Magnetic motion control has been actively studied mainly for the purpose of biomedical applications. However, in many cases, many actuator magnets surround a small magnet to be moved, and they ...consume large electric power. In some cases, complex calculations are required to estimate the control input of the actuator magnets. This study proposes a simple method to move a small magnet to the desired positions. For this, three cylindrical permanent magnets magnetized in the radial direction were positioned as the sides of a triangle; these actuator magnets were rotated using motors. By monitoring the position of the small magnet and through simple feedback control based on the angles of the three actuator magnets, the untethered small magnet could be moved along arbitrary three-dimensional (3D) paths. The control principle was established by calculating the magnetic force and torque acting on the small magnet for some sets of actuator-magnet angles.
The understanding of the swelling phenomenon of montmorillonite is essential to predict the physical and chemical behavior of clay-based barriers in geoenvironmental engineering. This study ...investigated the crystalline swelling behavior of montmorillonite with different interlayer cations including monovalent Na, K, and Cs and divalent Ca and Sr by molecular dynamics simulations and experimental measurements including X-ray diffraction and water vapor adsorption. The stepwise swelling behavior for Na- and Ca/Sr-montmorillonite demonstrated good agreement between molecular dynamics (MD) simulated and experimental results. The swelling curves of K- and Cs-montmorillonite remaining in the 1-hydrated state even at high relative humidity showed systematic discrepancies between MD simulations and experimental results. The comparative discussion between the experimental and MD derived swelling curves offer insights that may help to understand the swelling mechanism of montmorillonite and the dependence on interlayer cations. The water content in the interlayer and external surface in five homoionic montmorillonite was strongly correlated to the hydration number of each ion. On the basis of these comparisons, the hydration free energy of interlayer cations seems to contribute greatly to the total driving force for the crystalline swelling of montmorillonite. An additional key factor is the preference of an outer- or inner-sphere complex of interlayer cations and the distribution of cations in the interlayer space. This effect has a considerable impact in the case of monovalent cations and results in different swelling behavior between the outer-sphere Na and inner-sphere K and Cs ions.
•Effects of interlayer cations on swelling behaviors of montmorillonite were investigated.•Molecular dynamics simulations and experimental results are systematically compared.•Differences in measured stepwise swelling behaviors were interpreted by MD simulations.•Main factor affecting crystalline swelling behavior is the hydration free energy of interlayer cations.•Preference of outer- or inner-sphere complex of interlayer cations is an additional key factor.
•The rotation pattern for a mangle-type magnetic field source was optimized.•Optimization was performed using the covariance matrix adaptation evolution strategy.•A uniform magnetic field with an ...arbitrary magnitude and direction could be generated.
A mangle-type magnetic field source with four permanent magnets is capable of generating a magnetic field with an arbitrary magnitude and direction. In this study, the rotation pattern of magnets was optimized to maximize the field uniformity by using a covariance matrix adaptation evolution strategy. Starting with random angles of magnets, angles generating the highest magnitude of the magnetic field were calculated with values similar to those of a Halbach cylinder. Although reproducible results were not obtained for a zero magnetic field, a symmetric pattern about the origin after multiple trials of optimization is likely. As the rotation pattern for continuously varying magnitude and direction of the magnetic field could not be found using the covariance matrix adaptation evolution strategy alone, artificial initial guesses were introduced, and the optimization was successful. It was demonstrated that the application of an optimized pattern requires caution with regard to the degradation of the maximum magnetic field and linearity of change in the magnitude and direction of the magnetic field.
The distribution and dynamics of water molecules and monovalent cations (Li⁺, Na⁺, K⁺, Cs⁺, and H₃O⁺) on muscovite surfaces were investigated by molecular dynamics (MD) simulations. The direct ...comparison of calculated X-ray reflectivity profiles and electron density profiles with experiments revealed the precise structure at the aqueous monovalent electrolyte solutions/muscovite interface. To explain the experimentally observed electron density profiles for the CsCl solution–muscovite interface, the co-adsorption of Cs⁺ and Cl⁻ ion pairs would be necessary. Two types of inner-sphere complexes and one type of outer-sphere complex were observed for hydrated Li⁺ ions near the muscovite surface. For Na⁺, K⁺, Cs⁺, and H₃O⁺ ions, the inner-sphere complexes were stable on the muscovite surface. The density oscillation of water molecules was observed to approximately 1.5nm from the muscovite surface. The number of peaks and the locations for the density of water oxygen atoms were almost similar among the water molecules coordinated to Li⁺, Na⁺, K⁺, and H₃O⁺ ions adsorbed on the muscovite surfaces. The water molecules around Cs⁺ ions that were adsorbed to muscovite surfaces seemed to avoid coordinating with Cs⁺ ions on the surface, and the density of water oxygen near the muscovite surface decreased relative to that in a bulk state. There was no significant difference in self-diffusion, viscosity, retention time, and reorientation time of water molecules among different cations adsorbed to muscovite surfaces. These translational and rotational motions of water molecules located at less than 1nm from the muscovite surfaces were slower than those in a bulk state. A significant difference was observed for the exchange times of water molecules around monovalent cations. The exchange time of water molecules was long around Li⁺ ions and decreased with an increase in the ionic radius.
Salinity, pH, and redox states are fundamental properties that characterize natural waters. These properties of surface waters on early Mars reflect palaeoenvironments, and thus provide clues on the ...palaeoclimate and habitability. Here we constrain these properties of pore water within lacustrine sediments of Gale Crater, Mars, using smectite interlayer compositions. Regardless of formation conditions of smectite, the pore water that last interacted with the sediments was of Na-Cl type with mild salinity (~0.1-0.5 mol/kg) and circumneutral pH. To interpret this, multiple scenarios for post-depositional alterations are considered. The estimated Na-Cl concentrations would reflect hyposaline, early lakes developed in 10
-10
-year-long semiarid climates. Assuming that post-depositional sulfate-rich fluids interacted with the sediments, the redox disequilibria in secondary minerals suggest infiltration of oxidizing fluids into reducing sediments. Assuming no interactions, the redox disequilibria could have been generated by interactions of upwelling groundwater with oxidized sediments in early post-depositional stages.
Water in confining geometries shows various anomalous properties related to its structure and dynamics compared with bulk water. Here, the dielectric constant of water as a function of separation in ...a graphite slab geometry was studied using molecular dynamics simulations. The dielectric constants of water were calculated from the orientational polarization of water molecules when an external electric field was applied parallel and normal to the slabs. The reduction of the dielectric constant of water compared with bulk water can be explained by investigating the structure and dynamics of water in slab geometries. We found a preferred orientation of water molecules in the layer closest to the graphite surface. The self-diffusion coefficient distribution of water molecules along the direction normal to the slabs was also computed. Highly mobile water molecules in the intermediate region were generated by the weak hydrogen bonding produced by the preferred orientation of water molecules in the layer. We concluded that the dielectric constant of water in the slab geometry is lower than that of bulk water because of the reduction of the polarization of water and the highly mobile water molecules in the intermediate region arising from the preferred orientation of water molecules.
The cardinal symptom of acute encephalopathy is impairment of consciousness of acute onset during the course of an infectious disease, with duration and severity meeting defined criteria. Acute ...encephalopathy consists of multiple syndromes such as acute necrotizing encephalopathy, acute encephalopathy with biphasic seizures and late reduced diffusion and clinically mild encephalitis/encephalopathy with reversible splenial lesion. Among these syndromes, there are both similarities and differences. In 2016, the Japanese Society of Child Neurology published ‘Guidelines for the Diagnosis and Treatment of Acute Encephalopathy in Childhood’, which made recommendations and comments on the general aspects of acute encephalopathy in the first half, and on individual syndromes in the latter half. Since the guidelines were written in Japanese, this review article describes extracts from the recommendations and comments in English, in order to introduce the essence of the guidelines to international clinicians and researchers.
To investigate the role of atomic-scale structure on the frictional properties of gibbsite, a dioctahedral-type aluminum hydroxide, we calculated the atomic-scale interlayer shear properties using ...the first-principles method based on density functional theory. We found that the presence of vacant sites within the octahedral sheet of gibbsite enables hydroxyls to move to more stable positions and reduce the repulsive force, leading to a lower atomic-scale shear stress of gibbsite compared with brucite, a trioctahedral-type magnesium hydroxide. We also estimated the macroscopic single-crystal friction coefficient of gibbsite with the assumption that only the atomic-scale interlayer friction controls macroscopic friction. The estimated single-crystal friction coefficient for gibbsite is 0.36(6), which is clearly lower than the experimentally obtained friction coefficient of the powdered gouge of gibbsite (0.74). This difference between the interlayer friction coefficient and gouge friction coefficient suggests the presence of additional mechanisms that affect the frictional strength, such as microstructures within a fault gouge.
There is currently significant interest in adsorbents for selective removal of caffeine from water. Here, we examined caffeine adsorption in a natural montmorillonite (Mnt) smectite clay mineral. A ...simple exchange of the original monovalent sodium interlayer cations with polyvalent aluminum cations increased the caffeine adsorption rate of the smectite by approximately 1.6 times (maximum adsorption from a 1.5 mmol L–1 aqueous solution of caffeine: Na+Mnt, 57.1%; Al3+Mnt, 91.2%). These adsorptions were well fitted by the Langmuir adsorption model indicating, that the adsorptions were limited by equilibrium. Humidity-controlled X-ray diffraction confirmed that caffeine adsorption occurred mainly in the interlayer nanospace. 23Na and 27Al magic-angle spinning-nuclear magnetic resonance (MAS-NMR) analyses revealed an attractive interaction between the interlayer cations and the caffeine molecules. The 27Al MAS-NMR spectrum of Al3+Mnt indicated that most of the interlayer Al3+ was coordinated with six water molecules. From these findings, we developed an interaction model that simulated caffeine adsorption by Al3+Mnt. Molecular dynamics simulation revealed that adsorption occurred via electrostatic interactions between the caffeine molecules and the interlayer cations, not the basal planes of the clay. Optimization of the electrostatic interactions and nanospace available for the adsorption will be crucial for developing highly efficient, selective, clay-mineral-based adsorbents of caffeine molecules.
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