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Fabrication and Testing of Polymeric Flexible Sheets with Asymmetric Distributed Magnetic Particles for Biomedical Actuated Devices
This thesis explores a method to fabricate magnetic membranes with asymmetric distribution of particles and their testing as actuators. Focus of this research is to fabricate thin polymeric sheets and thickness range of 120-125µm, with asymmetric distribution of magnetic nano particles, employing micromagnets during the fabrication. The micromagnets are used to localize the magnetic particles during the curing process at selected locations. The effect of the asymmetric distribution of magnetic particles in the membrane is used for the first time. Magnetite (Fe3O4) is used as the magnetic particles that is embedded into a polymeric membrane made of polydimethylsiloxane (PDMS); the membrane is then tested in terms of deflection observed by using a high-resolution camera. From the perspective of the biomedical application, PDMS is chosen for its excellent biocompatibility and mechanical properties, and Fe3O4 for its non-toxic nature. Since magnetic actuation does not require onboard batteries or other power systems, it is very convenient to use in embedded devices or where the access is made difficult. A comparative study of membranes with asymmetric and randomly distributed particles is carried out in this thesis. The asymmetric distribution of magnetic particles can benefit applications involving localized and targeted treatments and precision medicine.
Study of the Corrosion Resistance of 316L Stainless Steel Made by Directed Energy Deposition for Applications at an Elevated Temperature
The corrosion resistance under elevated temperature of additively manufactured 316L stainless steel made by directed energy deposition was studied. Test samples were prepared in a hybrid additive manufacturing machine using standard deposition parameters recommended by the manufacturer. Control samples were cut from wrought material to compare the results. The test was performed under a corrosive atmosphere with a solution of water with 3.5 % in weight of salt (NaCl). The total duration of the test was 635 hours, divided in five stages of 12, 24, 48, 226, and 325 hours to analyze the samples between each stage. The samples were analyzed quantitatively measuring weight loss and surface topography, and qualitatively by macroscopic inspection with digital photography, and microscopic inspection with optical and scanning electron microscopy. The results show a higher corrosion rate for the additively manufactured samples compared to the control samples. An evident increase in the size of pits initially present on the samples was observed and quantified on the additively manufactured. Although the additively manufactured samples were more aggressively attacked by corrosion, they still presented a shiny surface finish at the end of the test, reinforcing the idea of the formation of a passive oxide layer and suggesting that the corrosion was focalized in the surface defects by pitting and crevice corrosion mechanisms.
Structural Analysis and Finite Element Modeling of Aluminum Honeycomb Sandwich Structures
The objective of this research is to determine how the sandwich's physical characteristics have an impact on the mechanical properties, determine under what conditions the specimens will be lighter and mechanically stronger, and determine if the use of an aluminum honeycomb sandwich as a construction material is feasible. The research has aimed at the use of aluminum sandwiches as light and strong material. The study of the structural layers' damage resistance and tolerance demonstrated that the top and bottom layers play a crucial role. The thesis presents three test results from aluminum honeycomb sandwich compression horizontal, compressive vertical, and bending tests. Also, each group was displayed mechanically and simulated in Abaqus. The study determines the mechanical properties such as maximum elastic stress-strain, ultimate stress-strain, fracture point, density, poison ration, young modulus, and maximum deflection was determined. The energy absorbed by the FEA, such modulus of elasticity, resilience, and toughness, the crack propagation, the test's view shows aluminum honeycomb behaved like a brittle material with both compression test. And the maximum deflection, crack propagation, shear forces, bending moment, and images illustrated that the layers play a crucial role in the 3-point bend test.
Modeling and Analysis of Prototype Shelter Structure on Abaqus
Due to the constraint of high costs and limitations of load conditions, experimental testing is not appropriate for the static study of shelter structures. Comparatively, an effective computational modeling and numerical solution demonstrates significant advantages for understanding the response of steel shelter structures. This study gives an insight into the structural integrity of the prototype shelter structure which is examined using computer simulation of the shelter structure on Abaqus/CAE 2019. The results of the computer modelling demonstrate the response of shelter structure under ten different loading conditions as per ISO 1496:2013 (E). The loading conditions are applied to various components of the shelter structure and corresponding deflection are observed.
Design Method for Cold-Formed Steel Shear Wall Sheathed with Polymer Composite Panel
In order to predict the strength of shear wall with cold-formed steel framing members, analytical models were reviewed. Multiple analytical models were studied, as well as twenty-one connection tests were performed. The connection tests consist of 50-ksi cold-formed steel framing track, different fastening configurations, and different sheathing thicknesses (1/8" and 1/2"). No.12 screw resulted in the highest peak load of all fastening configurations, while the rivet connection had the lowest peak load. In addition, failure modes were observed after conducting the connection tests including shear in fastening, screw pullout, and bearing in the sheathing. However, only the rivet and No.10 screw fastening configurations were used in the prediction analysis of the shear wall by the elastic model. Six shear wall tests were conducted on both panels (1/2"and 1/8" thickness). After doing the comparison between the experimental and the elastic model, the percentage difference for the 1/8" and the 1/2" polymer composite panels (3''along the edge and 6''along the chord stud), was very small. It was 6.2% for the 1/8" and 2.96% for the 1/2" panels. This means the analytical model can predict the shear wall peak load. However, the percentage difference was slightly higher being 7.4% for the 1/2" polymer composite panels with 6" along the perimeter with the 12" at the chord stud. After comparing the experimental values to the predicted value of shear walls, it was concluded that this model is the most appropriate analytical method for predicting the shear wall capacity framed with cold-formed steel sheathed with polymer composite panels. Many of these configurations were used in a prototype shelter that was constructed and built at the structural testing laboratory at the University of North Texas.
Structural, Thermal, and Corrosion Properties of a Cold-Formed Steel Rigid Wall Relocatable Shelter
A prototype rigid wall relocatable shelter was designed and constructed using cold-formed steel (CFS) construction techniques including shear walls with corrugated sheathings. The design of the shelter was to be mechanically sound with adequate thermal performance and resistance to corrosion. Modeling of structural shear walls was performed using ABAQUS and verified with experimental results. At the project's conclusion, a completed full-scale prototype shelter was constructed.
Construction Management Methods and Techniques in Army Tactical Shelter
This thesis presents a research effort aimed at developing using construction methods and techniques in army tactical shelter. The beginning step focuses on developing and identifying different activities and work breakdown structure applicable in shelter prototype. The next step focuses on identifying resource allocation. This include allocate resources based on the delivered project as per alternative one and for the second alternative as optimization, resource allocation modified and tried to level and minimize resource peak. In addition, the cost calculated for the whole project as well as for each WBS and activities which consider as alternative one and in the second alternative, cost mitigation applied according to available resources and adjusting predecessors and successors of each activity. In conclusion, two alternatives compared, available outcome presents, and future work suggested for the project team to continue this effort.
Fabrication and Testing of Biomimetic Microstructures for Walkway Tribometers
The main objective of this work is to give contribution in both additive manufacturing (AM) and tribometry derived from the application and study of materials available with the use of biomimetic designs. Additional contributions are determining what effects treatments for flooring surfaces may have on the dynamic coefficient of friction and the effects of these products on common surfaces. The validity of the proposed methodology for a proof of concept was demonstrated by comparing measured dynamic coefficient of friction for designs using standardized equipment and comparing these values to plantar skin tested using an accepted and standardized testing method that has been extensively researched and validated. Initial biomimetic designs and characteristics unique to each design were researched and compared. Eleven designs were selected to be fabricated, tested, and compared to select the most desirable applications for further investigation. Research into potential treatments commercially available for use was done to determine the efficacy of these products. Prototype sensor designs were selected and fabricated using direct light processing (DLP) technology. Examination of the measured values was done through an analysis of the variances in the response variable and comparisons using Fisher and Tukey pairwise comparison method. Future work recommendations are provided for further development and improvement of the topics presented in this thesis.
Design Method of Cold-Formed Steel Framed Shear Wall Sheathed by Structural Concrete Panel
The objective of this research is developing a new method of design for cold-formed steel framed shear wall sheathed by ¾" thick USG structural panel concrete subfloor using a predictive analytical model and comparing the results obtained from the model with those achieved from real testing to verify the analytical model and predicted lateral load-carrying capacity resulted from that. Moreover, investigating the impact of various screw spacings on shear wall design parameter such as ultimate strength, yield strength, elastic stiffness, ductility ratio and amount of energy dissipation is another purpose of this research.
Microfluidic-Based Fabrication of Photonic Microlasers for Biomedical Applications
Optical microlasers have been used in different engineering fields and for sensing various applications. They have been used in biomedical fields in applications such as for detecting protein biomarkers for cancer and for measuring biomechanical properties. The goal of this work is to propose a microfluidic-based fabrication method for fabricating optical polymer based microlasers, which has advantages, over current methods, such us the fabrication time, the contained cost, and the reproducibility of the microlaser's size. The microfluidic setup consisted of microfluidic pumps and a flow focusing droplet generator chip made of polydimethylsiloxane (PDMS). Parameters such as the flow rate (Q) and the pressure (P) of both continuous and dispersed phases are taken into account for determining the microlaser's size and a MATLAB imaging tool is used to reduce the microlaser's diameter estimation. In addition, two applications are discussed: i) electric field measurements via resonator doped with Di-Anepps-4 voltage sensitive dye, and ii) strain measurements in a 3D printed bone-like structure to mimic biomedical implantable sensors.
Cold-Formed Steel Member Connections Using BAC Screw Fasteners
In this project, the main research objective is intend to seek criteria for evaluating the capacity of BAC screw fasteners with mixed configuration of waterproof seal washer, sealer tape and different pre-drill holes to determine shear and tension strength values for the screws used in cold-formed steel connections. The thesis presents the design methods and test program conducted to investigate the behavior and strength of the screw connections in shear and tension test. Test results were compared with AISI design provisions to determine if new design equations will be developed for those screws used in BAC cooling tower applications. LRFD resistance factors and ASD safety factors were investigated to the proposed design equations.
Topology and Lattice-Based Structural Design Optimization for Additively Manufactured Medical Implants
Topology-based optimization techniques and lattice structures are powerful ways to accomplish lightweight components with enhanced mechanical performance. Recent developments in additive manufacturing (AM) have led the way to extraordinary opportunities in realizing complex designs that are derived from topology and lattice-based structural optimization. The main aim of this work is to give a contribution, in the integration between structural optimization techniques and AM, by proposing a setup of a proper methodology for rapid development of optimized medical implants addressing oseeointegration and minimization of stress shielding related problems. The validity of the proposed methodology for a proof of concept was demonstrated in two real-world case studies: a tibia intramedullary implant and a shoulder hemi prosthetics for two bone cancer patients. The optimization was achieved using topology optimization and replacement of solid volumes by lattice structures. Samples of three lattice unit cell configurations were designed, fabricated, mechanically tested, and compared to select the most proper configuration for the shoulder hemi prosthesis. Weight reductions of 30% and 15% were achieved from the optimization of the initial design of the tibia intramedullary implant and the shoulder hemiprosthesis respectively compared to initial designs. Prototypes were fabricated using selective laser melting (SLM) and direct light processing (DLP) technologies. Validation analysis was performed using finite element analysis and compressive mechanical testing. Future work recommendations are provided for further development and improvement of the work presented in this thesis.
Hydrophobicity of Magnetite Coating on Low Carbon Steel
Superhydrophobic coatings (SHC) with excellent self-cleaning and corrosion resistance property is developed on magnetite coated AISI SAE 1020 steel by using a simple immersion method. Roughness measurement, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), contact angle measurement (CAM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS), and qualitative characterization of self-cleaning behavior, antifouling property and durability of the coatings are assessed. A water contact angle as high as 152o on the coated surface with excellent self-cleaning and resistivity to corrosion and good longevity in atmospheric air is obtained. Self-cleaning test results prove that these surfaces can find applications in large scale production of engineering materials. Potentiodynamic polarization tests and EIS tests confirm that the superhydrophobic low carbon steel surfaces have better resistance to corrosion compared to bare steel and magnetite coated steel in 3.5% NaCl solution. But the longevity of the coated steel surfaces in 3.5% salt solution is limited, which is revealed by the immersion durability test. However, hydrophobic coatings (HC) have better stability in normal tap water, and it can stay unharmed up to 15 days. Finally, hydrophobic coatings on low carbon steel surface retains hydrophobic in open atmosphere for more than two months. Results of this investigation show surface roughness is a critical factor in manufacturing hydrophobic steel surfaces. Higher contact angles are obtained for rougher and more uniform surfaces. A linear mathematical relationship (y =6x+104; R2 = 0.93) is obtained between contact angle (y) and surface roughness (x).
The Design and Development of Lightweight Composite Wall, Roof, and Floor Panels for Rigid Wall Shelter
This thesis presents a research effort aimed at developing a stronger, lighter, and more economic shelter using rigid wall panels. Reported herein is insulation research, wall and roof panel design and testing, floor section modeling and strength calculations, and cost and weight calculations. Beginning stages focus on developing solid wall and roof panels using cold-formed steel corrugated sheathing and members, as well as polyurethane spray foam for insulation. This research includes calculating uniform load density, to determine the overall strength of the panel. The next stage focuses on the flexural strength of the wall and roof panels, as well as finalizing the floor design for the shelter. This includes determining maximum flexural strength required to meet the standards set by the project goal. Direct strength method determined the correct thickness of members to use based on the dimension selected for the design. All Phases incorporated different connection methods, with varied stud spacing, to determine the safest design for the new shelters. Previous research has shown that cold-formed steel corrugated sheathing performs better than thicker flat sheathing of various construction materials, with screw and spot weld connections. Full scale shear wall tests on this type of shear wall system have been conducted, and it was found that the corrugated sheathing had rigid board behavior before it failed in shear buckling in sheathing and sometimes simultaneously in screw connection failures. Another aspect of the research is on the insulation of the wall panels. Research was conducted on many different insulation options for the mobile facilities. Specifically, insulation made of lightweight material, is non-combustible, added rigidity to the structure, and has high thermal properties. Closed cell polyurethane spray foam was selected for full-scale testing in this research. Closed cell polyurethane adds extra rigidity, is lighter than common honeycomb insulation, and has a higher …
Shear and Bending Strength of Cold-Formed Steel Solid Wall Panels Using Corrugated Steel Sheets for Mobile Shelters
The objective of this thesis is to determine if the single sided resistance spot weld (RSW) can be used as a feasible connection method for cold formed steel (CFS) shear walls subject to lateral force of either seismic or wind loads on mobile shelters. The research consisted of three phases which include: a design as a 3D BIM model, connection tests of the resistance spot weld, and full-scale testing of the designed solid wall panels. The shear wall testing was conducted on specimens with both resistance spot weld and self-drilling screws and the results from tests gave a direct comparison of these connections when the solid wall panel was subjected to in-plane shear forces. The full-scale tests also included 4-point bending tests which was designed to investigate the wall panel's resistance to the lateral loads applied perpendicularly to the surface. The research discovered that the singled sided resistance spot weld achieved similar performance as the self-drilling screws in the applications of CFS wall panels for mobile shelters. The proposed single sided resistance spot weld has advantages of low cost, no added weight, fast fabrication, and it is a feasible connection method for CFS wall panels.
Shear and Compression Strength of Cold-formed Steel Clip Angles Subjected to Different Screw Patterns
This thesis presents experiments and numerical analysis of the cold-formed steel clip angle in three different limit states which are shear, compression, and combination of the screw connection. A previous cold-formed steel clip angle test program (which is Phase 1) developed design methods for clip angle. Therefore, the object of this thesis is to further investigate the behavior and design methods of loading-bearing cold-formed steel clip angles under different screw pattern. For each limit state, a test program was conducted to investigate the behavior, strength, and deflection of the clip angle. The test result were compared with previous CFS clip angle design method. Amending existing CFS clip angle method were developed by each of the four limit states studied in this project.
Two-Phase Spray Cooling with HFC-134a and HFO-1234yf for Thermal Management of Automotive Power Electronics using Practical Enhanced Surfaces
The objective of this research was to investigate the performance of two-phase spray cooling with HFC-134a and HFO-1234yf refrigerants using practical enhanced heat transfer surfaces. Results of the study were expected to provide a quantitative spray cooling performance comparison with working fluids representing the current and next-generation mobile air conditioning refrigerants, and demonstrate the feasibility of this approach as an alternative active cooling technology for the thermal management of high heat flux power electronics (i.e., IGBTs) in electric-drive vehicles. Potential benefits of two-phase spray cooling include achieving more efficient and reliable operation, as well as compact and lightweight system design that would lead to cost reduction. The experimental work involved testing of four different enhanced boiling surfaces in comparison to a plain reference surface, using a commercial pressure-atomizing spray nozzle at a range of liquid flow rates for each refrigerant to determine the spray cooling performance with respect to heat transfer coefficient (HTC) and critical heat flux (CHF). The heater surfaces were prepared using dual-stage electroplating, brush coating, sanding, and particle blasting, all featuring "practical" room temperature processes that do not require specialized equipment. Based on the obtained results, HFC-134a provided a better heat transfer performance through higher HTC and CHF values compared to HFO-1234yf at all tested surfaces and flow rates. While majority of the tested surfaces provided comparable HTC and modestly higher CHF values compared to the reference surface, one of the enhanced surfaces offered significant heat transfer enhancement.
Seismic Performance Evaluation of Novel Cold-Formed Steel Framed Shear Walls Sheathed with Corrugated Steel Sheets
This thesis presents experiments and numerical analysis of a novel cold-formed steel framed shear wall sheathed with corrugated steel sheets. The objective of this newly designed shear wall is to meet the growing demand of mid-rise buildings and the combustibility requirement in the International Building Code. The strength of the novel shear wall is higher than currently code certified shear wall in AISI S400-15 so that it could be more favorable for mid-rise building in areas that are prone to earthquakes and hurricanes. Full-scale monotonic and cyclic tests were conducted on bearing walls and shear walls under combined lateral and gravity loads. Though the gravity loads had negative effects on the strength and stiffness of the shear wall due to the buckling of the chord framing members, it still shows promise to be used in mid-rise buildings. The objective of numerical analysis is to quantify the seismic performance factors of the newly design shear wall lateral-force resisting system by using the recommended methodology in FEMA P695. Two groups of building archetypes, story varied from two to five, were simulated in OpenSees program. Nonlinear static and dynamic analysis were performed in both horizontal directions of each building archetype. Finally, the results of the performance evaluation verified the seismic performance factors(R=Cd=6.5 and Ω =3.0) were appropriate for the novel shear wall system.
Investigation of Immersion Cooled ARM-Based Computer Clusters for Low-Cost, High-Performance Computing
This study aimed to investigate performance of ARM-based computer clusters using two-phase immersion cooling approach, and demonstrate its potential benefits over the air-based natural and forced convection approaches. ARM-based clusters were created using Raspberry Pi model 2 and 3, a commodity-level, single-board computer. Immersion cooling mode utilized two types of dielectric liquids, HFE-7000 and HFE-7100. Experiments involved running benchmarking tests Sysbench high performance linpack (HPL), and the combination of both in order to quantify the key parameters of device junction temperature, frequency, execution time, computing performance, and energy consumption. Results indicated that the device core temperature has direct effects on the computing performance and energy consumption. In the reference, natural convection cooling mode, as the temperature raised, the cluster started to decease its operating frequency to save the internal cores from damage. This resulted in decline of computing performance and increase of execution time, further leading to increase of energy consumption. In more extreme cases, performance of the cluster dropped by 4X, while the energy consumption increased by 220%. This study therefore demonstrated that two-phase immersion cooling method with its near-isothermal, high heat transfer capability would enable fast, energy efficient, and reliable operation, particularly benefiting high performance computing applications where conventional air-based cooling methods would fail.
Investigation of Spray Cooling Schemes for Dynamic Thermal Management
This study aims to investigate variable flow and intermittent flow spray cooling characteristics for efficiency improvement in active two-phase thermal management systems. Variable flow spray cooling scheme requires control of pump input voltage (or speed), while intermittent flow spray cooling scheme requires control of solenoid valve duty cycle and frequency. Several testing scenarios representing dynamic heat load conditions are implemented to characterize the overall performance of variable flow and intermittent flow spray cooling cases in comparison with the reference, steady flow spray cooling case with constant flowrate, continuous spray cooling. Tests are conducted on a small-scale, closed loop spray cooling system featuring a pressure atomized spray nozzle. HFE-7100 dielectric liquid is selected as the working fluid. Two types of test samples are prepared on 10 mm x 10 mm x 2 mm copper substrates with matching size thick film resistors attached onto the opposite side, to generate heat and simulate high heat flux electronic devices. The test samples include: (i) plain, smooth surface, and (ii) microporous surface featuring 100 μm thick copper-based coating prepared by dual stage electroplating technique. Experimental conditions involve HFE-7100 at atmospheric pressure and 30°C and ~10°C subcooling. Steady flow spray cooling tests are conducted at flow rates of 2 - 5 ml/cm².s, by controlling the heat flux in increasing steps, and recording the corresponding steady-state temperatures to obtain cooling curves in the form of surface superheat vs. heat flux. Variable flow and intermittent flow spray cooling tests are done at selected flowrate and subcooling conditions to investigate the effects of dynamic flow conditions on maintaining the target surface temperatures defined based on reference steady flow spray cooling performance.
Design, Modeling, and Experiment of a Piezoelectric Pressure Sensor based on a Thickness-Shear Mode Crystal Resonator
This thesis presents the design, modeling, and experiment of a novel pressure sensor using a dual-mode AT-cut quartz crystal resonator with beat frequency analysis based temperature compensation technique. The proposed sensor can measure pressure and temperature simultaneously by a single AT-cut quartz resonator. Apart from AT-cut quartz crystal, a newly developed Langasite (LGS) crystal resonator is also considered in the proposed pressure sensor design, since LGS can operate in a higher temperature environment than AT-cut quartz crystal. The pressure sensor is designed using CAD (computer aided design) software and CAE software - COMSOL Multiphysics. Finite element analysis (FEA) of the pressure sensor is performed to analyze the stress- strain of the sensor's mechanical structure. A 3D printing prototype of the sensor is fabricated and the proposed sensing principle is verified using a force-frequency analysis apparatus. Next to the 3D printing model verification, the pressure sensor with stainless steel housing has been fabricated with inbuilt crystal oscillator circuit. The oscillator circuit is used to excite the piezo crystal resonator at its fundamental vibrational mode and give the frequency as an output signal. Based on the FEA and experimental results, it has been concluded that the maximum pressure that the sensor can measure is 45 (psi). The pressure test results performed on the stainless steel product shows a highly linear relationship between the input (pressure) and the output (frequency).
A Study on the System Reliability of Cold-Formed Steel Roof Trusses
This thesis presents a research project aimed at advancing the treatment of cold-formed steel (CFS) structural reliability in roof trusses. Structural design today relies almost exclusively on component-level design, so structural safety is assured by limiting the probability of failure of individual components. Reliability of the entire system is typically not assessed, so in a worst-case scenario the system reliability may be less than the component reliability, or in a best-case scenario the system reliability may be much greater than the component reliability. A roof truss itself, is a subsystem with several possible failure modes that are being studied in this test program. These trusses are constructed of CFS members that nest with one another at the truss nodes and are connected by drilling fasteners through the mated surfaces, as well as having steel sheathing fastened to the top chords for lateral bracing. Presented in this paper is a series of full-scale static tests on single cold-formed steel roof trusses with a unique experimental setup. The test specimens were carefully monitored to address multiple failure modes: buckling of the top chord, buckling of the truss webs, and any connection failures. This research includes the experimental results, the computed system reliability of the trusses as well as their relationship between the components reliability.
Design of a Monitoring System for a Plasma Cleaning Machine
Plasma cleaning is the most effective dry process to remove surface contaminates from a SAW (Surface Acoustical Wave) device. Consistent gas pressures, flows, and good electrical connections between the chamber shelves are necessary for the process to function predictably. In addition, operation of the monitoring system must be transparent to the plasma cleaning unit. This thesis describes a simple solution to the complex problem of monitoring a plasma cleaning system. The monitoring system uses the LabVIEW® G programming language and hardware, both products of National Instruments, Inc.®, to monitor critical parameters necessary to achieve a consistent process when cleaning these devices.
A Data Acquisition System Experiment for Gas Temperature and Pressure Measurements on a Liquid-Nitrogen-Powered Vehicle
A data acquisition system was set up to measure gas temperatures and pressures at various points on a liquid-nitrogen-powered vehicle. The experiment was attempted to develop a data acquisition method for applications on engines that use liquid air as the fuel. Two thermocouples and a pressure transducer were connected using data acquisition instruments interfaced to a laptop computer to acquire data.
A Computer-Based Process Control System for a Target Station in a LINAC Facility
An event-driven, sequential, process control system was designed for International Isotopes, Inc., to automate and remotely control a target station at the company's linear accelerator facility. The designed system consisted of two major sections: a software program (virtual instrument), which was developed by LabVIEW, and a hardware interface (FieldPoint Modular Distributed I/O System by National Instrument), which had to be a pre-developed system that did not require customization. The designed virtual instrument was tested on a simulation model that mimed the target station. The result was a valid design.
Development of a Simplified Fracture Toughness Tool for Polymers
This thesis presents research toward the development of a simple inexpensive fracture toughness tool for polymeric materials. Experiments were conducted to test the specimen configuration and the fracture toughness tool against an established ASTM standard for polymer fracture toughness, D5045, and a commonly used four-point bend method. The materials used in this study were polycarbonate and high density polyethylene. Reductions in both the production time and the variability resulting from the preparation of the specimens were addressed through the use of specially designed fixtures. The effects from the razor cut depths used in the chevron notch were compared to the fracture toughness values obtained in order to determine the effect upon the validity of the fracture toughness.
Fracture Toughness Testing of Plastics under Various Environmental Conditions
The primary objective of this study is to test the applicability to plastics of a fracture toughness testing tool developed for metals. The intent is to study pre-test conditioning of several plastic materials and the effect of the depth of the razor notch cut in the chevron notched fracture toughness test specimens. The study includes the careful preparation of samples followed by conditioning in various environments. Samples were subjected to laboratory air for a specific duration or to a controlled temperature-humidity condition as per the ASTM D1870. Some of the samples were subjected to vacuum conditioning under standard test specifications. Testing was conducted using the conventional three-point bend test as per ASTM D5045-95. ASTM E1304, which sets a standard for short rod and bar testing of metals and ceramics provides some basis for conducting chevron notched four-point bend tests to duplicate the toughness tool. Correlation of these results with the ASTM test samples is determined. The four-point bend test involves less specimen machining as well as time to perform the fracture toughness tests. This study of fracture toughness testing has potential for quality control as well as the fracture property determination.
A Study of the Synthesis and Surface Modification of UV Emitting Zinc Oxide for Bio-Medical Applications
This thesis presents a novel ZnO-hydrogel based fluorescent colloidal semiconductor nanomaterial system for potential bio-medical applications such as bio-imaging, cancer detection and therapy. The preparation of ZnO nanoparticles and their surface modification to make a biocompatible material with enhanced optical properties is discussed. High quality ZnO nanoparticles with UV band edge emission are prepared using gas evaporation method. Semiconductor materials including ZnO are insoluble in water. Since biological applications require water soluble nanomaterials, ZnO nanoparticles are first dispersed in water by ball milling method, and their aqueous stability and fluorescence properties are enhanced by incorporating them in bio-compatible poly N-isopropylacrylamide (PNIPAM) based hydrogel polymer matrix. The optical properties of ZnO-hydrogel colloidal dispersion versus ZnO-Water dispersion were analyzed. The optical characterization using photoluminescence spectroscopy indicates approximately 10 times enhancement of fluorescence in ZnO-hydrogel colloidal system compared to ZnO-water system. Ultrafast time resolved measurement demonstrates dominant exciton recombination process in ZnO-hydrogel system compared to ZnO-water system, confirming the surface modification of ZnO nanoparticles by hydrogel polymer matrix. The surface modification of ZnO nanoparticles by hydrogel induce more scattering centers per unit area of cross-section, and hence increase the luminescence from the ZnO-gel samples due to multiple path excitations. Furthermore, surface modification of ZnO by hydrogel increases the radiative efficiency of this hybrid colloidal material system thereby contributing to enhanced emission.
A Study of Laser Direct Writing for All Polymer Single Mode Passive Optical Channel Waveguide Devices
The objective of this research is to investigate the use of laser direct writing to micro-pattern low loss passive optical channel waveguide devices using a new hybrid organic/inorganic polymer. Review of literature shows previous methods of optical waveguide device patterning as well as application of other non-polymer materials. System setup and design of the waveguide components are discussed. Results show that laser direct writing of the hybrid polymer produce single mode interconnects with a loss of less 1dB/cm.
Investigation of the feasibility of non-invasive carbon dioxide detection using spectroscopy in the visible spectrum.
Pulse oximeters are used in operating rooms and recovery rooms as a monitoring device for oxygen in the respiratory system of the patient. The advantage of pulse oximeters over other methods of oxygen monitoring is that they are easy to use and they are non-invasive, which means it is not necessary break the skin to extract blood for information to be obtained. The standard for the measurement of partial pressure of CO2 and O2 is an arterial blood gas analysis (ABG). However routine monitoring using this method on a continuous basis is impractical since it is slow, painful and invasive. Measuring carbon dioxide is critical to preventing ailments such as carbon dioxide poisoning or hypoxia. The problem is, currently there is no known effective non-invasive method for accurately measuring carbon dioxide in the body to properly assess the adequacy of ventilation. The objective of this study was to experimentally use spectroscopy in the visible spectrum and the principles of operation of a pulse oximeter to incorporate a method of non-invasive real-time carbon dioxide monitoring that is as quick and easy to use.
Flow Accelerated Corrosion Experience at Comanche Peak Steam Electric Station
Flow accelerated corrosion (FAC) is a major concern in the power industry as it causes thinning of the pipes by the dissolution of the passive oxide layer formed on the pipe surface. Present research deals with comparing the protection offered by the magnetite (Fe3O4) versus maghemite (γ-Fe2O3) phases thickness loss measurements. Fourier transform infrared spectroscopy (FTIR) is used in distinguishing these two elusive phases of iron oxides. Representative pipes are collected from high pressure steam extraction line of the secondary cycle of unit 2 of Comanche Peak Steam Electric Station (CPSES). Environmental scanning electron microscopy (ESEM) is used for morphological analysis. FTIR and X-ray diffraction (XRD) are used for phase analysis. Morphological analysis showed the presence of porous oxide surfaces with octahedral crystals, scallops and "chimney" like vents. FTIR revealed the predominance of maghemite at the most of the pipe sections. Results of thickness measurements indicate severe thickness loss at the bend areas (extrados) of the pipes.
Liquid Nitrogen Propulsion Systems for Automotive Applications: Calculation of Mechanical Efficiency of a Dual, Double-acting Piston Propulsion System
A dual, double-acting propulsion system is analyzed to determine how efficiently it can convert the potential energy available from liquid nitrogen into useful work. The two double-acting pistons (high- and low-pressure) were analyzed by using a Matlab-Simulink computer simulation to determine their respective mechanical efficiencies. The flow circuit for the entire system was analyzed by using flow circuit analysis software to determine pressure losses throughout the system at the required mass flow rates. The results of the piston simulation indicate that the two pistons analyzed are very efficient at transferring energy into useful work. The flow circuit analysis shows that the system can adequately maintain the mass flow rate requirements of the pistons but also identifies components that have a significant impact on the performance of the system. The results of the analysis indicate that the nitrogen propulsion system meets the intended goals of its designers.
Radio frequency propagation differences through various transmissive materials.
The purpose of this research was to determine which of the commonly used wireless telecommunication site concealment materials has the least effect on signal potency. The tested materials were Tuff Span® fiberglass panels manufactured by Enduro Composite Systems, Lexan® XL-1 polycarbonate plastic manufactured by GE Corporation and Styrofoam™ polystyrene board manufactured by The Dow Chemical Company. Testing was conducted in a double electrically isolated copper mesh screen room at the University of North Texas Engineering Technology Building in Denton, Texas. Analysis of the data found no differences exist between the radio frequency transmissiveness of these products at broadband personal communication service frequencies. However, differences in the signal do exist with regards to the angle of incidence between the material and the transmitting antenna.
Evaluation of dynamic and static electrical characteristics for the DY8 and YI8 process gallium diodes in comparison to the DI8 process boron diodes.
A rectifier is an electrical device, comprising one or more semiconductor devices arranged for converting alternating current to direct current by blocking the negative or positive portion of the waveform. The purpose of this study would be to evaluate dynamic and static electrical characteristics of rectifier chips fabricated with (a) DY8 process and (b) YI8 process and compare them with the existing DI8 process rectifiers. These new rectifiers were tested to compare their performance to meet or exceed requirements of lower forward voltages, leakage currents, reverse recovery time, and greater sustainability at higher temperatures compared to diodes manufactured using boron as base (DI8 process diodes) for similar input variables.
Surface Plasmon Based Nanophotonic Optical Emitters
Group- III nitride based semiconductors have emerged as the leading material for short wavelength optoelectronic devices. The InGaN alloy system forms a continuous and direct bandgap semiconductor spanning ultraviolet (UV) to blue/green wavelengths. An ideal and highly efficient light-emitting device can be designed by enhancing the spontaneous emission rate. This thesis deals with the design and fabrication of a visible light-emitting device using GaN/InGaN single quantum well (SQW) system with enhanced spontaneous emission. To increase the emission efficiency, layers of different metals, usually noble metals like silver, gold and aluminum are deposited on GaN/InGaN SQWs using metal evaporator. Surface characterization of metal-coated GaN/InGaN SQW samples was carried out using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Photoluminescence is used as a tool for optical characterization to study the enhancement in the light emitting structures. This thesis also compares characteristics of different metals on GaN/InGaN SQW system thus allowing selection of the most appropriate material for a particular application. It was found out that photons from the light emitter couple more to the surface plasmons if the bandgap of former is close to the surface plasmon resonant energy of particular metal. Absorption of light due to gold reduces the effective mean path of light emitted from the light emitter and hence quenches the quantum well emission peak compared to the uncoated sample.
Development of a Hybrid Molecular Ultraviolet Photodetector based on Guanosine Derivatives
Modern studies on charge transfer reaction and conductivity measurements of DNA have shown that the electrical behavior of DNA ranges from that of an insulator to that of a wide bandgap semiconductor. Based on this property of DNA, a metal-semiconductor-metal photodetector is fabricated using a self-assembled layer of deoxyguanosine derivative (DNA base) deposited between gold electrodes. The electrodes are lithographically designed on a GaN substrate separated by a distance L (50nm < L < 100nm). This work examines the electrical and optical properties of such wide-bandgap semiconductor based biomaterial systems for their potential application as photodetectors in the UV region wherein most of the biological agents emit. The objective of this study was to develop a biomolecular electronic device and design an experimental setup for electrical and optical characterization of a novel hybrid molecular optoelectronic material system. AFM results proved the usage of Ga-Polar substrate in conjugation with DG molecules to be used as a potential electronic based sensor. A two-terminal nanoscale biomolectronic diode has been fabricated showing efficient rectification ratio. A nanoscale integrated ultraviolet photodetector (of dimensions less than 100 nm) has been fabricated with a cut-off wavelength at ~ 320 nm.
Nodal Resistance Measurement System
The latest development in the measurement techniques has resulted in fast improvements in the instruments used for measurement of various electrical quantities. A common problem in such instruments is the automation of acquiring, retrieving and controlling the measurements by a computer or a laptop. In this study, nodal resistance measurement (NRM) system is developed to solve the above problem. The purpose of this study is to design and develop a compact electronic board, which measures electrical resistance, and a computer or a laptop controls the board. For the above purpose, surface nodal points are created on the surface of the sample electrically conductive material. The nodal points are connected to the compact electronic board and this board is connected to the computer. The user selects the nodal points, from the computer, between which the NRM system measures the electrical resistance and displays the measured quantity on the computer.
Synthesis of cubic boron nitride thin films on silicon substrate using electron beam evaporation.
Cubic boron nitride (cBN) synthesis has gained lot of interest during the past decade as it offers outstanding physical and chemical properties like high hardness, high wear resistance, and chemical inertness. Despite of their excellent properties, every application of cBN is hindered by high compressive stresses and poor adhesion. The cost of equipment is also high in almost all the techniques used so far. This thesis deals with the synthesis of cubic phase of boron nitride on Si (100) wafers using electron beam evaporator, a low cost equipment that is capable of depositing films with reduced stresses. Using this process, need of ion beam employed in ion beam assisted processes can be eliminated thus reducing the surface damage and enhancing the film adhesion. Four sets of samples have been deposited by varying substrate temperature and the deposition time. scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) techniques have been used to determine the structure and composition of the films deposited. X-ray diffraction (XRD) was performed on one of the samples to determine the thickness of the film deposited for the given deposition rate. Several samples showed dendrites being formed as a stage of film formation. It was found that deposition at substrate temperature of 400oC and for a period of one hour yielded high quality cubic boron nitride films.
Characterization of Iron Oxide Deposits Formed at Comanche Peak Steam Electric Station
The presence of deposits leading to corrosion of the steam generator (SG) systems is a major contributor to operation and maintenance cost of pressurized water reactor (PWR) plants. Formation and transport of corrosion products formed due to the presence of impurities, metallic oxides and cations in the secondary side of the SG units result in formation of deposits. This research deals with the characterization of deposit samples collected from the two SG units (unit 1 and unit 2) at Comanche Peak Steam Electric Station (CPSES). X-ray diffraction (XRD), Fourier transform infrared spectrophotometry (FTIR), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) techniques have been used for studying the compositional and structural properties of iron oxides formed in the secondary side of unit 1 and unit 2. Magnetite (Fe3O4) was found to be predominant in samples from unit 1 and maghemite (g-Fe2O3) was found to be the dominant phase in case of unit 2. An attempt has been made to customize FTIR technique for analyzing different iron oxide phases present in the deposits of PWR-SG systems.
Propagation analysis of a 900 MHz spread spectrum centralized traffic signal control system.
The objective of this research is to investigate different propagation models to determine if specified models accurately predict received signal levels for short path 900 MHz spread spectrum radio systems. The City of Denton, Texas provided data and physical facilities used in the course of this study. The literature review indicates that propagation models have not been studied specifically for short path spread spectrum radio systems. This work should provide guidelines and be a useful example for planning and implementing such radio systems. The propagation model involves the following considerations: analysis of intervening terrain, path length, and fixed system gains and losses.
MBE Growth and Instrumentation
This thesis mainly aims at application of principles of engineering technology in the field of molecular beam epitaxy (MBE). MBE is a versatile technique for growing epitaxial thin films of semiconductors and metals by impinging molecular beams of atoms onto a heated substrate under ultra-high vacuum (UHV) conditions. Here, a LabVIEW® (laboratory virtual instrument engineering workbench) software (National Instruments Corp., http://www.ni.com/legal/termsofuse/unitedstates/usH) program is developed that would form the basis of a real-time control system that would transform MBE into a true-production technology. Growth conditions can be monitored in real-time with the help of reflection high energy electron diffraction (RHEED) technique. The period of one RHEED oscillation corresponds exactly to the growth of one monolayer of atoms of the semiconductor material. The PCI-1409 frame grabber card supplied by National Instruments is used in conjunction with the LabVIEW software to capture the RHEED images and capture the intensity of RHEED oscillations. The intensity values are written to a text file and plotted in the form of a graph. A fast Fourier transform of these oscillations gives the growth rate of the epi-wafer being grown. All the data being captured by the LabVIEW program can be saved to file forming a growth pedigree for future use. Unattended automation can be achieved by designing a control system that monitors the growth in real-time and compares it with the data recorded from the LabVIEW program from the previous growth and adjusts the growth parameters automatically thereby growing accurate device structures.
Indoor Propagation Modeling at 2.4 GHz for IEEE 802.11 Networks
Indoor use of wireless systems poses one of the biggest design challenges. It is difficult to predict the propagation of a radio frequency wave in an indoor environment. To assist in deploying the above systems, characterization of the indoor radio propagation channel is essential. The contributions of this work are two-folds. First, in order to build a model, extensive field strength measurements are carried out inside two different buildings. Then, path loss exponents from log-distance path loss model and standard deviations from log-normal shadowing, which statistically describe the path loss models for a different transmitter receiver separations and scenarios, are determined. The purpose of this study is to characterize the indoor channel for 802.11 wireless local area networks at 2.4 GHz frequency. This thesis presents a channel model based on measurements conducted in commonly found scenarios in buildings. These scenarios include closed corridor, open corridor, classroom, and computer lab. Path loss equations are determined using log-distance path loss model and log-normal shadowing. The chi-square test statistic values for each access point are calculated to prove that the observed fading is a normal distribution at 5% significance level. Finally, the propagation models from the two buildings are compared to validate the generated equations.
FEM of nanoindentation on micro- and nanocrystalline Ni: Analysis of factors affecting hardness and modulus values.
Nanoindentation is a widely used technique to measure the mechanical properties of films with thickness ranging from nanometers to micrometers. A much better understanding of the contact mechanics is obtained mostly through finite element modeling. The experiments were modeled using the software package Nano SP1 that is based on COSMOSM™ (Structural Research & Analysis Corp, www.cosmosm.com), a finite element code. The fundamental material properties affecting pile-up are the ratio of the effective modulus to yield stress Eeff/σ and the work hardening behavior. Two separate cases of work hardening rates were considered; one with no work hardening rate and other with a linear work hardening rate. Specifically, it is observed that pile up is large only when hf/hmax is close to one and degree of work hardening rate is small. It should also be noted that when hf/hmax < 0.7 very little pile-up is observed no matter what the work-hardening behavior of the material. When pile-up occurs the contact area is greater than that predicted by the experimental methods and both the hardness and modulus are overestimated. In this report the amount by which these properties are overestimated are studied and got to be around 22% approx. Bluntness of the tip often leads to the misinterpretation of the load-displacement data. Further analysis was done in order to find out the amount of deviation from the ideal tip due to tip bluntness. Radius of the tips were also calculated for cubecorner (41.35 nm) and conical indenter (986.05 nm).
Effect of Amines as Corrosion Inhibitors for a Low Carbon Steel in Power Industry
Commonly used amines in power industry, including morpholine, DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), and DMA (dimethylallylamine) were evaluated for their effect on AISI 1018 steel at 250oF. Samples were exposed to an autoclave containing amine added aqueous solution at pH of 9.5 for 1, 2, 4, 6, 8, and 12 hours. Morphology studies were carried using scanning electron microscope (SEM), phase analysis was done utilizing Fourier transform infrared spectroscopy (FTIR), and weight loss was performed to assess kinetics of oxidation. Control samples showed the highest metal dissolution rate. DBU showed the best performance in metal protection and SEM indicated the presence of a free-crack layer formed by fine particles in that set. FTIR showed that DBU apparently favored the formation of magnetite. It is believed that fine particles impede intrusion of aggressive ions into the metal surface by forming a barrier layer. FTIR demonstrated that DMA formed more oxyhydroxides, whereas morpholine presented magnetite to hematite transformation as early as 2 hours. SEM revealed that control and DMA produced acicular particles characteristic of oxyhydroxides while morpholine and DBU presented more equiaxed particles.
Computer Virus Spread Containment Using Feedback Control.
In this research, a security architecture based on the feedback control theory has been proposed. The first loop has been designed, developed and tested. The architecture proposes a feedback model with many controllers located at different stages of network. The controller at each stage gives feedback to the one at higher level and a decision about network security is taken. The first loop implemented in this thesis detects one important anomaly of virus attack, rate of outgoing connection. Though there are other anomalies of a virus attack, rate of outgoing connection is an important one to contain the spread. Based on the feedback model, this symptom is fed back and a state model using queuing theory is developed to delay the connections and slow down the rate of outgoing connections. Upon implementation of this model, whenever an infected machine tries to make connections at a speed not considered safe, the controller kicks in and sends those connections to a delay queue. Because of delaying connections, rate of outgoing connections decrease. Also because of delaying, many connections timeout and get dropped, reducing the spread. PID controller is implemented to decide the number of connections going to safe or suspected queue. Multiple controllers can be implemented to control the parameters like delay and timeout. Control theory analysis is performed on the system to test for stability, controllability, observability. Sensitivity analysis is done to find out the sensitivity of the controller to the delay parameter. The first loop implemented gives feedback to the architecture proposed about symptoms of an attack at the node level. A controller needs to be developed to receive information from different controllers and decision about quarantining needs to be made. This research gives the basic information needed for the controller about what is going on at individual nodes of …
Effects of Thickness and Indenter Tip Geometry in Nanoindentation of Nickel Films
Nanoindentation has become a widely used technique to measure the mechanical properties of materials. Due to its capability to deform materials in micro- and nano-scale, nanoindentation has found more applications in characterizing the deformation behavior and determining the mechanical properties of thin films and coatings. This research deals with the characterization of samples received from Center for Advanced Microstructures and Devices (CAMD) and Integran Technologies Inc., Toronto, Canada and the objective of this investigation was to utilize the experimental data obtained from nanoindentation to determine the deformation behavior, mechanical properties of thin films on substrates and bulk materials, and the effect of geometrically different indenters (Berkovich, cubecorner, and conical). X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) analysis were performed on these materials to determine the crystal orientation, grain size of the material, and also to measure any substrate effects like pile-up or sin-in respectively. The results indicate that indentation size effect (ISE) strongly depends on shape of the indenter and less sensitive to penetration depth where as the hardness measurements depends on shape of indenter and depth of penetration. There is a negligible strain rate dependency of hardness at deeper depths and a significant increase in the hardness due to the decrease in grain size and results also indicate that there is no significant substrate effect on thin films for 10% and 20% of film thicknesses. Nanocrystalline material could not validate a dislocation based mechanisms deformation for indentation made by cubecorner and conical indenters in depths less than 1mm.
Design of Power Amplifier Test Signals with a User-Defined Multisine
Cellular radio communication involves wireless transmission and reception of signals at radio frequencies (RF). Base stations house equipment critical to the transmission and reception of signals. Power amplifier (PA) is a crucial element in base station assembly. PAs are expensive, take up space and dissipate heat. Of all the elements in the base station, it is difficult to design and operate a power amplifier. New designs of power amplifiers are constantly tested. One of the most important components required to perform this test successfully is a circuit simulator model of an entire communication system that generates a standard test signal. Standard test signals 524,288 data points in length require 1080 hours to complete one test of a PA model. In order to reduce the time taken to complete one test, a 'simulated test signal,' was generated. The objective of this study is to develop an algorithm to generate this 'simulated' test signal such that its characteristics match that of the 'standard' test signal.
Sunlight readability and luminance characteristics of light-emitting diode push button switches.
Lighted push button switches and indicators serve many purposes in cockpits, shipboard applications and military ground vehicles. The quality of lighting produced by switches is vital to operators' understanding of the information displayed. Utilizing LED technology in lighted switches has challenges that can adversely affect lighting quality. Incomplete data exists to educate consumers about potential differences in LED switch performance between different manufacturers. LED switches from four different manufacturers were tested for six attributes of lighting quality: average luminance and power consumption at full voltage, sunlight readable contrast, luminance contrast under ambient sunlight, legend uniformity, and dual-color uniformity. Three of the four manufacturers have not developed LED push button switches that meet lighting quality standards established with incandescent technology.
Cost Savings Realized Through Proper Sizing of an Excessive Instrument Air System.
The purpose of this research was to determine if installing a smaller air compressor could reduce the electrical usage of a large semiconductor manufacturing plant. A 200 horsepower Atlas Copco compressor was installed with the existing 500 horsepower Ingersoll-Rand compressors. Testing was conducted during the regular manufacturing process at MEMC Southwest in Sherman, Texas. Analysis of the data found that installing the new compressor could reduce electrical consumption. The study also found there are specific operational setpoints that allow the compressor to operate more efficiently.
Susceptibility of a digital turbine control system to IEEE 802.11 compliant emissions.
Within the nuclear industry, there have been numerous instances of radio transmissions interfering with sensitive plant equipment. Instances documented vary from minor instrument fluctuations to major plant transients including reactor trips. With the nuclear power industry moving toward digital technologies for control and reactor protection systems, concern exists regarding their potential susceptibility to contemporary wireless telecommunications technologies. This study evaluates the susceptibility of Comanche Peak's planned turbine controls upgrade to IEEE 802.11 compliant wireless radio emissions. The study includes a review of previous research, industry emissions standards, and technical overview of the various IEEE 802.11 protocols and details the testing methodology utilized to evaluate the digital control system. The results of this study concluded that the subject digital control system was unaffected by IEEE 802.11 compliant emissions even when the transmitter was in direct contact with sensitive components.
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