Interfacial-Redox-Induced Tuning of Superconductivity in YBa2Cu3O7-δ.

Solid-state ionic approaches for modifying ion distributions in getter/oxide heterostructures offer exciting potentials to control material properties. Here, we report a simple, scalable approach allowing for manipulation of the superconducting transition in optimally doped YBa2Cu3O7-δ (YBCO) films via a chemically driven ionic migration mechanism. Using a thin Gd capping layer of up to 20 nm deposited onto 100 nm thick epitaxial YBCO films, oxygen is found to leach from deep within the YBCO. Progressive reduction of the superconducting transition is observed, with complete suppression possible for a sufficiently thick Gd layer. These effects arise from the combined impact of redox-driven electron doping and modification of the YBCO microstructure due to oxygen migration and depletion. This work demonstrates an effective step toward total ionic tuning of superconductivity in oxides, an interface-induced effect that goes well into the quasi-bulk regime, opening-up possibilities for electric field manipulation

Ionic Tuning of Cobaltites at the Nanoscale

Control of materials through custom design of ionic distributions represents a powerful new approach to develop future technologies ranging from spintronic logic and memory devices to energy storage. Perovskites have shown particular promise for ionic devices due to their high ion mobility and sensitivity to chemical stoichiometry. In this work, we demonstrate a solid-state approach to control of ionic distributions in (La,Sr)CoO$_{3}$ thin films. Depositing a Gd capping layer on the perovskite film, oxygen is controllably extracted from the structure, up-to 0.5 O/u.c. throughout the entire 36 nm thickness. Commensurate with the oxygen extraction, the Co valence state and saturation magnetization show a smooth continuous variation. In contrast, magnetoresistance measurements show no-change in the magnetic anisotropy and a rapid increase in the resistivity over the same range of oxygen stoichiometry. These results suggest significant phase separation, with metallic ferromagnetic regions and oxygen-deficient, insulating, non-ferromagnetic regions, forming percolated networks. Indeed, X-ray diffraction identifies oxygen-vacancy ordering, including transformation to a brownmillerite crystal structure. The unexpected transformation to the brownmillerite phase at ambient temperature is further confirmed by high-resolution scanning transmission electron microscopy which shows significant structural - and correspondingly chemical - phase separation. This work demonstrates room-temperature ionic control of magnetism, electrical resistivity, and crystalline structure in a 36 nm thick film, presenting new opportunities for ionic devices that leverage multiple material functionalities

Biological activity differences between TGF-β1 and TGF-β3 correlate with differences in the rigidity and arrangement of their component monomers

[Image: see text] TGF-β1, -β2, and -β3 are small, secreted signaling proteins. They share 71–80% sequence identity and signal through the same receptors, yet the isoform-specific null mice have distinctive phenotypes and are inviable. The replacement of the coding sequence of TGF-β1 with TGF-β3 and TGF-β3 with TGF-β1 led to only partial rescue of the mutant phenotypes, suggesting that intrinsic differences between them contribute to the requirement of each in vivo. Here, we investigated whether the previously reported differences in the flexibility of the interfacial helix and arrangement of monomers was responsible for the differences in activity by generating two chimeric proteins in which residues 54–75 in the homodimer interface were swapped. Structural analysis of these using NMR and functional analysis using a dermal fibroblast migration assay showed that swapping the interfacial region swapped both the conformational preferences and activity. Conformational and activity differences were also observed between TGF-β3 and a variant with four helix-stabilizing residues from TGF-β1, suggesting that the observed changes were due to increased helical stability and the altered conformation, as proposed. Surface plasmon resonance analysis showed that TGF-β1, TGF-β3, and variants bound the type II signaling receptor, TβRII, nearly identically, but had small differences in the dissociation rate constant for recruitment of the type I signaling receptor, TβRI. However, the latter did not correlate with conformational preference or activity. Hence, the difference in activity arises from differences in their conformations, not their manner of receptor binding, suggesting that a matrix protein that differentially binds them might determine their distinct activities

Ligand-Receptor Interactions

The formation and dissociation of specific noncovalent interactions between a variety of macromolecules play a crucial role in the function of biological systems. During the last few years, three main lines of research led to a dramatic improvement of our understanding of these important phenomena. First, combination of genetic engineering and X ray cristallography made available a simultaneous knowledg of the precise structure and affinity of series or related ligand-receptor systems differing by a few well-defined atoms. Second, improvement of computer power and simulation techniques allowed extended exploration of the interaction of realistic macromolecules. Third, simultaneous development of a variety of techniques based on atomic force microscopy, hydrodynamic flow, biomembrane probes, optical tweezers, magnetic fields or flexible transducers yielded direct experimental information of the behavior of single ligand receptor bonds. At the same time, investigation of well defined cellular models raised the interest of biologists to the kinetic and mechanical properties of cell membrane receptors. The aim of this review is to give a description of these advances that benefitted from a largely multidisciplinar approach

Nitrogen-Based Magneto-Ionic Manipulation of Exchange Bias in CoFe/MnN Heterostructures

Electric field control of the exchange bias effect across ferromagnet/antiferromagnet (FM/AF) interfaces has offered exciting potentials for low-energy-dissipation spintronics. In particular, the solid state magneto-ionic means is highly appealing as it may allow reconfigurable electronics by transforming the all-important FM/AF interfaces through ionic migration. In this work, we demonstrate an approach that combines the chemically induced magneto-ionic effect with the electric field driving of nitrogen in the Ta/Co$_{0.7}$Fe$_{0.3}$/MnN/Ta structure to electrically manipulate exchange bias. Upon field-cooling the heterostructure, ionic diffusion of nitrogen from MnN into the Ta layers occurs. A significant exchange bias of 618 Oe at 300 K and 1484 Oe at 10 K is observed, which can be further enhanced after a voltage conditioning by 5% and 19%, respectively. This enhancement can be reversed by voltage conditioning with an opposite polarity. Nitrogen migration within the MnN layer and into the Ta capping layer cause the enhancement in exchange bias, which is observed in polarized neutron reflectometry studies. These results demonstrate an effective nitrogen-ion based magneto-ionic manipulation of exchange bias in solid-state devices.Comment: 28 pages, 4 figures; supporting information: 17 pages, 11 figure

Aspectos metodológicos e aplicações clínicas dos exercícios com restrição do fluxo sanguíneo

The resistance training has been recommended in the prevention and rehabilitation of injuries, health promotion, and to improve sports performance. Low intensity resistance exercise with blood flow restriction is an alternative for people intolerant to traditional protocols recommended by the American College of Sports Medicine, advocating high intensity to increase strength and muscle hypertrophy. This method involves the application of cuff pressure on the proximal portion of the upper or lower extremities by promoting muscle ischemia with consequent increase in anabolic activity. The study aimed to review the literature on the methodological aspects of exercise with blood flow restriction, as well as verify the muscular and cardiovascular effects promoted by this type of training and its possible clinical applications. We can conclude that there are different methodological approaches used in this type of training, and therefore a need for a standard protocol. However, even with different methodologies, the results have shown that the low intensity exercise with blood flow restriction seems to promote muscle responses similar to those protocols with highloads, such as increased strength and muscle hypertrophy. On the other hand, caution must be taken when prescribing this type of exercise, especially to patients with cardiometabolic diseases due to possible reductions of flow mediated vasodilatation that may be associated with increased retrograde flow, leading to endothelial dysfunction through the mechanism of ischemia-reperfusion.O treinamento resistido vem despertando o interesse dos profissionais da saúde, sendo utilizado na prevenção e na reabilitação de lesões, na promoção da saúde e na melhora do desempenho desportivo. O exercício de baixa intensidade com restrição do fluxo sanguíneo representa uma alternativa para indivíduos intolerantes aos protocolos tradicionais recomendados pelo Colégio Americano de Medicina Desportiva, que preconizam alta intensidade para aumento da força e da hipertrofia muscular. Nesse método utiliza-se um manguito de pressão colocado no terço proximal dos membros superiores e/ou inferiores, promovendo uma isquemia muscular com consequente aumento da atividade anabólica. O presente estudo teve como objetivo fazer uma revisão da literatura sobre os aspectos metodológicos dos exercícios com restrição do fluxo sanguíneo, assim como verificar os efeitos musculares e cardiovasculares promovidos por esse tipo de treinamento e suas possíveis aplicações clínicas. Podemos concluir que existem diferentes propostas metodológicas utilizadas nesse tipo de treinamento, não havendo ainda, um protocolo “ideal”. No entanto, mesmo utilizando diferentes metodologias, os resultados sugerem que o exercício de baixa intensidade com restrição do fluxo sanguíneo promove respostas musculares semelhantes aos protocolos com cargas altas, como o aumento da força e hipertrofia muscular. No entanto, devem ser prescritos com cautela para indivíduos com doenças cardiovasculares, uma vez que parecem induzir ao aumento do fluxo retrógrado vascular, seguido de possível lesão endotelial por isquemia-reperfusão e consequente diminuição da vasodilatação endotélio-dependente.Descritores: Fluxo sanguíneo regional; Hipertrofia; Força muscular; Fluxo retrógrado. Revista HUPE, Rio de Janeiro, 2013;12(4):124-36doi:10.12957/rhupe.2013.871