4,379 research outputs found
A quantitative assessment of the ecological value of sycamore maple habitats in the French Alps
La naturalité est un critère important pour l'évaluation de mesures conservatoires des écosystèmes. Au niveau local, une telle évaluation doit être basée sur des indicateurs objectifs et quantifiables sur le terrain. Dans cette étude, nous avons utilisé une méthode multicritères basée sur la différence entre Valeur Naturelle (NV) et Valeur Conservatoire (CV) pour quantifier la valeur écologique des érablaies de versant à érable sycomore (Acer pseudoplatanus L.) par comparaison avec les peuplements mixtes de hêtraie-sapinière-pessière avoisinants. En effet, les naturalistes ainsi que l'Union Européenne considèrent que les érablaies de versant ont une valeur de conservation et de naturalité élevée. Nos résultats montrent que les valeurs naturelle et de conservation sont significativement plus élevées pour l'érablaie que pour la forêt mixte avoisinante et que cette évaluation ne dépend pas de facteurs abiotiques tels que l'altitude ou l'exposition. En fait, la naturalité de structure et de composition des érablaies de versant sont plus fortes que celles des forêts mixtes et permettent de différencier les deux habitats en termes de valeur écologique. Les gestionnaires peuvent facilement utiliser cette méthode pour évaluer la valeur écologique de petits habitats en zone de montagne, ce qui permet d'établir des orientations sylvicoles pour une gestion conservatoire et proche de la nature. / Naturalness is an important criterion in nature conservation assessment. At the stand-level, such assessment must be based on objective and quantifiable indicators measurable in the field. In this study, we used a multi-criterion method based on the difference between a Natural Value(NV) and a Conservation Value (CV) to quantify the ecological value of sycamore maple patches compared to the surrounding mixed forests. Indeed, sycamore habitats are considered of high natural and conservation value both by naturalists and by European institutions. Our results showed that the natural and conservation values were significantly higher for the sycamore forests than for the surrounding mixed forests and that this assessment did not depend on abiotic factors such as elevation or aspect. Actually, naturalness of structure and composition in the sycamore habitats was higher than for mixed forests and allowed us to differentiate between the two habitats. Managers could easily use this method in order to assess the ecological value of small habitats in mountainous regions and to provide guidelines for close-to-nature and conservation-related silviculture.FORET DE MONTAGNE;ECOLOGIE FORESTIERE;EVALUATION;PROTECTION DE LA NATURE;ACER PSEUDOPLATANUS;METHODOLOGIE;HABITAT;VALEUR ECOLOGIQUE;NATURALITE;ALPES FRANCAISES;CHARTREUSE MASSIF;ACER PSEUDOPLATANUS;CHARTREUSE;INDICATORS;NATURALNESS;ECOLOGICAL VALUE
The Fetal Allograft Revisited: Does the Study of an Ancient Invertebrate Species Shed Light on the Role of Natural Killer Cells at the Maternal-Fetal Interface?
Human pregnancy poses a fundamental immunological problem because the placenta and fetus are genetically different from the host mother. Classical transplantation theory has not provided a plausible solution to this problem. Study of naturally occurring allogeneic chimeras in the colonial marine invertebrate, Botryllus schlosseri, has yielded fresh insight into the primitive development of allorecognition, especially regarding the role of natural killer (NK) cells. Uterine NK cells have a unique phenotype that appears to parallel aspects of the NK-like cells in the allorecognition system of B. schlosseri. Most notably, both cell types recognize and reject "missing self" and both are involved in the generation of a common vascular system between two individuals. Chimeric combination in B. schlosseri results in vascular fusion between two individual colonies; uterine NK cells appear essential to the establishment of adequate maternal-fetal circulation. Since human uterine NK cells appear to de-emphasize primary immunological function, it is proposed that they may share the same evolutionary roots as the B. schlosseri allorecognition system rather than a primary origin in immunity
Interpretation of a low-lying excited state of the reaction center of Rb.sphaeroides as a double triplet
The recently observed transient absorption of the lowest excited state of the
special pair P* at 2710 cm-1 is assigned as a singlet which arises from the
coupling of the two lowest triplets from the two dimer halves. INDO
calculations are used to predict its intensity. The analogy of the coupling
mechanism to the trip-doublet spectrum from P+ is shown and the influence of
the double triplet on the Stark effect of P* is investigated.Comment: 10 pages Latex, 1 figure, to be published in Chemical Physics Letters
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Discovery of the Optical Counterparts to Four Energetic Fermi Millisecond Pulsars
In the last few years, over 43 millisecond radio pulsars have been discovered
by targeted searches of unidentified gamma-ray sources found by the Fermi
Gamma-Ray Space Telescope. A large fraction of these millisecond pulsars are in
compact binaries with low-mass companions. These systems often show eclipses of
the pulsar signal and are commonly known as black widows and redbacks because
the pulsar is gradually destroying its companion. In this paper, we report on
the optical discovery of four strongly irradiated millisecond pulsar
companions. All four sources show modulations of their color and luminosity at
the known orbital periods from radio timing. Light curve modelling of our
exploratory data shows that the equilibrium temperature reached on the
companion's dayside with respect to their nightside is consistent with about
10-30% of the available spin-down energy from the pulsar being reprocessed to
increase the companion's dayside temperature. This value compares well with the
range observed in other irradiated pulsar binaries and offers insights about
the energetics of the pulsar wind and the production of gamma-ray emission. In
addition, this provides a simple way of estimating the brightness of irradiated
pulsar companions given the pulsar spin-down luminosity. Our analysis also
suggests that two of the four new irradiated pulsar companions are only
partially filling their Roche lobe. Some of these sources are relatively bright
and represent good targets for spectroscopic follow-up. These measurements
could enable, among other things, mass determination of the neutron stars in
these systems.Comment: 11 pages, 5 tables, 1 figure, 4 online tables. ApJ submitted and
referee
A Low Power Multi-Channel Single Ramp ADC With Up to 3.2 GHz Virtual Clock
During the last decade, ADCs using single ramp architecture have been widely used in integrated circuits dedicated to nuclear science applications. These types of converters are actually very well suited for low power, multi-channel applications. Moreover their wide dynamic range and their very good differential non-linearity are perfectly matched to spectroscopy measurement. Unfortunately, their use is limited by their long conversion time, itself limited by their maximum clock frequency. A new architecture is described in this paper. It permits speeding up the conversion time of the traditional ramp ADC structures by a factor of 32 while keeping a low power consumption. Measurement results on a 4-channel, 12-bit prototype using a 3.2 GHz virtual clock are then presented in detail, showing excellent performances of linearity and noise
Metrics for quantifying the circularity of bioplastics: The case of bio-based and biodegradable mulch films
The concept of circularity and its quantification through the Material Circularity Indicator (MCI) is well established for traditional plastic products. In this paper a methodological approach for calculating the circularity of bio-based and biodegradable (BB) products is proposed and applied to BB mulch films. BB products are different from traditional products in as much as they are sourced and regenerated (recycled) not through technical cycles but the biological loop. The suggested method is an adaptation of the MCI where two major changes were made: (i) the mass of the bio-based component corresponds to the recycled material in input and (ii) the mass of the bio-based component leaving the system through composting or biodegradation in soil is accounted as recycled. The modified MCI supports the eco-design of innovative BB products and allows for the comparison of their circularity taking into account the biological source and the expected end of life process such as biodegradation. To demonstrate the adaptation, the method has been applied to BB mulch films. Results showed that the MCI of a biodegradable mulch film, characterized by an average bio-based feedstock content of 30% is 0.37 ± 0.04 in a 0–1 scale. For BB mulch film, the amount of bio-based feedstock is the most sensitive factor and controls linearly the value of the MCI
Tracking active nests in solar-type pulsators: Ensemble starspot modelling of Kepler asteroseismic targets
The satellite Planetary Transits and Oscillations of stars (PLATO), due to be
launched late 2026, will provide us with an unprecedented sample of light
curves of solar-type stars that will exhibit both solar-type oscillations and
signatures of activity-induced brightness modulations. Solar-type pulsators
only have moderate levels of activity because high levels of activity inhibit
oscillations. This means that these targets represent a specific challenge for
starspot modelling. In order to assess the possibilities that PLATO will soon
open, we wish to characterise the morphology of active regions at the surface
of stars for which we also have a detection of solar-like acoustic
oscillations. In this context, we report the results of an ensemble starspot
modelling analysis of the Sun and ten solar-type pulsators observed by the
Kepler satellite. We implement a Bayesian starspot modelling approach based on
a continuous-grid model, accounting for the combined starspot and facular
contribution to activity-induced brightness modulations. From our analysis, we
find that several stars of our sample exhibit clear signatures of stable
longitudinal active nests while sharing activity levels and convection versus
rotation regimes similar to the solar regime. By searching for modulations in
the reconstructed starspot coverage, we found significant periodicities that we
identify as possible signatures of cyclic modulations similar to the
quasi-biennal oscillation or the Rieger cycle. We can infer the corresponding
intensity of the magnetic field at the bottom of the convective envelope based
on the hypothesis that internal magneto-Rossby waves acting on the tachocline
cause these modulations.Comment: 18 pages, 23 figures, accepted for publication in A&
Stress response function of a two-dimensional ordered packing of frictional beads
We study the stress profile of an ordered two-dimensional packing of beads in
response to the application of a vertical overload localized at its top
surface. Disorder is introduced through the Coulombic friction between the
grains which gives some indeterminacy and allows the choice of one constrained
random number per grain in the calculation of the contact forces. The so-called
`multi-agent' technique we use, lets us deal with systems as large as
grains. We show that the average response profile has a double
peaked structure. At large depth , the position of these peaks grows with
, while their widths scales like . and are analogous to
`propagation' and `diffusion' coefficients. Their values depend on that of the
friction coefficient . At small , we get and , with , which means that the peaks get
closer and wider as the disorder gets larger. This behavior is qualitatively
what was predicted in a model where a stochastic relation between the stress
components is assumed.Comment: 7 pages, 7 figures, accepted version to Europhys. Let
The Double Pulsar Eclipses I: Phenomenology and Multi-frequency Analysis
The double pulsar PSR J0737-3039A/B displays short, 30 s eclipses that arise
around conjunction when the radio waves emitted by pulsar A are absorbed as
they propagate through the magnetosphere of its companion pulsar B. These
eclipses offer a unique opportunity to probe directly the magnetospheric
structure and the plasma properties of pulsar B. We have performed a
comprehensive analysis of the eclipse phenomenology using multi-frequency radio
observations obtained with the Green Bank Telescope. We have characterized the
periodic flux modulations previously discovered at 820 MHz by McLaughlin et
al., and investigated the radio frequency dependence of the duration and depth
of the eclipses. Based on their weak radio frequency evolution, we conclude
that the plasma in pulsar B's magnetosphere requires a large multiplicity
factor (~ 10^5). We also found that, as expected, flux modulations are present
at all radio frequencies in which eclipses can be detected. Their complex
behavior is consistent with the confinement of the absorbing plasma in the
dipolar magnetic field of pulsar B as suggested by Lyutikov & Thompson and such
a geometric connection explains that the observed periodicity is harmonically
related to pulsar B's spin frequency. We observe that the eclipses require a
sharp transition region beyond which the plasma density drops off abruptly.
Such a region defines a plasmasphere which would be well inside the
magnetospheric boundary of an undisturbed pulsar. It is also two times smaller
than the expected standoff radius calculated using the balance of the wind
pressure from pulsar A and the nominally estimated magnetic pressure of pulsar
B.Comment: 9 pages, 7 figures, 3 tables, ApJ in pres
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Subsurface Gas-Shale Samples Of The Upper Devonian And Lower Mississippian Woodford Shale, Permian Basin, West Texas And Southeastern New Mexico: Core Sampling For Measured Vitrinite-Reflectance (Ro) Determination
This report summarizes activities carried out by the Bureau of Economic Geology (BEG) during fiscal year (FY) 2012 for the National Coal Resources Data System State Cooperative Program (NCRDS project). In a continuation of the sampling strategy for measured vitrinite-reflectance (Ro) determination initiated 4 years ago (Hentz and others, 2009) and conducted during the following three years (Hentz and others, 2010, 2011, 2012), this report provides a collection of oil- and gas-shale samples from the oil- and gas-productive Upper Devonian Woodford Shale of the Permian Basin in Texas and New Mexico (Fig. 1).
In FY2009, 2010, and 2011, we provided samples of the Eagle Ford Shale from the San Marcos Arch and Maverick Basin areas, samples of the deeper Pearsall Formation from the Maverick Basin of the eastern part of Texas, and samples of the Smithwick Shale from the Fort Worth Basin of north Texas, respectively. As specified in our work plan for FY2010 through 2014 (Hentz, 2010), this year we have provided samples of the productive Upper Devonian Woodford Shale in the Permian Basin of West Texas and southeastern New Mexico.Bureau of Economic Geolog
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