17,401 research outputs found
Effects of Gamma Ray Bursts in Earth Biosphere
We continue former work on the modeling of potential effects of Gamma Ray
Bursts on Phanerozoic Earth. We focus on global biospheric effects of ozone
depletion and show a first modeling of the spectral reduction of light by NO2
formed in the stratosphere. We also illustrate the current complexities
involved in the prediction of how terrestrial ecosystems would respond to this
kind of burst. We conclude that more biological field and laboratory data are
needed to reach even moderate accuracy in this modelingComment: Accepted for publication in Astrophysics & Space Scienc
OH rotational lines as a diagnostic of the warm neutral gas in galaxies
We present Infrared Space Observatory (ISO) observations of several OH, CH
and H2O rotational lines toward the bright infrared galaxies NGC253 and
NGC1068. As found in the Galactic clouds in SgrB2 and Orion, the extragalactic
far-IR OH lines change from absorption to emission depending on the physical
conditions and distribution of gas and dust along the line of sight. As a
result, most of the OH rotational lines that appear in absorption toward NGC253
are observed in emission toward NGC1068. We show that the far-IR spectrum of OH
can be used as a powerful diagnostic to derive the physical conditions of
extragalactic neutral gas. In particular, we find that a warm (Tk~150 K, n(H2)<
5 10^4 cm^-3) component of molecular gas with an OH abundance of 10^{-7} from
the inner <15'' can qualitatively reproduce the OH lines toward NGC253. Similar
temperatures but higher densities (5 10^5 cm^-3) are required to explain the OH
emission in NGC1068.Comment: 5 pages, 4 figures, accepted in ApJ Part I (2004, October 6
Atmospheric lepton fluxes at ultrahigh energies
In order to estimate the possibility to observe exotic physics in a neutrino
telescope, it is essential to first understand the flux of atmospheric
neutrinos, muons and dimuons. We study the production of these leptons by
high-energy cosmic rays. We identify three main sources of muons of energy E >
10^6 GeV: the weak decay of charm and bottom mesons and the electromagnetic
decay of unflavored mesons. Contrary to the standard assumption, we find that
eta mesons, not the prompt decay of charm hadrons, are the dominant source of
atmospheric muons at these energies. We show that, as a consequence, the ratio
between the neutrino and muon fluxes is significantly reduced. For dimuons,
which may be a background for long-lived staus produced near a neutrino
telescope, we find that pairs of E ~ 10^7 GeV forming an angle above 10^-6 rad
are produced through D (80%) or B (10%) meson decay and through Drell-Yan
proceses (10%). The frequency of all these processes has been evaluated using
the jet code PYTHIA.Comment: 10 pages, 4 figures; published versio
Influence of oxidative stress, diaphragm fatigue, and inspiratory muscle training on the plasma cytokine response to maximum sustainable voluntary ventilation
The influence of oxidative stress, diaphragm fatigue, and inspiratory muscle training (IMT) on the cytokine response to maximum sustainable voluntary ventilation (MSVV) is unknown. Twelve healthy males were divided equally into an IMT or placebo (PLA) group, and before and after a 6-wk intervention they undertook, on separate days, 1h of (1) passive rest and (2) MSVV, whereby participants undertook volitional hyperpnea at rest that mimicked the breathing and respiratory muscle recruitment patterns commensurate with heavy cycling exercise. Plasma cytokines remained unchanged during passive rest. There was a main effect of time (P < 0.01) for plasma interleukin-1 (IL-1) and interleukin-6 (IL-6) concentrations and a strong trend (P = 0.067) for plasma interleukin-1 receptor antagonist concentration during MSVV. Plasma IL-6 concentration was reduced after IMT by 27 + 18% (main effect of intervention, P = 0.029), whereas there was no change after PLA (P = 0.753). There was no increase in a systemic marker of oxidative stress [DNA damage in peripheral blood mononuclear cells (PBMC)], and diaphragm fatigue was not related to the increases in plasma IL-1 and IL-6 concentrations. A dose-response relationship was observed between respiratory muscle work and minute ventilation and increases in plasma IL-6 concentration. In conclusion, increases in plasma IL-1 and IL-6 concentrations during MSVV were not due to diaphragm fatigue or DNA damage in PBMC. Increases in plasma IL-6 concentration during MSVV are attenuated following IMT, and the plasma IL-6 response is dependent upon the level of respiratory muscle work and minute ventilation
High prevalence of scrapie in a dairy goat herd: tissue distribution of disease-associated PrP and effect of PRNP genotype and age
Following a severe outbreak of clinical scrapie in 2006–2007, a
large dairy goat herd was culled
and 200 animals were selected for post-mortem examinations in order to
ascertain the prevalence of infection,
the effect of age, breed and PRNP genotype on the susceptibility to scrapie,
the tissue distribution of diseaseassociated
PrP (PrP), and the comparative efficiency of different diagnostic methods.
As determined by immunohistochemical (IHC) examinations with Bar224 PrP antibody, the
prevalence of preclinical infection
was very high (72/200; 36.0%), with most infected animals being positive
for PrP in lymphoreticular system
(LRS) tissues (68/72; 94.4%) compared to those that were positive in
brain samples (38/72; 52.8%). The
retropharyngeal lymph node and the palatine tonsil showed the highest
frequency of PrP accumulation (87.3%
and 84.5%, respectively), while the recto-anal mucosa-associated lymphoid
tissue (RAMALT) was positive in
only 30 (41.7%) of the infected goats. However, the efficiency of rectal
and palatine tonsil biopsies taken
shortly before necropsy was similar. The probability of brain and RAMALT
being positive directly
correlated with the spread of PrP within the LRS. The prevalence of
infection was influenced by PRNP
genetics at codon 142 and by the age of the goats: methionine carriers older
than 60 months showed a much
lower prevalence of infection (12/78; 15.4%) than those younger than 60 months (20/42; 47.6%); these last
showed prevalence values similar to isoleucine homozygotes of any age
(40/80; 50.0%). Two of seven goats
with definite signs of scrapie were negative for PrP in brain but positive
in LRS tissues, and one goat showed
biochemical and IHC features of PrP different from all other infected
goats. The results of this study have
implications for surveillance and control policies for scrapie in goats
Análisis estadístico multivariado para determinar la intencionalidad de pesca en congrio dorado (Genypterus blacodes) en la pesquería palangrera austral de Chile
The definition of catch intention in multispecies fisheries is a key step toward building abundance indexes based on commercial fishing data. Previous analysis to determine catch intention in the pink cusk-eel (Genypterus blacodes) has been based on the idea that fishing tactics remain constant over time (static fishing tactics). We propose a statistical procedure to determine the catch intention of each haul in the industrial longline fisheries in southern Chile, where fishing tactics may vary over time. This procedure is based on principal component analysis and agglomerative hierarchical analysis of the catch composition, and relaxes the assumption of static fishing tactics by selecting a subset of data that is informative for fishing intention (target versus by-catch) every year. Sensitivity analyses were conducted to assess the robustness of variable fishing tactics on the nominal catch rates in pink cusk-eel. Targeted and by-catch time series of nominal catch rates showed a different trend, so determining the catch intention became relevant. Sensitivity analyses showed that trends in targeted catch rates are robust to the variations of fishing tactic per year. We recommend the use of variable fishing tactics for further use in effort standardization and stock assessment of the pink cusk-eel fishery in southern Chile.La definición de intención de captura en pesquerías multi-específicas es un paso fundamental para la determinación de índices de abundancia con datos provenientes de pesca comercial. Los análisis previos para determinar la intencionalidad de captura en congrio dorado (Genypterus blacodes) han estado basados en la idea de que las tácticas de pescas permanecen constante a través del tiempo (táctica de pesca estática). Se propone un procedimiento estadístico para determinar la intencionalidad de captura en cada lance de pesca palangrero industrial en la zona austral de Chile, donde las tácticas de pesca pueden variar a través del tiempo. Este procedimiento está basado en análisis de componentes principales y aglomeración jerárquica de la composición de captura y relaja el supuesto de táctica de pesca estática seleccionando un sub-grupo de datos, los cuales son informativos para la intención de pesca (objetivo versus incidental) cada año. Se realizan análisis de sensibilidad para evaluar la robustez de las tácticas de pesca variables en las tasas de captura nominales de congrio dorado. Series de tiempo de pesca objetivo e incidental muestran diferentes tendencias, y por lo tanto, la determinación de táctica de pesca se hace relevante en esta pesquería. El análisis de sensibilidad muestra que las tendencias en las tasas de captura objetivo son robustas a las variaciones de tácticas de pesca por año. Se recomienda el uso de tácticas de pesca variable para su posterior uso en estandarización de esfuerzo y evaluación de stock en la pesquería de congrio dorado en la zona austral de Chile
Feasibility study into a scientific self-sampling programme for the pelagic sector : FIS020
Publisher PD
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