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51.
Porous carbon beads were prepared by carbonizing at 700 and 1000 °C under N2 (NN-series) or CO2 atmospheres (CO-series) and a subsequent oxidization with boiling nitric acid solution (13%, v/v) for 3 h (ANN- and ACO-series). BET surface area of both CO- and NN-series samples tends to increase with increasing carbonization temperature, but CO-series samples show higher BET surface areas (700 °C: 610 m2/g, 1000 °C: 780 m2/g) compared with those of NN-series samples (700 °C: 380 m2/g, 1000 °C: 580 m2/g). After acid oxidation, BET surface areas of NN-series samples increased from 580 to 650 m2/g, whereas those of CO-series samples decreased from 780 to 600 m2/g. On subsequent acid oxidation, acidic surface functional groups increased in both CO- and NN-series samples, but the CO-series samples tend to have much more acidic surface functional groups. Adsorption of halogenated methanes, such as tetra-, tri- and dichloromethanes, onto the samples of CO-, NN-, ACO- and ANN-series was thought to be driven initially by the basicity, but the acidic functional groups that could attract adsorbates via dipole-dipole interaction might hinder the adsorption of subsequently incoming adsorbates. 相似文献
52.
The effects of potassium on the catalytic behavior in CO hydrogenation over K-promoted Fe/carbon catalysts having low K/Fe
ratios were investigated. Even though the doses of potassium were low the promotional effects were pronounced, especially
on the olefin-to-paraffin ratio, and theC
3
toC
4
olefin selectivities of the K-promoted catalysts were as high as 51 to 66 mol%. Over the catalysts having no or low potassium
content the olefin-to-paraffin ratio and the ratio of the CO2 formation rate to the rate of CO conversion to hydrocarbons remained roughly the same regardless of temperature, while over
the K-promoted catalysts having higher potassium content they increased with temperature. Formation of significant amounts
of filamentous carbon was observed in the K-promoted catalysts; however, the carbon deposition did not appear to affect the
inherent activity and selectivity of the K-promoted catalysts. 相似文献
53.
Yanyan Dai Suk Gyu Lee 《International Journal of Control, Automation and Systems》2014,12(5):1077-1089
This paper deals with the problem of formation control for nonholonomic mobile robots under a cluttered environment. When the obstacles are not detected, the follower robot calculates its waypoint to track, based on the leader robot’s state. The proposed geometric obstacle avoidance control method (GOACM) guarantees that the robot avoids the static and dynamic obstacles using onboard sensors. Due to the difficulty for the robot to simultaneously get overall safe boundary of an obstacle in practice, a safe line, which is perpendicular to the obstacle surface, is used instead of the safe boundary. Since GOACM is executed to find a safe waypoint for the robot, GOACM can effectively cooperate with the formation control method. Moreover, the adaptive controllers guarantee that the trajectory and velocity tracking errors converge to zero with the consideration of the parametric uncertainties of both kinematic and dynamic models. Simulation and experiment results present that the robots effectively form and maintain formation avoiding the obstacles. 相似文献
54.
Ki Soo ParkMyung Hun Cho Sang Ho ParkKee Suk Nahm Yang Kook SunYun Sung Lee Masaki Yoshio 《Electrochimica acta》2002,47(18):2937-2942
Layered Li0.7[M1/6Mn5/6]O2 (M=Li, Ni) was synthesized using a sol-gel method. P2-Na0.7[M1/6Mn5/6]O2 precursor was first synthesized by a sol-gel method, and then O2-Li0.7[M1/6Mn5/6]O2 was prepared by an ion exchange of Li for Na in P2-Na0.7[M1/6Mn5/6]O2 precursor. From charge/discharge curves, it was seen that Li0.7[Li1/6Mn5/6]O2 has two plateaus similar to those observed from a spinel structure, but Li0.7[Ni1/6Mn5/6]O2 holds a single plateau as observed from a typical layered structure. It was considered that Li0.7[Li1/6Mn5/6]O2 undergoes a phase transformation from layered to spinel structure during the charge/discharge cycle, but Li0.7[Ni1/6Mn5/6]O2 maintains O2-layered structure after the cycles. Li0.7[Ni1/6Mn5/6]O2 was higher in discharge capacity and retention rate than Li0.7[Li1/6Mn5/6]O2. 相似文献
55.
Novel polyimides were synthesized from 1‐[3′,5′‐bis(trifluoromethyl)phenyl] pyromellitic dianhydride (6FPPMDA) by a conventional two‐step process: the preparation of poly(amic acid) followed by solution imidization via refluxing in p‐chlorophenol. The diamines used for polyimide synthesis included bis(3‐aminophenyl)‐3,5‐bis(trifluoromethyl)phenyl phosphine oxide, bis(3‐aminophenyl)‐4‐trifluoromethylphenyl phosphine oxide, and bis(3‐aminophenyl)phenyl phosphine oxide. The synthesized polyimides were designed to have a molecular weight of 20,000 g/mol by off‐stoichiometry and were characterized by Fourier transform infrared, NMR, differential scanning calorimetry, and thermogravimetric analysis. In addition, their intrinsic viscosity, solubility, water absorption, and coefficient of thermal expansion (CTE) were also measured. The adhesion properties of the polyimides were evaluated via a T‐peel test with bare and silane/Cr‐coated Cu foils, and the failure surfaces were investigated with scanning electron microscopy. The 6FPPMDA‐based polyimides exhibited high glass‐transition temperatures (280–299°C), good thermal stability (>530°C in air), low water absorption (1.46–2.16 wt %), and fairly low CTEs (32–40 ppm/°C), in addition to good adhesion properties (83–88 g/mm) with silane/Cr‐coated Cu foils. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1801–1809, 2005 相似文献
56.
Eun-Yong Ko Eun Duck Park Kyung Won Seo Hyun Chul Lee Doohwan Lee Soonho Kim 《Korean Journal of Chemical Engineering》2006,23(2):182-187
Selective CO oxidation in the presence of excess hydrogen was studied over supported Pt catalysts promoted with various transition
metal compounds such as Cr, Mn, Fe, Co, Ni, Cu, Zn, and Zr. CO chemisorption, XRD, TPR, and TPO were conducted to characterize
active catalysts. Among them, Pt-Ni/γ-Al2O3 showed high CO conversions over wide reaction temperatures. For supported Pt-Ni catalysts, Alumina was superior to TiO2 and ZrO2 as a support. The catalytic activity at low temperatures increased with increasing the molar ratio of Ni/Pt. This accompanied
the TPR peak shift to lower temperatures. The optimum molar ratio between Ni and Pt was determined to be 5. This Pt-Ni/γ A12O3 showed no decrease in CO conversion and CO2 selectivity for the selective CO oxidation in the presence of 2 vol% H2O and 20 vol% CO2. The bimetallic phase of Pt-Ni seems to give rise to stable activity with high CO2 selectivity in selective oxidation of CO in H2-rich stream. 相似文献
57.
Man-Hee HanJung-Whan Kim Jinwon KimJung Yoon Ko Jules J. MagdaIn Suk Han 《Polymer》2003,44(16):4541-4546
The acrylic comonomers hydroxypropyl methacrylate (HPMA) and N,N-dimethylaminoethyl methacrylate (DMA) have been used in several earlier studies to produce pH-responsive hydrogels. However, these same monomers can also be used to prepare hydrogels that are highly responsive to temperature. One manifestation of this temperature sensitivity is a sharp decrease in hydrogel optical transparency that occurs when the temperature exceeds a critical transition value. For example, a hydrogel that exhibits a swelling transition at the physiological pH value of 7.4 has a transition temperature of about 45 °C when the environmental salt concentration is 0.15 M. The value of the transparency transition temperature is shown to depend on hydrogel synthesis parameters such as comonomer mole ratio, crosslinker mole ratio, and even initiator concentration. By reducing the mole ratio of the crosslinker tetraethylene glycol dimethacrylate (TEGDMA), the transition temperature can be lowered by as much as 15 °C. Environmental salt concentration and solvent polarity are also shown to influence the transition temperature. 相似文献
58.
Min Chan Kim David M. Phillips Myung S. Jhon Xiaoding 《Chemical Engineering Communications》2004,191(1):1-16
The surface diffusion characteristics of nonpolar perfluoropolyether (PFPE) Z on carbon surfaces are investigated in two regimes, submonolayer and multilayer, for nano-thin films. For the submonolayer regime, the two-dimensional, cubic van der Waals equation of state is applied to determine the dependence of the surface diffusion coefficient on the film thickness, as experimental surface diffusion coefficients increase with increasing film thickness. For the multilayer regime, a conventional fluid mechanics analysis with position dependent viscosity and a van der Waals disjoining pressure gradient is applied to investigate the surface diffusion characteristics. The present theoretical analysis qualitatively agrees with the experimental results. 相似文献
59.
Soo‐kyung Shin Myung‐jin Jun Hyungki Hong 《Journal of the Society for Information Display》2014,22(2):122-128
In stereoscopic images, the crossing point of the viewing directions of the two eyes determines the perceived depth. Assuming that accommodation is affected by the positions of the crossing point, the effect of crossing point on minimum angle of resolution (MAR) was investigated. For 40 participants, MAR was measured by two‐alternative forced choice where Snellen optotype E of up and down directions were used as two kinds of stimuli. As the crossing point of the viewing direction of the left and right eyes moves farther from the sample display, the ability to identify the direction of letter E decreases at the optotype of the same line thickness. The change of MAR shows linear trends with respect to the optical power change that are the reciprocal of the distance from the participant to the crossing points located out of screen and on screen. 相似文献
60.
Ji Hoon Yang Min Hyung Yum Eun Jung Kim Myeung Hoi Kwon Cheol Woong Yang Ha-Jin Song Yong-Wan Jin 《Carbon》2006,44(11):2219-2223
Nitrogen molecules have been encapsulated into the central hollows of vertically aligned carbon nitride (CN) multiwalled nanofibers by dc plasma-enhanced chemical vapor deposition with C2H2, NH3, and N2 gases on a Ni/TiN/Si(1 0 0) substrate at 650 °C. X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectra showed the existence of nitrogen molecules in CN nanofibers. Elemental mapping images with electron energy loss spectroscopy of the CN nanofiber and catalyst metal, and optical emission spectroscopy spectra of the plasma showed the distribution of nitrogen atoms and molecules in the CN nanofiber, catalyst metal, and gaseous precursor, respectively. These studies showed that atomic nitrogen diffused into the catalytic metal particle because of the concentration gradient and then saturated at the bottom of the particle. Saturated nitrogen atom participated in the formation of the CN nanofiber wall but most of nitrogen was trapped in the central hollow of the nanofiber as molecules. 相似文献