emitted by the same ion, Fe, are shown to be useful for
deriving the isotopic fraction of Fe. We calculate the ratios of the
hyperfine line to the 2s--2p EUV lines at 192 \AA and 255 \AA, and the 2s--3p
X-ray doublet at 10.6 \AA.Comment: 28 pages text+figures, Accepted to ApJ in Jan 98, also at
http://www.astro.virginia.edu/~nld2n/research.htm
Interelectronic-interaction effects on the two-photon decay rates of heavy He-like ions
Based on a rigorous QED approach a theoretical analysis is performed for the
two-photon transitions in heavy He-like ions. Special attention is paid to the
interelectronic-interaction corrections to the decay rates that are taken into
account within the two-time Green-function method. Detailed calculations are
carried out for the two-photon transitions 2^1S_0 -> 1^1S_0 and 2^3S_1 ->
1^1S_0 in He-like ions within the range of nuclear numbers Z=28-92. The total
decay rates together with the spectral distributions are given. The obtained
results are compared with experimental values and previous calculations.Comment: 17 pages, 7 figure
Возобновляемая энергетика - эффективное направление повышения энергетической и экологической безопасности Республики Беларусь
The structure of the world electricity production is reviewed. It provides an assessment of actual use of the most promising renewable energy sources in Belarus; an environmental impact assessment of different power sources and fuels; an evaluation of economic efficiency of renewable energy considering environmental factors. It also presents an analysis of the reasons impeding the development of renewable energy in Belarus, and possible solutions.Рассмотрена структура мирового производства электроэнергии. Приведена оценка состояния использования наиболее перспективных для Беларуси возобновляемых источников энергии (ВИЭ). Дана оценка воздействия различных источников энергии и видов топлива на окружающую среду, оценка экономической эффективности использования ВИЭ с учетом экологических факторов. Представлен анализ причин, сдерживающих развитие ВИЭ в Беларуси, и меры для их устранения
CHIANTI - an Atomic Database for Emission Lines. Paper VI: Proton Rates and Other Improvements
The CHIANTI atomic database contains atomic energy levels, wavelengths,
radiative transition probabilities and electron excitation data for a large
number of ions of astrophysical interest. Version 4 has been released, and
proton excitation data is now included, principally for ground configuration
levels that are close in energy. The fitting procedure for excitation data,
both electrons and protons, has been extended to allow 9 point spline fits in
addition to the previous 5 point spline fits. This allows higher quality fits
to data from close-coupling calculations where resonances can lead to
significant structure in the Maxwellian-averaged collision strengths. The
effects of photoexcitation and stimulated emission by a blackbody radiation
field in a spherical geometry on the level balance equations of the CHIANTI
ions can now be studied following modifications to the CHIANTI software. With
the addition of H I, He I and N I, the first neutral species have been added to
CHIANTI. Many updates to existing ion data-sets are described, while several
new ions have been added to the database, including Ar IV, Fe VI and Ni XXI.
The two-photon continuum is now included in the spectral synthesis routines,
and a new code for calculating the relativistic free-free continuum has been
added. The treatment of the free-bound continuum has also been updated.Comment: CHIANTI is available at http://wwwsolar.nrl.navy.mil/chianti.htm
Dielectronic recombination data for dynamic finite-density plasmas I. Goals and methodology
A programme is outlined for the assembly of a comprehensive dielectronic
recombination database within the generalized collisional--radiative (GCR)
framework. It is valid for modelling ions of elements in dynamic finite-density
plasmas such as occur in transient astrophysical plasmas such as solar flares
and in the divertors and high transport regions of magnetic fusion devices. The
resolution and precision of the data are tuned to spectral analysis and so are
sufficient for prediction of the dielectronic recombination contributions to
individual spectral line emissivities. The fundamental data are structured
according to the format prescriptions of the Atomic Data and Analysis Structure
(ADAS) and the production of relevant GCR derived data for application is
described and implemented following ADAS. The requirements on the dielectronic
recombination database are reviewed and the new data are placed in context and
evaluated with respect to older and more approximate treatments. Illustrative
results validate the new high-resolution zero-density dielectronic
recombination data in comparison with measurements made in heavy-ion storage
rings utilizing an electron cooler. We also exemplify the role of the
dielectronic data on GCR coefficient behaviour for some representative light
and medium weight elements.Comment: 14 Pages, 9 Figures. Submitted to Astronomy & Astrophysics April 12,
200
DNA Barcoding Reveals Cryptic Diversity in Lumbricus terrestris L., 1758 (Clitellata): Resurrection of L. herculeus (Savigny, 1826)
The widely studied and invasive earthworm, Lumbricus terrestris L., 1758 has been the subject of nomenclatural debate for many years. However these disputes were not based on suspicions of heterogeneity, but rather on the descriptions and nomenclatural acts associated with the species name. Large numbers of DNA barcode sequences of the cytochrome oxidase I obtained for nominal L. terrestris and six congeneric species reveal that there are two distinct lineages within nominal L. terrestris. One of those lineages contains the Swedish population from which the name-bearing specimen of L. terrestris was obtained. The other contains the population from which the syntype series of Enterion herculeum Savigny, 1826 was collected. In both cases modern and old representatives yielded barcode sequences allowing us to clearly establish that these are two distinct species, as different from one another as any other pair of congeners in our data set. The two are morphologically indistinguishable, except by overlapping size-related characters. We have designated a new neotype for L. terrestris. The newly designated neotype and a syntype of L. herculeus yielded DNA adequate for sequencing part of the cytochrome oxidase I gene (COI). The sequence data make possible the objective determination of the identities of earthworms morphologically identical to L. terrestris and L. herculeus, regardless of body size and segment number. Past work on nominal L. terrestris could have been on either or both species, although L. herculeus has yet to be found outside of Europe
Selected Schizosaccharomyces pombe Strains Have Characteristics That Are Beneficial for Winemaking
At present, wine is generally produced using Saccharomyces yeast followed by Oenococus bacteria to complete malolactic fermentation. This method has some unsolved problems, such as the management of highly acidic musts and the production of potentially toxic products including biogenic amines and ethyl carbamate. Here we explore the potential of the fission yeast Schizosaccharomyces pombe to solve these problems. We characterise an extensive worldwide collection of S. pombe strains according to classic biochemical parameters of oenological interest. We identify three genetically different S. pombe strains that appear suitable for winemaking. These strains compare favourably to standard Saccharomyces cerevisiae winemaking strains, in that they perform effective malic acid deacidification and significantly reduce levels of biogenic amines and ethyl carbamate precursors without the need for any secondary bacterial malolactic fermentation. These findings indicate that the use of certain S. pombe strains could be advantageous for winemaking in regions where malic acid is problematic, and these strains also show superior performance with respect to food safety
Expression variability of co-regulated genes differentiates Saccharomyces cerevisiae strains
Background: Saccharomyces cerevisiae (Baker’s yeast) is found in diverse ecological niches and is characterized by
high adaptive potential under challenging environments. In spite of recent advances on the study of yeast
genome diversity, little is known about the underlying gene expression plasticity. In order to shed new light onto
this biological question, we have compared transcriptome profiles of five environmental isolates, clinical and
laboratorial strains at different time points of fermentation in synthetic must medium, during exponential and
stationary growth phases.
Results: Our data unveiled diversity in both intensity and timing of gene expression. Genes involved in glucose
metabolism and in the stress response elicited during fermentation were among the most variable. This gene
expression diversity increased at the onset of stationary phase (diauxic shift). Environmental isolates showed lower
average transcript abundance of genes involved in the stress response, assimilation of nitrogen and vitamins, and
sulphur metabolism, than other strains. Nitrogen metabolism genes showed significant variation in expression
among the environmental isolates.
Conclusions: Wild type yeast strains respond differentially to the stress imposed by nutrient depletion, ethanol
accumulation and cell density increase, during fermentation of glucose in synthetic must medium. Our results
support previous data showing that gene expression variability is a source of phenotypic diversity among closely
related organisms.Fundação para a Ciência e TecnologiaThe authors wish to thank Adega Cooperativa da Bairrada, Cantanhede,
Portugal, for providing the commercial strains
Long-term time-lapse live imaging reveals extensive cell migration during annelid regeneration
- …