Maximally-localized Wannier Functions in Antiferromagnetic MnO within the FLAPW Formalism

We have calculated the maximally-localized Wannier functions of MnO in its antiferromagnetic (AFM) rhombohedral unit cell, which contains two formula units. Electron Bloch functions are obtained with the linearized augmented plane-wave method within both the LSD and the LSD+U schemes. The thirteen uppermost occupied spin-up bands correspond in a pure ionic scheme to the five Mn 3d orbitals at the Mn_1 (spin-up) site, and the four O 2s/2p orbitals at each of the O_1 and O_2 sites. Maximal localization identifies uniquely four Wannier functions for each O, which are trigonally-distorted sp^3-like orbitals. They display a weak covalent bonding between O 2s/2p states and minority-spin d states of Mn_2, which is absent in a fully ionic picture. This bonding is the fingerprint of the interaction responsible for the AFM ordering, and its strength depends on the one-electron scheme being used. The five Mn Wannier functions are centered on the Mn_1 site, and are atomic orbitals modified by the crystal field. They are not uniquely defined by the criterion of maximal localization and we choose them as the linear combinations which diagonalize the r^2 operator, so that they display the D_3d symmetry of the Mn_1 site.Comment: 11 pages, 6 PostScript figures. Uses Revtex4. Hi-res figures available from the author

Facile route to effective antimicrobial aluminum oxide layer realized by co-deposition with silver nitrate

The emergence and spreading of the SARS-CoV-2 pandemic has forced the focus of attention on a significant issue: the realization of antimicrobial surfaces for public spaces, which do not require extensive use of disinfectants. Silver represents one of the most used elements in this context, thanks to its excellent biocidal performance. This work describes a simple method for the realization of anodized aluminum layers, whose antimicrobial features are ensured by the co-deposition with silver nitrate. The durability and the chemical resistance of the samples were evaluated by means of several accelerated degradation tests, such as the exposure in a salt spray chamber, the contact with synthetic sweat and the scrub test, highlighting the residual influence of silver in altering the protective behavior of the alumina layers. Furthermore, the ISO 22196:2011 standard was used as the reference protocol to set up an assay to measure the effective antibacterial activity of the alumina-Ag layers against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria, even at low concentrations of silver. Finally, the Ag-containing aluminum oxide layers exhibited excellent antimicrobial performances also following the chemical–physical degradation processes, ensuring good durability over time of the antimicrobial surfaces. Overall, this work introduces a simple route for the realization of anodized aluminum surfaces with excellent antibacterial properties

“Villas miseria” en Buenos Aires hacia mediados del siglo XX: tensiones políticas y primeras conceptualizaciones estatales

Este trabajo analiza las primeras conceptualizaciones estatales producidas en torno a asentamientos urbanos precarios en Buenos Aires. Se examina para ello el primer plan de desalojo masivo de “villas miseria” (el término local para urbanizaciones informales) en Argentina (Plan de Emergencia, 1956), junto con sus antecedentes conceptuales y su contexto político. Se propone que la idea estatal de “villa miseria” cristalizó en la Argentina de los años cincuenta en torno a dicho plan y en la intersección de dos escalas: nacional e interamericana. A nivel nacional, las tensiones entre adeptos y opositores al peronismo determinaron que este nuevo concepto urbano surgiría cargado de un fuerte sesgo político. Pero, además, en diálogo con organismos interamericanos, la matriz discursiva de esta conceptualización estuvo signada por agendas hemisféricas vinculadas a la Guerra Fría. A través de un estudio minucioso de fuentes históricas originales, el artículo reconstruye este proceso. This article analyzes the first state conceptualizations of precarious urban settlements in Buenos Aires. To this aim we examine the first plan for the eviction of “villas miseria” (the local term for informal urbanizations) in Argentina (Emergency Plan, 1956) together with its conceptual antecedents and political context. It is argued that the state idea of “villa” crystallized in Argentina in the 1950s around this plan and at the intersection of two scales: national and inter-American. At the national level, the tensions between supporters and opponents of Peronism determined that this new urban concept would emerge with a strong political bias. But also, in dialogue with inter-American organizations, the discursive matrix of this conceptualization was marked by hemispheric agendas linked to the Cold War. The article reconstructs this process using a meticulous study of original historical sources

The effect of magnetic impurities in a two-band superconductor: A point-contact study of Mn-substituted MgB2 single crystals

We present the first results of directional point-contact measurements in Mg_{1-x}Mn_{x}B_2 single crystals, with x up to 0.015 and bulk T_c down to 13.3 K. The order parameters Delta_{sigma} and Delta_{pi} were obtained by fitting the conductance curves with the two-band Blonder-Tinkham-Klapwijk (BTK) model. Both Delta_{pi} and Delta_{sigma} decrease with the critical temperature of the junctions T_c^A, but remain clearly distinct up to the highest Mn content. Once analyzed within the Eliashberg theory, the results indicate that spin-flip scattering is dominant in the sigma band, as also confirmed by first-principle band structure calculations.Comment: 4 pages, 5 eps figures. New theoretical results added, text and some figures changed. References adde

Influence of the MCT1 rs1049434 on Indirect Muscle Disorders/Injuries in Elite Football Players

The aim of this study was to investigate the association between MCT1 rs1049434 polymorphism and indirect muscle injuries in elite football players. One hundred and seventy-three male elite Italian football players (age = 19.2 ± 5.3 years) were recruited from a first-league football club participating at the Official National Italian Football Championship (Serie A, Primavera, Allievi, Giovanissimi). The cohort was genotyped for the MCT1 rs1049434 polymorphism, and muscle injuries data were collected during the period of 2009-2014 (five football seasons).Genomic DNA was extracted using a buccal swab, and genotyping was performed using PCR method. Structural-mechanical injuries and functional muscle disorder were included in the acute indirect muscle injury group.Participants with the MCT1 AA (AA = 1.57 ± 3.07, n = 69) genotype exhibit significantly higher injury incidents compared to participants with the TT genotype (TT = 0.09 ± 0.25, n = 22, P = 0.04).The MCT1 rs1049434 polymorphism is associated with the incidence of muscle injuries in elite football players. We anticipate that the knowledge of athletes' genetic predisposition to sports-related injuries might aid in individualizing training programs

Point defects, ferromagnetism and transport in calcium hexaboride

The formation energy and local magnetic moment of a series of point defects in CaB$_6$ are computed using a supercell approach within the generalized gradient approximation to density functional theory. Based on these results, speculations are made as to the influence of these defects on electrical transport. It is found that the substitution of Ca by La does not lead to the formation of a local moment, while a neutral B$_6$ vacancy carries a moment of 2.4 Bohr magnetons, mostly distributed over the six nearest-neighbour B atoms. A plausible mechanism for the ferromagnetic ordering of these moments is suggested. Since the same broken B-B bonds appear on the preferred (100) cleavage planes of the CaB$_6$ structure, it is argued that internal surfaces in polycrystals as well as external surfaces in general will make a large contribution to the observed magnetization.Comment: Calculated defect formation energies had to be corrected, due to the use of a wrong reference energy for the perfect crystal in the original pape

LocZ is a new cell division protein involved in proper septum placement in Streptococcus pneumoniae

How bacteria control proper septum placement at midcell, to guarantee the generation of identical daughter cells, is still largely unknown. Although different systems involved in the selection of the division site have been described in selected species, these do not appear to be widely conserved. Here, we report that LocZ (Spr0334), a newly identified cell division protein, is involved in proper septum placement in Streptococcus pneumoniae. We show that locZ is not essential but that its deletion results in cell division defects and shape deformation, causing cells to divide asymmetrically and generate unequally sized, occasionally anucleated, daughter cells. LocZ has a unique localization profile. It arrives early at midcell, before FtsZ and FtsA, and leaves the septum early, apparently moving along with the equatorial rings that mark the future division sites. Consistently, cells lacking LocZ also show misplacement of the Z-ring, suggesting that it could act as a positive regulator to determine septum placement. LocZ was identified as a substrate of the Ser/Thr protein kinase StkP, which regulates cell division in S. pneumoniae. Interestingly, homologues of LocZ are found only in streptococci, lactococci, and enterococci, indicating that this close phylogenetically related group of bacteria evolved a specific solution to spatially regulate cell division. IMPORTANCE Bacterial cell division is a highly ordered process regulated in time and space. Recently, we reported that the Ser/ Thr protein kinase StkP regulates cell division in Streptococcus pneumoniae, through phosphorylation of several key proteins. Here, we characterized one of the StkP substrates, Spr0334, which we named LocZ. We show that LocZ is a new cell division protein important for proper septum placement and likely functions as a marker of the cell division site. Consistently, LocZ supports proper Z-ring positioning at midcell. LocZ is conserved only among streptococci, lactococci, and enterococci, which lack homologues of the Min and nucleoid occlusion effectors, indicating that these bacteria adapted a unique mechanism to find their middle, reflecting their specific shape and symmetry

Excitonic order at strong-coupling: pseudo-spins, doping, and ferromagnetism

A tight binding model is introduced to describe the strong interaction limit of excitonic ordering. At stoichiometry, the model reduces in the strong coupling limit to a pseudo-spin model with approximate U(4) symmetry. Excitonic order appears in the pseudo-spin model as in-plane pseudo-magnetism. The U(4) symmetry unifies all possible singlet and triplet order parameters describing such states. Super-exchange, Hunds-rule coupling, and other perturbations act as anisotropies splitting the U(4) manifold, ultimately stabilizing a paramagnetic triplet state. The tendency to ferromagnetism with doping (observed experimentally in the hexaborides) is explained as a spin-flop transition to a different orientation of the U(4) order parameter. The physical mechanism favoring such a reorientation is the enhanced coherence (and hence lower kinetic energy) of the doped electrons in a ferromagnetic background relative to the paramagnet. A discussion of the physical meaning of various excitonic states and their experimental consequences is also provided.Comment: 16 pages, 5 figure

Electronic Fine Structure in the Electron-Hole Plasma in SrB6

Electron-hole mixing-induced fine structure in alkaline earth hexaborides leads to lower energy (temperature) scales, and thus stronger tendency toward an excitonic instability, than in their doped counterparts (viz. Ca(1-x)La(x)B(6), x=0.005), which are high Curie temperature, small moment ferromagnets. Comparison of Fermi surfaces and spectral distributions with de Haas - van Alphen (dHvA), optical, transport, and tunneling data indicates that SrB6 remains a fermionic semimetal down to (at least) 5 K, rather than forming an excitonic condensate. For the doped system the Curie temperature is higher than the degeneracy temperature.Comment: Four two-column pages, three postscript figures. Phys. Rev. Lett. (April 2000, in press

Ferromagnetism below the Stoner limit in La-doped SrB_6

Spin-polarized band calculations for LaSr_7B_{48} show a weak ferro-magnetic state. This is despite a low density-of-states (DOS) and a low Stoner factor. The reason for the magnetic state is found to be associated with a gain in potential energy in addition to the exchange energy, as a spin-splitting is imposed. An impurity like La DOS is essential for this effect. It makes a correction to the Stoner factor, and provides an explanation of the recently observed weak ferro-magnetism in doped hexaborides.Comment: 6 pages, 2 tables, 1 figur