Physics and Astronomy

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Open Access
Autonomous Sensor Tasking And Object Detection For Space Situational Awareness Using Machine Learning
(2025-04-10) Fairbrother, Michael Christopher; Lee, Regina S. K.
The space domain is becoming increasingly crowded due to the proliferation of man-made resident space objects. Our limited number of object-tracking resources is becoming overburdened by a growing catalog of space debris and active satellites. This problem necessitates the most effective use of available sensors and observatories for catalog maintenance through the optimization of sensor tasking schedules. Given the complexity of the tasking problem, autonomous scheduling is essential and creates a need for increasingly powerful computational optimization algorithms. This research explores one such optimization approach, deep reinforcement learning, as an effective solution for autonomous sensor tasking. In addition to scheduling, improved object detection algorithms are in constant demand in order to more accurately identify resident space objects in images produced by optical sensors. This research additionally explores region-based convolutional neural networks as a potential considerable improvement over traditional detection algorithms.
Open Access
The Past, Present And Future Of Neutrino Near Detectors
(2025-04-10) Zaki, Rowan; Harris, Deborah
This thesis covers two accelerator-driven long-baseline neutrino experiments. The Tokai-to-Kamioka (T2K) experiment uses a 0.6 GeV neutrino beam produced at the J-PARC beamline in Tokai, Japan to measure neutrino oscillation parameters. These parameters can be found by comparing the neutrino interaction rates at the ND280 near detector and the Super-Kamiokande far detector at 280 meters and 295 kilometers from the neutrino beam source, respectively. Accurately measuring these interaction rates and subsequently the oscillation probability is limited by the systematic uncertainties associated with the neutrino-nucleus interaction cross-sections. Hence, these interactions are studied in the high event rate environment of the ND280 near detector. In muon-neutrino-induced charged-current single positive pion production on hydrocarbon, both a muon and a positively charged pion are produced in the final state. The four dimensional differential cross-section for this process has been measured in muon and pion kinematic parameters for the full solid angle in the past, but has always been statistically limited. Here it is presented with the full available statistics including the use of pion properties derived from Michel electrons of their subsequent decay, which improved the statistics for pion momenta between 50-400 MeV by 50\%. The cross-section extraction is done with a binned log-likelihood minimization returning a $\chi^{2}/\text{Ndf}$ of 1.25, showing good agreement with the nominal Monte Carlo models. The future Deep Underground Neutrino Experiment (DUNE) relies on liquid argon as target material for the neutrino interactions in the near and far sites. The liquid argon near detector (NDLAr) has been given a modular design consisting of 35 modules (70 time-projection chambers) in a 7 by 5 array with novel pixelated charge readout systems in order to deal with the high interaction rates in the world's most intense neutrino beam. To understand the behavior of the drift fields and the pixel charge collection efficiencies inside these time-projection chambers, a series of prototypes have been studied. These studies ultimately converged into a diagnostic tool capable of identifying misbehavior in pixel trigger rates during operation.
Open Access
Characterizing the Martian Environment Through Surface Spacecraft Observations
(2024-07-18) Campbell, Charissa; Moores, John
Over the course of a Mars Year (MY) atmospheric temperatures vary enough between the furthest (Aphelion) and closest (Perihelion) points in Mars' orbit due to an Earth-like obliquity and elliptical orbit, creating two distinct seasons. Aphelion has cooler temperatures and a cross-equatorial Hadley cell revealing equatorial water-ice clouds. Perihelion has warmer temperatures that support increased dust activity such as dust-devils or dust storms. These two seasons have been observed from orbit and surface, with surface vehicles crucially important for understanding surface-to-atmosphere interactions. Aerosols were examined for wind direction and speed using movies from the Mars Science Laboratory (MSL) rover and InSight lander due to their proximity. Similar Easterly wind directions during the Aphelion season for both landing sites helped pinpoint that observed aerosols were most likely aloft in the middle atmosphere, affected by the same large-scale circulation via Hadley cells. However, mission constraints such as power and data volume limit the amount of returnable data and the ability to fully understand these aerosols. Automated methods appear to show promising results based on an algorithm developed by a team from Curtin university and tested with known wind directions from MSL atmospheric movies. The Onboard Rover Cloud Algorithm (ORCA) could be used on future missions to significantly decrease data volume by simply returning a set of wind parameters without first downlinking images. To further expand low-cost options, an optical meteorological station was created based on the Phoenix Mars mission experiment that imaged the lidar beam shining within aerosols to calculate ice-water content. The Mars Atmospheric Panoramic camera and Laser Experiment (MAPLE) has a panoramic camera and multiple class 3R lasers to maximize returnable science in a minimal way. Field testing in dense fog in Newfoundland showed that MAPLE's lasers could detect fog decks up to 100 m above the camera during nighttime conditions. The lasers were unable to be resolved during the day, but a power calculation determined that all three lasers on MAPLE could be suitable for Martian polar conditions. Understanding the constraints of obtaining Martian atmospheric data enables low-cost options such as MAPLE to further our knowledge of these aerosols.
Open Access
The Morphology-Density Relation of Galaxies at z~1.6
(2024-07-18) Brown, Westley Andrew Louise; Muzzin, Adam
The relationship between galaxy morphology and environment has been well-studied in the local universe and at low redshift, showing that galaxies in dense clusters tend to be elliptical and bulge-like while galaxies in low-density fields tend to be spiral and disk-like. However, this relationship is less understood at higher redshifts, and the few studies at high-z rely on samples with incomplete redshift measurements and poorly constrained stellar masses. We explore the morphology-density relation at z~1.6, the tail end of cosmic noon, using a sample of 3 SpARCS clusters and 2 fields from 3D-HST/CANDELS. Using Sersic index as a proxy for galaxy morphology, we find that the morphology-density relation is already in place in clusters at this epoch. Additionally, we find a significant difference in the relationship between galaxy morphology and stellar mass in clusters compared to field environments. This suggests that the morphology-density relation may be driven by mass-dependent environmental processes.
Open Access
Progress Towards a Precision Measurement of the n = 2 Triplet P0-to-n = 2 Triplet P1 Transition in Atomic Helium
(2024-03-16) Skinner, Taylor David Grant; Hessels, Eric
Significant progress towards a high-precision measurement of the 29.6 GHz 2^3P_1-to-2^3P_0 fine-structure interval in helium at an intended precision of 20 Hz is presented. The measurement is performed using a thermal beam of metastable helium atoms, and the transition is measured using the frequency-offset separated oscillatory fields (FOSOF) method, where the transition is driven by a pair of temporally separated microwave pulses. The two pulses are at slightly different frequencies, which can be viewed as a continuously advancing phase difference between the pulses. The advancing phase difference leads to a sinusoidally varying atomic signal due to quantum interference between atoms excited during the two pulses. The phase difference between the sinusoidal atomic signal and a reference signal generated by combining the two microwave frequencies is zero at resonance and approximately proportional to the difference between the applied microwave frequency and the centre frequency of the transition. A large number of experiment parameters which could lead to systematic effects have been investigated and shown to be sufficiently well-managed at the intended precision level of the intended measurement. One effect which causes the measured linecentre to depend on the range of microwave frequencies at which data is taken has been thoroughly investigated in both experiments and in a numerical simulation developed to investigate systematic effects. This effect is still not sufficiently well-understood or controlled to allow completion of a measurement at the 20 Hz level of precision. A completed measurement, at a precision of 20 Hz, would be able to be combined with our previous 25 Hz measurement of the 2.3 GHz 2^3P_2-to-2^3P_1 interval to obtain a part-per-billion (ppb) determination of the combined 31.9 GHz 2^3P_2-to-2^3P_0 interval. When compared to a sufficiently-precise theoretical calculation, the combined interval would allow a 0.5 ppb determination of the fine-structure constant, the most precise determination of the fine-structure constant in a two-electron system and within an order of magnitude of the most precise determinations of the fine-structure constant. This 0.5 ppb determination could be compared with other fine-structure constant determinations to test beyond-the-Standard-Model physics.
Open Access
Self-Similar Models of Quasar Outflow Shock Structures
(2024-03-16) Weiss, Erik Adam; Hall, Patrick B.
Supersonic winds of outflowing material are observed and/or predicted in a number of astrophysical systems; such winds may drive an expanding shock structure that shocks and pushes the ambient interstellar medium (ISM) outward. This thesis analyses, combines and expands on existing analytic self-similar models of these structures in the context of quasar accretion disk winds; we then search for the bulk acceleration (positive or negative) of low-velocity Ca II in the quasar SDSS J030000.0+004828.0 (J0300) and compare our results to model predictions. We find a strong upper limit on the acceleration magnitude, yielding plausible model constraints, but the observed range of gas velocities implies that the Ca II velocity profile does not coincide with that of the shocked ISM. We conclude with a discussion of recent results regarding J0300's outflow properties and briefly investigate the possibility of pre-existing ISM cloud disruption as an explanation for the observed Ca II velocity profile.
Open Access
Time-evolution of SU(2) lattice gauge theory on a quantum computer
(2024-03-16) Rahman, Sarmed A.; Lewis, Randy
Lattice Gauge Theory is a mathematical tool used to study the forces of nature, like Quantum Electrodynamics and Quantum Chromodynamics. Quantum computers offer an alternative to classical computers in studying these forces. In my thesis, a gate-based quantum computer was used to perform calculations of the propagation of an excitation in real-time. A new error mitigation method was developed to greatly extend the range of comprehensible data over time by using the physics circuits to estimate the accumulated error. I also developed the theoretical foundation for higher energy systems, as well as higher dimensional geometry.
Open Access
Structure and Local Properties of Dark Matter Halos
(2024-03-16) Smith-Orlik, Adam Jacob Ross; Tulin, Sean; Bozorgnia, Nassim
The structure and local properties of dark matter (DM) are important input variables for both direct and indirect detection experiments. Common assumptions about DM, such as, its particle nature being cold and collisionless–CDM–and its distribution in halos being isothermal and spherical, and well-modeled by an isotopic Maxwell-Boltzmann velocity distribution–the Standard Halo Model (SHM)–prove to be at odds with astrophysical observations. In this thesis I present work towards elucidating two areas of refinement to the above-mentioned assumptions regarding DM: 1) allowing moderate self-interactions between DM particles (SIDM), extending the semi-analytic Jeans modeling technique for SIDM halos to multiple dimensions and including baryons and nonspherical effects to study the resulting change in the DM halo structure; 2) quantifying the departure from the SHM by analyzing hydrodynamical simulations of Milky Way (MW) like halos to characterize the impact on local properties of DM induced by satellite galaxies like the Large Magellanic Cloud (LMC) and their implications for direct detection experiments.
Open Access
Extreme Emission Line Galaxies Observed with the James Webb Space Telescope's Medium-Band Filters
(2024-03-16) Withers, Cassandra Carol; Muzzin, Adam; Ravindranath, Swara
Since the beginning of the James Webb Space Telescope's science operations, there have been many observations dedicated to characterizing galaxies during the Epoch of Reionization (EoR). This thesis uses medium-band photometry from the JWST to search for Extreme Emission Line Galaxies (EELGs) in the EoR and analogues at lower redshifts. We present a sample of EELGs over 1.7 < z < 6.7 selected on their strong Halpha and [OIII] + Hbeta emission lines. We measure the equivalent widths (EWs) and physical properties of the galaxies in our sample, finding high EWs (median EW(Halpha) = 893 Angstroms, EW([OIII] + Hbeta) = 1255 Angstroms) and properties typical of EELGs: mostly compact with low stellar mass, low metallicity, little dust, and high specific star formation rates. Follow-up NIRSpec spectroscopy of 15 of the EELGs in our sample confirm the nature and EWs of the EELGs measured from medium-band photometry, demonstrating the accuracy of our colour selections.
Open 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.
Open 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.
Open 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.
Open 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.
Open 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.
Open 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.
Open 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.
Open 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.
Open 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.
Open 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.
Open 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.