Characterization of multiphase flows integrating X-ray imaging and virtual reality

Multiphase flows are used in a wide variety of industries, from energy production to pharmaceutical manufacturing. However, because of the complexity of the flows and difficulty measuring them, it is challenging to characterize the phenomena inside a multiphase flow. To help overcome this challenge, researchers have used numerous types of noninvasive measurement techniques to record the phenomena that occur inside the flow. One technique that has shown much success is X-ray imaging. While capable of high spatial resolutions, X-ray imaging generally has poor temporal resolution. This research improves the characterization of multiphase flows in three ways. First, an X-ray image intensifier is modified to use a high-speed camera to push the temporal limits of what is possible with current tube source X-ray imaging technology. Using this system, sample flows were imaged at 1000 frames per second without a reduction in spatial resolution. Next, the sensitivity of X-ray computed tomography (CT) measurements to changes in acquisition parameters is analyzed. While in theory CT measurements should be stable over a range of acquisition parameters, previous research has indicated otherwise. The analysis of this sensitivity shows that, while raw CT values are strongly affected by changes to acquisition parameters, if proper calibration techniques are used, acquisition parameters do not significantly influence the results for multiphase flow imaging. Finally, two algorithms are analyzed for their suitability to reconstruct an approximate tomographic slice from only two X-ray projections. These algorithms increase the spatial error in the measurement, as compared to traditional CT; however, they allow for very high temporal resolutions for 3D imaging. The only limit on the speed of this measurement technique is the image intensifier-camera setup, which was shown to be capable of imaging at a rate of at least 1000 FPS. While advances in measurement techniques for multiphase flows are one part of improving multiphase flow characterization, the challenge extends beyond measurement techniques. For improved measurement techniques to be useful, the data must be accessible to scientists in a way that maximizes the comprehension of the phenomena. To this end, this work also presents a system for using the Microsoft Kinect sensor to provide natural, non-contact interaction with multiphase flow data. Furthermore, this system is constructed so that it is trivial to add natural, non-contact interaction to immersive visualization applications. Therefore, multiple visualization applications can be built that are optimized to specific types of data, but all leverage the same natural interaction. Finally, the research is concluded by proposing a system that integrates the improved X-ray measurements, with the Kinect interaction system, and a CAVE automatic virtual environment (CAVE) to present scientists with the multiphase flow measurements in an intuitive and inherently three-dimensional manner

Atomic-scale and three-dimensional transmission electron microscopy of nanoparticle morphology

The burgeoning field of nanotechnology motivates comprehensive elucidation of nanoscale materials. This thesis addresses transmission electron microscope characterisation of nanoparticle morphology, concerning specifically the crystal- lographic status of novel intermetallic GaPd2 nanocatalysts and advancement of electron tomographic methods for high-fidelity three-dimensional analysis. Going beyond preceding analyses, high-resolution annular dark-field imaging is used to verify successful nano-sizing of the intermetallic compound GaPd2. It also reveals catalytically significant and crystallographically intriguing deviations from the bulk crystal structure. So-called ‘non-crystallographic’ five-fold twinned nanoparticles are observed, adding a new perspective in the long standing debate over how such morphologies may be achieved. The morphological complexity of the GaPd2 nanocatalysts, and many cognate nanoparticle systems, demands fully three-dimensional analysis. It is illustrated how image processing techniques applied to electron tomography reconstructions can facilitate more facile and objective quantitative analysis (‘nano-metrology’). However, the fidelity of the analysis is limited ultimately by artefacts in the tomographic reconstruction. Compressed sensing, a new sampling theory, asserts that many signals can be recovered from far fewer measurements than traditional theories dictate are necessary. Compressed sensing is applied here to electron tomographic reconstruction, and is shown to yield far higher fidelity reconstructions than conventional algorithms. Reconstruction from extremely limited data, more robust quantitative analysis and novel three-dimensional imaging are demon- strated, including the first three-dimensional imaging of localised surface plasmon resonances. Many aspects of transmission electron microscopy characterisation may be enhanced using a compressed sensing approach

Electron Beam Tomography of Recording Head Fields

The quantitative evaluation of inductive recording head fields has been achieved by electron beam tomography. The differential phase contrast (DPC) mode of Lorentz microscopy implemented on a 200 kV scanning transmission instrument provides a novel technique for recording head field investigations and in particular the acquisition of the experimental data sets required for field reconstruction. The absolute determination of the recording head field has been obtained by calibration of the DPC image contrast. This thesis starts with a brief discussion of the basics of ferromagnetism and the application of magnetic materials in magnetic recording technology. Development trends and some recent advances in magnetic recording head design are also discussed. The second chapter gives a review of two dimensional techniques developed previously for magnetic stray field measurement and particular attention is given to the DPC Lorentz microscopy, since it is the experimental basis of 3D field characterisation by means of electron beam tomography. The fundamental principles and the realisation of electron beam tomography for recording head field study are discussed in chapter 3. The two reconstruction algorithms of the RTM and the ART are introduced. The emphasis of this chapter is put upon the derivation of the magnetic field vector ART algorithm and the experimental implementation of the electron beam tomography using DPC Lorentz microscopy based on the modified JEOL 2000FX (S)TEM. The acquisition of the experimental data sets for tomographic reconstruction is also described in this chapter. The ART tomography program described in chapter 3 is tested and compared with the RTM in chapter 4. The performance of the tomography programs are evaluated by simulation of DPC data sets for a model thin film head using different reconstruction parameters. It is confirmed by these simulations that the ART and the RTM can produce satisfactory reconstruction of recording head fields. Reconstructions using fewer projections by the ART and using truncated input data sets by the ART and the RTM can still provide reasonable information on the major field distributions; this situation is encountered in practice. The computer simulations also provide information on the suitable reconstruction parameters which may be adopted in the experimental reconstruction of recording head fields. In chapter 5 the electron beam tomography method is applied to study the stray field from inductive thin film heads. A novel method of mounting the thin film head for data collection makes it possible to reconstruct the stray field on a plane ~0.25 mum from the head gap. By etching part of the alumina present in the vicinity of the poletips, it has proved possible to identify magnetic flux leakage from regions of the poles, other than the polegap. The saturation behaviour of the writing field can also be obtained by studying the integrated stray field in the head gap direction for different dc driving currents. Chapter 6 presents the experimental results from the study of the stray field from tape heads. The specimens used in this chapter are a pair of Metal-in-Gap write/ferrite read heads and laminated alloy film tape heads. Electron beam tomography and the DPC experiments can provide quantitative information on the stray field gradient and the half height of the field amplitude. The results obtained also show that DPC Lorentz microscopy is the most powerful tool to observe stray field defects, such as the secondary gap effect from the MIG head and the remanence effect from both the MIG and the laminated alloy film heads. A method to calibrate the relative value of the DPC signal acquired from a quadrant DPC detector is described in chapter 7. The actual value of the electron beam deflection at certain point(s) on the DPC image is measured in-situ as part of the DPC experiment. From the calibration data set obtained, which is consistent with the theoretical analysis of the detector response, the absolute determination of the 3D stray field is achieved. Conclusions and suggestions for further work are given in chapter 8

The mitral valve computational anatomy and geometry analysis

We present a novel methodology to characterize and quantify the Mitral Valve (MV) geometry and physical attributes in a multi-resolution framework. A multi-scale decomposition was implemented to model the MV geometry by using superquadric shape primitives and spectral reconstruction of the finer-scale geometric details. Superquadrics provide a basis to normalize the size and approximate a basic model of the MV geometry. The point-wise difference between the original geometry and the superquadric model denotes the finer-scale geometric details, which can be modeled as a scalar attribute for the MV model development. The additive decomposition of the basic MV geometry from geometric details (attributes) allows recovering the actual geometry by superposition of the superquadric approximation and the finer-details model. We implemented a lasso optimization algorithm to perform spectral analysis and develop the Fourier reconstruction of the geometric details. The spectral modeling enabled us to resample the geometric details or use spectral filters in order to adjust the spatial resolution in the model reconstruction. It also provides the basis to control the level of detail in the final model reconstruction by applying low-pass filters in the frequency domain. The higher-order attributes such as internal fiber architecture can be integrated with the geometric models using the same framework. We applied our pipeline to create models of three ovine MVs based on computed-tomography 3D images with micrometer resolution. We were able to quantify the MV leaflet geometry, reconstruct models with custom level of geometric details, and develop medial representation of the MV leaflet structure. The results show that our methodology for geometry analysis provides a basis for assessing patient-specific geometries and facilitates developing population-averaged models. Ultimately, this approach allows building personalized image-based computational models for medical device design and surgical treatment simulations.Mechanical Engineerin

Deep learning-based denoising for improved dose efficiency in EDX tomography of nanoparticles

Computer Science

Two dimensional angular domain optical imaging in biological tissues

Optical imaging is a modality that can detect optical contrast within a biological sample that is not detectable with other conventional imaging techniques. Optical trans-illumination images of tissue samples are degraded by optical scatter. Angular Domain Imaging (ADI) is an optical imaging technique that filters scattered photons based on the trajectory of the photons. Previous angular filters were limited to one dimensional arrays, greatly limiting the imaging capability of the system. We have developed a 2D Angular Filter Array (AFA) that is capable of acquiring two dimensional projection images of a sample. The AFA was constructed using rapid prototyping techniques. The contrast and the resolution of the AFA was evaluated. The results suggest that a 2D AFA can be used to acquire two dimensional projection images of a sample with a reduced acquisition time compared to a scanning 1D AFA

Computed Tomography of Chemiluminescence: A 3D Time Resolved Sensor for Turbulent Combustion

Time resolved 3D measurements of turbulent flames are required to further understanding of combustion and support advanced simulation techniques (LES). Computed Tomography of Chemiluminescence (CTC) allows a flame’s 3D chemiluminescence profile to be obtained by inverting a series of integral measurements. CTC provides the instantaneous 3D flame structure, and can also measure: excited species concentrations, equivalence ratio, heat release rate, and possibly strain rate. High resolutions require simultaneous measurements from many view points, and the cost of multiple sensors has traditionally limited spatial resolutions. However, recent improvements in commodity cameras makes a high resolution CTC sensor possible and is investigated in this work. Using realistic LES Phantoms (known fields), the CT algorithm (ART) is shown to produce low error reconstructions even from limited noisy datasets. Error from selfabsorption is also tested using LES Phantoms and a modification to ART that successfully corrects this error is presented. A proof-of-concept experiment using 48 non-simultaneous views is performed and successfully resolves a Matrix Burner flame to 0.01% of the domain width (D). ART is also extended to 3D (without stacking) to allow 3D camera locations and optical effects to be considered. An optical integral geometry (weighted double-cone) is presented that corrects for limited depth-of-field, and (even with poorly estimated camera parameters) reconstructs the Matrix Burner as well as the standard geometry. CTC is implemented using five PicSight P32M cameras and mirrors to provide 10 simultaneous views. Measurements of the Matrix Burner and a Turbulent Opposed Jet achieve exposure times as low as 62 μs, with even shorter exposures possible. With only 10 views the spatial resolution of the reconstructions is low. However, a cosine Phantom study shows that 20–40 viewing angles are necessary to achieve high resolutions (0.01– 0.04D). With 40 P32M cameras costing £40000, future CTC implementations can achieve high spatial and temporal resolutions