### Browsing by Subject "Holography"

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Item Beyond the Standard Model applications of holography(2020-07) Buyukdag, YusufShow more In this thesis, we explore beyond the Standard Model of particle physics by taking advantage of the holography approach. First of all, we consider a supersymmetric model that uses partial compositeness to explain the fermion mass hierarchy and predict the sfermion mass spectrum. Linear mixing between elementary superfields and supersymmetric operators with large anomalous dimensions is responsible for simultaneously generating the fermion and sfermion mass hierarchies. After supersymmetry is broken by the strong dynamics, partial compositeness causes the first- and second-generation sfermions to be split from the much lighter gauginos and third-generation sfermions. The sfermion mass scale is constrained by the observed 125 GeV Higgs boson, leading to stop masses and gauginos around 10--100 TeV and the first two generation sfermion masses around 100--1000 TeV. This gives rise to a splitlike supersymmetric model that explains the fermion mass hierarchy while simultaneously predicting an inverted sfermion mass spectrum consistent with the Large Hadron Collider and flavor constraints. The lightest supersymmetric particle is a gravitino in the keV to TeV range, which can play the role of dark matter. This brings us to the second topic that we consider, a novel realization of the Dynamical Dark Matter (DDM) framework in which the ensemble of particles collectively constitute dark matter and they are the composite states of a strongly-coupled conformal field theory. Cosmological abundances for these states are then generated through mixing with an additional, elementary state. As a result, the physical fields of the DDM dark sector at low energies are partially composite. We calculate the masses, lifetimes, and abundances of these states --- along with the effective equation of state of the entire ensemble. Our results suggest the existence of a potentially rich cosmology associated with partially composite DDM.Show more Item Computational Digital Inline Holography for In Situ Particle Tracking and Characterization(2020-05) Mallery, KevinShow more Digital inline holography (DIH) is a powerful single-camera 3D microscopic imaging tool that is able to digitally refocus a recorded image to reconstruct the 3D field of view. Compared to other single-camera techniques, DIH has a much larger depth of field in which objects can be seen, leading to drastically increased sampling volumes. Many particle features can be measured with DIH including size, shape, refractive index, identity, and motion. However, DIH has traditionally been limited by challenges related to the difficulty of accurately and quickly processing holographic images. In this thesis, I present technical developments focused on the digital processing of holographic images that are intended to alleviate these challenges and enable the application of DIH to new measurements. Specifically, a new approach for hologram reconstruction -- regularized holographic volume reconstruction (RIHVR) -- is introduced. This method is able to produce substantially noise-free reconstructions of particle fields. A data-driven approach to predictive particle tracking is also introduced in order to enable increased particle concentrations for particle tracking velocimetry applications. Each of these developments is validated using synthetic data and experimental demonstrations. Three applications of holographic imaging are presented to demonstrate the broad applicability of the method. The effect of temperature on the density of colonial cyanobacteria is identified by measuring the buoyant velocity and size of individual colonies. This could lead to better modelling of toxic algal blooms. Another type of algae, \emph{Dunaliella primolecta}, is useful and can be farmed for materials used in nutritional supplements, pharmaceuticals, and biodiesel. DIH is used to identify behavior signatures that could be used as indicators of optimal lipid production. This could enable optimal harvest timing leading to improved biodiesel yield. Finally, a low-cost miniature underwater holographic microscope was developed for \emph{in situ} field applications. This microscope is paired with a robotic platform to enable autonomous exploration of lakes or other aquatic environments. Despite its handheld size, the sensor is able to perform real-time particle concentration measurements using a deep neural network. The recorded images can also be used to identify the type of microorganisms found in the water.Show more Item Database of snow holograms collected from 2019 to 2022 for machine learning training or other purposes(2022-10-06) Li, Jiaqi; Guala, Michele; Hong, Jiarong; li001334@umn.edu; Li, Jiaqi; University of Minnesota Flow Field Imaging LabShow more This dataset includes the original combined snow holograms and holograms with image augmentation (rotation, exposure, blur, noise) for YOLOv5 model training to detect and classify snow particles. The individual snow particles are cropped and combined to enrich the particle numbers in each image for the ease of manual labeling. The snow particles are classified into six categories, including aggregate/irregular (I), dendrite (P2), graupel/rime (R), plate (P1), needle/column (N/C), and small particles/germ (G).Show more Item Development of High Fidelity Digital Inline Holographic Particle Tracking Velocimetry for 3D Flow Measurements(2016-03) Toloui, MostafaShow more Three-dimensional non-invasive measurement capability is often a necessity to unravel the physical phenomenon in fluid mechanic problems such as flow field characterization in wall-bounded turbulent flows and microfluidic devices. Among all the 3D optical flow diagnostic techniques, digital inline holographic particle tracking velocimetry (DIH-PTV) provides the highest spatial resolution with low cost, simple and compact optical setups. Despite these advantages, DIH-PIV suffers from major limitations including poor longitudinal resolution, human intervention (i.e. requirement for manually determined tuning parameters during tracer field reconstruction and extraction), limited tracer concentration, small sampling volume and expensive computations. These limitations have prevented this technique from being widely implemented for high resolution 3D flow measurements. In this study, we present our novel high-fidelity DIH-PTV algorithm with the goal of overcoming all the above mentioned limitations. Specifically, the proposed particle extraction method consists of multiple steps including 3D reconstruction, 3D deconvolution, automatic signal-to-noise ratio enhancement and thresholding, particle segmentation and centroid cacluation, and inverse iterative particle extraction. In addition, the processing package is enriched with a multi-pass 3D tracking method and a cross-correlation based longitudinal displacement refinement scheme. The entire method is implemented using GPU-based algorithm to increase the computational speed significantly. Validated with synthetic particle holograms, the proposed method can achieve particle extraction rate above 95% with ghost particles less than 3% and maximum position error below a particle diameter for holograms with particle concentration above 3000 particles/mm3 within sampling volumes of ~1 mm longitudinal length. Such improvements will substantially enhance the implementation of DIH-PTV for 3D flow measurements and enable the potential commercialization of this technique. The applicability of the technique is validated using the experiment of laminar flow in a microchannel and the synthetic tracer flow fields generated using a DNS turbulent channel flow database. In addition, the proposed method is applied to smooth- and rough-wall turbulent channel flows under two different settings of high-resolution near-wall and whole-channel measurements (i.e. sampling volume is extended to the entire depth of the channel). In the first case, using a microscopic objective and local seeding mechanism, DIH-PTV resolves near-wall flow structures within a sampling volume of 1 × 1.5 × 1 mm3 (streamwise × wall-normal × spanwise) with velocity resolution of ~100 μm (vector spacing). In the second case, the measurement volume is extended to the whole-channel depth by seeding the entire channel. Under this setting, the 3D velocity fields are obtained within a sampling volume of 14.7 × 50.0 × 14.4 mm3 with a velocity resolution of ~ <1.3 mm per vector, comparable to other the-state-of-the-art 3D whole-field flow measurement techniques. Overall, the presented DIH-PTV measurements under two different settings highlight the potential of DIH-PTV to obtain 3D characterization of the turbulent structures over a full range of scales, covering both the near wall and the out-layer regions of wall-bounded turbulent flows.Show more Item Holography: Encoding Quantum Information In Classical Gravity(2023-06) Dhumuntarao, AdityaShow more We explore the intersections between classical gravity and quantum information via holographic dualities. Such dualities provide a sophisticated mathematical dictionary which encodes information from a d-dimensional quantum theory onto a (d+1)-dimensional theory of gravity via equivalence of their partition functions. In this dissertation, we bridge geometry and quantum information in three parts. In Part I, we elucidate the connection between geometry and thermodynamics. Using the laws of black hole thermodynamics, we prove the existence of novel liquid-gas phase transitions in the phase diagram for lower dimensional AdS black holes. We further establish a proof that thermodynamic instabilities for AdS uniform black strings are correlated with classical gravitational instabilities. In Part II, we focus on applications of holographic quantum/classical dualities. Specifically, we study putative gravitational duals to 4d SU(N_c) Yang-Mills under various deformations. First, we demonstrate that deforming the bulk gravity dual with codimension one branes yields a scalar mass spectra concordant with lattice data at zero temperature. Next, at finite temperature, we show the presence of such branes imposes an upper bound on the thermal Bekenstein-Hawking entropy. We further prove that deforming the R-charge for 4d N=4 Super Yang-Mills on S^1_\beta\times S_R^3 avoids the deconfinement/Hagedorn phase transition at weak coupling and the Hawking/Page phase transition at strong coupling. These results connect quantum statistical systems and equilibrium gravitational systems. In Part III, we link quantum information and classical geometry holographically. Using geometric flows of extremal surfaces in asymptotically AdS spacetimes, we prove novel speed limits on the growth of entanglement entropy, equal time correlators, and spacelike Wilson loops for strongly coupled, far from equilibrium quantum systems admitting holographic duals. Our results imply new bounds on the entanglement velocity, prove the entanglement tsunami conjecture for a large class of states in 2d, and uncover a new momentum-entanglement correspondence, proving that entanglement growth is directly related to the momentum flux crossing an extremal surface.Show more Item Meson spectra from a dynamical three-field model of AdS/QCD(2014-08) Bartz, Sean PeterShow more Gauge/gravity dualities are tools that allow for the analytic study of strongly- coupled gauge theories. The Anti-de Sitter Space/Conformal Field Theory conjecture posits a duality between ten-dimensional string theory and a super Yang-Mills theory. A phenomenologically-motivated modification of this correspondence is known as AdS/QCD, a proposed duality between strongly-coupled QCD-like theories and weakly- coupled gravitational theories in an additional dimension. QCD is not scale-invariant, so the dual theory must be modified in the conformal dimension to reflect this.This thesis examines soft-wall models of AdS/QCD, wherein the conformal symmetry is broken by a field known as a dilaton. The dynamics of the dilaton and other background fields are examined, and a potential for these fields is determined. The back- ground fields are numerically derived from this potential and used in the calculation of meson spectra, which match experiment well.Show more Item Microalgal swimming in fluid environments: experimental and numerical investigations(2013-09) Chengala, Ahammed AnwarShow more The objective of this research was to examine the effects of small-scale fluid motion on the kinetic behavior and some key physiological aspects of Dunaliella primolecta Butcher (D. primolecta / Dunaliella). D. primolecta, a fast growing microalga, is a promising organism for alternative energy production because of its capability to accumulate significant amount of "lipids", a major prerequisite for commercial production of microalgal oil-derived biofuel. For kinetic response studies of Dunaliella, flow visualization and quantification techniques such as Particle Image Velocimetry (PIV) and Digital Holographic microscopy were employed. The two-dimensional PIV results showed that Dunaliella were influenced by the fluid flow as soon as the local (or ambient) flow velocities surrounding the cells exceeded the individual (flow subtracted) swimming velocity of Dunaliella. Further inspection of the swimming characteristics of Dunaliella under shear flow in a three-dimensional holography revealed that Dunaliella preferred to swim cross-stream (i.e. also the direction of local vorticity) when the shear flow exceeded a critical value, and this resulted in Dunaliella dispersing in a thin two-dimensional horizontal layer. The cell body rotation was absent during this display in shear flow, although the cell body rotation was evident while swimming in stagnant fluid. A physical model was developed that provided a possible explanation for the cell orienting and swimming in the cross-stream direction in a shear flow while cell body remained irrotational. The experimental swimming data also showed good agreement with the computational results. In order to investigate the biochemical composition and some physiological aspects in Dunaliella under different flow conditions, a laboratory bioreactor equipped with speakers was utilized. The fluid flow velocities in the proximity of the cells generated by the speaker bioreactor are observable in natural water ecosystems. The results showed that the flow condition with the highest turbulence investigated favored the growth and lipid accumulation in Dunaliella.Show more Item Multi-Exposure Darkfield Digital Inline Holography for Ultrafast Microparticle Tracking(2022-10) Grazzini Placucci, RafaelShow more Current imaging solutions are unable to characterize complex and 3D ultra-highspeedmicroscopic flows with sufficient sampling rate, spatial resolution or depth-offield. Options that overcome the challenge in temporal resolution typically sacrifice depth-of-field and spatial resolution for increased framerate, and employ an array of sensors to extend measurements to three dimensions, further aggravating system cost and complexity. Systems that can overcome these challenges without compromising image resolution or affordability are therefore indispensable to advance fluid dynamics, aerosol, and biological research, among others. In fact, they are a essential in challenging flow scenarios such as laminar-turbulent transition in the hypersonic boundary layer, where megahertz frequencies, micron-scale resolution, and a depth-of-field extended to the centimeter range is essential to capture high frequency and 3D small-scale instabilities with sufficient fidelity. In this thesis, a unique holographic imaging technique named multi-exposure darkfield digital inline holography was developed to deliver 3D microparticle tracking at megahertz frequencies over an extended depth-of-field with high resolution using a single-camera setup. The proposed system integrates a low-cost nanosecond pulsed laser and a high-resolution digital camera operating at a prolonged exposure time to capture multiple particle exposures per image frame. A high-pass spatial frequency filter is introduced prior to the camera to prevent the saturation of the sensor and allow the acquisition of full-frame images at megahertz frequencies. The optical system is accompanied by a deep learning framework that incorporates a physics-based synthetic hologram generation algorithm and a conditional generative adversarial network to create a vast dataset of labeled darkfield holograms that are subsequently used to train a regression convolutional neural network for particle depth estimation. Finally, the innovation is demonstrated by imaging 300-350 μm tracers in a 12 × 10 × 30 mm3 measurement volume located above a magnetic rod rotating at 3,000 RPM. Particle trajectories were acquired with a frequency of 750 Hz and spatial resolutions of 2.27 μm and 20 μm in the planar and axial directions, respectively, and used to calculate statistics on particle velocities for a total of 124 trajectories.Show more Item Multiplexed Volume Bragg Gratings in Narrow- and Broad-band Spectral Systems: Analysis and Application(2015-05) Ingersoll, GregoryShow more Volume Bragg gratings (VBGs) are important holographic optical elements in many spectral systems. Using multiple volume gratings, whether multiplexed or arranged sequentially, provides advantages to many types of systems in overall efficiency, dispersion performance, flexibility of design, etc. However, the use of multiple gratings---particularly when the gratings are multiplexed in a single holographic optical element (HOE)---is subject to inter-grating coupling effects that ultimately limit system performance. Analyzing these coupling effects requires a more complex mathematical model than the straightforward analysis of a single volume grating. We present a matrix-based algorithm for determining diffraction efficiencies of significant coupled waves in these multiplexed grating holographic optical elements (HOEs). Several carefully constructed experiments with spectrally multiplexed gratings in dichromated gelatin verify our conclusions. Applications of this theory to broad- and narrow-band systems are explored in detailed simulations. Broadband systems include spectrum splitters for diverse-bandgap photovoltaic (PV) cells. Volume Bragg gratings can serve as effective spectrum splitters, but the inherent dispersion of a VBG can be detrimental given a broad-spectrum input. The performance of a holographic spectrum splitter element can be improved by utilizing multiple volume gratings, each operating in a slightly different spectral band. However, care must be taken to avoid inter-grating coupling effects that limit ultimate performance. We explore broadband multi-grating holographic optical elements (HOEs) in sandwiched arrangements where individual single-grating HOEs are placed in series, and in multiplexed arrangements where multiple gratings are recorded in a single HOE. Particle swarm optimization (PSO) is used to tailor these systems to the solar spectrum taking into account both efficiency and dispersion. Both multiplexed and sandwiched two-grating systems exhibit performance improvements over single-grating solutions, especially when reduced dispersion is required. Dispersion performance can be further improved by employing more than two VBGs in the spectrum splitter, but efficiency is compromised by additional cross-coupling effects. Narrow-band applications of the multi-grating theory include spectral beam combining (SBC) systems. SBC systems utilizing multiple VBGs must be carefully analyzed to maximize channel density and efficiency, and thus output radiance. This analysis grows increasingly difficult as the number of channels in the system increases, and heuristic optimization techniques (e.g. PSO) are again useful tools for exploring the limits of these systems. We explore three classes of multi-grating SBC systems: "cascaded" where each grating adds a new channel to the system in sequence, "sandwiched" where several individual gratings are placed together and all channels enter the system at the same facet, and "multiplexed" where all of the gratings occupy the same holographic optical element (HOE). Loss mechanisms differ among these three basic classes, and the optimization algorithm shows that the highest channel density for a given minimum efficiency and fixed operating bandwidth is achieved for a cascaded-grating system. The multiplexed-grating system exhibits the lowest channel density under that same constraints but has the distinct advantage of being realized by a single HOE. For a particular application, one must weigh channel density and efficiency versus system complexity when choosing among these basic classes of SBC system. Additionally, one may need to consider the effects of finite-width input beams. As input beam radius is reduced, angular clipping effects begin to dominate over spectral interference and crosstalk effects, limiting all three classes of SBC systems in a similar manner.Show more