Effects of ultrasound on the synthesis of silicalite-1 nanocrystals

Application of power ultrasound, offers potential in the degree of control over the preparation and properties of nanocrystalline zeolites, which have become increasingly important due to their diverse emerging applications. Synthesis of silicalite-1 nanocrystals from a clear solution was carried out at 348 K in the absence and presence of ultrasound of 300 and 600 W, in an attempt to investigate the effects of sonication, in this respect. Variation of the particle size and particle size distribution was followed with respect to time using a laser light scattering device with a detector set to collect back-scattered light at an angle of 173°. Product yield was determined and the crystallinity was analyzed by X-ray diffraction for selected samples collected during the syntheses. Nucleation, particle growth and crystallization rates all increased as a result of the application of ultrasound and highly crystalline silicalite-1 of smaller average particle diameter could be obtained at shorter synthesis times. The particle size distributions of the product populations, however, remained similar for similar average particle sizes. The rate of increase in yield was also speeded up in the presence of ultrasound, while the final product yield was not affected. Increasing the power of ultrasound, from 300 to 600 W, increased the particle growth rate and the crystalline domain size, and decreased both the final particle diameter and the time required for the particle growth to reach completion, while its effect on nucleation was unclear.     

Approximation of fixed points of uniformly R-subweakly commuting mappings

We introduce a new class of uniformly R-subweakly commuting mappings and then using this class study the problem of approximation of common fixed points of asymptotically S-nonexpansive mappings in a Banach space with uniformly Gâteaux differentiable norm.     

Changes in the zeta-potential of copper ferrocyanide sol by gradual addition of electrolytes

Summary Zeta-potential of copper ferrocyanide sol falls, and its hydrogen ion concentration increases continuously with the addition of chlorides of potassium, barium, and aluminium till the sol falls to coalescence. The effect of thorium nitrate on the above sol is quite distinct from the rest in the sense that with its addition zeta-potential first falls rapidly, attains a minima, and then it again rises. The lowering of zeta-potential as well as the increase in hydrogen ion concentration of this sol by the cations of different valencies follows the Hardy-Schulze rule.

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Zusammenfassung Das Zeta-Potential von Kupfer-Ferro-Cyanid-Sol sinkt, und seine Wasserstoffkonzentration steigt kontinuierlich mit Zufügung der Chloride von Kalium, Barium und Aluminium, bis das Sol ausf?llt. Der Effekt von Thoriumnitrat ist v?llig verschieden. Das Zeta-Potential f?llt zuerst sehr stark, erreicht ein Minimum und steigt dann wieder. Die Erniedrigung des Zeta-Potentials wie auch der Anstieg der Wasserstoffionenkonzentration dieses Soles durch Kationen verschiedener Wertigkeit entspricht der Hardy-SchulzeRegel.

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We thank Dr. M. O. Farooq for his kind interest in the work.     

An application of a fixed point theorem to best simultaneous approximation

Using a recent result regarding the fixed points of multivalued mappings, the existence of invariant best simultaneous approximation in chainable metric space is proved.     

Common fixed points of two maps in cone metric spaces

We prove the existence of points of coincidence and common fixed points of a pair of self-mappings satisfying a generalized contractive condition in cone metric spaces. Our results generalize several well-known recent and classical results.      

A novel technique for mass transfer studies

An optical technique using microdensitometer has been demonstrated to measure mass transfer rates to a flat plate. Not only that this technique enabled measurements from extremely small areas but also the accuracy and reproducibility of the results were found to be excellent. A dyeing process consisting of a flat polymer film held parallel to the direction of liquid flow was chosen as a model system in which the mass transfer rates are determined by a number of mechanisms. The fundamental concepts thus obtained can be extended to apply more generally to all mass transfer processes.

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Zusammenfassung Mit Hilfe eines Mikrodichtemessers wird eine neue Technik demonstriert, um Stoffübertragungsdaten auf eine ebene Platte zu messen. Diese Technik ermöglicht nicht nur Messungen bei extrem kleinen Mächen, auch die Genauigkeit und Reproduzierbarkeit der Ergebnisse ist ausgezeichnet. Ein Färbungsprozeß, bei dem ein ebener, polymerer Film parallel zur Richtung des Flüssigkeitsstromes gehalten wird, wird als Modellsystem gewählt. Die Stoffübertragungsraten werden durch eine Anzahl von Mechanismen bestimmt. Die so erhaltenen grundlegenden Begriffe können erweitert werden, um sie allgemein auf alle Stoffübertragungsvorgänge anzuwenden.

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Effect of CuO Doping on the Electrical Behavior of ZrO2

Electrical conductivity has been measured at different temperatures for ZrO2 doped with various molar ratios of CuO. The conductivity increases due to migration of vacancies, created by doping. The conductivity was found to increase with increase in temperature till 220℃ and thereafter decrease due to collapse of the fluorite framework. A second rise in conductivity around 500 ℃ was observed due to phase transition of ZrO2. X-ray powder diffraction, DTA and IR studies were carried out for confirming doping effect and phase transition in ZrO2.     

Role of Magnetic Exchange Interactions in the Magnetization Relaxation of {3d–4f} Single‐Molecule Magnets: A Theoretical Perspective

Combined density functional and ab initio calculations are performed on two isomorphous tetranuclear {Ni₃^IIILn^III} star‐type complexes [Ln=Gd ( 1 ), Dy ( 2 )] to shed light on the mechanism of magnetic exchange in 1 and the origin of the slow magnetization relaxation in complex 2 . DFT calculations correctly reproduce the sign and magnitude of the J values compared to the experiments for complex 1 . Acute ?Ni?O?Gd bond angles present in 1 instigate a significant interaction between the 4f_xyz orbital of the Gd^III ion and 3d orbital of the Ni^II ions, leading to rare and strong antiferromagnetic Ni???Gd interactions. Calculations reveal the presence of a strong next‐nearest‐neighbour Ni???Ni antiferromagnetic interaction in complex 1 leading to spin frustration behavior. CASSCF+RASSI‐SO calculations performed on complex 2 suggest that the octahedral environment around the Dy^III ion is neither strong enough to stabilize the m_J |±15/2〉 as the ground state nor able to achieve a large ground‐state–first‐excited‐state gap. The ground‐state Kramers doublet for the Dy^III ion is found to be the m_J |±13/2〉 state with a significant transverse anisotropy, leading to very strong quantum tunneling of magnetization (QTM). Using the POLY_ANISO program, we have extracted the J_NiDy interaction as ?1.45 cm^?1. The strong Ni???Dy and next‐nearest‐neighbour Ni???Ni interactions are found to quench the QTM to a certain extent, resulting in zero‐field SMM behavior for complex 2 . The absence of any ac signals at zero field for the structurally similar [Dy(AlMe₄)₃] highlights the importance of both the Ni???Dy and the Ni???Ni interactions in the magnetization relaxation of complex 2 . To the best of our knowledge, this is the first time that the roles of both the Ni???Dy and Ni???Ni interactions in magnetization relaxation of a {3d–4f} molecular magnet have been established.