Matching Items (134)
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Description
In this research, our goal was to fabricate Josephson junctions that can be stably processed at 300°C or higher. With the purpose of integrating Josephson junction fabrication with the current semiconductor circuit fabrication process, back-end process temperatures (>350 °C) will be a key for producing large scale junction circuits reliably,

In this research, our goal was to fabricate Josephson junctions that can be stably processed at 300°C or higher. With the purpose of integrating Josephson junction fabrication with the current semiconductor circuit fabrication process, back-end process temperatures (>350 °C) will be a key for producing large scale junction circuits reliably, which requires the junctions to be more thermally stable than current Nb/Al-AlOx/Nb junctions. Based on thermodynamics, Hf was chosen to produce thermally stable Nb/Hf-HfOx/Nb superconductor tunnel Josephson junctions that can be grown or processed at elevated temperatures. Also elevated synthesis temperatures improve the structural and electrical properties of Nb electrode layers that could potentially improve junction device performance. The refractory nature of Hf, HfO2 and Nb allow for the formation of flat, abrupt and thermally-stable interfaces. But the current Al-based barrier will have problems when using with high-temperature grown and high-quality Nb. So our work is aimed at using Nb grown at elevated temperatures to fabricate thermally stable Josephson tunnel junctions. As a junction barrier metal, Hf was studied and compared with the traditional Al-barrier material. We have proved that Hf-HfOx is a good barrier candidate for high-temperature synthesized Josephson junction. Hf deposited at 500 °C on Nb forms flat and chemically abrupt interfaces. Nb/Hf-HfOx/Nb Josephson junctions were synthesized, fabricated and characterized with different oxidizing conditions. The results of materials characterization and junction electrical measurements are reported and analyzed. We have improved the annealing stability of Nb junctions and also used high-quality Nb grown at 500 °C as the bottom electrode successfully. Adding a buffer layer or multiple oxidation steps improves the annealing stability of Josephson junctions. We also have attempted to use the Atomic Layer Deposition (ALD) method for the growth of Hf oxide as the junction barrier and got tunneling results.
ContributorsHuang, Mengchu, 1987- (Author) / Newman, Nathan (Thesis advisor) / Rowell, John M. (Committee member) / Singh, Rakesh K. (Committee member) / Chamberlin, Ralph (Committee member) / Wang, Robert (Committee member) / Arizona State University (Publisher)
Created2013
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Description
The ability to shift the photovoltaic (PV) power curve and make the energy accessible during peak hours can be accomplished through pairing solar PV with energy storage technologies. A prototype hybrid air conditioning system (HACS), built under supervision of project head Patrick Phelan, consists of PV modules running a DC

The ability to shift the photovoltaic (PV) power curve and make the energy accessible during peak hours can be accomplished through pairing solar PV with energy storage technologies. A prototype hybrid air conditioning system (HACS), built under supervision of project head Patrick Phelan, consists of PV modules running a DC compressor that operates a conventional HVAC system paired with a second evaporator submerged within a thermal storage tank. The thermal storage is a 0.284m3 or 75 gallon freezer filled with Cryogel balls, submerged in a weak glycol solution. It is paired with its own separate air handler, circulating the glycol solution. The refrigerant flow is controlled by solenoid valves that are electrically connected to a high and low temperature thermostat. During daylight hours, the PV modules run the DC compressor. The refrigerant flow is directed to the conventional HVAC air handler when cooling is needed. Once the desired room temperature is met, refrigerant flow is diverted to the thermal storage, storing excess PV power. During peak energy demand hours, the system uses only small amounts of grid power to pump the glycol solution through the air handler (note the compressor is off), allowing for money and energy savings. The conventional HVAC unit can be scaled down, since during times of large cooling demands the glycol air handler can be operated in parallel with the conventional HVAC unit. Four major test scenarios were drawn up in order to fully comprehend the performance characteristics of the HACS. Upon initial running of the system, ice was produced and the thermal storage was charged. A simple test run consisting of discharging the thermal storage, initially ~¼ frozen, was performed. The glycol air handler ran for 6 hours and the initial cooling power was 4.5 kW. This initial test was significant, since greater than 3.5 kW of cooling power was produced for 3 hours, thus demonstrating the concept of energy storage and recovery.
ContributorsPeyton-Levine, Tobin (Author) / Phelan, Patrick (Thesis advisor) / Trimble, Steve (Committee member) / Wang, Robert (Committee member) / Arizona State University (Publisher)
Created2012
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Description
The study of high energy particle irradiation effect on Josephson junction tri-layers is relevant to applications in space and radioactive environments. It also allows us to investigate the influence of defects and interfacial intermixing on the junction electrical characteristics. In this work, we studied the influence of 2MeV Helium ion

The study of high energy particle irradiation effect on Josephson junction tri-layers is relevant to applications in space and radioactive environments. It also allows us to investigate the influence of defects and interfacial intermixing on the junction electrical characteristics. In this work, we studied the influence of 2MeV Helium ion irradiation with doses up to 5.2×1016 ions/cm2 on the tunneling behavior of Nb/Al/AlOx/Nb Josephson junctions. Structural and analytical TEM characterization, combined with SRIM modeling, indicates that over 4nm of intermixing occurred at the interfaces. EDX analysis after irradiation, suggests that the Al and O compositions from the barrier are collectively distributed together over a few nanometers. Surprisingly, the IV characteristics were largely unchanged. The normal resistance, Rn, increased slightly (<20%) after the initial dose of 3.5×1015 ions/cm2 and remained constant after that. This suggests that tunnel barrier electrical properties were not affected much, despite the significant changes in the chemical distribution of the barrier's Al and O shown in SRIM modeling and TEM pictures. The onset of quasi-particle current, sum of energy gaps (2Δ), dropped systematically from 2.8meV to 2.6meV with increasing dosage. Similarly, the temperature onset of the Josephson current dropped from 9.2K to 9.0K. This suggests that the order parameter at the barrier interface has decreased as a result of a reduced mean free path in the Al proximity layer and a reduction in the transition temperature of the Nb electrode near the barrier. The dependence of Josephson current on the magnetic field and temperature does not change significantly with irradiation, suggesting that intermixing into the Nb electrode is significantly less than the penetration depth.
ContributorsZhang, Tiantian (Author) / Newman, Nathan (Thesis advisor) / Rowell, John M (Committee member) / Singh, Rakesh K. (Committee member) / Chamberlin, Ralph (Committee member) / Wang, Robert (Committee member) / Arizona State University (Publisher)
Created2012
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Description
Defending against spoofing is an important part of security throughout the internet. With- out the ability to authenticate, within a certain confidence, that a person is in fact who they say are, can allow attackers to go unrecognized after performing an attack. It is much too easy for attackers today

Defending against spoofing is an important part of security throughout the internet. With- out the ability to authenticate, within a certain confidence, that a person is in fact who they say are, can allow attackers to go unrecognized after performing an attack. It is much too easy for attackers today to hide their identity or pretend to be someone else through the means of spoof- ing. Researchers must focus their efforts on defenses that are scalable and effective in counter- ing spoofing. This thesis focuses on surveying different types of spoofing as well as attacks that lever- age spoofing with the hopes to hide the attacker's identity or leverage identity theft to perform an attack. It also looks at current defenses that hope to counter attacks that leverage spoofing and evaluates how realistic is to implement the defenses in terms of scalability and effective- ness. By surveying different attacks and defenses, researchers will be able to better focus their efforts on more effective and scalable defenses to spoofing and attacks that leverage spoofing.
ContributorsTorrence, Ryan Michael (Author) / Dasgupta, Partha (Thesis director) / Doupe, Adam (Committee member) / Barrett, The Honors College (Contributor) / Computer Science and Engineering Program (Contributor)
Created2015-05
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Description
With the world's ever growing need for sustainable energy solutions, the field of thermoelectrics has seen rejuvenated interest. Specifically, modern advances in nanoscale technology have resulted in predictions that thermoelectric devices will soon become a viable waste heat recovery energy source, among other things. In order to achieve these predictions,

With the world's ever growing need for sustainable energy solutions, the field of thermoelectrics has seen rejuvenated interest. Specifically, modern advances in nanoscale technology have resulted in predictions that thermoelectric devices will soon become a viable waste heat recovery energy source, among other things. In order to achieve these predictions, however, key structure-property relationships must first be understood. Currently, the Thermal Energy and Nanomaterials Lab at Arizona State University is attempting to solve this problem. This project intends to aid the groups big picture goal by developing a robust and user friendly measurement platform which is capable of reporting charge carrier mobility, electrical conductivity, and Seebeck coefficient values. To date, the charge carrier mobility and electrical conductivity measurements have been successfully implemented and validated. First round analysis has been performed on β-In2Se3 thin film samples. Future work will feature a more comprehensive analysis of this material.
ContributorsNess, Kyle David (Author) / Wang, Robert (Thesis director) / Chan, Candace (Committee member) / Barrett, The Honors College (Contributor) / Mechanical and Aerospace Engineering Program (Contributor)
Created2014-05
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Description

The rampant occurrence of spam telephone calls shows a clear weakness of authentication and security in our telephone systems. The onset of cheap and effective voice over Internet Protocol (VoIP) technology is a major factor in this as our existing telephone ecosystem is virtually defenseless by many features of this

The rampant occurrence of spam telephone calls shows a clear weakness of authentication and security in our telephone systems. The onset of cheap and effective voice over Internet Protocol (VoIP) technology is a major factor in this as our existing telephone ecosystem is virtually defenseless by many features of this technology. Our telephone systems have also suffered tremendously from a lack of a proper Caller ID verification system. Phone call spammers are able to mask their identities with relative ease by quickly editing their Caller ID. It will take a combination of unique innovations in implementing new authentication mechanisms in the telephone ecosystem, novel government regulation, and understanding how the people behind the spam phone calls themselves operate.<br/><br/>This study dives into the robocall ecosystem to find more about the humans behind spam telephone calls and the economic models they use. Understanding how the people behind robocalls work within their environments will allow for more insight into how the ecosystem works. The study looks at the human component of robocalls: what ways they benefit from conducting spam phone calls, patterns in how they identify which phone number to call, and how these people interact with each other within the telephone spam ecosystem. This information will be pivotal to educate consumers on how they should mitigate spam as well as for creating defensive systems. In this qualitative study, we have conducted numerous interviews with call center employees, have had participants fill out surveys, and garnered data through our CallFire integrated voice broadcast system. While the research is still ongoing, initial conclusions in my pilot study interview data point to promising transparency in how the voices behind these calls operate on both a small and large scale.

ContributorsUsman, Ahmed (Author) / Doupe, Adam (Thesis director) / Bazzi, Rida (Committee member) / Computer Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
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Description
Apple’s HomeKit framework centralizes control of smart home devices and allows users to create home automations based on predefined rules. For example, a user can add a rule to turn off all the lights in their house whenever they leave. Currently, these rules must be added through a graphical user

Apple’s HomeKit framework centralizes control of smart home devices and allows users to create home automations based on predefined rules. For example, a user can add a rule to turn off all the lights in their house whenever they leave. Currently, these rules must be added through a graphical user interface provided by Apple or a third-party app on iOS. This thesis describes how a text-based language provides users with a more expressive means of creating complex home automations and successfully implements such a language. Rules created using this text-based format are parsed and interpreted into rules that can be added directly into HomeKit. This thesis also explores how security features should be implemented with this text-based approach. Since automations are run by the system without user interaction, it is important to consider how the system itself can provide functionality to address the unintended consequences that may result from running an automation. This is especially important for the text-based approach since its increase in expressiveness makes it easier for a user to make a mistake in programming that leads to a security concern. The proposed method for preventing unintended side effects is using a simulation to run every automation prior to actually running the automation on real-world devices. This approach allows users to code some conditions that must be satisfied in order for the automation to run on devices in the home. This thesis describes the creation of such a program that successfully simulates every device in the home. There were limitations, however, with Apple's HomeKit framework, which made it impractical to match the state of simulated devices to real devices in the home. Without being able to match the current state of the home to the current state of the simulation, this method cannot satisfy the goal of ensuring that certain adverse effects will not occur as a result of automations. Other smart home control platforms that provide more extensibility could be used to create this simulation-based security approach. Perhaps as Apple continues to open up their HomeKit platform to developers, this approach may be feasible within Apple's ecosystem at some point in the future.
ContributorsSharp, Trevor Ryan (Co-author) / Sharp, Trevor (Co-author) / Bazzi, Rida (Thesis director) / Doupe, Adam (Committee member) / Economics Program in CLAS (Contributor) / Department of Management and Entrepreneurship (Contributor) / Computer Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2020-05
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Description
A web server is a program that responds to your browser's
requests. Often, the response is a HTML document that the browser
renders in a way that looks pleasant to humans. The manner in which it
responds is generally determined before the server is started up; it
is static. The content may change arbitrarily,

A web server is a program that responds to your browser's
requests. Often, the response is a HTML document that the browser
renders in a way that looks pleasant to humans. The manner in which it
responds is generally determined before the server is started up; it
is static. The content may change arbitrarily, but the actual logic
that the server follows resists change while the server is still
running. The goal of this thesis is to explore the possibility of
removing this restriction, allowing a web server's logic to be
modified arbitrarily during runtime by select users. This is why the
term ``Federated'' appears in the title: my goal is to create a system
that can be developed in a decentralized manner, by multiple entities
with similar high-level goals but different ideas at the lower level.
ContributorsKulkarni, Sidharth (Author) / Bazzi, Rida (Thesis director) / Doupe, Adam (Committee member) / Computer Science and Engineering Program (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2019-05
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Description
This thesis project explains what thermal interface materials (TIMs) are, what they are used for, and how to measure their properties. Thermal interface materials are typically either a grease like paste or a soft polymer pad that is placed between two solids to increase the heat transfer rate. Solids in

This thesis project explains what thermal interface materials (TIMs) are, what they are used for, and how to measure their properties. Thermal interface materials are typically either a grease like paste or a soft polymer pad that is placed between two solids to increase the heat transfer rate. Solids in contact with each other experience a very large thermal contact resistance, this creates a thermal bottleneck which severely decreases the heat transfer from one solid to another. To solve this, particles with a high thermal conductivity are used as filler material in either a grease or polymer. A common application for TIMs is in computer components, where a TIM is used to remove the heat generated from computer chips. These materials allow for computer chips to run faster without overheating or throttling performance. However, further improvements to TIMs are still desired, which are needed for more powerful computer chips. In this work, a Stepped Bar Apparatus (SBA) is used to evaluate the thermal properties of TIMs. The SBA is based on Fourier’s Law of one-dimensional heat transfer. This work explains the fundamentals of the SBA measurement, and develops a reliable way to confirm the SBA’s measurement consistency through the use of reference samples. Furthermore, this work evaluates the effects of volume fraction and magnetic alignment on the performance of nickel flakes mixed into a polymer to create a soft TIM composite pad. Magnets are used to align the nickel flakes into a column like arrangement in the direction that heat will travel. Magnetic alignment increases the thermal conductivity of the composite pads, and has peak performance at low compression.
ContributorsHart, Matthew (Author) / Rykaczewski, Konrad (Thesis director) / Wang, Robert (Committee member) / Mechanical and Aerospace Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2019-12
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Description
Despite the more tightly controlled permissions and Java framework used by most programs in the Android operating system, an attacker can use the same classic vulnerabilities that exist for traditional Linux binaries on the programs in the Android operating system. Some classic vulnerabilities include stack overows, string formats, and hea

Despite the more tightly controlled permissions and Java framework used by most programs in the Android operating system, an attacker can use the same classic vulnerabilities that exist for traditional Linux binaries on the programs in the Android operating system. Some classic vulnerabilities include stack overows, string formats, and heap meta-information corruption. Through the exploitation of these vulnerabilities an attacker can hijack the execution ow of an application. After hijacking the execution ow, an attacker can then violate the con_dentiality, integrity, or availability of the operating system. Over the years, the operating systems and compliers have implemented a number of protections to prevent the exploitation of vulnerable programs. The most widely implemented protections include Non-eXecutable stack (NX Stack), Address Space Layout Randomization (ASLR), and Stack Canaries (Canaries). NX Stack protections prevent the injection and execution of arbitrary code through the use of a permissions framework within a program. Whereas, ASLR and Canaries rely on obfuscation techniques to protect control ow, which requires su_cient entropy between each execution. Early in the implementation of these protections in Linux, researchers discovered that without su_cient entropy between executions, ASLR and Canaries were easily bypassed. For example, the obfuscation techniques were useless in programs that ran continuously because the programs did not change the canaries or re-randomize the address space. Similarly, aws in the implementation of ASLR and Canaries in Android only re-randomizes the values after rebooting, which means the address space locations and canary values remain constant across the executions of an Android program. As a result, an attacker can hijack the control ow Android binaries that contain control ow vulnerabilities. The purpose of this paper is to expose these aws and the methodology used to verify their existence in Android versions 4.1 (Jelly Bean) through 8.0 (Oreo).
ContributorsGibbs, Wil (Author) / Doupe, Adam (Thesis director) / Shoshitaishvili, Yan (Committee member) / Barrett, The Honors College (Contributor) / Computer Science and Engineering Program (Contributor)
Created2018-12