Mössbauer study of orientation of particles in magnetic recording tapes

Mössbauer spectrum method was applied on tapes prepared using γ-Fe2O3, cobalt-epitaxial iron oxides and Fe particles to estimate the direction of orientation of the particles in the tapes. The coercivity and the squareness of the tapes was in the range of about 340 to 1140 Oe and 0.82 to 0.86, respectively. The γ-ray was applied to the tapes from the direction of the tape travel and the direction perpendicular to the tape plane. The angle of the orientation of the particles in the tapes was 29 -34 degree from the direction of the tape travel. The direction of magnetic moment in remanent state determined by Mössbauer method nearly agreed with that determined by hysteresis measurement. In the remanent state, the degree of discrepancy between the direction of orientation of particles and the direction of magnetic moment in particles increased with decreasing coercivity. It was considered that the magnetic moment in particles with lower coercivity tended to be inclined to the direction of tape plane.     

X-ray and Mössbauer study of alnico 8

Mössbauer spectroscopy and X-ray studies have been used to investigate two Alnico 8 alloys in different stages of a thermomagnetic treatment cycle. It is revealed that the first low-temperature aging subsequent to magnetic field hardening results in redistribution of components among the alloy phases, while the second low-temperature aging causes the variation in the degree of weak magnetic phase order. The temperature range of developing effective magnetic fields on iron nuclei in the α phase is shown to lower with an increase in the degree of Fe3Al-type order.     

The photomagnetic effect detected by nuclear magnetic resonance

The results of experiments with transparent easy-plane antiferromagnetic iron borate (FeBO₃) show that nuclear magnetic resonance (NMR) offers an effective tool for the study of photomagnetism in magnetically ordered materials. It is established that illumination of a FeBO₃ sample leads to a shift of the ⁵⁷Fe NMR frequency due to a change in the electron magnetization and significantly increases the nuclear induction signal intensity in the range of existence of the domain boundaries.     

Analysis of antimycin A by reversed-phase liquid chromatography/nuclear magnetic resonance spectrometry

A mixture of closely related streptomyces fermentation products, antimycin A, is separated, and the components are identified by using reversed-phase high-performance liquid chromatography with directly linked 400-MHz proton nuclear magnetic resonance detection. Analyses of mixtures of three amino acids, alanine, glycine, and valine, are used to determine optimal measurement conditions. Sensitivity increases of as much as a factor of 3 are achieved, at the expense of some loss in chromatographic resolution, by use of an 80-microL NMR cell, instead of a smaller 14-microL cell. Analysis of the antimycin A mixture, using the optimal analytical high-performance liquid chromatography/nuclear magnetic resonance conditions, reveals it to consist of at least 10 closely related components.     

MS/NMR: a structure-based approach for discovering protein ligands and for drug design by coupling size exclusion chromatography, mass spectrometry, and nuclear magnetic resonance spectroscopy

A protocol is described for rapidly screening small organic molecules for their ability to bind a target protein while obtaining structure-related information as part of a structure-based drug discovery and design program. The methodology takes advantage of and combines the inherent strengths of size exclusion gel chromatography, mass spectrometry, and NMR to identify bound complexes in a relatively universal high-throughput screening approach. Size exclusion gel chromatography in the spin column format provides the high-speed separation of a protein-ligand complex from free ligands. The spin column eluent is then analyzed under denaturing conditions by electrospray ionization mass spectrometry (MS) for the presence of small molecular weight compounds formerly bound to the protein. Hits identified by MS are then individually assayed by chemical shift perturbations in a 2D 1H-15N HSQC NMR spectrum to verify specific interactions of the compound with the protein and identification of the binding site on the protein. The utility of the MS/NMR assay is demonstrated with the use of the catalytic fragment of human fibroblast collagenase (MMP-1) as a target protein and the screening of a library consisting of approximately 32 000 compounds for the identification of molecules that exhibit specific binding to the RGS4 protein.     

Solid state spatially resolved 1H and 19F nuclear magnetic resonance spectroscopy of dental materials by stray-field imaging

As part of a program to evaluate the use of stray-field magnetic resonance microimaging (STRAFI) in dental materials research spatially resolved nuclear magnetic resonance (NMR) for solid dental cements has been investigated. By applying a quadrature echo pulse sequence to a specimen positioned in the stray-field of a NMR spectrometer superconducting magnet the magnetic resonance within a thin slice was obtained. The specimen was stepped through the field in 500 m increments to record ¹ and ¹⁹F profiles and T₂ values at each point. The specimens were fully cured cylinders made from four types of restorative material (glass ionomer, resin modified glass ionomer, compomer, composite). The values for F¹⁹T₂ varied with material type and reflected the nature of the matrix structure. For all materials containing ¹⁹F in the glass two values were calculated for ¹⁹F T₂, one short and one long. These were relatively invariant. Solid state magic angle spinning (MAS)-NMR showed that they came from the glass. This suggests that a proportion of the element is relatively mobile (in a glass phase) and the remainder is more tightly bound (in a compound dispersed in the glass). This demonstration, that NMR microimaging of both ¹H and ¹⁹F in solid dental cements is possible, opens up exciting new possibilities for investigating the distribution of these elements (in particular fluorine) in solid dental materials. ©©1999©Kluwer Academic Publishers     

Magnetic junction switching by joint action of current pulse and magnetic field: numerical simulation

The process of magnetic junction switching by a spin-polarized current pulse in the presence of an external magnetic field has been numerically simulated at the current densities and magnetic fields below the corresponding threshold values for separate effects. It is established that the switching can be performed with controlled delay relative to the current pulse.     

Self Organising Maps for variable selection: Application to human saliva analysed by nuclear magnetic resonance spectroscopy to investigate the effect of an oral healthcare product

SOMs (Self Organising Maps) are derived from the machine learning literature and serve as a valuable method for representing data. In this paper, the use of SOMs as a technique for determining the most significant variables (or markers) in a dataset is described. The method is applied to the NMR spectra of 96 human saliva samples, half of which have been treated with an oral rinse formulation and half of which are controls, and 49 variables consisting of bucketed intensities. In addition, three simulations, two of which consist of the same number of samples and variables as the experimental dataset and a third that contains a much larger number of variables, are described. Two of the simulations contain known discriminatory variables, and the remaining is treated as a null dataset without any specific discriminatory variables added. The described SOM method is contrasted to Partial Least Squares Discriminant Analysis, and a list of the markers determined to be most significant using both approaches was obtained and the differences arising are discussed. A SOM Discrimination Index (SOMDI) is defined, whose magnitude relates to how strongly a variable is considered to be a discriminator. In order to ensure that the model is stable and not dependent on the random starting point of the SOM, one hundred iterations were performed and variables that were consistently of high rank were selected. A variety of approaches for data representation are illustrated, and the main theoretical principles of employing SOMs for determining which variables are most significant are outlined. Software used in this paper was written in-house, allowing greater flexibility over existing packages, and tailored for the specific application in hand.     

Protein structure determination in solution by two-dimensional and three-dimensional nuclear magnetic resonance spectroscopy

Over the last decade, nuclear magnetic resonance (NMR) spectroscopy has evolved into a powerful method for determining structures of biological macromolecules. This has opened a unique opportunity for obtaining high-resolution three-dimensional structures in solution, in contrast to the well-established methods of X-ray diffraction, which are applicable only to solids and in particular single crystals. This rapid development has been spurred by several key advances in the field, especially the introduction of two- and three-dimensional NMR experiments, high field spectrometers (500 and 600 MHz), and computational algorithms for converting NMR derived restraints into three-dimensional structures. This review outlines the methodology employed for solving protein structures in solution, describing the basic NMR experiments necessary as well as introducing the concepts upon which the computational algorithms are founded. A variety of examples is discussed, illustrating the present state of the art, and future possibilities are indicated.     

A study of the oxidation curing mechanism of polycarbosilane fibre by solid-state high-resolution nuclear magnetic resonance

The chemical structure of oxidation-cured polycarbosilane fibres has been studied by IR and chemical analysis, but its structure has not been identified in detail. In this work, the molecular structure was examined by chemical analysis, and solid state¹³C and²⁹Si nuclear magnetic resonance (NMR) spectroscopy. Si-O-Si, Si-O-C(I) and Si-O-C(II) bonds were formed by the oxidation curing process. The six chemical bonds (Si-C, Si-H, Si-Si, Si-O-Si, Si-O-C(I) and Si-O-C(II)) in oxidation-cured polycarbosilane were determined quantitatively, and the chemical structural model was shown. Solid state²⁹Si resolution NMR spectroscopy has proved to be a powerful tool for investigating the curing mechanism of oxidation-cured polycarbosilane fibres.     

The effect of caesium on barium hollandites studied by neutron diffraction and magic-angle spinning (MAS) nuclear magnetic resonance

The structural effects of incorporating Cs into the monoclinic and tetragonal hollandites Ba_1.2−x Cs _x Mg_1.2−x/2Ti_6.8+x/2O₁₆ and Ba_1.2−x Cs _x Al_2.4−x Ti_5.6+x O₁₆ have been studied using powder neutron diffraction and ¹³³Cs and ²⁷Al MAS NMR. Addition of Cs to the monoclinic structure induces a ‘shear-type collapse’, in agreement with previously published results. NMR spectra show that the addition of Cs does not change the local structure around the Al cations within the tunnel walls. An algorithm is given that allows a prediction of unit cell parameters to be made for tetragonal hollandites containing barium.     

A chemometric approach for brain tumor classification using magnetic resonance imaging and spectroscopy

A new classification approach was developed to improve the noninvasive diagnosis of brain tumors. Within this approach, information is extracted from magnetic resonance imaging and spectroscopy data, from which the relative location and distribution of selected tumor classes in feature space can be calculated. This relative location and distribution is used to select the best information extraction procedure, to identify overlapping tumor classes, and to calculate probabilities of class membership. These probabilities are very important, since they provide information about the reliability of classification and might provide information about the heterogeneity of the tissue. Classification boundaries were calculated by setting thresholds for each investigated tumor class, which enabled the classification of new objects. Results on histopathologically determined tumors are excellent, demonstrated by spatial maps showing a high probability for the correctly identified tumor class and, moreover, low probabilities for other tumor classes.     

A study of the pozzolanic reaction by solid-state 29Si nuclear magnetic resonance using selective isotopic enrichment

The hydration of a mixture of tricalcium silicate and silica has been studied by ²⁹Si solid-state nuclear magnetic resonance, using selective enrichment of the reactants with ²⁹Si in order to follow and compare the behaviour of the silicon nuclei originating from either source. This approach shows for the first time that the silicon atoms from the two components are not equilibrated throughout the hydration products but are preferentially located in distinct species. In particular, from the distinctive spectra observed when the silica only is enriched, it is concluded that the part of the calcium silicate hydrate gel formed which incorporates silicon from this source has a longer chain length and a slightly better-ordered structure than the remainder. The spectra obtained with selective enrichment are interpreted in terms of a model based on a dreierkette chain structure for C-S-H.     

Magnetic field dependence of the Leggett angle,the susceptibility,and the longitudinal nuclear magnetic resonance of3He-B

The magnetic field dependences of the Leggett angle, the susceptibility, the free energy, and the longitudinal NMR frequency of³He-B are calculated from a generalized weak coupling theory. Employing the experimental values for the Landau parametersF ₀ ^a andF ₂ ^a , reasonable agreement with the susceptibility data measured recently by Hoyt, Scholz, and Edwards is obtained. Substantial field dependence of the Leggett angle and the longitudinal NMR frequency is predicted.