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In-plane to out-of-plane magnetization switching in a single nickel nanorod affixed to an attonewton-sensitivity cantilever was studied at cryogenic temperatures. We observe multiple sharp, simultaneous transitions in cantilever frequency, dissipation, and frequency jitter associated with magnetic switching through distinct intermediate states. These findings suggest a new route for detecting magnetic fields at the nanoscale. [ABSTRACT FROM AUTHOR]

Abstract: The measurement of surface charge on nanofibers was achieved by characterizing zeta potential of the nanofibers via a newly developed device for streaming current measurement. Low flow rates were sufficient to generate detectable streaming currents in the absence of an externally applied voltage without damaging nanofiber samples. Zeta potential was calculated by using the Helmholtz–Smoluchowski equation and the measured streaming currents. Two acrylic plates were machined and assembled to form a microfluidic channel that is 150μm high, 2.0mm wide, and 30mm long. Two electrodes for the measurement of streaming currents were housed in the top plate. Two nanofibers of pure polyacrylonitrile (PAN) fibers and charged (TiO2 incorporated) PAN fibers were prepared and characterized in the device. Monobasic sodium phosphate and dibasic sodium phosphate were used to prepare four different pH buffer solutions ranging from pH 5 to pH 8 in order to characterize the zeta potentials. The pure PAN nanofibers had negatively-charged surfaces regardless of pH. However, the zeta potentials of PAN/TiO2 nanofibers changed from positive to negative at pH 6.5. The zeta potential measurements made on the nanofibers in this new microfluidic device matched with those of the powdered raw materials using a commercial Zetasizer. [Copyright &y& Elsevier]

Abstract: We report an inductive method detecting a magnetostrictive resonance signal, which is applied to an ultrasonic magnetostrictive transducer sample. Slab shaped ferrite samples are mounted in a rf coil and actuated by a pulsed rf magnetic field. A dc magnetic field is also applied and the resonance signal from the sample is detected by the same coil after the rf field is turned off. The detector system is identical to a conventional pulse NMR system with quadrature detection. The detected signal is Fourier transformed and wide band spectrum data are obtained. The resonance spectrum data show strong dependencies on the bias dc field strength and direction as well as the dimension of the sample. [Copyright &y& Elsevier]

This paper reports the effects of a current sweep cycle method on reducing the screening current induced field (SCF) in a (RE)Ba2Cu3Ox (REBCO) coil. The screening current induced field in a REBCO coil causes two major problems: temporal magnetic field drift and a reduction of the central magnetic field. This is a critical problem in relation to REBCO coils, which require a homogeneous and stable magnetic field, during, for instance, nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) applications (Itoh et al., 2013; Hemmi et al., 2005; Hahn et al., 2008; Amemiya et al., 2008; Otsuka et al., 2011; Yang et al., 2013; Ahn et al., 2009; Koyama et al., 2009; Kajikawa et al., 2015). In an effort to circumvent the SCF problem, the current sweep cycle method is investigated based on experiments in this study. The experimental results show that a greater SCF reduction in a REBCO coil can be obtained by increasing the overshooting of the current sweep cycle. [ABSTRACT FROM AUTHOR]

This paper reports the feasibility of the impregnation of no-insulation (NI) high-temperature superconducting (HTS) coils using an electrically conductive epoxy resin. Recently, several studies of HTS coils without turn-to-turn insulation have been reported for field coils used in rotating machines such as motors and generators. The NI winding technique enhances the thermal stability of the HTS coil without requiring complicated protection techniques because the quench current is automatically bypassed through the turn-to-turn contacts within the HTS coil. Nevertheless, there is still a question as to whether the NI technique can be applied to rotating machines. To utilize an HTS coil under high mechanical loads such as field coils for rotating machines, the HTS tapes must be stabilized mechanically. For HTS field coils intended for use in rotating machines, epoxy impregnation is generally necessary to protect the HTS field coil from mechanical disturbances caused by the magnetic field and rotational vibration of the rotor to enhance the mechanical stability [1], [2] . However, the NI HTS coil cannot be fabricated by wet winding using epoxy resin because epoxy resins such as Stycast 2850 FT and CTD 521 are electrically insulating materials. This study examines the electrical stability of an NI HTS coil impregnated with an epoxy resin containing electrically conductive particles. The results are likely to present useful data for the application of electrically conductive epoxy impregnated NI HTS coils to rotating machines. [ABSTRACT FROM PUBLISHER]

A 3-T 100-mm winding bore conduction-cooled REBCO magnet has been designed, constructed, and tested. It consists of a stack of double pancake coils wound with metallic cladding (MC) REBCO tapes, for which 1–2 \mu \textm stainless steel was clad in a hermetic way around the tapes. This approach, first proposed by the SuNAM Company Ltd. in 2015, is expected to substantially reduce the charging time delay of a no-insulation magnet, which in turn will be effective in the manipulation of screening currents in such a way as to improve the field homogeneity of magnets, particularly for nuclear magnetic resonance or MRI. This paper presents test results for our approach on the current sweep cycling, which is used to reduce the screening current-induced fields in a newly constructed 3-T 100-mm MC all-REBCO magnet [ABSTRACT FROM PUBLISHER]

Because low-temperature superconducting (LTS) magnets can conduct large electric current and generate intense magnetic fields under cryogenic conditions, such magnets are used in many applications such as MRI, nuclear magnetic resonance spectrometers, and mass spectrometers. However, an abnormal termination called “quench” disturbs the normal operation and increases the magnet temperature. To protect the LTS magnet from excessive heat, the maximum temperature of a magnet under the quench process should be calculated. The design of a superconducting magnet protection system is performed according to the calculated maximum temperature. This is why accurate estimation of magnet temperature is important. The quench process of a superconducting magnet involves complex physical mechanisms, which requires a thermal–electrical simulation using computational analysis. We propose a highly efficient and reliable three-dimensional quench calculation method that can calculate the magnet temperature in the quench process. The LTS magnet is divided into many unit nodes; multiphysics analysis at each node is carried out with respect to the elapsed time. To verify the feasibility of the simulation, LTS magnet quench experimental results were compared with the simulation results. This study has the potential to develop a computational method for heat propagation analysis of a superconducting magnet. [ABSTRACT FROM PUBLISHER]

Abstract: The temperature dependences of the resonance frequency, line width, and spin–lattice relaxation time T 1 of the ferroelectric and paraelectric phases of RbH2AsO4 crystals are investigated. The 87Rb NMR line at the phase transition temperature T C (=110K) splits into two lines, which indicates the occurrence of phase transition from tetragonal to orthorhombic phase. In addition, T 1 for the 87Rb nucleus undergoes remarkable changes near T C , which indicates drastic alterations of the spin dynamics at T C . At T C , changes occur in the resonance frequency and T 1, which are related to variations in the symmetry of the environments of the 87Rb ions. [Copyright &y& Elsevier]

We report that the field homogeneity of a large-scale metal-clad no-insulation all-ReBa2Cu3O7−x magnet is reproducible after occasional operating conditions, in this case the current ramp down/up and magnet warm-up/cool-down conditions. First, we shimmed the magnet by cylindrically arraying ferromagnetic shims on the wall of the room-temperature bore of the magnet to improve the spatial field homogeneity. As a result, the field homogeneity of the magnet was improved from 557.7 to 14.1 ppm in a 10 mm diameter spherical volume. The resultant acquisition of field homogeneity tremendously enhanced from an inhomogeneous state greatly degraded by screening currents qualified us to study the temporal stability of the field homogeneity. We used a magnet-energizing protocol with the field drift minimized to shrink a nuclear magnetic resonance (NMR) lineshape into a much narrower super-imposable lineshape. We demonstrate the technique by NMR experiments, showing excellent reproducibility in every case, presenting strong evidence of recovery to certain time-unvarying field gradients and to a state of homogeneity. These findings suggest a new route for high-resolution high-temperature superconducting NMR and magnetic-resonance-imaging magnet technology. [ABSTRACT FROM AUTHOR]

Due to the self-protecting feature, no-insulation (NI) high-temperature superconductor magnets have been regarded as a reliable option to generate high fields, yet their intrinsic charging delay still remains a major drawback. To apply the NI technique for actual high-field user magnets, however, postquench transient behavior of such magnets need to be fully understood, particularly the electromagnetic interaction among magnetically coupled subcoils. Recent publications have shown successful simulations of the transient behavior of a single NI coil or a multicoil magnet using distributed network models. Even though these approaches are very accurate, they often require substantial computation time, especially when multiple iterations are required during design or analysis of an NI magnet having a large number of coils. This paper presents a simple circuit approach that may be effective for quench simulation of multicoil NI magnets. Each NI subcoil in a magnet is lumped into a single inductor with a resistor in series and a resistor in parallel. This approach has allowed us to simulate the whole magnet system within reasonable time without compromising the understanding of mutual interactions of all of the subcoils after quench, namely change in parameters such as voltage, current, and temperature with respect to time and coil to coil normal zone propagation in an electromagnetic manner. We verified the proposed approach by analyzing the quench process in a previously built 7 T, 78 mm all-REBCO NI magnet (by MIT), and by doing the first ever comparison between the simulated results with the data measured from actual experiment. [ABSTRACT FROM PUBLISHER]

A nuclear magnetic resonance (NMR) magnet composed of a high-temperature superconductor (HTS) is expected to contribute to a smaller size and a higher magnetic field (>1 GHz) of the NMR magnet due to its high critical current density under high magnetic field and better mechanical properties. The high operating temperature of HTS NMR magnets also makes conduction cooling by a cryocooler available. The conduction cooling system combined with a cryocooler is compact and user-friendly but has critical issues about the design of conduction cooling passages and the mechanical vibration. The small-scale HTS magnet with the conduction cooling system is fabricated and tested to check the issues and establish the design basis as a preliminary step for the development of a 400-MHz HTS NMR magnet. Thermal analysis for heat loads and thermal resistances at main joints is performed from the temperature distribution of the cooling system. The vibration levels at the crycooler and the vacuum chamber are discussed in comparison to the vibration criterion of NMR magnets. In addition, the design approach to the conduction cooling system for the HTS NMR magnet is discussed. [ABSTRACT FROM PUBLISHER]

In this work, a facile synthetic process is reported for the large-scale synthesis of Fe3O4 nanocrystals. Thermal decomposition of Fe(acac)3 (100 g) in 1-hexadecanol produced Fe3O4 nanocrystals with well-controlled sizes and morphologies. The nanocrystals were spherically shaped with average diameters of 7.8 ± 0.6, 6.5 ± 0.4, and 5.9 ± 0.2 nm when prepared at 300°C, 270°C, and 250°C, respectively. Mechanisms of crystal formation were elucidated on the basis of gas chromatography-mass spectroscopy analysis, enabling the large-scale preparation of Fe3O4 nanocrystals. To provide an environmentally benign route, Fe3O4 nanocrystals were prepared with recycled solvent which was recovered from the initial experiment. The resulting porous Fe3O4 nanocrystals had larger average sizes than those of the initial nanocrystals. Structural characterization was performed using transmission electron microscopy and powder X-ray diffraction. [ABSTRACT FROM AUTHOR]

Highlights: [•] The T–FC was firstly synthesized by wet-chemical processing and ultrasound irradiation. [•] This T–FC exhibited higher visible-light photocatalytic and antibacterial activities. [•] The T–FC can be easily recovered from water using a magnet. [•] Moreover, the T–FC exhibits excellent photocatalytic stability. [ABSTRACT FROM AUTHOR]

Highlights: [•] The u-MFN were synthesized via a ultrasound irradiation and/or calcinations process. [•] The u-MFN exhibited excellent adsorption capacities. [•] The u-MFN also displayed excellent adsorption of organic polluent after recycling. [•] The u-MFN has the potential to be used as an efficient adsorbent material. [Copyright &y& Elsevier]