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Physics and Astronomy

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  • ItemOpen Access
    Cellular Cooperativity
    (2023-12-08) Fedoryk, Olha; Bergevin, Christopher
    The ear is sound detector that is remarkably sensitive and selective. As a nonlinear and active system, ears also emit sound, known as otoacoustic emission (OAEs). We investigated the theoretical origins of spontaneous emissions (SOAEs), which appear as idiosyncratic peaks unique to a given ear. Using an established model of locally coupled limit cycle oscillators, we adapted and extended the framework for describing an Anolis lizard ear and explored several specific hypotheses. We observed that depending on the set of parameters and number of oscillators, the system could become sensitive to initial conditions and stay either stable or unstable. We also conclude that embedding only morphological differences (via frequency or hair cell bundle height) is not enough to generate "unique ears". Finally, we achieved a peak broadening by presenting additive noise to the system both as external and local thermal noise.
  • ItemOpen Access
    Surface Water Investigations on Mars
    (2023-12-08) Saive, Elliot Edward; Whiteway, James A.
    Experiments are presented which explore whether a layer of liquid water forms at the ice table in the shallow subsurface due to contact between perchlorate and water ice on Mars. Samples of regolith simulant were mixed with varying concentrations of magnesium perchlorate and deposited over ice to simulate the ice-regolith interface as was seen on Mars. Over multiple temperature cycles, the temperatures of melting of the ice and full freezing of the resulting brine were recorded using an embedded moisture sensing device. Based on temperatures simulated to constrain the ice table at the Phoenix landing site, a perchlorate concentration of 5% is sufficient for a layer of liquid water to form which can persist for days at a time, while no liquid forms for a Mars-measured concentration of 0.6%. Other concentrations are also explored.
  • ItemOpen Access
    Search for Magnetic Monopoles and Other Highly Ionizing Particles in 13 TeV Centre-of-Mass Energy Proton-Proton Collisions with the ATLAS Detector at the LHC
    (2023-12-08) Rodriguez Vera, Ana Maria; Taylor, Wendy J.
    Among the outstanding questions of particle physics, proof of the existence of a magnetic monopole is still one of great interest. One compelling argument that motivates the search for magnetic monopoles is Paul Dirac's finding that the seemingly inexplicable quantized nature of the electric charge can be explained through the existence of magnetic monopoles. TeV-mass Dirac magnetic monopoles could potentially be produced by the sqrt{s} = 13 TeV proton-proton collisions at the LHC. This thesis documents a search for magnetic monopoles using a 138 fb^-1 dataset of Run 2 proton-proton collisions at the LHC collected by the ATLAS experiment. Due to the highly ionizing nature of the interaction of magnetic monopoles with matter, the search is extended to include other highly ionizing particles known as high electric charge objects. Two production mechanisms are considered as benchmark models to interpret the results, Drell-Yan and photon fusion. No spin constraints are imposed by Dirac's theory, and therefore both spin-0 and spin-1/2 are modelled. The collision conditions allow for masses between 0.2 and 4TeV to be studied. Theoretical considerations and experimental constraints motivate studying magnetic charges |g|= 1 and 2 g_D for magnetic monopoles and the range of |z| = 20 through |z| = 100 for high electric charge objects. Detection is based on the particle's characteristic high ionization of matter, penetration distance in the detector and lack of calorimeter shower. A data driven method is used to estimate the background contamination. No excess events are found in the signal region. Cross-section limits are computed through the CLs method with 95% confidence level. The highest mass limits to date for particle collider highly ionizing particle searches are presented.
  • ItemOpen Access
    Investigating how to simulate gauge theories on a quantum computer
    (2023-12-08) Mendicelli, Emanuele; Lewis, Randy
    Quantum computers have the potential to expand the utility of lattice gauge theory to investigate non-perturbative particle physics phenomena that cannot be accessed using a standard Monte Carlo method due to the sign problem. Thanks to the qubit, quantum computers can store Hilbert space in a more efficient way compared to classical computers. This allows the Hamiltonian approach to be computationally feasible, leading to absolute freedom from the sign-problem. But what the current noisy intermediate scale quantum hardware can achieve is under investigation, and therefore we chose to study the energy spectrum and the time evolution of an SU(2) theory using two kinds of quantum hardware: the D-Wave quantum annealer and the IBM gate-based quantum hardware.
  • ItemOpen Access
    Search for Magnetic Monopoles and Stable High-Electric-Charge Objects in 13 TeV Centre-of-Mass Energy Proton-Proton Collisions with the ATLAS Detector at the LHC
    (2023-12-08) Song, Wen-Yi; Taylor, Wendy J.
    One asymmetry of the current formulation of classical electrodynamics is the absence of a magnetic monopole, despite the existence of isolated electric charges. The existence of such a particle with net magnetic charge not only restores the symmetry between electricity and magnetism but also provides an explanation for the quantization of electric charges due to a correlation between the magnitude of a magnetic charge and that of an electric charge. Magnetic monopoles do not decays and lose kinetic energy in matter similarly as ions with high electric charge. This work presents the strategy and results of a search for magnetic monopoles and stable high-electric-charge objects with mass up to 4000 GeV. It is performed with 137 fb −1 of proton-proton collision data at a centre-of-mass energy of 13 TeV, collected during 2015 – 2018 with the ATLAS Detector at the Large Hadron Collider. No deviation from Standard Model predictions are observed, thus exclusion limits are placed on production models. These limits surpass the ones obtained in the previous search. With the increase in statistics and an interest in heavy-ion collisions, the search for magnetic monopoles and stable high-electric-charge objects will continue to play an important role in the quest for physics beyond the Standard Model.
  • ItemOpen Access
    Stars Versus Quasar Accretion Disks
    (2023-08-04) Seaton, Lucas Matthew; Hall, Patrick B.
    This thesis investigates the astrophysical effects of stars colliding with the accretion disks of supermassive black holes (SMBH) in active galactic nuclei (AGN). In this work, we model the AGN to have a thin accretion disk surrounded by a stellar nuclear cluster (SNC) containing stars on various orbital eccentricities and inclination angles striking the disk at periapse. An impacting star carves a tilted cylindrical tunnel out of the disk material and loses up to $6\times10^{-4}\%$ of its stellar mass. The time-averaged collisional luminosity is at most $10^{-2}$ times the entire disk's expected luminosity, while the emission profile of an impact site initially flares before quickly dimming to the brightness of the local disk. The parameters of the SMBH, accretion disk, SNC, and impacting stars are altered to reveal that star-disk collisions from a densely populated SNC can outshine the disk luminosity.
  • ItemOpen Access
    One Star Shines on Many Worlds: Exploring Extraterrestrial Water Through Observations of Scattered Light on the Moon and Mars
    (2022-12-14) Hayes, Conor William; Moores, John
    We investigate interactions between scattered light and water on the Moon and Mars. On the Moon, we develop an illumination and thermal model to examine small-scale temperatures and the thermal stability of volatile molecules at the Lunar Crater Observation and Sensing Satellite (LCROSS) impact site. We find that small-scale surface roughness creates a maximum temperature spread of approximately 10 K. On Mars, we derive a scattering phase function for Aphelion Cloud Belt water-ice clouds (WICs) during Mars Years 34 – 36 using Mars Science Laboratory cloud movies. We compared our phase functions with seven previously-derived Martian WIC phase functions and two Martian dust phase functions, as well as modeled phase functions for seven different ice crystal geometries. We find poor to moderate agreement with our phase functions. We also investigate interannual and diurnal variability of our phase functions, finding that any variability is minimal, consistent with previous results.
  • ItemOpen Access
    Retrieval of Water-Ice Cloud Opacity at the Phoenix Mars Landing Site from Radiative Transfer in Thermal and Visible Wavelengths
    (2022-12-14) Bischof, Grace Ann; Moores, John
    Water-ice clouds at the Phoenix landing site are investigated by considering radiative transfer in thermal and visible wavelengths. First, we reconstruct a record of water-ice clouds at the Phoenix landing site by examining the radiative contribution to the surface energy balance and compare our results to the Phoenix lidar. We find that clouds, radiating between 0 and 30 W m^-2, were present earlier in the mission than previously known and that optically thicker clouds emitted more radiation toward the surface. Next, we use a doubling-and-adding radiative transfer model to derive the visible opacities of the water-ice clouds in images. The derived opacities are consistent with prior studies during the daytime, but give higher opacities between 2:00 - 10:00 LTST. This work allows us to make a direct comparison between the visible opacity of the cloud and the thermal radiation emitted by the cloud to better constrain their effect on the atmosphere.
  • ItemOpen Access
    Scattering Amplitude Techniques in Classical Gauge Theories and Gravity
    (2022-12-14) Bautista Chivata, Yilber Fabian; Tulin, Sean
    In this thesis we present a study of the computation of classical observables in gauge theories and gravity directly from scattering amplitudes. In particular, we discuss the direct application of modern amplitude techniques in the one, and two-body problems for both, scattering and bounded scenarios, and in both, classical electrodynamics and gravity, with particular emphasis on spin effects in general, and in four spacetime dimensions. Among these observables we have the conservative linear impulse and the radiated waveform in the two-body problem, and the differential cross section for the scattering of waves off classical spinning compact objects. The implication of classical soft theorems in the computation of classical radiation is also discussed. Furthermore, formal aspects of the double copy for massive spinning matter, and its application in a classical two-body context are considered. Finally, the relation between the minimal coupling gravitational Compton amplitude and the scattering of gravitational waves off the Kerr black hole is presented.
  • ItemOpen Access
    Optimizing Top-down Airborne Retrievals through High and Super-Resolution Numerical Modelling
    (2022-12-14) Fathi, Sepehr; Gordon, Mark
    A multi-scale-modelling study of conventional top-down source emission-rate estimation methodologies was conducted. Two modelling systems were employed: Environment and Climate Change Canada's regional air quality model GEM-MACH at 2.5km resolution (high-resolution), and Weather Research and Forecasting (WRF) with ARW dynamical core at 50m resolution (super-resolution). Using GEM-MACH, high-resolution air-quality model simulations were conducted for the period of an airborne campaign in 2013 over the Canadian oil sands facilities. Modelling products from these simulations were analyzed to investigate the application of the mass-balance technique in aircraft-based retrievals. The focus was on exploring the theoretical aspects and the underlying assumptions of the mass-balance technique. An extensive range of realistic meteorological and source emission conditions were considered. It was demonstrated how temporal variability in meteorology/emission conditions can give rise to storage-and-release events, where mass-balancing using only aircraft measurements can result in significant under-/over-estimates. Using WRF-ARW, super-resolution (<100 m) model simulations with Large-Eddy-Simulation (LES) subgrid-parameterization were developed/implemented. The objective was to resolve smaller dynamical processes at the spatio-temporal scales of the airborne measurements. This was achieved by multi-domain model nesting in the horizontal, grid-refining in the vertical, and down-scaling of reanalysis data from 31.25 km to 50 m. Further, WRF dynamical-solver source code was modified to simulate passive-tracer emissions within the finest resolution domain. Different meteorological case studies and several tracer emission sources were considered. Model-generated fields were evaluated against observational data and also in terms of tracer mass-conservation, results indicated high model performance. Using the model output from the WRF super-resolution simulations, conventional aircraft-based retrievals were simulated/evaluated. It was shown that conventional methods can result in estimates with 30-50% uncertainty/error. Two major sources of uncertainty were identified: (a) the spatio-temporal variability in the sampled fields, and (b) the gap of information below the flight level. Optimal flight-time around one hour and sampling-distance between 10-15 km, were shown to minimize the uncertainty arising from (a)-(b). Finally, a new sampling/retrieval strategy is introduced where aircraft-based in-situ and remote measurements can be combined to improve the accuracy of top-down estimates by up to 30%. This method utilizes remote sensing to fill the information gap below flight level, characterize temporal trends in the environmental fields during flight-time (to estimate storage-rate), while reducing the required flight-time for more accurate source emission rate estimates.
  • ItemOpen Access
    Modeling and Compensation of Hysteresis In Piezoelectric Actuators: A Physical Approach
    (2022-12-14) Savoie, Marc; Shan, Jinjun
    A study in the polarization domain is conducted by probing the impedance of the piezoelectric actuator as it moves along its trajectory. A sensing signal is overlaid over a driving signal that is used to vary the position of the device. The electric polarisation is extracted from the capacitance measurement calculated from the impedance. These polarisation curves are then modelled using the Jiles-Atherton model and compensated for using the inverse model. These measurements give insight into the ferroelectric processes within the piezoelectric actuator, which operate on the polarisation state. In addition, research has been conducted on the topic of parameter estimation of hysteresis models. This dissertation proposes a Monte Carlo study on a novel normalised Jiles-Atherton model to generate a statistical set of model solutions to compare area and remnant displacement characteristics for different parameter selections. Two parameters were found to be the most responsible for changes in these characteristics, and solutions near the desired values of the measured hysteresis curves were found to be densely distributed in certain areas of the parameter space. Different parameter estimation techniques are proposed for the Prandtl-Ishlinskii model. For this model, the parameters have geometrical significance in the slope of certain points of the hysteresis curve. A novel rescaling procedure is developed to scale a Prandtl-Ishlinskii model hysteresis curve area to a new value without requiring a refitting of the coefficients and a frequency-dependent Prandtl-Ishlinskii model is developed. Finally, a temperature-dependent, asymmetric Prandtl-Ishlinskii (TAPI) model is developed to account for the changes in hysteresis due to the external temperature. These effects are modelled in the charge domain as an extra bound charge that appears as a result of domain reorientation effects. The temperature effectively changes the amount of energy required to break pinning sites in the actuator which changes the shape of the curve. The TAPI model is then implemented on a Fabry-Perot interferometer system consisting of three piezoelectric actuators controlling the placement of a mirror forming the etalon. A decoupled inverse TAPI model is shown to effectively linearise the output of this system at different temperatures.
  • ItemOpen Access
    Strong Field Interactions with Atoms and Molecules
    (2022-12-14) Arias Laso, Susana; Horbatsch, Marko M.
    Atoms and molecules exposed to strong fields of magnitude comparable to their internal binding forces undergo ionization. This process sets the ground for multiple strong-field ionization phenomena such as above threshold ionization (ATI). This dissertation addresses two separate ionization problems, the dc Stark ionization of H2O valence orbitals, 1b1, 1b2, and 3a1, within the framework of non-Hermitian quantum mechanics, and ATI for a model-helium atom as part of a review of a previous quantitative approach based on the strong-field approximation (SFA). Calculations of the dc ionization parameters, dc Stark shift and exponential decay rates, for the H2O valence orbitals are carried out by solving the Schrödinger equation in the complex domain. Two independent models are implemented in the study of static ionization of the molecular orbitals (MOs). In the first one, a spherical effective potential obtained from a self-consistent calculation of H2O orbital energies is combined with an exterior complex scaling approach to express the problem as a system of partial differential equations that is solved numerically using a finite-element method. In the second approach, a model potential for the H2O molecule is expanded in a basis of spherical harmonics and combined with a complex absorbing potential that results in a complex eigenvalue problem for the Stark resonances. The second part of this investigation is concerned with the study of ATI for atoms subjected to a strong laser field. The convergence of the ionization spectrum for a model-helium atom is addressed in a systematic study that is carried out following Keldysh's formalism of SFA. A generalized compact expression for the ionization amplitude that incorporates electron rescattering into the analysis is explored as well. Additionally, a model based on the concept of quantum paths is implemented in the numerical evaluation of the SFA transition amplitude. In this analysis, a coherent sum over all allowed quantum trajectories that render the action stationary is carried out. This calculation allows to generate an ATI spectrum that converges to the numerical Keldysh amplitude as the number of trajectories increases.
  • ItemOpen Access
    Measuring the Muon Neutrino and Muon Antineutrino Induced Charged-Current Coherent Pion Production Cross Section on Carbon at the T2K Experiment
    (2022-08-08) Mitchell Yu; Sampa Bhadra
    The Tokai-to-Kamioka (T2K) experiment is a long-baseline neutrino oscillation experiment located in Japan. The experiment aims to measure neutrino oscillation parameters through measurements of neutrino interaction rates at various locations after production. In addition, the T2K near detector ND280 can also perform neutrino cross-section measurements. The muon neutrino induced charged-current coherent pion production (COH) process and the muon antineutrino induced coherent pion production process are not well modelled, and only a handful of experimental measurements are available to set constraints in the theoretical models. This thesis describes two new measurements of muon neutrino and muon antineutrino induced CC-COH using the T2K near detector ND280. Both measurements are performed with a binned likelihood fitter framework developed by the T2K collaboration. The theoretical model used in the neutrino event generator for the COH process is the Berger-Sehgal model. The first measurement uses the ND280 data taken with the muon neutrino enhanced beam, with a mean neutrino energy of 0.849 GeV, and the measured CC-COH cross section on carbon is 2.98 ± 0.37 (stat.) ± 0.58 (syst.) X 10^-40 cm^2. This is an updated measurement of a previously published T2K result with doubled statistics and an improved understanding of the systematic uncertainties. The second measurement uses the ND280 data taken with the muon antineutrino enhanced beam, with a mean neutrino energy of 0.849 GeV, and the measured CC-COH cross section on carbon is 3.05 ± 0.71 (stat.) ± 0.84 (syst.) X 10^-40 cm^2. This is the first measurement of muon antineutrino CC-COH at the sub-GeV neutrino energy range.
  • ItemOpen Access
    Electronic Properties of Anatase TiO2 and Iron (III) Doped TiO2 Nanoparticles
    (2022-08-08) Gong, Tuochen; Morin, Sylvie
    Since its discovery by Fujishima and Honda in 1972, titanium dioxide (TiO2) has been studied extensively due to its ability to split water and decompose dyes as a photocatalyst. Among all phases, TiO2 in the anatase phase displayed the highest photocatalytic rates for dye decompositions. Iron is selected as a dopant to maximize the efficiency under solar light. In this study, we use structural, morphological, chemical methods to study nanoparticles prepared using the sol-gel method, to confirm their phases, crystallite sizes, appearance, and detailed chemical compositions. To understand the effect of iron doping on photocatalysis, band gaps and valence band structures are obtained using state-of-the -art spectroscopy techniques. Models of electronic band structures of anatase TiO2 with various iron doping percentages are proposed, and effects of iron dopants on photodegradation are discussed using experimental results. Our study will benefit water purification industries, especially for on-site water treatments.
  • ItemOpen Access
    SPHerical: A Python Package For Exploring Alternative Dark Matter Models
    (2022-03-03) Blaff, Reuben David; Tulin, Sean
    Cold dark matter (CDM) cosmological N-body simulations have proved to be powerful tools for studying the evolution and structure of the universe. These simulations, however, predict certain small-scale structure that disagrees with observation. They are also computationally expensive. Thus, the majority of efforts have focused upon the vanilla CDM model. There are, however, a variety of DM models beyond CDM, such as self-interacting dark matter (SIDM), which has shown promise in resolving some of the aforementioned small-scale structure problems. Our new Python package, SPHerical, which we present in this paper, aims to allow for further exploration of SIDM and other alternative DM models. The package is used to simulate the evolution of isolated spherically symmetric DM halos using a Smoothed Particle Hydrodynamics (SPH) framework and gravothermal fluid model. In this paper, we limit our scope to SIDM and compare SPHerical's results with those of similar simulations.
  • ItemOpen Access
    Development of Software to Measure the Gravitational Redshift with RadioAstron
    (2022-03-03) Nunes, Nelson Vitoria; Bartel, Norbert H.
    The incompatibility of General Relativity (GR) and quantum theory continues to be a stumbling block in the unification of our understanding of the physical world. Tests of the Einstein Equivalence Principle, lying at the core of GR, are vital to constrain new theories that require departures from GR's predictions. One such test is measuring the gravitational redshift using RadioAstron – a space-VLBI mission launched in 2011 into a highly elliptical orbit. Utilizing the onboard H-maser frequency standard along with a Doppler compensation scheme that minimizes systematics, the gravitational redshift is anticipated to be determined with a relative accuracy of 10^-5. A third-order dynamical model has been implemented to predict frequency shifts in the spacecraft's carrier signal needed to conduct the experiment. The theory behind this model is developed, the software implementation described and third-order effects necessary to achieve the desired measurement accuracy are discussed.
  • ItemOpen Access
    Apparatus for Positronium Production via Rydberg Cesium Charge-Exchange
    (2021-11-15) Thai, Richard; Storry, Cody H.
    This dissertation outlines research conducted with positrons towards the production of positronium via charge-exchange with Rydberg cesium atoms. Positronium is a purely leptonic atomic system that is ideal for tests of quantum electrodynamics (QED) theory. A frozen neon crystal moderator produces low-energy positrons from a radioactive source that are magnetically guided towards a buffer-gas accumulator. The buffer-gas accumulator has been optimized to store large numbers of positrons (>40 million in 2 minutes) for a long time to perform a variety of experiments. The 200 meV energy width of the accumulated positrons is suitable for charge-exchange experiments. The positrons are then magnetically guided through a 90 bend towards an apparatus where charge-exchange takes place. The experimental techniques to produce and detect Rydberg positronium are described and the progress is presented. A data acquisition system has been developed to detect positron signatures based on the coincidence-timing of back-to-back annihilations on a single-event basis where time and energy analysis cuts allow strict criteria to distinguish signal from background. The long-term goal of the research program is to perform precision spectroscopy of the internal structure of Rydberg positronium. These measurements can be used to determine fundamental constants of nature and to test QED theory. A deviation from the QED predictions can be an indication of physics beyond the Standard Model. Physics beyond the Standard Model can provide a solution to unsolved problems, such as the matter-antimatter imbalance that is observed today.
  • ItemOpen Access
    Role of water in radiochromic LiPCDA monomer crystal packing and radiotherapy dose response
    (2021-07-06) Kaiyum, Rohith Ahmmed; Mermut, Ozzy
    Radiochromic films comprised of lithium-10,12-pentacosa diynoate (LiPCDA) crystals, a form of diacetylene, have been developed for in vivo real-time dosimetry. The polymerization of LiPCDA results in a change in optical density that is related to the absorbed dose. The dose response of diacetylene monomers is dependent on their packing, determined by the R groups. LiPCDA used in commercial film can have two distinct dose sensitive forms, 635LiPCDA and 674LiPCDA, with peak absorbances occurring at 635 nm and 674 nm, respectively. While the two forms do not differ in their R groups, they have different dosimetric behaviours. The 674LiPCDA achieved through desiccation of 635LiPCDA was 3-fold less sensitive to dose and had ~7-fold higher dynamic range. This indicates that the dosimetric behaviour of radiochromic crystals is primarily dependent on structure, controlled by more than just the chemical composition of individual monomers as water appears to have a role in the packing.
  • ItemOpen Access
    Atmospheric Temperature Profiling using Rotational Raman Lidar Measurements with a 32-Channel Spectral Detector
    (2021-07-06) Seth, Kanupria; Whiteway, James A.
    Atmospheric backscatter measurements with lidar at 355 nm laser wavelength were conducted at York University. The novel combination of the lidar system with a new 32-channel spectral detector made possible detecting photon-counting signals for multiple wavelengths simultaneously. The goal of this research was to derive atmospheric temperature profiles using the rotational Raman backscatter signal. The temperature was derived using the ratio of two wavelength intervals in the rotational Raman backscatter spectrum. A calibration function for the signal ratio and temperature on June 6, 2019 was found using temperature data from radiosonde measurements in Buffalo. The calibration function was used to derive temperature from ground up to 1200 m using lidar measurements on April 18, June 11 and June 12 in 2019. The lidar-calculated temperature profile had a mean deviation of 2.14 K from the radiosonde temperature values. The method requires improvements, such as controlling the temperature of the edge filter to minimize changes in the calibration from day to day.
  • ItemOpen Access
    Exterior Complex Scaling Approach for Atoms and Molecules in Strong DC Fields
    (2021-07-06) Pirkola, Patrik Cristian; Horbatsch, Marko M.
    We perform a short review of the history of quantum mechanics, with a focus on the historical problems with describing ionization theoretically in the context of quantum mechanics. The essentials of the theory of resonances are presented. The exterior complex scaling method for obtaining resonance parameters within the context of the Schrodinger equation is detailed. We explain how this is implemented for a numerical solution using a finite element method for the scaled variable. Results for the resonance parameters of a one-dimensional hydrogen model in an external direct current (DC) electric field are presented as proof of the independence of the theory from the scaling angle. We apply the theory to the real hydrogen atom in a DC field and present results which agree with literature values. The resonance parameters for singly ionized helium are also presented. Using a model potential energy for the water molecule, we solve for the energy eigenvalues. We then solve for the resonance parameters of the water molecule in a DC field and compare to literature results. Our widths for the valence orbital are shown to agree well with the so-called "coupled-cluster singles and doubles with perturbative triples excitations" method.