8,429 research outputs found
Microporous cesium salts of tetravalent Keggin-type polyoxotungstates Cs-4[SiW12O40], Cs-4[PW11O39(Sn-n-C4H9)], and Cs-4[PW11O39(Sn-OH)] and their adsorption properties
No full textMicroporous cesium salts of modified and unmodified tetravalent Keggin-type polyoxometalates, including Cs-4[SiW12O40], Cs-4[PW11O39(Sn-n-C4H9)], and Cs-4[PW11O39(Sn-OH)], were synthesized. The crystalline structures, which had body-centered cubic (bcc) arrangements, the lattice constants, and the pore-size distributions of the three Cs salts were similar, regardless of the presence or absence and types of functional groups introduced. The Cs salts had only micropores and no mesopores. The micropore size distributions were determined from adsorption isotherms of Ar, which showed a sharp peak at 0.59 nm and a shoulder at 0.62 nm. The fractions of the external surface areas to the total surface areas of the Cs salts were less than 6%. It is plausible that the micropores originate from the heteropoly anion defects in the crystallite, which form to avoid mismatches in the Cs+/(heteropoly anion) ratio required for charge balance (=4) and for a bcc structure (=3). The surface of the Cs salt introduced with n-butyl groups was hydrophobic, although the surface density of the n-butyl groups was low. On the other hand, the hydroxyl groups present on the surface of Cs-4[PW11O39(Sn-OH)] had little effect on the adsorption of water, methanol, ethanol, and hexane but a great impact on that for benzene due to the interactions between the -OH groups and the aromatic rings (-OH center dot center dot center dot pi). (C) 2013 Elsevier Inc. All rights reserved
Predictive control for the attitude maneuver of a flexible spacecraft
No full textPredictive control for the attitude maneuver of a flexible spacecraft model is proposed. The predictive control law takes the flexibility into account which is caused by the rotational maneuver of spacecraft body. In fact, the new control law is an extension of a previous predictive control law applied to a pure rigid model. The flexible spacecraft model consists of a rigid center body with two identical flexible structures attached. The resultant control law is an output feedback with robustness in the sense that state estimation is not needed for actual implementation of the control law. The control law therefore may be claimed to maintain the inherent properties of nonlinear predictive controllers as well as robust output feedback for the flexible spacecraft model. (C) 2004 Elsevier SAS. All rights reserved.The present study was supported by National Research
Lab. (NRL) Program (2002, M1-0203-00-0006) by the Ministry
of Science and Technology,Korea. Authors fully appreciate
the financial support. Also, effort made by anonymous
reviewers for careful review is highly appreciated
Structures and stabilities of C60(OH)6 and C60(OH)12 fullerenols
No full textRecently, Chiang's group have prepared water-soluble polyhydroxylated C60 derivatives (Fullerenols) in fuming sulfuric acid via hydrolysis of polycyclosulfated precursors. A suggested reaction mechanism is proposed. The calculation of different isomers of C60(OH)6 and C60(OH)12 fullerenols has been carried out using the semiempirical MNDO and MM2 methods with two different approaches:
1.(a) consideration of the geometries and thermodynamic stabilities;
2.(b) consideration of the cyclosulfation and hydrolysis reaction mechanisms.
For (a), the double bonds in the pentagon lead to a decrease in the electron delocalization energy. Thus, the ΔHfO values of fullerenol are predicted to increase for each double bond placed in the pentagon for these fullerenols. According to the ΔHfo values, the most stable structures of C60(OH)6 and C60(OH)12 with externally bound hydroxyl groups have been generated, with Cs and S6 symmetries respectively. The ΔHfOvalues for these fullerenols are 503 kcal mol−1 (C60(OH)6) and 131.8 kcal mol−1 (C60(OH)12). According to the geometric structure of C60(OH)6 and C60(OH)12 fullerenol, multi-hydroxy additions follow 1,2- or 1,4- addition to a cyclohexatriene. For (b) the most likely products in this reaction are C60(OH)6 (Cs) and C60(OH)12 (S6), whose ΔHfOvalues are 573 and 141.5 kcal mol−1, respectively. These stable structures could contain exact hydroxyl group sites in C60, and they may be helpful in the investigation of the physical properties of polymers or other groups substituted onto fullerenols (called star-like polymers).補正完
Modified Grid Algorithm for Star Pattern Identification by using Star Trackers
No full textNational Research Lab.(") Program(2002, MI -0203-00-0006)by the Ministry of Science and Technology, Korea
THE VIBRATIONAL STARK EFFECT AND AND ION CLUSTERS
No full text D. M. Bishop, J. Chem. Phys. 98(4), 3179, 1992.Author Institution: School of Chemical Sciences, University of Illinois at Urbana-ChampaignThe vibrational Stark has been used to calculate the frequency shifts observed in the vibrational predissociation spectra of , and , ion clusters. The electric field was obtained for each cluster by averaging over 400 Monte Carlo generated configurations. The ligands were approximated by polarizable dipoles and the ion was treated as a point charge. Experimental results will be compared to calculated frequency shifts and ligand effects will also be discussed
FDTD simulation to analyze the optical characteristics of an OLED structure with a perforated WO3 layer
No full textDesign of Chitosan-Grafted Carbon Nanotubes: Evaluation of How the –OH Functional Group Affects Cs+ Adsorption
No full textIn order to explore the effect of –OH functional groups in Cs+ adsorption, we herein used the low temperature plasma-induced grafting method to graft chitosan onto carbon nanotubes (denoted as CTS-g-CNTs), as raw-CNTs have few functional groups and chitosan has a large number of –OH functional groups. The synthesized CTS-g-CNT composites were characterized using different techniques. The effect of –OH functional groups in the Cs+ adsorption process was evaluated by comparison of the adsorption properties of raw-CNTs with and without grafting chitosan. The variation of environmental conditions such as pH and contact time was investigated. A comparison of contaminated seawater and simulated groundwater was also evaluated. The results indicated that: (1) the adsorption of Cs+ ions was strongly dependent on pH and the competitive cations; (2) for CNT-based material, the –OH functional groups have a positive effect on Cs+ removal; (3) simulated contaminated groundwater can be used to model contaminated seawater to evaluate the adsorption property of CNTs-based material. These results showed direct observational evidence on the effect of –OH functional groups for Cs+ adsorption. Our findings are important in providing future directions to design and to choose effective material to remedy the removal of radioactive cesium from contaminated groundwater and seawater, crucial for public health and the human social environment
Quantum dynamics study on the exchange H + OH+ reaction
No full textThe time-dependent wave packet quantum method under centrifugal sudden (CS) approximation has been employed to investigate the dynamics of the exchange reaction H + OH+ based on an accurate potential energy surface [Martinez et al., J. Chem. Phys. 120 (2004) 4705]. The reaction probability dependence with collision energy, the weighed partial wave contributions to the integral cross sections, and the integral cross sections of the exchange reaction H + OH+ in the collision energy range of 0.0-1.0 eV with reactant OH+ in the rotational state j(i) = 0 and vibrational states v(i) = 0-4 are calculated. The calculated time evolution of CS probability density distribution in logarithmic scales at total angular momentum J = 0 clearly indicates that the convex structure in the reaction path of the exchange H + OH+ reaction has significant influence on the dynamics of title reaction. (c) 2013 Elsevier B.V. All rights reserved
An electrochemical capacitor based on a Ni(OH)(2)/activated carbon composite electrode
No full textIn order to enhance energy density, a hybrid type pseudocapacitor/electric double layer capacitor (EDLC) was considered and its electrochemical properties were investigated. At various current densities, stable charge/discharge behaviors were observed with much higher specific capacitance values of 530 F/g compared with that of EDLC (230 F/g), by introducing Ni(OH)(2) as a cathode material. By using the modified cathode of a Ni(OH)(2)/activated carbon composite electrode, the specific capacitance was less sensitive to charge/discharge current density exhibiting stable power characteristics. (C) 2001 The Electrochemical Society
A filter bank approach to independent component analysis for convolved mixtures
No full textWe present a filter bank approach to perform independent component analysis (ICA) for convolved mixtures. Input signals are split into subband signals and subsampled. A simplified network performs ICA on the subsampled signals, and finally independent components are synthesized. The proposed approach achieves superior performance than the frequency domain approach and faster convergence with less computational complexity than the time domain approach. Furthermore, it requires shorter unmixing filter length and less computational complexity than other filter bank approaches by designing efficient filter banks. Also, a method is proposed to resolve the permutation and scaling problems of the filter bank approach. (c) 2006 Elsevier B.V. All rights reserved.This work was supported as the Brain Neuroinformatics Research Program sponsored by Korean Ministry of Science and Technology
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