Electrotransport and magnetic properies of Cr-GaSb spintronic materials synthesized under high pressure

Electrotarnsport and magnetic properties of new phases in the system Cr-GaSb were studied. The samples were prepared by high-pressure (P=6-8 GPa) high-temperature treatment and identified by x-ray diffraction and scanning electron microscopy (SEM). One of the CrGa$_2$Sb$_2$ phases with an orthorhombic structure $Iba2$ has a combination of ferromagnetic and semiconductor properties and is potentially promising for spintronic applications. Another high-temperature phase is paramagnetic and identified as tetragonal $I4/mcm$

Study of the Distribution of Organic Molecules in the Porous Space of Vycor Glasses

© 2014, Springer-Verlag Wien. The melting crystallization processes of cyclohexane and dimethylsulfoxide adsorbed in porous glasses Vycor have been investigated by nuclear magnetic resonance method in a wide temperature range. It has been established that the adsorbed molecules form aggregates or clusters of different sizes depending on the polarity of the adsorbed fluid. In addition, this effect leads to an inhomogeneous distribution of the adsorbed non-polar molecules in the porous volume of porous glasses Vycor. It has been shown based on the analysis of the temperature dependence of the relative proportion of the amorphous component that the molecules of the adsorbed fluid can be part of different “phases” below the melting temperature at concentration corresponding to the monolayer filling: (1) the molecules in the crystalline state, (2) the molecules in amorphous “non-frozen” layer, (3) molecules in the amorphous state on the surface which are not included in the “non-frozen” layer, and (4) the molecules in the nanopores

Nuclear magnetic relaxation and phase transitions of diethylene glycol in Vycor porous glasses

The times of longitudinal T 1 and transverse T 2 magnetic relaxation of protons of diethylene glycol in the bulk phase and in Vycor porous glasses with average pore radii of 4, 11, and 32 nm are measured by the pulse NMR method in the 172-350 K temperature range. It is found that, for all samples of porous glasses, the crystallization of diethylene glycol is not observed if its content corresponds to the monolayer surface filling. The minimum content of diethylene glycol, which makes it possible to cause its crystallization in porous glass, is determined. By analyzing the dependence of the characteristics of a component with T 2b = 20-40 μs in the transverse magnetization decay on the content of diethylene glycol in porous glasses, the volume of nanopores comparable in size with diethylene glycol molecule is estimated. © 2010 Pleiades Publishing, Ltd

Climate Change Adaptation in Africa Program : 2009-10 annual report

Coastal West Africa, from Mauritania to Guinea, benefits from a marine upwelling of nutrient-rich cold water which makes it one of the world’s most productive fishing zones. The fisheries sector is therefore extremely important to both national and local economies and to the food security of local people. But fish stocks are threatened by destructive fishing practices, ecosystem decline and competition within the sector. This crucial resource faces further uncertainties because of climate change

Effect of a porous medium on the phase transitions and mobility of cyclohexane molecules

The effect of a porous medium on the phase transitions and molecular mobility of cyclohexane at a liquid content corresponding to a monolayer is studied by pulsed NMR. The times of longitudinal T 1 and transverse T 2 magnetic relaxation of protons of cyclohexane introduced into granulated porous glasses of the Vycor type with average pore diameters of 4, 11, and 32 nm are measured in the temperature range of 128-293 K. In spite of a relatively low liquid content, two phase transitions are observed for all porous glass samples at temperatures lower than those inherent in pure cyclohexane. At low temperatures, nonfreezing cyclohexane volumes with characteristic times of T 2 ∼100-200 μs and relative populations of 5-10% remain preserved due to the presence of a small number of micropores commensurable with molecular sizes. The appearance of an additional component with T 2 ∼200 μs upon temperature elevation to 148 K attests to thawing out of some cyclohexane volumes, which begins long before the crystal-plastic crystal phase transition. The nonexponential character of the transverse magnetization decay of cyclohexane above the temperature of the plastic crystal-liquid phase transition in the porous glass with a pore diameter of 4 nm suggests the existence of barriers for rapid molecular exchange. The obtained experimental results are indicative of the cluster mechanism of cyclohexane adsorption in the studied porous glasses. © 2009 Pleiades Publishing, Ltd

Disordering of phospholipid headgroups induced by a small amount of polyethylene oxide

We present a 31P NMR spectroscopy study of planar glass-plate-oriented multi-bilayers of dimyristoylphosphatidylcholine (DMPC) with addition of polyethylene oxide (PEO). This work revealed the presence of a new component in the spectra that appeared only with addition of a small fraction of PEO (up to one PEO segment per dimyristoylphosphatidylcholine molecule) and disappeared when larger amounts of PEO were added. We explained this phenomenon as an effect of an inhomogeneous force field induced by the PEO molecules located at a certain depth in the lipid membrane interface region. Copyright © 2012 John Wiley & Sons, Ltd

Application of the LASSO algorithm for fitting the multiexponential data of the NMR relaxometry

© 2018 Institute of Physics Publishing. All rights reserved. The problem of time series fitting by the sum of several exponentials with different decay parameters often arises analyzing the data of a physical experiment. In particular, such a problem arises determining the nuclear transverse relaxation times from the spin-echo decay NMR data. Mathematically, the problem can be formulated as a solution of the Fredholm integral equation of the first kind with an exponential kernel, or an equivalent system of linear equations. To solve this equation, various regularization methods are used, based on the L2-norm in most cases. We report the application of the L1-regularization for the problem, using the LASSO algorithm. A comparison was made between the results of L1- and L2-regularization on model time series, which were the sum of several exponential decays with noise. Also the L1- and L2-regularization were applied to analyze the 1H NMR experimental data of the spin-echo decays of n-hexane adsorbed in the porous volume of aluminium poor MFI-type zeolites known as ZSM-5. It was found out that the L1-regularization is effective method for determination of the transverse relaxation times from NMR data

Study of correlation of oil flow properties with nuclear magnetic resonance and self-diffusion characteristics

© Copyright 2016.Correlation curves of viscosity, average spin-spin relaxation time, and average self-diffusion for crude oil samples from Tatarstan oil fields have been obtained. Two different averaging models were used to calculate mean values. It has been found that self-diffusion D and average spin-spin relaxation time R2 are best correlated in case reciprocal values 1/R and 1/D are averaged

Paper estimability of heavy oil viscosity by nuclear magnetic resonances researchestitle

Copyright © 2014, Society of Petroleum Engineers. This paper presents the results of laboratory and nuclear magnetic resonances researches of seventy-seven crude oil samples from the Devonian, Carboniferous and Permian formations of Tatarstan oil fields with a wide range of viscosity varying from several cps to 60,000 cps. The results can be used to estimate the viscosity of the oil, including in situ viscosity. It has been found that the NMR relaxation characteristics of the tested samples presented in the form of T2 time distribution spectra confirm that crude oil is multicomponent. Numerical characteristics resulting from the analysis of the spectrum of spin-spin relaxation time T2 have been determined, which show good correlation with the viscosity of the hydrocarbon fluid. The paper presents the obtained experimental correlations between the rheological properties and NMR characteristics for oil samples studied

Proton-Radical Interaction in Crude Oil - A Combined NMR and EPR Study

© 2018 American Chemical Society. We present a detailed study of electron/nuclear interaction in a specific crude oil by continuous-wave and pulsed EPR, electron-nuclear double resonance (ENDOR) at W-band (94 GHz), and fast field-cycling dynamic nuclear polarization (FFC-DNP) at X-band. A perceptible non-Overhauser (solid) effect is found at room temperature as a result of the polarization transfer from the intrinsic oil "free" radicals to the 1H nuclei with different dynamics. On the basis of the analysis of the longitudinal nuclear relaxation times, three dynamical components described by different electron-proton coupling parameters were found, which in combination with ENDOR provides information about the distribution of the radicals in the high-molecular oil components