998 research outputs found
Production primaire, secondaire et régéneration des sels nutritifs dans l'upwelling de Mauritanie
Primary and secondary productions and nutrient regeneration in the Mauritanian upwelling area were studied by following a drogue for 9 days, from the point of upwelling till the water mass dives under offshore waters. The lag between phytoplanktonic bloom, zooplanktonic peak and bacterial activity is very short and may be explained by a well-settled biological cycle connected with an undercurrent. Organic production was estimated in two ways: (1) from chlorophyll 'a' values, considering a C/Chla ratio of 25 during the 5.5 day phytoplankton growth period, primary production computed by this method reaches 13.5 g C/m2; (2) from 14C values net primary production calculated for the same period reaches 10.5 g C/m2 and total organic production (net production + organic excretion) reaches 19.5 g C/m2. Organic production computed ratios, delta O/ delta C/ delta N/ delta Si/ delta P are equal to 130/43/11/7.4/1. Secondary production and 'grazing' are estimated from mesozooplankton respiration values and have a huge increase during the bloom. Net secondary production is assessed to be 1.0-4.2 g C/m2 for 6 days. Evidence of nutrient regeneration as ammonia, phosphate and silicate is given and regeneration rates are calculated. Zooplankton excretion plays an important part in nitrogen and phosphorus regeneration. Bacterial activity is induced by zooplankton organic excretion, then increased by phytoplankton decomposition at the end of the bloom
Echec de la baisse de la TVA en restauration : mat ou pat ?
Cette étude de cas permet une approche chiffrée de l\u27impact supposée de la baisse de la TVA en restauration commerciale sur l\u27emploi, les investissements et la baisse des prix pour le client
An Updated View on an Emerging Target: Selected Papers from the 8th International Conference on Protein Kinase CK2
The 8th International Conference on Protein Kinase CK2 took place in Homburg, Germany, from 6 September to 9 September 2016. Over 80 scientists from Australia, China, Japan, USA, Canada, Denmark, France, Italy, Spain, Poland and Germany participated. After the opening lecture by Lorenzo A. Pinna, Padova, Italy, entitled Exploring the CK2 Paradox: Restless, Dangerous, Dispensable, the scientists reported their latest research on the structural characterization of CK2, hence leading directly to the development of CK2 inhibitors. The driving force behind the development of inhibitors is their use in the treatment of various diseases, which was the next topic of the conference. New findings on protein kinase CK2 were addressed in the following session. The final topic of the conference addressed the role of CK2 in differentiation and development
Ultraviolet to infrared emission of z>1 galaxies: Can we derive reliable star formation rates and stellar masses?
We seek to derive star formation rates (SFR) and stellar masses (M_star) in
distant galaxies and to quantify the main uncertainties affecting their
measurement. We explore the impact of the assumptions made in their derivation
with standard calibrations or through a fitting process, as well as the impact
of the available data, focusing on the role of IR emission originating from
dust. We build a sample of galaxies with z>1, all observed from the UV to the
IR (rest frame). The data are fitted with the code CIGALE, which is also used
to build and analyse a catalogue of mock galaxies. Models with different SFHs
are introduced. We define different set of data, with or without a good
sampling of the UV range, NIR, and thermal IR data. The impact of these
different cases on the determination of M_star and SFR are analysed.
Exponentially decreasing models with a redshift formation of the stellar
population z ~8 cannot fit the data correctly. The other models fit the data
correctly at the price of unrealistically young ages when the age of the single
stellar population is taken to be a free parameter. The best fits are obtained
with two stellar populations. As long as one measurement of the dust emission
continuum is available, SFR are robustly estimated whatever the chosen model
is, including standard recipes. M_star measurement is more subject to
uncertainty, depending on the chosen model and the presence of NIR data, with
an impact on the SFR-M_star scatter plot. Conversely, when thermal IR data from
dust emission are missing, the uncertainty on SFR measurements largely exceeds
that of stellar mass. Among all physical properties investigated here, the
stellar ages are found to be the most difficult to constrain and this
uncertainty acts as a second parameter in SFR measurements and as the most
important parameter for M_star measurements.Comment: 14 pages, 14 figures, accepted for publication A&
EROs found behind lensing clusters: II.Empirical properties, classification, and SED modelling based on multi-wavelength observations
We study the properties and nature of extremely red galaxies (ERO, R-K>5.6)
found behind two lensing clusters and compare them with other known galaxy
populations. New HST/ACS observations, Spitzer IRAC and MIPS, and Chandra/ACIS
observations of the two lensing clusters Abell 1835 and AC114 contemplate our
earlier optical and near-IR observations and have been used to study extremely
red objects (EROs) in these deep fields. We have found 6 and 9 EROs in Abell
1835 and AC114. Several (7) of these objects are undetected up to the I and/or
z band, and are hence ``optical'' drop-out sources. The photometric redshifts
of most of our sources (80%) are z~0.7-1.5. According to simple colour-colour
diagrams the majority of our objects would be classified as hosting old stellar
populations. However, there are clear signs of dusty starbursts for several
among them. These objects correspond to the most extreme ones in R-K colour. We
estimate a surface density of (0.97+-0.31) arcmin-2 for EROs with (R-K>5.6) at
K<20.5. Among our 15 EROs 6 (40 %) also classify as distant red galaxies
(DRGs). 11 of 13 EROs with available IRAC photometry also fulfil the selection
criteria for IRAC selected EROs (IEROs) of Yan et al. (2004). SED modelling
shows that ~ 36 % of the IEROs in our sample are luminous or ultra-luminous
infrared galaxies ((U)LIRG). Some very red DRGs are found to be very dusty
starbursts, even (U)LIRGs, as also supported by their mid-IR photometry. No
indication for AGNs is found, although faint activity cannot be excluded for
all objects. From mid-IR and X-ray data 5 objects are clearly classified as
starbursts. The derived properties are quite similar to those of DRGs and
IEROs, except for 5 extreme objects in terms of colours, for which a very high
extinction (Av>3) is found.Comment: 20 pages, 10 figures, accepted for publication in A&
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