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We report on our progress in measuring the Boltzmann’s constant by Johnson noise thermometry (JNT) using an integrated quantum voltage noise source (IQVNS) that is fully implemented with superconducting integrated circuit technology. The IQVNS generates calculable pseudo white noise voltages to calibrate the JNT system. Thermal noise of a resistor placed at the temperature of the triple point of water was measured precisely by the IQVNS-based JNT. We accumulated more than 2000 data points to determine the Boltzmann’s constant. The experimentally obtained Boltzmann’s constant was kexp = 1.3806493 × 10−23 J/K with a relative statistical uncertainty of 8.6 × 10−6, which agreed well with the 2014 Committee on Data for Science and Technology value with a relative offset of +0.6 × 10−6. [ABSTRACT FROM AUTHOR]

A 10-V programmable Josephson voltage standard (PJVS) circuit including 524 288 vertically stacked NbN/TiN/NbN Josephson junctions was successfully fabricated without any defects. The chip was cooled with a compact cryocooler at a temperature of 9.8 K and generated an output voltage of 17.3 V with the first Shapiro step height of 1.0 mA under microwave irradiation at 16 GHz. Furthermore, the circuit design having the high output voltage increased the number of available chips for the 10-V PJVS. The fabrication yield for the chip, which generates greater than 10 V, was 36%, which is ten times greater than that for a perfect chip without any defects. This method was not effective for the chip that had serious defects, such as a disconnection across the array or short between the array and ground; thus, efforts to reduce such defects, e.g., frequent maintenance inside vacuum chambers for film preparation and etching, were found to be essential. [ABSTRACT FROM AUTHOR]

We precisely evaluated a single-chip 10-V programmable Josephson voltage standard (PJVS) system based on a closed-cycle refrigerator by directly comparing it with a conventional Josephson voltage standard system. The PJVS chip fabricated using NbN/TiNx/NbN junction technology was used. The result of the measurement showed a good agreement with a combined standard uncertainty of 3.1 parts in 1010 at 10 V. [ABSTRACT FROM AUTHOR]

We developed a 10-V dc programmable Josephson voltage standard (PJVS) using a multichip technique. The PJVS was based on NbN/TiNx /NbN junctions and operated using a 10-K compact cryocooler. We carried out an indirect comparison with a superconductor-insulator-superconductor-based conventional Josephson voltage standard (JVS) by measuring the voltage of a 10-V zener diode reference standard. The combined standard uncertainty of the comparison was uc = 0.03 μV(k = 1), and the relative combined standard uncertainty was 3 × 10-9. [ABSTRACT FROM AUTHOR]

Basic characteristic of electromagnetic force in induction heating application of single-sided linear induction motor (SLIM) which uses electromagnetic AC field is investigated by means of 2-D and 3-D numerical electromagnetic FEM calculation. The electromagnetic force in the normal direction consists of the attractive force caused by magnetization and the repelling force caused by Lorentz force. Although the normal force is canceled by them and becomes zero at crossover frequency, the value is different, which is 2 kHz in 2-D model and is 5 kHz in 3-D one respectively. Since 2-D model expresses only center section of 3-D model and can not express the complex behavior of the eddy current in the whole model, the repelling force caused by Lorentz force is considered to be overestimated when the electromagnetic force value of 2-D model is converted into 3-D one. As a result, the crossover frequency of 3-D model becomes large in comparison with 2-D one. This means that an evaluation by using 3-D model is demanded in order to correctly evaluate the crossover frequency. On the other hand, at low frequency in which the attractive force caused by magnetization becomes dominant, the normal forces of the 2-D and 3-D model are in good agreement. This means that the evaluation by using 2-D model is effective at low frequency. [ABSTRACT FROM AUTHOR]

Proposes a fault-tolerant method and stepwise negotiating voting (SNV) method which provides both permanent and transient fault-tolerance. Technical issues in conventional fault-tolerance techniques; How SNV was developed; Hiten onboard computer (OBC); Contents and results of fault-tolerance experiments; Analysis on the experimental results.

Purpose: In the conventional techniques for determining the calibration factors of positron emission tomography (PET) scanners, cylindrical water and resin phantoms with radioisotope ^18 F or ^68Ge/^68Ga are used. In these methods, however, the results depend on attenuation and scatter correction. The purpose of this study is to develop a point-like ^68Ge/^68Ga radioactive source that can be used to determine the calibration factors of PET scanners without the uncertainty of attenuation and scatter correction. Methods: A spherical absorber design was employed to realize a symmetric angular distribution of emitted annihilation photons. A Geant4-based Monte Carlo simulation code was used to compare physics characteristics of point-like sources with various absorber materials. On the basis of this simulation, a point-like ^68Ge/^68Ga source with a spherical aluminum absorber was manufactured. Its radioactivity was calibrated at an accredited national calibration facility. A calibration factor of a clinical PET scanner was then obtained with a point-like source and compared with that obtained by a standard cross-calibration method. Results: The emission probability of 0.511 MeV annihilation photon pairs per positron decay was typically 0.6–0.8. The fraction of background photon pairs was 6–8% in the energy region of 0.4–0.6 MeV. Considering these two figures, lower density materials such as aluminum and pol(ymethyl methacrylate) (PMMA) were preferable. For the aluminum absorber, a diameter of 8 mm was suitable to prevent positrons from escaping. The calibration factor obtained with the point-like source agreed with that obtained by the standard method within 2–3%. Conclusion: A point-like ^68Ge/^68Ga radioactive source was successfully designed, manufactured, and used for determining a calibration factor of a PET scanner. It can be considered a practical tool for calibrating and evaluating the quantitative aspects of PET scanners. [ABSTRACT FROM PUBLISHER]

Purpose: Point-like ^22Na radioactive sources have been widely used for checking radiation detectors that measure annihilation photons and for evaluating PET scanners. We developed new types of ^22Na point-like radioactive sources that are expected to be more symmetric than conventional source types in the angular distribution of the emitted photons. The purpose of this study is to use Monte Carlo simulation to investigate the basic characteristics of the photons emitted from the new type ^22Na point-like radioactive sources. Methods: Two new types of ^22Na point-like sources, a cylinder type and a sphere type, were considered in comparison with two conventional source types, a disk type and a cube type. The angular distribution and energy spectra of the emitted 0.511 MeV annihilation photons and 1.275 MeV gamma rays were calculated using a Monte Carlo code based on Geant4. Results: The angular distribution of the emitted photons was more symmetric in the new type point-like sources than in the conventional types. The asymmetry of the angular distribution of the unscattered 0.511 MeV annihilation photon pairs counted in coincidence was 0.1 \pm 0.1\% and 1.6\pm 0.1\% in the sphere and cylinder types, compared with 4.1\pm 0.1\% and 22.6\pm 0.1\% for the cube and disk types. The scatter components around the 0.511 MeV photopeaks in the new source types were typically less than 2/3 and 1/2 of those in the disk and cube types, respectively. Conclusion: The new point-like ^22Na sources offer a more symmetric angular distribution of the emitted photons with fewer scatter components. They are useful for applications where the symmetry of the emitted photons is crucial. [ABSTRACT FROM AUTHOR]

We are developing a programmable Josephson voltage standard (PJVS) system based on a compact cryocooler. The system is capable of generating two arbitrary waveforms by use of a dual-output PJVS (DO-PJVS) device. Owing to this dual-output feature of the PJVS system, the low-frequency characteristic in the ac–dc transfer difference of a thermal converter has been investigated using the 90^\circ addition method. The evaluation of the low-frequency characteristic of a thermal converter is of great importance for connecting conventional ac–dc transfer standards and new Josephson-based ac voltage standards. To fulfill this purpose, a dual-heater thermal voltage converter (DH-TVC) with improved low-frequency performance has been developed. The low-frequency ac–dc transfer difference of the DH-TVC was evaluated to be smaller than 1 \mu\V/V at frequencies of as low as 1 Hz. [ABSTRACT FROM PUBLISHER]

We evaluated timing jitter based on a time-to-digital converter (TDC) having sub-pico seconds time resolution. The measured jitter at liquid helium temperature was 65 fs for an optimally damped simple junction composing a conventional Josephson transmission line fabricated with the NEC standard process. The temperature dependence and shunt resistance dependence of jitter indicate that the jitter originates from thermal noise generated at the shunt resistor of the junction. We also found that the timing jitter of a balanced comparator is much larger than that of a JTL. The jitter of a balanced comparator is independent of temperature. This means that the jitter of a balanced comparator does not arise from thermal noise. [ABSTRACT FROM AUTHOR]

A space vector modulation (SVM) technique of a dual-inverter system for an open-end winding motor drive is described in this paper, where one inverter has a battery power source and the other has an only capacitor across the dc bus. The SVM must be achieved to operate the motor with field-oriented control and simultaneously to control the capacitor voltage at a constant value by using redundant switching states of the dual-inverter system. The control of the capacitor voltage is carried out by selecting a charging or a discharging mode in each redundant switching state, taking the instantaneous motor power factor into account. In addition, it is also required to reduce the error voltage pulses, which are generated in output multilevel voltage waveforms during the dead time. The compensation method of the existing dead-time scheme and the improved SVM sequence to reduce the error voltage vectors are proposed in this paper. The proposed methods are examined through several experimental tests and are confirmed to generate superior output voltage waveforms from the viewpoint of the measured total harmonic distortion and dv/dt. [ABSTRACT FROM AUTHOR]

A cryogenic current comparator (CCC) is an instrument of great importance in electrical metrology, which provides a ratio of two currents with ultimate accuracy based on superconductivity. It is used for dc resistance calibration in many national metrology institutes. Conventional CCCs consist of multi-turn coils of wire windings, a multi-layered shield of superconductor foils and a separate SQUID sensor. This implementation results in a bulky device too massive to cool with a mechanical cryocooler, making a system inconvenient. A new implementation of CCC, an integrated CCC (ICCC) consisting of thin-film spiral coils, a thin-film superconducting shield and a SQUID sensor integrated on a single chip, enables a user-friendly system operated with a compact cryocooler. Prototype ICCC chips were designed and fabricated by using a superconducting Nb integrated circuit technology with chemical-mechanical polishing. The basic operation of the prototype ICCCs was confirmed by monitoring periodic flux-voltage characteristics of the SQUIDs. [ABSTRACT FROM AUTHOR]

Stacked (NbN/TiNX)N/NbN (N = 2, 3, 4, 5 and 10) Josephson junctions and their arrays have been fabricated on a Si chip and their microwave-induced characteristics were measured at a temperature around 10 K. To achieve a vertical and smooth edge of an NbN - TiNX multilayer, an inductively coupled plasma reactive ion etching (ICP-RIE) technique was used. Current-voltage characteristics measured for stacks of (NbN/TiNX)N/NbN Josephson junctions without microwave indicated that critical currents for those junctions distribute in a certain range. We defined Ic - spread as (Ic MAX - Ic MIN)/Ic Average to measure the distribution of Ic. The Ic, - spread was minimized when the thickness of intermediate electrodes was d = 50 nm. We also evaluated values of Ic - spread for stacks prepared at different fabrication runs as a function of the number of junctions in a stack N. As a result, we found N = 3 is the maximum for practical use. For arrays, we obtained a constant-voltage step height of about 2 mA for 2048 stacks of double-barrier junctions (N = 2), and about 1 mA for 1 024 stacks of triple-barrier junctions (N = 3). [ABSTRACT FROM AUTHOR]