Structural characterization of nanosized CeO(2)-SiO(2), CeO(2)-TiO(2), and CeO(2)-ZrO(2) catalysts by XRD, Raman, and HREM techniques

Structural characteristics of nanosized ceria-silica, ceria-titania, and ceria-zirconia mixed oxide catalysts have been investigated using X-ray diffraction (XRD), Raman spectroscopy, BET surface area, thermogravimetry, and high-resolution transmission electron microscopy (HREM). The effect of support oxides on the crystal modification of ceria cubic lattice was mainly focused. The investigated oxides were obtained by soft chemical routes with ultrahighly dilute solutions and were subjected to thermal treatments from 773 to 1073 K. The XRD results suggest that the CeO(2)-SiO(2) sample primarily consists of nanocrystalline CeO(2) on the amorphous SiO(2) surface. Both crystalline CeO(2) and TiO(2) anatase phases were noted in the case of CeO(2)-TiO(2) sample. Formation of cubic Ce(0.75)Zr(0.25)O(2) and Ce(0.6)Zr(0.4)O(2) (at 1073 K) were observed in the case of the CeO(2)-ZrO(2) sample. Raman measurements disclose the fluorite structure of ceria and the presence of oxygen vacancies/Ce(3+). The HREM results reveal well-dispersed CeO(2) nanocrystals over the amorphous SiO(2) matrix in the cases of CeO(2)-SiO(2), isolated CeO(2), and TiO(2) (anatase) nanocrystals, some overlapping regions in the case of CeO(2)-TiO(2), and nanosized CeO(2) and Ce-Zr oxides in the case of CeO(2)-ZrO(2) sample. The exact structural features of these crystals as determined by digital diffraction analysis of HREM experimental images reveal that the CeO(2) is mainly in cubic fluorite geometry. The oxygen storage capacity (OSC) as determined by thermogravimetry reveals that the OSC of the mixed oxide systems is more than that of pure CeO(2) and is system dependent.     

Chaos in thermal pulse combustion

An experimental thermal pulse combustor and a differential equation model of this device are shown to exhibit chaotic behavior under certain conditions. Chaos arises in the model by means of a progression of period-doubling bifurcations that occur when operating parameters such as combustor wall temperature or air/fuel flow are adjusted to push the system toward flameout. Bifurcation sequences have not yet been reproduced experimentally, but similarities are demonstrated between the dynamic features of pressure fluctuations in the model and experiment. Correlation dimension, Kolmogorov entropy, and projections of reconstructed attractors using chaotic time series analysis are demonstrated to be useful in classifying dynamical behavior of the experimental combustor and for comparison of test data to the model results. Ways to improve the model are suggested. (c) 1995 American Institute of Physics.     

Acid activated montmorillonite and vermiculite clays as dehydration and cracking catalysts

Treatment of montmorillonite and vermiculite with hydrochloric acid results in an overall increase in acidity and acidic sites. IR and DSC studies of base adsorbed catalysts have revealed the heterogeneity of surface acidity on the activated catalysts. Clay catalysts have been found to dehydrate 1-butanol to 1-butene, which directly isomerizes tocis- andtrans-2-butenes, confirming the presence of Lewis and Brönsted acid sites. Cumene cracking studies using the clay catalyst also confirm the presence of Brönsted acid sites. The temperature and concentration of acid have been found to have a significant influence on the catalytic activity.     

Method of action-angle variables and the classical dynamics of a nonlinear lagrangian

The method of action-angle variables is used to obtain the complete periodic solutions of a nonlinear chiral Lagrangian system with the Lagrangian of the formL=1/2 {q² [(q · q)²/(1 - q²)] - [k ₀q²/(1 - q²)]q=(q ₁,q ₂,q ₃) by making suitable canonical transformations. Usual semiclassical quantization procedure may then be applied to obtain the energy levels, which is shown to be in good agreement with exact results.     

Synthesis,characterization, and anti-cancer activity of chalcone derivatives as-potent anaplastic lymphoma kinase inhibitors

Structural Chemistry - Chalcone derivatives (7a–k) have been synthesized and characterized by 1H-NMR, 13C-NMR, mass, and elemental analysis. The synthesized compounds 7a, 7d, and 7g have been...     

A class of solvable coupled nonlinear oscillators with amplitude independent frequencies

Existence of amplitude independent frequencies of oscillation is an unusual property for a nonlinear oscillator. We find that a class of N coupled nonlinear Liénard type oscillators exhibit this interesting property. We show that a specific subset can be explicitly solved from which we demonstrate the existence of periodic and quasiperiodic solutions. Another set of N coupled nonlinear oscillators, possessing the amplitude independent nature of frequencies, is almost integrable in the sense that the system can be reduced to a single nonautonomous first order scalar differential equation which can be easily integrated numerically.     

Synchrotron Radiation Provides a Plausible Explanation for the Generation of a Free Radical Adduct of Thioxolone in Mutant Carbonic Anhydrase II

Thioxolone acts as a prodrug in the presence of carbonic anhydrase II (CA II), whereby the molecule is cleaved by thioester hydrolysis to the carbonic anhydrase inhibitor, 4-mercaptobenzene-1,3-diol (TH0). Thioxolone was soaked into the proton transfer mutant H64A of CA II in an effort to capture a reaction intermediate via X-ray crystallography. Structure determination of the 1.2 ? resolution data revealed the TH0 had been modified to a 4,4'-disulfanediyldibenzene-1,3-diol, a product of crystallization conditions, and a zinc ligated 2,4-dihydroxybenzenesulfenic acid, most likely induced by radiation damage. Neither ligand was likely a result of an enzymatic mechanism.     

Improved results on robust stability of neutral systems with mixed time-varying delays and nonlinear perturbations

This paper considers the problem of robust stability of neutral systems with mixed time-varying delays and nonlinear perturbations. Two type uncertainties such as nonlinear time-varying parameter perturbations and norm-bounded uncertainties have been discussed. Based on the new Lyapunov–Krasovskii functional with triple integral terms, some integral inequalities and convex combination technique, a new delay-dependent stability criterion for the system is established in terms of linear matrix inequalities (LMIs). Finally, four numerical examples are given to illustrate the effectiveness and an improvement over some existing results in the literature with the proposed results.     

Surface stabilized nanosized Ce(x)Zr(1-x)O(2) solid solutions over SiO(2): characterization by XRD, Raman, and HREM techniques

Ce(x)Zr(1)(-)(x)O(2) solid solutions deposited over silica surface were investigated by X-ray diffraction (XRD), Raman spectroscopy (RS), and high-resolution transmission electron microscopy (HREM) techniques in order to understand the role of silica support and the temperature stability of these composite oxides. For the purpose of comparison, an unsupported Ce(x)Zr(1)(-)(x)O(2) was also synthesized and subjected to characterization by various techniques. The Ce(x)Zr(1)(-)(x)O(2)/SiO(2) (CZ/S) (1:1:2 mole ratio based on oxides) was synthesized by depositing Ce(x)Zr(1)(-)(x)O(2) solid solution over a colloidal SiO(2) support by a deposition precipitation method and unsupported Ce(x)Zr(1)(-)(x)O(2) (CZ) (1:1 mole ratio based on oxides) was prepared by a coprecipitation procedure, and the obtained catalysts were subjected to thermal treatments from 773 to 1073 K. The XRD measurements disclose the presence of cubic phases with the composition Ce(0.75)Zr(0.25)O(2) and Ce(0.6)Zr(0.4)O(2) in CZ samples, while CZ/S samples possess Ce(0.75)Zr(0.25)O(2), Ce(0.6)Zr(0.4)O(2), and Ce(0.5)Zr(0.5)O(2) in different proportions. The crystallinity of these phases increased with increasing calcination temperature. The cell a parameter estimations indicate contraction of ceria lattice due to the incorporation of zirconium cations into the CeO(2) unit cell. Raman measurements indicate the presence of oxygen vacancies, lattice defects, and displacement of oxygen ions from their normal lattice positions in both the series of samples. The HREM results reveal, in the case of CZ/S samples, a well-dispersed nanosized Ce-Zr-oxides over the surface of amorphous SiO(2). The structural features of these crystals as determined by digital diffraction analysis of experimental images reveal that the Ce-Zr-oxides are mainly in the cubic geometry and exhibit high thermal stability. Oxygen storage capacity measurements by a thermogravimetric method reveal a substantial enhancement in the oxygen vacancy concentration of CZ/S sample over the unsupported CZ sample.