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Deformation of the semisolid mush during solidification is a common phenomenon in metal casting and can lead to defects such as hot tears, macrosegregation, and porosity. The morphology of the solidifying mush, including the shape of the dendrites and the distribution of grain boundaries, plays a key role in determining its mechanical behavior. In the current study, a polycrystalline phase-field model is combined with a material point method stress analysis to numerically simulate the fully coupled dendritic solidification and elasto-viscoplastic deformation behavior of a pure substance in two dimensions. It is shown that solid compressive and shear deformations result in variations in the crystallographic orientation angle within a single dendrite that, in turn, affect the subsequent solidification behavior. Shearing of a dendritic structure occurs primarily in relatively narrow bands near or inside the grain boundaries or the thin junctions between different dendrite arms. The deformations can cause the formation of low-angle tilt grain boundaries inside of individual dendrite arms. In addition, grain boundaries form when different arms of a deformed single dendrite impinge. During compression of a high-solid-fraction dendritic structure, the deformations are limited to a relatively thin layer along the compressing boundary. The compression causes consolidation of this layer into a fully solid structure that consists of numerous subgrains.

Uniform InAs quantum dots (QDs) have been realized on GaAs by molecular beam epitaxy, which can increase maximum optical gain in laser diodes without sacrificing original high-density and high optical quality characteristics. This improvement enables laser operation under higher environment temperature. In order to improve QD uniformity, we searched for a proper growth condition and sequence for suppressing In out-diffusion during QD coverage. Although the same initial InAs QD structure on GaAs was used, PL linewidth was reduced after coverage under such improved conditions. In QD lasers, higher optical gain as large as 54 cm −1 at room temperature which is about 10 cm −1 larger than our previous data was realized. Those improved QDs are attractive for realizing novel optical devices.

A method is developed to numerically simulate coupled solidification and deformation of dendrites. Dendritic solidification is modeled using the phase-field method. The elasto-viscoplastic deformation of the growing solid is computed using the material point method. The stress analysis assumes a sharp and stress free solid–liquid interface, with the zero contour line of the phase field used to identify the interface. The deformation-induced flow in the liquid is approximated through a zero-gradient extension of the deformation velocities in the solid. Changes in the crystallographic orientation angle and advection of the phase and temperature fields due to solid deformation are all accounted for. Numerous tests are performed to validate the various numerical procedures. The full model is then applied to simulate in two dimensions the compression of a single dendrite of a pure substance growing in an undercooled melt. The development of complex stress and strain distributions is observed. The deformations result in variations in the crystallographic orientation angle within the dendrite that, in turn, affect the subsequent solidification behavior. The modeling of the deformation of polycrystalline solidifying structures, including the formation of grain boundaries, is described in a companion paper.

Deformation of the semi-solid mush during solidification is a common phenomenon in metal casting. At relatively high fractions of solid, grain boundaries play a key role in determining the mechanical behavior of solidifying structures, but little is known about the interplay between solidification and deformation. In the present study, a polycrystalline phase-field model is combined with a material point method stress analysis to numerically simulate the coupled solidification and elasto-viscoplastic deformation behavior of a pure substance in two dimensions. It is shown that shearing of a semi-solid structure occurs primarily in relatively narrow bands near or inside the grain boundaries or in the thin junctions between different dendrite arms. The deformations can cause the formation of low-angle tilt grain boundaries inside individual dendrite arms. In addition, grain boundaries form when different arms of a deformed single dendrite impinge. During compression of a high-solid fraction dendritic structure, the deformations are limited to a relatively thin layer along the compressing boundary. The compression causes consolidation of this layer into a fully solid structure that consists of numerous sub-grains. It is recommended that an improved model be developed for the variation of the mechanical properties inside grain boundaries.

Sn-based sheets with Ta, B or Nb particle dispersion have been prepared from consolidated alloys. A small amount of Ti addition strengthened the bonding between dispersed particles and the Sn matrix, which improved the workability of the sheet. The sheet was laminated with a Nb sheet, and wound into a Jelly Roll (JR) composite. The composite was easily fabricated to a wire without intermediate annealing. Thick and uniform Nb3Sn layers with nearly stoichiometric Sn concentration were synthesized by the mutual diffusion between Nb and Sn-based alloy layers. An offset Tc of ~18.1 K and an offset Bc2 (4.2 K) of ~26.5 T have been obtained after the heat treatment. The non-Cu Jc of the wires increased with decreasing the wire diameter. A non-Cu Jc of ~150 A/mm2 has been obtained at 4.2 K and 22 T. The Sn-Ta, Sn-B and Sn-Nb based sheet JR wires exhibited similar microstructures and superconducting performances.

A real-space mapping of photovoltage near the edge of the Hall-bar of a GaAs/AlGaAs single heterojunction has been obtained using a dilution-refrigerator-based near-field scanning optical microscope in magnetic fields. The optical probe-sample surface distance dependence of photovoltage is investigated. We obtain photovoltage profile in the vicinity of the edge, which reflects the local chemical potential of the two-dimensional electron gas determined by the distribution of the compressible and incompressible strips.

We measured the photoluminescence (PL) of a GaAs quantum well (QW) with a lateral potential modulation by the front-gate bias while changing both the electron density and electric field at low temperature. Near the onset of the two-dimensional electron gas, we observed an anomalous enhancement of PL intensity of the neutral exciton X 0 accompanied by a decrease in the intensity of the charged exciton X - . The sample was a 20-nm GaAs back-gate undoped QW with semi-transparent square-mesh surface gates. By comparing the results with those for a flat transparent surface gate sample we discuss the origin of this anomalous phenomenon. We present a possible explanation for this phenomenon, which is attributed to lateral drift motion of the X 0 in a laterally modulated exciton potential.

We report the high-frequency properties of sub-micron-sized Fe-Co particles synthesized with a polyol process, and what influence hard magnetic and non-magnetic oxide layers had on those high-frequency properties. The Fe-Co particles exhibited a resonance peak in the range of a few gigahertz, and the resonance peak shifted to a higher region for decreasing particle size. Furthermore, the presence of a multi-resonance peak in the gigahertz range was recorded. The permeability of surface-oxidized particles decreased and the resonant frequency shifted to a higher region for increasing CoFe2O4 layer thickness on the surface of the particles. However, SiO2 coating did not influence the resonant frequency even though the permeability decreased due to the decrease in the volume fraction of FeCo particles in the sample.

The effect of microbubble emission boiling (MEB) on the mixing of two fluids in a microfluidic device was studied experimentally. When MEB occurred on an electric heater made of a platinum wire with a diameter of 30 micrometers, the mixing of the two fluids increased markedly. However, nucleate boiling had no significant effect on the mixing. A high-speed video showed that the very rapid growth and collapse of micro boiling bubbles on the heater causes the strong mixing of the two fluids. The coexistence of highly superheated and highly subcooled water near the heater seems to be the reason for such enhanced mixing.

Sn-Ta based quaternary alloys were prepared by the reaction of constituent metal powders. The alloys were fabricated into sheet or rod forms. In addition, Sn-Ti based ternary alloys prepared by melt and cast procedure were fabricated into sheets. Jelly Roll (JR) composites were prepared using Sn-based alloy sheet and Nb sheet, and then fabricated into wires. A Bc2 (4.2 K) of 26.9 T (mid) has been obtained in the JR wire using Sn-Ta based alloy sheet. Thick Nb3Sn layers were formed by the mutual diffusion between Sn-based alloy sheet and Nb sheet. Stoichiometric Sn concentration with no gradient was obtained throughout the Nb3Sn layers, which may be the main origin of excellent high-field performance of the JR wires. Meanwhile, 19 and 37 filamentary Nb3Sn wires have been fabricated using Sn-Ta based alloy rods. An equivalent high-field performance has been obtained in the multi-rod wires as that of JR wires.

CdS thin films grown on ITO/glass substrates by using chemical bath (CB) were boron-implanted employing 100 keV beam of boron ions (B + ) with fluences in the range 1.0×10 15 –1.0×10 16 ions/cm 2 . The B doping was successfully carried out, as was proved by the major carrier density introduced in the range 0.8×10 18 –5.4×10 18 cm −3 , which was calculated from thermo power measurements. Raman spectroscopy results support the assumption that triply ionized boron (B 3+ ) enters into the CdS lattice occupying Cd 2+ sites, which create shallow donor levels in the forbidden energy band gap.

Ti–Al–Si–N films with various composition ratios were deposited by a specially designed cosputtering system with three magnetron cathodes by controlling the impressed power ratios on each cathode independently. All the films were deposited on Si wafers at 300°C under a total gas pressure of 0.5Pa with a nitrogen flow ratio [N2∕(N2+Ar)] of 70% using Ti, Al, and Si targets. Hardness and Young’s modulus normal to the surface of the Ti–Al–Si–N films were analyzed by nanoindentation equipped with a Berkovich diamond indenter. It was clarified that the hardest condition of the films with different Ti∕Al ratios could be obtained when the Si content was about 10–20at.%, whereas the maximum values of the hardness did not depend on the Al content. Nanocomposite structures where Ti–Al–N or Ti–Al–Si–N nanocrystallites were embedded in an amorphous Si3N4 matrix were clearly observed by transmission electron microscopy which must contribute largely on the hardening of the films. The size of the nanocrystallites for the...

This paper presents the mechanical properties of silicon-based membranes windows applied for miniature electron beam radiation system. The membranes were used for the physical separation between the vacuum and atmosphere, and used as an EB-permeable membrane window. We used MEMS technologies to fabricate the thin Si-based membrane window structure. The size of each window is 6 mm in length and 2 mm in width. Four different types of membrane windows were fabricated to compare the mechanical properties. Residential stress, Young's modulus, and breakage pressure were evaluated by using bulge test technique. SiN/SiO2/Si membrane showed the highest breakage pressure and operated more than one thousand hours.

We demonstrated the RF integrated noise suppressor and thin-film inductor using ferromagnetic film. The transmission parameter (S 21) of the integrated noise suppressor was compared with that of the nonintegrated noise suppressor. The magnitude of signal attenuation at the resonance point was greatly increased by the integration up to −30 and −57 dB for the 1-µm-thick and 2-µm-thick CoNbZr films, respectively. The closed magnetic circuit type GHz-drive integrated spiral inductors were fabricated with a four-turn and 380 × 380 µm2 two-port-type inductor with ground guards, which consisted of a sandwich 2-µm-thick Cu coil in between a patterned 1-µm-thick CoNbZr film. The 10/3 (line/space [µm]) designs with 2-µm-thick SiO2 insulating layers exhibited a quality factor Q = 14.7, being highest among the published data at 1 GHz.

The electron–hole states in the fractional quantum Hall regime is investigated with a back-gated undoped quantum well by photoluminesccence in magnetic fields. The evolution of the photoluminescence spectra is discussed depending on the electron density. We find anomalies of the photoluminescence at the integer as well as the fractional filling factors.

We report the magneto-optical measurement of GaAs quantum wire lattices of 0.7 micrometer period grown on GaAs(111)B substrates by using the selective-area MOVPE technique. We measure the photoluminescence (PL) spectra at 60 mK from the triangular and the Kagome lattice patterns as well as from the unpatterned single quantum well (SQW) as a reference. While the PL from acceptors is dominant in all the samples, the PL spectra have a different peak between the wire structures and the SQW. When we apply a perpendicular magnetic field to the samples, the PL intensities slightly decrease up to 100 mT and then increase at higher magnetic fields with periodic oscillations in the triangular and the Kagome lattices. This oscillation is possibly attributed to the interference effect of electrons in the lattice patterns threaded by the magnetic flux.

Ag and Ag-Ni films (Ni: 0.6, 2.0 and 4.8at.%) with a thickness of 95nm were deposited on SiO"2/Si substrates and the thermal stability of the films was evaluated. The films were annealed at temperatures from 400 to 700^oC for 1h in vacuum. The as-deposited Ag and Ag-Ni films had a smooth surface. The Ag-Ni films had an electrical resistivity higher than that of the Ag film because of the impurity scattering effect. However, the resistivity of Ag-Ni films decreased until 600^oC by annealing. As the morphological change after annealing, void formation was observed for the Ag film at 500^oC. Then after the annealing at 600^oC, agglomeration with a partly uncovered substrate was clearly observed for the Ag film. On the other hand, void formation was also observed for the Ag-Ni films at 600^oC. Further annealing at 650^oC caused agglomeration of the Ag-Ni films with an increase in their resistivity. Due to the insolubility of Ni into Ag, small islands of Ni appeared at this temperature. Consequently, Ag-Ni films are useful for suppressing agglomeration up to the annealing temperature of 600^oC. The resistivity of the Ag-Ni (0.6at.%) film was 2.1-2.4@m@Wcm after annealing from 400 to 550^oC comparable with that of the Ag film (1.9-2.2@m@Wcm) and it remained low, though that of the pure Ag film increased significantly at 600^oC.

We measured the photoluminescence (PL) spectra of a two-dimensional electron system induced in a Be-δ-doped GaAs/AlGaAs quantum well (QW) with a back gate. The electron density is controlled by means of the back-gate voltage. We estimated the electron density using the magneto-optical method and the PL linewidth, and also by undertaking transport measurements. We show that a uniform 2DES as large as 1 mm 2 is induced by the back-gate operation from 2.5 × 10 10 cm −2 . This experiment indicates that optical measurement with a back-gated QW is advantageous for studying the low-density 2DES.

A numerical model to calculate current density distribution in a parallel conductor assembled by multiple high temperature superconducting tapes was proposed. The numerical calculations on the current distribution in the parallel conductor of three high-temperature superconducting tapes were performed by using the developed model. The numerical results showed that the current density distribution in the parallel conductor were affected by the tape arrangement in the conductor.

A GaAs/AlGaAs quantum well (QW) was grown on a stripe-patterned (0 0 1) GaAs substrate with conventional molecular beam epitaxy. A mesa structure was formed with (0 0 1) facet on the top and (1 1 1) facet on the sides. It was found that the thickness of the QW layer on the (0 0 1) facet is controlled by the inter-surface diffusion of Ga adatoms from the (1 1 1) side facets. The behavior was investigated as a function of V/III ratio and the growth temperature.

Dyneema fiber has a high thermal conduction property. Using the property, we applied a Dyneema fiber reinforced plastic (DFRP) as a heat drain material for a conduction-cooled magnet. In the experiments, the DFRP was contacted on a surface of HTS tape, and a short-time over current exceeding its critical current was applied to the tape. The heat drain effect was measured from a voltage of the tape and a thermocouple. The experimental results showed that the effects depended on the fiber directions in the plastic. In case that the fibers in the plastic contacted perpendicular to the tape's face, the effect was good. When the DFRP is used as the heat-drain material, we should pay attention to the fiber directions in the DFRP.

An approximated method to estimate the electro-magnetic AC loss in high temperature superconducting coil was proposed. We applied this method to estimate the AC loss characteristics of the high temperature superconducting coil made by stacking pancake coils which are wound by Bi2223/Ag tape. The analytical AC losses of the HTS coil were compared with the measured AC losses before and after impregnation by epoxy resin obtained in the previous work by National Institute of Advanced Industrial Science and Technology. The analytically estimated electro-magnetic AC losses in the HTS coil were much smaller than the measured AC loss of the coil. The AC loss characteristics could not be explained by the method proposed in this paper. The main reason of this discrepancy was considered that the measured AC losses in the HTS coil contained large amount of the mechanical AC loss due to the AC vibration of the winding even if the HTS coil was impregnated.

Ultrasonic inactivation of Escherichia coli XL1-Blue has been investigated by high-intensity ultrasonic waves from horn type sonicator (27.5 kHz) utilizing the "squeeze-film effect". The amplitude of the vibration face contacting the sample solution was used as an indication of the ultrasonic power intensity. The inactivation of the E. coli cells by ultrasonic irradiation shows pseudo first-order behavior. The inactivation rate constant gradually increased with increasing amplitude of the vibration face and showed rapid increase above 3 microm (p-p). In contrast, the H2O2 formation was not observed below 3 microm (p-p), indicating that the ultrasonic shock wave might be more important than indirect effect of OH radicals formed by ultrasonic cavitation in this system. The optimal thickness of the squeeze film was determined as 2 mm for the E. coli inactivation. More than 99% of E. coli cells was inactivated within 180-s sonication at the amplitude of 3 microm (p-p) and 2 mm of the thickness of the squeeze film.

Oxide catalyst materials for methane oxidation were examined in order to develop the anode electrode for molten carbonate type fuel cell (MCFC). As a primary selection, oxides such as lanthanum (La 2 O 3 ) and samarium (Sm 2 O 3 ) were selected from screening experiments of TPD, TG and tubular reactor. Composite materials of these oxides with titanium fine powder were assembled into a cell unit for MCFC as the anode electrode. Steady-state activities were observed with these anode electrode materials when hydrogen was used as a fuel. When methane was directly charged to anode as a fuel (dry methane operation), a power generation with steady state was observed on both lanthanum and samarium composites after gradual decrease of open circuit electromotive force (OCV) and closed circuit current (CCI). The steady-state activity held as long as 144 h of continuous operation.

We have studied the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) of single spin-valve (SV) films with two different free layers : one is a single ferromagnet layer (conventional), and the other is a ferromagnetic layer with a ruthenium cap layer (Ru cap). When the spacer Cu layer thickness is 2.5 nm and the Ru layer is 0.45 nm, the Ru cap-type greatly enhances the CPP-GMR, with increasing its value up to 4.3%. We argue that the MR enhancement is probably caused by the spin-dependent scattering due to the strong reflection of majority spins at the Co90Fe10/Ru interface.

An open gradient magnetic separator using solenoid magnet was proposed. Simulation study was performed to investigate the basic separation characteristics of our separation method by analyzing the dynamic motion of magnetic particles. The simulation results show that the separation of ferromagnetic particles of several tens micrometer diameter is enough feasible. Separation experiment using a high-temperature superconducting magnet was performed to verify the validity of our method.

Numerical study to evaluate the validity of the measurement method of AC loss in high temperature superconducting tapes in external AC magnetic field carrying AC transport current was done. The AC transport current loss and the magnetization loss in a conventional Bi2223/Ag-sheathed multifilamentary tape in the external AC magnetic field carrying the AC transport current were measured by the four terminal method and the pick-up coil method respectively. Numerical calculations on the AC losses in the tape were performed by using our previously developed analytical model. The measured losses were compared with the analytical results and the errors of the AC loss measurement were evaluated.

Diffusion of 59 Fe in single crystalline γ-TiAl intermetallic compound has been investigated by the ion-beam sputter-sectioning technique in the temperature range from 1123 to 1303 K. The diffusion coefficients measured in the directions parallel ( D 33 ) and perpendicular ( D 11 ) to the [001] axis exhibit significant anisotropy; the diffusion of 59 Fe parallel to the [001] direction is faster than that perpendicular to the [001] direction. The activation energy for diffusion of 59 Fe parallel to the [001] direction is smaller than that perpendicular to that direction. The anisotropy of 59 Fe diffusion was opposite to that of 44 Ti self-diffusion. It is suggested that this anisotropy is related to site occupation of Fe in TiAl and the jumps of atoms through vacancy jumps.

AC loss characteristics of high temperature superconducting tape in external AC magnetic field carrying AC transport current were theoretically and experimentally studied. We measured the AC transport current and magnetization losses in a conventional Bi2223/Ag multifilamentary tape in the external AC magnetic field carrying the AC transport current. The measured AC magnetization loss, AC transport current loss and total AC loss were compared with the numerical results. The measured AC loss characteristics of the tape can not be explained by the critical state model. Numerical calculations on the AC losses in the tape were performed by using our analytical model introducing the electric field and current density relation locally determined in the filamentary region of the tape. The numerical losses by our model reasonably agree with the measured data.

We have fabricated two kinds of Nb/sub 3/Sn superconductors having the same diameter; one superconductor is reinforced by center-gathered tantalum (Ta) in a cross-section of the conductor, and the other is reinforced by distributed Ta in the cross-section. We applied compressive force to the conductors, and measured degradation of the conductors. When the conductor's strain due to the compressive force to the conductors was zero, a critical current (I/sub c/) of the distributed Ta conductor was larger than that of the center-gathered Ta conductor. However, an I/sub c/ of the distributed-Ta type conductor rapidly decreased, and when the compressive strain became approximately 5 or 6%, the I/sub c/ of the center-gathered Ta conductor exceeded that of the distributed-Ta type. It was experimentally shown that the center-gathered Ta conductor was more tolerant than the distributed Ta conductor about the compressive strain to the conductor.

We have measured contact resistance between superconducting strands that was a parameter of coupling losses in cable-in-conduit conductors. Assuming some kinds of twist pitches of sub-cables in the multi-stranded cables, we measured the contact resistance under the condition of the intersecting strands. Since not only the resistance but also mechanical properties of the strands (applied force to the strands and deformation of the strands due to the force) were measured, the contact area could be precisely estimated, and then the surface resistance was also evaluated. The experimental results showed that the surface resistance hardly depended on the twist pitches of the sub-cables at both liquid nitrogen and liquid helium temperatures. The results become fundamental data to estimate the coupling losses caused by current loops including more than one sub-cable with long-time constants of current decay.

AC loss characteristics of the twisted multifilamentary high temperature superconducting tape with different twist pitches in external AC longitudinal magnetic field as well as those of the nontwisted tape were experimentally investigated. We measured the AC transport current loss and the AC magnetization loss in the twisted and nontwisted Bi2223 multifilamentary tapes in the external AC longitudinal magnetic field. The measured transport loss and magnetization loss in the twisted tapes were affected by the amplitude and the direction of the AC longitudinal field. It was also shown that the AC losses in the tapes under the external AC longitudinal field depended on the twist pitch.

Local temperature rise due to insufficient cooling is one of the important problems in conduction-cooled high-temperature superconducting (HTS) coils. Assuming two types of plastics having high thermal conductivity as spacers in HTS coils, we measured temperature rises of a conduction-cooled HTS tape under various contact conditions between the plastics and the HTS tape. The cooling performance from the Zylon fiber reinforced plastic to the HTS tape was not so good, since the fibers in the plastic were oriented in one direction. The Dyneema fiber reinforced plastic effectively cooled the HTS tape, because the fibers in the plastic were two dimensions. The possibility to use the plastics with high thermal conductivity as the spacers in the conduction-cooled HTS coils was demonstrated.

It is of great concern for magnet designers to address their critical currents at a given field and bore size. In the case of high temperature superconducting magnets wound with BSCCO Ag-sheathed tapes, they have a strong magnetic anisotropy and therefore the critical current of magnets defined by an average voltage drop over an entire coil cannot be easily determined like low temperature superconducting magnets. An analytical way to obtain the critical current of HTS magnets is described by means of the electric and magnetic field analyzes based on the measured data of BSCCO Ag-sheathed tapes. A performance improvement of HTS magnet is studied by pursuing an optimum coil cross section.

Microstructure and thermoelectric properties were investigated on Zn4Sb3 thin films prepared by co-deposition of Zn and Sb by magnetron sputtering. The as-deposited amorphous thin films were annealed at temperatures between 573 and 673 K so that they crystallized in the form of β-Zn4Sb3. The Zn4Sb3 thin films have a relatively high power factor and a low thermal conductivity. Microstructure of the thin films can be controlled by changing sputtering power and deposition time. The thin films investigated are all Zn-rich with respect to the stoichiometric Zn4Sb3. Their electrical resistivity decreases as film thickness increases and Zn-rich particles in the matrix grow coarse. Their Seebeck coefficient decreases as electrical resistivity decreases. Low electrical resistivity and high Seebeck coefficient can be achieved simultaneously in a film specimen with properly controlled thickness and microstructure. A nano-scale grain size in a ∼300 nm-thick film specimen gives rise to an almost 50% reduction in its thermal conductivity. A ZT of 1.2 at ∼460 K has been obtained for a 349 nm-thick Zn4Sb3 film specimen.

A preparation method has been developed for thin foils for transmission electron microscopy (TEM) from powdered intermetallic compounds as a result of hydrogenation, in which powder samples are embedded in a Ni plate formed by electroless plating and then the assembly consisting of the Ni plate and the embedded powder samples are ion-milled. This method is successfully applied to some typical hydrogen-absorbing intermetallic compounds such as LaNi5, FeTi and TiMn2. In this method, Ni plating is carried out at ambient temperature, at which possible rearrangement of lattice defects that are introduced during hydrogenation is minimized and areas thin and wide enough for TEM observations are successfully produced because of the small difference in the sputtering yield between the Ni plate and these intermetallics. For thin foils produced by this method, not only lattice defects such as dislocations introduced into the bulk of powder samples can be characterized but also the crystallography of cracking and surface layers of powder samples can be characterized.

Temperature-dependence of a 1.3 µm external-cavity quantum-dot laser was evaluated. Four-wavelength simultaneous oscillation and wide-eye openings under 25-Gbps NRZ signal using the filtered individual longitudinal mode were demonstrated between 40 °C and 80 °C.

Electron paramagnetic resonance (EPR) measurements have been performed to investigate the effect of annealing on paramagnetic defect center in P+-implanted C60 films, in order to control and improve the electronic properties of the implanted films towards photovoltaic applications. We have found a reduction in the dangling bond density upon annealing by approximately a one order of magnitude, in the temperature range between 100°C and 700°C, regardless of the annealing media whether vacuum or forming gas (N2/H2). The reduction in spin defect density was ascribed to the decrease in disordered dangling bond as a consequence of the reconstruction of the less stable defect sites. Indeed the modification in the spin density is accompanied with an improvement in the electrical conductivity and band structure of the films. Also, in the annealed carbon films, a correlation was observed among linewidth, relaxation times, and optical gap. In addition, we report about the temperature dependence of the linewidth, signal intensity and the susceptibility of annealed films. The susceptibility follows the Curie-law at sufficiently low temperature, while above 180 K a deviation was observed. The prime novelty of this study is that it is the first EPR study of effects of annealing on defect center in P+- implanted C60 films.

Many research and development projects on high-temperature superconducting apparatus such as a transformer, fault current limiter, and cable are being actively pursued in the power field as a result of performance improvement of Bi silver sheath high-temperature superconducting (HTS) wire. HTS transformers are considered to be among the most promising applications in view of efficiency improvement, the interface with cryogenic cable and normal temperature devices, incombustibility, overload capability, the function as a reactor, and the possibility of use as a fault current limiter. The necessary technical development items of an HTS transformer in order to achieve performance superior to conventional devices are examined. For this purpose, three-phase 66-kV 100-MVA transformers were designed for the comparison of an HTS transformer and a conventional one with oil cooling. The desirable development items are an HTS wire current density of about 40 A/mm2, an allowable winding strain of about 0.5%, a percent impedance of 7.5%, an air gap flux density of about 0.3 T, and AC losses of about 0.3 W/km-A. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(1): 25–31, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10087

We studied the technical design targets of high temperature superconducting (HTS) large capacity transformers through the design of 3-phase 66 kV–100 MVA transformers, expecting further performance progress of HTS tapes. It is required for large capacity transformers installed in a power system to have enough percent impedance %IX in order to limit a fault current in the power system at the time of a short circuit accident. It is not easy at the present technical level for HTS transformers wound with Bi-2223/Ag tapes to secure enough percent impedance due to low air gap fields. The design targets are a percent impedance of 7.5%, an air gap flux density of 0.3 T, tape current density of about 40 A/mm 2 , winding strain of about 0.5% and AC losses of about 0.3 W/km A.