Massey Documents by Type
Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294
Browse
10 results
Search Results
Item Susceptibility, diffusion and relaxation contrast in NMR microscopy at high resolution : a thesis presented in partial fulfilment of the requirement for the degree of Master of Science in physics at Massey University(Massey University, 1994) Forde, Lucy CatherineAn integrated approach to the functional NMR imaging of plant tissue at moderately-high transverse resolution (23 µm) was undertaken. Attention was paid to all the possible commonly-known influences, such as sources of nuclear spin relaxation or of artefacts, relevant to the final image intensity of the different tissues. While it was not clear at the outset which influences might prove to be significant, two phenomena in particular, susceptibility inhomogeneity and correlated diffusion effects, were selected for detailed investigation using simple model systems constructed from small glass tubes and rods combined with aqueous solutions, before continuing on to more complex plant samples. Simulated images compared well with the experimental results in these studies. Preliminary images of a stem of an intact Stachys sylvatica L. plant showed that the apparent T₂ relaxation time is much less (an order of magnitude) than the T₁ relaxation time in all tissues. A range of diagnostic pulse sequences was then carried out on this and similar stems in order to reveal the signatures for different models of T₂ relaxation which might explain this fact (assuming that the water protons imaged fall within the extreme-narrowed region of Bloembergen, Purcell and Pound theory). It was found that measures were necessary to avoid the complicating factor of attenuation due to diffusion in the applied read gradient, specifically the use of Carr-Purcell-Meiboom-Gill (CPMG) refocusing pulses. Susceptibility inhomogeneity seemed important in sensitive gradient echo images, but further experiments at different B₀ strengths revealed that it (and chemical shift exchange) does not contribute significantly to the spin echo image contrast. The Brownstein-Tarr model of relaxation at boundaries and surfaces (without local field offsets) was also considered as a possibility, but was ruled out for at least some of the tissues (those which display a CPMG pulse-spacing dependence). Another alternative explanation is short-range dipole interactions between water protons and protons of more slowly-moving molecules, which should be abundant in the particular cells which escape the other hypotheses, but it is difficult to confirm this within the scope of the pulse sequences used here. More progress might be possible with proper multicomponent T₂ analysis and improved knowledge of subcellular structure of our particular tissues.Item Molecular diffusion as measured by pulsed field gradient nuclear magnetic resonance : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Chemistry at Massey University(Massey University, 1982) Kissock, Jeremy Samuel DruceThe work presented in this thesis may be conveniently divided into three sections. Firstly the development of a Carr-Purcell-Meiboom-Gill pulse sequence for use in the pulsed field gradient experiment in order to examine diffusion over long diffusion times is described. Secondly diffusion coefficients of both components of binary mixtures of methanol and benzene have been measured using pulsed field gradient fourier transform NMR. Results showed self-association to be dominant over AB association and a brief qualitative explanation of the reasons for this is given. In the third section, which is the major part of this thesis, diffusion coefficients of water in the caesium perfluoro-octanoate, water system have been determined at various weight fractions and temperatures by pulsed field gradient NMR. The liquid crystalline phases occuring within the system are the isotropic micellar solution, the nematic amphiphilic mesophase and the smetic lamellar mesophase. Water was found to pass through the system in an unrestricted and virtually unhindered manner. These results were discussed in terms of the known structures of the phases and with respect to possible permeation mechanisms. No definite conclusion as to the permeation mechanism is possible. The limitations in the use of surfactants as membrane models is discussed.Item A nuclear magnetic resonance investigation of brine inclusions in Antarctic and artificial sea ice : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in Physics at Massey University(Massey University, 2000) Furkert, Suzanne AliceThe aim of this thesis is to use Nuclear Magnetic Resonance (NMR) techniques to examine the brine pockets in sea ice. Both the movement of the brine pockets within the ice, and the movement of the brine within the brine pockets is examined. The experiments are carried out using Earth's field NMR on sea ice in situ in Antarctica, and high field NMR equipment on artificially grown sea ice in New Zealand. The field work involved probe design, construction, and use. Investigations were carried out on brine content, and brine diffusion rates. The laboratory work involved growing realistic artificial sea ice, designing and constructing a temperature control system for the high field NMR machine, and carrying out experiments on the artificial sea ice samples. The brine pockets' morphology and distribution was examined. The brine and brine pocket movements over time, with a controlled temperature gradient, were also investigated. The results from the field work clearly showed multiple diffusion rates in sea ice, both faster and slower than that of water. The lab work showed that realistic sea ice had been grown, and that there was a migration of brine pockets in the direction of the temperature gradient.Item The development of a portable Earth's field NMR system for the study of Antarctic sea ice : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Electronics at Massey University(Massey University, 2001) Dykstra, RobinA portable Nuclear Magnetic Resonance (NMR) spectrometer based on digital signal processor (DSP) technology has been developed and applied to the study of the structure of Antarctic sea ice. The portability of this system means that external sources of noise can be minimised and remote sites can be investigated. A new sea-ice probe has been developed in conjunction with the spectrometer allowing in-situ measurement of water content, relaxation times and self diffusion. The new probe minimises disturbances to the sea ice sample which have been a problem with previous techniques. The core of the spectrometer consists of a Motorola DSP56303 DSP which controls the NMR experiment under the supervison of a host computer which in this case is a PC laptop. Communication between host and DSP is via either a PCMCIA card or USB interface. DSP software runs the experiment, controls acquisition and performs digital filtering of the NMR data before sending it to the PC for analysis and display. The flexibility of the DSP based core means that this system could be adapted to other control applications with relative ease.Item q-space, restricted diffusion and pulsed gradient spin echo nuclear magnetic resonance : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Physics at Massey University(Massey University, 1995) Coy, AndrewThe theory and technique of Pulsed Gradient Spin Echo (PGSE) Nuclear Magnetic Resonance (NMR) are presented. Particular attention is paid to the Fourier relationship between the average propagator of motion and the echo attenuation function. Using the q-space formalism, existing PGSE theory for diffusing molecules trapped between parallel barriers is extended to include the effects of relaxation at the walls. Computer simulations have been performed to test this extension to the theory and also to investigate the effect of finite gradient pulses in such an experiment. PGSE experiments were performed on pentane inside rectangular microslides of 100 μm width. Diffraction-like effects predicted by theory for such experiments were observed where the PGSE data has a minimum when the gradient wavevector q is equal to the reciprocal width of the microslides. Through the use of non-linear least squares fitting techniques the PGSE data is fitted to theories for perfectly reflecting walls, partially reflecting walls and wall with variable spacings. NMR microimaging experiments were performed on the microslide capillaries. The images revealed edge enhancement effects which can be explained through the signal attenuation expressions used in PGSE experiments. A brief theoretical discussion shows that the effect is due to the restricted diffusion of the molecules at the boundaries compared with the center of the sample. A pore hopping technique is presented which allows analytic expressions to be found for diffusion in porous media. PGSE experiments are performed on water diffusing in the interconnecting voids formed by close packed, monodisperse, micron sized polystyrene spheres. Diffraction-like interference effects predicted by theory are obsevered where the PGSE data has a maximum when q is equal to the reciprocal lattice spacing of the porous network. Using non-linear least squares fitting techniques the PGSE data is fitted to the pore hopping theory for a pore glass with some variation in pore spacing. The use of an appropriate structure function for the pore shape is analysed by modelling the true pore shape and comparing it to the structure function for a sphere. The parameters revealed by fitting theory to data are consistent with the known dimensions and show that important structural information can be revealed by this technique. Electron Spin Resonance (ESR) experiments are performed on the quasi-one-dimensional organic conductor (FA)2PF6. PGSE experiments on the conduction electrons show restricted diffusion effects. The PGSE data is analysed using both an impermeable relaxing wall model and a permeable pore hopping model. Fitting the data to these models show that a hopping model is more consistent with the data. PGSE experiments are performed on semi-dilute solutions of high molecular weight polystyrene dissolved in CCl4. The reptation model of diffusion is reviewed and features of this model relevant to PGSE experiments are detailed. PGSE experiments are performed and the mean square displacement of the entangled polymers is obtained as a function of diffusion time. Transitions from t to t1/2 scaling of the mean square displacement are found, and a region exhibiting t1/4 scaling is also observed, this region often being considered the signature for reptation. The PGSE-MASSEY technique, which pervides a method to correct for gradient pulse mismatch, is described. The details of the hardware and software implementation of this technique are also give. PGSE-MASSEY experiments are performed on the semi-dilute polymer solutions and enable structure functions to be acquired. These structure functions are compared to the primitive chain structure function enabling an estimate of the Doi-Edwards tube diameter to be made.Item Dynamic NMR microscopy : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Physics at Massey University(Massey University, 1992) Xia, YangThe theory and practice of Dynamic NMR Microscopy are described in detail. The description consists of a brief presentation of k-space imaging which includes the 2-D filtered back-projection (PR) reconstruction algorithm as well as the influence of various image contrast factors, a detailed discussion of q-space imaging which employs the Pulsed-Gradient Spin-Echo (PGSE) sequence and a thorough description of Dynamic NMR Microscopy which combines both k-space and q-space mapping. The velocity and self-diffusion image artifacts and errors associated with Dynamic NMR Microscopy have also been investigated extensively. As part of this work, various modifications to and developments of the existing imaging system have been made. These include the probe design for 'non-trivial' flow imaging experiments and software programming using assembly, BASIC, FORTRAN and PASCAL languages. Several instrument-related issues in NMR microscopy have also been investigated. They include the attempt to improve spatial resolution by scaling down the receiver coil, the zero-frequency 'glitch' artifact in images and the effect of induced eddy current in imaging experiments. The results of the comprehensive water capillary flow experiments have shown that simultaneous measurement of velocity and self-diffusion coefficient can be made both accurately and precisely using Dynamic NMR Microscopy. Imaging experiments which investigate molecular motion of relevance to plant physiology, fluid dynamics and polymer physics have been carried out. In the in vivo botanical studies, velocities of approximately 10 µm/s in the castor bean experiment and 45 µm/s in the Stachys experiment have been measured. In the rheological studies, induced secondary flow (eddy) around the abrupt junction in a tube was observed, which has agreed well with numerical simulation of the Navier-Stokes equation. In the studies of unusual rheological properties of high molar mass polymer solutions, velocity profiles for WSR301 polyethylene oxide (PEO)/H2O in capillary flow were measured and fitted using the power law model. The measurement of self-diffusion profiles for monodisperse PEO standards in D2O has shown clear evidence for the breakdown of molecular entanglements in semi-dilute solutions once the shear rate exceeds the equilibrium tube renewal rate, τd-1.Item Microscopic NMR imaging : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Physics at Massey University(Massey University, 1987) Eccles, Craig DavidIn the process of developing the imaging system it was necessary to write an extensive range of software. Our only access to the TI-980A was via a series of bit switches and so the first task was to write a hex monitor which would speed program entry. A fairly extensive software package was provided with the system for the purpose of performing NMR spectroscopy and so rather than rewrite FFTs etc from scratch much of this software (conveniently in the form of subroutines) was used by the imaging system. The Hitachi was supplied without any software apart from BASIC and MSDOS. IBM PC Fortran, Pascal and assembler were obtained which ran on this machine but because of graphics and I/O incompatibilities no graphics library was available. It was therefore necessary to write a number of 8088 assembly language routines to perform these essential functions. All those routines (such as image display, backprojections and FFTs) which required rapid execution were written in assembler and called as subroutines from Fortran (this programmers language of choice). Those routines for which speed is not a primary requirement or which are currently in the development stage have been written in Hitachi Basic. This volume is divided into 2 sections. The first part contains the TI-980A routines which are used to control the imaging experiment. The second contains listings and flowcharts for programs written on the Hitachi in Fortran, Basic and assembler.Item Development and applications of a low-field portable NMR system : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Physics at Massey University, Manawatu, New Zealand(Massey University, 2011) Ward, Robert LNuclear magnetic resonance (NMR) is a phenomenon similar to MRI in which radio frequency signals are used to excite and manipulate atomic nuclei within a static magnetic field. Following excitation, the nuclei return to equilibrium, all the while offering valuable molecular level information pertaining to the sample. Within the last decade, the development of small and inexpensive NMR spectrometers and permanent magnet NMR sensors has been a significant focus within the NMR community. More recently, application scientists have sought practical applications for the new technologies. In this thesis, a prototype NMR apparatus consisting of a spectrometer and 3.2MHz permanent magnet sensor was extended to enable scientifc measurements. This involved developing radio frequency electronic circuitry for the spectrometer front-end, and electromagnetic noise shielding and temperature regulation for the magnetic sensor. Experimental results confirmed that repeatable measurements using the modified apparatus were indeed possible. The NMR apparatus was thereafter successfully used to study flow, diffusion and kiwifruit using several different experimental techniques. A significantly larger effort was then expended upon the study of T2 relaxation in pectin model systems using pH as the adjustable parameter. The fascinating experimental results were successfully interpreted and modeled across three pH zones in terms of a proton chemical exchange model and molecular conformational changes. In addition, it was found that pectin carboxyl de-protonation was significantly less than expected. Further experiments performed upon galacturonic acid monomers, dimers and trimers appeared to further illuminate the pectin results. Future experiments are planned. Also while studying pectin solutions, an unexpected pH-dependent water transverse relaxation behavior was observed at both 3.2MHz and 400MHz. The only references found in the literature were from a small publication almost 50 years ago, and a 2011 publication. Altogether, this thesis contributed to original knowledge in several ways: it showed how a low- eld apparatus and single-sided sensor could be improved and utilized for a variety of scientific measurements; it showed both experimentally and theoretically how T2 for pectin solutions change with pH; it revealed an unexpected de-protonation limit for pectin molecules; it revealed a T2 pH dependence for water.Item Characterisation of lactose in the liquid and solid state using nuclear magnetic resonance and other methods : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University(Massey University, 1995) Hargreaves, JimThe anomeric composition of lactose is studied using polarimetry, gas liquid chromatography and a variety of nuclear magnetic resonance (NMR) methods and the results compared. As a result reliable characterisation based on solution methods is obtained. The measurement of the spectrum of nuclear spin-lattice relaxation times (T1) of lactose powders demonstrate significant differences between crystalline and amorphous species and between the different crystalline forms of lactose. These differences form the basis of a new characterisation methodology of powdered lactose ẁhere measurements are performed in the solid state. The use of linear multiexponential curve fitting algorithms (NNLS and Contin) to deduce the "relaxation spectrum" from the multiexponential decay curve (obtained using a low-cost wideline NMR machine) allows for the reliable interpretation of noisy and drift-affected inversion recovery data. The absence of spin-diffusion between crystalline and amorphous species enables the determination of the relative weight fractions of several lactose species in a mixed powder sample with a simple correlation to the relative intensities of relaxation time components of the T1 spectrum. The T1 values of amorphous lactoseareshown to be sensitive to moisture content and the glass transition process. The quantitative results gained from using the T1 method to characterise lactose can be applied to improve the functionality of lactose and lactose-containing powders.Item Physicochemical changes in a model protein bar during storage(Elsevier, 2009) Loveday, SM; Hindmarsh, Jason; Creamer, Lawrence K; Singh, HarjinderHigh-protein snack bars (protein bars) contain high-quality protein, sugars and other low molecular weight polyhydroxy compounds (PHCs), high-energy confectionary fats, and a minimum of water (water activity ≤ 0.65). The consequence of the intimate mixing of these components in protein bars is that they can react together, creating sensory characteristics that are unacceptable to consumers. This study examined the changes occurring in a model protein bar during storage for 50 days at 20 °C. Over this time, fracture stress increased from 20.1 +/- 1.8 Pa to 201 +/- 75 Pa at a rate that decreased slightly over time. 1H nuclear magnetic resonance (NMR) showed that the molecular mobility of PHCs decreased dramatically over the first 5 days as the batter set into a solid bar. Over the first 17 hours after manufacturing, protein particles became more clustered, and soluble protein appeared to precipitate, as shown by confocal microscopy. Reactive lysine fell 38% in the first 10 days of storage and was approximately constant thereafter. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed little change in protein molecular weights. Following the initial ‘setting’ phase of 5-10 days, fracture stress continued to increase and the molecular mobility of PHCs decreased. Changes in PHC molecular mobility were consistent with glucose crystallisation. Chemical changes were minimal during this phase, which suggests that chemical reactions play little part in the hardening of protein bars and that changes in molecular mobility and changes in microstructure driven by moisture migration may be more important.