59 research outputs found
Experimental procedures for precision measurements of the Casimir force with an Atomic Force Microscope
Experimental methods and procedures required for precision measurements of
the Casimir force are presented. In particular, the best practices for
obtaining stable cantilevers, calibration of the cantilever, correction of
thermal and mechanical drift, measuring the contact separation, sphere radius
and the roughness are discussed.Comment: 14 pages, 7 figure
Chiral symmetry breaking for deterministic switching of perpendicular magnetization by spin-orbit torque
Symmetry breaking is a characteristic to determine which branch of a
bifurcation system follows upon crossing a critical point. Specifically, in
spin-orbit torque (SOT) devices, a fundamental question arises: how to break
the symmetry of the perpendicular magnetic moment by the in-plane spin
polarization? Here, we show that the chiral symmetry breaking by the DMI can
induce the deterministic SOT switching of the perpendicular magnetization. By
introducing a gradient of saturation magnetization or magnetic anisotropy,
non-collinear spin textures are formed by the gradient of effective SOT
strength, and thus the chiral symmetry of the SOT-induced spin textures is
broken by the DMI, resulting in the deterministic magnetization switching. We
introduce a strategy to induce an out-of-plane (z) gradient of magnetic
properties, as a practical solution for the wafer-scale manufacture of SOT
devices.Comment: 16 pages, 4 figure
Distinguishing two-component anomalous Hall effect from topological Hall effect in magnetic topological insulator MnBi2Te4
In transport, the topological Hall effect (THE) is widely interpreted as a
sign of chiral spin textures, like magnetic skyrmions. However, the
co-existence of two anomalous Hall effects (AHE) could give rise to similar
non-monotonic features or "humps", making it difficult to distinguish between
the two. Here we demonstrate that the "artifact" two-component anomalous Hall
effect can be clearly distinguished from the genuine topological Hall effect by
three methods: 1. Minor loops 2. Temperature dependence 3. Gate dependence. One
of the minor loops is a single loop that cannot fit into the full AHE loop
under the assumption of AHE+THE. In addition, by increasing the temperature or
tuning the gate bias, the emergence of humps is accompanied by a polarity
change of the AHE. Using these three methods, one can find the humps are from
another AHE loop with a different polarity. Our material is a magnetic
topological insulator MnBi2Te4 grown by molecular beam epitaxy, where the
presence of the secondary phase MnTe2 on the surface contributes to the extra
positive AHE component. Our work may help future researchers to exercise
cautions and use these three methods to examine carefully in order to ascertain
genuine topological Hall effect
Giant Hall Switching by Surface-State-Mediated Spin-Orbit Torque in a Hard Ferromagnetic Topological Insulator
Topological insulators (TI) can apply highly efficient spin-orbit torque
(SOT) and manipulate the magnetization with their unique topological surface
states, and their magnetic counterparts, magnetic topological insulators (MTI)
offer magnetization without shunting and are one of the highest in SOT
efficiency. Here, we demonstrate efficient SOT switching of a hard MTI, V-doped
(Bi,Sb)2Te3 (VBST) with a large coercive field that can prevent the influence
of an external magnetic field and a small magnetization to minimize stray
field. A giant switched anomalous Hall resistance of 9.2 is realized,
among the largest of all SOT systems. The SOT switching current density can be
reduced to , and the switching ratio can be enhanced to
60%. Moreover, as the Fermi level is moved away from the Dirac point by both
gate and composition tuning, VBST exhibits a transition from
edge-state-mediated to surface-state-mediated transport, thus enhancing the SOT
effective field to and the spin Hall angle to
at 5 K. The findings establish VBST as an extraordinary candidate
for energy-efficient magnetic memory devices
Axonal Fiber Terminations Concentrate on Gyri
Convoluted cortical folding and neuronal wiring are 2 prominent attributes of the mammalian brain. However, the macroscale intrinsic relationship between these 2 general cross-species attributes, as well as the underlying principles that sculpt the architecture of the cerebral cortex, remains unclear. Here, we show that the axonal fibers connected to gyri are significantly denser than those connected to sulci. In human, chimpanzee, and macaque brains, a dominant fraction of axonal fibers were found to be connected to the gyri. This finding has been replicated in a range of mammalian brains via diffusion tensor imaging and high–angular resolution diffusion imaging. These results may have shed some lights on fundamental mechanisms for development and organization of the cerebral cortex, suggesting that axonal pushing is a mechanism of cortical folding
Electric-Field Control of Spin Diffusion Length and Electric-Assisted D’yakonov–Perel’ Mechanism in Ultrathin Heavy Metal and Ferromagnetic Insulator Heterostructure
Electric-field control of spin dynamics is significant for spintronic device applications. Thus far, effectively electric-field control of magnetic order, magnetic damping factor and spin-orbit torque (SOT) has been studied in magnetic materials, but the electric field control of spin relaxation still remains unexplored. Here, we use ionic liquid gating to control spin-related property in the ultra-thin (4 nm) heavy metal (HM) platinum (Pt) and ferromagnetic insulator (FMI) yttrium iron garnet (Y3Fe5O12, YIG) heterostructure. It is found that the anomalous Hall effect (AHE), spin relaxation time and spin diffusion length can be effectively controlled by the electric field. The anomalous Hall resistance is almost twice as large as at 0 voltage after applying a small voltage of 5.5 V. The spin relaxation time can vary by more than 50 percent with the electric field, from 41.6 to 64.5 fs. In addition, spin relaxation time at different gate voltage follows the reciprocal law of the electron momentum scattering time, which indicates that the D'yakonov-Perel' mechanism is dominant in the Pt/YIG system. Furthermore, the spin diffusion length can be effectively controlled by an ionic gate, which can be well explained by voltage-modulated interfacial spin scattering. These results help us to improve the interface spin transport properties in magnetic materials, with great contributions to the exploration of new physical mechanisms and spintronics device
pH-Dependent Aggregation and Disaggregation of Native β‑Lactoglobulin in Low Salt
The
aggregation of β-lactoglobulin (BLG) near its isoelectric
point was studied as a function of ionic strength and pH. We compared
the behavior of native BLG with those of its two isoforms, BLG-A and
BLG-B, and with that of a protein with a very similar pI, bovine serum
albumin (BSA). Rates of aggregation were obtained through a highly
precise and convenient pH/turbidimetric titration that measures transmittance
to ±0.05 %T. A comparison of BLG and BSA suggests that the difference
between pH<sub>max</sub> (the pH of the maximum aggregation rate)
and pI is systematically related to the nature of protein charge asymmetry,
as further supported by the effect of localized charge density on
the dramatically different aggregation rates of the two BLG isoforms.
Kinetic measurements including very short time periods show well-differentiated
first and second steps. BLG was analyzed by light scattering under
conditions corresponding to maxima in the first and second steps.
Dynamic light scattering (DLS) was used to monitor the kinetics, and
static light scattering (SLS) was used to evaluate the aggregate structure
fractal dimensions at different quench points. The rate of the first
step is relatively symmetrical around pH<sub>max</sub> and is attributed
to the local charges within the negative domain of the free protein.
In contrast, the remarkably linear pH dependence of the second step
is related to the uniform reduction in global protein charge with
increasing pH below pI, accompanied by an attractive force due to
surface charge fluctuations
Alveolar Type II Epithelial Cell Dysfunction in Rat Experimental Hepatopulmonary Syndrome (HPS)
<div><p>The hepatopulmonary syndrome (HPS) develops when pulmonary vasodilatation leads to abnormal gas exchange. However, in human HPS, restrictive ventilatory defects are also observed supporting that the alveolar epithelial compartment may also be affected. Alveolar type II epithelial cells (AT2) play a critical role in maintaining the alveolar compartment by producing four surfactant proteins (SPs, SP-A, SP-B, SP-C and SP-D) which also facilitate alveolar repair following injury. However, no studies have evaluated the alveolar epithelial compartment in experimental HPS. In this study, we evaluated the alveolar epithelial compartment and particularly AT2 cells in experimental HPS induced by common bile duct ligation (CBDL). We found a significant reduction in pulmonary SP production associated with increased apoptosis in AT2 cells after CBDL relative to controls. Lung morphology showed decreased mean alveolar chord length and lung volumes in CBDL animals that were not seen in control models supporting a selective reduction of alveolar airspace. Furthermore, we found that administration of TNF-α, the bile acid, chenodeoxycholic acid, and FXR nuclear receptor activation (GW4064) induced apoptosis and impaired SP-B and SP-C production in alveolar epithelial cells <i>in vitro</i>. These results imply that AT2 cell dysfunction occurs in experimental HPS and is associated with alterations in the alveolar epithelial compartment. Our findings support a novel contributing mechanism in experimental HPS that may be relevant to humans and a potential therapeutic target.</p></div
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