Structural changes at the semiconductor-insulator phase transition in the single layered La0.5Sr1.5MnO4 perovskite

The semiconductor-insulator phase transition of the single-layer manganite La0.5Sr1.5MnO4 has been studied by means of high resolution synchrotron x-ray powder diffraction and resonant x-ray scattering at the Mn K edge. We conclude that a concomitant structural transition from tetragonal I4/mmm to orthorhombic Cmcm phases drives this electronic transition. A detailed symmetry-mode analysis reveals that condensation of three soft modes -Delta_2(B2u), X1+(B2u) and X1+(A)- acting on the oxygen atoms accounts for the structural transformation. The Delta_2 mode leads to a pseudo Jahn-Teller distortion (in the orthorhombic bc-plane only) on one Mn site (Mn1) whereas the two X1+ modes produce an overall contraction of the other Mn site (Mn2) and expansion of the Mn1 one. The X1+ modes are responsible for the tetragonal superlattice (1/2,1/2,0)-type reflections in agreement with a checkerboard ordering of two different Mn sites. A strong enhancement of the scattered intensity has been observed for these superlattice reflections close to the Mn K edge, which could be ascribed to some degree of charge disproportion between the two Mn sites of about 0.15 electrons. We also found that the local geometrical anisotropy of the Mn1 atoms and its ordering originated by the condensed Delta_2 mode alone perfectly explains the resonant scattering of forbidden (1/4,1/4,0)-type reflections without invoking any orbital ordering.Comment: 3 tables and 10 figures; accepted in Phys. Rev.

Financial VAT may improve trade openness

This paper theoretically and empirically analyzes how the taxation of financial services under VAT (‘financial VAT’) influences trade openness. The empirical analysis uses data from the OECD and 36 European Union countries for the period 1960–2019. Dynamic panel data techniques are used, concretely the GMM System, and an unbalanced panel is handled. The results corroborate that financial VAT, and in particular the ‘option-to-tax’ method applied by some countries in the European Union, are positively associated with a country’s trade openness. © 2021 Informa UK Limited, trading as Taylor & Francis Group

Proteins influencing foam formation in wine and beer: the role of yeast

This review focuses on the role of proteins in the production and maintenance of foam in both sparkling winesand beer. The quality of the foam in beer but especially in sparkling wines depends, among other factors, on the presence ofmannoproteins released from the yeast cell walls during autolysis. These proteins are hydrophobic, highly glycosylated, andtheir molecular masses range from 10 to 200 kDa- characteristics that allow mannoproteins to surround and thus stabilizethe gas bubbles of the foam. Both the production and stabilization of foam also depend on other proteins. In wine, theseinclude grape-derived proteins such as vacuolar invertase; in beer, barley-derived proteins, such as LTP1, protein Z, andhordein-derived polypeptides, are even more important in this respect than mannoproteins

Stability of Jahn-Teller distortion ordering in LaMn1-x ScxO3

We have investigated the role of Mn3+ Jahn-Teller distortion in driving ferromagnetism in the LaMn1-xScxO3 series. The replacement of Mn by Sc in LaMnO3 decreases the orthorhombic distortion of the Pbnm cell, but the unit cell remains distorted even in the LaScO3 sample. The analysis of the x-ray diffraction patterns indicates a continuous evolution from the typical Jahn-Teller distorted octahedron in LaMnO3 into a nearly regular one in LaScO3. Surprisingly, x-ray absorption spectroscopy measurements at the Mn and Sc K edges reveal the stability of both Jahn-Teller distorted MnO6 octahedron and nearly regular ScO6 octahedron along the whole Sc-substituted series. Moreover, the structure is described as a random distribution of Jahn-Teller distorted MnO6 octahedra spatially ordered as in LaMnO3 and nearly regular ScO6 octahedra. This result contrasts with the pseudocubic phase and the appearance of regular MnO6 octahedra in LaMn1-xGaxO3 for x>0.5. Thus the occurrence of Jahn-Teller distortion strongly depends on the distorted orthorhombic crystallographic structure of the matrix in which the Mn3+ atom is allocated. Besides, a ferromagnetic ground state is observed for x>0.5 in both series independently of the presence (or not) of Jahn-Teller distortions around Mn3+, which discards either the spin flipping or the vibronic superexchange models proposed for the ferromagnetism in LaMn1-xBxO3 (B=Sc or Ga).The authors thank ESRF, ALBA, and Elettra Synchrotrons for granting beam time. Financial support from the Spanish MINECO (Projects No. MAT2012-38213-C02-01 and No. MAT2011-23791) and the Diputacion General de Aragón (CAMRADS) are acknowledged.Peer Reviewe

Resonant x-ray scattering study of charge superstructures in layered L a2-x C axCo O4±d (0.4=x=0.7) and L a1.5 S r0.5Co O4 compounds

We propose a model for the Co charge disproportionation in La2-xCaxCoO4±d (0.4=x=0.7) and La1.5Sr0.5CoO4 layered cobaltites based on the photon energy, azimuthal angle, and polarization dependence of the scattered intensity of selected reflections in a resonant x-ray scattering experiment. Tetragonal superlattice (h/2, h/2, l)-type reflections were detected at room temperature for all the samples independently from the Ca (or Sr) doping rate in agreement with a checkerboard ordering of two different Co sites. The corresponding average charge disproportion is accounted for by a semiempirical model from which the imaginary part of the resonant atomic scattering factors of each of the two Co atoms is obtained resulting in about 0.5±0.1 electron. Moreover, no forbidden (h/4, h/4, l)-type reflections were observed at room temperature indicating the lack of any local anisotropy ordering in contrast with the behavior found in the related layered manganites. Finally, we found the pattern of small distortions (~0.05Å) around the two Co sites compatible with the resonant x-ray scattering results. The symmetry of this displacement pattern is consistent with the A2mm (or Ammm) orthorhombic structure of the ordered phase and the structural transition is accounted for by the condensation of two soft modes - X1+(B2u) and X1+(A1) - acting on the oxygen atoms

Utilización de fijadores externos circulares en el tratamiento de la pseudoartrosis infectada de tibia secuela de aplastamiento de miembros

Se revisan 7 casos de pseudoartrosis infectada de tibia, secuela de aplastamiento de miembros, tratadas inicialmente en el momento de la fractura con desbridamiento y fijador externo monolateral. Todos los casos eran iniciamente fracturas abiertas grado III de Gustilo. El tratamiento de la pseudoartrosis se realizó mediante desbridamiento, estabilización con fijador externo circular, cobertura de partes blandas e injerto óseo. La unión ósea se consiguió en todos los casos con una buena recuperación funcional. Se discuten las ventajas del fijador externo circular en estos casos.Seven patients with infected tibial pseuarthrosis due to crush injuries of the lower extremity and treated by using circular cxternal fixators were reviewed. All cases had tibial open fractures, Gustillo's type III. Treatment consisted of debridement, stabilization with a circular device, bone graft and coverage of soft tissues. Bone union «as achieved in all cases with a satisfactory functional recovery. The advantages of external fixators for this type of lesion are addressed

Putative ancient microorganisms from amber nuggets

Evolutionary microbiology studies based on the isolation of ancient DNA and/or microbial samples are scarce due to the difficulty of finding well preserved biological specimens. However, amber is a fossil resin with natural preserving properties for microbial cells and DNA. The visualization by transmission electron microscopy of different microorganismlike specimens found in amber nuggets from both the Miocene and the Cretaceous periods was accompanied by studies of ancient DNA obtained from the nuggets. After the design of specific primers based on the present sequences of both genes in Saccharomyces cerevisiae, the ancestral AGP2 sequence from the Miocene, as well as the 18S rRNA from the Cretaceous, were amplified. [Int Microbiol 2007; 10(2):117-122

Dependence of the Jahn-Teller distortion in LaMn1-xScxO3 on the isovalent Mn-site substitution

We investigated the relative importance of removing the Mn3+ Jahn-Teller distortion in driving ferromagnetism in LaMn1-xScxO3 combining x-ray powder diffraction and x-ray absorption spectroscopy at the Mn and Sc K-edges. By increasing the Sc content, the orthorhombic distortion of the Pbnm cell in LaMnO3 decreases but the unit-cell remains slightly distorted in LaScO3. Besides, the nearly tetragonal-distorted MO6 in LaMnO3 continuously evolves into a nearly regular one in LaScO3. On the other hand, x-ray absorption spectra show that the MnO6 octahedron remains Jahn-Teller distorted and the ScO6 octahedron is nearly regular along the whole series. Moreover, the ordering of the Mn3+ Jahn-Teller distortion is not disrupted in the ab plane for any Sc concentration. This contrasts with the Gasubstituted compounds, where a regular MnO6 is found for x > 0.5. However, both LaMn0.5Sc0.5O3 and LaMn0.5Ga0.5O3 show ferromagnetic behavior independently of the presence (or not) of Jahn-Teller distorted Mn3+. Thus, our results point to the Mn-sublattice dilution as the main effect in driving ferromagnetism in these manganites over local structure effects previously proposed by the spin flipping or the vibronic superexchange models