Electric and magnetic polarizabilities of hexagonal Ln(2)CuTiO(6)(Ln = Y, Dy, Ho, Er, and Yb)

We investigated the rare-earth transition-metal oxide series, Ln(2)CuTiO(6) (Ln = Y, Dy, Ho, Er, and Yb), crystallizing in the hexagonal structure with noncentrosymmetric P6(3)cm space group for possible occurrences of multiferroic properties. Our results show that while these compounds, except Ln = Y, exhibit a low-temperature antiferromagnetic transition due to the ordering of the rare-earth moments, the expected ferroelectric transition is frustrated by the large size difference between Cu and Ti at the B site. Interestingly, this leads these compounds to attain a rare and unique combination of desirable paraelectric properties with high dielectric constants, low losses, and weak temperature and frequency dependencies. First-principles calculations establish these exceptional properties result from a combination of two effects. A significant difference in the MO5 polyhedral sizes for M = Cu and M = Ti suppress the expected cooperative tilt pattern of these polyhedra, required for the ferroelectric transition, leading to relatively large values of the dielectric constant for every compound investigated in this series. Additionally, it is shown that the majority contribution to the dielectric constant arises from intermediate-frequency polar vibrational modes, making it relatively stable against any temperature variation. Changes in the temperature stability of the dielectric constant among different members of this series are shown to arise from changes in relative contributions from soft polar modes.

Impact of water drops onto the junction of a hydrophobic texture and a hydrophilic smooth surface

Wettability gradient surfaces play a significant role in control and manipulation of liquid drops. The present work deals with the analysis of water drops impacting onto the junction line between hydrophobic texture and hydrophilic smooth portions of a dual-textured substrate made using stainless steel material. The hydrophobic textured portion of the substrate comprised of unidirectional parallel groove-like and pillar-like structures of uniform dimensions. A high-speed video camera recorded the spreading and receding dynamics of impacting drops. The drop impact dynamics during the early inertia driven impact regime remains unaffected by the dual-texture feature of the substrate. A larger retraction speed of drop liquid observed on the hydrophobic portion of the substrate during the impact of low velocity drops makes the drop liquid on the higher wettability portion to advance further (secondary drop spreading). The net horizontal drop velocity towards the hydrophilic portion of the dual-textured substrate decreases with increasing drop impact velocity. The available experimental results suggest that the movement of bulk drop liquid away from the impact point during drop impact on the dual-textured substrate is larger for the impact of low inertia drops. (C) 2010 Elsevier B.V. All rights reserved.

Modelling, Design and Analysis of Low Frequency Platform for Attenuating Micro-Vibration in Spacecraft

One of the most important factors that affect the pointing of precision payloads and devices in space platforms is the vibration generated due to static and dynamic unbalanced forces of rotary equipments placed in the neighborhood of payload. Generally, such disturbances are of low amplitude, less than 1 kHz, and are termed as ‘micro-vibrations’. Due to low damping in the space structure, these vibrations have long decay time and they degrade the performance of payload. This paper addresses the design, modeling and analysis of a low frequency space frame platform for passive and active attenuation of micro-vibrations. This flexible platform has been designed to act as a mount for devices like reaction wheels, and consists of four folded continuous beams arranged in three dimensions. Frequency and response analysis have been carried out by varying the number of folds, and thickness of vertical beam. Results show that lower frequencies can be achieved by increasing the number of folds and by decreasing the thickness of the blade. In addition, active vibration control is studied by incorporating piezoelectric actuators and sensors in the dynamic model. It is shown using simulation that a control strategy using optimal control is effective for vibration suppression under a wide variety of loading conditions.

Nucleation and growth of Al2O3/metal composites by oxidation of aluminum alloys

The nucleation and growth mechanisms during high temperature oxidation of liquid Al-3% Mg and Al-3% Mg-3% Si alloys were studied with the aim of enhancing our understanding of a new composite fabrication process. The typical oxidation sequence consists of an initial event of rapid but brief oxidation, followed by an incubation period of limited oxide growth after which bulk Al2O3/Al composite forms. A duplex oxide layer, MgO (upper) and MgAl2O4 (lower), forms on the alloy surface during initial oxidation and incubation. The spinel layer remains next to the liquid alloy during bulk oxide growth and is the eventual repository for most of the magnesium in the original alloy. Metal microchannels developed during incubation continuously supply alloy through the composite to the reaction interface. During the growth process, a layered structure exists at the upper extremity of the composite, consisting of MgO at the top surface, MgAl2O4 (probably discontinuous), Al alloy, and finally the bulk Al2O3 composite containing microchannels of the alloy. The bulk oxide growth mechanism appears to involve continuous formation and dissolution of the Mg-rich oxides at the surface, diffusion of oxygen through the underlying liquid metal, and epitaxial growth of Al2O3 on the existing composite body. The roles of Mg and Si in the composite growth process are discussed.

Preparation and characterization of hydrazine derivatives. Part-II: Reaction of transition metal ammonium double sulphates with hydrazine hydrate

Transition metal ammonium double sulphates (NH4)2M(SO4)2· 6H2O, where M = Fe, Co and Ni react with hydrazine hydrate in air giving crystalline compounds of the general formula (N2H5) [M(N2H3COO)3] H2O. The reaction proceeds through (N2H5)2 M(SO4)2, · 3N2H4, (N2H5)2 [M(OH)4 · (N2H4)2], M(N2H3COO)2 · (N2H4)2 and N2H5 [M(N2 H3 COO)3] intermediates. The reaction sequence is followed by chemical analysis and infrared spectra. A possible reaction mechanism has been suggested.

Use of adult male bonnet monkeys (Macaca radiata) for testing the biological activity of gonadotropin releasing hormone and its analogues

The effect of injecting agonistic and antagonistic analogues of gonadotropin releasing hormone analogues on serum testosterone levels was checked in adult and immature male bonnet monkeys. Of the agonistic analogues Buserelin, Ovurelin and D-Phe6 Gln8 GnRH were found to be most potent in increasing serum testosterone levels in the adult male bonnet monkeys. While 27-month-old monkeys responded well to des Gly10 GnRH, only marginal response was observed in the case of 15-month-old monkeys. Studies carried out with Ovurelin indicated that it was not effective in causing desensitization in adult monkeys. The antagonistic analogue was effective in blocking nocturnal surge of serum testosterone. Based on these studies it is suggested the adult male bonnet monkeys can be effectively used for testing the activity of GnRH analogues.

Protein Hydration and Water Structure: X-ray Analysis of a Closely Packed Protein Crystal with Very Low Solvent Content

Low-humidity monoclinic lysozyme, resulting from a water-mediated transformation, has one of the lowest solvent contents (22% by volume) observed in a protein crystal. Its structure has been solved by the molecular replacement method and refined to an R value of 0.175 for 7684 observed reflections in the 10–1.75 Å resolution shell. 90% of the solvent in the well ordered crystals could be located. Favourable sites of hydration on the protein surface include side chains with multiple hydrogen-bonding centres, and regions between short hydrophilic side chains and the main-chain CO or NH groups of the same or nearby residues. Major secondary structural features are not disrupted by hydration. However, the free CO groups at the C terminii and, to a lesser extent, the NH groups at the N terminii of helices provide favourable sites for water interactions, as do reverse turns and regions which connect β-structure and helices. The hydration shell consists of discontinuous networks of water molecules, the maximum number of molecules in a network being ten. The substrate-binding cleft is heavily hydrated, as is the main loop region which is stabilized by water interactions. The protein molecules are close packed in the crystals with a molecular coordination number of 14. Arginyl residues are extensively involved in intermolecular hydrogen bonds and water bridges. The water molecules in the crystal are organized into discrete clusters. A distinctive feature of the clusters is the frequent occurrence of three-membered rings. The protein molecules undergo substantial rearrangement during the transformation from the native to the low-humidity form. The main-chain conformations in the two forms are nearly the same, but differences exist in the side-chain conformation. The differences are particularly pronounced in relation to Trp 62 and Trp 63. The shift in Trp 62 is especially interesting as it is also known to move during inhibitor binding.

A comparative study of the interaction of nickel clusters with buckminsterfullerene, C60, and graphite

Interaction of nickel deposited on multilayer films of C60 has been investigated in comparison with that on amorphized graphite by employing photoemission spectroscopy. It is shown that unlike with graphite, Ni interacts strongly with C60 causing large changes in C(1s) and C(2p) binding energies. The increase in the Ni(2p) binding energy at small Ni coverages is also far greater on c60 than on graphite.

Addition of amines and halogens to fullerenes C60 and C70

In solution phase, aliphatic amines add on to fullerenes; vapourization of graphite in presence of methylamine gives nitrogeneous C60 derivatives. Reactions of C60 with SbCl5 and liquid Br2 yield halogen adducts.

Cloning, expression, purification, crystallization and preliminary X-ray studies of a secreted lectin (Rv1419) from Mycobacterium tuberculosis

A secreted lectin, Rv1419, from Mycobacterium tuberculosis has been cloned, expressed, purified and crystallized and the crystals have been characterized. This represents the first X-ray investigation of a lectin or lectin-like molecule from the pathogen. The cubic crystals contain one molecule in the asymmetric unit. Sequence comparisons indicate that the lectin has a beta-trefoil fold and belongs to a well characterized family of carbohydrate-binding modules. Structural analysis of the crystals is in progress.