367 research outputs found
Synthesis and characterization of multiferroic BiMnO
We report on the high pressure synthesis of BiMnO, a manganite
displaying a "quadruple perovskite" structure. Structural characterization of
single crystal samples shows a distorted and asymmetrical coordination around
the Bi atom, due to presence of the lone pair, resulting in
non-centrosymmetric space group Im, leading to a permanent electrical dipole
moment and ferroelectric properties. On the other hand, magnetic
characterization reveals antiferromagnetic transitions, in agreement with the
isostructural compounds, thus evidencing two intrinsic properties that make
BiMnO a promising multiferroic material.Comment: 4 pages, 3 figure
Instrumentos de gestión de recursos bentónicos del litoral atlántico uruguayo con respecto al impacto de las floraciones algales nocivas
Tesis dirigida por Carlos Montes, tutora Clarisse Odebrecht. El litoral Atlántico uruguayo es una zona de importancia económica y ecológica en contínua transformación, debido a la gran dinámica y funcionamiento natural del medio y la provocada por la explotación de sus recursos naturales. Los recursos bentónicos del área han sido gestionados por el Instituto Nacional de Pesca en lo que se refiere a la evaluación biológica, explotación comercial y calidad. Si bien estos recursos han sido afectados por la explotación controlada durante las dos últimas décadas, se han producido episodios de mortandades masivas de algunas especies o accidentes ambientales de origen antrópico que afectaron drásticamente algunos recursos, los cuales se encuentran aún en vías de recuperación. Por otra parte, fenómenos naturales como las floraciones algales nocivas han afectado la explotación de los recursos, su calidad para el consumo, la salud del consumidor y la economía de los pescadores que viven de estos. La gestión adecuada de estos recursos (mejillón berberecho, almeja, caracol, etc.) pretende asegurar la conservación de los mismos mediante una explotación controlada, en beneficio de la comunidad de pescadores y consumidores, y garantizar la calidad de los mismos de acuerdo a normas internacionales. Se consideran instrumentos de gestión de los recursos bentónicos y se analizarán en el presente trabajo, aquellos elementos claves para la toma de decisiones, para proteger al recurso, a los que viven de su explotación y fundamentalmente al consumidor. Entre estos elementos se destacan las reglamentaciones existentes sobre la explotación de los recursos, la información procedente de trabajos de investigación sobre la dinámica de la población de los recursos y el plancton nocivo en esa área y las normas y programas para el control de calidad de los recursos a nivel nacional e internacional, para considerarlos aptos para el consumo
Internal-strain mediated coupling between polar Bi and magnetic Mn ions in the defect-free quadruple-perovskite BiMnMnO
By means of neutron powder diffraction, we investigated the effect of the
polar Bi ion on the magnetic ordering of the Mn ions in
BiMnMnO, the counterpart with \textit{quadruple} perovskite
structure of the \textit{simple} perovskite BiMnO. The data are consistent
with a \textit{noncentrosymmetric} spacegroup which contrasts the
\textit{centrosymmetric} one previously reported for the isovalent and
isomorphic compound LaMnMnO, which gives evidence of a
Bi-induced polarization of the lattice. At low temperature, the two
Mn sublattices of the and sites order antiferromagnetically
(AFM) in an independent manner at 25 and 55 K, similarly to the case of
LaMnMnO. However, both magnetic structures of
BiMnMnO radically differ from those of LaMnMnO.
In BiMnMnO the moments of the sites form
an anti-body AFM structure, whilst the moments \textbf{M} of the
sites result from a large and \textit{uniform} modulation along the b-axis of the moments \textbf{M} in the
-plane. The modulation is strikingly correlated with the displacements of
the Mn ions induced by the Bi ions. Our analysis unveils a strong
magnetoelastic coupling between the internal strain created by the Bi
ions and the moment of the Mn ions in the sites. This is ascribed to
the high symmetry of the oxygen sites and to the absence of oxygen defects, two
characteristics of quadruple perovskites not found in simple ones, which
prevent the release of the Bi-induced strain through distortions or
disorder. This demonstrates the possibility of a large magnetoelectric coupling
in proper ferroelectrics and suggests a novel concept of internal strain
engineering for multiferroics design.Comment: 9 pages, 7 figures, 5 table
On the temperature behavior of shunt-leakage currents in Cu(In,Ga)Se2 solar cells: The role of grain boundaries and rear Schottky contact
By comparing simulated and measured dark current-voltage (I-V) characteristics of CIGS cells at different temperatures, we investigate the temperature behavior of the shunt leakage current, and find that it can be explained by large donor trap concentrations at grain boundaries (GBs), and by a Schottky barrier at the backside contact where the GBs meets the anode metallization. We studied the I-V characteristics in the temperature range 280 K - 160 K achieving good fits of the measured I-V curves, especially for reverse bias and low forward bias, where the shunt leakage current dominates. The most important parameters determining the shunt leakage current value and its temperature dependence are the peak energy and density of the GB donor distribution, which control the inversion of GBs and the pinning of Fermi level at the anode/GB contact
Results on MOVPE SiGeSn deposition for the monolithic integration of III-V and IV elements in multi-junction solar cells
Abstract In order to produce a step forward towards the monolithic integration of III-V and IV compounds in multijunction solar cells, a first assessment of SiGeSn deposition in a metal organic vapour phase epitaxy (MOVPE) chamber also used for III-V growth has been carried out. The study brings insights on several aspects of the MOVPE SiGeSn growth in order to get a better control of SiGeSn composition and to obtain epitaxial layers with improved morphology. In particular, it is shown that the gas source Si2H6 is more influenced by the growth temperature compared to GeH4 and SnCl4, moreover, its competition with SnCl4 makes it difficult to incorporate Si in SiGeSn, as SnCl4 partial pressure is increased. SiGeSn morphology is shown to be strongly dependent on temperature, As carry-over and growth rate. A new growth model is introduced in order to explain the importance of the adatom bond lengths in inhibiting tin segregation when SiGeSn is grown at relatively high growth temperatures (>480 °C). In order to investigate the photovoltaic behaviour of SiGeSn, a single-junction GaAs/InGaP/SiGeSn/Ge functional device has been manufactured and characterized by external quantum efficiency (EQE) and current-voltage measurements. The experimental and the simulated EQE show the higher absorption coefficient of SiGeSn with respect to Ge, which allows using SiGeSn layers with a thickness three times lower than Ge to produce the same photovoltaic current
Intronic determinants coordinate charme lncRNA nuclear activity through the interaction with MATR3 and PTBP1
Chromatin architect of muscle expression (Charme) is a muscle-restricted long noncoding RNA (lncRNA) that plays an important role in myogenesis. Earlier evidence indicates that the nuclear Charme isoform, named pCharme, acts on the chromatin by assisting the formation of chromatin domains where myogenic transcription occurs. By combining RNA antisense purification (RAP) with mass spectrometry and loss-of-function analyses, we have now identified the proteins that assist these chromatin activities. These proteins—which include a sub-set of splicing regulators, principally PTBP1 and the multifunctional RNA/DNA binding protein MATR3—bind to sequences located within the alternatively spliced intron-1 to form nuclear aggregates. Consistent with the functional importance of pCharme interactome in vivo, a targeted deletion of the intron-1 by a CRISPR-Cas9 approach in mouse causes the release of pCharme from the chromatin and results in cardiac defects similar to what was observed upon knockout of the full-length transcript
First Results from the TOTEM Experiment
The first physics results from the TOTEM experiment are here reported,
concerning the measurements of the total, differential elastic, elastic and
inelastic pp cross-section at the LHC energy of = 7 TeV, obtained
using the luminosity measurement from CMS. A preliminary measurement of the
forward charged particle distribution is also shown.Comment: Conference Proceeding. MPI@LHC 2010: 2nd International Workshop on
Multiple Partonic Interactions at the LHC. Glasgow (UK), 29th of November to
the 3rd of December 201
Elastic Scattering and Total Cross-Section in p+p reactions measured by the LHC Experiment TOTEM at sqrt(s) = 7 TeV
Proton-proton elastic scattering has been measured by the TOTEM experiment at
the CERN Large Hadron Collider at TeV in special runs with the
Roman Pot detectors placed as close to the outgoing beam as seven times the
transverse beam size. The differential cross-section measurements are reported
in the |t|-range of 0.36 to 2.5 GeV^2. Extending the range of data to low t
values from 0.02 to 0.33 GeV^2,and utilizing the luminosity measurements of
CMS, the total proton-proton cross section at sqrt(s) = 7 TeV is measured to be
(98.3 +- 0.2(stat) +- 2.8(syst)) mb.Comment: Proceedings of the XLI International Symposium on Multiparticle
Dynamics. Accepted for publication in Prog. Theor. Phy
Proton-proton elastic scattering at the LHC energy of {\surd} = 7 TeV
Proton-proton elastic scattering has been measured by the TOTEM experiment at
the CERN Large Hadron Collider at {\surd}s = 7 TeV in dedicated runs with the
Roman Pot detectors placed as close as seven times the transverse beam size
(sbeam) from the outgoing beams. After careful study of the accelerator optics
and the detector alignment, |t|, the square of four-momentum transferred in the
elastic scattering process, has been determined with an uncertainty of d t =
0.1GeV p|t|. In this letter, first results of the differential cross section
are presented covering a |t|-range from 0.36 to 2.5GeV2. The differential
cross-section in the range 0.36 < |t| < 0.47 GeV2 is described by an
exponential with a slope parameter B = (23.6{\pm}0.5stat {\pm}0.4syst)GeV-2,
followed by a significant diffractive minimum at |t| =
(0.53{\pm}0.01stat{\pm}0.01syst)GeV2. For |t|-values larger than ~ 1.5GeV2, the
cross-section exhibits a power law behaviour with an exponent of -7.8_\pm}
0.3stat{\pm}0.1syst. When compared to predictions based on the different
available models, the data show a strong discriminative power despite the small
t-range covered.Comment: 12pages, 5 figures, CERN preprin
- …