R. P. Millane

University of Canterbury, Christchurch, Canterbury Region, New Zealand

Are you R. P. Millane?

Claim your profile

Publications (161)586.21 Total impact

  • Rick P Millane, Joe P J Chen
    [Show abstract] [Hide abstract]
    ABSTRACT: X-ray free-electron laser diffraction patterns from protein nanocrystals provide information on the diffracted amplitudes between the Bragg reflections, offering the possibility of direct phase retrieval without the use of ancillary experimental data. Proposals for implementing direct phase retrieval are reviewed. These approaches are limited by the signal-to-noise levels in the data and the presence of different and incomplete unit cells in the nanocrystals. The effects of low signal to noise can be ameliorated by appropriate selection of the intensity data samples that are used. The effects of incomplete unit cells may be small in some cases, and a unique solution is likely if there are four or fewer molecular orientations in the unit cell.
    Philosophical transactions of the Royal Society of London. Series B, Biological sciences. 07/2014; 369(1647).
  • Chunhong Yoon, Rick P. Millane
    [Show abstract] [Hide abstract]
    ABSTRACT: Expressions are derived for diffraction by the triangular Ising antiferromagnet, a disordered lattice system consisting of two kinds of scatterer and exhibiting geometric frustration. Analysis of the expressions shows characteristics of the diffraction patterns, including the presence of Bragg and diffuse diffraction, superlattice reflections, and their behavior with temperature. These characteristics are illustrated by numerical simulations. The results have application to diffraction imaging of disordered systems.
    Journal of the Optical Society of America A 07/2014; 31(7). · 1.67 Impact Factor
  • Joe P J Chen, John C H Spence, Rick P Millane
    [Show abstract] [Hide abstract]
    ABSTRACT: X-ray free-electron laser diffraction patterns from protein nanocrystals provide information on the diffracted amplitudes between the Bragg reflections, offering the possibility of direct phase retrieval without the use of ancillary experimental diffraction data [Spence et al. (2011). Opt. Express, 19, 2866-2873]. The estimated continuous transform is highly noisy however [Chen et al. (2014). Acta Cryst. A70, 143-153]. This second of a series of two papers describes a data-selection strategy to ameliorate the effects of the high noise levels and the subsequent use of iterative phase-retrieval algorithms to reconstruct the electron density. Simulation results show that employing such a strategy increases the noise levels that can be tolerated.
    Acta crystallographica. Section A, Foundations and advances. 03/2014; 70(Pt 2):154-61.
  • Joe P J Chen, John C H Spence, Rick P Millane
    [Show abstract] [Hide abstract]
    ABSTRACT: X-ray free-electron lasers solve a number of difficulties in protein crystallography by providing intense but ultra-short pulses of X-rays, allowing collection of useful diffraction data from nanocrystals. Whereas the diffraction from large crystals corresponds only to samples of the Fourier amplitude of the molecular transform at the Bragg peaks, diffraction from very small crystals allows measurement of the diffraction amplitudes between the Bragg samples. Although highly attenuated, these additional samples offer the possibility of iterative phase retrieval without the use of ancillary experimental data [Spence et al. (2011). Opt. Express, 19, 2866-2873]. This first of a series of two papers examines in detail the characteristics of diffraction patterns from collections of nanocrystals, estimation of the molecular transform and the noise characteristics of the measurements. The second paper [Chen et al. (2014). Acta Cryst. A70, 154-161] examines iterative phase-retrieval methods for reconstructing molecular structures in the presence of the variable noise levels in such data.
    Acta crystallographica. Section A, Foundations and advances. 03/2014; 70(Pt 2):143-53.
  • Source
    Joe P J Chen, Rick P Millane
    [Show abstract] [Hide abstract]
    ABSTRACT: X-ray femtosecond nanocrystallography is a new, potentially powerful technique for imaging biological macromolecules that uses ensemble-averaged measurements of diffraction of x-ray free-electron laser pulses from nanocrytalline specimens. Nanocrystals have some diffraction characteristics that are distinct from those of macroscopic crystals, due to the presence of different kinds of unit cell in the crystal and of truncated unit cells on the crystal surface. Expressions are derived for diffraction by nanocrystals with variable and incomplete unit cells, averaged over a distribution of crystal sizes and shapes. The diffraction contains differently modulated Bragg components that are due to interference effects within and between the full and incomplete unit cells. Estimates are obtained for the relative magnitudes of the components. The nature of the diffraction is illustrated by two-dimensional simulations. Implications for molecular imaging are discussed.
    Journal of the Optical Society of America A 12/2013; 30(12):2627-34. · 1.67 Impact Factor
  • Rick P. Millane, Victor L. Lo
    [Show abstract] [Hide abstract]
    ABSTRACT: A general class of iterative projection algorithms is described and proposed as a tool for phasing in protein crystallography in order to improve the radius of convergence over that of conventional density‐modification algorithms. Their relationship to conventional density modification is described. The common iterative projection algorithms, their convergence properties and their application to protein crystallography are described. These algorithms offer the possibility of protein structure determination starting with only information on the molecular envelope and low‐order non‐crystallographic symmetry.
    Acta Crystallographica Section A Foundations of Crystallography 01/2013; 69(5). · 2.24 Impact Factor
  • Joe P. J. Chen, John C. H. Spence, Rick P. Millane
    [Show abstract] [Hide abstract]
    ABSTRACT: Protein X-ray crystallography is a method for determining the 3-dimensional structures of large biological molecules arranged in regular arrays inside a crystal. Samples of the Fourier magnitude of the molecular charge density can be measured from the amplitudes of the scattered X-rays but the determination of the Fourier phases requires chemical modification to the sample and collection of additional data. There is thus a need for a direct digital phasing method that does not require modified specimens. The diffraction from very small crystals allows for a finer sampling of the diffraction amplitude and although highly attenuated, these additional samples offer the possibility of iterative phase retrieval without the use of ancillary experimental data. Following on from a previous study [6], we examine in detail the noise characteristics of finite crystal diffraction and propose a data selection strategy to improve 3-dimensional reconstructions of the molecular charge density using iterative phase retrieval algorithms. Simulation results verify that higher noise levels can indeed be tolerated by employing such a strategy to precondition the data.
    Proceedings of the 27th Conference on Image and Vision Computing New Zealand; 11/2012
  • [Show abstract] [Hide abstract]
    ABSTRACT: The problem of estimating wind velocities from limited flight data recordings is considered, with application to sailplane flights in high-altitude atmospheric mountain waves. Sailplane flight recorders routinely measure only GPS position and the problem is highly underdetermined. The nature of this problem is studied and a maximum a posteriori estimator is developed using prior information on the wind velocity and the sailplane airspeed and heading. The method is tested by simulation and by application to sailplane flight data.
    Proc SPIE 10/2012;
  • Joe P. J. Chen, John C. H. Spence, Rick P. Millane
    [Show abstract] [Hide abstract]
    ABSTRACT: Protein X-ray crystallography is a method for determining the three-dimensional structures of large biological molecules by analysing the amplitudes of X-rays scattered from a crystalline specimen of the molecule under study. Conventional structure determination in protein crystallography requires chemical modification to the sample and collection of additional data in order to solve the corresponding phase problem. There is an urgent need for a direct (digital) low-resolution phasing method that does not require modified specimens. Whereas diffraction from large crystals corresponds to samples (so-called Bragg samples) of the amplitude of the Fourier transform of the scattering density, the diffraction from very small crystals allows measurement of the diffraction amplitude between the Bragg samples. Although highly attenuated, these additional measurements offer the possibility of iterative phase retrieval without the use of ancillary experimental data. In this study we examine the noise characteristics of small-crystal diffraction and propose a data selection strategy to improve the quality of reconstructions using iterative phase retrieval algorithms. Simulation results verify that a higher noise level can be tolerated by using such a data selection strategy.
    Proc SPIE 10/2012;
  • Victor Lo, Rick P. Millane
    [Show abstract] [Hide abstract]
    ABSTRACT: A brief description of various iterative projection algorithms and the relationships between them is given, along with some possible reasons for their ability to solve non-convex problems. An empirical model of their behaviour when applied to non-convex problems is also described.
    Proc SPIE 10/2012;
  • Ni Zhang, Rick P. Millane, Alan J. Hunter
    [Show abstract] [Hide abstract]
    ABSTRACT: The problem of estimating wind velocities from limited flight data recordings is considered, with application to sailplane flights in high-altitude mountain waves. Sailplane flight recorders routinely measure only GPS position and, infrequently, also airspeed and the problem is underdeter- mined. Maximum likelihood and maximum a posteriori estimators are developed for these kinds of data and tested by simulation and by application to sailplane flight data.
    12/2011;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Two improved compressed sensing (CS)-based image reconstruction methods for MRI are proposed: prior estimate-based compressed sensing (PECS) and sensitivity encoding-based compressed sensing (SENSECS). PECS allows prior knowledge of the underlying image to be intrinsically incorporated in the image recovery process, extending the use of data sorting as first proposed by Adluru and DiBella (Int J Biomed Imaging 2008: 341648). It does so by rearranging the elements in the underlying image based on the magnitude information gathered from a prior image estimate, so that the underlying image can be recovered in a new form that exhibits a higher level of sparsity. SENSECS is an application of PECS in parallel imaging. In SENSECS, image reconstruction is carried out in two stages: SENSE and PECS, with the SENSE reconstruction being used as a image prior estimate in the following PECS reconstruction. SENSECS bypasses the conflict of sampling pattern design in directly applying CS recovery in multicoil data sets and exploits the complementary characteristics of SENSE-type and CS-type reconstructions, hence achieving better image reconstructions than using SENSE or CS alone. The characteristics of PECS and SENSECS are investigated using experimental data.
    Magnetic Resonance in Medicine 10/2010; 65(1):83-95. · 3.27 Impact Factor
  • Source
    Philip J. Bones, Michael A. Fiddy, Rick P. Millane
    Proc SPIE 08/2010;
  • Ni Zhang, Rick P. Millane, Alan J. Hunter
    [Show abstract] [Hide abstract]
    ABSTRACT: The problem of estimating the wind velocity from measurement of limited flight data from a sailplane flight in atmospheric mountain waves is considered. A Sailplane are often equipped with a flight recorder that records position, and sometimes other information, at regular intervals during the flight. These data contain information on the state of the atmosphere during the flight. A maximum likelihood method is developed for estimating wind fields using such sailplane flight data. The methods are evaluated by application to simulated flight data.
    Proc SPIE 08/2010;
  • V. L. Lo, R. P. Millane
    [Show abstract] [Hide abstract]
    ABSTRACT: Symmetry provides a source of redundancy which can be exploited in image reconstruction. In particular, internal symmetries in molecules can help to compensate for the loss of Fourier phase information in macromolecular x-ray crystallography. Symmetry projections are incorporated into iterative projection algorithms for reconstruction of macromolecular electron densities from x-ray diffraction amplitudes from crystals. The effects of interpolation are studied and the algorithms are applied to reconstruction of an icosahedral virus.
    Proc SPIE 08/2010;
  • Joe Chen, Veit Elser, R. P. Millane
    [Show abstract] [Hide abstract]
    ABSTRACT: The problem of optimizing antenna locations in a radio telescope with a large number of antennas is addressed. An algorithm is developed that first optimizes the probability density function of the antenna positions and this distribution is subsequently sampled. This approach avoids the large number of variables with many antennas. The density function is optimized subject to terrain constraints and the distribution of visibility samples. The optimization is solved by mapping the problem to a phase retrieval problem which is solved using an iterative projection algorithm.
    01/2010;
  • Journal of Atmospheric and Oceanic Technology 01/2010; 27(1). · 1.69 Impact Factor
  • N. Zhang, R. P. Millane, A. J. Hunter
    [Show abstract] [Hide abstract]
    ABSTRACT: Maximum likelihood (ML) and maximum a posteriori (MAP) estimators are described for the estimation of wind velocity using position, and airspeed measurements from flight data recordings. The estimators are demonstrated using simulated flight data and experimental flight data from a high-altitude sailplane flight.
    01/2010;
  • Source
    B. Wu, R. Watts, R. P. Millane, P. J. Bones
    International Society for Magnetic Resonance in Medicine, Stockholm, Sweden; 01/2010
  • Source
    International Society for Magnetic Resonance in Medicine, Stockholm, Sweden; 01/2010

Publication Stats

1k Citations
586.21 Total Impact Points

Institutions

  • 1980–2013
    • University of Canterbury
      • Department of Electrical and Computer Engineering
      Christchurch, Canterbury Region, New Zealand
  • 2010
    • Duke University Medical Center
      • Brain Imaging and Analysis Center
      Durham, NC, United States
  • 2008
    • Cornell University
      • Department of Physics
      Ithaca, NY, United States
  • 2005
    • Canterbury Christ Church University
      Cantorbery, England, United Kingdom
    • Girne American University Canterbury
      Cantorbery, England, United Kingdom
  • 1983–2004
    • Purdue University
      • • School of Electrical and Computer Engineering
      • • Whistler Center for Carbohydrate Research
      • • Department of Biological Sciences
      West Lafayette, IN, United States