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Exploring The Effectiveness Of Model-Based Instruction To Improve Sixth-Grade Students’ Science Content Knowledge, Scot D. Ewen
Exploring The Effectiveness Of Model-Based Instruction To Improve Sixth-Grade Students’ Science Content Knowledge, Scot D. Ewen
UNLV Theses, Dissertations, Professional Papers, and Capstones
The economy of tomorrow is uncertain, so students today need to be prepared for the known and unknown careers that lie ahead. Currently, not all students are expected to have equal career opportunities based on evidence from dropout and testing data (Brown & Brown, 2007; Kirsch, Braun, Yamamoto, & Sum, 2007), so educators should consider different methods of helping all students reach their potential. Modeling instruction is one method that might help diverse learners improve their scientific understandings and allow them to pursue careers in technology-oriented fields. A quasi-experimental study was conducted with 128 sixth grade students as participants. A …
The Design, Modeling, And Optimization Of A Biomimetic Soft Robot For Fluid Pumping And Thrust Generation Using Electroactive Polymer Actuators, Zakai Jedidiah Olsen
The Design, Modeling, And Optimization Of A Biomimetic Soft Robot For Fluid Pumping And Thrust Generation Using Electroactive Polymer Actuators, Zakai Jedidiah Olsen
UNLV Theses, Dissertations, Professional Papers, and Capstones
Nature is a constant source of inspiration for engineers and scientists through its simple, effective, and elegant solutions to many complex problems. Smart materials and soft robotics have been seen to be particularly well suited for developing biomimetic devices and are active fields of research. In this study, the design, modeling, and optimization of a new biomimetic soft robot is described. Preliminary work was made in the modeling of a biomimetic robot based on the locomotion and kinematics of jellyfish. Modifications were made to the governing equations for jellyfish locomotion that accounted for geometric differences between biology and the robotic …
Mapping The Landscape For Archaeological Detection, Preservation, And Interpretation: A Case Study In High Resolution Location Modeling From The Blue Mountains Of Northeastern Oregon, Trent Skinner
UNLV Theses, Dissertations, Professional Papers, and Capstones
Archaeological location modeling (ALM) is an important tool in most survey strategies, and has contributed substantially to economizing efforts to locate and characterize the archaeological record. The increasing availability of high resolution (<3m) airborne light detection and ranging (lidar) data has the potential to refine the application and ultimately the role of ALM. This research tests the precision and accuracy gained by incorporating lidar derived data into an ALM. The site records and other environmental data used in this study were all generated over the last four decades by the resource specialists of the Malheur National Forest. The Weights-of-Evidence (WofE) probability method (Bonham-Carter 1994) was used to produce two ALMs; one based on a 10m digital elevation model (DEM) created from satellite imaging, and the second from a 3m resolution lidar derived DEM. Independent variables (e.g., slope, aspect, distance to water, etc.) commonly used in ALM were largely replaced by index variables (e.g., slope position classification, topographic wetness index, etc.). The final models were classified into areas of high, medium, and low archaeological potential, then cross-validated against a reserved random dataset. Models were then compared using the Kvamme gain statistic and site to area frequency ratio. The 3m model demonstrated a significant improvement over the results obtained from the 10m model and the current probability model used in the study area. A number of factors including model resolution, statistical methodology, and the character of the independent and dependent variables all contributed to the increase in precision and accuracy. The incremental improvement in modeling efficiency demonstrated here will create time and cost saving in the management and preservation of cultural resources, and ultimately contribute to a better understanding of patterns of past human land use.
Relationships Between The Groundwaters Of Ash Meadows, Death Valley, Pahranagat Valley And The Nevada Test Site Based On Statistical Analysis And Modeling Of Trace Element Data, Sara Michelle Cox
UNLV Retrospective Theses & Dissertations
Relationships between the groundwaters of the Nevada Test Site, Ash Meadows, Pahranagat, and Death Valley have been studied by many people over many years. Using hydrogeochemical data from these areas (sampled and analyzed by the Harry Reid Center for Environmental Studies) hydrologic subbasins were classified on the basis of trace element concentrations and compare these to previous classification systems. In addition, previously suggested flow relationships were examined on the basis of trace element concentrations, in particular those elements which are thought to behave conservatively in oxidizing environments. These efforts were made with the aid of statistical analyses such as principal …
Experimental And Numerical Study Of A Proton Exchange Membrane Electrolyzer For Hydrogen Production, Sachin S. Deshmukh
Experimental And Numerical Study Of A Proton Exchange Membrane Electrolyzer For Hydrogen Production, Sachin S. Deshmukh
UNLV Theses, Dissertations, Professional Papers, and Capstones
Hydrogen as a fuel source has received attention from researchers globally due to its potential to replace fossil based fuels for energy production. Research is being performed on hydrogen production, storage and utilization methods to make its use economically feasible relative to current energy sources. The PEM electrolyzer is used to produce hydrogen and oxygen using water and electricity. Focus of our study is to provide a benchmark experiment and numerical model of a single cell electrolyzer that can assist in improving the current state of understanding of this system. Parametric analysis of an experimental cell was performed to understand …
Numerical Modeling Of High Temperature Shell And Tube Heat Exchanger And Chemical Decomposer For Hydrogen Production, Gayatri Kuchi
Numerical Modeling Of High Temperature Shell And Tube Heat Exchanger And Chemical Decomposer For Hydrogen Production, Gayatri Kuchi
UNLV Retrospective Theses & Dissertations
This thesis deals with the development of a three-dimensional numerical model of high temperature shell and tube heat exchanger and chemical decomposer to examine the percentage decomposition of a sulfur trioxide gaseous mixture for the production of hydrogen by the sulfur-iodine thermochemical water splitting cycle, a candidate cycle in the U.S. Department of Energy Nuclear Hydrogen Initiative. A counter flow type straight tube shell and heat exchanger concept is chosen for the analysis. The reacting fluid is a mixture of sulfur trioxide gas and water vapor inside the tubes of the heat exchanger and high temperature helium is the gas …
Thermal Modeling Of A High Concentration Photovoltaic System, Aaron M Sahm
Thermal Modeling Of A High Concentration Photovoltaic System, Aaron M Sahm
UNLV Retrospective Theses & Dissertations
A two-dimensional numerical model was developed to simulate a single chamber with an array of cells for a high concentration photovoltaic system. Gambit was used to generate the computational mesh and Fluent was used to obtain the numerical simulation results. The cells were treated as heat sources with efficiencies that change as a function of temperature. Initially a simulation was run with an assumed cell efficiency of 25%. After the maximum temperature was determined, the cell efficiency was calculated and input into the model to recalculate the temperature solution. Radiation and convection modes of heat transfer were the primary focus …
Monitoring And Modeling The Performance Of A Solar Powered Hydrogen Filling Station, Mark R Campbell
Monitoring And Modeling The Performance Of A Solar Powered Hydrogen Filling Station, Mark R Campbell
UNLV Retrospective Theses & Dissertations
A hydrogen filling station (HFS) has been constructed in Las Vegas to demonstrate how solar energy can be used to generate and store hydrogen as an energy carrier for transportation. This thesis presents a description of the station and the data acquisition system used to monitor its performance. Energy consumption by the hydrogen generation and storage equipment and energy production from a solar photovoltaic (PV) array were measured, and based on the characteristics of the different system components, a computer model was created to predict the amount of hydrogen that could be produced from the solar array. The hydrogen produced …
Modeling The Unsaturated Zone At The Area 5 Radioactive Waste Management Site: Effects Of Climate Change And Vegetation On Flow Conditions, Amanda Marie Brandt
Modeling The Unsaturated Zone At The Area 5 Radioactive Waste Management Site: Effects Of Climate Change And Vegetation On Flow Conditions, Amanda Marie Brandt
UNLV Retrospective Theses & Dissertations
This thesis tests a series of potential future climate scenarios and associated environmental conditions that could result in the reversal of the present upward hydraulic gradient in the vadose zone at the Area 5 Radioactive Waste Management Site (RWMS) by implementing a one-dimensional model developed using the HYDRUS 1-D numerical modeling package. The research is divided into two phases. Phase I simulates the system from the Pleistocene to Holocene transition (approximately 13,000 years ago) to the present and is tested by independently varying precipitation, evaporation and transpiration rates. The results provide initial conditions for subsequent modeling under Phase II, which …
Statistical Modeling Of Skewed Data Using Newly Formed Parametric Distributions, Kahadawala Cooray
Statistical Modeling Of Skewed Data Using Newly Formed Parametric Distributions, Kahadawala Cooray
UNLV Retrospective Theses & Dissertations
Several newly formed continuous parametric distributions are introduced to analyze skewed data. Firstly, a two-parameter smooth continuous lognormal-Pareto composite distribution is introduced for modeling highly positively skewed data. The new density is a lognormal density up to an unknown threshold value and a Pareto density for the remainder. The resulting density is similar in shape to the lognormal density, yet its upper tail is larger than the lognormal density and the tail behavior is quite similar to the Pareto density. Parameter estimation methods and the goodness-of-fit criterion for the new distribution are presented. A large actuarial data set is analyzed …
Modeling Natural Resource Scarcity And Poverty Effects On Fertility In Honduras, Nepal, And Tanzania, Ayoub Shaban Ayoub
Modeling Natural Resource Scarcity And Poverty Effects On Fertility In Honduras, Nepal, And Tanzania, Ayoub Shaban Ayoub
UNLV Retrospective Theses & Dissertations
This dissertation examines whether the vicious circle theory applies in three developing countries characterized by high population growth. According to the vicious circle theory, natural resource scarcity coupled with poverty leads to population growth via positive effects on fertility particularly in rural areas of developing countries. Population growth then leads to a further increase in natural resource scarcity, creating a "feedback loop." This is the first study to use micro-level data to test and control for endogeneity using a two-stage Probit model (IVPROBIT). The existing literature has largely failed to address endogeneity in the relationship between natural resource scarcity and …
Geochemical And Transport Modeling Of Selected Radionuclides At Yucca Mountain, Yuyu Lin
Geochemical And Transport Modeling Of Selected Radionuclides At Yucca Mountain, Yuyu Lin
UNLV Retrospective Theses & Dissertations
Yucca Mountain, Nevada has been selected as a potential high-level nuclear waste repository. The groundwater system at Yucca Mountain is a primary medium through which radionuclides might move away from the potential repository. Characterization studies have identified 237Np, 235 U and 239Pu as radionuclides of concern. In this study, simulations of solid solubility, solution speciation, and transport of selected radionuclides are conducted with PHREEQC, a geochemical modeling system. Results from solubility and speciation simulations indicate the influence of pH value and CO2 fugacity on radionuclide dissolution and aqueous species in solution. Kinetic transport simulations produced radionuclide breakthrough curves under various …
Mathematical Modeling Of Magnetohydrodynamic Micropumps, Juan Katoff Afonien
Mathematical Modeling Of Magnetohydrodynamic Micropumps, Juan Katoff Afonien
UNLV Retrospective Theses & Dissertations
A lab-on-a-chip (LOC) system is a minute chemical processing plant consisting of interconnected networks of microchannels and reservoirs operating with small volumes of reagents. In many LOC systems, it is necessary to propel fluids from one part of the device to another, control fluid motion, stir and interact various reagents, and detect the presence of target analytes. In LOC systems, these tasks are far from trivial; This thesis focuses on fluid propulsion under the action of electric and magnetic fields. Both Non-RedOx and RedOx-based Magneto-hydrodynamic (MHD) micropumps, in which the flow is directed by judicious interplay between electric and magnetic …
Evaluation And Modeling Of The Effect Of Midblock Pedestrian Crossings On Arterial Traffic, Naveen Kumar Veeramisti
Evaluation And Modeling Of The Effect Of Midblock Pedestrian Crossings On Arterial Traffic, Naveen Kumar Veeramisti
UNLV Retrospective Theses & Dissertations
Unsignalized midblock pedestrian crossings are one of the critical components of arterial streets designed to provide for safer crossing locations for pedestrians. These crossings are often placed between signalized intersections that are far apart. However when arterial segments with such crossings are being analyzed or designed, the effect of the crossings was not normally taken into consideration. This is primarily due to the inability of current traffic software in modeling these locations; The objective of this study was to evaluate the effect of midblock pedestrian crossings on the measures of effectiveness of arterial traffic flow using a computer simulation model. …
Modeling A Passive Cooling System For Photovoltaic Cells Under Concentration, Allison K Gray
Modeling A Passive Cooling System For Photovoltaic Cells Under Concentration, Allison K Gray
UNLV Retrospective Theses & Dissertations
An analysis of the Amonix high concentration photovoltaic (HCPV) passive cooling system was performed in order to obtain a better understanding of the present design and identify poor areas of dissipation. Cooling of photovoltaic tells under high intensity solar irradiance is a major concern when designing concentrating photovoltaic systems. Solar tell temperatures increase if the waste heat is not removed causing the cell voltage to decrease lowering the power generated. The concentrator geometry was studied so a model of the HCPV passive cooling system could be generated to analyze the system numerically. In addition to this experiments were conducted in …
Physics Based Modeling Of The Charging Dynamics In Silicon Nanocrystal Non-Volatile Flash Memory Cell, Pavan Kumar Singaraju Venkata Sai
Physics Based Modeling Of The Charging Dynamics In Silicon Nanocrystal Non-Volatile Flash Memory Cell, Pavan Kumar Singaraju Venkata Sai
UNLV Retrospective Theses & Dissertations
Flash memory devices based on continuous floating gate are rapidly approaching their technological limitations due to excessive gate leakage currents, resulting from reduced tunnel oxide thickness. A new architecture based on Si-Nanocrystal floating gate has shown promise through realization of devices with reduced gate leakage current and lower programming and erase voltages. The dominant transport mechanisms in this device are tunneling of electrons from the (3-D) silicon into the (0-D) nanocrystals and Fowler-Nordheim tunneling of carriers from nanocrystals to the bulk Si. In order to accurately model the charging dynamics of such devices, size based quantum confinement effects should be …
Computational Modeling Of Proton Exchange Membrane Electrolysis Cell For Hydrogen Production, Shanthi P Katukota
Computational Modeling Of Proton Exchange Membrane Electrolysis Cell For Hydrogen Production, Shanthi P Katukota
UNLV Retrospective Theses & Dissertations
Numerical simulations of electrochemical process for hydrogen production were performed for the purpose of examining the phenomena occurring within the proton exchange membrane (PEM) water splitting cell. A steady-state isothermal two dimensional model of the cell is developed. Finite element method was used to solve the multi-component transport model coupled with flow in porous medium, charge balance and electrochemical kinetics; Parametric studies were performed based on appropriate mass balances, transport, and electrochemical kinetics applied to the cell. It is observed that, as the water on the anode side flows from the inlet to the outlet, the mass fraction of oxygen …
Statistical Modeling Via Empirical Recurrence Rate, Hui Wang
Statistical Modeling Via Empirical Recurrence Rate, Hui Wang
UNLV Retrospective Theses & Dissertations
A key parameter, most sought after by the modelers of reliability, is the failure rate of a targeted repairable system. Popular modeling techniques based on a point process such as the Power-law process often are handicapped by the requirement of a monotonic failure rate. In this thesis, we show the potential of building a linking bridge between the traditional homogeneous and nonhomogeneous Poisson processes and the classical time series via a sequence of the empirical recurrence rates, calculated at equally spaced intervals of time. The distinctive signature, marking the unique failure pattern of a repairable system, is displayed with an …
Optimization For Finite Element Modeling Of Electronic Components Under Dynamic Loading, Srujanbabu Sridharala
Optimization For Finite Element Modeling Of Electronic Components Under Dynamic Loading, Srujanbabu Sridharala
UNLV Retrospective Theses & Dissertations
Usage of electronic components in the U.S. ARMY applications is becoming more challenging due to their usage in harsh environments. Experimental verification of these components is expensive and it can yield information about specific locations only. This research outlines the finite element modeling methodology for these electronic components that are subjected to high acceleration loads that occur over extremely short time such as impact, gun firing and blast events. Due to their miniature size these finite element models are computationally expensive. An optimization engine was presented to have an efficient analysis procedure that provides a combination of accuracy, computational speed …
Synthesizing A Piccolo Using Physical Modeling Techniques, Pamela Pnina Mandelbaum
Synthesizing A Piccolo Using Physical Modeling Techniques, Pamela Pnina Mandelbaum
UNLV Retrospective Theses & Dissertations
Physical modeling is a very affective technique used to simulate a musical instrument. It is different than most synthesizing techniques, because the synthesized sound is completely computer generated. It works by starting with a pure frequency and then applying a physical model to this signal. The physical model is created by analyzing the effects that the real instrument would have on a pure signal and then designing a model to simulate these effects using signal processing techniques; The piccolo is an instrument similar to the flute. Music synthesizers will use synthesized flute sounds for music that requires a synthesized piccolo. …
Virtual Design And Modeling Of Various Manufacturing Processes For Remote Fabrication Of Transmuter Fuel, Jamil Mohamad Renno
Virtual Design And Modeling Of Various Manufacturing Processes For Remote Fabrication Of Transmuter Fuel, Jamil Mohamad Renno
UNLV Retrospective Theses & Dissertations
As currently envisioned, over 70,000 tons of high-level nuclear waste would be stored inside the planned Yucca Mountain repository. After emplacement, the site must be maintained and guarded for over 10,000 years; The reprocessing of spent nuclear fuel is a possible alternative to geological storage. Here, depleted Uranium would be separated from Plutonium and Minor Actinides. While Plutonium can be 'burned' in commercial nuclear reactors, the minor actinides would be transmuted into other elements. The large-scale deployment of remote fabrication and refabrication processes (approx. 100 tons of Minor Actinides (MA) annually) will be required. Process automation has the potential to …
Cfd Modeling Of Compact Offset Strip-Fin High Temperature Heat Exchanger, Sundaresan Subramanian
Cfd Modeling Of Compact Offset Strip-Fin High Temperature Heat Exchanger, Sundaresan Subramanian
UNLV Retrospective Theses & Dissertations
This thesis deals with the development of a numerical model to predict the overall performance of an advanced high temperature heat exchanger (HTHX) design, up to 1000°C, for the production of hydrogen by the sulfur iodine thermo-chemical cycle. The present study considers an offset strip-fin type compact high temperature heat exchanger made of liquid silicon impregnated carbon composite (SiC). The ceramic matrix composite material (CMC) is manufactured by impregnating the silicon into the pores of the carbon composites. The prototype heat exchanger is designed to operate at a thermal power of 50 MW. The design is an offset strip-fin, hybrid …
Conceptual Modeling And Analysis Of A Solar Receiver For Thermochemical Hydrogen Generation, Derek Satoru Taguchi
Conceptual Modeling And Analysis Of A Solar Receiver For Thermochemical Hydrogen Generation, Derek Satoru Taguchi
UNLV Retrospective Theses & Dissertations
Hydrogen has the potential to revolutionize the way we live our everyday lives in the near future. With the global demand for oil increasing and pumping capabilities running at, or almost at full capacity, the world will eventually have to turn to alternative energy sources to satisfy the need for fuel in the near future; The processes involved in designing a system capable of hydrogen production include many different components. For the generation of hydrogen through a solar process, one of these components is the design and analysis of the solar receiver. The solar receiver is the component of the …
Reactor Modeling And Simulation For The Copper-Chlorine Thermochemical Solar Hydrogen Generation Process, Mohammed Yassin
Reactor Modeling And Simulation For The Copper-Chlorine Thermochemical Solar Hydrogen Generation Process, Mohammed Yassin
UNLV Retrospective Theses & Dissertations
Interest in hydrogen as a clean fuel has surged in the recent past as concerns over the costs of fossil fuels to the economy and environment have become paramount. As hydrogen burns only to produce water and can be used in efficient fuel cells, it has a great opportunity to be the replacement for carbon-based fuels in the twenty-first century. Hydrogen is an attractive fuel because it is renewable as an energy resource and it is also flexible as an energy carrier; Quantities of hydrogen gas on earth are limited, so it must be chemically derived from some other sources. …
Radiation Transport And Finite Element Modeling Of A Detector Shield For Sandia National Laboratory, Daniel Robert Lowe
Radiation Transport And Finite Element Modeling Of A Detector Shield For Sandia National Laboratory, Daniel Robert Lowe
UNLV Retrospective Theses & Dissertations
The Z Machine at Sandia National Laboratory is a pulsed powered electron accelerator that is able to produce fusion neutrons by pinching the deuterium and tritium gas with the surrounding high temperature plasma. Neutron detectors are placed in various locations throughout the room in order to detect these fusion neutrons. Plastic scintillating neutron detectors are sensitive to other types of unwanted radiations however. The purpose of this project was to design a shield that would allow the fusion neutrons to enter the detector while preventing the other types of unwanted radiation from getting to that same detector. A shield was …
Three-Dimensional Modeling And Simulation Of Manufacturing Processes For Transmuter Fuel Fabrication, Richard Arthur Silva
Three-Dimensional Modeling And Simulation Of Manufacturing Processes For Transmuter Fuel Fabrication, Richard Arthur Silva
UNLV Retrospective Theses & Dissertations
A proposed method of converting long-lived radionuclides contained within spent nuclear fuel into shorter-lived radionuclides is known as transmutation. The feasibility assessment of fuel manufacturing for transmutation is necessary for the overall success of the transmutation project. As part of that assessment, this paper reviews current methodologies for handling spent nuclear fuel and other highly radioactive material. While not exhaustive, the review encompassed facilities within the U.S. Department of Energy, international operations, as well as, work performed collegiately; The manufacturing of fuel for transmutation will certainly utilize automation and robotics. A simplified 3-D model of a fuel handling operation was …
Modeling Consumer Choices Between Domestic And Foreign Automobiles, Cagla Hirschman
Modeling Consumer Choices Between Domestic And Foreign Automobiles, Cagla Hirschman
UNLV Retrospective Theses & Dissertations
This paper analyzes survey data to determine the factors that impact the probability of purchasing a domestic versus foreign brand of automobile. It includes dynamic variables reflecting purchase history and thus the effect past choices may have on current behavior. Some of these factors are shown to be statistically significant. The paper also looks at key subpopulations. We see that preferences in the luxury segment are far better explained by economic, demographic, and dynamic variables than are preferences in the non-luxury market. The paper also looks at switching behavior---domestic owners who switch to foreign brands. The key finding is that …
Finite Element Modeling Of Energy-Absorbing Materials In Blast-Loaded Structures, Michael Jason Mullin
Finite Element Modeling Of Energy-Absorbing Materials In Blast-Loaded Structures, Michael Jason Mullin
UNLV Retrospective Theses & Dissertations
Energy absorbing materials such as foam or honeycomb are of interest in blast protection because of their ability to absorb energy through plastic deformation. They absorb a considerable amount of energy relative to their low density, and are investigated to determine if their energy absorbing abilities can be used to mitigate blast damage. Ballistic pendulum experiments show that energy absorbing materials increase the energy transferred from a blast. This behavior was contrary to expected results so computational models were created in LS-DYNA to understand the phenomenon that causes an increase in transferred energy. Many models using ConWep and Arbitrary-Lagrangian-Eulerian (ALE) …
Numerical Modeling Of Unsteady Compressible Gas Flow Around A Projectile, Valery Ivanovich Ponyavin
Numerical Modeling Of Unsteady Compressible Gas Flow Around A Projectile, Valery Ivanovich Ponyavin
UNLV Retrospective Theses & Dissertations
In this project, an attempt to calculate the characteristics of compressible gas flow around a projectile during the motion of the projectile in the gun barrel is undertaken. The flow is considered axisymmetrical, nonstationary, nonisothermal, compressible, and turbulent. For calculating the compressible gas flow around a projectile, the finite volume method was employed. An h-adaptive mesh refinement scheme based on elemental flow feature gradients is utilized for greater solution accuracy. For modeling flow around the moving projectile both sliding and dynamic meshes were used; The application of the calculations is in support of the Joint Actinide Shock Physics Experimental Research …
Flux Profile Modeling Using Monte Carlo Simulation, Ramprasad Vijayagopal
Flux Profile Modeling Using Monte Carlo Simulation, Ramprasad Vijayagopal
UNLV Retrospective Theses & Dissertations
Molecular beam Epitaxy (MBE) is a process by which semiconductor films are grown on the substrate by physical vapor deposition of the source material in an ultra high vacuum environment. Spatial variations in flux are a result of the shape of the crucible and the geometry of the growth chamber. In this study a process simulation tool for MBE based on a phenomenological model is proposed and elaborated; Two different models based on physical principles are investigated. Model I includes the primary flux from the liquid surface and a secondary flux re-emitted from the crucible walls for the total flux …