Structural and Electrical Characterization of LaSrAl1-xMgxO4-δ Layered Perovskites Obtained by Mechanical Synthesis.

This work presents the structural and electrical characterization of K2NiF4-type layered perovskites of LaSrAl1-xMgxO4-δ composition to be used as oxide-ion electrolytes for a solid-oxide fuel cell (SOFC). These perovskites were prepared by mechano-chemical synthesis (ball milling), an alternative to traditional synthesis methods such as citrate-nitrates and solid-state reaction. With these methods, two things are avoided: first, the use of nitrate salts, which are more environmentally harmful than oxide precursors, and second, it saves the series of long thermal treatments associated with solid-state reactions. After grinding the precursors, nanometric particles were obtained with a combination of crystalline regions and amorphous regions; this effect was determined by XRD and TEM, showing that Mg has a positive effect on the phase formation by only mechanical synthesis. R2C4: After sintering, it was found by XRD that the sample x = 0.1 only presents the diffraction peaks corresponding to the desired phase, which shows a phase purity greater than 97%, even higher than that of the standard undoped sample. For x = 0.2 and 0.3, there was a segregation of impurities, possibly by the local migration of La and Sr heavy cations; this was determined by SEM and EDS. The electrical characterization of the sintered pellets was carried out by electrochemical impedance spectroscopy, which determined that the incorporation of Mg in the structure improves the ionic conductivity by three orders of magnitude, obtaining conductivities of 1.6 mS/cm at 900 °C for x = 0.2. Although the improvement in conductivity is considerable, many challenges such as densification, the segregation of impurities, and the study of mechanical and thermal properties must be carried out on these materials to endorse them as solid electrolytes in SOFC.

Structure-properties relationship in the hydronium-containing pyrochlores (H3O)1+pSb1+pTe1-pO6 with catalytic activity in the fructose dehydration reaction.

A series of defect pyrochlores of the composition (H3O)1+pSb1+pTe1-pO6 have been prepared by ion exchange from K-containing pyrochlores K1+pSb1+pTe1-pO6 in sulfuric acid at 280 °C for 24 h. The structural characterization of the hydronium-containing pyrochlores, including the location of the H3O+ units within the three-dimensional framework, was possible from neutron powder diffraction data in undeuterated samples. The crystal structure for all the compounds is defined in the Fd3[combining macron]m space group, and consists of a covalent framework of SbVO6 and TeVIO6 octahedra distributed at random and connected by their vertices with (Sb,Te)-O1-(Sb,Te) angles close to 136°, conforming to large cages where the hydronium species are located off-center. The absence of K+ ions in the ion-exchanged pyrochlores was confirmed by inductively coupled plasma optical emission spectroscopy and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy. The shape and size of the hydronium units evolve along with the series, becoming more compact as the framework covalence and Lewis-basicity decrease upon Sb enrichment of the structure (for greater p values). The amount and lability of the H3O+ species also increase throughout the series, as wanted: a straightforward correlation of the catalytic activity in the fructose dehydration reaction to 5-hydroxymethylfurfural has been observed, reaching conversion rates up to 88.5% of concentrated fructose solution for the p = 0.25 catalyst. Moreover, a pseudo-first-order kinetic mechanism was simulated, and the kinetic constants obtained from diluted and concentrated enhanced reaction systems were determined and compared.

¿Limitar la presión de distensión protege contra la lesión pulmonar adquirida por la ventilación mecánica (VALI)? / Does limiting the distension pressure protect against lung injury acquired by mechanical ventilation (VALI)? / A limitação da pressão de distensão protege contra lesão pulmonar adquirida por ventilação mecânica (VALI)?

Resumen: El incremento en la presión de las vías respiratorias causa lesión de la membrana alveolar proponiendo el barotrauma como causa de lesión pulmonar adquirida por el ventilador (VALI), esta afección se presenta de forma frecuente, lo que conduce a entender mejor el papel desempeñado por los ajustes del ventilador mecánico, la fisiopatología pulmonar subyacente y su interacción. En la última década se ha dado relevancia al término presión de distensión (PD), que surge del cálculo del delta de presión (∆P = Vt/CRS). La PD representa los cambios dinámicos de la presión que se genera en la vía aérea en cada ciclo ventilatorio. Aunque se instalen medidas de protección pulmonar de manera inicial, existen diversas condiciones que modifican las propiedades elásticas, tales como reanimación hídrica y el balance positivo de líquidos, procesos infecciosos agregados, etc. Sin embargo, aun cuando se cumplan estas medidas de protección puede haber distensión pulmonar excesiva, por lo que la monitorización de la PD puede ser una herramienta útil para determinar de manera sistemática los cambios en la rigidez pulmonar, estableciendo intervenciones. En ausencia de ensayos que usen PD como objetivo al establecer el ventilador, se sugiere que se utilice como complemento y no como un sustituto de parámetros de protección pulmonar.

Abstract: The increase in airway pressure causes injury in the alveolar membrane by proposing barotrauma as the cause of ventilator-acquired Lung Injury (VALI), this condition occurs frequently, which leads to a better understanding of the roles played by the mechanical ventilator settings, underlying lung pathophysiology and their interaction. In the last decade, the term pressure of distension (PD) has emerged, arising from the calculation of the pressure delta (ΔP = Vt/CRS). The PD represents the dynamic changes of the pressure that is generated in the airway in each ventilatory cycle. Although pulmonary protection measures are initially installed, there are several conditions that modify elastic properties, such as fluid resuscitation and positive fluid balance, aggregated infectious processes, etc. However, even if these protective measures are met, excessive pulmonary distention may occur, so PD monitoring may be a useful tool for systematically determining changes in pulmonary stiffness by establishing interventions. In the absence of assays using PD as a target when establishing the ventilator, it is suggested that it be used as a complement and not as a substitute for pulmonary protection parameters.

Resumo: O aumento da pressão das vias aéreas causa lesão da membrana alveolar, propondo o barotrauma como causa de Lesão Pulmonar Adquirida pelo Ventilador (VALI), esta condição ocorre com frequência, o que leva a uma melhor compreensão dos papéis desempenhados pelos ajustes do ventilador mecânico, a fisiopatologia pulmonar subjacente e sua interação. Na última década, o termo pressão de distensão (PD) tem recebido relevância decorrente do cálculo do delta de pressão (ΔP = Vt/CRS). A DP representa as mudanças dinâmicas da pressão gerada na via aérea em cada ciclo ventilatório. Embora as medidas de proteção pulmonar sejam instaladas inicialmente, existem várias condições que modificam as propriedades elásticas, tais como ressuscitação hídrica e balanço hídrico positivo, processos infecciosos agregados, etc. No entanto, mesmo que essas medidas de proteção sejam atendidas, pode haver distensão pulmonar excessiva, de modo que a monitorização da DP possa ser uma ferramenta útil para determinar sistematicamente as mudanças na rigidez pulmonar, estabelecendo intervenções. Na ausência de ensaios que utilizem a PD como objetivo no estabelecimento do ventilador, sugere-se que seja utilizado como complemento e não como substituto dos parâmetros de proteção pulmonar.

Phonons and hybrid modes in the high and low temperature far infrared dynamics of hexagonal TmMnO3.

We report on temperature dependent TmMnO3 far infrared emissivity and reflectivity spectra from 1910 K to 4 K. At the highest temperature the number of infrared bands is lower than that predicted for centrosymmetric P63/mmc (D(4)(6h)) (Z = 2) space group due to high temperature anharmonicity and possible defect induced bitetrahedra misalignments. On cooling, at ~1600 ± 40 K, TmMnO3 goes from non-polar to an antiferroelectric-ferroelectric polar phase reaching the ferroelectric onset at ~700 K. Room temperature reflectivity is fitted using 19 oscillators and this number of phonons is maintained down to 4 K. A weak phonon anomaly in the band profile at 217 cm(-1) (4 K) suggests subtle Rare Earth magneto-electric couplings at ~TN and below. A low energy collective excitation is identified as a THz instability associated with room temperature eg electrons in a d-orbital fluctuating environment. It condenses into two modes that emerge pinned to the E-type antiferromagnetic order hardening simultaneously down to 4 K. They obey power laws with TN as the critical temperature and match known zone center magnons. The one peaking at 26 cm(-1), with critical exponent ß=0.42 as for antiferromagnetic order in a hexagonal lattice, is dependent on the Rare Earth ion. The higher frequency companion at ~50 cm(-1), with ß=0.25, splits at ~TN into two peaks. The weaker band of the two is assimilated to the upper branch of the gap opening in the transverse acoustical (TA) phonon branch crossing the magnetic dispersion found in YMnO3. (Petit et al 2007 Phys. Rev. Lett. 99 266604). The stronger second band at ~36 cm(-1) corresponds to the lower branch of the TA gap. We assign both excitations as zone center magneto-electric hybrid quasiparticles, concluding that in NdMnO3 perovskite the equivalent picture corresponds to an instability which may be driven by an external field to transform NdMnO3 into a multiferroic compound by perturbation enhancing the TA phonon-magnetic correlation.

Paramagnetic collective electronic mode and low temperature hybrid modes in the far infrared dynamics of orthorhombic NdMnO3.

We report on the far- and mid-infrared reflectivity of NdMnO3 from 4 to 300 K. Two main features are distinguished in the infrared spectra: active phonons in agreement with expectations for the orthorhombic [Formula: see text]-Pbnm (Z = 4) space group remaining constant down to 4 K and a well defined collective excitation in the THz region due to eg electrons in a d-orbital fluctuating environment. We trace its origin to the NdMnO3 high-temperature orbital disordered intermediate phase not being totally dynamically quenched at lower temperatures. This results in minute orbital misalignments that translate into randomized non-static eg electrons within orbitals yielding a room-temperature collective excitation. Below TN ∼ 78 K, electrons gradually localize, inducing long-range magnetic order as the THz band condenses into two modes that emerge pinned to the A-type antiferromagnetic order. They harden simultaneously down to 4 K, obeying power laws with TN as the critical temperature and exponents ß âˆ¼ 0.25 and ß âˆ¼ 0.53, as for a tri-critical point and Landau magnetic ordering, respectively. At 4 K they match known zone center spin wave modes. The power law dependence is concomitant with a second order transition in which spin modes modulate orbital instabilities in a magnetoelectric hybridized orbital-charge-spin-lattice scenario. We also found that phonon profiles also undergo strong changes at TN ∼ 78 K due to magnetoelasticity.

High temperature far-infrared dynamics of orthorhombic NdMnO3: emissivity and reflectivity.

We report on near normal far- and mid-infrared emission and reflectivity of NdMnO3 perovskite from room temperature to sample decomposition above 1800 K. At 300 K the number of infrared active phonons is in close agreement with the 25 calculated for the orthorhombic D(2h)(16)-Pbnm (Z = 4) space group. Their number gradually decreases as we approach the temperature of orbital disorder at ~1023 K where the orthorhombic O' lower temperature cooperative phase coexists with the cubic orthorhombic O. At above ~1200 K, the three infrared active phonons coincide with that expected for cubic Pm-3m (Z = 1) in the high temperature insulating regime. Heating samples in dry air triggers double exchange conductivity by Mn(3+) and Mn(4+) ions and a small polaron mid-infrared band. Fits to the optical conductivity single out the octahedral antisymmetric and symmetric vibrational modes as the main phonons in the electron-phonon interactions at 875 K. For 1745 K, it is enough to consider the symmetric stretching internal mode. An overdamped defect induced Drude component is clearly outlined at the highest temperatures. We conclude that rare earth manganite eg electrons are prone to spin, charge, orbital, and lattice couplings in an intrinsic orbital distorted perovskite lattice, favoring embryonic low energy collective excitations.

Collective phase-like mode and the role of lattice distortions at TN ~TC in RMn2O5 (R= Pr, Sm, Gd, Tb, Bi).

We report on electronic collective excitations in RMn(2)O(5) (R =Pr, Sm, Gd, Tb) showing condensation starting at and below ~T(N) ~T(C)~ 40-50 K. Their origin is understood as partial delocalized e(g) electron orbitals in the Jahn-Teller distortion of the pyramid dimer with strong hybridized Mn(3+)-O bonds. Our local probes, Raman, infrared, and x-ray absorption, back the conclusion that there is no structural phase transition at T(N)~T(C). Ferroelectricity is magnetically assisted by electron localization triggering lattice polarizability by unscreening. We have also found phonon hardening as the rare earth is sequentially replaced. This is understood as a consequence of lanthanide contraction. It is suggested that partially f-electron screened rare earth nuclei might be introducing a perturbation to e(g) electrons prone to delocalize as the superexchange interaction takes place.

Energy-dispersive X-ray absorption spectroscopy at LNLS: investigation on strongly correlated metal oxides.

An energy-dispersive X-ray absorption spectroscopy beamline mainly dedicated to X-ray magnetic circular dichroism (XMCD) and material science under extreme conditions has been implemented in a bending-magnet port at the Brazilian Synchrotron Light Laboratory. Here the beamline technical characteristics are described, including the most important aspects of the mechanics, optical elements and detection set-up. The beamline performance is then illustrated through two case studies on strongly correlated transition metal oxides: an XMCD insight into the modifications of the magnetic properties of Cr-doped manganites and the structural deformation in nickel perovskites under high applied pressure.

The role of the Pb2+ 6s lone pair in the structure of the double perovskite Pb2ScSbO6.

The new double perovskite Pb2ScSbO6 was synthesized by standard ceramic procedures; the Rietveld refinement of room temperature neutron powder diffraction data shows that the crystal structure is well defined in the space group Fm3[combining macron]m. It contains a completely ordered array of alternating ScO6 and SbO6 octahedra sharing corners; the PbO12 polyhedra present an off-center displacement of the lead atoms along the [111] direction, due to the electrostatic repulsion between the Pb2+ 6s lone pair and the Pb-O bonds of the cuboctahedron. Dielectric permittivity measurements show a peak near 343 K, with a Curie-Weiss response above this temperature, which suggests an antiferroelectric behavior. Finally we present a DFT study of the electronic structure of Pb2ScSbO6, showing a great difference between the electronic density within SbO6 and ScO6 octahedra.

A produção de informação e conhecimento: Fundação de Economia e Estatística / x

A informação e o conhecimento sempre foram elementos estratégicos no desenvolvimento da humanidade, tendo sido fatores relevantes em todas as revoluções tecnológicas, e assumido, nesta última, o caráter de revolução da própria informação. Neste texto, são discutidos o modo de produção de estatísticas e do conhecimento e os veículos de disseminação mais utilizados.

Information and knowledge have always been fundamental to human development, strategically present in all technological revolutions. In the most recent revolution, the very nature of information itself was redefined. Also examined is how statistics and knowledge are produced and most commonly disseminated.

As mudanças econômicas em Porto Alegre e a questäo do financiamento da cidade / The economic changes in Porto Alegre and the question of city financing

Discute alguns aspectos que envolvem a questäo do financiamento da cidade em Porto Alegre. Estuda os efeitos das mudanças na estrutura econômica da metrópole, nas últimas décadas, sobre a capacidade do poder público financiar a organizaçäo e o financiamento da cidade. Desenvolve uma análise da evoluçäo econômica do município associada ao comportamento das principais fontes de receita do governo local. Discute alguns aspectos conceituais sobre os custos do crescimento urbano juntamente com uma análise qualitativa de algumas fontes de elevaçäo do gasto público com a cidade.