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排序方式: 共有5005条查询结果,搜索用时 484 毫秒
901.
Taeseon Hwang Joon Suk Oh Jung-Pyo Hong Gi-Yong Nam Ah-Hyun Bae Sang-Ik Son Geun-Ho Lee Hak-Kyung Sung Youngkwan Lee Jae-Do Nam 《Carbon》2012,50(2):612-621
Few-layer graphene (FLG) was investigated as an electrically-conductive interleaf layer for one-step electroplating and patterning of metal on nonconductive polymer substrates without using multiple and toxic pretreatment processes in traditional electroplating. An individual FLG (5–10 nm of thickness with 6.4% of oxygen content) was obtained by expanding graphite with microwave followed by exfoliating the expanded graphite with sonication in N-methyl-pyrrolidone. Stacking FLG in the in-plane direction, a robust FLG film was obtained by the vacuum-assisted filtering and drying methods, and transferred to a polyethylene terephthalate (PET) substrate via an intermediate transfer to the water surface. The sheet resistance of the FLG film on the PET substrate was 0.9 kΩ/sq with a thickness of 80 nm and the root-mean-square roughness of 29 nm. In the electroplating of nickel on the FLG film, hemisphere-shape metal seeds appeared in the early stage of electroplating and they subsequently grew up to 200–480 nm, which became connected to form a continuous nickel layer. The thickness of the continuous nickel layer increased linearly with electroplating time. The developed electroplating method demonstrated its capability of selective patterning on nonconductive substrates using a simple masking technique. 相似文献
902.
Tae-Jun Ko Eun Kyu Her Bongsu Shin Ho-Young Kim Kwang-Ryeol Lee Bo Ki Hong Sae Hoon Kim Kyu Hwan Oh Myoung-Woon Moon 《Carbon》2012,50(14):5085-5092
We have explored the condensation behavior of water on a superhydrophobic carbon fiber (CF) network with high-aspect-ratio hair-like nanostructures. Nanostructures ranging from nanopillars to hairy shapes were grown on CFs by preferential oxygen plasma etching. Superhydrophobic CF surfaces were achieved by application of a hydrophobic siloxane-based hydrocarbon coating, which increased the water contact angle from 147° to 163° and decreased the contact angle hysteresis from 71° to below 5°, sufficient to cause droplet roll-off from the surface. Water droplet nucleation and growth on the superhydrophobic CF were significantly retarded due to the high-aspect-ratio nanostructures under super-saturated vapor conditions. CFs are observed to wet with condensation between fibers of the pristine surface under super-saturated vapor conditions, which eventually leads to flooding. However, dropwise condensation became dominant in the superhydrophobic CF network, allowing for easy removal of the condensed droplets, which largely allowed the interstitial spaces of the fiber network to remain dry. It is implied that superhydrophobic CF can provide a passage for vapor or gas flow in wet environments such as a gas diffusion layer requiring the effective water removal in the operation of proton exchange membrane fuel cell. 相似文献
903.
Polyaniline (PANI)/activated carbon (AC) composites are prepared by in situ emulsion polymerization using dodecyl benzenesulfonic acid (DBSA). DBSA can play a role as both surfactant and dopant in the process of PANI synthesis. The effect of DBSA on the preparation of PANI/AC composites is investigated in this research. For this purpose, the composites are prepared in micellar solutions with various concentrations of DBSA. It is confirmed using X-ray diffraction (XRD) analysis and Fourier-transform IR (FT-IR) spectroscopy that DBSA actually participates in the PANI doping process. The PANI doped with DBSA (DBSA-PANI) covering the AC surfaces is observed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical properties of the composites are studied by cyclic voltammetry (CV). The composites show different values of specific capacitance, which was found to be a function of DBSA concentration. The composite prepared in 0.045 M DBSA solution shows the highest specific capacitance (115.2 F g?1) among the prepared composites. The doping level of DBSA-PANI is increased with the concentration of DBSA in solution. 相似文献
904.
An optical emission spectrometer (OES) was designed and constructed to detect the absolute spectral radiant exitance of UV signatures for a wavelength range of 240 nm to 440 nm. Using a directly heated graphite black body furnace operating at a temperature of 3000 K, the spectral response of the OES in the UV range was calibrated. To evaluate the performance of the OES system, the emission spectra of molecules were measured in a butane flame and the absolute emissions of the UV signatures were calculated. The uncertainty of the absolute measurement of the UV signature was analyzed by considering various uncertainty budgets, and the total uncertainty of the OES was found to be 1.66 %. 相似文献
905.
Active and stable cobalt-based non-precious metal catalysts for the oxygen reduction reaction (ORR) in PEM fuel cells were
developed through high-temperature pyrolysis of metal-porphyrins supported on carbon. The roles of substituted porphyrins,
carbon support, and catalyst loading on ORR activity were studied using rotating disc electrode (RDE) measurements. It was
observed that the carbon support plays a major role in improving the catalytic activity. The results showed that among the
supported catalysts, the homemade mesocarbon-supported cobalt-porphyrin catalyst with 20 wt% loading displayed higher ORR
activity; the cell performance showed maximum current density of 1.1 A cm−2 at 0.13 V in H2/O2 fuel cells. 相似文献
906.
907.
Byung-Seung Yim Yumi Kwon Seung Hoon Oh Jooheon Kim Yong-Eui Shin Seong Hyuk Lee Jong-Min Kim 《Microelectronics Reliability》2012,52(6):1165-1173
This study investigated the effect of the viscosity of the ECAs using a low-melting-point alloy (LMPA) filler on its bonding characteristics. The curing behaviors of the ECAs were determined using Differential Scanning Calorimetry (DSC), and ECA temperature-dependant viscosity characteristics were observed using a torsional parallel rheometer. The wetting test was conducted to investigate the reduction capability of ECAs and the flow-coalescence-wetting behavior of the LMPAs in ECAs. Electrical and mechanical properties were determined and compared to those with commercial ECAs and eutectic tin/lead (Sn/Pb) solder. In the metallurgically interconnected Quad Flat Package (QFP) joint, a typical scallop-type Cu–Sn intermetallic compound (IMC) layer formed at the upper SnBi/Cu interface after curing process. On the other hand, a (Cu, Ni)6Sn5 IMC layer formed on the SnBi/ENIG interface. In addition, the fracture surface exhibited by cleavage fracture mode and the fracture was propagated along the Cu–Sn IMC/SnBi interface. The extremely low-level viscosity of ECAs had a significant influence on the flow-coalescence-wetting behavior of the LMPAs in ECAs and also on the interconnection properties. Stable interconnected assemblies showed good electrical and mechanical properties. 相似文献
908.
Regularized signal reconstruction for level-crossing sampling using Slepian functions 总被引:1,自引:0,他引:1
In this paper, we propose a method for efficient signal reconstruction from non-uniformly spaced samples collected using level-crossing sampling. Level-crossing (LC) sampling captures samples whenever the signal crosses predetermined quantization levels. Thus the LC sampling is a signal-dependent, non-uniform sampling method. Without restriction on the distribution of the sampling times, the signal reconstruction from non-uniform samples becomes ill-posed. Finite-support and nearly band-limited signals are well approximated in a low-dimensional subspace with prolate spheroidal wave functions (PSWF) also known as Slepian functions. These functions have finite support in time and maximum energy concentration within a given bandwidth and as such are very appropriate to obtain a projection of those signals. However, depending on the LC quantization levels, whenever the LC samples are highly non-uniformly spaced obtaining the projection coefficients requires a Tikhonov regularized Slepian reconstruction. The performance of the proposed method is illustrated using smooth, bursty and chirp signals. Our reconstruction results compare favorably with reconstruction from LC-sampled signals using compressive sampling techniques. 相似文献
909.
Lee JH Choi JG Kim YS Kim KR Kim SW Oh DK 《Journal of Bioscience and Bioengineering》2012,113(4):461-466
The optimal temperature and pH for retinal production using metabolically engineered Escherichia coli in a 7-l fermentor were found to be 30°C and 7.0, respectively. The agitation speed was a critical factor for retinal production. The optimal agitation speed was 400 rpm (oxygen transfer coefficient, k(L)a, = 92 1/h) in batch culture and 600 rpm (k(L)a=148 1/h) in a fed-batch culture of glycerol. Span 80 was selected as a surfactant for retinal production in metabolically engineered E. coli because Span 80 had proven the most effective for increased retinal production among the tested surfactants. Under the optimal conditions in the fed-batch culture with 5 g/l Span 80, the cell mass and the concentration, content, and productivity of retinal were 24.7 g/l, 600 mg/l, 24.3mg/g-cells, and 18 mg l(-1)h(-1) after 33 h, respectively. They were 1.2-, 2.7-, 2.3-, and 2.7-fold higher than those in the fed-batch culture without Span 80, respectively. The concentration and productivity of retinal in this study were the highest ever reported. The hydrophilic portion of Span 80 (sorbitan) did not affect cell growth and retinal production, but the hydrophobic portion (oleic acid) stimulated cell growth. However, oleic acid plus sorbitan did not stimulate retinal production. Thus, Span 80, as a linked compound of oleic acid and sorbitan produced by esterification, proved to be an effective surfactant for the enhancement of retinal production. 相似文献
910.
In Advanced Television Systems Committee (ATSC) terrestrial digital television (DTV) systems, additional very low‐rate data can be transmitted by modulating the amplitude and polarity of the transmitter identification (TxID) signal. Although the additional data transmission scheme offers reliable transmission and has a very large coverage area, it has a limitation on the data rate. In this paper, we propose a novel additional data transmission scheme based on the TxID sequences of the ATSC DTV system and Walsh modulation. The proposed scheme not only increases the data rate significantly, but also offers a virtually identical coverage area compared to a conventional scheme. 相似文献