Search NASA⌕ Search

SEARCH · Search NASA

Results for “geometrical optics”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Spectral shape corrections for SDSS BOSS quasars

Modifications were made to the Sloan Digital Sky Survey’s Baryonic Oscillations Spectroscopic Survey (SDSS/BOSS) optical fibres assigned to quasar targets in order to improve the signal-to-noise ratio in the Ly-α forest. However, the consequence of these modifications is that quasars observed in this way require additional flux correction procedures in order to recover the correct spectral shapes. Here, in this paper, we describe such a procedure, based on the geometry of the problem, and other observational parameters. Applying several correction methods to four SDSS quasars with multiple observations permits a detailed verification of the relative performances of the different flux correction procedures. We contrast our method (which takes into account a wavelength-dependent seeing profile) with the BOSS pipeline approach (which does not). Our results provide independent confirmation that the geometric approach employed in the SDSS pipeline works well, although with room for improvement. By separating the contributions from four effects, we are able to quantify their relative importance. Most importantly, we demonstrate that wavelength dependence has a significant impact on the derived spectral shapes and thus should not be ignored.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

An empirical method for geometric calibration of a photon counting detector-based cone beam CT system

BACKGROUND: Geometric calibration is essential in developing a reliable computed tomography (CT) system. It involves estimating the geometry under which the angular projections are acquired. Geometric calibration of cone beam CTs employing small area detectors, such as currently available photon counting detectors (PCDs), is challenging when using traditional-based methods due to detectors’ limited areas. OBJECTIVE: This study presented an empirical method for the geometric calibration of small area PCD-based cone beam CT systems. METHODS: Unlike the traditional methods, we developed an iterative optimization procedure to determine geometric parameters using the reconstructed images of small metal ball bearings (BBs) embedded in a custom-built phantom. An objective function incorporating the sphericities and symmetries of the embedded BBs was defined to assess performance of the reconstruction algorithm with the given initial estimated set of geometric parameters. The optimal parameter values were those which minimized the objective function. The TIGRE toolbox was employed for fast tomographic reconstruction. To evaluate the proposed method, computer simulations were carried out using various numbers of spheres placed in various locations. Furthermore, efficacy of the method was experimentally assessed using a custom-made benchtop PCD-based cone beam CT. RESULTS: Computer simulations validated the accuracy and reproducibility of the proposed method. The precise estimation of the geometric parameters of the benchtop revealed high-quality imaging in CT reconstruction of a breast phantom. Within the phantom, the cylindrical holes, fibers, and speck groups were imaged in high fidelity. The CNR analysis further revealed the quantitative improvements of the reconstruction performed with the estimated parameters using the proposed method. CONCLUSION: Apart from the computational cost, we concluded that the method was easy to implement and robust.

Instruments & Instrumentation↗
DOE OSTI2024

Epitaxial Thin Film Growth on Recycled SrTiO 3 Substrates Toward Sustainable Processing of Complex Oxides

Complex oxide thin films cover a range of physical properties and multifunctionalities that are critical for logic, memory, and optical devices. Typically, the high‐quality epitaxial growth of these complex oxide thin films requires single crystalline oxide substrates such as SrTiO 3 (STO), MgO, LaAlO 3 , a‐Al 2 O 3, and many others. Recent successes in transferring these complex oxides as free‐standing films not only offer great opportunities in integrating complex oxides on other devices, but also present enormous opportunities in recycling the deposited substrates after transfer for cost‐effective and sustainable processing of complex oxide thin films. In this work, the surface modification effects introduced on the recycled STO are investigated, and their impacts on the microstructure and properties of subsequently grown epitaxial oxide thin films are assessed and compared with those grown on the pristine substrates. Detailed analyses using high‐resolution scanning transmission electron microscopy and geometric phase analysis demonstrate distinct strain states on the surfaces of the recycled STO versus the pristine substrates, suggesting a pre‐strain state in the recycled STO substrates due to the previous deposition layer. These findings offer opportunities in growing highly mismatched oxide films on the recycled STO substrates with enhanced physical properties. Specifically, yttrium iron garnet (Y 3 Fe 5 O 12 ) films grown on recycled STO present different ferromagnetic responses compared to that on the pristine substrates, underscoring the effects of surface modification. The study demonstrates the feasibility of reuse and redeposition using recycled substrates. Via careful handling and preparation, high‐quality epitaxial thin films can be grown on recycled substrates with comparable or even better structural and physical properties toward sustainable process of complex oxide devices.

pre-strained STO surfaces↗
DOE OSTI2024

Charge state-dependent symmetry breaking of atomic defects in transition metal dichalcogenides

Abstract The functionality of atomic quantum emitters is intrinsically linked to their host lattice coordination. Structural distortions that spontaneously break the lattice symmetry strongly impact their optical emission properties and spin-photon interface. Here we report on the direct imaging of charge state-dependent symmetry breaking of two prototypical atomic quantum emitters in mono- and bilayer MoS 2 by scanning tunneling microscopy (STM) and non-contact atomic force microscopy (nc-AFM). By changing the built-in substrate chemical potential, different charge states of sulfur vacancies (Vac S ) and substitutional rhenium dopants (Re Mo ) can be stabilized. $${\mathrm{Vac}}_{{{{{{{{\rm{S}}}}}}}}}^{-1}$$ Vac S − 1 as well as $${{\mathrm{Re}}}_{{{{{{{{\rm{Mo}}}}}}}}}^{0}$$ Re Mo 0 and $${\mathrm{Re}}_{{\rm{Mo}}}^{-1}$$ Re Mo − 1 exhibit local lattice distortions and symmetry-broken defect orbitals attributed to a Jahn-Teller effect (JTE) and pseudo-JTE, respectively. By mapping the electronic and geometric structure of single point defects, we disentangle the effects of spatial averaging, charge multistability, configurational dynamics, and external perturbations that often mask the presence of local symmetry breaking.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Terahertz-polarizing effect based on geometric anisotropy of Ti 3 C 2 T x MXene nanosheets

Two-dimensional (2D) nanomaterials have garnered considerable attention due to their unique properties, such as thinness and excellent electronic properties. The inherent anisotropy of 2D nanomaterials, which is characterized by their high aspect ratio, can maximize the directional functionality to enhance the conductivity and utilization of edges. Here, we demonstrate how to utilize the edges of titanium carbide (Ti 3 C 2 T x ) MXene nanosheet to control the linear polarization in the terahertz (THz) frequency range. By a simple and unique vertical alignment exploiting the high surface charge and excellent colloidal dispersibility of MXene nanosheets, MXene nanosheets are vertically oriented along an applied AC electric field. The well-aligned edges justify the THz polarizing effect, revealing outstanding performances such as the broadband coverage in 0.2–1.5 THz and an exceptional extinction ratio reaching 20 dB. Furthermore, we vary the local orientation of the vertical MXene nanosheets by tailoring the applied electric field, enabling spatially controllable polarization capabilities. Our results can provide a generic tool for the utilization of 2D nanomaterials in diverse potential applications in optics and electronics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

The ambiguous AT2022rze: changing-look AGN mimicking a supernova in a merging galaxy system

AT2022rze is a luminous, ambiguous transient located south-east of the geometric centre of its host galaxy at redshift $z = 0.08$. The host appears to be formed by a merging galaxy system. The observed characteristics of AT2022rze are reminiscent of active galactic nuclei (AGNs), tidal disruption events, and superluminous supernovae. The transient reached a peak absolute magnitude of $-$20.2 $\pm$ 0.2 mag, showing a sharp rise (t$_{\mathrm{rise,1/e}} = 27.5 \pm 0.6$ d) followed by a slow decline (t$_{\mathrm{dec,1/e}} = 382.9 \pm 0.6$). Its bumpy light curve and narrow Balmer lines indicate the presence of gas (and dust). Its light curve shows rather red colours, indicating that the transient could be affected by significant host extinction. The spectra reveal coronal lines, indicative of high-energy (X-ray/UV) emission. Archival data reveal no prior activity at this location, disfavouring a steady-state AGN, although an optical spectrum obtained prior to the transient is consistent with an AGN classification of the host. Based on this, we conclude that the transient most likely represents a changing-look AGN at the centre of the smallest component of the merging system.

galaxies: active↗
DOE OSTI2020

Three-dimensional super line-localization in low signal-to-noise microscope images via prior-apprised unsupervised learning (PAUL)

Biological processes such as processive enzyme turnover and intracellular cargo tracking involve the dynamic motion of a small "article" along a curvilinear biopolymer track. To understand these processes that occur across multiple length and time scales, one must acquire both the trajectory of the particle and the position of the track along which it moves, possibly by combining high-resolution single-particle tracking with conventional microscopy. Yet, usually there is a significant resolution mismatch between these modalities: while the tracked particle is localized with a precision of 10 nm, the image of the surroundings is limited by optical difraction, with 200 nm lateral and 500 nm axial resolutions. Compared to the particle's trajectory, the surrounding curvilinear structure appears as a blurred and noisy image. This disparity in the spatial resolutions of the particle trajectory and the surrounding curvilinear structure image makes data reconstruction, as well as interpretation, particularly challenging. Analysis is further complicated when the curvilinear structures are oriented arbitrarily in 3D space. Here, we present a prior-apprised unsupervised learning (PAUL) approach to extract information from 3D images where the underlying features resemble a curved line such as a filament or microtubule. This three-stage framework starts with a Hessian-based feature enhancement, which is followed by feature registration, where local line segments are detected on repetitively sampled subimage tiles. In the final stage, statistical learning, segments are clustered based on their geometric relationships. Principal curves are then approximated from each segment group via statistical tools including principal component analysis, bootstrap and kernel transformation. This procedure is characterized on simulated images, where sub-voxel medium deviations from true curves have been achieved. The 3D PAUL approach has also been implemented for successful line localization in experimental 3D images of gold nanowires obtained using a multifocal microscope. Lastly, this work not only bridges the resolution gap between two microscopy modalities, but also allows us to conduct 3D super line-localization imaging experiments, without using super-resolution techniques.

42 ENGINEERING↗
DOE OSTI2025

Designing molecular qubits: computational insights into first-row and group 6 transition metal complexes

In the realm of optically addressable qubits, a previously synthesized and characterized Cr( IV ) pseudo-tetrahedral complex, featuring four strongly donating ligands surrounding the chromium center, has demonstrated potential as a qubit candidate. This study proposes analogs of this complex through a metal substitution strategy, extending the investigation to different complexes based on metal centers selected from first-row and Group 6 transition metals. Computational modeling based on multiconfigurational methods CASPT2 and MC-PDFT was utilized to calculate energy gaps between ground and excited electronic spin states, and zero-field splitting parameters. Simulations were applied to each equilibrium geometry and related deformations based on vibrational modes. All results align with previous experimental findings, but also show that qubits based on V and Ti centers could be more electronically stable than the Cr one, suggesting a lower electronic features dependency from their related geometry. In some cases geometrical deformations provide changes in relative energy gaps between triplet and singlet excited state, that could potentially swap, offering a different initialization process, and some inspiration for ligand design based on such deformations. Additionally, this study identifies an unsynthesized Ti( II ) compound as a promising candidate for molecular qubits. This finding highlights the role of computational multireference methods in the rational design of qubit systems.

Sauza-de la Vega, Arturo [Univ. of Chicago, IL (Un↗
DOE OSTI2020

Microscopic force driving the photoinduced ultrafast phase transition: Time-dependent density functional theory simulations of IrTe 2

Photoinduced phase transitions can have complex and intriguing behaviors more than material ground-state dynamics. Understanding the underlying mechanism can help us to design new ways to manipulate the materials. A variety of mechanisms has been proposed to explain the photoinduced phase transitions of IrTe 2 , but a consensus has yet to be reached. Here, we study the photo-induced phase transitions of IrTe 2 by performing the real-time time-dependent density functional theory (rt-TDDFT) simulations in combination with the occupation constrained DFT method. We reveal that the microscopic driving force for the photo-induced phase transitions arises from the tendency to lower the energy levels occupied by the excited carriers, through the increase or decrease of the associated atomic pair distances, depending on whether the newly occupied states are antibonding or bonding states, respectively. The geometric constraints between different bonds represented by the Poisson ratio can bring together different tendencies from different atomic pairs, thus forming a complex intriguing dynamic picture depending on the intensity of the excitation. Furthermore, we also find that phonons don't play a primary role, but can assist the phase transition. These findings imply that one can control the structural phase transitions by selectively exciting photocarriers into designated atomic states using appropriate photon sources.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Probing the impact of oxygen negative ions on the self-organized pattern in 1 atm DC glow with liquid anode

In an atmospheric DC glow discharge with a liquid anode, the plasma anode glow attached to the grounded liquid surface under certain conditions self-organizes into coherent patterns. Optical emission spectroscopy revealed that the emission consists primarily of the second positive system of nitrogen, N 2 (C-B), whose excitation energy is low and sensitive to changes in the electron energy distribution. In addition to electrons, negative ions can accumulate in the anode sheath and affect the local space charge. It has been speculated that these negative ions play a role in pattern formation at the anode surface. In this work, the role of oxygen negative ions was explored. It was found that the formation of anode patterns requires at least a 7% volume fraction of oxygen in the ambient gas. Results showed that O 2 - is the dominant negative ion species in atmospheric DC glow discharge, with a density of ~10 12 cm -3 . While the presence of oxygen appears to be crucial for pattern formation, this study indicated that patterns still formed without geometric changes even when 62% of negative ions in the plasma were detached by a laser. This suggests that negative ions do not support the patterns, while oxygen's heating effect may induce instability at the anode.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

Improved Productivity with Multilaser Rotary Powder Bed Fusion Additive Manufacturing

Laser powder bed fusion (LPBF) enables the fabrication of intricate, geometrically complex structures with a sufficiently fine surface finish for many engineering applications with a diversity of available feedstock metals. However, the production rate of LPBF systems is not well suited for mass production in comparison to traditional manufacturing methods. LPBF systems measure their deposition rates in 100's of grams per hour, while other processes measure in kilograms per hour or even in the case of processes such as forming, stamping, and casting, 100's of kilograms per hour. To be widely adopted in industry for mass production, LPBF requires a new scalable architecture that enables many orders of magnitude improvement in deposition rate, while maintaining the geometry freedom of additive manufacturing. This article explores concepts that could achieve as much as four orders of magnitude increase in the production rate through the application of (1) rotary table kinematic arrangements; (2) a dramatic number of simultaneously operating lasers; (3) reductions of laser optic size; (4) improved scanning techniques; and (5) an optimization of toroidal build plate size. To theoretically demonstrate the possibilities of production improvements, a productivity analysis is proposed for synchronous reluctance motors with relevance to the electric vehicle industry, given the recent increase in the diversity of printable soft magnetic alloys. The analysis provides insights into the impact of the architecture and process parameters necessary to optimize rotary powder bed fusion for mass production.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Validating a microphysical prognostic stratospheric aerosol implementation in E3SMv2 using observations after the Mount Pinatubo eruption

Abstract. This paper describes the addition of a stratospheric prognostic aerosol (SPA) capability – developed with the goal of accurately simulating sulfate aerosol formation and evolution in the stratosphere – in the Department of Energy (DOE) Energy Exascale Earth System Model, version 2 (E3SMv2). The implementation includes changes to the four-mode Modal Aerosol Module microphysics in the stratosphere to allow for larger particle growth and more accurate stratospheric aerosol lifetime following the Pinatubo eruption. E3SMv2-SPA reasonably reproduces stratospheric aerosol lifetime, burden, aerosol optical depth, and top-of-atmosphere flux when compared to remote sensing observations. E3SMv2-SPA also has close agreement with the interactive chemistry–climate model CESM2-WACCM (Community Earth System Model version 2–Whole Atmosphere Community Climate Model) – which has a more complete chemical treatment – and the observationally constrained, prescribed volcanic aerosol treatment in E3SMv2. Global stratospheric aerosol size distributions identify the nucleation and growth of sulfate aerosol from volcanically injected SO2 from both major and minor volcanic eruptions from 1991 to 1993. The modeled aerosol effective radius is consistently lower than satellite and in situ measurements (max differences of ∼ 30 %). Comparisons with in situ size distribution samples indicate that this simulated underestimation in both E3SMv2-SPA and CESM2-WACCM is due to overly small accumulation and coarse-mode aerosols 6–18 months post-eruption, with E3SMv2-SPA simulating ∼ 50 % of the coarse-mode geometric mean diameters of observations 11 months post-eruption. Effective radii from the models and observations are used to calculate offline scattering and absorption efficiencies to explore the implications of smaller simulated aerosol size for the Pinatubo climate impacts. Scattering efficiencies at wavelengths of peak solar irradiance (∼ 0.5 µm) are 10 %–80 % higher for daily samples in models relative to observations through 1993, suggesting higher diffuse radiation at the surface and a larger cooling effect in the models due to the smaller simulated aerosol; absorption efficiencies at the peak wavelengths of outgoing terrestrial radiation (∼ 10 µm) are 15 %–40 % lower for daily samples in models relative to observations, suggesting an underestimation in stratospheric heating in the models due to the smaller simulated aerosol. These potential biases are based on aerosol size alone and do not take into account differences in the aerosol number. The overall agreement of E3SMv2-SPA with observations and its similar performance to the well-validated CESM2-WACCM makes E3SMv2-SPA a viable alternative to simulating climate impacts from stratospheric sulfate aerosols.

Brown, Hunter York (ORCID:0000000218147874)↗
DOE OSTI2026

The role of source geometry and atmospheric propagation in global bolide infrasound detectability

Global infrasound monitoring provides a persistent means of detecting energetic bolide atmospheric entries, complementing optical observations and extending coverage over remote regions. We present a global assessment of the physical factors governing bolide infrasound detectability by correlating 623 bolide events reported by the Center for Near-Earth Object Studies between 2007 and 2025 with waveform data from the International Monitoring System. We identify 311 events with confirmed infrasound detections, corresponding to a detection rate of approximately 50%, substantially higher than inferred from earlier surveys, reflecting both the maturation of the global infrasound network and advances in automated, multi-frequency array processing. Analysis of flight parameters shows that infrasound detectability is selective rather than uniform across the bolide population. Detected events are preferentially associated with steeper entry angles and lower-altitude energy deposition, while shallow, high-altitude trajectories are less consistently observed. Very high-energy events remain detectable regardless of geometry, but for the more common lower-energy regime, observability depends on specific combinations of entry parameters and propagation conditions. This geometric dependence persists across comparable energy ranges and atmospheric conditions, indicating that entry angle exerts a primary control on detectability, with energy and propagation acting as secondary modulating factors. Furthermore, these results provide new physical constraints on bolide-atmosphere interactions and improve interpretation of global infrasound observations for planetary defense and atmospheric-entry studies.

Bolides↗
DOE OSTI2021

Topology and geometry under the nonlinear electromagnetic spotlight

For many materials, a precise knowledge of their dispersion spectra is insufficient to predict their ordered phases and physical responses. Instead, these materials are classified by the geometrical and topological properties of their wavefunctions. A key challenge is to identify and implement experiments that probe or control these quantum properties. In this Review, we describe recent progress in this direction, focusing on nonlinear electromagnetic responses that arise directly from quantum geometry and topology. Furthermore, we give an overview of the field by discussing theoretical ideas, experiments and the materials that drive them. We conclude by discussing how these techniques can be combined with device architectures to uncover, probe and ultimately control quantum phases with emergent topological and correlated properties.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The TESS Phase Curve of KELT-1b Suggests a High Dayside Albedo

We measured the optical phase curve of the transiting brown dwarf KELT-1b (TOI 1476) using data from the TESS spacecraft. We found that KELT-1b shows significant phase variation in the TESS bandpass, with a relatively large phase amplitude of 234{sub −44}{sup +43} ppm and a secondary eclipse depth of 371{sub −49}{sup +47} ppm. We also measured a marginal eastward offset in the dayside hot spot of 18.°3 ± 7.°4 relative to the substellar point. We detected a strong phase-curve signal attributed to ellipsoidal distortion of the host star with an amplitude of 399 ± 19 ppm. Our results are roughly consistent with the Spitzer phase curves of KELT-1b, but the TESS eclipse depth is deeper than expected. Our cloud-free 1D models of KELT-1b’s dayside emission are unable to fit the full combined eclipse spectrum. Instead, the large TESS eclipse depth suggests that KELT-1b may have a significant dayside geometric albedo of A {sub g} ∼ 0.5 in the TESS bandpass, which would agree with the tentative trend between equilibrium temperature and geometric albedo recently suggested by Wong et al. We posit that if KELT-1b has a high dayside albedo, it is likely due to silicate clouds that form on KELT-1b’s nightside and are subsequently transported onto the western side of KELT-1b’s dayside hemisphere before breaking up.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Geometrical Frustration and Defect Formation in Growth of Colloidal Nanoparticle Crystals on a Cylinder: Implications for Assembly of Chiral Nanomaterials

Using a combination of experiment and simulation, we study how two-dimensional (2D) crystals of colloidal nanoparticles grow on cylindrical substrates. The cylindrical geometry allows us to examine growth in the absence of Gaussian curvature but in the presence of a closure constraint - the requirement that a crystal loops back onto itself. In some cases, this constraint results in structures that have been observed previously in theory and nonequilibrium packing experiments: chiral crystals and crystals with linear defects known as "line slips". More generally, though, the structures we see differ from those that have been observed: the line slips are kinked and contain partial vacancies. We show that these structures arise because the cylinder changes how the crystal grows. After a crystal wraps around the cylinder and touches itself, it must grow preferentially along the cylinder axis. As a result, crystals with a chiral line slip tend to trap partial vacancies. Indeed, we find that line slips that are less aligned with the cylinder axis incorporate more partial vacancies on average than the ones that are more aligned. Here, these results show that crystal growth on a cylinder is frustrated by the closure requirement, a finding that may shed some light on the assembly of biological nanosystems such as tobacco mosaic virus and might inform ways to fabricate chiral optical nanomaterials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Dual-polarization Dirac cones in a simple 2D square lattice photonic crystal

We report on dual-polarization Dirac cones in a simple square lattice two-dimensional (2D) photonic crystal (PC) based on transmission at accidental degeneracies centered at the k = 0 symmetry ( Γ <#comment/> ) point. Finite difference time domain simulations are used to identify the material and geometric parameters for Dirac-like dispersion. A configuration that produces a Dirac-like point for both transverse electric and transverse magnetic polarizations at the same frequency is presented. The PC dispersion shows the expected threefold degenerate linear branch crossings at the Dirac-like point. Full-field electromagnetic wave simulations exhibit some common behaviors of devices based on Dirac-like dispersion, such as cloaking and waveguiding. The configuration works for a considerable range of the parameter space, and thus is experimentally realizable with a wide range of materials.

Rodríguez, J. A. (ORCID:0000000178926207)↗
DOE OSTI2024

Integrated positron emission particle tracking (PEPT) and X-ray computed tomography (CT) imaging of flow phenomena in twisted tape swirl flow

Abstract A combined positron emission particle tracking (PEPT) and X-ray computed tomography (CT) technique is presented, and its utility is demonstrated through investigation of flow in a pipe with twisted tape swirl insert with varying flow conditions (diameter-based Reynolds numbers 16,300–63,300). A description of this technique is given, as well as data handling practices used to relate geometric information captured by CT to fluid flow data gathered via PEPT. It is found that the CT component is readily capable of capturing the stainless steel insert geometry in this present system, but the use of combined plastic and metal materials leads to artifacts in imaging of the plastic surface. Nonetheless, CT data are related to PEPT flow measurements, and average velocity fields are calculated via a pseudo-framing and interpolation scheme and used to visualize and interrogate key flow phenomena within the system. Radial velocity profiles of the mean flow characteristics are seen to collapse to a nearly common form across all flow conditions considered. Helical vortices are seen propagating through the flow field, generated by bypass flow around the gap between the insert and pipe wall, with additional coherent secondary flow structures seen in the higher Reynolds number cases. These findings enhance the understanding of the mixing mechanisms in these swirl flows and encourage the continued development of PEPT-CT methodologies for 3D flow measurements in optically inaccessible systems.

42 ENGINEERING↗