2,062 research outputs found
Sargassum polyceratium (Phaeophyceae, Fucaceae) surface molecule activity towards fouling organisms and embryonic development of benthic species
International audienceCoral reefs have undergone profound ecological changes over recent decades. Areas formerly covered by scleractinian coral species are now often overgrown by macroalgae. In Martinique (West Indies), this phenomenon has lead to the colonisation of numerous coral reefs by algae, amongst which Sargassum is one of the most prominent. This study focuses on potential defence molecules produced by Sargassum polyceratium. The hexane dipping method was employed to extract surface molecules on fresh material, and their bioactivities were assessed against bacteria (marine and estuarine), and marine tropical invertebrates wan annelid (Pseudonereis sp.), a bivalve (Codakia orbicularis) and a sea urchin (Diadema antillarum)x. Extracts were active against all microorganisms tested (MICs150 or 300 mg ml-1), early stages of development in Pseudonereis sp. (MICs100 mg ml-1) and embryos of C. orbicularis and D. antillarum (MICs5 mg ml-1), suggesting the production of defence compounds by S. polyceratium
Statistics of the electromagnetic response of a chaotic reverberation chamber
This article presents a study of the electromagnetic response of a chaotic
reverberation chamber (RC) in the presence of losses. By means of simulations
and of experiments, the fluctuations in the maxima of the field obtained in a
conventional mode-stirred RC are compared with those in a chaotic RC in the
neighborhood of the Lowest Useable Frequency (LUF). The present work
illustrates that the universal spectral and spatial statistical properties of
chaotic RCs allow to meet more adequately the criteria required by the Standard
IEC 61000-4-21 to perform tests of electromagnetic compatibility.Comment: 6 pages, 9 figure
Mott correlated states in the underdoped two-dimensional Hubbard model: variational Monte Carlo versus a dynamical cluster approximation
We investigate the properties of the frustrated underdoped Hubbard model on
the square lattice using two complementary approaches, the dynamical cluster
extension of dynamical mean field theory, and variational Monte Carlo
simulations of Gutzwiller-Jastrow wavefunctions with backflow corrections. We
compare and discuss data for the energy and the double occupancies, as obtained
from both approaches. At small dopings, we observe a rapid crossover from a
weakly correlated metal at low interaction strength U to a non-Fermi liquid
correlated state with strong local spin correlations. Furthermore, we
investigate the stability of the correlated state against phase separation. We
observe phase separation only for large values of U or very large frustration.
No phase separation is present for the parameter range relevant for the
cuprates.Comment: 8 pages, 8 figure
Possible effects of charge frustration in NaCoO: bandwidth suppression, charge orders and resurrected RVB superconductivity
Charge frustration due to further neighbor Coulomb repulsion can have
dramatic effects on the electronic properties of NaCoO in the full
doping range. It can significantly reduce the effective mobility of the charge
carriers, leading to a low degeneracy temperature . Such
strongly renormalized Fermi liquid has rather unusual properties--from the
point of view of the ordinary metals with --but similar to
the properties that are actually observed in the NaCoO system. For
example, we show that the anomalous thermopower and Hall effect observed in
NaCoO may be interpreted along these lines. If the repulsion is
strong, it can also lead to charge order; nevertheless, away from the
commensurate dopings, the configurational constraints allow some mobility for
the charge carriers, i.e., there remains some ``metallic'' component. Finally,
the particularly strong bandwidth suppression around the commensurate
can help resurrect the RVB superconductivity, which would otherwise not be
expected near this high doping. These suggestions are demonstrated specifically
for a -like model with an additional nearest neighbor repulsion.Comment: 15 pages, 17 figure
Na2V3O7, a frustrated nanotubular system with spin-1/2 diamond rings
Following the recent discussion on the puzzling nature of the interactions in
the nanotubular system Na2V3O7, we present a detailed ab-initio microscopic
analysis of its electronic and magnetic properties. By means of a non-trivial
downfolding study we propose an effective model in terms of tubes of nine-site
rings with the geometry of a spin-diamond necklace with frustrated inter-ring
interactions. We show that this model provides a quantitative account of the
observed magnetic behavior.Comment: 5 pages, 5 figures. Phys. Rev. Lett. (in press
Modeling the electronic behavior of -LiV2O5: a microscopic study
We determine the electronic structure of the one-dimensional spin-1/2
Heisenberg compound -LiVO, which has two inequivalent vanadium
ions, V(1) and V(2), via density-functional calculations. We find a relative
V(1)-V(2) charge ordering of roughly . We discuss the influence of the
charge ordering on the electronic structure and the magnetic behavior. We give
estimates of the basic hopping matrix elements and compare with the most
studied -NaVO.Comment: Final version. To appear in Phys. Rev. Let
Case report: Stenosis turned leak … and turned stenosis-complications of paravalvular prosthetic leak closure with a plug device.
Paravalvular leak is one of the most common complications and is among the most important prognostic factors of short- and long-term mortality after transcatheter aortic valve implantation (TAVI). Percutaneous valvular leak repair constitutes a first-line treatment for paravalvular leaks and is associated with high success rates and few serious complications nowadays. To the best of our knowledge, this is the first case where placement of the device through the stenting of the bioprosthesis resulted in creating a new symptomatic stenosis that required surgery.
We present a case of a patient with low-flow, low-gradient aortic stenosis treated with transfemoral implantation of a biological aortic prosthesis. One month after the procedure, the patient presented with acute pulmonary oedema and a paravalvular leak was discovered, which was corrected by percutaneous repair with a plug device. Five weeks after the valvular leak repair, the patient was readmitted for heart failure. At this time, a new aortic stenosis and paravalvular leak were diagnosed and the patient was referred for surgery. The new aortic mixed diseased was caused by the positioning of the plug device through the valve's metal stenting, which resulted in a paravalvular leak and pressed against the valve's leaflets, causing valvular stenosis. The patient was referred for surgical replacement and evolved well afterward.
This case illustrates a rare complication of a complex procedure, and it highlights the need for multidisciplinary decisions and good cooperation between the cardiology and cardiac surgery teams to develop better criteria in the selection of the appropriate technique for managing paravalvular leaks after TAVI
Discovery of a new INTEGRAL source: IGR J19140+0951
IGR J19140+0951 (formerly known as IGR J19140+098) was discovered with the
INTEGRAL satellite in March 2003. We report the details of the discovery, using
an improved position for the analysis. We have performed a simultaneous study
of the 5-100 keV JEM-X and ISGRI spectra from which we can distinguish two
different states. From the results of our analysis we propose that IGR
J19140+0951 is a persistent Galactic X-ray binary, probably hosting a neutron
star although a black hole cannot be completely ruled out.Comment: 4 pages, 4 figures. Accepted for publication in A&A
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