Paul T. Callaghan

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In pulsed-gradient spin-echo NMR, one measures the dis-of rotational dipolar auto-correlation spectral density via the ''probe'' of the spin relaxation times, where T 1 samples at placement of nuclear spins over the time interval, D, between two gradient pulses, of duration d and amplitude g, positions v 0 and 2v 0 , while T 1r samples at v 1 and 2v 1. The(More)
The long time tail of molecular velocity correlation in a con"ned #uid: observation by modulated gradient spin-echo NMR Abstract In addition to the fast correlation for local stochastic motion the molecular velocity correlation function in a #uid enclosed within the pore boundaries features a slow long time tail decay [1,2]. This article presents a study by(More)
Two different multidimensional pulsed field gradient sequences are compared which have the purpose of correlating spin displacements in different time intervals with each other. The simplest possible sequence, three-pulse SERPENT, measures displacements in two interleaved time intervals, while in VEXSY, consisting of two independent pairs of gradient pulses(More)
We demonstrate the first two-dimensional correlation NMR (COSY) spectra obtained at ultra low frequencies (ULF) using the Earth's magnetic field. Using a specially developed spectrometer with multiple audio-frequency pulses under controlled pulse phase, we observe magnetisation transfer arising from heteronuclear J-couplings in trifluoroethanol and(More)
The Earth's magnetic field, though weak, is appealing for NMR applications because it is highly homogeneous, globally available and free. However, the practicality of Earth's field NMR (EFNMR) has long been limited by the need to perform experiments in outdoor locations where the local field homogeneity is not disrupted by ferrous or magnetic objects and(More)
The use of the pulsed gradient spin-echo sequence in NMR microscopy enables the measurement of molecular translational motion and simultaneous construction of velocity and self-diffusion images, a technique that has been termed dynamic NMR microscopy. In this method the PGSE contrast gradient is stepped in a fourth dimension (q space) and so is inherently(More)
Diffusion exchange of dextran with molecular weights 4.4 and 77 kDa through polyelectrolyte multilayer (PEM) hollow capsules consisting of four bilayers of polystyrene sulfonate/polydiallyldimethylammonium chloride has been investigated using two-dimensional nuclear-magnetic-resonance methods: diffusion-diffusion exchange spectroscopy (DEXSY) and(More)
The effects of independent encoding for relaxation and for diffusion using separate time and gradient dimensions are calculated for spins diffusing in plane parallel and spherical pores with relaxing walls. Two-dimensional inverse Laplace transformation is used to obtain computed (D,T(2)) maps for both geometries, in the regime in which the dimensionless(More)
Poiseuille's equation describes the relationship between fluid viscosity, pressure, tubing diameter, and flow, yet it is not known if cold organ perfusion systems follow this equation. We investigated these relationships in an ex vivo model and aimed to offer some rationale for equipment selection. Increasing the cannula size from 14 to 20 Fr increased flow(More)
We use the propagator-resolved transverse relaxation exchange experiment to characterize the pore space and fluid behavior of water saturated, tight-packed quartz sand. The experiment uses T2 exchange plots to observe the number of molecules that shift their environment for a range of mixing times. The propagator dimension allows us to determine how far the(More)