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Shaking and pushing skyrmions: Formation of a nonequilibrium phase with zero critical current
No full textIn three-dimensional chiral magnets, skyrmions are line-like objects oriented parallel to the applied magnetic field. The efficient coupling of magnetic skyrmion lattices to spin currents and magnetic fields permits their dynamical manipulation. Here, we explore the dynamics of skyrmion lattices when slowly oscillating the field direction by up to a few degrees on millisecond timescales while simultaneously pushing the skyrmion lattice by electric currents. The field oscillations induce a shaking of the orientation of the skyrmion lines, leading to a phase where the critical depinning current for translational motion vanishes. We measure the transverse susceptibility of MnSi to track various depinning phase transitions induced by currents, oscillating fields, or combinations thereof. An effective slip–stick model for the bending and motion of the skyrmion lines in the presence of disorder explains main features of the experiment and predicts the existence of several dynamical skyrmion lattice phases under shaking and pushing representing phases of matter far from thermal equilibrium
Volatile resistive switching characteristics of molecular beam epitaxy grown HfO2 thin films
No full textIn this work, we have explored the structure, morphology and resistive switching aspects of molecular beamepitaxy grown HfO2 thin films fabricated on highly doped p-type Si substrate at substrate temperatures of 300and 500 ◦C. Both films correspond to the monoclinic phase (P21/c) of HfO2 and exhibit single crystallinestructure with a preferred orientation along (111). The density of the HfO2 layer is found to be 9.1 and 9.2 g/cm3,whereas the root mean square roughness is 1.3 and 2.4 nm in the films grown at 300 and 500 ◦C, respectively.Both films have an average grain size of ~ 140 nm. These HfO2 films demonstrate forming free volatile resistiveswitching behavior with SET voltage of − 3.1 and − 3.6 V, along with the ON/OFF ratio of ~ 2 and ~ 4 for thefilms deposited at substrate temperatures of 300 and 500 ◦C, respectively. For the films grown at 300 ◦C and500 ◦C, the retention time is found to be 20 and 30 s, respectively. Memory device based on HfO2 film withhigher substrate temperature exhibits a better ON/OFF ratio due to higher crystallinity and the availability ofmore oxygen vacancies. A comprehensive mechanism of resistive switching is also discussed in this article,considering the transport of oxygen vacancies and the electromigration of Ag ions
From cathode to anode: Understanding lithium loss in 21700-type Ni-rich NCM||Graphite-SiO cells
No full textMoving to larger cell formats in lithium-ion batteries increases overall useable energy but introduces inhomogeneities that influence aging. This study investigates degradation in 21700-type cells with NCM cathodes and graphite/SiOx anodes under cyclic aging, using in operando neutron diffraction, neutron depth profiling, and X-ray computed tomography. Prolonged cycling causes lithium loss, observed on the cathode side as reduced NCM unit cell change during cycling. On the anode side, this loss appears as diminished formation of the fully lithiated LiC6 phase. Differential voltage analysis during aging reveals not only lithium inventory loss but also active anode material loss. Diffraction data confirm this through shifts in the LiC12 transition and LiC6 onset to lower capacities, requiring less lithium to trigger the transitions. Lithium concentration profiles across electrode positions show depletion in the cathode, while elevated concentrations in the anode indicate increased solid-electrolyte interphase formation, suggesting lithium consumed from the cathode deposits on the anode side. CT measurements show that intrinsic inhomogeneities inside the cells have a stronger influence on the macroscopic structure than aging-induced changes, indicating that the observed capacity fade primarily originates from microscopic degradation processes within the electrodes. Overall, the combined techniques provide direct evidence of lithium loss, active material degradation, and spatially dependent aging mechanisms in large-format cylindrical cells
Structural basis of hydride and proton transfer reactions revealed by the detection of hydrogen atoms in mammalian NADH-cytochrome b5 reductase
No full textMany structural studies have been reported for ferredoxin:NADP + reductase family members, but an experimental validation of the catalytic hydride and proton transfer steps through a direct detection of the involved hydrogen atoms has not been achieved so far. Here, we determined high-resolution X-ray and neutron crystal structures of NADH-cytochrome b5 reductase, which acts as an electron supplier for various metabolic processes and mediates hydride and proton transfer reactions via its FAD and NADH cofactors. The X-ray structures identify the FADH − -NAD + and FAD-NADH complexes based on the electron densities of the hydrogen atoms bound to the cofactors. The neutron structures determined at different pD-values show a difference in the protonation state of the histidine residue in the hydrogen-bond network from FAD to the protein surface. The observation of the hydrogen atoms reveals the structural basis for the hydride and proton transfer reactions catalyzed by NADH-cytochrome b5 reductase
Curcumin distribution influences the properties of oil-water interfaces formed by kafirin nanoparticles
No full textIndividual and simultaneous encapsulation and delivery of incompatible dyes in biocompatible multicompartment terpolymer micelles
No full textDual-scale selection of martensite variants in shape memory intermetallic compounds during thermomechanical loading
No full textGenerating a pre-strain by mechanical loading during martensitic transformation stands as a crucial strategy to obtain memory effect in shape memory alloys (SMAs). As martensitic transformation is realized by an anisotropic lattice deformation, the formation of martensite variants is always governed by strain accommodation. In a stress-free state, the orientation variants are organized hierarchically into colonies with a fixed number of variants. Under an external load, the transformation becomes selective. Although variant selection has long been a subject of interest, knowledge on selection via the activation of the transformation shear system under a load and by local strain mitigation is limited. Here, by a combined in-situ neutron diffraction and exhaustive EBSD crystallographic examination, the variant selection under a compressive load during martensitic transformation was thoroughly investigated using Ni51Mn34In15 as an example alloy. Remarkably, a dual-scale selection mechanism, i.e., colony and intra-colony variants, was revealed, which is in stark contrast to the stress-free scenario. For colonies, those containing variants receiving the highest resolved shear stress on their dominant transformation shear system were selected. Within the colonies, the selection is on variant volume fraction. Those making the maximum contribution to the external compression strain were majorly selected. Nevertheless, due to local incompatible strains created by the favorable variants, the variants with deformation opposite to the external compression were also selected to mitigate local incompatible strain and promote further formation of the favorable variants. This study provides useful experimental evidence and analysis data for related crystal plasticity modeling and simulation
Thermochronological constraints for reconstructing the tectonic history of the northern Central Cordillera (Serranía de San Lucas), Colombia
No full textThe Northern Andes are characterized by episodes of exhumation at around 80, 60–50, 40, 25 and 15–0 Ma in the Central and Eastern Cordilleras, Santander Massif, Sierra Nevada de Santa Marta and Merída Andes. Here we present a preliminary set of low-temperature thermochronological data from the Serranía de San Lucas in the northern Central Cordillera, which demonstrate that the timing of exhumation of this region is different from that of the surrounding massifs such as the Antioquia batholith, the Santander Massif or the Sierra Nevada de Santa Marta. The thermochronological data show that the volcanic rocks of the Early Jurassic Noreán Formation exposed in the Serranía de San Lucas to the west of the Middle Magdalena River basin and the northern Santander Massif were buried beneath 6–7 km of Upper Jurassic to Upper Cretaceous/Paleocene sedimentary rocks, then slow erosional exhumation resumed at about 80–60 Ma as reflected by slow cooling rates of 2–4°C/myr. No evidence is found for exhumation at 25 Ma as it has been previously detected in the Antioquia batholith or the Santander Massif. The Serranía de San Lucas tectonic evolution is seen in connection with Mid-Late Jurassic to Early Cretaceous extension and Late Cretaceous compression and accretion of oceanic blocks to the western margin of the South American plate, and flat slab subduction of the Caribbean plate during the Eocene–Oligocene