The nature of dislocation motion in quasicrystals

Calculations in a hydrodynamic model of quasicrystal dynamics show that dislocation motion in these systems is impeded by a drag far greater than that in crystals.

Observation of crack closure using a crack mouth opening displacement gauge

A crack mouth opening displacement (CMOD) gauge has been designed to estimate the crack length as well as the crack opening stress level in an automated fatigue crack propagation test programme. The CMOD gauge accurately predicts crack tip opening levels in K-controlled tests with constant K, K increasing or K decreasing. In all three K-controlled tests with a single 100% overload cycle, the CMOD gauge does not measure the crack tip opening stress level over a large range of crack lengths after the application of the overload. The CMOD gauge measures the stress level at which the overload plastic zone site opens. Caution should thus be exercised in using the crack opening stress level, estimated by the CMOD gauge, to explain fatigue crack propagation under arbitrary load sequences from the viewpoint of crack closure phenomena.

Reactivity studies of highly electrophilic ruthenium complexes

The 16-electron, coordinatively unsaturated, dicationic ruthenium complex Ru(P(OH)(2)(OMe))(dppe)(2)]OTf](2) (1a) brings about the heterolysis of the C-H bond in phenylacetylene to afford the phenylacetylide complex trans-Ru(C CPh)(P(OH)(2)(OMe))(dppe)(2)]OTf] (2). The phenylacetylide complex undergoes hydrogenation to give a ruthenium hydride complex trans-Ru(H)(P(OH)(2)(OMe))(dppe)(2)]OTf] (3) and phenylacetylene via the addition of H-2 across the Ru-C bond. The 16-electron complex also reacts with HSiCl3 quite vigorously to yield a chloride complex trans-Ru(Cl)(P(OH)(2)(OMe))(dppe)(2)]OTf] (4). On the other hand, the other coordinatively unsaturated ruthenium complex Ru(P(OH)(3))(dppe)(2)]OTf](2) (1b) reacts with a base N-benzylideneaniline to afford a phosphonate complex Ru(P(O)(OH)(2))(dppe)(2)]OTf] (5) via the abstraction of one of the protons of the P(OH)(3) ligand by the base. The phenylacetylide, chloride, and the phosphonate complexes have been structurally characterized. The phosphonate complex reacts with H-2 to afford the corresponding dihydrogen complex trans-Ru(eta(2)-H-2)(P(O)(OH)(2))(dppe)(2)]OTf] (5-H2). The intact nature of the H-H bond in this species was established using variable temperature H-1 spin-lattice relaxation time measurements and the observation of a significant J(H,D) coupling in the HD isotopomer trans-Ru(eta(2)-HD)(P(O)(OH)(2))(dppe)(2)]OTf] (5-HD). (C) 2010 Elsevier B. V. All rights reserved.

Facile hydrothermal synthesis and observation of bubbled growth mechanism in nano-ribbons aggregated microspherical Covellite blue-phosphor

Well uniform microspheres of phase pure Covellite were synthesized through a simple hydrothermal approach using poly vinyl pyrrolidone (PVP) as surfactant. The micro-spheres were constituted of numerous self-organized knitted nano-ribbons of similar to 30 nm thickness. The effect of conc. PVP in the hydrothermal precursor solution on the product morphology was investigated. Based on the out-coming product micro-architecture a growth mechanism was proposed which emphasized bubbled nucleation inside the hydrothermal reactor. In a comparative study on linear optical properties, enhancement of luminescent intensity was observed for nano-ribbon clung microspheres rather than that of agglomerates of distorted particles, which may be attributed to better crystallinity as well as reduced surface defects and ionic vacancies for ribbon-like nano-structures.

Investigations of the Nature of Critical Line Very Close to a Double Critical Point

The curvature of the line of critical points in a reentrant ternary mixture is determined by approaching the double critical point (DCP) extremely closely. The results establish the continuous and quadratic nature of this line. Out study encompasses as small a loop size (ΔT) as 663 mK. The DCP is realized when ΔT becomes zero.

Nature of nitrogen adsorbed on transition metal surfaces as revealed by electron spectroscopy and cognate techniques

The nature of the chemisorbed states of nitrogen on various transition metal surfaces is discussed comprehensively on the basis of the results of electron spectroscopic investigations augmented by those from other techniques such as LEED and thermal desorption. A brief discussion of the photoemission spectra of free N2, a comparison of adsorbed N2 and CO as well as of physisorption of N2 on metal surfaces is also presented. We discuss the chemisorption of N2 on the surfaces of certain metals (e.g. Ni, Fe, Ru and W) in some detail, paying considerable attention to the effect of electropositive and electronegative surface modifiers. Features of the various chemisorbed states (one or more weakly chemisorbed gamma-states, strongly chemisorbed alpha-states with bond orders between 1 and 2. and dissociative chemisorbed beta-states) on different surfaces are described and relations between them indicated. While the gamma-state could be a precursor of the alpha-state, the alpha-state could be the precursor of the beta-state and this kind of information is of direct relevance to ammonia synthesis. The nature of adsorption of N2 on the surfaces of some metals (e.g. Cr, Co) deserves further study and such investigations might as well suggest alternative catalysts for ammonia synthesis.

The nature of inhibition of 3-hydroxy-3-methylglutaryl CoA reductase by garlic-derived diallyl disulfide

A concentration dependent inhibition of 3-hydroxy-3-methylglutaryl CoA (HMG CoA) reductase was found on preincubation of microsomal preparations with diallyl disulfide, a component of garlic oil. This inhibited state was only partially reversed even with high concentrations of DTT. Glutathione, a naturally occurring reducing thiol agent, was ineffective. The substrate, HMG CoA, but not NADPH, was able to give partial protection for the DTT-dependent, but not glutathione-dependent activity. The garlic-derived diallyl disulfide is the most effective among the sulfides tested for inhibition of HMG CoA reductase. Formation of protein internal disulfides, inaccessible for reduction by thiol agents, but not of protein dimer, is likely to be the cause of this inactivation.

Lyophilized disaccharides – the effect of water during storage

Nearly one fourth of new medicinal molecules are biopharmaceutical (protein, antibody or nucleic acid derivative) based. However, the administration of these compounds is not always that straightforward due to the fragile nature of aforementioned domains in GI-tract. In addition, these molecules often exhibit poor bioavailability when administered orally. As a result, parenteral administration is commonly preferred. In addition, shelf-life of these molecules in aqueous environments is poor, unless stored in low temperatures. Another approach is to bring these molecules to anhydrous form via lyophilization resulting in enhanced stability during storage. Proteins cannot most commonly be freeze dried by themselves so some kind of excipients are nearly always necessary. Disaccharides are commonly utilized excipients in freeze-dried formulations since they provide a rigid glassy matrix to maintain the native conformation of the protein domain. They also act as "sink"-agents, which basically mean that they can absorb some moisture from the environment and still help to protect the API itself to retain its activity and therefore offer a way to robust formulation. The aim of the present study was to investigate how four amorphous disaccharides (cellobiose, melibiose, sucrose and trehalose) behave when they are brought to different relative humidity levels. At first, solutions of each disaccharide were prepared, filled into scintillation vials and freeze dried. Initial information on how the moisture induced transformations take place, the lyophilized amorphous disaccharide cakes were placed in vacuum desiccators containing different relative humidity levels for defined period, after which selected analyzing methods were utilized to further examine the occurred transformations. Affinity to crystallization, water sorption of the disaccharides, the effect of moisture on glass transition and crystallization temperature were studied. In addition FT-IR microscopy was utilized to map the moisture distribution on a piece of lyophilized cake. Observations made during the experiments backed up the data mentioned in a previous study: melibiose and trehalose were shown to be superior over sucrose and cellobiose what comes to the ability to withstand elevated humidity and temperature, and to avoid crystallization with pharmaceutically relevant moisture contents. The difference was made evident with every utilized analyzing method. In addition, melibiose showed interesting anomalies during DVS runs, which were absent with other amorphous disaccharides. Particularly fascinating was the observation made with polarized light microscope, which revealed a possible small-scale crystallization that cannot be observed with XRPD. As a result, a suggestion can safely be made that a robust formulation is most likely obtained by utilizing either melibiose or trehalose as a stabilizing agent for biopharmaceutical freeze-dried formulations. On the other hand, more experiments should be conducted to obtain more accurate information on why these disaccharides have better tolerance for elevating humidities than others.

Surprising observation of large anthropogenic aerosol fraction over the ``near-pristine'' southern Bay of Bengal: Climate implications

The Bay of Bengal (BoB), a small oceanic region surrounded by landmasses with distinct natural and anthropogenic activities and under the influence of seasonally changing airmass types, is characterized by a rather complex and highly heterogeneous aerosol environment. Concurrent measurements of the physical, optical, and chemical (offline analysis) properties of BoB aerosols, made onboard extensive ship-cruises and aircraft sorties during Integrated Campaign for Aerosols, gases and Radiation Budget of March-April 2006, and satellite-retrieved aerosol optical depths and derived parameters, were synthesized following a synergistic approach to delineate the anthropogenic fraction to the composite aerosol parameters and its spatial variation. Quite interestingly and contrary to the general belief, our studies revealed that, despite of the very high aerosol loading (in the marine atmospheric boundary layer as well as in the vertical column) over the northern BoB and a steep decreasing gradient toward the southern latitudes, the anthropogenic fraction showed a steady increase from North to South (where no obvious anthropogenic source regions exist). Consequently, the direct radiative forcing at the top of the atmosphere due to anthropogenic aerosols remained nearly constant over the entire BoB with values in the range from -3.3 to -3.6 Wm(-2). This interesting finding, beyond doubts calls for a better understanding of the complex aerosol system over the BoB through more focused field campaigns.

Polarization studies in electromagnetic scattering by small Solar-system particles

In remote-sensing studies, particles that are comparable to the wavelength exhibit characteristic features in electromagnetic scattering, especially in the degree of linear polarization. These features vary with the physical properties of the particles, such as shape, size, refractive index, and orientation. In the thesis, the direct problem of computing the unknown scattered quantities using the known properties of the particles and the incident radiation is solved at both optical and radar spectral regions in a unique way. The internal electromagnetic fields of wavelength-scale particles are analyzed by using both novel and established methods to show how the internal fields are related to the scattered fields in the far zone. This is achieved by using the tools and methods that were developed specifically to reveal the internal field structure of particles and to study the mechanisms that relate the structure to the scattering characteristics of those particles. It is shown that, for spherical particles, the internal field is a combination of a forward propagating wave with the apparent wavelength determined by the refractive index of the particle, and a standing wave pattern with the apparent wavelength the same as for the incident wave. Due to the surface curvature and dielectric nature of the particle, the incident wave front undergoes a phase shift, and the resulting internal wave is focused mostly at the forward part of the particle similar to an optical lens. This focusing is also seen for irregular particles. It is concluded that, for both spherical and nonspherical particles, the interference at the far field between the partial waves that originate from these concentrated areas in the particle interior, is responsible for the specific polarization features that are common for wavelength-scale particles, such as negative values and local extrema in the degree of linear polarization, asymmetry of the phase function, and enhancement of intensity near the backscattering direction. The papers presented in this thesis solve the direct problem for particles with both simple and irregular shapes to demonstrate that these interference mechanisms are common for all dielectric wavelength-scale particles. Furthermore, it is shown that these mechanisms can be applied to both regolith particles in the optical wavelengths and hydrometeors at microwave frequencies. An advantage from this kind of study is that it does not matter whether the observation is active (e.g., polarimetric radar) or passive (e.g., optical telescope). In both cases, the internal field is computed for two mutually perpendicular incident polarizations, so that the polarization characteristics can then be analyzed according to the relation between these fields and the scattered far field.

Nature of the inhibition by noradrenaline of induction by cortisol of hepatic tryptophan pyrrolase

Administration of noradrenaline inhibited the induction of hepatic trytophan pyrrolase by Cortisol but not by tryptophan. The selective inhibition of pyrrolase was specific to noradrenaline, whereas adrenaline and rat growth hormone also inhibited tyrosine aminotransferase. None of those three hormones had any effect on the incorporation of [32P]-orthophosphate into RNA, stimulated by cortisol. Other biogenic amines, polypeptide hormones and steroid analogues were not inhibitory to the induction of tryptophan pyrrolase by cortisol. The α-adrenergic agonist, phenylephrine, potentiated the noradrenaline inhibition whereas Image -threo-3,4-dihydroxyphenylserine, its precursor, together with pargyline had no effect on the induction process of pyrrolase. These results support the view that noradrenaline exerts its inhibitory action at the cell membrane via the α-receptor, and is not mediated directly by an intracellular mechanism.

Composite MR image reconstruction and unaliasing for general trajectories using neural networks

In rapid parallel magnetic resonance imaging, the problem of image reconstruction is challenging. Here, a novel image reconstruction technique for data acquired along any general trajectory in neural network framework, called ``Composite Reconstruction And Unaliasing using Neural Networks'' (CRAUNN), is proposed. CRAUNN is based on the observation that the nature of aliasing remains unchanged whether the undersampled acquisition contains only low frequencies or includes high frequencies too. Here, the transformation needed to reconstruct the alias-free image from the aliased coil images is learnt, using acquisitions consisting of densely sampled low frequencies. Neural networks are made use of as machine learning tools to learn the transformation, in order to obtain the desired alias-free image for actual acquisitions containing sparsely sampled low as well as high frequencies. CRAUNN operates in the image domain and does not require explicit coil sensitivity estimation. It is also independent of the sampling trajectory used, and could be applied to arbitrary trajectories as well. As a pilot trial, the technique is first applied to Cartesian trajectory-sampled data. Experiments performed using radial and spiral trajectories on real and synthetic data, illustrate the performance of the method. The reconstruction errors depend on the acceleration factor as well as the sampling trajectory. It is found that higher acceleration factors can be obtained when radial trajectories are used. Comparisons against existing techniques are presented. CRAUNN has been found to perform on par with the state-of-the-art techniques. Acceleration factors of up to 4, 6 and 4 are achieved in Cartesian, radial and spiral cases, respectively. (C) 2010 Elsevier Inc. All rights reserved.

Nature inspired optimization techniques for the design optimization of laminated composite structures using failure criteria

The design optimization of laminated composites using naturally inspired optimization techniques such as vector evaluated particle swarm optimization (VEPSO) and genetic algorithms (GA) are used in this paper. The design optimization of minimum weight of the laminated composite is evaluated using different failure criteria. The failure criteria considered are maximum stress (MS), Tsai-Wu (TW) and failure mechanism based (FMB) failure criteria. Minimum weight of the laminates are obtained for different failure criteria using VEPSO and GA for different combinations of loading. From the study it is evident that VEPSO and GA predict almost the same minimum weight of the laminate for the given loading. Comparison of minimum weight of the laminates by different failure criteria differ for some loading combinations. The comparison shows that FMBFC provide better results for all combinations of loading. (C) 2010 Elsevier Ltd. All rights reserved.