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Results for "Daniel J. Saunders"

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Investigating the Power of Circuits with $MOD_6$ GatesOct 12 2018We consider the power of Boolean circuits with MOD$_{6}$ gates. First, we introduce a few basic notions of computational complexity, and describe the standard models with which we study the complexity of problems. We then define the model of Boolean circuits, ... More
STDP Learning of Image Patches with Convolutional Spiking Neural NetworksAug 24 2018Spiking neural networks are motivated from principles of neural systems and may possess unexplored advantages in the context of machine learning. A class of \textit{convolutional spiking neural networks} is introduced, trained to detect image features ... More
Diophantine Equations Involving the Euler Totient FunctionFeb 05 2019We deal with various Diophantine equations involving the Euler totient function and various sequences of numbers, including factorials, powers, and Fibonacci sequences.
Double structures and jetsAug 30 2011We show how the double vector bundle structure of the manifold of double velocities, with its submanifolds of holonomic and semiholonomic double velocities, is mirrored by a structure of holonomic and semiholonomic subgroups in the principal prolongation ... More
Homogeneous variational complexes and bicomplexesDec 16 2005We present a family of complexes playing the same role, for homogeneous variational problems, that the horizontal parts of the variational bicomplex play for variational problems on a fibred manifold. We show that, modulo certain pullbacks, each of these ... More
The fundamental form of a second-order homogeneous Lagrangian in two variablesDec 16 2005We construct, for a second-order homogeneous Lagrangian in two independent variables, a differential 2-form with the property that it is closed precisely when the Lagrangian is null. This is similar to the property of the 'fundamental Lepage equivalent' ... More
On Lagrangians with reduced-order Euler-Lagrange equationsJan 21 2018If a Lagrangian defining a variational problem has order $k$ then its Euler-Lagrange equations generically have order $2k$. This paper considers the case where the Euler-Lagrange equations have order strictly less than $2k$, and shows that in such a case ... More
Homogeneous variational problems: a minicourseAug 30 2011A Finsler geometry may be understood as a homogeneous variational problem, where the Finsler function is the Lagrangian. The extremals in Finsler geometry are curves, but in more general variational problems we might consider extremal submanifolds of ... More
How to recover a Lagrangian using the homogeneous variational bicomplexDec 20 2006We show how the homogeneous variational bicomplex provides a useful formalism for describing a number of properties of single-integral variational problems, and we introduce a subsequence of one of the rows of the bicomplex which is locally exact with ... More
Locally Connected Spiking Neural Networks for Unsupervised Feature LearningApr 12 2019In recent years, Spiking Neural Networks (SNNs) have demonstrated great successes in completing various Machine Learning tasks. We introduce a method for learning image features by \textit{locally connected layers} in SNNs using spike-timing-dependent ... More
BindsNET: A machine learning-oriented spiking neural networks library in PythonJun 04 2018Dec 10 2018The development of spiking neural network simulation software is a critical component enabling the modeling of neural systems and the development of biologically inspired algorithms. Existing software frameworks support a wide range of neural functionality, ... More
Unsupervised Learning with Self-Organizing Spiking Neural NetworksJul 24 2018We present a system comprising a hybridization of self-organized map (SOM) properties with spiking neural networks (SNNs) that retain many of the features of SOMs. Networks are trained in an unsupervised manner to learn a self-organized lattice of filters ... More
Improved robustness of reinforcement learning policies upon conversion to spiking neuronal network platforms applied to ATARI gamesMar 26 2019Various implementations of Deep Reinforcement Learning (RL) demonstrated excellent performance on tasks that can be solved by trained policy, but they are not without drawbacks. Deep RL suffers from high sensitivity to noisy and missing input and adversarial ... More
Holonomy of a class of bundles with fibre metricsMay 29 2010This paper is concerned with the holonomy of a class of spaces which includes Landsberg spaces of Finsler geometry. The methods used are those of Lie groupoids and algebroids as developed by Mackenzie. We prove a version of the Ambrose-Singer Theorem ... More
Homogeneity and projective equivalence of differential equation fieldsSep 16 2011We propose definitions of homogeneity and projective equivalence for systems of ordinary differential equations of order greater than two, which allow us to generalize the concept of a spray (for systems of order two). We show that the Euler-Lagrange ... More
The fundamental form of a homogeneous Lagrangian in two independent variablesSep 19 2007We construct, for a homogeneous Lagrangian of arbitrary order in two independent variables, a differential 2-form with the property that it is closed precisely when the Lagrangian is null. This is similar to the property of the `fundamental Lepage equivalent' ... More
A sample of 6C radio sources designed to find objects at redshift > 4: II --- spectrophotometry and emission line propertiesJun 07 2001(Abridged) This is the second in a series of three papers which present and interpret basic observational data on the 6C* 151-MHz radio sample: a low-frequency selected sample which exploits filtering criteria based on radio properties (steep spectral ... More
On (a,b) Pairs in Random Fibonacci SequencesAug 11 2016We study the random Fibonacci tree, which is an infinite binary tree with non-negative numbers at each node defined as follows. The root consists of the number 1 with a single child also the number 1. Then we define the tree recursively in the following ... More
The multiplier approach to the projective Finsler metrizability problemMar 14 2012This paper is concerned with the problem of determining whether a projective-equivalence class of sprays is the geodesic class of a Finsler function. We address both the local and the global aspects of this problem. We present our results entirely in ... More
Stages of Homogeneous Nucleation in Solid Isotopic Helium MixturesNov 21 2007We have made pressure and NMR measurements during the evolution of phase separation in solid helium isotopic mixtures. Our observations indicate clearly all three stages of the homogeneous nucleation - growth process: 1) creation of nucleation sites; ... More
Disordering to Order: de Vries behavior from a Landau theory for smecticsDec 20 2006We show that Landau theory for the isotropic, nematic, smectic A, and smectic C phases generically, but not ubiquitously, implies de Vries behavior. I.e., a continuous AC transition can occur with little layer contraction; the birefringence decreases ... More
Muon Calibration at SoLidFeb 06 2016The SoLid experiment aims to make a measurement of very short distance neutrino oscillations using reactor antineutrinos. Key to its sensitivity are the experiments high spatial and energy resolution, combined with a very suitable reactor source and efficient ... More
Hilbert forms for a Finsler metrizable projective class of spraysJun 29 2012Jan 11 2013The projective Finsler metrizability problem deals with the question whether a projective-equivalence class of sprays is the geodesic class of a (locally or globally defined) Finsler function. In this paper we use Hilbert-type forms to state a number ... More
Real-time processing of the imaging data from the network of Las Cumbres Observatory Telescopes using BANZAINov 10 2018Work in time-domain astronomy necessitates robust, automated data processing pipelines that operate in real time. We present the BANZAI pipeline which processes the thousands of science images produced across the Las Cumbres Observatory Global Telescope ... More
Responses to ``Theoretical Mathematics: Toward a cultural synthesis of mathematics and theoretical physics'', by A. Jaffe and F. QuinnApr 01 1994This article is a collection of letters solicited by the editors of the Bulletin in response to a previous article by Jaffe and Quinn [math.HO/9307227]. The authors discuss the role of rigor in mathematics and the relation between mathematics and theoretical ... More
Towards Completing a Large Area ULIRG SurveyAug 27 1998We present the latest results in our efforts to produce a complete, large sample of Ultraluminous Infrared Galaxies (ULIRGs, L60 > 10^11.4 Lsun for H0=100kms^-1 Mpc^-1, q0=0.5) for use in the study of these objects and their evolution. We have been using ... More
Pattern stabilization through parameter alternation in a nonlinear optical systemFeb 22 2006We report the first experimental realization of pattern formation in a spatially extended nonlinear system when the system is alternated between two states, neither of which exhibits patterning. Dynamical equations modeling the system are used for both ... More
A New Twist on the Electroclinic Critical Point: Type I and Type II Smectic $C^*$ SystemsFeb 14 2019This analysis of the electroclinic effect in ferroelectric liquid crystals with a first order Smectic-$A^*$--Smectic-$C^*$ (Sm-$A^*$--Sm-$C^*$) transition, shows they can be either Type I or Type II. In temperature--field parameter space Type I systems ... More
Spin glass transition in geometrically frustrated antiferromagnets with weak disorderSep 28 2009May 04 2010We study the effect in geometrically frustrated antiferromagnets of weak, random variations in the strength of exchange interactions. Without disorder the simplest classical models for these systems have macroscopically degenerate ground states, and this ... More
Shape maps for second order partial differential equationsDec 15 2015We analyse the singularity formation of congruences of solutions of systems of second order PDEs via the construction of \emph{shape maps}. The trace of such maps represents a congruence volume whose collapse we study through an appropriate evolution ... More
Tangent bundle geometry induced by second order partial differential equationsDec 07 2014Dec 16 2015We show how the tangent bundle decomposition generated by a system of ordinary differential equations may be generalized to the case of a system of second order PDEs `of connection type'. Whereas for ODEs the decomposition is intrinsic, for PDEs it is ... More
A ROC-based Approximate Bayesian Computation algorithm for model selection: application to fingerprint comparisons in forensic scienceMar 27 2018Feb 08 2019Approximate Bayesian Computation enables inference in complex feature spaces where likelihood-based inference cannot be performed. However, ABC methods are sensitive to the curse of dimensionality resulting from the use of large vectors of insufficient ... More
An update to the EVEREST K2 pipeline: Short cadence, saturated stars, and Kepler-like photometry down to Kp = 15Feb 17 2017We present an update to the EVEREST K2 pipeline that addresses various limitations in the previous version and improves the photometric precision of the de-trended light curves. We develop a fast regularization scheme for third order pixel level decorrelation ... More
de Vries behavior of the electroclinic effect in the smectic-A* phase near a biaxiality-induced smectic-A* -- smectic-C* tricritical pointOct 20 2011Using a generalized Landau theory involving orientational, layering, tilt, and biaxial order parameters we analyze the smectic-A* and smectic-C* (Sm-A* -- Sm-C*) transition, showing that a combination of small orientational order and large layering order ... More
IndistinguishabilitySep 18 2016This is a systematic review of the concept of indistinguishability in both classical and quantum mechanics, with particular attention to Gibbs' paradox. Section 1 is on the Gibbs paradox; section 2 is a defense of the concept of classical indistinguishability, ... More
Minimal Faithful Permutation Degrees for Irreducible Coxeter Groups and Binary Polyhedral GroupsNov 30 2008Mar 21 2014In this article we calculate the minimal faithful permutation degree for all of the irreducible Coxeter groups. We also exhibit new examples of finite groups that possess a quotient whose minimal degree is strictly greater than that of the group.
Space-Time and ProbabilityDec 14 2001Special relativity is most naturally formulated as a theory of space-time geometry, but within the space-time framework probability apears to be at best an epistemic notion - a matter of what can be known, not of the status of events in themselves. However, ... More
What is Probability?Dec 24 2004Probabilities may be subjective or objective; we are concerned with both kinds of probability, and the relationship between them. The fundamental theory of objective probability is quantum mechanics: it is argued that neither Bohr's Copenhagen interpretation, ... More
Derivation of the Born Rule from Operational AssumptionsNov 21 2002Nov 21 2002The Born rule is derived from operational assumptions, independent of the normalization of the state. Unlike Gleason's theorem, the argument applies even if probabilities are defined for only a single resolution of the identity, so it applies to all the ... More
On the explanation for quantum statisticsNov 15 2005The concept of classical indistinguishability is analyzed and defended against a number of well-known criticisms, with particular attention to the Gibbs' paradox. Granted that it is as much at home in classical as in quantum statistical mechanics, the ... More
De Vries Behavior in Smectics near a Biaxiality Induced Smectic A - Smectic C Tricritical PointDec 15 2008We show that a generalized Landau theory for the smectic A and C phases exhibits a biaxiality induced AC tricritical point. Proximity to this tricritical point depends on the degree of orientational order in the system; for sufficiently large orientational ... More
Very fast transmissive spectrograph designs for highly multiplexed fiber spectroscopyJul 26 2016Very fast (f/1.2 and f/1.35) transmissive spectrograph designs are presented for Hector and MSE. The designs have 61mm x 61mm detectors, 4 or 5 camera lenses of aperture less than 228mm, with just 6 air/glass surfaces, and rely on extreme aspheres for ... More
Complementarity and Scientific RationalityDec 24 2004Bohr's interpretation of quantum mechanics has been criticized as incoherent and opportunistic, and based on doubtful philosophical premises. If so Bohr's influence, in the pre-war period of 1927-1939, is the harder to explain, and the acceptance of his ... More
Rethinking Newton's $\textit{Principia}$Sep 20 2016It is widely accepted that the notion of an inertial frame is central to Newtonian mechanics and that the correct space-time structure underlying $\text{Newton's}$ methods in $\textit{Principia}$ is neo-Newtonian or Galilean space-time. I argue to the ... More
Experimental device-independent verification of quantum steeringAug 04 2014Aug 07 2014Bell nonlocality between distant quantum systems---i.e., joint correlations which violate a Bell inequality---can be verified without trusting the measurement devices used, nor those performing the measurements. This leads to unconditionally secure protocols ... More
Experimental EPR-Steering of Bell-local StatesSep 04 2009Jan 24 2011Entanglement is the defining feature of quantum mechanics, and understanding the phenomenon is essential at the foundational level and for future progress in quantum technology. The concept of steering was introduced in 1935 by Schr\"odinger as a generalization ... More
PILOT: design and capabilitiesJan 29 2008The proposed design for PILOT is a general-purpose, wide-field 1 degree 2.4m, f/10 Ritchey-Chretien telescope, with fast tip-tilt guiding, for use 0.5-25 microns. The design allows both wide-field and diffraction-limited use at these wavelengths. The ... More
Experimental demonstration of non-bilocal quantum correlationsOct 26 2016Quantum mechanics admits correlations that cannot be explained by local realistic models. Those most studied are the standard local hidden variable models, which satisfy the well-known Bell inequalities. To date, most works have focused on bipartite entangled ... More
The Biaxial Smectic-A* Phase -- A New Phase, Already But Unknowingly Discovered?Oct 19 2011The biaxial smectic-A* (Sm-A_B*) phase, appearing in the phase sequence Sm-A*--Sm-A*_B--Sm-C*, is analyzed using Landau theory. It is found to possess a helical superstructure with a pitch that is significantly shorter than the pitch of the Sm-C* helical ... More
Time, Quantum Mechanics, and ProbabilityNov 07 2001A "geometric" intepretation of probability is proposed, modelled on the treatment of tense in 4-dimensional spacetime. It is applied to Everett's approach to quantum mechanics, as formulated in terms of consistent histories. Standard objections to Everett's ... More
Chance in the Everett interpretationSep 15 2016The notion of objective probability or chance, as a physical trait of the world, has proved elusive; the identification of chances with actual frequencies does not succeed. An adequate theory of chance should explain not only the connection of chance ... More
The Minimal Degree for a Class of Finite Complex Reflection GroupsMar 13 2008We calculate the minimal degree for a class of finite complex reflection groups $G(p,p,q)$, for $p$ and $q$ primes and establish relationships between minimal degrees when these groups are taken in a direct product.
Maximal Cocliques in $\operatorname{PSL}_2(q)$Feb 26 2018Jan 14 2019The generating graph of a finite group is a structure which can be used to encode certain information about the group. It was introduced by Liebeck and Shalev and has been further investigated by Lucchini, Mar\'oti, Roney-Dougal and others. We investigate ... More
A Strict Inequality for a Minimal Degree of a Direct ProductAug 06 2007Aug 07 2007The minimal faithful permutation degree of a finite group G is the least non-negative integer n such that G embeds in the symmetric group Sym(n). Work of Johnson and Wright established conditions for when the minimal degree of a direct product equals ... More
The Gibbs ParadoxAug 06 2018The Gibbs Paradox is essentially a set of open questions as to how sameness of gases or fluids (or masses, more generally) are to be treated in thermodynamics and statistical mechanics. They have a variety of answers, some restricted to quantum theory ... More
Application of the Signature Method to Pattern Recognition in the CEQUEL Clinical TrialJun 07 2016The classification procedure of streaming data usually requires various ad hoc methods or particular heuristic models. We explore a novel non-parametric and systematic approach to analysis of heterogeneous sequential data. We demonstrate an application ... More
Quantum transport in mesoscopic $^3$He films: experimental study of the interference of bulk and boundary scatteringOct 28 2010Jul 22 2011We discuss the mass transport of a degenerate Fermi liquid $^3$He film over a rough surface, and the film momentum relaxation time, in the framework of theoretical predictions. In the mesoscopic r\'egime, the anomalous temperature dependence of the relaxation ... More
Experimental semi-device-independent certification of entangled measurementsApr 05 2014Certifying the entanglement of quantum states with Bell inequalities allows one to guarantee the security of quantum information protocols independently of imperfections in the measuring devices. Here we present a similar procedure for witnessing entangled ... More
Construction and evaluation of classifiers for forensic document analysisApr 05 2010Jun 28 2011In this study we illustrate a statistical approach to questioned document examination. Specifically, we consider the construction of three classifiers that predict the writer of a sample document based on categorical data. To evaluate these classifiers, ... More
Spin Dynamics of Rare Earth Ions in Phosphate Laser GlassesAug 24 1999The spin dynamics of rare earth ions (Er, Nd, Sm and Gd) in heavily doped phosphate glasses have been investigated using 31P NMR. Correlation times in the range 10^-2 to 10^-12 s have been obtained for temperatures between 4 K and 100 K. No evidence of ... More
Charge density waves in graphite; towards the magnetic ultra-quantum limitNov 12 2014Jul 26 2016Graphite is a model system for the study of three-dimensional electrons and holes in the magnetic quantum limit, in which the charges are confined to the lowest Landau levels. We report magneto-transport measurements in pulsed magnetic fields up to 60 ... More
Mean Field Theory of Collective Transport with Phase SlipsNov 12 2003The driven transport of plastic systems in various disordered backgrounds is studied within mean field theory. Plasticity is modeled using non-convex interparticle potentials that allow for phase slips. This theory most naturally describes sliding charge ... More
Empirical isochrones and relative ages for young stars, and the radiative-convective gapDec 04 2006We have selected pre-main-sequence stars in 12 groups of notional ages ranging from 1 Myr to 35 Myrs, using heterogeneous membership criteria. Using these members we have constructed empirical isochrones in V, V-I colour magnitude diagrams (CMDs). This ... More
Fractional resonances in the atom-optical delta-kicked acceleratorJun 24 2008Sep 23 2008We consider resonant dynamics in a dilute atomic gas falling under gravity through a periodically pulsed standing-wave laser field. Our numerical calculations are based on a Monte Carlo method for an incoherent mixture of noninteracting plane waves, and ... More
New Methods for Determining the Ages of PMS StarsSep 09 2009We present three new methods for determining the age of groups of pre-main-sequence stars. The first, creating empirical isochrones allows us to create a robust age ordering, but not to derive actual ages. The second, using the width of the gap in colour-magnitude ... More
Rotation of young stars in Cepheus OB3bNov 18 2009We present a photometric study of I-band variability in the young association Cepheus OB3b. The study is sensitive to periodic variability on timescales of less than a day, to more than 20 days. After rejection of contaminating objects using V, I, R and ... More
Accretion-induced luminosity spreads in young clusters: evidence from stellar rotationFeb 18 2011We present an analysis of the rotation of young stars in the associations Cepheus OB3b, NGC 2264, NGC 2362 and the Orion Nebula Cluster (ONC). We discover a correlation between rotation rate and position in a colour-magnitude diagram (CMD) such that stars ... More
Power-law behavior in the quantum-resonant evolution of the delta-kicked acceleratorJul 16 2008Sep 25 2008We consider the atom-optical delta-kicked accelerator when the initial momentum distribution is symmetric. We demonstrate the existence of quantum-resonant dynamics, and derive analytic expressions for the system evolution. In particular, we consider ... More
The manifestation of quantum resonances and antiresonances in a finite temperature dilute atomic gasJul 06 2007Aug 07 2007We investigate the effect of temperature on resonant and antiresonant dynamics in a dilute atomic gas kicked periodically by a standing wave laser field. Our numerical calculations are based on a Monte Carlo method for an incoherent mixture of non-interacting ... More
Driven depinning of strongly disordered media and anisotropic mean-field limitsFeb 14 2003Extended systems driven through strong disorder are modeled generically using coarse-grained degrees of freedom that interact elastically in the directions parallel to the driving force and that slip along at least one of the directions transverse to ... More
Maximum-likelihood astrometric geometry calibration of interferometric telescopes: application to the Very Small ArrayDec 09 2002Interferometers require accurate determination of the array configuration in order to produce reliable observations. A method is presented for finding the maximum-likelihood estimate of the telescope geometry, and of other instrumental parameters, astrometrically ... More
Measurement requirements for a near-Earth asteroid impact mitigation demonstration missionJul 21 2011A concept for an Impact Mitigation Preparation Mission, called Don Quijote, is to send two spacecraft to a Near-Earth Asteroid (NEA): an Orbiter and an Impactor. The Impactor collides with the asteroid while the Orbiter measures the resulting change in ... More
Detecting early signs of depressive and manic episodes in patients with bipolar disorder using the signature-based modelAug 03 2017Recurrent major mood episodes and subsyndromal mood instability cause substantial disability in patients with bipolar disorder. Early identification of mood episodes enabling timely mood stabilisation is an important clinical goal. Recent technological ... More
The Simplest Demonstrations of Quantum NonlocalityMar 01 2011Jul 06 2012We investigate the complexity cost of demonstrating the key types of nonclassical correlations --- Bell inequality violation, EPR-steering, and entanglement --- with independent agents, theoretically and in a photonic experiment. We show that the complexity ... More
In Situ Characterisation of an Optically Thick Atom-Filled CavityNov 17 2015Feb 02 2016A means for precise experimental characterization of the dielectric susceptibility of an atomic gas inside and optical cavity is important for design and operation of quantum light matter interfaces, particularly in the context of quantum information ... More
Arbitrarily loss-tolerant Einstein-Podolsky-Rosen steering allowing a demonstration over 1 km of optical fiber with no detection loopholeNov 03 2011Jul 03 2012Demonstrating nonclassical effects over longer and longer distances is essential for both quantum technology and fundamental science. The main challenge is loss of photons during propagation, because considering only those cases where photons are detected ... More
Redshifts and Velocity Dispersions of Galaxy Clusters in the Horologium-Reticulum SuperclusterDec 06 2005We present 118 new optical redshifts for galaxies in 12 clusters in the Horologium-Reticulum supercluster (HRS) of galaxies. For 76 galaxies, the data were obtained with the Dual Beam Spectrograph on the 2.3m telescope of the Australian National University ... More
Large-Scale Velocity Structures in the Horologium-Reticulum SuperclusterMay 17 2005We present 547 optical redshifts obtained for galaxies in the region of the Horologium-Reticulum Supercluster (HRS) using the 6dF multi-fiber spectrograph on the UK Schmidt Telescope at the Anglo Australian Observatory. The HRS covers an area of more ... More
Galaxy and Cluster Biasing from Local Group DynamicsDec 19 1999Comparing the gravitational acceleration induced on the Local Group of galaxies by different tracers of the underline density field we estimate, within the linear gravitational instability theory and the linear biasing ansatz, their relative bias factors. ... More
Bayesian modelling of clusters of galaxies from multi-frequency pointed Sunyaev--Zel'dovich observationsNov 07 2008We present a Bayesian approach to modelling galaxy clusters using multi-frequency pointed observations from telescopes that exploit the Sunyaev--Zel'dovich effect. We use the recently developed MultiNest technique (Feroz, Hobson & Bridges, 2008) to explore ... More
Exploring Novel Game Spaces with Fluidic GamesMar 04 2018With the growing integration of smartphones into our daily lives, and their increased ease of use, mobile games have become highly popular across all demographics. People listen to music, play games or read the news while in transit or bridging gap times. ... More
Global Extinction in Spiral GalaxiesFeb 19 1998Magnitude-limited samples of spiral galaxies drawn from the Ursa Major and Pisces clusters are used to determine their extinction properties as a function of inclination. Imaging photometry is available for 87 spirals in B,R,I and K' bands. Extinction ... More
A physics-based life prediction methodology for thermal barrier coating systemsMar 02 2007A novel mechanistic approach is proposed for the prediction of the life of thermal barrier coating (TBC) systems. The life prediction methodology is based on a criterion linked directly to the dominant failure mechanism. It relies on a statistical treatment ... More
Bayes-X: a Bayesian inference tool for the analysis of X-ray observations of galaxy clustersOct 07 2013Oct 16 2014We present the first public release of our Bayesian inference tool, Bayes-X, for the analysis of X-ray observations of galaxy clusters. We illustrate the use of Bayes-X by analysing a set of four simulated clusters at z=0.2-0.9 as they would be observed ... More
LSMR: An iterative algorithm for sparse least-squares problemsJun 04 2010Jun 10 2011An iterative method LSMR is presented for solving linear systems $Ax=b$ and least-squares problem $\min \norm{Ax-b}_2$, with $A$ being sparse or a fast linear operator. LSMR is based on the Golub-Kahan bidiagonalization process. It is analytically equivalent ... More
Starbug fibre positioning robots: performance and reliability enhancementsMay 28 2018Starbugs are miniature piezoelectric walking robots that can be operated in parallel to position many payloads like optical fibers across a telescopes focal plane. They consist of two concentric piezoelectric ceramic tubes that walk with micron step size. ... More
Optical designs for the Maunakea Spectroscopic Explorer TelescopeJun 23 2016Jul 27 2016Optical designs are presented for the Maunakea Spectroscopic Explorer (MSE) telescope. The adopted baseline design is a prime focus telescope with a segmented primary of 11.25m aperture, with speed f/1.93 and 1.52deg field-of-view, optimized for wavelengths ... More
The Smallest Faithful Permutation Degree for a Direct Product Obeying an Inequality ConditionOct 29 2014The minimal faithful permutation degree $\mu(G)$ of a finite group $G$ is the least nonnegative integer $n$ such that $G$ embeds in the symmetric group $\Sym(n)$. Clearly $\mu(G \times H) \le \mu(G) + \mu(H)$ for all finite groups $G$ and $H$. Wright ... More
The Surface Electroclinic Effect near the First Order Smectic-A*--Smectic-C* transitionOct 19 2011We analyze the surface electroclinic effect (SECE) in a material that exhibits a first order bulk smectic-$A^*$ (Sm-$A^*$) -- smectic-$C^*$ (Sm-$C^*$) transition. The effect of a continuously varying degree of enantiomeric excess on the SECE is also investigated. ... More
Aggregation-fragmentation model of robust concentration gradient formationFeb 06 2015Concentration gradients of signaling molecules are essential for patterning during development and they have been observed in both unicellular and multicellular systems. In subcellular systems, clustering of the signaling molecule has been observed. We ... More
Sums of Digits in q-ary ExpansionsNov 03 2013Aug 01 2014Let $s_q(n)$ denote the sum of the digits of a number $n$ expressed in base $q$. We study here the ratio $\frac{s_q(n^\alpha)}{s_q(n)}$ for various values of $q$ and $\alpha$. In 1978, Kenneth B. Stolarsky showed that $\lim\inf_{n\rightarrow\infty}\frac{s_2(n^2)}{s_2(n)}=0$ ... More
A wide field corrector with loss-less and purely passive atmospheric dispersion correctionJul 08 2014A 2.5 degree field diameter corrector lens design for the Cassegrain focus of the VISTA 4 meter telescope is presented. It comprises four single elements of glasses with high UV transmission, all axi-symmetric for operation at the zenith. One element ... More
A nuclear magnetic resonance spectrometer for operation around 1 MHz with a sub 10 mK noise temperature based on a two stage dc SQUIDOct 24 2007Nov 23 2007We have developed a nuclear magnetic resonance spectrometer with a series tuned input circuit for measurements on samples at millikelvin temperatures based on an integrated two-stage superconducting quantum interference device current sensor, with an ... More
Annotating Synapses in Large EM DatasetsSep 05 2014Dec 04 2014Reconstructing neuronal circuits at the level of synapses is a central problem in neuroscience and becoming a focus of the emerging field of connectomics. To date, electron microscopy (EM) is the most proven technique for identifying and quantifying synaptic ... More
LHCb VELO Timepix3 TelescopeFeb 26 2019The LHCb VELO Timepix3 telescope is a silicon pixel tracking system constructed initially to evaluate the performance of LHCb VELO Upgrade prototypes. The telesope consists of eight hybrid pixel silicon sensor planes equipped with the Timepix3 ASIC. The ... More
Hidden variable interpretation of spontaneous localization theoryApr 11 2011The spontaneous localization theory of Ghirardi, Rimini, and Weber (GRW) is a theory in which wavepacket reduction is treated as a genuine physical process. Here it is shown that the mathematical formalism of GRW can be given an interpretation in terms ... More
MOS: A critical tool for current and future radio surveysJun 18 2015Since radio continuum observations are not affected by dust obscuration, they are of immense potential diagnostic power as cosmological probes and for studying galaxy formation and evolution out to high redshifts. However, the power-law nature of radio ... More
Completing the Liénard-Wiechert potentials: The origin of the delta function fields for a charged particle in hyperbolic motionSep 04 2014Dec 03 2014Calculating the electromagnetic field of a uniformly accelerated charged particle is a surprisingly subtle problem that has been long discussed in the literature. While the correct field has been obtained many times and through various means, it remains ... More
Quasars as probes of cosmological reionizationNov 03 2015Quasars are the most luminous non-transient sources in the epoch of cosmological reionization (i.e., which ended a billion years after the Big Bang, corresponding to a redshift of z ~ 5), and are powerful probes of the inter-galactic medium at that time. ... More
Deprojecting Densities from Angular Cross-CorrelationsDec 03 2002I present a model-independent spherically symmetric density estimator to be used in the cross-correlation of imaging catalogs with objects of known redshift. The estimator is a simple modification of the usual projected density estimator, with weightings ... More