Institutional Repository

The University of Houston Institutional Repository (UHIR) collects, preserves and distributes scholarly output and creative works produced by the University of Houston community. UHIR provides free and open online access to the university’s research and scholarship, including electronic theses and dissertations.


Recent Submissions

Dense Time Series Generation of Surface Water Extents through Optical–SAR Sensor Fusion and Gap Filling
(2024-04-03) Markert, Kel N.; Williams, Gustavious P.; Nelson, E. James; Ames, Daniel P.; Lee, Hyongki; Griffin, Robert E.
Surface water is a vital component of the Earth’s water cycle and characterizing its dynamics is essential for understanding and managing our water resources. Satellite-based remote sensing has been used to monitor surface water dynamics, but cloud cover can obscure surface observations, particularly during flood events, hindering water identification. The fusion of optical and synthetic aperture radar (SAR) data leverages the advantages of both sensors to provide accurate surface water maps while increasing the temporal density of unobstructed observations for monitoring surface water spatial dynamics. This paper presents a method for generating dense time series of surface water observations using optical–SAR sensor fusion and gap filling. We applied this method to data from the Copernicus Sentinel-1 and Landsat 8 satellite data from 2019 over six regions spanning different ecological and climatological conditions. We validated the resulting surface water maps using an independent, hand-labeled dataset and found an overall accuracy of 0.9025, with an accuracy range of 0.8656–0.9212 between the different regions. The validation showed an overall false alarm ratio (FAR) of 0.0631, a probability of detection (POD) of 0.8394, and a critical success index (CSI) of 0.8073, indicating that the method generally performs well at identifying water areas. However, it slightly underpredicts water areas with more false negatives. We found that fusing optical and SAR data for surface water mapping increased, on average, the number of observations for the regions and months validated in 2019 from 11.46 for optical and 55.35 for SAR to 64.90 using both, a 466% and 17% increase, respectively. The results show that the method can effectively fill in gaps in optical data caused by cloud cover and produce a dense time series of surface water maps. The method has the potential to improve the monitoring of surface water dynamics and support sustainable water management.
Asymptotically Newton-Type Methods without Inverses for Solving Equations
(2024-04-02) Argyros, Ioannis K.; George, Santhosh; Shakhno, Stepan; Regmi, Samundra; Havdiak, Mykhailo; Argyros, Michael I.
The implementation of Newton’s method for solving nonlinear equations in abstract domains requires the inversion of a linear operator at each step. Such an inversion may be computationally very expensive or impossible to find. That is why alternative iterative methods are developed in this article that require no inversion or only one inversion of a linear operator at each step. The inverse of the operator is replaced by a frozen sum of linear operators depending on the Fréchet derivative of an operator. The numerical examples illustrate that for all practical purposes, the new methods are as effective as Newton’s but much cheaper to implement. The same methodology can be used to create similar alternatives to other methods using inversions of linear operators such as divided differences or other linear operators.
Laminin Alpha 2 Enhances the Protective Effect of Exosomes on Human iPSC-Derived Cardiomyocytes in an In Vitro Ischemia-Reoxygenation Model
(2024-03-28) Mesquita, Fernanda C. P.; King, Madelyn; da Costa Lopez, Patricia Luciana; Thevasagayampillai, Shiyanth; Gunaratne, Preethi H.; Hochman-Mendez, Camila
Ischemic heart disease, a leading cause of death worldwide, manifests clinically as myocardial infarction. Contemporary therapies using mesenchymal stromal cells (MSCs) and their derivative (exosomes, EXOs) were developed to decrease the progression of cell damage during ischemic injury. Laminin alpha 2 (LAMA2) is an important extracellular matrix protein of the heart. Here, we generated MSC-derived exosomes cultivated under LAMA2 coating to enhance human-induced pluripotent stem cell (hiPSC)-cardiomyocyte recognition of LAMA2-EXOs, thus, increasing cell protection during ischemia reoxygenation. We mapped the mRNA content of LAMA2 and gelatin-EXOs and identified 798 genes that were differentially expressed, including genes associated with cardiac muscle development and extracellular matrix organization. Cells were treated with LAMA2-EXOs 2 h before a 4 h ischemia period (1% O2, 5% CO2, glucose-free media). LAMA2-EXOs had a two-fold protective effect compared to non-treatment on plasma membrane integrity and the apoptosis activation pathway; after a 1.5 h recovery period (20% O2, 5% CO2, cardiomyocyte-enriched media), cardiomyocytes treated with LAMA2-EXOs showed faster recovery than did the control group. Although EXOs had a protective effect on endothelial cells, there was no LAMA2-enhanced protection on these cells. This is the first report of LAMA2-EXOs used to treat cardiomyocytes that underwent ischemia-reoxygenation injury. Overall, we showed that membrane-specific EXOs may help improve cardiomyocyte survival in treating ischemic cardiovascular disease.
Visual input for inspection and closed loop control of a hybrid circuit printer
(1985) Nguyen, Cap Van; Lee, Kwang Y.; Shieh, Leang-San; Rajaram, Navaratna S.
A machine vision system is used to inspect thick film printed circuit boards. Inspection functions detect defects and misalignment and feed corrective data back to the processing facility. This thesis describes a visual Inspection system for the thick film screen printing process in which complex patterns are printed on ceramic substrates. The image algebra, based on set theory, is utilized as a vehicle for image processing and analysis algorithm. A predefined shape is used as a probe to test the nature of a circuit pattern. A computerized visual inspection specification is created to define the inspection criteria and the system requirements. An algorithm is developed to snap the image and to detect faults based on programmable parameters. It also measures the misregistration of the circuit with respect to the edge of the substrate. A computer control algorithm, utilizing digital control theory, has been developed to control an alignment system of a screen printer. The control algorithm has the capability of accepting visual feedback input signals for a real-time closed-loop control system.
Single trial evoked potential analysis by means of cross-correlation and dynamic time-warping
(1985) Yeh, Youn-Sing; Jansen, Ben H.; Glover, John R., Jr.; Sheer, Daniel. E.
This thesis describes and evaluates a new approach to obtain evoked potential (EP) estimates. EPs are minute voltage fluctuations in the electrical activity of the brain in response to an external stimulus. EPs are often buried in the spontaneous brain activity and special techniques are required to improve the signal-to-noise ratio. The method presented here uses a dynamic time warping (DTW) algorithm to maximize the crosscorrelation between a template and the recorded block. Several modifications of the basic algorithm are proposed and evaluated using simulated data consisting of triangular shapes superimposed on white noise. One of the most promising versions was subjected to further testing using a more realistic model of the EP and background activity. It was found that warping increased the crosscorrelation between the template and single trial, however, the template occassionally converged to the background noise especially for low signal-to-noise ratios.