577 research outputs found
Symbiont diversity is not involved in depth acclimation in the Mediterranean sea whip Eunicella singularis
In symbiotic cnidarians, acclimation to depth and lower irradiance can involve physiological changes in the photosynthetic dinoflagellate endosymbiont, such as increased chlorophyll content, or qualitative modifications in the symbiont population in favour of better adapted strains. It has been argued that a lack of capacity to acquire new symbionts could limit the bathymetric distribution of the host species, or compromise its long-term survival in a changing environment. But is that always true? To address this question, we investigated the symbiont genetic diversity in Eunicella singularis, a Mediterranean sea whip species with a wide bathymetric distribution (10 to 50 m depth), which has recently suffered from mass mortalities after periods of abnormally high sea temperatures. We measured symbiont population densities and chlorophyll content in natural populations, and followed the response of the holobionts after reciprocal transplantations to deep and shallow depths. A total of 161 colonies were sampled at 2 depths (10 and 30 m) at 5 sites in the northwestern Mediterranean. All colonies harboured a single ribosomal Symbiodinium clade (A'), but a relatively high within-clade genetic diversity was found among and within colonies. This diversity was not structured by depth, even though the deeper colonies contained significantly lower population densities of symbionts and less chlorophyll. We did, however, reveal host-symbiont specificity among E. singularis and other Mediterranean cnidarian species. Transplantation experiments revealed a limit of plasticity for symbiont population density and chlorophyll content, which in turn questions the importance of the trophic role of Symbiodinium in E. singularis
Control of Pre-mRNA Splicing by the General Splicing Factors PUF60 and U2AF65
Pre-mRNA splicing is a crucial step in gene expression, and accurate recognition of splice sites is an essential part of this process. Splice sites with weak matches to the consensus sequences are common, though it is not clear how such sites are efficiently utilized. Using an in vitro splicing-complementation approach, we identified PUF60 as a factor that promotes splicing of an intron with a weak 3' splice-site. PUF60 has homology to U2AF(65), a general splicing factor that facilitates 3' splice-site recognition at the early stages of spliceosome assembly. We demonstrate that PUF60 can functionally substitute for U2AF(65)in vitro, but splicing is strongly stimulated by the presence of both proteins. Reduction of either PUF60 or U2AF(65) in cells alters the splicing pattern of endogenous transcripts, consistent with the idea that regulation of PUF60 and U2AF(65) levels can dictate alternative splicing patterns. Our results indicate that recognition of 3' splice sites involves different U2AF-like molecules, and that modulation of these general splicing factors can have profound effects on splicing
Induced Magnetic Ordering by Proton Irradiation in Graphite
We provide evidence that proton irradiation of energy 2.25 MeV on
highly-oriented pyrolytic graphite samples triggers ferro- or ferrimagnetism.
Measurements performed with a superconducting quantum interferometer device
(SQUID) and magnetic force microscopy (MFM) reveal that the magnetic ordering
is stable at room temperature.Comment: 3 Figure
Optimal Operation of the Multireservoir System in the Seine River Basin Using Deterministic and Ensemble Forecasts
International audienceThis article investigates the improvement of the operation of a four-reservoir system in the Seine River basin, France, by use of deterministic and ensemble weather forecasts and real-time control. In the current management, each reservoir is operated independently from the others and following prescribed rule-curves, designed to reduce floods and sustain low flows under the historical hydrological conditions. However, this management system is inefficient when inflows are significantly different from their seasonal average and may become even more inadequate to cope with the predicted increase in extreme events induced by climate change. In this work, a centralized real-time control system is developed to improve reservoirs operation by exploiting numerical weather forecasts that are becoming increasingly available. The proposed management system implements a well-established optimization technique, model predictive control (MPC), and its recently modified version that can incorporate uncertainties, tree-based model predictive control (TB-MPC), to account for deterministic and ensemble forecasts respectively. The management system is assessed by simulation over historical events and compared to the no-forecasts strategy based on rule-curves. Simulation results show that the proposed real-time control system largely outperforms the no-forecasts management strategy, and that explicitly considering forecast uncertainty through ensembles can compensate for the loss in performance due to forecast inaccuracy
Possible Superconductivity at 37 K in Graphite-Sulfur Composite
Sulfur intercalated graphite composites with diamagnetic transitions at 6.7 K
and 37 K are prepared. The magnetization hysteresis loops (MHL), Xray
diffraction patterns, and resistance were measured. From the MHL, a slight
superconducting like penetration process is observed at 15 K in low field
region. The XRD shows no big difference from the mixture of graphite and sulfur
indicating that the volume of the superconducting phase (if any) is very small.
The temperature dependence of resistance shows a typical semiconducting
behavior with a saturation in low temperature region. This saturation is either
induced by the de-localization of conducting electrons or by possible
superconductivity in this system.Comment: CHIN. PHYS.LETT v18 1648 (2001
FAO/WHO GIFT (Global Individual Food consumption data Tool): a global repository for harmonised individual quantitative food consumption studies
Knowing who eats what, understanding the various eating habits of different population groups, according to the geographical area, is critical to develop evidence-based policies for nutrition and food safety. The FAO/WHO Global Individual Food consumption data Tool (FAO/WHO GIFT) is a novel open-access online platform, hosted by FAO and supported by WHO, providing access to harmonised individual quantitative food consumption (IQFC) data, especially in low- and middle-income countries (LMIC). FAO/WHO GIFT is a growing repository, which will serve as the global FAO/WHO hub to disseminate IQFC microdata. Currently five datasets from LMIC are available for dissemination, and an additional fifty datasets will be made available by 2022. To facilitate the use of these data by policy makers, ready-to-use food-based indicators are provided for an overview of key data according to population segments and food groups. FAO/WHO GIFT also provides an inventory of existing IQFC data worldwide, which currently contains detailed information on 188 surveys conducted in seventy-two countries. In order for end-users to be able to aggregate the available data, all datasets are harmonised with the European Food Safety Authority's food classification and description system FoodEx2 (modified for global use). This harmonisation is aimed at enhancing the consistency and reliability of nutrient intake and dietary exposure assessments. FAO/WHO GIFT is developed in synergy with other global initiatives aimed at increasing the quality, availability and use of IQFC data in LMIC to enable evidence-based decision-making and policy development for better nutrition and food safety
Two-phase stretching of molecular chains
While stretching of most polymer chains leads to rather featureless
force-extension diagrams, some, notably DNA, exhibit non-trivial behavior with
a distinct plateau region. Here we propose a unified theory that connects
force-extension characteristics of the polymer chain with the convexity
properties of the extension energy profile of its individual monomer subunits.
Namely, if the effective monomer deformation energy as a function of its
extension has a non-convex (concave up) region, the stretched polymer chain
separates into two phases: the weakly and strongly stretched monomers.
Simplified planar and 3D polymer models are used to illustrate the basic
principles of the proposed model. Specifically, we show rigorously that when
the secondary structure of a polymer is mostly due to weak non-covalent
interactions, the stretching is two-phase, and the force-stretching diagram has
the characteristic plateau. We then use realistic coarse-grained models to
confirm the main findings and make direct connection to the microscopic
structure of the monomers. We demostrate in detail how the two-phase scenario
is realized in the \alpha-helix, and in DNA double helix. The predicted plateau
parameters are consistent with single molecules experiments. Detailed analysis
of DNA stretching demonstrates that breaking of Watson-Crick bonds is not
necessary for the existence of the plateau, although some of the bonds do break
as the double-helix extends at room temperature. The main strengths of the
proposed theory are its generality and direct microscopic connection.Comment: 16 pges, 22 figure
Critical exponents at the ferromagnetic transition in tetrakis(diethylamino)ethylene-C (TDAE-C)
Critical exponents at the ferromagnetic transition were measured for the
first time in an organic ferromagnetic material tetrakis(dimethylamino)ethylene
fullerene[60] (TDAE-C). From a complete magnetization-temperature-field
data set near we determine the susceptibility and
magnetization critical exponents and respectively, and the field vs. magnetization exponent at of
. Hyperscaling is found to be violated by , suggesting that the onset of ferromagnetism can be
related to percolation of a particular contact configuration of C
molecular orientations.Comment: 5 pages, including 3 figures; to appear in Phys. Rev. Let
Gate-induced band ferromagnetism in an organic polymer
We propose that a chain of five-membered rings (polyaminotriazole) should be
ferromagnetic with an appropriate doping that is envisaged to be feasible with
an FET structure. The ferromagnetism is confirmed by a spin density functional
calculation, which also shows that ferromagnetism survives the Peierls
instability. We explain the magnetism in terms of Mielke and Tasaki's flat-band
ferromagnetism with the Hubbard model. This opens a new possibility of band
ferromagnetism in purely organic polymers.Comment: 4 pages, 7 figure
Electronic properties of alkali-metal loaded zeolites -- a "supercrystal" Mott insulator
First-principles band calculations are performed for the first time for an
open-structured zeolite (LTA) with guest atoms (potassium) introduced in their
cages. A surprisingly simple band structure emerges, which indicates that this
system may be regarded as a "supercrystal", where each cluster of guest atoms
with diameter 10\AA acts as a "superatom" with well-defined - and
-like orbitals, which in turn form the bands around the Fermi energy. The
calculated Coulomb and exchange energies for these states turn out to be in the
strongly-correlated regime. With the dynamical mean-field theory we show the
system should be on the Mott-insulator side, and, on a magnetic phase diagram
for degenerate-orbital systems, around the ferromagnetic regime, in accord with
experimental results. We envisage this class of systems can provide a new
avenue for materials design.Comment: 4 pages, 4 figure
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