Computational Researchers develop and use software that implements known physical laws to model nature or simulate the workings of nature, thereby making possible approaches to problems that are analytically intractable. Also, some computational researchers develop and implement algorithms for exploring "big data". For example, computational particle physicists have studied the interactions of quarks in hadrons to identify how much mass is attributable to energy and to predict the existence of multi-quark particles that are stable but not yet discovered. Computational atomic and molecular physicists have guided experimental research by evaluating the cross section for an interaction from simulations of millions of events with a wide range of initial conditions. Computational astronomers "created" the current Universe by gravitationally evolving from the Big Bang to the present a cube containing a billion particles of dark and normal matter. Then, they "explored" the simulated Universe to identify galaxies and study their large-scale distribution.
Here are the Computational Researchers who are able to supervise graduate students. To see a detailed profile of anyone, including contact information, click on the title bar or portrait. To see a personal research website (if available), click on the research picture.
Supernovae and their remnants; Pulsars; Active Galactic Nuclei; Observational tests of general relativity; Radio continuum astronomy; Very Long Baseline Interferometry.
I study galactic and extragalactic compact, celestial sources of radio waves such as supernovae, pulsars, black hole candidates, radio stars and the powerful cores of radio galaxies and quasars. With the technique of very-long-baseline interferometry (VLBI) and a network of several large radio telescopes girdling the globe, it is possible to image the areas of activity of these sources and determine their positions with an angular resolution 1,000 times better than with any optical telescope on Earth. In particular, this allows us to make sequences of images of young, rapidly expanding supernovae, study the interaction of their shock fronts with the circumstellar medium, search for pulsars in their centres and compose the results in a "movie of an exploding star." As a spin-off, we obtain vital information for determining the distance to the host galaxy, which helps to anchor the extragalactic distance scale. We have developed a novel data acquisition system for phase-coherent baseband recording of pulsars to complement our VLBI observations and extend our studies to searches for new millisecond pulsars and their possible companion planets and black holes. Also, we investigate the cosmological jets of energetic particles which emanate from the active centers of so-called superluminal radio galaxies and quasars with speeds that appear to be faster than the speed of light. These studies help us to understand the physics of the immediate environment of these centres which are believed to be supermassive black holes.
Auditory biophysics, especially otoacoustic emissions; Tuvan throat singing; Coupled/nonlinear oscillators; Signal processing in sensory physiology.
I am primarily interested in auditory biophysics, chiefly in the context of how sound is transduced by the ear into neural impulses going to the brain. Remarkably, somehow in the process of being a very sensitive detector, the (healthy) ear generates and subsequently emits sounds that can be detected non-invasively using a sensitive microphone. These sounds, known as otoacoustic emissions (OAEs), reveal many aspects of the inner workings of the ear and also have many translational applications (e.g., clinical audiology). Our lab combines both experimental and theoretical/modeling approaches across a broad comparative framework so to help us better understand OAEs and thereby the key biophysical processes at work that allow us to hear the world around us.
Applications of Global Navigation Satellite Systems (GNSS), especially to positioning and navigation.
My research interests centre on the use of Global Navigation Satellite Systems (GNSSs), most notably GPS, for a multitude of precise positioning and navigation applications. Specific application areas include crustal deformation monitoring, precise orbit determination, and precise positioning of offshore platforms. This research requires development of positioning algorithms, which include filters, functional models, stochastic models, and prediction models to mitigate physical affects. Recent algorithm research has focused on improving the robustness of precise point positioning, and extending the range of single-baseline, real-time kinematic (RTK) GPS.
Atomic and molecular collisions, especially involving positrons.
In recent years, the availability of intense positron beams allowed for an increase in the number of ionization experiments. The first experiments, which studied noble gases, were followed by measurements of the ionization cross sections for other atoms and molecules and for triple differential cross section measurements. Our work uses various theoretical models to reproduce the existing experimental cross sections. For the calculation of the total ionization cross sections of atoms and molecules, we have explored the use of distorted-wave models, containing a realistic description of the final state of the system and including distortion and polarization effects. Recently, we expanded our work to the study of the electron-capture-in-the-continuum (ECC) phenomenon in positron impact ionization of helium and molecular hydrogen. We employed a 3C theoretical model in representing the final state of the ionization system, which allowed us to obtain good agreement with the existing "triple differential cross section" experiments.
I am an active developer of advanced numerical modeling and data assimilation systems for studying weather and climate. I utilize state-of-the-art numerical models and ensemble-based data assimilation techniques to improve weather forecasts, regional climate predictions, and air-quality forecasts. Particularly, I am interested in mesoscale dynamics and severe weather.
Quantum field theory; Positron interactions; Quantum scattering theory.
My current research is concerned with the development and application of variational (i.e non-perturbative) methods in quantum field theory. I am particularly interested in using the variational method to derive (and solve) relativistic few-body wave equations from the underlying quantum field theory. I investigate model quantum field theories, such as the Yukawa model, as well as QED and various sectors of the standard model. In addition, I am interested in positron interactions with simple molecules and atoms, particularly ionization and annihilation, as well as bounded variational methods in quantum scattering theory.
Active Galactic Nuclei, especially Seyfert galaxies; Cool dwarf stars; Structure of the Milky Way galaxy.
I am interested in the nuclei of galaxies, especially the nature and origin of nuclear activity. Active Galactic Nuclei (AGN) are the centres of some galaxies which emit tremendous amounts of non-stellar radiation. Such radiation is believed to be generated by the accretion of matter -- gas and stars -- onto supermassive black holes. This intense radiation has profound effects on the circumnuclear environment of these galaxies. There are numerous members of the AGN family, including relatively nearby Seyfert galaxies and the more distant quasars. Of particular interest to me is the origin of activity in Seyfert galaxies, especially the role played by the environment in which such galaxies are situated.
I am interested also in aspects of Galactic structure, particularly M dwarf stars. The overwhelming majority of stars in the solar neighbourhood, and indeed in the Milky Way Galaxy itself, are cool, relatively unspectacular stars called late-type (M) dwarfs and subdwarfs. These stars are so faint that they cannot be seen to great distances and are consequently difficult to detect. I am involved in studying how these stars behave within the Milky Way (kinematics), as well as determining their surface temperature and metal abundance using imaging techniques.
Computational chemistry, especially applications to atomic clusters, molecular ions, and transition metal complexes.
Using various methods of computational chemistry in combination with global optimization and simulation methods, I study atomic clusters that range in size from 3 atoms to a few hundred atoms. The geometric structure and properties of small clusters are very different from those of the corresponding bulk materials. For example, silver clusters are not fragments of the fcc crystal, and clusters of rhodium are magnetic. Our theoretical predictions of vibrational spectra and electron detachment energies are compared to experiment for structure elucidation. We try to understand the factors controlling stability, so that we might predict cluster sizes and compositions that are particularly stable. We also model surfaces and noncrystalline materials with clusters having a hundred or more atoms using more approximate theoretical models, such as empirical potentials and model hamiltonians. I am also interested in molecular ions and transition metal complexes.
Active Galactic Nuclei, especially quasars; Black holes; Gravitational lensing.
When matter spirals into a supermassive black hole at the centre of a galaxy, a kind of friction can heat the matter up until it shines brightly enough to be seen all the way across the universe. We call such objects quasars. I am interested in understanding more clearly the dynamics of gas spiralling around black holes in quasars. That knowledge will improve our ability to infer the physical properties of quasars and their black holes (such as mass and spin) from the details of the light they produce. I am particularly interested in outflows of gas from quasars. Much of the mass spiralling around in a quasar ends up in the black hole, but some of it is flung outwards and is sometimes visible in the spectrum of the quasar. Establishing the connections between those absorption lines and the emission lines seen in most quasars will help us understand how quasars work and how galaxies form. I am also interested in gravitational lensing, which can take a small, faint galaxy and stretch it out into a long, luminous arc. My research is both experimental and theoretical. I do much of my experimental work using online databases from large astronomical surveys, supplementing data as necessary with modern instruments on large telescopes.
Neutrino masses and mixing; Neutrino interactions with nuclei.
My research aims to understand the neutrino, the most abundant particle in the universe that has any mass. Because the neutrino almost never interacts, we know very little about it. However, that same characteristic also means that we can study them by making a beam of neutrinos and shooting them long distances through the earth and studying their composition after they have had time to evolve over time. These measurements can tell us more precisely what the mass differences are between different neutrinos, whether their masses are like the charged fermion mass spectra or the inverse, and whether neutrinos and antineutrinos evolve the same way over time. Because neutrinos have mass, they have a huge impact on galaxy formation in the universe, and if neutrinos and antineutrinos evolve differently, they may be the reason that the universe today is dominated by matter rather than simply being full of light from matter-antimatter annihilations.
The Deep Underground Neutrino Experiment (DUNE) combines an enormous fine-grained neutrino detector with an intense broad-band neutrino beam that has traveled over 1300 km by the time it reaches that detector. DUNE will enable us to test the neutrino oscillation framework at a level of detail and precision that is simply not possible with today’s suite of very capable narrow-band neutrino beam experiments. I will be working on DUNE’s near detector, because the best predictions for what the far detector will see come from an accurate (and tested) description of how neutrinos interact and from extensive measurements from the DUNE Near Detector Complex. My ultimate research plan is to do precision oscillation measurements on DUNE.
However, just as the detector and beamline for DUNE are not yet ready today, the field of neutrino physics as a whole is not yet ready to predict oscillated neutrino event rates over a broad range of energies at the required level of precision. In order to fulfill DUNE's promise of precision we not only have to build the detector and neutrino beamline, but we also have to understand the way neutrinos will interact in that detector. The MINERvA experiment, located at Fermilab, has started writing the book on neutrino interactions and how the nuclear environment affects those interactions. We have collected a huge sample of neutrino and antineutrino interactions on many different nuclei, and are able to shine a much brighter light on neutrinos than ever before. I am currently the co-spokesperson of MINERvA and I am making sure many more neutrino interaction measurements come from MINERvA to best prepare for DUNE.
My professional research goals centre around the investigation and solution of mathematical and computational problems of scientific and engineering relevance. During the last few years, I have worked on a variety of highly applied and very challenging problems in electromagnetics, hydrodynamics, and combinations of both. For example, I have researched wire antenna problems, numerical methods for optical gratings, enhanced radar backscatter from the ocean surface, hydrodynamic stability problems, blood flow in compressed vessels, and the hydrodynamics of expanding universes. Certainly, computational science lies at the core of my research interests.
The main goal of computational electromagnetics, for example, is the design and implementation of numerical methods that can be used to efficiently simulate electromagnetic wave interactions with complex material structures. This field has shown an impressive growth in recent years, as improved numerical algorithms enable accurate simulation of the ever more complex phenomena arising in an ever growing number of applications. The numerical methods used in this area draw from the classical approaches, such as the method of moments and finite-element based algorithms into the efficient high-order/accelerated algorithms that have arisen over the last two decades. Applications are found in communications (transmission through optical fiber or wireless communication), remote sensing and surveillance (radar and sonar systems), geophysical prospecting, materials science, and biomedical imaging (optical coherence tomography), to name but a few.
Significant challenges arise in the design of reliable numerical algorithms for engineering and industrial applications such as those mentioned above. These challenges are largely due to the necessity of numerical methods to resolve wave oscillations and interactions of these with geometrically and/or compositionally complex structures, which lead to very high (often prohibitive) computational costs for many problems of interest. The focus of my work has been and will continue to be the development and implementation of efficient, fast and accurate numerical algorithms to enable treatment of challenging engineering and scientific applications.
High-precision laser spectroscopy of atoms; Experimental tests of Quantum Electrodynamics and the Standard Model; Antimatter, especially antihydrogen; Proton radius; Laser cooling and atom trapping.
I employ lasers to make high-precision measurements of atomic properties to test the predictions of Quantum Electrodynamics and the Standard Model of particle physics. Currently, I am studying atomic hydrogen to make a new measurement of the radius of the proton to try to understand the deviant value recently obtained from muonic hydrogen. If the discrepancy is real, it may herald the discovery of a new boson or even gravity in higher dimensions. Also, I am part of a collaboration whose goal is to hold antihydrogen atoms (antimatter versions of the element hydrogen) in a magnetic trap and use them to conduct precise spectroscopic tests of the symmetries and physics of antimatter. Additionally, I am involved in measuring the energies and orbits of helium atoms to provide the most accurate measurement of the "fine structure constant,” the fundamental constant of nature that determines the strength of the electric and magnetic forces between charged objects. The fine structure constant is not only relevant to magnets and electricity, but to how atoms, chemicals, and solid objects are held together.
Collisions of ions with atoms and molecules; Ionization and electron capture; Interactions of matter with strong laser fields; Quantum optics.
I study interactions of atoms and simple molecules in collisions with ions or in exposure to strong laser fields by theoretical and computational methods. My particular interests are in the areas of multiple ionization and capture of electrons in collisions of highly charged ions. Also, I am interested in quantum optics, especially in measurements of the radius of the proton and the line shape problem for high-precision spectroscopy, as well as the problem of electron-positron pair creation in ultra-strong fields. My emphasis is on developing new computational methods and testing time-dependent density functional theory.
I study biologically-inspired imaging systems, i.e., electronic camera chips and networks of cameras. My work encompasses distributed sensor systems based on insect and spider eyes, sensor swarms, clouds and "smart dust" modelled on ant colonies and schools of fish, high performance integrated sensor design, on-chip image processing methodologies, semiconductor device modelling and simulation, and radiation tolerant design and manufacturing. Applications include aircraft collision avoidance, space systems, industrial inspection, machine vision, and vision rehabilitation.
Theoretical cosmology, especially cosmic inflation, eternal inflation, dark energy, and confrontations with observations; Field theory; String theory; Gravitation.
The goal of my research is to understand the fundamental laws of nature through their impact on cosmology. I am primarily a theorist, dabbling in cosmology, field theory, string theory, and gravitation. I am actively engaged in research on cosmic inflation, eternal inflation, topological defects, and models of dark energy. I also design data analysis algorithms to confront fundamental theory with observations of the Cosmic Microwave Background (CMB) radiation. Here is a sampling of the questions that drive my research: How big is the universe? What might lie beyond our observable universe, and how could we confirm or disprove various proposals? What role do the extra dimensions predicted by string theory play in cosmology? What is the fundamental nature of space-time singularities? Are there new ways of looking at cosmological datasets that could be useful when confronting theories with data? Can computer simulations of the very early universe shed light on its possible initial conditions and evolution?
Interactions of atomic and molecular few-body systems with particles and fields; Ionization and fragmentation of molecules; Density functional theory; Time-resolved quantum dynamics.
My research is concerned with the question of how atomic and molecular few-body systems respond to perturbations exerted on them by impinging particles and external fields. Quantum dynamics induced by collisions or laser fields have implications for a variety of topics and applications ranging from plasma diagnostics to radiation biology. What is more, they constitute a problem of fundamental importance: How do the building blocks of matter interact and evolve in space and time? The better this question is answered, the more is learned about a further issue that receives considerable attention: Can few-body quantum dynamics be manipulated purposefully and controlled actively?
I have participated in a number of projects and activities to elucidate these topics by theoretical analysis and computations. Methods based on density functional theory deal with the many-electron problem, and both nonperturbative and perturbative quantum methods describe the dynamics of the systems. Currently, we are working on a method to describe ionization and fragmentation of multi-center molecules. First applications are concerned with ion-induced fragmentation of water, which is a relevant process in the radiation damage of biological tissue. In the long run we hope to study even more complex systems, thereby exploring the transition from correlated to collective dynamics. Our central goal is to contribute to a microscopic understanding of time-resolved quantum dynamics, and to investigate applicability and limitations of density functional theory by practical calculations.
Strongly-coupled quantum field theories, especially qantum chromodynamics; Lattice field theory simulations.
I aim to understand strongly coupled quantum field theories, quantum chromodynamics (QCD) in particular. QCD is the theory of the nuclear and sub-nuclear strong force, the force that binds protons and neutrons to form nuclei and at a deeper level, the force that binds quarks to form neutrons and protons. Although the theory can be stated very compactly and elegantly, its solution has eluded physicists for decades. This is perhaps not surprising as QCD can be thought of as a theory of 104 complex-valued quantum variables at each point in space. One of the most promising approaches for studying QCD is Monte-Carlo simulation of the field theory on a space-time lattice. I use this technique to study nuclear forces, colour-flux-tube breaking and other problems.
Micro- and nano-structuring of polymer material systems; Bio-based and smart multifunctional materials; Advanced thermal management materials.
My research is focussed on micro- and nano-structuring of polymer material systems, with the emphasis on tailoring and optimizing their multifunctional properties for a wide spectrum of applications (e.g., energy storage and harvesting, sensing and actuation, biomedical devices, thermal management, and environmentally benign packaging). This highly interdisciplinary research area requires integrating the principles and techniques of advanced manufacturing, materials science, fluid mechanics, thermodynamics, and rheological sciences.
Quantum chromodynamics (QCD); Lattice quantum field theories; Physics beyond the Standard Model, including dark matter.
Inside the protons and neutrons of every atom's nucleus, there are quarks. The strong force that is responsible for the perpetual confinement of quarks is described by Quantum Chromodynamics (QCD). My recent research has combined theoretical methods with supercomputer simulations to explore this quantum theory of quarks via lattice QCD computations, chiral perturbation theory, and heavy quark symmetry. My work also extends to theories beyond the Standard Model of particle physics.
I am interested in the consequences of the Standard Model of particle physics for few-body nuclear systems and low-energy particle physics and dynamics. My recent research has focussed on Quantum Chromodynamics (QCD), the theory of the strong interactions, using the techniques of chiral perturbation theory and various versions of QCD sum rules to study weak, strong, and electromagnetic observables.
High-precision optical and microwave spectroscopy of atoms; Atomic clocks and time standards; Instrument interfaces and real-time digital control.
I carry out experimental research in atomic physics, especially high-precision spectroscopic measurements and frequency generation. My background is in nonlinear optics and optical cooling. I bring this knowledge to bear on developing atomic clocks to obtain a physical realization of the international SI second. Currently, I am improving on a primary time standard which does not lose or gain more than a millionth of a second in five years.
Formation, evolution, and structure of galaxies; Aggregates of galaxies, especially the Local Sheet and analogues; Interstellar matter, especially gaseous nebulae.
I study the formation, evolution, and organization of galaxies large and small, with the objective of elucidating how we came to be. Insights into the mechanisms driving evolution are gained by utilizing gaseous nebulae (planetary nebulae and HII regions) to probe chemical compositions. Surface photometry, particularly at near-infrared wavelengths, is combined with dynamical measurements to seek a unified description of normal galaxies, which facilitates examination of how different kinds of galaxies are related and which ultimately confronts the “nature versus nurture” debate over origins. To refine knowledge about our place in the Cosmic Web, I implement improved methodologies for determining the distances of galaxies. A recent outcome is a precise three-dimensional map of the Local Sheet of galaxies that reveals that the development of our own galaxy, the Milky Way, was influenced by an environment of far greater extent than hitherto recognized. Now, my students and I are finding and studying analogues of the Local Sheet in the greater Universe to learn what attributes of the Local Sheet were most relevant to the realization of the Milky Way as it exists today. Modern simulations of structure formation are utilized as “virtual universes” to guide the interpretation of measurements and to test theoretical foundations. Much of the work on individual galaxies and the structures in which they are embedded also leads to insights about the origin of spin and the nature, localization, and preponderance of dark matter in the Universe. My primary research adversary is interstellar dust, and I have spent a good deal of time uncovering what lies behind it, including two hitherto unknown galaxies in the backyard of the Milky Way as well as the Council of Giants surrounding us.
Atomic processes, especially electron and positron scattering; Plasma physics.
My work is in theoretical atomic physics. I am particularly interested in electron and positron scattering, both elastic and inelastic, and I endeavour to calculate cross sections for a wide range of targets. Such cross sections are essential to understanding how matter behaves in a wide range of environments, be they natural (e.g., the Earth’s atmosphere, or astrophysical plasmas) or constructs of humans (e.g., fission or fusion reactors).
Space-based remote sensing of Earth's atmosphere, especially low-altitude pollution; Evolution of ozone layer; Information retrieval from atmospheric spectra.
I use remote sensing observations by satellites to better quantify and understand the distribution, evolution, sources and sinks of air pollutants. Primarily, I develop models for the retrieval of atmospheric composition from UV-visible spectra acquired by satellites, and then use the results to quantify, map, and evaluate trends in emissions of surface pollutants over urban and industrial locations. I am also interested in understanding and quantifying the evolution of stratospheric ozone and ozone-related trace gases, especially those composed of species of nitrogen and bromine. Additionally, I am engaged in monitoring how the extraction of oil from oil sands is affecting atmospheric composition.
Planetary volatiles, from ices to atmospheres; Laboratory simulation of planetary bodies; Space mission operations, design, and data analysis; Planetary instrument design and development.
My research interests lie in the planetary sciences, particularly planetary atmospheres and interactions with planetary surfaces. Questions that I address span the solar system, from Earth to Mars to Comets to Ceres to Giant Planets and their icy satellites. For example, how is it that Mars went from being a warm and wet world in the ancient past to the dry and frozen desert world of today? How is it that an icy body like Enceladus can geyser water droplets out into space, and what can that material tell us about the ocean that lies within? In order to find answers to such questions, it is necessary to send spacecraft out to explore and to establish ground-based facilities to interpret returned data.
I am currently supporting Surface Operations on the Mars Science Laboratory Rover (Curiosity) and developing planetary simulation facilities at York University as part of the Planetary Volatile Laboratory. Previously, I have led experimental studies into interactions of volatiles with the Martian surface and polar caps. After my training with the Mars Exploration Rovers, I worked on the Huygens probe to Titan and I also participated in the development of the Surface Stereo Imager for the Phoenix Mars Lander. Also, I have been involved in several conceptual space mission design studies and analogue planetary missions. I have experience modeling scattering in the atmospheres of Earth and of Mars from the ultraviolet into the near infra-red and dynamical modeling of the Martian atmosphere. Recently, my work has led to the first direct detection of fog on Mars, to estimates of the methane content of the martian atmosphere from exogenous sources, and to an understanding of the origin of ridges of ice on the surface of Pluto.
Distant galaxies and clusters of galaxies; Formation and evolution of galaxies, especially environmental influences.
Most of my work is on how distant galaxies form and evolve, and how that evolution is related to their larger scale environment. Because light is redshifted by the expansion of the Universe, studies of distant galaxies almost always involve infrared observations. I use sophisticated instrumentation on ground-based and space-based telescopes to conduct multi-wavelength surveys of galaxies and galaxy clusters. In so doing, I am able to constrain star formation rates and galaxy masses as a function of redshift and thereby ascertain how galaxies grow and at what rate.
Space instrumentation; Space test processes; Planetary atmospheres; Radio astronomy.
My research focuses on the development of space-based instrumentation, data analysis techniques and tools, and space test processes to advance planetary research and to improve the performance and reliability of space systems. For example, I am a member of the York University Argus team that is currently operating a pollution monitoring spectrometer in low Earth orbit on the CanX-2 spacecraft. This technology was awarded the Canadian Astronautics and Space Institute Alouette award in 2010. Also, I am the inventor of a novel construction technology for a space elevator which has attracted world-wide interest. In collaboration with Thoth Technology, Inc., I am currently developing a mission to Mars called Northern Light which will explore new regions of the planet. In the process, I have revived Algonquin Park Radio Observatory, and am presently using it for endeavours ranging from spacecraft tracking to very-long-baseline interferometry of pulsars.
Spacecraft dynamics, control and navigation; Formation flying; Active vibration control; Membrane structures; Smart materials and structures; Multi-agent systems; Motion synchronization; Trajectory design and optimization.
I conduct research in spacecraft dynamics, control and navigation. I am particularly interested in cooperative and coordinated control of multiple vehicles, i.e., formation flying. Consequently, I must delve into such areas as active vibration control, smart materials and structures, membrane structures, and motion synchronization. For this purpose, I founded and direct the Spacecraft Dynamics Control and Navigation Laboratory at York University.
Airglow; Aurorae; Atmospheric dynamics and composition; Space instrumentation.
I am interested in the properties of the upper atmosphere, and develop ground- and space-based instruments for conducting measurements. The upper atmosphere, in the region from 80 to 300 km, is where solar energy input first begins to interact with the atmosphere, producing optical emission known as airglow, and aurora. With specialized instrumentation, this emitted light can be used as a diagnostic tool to determine the properties of the atmosphere in this region. With support from NSERC, and the Canadian Space Agency, the Doppler Michelson Interferometer technique was developed for spectral imaging of the atmosphere, yielding images of optical emission rate, temperature and wind. As Principal Investigator for WINDII, the Wind Imaging Interferometer, a joint Canada-France instrument was placed in orbit from 1991 to 2003 on NASA’s Upper Atmosphere Research Satellite and acquired 23 million images of the atmosphere. The data are still providing exciting new information on the dynamics of the upper atmosphere, and how these dynamics influence the distribution of atmospheric species, such as atomic oxygen. Ground-based instruments have been deployed also. For example, an optical observatory was operated at Resolute Bay in Northern Canada to study the polar upper atmosphere. More recently a derivative of WINDII, the Spectral Heterodyne Spectrometer (SHS), has been developed and flown on a high altitude balloon for the measurement of water vapour in the lower atmosphere. Currently, a collaboration with Germany is in place, intended to lead to the launch of a Cubesat satellite carrying an SHS instrument to measure waves in the upper atmosphere.
Atomic and molecular processes, especially electron and positron scattering; Plasma physics.
I carry out theoretical research on the scattering of electrons and positrons from atoms and simple molecules. I am particularly interested in scattering from heavy atoms, and use the relativistic Dirac equations as the basis for computation of scattering parameters. Collaborating with graduate students and international co-workers, we perform large scale numerical computations of these processes and develop theoretical and numerical methods to carry them out. For example, we have developed the very successful Relativistic Distorted-Wave Method for evaluating the scattering cross sections as well as the spin polarization parameters for the scattered electrons and the Stokes parameters for the light emitted from atoms excited during the scattering interactions. I am also involved in projects which make use of the atomic data we generate. Much of our work is of use in plasma physics, particularly in the modeling of low pressure plasmas. One example is a large-scale Monte Carlo simulation of gas-filled X-ray detectors. I maintain close contact with various experimental groups and often publish joint papers with these groups where theory and experiment can be directly compared.
Magnetic monopoles and Q-balls; Supersymmetry and Higgs bosons; Electronics for high-energy physics experiments.
I am an experimental high-energy particle physicist. I am particularly interested in searching for new particles predicted by some theories, such as magnetic monopoles and supersymmetric particles. I am also interested in the development of custom electronics for particle searches. I am a member of the ATLAS experiment at the Large Hadron Collider (LHC) at CERN in Geneva, Switzerland, which is the world’s highest energy particle accelerator. As such, I contributed to the 2012 discovery of a new particle believed to be the Higgs boson.
Particle physics is the study of the smallest constituents of matter and the four fundamental forces between them. Our current understanding is that the world is made up of six quarks and six leptons, each apparently grouped into pairs, forming three similar families of matter. Research shows that quarks and leptons do not have any substructure, that is, that they are the fundamental particles. Each of these particles is partnered with an antiparticle with the same mass but the opposite charge. The standard theoretical model of particle physics does not explain why these particles appear in three families, nor does it predict the particle masses. At a cosmological level, we do not understand why the Universe appears to be dominated by matter as opposed to antimatter, nor do we understand the source of the “dark matter” that represents 23% of the matter in the universe. Perhaps there are particles we have yet to discover. To help answer these questions, we need to go back to the Big Bang, when the universe was minute and the temperatures and densities of matter were enormous. Particle accelerators are the tools we use to recreate the conditions of the universe shortly after the Big Bang.
Presently, the York ATLAS group is engaged in a search for magnetic monopoles. All magnetic objects that have ever been observed have a north pole at one end and a south pole at the other end. A magnetic monopole is a particle postulated to carry only a south or a north pole. If a magnetic monopole exists, theory shows that this would explain why there appears to be a fundamental unit of electric charge. This is one of the outstanding mysteries in particle physics today!
We are also involved in searches for particles predicted by Supersymmetry, which is an attempt to unify the strong and weak forces in the Standard Model. One of the particles predicted by Supersymmetry could be the source of dark matter. Whether or not Supersymmetry exists, ATLAS is certain to discover new physics. So far, we have focussed on searching for a counterpart of the Z boson predicted by a version of Supersymmetry called LeptoSUSY.
We also create custom electronics for particle detection with ATLAS. To that end, I established an electronics test and development laboratory that includes the state of the art equipment necessary for such leading edge electronics projects. For example, we have worked on readout electronics (including firmware development) for the Transition Radiation Tracker in the ATLAS inner detector. We are currently building electronics to select magnetic monopoles in real time at ATLAS.
Dark matter; Physics of the weak scale; Matter/Antimatter asymmetry.
Dark matter makes up around 85% of the matter in the Universe and yet we have no explanation for it in the Standard Model of particle physics. As a particle theorist, my research focuses on proposing new ideas and new tests for dark matter in order to illuminate what this mysterious stuff actually is. Recently, I have become interested in using astronomical observations of galaxies and clusters to determine whether dark matter particles interact with each other through forces other than gravity. It is remarkable that the largest structures in the Universe, millions of light years in size, can be a laboratory to study the microscopic properties of dark matter particles. I also explore the idea that dark matter is made up of strongly-interacting constituents, much like protons and neutrons. Theories of this nature cannot be worked out using paper-and-pencil and I collaborate with lattice theorists to simulate dark matter's properties using supercomputers.
Atmospheres of Earth and Mars; Applications of lasers to remote sensing (LIDAR); Laboratory simulations of the Martian environment.
I specialize in the study of the atmospheres of Earth and Mars, primarily compositions, climate, and dynamics. To further atmospheric measurements, my group develops and applies laser remote sensing (or LIDAR) instruments for use from the ground, from aircraft, and on Mars. I led the design, testing, and implementation of a LIDAR system on the Phoenix Mars Lander to measure the distribution of dust and clouds. It resulted in the discovery of snow falling from Martian clouds. The next generation of Mars LIDAR will be directed at the surface of Mars to detect the deposition of water. It is being tested in a chamber that simulates the environment on Mars. Scientific progress is already being made with the finding that water can condense out of the atmosphere onto salts on the surface of Mars. To measure ozone, clouds, and aerosols in the Earth’s atmosphere, we have built a LIDAR system for installation on various aircraft. Recently, it was installed on the Polar-5 aircraft (DC-3) and on the Amundsen icebreaker for measurements of the impact of sea ice on air chemistry and ozone. Another recent field campaign has involved installing a LIDAR instrument on a Twin Otter aircraft for measurements of air pollution form the oil sands industry in northern Alberta.
My research interests include computational solid mechanics, dynamics of mechanical systems, and numerical methods and their applications in the aerospace and defence industries. I am particularly interested in space tethers, such as the dynamics and control of tethered spacecraft systems and the application of electrodynamic tether control to the removal of space debris. Other applications include aerial refuelling systems, aerial cable-towed instruments, and underwater cable-towed systems. Additionally I am engaged in developing autonomous space robotics for on-orbit servicing. In support of many of these endeavours, I also study multi-functional composite materials and additive manufacturing in space.
I study the way the brain represents information about the outside world, and the way in which those representations are learned. My immediate goal is to build on my expertise in machine learning and sensory neuroscience to create a camera to brain translator that could restore sight to the blind, and could be used in computer vision systems. In parallel, I will develop new data science methods that will infer the brain’s learning rules from in vivo neural data, and use those methods to determine how behavioural context affects synaptic plasticity in the visual cortex. Next, I will use the brain’s learning rules to make next-generation machine learning algorithms that will be more flexible and efficient than the current state of the art. Finally, I will reveal how the interaction between different retinal ganglion cell types supports the communication of visual information from the eyes to the brain. That work may have strong implications for the development of next-generation retinal prosthetics.