240 research outputs found
X-Ray Photoabsorption in KLL Resonances of O VI And Abundance Analysis
It is shown that photoabsorption via autoionizing resonances may be
appreciable and used for abundance analysis. Analogous to spectral lines, the
`resonance oscillator strength' f_r may be defined and evaluated in terms of
the differential oscillator strength df/d(epsilon) that relates bound and
continuum absorption. X-ray photoabsorption in KLL (1s2s2p) resonances of O VI
is investigated using highly resolved relativistic photoionization cross
sections with fine structure. It is found that f_r is comparable to that for UV
dipole transition in O VI (2s - 2p) and the X-ray (1s^2 ^1S_0 - 1s2p ^1P^o_1)
transition in O VII. The dominant O VI(KLL) components lie at 22.05 and 21.87
Angstroms. These predicted absorption features should be detectable by the
Chandra X-Ray Observatory (CXO) and the X-Ray Multi-Mirror Mission (XMM). The
combined UV/X-ray spectra of O VI/O VII should yield valuable information on
the ionization structure and abundances in sources such as the `warm absorber'
region of active galactic nuclei and the hot intergalactic medium. Some general
implications of resonant photoabsorption are addressed.Comment: Astrophys. J. Letters (in press), 9 pages, 3 figure
Thin deformable mirrors for a reconfigurable space telescope
As part of a small satellite technology demonstration that will utilize autonomous assembly, reconfiguration, and docking technology to form the primary mirror for the mission’s telescope payload, the mirror segments are required to modify and control their shape, in order to allow for imaging in different configurations. This paper focuses on the development of 10 cm diameter active lightweight mirrors. The current mirror design, control scheme, and fabrication methods are described, as well as experimental results on initial samples. The data demonstrates that the mirrors are capable of at least 100 microns of displacement during operation, and that fabrication on polished molds can result in high quality reflective surfaces
K-shell dielectronic resonances in photoabsorption: differential oscillator strengths for Li-like C IV, O VI, and Fe XXIV
Recently X-ray photoabsorption in KLL resonances of O VI was predicted
[Pradhan, Astrophys.J. Lett. 545, L165 (2000)], and detected by the Chandra
X-ray Observatory [Lee et al, Astrophys. J. {\it Lett.}, submitted].
The required resonance oscillator strengths f_r, are evaluated in terms of
the differential oscillator strength df/de that relates bound and continuum
absorption. We present the f_r values from radiatively damped and undamped
photoionization cross sections for Li-like C,O, and Fe calculated using
relativistic close coupling Breit-Pauli R-matrix method. The KLL resonances of
interest here are: 1s2p (^3P^o) 2s [^4P^o_{1/2,3/2}, ^2P^o_{1/2,3/2}] and 1s2p
(^1P^o) 2s [^2P^o_{1/2,3/2}]. The KLL photoabsorption resonances in Fe XXIV are
fully resolved up to natural autoionization profiles for the first time. It is
demonstrated that the undamped f_r independently yield the resonance radiative
decay rates, and thereby provide a precise check on the resolution of
photoionization calculations in general. The predicted photoabsorption features
should be detectable by the X-ray space observatories and enable column
densities in highly ionized astrophysical plasmas to be determined from the
calculated f_r. The dielectronic satellites may appear as redward broadening of
resonances lines in emission and absorption.Comment: 9 pages, 2 figurs, Phys. Rev. A, Rapid Communication (submitted
Growth and fermentation patterns of Saccharomyces cerevisiae under different ammonium concentrations and its implications in winemaking industry
To study the effects of assimilable nitrogen concentration on growth profile and on fermentation kinetics of Saccharomyces cerevisiae. Aims: To study the effects of assimilable nitrogen concentration on growth profile and on fermentation kinetics of Saccharomyces cerevisiae.
Methods and Results: Saccharomyces cerevisiae was grown in batch in a defined medium with glucose (200 g l−1) as the only carbon and energy source, and nitrogen supplied as ammonium sulphate or phosphate forms under different concentrations. The initial nitrogen concentration in the media had no effect on specific growth rates of the yeast strain PYCC 4072. However, fermentation rate and the time required for completion of the alcoholic fermentation were strongly dependent on nitrogen availability. At the stationary phase, the addition of ammonium was effective in increasing cell population, fermentation rate and ethanol.
Conclusions: The yeast strain required a minimum of 267 mg N l−1 to attain complete dryness of media, within the time considered for the experiments. Lower levels were enough to support growth, although leading to sluggish or stuck fermentation.
Significance and Impact of the Study: The findings reported here contribute to elucidate the role of nitrogen on growth and fermentation performance of wine yeast. This information might be useful to the wine industry where excessive addition of nitrogen to prevent sluggish or stuck fermentation might have a negative impact on wine stability and quality
On inelastic hydrogen atom collisions in stellar atmospheres
The influence of inelastic hydrogen atom collisions on non-LTE spectral line
formation has been, and remains to be, a significant source of uncertainty for
stellar abundance analyses, due to the difficulty in obtaining accurate data
for low-energy atomic collisions either experimentally or theoretically. For
lack of a better alternative, the classical "Drawin formula" is often used.
Over recent decades, our understanding of these collisions has improved
markedly, predominantly through a number of detailed quantum mechanical
calculations. In this paper, the Drawin formula is compared with the quantum
mechanical calculations both in terms of the underlying physics and the
resulting rate coefficients. It is shown that the Drawin formula does not
contain the essential physics behind direct excitation by H atom collisions,
the important physical mechanism being quantum mechanical in character.
Quantitatively, the Drawin formula compares poorly with the results of the
available quantum mechanical calculations, usually significantly overestimating
the collision rates by amounts that vary markedly between transitions.Comment: 9 pages, 6 figures, accepted for A&
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
Oenological characterisation of indigenous strains of S. cerevisiae isolated in a biodynamic winery in the Cortona DOC area
Genotypic and technological characterisation of the S. cerevisiae population isolated in a biodynamic winery in the Cortona DOC area was performed to gain better knowledge of the variables that influence winemaking. The oenological performance of 11 S. cerevisiae strains was evaluated with physiological tests; strain typing was performed through analysis of interdelta sequences and 26S rDNA sequencing. The analysis revealed a remarkable variability in terms of S. cerevisiae strains, despite the homogeneity of wine features, underlining the high levels of biodiversity characterising biodynamic agriculture. Some strains were found in wines of different vintages, suggesting the presence of an established microbiota in the winery. Oenological tests demonstrated that while some yeasts provided reliable oenological performance, other strains were not able to accomplish prompt and effective alcoholic fermentation, or were characterised by spoilage characteristics, such as excessive production of volatile phenols or acetic acid. Indigenous strains of S. cerevisiae could be a useful instrument for reliable winemaking without altering the native microbiota of each oenological environment. However, characterisation of their oenological suitability, and the application of practices able to drive the evolution of microbiota, must be employed to reduce the risk of wine spoilage
НОВЫЕ ДАННЫЕ О ЛИШАЙНИКАХ РОДА CETRELIA (LECANORALES, ASCOMYCOTA) В БЕЛАРУСИ
Two hundred and ten lichen specimens of Cetrelia collected in Belarus during 1954–2012 were examined based on morphological and chemical characters. Three species of Cetrelia (C. cetrarioides, C. monachorum, and C. olivetorum) have been identified in this study. The occurrence of detected species in Belarus is reviewed and distribution maps are provided.Ревизия гербарного материала по роду Cetrelia в Беларуси выявила неполноту опубликованных флористических данных по рассматриваемому роду. Установлено, что большинство гербарных образцов, определенных ранее как C. cetrarioides, относится к другому виду – C. monachorum. Таким образом, в настоящее время в состав рода Cetrelia на территории Беларуси входит три вида: C. cetrarioides, C. monachorum и C. olivetorum. Полученные в ходе исследования данные уточняют представления о таксономических особенностях и ареалах лишайников рода Cetrelia в Европе и, кроме того, могут быть использованы при составлении Красной книги Республики Беларусь, а также фундаментального многотомного издания "Флора БеларусиЙ"
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
The UniProt-GO Annotation database in 2011
The GO annotation dataset provided by the UniProt Consortium (GOA: http://www.ebi.ac.uk/GOA) is a comprehensive set of evidenced-based associations between terms from the Gene Ontology resource and UniProtKB proteins. Currently supplying over 100 million annotations to 11 million proteins in more than 360 000 taxa, this resource has increased 2-fold over the last 2 years and has benefited from a wealth of checks to improve annotation correctness and consistency as well as now supplying a greater information content enabled by GO Consortium annotation format developments. Detailed, manual GO annotations obtained from the curation of peer-reviewed papers are directly contributed by all UniProt curators and supplemented with manual and electronic annotations from 36 model organism and domain-focused scientific resources. The inclusion of high-quality, automatic annotation predictions ensures the UniProt GO annotation dataset supplies functional information to a wide range of proteins, including those from poorly characterized, non-model organism species. UniProt GO annotations are freely available in a range of formats accessible by both file downloads and web-based views. In addition, the introduction of a new, normalized file format in 2010 has made for easier handling of the complete UniProt-GOA data set
- …