Naoki Ide

High-Density Near-Field Optical Disc Recording

We developed a high-density near-field optical recording disc system using a solid immersion lens. The near-field optical pick-up consists of a solid immersion lens with a numerical aperture of 1.84. The laser wavelength for recording is 405 nm. In order to realize the near-field optical recording disc, we used a phase-change recording media and a molded polycarbonate substrate. A clear eye pattern of 112 GB capacity with 160 nm track pitch and 50 nm bit length was observed. The equivalent areal density is 80.6 Gbit/in2. The bottom bit error rate of 3 tracks-write was 4.5×10-5. The readout power margin and the recording power margin were ±30.4% and ±11.2%, respectively.

Thermoelectric properties of Heusler-type off-stoichiometric Fe2V1+xAl1−x alloys

We report the thermoelectric properties of Heusler-type off-stoichiometric Fe2V1+xAl1�x alloys. Due to the off-stoichiometric effect, which is the substitution of V/Al atoms with Al/V atoms, semiconductor-like electric resistivity behavior in Fe2VAl is changed to metallic behavior in Fe2V1+xAl1�x alloys and both positive and negative absolute Seebeck coefficients are drastically increased. The maximum thermoelectric power factor of Fe2V1+xAl1�x alloys is 4.3 × 10 �3 (x = �0.03: p-type) and 6.8 × 10 �3 WmK �2 (x = 0.05: n-type) with a peak temperature in the range 300–600 K, exceeding the values of previously reported Fe-based Heusler alloys as well as those of available thermoelectric materials such as Bi-Te semiconductors. Based on x-ray diffraction and photoemission spectroscopy results, it is thought that the maintenance of the Heusler-type (L21) crystal structure and the modification of the electronic structure due to the offstoichiometry could explain the large thermoelectric power factor and high peak temperature in Fe2V1+xAl1�x alloys.

Signal Quality Evaluation Method for Over-30-GB Blu-ray Discs

We proposed a new signal quality evaluation method applying a sequenced amplitude margin (SAM) for over 30-GB Blu-ray discs (BDs), where the dominant error pattern differs from lower-density discs (23–27-GB BDs), and conventional signal quality evaluation method such as maximum-likelihood sequence error (MLSE) lose accuracy. We experimentally confirmed the effectiveness of our new method for 30–31.5-GB BDs.

Adaptive Partial-Response Maximum-Likelihood Detection in Optical Recording Media

We developed an adaptive partial-response maximum-likelihood (PRML) detector. This detector learns the reference levels for the calculation of branch metrics from past RF samples. Therefore, it enables asymmetry and level fluctuation compensation. In this paper, we report the results of applying adaptive PRML detection to error rate measurements of 20 Gbyte optical discs.

Computer Simulation of Core Structure of Screw Dislocations in C60 Crystals Using Girifalco Potential.

The equilibrium molecular configuration around a 1/2[101] screw dislocation in C60 crystals in a fcc phase was calculated by means of molecular dynamics. The molecules were assumed to be rigid and the spherical intermolecular potential derived by Girifalco was utilized. The dislocation was found to dissociate into two Shockley partials. The partial dislocation had a spreadout core and the width of the Burgers vector density at the half-peak height reached 13 times the magnitude of the Burgers vector.

Solid solution hardening evaluated from amplitude-dependent internal friction in polycrystalline copper alloys

In the present study, the authors evaluated plastic strain as a function of stress from data of the amplitude-dependent internal friction in polycrystalline Cu alloys under the condition that the flow stress is controlled only by the mobility of dislocations. The polycrystalline alloys were employed as specimens in the measurements, because the amplitude dependence of internal friction is too structure-sensitive to show reproducible results in highly pure monocrystals. In addition, the application of the present evaluation of plastic strain to engineering materials is expected as a new non-destructive strength test. The solute elements were restricted within IVb group and the concentration was fixed at 0.3% in order to examine the dependence of flow stress on the size misfit between solute and solvent atoms.

COMPUTER SIMULATION OF CORE STRUCTURE AND STRESS FIELD OF EDGE DISLOCATIONS IN C60 CRYSTALS USING GIRIFALCO POTENTIAL

The equilibrium molecular configuration around a 1/2[101](111) edge dislocation in fcc C60 crystals was calculated using molecular dynamics with the Girifalco potential. The dislocation was found to dissociate into two Shockley partials. The core of the partial dislocation was wider than that of the screw dislocation and its width was 17.5 times the Burgers vector. The compressive stress at the core reached 0.74 GPa at maximum. The extent of redshift of photoluminescence spectra was estimated.

Internal Friction Peak in FCC Fe–Cr–Ni Alloys Hydrogen-Charged by Gas-Equilibration Method

An internal friction peak due to hydrogen in Fe55Cr45-xNix (x=20–45) and Fe100-xNix (x=35–100) alloys was observed. A gas-equilibration method was employed in order to charge specimens homogeneously with hydrogen. In Fe55Cr45-xNix alloys, the peak height significantly increased as the nickel content increased, whereas in Fe100-xNix alloys the peak height did not show a monotonic change versus the increasing nickel content. In both alloys the peak height depended strongly on the alloy composition.

Interaction Potential between a Dislocation and a Pinning Atom in FCC Metals

Amplitude dependent internal friction (ADIF) was measured on 4N and 6N Cu crystals at 4K–40 K to study the interaction between a dislocation and a pinning atom. The temperature dependence of the stress amplitude necessary to produce a constant ADIF was well explained by assuming the Cottrell type interaction potential based on linear elasticity. This is clearly different from the case of Al crystals where it was necessary to consider a modified Cottrell potential including a deviation from linear elasticity near the dislocation center.

Maximum-Likelihood Detection for Information Channels with Colored Noise

We developed a new partial-response maximum-likelihood (PRML) detector more suitable for data storage systems than conventional PRML detectors. This detector calculates the likelihood of data sequences from both the direct and the differential partial-response. Therefore, it enables the noise in the likelihood to be made close to white noise. In this paper, we report the mechanism of the new method and the experimental results of applying this method to a 25 Gbyte optical disc playback system.