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Articles 43321 - 43350 of 294774

Full-Text Articles in Physical Sciences and Mathematics

Win: Weight-Decay-Integrated Nesterov Acceleration For Adaptive Gradient Algorithms, Pan Zhou, Xingyu Xie, Shuicheng Yan May 2023

Win: Weight-Decay-Integrated Nesterov Acceleration For Adaptive Gradient Algorithms, Pan Zhou, Xingyu Xie, Shuicheng Yan

Research Collection School Of Computing and Information Systems

Training deep networks on large-scale datasets is computationally challenging. In this work, we explore the problem of “how to accelerate adaptive gradient algorithms in a general manner”, and aim to provide practical efficiency-boosting insights. To this end, we propose an effective and general Weight-decay-Integrated Nesterov acceleration (Win) to accelerate adaptive algorithms. Taking AdamW and Adam as examples, we minimize a dynamical loss per iteration which combines the vanilla training loss and a dynamic regularizer inspired by proximal point method (PPM) to improve the convexity of the problem. To introduce Nesterov-alike-acceleration into AdamW and Adam, we respectively use the first- and …

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Two Sides Of The Same Coin: Exploiting The Impact Of Identifiers In Neural Code Comprehension, Shuzheng Gao, Cuiyun Gao, Chaozheng Wang, Jun Sun, David Lo, Yue Yu May 2023

Two Sides Of The Same Coin: Exploiting The Impact Of Identifiers In Neural Code Comprehension, Shuzheng Gao, Cuiyun Gao, Chaozheng Wang, Jun Sun, David Lo, Yue Yu

Research Collection School Of Computing and Information Systems

Previous studies have demonstrated that neural code comprehension models are vulnerable to identifier naming. By renaming as few as one identifier in the source code, the models would output completely irrelevant results, indicating that identifiers can be misleading for model prediction. However, identifiers are not completely detrimental to code comprehension, since the semantics of identifier names can be related to the program semantics. Well exploiting the two opposite impacts of identifiers is essential for enhancing the robustness and accuracy of neural code comprehension, and still remains under-explored. In this work, we propose to model the impact of identifiers from a …

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A Comprehensive Review On Machine Learning In Healthcare Industry: Classification, Restrictions, Opportunities And Challenges, Qi An, Saifur Rahman, Jingwen Zhou, James Jin Kang May 2023

A Comprehensive Review On Machine Learning In Healthcare Industry: Classification, Restrictions, Opportunities And Challenges, Qi An, Saifur Rahman, Jingwen Zhou, James Jin Kang

Research outputs 2022 to 2026

Recently, various sophisticated methods, including machine learning and artificial intelligence, have been employed to examine health-related data. Medical professionals are acquiring enhanced diagnostic and treatment abilities by utilizing machine learning applications in the healthcare domain. Medical data have been used by many researchers to detect diseases and identify patterns. In the current literature, there are very few studies that address machine learning algorithms to improve healthcare data accuracy and efficiency. We examined the effectiveness of machine learning algorithms in improving time series healthcare metrics for heart rate data transmission (accuracy and efficiency). In this paper, we reviewed several machine learning …

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Determinants Of Cloud Computing Integration And Its Impact On Sustainable Performance In Smes: An Empirical Investigation Using The Sem-Ann Approach, Mohammed A. Al-Sharafi, Mohammad Iranmanesh, Mostafa Al-Emran, Ahmed I. Alzahrani, Fadi Herzallah, Norziana Jamil May 2023

Determinants Of Cloud Computing Integration And Its Impact On Sustainable Performance In Smes: An Empirical Investigation Using The Sem-Ann Approach, Mohammed A. Al-Sharafi, Mohammad Iranmanesh, Mostafa Al-Emran, Ahmed I. Alzahrani, Fadi Herzallah, Norziana Jamil

Research outputs 2022 to 2026

Although extant literature has thoroughly investigated the incorporation of cloud computing services, examining their influence on sustainable performance, particularly at the organizational level, is insufficient. Consequently, the present research aims to assess the factors that impact the integration of cloud computing within small and medium-sized enterprises (SMEs) and its subsequent effects on environmental, financial, and social performance. The data were collected from 415 SMEs and were analyzed using a hybrid SEM-ANN approach. PLS-SEM results indicate that relative advantage, complexity, compatibility, top management support, cost reduction, and government support significantly affect cloud computing integration. This study also empirically demonstrated that SMEs …

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Another Shipment Of Six Short-Period Giant Planets From Tess, Joseph E. Rodriguez, Samuel N. Quinn, Andrew Vanderburg, George Zhou, Jason D. Eastman, Erica Thygesen, Bryson Cale, David R. Ciardi, Phillip A. Reed, Ryan J. Oelkers May 2023

Another Shipment Of Six Short-Period Giant Planets From Tess, Joseph E. Rodriguez, Samuel N. Quinn, Andrew Vanderburg, George Zhou, Jason D. Eastman, Erica Thygesen, Bryson Cale, David R. Ciardi, Phillip A. Reed, Ryan J. Oelkers

Physics & Astronomy Faculty Publications

We present the discovery and characterization of six short-period, transiting giant planets from NASA’s Transiting Exoplanet Survey Satellite (TESS) -- TOI-1811 (TIC 376524552), TOI-2025 (TIC 394050135), TOI-2145 (TIC 88992642), TOI-2152 (TIC 395393265), TOI-2154 (TIC 428787891), and TOI-2497 (TIC 97568467). All six planets orbit bright host stars (8.9 <G < 11.8, 7.7 <K < 10.1). Using a combination of time-series photometric and spectroscopic follow-up observations from the TESS Follow-up Observing Program Working Group, we have determined that the planets are Jovian-sized (RP = 0.99--1.45 RJ), have masses ranging from 0.92 to 5.26 MJ, and orbit F, G, and K stars (4766 ≤ Teff ≤ 7360 K). We detect a significant orbital …

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Repytah: An Open-Source Python Package For Building Aligned Hierarchies For Sequential Data, Chenhui Jia, Lizette Carpenter, Thu Tran, Amanda Y. Liu, Sasha Yeutseyva, Mariun Tapal, Yingke Wang, Zoie Kexin Zhou, Jordan Moody, Denise Nava, Eleanor Donaher, Lillian Yusha Jiang, Ben Bruncati, Katherine M. Kinnaird May 2023

Repytah: An Open-Source Python Package For Building Aligned Hierarchies For Sequential Data, Chenhui Jia, Lizette Carpenter, Thu Tran, Amanda Y. Liu, Sasha Yeutseyva, Mariun Tapal, Yingke Wang, Zoie Kexin Zhou, Jordan Moody, Denise Nava, Eleanor Donaher, Lillian Yusha Jiang, Ben Bruncati, Katherine M. Kinnaird

Computer Science: Faculty Publications

We introduce repytah, a Python package that constructs the aligned hierarchies representation that contains all possible structure-based hierarchical decompositions for a finite length piece of sequential data aligned on a common time axis. In particular, this representation–introduced by Kinnaird (2016) with music-based data (like musical recordings or scores) as the primary motivation–is intended for sequential data where repetitions have particular meaning (such as a verse, chorus, motif, or theme). Although the original motivation for the aligned hierarchies representation was finding structure for music-based data streams, there is nothing inherent in the construction of these representations that limits repytah to only …

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Design And Synthesis Of Novel Peptide-Metal Organic Frameworks, Moustafa Mahmoud Abdel Wahid Hamaad May 2023

Design And Synthesis Of Novel Peptide-Metal Organic Frameworks, Moustafa Mahmoud Abdel Wahid Hamaad

Theses and Dissertations

Metal-organic frameworks (MOFs) are a class of crystalline porous materials with extended network structures formed through the reticular assembly of inorganic and organic molecular building blocks through strong coordination bonds. Compared to other porous materials, MOFs offer a high degree of structural diversity as their shape and pore size as well as functionality can tuned by the precise selection and design of their metal centers and organic struts. Due to their high surface areas, pore volumes, and the possibility of introduction of a myriad of chemical functionalities in their structures, MOFs have gained popularity for applications in many fields such …

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Anti-Doping Crisis In Sports, What's Next? Ion Mobility-Mass Spectrometry For The Study Of Anabolic Androgenic Steroids, Diana Constanza Velosa May 2023

Anti-Doping Crisis In Sports, What's Next? Ion Mobility-Mass Spectrometry For The Study Of Anabolic Androgenic Steroids, Diana Constanza Velosa

Theses and Dissertations

The main objective of this work is to augment both qualitative and quantitative measures of anabolic androgenic steroids (AAS) with ion mobility-mass spectrometry (IM-MS), laying the foundation for implementation into analytical drug testing laboratories. AAS testing requires high sensitivity and specificity. IM-MS is presented as an emerging technology workflow capable of targeted quantification of AAS and structural elucidation for potential unknowns, allowing ions to be separated and characterized based on their rotationally averaged collision cross section (CCS). Chapter 1 provides a background of the basic principles of IMS and the different types of analytical methods used for doping analysis currently …

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Global Upper Bounds For The Landau Equation Of Plasma Physics In The Very Soft Potentials Case, Caleb Solomon May 2023

Global Upper Bounds For The Landau Equation Of Plasma Physics In The Very Soft Potentials Case, Caleb Solomon

Theses and Dissertations

This paper explores global upper bounds for solutions of the Landau equation in the soft potentials case (γ < −2). In particular, this paper explores the case of γ ∈ [−3,−2). Working with a classical solution to the Landau equation weighted by a cut-off function χ and using the Moser iteration, an upper bound for the L∞v norm of the solution to the Landau equation f is obtained proportianally to the L2 v norm of f with the assumptions of positive, essentially bounded coefficients. The supremum of f for t ∈ [0, T], x ∈ R3, v ∈ BR for some large radius R is shown to be bounded polynomially in R.

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1. Influence Of Metal Ions And Solvents On The Photo-Generation Of Reactive Oxygen Species In Mesoporous Silicate Embedded Porphyrins 2.Water-Soluble Rhodium(Iii) Porphyrin Complex For The Biological Inactivation Of Fentanyl, Hemant Pal May 2023

1. Influence Of Metal Ions And Solvents On The Photo-Generation Of Reactive Oxygen Species In Mesoporous Silicate Embedded Porphyrins 2.Water-Soluble Rhodium(Iii) Porphyrin Complex For The Biological Inactivation Of Fentanyl, Hemant Pal

Theses and Dissertations

Porphyrins are differentiated π-conjugated compounds with unique photochemical and redox properties. The tetrapyrrole macrocycle core of porphyrins is extremely favorable for the complexation of metal ions, resulting in hybrid metal-organic molecules with good catalytic properties. Porphyrin-based systems are known for their oxidative properties and are frequently utilized as bio-mimicking catalysts and environmental remediation agents. My current research aims at both of these aspects. One of the most efficient methods to create photocatalytic systems with outstanding features and applicability is the use of porphyrins on supported solid materials. A series of novel mesoporous silicate-embedded metalloporphyrins were prepared via conjugation of novel …

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Monte-Carlo Modeling Of Bidirectional Reflectance In Shallow Turbid Water, Tyler Anthony Rotkiske May 2023

Monte-Carlo Modeling Of Bidirectional Reflectance In Shallow Turbid Water, Tyler Anthony Rotkiske

Theses and Dissertations

The ability to model surface and bottom boundary layers using water column information in shallow waters is mathematically approached using a Monte-Carlo model. The hyperspectral Monte-Carlo model used in this research was previously developed and analytically validated. This mathematical model tracks photons in 3-dimensional space and includes the effects of small gravity waves on the water surface, the bottom reflectance, and constituents within the water column. This type of modeling uses a probabilistic approach and is the only method used to calculate shape factors and mean cosines in a water column and then verified using hyperspectral remote sensing reflectance measurements. …

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Optimal R&D Investment In The Management Of Invasive Species, William Haden Chomphosy, Dale T. Manning, Stephanie A. Shwiff, Stephan Weiler May 2023

Optimal R&D Investment In The Management Of Invasive Species, William Haden Chomphosy, Dale T. Manning, Stephanie A. Shwiff, Stephan Weiler

United States Department of Agriculture Wildlife Services: Staff Publications

Invasive alien species (IAS) threaten world biodiversity, ecosystem services, and economic welfare. While existing literature has characterized the optimal control of an established IAS, it has not considered how research and development (R&D) into new removal methods or technologies can affect management decisions and costs over time. R&D can lower the costs of control in a management plan and creates an intertemporal trade-off between quick but costly control and gradual but cheaper removal over time. In this paper, we develop and solve a continuous time dynamic optimization model to study how investment in R&D influences the optimal control of an …

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Stoichiometric Determination Of Hydride Materials At Extreme Conditions, Gregory Alexander Smith May 2023

Stoichiometric Determination Of Hydride Materials At Extreme Conditions, Gregory Alexander Smith

UNLV Theses, Dissertations, Professional Papers, and Capstones

Hydrogen was predicted to be a high-temperature superconductor at near-megabar conditions in 1968,[1] but only recently was been experimentally observed.[2] This is due to the extraneous metrological constraint of requiring 5 megabars of pressure to stabilize. A more practical approach for synthesis of high-temperature superconductors has been pro-posed through the use of hydride compounds. Recently, a surge of rare earth hydrides have achieved critical superconducting transition temperatures (T_C ) close to room temperature.[3, 4, 5, 6] However, due to limitations of the necessary instrumentation to achieve megabar pressures, many techniques traditionally used to measure stoichiometry are unavailable.Three works presented in …

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High Clearance Collision-Free Paths, Barun Thapa May 2023

High Clearance Collision-Free Paths, Barun Thapa

UNLV Theses, Dissertations, Professional Papers, and Capstones

Path Planning is one of the widely investigated research areas in computational geometry and robotics. Given a set of polygonal obstacles inside a rectangular box, and start & goal points, the path planning problem is to construct a collision-free path connecting the start point to the goal point. We review existing well known algorithms for solving the path planning problem. We propose new approaches for constructing a collision-free path with high clearance from obstacles. The main idea of the proposed algorithm is the appropriate generation free-region nodes which can be processed to construct high clearance paths. Neighbors of free-region nodes …

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The Effects Of Habitat Isolation On Fine-Scale Genetic And Geographic Structure Of Populations Of Two Threatened Endemic Insects In Southern Nevada, Pseudocotalpa Giulianii And Icaricia Shasta Charlestonensis, Kristen Tovar May 2023

The Effects Of Habitat Isolation On Fine-Scale Genetic And Geographic Structure Of Populations Of Two Threatened Endemic Insects In Southern Nevada, Pseudocotalpa Giulianii And Icaricia Shasta Charlestonensis, Kristen Tovar

UNLV Theses, Dissertations, Professional Papers, and Capstones

Assessing the role geographic isolation and ecological specialization have on phylogeographic patterns contributes to our understanding of the evolutionary history of a species and the processes that erode genetic diversity. I used mitochondrial and nuclear genomic sequences to assess whether habitat isolation has shaped the fine-scale patterns of present-day genetic structure and diversity in two threatened insect species endemic to southern Nevada. Pseudocotalpa giulianii (Coleoptera; Scarabaeidae) is a dune obligate scarab beetle endemic to only two small, isolated sand dunes in Nye County, Nevada, with a usable habitat of less than 4.2 km sq that is impacted by on-going degradation. …

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Analysis And Application Of Finite Element And High-Order Finite Difference Methods For Maxwell’S Equations In Complex Media, Li Zhu May 2023

Analysis And Application Of Finite Element And High-Order Finite Difference Methods For Maxwell’S Equations In Complex Media, Li Zhu

UNLV Theses, Dissertations, Professional Papers, and Capstones

The Perfectly Matched Layer (PML) technique is an effective tool introduced by B´erenger [13] to reduce the unbounded wave propagation problem to a bounded domain problem. This dissertation focuses on two different PML models and their applications to wave propagation problems with Maxwell’s equation in complex media. We investigate these models using two popular numerical methods: the Finite Difference Method (FDM) in Chapters 2 and 3, and the Finite Element Method (FEM) in Chapters 4 and 5.In Chapter 2, we focus on analyzing the stability of a PML developed by B’ecache et al. [10] for simulating wave propagation in the …

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The Transaction Costs Of Federal Environmental Policy Changes: The Effects Of The Temporary Covid-19 Cwa Rollback On Local Water Systems, Jesse Lee Barnes May 2023

The Transaction Costs Of Federal Environmental Policy Changes: The Effects Of The Temporary Covid-19 Cwa Rollback On Local Water Systems, Jesse Lee Barnes

UNLV Theses, Dissertations, Professional Papers, and Capstones

An institutional dilemma exists between the Clean Water Act (CWA) and the Safe Drinking Water Act (SDWA). US surface waters are protected from point-source pollution by the CWA. Community Water Systems (CWSs) that draw from these surface waters for potable purposes are required to treat that water to a level that meets SDWA health standards. Therefore, decreases in CWA regulations could lead to surface water quality declines and, thus, higher SDWA compliance costs for CWSs. This area of inquiry has become increasingly relevant due to Trump-era executive actions to try to decrease the federal government's role in multiple environmental policies, …

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Trajectory Analysis For Driving Safety Quantification, Michael I. Chang May 2023

Trajectory Analysis For Driving Safety Quantification, Michael I. Chang

UNLV Theses, Dissertations, Professional Papers, and Capstones

In order to evaluate the efficacy of the skid recovery exercise in the Driver’s Edge teenage driving program, a process is established to determine the trajectories of vehicles from recorded videos, compare them in terms of similarity through dynamic time warping (DTW), and then analyze the similarity measurements to assess whether the program has a significant effect on driving ability by repeated measures analysis of variance (rANOVA). The video is analyzed by Harris corner detection and Lucas-Kanade optical flow method to ascertain the vehicle trajectories. A homography is then estimated to translate coordinates from video into real-world. The instructor and …

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Information-Theoretic Model Diagnostics (Infomod), Armin Esmaeilzadeh May 2023

Information-Theoretic Model Diagnostics (Infomod), Armin Esmaeilzadeh

UNLV Theses, Dissertations, Professional Papers, and Capstones

Model validation is a critical step in the development, deployment, and governance of machine learning models. During the validation process, the predictive power of a model is measured on unseen datasets with a variety of metrics such as Accuracy and F1-Scores for classification tasks. Although the most used metrics are easy to implement and understand, they are aggregate measures over all the segments of heterogeneous datasets, and therefore, they do not identify the performance variation of a model among different data segments. The lack of insight into how the model performs over segments of unseen datasets has raised significant challenges …

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Desert Spring Prokaryotes And Benthic Macroinvertebrates: Geological And Ecological Controls, Ariel D. Friel May 2023

Desert Spring Prokaryotes And Benthic Macroinvertebrates: Geological And Ecological Controls, Ariel D. Friel

UNLV Theses, Dissertations, Professional Papers, and Capstones

Desert springs are aquatic oases, being considered among the most diverse and imperiled ecosystems on Earth. Despite the ecological significance and threatened status of desert springs, few studies have surveyed the microorganisms in these systems or their interactions with other community members. The primary goal of this dissertation was to describe the major controls influencing the community ecology of prokaryotic and BMI communities in cold- and moderate-temperature desert springs of the southern hydrographic Great Basin. Chapter 1 provides a broad overview of spring ecosystems and of each chapter included in this dissertation. Chapter 2 documents the first-ever, regional-scale survey of …

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Response Of The Isothermal Mode Grüneisen Tensor Across Phase Boundaries, Jasmine K. Hinton May 2023

Response Of The Isothermal Mode Grüneisen Tensor Across Phase Boundaries, Jasmine K. Hinton

UNLV Theses, Dissertations, Professional Papers, and Capstones

The assumptions for the 1912 Grüneisen parameter are reviewed, particularly in the cases of anisotropy, high temperatures, and across phase boundaries. Two main case studies are shown: β-Sn, and Cd. The main techniques of this work involve resistively heated diamond anvil cells with both optical Raman spectroscopy and x-ray diffraction. It is found in Sn that the isothermal mode Grüneisen tensor along increasing isotherms diverges from the single-valued temperature aggregate at the onset of melt, and this is proposed to use as a method of exploring melt phase boundaries in other systems. This method is examined once again on another …

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Spectroscopic Studies On Silicon And Chalcopyrite Materials For Solar Energy Applications, Amandee Hua May 2023

Spectroscopic Studies On Silicon And Chalcopyrite Materials For Solar Energy Applications, Amandee Hua

UNLV Theses, Dissertations, Professional Papers, and Capstones

In this dissertation, silicon-based materials for photovoltaics and chalcopyrite-based materials for photoelectrochemical water splitting are investigated using various spectroscopic and microscopic techniques. Although silicon dominates the photovoltaic market, further improvement can be made by using an alternative low temperature passivation approach. Currently, thermally grown SiO2 passivation is commonly used for silicon solar cells. However, this technique requires high processing temperatures (>800 °C), which increases the thermal budget, potentially decreases the bulk quality of Si, and can lead to difficulties in implementing in production lines. Here, a S-based passivation approach is studied that require lower processing temperatures of ~550 °C. …

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Applying Instrumental Neutron Activation Analysis To Assess Air Pollution With Spanish Moss As A Bioindicator In The Low Country Of The Savannah River Basin, Christina Jiang May 2023

Applying Instrumental Neutron Activation Analysis To Assess Air Pollution With Spanish Moss As A Bioindicator In The Low Country Of The Savannah River Basin, Christina Jiang

UNLV Theses, Dissertations, Professional Papers, and Capstones

The Savanah River Basin is an area of 9,850 square miles that stretches from the border between South Carolina and Georgia, which empties into the Atlantic Ocean near Savannah, Ga. This area is home to surrounding cities, industrial sites, and the Savanah River Site. It is well documented that traffic, industrial operations, and agriculture contribute to worsening air pollution that needs to be monitored. While Tillandsia usneoides (Spanish moss) has been used in previous studies that prove it to be an effective biomonitor for air pollution and an accumulator of heavy metals, there have been no biomonitoring studies in the …

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Solving Boundary Value And Initial Boundary Value Problems Of Partial Differential Equations Using Meshless Methods, Adam Johnson May 2023

Solving Boundary Value And Initial Boundary Value Problems Of Partial Differential Equations Using Meshless Methods, Adam Johnson

UNLV Theses, Dissertations, Professional Papers, and Capstones

In this dissertation, the methods of fundamental solutions (MFS) and the methods of particular solutions (MPS) are used to solve the boundary value problems of the Poisson and Helmholtz equations, where the particular solutions of the Poisson and Helmholtz equations in [13, 14] are used. Then the initial boundary value problems of the diffusion and wave equations are discretized into a sequence of boundary value problems of the Helmholtz equation by using either the Laplace transform or time difference methods along the lines of [8]. The Helmholtz problems are solved consequently in an iterative manner which leads to the solution …

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A Generalized Family Of Exponentiated Composite Distributions With Applications To Insurance And Survival Data, Bowen Liu May 2023

A Generalized Family Of Exponentiated Composite Distributions With Applications To Insurance And Survival Data, Bowen Liu

UNLV Theses, Dissertations, Professional Papers, and Capstones

The concept of composite distributions was proposed in the early 2000s as a good parametric solution to model the data with heavy tails. Since the concept was proposed, it has been widely used in different areas, such as modeling insurance claim size data, predicting the risk measures in insurance data analysis, fitting survival time data, and modeling precipitation data. While a lot of the composite distributions demonstrated great performances in real applications, many commonly used composite distributions such as the inverse gamma-Pareto (IGP) or exponential-Pareto (EP), did not demonstrate great performances when fitting to several particular data sets. In order …

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Critical Metals: From Granitic Pegmatites To The Anthropogenic Cycle, Dalton Mccaffrey May 2023

Critical Metals: From Granitic Pegmatites To The Anthropogenic Cycle, Dalton Mccaffrey

UNLV Theses, Dissertations, Professional Papers, and Capstones

Critical metals are vital to the functionality of the modern world. The increased diversity and usage intensity of these commodities in defense-related and strategic technologies (e.g., jet engines, rocket assemblies), modern infrastructure and products (e.g., high-strength steel, cellular phones, laptop computers), and energy-related, low-emissions technologies (e.g., nuclear reactors, solar panels, wind turbines, hybrid and electric vehicles) has drastically increased our reliance on critical metals and, thus, the United States (and global) exposure to supply restrictions. Granitic pegmatites are unique mineral deposits that represent a past, present and future resource for many (approximately half) of these critical resources. Even with the …

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Algorithmic Approaches To Battery Consolidation In A Smart Grid, Dara Nyknahad May 2023

Algorithmic Approaches To Battery Consolidation In A Smart Grid, Dara Nyknahad

UNLV Theses, Dissertations, Professional Papers, and Capstones

The concept of the battery exchange station (BES) as a part of the battery consolidation system (BCS) has certain criteria that make it a significant player in the better adaptation plan of electric vehicles (EVs) in the grid toward the smart grid. In this dissertation, we study the BES optimization problem as a promising approach for EV adaptation in a smart grid. We introduce the concept of BCS, which focuses on optimizing the incorporation and transaction of all of the components in a smart grid. Accordingly, we address three BES optimization problems in the BCS. In the first problem, we …

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Characterization Of Hematite Coated Bedrock Fault Scarps In The Northern Colorado River Extensional Corridor Near Lake Mead, Nevada, Molly E. Pickerel May 2023

Characterization Of Hematite Coated Bedrock Fault Scarps In The Northern Colorado River Extensional Corridor Near Lake Mead, Nevada, Molly E. Pickerel

UNLV Theses, Dissertations, Professional Papers, and Capstones

Fault mirrors are reflective, thin, typically <1 mm thick, fault slip surfaces in exhumed fault zones that can provide a record of thermal, chemical, and rheological changes to fault materials during deformation. This study investigates a series of hematite coated fault mirrors along bedrock fault scarps in Miocene volcanic rocks near Lake Mead, Nevada. The studied faults are located in a structurally complex area that includes NE-SW trending left-lateral strike-slip faults of the Lake Mead fault system, NW-SE right-lateral strike-slip faults of the Las Vegas Shear Zone, and N-S striking extensional faults of the Northern Colorado River Extensional Corridor.New zircon U-Pb ages from fault scarp host rocks 21-BC-03 and 21-BC-05 are and 13.86 ± 0.27 Ma and 12.90 ± 0.31 Ma (2σ standard error), respectively. New apatite (U-Th)/He dates range from 5.64 ± 0.46 Ma to 12.4 ± 0.36 Ma (2σ standard error) and are interpreted to be partially reset after eruption due to reheating. Inverse thermal history modeling in HeFTy of apatite He dates indicates a thermal history of reheating to ~65 °C which is interpreted as shallow burial around ~11 - 5 Ma followed by cooling to the surface, interpreted as exhumation between ~4.5 - 2 Ma. The zircon U-Pb ages, apatite He dates, and inverse thermal history models indicate the fault host rocks were erupted to the surface and stayed within the upper ~2 km of the crust since the Miocene. Nearly vertical fault scarps that host the fault mirror surfaces exhibit two sets of slickenlines, indicating oblique and strike-slip motion, with different orientations indicating that there have been multiple episodes of deformation along the surfaces. Three of the five studied fault scarps have E-W orientations, and one scarp is NW-SE, and one is NE-SW striking. The studied faults are interpreted to have been active during deformation associated with the Lake Mead Fault System and the Las Vegas Valley Shear Zone at 13 – 9 Ma and record both strike slip and oblique slip events in the complex strain field during this time. Micro-nano scale texture and grain morphology analysis of the hematite fault mirror volumes shows extreme strain localization along the fault mirror surface. Some fault mirrors exhibit multiple domains separated by discrete slip surfaces. Comminution and cataclasis appear to be the dominant deformation mechanisms in the fault mirror volume. Hematite textures and morphologies are consistent with observations from other fault systems that are interpreted to record aseismic to sub-seismic slip rates, and relatively low coseismic temperature rise. Fluid injection veins and post-deformation FeO mineralization in fractures are interpreted as evidence of high fluid pressures during slip and fluid circulation postdeformation. The new geochronologic and microstructural data inform on the processes operating along discrete fault surfaces in the shallow crust since the Miocene in the Lake Mead region.

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Mathematical Modeling: Finite Element Analysis And Computations Arising In Fluid Dynamics And Biological Applications, Jorge Reyes May 2023

Mathematical Modeling: Finite Element Analysis And Computations Arising In Fluid Dynamics And Biological Applications, Jorge Reyes

UNLV Theses, Dissertations, Professional Papers, and Capstones

It is often the case when attempting to capture real word phenomena that the resulting mathematical model is too difficult and even not feasible to be solved analytically. As a result, a computational approach is required and there exists many different methods to numerically solve models described by systems of partial differential equations. The Finite Element Method is one of them and it was pursued herein.This dissertation focuses on the finite element analysis and corresponding numerical computations of several different models. The first part consists of a study on two different fluid flow models: the main governing model of fluid …

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Morphologic Comparisons Of Recrystallized And Neocrystallized Fibrous Amphibole Asbestos: Implications For Corresponding Health Risk Potential, Natalie G. Renkes May 2023

Morphologic Comparisons Of Recrystallized And Neocrystallized Fibrous Amphibole Asbestos: Implications For Corresponding Health Risk Potential, Natalie G. Renkes

UNLV Theses, Dissertations, Professional Papers, and Capstones

The presence of naturally-occurring asbestos (NOA) is increasingly concerning for scientists, health and regulatory agencies, and citizens living in impacted areas. It is commonly believed that fibrous amphibole asbestos can only form through neocrystallization. In southern Nevada, NOA occurs as a result of hydrothermal alteration of granitic rock producing fibrous amphibole both as cross-cutting neocrystallized veins and via recrystallization of original magmatic hornblende crystals. Fibers with a greater aspect ratio are known to have increased toxicity. This study measured the maximum length and average width of both neocrystallized and recrystallized fibers to see if the morphologies were similar. Neocrystallized and …

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