1,696 research outputs found
Effects of upwelling duration and phytoplankton growth regime on dissolved-oxygen levels in an idealized Iberian Peninsula upwelling system
Abstract. We apply a coupled modelling system composed of a
state-of-the-art hydrodynamical model and a low-complexity biogeochemical
model to an idealized Iberian Peninsula upwelling system to identify the
main drivers of dissolved-oxygen variability and to study its response to
changes in the duration of the upwelling season and in the phytoplankton growth
regime. We find that the export of oxygenated waters by upwelling front
turbulence is a major sink for nearshore dissolved oxygen. In our
simulations of summer upwelling, when the phytoplankton population is generally
dominated by diatoms whose growth is boosted by nutrient input, net
primary production and air–sea exchange compensate dissolved-oxygen
depletion by offshore export over the shelf. A shorter upwelling duration
causes a relaxation of upwelling winds and a decrease in offshore export,
resulting in a slight increase of net dissolved-oxygen enrichment in the
coastal region as compared to longer upwelling durations. When phytoplankton
is dominated by groups less sensitive to nutrient inputs, growth rates
decrease, and the coastal region becomes net heterotrophic. Together with the
physical sink, this lowers the net oxygenation rate of coastal waters, which
remains positive only because of air–sea exchange. These findings help in
disentangling the physical and biogeochemical controls of dissolved oxygen
in upwelling systems and, together with projections of increased duration of
upwelling seasons and phytoplankton community changes, suggest that the
Iberian coastal upwelling region may become more vulnerable to hypoxia and
deoxygenation.
This research has been supported by the IDEX UNITI – University of Toulouse (TEASAO IDEX UNITI – Univer- sity of Toulouse)
A combined FEG-SEM and TEM study of silicon nanodot assembly
Nanodots forming dense assembly on a substrate are difficult to characterize in terms of size, density, morphology and cristallinity. The present study shows how valuable information can be obtained by a combination of electron microscopy techniques. A silicon nanodots deposit has been studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) to estimate essentially the dot size and density, quantities emphasized because of their high interest for application. High resolution SEM indicates a density of 1.6 × 1012 dots/cm2 for a 5 nm to 10 nm dot size. TEM imaging using a phase retrieval treatment of a focus series gives a higher dot density (2 × 1012 dots/cm2) for a 5 nm dot size. High Resolution Transmission Electron Microscopy (HRTEM) indicates that the dots are crystalline which is confirmed by electron diffraction. According to HRTEM and electron diffraction, the dot size is about 3 nm which is significantly smaller than the SEM and TEM results. These differences are not contradictory but attributed to the fact that each technique is probing a different phenomenon. A core-shell structure for the dot is proposed which reconcile all the results. All along the study, Fourier transforms have been widely used under many aspects
S30 The Bauschinger Effect in Nanofilamentary Cu/Nb Wires Evidenced By In-Situ Tensile Tests Under Synchrotron Radiation
Constrained Dynamics of Universally Coupled Massive Spin 2-spin 0 Gravities
The 2-parameter family of massive variants of Einstein's gravity (on a
Minkowski background) found by Ogievetsky and Polubarinov by excluding lower
spins can also be derived using universal coupling. A Dirac-Bergmann
constrained dynamics analysis seems not to have been presented for these
theories, the Freund-Maheshwari-Schonberg special case, or any other massive
gravity beyond the linear level treated by Marzban, Whiting and van Dam. Here
the Dirac-Bergmann apparatus is applied to these theories. A few remarks are
made on the question of positive energy. Being bimetric, massive gravities have
a causality puzzle, but it appears soluble by the introduction and judicious
use of gauge freedom.Comment: 6 pages; Talk given at QG05, Cala Gonone (Italy), September 200
S31 Size Effect in the Plasticity of Multiscale Nanofilamentary Cu/Nb Composite Wires During In-Situ Tensile Tests Under Neutron Beam
An insight into polarization states of solid-state organic lasers
The polarization states of lasers are crucial issues both for practical
applications and fundamental research. In general, they depend in a combined
manner on the properties of the gain material and on the structure of the
electromagnetic modes. In this paper, we address this issue in the case of
solid-state organic lasers, a technology which enables to vary independently
gain and mode properties. Different kinds of resonators are investigated:
in-plane micro-resonators with Fabry-Perot, square, pentagon, stadium, disk,
and kite shapes, and external vertical resonators. The degree of polarization P
is measured in each case. It is shown that although TE modes prevail generally
(P>0), kite-shaped micro-laser generates negative values for P, i.e. a flip of
the dominant polarization which becomes mostly TM polarized. We at last
investigated two degrees of freedom that are available to tailor the
polarization of organic lasers, in addition to the pump polarization and the
resonator geometry: upon using resonant energy transfer (RET) or upon pumping
the laser dye to an higher excited state. We then demonstrate that
significantly lower P factors can be obtained.Comment: 12 pages, 12 figure
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A 3-Mb High-Resolution BAC/PAC Contig of 12q22 Encompassing the 830-kb Consensus Minimal Deletion in Male Germ Cell Tumors
Cytogenetic and molecular genetic analyses have shown that the 12q22 region is recurrently deleted in male germ cell tumors (GCTs), suggesting that this site may harbor a tumor suppressor gene (TSG). Previous loss of heterozygosity (LOH) analyses identified a consensus minimal deleted region between the markers D12S377 and D12S296, and a YAC clone contig covering the region was generated. Here, we describe a high-resolution sequence-ready physical map of this contig covering a 3-Mb region. The map comprised of 52 cosmids, 49 PACs, and 168 BACs that were anchored to the previous YAC contig; 99 polymorphic, nonpolymorphic, EST, and gene-based markers are now placed on this map in a unique order. Of these, 61 markers were isolated in the present study, including one that was polymorphic. In addition, we have narrowed the minimal deletion to ∼830 kb between D12S1716 (proximal) and P382A8-AG (distal) by LOH analysis of 108 normal-tumor DNAs from GCT patients using 21 polymorphic STSs. These physical and deletion maps should prove useful for identification of the candidate TSG in GCTs, provide framework to generate complete DNA sequence, and ultimately generate a gene map of this segment of the chromosome 12
Type I D-branes in an H-flux and twisted KO-theory
Witten has argued that charges of Type I D-branes in the presence of an
H-flux, take values in twisted KO-theory. We begin with the study of real
bundle gerbes and their holonomy. We then introduce the notion of real bundle
gerbe KO-theory which we establish is a geometric realization of twisted
KO-theory. We examine the relation with twisted K-theory, the Chern character
and provide some examples. We conclude with some open problems.Comment: 23 pages, Latex2e, 2 new references adde
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