Magritek Ltd

Wellington, New Zealand

Magritek Ltd

Wellington, New Zealand
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Pielot R.,Leibniz Institute of Plant Genetics and Crop Plant Research | Pielot R.,Leibniz Institute for Neurobiology | Kohl S.,Leibniz Institute of Plant Genetics and Crop Plant Research | Manz B.,Fraunhofer Institute for Biomedical Engineering | And 9 more authors.
Journal of Experimental Botany | Year: 2015

The shape of the maternal pericarp affects cereal grain mass and yield. Pericarp growth was analysed by magnetic resonance imaging (MRI), revealing topological maps of mobile water in developing pericarp of barley (Hordeum vulgare) and displaying tissue regions actively elongating in specific temporal-spatial patterns. Correlation analysis of MRI signals and growth rates reveals that growth in length is mediated by dorsal and also lateral rather than ventral regions. Growth in thickness is related to ventral regions. Switching from dorsal to ventral growth is associated with differential expression of axial regulators of the HD-ZipIII and Kanadi/Ettin types, and NPH3 photoreceptors, suggesting light-mediated auxin re-distribution. Auxin increases with the highest levels in the basal pericarp at 6 days after fertilization (DAF), together with transcriptionally up-regulated auxin transport and signalling. Gibberellin biosynthesis is transcriptionally up-regulated only later, and levels of bioactive gibberellins increase from 7 to 13 DAF, with higher levels in ventral than dorsal regions. Differential gene expression related to cell expansion indicates genes related to apoplast acidification, wall relaxation, sugar cleavage, water transport, and cell wall biosynthesis. Candidate genes potentially involved in pericarp extension are distinguished by their temporal expression, representing potential isoforms responsible for dorsal-mediated early growth in length or ventral-mediated late growth in thickness. © 2015 The Author.


Teal P.D.,Victoria University of Wellington | Eccles C.,Magritek Ltd
Inverse Problems | Year: 2015

The two most successful methods of estimating the distribution of nuclear magnetic resonance relaxation times from two dimensional data are data compression followed by application of the Butler-Reeds-Dawson algorithm, and a primal-dual interior point method using preconditioned conjugate gradient. Both of these methods have previously been presented using a truncated singular value decomposition of matrices representing the exponential kernel. In this paper it is shown that other matrix factorizations are applicable to each of these algorithms, and that these illustrate the different fundamental principles behind the operation of the algorithms. These are the rank-revealing QR (RRQR) factorization and the LDL factorization with diagonal pivoting, also known as the Bunch-Kaufman-Parlett factorization. It is shown that both algorithms can be improved by adaptation of the truncation as the optimization process progresses, improving the accuracy as the optimal value is approached. A variation on the interior method viz, the use of barrier function instead of the primal-dual approach, is found to offer considerable improvement in terms of speed and reliability. A third type of algorithm, related to the algorithm known as Fast iterative shrinkage-thresholding algorithm, is applied to the problem. This method can be efficiently formulated without the use of a matrix decomposition. © 2015 IOP Publishing Ltd.


Kittler W.C.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Galvosas P.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Hunter M.W.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Hunter M.W.,Magritek Ltd.
Microporous and Mesoporous Materials | Year: 2014

Acquisition of displacement space with NMR, the conjugate of q-space, has many applications including diffusion, dispersion, velocimetry, tortuosity, and surface to volume ratio measurements in porous media and emulsions. Normally, acquisition of q-space data requires a series of scans over which current pulsed through a gradient coil producing a constant magnetic field gradient is varied to step through q-space. By replacing the constant magnetic field gradient with a second order field whose gradient strength varies in space, a range of gradient values are applied over the sample in a single experiment, and q-space encoded into real space. Using slice selection and a read gradient in conjunction with the second order field, a modified PGSE sequence has been developed which allows the parallel acquisition of q-space in a single-shot experiment for a homogeneous medium. A proof of concept is presented for the parallel acquisition of q-space under the diffusive process, allowing a single-shot, single-excitation, single observation time diffusion measurement to be made. In addition to this, the mapping between real space and q-space leads to a mapping between displacement space and time. This means that for this experiment, without the use of any Fourier transforms, the average propagator may be obtained simply by normalising the acquired echo and plotting it against displacement space. © 2014 Elsevier Inc. All rights reserved.


Hertel S.A.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Hunter M.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Hunter M.,Magritek Ltd. | Galvosas P.,MacDiarmid Institute for Advanced Materials and Nanotechnology
Microporous and Mesoporous Materials | Year: 2014

The structure of porous materials is important in many areas of basic and applied science. Various Nuclear Magnetic Resonance (NMR) techniques are applied to study porous media on different length scales. Among them, diffusive-diffraction Pulsed Gradient Spin Echo (PGSE) NMR is able to resolve features of the pore space on the micrometer scale. However, this technique only measures the modulus square of the structure factor, which leaves the exact pore structure obscured due to the lack of phase information. In this contribution, we present experimental evidence that it is possible to obtain the full structure factor with a recently suggested modification of the PGSE NMR experiment. Our adaptation which we call Magnetic Resonance Pore Imaging (MRPI), creates a hybrid between Magnetic Resonance Imaging (MRI) and PGSE NMR. This allowed us to obtain two-dimensional average pore images with an unprecedented resolution as compared to conventional MRI. Based on these advances we demonstrate that MRPI integrates well with proven concepts of MRI and offers great potential to characterize even heterogeneous porous structures by mapping the MRPI signal on MRI images. © 2014 Elsevier Inc. All rights reserved.


Zhen J.,Victoria University of Wellington | Gouws G.,Victoria University of Wellington | Dykstra R.,Victoria University of Wellington | Eccles C.,Magritek Ltd
Proceedings of the International Conference on Sensing Technology, ICST | Year: 2012

A 20 MHz Class D RF amplifier has been developed to work with an NMR MOUSE sensor. The prototype has been built on a 4-layer PCB with an area of 50 cm 2 and weighs less than 120 g; it outputs 100 W into a 50Ω load using a single 24 V DC supply. Even with the high switching power losses at that frequency, the amplifier is able to achieve 73% efficiency. Test results from the MOUSE sensor show the class D amplifier is operating well at 20 MHz with fast turn on and turn off times, producing constant amplitude pulses as short as 2 μs. and is able to run long CPMG experiments with hundreds of echoes. The results confirm that the Class D amplifier is a worthy replacement for the existing, market available Class A amplifier, which is running at 19% efficiency and weighs 480 g with a PCB area of 160 cm2. © 2012 IEEE.


Kittler W.C.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Galvosas P.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Hunter M.W.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Hunter M.W.,Magritek Ltd.
Journal of Magnetic Resonance | Year: 2014

A proof of concept is presented for the parallel acquisition of q-space under diffusion using a second order magnetic field. The second order field produces a gradient strength which varies in space, allowing a range of gradients to be applied in a single pulse, and q-space encoded into real space. With the use of a read gradient, the spatial information is regained from the NMR signal, and real space mapped onto q-space for a thin slice excitation volume. As the diffusion encoded image for a thin slice can be mapped onto q-space, and the average propagator is the inverse Fourier transform of the q-space data, it follows that the acquisition of the echo is a direct measurement of the average propagator. In the absence of a thin slice selection, the real space to q-space mapping is lost, but the ability to measure the diffusion coefficient retained with an increase in signal to noise. © 2014 Elsevier Inc. All rights reserved.


Hertel S.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Hunter M.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Hunter M.,Magritek Ltd | Galvosas P.,MacDiarmid Institute for Advanced Materials and Nanotechnology
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2013

The internal structure of porous materials is of importance in many areas such as medicine, chemical engineering, and petrophysics. While diffraction methods such as x ray are widely used to study the internal pore space, these methods suffer from the loss of the phase information in the detected signals. Recently, an advanced diffusive diffraction NMR method was proposed which is predicted to preserve the phase information, thus overcoming this severe limitation of diffraction methods in general. Here we provide experimental confirmation that the suggested approach is indeed able to acquire the diffractive signal including its phase which allows the direct image reconstruction of the pore space, averaged over all pores. We furthermore prove that this approach may combine the advantages of magnetic resonance imaging, namely, its robust and straightforward image reconstruction via a Fourier transformation with the much improved spatial resolution of pulsed gradient spin echo NMR. © 2013 American Physical Society.


Kittler W.C.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Obruchkov S.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Galvosas P.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Hunter M.W.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Hunter M.W.,Magritek Ltd.
Journal of Magnetic Resonance | Year: 2014

Pulsed field gradient nuclear magnetic resonance provides a powerful tool for the measurement of particle diffusion and mobility. When these particles are contained in a porous medium, the diffusive process is influenced by the pore boundaries, and their effect on diffusion measurements provides information about the pore space. The acquisition of the apparent diffusion coefficient and its dependence on time, in the short time limit, reveals the surface to volume ratio of the porous medium, and in the long time limit, its tortuosity. With conventional pulsed field gradient techniques, processes where pore boundaries are evolving on the sub-second time scale cannot be resolved. Using pulsed second order magnetic fields in conjunction with one-dimensional imaging and the pulse sequence Difftrain, this paper presents a proof of concept for the first ever real time single-shot surface to volume NMR measurement. © 2014 Elsevier Inc.


Kittler W.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Hunter M.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Hunter M.,Magritek Ltd | Galvosas P.,MacDiarmid Institute for Advanced Materials and Nanotechnology
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2015

Brownian motion (diffusion) and coherent flow are fundamental for many natural and artificial processes. Therefore, its accurate measurement and description is highly desirable in many areas of science, engineering, and technology. Currently available methods commonly involve multiple experiments and substantial processing of acquired data. This contribution proposes a theoretical and experimental framework that enables one to directly examine the dynamics of fluid matter subject to diffusion and flow through the acquisition of the so-called averaged propagator. This statistical function holds all information on particle mobility due to flow and diffusion averaged over the observed fluid. The proposed method is based on a single instantaneous nuclear magnetic resonance measurement event. It also removes the need for data postprocessing by capturing the averaged propagator directly as the acquired signal, which enables the monitoring of diffusion and flow in real time. © 2015 American Physical Society.


Hertel S.A.,MacDiarmid Institute for Advanced Materials and Nanotechnology | Wang X.,University of Auckland | Hosking P.,University of Auckland | Simpson M.C.,University of Auckland | And 3 more authors.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2015

Imaging of the microstructure of porous media such as biological tissue or porous solids is of high interest in health science and technology, engineering and material science. Magnetic resonance pore imaging (MRPI) is a recent technique based on nuclear magnetic resonance (NMR) which allows us to acquire images of the average pore shape in a given sample. Here we provide details on the experimental design, challenges, and requirements of MRPI, including its calibration procedures. Utilizing a laser-machined phantom sample, we present images of microscopic pores with a hemiequilateral triangular shape even in the presence of NMR relaxation effects at the pore walls. We therefore show that MRPI is applicable to porous samples without a priori knowledge about their pore shape and symmetry. Furthermore, we introduce "MRPI mapping," which combines MRPI with conventional magnetic resonance imaging (MRI). This enables one to resolve microscopic pore sizes and shapes spatially, thus expanding the application of MRPI to samples with heterogeneous distributions of pores. © 2015 American Physical Society.

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