Omnidirectional Control of Large Electrical Output in a Topological Antiferromagnet

Control of magnetization direction is essential for the wide application of ferromagnets; it defines the signal size of memory and sensor. However, the magnetization itself causes a dilemma. While its size matters to obtain strong responses upon its reversal, the large magnetization concomitantly suppresses the range of its directional control because of the demagnetizing field. On the other hand, realization of the desired magnetic anisotropy requires careful engineering of crystalline and interfacial effects to overcome the demagnetization barrier. Thus, it would be ideal if one could find alternative magnets that carry no magnetization but strong responses. The discovery of a topological metallic state in the antiferromagnet Mn₃Sn is significant; they host a large Berry curvature in momentum space, enabling the observation of disproportionately large transverse responses such as anomalous Hall and Nernst effects, the key functionalities for replacing ferromagnets in the magnetic devices. Here, the experimental realization of omnidirectional control of the large responses in an antiferromagnet is reported. In particular, it is demonstrated that the absence of shape anisotropy enables the omnidirectional control, and lifts the shape constraint in designing the magnetic devices. This work lays the technological foundation for developing simple-structured high-performance devices including multi-level memory and heat flux sensor.     

The in vitro and in vivo indomethacin release from self-setting bioactive glass bone cement

The in vivo and in vitro drug release profiles from a self-setting bioactive CaO-SiO2-P2O5 glass bone cement containing indomethacin as a model drug were investigated. The cement containing 2% and 5% indomethacin (IMC) powder hardened within 5 min after mixing with ammonium phosphate buffer. After setting, in vitro drug release from drug-loaded cement pellets in a simulated body fluid (SBF) at pH 7.25 and 37 degrees C continued for two weeks. The hardened cement gradually formed low-crystallinity hydroxyapatite during the drug release test in SBF. An IMC-loaded cement device (2% and 5% drug) was implanted in the subcutaneous tissue on the back of rats. The in vivo IMC release from the cement increased and attained maximum levels (Cmax of 2% and 5% drug-loaded cements was 0.27 and 3.37 micrograms/ml, respectively) at Tmax, 3 and 0.5 d, respectively, upon subcutaneous (s.c.) administration in rats. This suggested that the s.c. administration of the cement provided IMC release for a much longer period than s.c. administration of the solution, and the plasma IMC concentration was dependent on the drug concentration in the cement. The plasma IMC concentration and the area under the curve from 2% and 5% IMC-loaded cements in rats were dependent on the concentration of IMC in the cements. The in vivo IMC concentration in plasma obtained by the deconvolution method was much lower than that delivered in SBF in vitro. Scanning electron microscopy and photomicrographs of cross sections showed that the bioactive bone cement had excellent biocompatibility with the surrounding soft tissues.     

Spherical tokamak generation and merging on UTST using ex‐vessel poloidal field coils only

We successfully generated two spherical tokamaks (ST) at two null points by using ex‐vessel poloidal field (PF) coils only and succeeded in merging them. This scheme is called a double null merging (DNM) scheme. First, two pairs of ex‐vessel PF coils generate two null points where the poloidal field is zero at the upper and lower regions inside the vacuum vessel. Then a poloidal flux swing generates two STs at two null points, because the distance to the wall along the magnetic field is long at the null points. Finally, the coil currents push two STs toward the mid‐plane and merge them into a single ST. Since a magnetic reconnection during merging transforms magnetic energy into thermal energy, this merged ST plasma is expected to have a high beta. It must be noted that the DNM scheme generates an ST without a center solenoid coil. The DNM scheme was demonstrated on the TS‐3/4 (Japan) and MAST (UKAEA). However, these devices have all PF coils inside the vacuum vessels, and the initial plasmas were generated around the PF coils, not the null points. Since internal coils are not feasible in a fusion reactor due to high neutron flux, it is important to demonstrate the DNM scheme by using ex‐vessel PF coils. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 179(4): 18–24, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21254     

Examination of vibration control of linear oscillatory actuator

Linear oscillatory actuators (LOAs) are widely used in linear motor shavers, electric toothbrushes, and mobile phone vibrators as high‐speed oscillatory driving devices. The maximum amplitude of the motor is obtained at a resonant frequency that is determined from the spring constant and the mass of the motor. However, there is a problem with these actuators: the amplitude decreases sharply when the driving frequency differs from the resonant frequency in a mechanical vibration system with minimal damping. In this paper, we propose a control method for the resonant frequency in which the thrust, which shows the characteristics of a spring, is generated on the basis of the displacement of the mover and the damping factor, in which the thrust, which shows the characteristics of damping, is generated based on the velocity of the mover. The proposed method assures that the resonant frequency always corresponds to the driving frequency and that rapid changes in the amplitude are avoided. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(4): 55–62, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21172     

Nucleation and Avalanche of 4He Crystals in Aerogel

Dynamical transition of ⁴He crystals in aerogel was reported recently (Nomura et al. Phys. Rev. Lett. 101:175703, 2008). Bare aerogel, which was placed in the bulk ⁴He crystals, was used in the report. ⁴He crystals inside the aerogel grew via creep at high temperatures and via avalanche at low temperatures owing to the competition between thermal fluctuation and quenched disorder. Crystal-liquid interface advanced from the edge to inside of the aerogel. Crystal has a greater density than liquid so that the extra mass has to be transported in the crystallization process. It is not known how the mass is transported in the aerogel. To find a clue to this issue, we did an experiment with aerogel in a glass tube so that the aerogel had contact with the bulk on only one surface. In this case, a similar dynamical transition was observed at low temperatures. In the avalanche region, however, ⁴He crystals did not grow from the outer surface of the aerogel but nucleated at various sites inside the aerogel. This means that crystallization in aerogel does not occur by the forced invasion of ⁴He crystal but by a process of the bulk crystal once being melted and transported to increase the pressure of the liquid in the aerogel. Thus, a mass transport mechanisms for the crystallization has been revealed by this observation.     

Sugar response of boronic acid-substituted azobenzene dye-modified polymer

We synthesized a boronic acid-appended azobenzene dye (BA) and attached it to poly(ethyleneimine) (polyBA) for studying its sugar response. The addition of d-glucose induced a significant change in the UV–visible absorption spectra of the polyBA solution. The binding constants for d-glucose (K_glu) and d-fructose (K_fru) were calculated to be 54 M^? 1 and 110 M^? 1, respectively. The selectivity for d-glucose was higher in polyBA as compared with that of monomeric BA (K_glu = 1.2 M^? 1, K_fru = 17 M^? 1). We also fabricated multilayered films composed of polyBA and polyanions {poly(vinyl sulfate) (PVS), carboxymethylcellulose (CMC)} using a layer-by-layer deposition technique. In (PVS/polyBA)₁₀ films, the affinity for d-glucose was relatively low (K_glu = 1.7 M^? 1, K_fru = 28 M^? 1). In contrast, (CMC/polyBA)₅ films showed a high affinity for d-glucose (K_glu = 18 M^? 1, K_fru = 42 M^? 1). The loosely packed structure of the (CMC/polyBA)₅ film and the suitable chemical structures of CMC probably led to a high affinity for d-glucose.