Localized electronic vacancy level and its effect on the properties of doped manganites.

Oxygen vacancies are common to most metal oxides and usually play a crucial role in determining the properties of the host material. In this work, we perform ab initio calculations to study the influence of vacancies in doped manganites [Formula: see text], varying both the vacancy concentration and the chemical composition within the ferromagnetic-metallic range ([Formula: see text]). We find that oxygen vacancies give rise to a localized electronic level and analyse the effects that the possible occupation of this defect state can have on the physical properties of the host. In particular, we observe a substantial reduction of the exchange energy that favors spin-flipped configurations (local antiferromagnetism), which correlate with the weakening of the double-exchange interaction, the deterioration of the metallicity, and the degradation of ferromagnetism in reduced samples. In agreement with previous studies, vacancies give rise to a lattice expansion when the defect level is unoccupied. However, our calculations suggest that under low Sr concentrations the defect level can be populated, which conversely results in a local reduction of the lattice parameter. Although the exact energy position of this defect level is sensitive to the details of the electronic interactions, we argue that it is not far from the Fermi energy for optimally doped manganites ([Formula: see text]), and thus its occupation could be tuned by controlling the number of available electrons, either with chemical doping or gating. Our results could have important implications for engineering the electronic properties of thin films in oxide compounds.

The magnetic structure of ß-cobalt hydroxide and the effect of spin-orientation.

Synchrotron X-ray and neutron diffraction experiments at various temperatures, down to 3 K, along with ab initio calculations, are carried out to elucidate the magnetic order of layered ß-cobalt-hydroxide. This combination of techniques allows for the unambiguous assignment of the magnetic structure of this material. Our results confirm that below the Néel temperature high-spin cobalt centers are ferromagnetically coupled within a layer, and antiferromagnetically coupled across layers (magnetic propagation vector k = (0,0,½)), in agreement with the indirect interpretation based on magnetic susceptibility measurements. A paramagnetic/antiferromagnetic transition is observed at around 15 K. Moreover, the thermal expansion behavior along the c-lattice direction, perpendicular to the layers, shows an inflection slightly above this temperature, at around 30 K. The neutron diffraction patterns and the non-collinear DFT+U calculations indicate that the magnetization forms an angle of about 35° with the cobalt planes. In particular, for an isolated ferromagnetic layer, the electronic structure calculations reveal sharp cusps on the potential energy surface when the spins point parallel or perpendicular to the planes, suggesting that the ferromagnetic superexchange mechanism is strongly sensitive to the orientation of the magnetic moment.

Distinct patterns of regeneration of central memory, effector memory and effector TCD8+ cell subsets after different hematopoietic cell transplant types: possible influence in the recovery of anti-cytomegalovirus immune response and risk for its reactivation.

TCD8+ cells may be divided into subsets with different phenotypes and functions: naive, central memory, effector memory and effector. Aiming to better understand the differences in early reconstitution of these TCD8+ cell subsets and their relationship with post-transplant anti-cytomegalovirus (CMV) immune responses recovery, we prospectively analyzed the transfer and expansion of these subsets in different transplant types. We found that graft cells from donor's peripheral blood, either allogeneic or autologous, were enriched for central memory, effector memory and effector phenotypes compared to allogeneic bone marrow grafts, as assessed by surface markers phenotyping and granzyme B expression. However, post-transplant, these subsets expanded in autologous recipients only, reaching numbers much greater than in allo-recipients at days +29 and +96. At the same time, autologous recipients presented less CMV reactivation and more vigorous CMV-induced interferon-gamma and lymphoproliferative responses. The marked loss of allo-transferred memory TCD8+ cells was probably due to the fact that they were more activated and more prone to apoptosis than auto-transferred TCD8+ cells as assessed by CD69 and active caspase 3 expression. Thus, transfer of peripheral blood stem cells in the allogeneic but not autologous setting is associated with poor expansion of memory TCD8+ cells, probably delaying antiviral immune reconstitution. These data may have important implications for the design of better strategies to immunoprotect this population against infectious challenges since different transplant types have different potentials for memory TCD8+ cells transfer and expansion.

Avaliação da reconstituição imunológica e da resposta anti-citomegalovirus nos receptores de transplante de medula óssea / Anti-cytomegalovirus immunity reconstitution following autologous and allogeneic stem cell and bone marrow transplantation as assessed by CD8+ T cell phenotyping and function

O citomegalovírus é uma séria ameaça aos receptores de transplante de medula óssea. A reativação está associada com uma imunidade mediada por células TCD8+ defeituosa. Nosso objetivo foi correlacionar as diferentes subpopulações de células TCD8+ com a reconstituição imunológica dos pacientes, especificamente a imunidade anti-citomegalovírus, analisando as subpopulações de células T infundidas nas diferentes modalidades de transplante de medula óssea. Receptores de transplante alogênico de células tronco mobilizadas para o sangue periférico (n=16) ou coletadas diretamente da medula óssea (n=28) e receptores de transplante autólogo de células tronco mobilizadas para o sangue periférico (n=22) foram avaliados. Nós mostramos que os receptores de células mobilizadas para o sangue periférico dos doadores, tanto nos transplantes alogênicos como nos autólogos, são proporcionalmente enriquecidos por fenótipos de células memória efetora e efetora, comparada aos receptores de células procedentes diretamente da medula óssea. Este maior número das subpopulações de células TCD8+ mais diferenciadas foi também correlacionado com maior número de células contendo altos níveis de granzima B, a qual é um outro marcador de valor dos linfócitos citotóxicos, sendo mais evidente nos receptores de transplante autólogo. Ao mesmo tempo, eles apresentaram menos freqüentemente reativação pelo citomegalovírus, e mais freqüentemente produziram interferon-gama em resposta ao antígeno do citomegalovírus / Cytomegalovirus is a serious threat to the recipients of bone marrow transplantation. Reactivation is associated with defective CD8+ T cell-mediated immunity. We aimed to correlate the different subsets of CD8+ T cells with the patients’ immune reconstitution, specifically anti CMV immunity, by analyzing the CD8+ T cell subsets infused in the different types of bone marrow transplantation. Recipients of allogeneic transplant of peripheral blood stem cells (n=16) or bone marrow (n=28) and recipients of autologous transplant of peripheral blood stem cells (n=22) were evaluated. We show that recipients of stem cells from donor’s peripheral blood, either allogeneic or autologous, are proportionally enriched for effector memory and effector phenotypes, compared to the recipients of stem cells of bone marrow origin...