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961.
Yazan Al-ZainYosuke Sato Hee Young Kim Hideki HosodaTae Hyun Nam Shuichi Miyazaki 《Acta Materialia》2012,60(5):2437-2447
The effect of room temperature (RT) aging on the superelasticity of Ti-Nb-Mo-based superelastic alloys is investigated. The results show that annealing at relatively low temperatures such as 973 K after severe cold rolling results in poor resistance to the effect of RT aging. The transformation stress increases considerably due to the formation of an isothermal ω phase at RT. Addition of Sn is partially effective in suppressing the RT aging effect in the specimens annealed at 973 K. The RT aging effect is suppressed by increasing the annealing temperature, due to the annihilation of lattice defects or non-equilibrium vacancies introduced during cold rolling, which are responsible for accelerating the diffusion process, however, superelasticity is reduced by annealing at higher temperatures, due to a decrease in the critical stress for slip deformation (σCSS). The specimen annealed at 1173 K followed by aging at 773 K exhibits stable superelasticity with a high resistance to the effect of RT aging. Annealing at 1173 K causes the annihilation of lattice defects or non-equilibrium vacancies, while aging at 773 K induces precipitation of the α phase, which in turn causes an increase in σCSS, and further enhances the resistance to the RT aging effect by enriching the matrix with β-stabilizing elements. 相似文献
962.
Baek Hyun Kim Jong Hoon Park Byungkyu Kim Do-Kyun Kwon 《Metals and Materials International》2012,18(6):1067-1072
Liquid phase sintering of lead zirconate titanate (abbreviated as PZT) ceramics with a 0.78 PbO-0.22 CuO (10:1 in weight ratio) flux was investigated. A small amount sintering flux consisting of a stoichiometrically mixed oxide of PbO-CuO with a eutectic composition successfully accelerated densification of the PZT ceramics far below the conventional sintering temperature. With the 3 wt% flux additions, full densifications of the PZT ceramics were achieved at temperatures as low as 825 °C. The results obtained in the crystal structure, microstructure, and electrical property analyses suggest that the Cu2+ impurity ion substitutes as an acceptor center for the perovskite B-site without forming isolated secondary phases. Defect associates of the Cu2+ impurities and charge compensating oxygen vacancies appear to affect dielectric and piezoelectric properties of the sintered PZT samples in both positive and negative ways by forming defect dipoles. When the Cu2+ content is small, slightly improved dielectric and piezoelectric performances were achieved, though ferroelectric relaxation was obviously developed at the higher Cu2+ contents. For the PZT samples sintered at 825 °C with 3 wt% flux addition, relative dielectric permittivity was 2200 and dielectric loss was less than 2%. Remnant polarization, coercive fields, and piezoelectric coefficient (d33) were 32 μC/cm2, 8.9 kV/cm and 373 pC/N, respectively. 相似文献
963.
Nam Suk Lim Chan Woo Bang Sanjeev Das Hyun Woo Jin Raghavan Ayer Chan Gyung Park 《Metals and Materials International》2012,18(1):87-94
In the present study, the influence of tempering temperature on the microstructural evolution and prior austenite grain boundary
segregation of AISI 4340 steels was investigated by transmission electron microscope and atom probe. The transmission electron
microscopy results showed a variation in the microstructure and the morphology of carbides with a change in tempering temperature.
Additionally, the chemical compositions of the prior austenite grain boundaries and carbides were quantified by atom probe
tomography. An increase in the tempering temperature led to a decrease in the amount of carbon segregated at the prior austenite
grain boundary from 7.9 to 1.3 at.%. It was found that a higher tempering temperature can accelerate the diffusion of carbon
from the prior austenite grain boundary into carbide. However, phosphorus atoms were segregated mainly at the prior austenite
grain boundary in steel tempered at 400°C (up to 0.18 at.%). It was found that formation of film-like carbide and phosphorus
segregation along the prior austenite grain boundary is the main cause of embrittlement in steel tempered at 400°C. 相似文献
964.
We propose a new method for performing in-channel electrochemical detection under a high electric field using a polyelectrolytic gel salt bridge (PGSB) integrated in the middle of the electrophoretic separation channel. The finely tuned placement of a gold working electrode and the PGSB on an equipotential surface in the microchannel provided highly sensitive electrochemical detection without any deterioration in the separation efficiency or interference of the applied electric field. To assess the working principle, the open circuit potentials between gold working electrodes and the reference electrode at varying distances were measured in the microchannel under electrophoretic fields using an electrically isolated potentiostat. In addition, "in-channel" cyclic voltammetry confirmed the feasibility of electrochemical detection under various strengths of electric fields (~400 V/cm). Effective separation on a microchip equipped with a PGSB under high electric fields was demonstrated for the electrochemical detection of biological compounds such as dopamine and catechol. The proposed "in-channel" electrochemical detection under a high electric field enables wider electrochemical detection applications in microchip electrophoresis. 相似文献
965.
For the rapid multiplex analysis of pathogens, 16S rRNAs from cell lysates were directly applied onto a DNA microarray at room temperature (RT) for RNA-DNA hybridization. To eliminate the labeling step, seven fluorescent-labeled detector probes were cohybridized with 16S rRNA targets and adjacent specific capture probes. We found that eight pathogens were successfully discriminated by the 16S rRNA-based direct method, which showed greater specificity than the polymerase chain reaction (PCR)-labeled method due to chaperone and distance effects. A new specificity criterion for a perfect match between RNA and DNA was suggested to be 21-41% dissimilarity using correlation analysis between the mismatch and the sequence according to the guanine-cytosine (GC) percentage or the distribution of mismatches. Six categories of food matrix (egg, meat, milk, rice, vegetable, and mixed) were also tested, and the target pathogen was successfully discriminated within statistically significant levels. Finally, we found that the intrinsic abundance of 16S rRNA molecules successfully substituted PCR-based amplification with a low limit of detection of 10-10(3) cells mL(-1) and a high quantitative linear correlation. Collectively, our suggested 16S rRNA-based direct method enables the highly sensitive, specific, and quantitative analysis of selected pathogens at RT within 2 h, even in food samples. 相似文献
966.
K. K. Viswanathan Jang Hyun Lee Zainal Abdul Aziz I. Hossain Wang Rongqiao H. Y. Abdullah 《Journal of Engineering Mathematics》2012,76(1):139-156
Free vibration of symmetric and antisymmetric cross-ply composite laminated truncated conical shells using the spline function technique is studied. The equilibrium equations for a truncated conical shells are formulated including first-order shear deformation theory. The equations of motion are derived in terms of displacement functions and rotational functions using stress–strain and strain–displacement relationships. The coupled differential equations are solved using Bickley-type splines to obtain the generalized eigenvalue problem by combining suitable boundary conditions. The convergence and comparative results are presented. Both symmetric and anti-symmetric cross-ply shells are considered using various types of material properties. Parametric studies are made to investigate the effect of transverse shear deformation on the frequency parameter with respect to the thickness ratio, length ratio, cone angle, and circumferential mode number using different numbers of layers under various types of boundary conditions. 相似文献
967.
Jae-ha Myung Hyun Jun Ko Hae-Gu Park Moon Hwan Sang-Hoon Hyun 《International Journal of Hydrogen Energy》2012,37(1):498-504
In this study, solid oxide fuel cells (SOFCs) consisting of a NiO-YSZ anode, a NiO/YSZ-YSZ functional layer, YSZ electrolyte and a (La0.8Sr0.2)MnO3 + yttria-stabilized zirconia (LSM-YSZ) cathode were fabricated by tape-casting, lamination, and a co-firing process. NiO/YSZ-YSZ nano-composite powder was synthesized for the anode functional layer via the Pechini process in order to improve cell performance. After optimization of the slurries for the anode functional anode, electrolyte and cathode, all components were casted so as to fabricate the monolithic laminate. The co-firing temperature was optimized to minimize second phase formation between the (La0.8Sr0.2)MnO3 (LSM) and yttria-stabilized zirconia (YSZ) and to increase the sinterability of the YSZ electrolyte. The YSZ electrolyte was fully sintered with the addition of 0.5 wt% CuO, and the second phases of La2Zr2O7 and SrZrO3 did not form at 1350 °C. Ni-YSZ anode-supported unit cells were fabricated by co-firing at 1250-1400 °C. The unit cells co-fired at 1250 °C, 1300 °C, 1325 °C, 1350 °C and 1400 °C had maximum power densities of 0.18, 0.18, 0.30, 0.46 and 0.036 W/cm2, respectively, in humidified hydrogen (∼3% H2O) and air at 800 °C. 相似文献
968.
Seong-Ho Baek Bum-Young Noh Jang-Kyoo Shin Jae Hyun Kim 《Journal of Materials Science》2012,47(9):4138-4145
We introduce a new type of silicon micro-wire (SiMW) solar cell with a conformal zinc oxide (ZnO) nanorods anti-reflection
coating (ARC) and discuss the optical and photovoltaic properties of the SiMW solar cells with controlled ZnO nanorods. The
fabrication processes were composed of metal-assisted electroless etching combined with photolithography, spin-on-dopant diffusion,
and hydrothermal synthesized ZnO nanorods growth. We found that the combination of Si wire geometry and ZnO ARC was able to
maximize the light absorption and to minimize the light reflectance. Illuminated current–voltage (I–V) results show that the photovoltaic efficiency of SiMW solar cells with optimized ZnO ARC was enhanced more than 50% and
the short-circuit current density was improved by over 43% compared to SiMW solar cells without ZnO ARC. This is mainly attributed
to the reduced light reflectance and enhanced photon absorption. These hybrid structures are promising for making low-cost
Si wire solar cells and making them applicable to photovoltaic devices with large areas. 相似文献
969.
Wanwan Xia Xiaojie Wang Zuoling Fu Shihong Zhou Siyuan Zhang Jung Hyun Jeong 《Materials Research Bulletin》2012,47(9):2535-2540
The orthorhombic and monoclinic Gd2(MoO4)3:Dy3+ were successfully synthesized by a hydrothermal process with a subsequent annealing treatment at 800 °C for 4 h. The crystal phase of Gd2(MoO4)3:Dy3+ was controlled as a function of the pH value of the solution. The crystallization and microstructures of the samples were characterized by Powder X-ray diffraction (XRD) and scanning electron micrograph (SEM). Furthermore, the optical properties were investigated by the diffuse reflection, excitation and emission spectra. The mechanisms of different crystal phases affected on the luminescence properties of Gd2(MoO4)3:Dy3+ were discussed. The electric dipole–dipole interaction between Dy3+ ions was identified as the main mechanism for the concentration quenching of the two structures. Finally, the chromatic natures of all the samples were analyzed in detail. The results indicate that the orthorhombic phosphor Gd1.84(MoO4)3:Dy0.163+ can be considered as a suitable candidate for white light emitting diodes (W-LEDs). 相似文献
970.
Wei Hu Yong Choi Key Jo HongJihoon Kang Jin Ho JungYoun Suk Huh Hyun Keong LimSang Su Kim Byung-Tae KimYonghyun Chung 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2012,664(1):370-375
Currently, for most photomultiplier tube (PMT)-based PET systems, constant fraction discriminators (CFD) and time to digital converters (TDC) have been employed to detect gamma ray signal arrival time, whereas anger logic circuits and peak detection analog-to-digital converters (ADCs) have been implemented to acquire position and energy information of detected events. As compared to PMT the Geiger-mode avalanche photodiodes (GAPDs) have a variety of advantages, such as compactness, low bias voltage requirement and MRI compatibility. Furthermore, the individual read-out method using a GAPD array coupled 1:1 with an array scintillator can provide better image uniformity than can be achieved using PMT and anger logic circuits. Recently, a brain PET using 72 GAPD arrays (4×4 array, pixel size: 3 mm×3 mm) coupled 1:1 with LYSO scintillators (4×4 array, pixel size: 3 mm×3 mm×20 mm) has been developed for simultaneous PET/MRI imaging in our laboratory. Eighteen 64:1 position decoder circuits (PDCs) were used to reduce GAPD channel number and three off-the-shelf free-running ADC and field programmable gate array (FPGA) combined data acquisition (DAQ) cards were used for data acquisition and processing. In this study, a free-running ADC- and FPGA-based signal processing method was developed for the detection of gamma ray signal arrival time, energy and position information all together for each GAPD channel. For the method developed herein, three DAQ cards continuously acquired 18 channels of pre-amplified analog gamma ray signals and 108-bit digital addresses from 18 PDCs. In the FPGA, the digitized gamma ray pulses and digital addresses were processed to generate data packages containing pulse arrival time, baseline value, energy value and GAPD channel ID. Finally, these data packages were saved to a 128 Mbyte on-board synchronous dynamic random access memory (SDRAM) and then transferred to a host computer for coincidence sorting and image reconstruction. In order to evaluate the functionality of the developed signal processing method, energy and timing resolutions for brain PET were measured via the placement of a 6 μCi 22Na point source at the center of the PET scanner. Furthermore the PET image of the hot rod phantom (rod diameter: from 2.5 mm to 6.5 mm) with activity of 1 mCi was simulated, and then image acquisition experiment was performed using the brain PET. Measured average energy resolution for 1152 GAPD channels and system timing resolution were 19.5% (FWHM%) and 2.7 ns (FWHM), respectively. With regard to the acquisition of the hot rod phantom image, rods could be resolved down to a diameter of 2.5 mm, which was similar to simulated results. The experimental results demonstrated that the signal processing method developed herein was successfully implemented for brain PET. This reduced the complexity, cost and developing duration for PET system relative to normal PET electronics, and it will obviously be useful for the development of high-performance investigational PET systems. 相似文献