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Articles 271 - 299 of 299

Full-Text Articles in Mechanical Engineering

Enhanced Tribological Properties Of Surfaces Patterned With Dlc/Su8 Microstructures, Luke Osborn May 2012

Enhanced Tribological Properties Of Surfaces Patterned With Dlc/Su8 Microstructures, Luke Osborn

Mechanical Engineering Undergraduate Honors Theses

Textured surfaces can reduce friction due to decreased contact area between two surfaces, and could therefore increase the reliability of micro-electro-mechanical systems (MEMS). The problem with some microtextures is their inability to withstand significant amounts of wear, often deforming or breaking, thus limiting their potential uses and overall effectiveness. In this study, connected and isolated SU8 microstructures with and without diamond-like coating (DLC) were designed to investigate the effects of these microstructures on the tribological performance of a surface. Friction studies were conducted using a tribometer, while surface topography and wear were characterized by scanning electron microscopy (SEM), optical microscope, …

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Surface Wetting And Friction Studies Of Nano-Engineered Surfaces On Copper Substrate, Julius Sheldon Morehead Dec 2011

Surface Wetting And Friction Studies Of Nano-Engineered Surfaces On Copper Substrate, Julius Sheldon Morehead

Graduate Theses and Dissertations

Nano-engineered-textures on a material surface can dramatically improve the wetting and non-wetting properties of a surface, and they also show promise to address friction issues that affect surfaces in contact. In this work, aluminum-induced crystallization (AIC) of amorphous silicon (a-Si) was used to produce nano-textures on copper (Cu) substrates. A study was performed to examine the effects of changing the annealing conditions and a-Si thickness on nano-texture formation. The creation of various nano-topographies and chemically modifying them using octafluorocyclobutane (C4F8) was performed to control hydrophilicity, hydrophobicity, and oil affinity of nano-textured surfaces. A video-based contact angle measurement system was used …

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Development Of A Structured Concrete Thermocline Thermal Energy Storage System, Bradley M. Brown Dec 2011

Development Of A Structured Concrete Thermocline Thermal Energy Storage System, Bradley M. Brown

Graduate Theses and Dissertations

The past couple of decades have shown a concern when considering the way the world obtains its power. The focus has been switching from fossil fuels that have been used for hundreds of years to renewable energy sources, such as the sun. Solar energy is readily and infinitely available for harnessing. One problem with solar energy, though, is its inability to be used during the night time and during cloud covered weather. A solution to this problem is the use of energy storage mechanisms. For solar plants that use solar thermal energy (concentrating solar power plants), thermal energy storage (TES) …

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Development Of Spray Cooling For High Heat Flux Electronics, Jeremy Scott Junghans Dec 2011

Development Of Spray Cooling For High Heat Flux Electronics, Jeremy Scott Junghans

Graduate Theses and Dissertations

The thermal demands of modern day electronic systems require innovative thermal solutions. Spray cooling has proven to be able to cool heat fluxes orders of magnitude higher than traditional cooling methodologies. This work includes a comparison of spray cooling to standard thermal management methodologies. Key system parameters and considerations are discussed. The properties of available packaging materials and their effect on the reliability of a spray cooled system are presented. Parameters such as fluid temperature, droplet size, fluid velocity and flow rate all directly impact performance and are detailed in this work. Finally, results from of a wide range of …

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Understanding The Role Of A Bio-Inspired Surface Modification For Delayed Icing, Clayton Schenk Aug 2011

Understanding The Role Of A Bio-Inspired Surface Modification For Delayed Icing, Clayton Schenk

Graduate Theses and Dissertations

Atmospheric icing event is problematic for outdoor structures because it can damage, slow, impede, and danger general routine. For a wind turbine blade, it can damage, disrupt movement, and cause potentially dangerous ice throw. Anti-icing based on a surface texture is advantageous due to the low cost of maintenance and there is no additional requirement of energy output for preventing the icing problem. This work is based on the biomimicry of the superhydrophobic nature of the lotus leaf, whereas the limited wettability supports the water to flow freely from the surface structure. The phenomenon is based on a morphology and …

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A Solid State Nitrogen Gas Generating Chip And Applications For Picosatellites, Kyle Godin Aug 2011

A Solid State Nitrogen Gas Generating Chip And Applications For Picosatellites, Kyle Godin

Graduate Theses and Dissertations

A microscale gas generating chip has many applications; in this study, applications relating to picosatellites have been considered. Cube satellites, a type of picosatellite, are of mass around one kilogram and side length 10cm x 10cm x 10cm. Their launches are becoming more numerous since their debut ten years ago. Their low cost and deployment system makes space accessible to agencies hitherto barred from it, such as universities and small governments. However, their power, mass, and volume budget is extremely tight. A microscale gas chip could compete with other designs for attitude control devices, most not flown yet as cube …

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Gimbaled Permanent Magnet-Based Attitude Control For Pico/Nano-Satellites, Rex Bair May 2011

Gimbaled Permanent Magnet-Based Attitude Control For Pico/Nano-Satellites, Rex Bair

Mechanical Engineering Undergraduate Honors Theses

As man-made satellites grow continually smaller and smaller, new, lower mass, volume, and power solutions must be devised to give these satellites the same performance capabilities as larger satellites. One subsystem that is especially difficult to shrink is the Attitude Determination and Control System (ADACS), which is used to position the satellite in a given orientation with respect to a specific reference frame. This paper explores a novel mechanism which combines both of these functions into one device. A permanent magnet is used in conjunction with the geomagnetic reference frame to provide magnetic torque to change the spacecraft's attitude. By …

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Carbon Nanotube Based Ion Sensitive Field Effect Transistor, Matthew Margis May 2011

Carbon Nanotube Based Ion Sensitive Field Effect Transistor, Matthew Margis

Mechanical Engineering Undergraduate Honors Theses

Carbon nanotubes (CNTs) have been the subject of much research in the past two decades. Due to their extraordinary mechanical and electrical properties, CNTs are ideal candidates for various sensors and electronic device applications. The purpose of this research is to overcome the difficulties in separating and aligning CNTs so that they can be implemented in an ion sensitive field effect transistor (ISFET). A solution to the alignment process has been presented that involves cutting nano channels on a microelectrode chip with an Atomic Force Microscope (AFM) in order to nanomanipulate the CNTs into the nano channels. Upon successfully cutting …

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Tribological Behavior Of Lubricants With And Without Nanoadditives: A Compartive Study, Kevin Carlson May 2011

Tribological Behavior Of Lubricants With And Without Nanoadditives: A Compartive Study, Kevin Carlson

Mechanical Engineering Undergraduate Honors Theses

Nano particle based additives have become a main focal point in the design of new lubricants, in order to better achieve reduction in both friction and wear. Previous research has led to the development of one such lubricant known as NanoGlide® by a company called NanoMech, Inc. The success of this initial lubricant design encouraged the research and potential development of new formulations of nano particle based lubricants by NanoMech, Inc. Using tribological testing, and Scanning Electron Microscopy (SEM), this research analyzed the behavior and performance of three new nano additives (NanoGlide 1, NanoGlide2, and NanoGlide3) in three different lubricant …

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Spectral Characterization Of Venusian Surface Mineralogy, Johnathon Conley May 2011

Spectral Characterization Of Venusian Surface Mineralogy, Johnathon Conley

Mechanical Engineering Undergraduate Honors Theses

While the atmospheric chemical composition of the Venusian atmosphere has been characterized at length by probes and ground-based equipment, the surface mineralogy of Venus is not yet well understood. The extremely thick atmosphere of Venus shields the surface from direct observation. While radar imaging of the surface reveals surface morphology, surface composition is difficult to characterize at a distance. Observation is also difficult due to the intense temperature (approximately 480°C) and pressure (approximately 90 atm) found on the surface. This has prompted NASA and other institutions around the world to begin planning for new missions to land on the surface …

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The Effects Of Roof Solar Absorptance On Building Energy Performance In A Variety Of U.S. Climate Zones, Zachary Eubanks Dec 2010

The Effects Of Roof Solar Absorptance On Building Energy Performance In A Variety Of U.S. Climate Zones, Zachary Eubanks

Mechanical Engineering Undergraduate Honors Theses

The solar absorptance of a roof surface directly affects the solar heat gain through the roof. It has been shown that buildings in hot climates benefit from roofs with low absorptance. Cold and moderate climates have received less attention in previous studies. This paper simulates the effects on annual energy use, carbon dioxide emission, and utility cost of varying the solar absorptance of warehouse and small office building roofs in a wide variety of U.S. climate zones using EnergyPlus software and the DOE Commercial Building Benchmark Models. Results show that the optimum absorptance not only depends on the climate zone, …

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Factors Affecting Redox Magnetohydrodynamics For Flow In Small Volumes, Matthew D. Gerner Aug 2009

Factors Affecting Redox Magnetohydrodynamics For Flow In Small Volumes, Matthew D. Gerner

Graduate Theses and Dissertations

Lab-on-a-chip technologies offer the possibility of developing analytical devices that are low-cost, portable, disposable, fast, and operable by non-technical personnel. Such devices require automated methods to manipulate ultra-small volumes (picoliters) of samples and solution, including pumping, stirring, and positioning. Current methods for ultra-small volume microfluidics have limitations that restrict their use including high voltage requirements, disadvantageous flow profiles or rates, and relatively complicated fabrication due to mechanical parts. Redox magnetohydrodyanmics (RMHD) that utilizes permanent magnets for portability shows promise as a micropump with ease of switching flow direction, no moving parts, compatibility with both aqueous and non-aqueous solutions, low voltages …

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Automated Flight Through Inertial Navigation And Digital Fly-By-Wire Systems, Aaron French May 2009

Automated Flight Through Inertial Navigation And Digital Fly-By-Wire Systems, Aaron French

Mechanical Engineering Undergraduate Honors Theses

With technology advancing by leaps and bounds by the year, the uses of Unmanned Aerial Vehicles are becoming more apparent. The possibilities for an aerial vehicle that is fully autonomous are endless. Such aerial vehicles could divert manpower to humanitarian efforts, airlift, and other non‐attack operations. Leaders can put their focus elsewhere on the battlefield with the knowledge that the skies over their heads will be well guarded. These desires give life to projects such as this. No advancement in civilization has ever been made without the collective revolutionary research of great minds, trial by fire, and daring to dream.

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Free Fridays: An Alternative Way To Conserve Energy, Lauren Kuenzel May 2009

Free Fridays: An Alternative Way To Conserve Energy, Lauren Kuenzel

Mechanical Engineering Undergraduate Honors Theses

In February 2007, the University of Arkansas at Fayetteville (UAF) signed the President's Climate Commitment to set a goal of becoming climate neutral. A large part of any strategy to become climate neutral includes energy conservation. In light of that, a four-day school week is proposed for UAF as an alternative energy savings possibility. This reduced schedule has been applied to K-12 schools and state government institutions, but not yet to universities. Along with numerous benefits such as energy conservation of buildings on the free day, a more effective use of time and building space and the positive emotional repercussions …

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Nickel-Induced Crystallization Of Amorphous Silicon, Robert Fleming May 2009

Nickel-Induced Crystallization Of Amorphous Silicon, Robert Fleming

Mechanical Engineering Undergraduate Honors Theses

One- and two-dimensional silicon nanostructures, such as nanodots, nanowires, and surface topography, have potential uses in a variety of fields, including microelectronics, photonics, and tribology. In this thesis research, nickel-induced crystallization (NIC) of amorphous silicon (a-Si) was investigated to determine the suitability of NIC of a-Si to produce silicon nanostructures on silicon substrates. The results show that formation of both surface topography and nanowires is possible with NIC of a-Si. In addition, the formation of nanostructures is very sensitive to Ni thickness, and the resulting nanostructures and films display a high degree of repeatability. The results obtained from this research …

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A Review Of Variable Valve Timing Devices, Paul Shelton May 2008

A Review Of Variable Valve Timing Devices, Paul Shelton

Mechanical Engineering Undergraduate Honors Theses

Variable valve timing (VVT) has evolved from simple, manual controlled engine management to automatic, electronic works of engineering. Starting from the need for more power and extending into fuel efficiency and low emissions, VVT has evolved from the constant changing of needs. This paper summarizes various devices used to control the timing of valves from the early 1920s up until 2007.

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Restart Capabilities Of Hybrid Rocket Motor Utilizing Gaseous Propane And Oxygen Injection System, Joseph Gracy May 2008

Restart Capabilities Of Hybrid Rocket Motor Utilizing Gaseous Propane And Oxygen Injection System, Joseph Gracy

Mechanical Engineering Undergraduate Honors Theses

Hybrid rockets have become an increasingly popular application in professional and amateur rocketry for their outstanding performance and reliability. An issue pressing the marketability and functionality of these rockets is the ability to restart with an exclusive system after primary ignition. Research and development of a system that can be used reliably in either application to achieve restart under various conditions has been made recently using dual injection of GOX and C3H8 using a 200kV ignition system while implementing a polymethylmethacrylate (PMMA) formable polymer as primary fuel. The system used a manual valve arrangement for control. The design features most …

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Development Of Miniature Hybrid Rockets For Orbital Upkeep And Transfer Applications In Nano/Pico-Satellites, Derek Willingham May 2008

Development Of Miniature Hybrid Rockets For Orbital Upkeep And Transfer Applications In Nano/Pico-Satellites, Derek Willingham

Mechanical Engineering Undergraduate Honors Theses

This research has developed and constructed a successful miniature hybrid rocket test assembly for research into hybrid rocket scaling issues. It is hoped that such systems will find eventual integration into small satellites. The test assembly houses 3" fuel grains and provides an inlet for gaseous oxidizer. Although far from complete, preliminary data were taken with PMMA and GOx and some useful conclusions were drawn that will benefit future research into this topic. Fuel grains with combustion chambers whose diameters range from 1/16" to 3/8" were tested at different flow rates and thrust data gathered. Maximum flow information was gathered …

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Benefits Of Leed Designs In Arkansas K-12 Schools, Philip Thrift May 2008

Benefits Of Leed Designs In Arkansas K-12 Schools, Philip Thrift

Mechanical Engineering Undergraduate Honors Theses

This paper provides and evaluation of an existing LEED certified sustainable green building for energy-efficiency, environmental impact, economic value, and occupant health. The new Bethel Middle School located in Bryant, Arkansas was the first LEED (Leadership in Energy and Environmental Design) certified public school building in the state. Based on actual building specifications and validated with the first year's utility bills, a simulation model was used to evaluate various design aspects of the school building. The building's baseline energy usage was compared with numerous energy and environmental scenarios. Results include both environmental and economic assessments. Overall, the study found that …

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Numerical Thermal-Fluid Analysis Of A Liquid Cooled Novel 3-D Electronic Package, Aron Meyer May 2008

Numerical Thermal-Fluid Analysis Of A Liquid Cooled Novel 3-D Electronic Package, Aron Meyer

Mechanical Engineering Undergraduate Honors Theses

The need for smaller and more powerful processors has become more and more important in recent times. This need is nowhere more evident than in the military where the ability to process large amounts of data quickly and accurately can save lives. So the University of Arkansas has been researching a new chip design, the 3-D stack-up thru-silicon via chip. This has several benefits over the traditional chip designs, but comes at the price of having more heat to be dissipated. Due to the need to dissipate up to 20 watts per wafer a liquid cooling system was used with …

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Factors Affecting The Spread Of A Bioterrorist Agent Throughout A Building, William A. Cantrell Jan 2008

Factors Affecting The Spread Of A Bioterrorist Agent Throughout A Building, William A. Cantrell

Inquiry: The University of Arkansas Undergraduate Research Journal

Bioterrorism has become a greater concern for Americans since the 2001 anthrax letters. Recent studies have explored the possibilities of biological attacks, and most deal with possible large-scale attacks. However, there is reason to believe that small-scale attacks are more likely. Even though there have been investigations of the postal delivery system and the spread of bioagents through mail, few if any studies have looked at attack on a single building and the resultant spread form room to room. One particular method of attacking a building would be a single-even release of an aerosol bioagent in the building. This paper …

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Factors Affecting The Spread Of A Bioterrorist Agent Through A Building, William Cantrell May 2007

Factors Affecting The Spread Of A Bioterrorist Agent Through A Building, William Cantrell

Mechanical Engineering Undergraduate Honors Theses

Bioterrorism has become a concern for Americans since the 2001 anthrax letters. Many studies have been done regarding the possibilities of biological attacks since, and most deal with possibilities of large scale attacks. However, there is reason to believe that small scale attacks are more likely. Even though studies have been done revolving around the postal system and the spread of bioagents through mail, few if any studies have looked at an attack on a single building. One particular method of attacking a building would be simply releasing an aerosoled contaminant in the building. This purpose of this project is …

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A Study On The Application Of Thermoelectric Heat Pumps For Heating Applications, James Lincicome May 2007

A Study On The Application Of Thermoelectric Heat Pumps For Heating Applications, James Lincicome

Mechanical Engineering Undergraduate Honors Theses

Typically, thermoelectric heat pumps are used in cooling applications where space and portability are important, but they can be used efficiently in heating applications under the right conditions. This paper explains the origins of the thermoelectric heat pump, its applications in society, and the technical aspects of the device. The many different appurtenances that the device requires will be discussed along with their drawbacks. The single-stage data for the cells will be compared to the two-stage configuration data, and the data gathered for a specific thermoelectric device will be compared to the manufacturer's published data for the different configurations of …

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Atomic Force Microscope Imaging Of Dna And Multi Walled Carbon Nanotubes, Jacob Hohnbaum May 2007

Atomic Force Microscope Imaging Of Dna And Multi Walled Carbon Nanotubes, Jacob Hohnbaum

Mechanical Engineering Undergraduate Honors Theses

The Micro and Nano System Laboratory at the University of Arkansas currently is equipped with an Atomic Force Microscope (AFM). This device can be used to measure objects with resolution on the nanometer scale, but there are a number of technical difficulties in performing scans of carbon nanotubes and DNA. The goal of this research is to successfully perform scans on both carbon nanotubes and DNA and to also establish laboratory processing protocols to re-perform such scans in the future. Previous works performed by other researchers in the laboratory provided basic protocols with which to begin the present research. These …

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Design Of A Supersonic Wind Tunnel, Jay Pascual May 2007

Design Of A Supersonic Wind Tunnel, Jay Pascual

Mechanical Engineering Undergraduate Honors Theses

A supersonic wind tunnel was to be designed using the existing compressed air tank at the Mechanical Engineering building at the University of Arkansas. A throat area of 0.000375 m2 was used in the design process. The properties of the air were calculated using various Mach numbers. These results are used to determine if a wind tunnel of Mach numbers between one and five can be built at the University of Arkansas and can run for a sufficient amount of time. Also, the dimensions of the supersonic wind tunnel were calculated for these various Mach numbers.

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Design Of Novel Experimental Techniques To Investigate The Formation Of Nanoparticle-Based Tribofilms, Corey Thompson Dec 2006

Design Of Novel Experimental Techniques To Investigate The Formation Of Nanoparticle-Based Tribofilms, Corey Thompson

Mechanical Engineering Undergraduate Honors Theses

Nano-engineered lubricant additives such as organically-active nanoparticles of molybdenum disulphide (Hybrid-milled MoS2) are becoming increasingly popular in the fight against harsh friction and wear that occurs during boundary-layer lubrication. A previous paper (Verma, 2007), has reported improvements in both coefficient of friction and wear scar diameter; however, there exists very little data concerning the methods through which this improvement is achieved. Using techniques such as atomic force microscopy (AFM), nanoindentation, scanning electron microscopy (SEM), focused ion beam (FIB), high resolution transmission electron microscopy (HRTEM) as well as tribometery, the chemical and mechanical characteristics of the nanoparticle based tribofilm are characterized. …

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Mechatronic Design Of A Treaded Mobile Robot For Mine Sweeping, Andrew B. Wright Jan 2000

Mechatronic Design Of A Treaded Mobile Robot For Mine Sweeping, Andrew B. Wright

Journal of the Arkansas Academy of Science

Autonomous mobile robots, which can be programmed to exhibit cooperative behaviors, are ideal mechanisms for sweeping land mines. They can spread out to hunt for the mines, using a dispersal rule. Once a mine is located, they can congregate to surround it using a clustering rule. Should a robot be destroyed by tripping an unseen mine, the cost is minimal compared to a human life. UALR has been experimenting with coupled oscillator based rule generators for several years using fragile, indoor robots in a laboratory setting to validate the clustering and dispersal behaviors. In order to accomplish outdoor trials, a …

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Evaluation Of Photodiode Arrays For Use In Rocket Plume Monitoring And Diagnostics, Dallas Snider, M. Keith Hudson, Robert B. Shanks, Reagan Cole Jan 1994

Evaluation Of Photodiode Arrays For Use In Rocket Plume Monitoring And Diagnostics, Dallas Snider, M. Keith Hudson, Robert B. Shanks, Reagan Cole

Journal of the Arkansas Academy of Science

The spectroscopic analysis of plume emissions is a non-intrusive method which has been used to check for fatigue and possible damage throughout the pumps and other mechanisms in a rocket motor or engine. These components are made of various alloys. Knowing the composition of the alloys and for which parts they are used, one can potentially determine from the emissions in the plume which component is failing. Currently, Optical Multichannel Analyzer systems are being used which utilize charge coupled devices, cost tens of thousands of dollars, are somewhat delicate, and usually require cooling. We have developed two rugged instruments using …

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Measurement Of The Coefficient Of Thermal Expansion Of Superconducting Thin Films Using Powder X-Ray Diffraction, Biju Chandran, R. Calvin Goforth, S. Nasrazadani Jan 1992

Measurement Of The Coefficient Of Thermal Expansion Of Superconducting Thin Films Using Powder X-Ray Diffraction, Biju Chandran, R. Calvin Goforth, S. Nasrazadani

Journal of the Arkansas Academy of Science

The High Density Electronics Center (HiDEC) at the University of Arkansas, Fayetteville is developing the technology for High Temperature Superconductor Multi-Chip Modules (HTSC-MCM's). As part of this work, we are looking at the mechanical properties of HTSC materials. An important mechanical property which influences the mechanical integrity of the hybrid MCMis the coefficient of thermal expansion (CTE) of the HTSC films. As a first step in developing a procedure for the determination of the CTE of HTSC materials, the lattice parameters and the CTE of an alpha-alumina substrate have been determined by powder x-ray diffraction technique. An extension of this …

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