Small nickel metal particles in Ni---Al2O3 metal-ceramic composites

Magnetic measurements have been used in combination with transmission electron microscopy to investigate small nickel metal particles in metal-ceramic composites. Estimates of the average number of atoms in the particles are given for nonmagnetic samples with low Ni content.

Direct estimation of an element of order matrix from H-1 NMR spectra of strongly dipolar coupled spins

NMR spectra of molecules oriented in thermotropic liquid crystalline media provide information on the molecular structure and order. The spins are generally strongly dipolar coupled and the spectral analyse require the tedious and time consuming numerical iterative calculations. The present study demonstrates the application of multiple quantum spin state selective detection of single quantum transitions for mimicking the homonuclear decoupling and the direct estimation of an element of ordering matrix. This information is utilized to estimate the nearly accurate starting dipolar couplings for iterative calculations. The studies on the spectra of strongly dipolar coupled five and six interacting spin systems are reported.

Superstructures exhibited by oxides of the aurivillius family, (Bi2O2)2+ (Anâ 1BnO3n+1)2â

Bi5Ti3FeO15 and Bi7Ti3Fe3O21 which are n=4 and n=6 members of the family of oxides of the general formula (Bi2O2)2+(An−1BnO3n+1)2− show unusual superstructures, possibly due to cation ordering. Bi5Ti3FeO15; Bi7Ti3Fe3O21; oxides.

TlCaBa2Cu2O7: The 1122 (90 K) superconductor in the new Tl(Ca,Ba)n+1CunO2n+3 seriesstar, open

The 1122 (n=2) member of the Tl(Ca,Ba)n+1CunO2n+3 series containing a single Tl-O layer is shown to be associated with a Tc of 90 K. This value of Tc is significantly lower than that of the 2122 phase (Tcnot, vert, similar110 K) with two Tl-O layers.

Preparation, structure, microwave absorption and other properties of the 125K superconductor Tl2Ca2Ba2Cu3O10+δ*1

It is shown that Tl2Ca2Ba2Cu3O10+δ (2223), the n=3 member of the Tl2O2. Can�1Ba2CunO2n+2 family shows a Tc (zero-resistance) of 125K (onset 140K) only when it is prepared by the sealed tube ceramic method starting from the 1313 composition. The structure is orthorhombic (Image compared to 30� of 2122), but electron diffraction patterns show two possible orthorhombic structures. Lattice images show the expected local structure and also the presence of dislocations and intergrowths. Both 2223 and 2122 oxides absorb microwaves (9.1GHz) intensely in the superconducting state, with some hysteresis. XPS measurements show Cu mainly in the 1+ state, suggesting the important role of oxygen holes.

An Electron-Microscopic Investigation Of Oxides Related To Beta-Alumina

High resolution electron microscopic (HREM) investigation of potassiumbeta-alumina and the related gallate and ferrite has revealed that whereas the aluminate and gallate are highly disordered, consisting of random sequence ofbeta andbetaPrime units, the ferrite is more ordered. The aluminate and gallate are sensitive to electron beam irradiation exhibiting beam-induced damage similar to sodiumbetaPrime-alumina. Significantly, the ferrite is beamstable, the difference in behaviour amongst these related oxides arising from the different mechanisms by which alkali metal nonstoichiometry is accommodated. Barium hexaaluminate and hexaferrite are both highly ordered; specimens prepared by the barium borate flux method exhibit a new radic3a×radic3a superstructure of the hexagonal magnetoplumbite cell.

An electron microscopic study of quasicrystals in a quaternary alloy : Mg32(Al, Zn, Cu)49

The discovery of a solid exhibiting m 3 5 point group symmetry by Shechtman et. al. (l) in a rapidly solidified Al-14at%Mn alloy has activated intensive studies of a new class of solids, termed as quasicrystals (2). While the original discovery reported the existence of quasicrystals in AI-Mn. AI-Fe and AI-Cr alloys, subsequent work has revealed their existence in Mg-Zn-Al(3,4), Mg-A]-Cu(5), AI-Mn-Si(6) and Ti-Ni-V(7) alloys (Table l).

Proton NMR studies of dihalogenated phenyl benzamides: two-dimensional higher quantum methodologies

The scalar coupled proton NMR spectra of many organic molecules possessing more than one phenyl ring are generally complex due to degeneracy of transitions arising from the closely resonating protons, in addition to several short- and long- range couplings experienced by each proton. Analogous situations are generally encountered in derivatives of halogenated benzanilides. Extraction of information from such spectra is challenging and demands the differentiation of spectrum pertaining to each phenyl ring and the simplification of their spectral complexity. The present study employs the blend of independent spin system filtering and the spin-state selective detection of single quantum (SO) transitions by the two-dimensional multiple quantum (MQ) methodology in achieving this goal. The precise values of the scalar couplings of very small magnitudes have been derived by double quantum resolved experiments. The experiments also provide the relative signs of heteronuclear couplings. Studies on four isomers of dilhalogenated benzanilides are reported in this work.

High Resoulution Electron Microscopy of Chloritoid Minerals From Different Geological Melieu

Structural defects of three chloritoid minerals from distinet geologic melieu have been investigated by high resolution electron microscopy. X-ray powder and electron diffraction patterns indicate that the chloritoid from one geological source (A) is2M 1+2M2 monoclinic variant while those from another geological source (B) are 2M 2 monoclinic variants. In a typical one-dimensional lattice image of a crystal from sourceA, the 2M 2 matrix is broken by insertion of triclinic inter-growths. Another crystal with the 2M 2 matrix showed single, triple, quadruple and quintuple layers displaying an unusually high degree of disorder. Lattice images of 2M 2 monoclinic variants from sourceB yielded more homogeneous micrographs. The important finding from the present studies is that the chloritoid from sourceA is a severely disordered low-temperature intermediate phase in the conversion of the triclinic chloritoid to the high-temperature ordered monoclinic variants of sourceB. Severely disordered chloritoids, marking the beginning of low grade metamorphism, are generated as intermediates between the state of complete disordered arrangement towards the end of low grade metamorphism within the narrow stability range of 400°–500°C.

In planta localization and interactions of impatiens necrotic spot tospovirus proteins

Impatiens necrotic spot tospovirus (INSV) is a significant pathogen of ornamentals. The tripartite negative- and ambi-sense RNA genome encodes six proteins that are involved in cytoplasmic replication, movement, assembly, insect transmission and defence. To gain insight into the associations of these viral proteins, we determined their intracellular localization and interactions in living plant cells. Nucleotide sequences encoding the nucleoprotein N, non-structural proteins NSs and NSm, and glycoproteins Gn and Gc of a Kentucky isolate of INSV were amplified by RTPCR, cloned, sequenced and transiently expressed as fusions with autofluorescent proteins in leaf epidermal cells of Nicotiana benthamiana. All proteins accumulated at the cell periphery and co-localized with an endoplasmic reticulum marker. The Gc protein fusion also localized to the nucleus. N and NSm protein self-interactions and an NSm-N interaction were observed by using bimolecular fluorescence complementation. A tospovirus NSm homotypic interaction had not been reported previously.

A hypothesis on the role of hydroxyproline in stabilizing collagen structure

The possibility of hydroxyproline residues stabilizing the collagen triple-helical structure by the formation of additional hydrogen bonds through their γ-hydroxyl group has been studied from structural considerations. It is not possible for this hydroxyl group to form a direct hydrogen bond with a suitable group in a neighbouring chain of the triple-helical protofibril. However, in the modified one-bonded structure, which is stabilized by additional hydrogen bonds being formed through water molecules as intermediaries (put forward in 1968 by Ramachandran, G. N. and Chandrasekharan, R.), it is found that the γ-hydroxyl group of hydroxyproline can form a good hydrogen bond with the water oxygen as acceptor, the hydrogen bond length being 2.82 Å. It is proposed that, in addition to stabilizing the collagen triple-helical structure due to the stereochemical properties of the pyrrolidine ring, hydroxyproline gives added stability by the formation of an extra hydrogen bond. Experimental studies on the determination of shrinkage and denaturation temperatures of native collagen and its synthetic analogues, as a function of their hydroxyproline content, are being undertaken to test this hypothesis.

The mean geometry of the peptide unit from crystal structure data

The average dimensions of the peptide unit have been obtained from the data reported in recent crystal structure analyses of di- and tripeptides. The bond lengths and bond angles agree with those in common use, except for the bond angle C---N---H, which is about 4° less than the accepted value, and the angle C2α---N---H which is about 4° more. The angle τ (Cα) has a mean value of 114° for glycyl residues and 110° for non-glycyl residues. Attention is directed to these mean values as observed in crystal structures, as they are relevant for model building of peptide chain structures.

The non-planar peptide unit II. Comparison of theory with crystal structure datastar, open

The theoretical results derived in Part I (Ramachandran, G.N., Lakshminarayan, A.V. and Kolaskar, A.S. (1973) Biochim. Biophys. Acta 303, 8–13) that the three bonds of the peptide unit meeting at N can have a pyramidal structure is confirmed by an analysis of 14 published crystal structures of small peptides. It is shown that the dihedral angles θN and Δω are correlated, while θC, is small and is uncorrelated with Δω, showing that the non-planar distortion at C′ is generally small.

Theory of the non-planar peptide unitstar, open

By means of CNDO/2 calculations on N-methyl acetamide, it is shown that the state of minimum energy of the trans-peptide unit is a non-planar conformation, with the NH and NC2α bonds being significantly out of the plane formed by the atoms C1α, C′, O and N.