Synthesis and characterization of multiferroic BiMn7_7O12_{12}

We report on the high pressure synthesis of BiMn$_7$O$_{12}$, 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 $6s^{2}$ 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 BiMn$_7$O$_{12}$ 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 BiMn3_3Mn4_4O12_{12}

By means of neutron powder diffraction, we investigated the effect of the polar Bi$^{3+}$ ion on the magnetic ordering of the Mn$^{3+}$ ions in BiMn$_3$Mn$_4$O$_{12}$, the counterpart with \textit{quadruple} perovskite structure of the \textit{simple} perovskite BiMnO$_3$. The data are consistent with a \textit{noncentrosymmetric} spacegroup $Im$ which contrasts the \textit{centrosymmetric} one $I2/m$ previously reported for the isovalent and isomorphic compound LaMn$_3$Mn$_4$O$_{12}$, which gives evidence of a Bi$^{3+}$-induced polarization of the lattice. At low temperature, the two Mn$^{3+}$ sublattices of the $A'$ and $B$ sites order antiferromagnetically (AFM) in an independent manner at 25 and 55 K, similarly to the case of LaMn$_3$Mn$_4$O$_{12}$. However, both magnetic structures of BiMn$_3$Mn$_4$O$_{12}$ radically differ from those of LaMn$_3$Mn$_4$O$_{12}$. In BiMn$_3$Mn$_4$O$_{12}$ the moments $\textbf{M}_{A'}$ of the $A'$ sites form an anti-body AFM structure, whilst the moments \textbf{M}$_{B}$ of the $B$ sites result from a large and \textit{uniform} modulation $\pm \textbf{M}_{B,b}$ along the b-axis of the moments \textbf{M}$_{B,ac}$ in the $ac$-plane. The modulation is strikingly correlated with the displacements of the Mn$^{3+}$ ions induced by the Bi$^{3+}$ ions. Our analysis unveils a strong magnetoelastic coupling between the internal strain created by the Bi$^{3+}$ ions and the moment of the Mn$^{3+}$ ions in the $B$ 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$^{3+}$-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 $\sqrt{s}$ = 7 TeV, obtained using the luminosity measurement from CMS. A preliminary measurement of the forward charged particle $\eta$ 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 $\sqrt{s} = 7$ 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