Hiroki Sato

Effects of nanofiller loading on the molecular motion and carrier transport in polyamide

Effects of nanofiller loading on the molecular motion and carrier transport in polyamide-6/mica nanocomposites were discussed by analyzing their complex permittivity spectra. As a result, the following four dielectric polarization processes were observed; space charge polarization, interfacial polarization at crystalline/amorphous boundaries, alpha relaxation due to dipolar orientation, and beta relaxation due to rotation of amide groups bonded with water molecules. The enhancement of dielectric constant and that of loss factor due to abundance of mobile charge carriers are suppressed by the nanofiller loading. Furthermore, it was found that the relaxation time becomes longer by the mica nanofiller loading both for the dipolar orientation and for the rotation of amide groups. These results suggest that molecular motion that assists carrier transport is suppressed in nanocomposites, which indicates a strong interaction between the resin and filler.

Anomalous magnetic properties of Heusler superconductor YbPd2Sn

Abstract We have investigated the magnetic properties of the Heusler compound YbPd2Sn, which exhibits coexistence of superconductivity (Tc=2.3 K) and antiferromagnetism (TN=0.22 K). In the temperature dependence of the specific heat in applied magnetic fields, we found an anomalous broadening of the Schottky peak caused by the Zeeman splitting of the Γ7 crystalline–electric-field (CEF) ground state of the Yb3+ ions. This fact indicates the existence of antiferromagnetic (AF) short-range correlations, which are hardly destroyed by magnetic field. An anomalous temperature dependence of the upper critical field Bc2 with a maximum around 0.8 K can be explained by taking into account the pair breaking effect of Cooper pairs caused by the Yb-moment fluctuation through an exchange interaction. We propose that a weak magnetic coupling between the cubic Pd sublattice responsible for superconductivity and the NaCl-type Yb–Sn sublattice responsible for the AF magnetic ordering play an essential role for the coexistence.

Valence State of Ce in the C14 and C15 Phases CeOs2.

We have measured the temperature dependence of the electrical resistivity, Hall coefficient, thermoelectric power, magnetic susceptibility and specific heat of CeOs 2 in the two different crystallographic structures C14 and C15. We observed clear differences in all the transport properties between the two phases. The C14 phase behaves like a normal metal with a stable Ce 4+ valence, while the C15 exhibits various features characteristic of valence fluctuating compounds. This fact explains why only the C14 becomes superconductive.

Secure Frequent Pattern Mining by Fully Homomorphic Encryption with Ciphertext Packing

We propose an efficient and secure frequent pattern mining protocol with fully homomorphic encryption (FHE). Nowadays, secure outsourcing of mining tasks to the cloud with FHE is gaining attentions. However, FHE execution leads to significant time and space complexities. P3CC, the first proposed secure protocol with FHE for frequent pattern mining, has these particular problems. It generates ciphertexts for each component in item-transaction data matrix, and executes numerous operations over the encrypted components. To address this issue, we propose efficient frequent pattern mining with ciphertext packing. By adopting the packing method, our scheme will require fewer ciphertexts and associated operations than P3CC, thus reducing both encryption and calculation times. We have also optimized its implementation by reusing previously produced results so as not to repeat calculations. Our experimental evaluation shows that the proposed scheme runs 430 times faster than P3CC, and uses 94.7 % less memory with 10,000 transactions data.

Features of electronic states in the highly-correlated electronic system Sr1-xNdxMnO3 around x = 0.50

In the highly-correlated electron system Sr1-xNdxMnO3 (SNMO) having the simple perovskite structure, there are interesting electronic states, which are related to degrees of charge, orbital, and spin freedoms for eg electrons in Mn ions. Among these states, in the case of SNMO, the C-, A-and CE-type antiferromagnetic states were reported for 0.20 ≤ x ≤ 0.38, for 0.38 ≤ x ≤ 0.48, and for 0.48 ≤ x ≤ 0.52, respectively. The points to note here are that these antiferromagnetic states are directly associated with corresponding orbital orderings, and that the CE-type state also accompanies charge ordering. Because of these features, we were interested in the (A → CE) state change in SNMO. The crystallographic features of prepared SNMO samples with 0.46 ≤ x ≤ 0.50 have thus been investigated mainly by means of a transmission electron microscope equipped with a low-temperature holder. As a result, the state around 100 K for x = 0.48 was first understood to be identified as the Imma state, which includes a large number of orbital-modulated (OM) regions with an average size of about 10 nm. The feature of such regions is that the orbital modulation has an incommensurate periodicity and a charge modulation is absent in them. On the other hand, the CE-type state having the commensurate orbital and charge modulations was also confirmed to be present for x = 0.50. In addition to these two states, the state around 100 K for x = 0.46 was found to be characterized by the coexistence state consisting of the C-type orbital-ordered state and the Imma states including OM regions. In other words, the presence of the A-type orbital-ordered state could not be confirmed in the temperature range between 300 K and about 100 K for 0.46 ≤ x ≤ 0.50 in this study.

Relaxation phenomenon in the formation of the C-type orbital-ordered state in the simple perovskite manganite Sr1-xNdxMnO3

The formation of the C-type orbital-ordered (COO) state from the disordered cubic (DC) state in Sr1−xNdxMnO3 (SNMO) with the simple perovskite structure has been examined mainly by transmission electron microscopy. As the COO state has tetragonal I4/mcm symmetry, its formation is associated with the cubic-to-tetragonal structural transition. It was found that, when SNMO samples were cooled down from the DC state, the R25-type rotational displacement of MnO6 octahedra was first induced, together with the symmetry change into the tetragonal I4/mcm structure. The C-type orbital ordering then appeared due to the induction of the Jahn–Teller distortion as a response of a lattice system to this orbital ordering. Because no symmetry change occurred in the latter case, the Jahn–Teller distortion can be regarded as a dilatational distortion. One interesting feature is that the appearance of the dilatational Jahn–Teller distortion led to a nanometer-scale banded structure, characterized by an alternating array of t...

Detailed Modeling of Motor System of Plug-In Hybrid Vehicle: Study of Detailed Modeling of Inverter and Boost Converter Losses

This paper addresses the method of detailing the motor system including the inverter and the boost converter of plug-in hybrid vehicles (PHVs). In the past, we had to use the actual measurement data such as efficiency map to calculate the loss of a motor system. However, by estimating the output current of the motor system, allows us to separate the one loss into losses caused by the inverter, the boost converter and the motor. Based on the separation of the losses, we can then build a multi-voltage motor system or estimate the losses of the different ranks of vehicles.

Characteristic features of the C-type orbital-ordered state in the simple perovskite manganite Sr1-xNdxMnO3

In the highly-correlated electronic system Sr1-xNdxMnO3, the C-type orbital-ordered (COO) state is present for 0.15<x<0.38, and its crystal structure with the tetragonal-I4/mcm symmetry involves both the R25-type rotational displacement of MnO6 octahedra and the Jahn-Teller distortion as a response of a lattice system to orbital ordering. To understand the details of the competition between the rotational displacement and the Jahn-Teller distortion, the formation of the COO state from the disordered cubic (DC) state with the space group Pm3m has been investigated mainly by transmission electron microscopy. It was found that, when the temperature was lowered from the DC state for x = 0.20, for instance, COO regions with the tetragonal symmetry, exhibiting a {110}DC banded structure, were locally formed in the matrix below about 330 K. The subsequent aging at 300 K resulted in the growth of COO regions; that is, the time-relaxation phenomenon. Because of the presence of antiphase boundaries for the rotational displacement in the matrix, the crystal structure of the matrix should also have the tetragonal symmetry. In other words, it is understood that the coexistence state appearing just after cooling from the DC state consists of two tetragonal regions with different c/a values. The coexistence state is apparently characteristic of the competition between the rotational displacement and the Jahn-Teller distortion for the formation of the COO state.

Specific Heat Study on Magnetic Superconductor YbPd2Sn

To investigate the magnetic ground state coexisting with superconductivity (Tc=2.5 K) in Heusler compound ybpd2Sn, we have measured the specific heat C in magnetic fields. In zero field, above the antiferromagnetic (AF) transition temperature TN=0.22 K, tail in C is observed indicating a short-range AF correlation. This could be the origin of the anomalous temperature dependence of the upper critical field Bc2.Using a peak in C(T) observed for B>0.3 T, we confirmed that the crystalline-field ground state of Yb3+ is г7 doublet. The broad peak-shape caused by a internal-field fluctuation at the Yb-ions indicates that the short-range correlation is not destroyed even in higher fields.

Evidence of the different valence states in the C14 and C15 phases CeOs2

We have measured the temperature dependence of the electrical resistivity, thermoelectric power and Hall coefficient of CeOs2 in two deferent crystallographic structures C14 and C15. We observed clear differences in all the transport properties between the two phases. The C14 phase behaves like a normal metal with a stable Ce4+, while the C15 exhibits various features characteristic of valence fluctuating compounds. This fact explains why only the C14 becomes superconductive.