Theoretical analysis and Lorentz transmission electron microscopy (LTEM) investigations in an FeGe wedge demonstrate that chiral twists arising near the surfaces of noncentrosymmetric ferromagnets ...Meynell et al., Phys. Rev. B 90, 014406 (2014) provide a stabilization mechanism for magnetic Skyrmion lattices and helicoids in cubic helimagnet nanolayers. The magnetic phase diagram obtained for freestanding cubic helimagnet nanolayers shows that magnetization processes differ fundamentally from those in bulk cubic helimagnets and are characterized by the first-order transitions between modulated phases. LTEM investigations exhibit a series of hysteretic transformation processes among the modulated phases, which results in the formation of the multidomain patterns.
Using Lorenz microscopy and small-angle electron diffraction, we directly present that the chiral magnetic soliton lattice (CSL) continuously evolves from a chiral helimagnetic structure in small ...magnetic fields in Cr(1/3)NbS2. An incommensurate CSL undergoes a phase transition to a commensurate ferromagnetic state at the critical field strength. The period of a CSL, which exerts an effective potential for itinerant spins, is tuned by simply changing the field strength. Chiral magnetic orders observed do not exhibit any structural dislocation, indicating their high stability and robustness in Cr(1/3)NbS2.
We propose a new mechanism for the formation of Tb-rich shell in the Nd–Fe–B sintered magnet that was subjected to the grain boundary diffusion (GBD) process using TbH2. Tb-enriched liquid films form ...along grain boundaries during the GBD process, which migrate by chemically induced liquid film migration (CILFM) to form Tb-rich shells behind. As a result, the Tb-rich shell form asymmetrically along a grain boundary with an abrupt concentration change at a core/shell interface with a gradual decrease of Tb concentration toward a grain boundary. These microstructure features can be reproduced with phase-field simulations.
SEM back scattered electron image of grain boundary diffusion procesd Nd-Fe-B sintered magnets and phase field simulation result of solute concentration formed by chemically induced liquid film migration. Display omitted
The spin transfer torque is essential for electrical magnetization switching. When a magnetic domain wall is driven by an electric current through an adiabatic spin torque, the theory predicts a ...threshold current even for a perfect wire without any extrinsic pinning. The experimental confirmation of this 'intrinsic pinning', however, has long been missing. Here, we give evidence that this intrinsic pinning determines the threshold, and thus that the adiabatic spin torque dominates the domain wall motion in a perpendicularly magnetized Co/Ni nanowire. The intrinsic nature manifests itself both in the field-independent threshold current and in the presence of its minimum on tuning the wire width. The demonstrated domain wall motion purely due to the adiabatic spin torque will serve to achieve robust operation and low energy consumption in spintronic devices.
Context.
The Hayabusa2 spacecraft launched by Japan Aerospace Exploration Agency has been conducting observations of the asteroid (162173) Ryugu since June 2018. The Telescopic Optical Navigation ...Camera (ONC-T) onboard Hayabusa2 has obtained thousands of images under a variety of illumination and viewing conditions.
Aims.
Our objective is to examine and validate the camera calibration, derive a photometric correction for creating global albedo maps, and to interpret the photometric modeling results to characterize the surface of Ryugu.
Methods.
We observed (162173) Ryugu with the Gemini-South telescope, and combined these measurements with other published ground-based observations of the asteroid. The ground-based observations were compared with the data obtained by ONC-T in order to validate the radiometric calibration mutually. We used a combination of the Hapke disk-integrated and disk-resolved model equations to simultaneously analyze the combined ground- and spacecraft-based data.
Results.
The average spectrum of Ryugu was classified as Cb-type following the SMASSII taxonomy and C/F-type following the Tholen taxonomy based on spacecraft observations. We derived Hapke model parameters for all seven color filters, which allowed us to photometrically correct images to within an error of <10% for ~80% of the image pixels used in the modeling effort. Using this model, we derived a geometric albedo of 4.0 ± 0.5% (
v
band) for Ryugu. The average reflectance factor at the standard illumination condition was 1.87 ± 0.14% in the
v
band. Moreover we measured a phase reddening of (2.0 ± 0.7) × 10
−3
μ
m
−1
deg
−1
for Ryugu, similar to that observed for the asteroid (101955) Bennu.
Conclusions.
The global color map showed that the general trend was for darker regions to also be redder regions, however there were some distinct exceptions to this trend. For example, Otohime Saxum was bright and red while Kibidango crater was dark and blue. The darkness and flatness of Ryugu’s reflectance might be caused by a high abundance of organic materials.
Iwo‐yama volcano, part of the Kirishima Volcanic Complex, has recently shown signs of unrest. We conducted a hypocenter relocation of shallow earthquakes and broadband magnetotelluric measurements ...around Iwo‐yama. Three‐dimensional inversion of magnetotelluric data revealed an electrically conductive layer that is interpreted as a hydrothermally altered clay‐dominated unit. Shallow earthquakes occur beneath this layer, suggesting that it controls the location of seismicity. The base of the layer corresponds to the depth of a pressure source identified by a leveling survey. These observations suggest that the supply of high‐temperature fluids has increased over time beneath Iwo‐yama, causing an increase in pore pressure beneath the clay‐rich layer and resulting in tectonic earthquakes and ground inflation. Increased upwelling of fluids through a fracture in the clay‐rich layer may have caused a vigorous liquid‐gas phase transition near the surface, which in turn might have led to the small phreatic eruption on 19 April 2018.
Plain Language Summary
Phreatic eruptions result from the sudden release of pressurized fluid into the air. Imaging the pressurized region is important to predict future phreatic eruptions. We studied Iwo‐yama volcano, Kirishima, Japan, where recent volcanic unrest has led to a small phreatic eruption. By imaging the subsurface electrical resistivity structure using the magnetotelluric technique, we have identified a low‐permeability clay‐rich layer at depths of 200–700 m below the surface. Earthquake hypocenters and one of the sources of surface uplift are located beneath this clay layer, so we conclude that the layer caps deep hydrothermal fluids and allows the buildup of pressure beneath it. If this clay‐rich layer suddenly breaks, or if the fluid supply through the deeper conductor suddenly increases, a larger phreatic eruption could occur in the future. Imaging and monitoring of such clay‐rich layers is important to our understanding of shallow activity beneath volcanoes.
Key Points
We conducted earthquake hypocenter relocations and broadband magnetotelluric measurements
Two electrical conductors are, respectively, interpreted to be an altered clay layer and a fluid pathway
The altered layer acts as a cap structure that controlled shallow seismicity, surface deformation, and a small phreatic eruption at Iwo‐yama
Generation and transmission of voltage signals in a kinetic inductance detector made of a superconducting nanowire stripline is investigated on the basis of superconducting electromagnetism. We show ...that electric signals traveling along the stripline in this detector can be regarded as a Swihart mode. An equation which can describe the generation and transmission of voltage pulses in this detector is derived. A pair of voltage pulses with opposite polarities are created when a spatiotemporal variation in the density of the superconducting condensate occurs in a small region of this superconducting nanowire. The voltage pulses propagate along the stripline in the directions opposite to each other with the Swihart velocity. The characteristic of the radiation detector named current-biased kinetic inductance detector (CB-KID) is well described by our model.
The results of an international review of separation processes for spent nuclear fuel (SNF) recycling in future closed fuel cycles are reported. This study was made by the Expert Group on Fuel ...Recycling Chemistry (EGFRC) organised by the Nuclear Energy Agency (NEA) of the Organisation for Economic Co-operation and Development (OECD). A unique feature of this study was that processes were classified according to a hierarchy of separations aimed at different elements within spent fuel (uranium; uranium-plutonium co-recovery; minor actinides; high heat generating radionuclides) and also the Head-end processes, used to prepare the SNF for chemical separation, were included. Separation processes covered both wet (hydrometallurgical) and dry (pyro-chemical) processes.
A bespoke methodology suitable for assessing the technological maturities of separation processes for SNF recycling was then designed based on the well-established Technology Readiness Level (TRL) scale but adapted for spent nuclear fuel separations. The innovative feature of this was the use of a matrix approach that enabled information on both the scale of testing and materials used in testing to be combined in the evaluation of the TRL. TRLs for the Head-end, hydrometallurgical and pyrochemical processes that had been reviewed by the study have been evaluated. It is clear that, whilst more R&D is needed in most cases to raise TRLs, suitable options exist to enable the recovery of all actinide elements plus the HHRs by wet or dry processes, even up to the extraordinarily difficult isolation of americium alone. The technology readiness levels (TRL) for most processes fall in the ‘proof of principle’ range with TRLs between 4 and 6, although this is an evaluation at the system level and some gaps in the individual process steps may still exist that strictly would reduce the overall TRL. That is, flowsheets have been proposed for processes and tested with active materials under increasingly relevant conditions, through to initial hot tests with small quantities of SNF. The results of this work were shown to be comparable to a parallel European study that evaluated TRLs for minor actinide partitioning processes.
Display omitted
•Results of an international study.•Advanced reprocessing and minor actinide partitioning technologies.•Review of progress in R&D on separation processes for advanced nuclear fuel cycles.•Technology Readiness Level assessment of separation processes.•Status of head-end, aqueous and pyro-chemical processes reviewed.
A method of fabricating multilayer focusing mirrors that can focus X-rays down to 10 nm or less was established in this study. The wavefront aberration induced by multilayer Kirkpatrick-Baez mirror ...optics was measured using a single grating interferometer at a photon energy of 9.1 keV at SPring-8 Angstrom Compact Free Electron Laser (SACLA), and the mirror shape was then directly corrected by employing a differential deposition method. The accuracies of these processes were carefully investigated, considering the accuracy required for diffraction-limited focusing. The wavefront produced by the corrected multilayer focusing mirrors was characterized again in the same manner, revealing that the root mean square of the wavefront aberration was improved from 2.7 (3.3) rad to 0.52 (0.82) rad in the vertical (horizontal) direction. A wave-optical simulator indicated that these wavefront-corrected multilayer focusing mirrors are capable of achieving sub-10-nm X-ray focusing.
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