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排序方式: 共有898条查询结果,搜索用时 109 毫秒
721.
Kazuki Maruhashi Kei S. Takahashi Mohammad Saeed Bahramy Sunao Shimizu Ryosuke Kurihara Atsushi Miyake Masashi Tokunaga Yoshinori Tokura Masashi Kawasaki 《Advanced materials (Deerfield Beach, Fla.)》2020,32(24):1908315
Magnetic semiconductors are a vital component in the understanding of quantum transport phenomena. To explore such delicate, yet fundamentally important, effects, it is crucial to maintain a high carrier mobility in the presence of magnetic moments. In practice, however, magnetization often diminishes the carrier mobility. Here, it is shown that EuTiO3 is a rare example of a magnetic semiconductor that can be desirably grown using the molecular beam epitaxy to possess a high carrier mobility exceeding 3000 cm2 V−1 s−1 at 2 K, while intrinsically hosting a large magnetization value, 7 μB per formula unit. This is demonstrated by measuring the Shubnikov–de Haas (SdH) oscillations in the ferromagnetic state of EuTiO3 films with various carrier densities. Using first-principles calculations, it is shown that the observed SdH oscillations originate genuinely from Ti 3d-t2g states which are fully spin-polarized due to their energetical proximity to the in-gap Eu 4f bands. Such an exchange coupling is further shown to have a profound effect on the effective mass and fermiology of the Ti 3d-t2g electrons, manifested by a directional anisotropy in the SdH oscillations. These findings suggest that EuTiO3 film is an ideal magnetic semiconductor, offering a fertile field to explore quantum phenomena suitable for spintronic applications. 相似文献
722.
Biodiesel fuel has become more attractive recently because of its environmental benefits and the fact that it is a product made from renewable resources. However the less favorable cold flow properties or the low temperature operability of biodiesel fuel compared to conventional diesel is a major drawback limiting its use. The poor flow properties of biodiesel at cold temperatures are mainly due to biodiesel fuel being composed of long-chain fatty acids with an alcohol molecule attached. If the double bond of unsaturated fatty acids in these long-chain fatty acids could be ruptured selectively, then the cold flow properties of biodiesel fuel would be enhanced by reducing its viscosity.In this study, the selective hydrothermal oxidation of oleic acid, as a model compound of unsaturated high molecular weight carboxylic acids, was studied experimentally. The objective was to use this as a model to investigate whether the double bond of unsaturated fatty acids can be ruptured selectively by partial hydrothermal oxidation. Demonstration of this method could then be used to show the potential to improve the cold flow properties of biodiesel. Results showed that the amount of mono-carboxylic acids, aldehyde, di-carboxylic acids, and aldehyde-acids with a carbon number of 9 was significantly higher than other oxidative products. This suggests that the oxidative cleavage may principally occur at the double bond in hydrothermal conditions. The cloud and pour points for biodiesel fuel (B100) and B100 blend with a mixture of methyl esters or acetals were measured. These are the most important indicators for the cold flow properties of biodiesel fuel. The methyl esters or acetals used were made from the esterification of carboxylic acids or aldehydes by simulating the major oxidation products. These were obtained from the hydrothermal oxidation of oleic acid at different oxygen supply rates. Results showed that the cloud and pour points of the blend were significantly enhanced compared to those of B100. 相似文献
723.
Aluminum (Al) matrix composite materials reinforced with carbon nanotubes (CNT) and silicon carbide nanoparticles (nano-SiC) were fabricated by mechanical ball milling, followed by hot-pressing. Nano-SiC was used as an active mixing agent for dispersing the CNTs in the Al powder. The hardness of the produced composites was dramatically increased, up to eight times higher than bulk pure Al, by increasing the amount of nano-SiC particles. A small quantity of aluminum carbide (Al(4)C(3)) was observed by TEM analysis and quantified using x-ray diffraction. The composite with the highest hardness values contained some nanosized Al(4)C(3). Along with the CNT and the nano-SiC, Al(4)C(3) also seemed to play a role in the enhanced hardness of the composites. The high energy milling process seems to lead to a homogeneous dispersion of the high aspect ratio CNTs, and of the nearly spherical nano-SiC particles in the Al matrix. This powder metallurgical approach could also be applied to other nanoreinforced composites, such as ceramics or complex matrix materials. 相似文献
724.
Shunichi Nakamura Toshitsugu Kawasaki 《Journal of Constructional Steel Research》2009,65(8-9):1705-1711
A numerical method is proposed to predict the lateral girder response induced by pedestrians on footbridges. The method is based on the motion of equations including the coefficients of the rate of a pedestrian’s lateral force, pedestrian density, rate of synchronized pedestrians, and pedestrians’ attitude to large vibration amplitude. These coefficients were determined by the field measured data of two slender footbridges and the experimental data of pedestrian induced forces. The lateral girder responses were then predicted for these bridges with different pedestrian densities by the proposed numerical method. They agreed reasonably well with the field measured girder responses of these bridges, which verified the proposed prediction method. 相似文献
725.
Naohiro Nakamura Naohiko Tsunashima Tomio Nakano Eizaburo Tachibana 《Engineering Structures》2009,31(4):999-1009
An analytical study using the nonlinear finite-element method was conducted for reinforced concrete shear wall tests under cyclic loading to estimate the damage from the aspect of energy consumption. First, the validity of the analytical method was confirmed by studying the load–displacement relationship, the condition of the cracking, and a comparison between the total strain energy of the analysis and the loaded energy of the test. Next, the distribution of the energy consumption was investigated, and the division between rebars and concrete was studied. It was determined that energy consumption is an effective method for estimating damage of shear walls. 相似文献
726.
Megumi Kawasaki Roberto B. Figueiredo Terence G. Langdon 《Journal of Materials Science》2012,47(22):7719-7725
The processing of disks by high-pressure torsion leads to an inhomogeneous distribution in strain with a high strain around the perimeter of the disk and a zero strain in the center. Despite this apparent inhomogeneity, there are now many experiments showing that the hardness values on the surfaces of disks gradually evolve with increasing strain to give a reasonably high level of homogeneity. Experiments were conducted to determine whether this high level of homogeneity extends also through the thickness of the disks or whether inhomogeneities occur in the axial direction. Results are presented for high-purity aluminum and a magnesium AZ31 alloy as two representative materials showing different hardness characteristics. 相似文献
727.
Operational stability enhancement of white OLEDs with single solution‐processed emitting layer fabricated by “self‐layered technique”
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Sukekazu Aratani Hirotaka Sakuma Motoko Harada Hironori Wakana Shunichiro Nobuki Masahiro Kawasaki 《Journal of the Society for Information Display》2015,23(6):273-276
Abstract — We achieved operationally stable white OLEDs with a single solution processed EML fabricated using a self‐layered technique. An LT70 of 10 khr at an initial luminance of 1000 cd/m2 was obtained by suppressing the exciplex formation between the EML and ETL, preventing Li diffusion into the EMLs, and using red dopants with shallow LUMO levels and stable host materials. 相似文献
728.
We obtained room-temperature red emission from GaN-based light-emitting diodes (LEDs) using a Eu-doped GaN (GaN:Eu) as an active layer. The bright emission was observed under normal lighting condition, which is associated with the intra-4f shell transition of Eu3+ ions. The LED properties depends on the growth condition of GaN:Eu layer. Since the high-quality GaN can be grown at higher growth pressure, the intense electroluminescence (EL) was observed in the LED with a GaN:Eu active layer grown at atmospheric pressure, which is due to the enhancement of the energy transfer efficiency from the GaN host material to the Eu ions. At a d.c. current of 20 mA, the light output power and external quantum efficiency were 17 μW and 0.04%, respectively. These results indicate the feasibility of GaN:Eu to realize a GaN-based red emitter for fabrication of nitride-based monolithic optical devices. 相似文献
729.
Grain Boundary Phenomena in an Ultrafine‐Grained Al–Zn Alloy with Improved Mechanical Behavior for Micro‐Devices
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730.
To improve the unconfined compressive strength (UCS) of a novel chemical grout composed of a calcium phosphate compound (CPC-Chem), we performed UCS tests and scanning electron microscopy (SEM) observations on sand test pieces cemented with CPC-Chem and four kinds of powders (tricalcium phosphate, TCP; magnesium phosphate, MgP; calcium carbonate, CC and magnesium carbonate, MgC) as seed crystals. The UCS of the CPC-Chem test pieces cemented with TCP and CC was significantly greater than that of the test pieces with no added powders. The UCS of the test pieces with TCP and CC additives exceeded the targeted value of 100 kPa and increased to a maximum of 261.4 kPa and 209.7 kPa for the test pieces with TCP and CC additives, respectively. Furthermore, the UCS of test pieces with 1 wt% or 5 wt% TCP and 1 wt% CC additives was maintained at a level exceeding 200 kPa for 168 days. SEM observations revealed net-like and three-dimensional structures in segments of test pieces cemented with 1 wt% or 5 wt% TCP and 1 wt% CC in CPC-Chem, which could have been the reason of the long-term stability of UCS (over 200 kPa for 168 days) observed in this study. These results suggest that the addition of TCP and CC significantly enhances the ground improvement afforded by CPC-Chem. 相似文献