Matching Items (156)
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Description
The theme for this work is the development of fast numerical algorithms for sparse optimization as well as their applications in medical imaging and source localization using sensor array processing. Due to the recently proposed theory of Compressive Sensing (CS), the $\ell_1$ minimization problem attracts more attention for its ability

The theme for this work is the development of fast numerical algorithms for sparse optimization as well as their applications in medical imaging and source localization using sensor array processing. Due to the recently proposed theory of Compressive Sensing (CS), the $\ell_1$ minimization problem attracts more attention for its ability to exploit sparsity. Traditional interior point methods encounter difficulties in computation for solving the CS applications. In the first part of this work, a fast algorithm based on the augmented Lagrangian method for solving the large-scale TV-$\ell_1$ regularized inverse problem is proposed. Specifically, by taking advantage of the separable structure, the original problem can be approximated via the sum of a series of simple functions with closed form solutions. A preconditioner for solving the block Toeplitz with Toeplitz block (BTTB) linear system is proposed to accelerate the computation. An in-depth discussion on the rate of convergence and the optimal parameter selection criteria is given. Numerical experiments are used to test the performance and the robustness of the proposed algorithm to a wide range of parameter values. Applications of the algorithm in magnetic resonance (MR) imaging and a comparison with other existing methods are included. The second part of this work is the application of the TV-$\ell_1$ model in source localization using sensor arrays. The array output is reformulated into a sparse waveform via an over-complete basis and study the $\ell_p$-norm properties in detecting the sparsity. An algorithm is proposed for minimizing a non-convex problem. According to the results of numerical experiments, the proposed algorithm with the aid of the $\ell_p$-norm can resolve closely distributed sources with higher accuracy than other existing methods.
ContributorsShen, Wei (Author) / Mittlemann, Hans D (Thesis advisor) / Renaut, Rosemary A. (Committee member) / Jackiewicz, Zdzislaw (Committee member) / Gelb, Anne (Committee member) / Ringhofer, Christian (Committee member) / Arizona State University (Publisher)
Created2011
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Description
A general continuum model for simulating the flow of ions in the salt baths that surround and fill excitable neurons is developed and presented. The ion densities and electric potential are computed using the drift-diffusion equations. In addition, a detailed model is given for handling the electrical dynamics on interior

A general continuum model for simulating the flow of ions in the salt baths that surround and fill excitable neurons is developed and presented. The ion densities and electric potential are computed using the drift-diffusion equations. In addition, a detailed model is given for handling the electrical dynamics on interior membrane boundaries, including a model for ion channels in the membranes that facilitate the transfer of ions in and out of cells. The model is applied to the triad synapse found in the outer plexiform layer of the retina in most species. Experimental evidence suggests the existence of a negative feedback pathway between horizontal cells and cone photoreceptors that modulates the flow of calcium ions into the synaptic terminals of cones. However, the underlying mechanism for this feedback is controversial and there are currently three competing hypotheses: the ephaptic hypothesis, the pH hypothesis and the GABA hypothesis. The goal of this work is to test some features of the ephaptic hypothesis using detailed simulations that employ rigorous numerical methods. The model is first applied in a simple rectangular geometry to demonstrate the effects of feedback for different extracellular gap widths. The model is then applied to a more complex and realistic geometry to demonstrate the existence of strictly electrical feedback, as predicted by the ephaptic hypothesis. Lastly, the effects of electrical feedback in regards to the behavior of the bipolar cell membrane potential is explored. Figures for the ion densities and electric potential are presented to verify key features of the model. The computed steady state IV curves for several cases are presented, which can be compared to experimental data. The results provide convincing evidence in favor of the ephaptic hypothesis since the existence of feedback that is strictly electrical in nature is shown, without any dependence on pH effects or chemical transmitters.
ContributorsJones, Jeremiah (Author) / Gardner, Carl (Committee member) / Baer, Steven (Committee member) / Crook, Sharon (Committee member) / Kostelich, Eric (Committee member) / Ringhofer, Christian (Committee member) / Arizona State University (Publisher)
Created2013
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Description
In vertebrate outer retina, changes in the membrane potential of horizontal cells affect the calcium influx and glutamate release of cone photoreceptors via a negative feedback. This feedback has a number of important physiological consequences. One is called background-induced flicker enhancement (BIFE) in which the onset of dim background enhances

In vertebrate outer retina, changes in the membrane potential of horizontal cells affect the calcium influx and glutamate release of cone photoreceptors via a negative feedback. This feedback has a number of important physiological consequences. One is called background-induced flicker enhancement (BIFE) in which the onset of dim background enhances the center flicker response of horizontal cells. The underlying mechanism for the feedback is still unclear but competing hypotheses have been proposed. One is the GABA hypothesis, which states that the feedback is mediated by gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter released from horizontal cells. Another is the ephaptic hypothesis, which contends that the feedback is non-GABAergic and is achieved through the modulation of electrical potential in the intersynaptic cleft between cones and horizontal cells. In this study, a continuum spine model of the cone-horizontal cell synaptic circuitry is formulated. This model, a partial differential equation system, incorporates both the GABA and ephaptic feedback mechanisms. Simulation results, in comparison with experiments, indicate that the ephaptic mechanism is necessary in order for the model to capture the major spatial and temporal dynamics of the BIFE effect. In addition, simulations indicate that the GABA mechanism may play some minor modulation role.
ContributorsChang, Shaojie (Author) / Baer, Steven M. (Thesis advisor) / Gardner, Carl L (Thesis advisor) / Crook, Sharon M (Committee member) / Kuang, Yang (Committee member) / Ringhofer, Christian (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

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
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
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Description
Third-party mixers are used to heighten the anonymity of Bitcoin users. The mixing techniques implemented by these tools are often untraceable on the blockchain, making them appealing to money launderers. This research aims to analyze mixers currently available on the deep web. In addition, an in-depth case study is done

Third-party mixers are used to heighten the anonymity of Bitcoin users. The mixing techniques implemented by these tools are often untraceable on the blockchain, making them appealing to money launderers. This research aims to analyze mixers currently available on the deep web. In addition, an in-depth case study is done on an open-source bitcoin mixer known as Penguin Mixer. A local version of Penguin Mixer was used to visualize mixer behavior under specific scenarios. This study could lead to the identification of vulnerabilities in mixing tools and detection of these tools on the blockchain.
ContributorsPakki, Jaswant (Author) / Doupe, Adam (Thesis director) / Shoshitaishvili, Yan (Committee member) / Computer Science and Engineering Program (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2018-12
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Description
Ethereum smart contracts are susceptible not only to those vulnerabilities common to all software development domains, but also to those arising from the peculiar execution model of the Ethereum Virtual Machine. One of these vulnerabilities, a susceptibility to re-entrancy attacks, has been at the center of several high-profile contract exploits.

Ethereum smart contracts are susceptible not only to those vulnerabilities common to all software development domains, but also to those arising from the peculiar execution model of the Ethereum Virtual Machine. One of these vulnerabilities, a susceptibility to re-entrancy attacks, has been at the center of several high-profile contract exploits. Currently, there exist many tools to detect these vulnerabilties, as well as languages which preempt the creation of contracts exhibiting these issues, but no mechanism to address them in an automated fashion. One possible approach to filling this gap is direct patching of source files. The process of applying these patches to contracts written in Solidity, the primary Ethereum contract language, is discussed. Toward this end, a survey of deployed contracts is conducted, focusing on prevalence of language features and compiler versions. A heuristic approach to mitigating a particular class of re-entrancy vulnerability is developed, implemented as the SolPatch tool, and examined with respect to its limitations. As a proof of concept and illustrative example, a simplified version of the contract featured in a high-profile exploit is patched in this manner.
ContributorsLehman, Maxfield Chance Christian (Author) / Bazzi, Rida (Thesis director) / Doupe, Adam (Committee member) / School of Mathematical and Statistical Sciences (Contributor) / Computer Science and Engineering Program (Contributor) / Barrett, The Honors College (Contributor)
Created2018-12