Search results for: Veit Elser

Items from 1 to 16 out of 16 results

article

Reconstructing three‐dimensional protein crystal intensities from sparse unoriented two‐axis X‐ray diffraction patterns. Corrigendum

Ti-Yen Lan, Jennifer L. Wierman, Mark W. Tate, Hugh T. Philipp, more

Journal of Applied Crystallography > 51 > 1 > 230 - 230

A figure in the article by Lan, Wierman, Tate, Philipp, Elser & Gruner [J. Appl. Cryst. (2017), 50, 985–993] is corrected.

article

The Complexity of Bit Retrieval

Veit Elser

IEEE Transactions on Information Theory > 2018 > 64 > 1 > 412 - 428

Bit retrieval is the problem of reconstructing a periodic binary sequence from its periodic autocorrelation, with applications in cryptography and x-ray crystallography. After defining the problem, with and without noise, we describe and compare various algorithms for solving it. A geometrical constraint satisfaction algorithm, relaxed-reflect-reflect, is currently the best algorithm for noisy bit...

article

Reconstructing three‐dimensional protein crystal intensities from sparse unoriented two‐axis X‐ray diffraction patterns

Ti-Yen Lan, Jennifer L. Wierman, Mark W. Tate, Hugh T. Philipp, more

Journal of Applied Crystallography > 50 > 4 > 985 - 993

Recently, there has been a growing interest in adapting serial microcrystallography (SMX) experiments to existing storage ring (SR) sources. For very small crystals, however, radiation damage occurs before sufficient numbers of photons are diffracted to determine the orientation of the crystal. The challenge is to merge data from a large number of such `sparse' frames in order to measure the full...

article

Matrix product constraints by projection methods

Veit Elser

Journal of Global Optimization > 2017 > 68 > 2 > 329-355

The decomposition of a matrix, as a product of factors with particular properties, is a much used tool in numerical analysis. Here we develop methods for decomposing a matrix C into a product XY, where the factors X and Y are required to minimize their distance from an arbitrary pair $$X_0$$ X 0 and $$Y_0$$ Y 0 . This type of decomposition, a projection to a matrix product constraint,...

book

Fixed-Point Algorithms for Inverse Problems in Science and Engineering

Heinz H. Bauschke, Regina S. Burachik, Patrick L. Combettes, Veit Elser, more

Nonconvex Optimization and Its Applications

Fixed-Point Algorithms for Inverse Problems in Science and Engineering presents some of the most recent work from leading researchers in variational and numerical analysis. The contributions in this collection provide state-of-the-art theory and practice in first-order fixed-point algorithms, identify emerging problems driven by applications, and discuss new approaches for solving these problems...

article

Exotic Self-trapped States of an Electron in Superfluid Helium

Veit Elser

Journal of Low Temperature Physics > 2015 > 180 > 5-6 > 363-376

We explore the possibility that the fast and exotic negative ions in superfluid helium are electrons bound to quantized vortex structures, the simplest being a ring. In the states we consider, the electron energy is only slightly below the conduction band minimum of bulk helium. To support our proposal, we present two calculations. In the first, we show that the electron pressure on the vortex core...

article

Breaking the Crowther limit: Combining depth-sectioning and tilt tomography for high-resolution, wide-field 3D reconstructions

Robert Hovden, Peter Ercius, Yi Jiang, Deli Wang, more

Ultramicroscopy > 2014 > 140 > C > 26-31

To date, high-resolution (<1nm) imaging of extended objects in three-dimensions (3D) has not been possible. A restriction known as the Crowther criterion forces a tradeoff between object size and resolution for 3D reconstructions by tomography. Further, the sub-Angstrom resolution of aberration-corrected electron microscopes is accompanied by a greatly diminished depth of field, causing regions...

article

Direct phasing of nanocrystal diffraction

Veit Elser

Acta Crystallographica Section A > 69 > 6 > 559 - 569

Recent experiments at free‐electron laser X‐ray sources have been able to resolve the intensity distributions about Bragg peaks in nanocrystals of large biomolecules. Information derived from small shifts in the peak positions augment the Bragg samples of the particle intensity with samples of its gradients. Working on the assumption that the nanocrystal is entirely generated by lattice translations...

article

Strategies for processing diffraction data from randomly oriented particles

Veit Elser

Ultramicroscopy > 2011 > 111 > 7 > 788-792

The high intensity of free-electron X-ray light sources may enable structure determinations of viruses or even individual proteins without the encumbrance of first forming crystals. This note compares two schemes of non-crystalline diffraction data collection that have been proposed: serial single-shot data from individual particles, and averaged cross-correlation data from particle ensembles. The...

chapter

A probabilistic approach to antenna location for large radio telescopes

Joe Chen, Veit Elser, R. P. Millane

2010 25th International Conference of Image and Vision Computing New Zealand > 1 - 6

2010 25th International Conference of Image and Vision Computing New Zealand (IVCNZ)

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...

article

Upper Bound on the Packing Density of Regular Tetrahedra and Octahedra

Simon Gravel, Veit Elser, Yoav Kallus

Discrete & Computational Geometry > 2011 > 46 > 4 > 799-818

Aristotle contended that (regular) tetrahedra tile space, an opinion that remained widespread until it was observed that non-overlapping tetrahedra cannot subtend a solid angle of 4π around a point if this point lies on a tetrahedron edge. From this 15th century argument, we can deduce that tetrahedra do not tile space but, more than 500 years later, we are unaware of any known non-trivial upper bound...

article

Dense Periodic Packings of Tetrahedra with Small Repeating Units

Yoav Kallus, Veit Elser, Simon Gravel

Discrete & Computational Geometry > 2010 > 44 > 2 > 245-252

We present a one-parameter family of periodic packings of regular tetrahedra, with the packing fraction 100/117≈0.8547, that are simple in the sense that they are transitive and their repeating units involve only four tetrahedra. The construction of the packings was inspired from results of a numerical search that yielded a similar packing. We present an analytic construction of the packings and a...

article

Laminating Lattices with Symmetrical Glue

Veit Elser, Simon Gravel

Discrete & Computational Geometry > 2010 > 43 > 2 > 363-374

We use the automorphism group Aut(H), of holes in the lattice L₈=A₂⊕A₂⊕D₄, as the starting point in the construction of sphere packings in 10 and 12 dimensions. A second lattice, L₄=A₂⊕A₂, enters the construction because a subgroup of Aut(L₄) is isomorphic to Aut(H). The lattices L₈ and L₄, when glued together through this relationship, provide an alternative construction of the laminated lattice...

article

The Mermin Fixed Point

Veit Elser

Foundations of Physics > 2003 > 33 > 11 > 1691-1698

The most efficient known method for solving certain computational problems is to construct an iterated map whose fixed points are by design the problem's solution. Although the origins of this idea go back at least to Newton, the clearest expression of its logical basis is an example due to Mermin. A contemporary application in image recovery demonstrates the power of the method.

article

An ab initio based structure model of i(Al-Pd-Mn)

Alexander Quandt, Veit Elser, Georg Kresse, Jürgen Hafner

Materials Science & Engineering A > 2000 > 294-296 > 351-354

We illustrate how ab initio numerical simulation methods can be used to check and improve structure models for i(Al-Pd-Mn). By focusing our study on the optimization of a small approximant, we obtain a number of general structural and compositional rules simple enough to be applicable to the quasicrystalline structure itself.

article

The growth of entropically stabilized quasicrystals

Dieter Joseph, Veit Elser

Materials Science & Engineering A > 2000 > 294-296 > 254-257

We introduce a growth model for entropically stabilized quasicrystals. The dominating feature of this model is a fluctuating growth front which enables growth near equilibrium with small phason components. We summarize the results obtained for 2D and give a first presentation of 3D calculations.

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