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181.
Jung Woo Lee Ravindranath Viswan Yoon Jeong Choi Yeob Lee Se Yun Kim Jaehun Cho Younghun Jo Jeung Ku Kang 《Advanced functional materials》2009,19(14):2213-2218
Using conventional methods to synthesize magnetic nanoparticles (NPs) with uniform size is a challenging task. Moreover, the degradation of magnetic NPs is an obstacle to practical applications. The fabrication of silica‐shielded magnetite NPs on carbon nitride nanotubes (CNNTs) provides a possible route to overcome these problems. While the nitrogen atoms of CNNTs provide selective nucleation sites for NPs of a particular size, the silica layer protects the NPs from oxidation. The morphology and crystal structure of NP–CNNT hybrid material is investigated by transmission electron microscopy (TEM) and X‐ray diffraction. In addition, the atomic nature of the N atoms in the NP–CNNT system is studied by near‐edge X‐ray absorption fine structure spectroscopy (nitrogen K‐edge) and calculations of the partial density of states based on first principles. The structure of the silica‐shielded NP–CNNT system is analyzed by TEM and energy dispersive X‐ray spectroscopy mapping, and their magnetism is measured by vibrating sample and superconducting quantum interference device magnetometers. The silica shielding helps maintain the superparamagnetism of the NPs; without the silica layer, the magnetic properties of NP–CNNT materials significantly degrade over time. 相似文献
182.
While an equation of state (EOS) plays a critical role in estimating thermodynamic properties, employing it in the determination
of binary interaction parameters is extremely important. In general, these parameters can be determined from phase equilibrium
data. However, data collection from experiments is a time-consuming and tedious process. In this study, after measuring the
excess enthalpies of binary systems containing CO2 by high-pressure flow isothermal microcalorimetry (IMC), we determined the EOS binary interaction parameters, specifically,
the Peng-Robinson EOS binary interaction parameters. These binary interaction parameters obtained by IMC were compared with
those obtained by vapor-liquid equilibrium (VLE) experiments. Hence, high-pressure flow IMC appears to be an effective method
for the determination of interaction parameters that are used in the estimation of thermodynamic properties. Further, the
Flory-Huggins interaction parameters of a binary mixture CO2 containing with various mole compositions were also estimated by employing high-pressure IMC. 相似文献
183.
We investigate the physical parameters controlling the low-energy screening in carbon nanotubes via electron energy loss spectroscopy and inelastic X-ray scattering. Two plasmon-like features are observed, one near 9 eV (the so-called π plasmon) and one near 20 eV (the so-called π + σ plasmon). At large nanotube diameters, the π + σ plasmon energies are found to depend on the number of walls and not on the radius or chiral vector. The observed shift with number of walls indicates a change in the strength of the screening and in the effective interaction at inter-atomic distances; thus this result suggests a mechanism for tuning the properties of nanotubes. 相似文献
184.
Min Ku Jeon 《Electrochimica acta》2009,54(10):2837-2842
The effect of reduction conditions on a Pt28Ni36Cr36/C catalyst was investigated by using two different reduction methods: hydrogen reduction and NaBH4 reduction. In hydrogen reduced catalysts, dissolution of metallic Ni and Cr was observed during cyclic voltammetry (CV) tests, and a larger amount of Ni and Cr was dissolved when reduced at higher temperatures. For methanol electro-oxidation, the highest specific current density of 1.70 A m−2 at 600 s of the chronoamperometry tests was observed in the catalyst reduced at 300 °C, which was ∼24 times that of a Pt/C catalyst (0.0685 A m−2). In NaBH4 reduced catalysts, formation of an amorphous phase and a more Pt-rich surface was observed in X-ray diffraction and CV results, respectively, with increasing amounts of NaBH4. When reduced by 50 times of the stoichiometric amount of NaBH4, the PtNiCr/C catalyst (PtNiCr-50t) showed a current density of 34.1 A gnoble metal−1, which was 81% higher than the 18.8 A gnoble metal−1 value of a PtRu/C catalyst at 600 s of the chronoamperometry tests. After 13 h of chronoamperometry testing, the activity of the PtNiCr-50t (15.0 A gnoble metal−1) was 110% higher than the PtRu/C catalyst (7.15 A gnoble metal−1). The PtNiCr/C catalyst shows promise as a Ru-free methanol oxidation catalyst. 相似文献
185.
Composite photocatalysts of palladium oxide and nitrogen-doped titanium oxide (PdO/TiON) were synthesized by a sol–gel process, as convenient forms of nanopowder or immobilized powder on nanofiber. The PdO/TiON catalysts were tested for visible-light-activated photocatalysis using different bacterial indicators, including gram-negative cells of Escherichia coli and Pseudomonas aeruginosa, and gram-positive cells of Staphylococcus aureus. Disinfection data indicated that PdO/TiON composite photocatalysts have a much better photocatalytic activity than either palladium-doped (PdO/TiO2) or nitrogen-doped titanium oxide (TiON) under visible-light illumination. The roles of Pd and N were discussed in terms of the production and separation of the charge carriers under visible-light illumination. The photocatalytic activity was thus dependent on dopants and light intensity. Microscopic characterization demonstrated that visible-light photocatalysis on PdO/TiON caused drastic damage on the bacteria cell wall and the cell membrane. 相似文献
186.
The decomposition of 2-chlorophenol by UV/TiO2 process with the application of external bias voltage was examined in this study. Experiments were conducted in a batch reactor using TiO2-coated titanium sheet as anode and platinum sheet as cathode. The anode photocatalysis of 2-chlorophenol was totally inhibited for experiments conducted with the application of external anodic bias voltage lower than the flat band potential of TiO2. The decomposition rate of 2-chlorophenol was then increased with increasing external anodic bias voltage applied up to 0.0 V (versus SCE). The application of external bias voltage higher than 1.0 V did not markedly promote the photocatalysis of 2-chlorophenol possibly because the photocurrent induced was constant. Experimental results indicated that the decomposition of 2-chlorophenol was more effective for experiments conducted in acidic solutions due to the lower flat band potential of TiO2 and the higher photocurrent induced. The presence of electron scavengers in aqueous solution, such as oxygen molecules, may increase the decomposition rate of 2-chlorophenol. However, the effect of dissolved oxygen was diminished for experiments conducted with applied external bias voltage. The photocatalytic decomposition rate of 2-chlorophenol was enhanced linearly with the increasing UV light intensity when the external bias voltage was applied. 相似文献
187.
188.
In this research, we showed that the different stress buffer configurations in the analog device will change the magnitude of the mechanical stress effect on the device surface, which will cause the variation in the output voltage characteristic of the device as well. And, the experimental results reveal that the different stress buffer configurations provide the difference of the mechanical stress resistance capability on the LDO (Low Drop Out) analog device. The stress buffer structure can reduce the stress effect to the LDO analog device effectively, i.e., the variation of the output voltage character of the LDO analog device will be larger if there is no stress buffer structure on the LDO analog device. Our results could be a reference for the design of an analog device and its packaging to improve the performance of the analog device. 相似文献
189.
Yung-Hsien Wu Chih-Ming Chang Chun-Yao Wang Chien-Kang Kao Chia-Ming Kuo Ku A. Tensor Huang 《Electron Device Letters, IEEE》2008,29(2):149-151
Owing to the delayed introduction of high-kappa storage dielectric for trench DRAM, a new technology to extend the existing NO storage dielectric becomes a prerequisite. For trench DRAM, the nitride film of NO-based storage dielectric has been proved to possess higher quality by proper treatment, which enables further reduction in nitride thickness and extension of scaling limit for the existing storage dielectric. A 164% leakage current improvement without sacrificing the cell capacitance can be achieved through this process, while keeping the outstanding reliability performance of less than 438 ppm failure rate after a ten-year operation. Most importantly, this new process can be fully integrated into incumbent furnace process, which means that no additional tool investment is required, and it is crucial for trench DRAM manufacturers to maintain their competitive advantage before the high-k material prevails at 65 nm technology node. 相似文献
190.
Multi-cell uplink-downlink beamforming throughput duality based on Lagrangian duality with per-base station power constraints 总被引:1,自引:0,他引:1
Janghoon Yang Dong Ku Kim 《Communications Letters, IEEE》2008,12(4):277-279
Despite significant research efforts in beamforming, the maximum achievable downlink throughput with beamforming in a multi-cell environment is not available due to difficulty in finding optimal downlink beamforming. Thus, to reformulate the problem into a more solvable form, we derive dual uplink throughput optimization problem to multi-cell downlink beam- forming throughput maximization with per-base station (BS) power constraints based on Lagrangian duality. The optimal downlink beamforming is shown to be a minimum mean squared error (MMSE) beamforming in the dual uplink. It is also shown that the dual uplink problem achieves the same optimal throughput as the primal downlink problem. 相似文献