2,643 research outputs found
A new model of cosmogenic production of radiocarbon 14C in the atmosphere
We present the results of full new calculation of radiocarbon 14C production
in the Earth atmosphere, using a numerical Monte-Carlo model. We provide, for
the first time, a tabulated 14C yield function for the energy of primary cosmic
ray particles ranging from 0.1 to 1000 GeV/nucleon. We have calculated the
global production rate of 14C, which is 1.64 and 1.88 atoms/cm2/s for the
modern time and for the pre-industrial epoch, respectively. This is close to
the values obtained from the carbon cycle reservoir inventory. We argue that
earlier models overestimated the global 14C production rate because of outdated
spectra of cosmic ray heavier nuclei. The mean contribution of solar energetic
particles to the global 14C is calculated as about 0.25% for the modern epoch.
Our model provides a new tool to calculate the 14C production in the Earth's
atmosphere, which can be applied, e.g., to reconstructions of solar activity in
the past.Comment: Published in EPSL, 337, 114, 201
New nonadiabatic pulsation computations on full PG1159 evolutionary models: the theoretical GW Vir instability strip revisited
We reexamine the theoretical instability domain of pulsating PG1159 stars (GW
Vir variables). We performed an extensive g-mode stability analysis on PG1159
evolutionary models with stellar masses ranging from 0.530 to 0.741 Mo for
which the complete evolutionary stages of their progenitors from the ZAMS,
through the thermally pulsing AGB and born-again phases to the domain of the
PG1159 stars have been considered. We found that pulsations in PG1159 stars are
excited by the kappa-mechanism due to partial ionization of carbon and oxygen,
and that no composition gradients are needed between the surface layers and the
driving region, much in agreement with previous studies. We show, for the first
time, the existence of a red edge of the instability strip at high
luminosities. We found that all of the GW Vir stars lay within our theoretical
instability strip. Our results suggest a qualitative good agreement between the
observed and the predicted ranges of unstable periods of individual stars.
Finally, we found that generally the seismic masses (derived from the period
spacing) of GW Vir stars are somewhat different from the masses suggested by
evolutionary tracks coupled with spectroscopy. Improvements in the evolution
during the thermally pulsing AGB phase and/or during the core helium burning
stage and early AGB could help to alleviate the persisting discrepancies.Comment: 10 pages, 8 figures. To be published in Astronomy and Astrophysic
Pathogen burden, inflammation, proliferation and apoptosis in human in-stent restenosis - Tissue characteristics compared to primary atherosclerosis
Pathogenic events leading to in-stent restenosis (ISR) are still incompletely understood. Among others, inflammation, immune reactions, deregulated cell death and growth have been suggested. Therefore, atherectomy probes from 21 patients with symptomatic ISR were analyzed by immunohistochemistry for pathogen burden and compared to primary target lesions from 20 stable angina patients. While cytomegalovirus, herpes simplex virus, Epstein-Barr virus and Helicobacter pylori were not found in ISR, acute and/or persistent chlamydial infection were present in 6/21 of these lesions (29%). Expression of human heat shock protein 60 was found in 8/21 of probes (38%). Indicated by distinct signals of CD68, CD40 and CRP, inflammation was present in 5/21 (24%), 3/21 (14%) and 2/21 (10%) of ISR cases. Cell density of ISR was significantly higher than that of primary lesions ( 977 +/- 315 vs. 431 +/- 148 cells/mm(2); p < 0.001). There was no replicating cell as shown by Ki67 or PCNA. TUNEL+ cells indicating apoptosis were seen in 6/21 of ISR specimens (29%). Quantitative analysis revealed lower expression levels for each intimal determinant in ISR compared to primary atheroma (all p < 0.05). In summary, human ISR at the time of clinical presentation is characterized by low frequency of pathogen burden and inflammation, but pronounced hypercellularity, low apoptosis and absence of proliferation. Copyright (C) 2004 S. Karger AG, Basel
Continuous synthesis of pyridocarbazoles and initial photophysical and bioprobe characterization
Pyridocarbazoles when ligated to transition metals yield high affinity kinase
inhibitors. While batch photocyclizations enable the synthesis of these
heterocycles, the non-oxidative Mallory reaction only provides modest yields
and difficult to purify mixtures. We demonstrate here that a flow-based
Mallory cyclization provides superior results and enables observation of a
clear isobestic point. The flow method allowed us to rapidly synthesize ten
pyridocarbazoles and for the first time to document their interesting
photophysical attributes. Preliminary characterization reveals that these
molecules might be a new class of fluorescent bioprobe
Contrasting origin of B chromosomes in two cervids (Siberian roe deer and grey brocket deer) unravelled by chromosome-specific DNA sequencing.
BACKGROUND: B chromosomes are dispensable and variable karyotypic elements found in some species of animals, plants and fungi. They often originate from duplications and translocations of host genomic regions or result from hybridization. In most species, little is known about their DNA content. Here we perform high-throughput sequencing and analysis of B chromosomes of roe deer and brocket deer, the only representatives of Cetartiodactyla known to have B chromosomes. RESULTS: In this study we developed an approach to identify genomic regions present on chromosomes by high-throughput sequencing of DNA generated from flow-sorted chromosomes using degenerate-oligonucleotide-primed PCR. Application of this method on small cattle autosomes revealed a previously described KIT gene region translocation associated with colour sidedness. Implementing this approach to B chromosomes from two cervid species, Siberian roe deer (Capreolus pygargus) and grey brocket deer (Mazama gouazoubira), revealed dramatically different genetic content: roe deer B chromosomes consisted of two duplicated genomic regions (a total of 1.42-1.98 Mbp) involving three genes, while grey brocket deer B chromosomes contained 26 duplicated regions (a total of 8.28-9.31 Mbp) with 34 complete and 21 partial genes, including KIT and RET protooncogenes, previously found on supernumerary chromosomes in canids. Sequence variation analysis of roe deer B chromosomes revealed a high frequency of mutations and increased heterozygosity due to either amplification within B chromosomes or divergence between different Bs. In contrast, grey brocket deer B chromosomes were found to be more homogeneous and resembled autosomes in patterns of sequence variation. Similar tendencies were observed in repetitive DNA composition. CONCLUSIONS: Our data demonstrate independent origins of B chromosomes in the grey brocket and roe deer. We hypothesize that the B chromosomes of these two cervid species represent different stages of B chromosome sequences evolution: probably nascent and similar to autosomal copies in brocket deer, highly derived in roe deer. Based on the presence of the same orthologous protooncogenes in canids and brocket deer Bs we argue that genomic regions involved in B chromosome formation are not random. In addition, our approach is also applicable to the characterization of other evolutionary and clinical rearrangements
Waves in Guinness
We describe a simple model of a bubbly two-phase flow which is able to explain why waves propagate downward when a pint of Guinness is poured, and also how the waves are generated. Our theory involves a physically based regularization of the basic equations of the two-phase flow, using interphasic pressure difference and virtual mass terms, together with bulk or eddy viscosity terms. We show that waves can occur through an instability analogous to that which forms roll waves in inclined fluid flows, and we provide a description of the form of these waves, and compare them to observations. Our theory provides a platform for the description of waves in more general bubbly two-phase flows, and the way in which the flow breaks down to form slug flow. © 2008 American Institute of Physics
Perceived responder legitimacy and group identification predict cooperation and compliance in a mass decontamination field exercise
Emergency responders’ failure to communicate effectively during decontamination following a chemical or biological incident has been associated with increased public anxiety and reduced public compliance. In this study we applied the social identity approach to evaluating a field exercise that involved mass decontamination. Questionnaires were collected from 115 volunteers, who participated in the exercise as simulated casualties. Volunteers’ perceptions of effective responder communication predicted increased self-reported compliance with decontamination, mediated by perceived responder legitimacy and identification with other group members. Developing effective communication strategies using a social psychology perspective could improve the way in which incidents are managed
Spectral Optical Monitoring of the Narrow Line Seyfert 1 galaxy Ark 564
We present the results of a long-term (1999--2010) spectral optical
monitoring campaign of the active galactic nucleus (AGN) Ark 564, which shows a
strong Fe II line emission in the optical. This AGN is a narrow line Seyfert 1
(NLS1) galaxies, a group of AGNs with specific spectral characteristics. We
analyze the light curves of the permitted Ha, Hb, optical Fe II line fluxes,
and the continuum flux in order to search for a time lag between them.
Additionally, in order to estimate the contribution of iron lines from
different multiplets, we fit the Hb and Fe II lines with a sum of Gaussian
components. We found that during the monitoring period the spectral variation
(F_max/F_min) of Ark 564 was between 1.5 for Ha to 1.8 for the Fe II lines. The
correlation between the Fe II and Hb flux variations is of higher significance
than that of Ha and Hb (whose correlation is almost absent). The permitted-line
profiles are Lorentzian-like, and did not change shape during the monitoring
period. We investigated, in detail, the optical Fe II emission and found
different degrees of correlation between the Fe II emission arising from
different spectral multiplets and the continuum flux. The relatively weak and
different degrees of correlations between permitted lines and continuum fluxes
indicate a rather complex source of ionization of the broad line emission
region.Comment: Accepted for publication in ApJ
a standardized assessment of forest mammal communities reveals consistent functional composition and vulnerability across the tropics
Understanding global diversity patterns has benefitted from a focus on functional traits and how they relate to variation in environmental conditions among assemblages. Distant communities in similar environments often share characteristics, and for tropical forest mammals, this functional trait convergence has been demonstrated at coarse scales (110-200 km resolution), but less is known about how these patterns manifest at fine scales, where local processes (e.g., habitat features and anthropogenic activities) and biotic interactions occur. Here, we used standardized camera trapping data and a novel analytical method that accounts for imperfect detection to assess how the functional composition of terrestrial mammal communities for two traits – trophic guild and body mass – varies across 16 protected areas in tropical forests and three continents, in relation to the extent of protected habitat and anthropogenic pressures. We found that despite their taxonomic differences, communities generally have a consistent trophic guild composition, and respond similarly to these factors. Insectivores were found to be sensitive to the size of protected habitat and surrounding human population density. Body mass distribution varied little among communities both in terms of central tendency and spread, and interestingly, community average body mass declined with proximity to human settlements. Results indicate predicted trait convergence among assemblages at the coarse scale reflects consistent functional composition among communities at the local scale, suggesting that broadly similar habitats and selective pressures shaped communities with similar trophic strategies and responses to drivers of change. These similarities provide a foundation for assessing assemblages under anthropogenic threats and sharing conservation measures.Understanding global diversity patterns has benefitted from a focus on functional traits and how they relate to variation in environmental conditions among assemblages. Distant communities in similar environments often share characteristics, and for tropical forest mammals, this functional trait convergence has been demonstrated at coarse scales (110-200 km resolution), but less is known about how these patterns manifest at fine scales, where local processes (e.g., habitat features and anthropogenic activities) and biotic interactions occur. Here, we used standardized camera trapping data and a novel analytical method that accounts for imperfect detection to assess how the functional composition of terrestrial mammal communities for two traits – trophic guild and body mass – varies across 16 protected areas in tropical forests and three continents, in relation to the extent of protected habitat and anthropogenic pressures. We found that despite their taxonomic differences, communities generally have a consistent trophic guild composition, and respond similarly to these factors. Insectivores were found to be sensitive to the size of protected habitat and surrounding human population density. Body mass distribution varied little among communities both in terms of central tendency and spread, and interestingly, community average body mass declined with proximity to human settlements. Results indicate predicted trait convergence among assemblages at the coarse scale reflects consistent functional composition among communities at the local scale, suggesting that broadly similar habitats and selective pressures shaped communities with similar trophic strategies and responses to drivers of change. These similarities provide a foundation for assessing assemblages under anthropogenic threats and sharing conservation measures
The formation and evolution of hydrogen-deficient post-AGB white dwarfs: the emerging chemical profile and the expectations for the PG1159-DB-DQ evolutionary connection
This paper is designed to explore the formation and evolution of
hydrogen-deficient post-AGB white dwarfs. To this end, we compute the complete
evolution of an initially 2.7 M_sun star from the zero-age main sequence
through the thermally pulsing and mass-loss phases to the white dwarf stage.
Particular attention is given to the chemical abundance changes during the
whole evolution. A time-dependent scheme for the simultaneous treatment of
abundance changes caused by nuclear reactions, diffusive overshooting, salt
fingers and convection is considered. We employed the double-diffusive
mixing-length theory of convection for fluids with composition gradients
(Grossman & Taam 1996). The study can therefore be considered as a test of its
performance in low-mass stars. Also, time-dependent element diffusion for
multicomponent gases is taken into account during the white dwarf evolution.
The evolutionary stages corresponding to the last helium thermal pulse on the
early white-dwarf cooling branch and the following born-again episode are
carefully explored. Relevant aspects for PG1159 stars and DB white dwarf
evolution are studied in the frame of these new evolutionary models that take
into account the history of the white dwarf progenitor. The scope of the
calculations is extended to the domain of the helium-rich, carbon-contaminated
DQ white dwarfs with the aim of exploring the plausibility of the evolutionary
connection PG1159-DB-DQ. In this regard, the implications for the
double-layered chemical structure in pulsating DB white dwarfs is investigated.
Another aspect of the investigation concerned the consequences of mass-loss
episodes during the PG1159 stage for the chemical stratification of the outer
layer of DB and DQ white dwarfs.Comment: 20 pages, 15 figures. Accepted by Astronomy & Astrophysic
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