Matching Items (1,210)
Filtering by
- All Subjects: Electrical Engineering
Description
Dual language use is thought to afford certain cognitive advantages to bilingual children and may function as an additional resource to help low-income Mexican-American children achieve academically. Emotion regulation and executive functioning (e.g., inhibition) have been found to be particularly important in studies investigating pathways to early academic achievement. Understanding how we can capitalize on children’s bilingual abilities to strengthen their executive functioning and emotion regulation, or to offset problems in these domains, may be important to promote better educational outcomes and inform policy. Thus, the current study investigated the relation between emerging bilingualism, inhibition, emotion regulation, and academic achievement across early childhood in sample of 322 low-income, Mexican-American children. Data were collected in a laboratory space at child ages 36-, 54-, and 72-months. Bilingualism was indexed as the interaction of Spanish and English vocabulary, and a mediated moderation model was examined. Results provided further evidence that inhibition positively predicts academic achievement during early childhood. Greater Spanish language vocabulary indirectly predicted academic achievement while controlling for English language vocabulary, suggesting that children from immigrant families may benefit from maintaining their Spanish language abilities as they begin to immerse themselves in an English-speaking classroom. Advancing our understanding of the development of self-regulatory abilities within bilingual, immigrant populations could have significant implications for educational policy.
ContributorsWinstone, Laura K (Author) / Crnic, Keith (Thesis advisor) / Gonzales, Nancy (Committee member) / Benitez, Viridiana (Committee member) / Arizona State University (Publisher)
Created2018
Description
Digital signal processing accelerator architectures are designed to provide either high-energy efficiency or high programmability depending on the targeted application and use case. For example, Domain Adaptive Processor (DAP), a highly reconfigurable array architecture, designed by University of Michigan, for signal processing workloads is highly energy efficient but difficult to program. DAP consists of 8x8 array of Processing elements (PE) with each PE containing four heterogeneous SUB-PEs. Each SUB-PE has its own instruction memory and is capable of executing Very Large Instruction Word (VLIW) instructions. Unfortunately, instructions have to be written for every cycle of computation for each SUB-PE used in the application and handcrafted such that all the inter-PE dependencies are synchronized. This thesis builds up on prior work at Arizona State University(ASU) to make DAP more programmable. First, the compiler back-end developed at ASU is extended with more features. Prior work introduced DAP Instruction Set Architecture (ISA), an assembly instruction format, and proposed a compiler framework, called DAP Assembler, with optimization passes to reduce the complexity of programming applications in DAP. While this back-end infrastructure helped generated code with relative ease compared to Very Large Instruction Word (VLIW) code by hand, the output of the code generated was not software-pipelined and the code generated for each Processing Element(PE) had to be manually synchronized. So in this thesis, DAP Assembler tool is extended to support software-pipelining for high throughput applications. Further, a generic synchronization tool is proposed to synchronize instructions in a multi-PE setup and integrated with DAP Assembler to generate synchronized high-throughput application code. Second, a Multi-Level Intermediate Representation(MLIR) based compiler front-end infrastructure is proposed to first lower the application code written by the programmer to an Intermediate Representation (IR) that is suitable for generic array architectures and then further converted to DAP-specific IR that can be used for generating machine code for DAP using DAP ISA. This two stage process enables this infrastructure to be more easily adapted to other array architectures. The first conversion pass uses a designer-provided modular hardware architecture information, called Resource Registry, to allocate operations in the input IR to resources in the Resource registry and capture all data movement. While the resource registry changes from architecture to architecture, the conversion pass algorithm is generic and can be used for other architectures. The second conversion pass is more geared towards DAP and integrates DAP specific constructs to generate optimized instruction in DAP ISA. Multiple kernels such as matrix multiplication, vector-vector addition were implemented using this infrastructure and the code generated by the tool verified to be functionally correct.
ContributorsMurugan, Narayanan (Author) / Chakrabarti, Chaitali Dr (Thesis advisor) / Akoglu, Ali Dr (Committee member) / Bliss, Daniel Dr (Committee member) / Arizona State University (Publisher)
Created2023
Description
Kuwait is committed to implementing the Kyoto Protocol in “Vision 2035” to reduce greenhouse gas emissions by shifting to the use of wind and solar energies [1]. The specific goal of the Vision 2035 is for renewables to comprise 15% of Kuwait’s electrical generation by 2030. Wind and solar are abundant in Kuwait and can easily provide 15% of the total electrical generation. However, there are three significant obstacles. The first is Kuwait currently depends heavily on rapidly diminishing fossil fuels which are the major sources of CO2, NOx, and SOx emissions. Unfortunately, current plans are to build two conventional power stations by 2024. The purpose is to cover the energy needs for growing population. The second problem is that Kuwait has a very small land area. Consequently, there is limited space to build new utility-scale renewable power stations. The third issue is the low electricity tariff provides little incentive for the population to save energy. Offshore wind farms have the potential to provide thousands of GWh/yr to accomplish the goals of Vision 2035. Kuwait has a vast untapped supply of offshore wind energy. Specifically, there are eight offshore locations in which 50 turbines could be built each, for a total of 400 turbines. Using 4.2 MW turbines, this would provide 1.68 GW of wind energy, and increase the renewable portion of the electrical energy production to 13.93% (including Shagaya renewable park). Installing battery storage with the proposed wind turbines could provide fast ramp response which would serve to complement existing power production on Kuwait’s grid. In this work, six different turbines with different sizes are considered from 2.5 MW to 4.2 MW (from well-known manufacturers, such as, Nordex and Vestas), but ultimately 4.2 MW turbines are recommended. Data for this study has been supplied by: A) Civil Aviation -- temperature and wind speed, B) Ministry of Electricity and Water (MEW) -- electricity data, and C) Public Authority for Civil Information -- population data.
ContributorsAlotaibi, Abdullah Saqer (Author) / Calhoun, Ronald (Thesis advisor) / Kitchen, Jennifer (Thesis advisor) / Roedel, Ronald (Committee member) / Mayyas, Abdul Ra'ouf (Committee member) / Arizona State University (Publisher)
Created2020
Description
In this dissertation, I investigate the electronic properties of two important silicon(Si)-based heterojunctions 1) hydrogenated amorphous silicon/crystalline silicon (a-Si:H/c-Si) which has already been commercialized in Heterojunction with Intrinsic Thin-layer (HIT) cells and 2) gallium phosphide/silicon (GaP/Si) which has been suggested to be a good candidate for replacing a-Si:H/c-Si in HIT cells in order to boost the HIT cell’s efficiency.
In the first part, the defect states of amorphous silicon (a-Si) and a-Si:H material are studied using density functional theory (DFT). I first employ simulated annealing using molecular dynamics (MD) to create stable configurations of a-Si:H, and then analyze the atomic and electronic structure to investigate which structural defects interact with H, and how the electronic structure changes with H addition. I find that H atoms decrease the density of mid-gap states and increase the band gap of a-Si by binding to Si atoms with strained bonds. My results also indicate that Si atoms with strained bonds creates high-localized orbitals in the mobility gap of a-Si, and the binding of H atoms to them can dramatically decrease their degree of localization.
In the second part, I explore the effect of the H binding configuration on the electronic properties of a-Si:H/c-Si heterostructure using density functional theory studies of models of the interface between a-Si:H and c-Si. The electronic properties from DFT show that depending on the energy difference between configurations, the electronic properties are sensitive to the H binding configurations.
In the last part, I examine the electronic structure of GaP/Si(001) heterojunctions and the effect of hydrogen H passivation at the interface in comparison to interface mixing, through DFT calculations. My calculations show that due to the heterovalent mismatch nature of the GaP/Si interface, there is a high density of localized states at the abrupt GaP/Si interface due to the excess charge associated with heterovalent bonding, as reported elsewhere. I find that the addition of H leads to additional bonding at the interface which mitigates the charge imbalance, and greatly reduces the density of localized states, leading to a nearly ideal heterojunction.
In the first part, the defect states of amorphous silicon (a-Si) and a-Si:H material are studied using density functional theory (DFT). I first employ simulated annealing using molecular dynamics (MD) to create stable configurations of a-Si:H, and then analyze the atomic and electronic structure to investigate which structural defects interact with H, and how the electronic structure changes with H addition. I find that H atoms decrease the density of mid-gap states and increase the band gap of a-Si by binding to Si atoms with strained bonds. My results also indicate that Si atoms with strained bonds creates high-localized orbitals in the mobility gap of a-Si, and the binding of H atoms to them can dramatically decrease their degree of localization.
In the second part, I explore the effect of the H binding configuration on the electronic properties of a-Si:H/c-Si heterostructure using density functional theory studies of models of the interface between a-Si:H and c-Si. The electronic properties from DFT show that depending on the energy difference between configurations, the electronic properties are sensitive to the H binding configurations.
In the last part, I examine the electronic structure of GaP/Si(001) heterojunctions and the effect of hydrogen H passivation at the interface in comparison to interface mixing, through DFT calculations. My calculations show that due to the heterovalent mismatch nature of the GaP/Si interface, there is a high density of localized states at the abrupt GaP/Si interface due to the excess charge associated with heterovalent bonding, as reported elsewhere. I find that the addition of H leads to additional bonding at the interface which mitigates the charge imbalance, and greatly reduces the density of localized states, leading to a nearly ideal heterojunction.
ContributorsVatan Meidanshahi, Reza (Author) / Goodnick, Stephen Marshall (Thesis advisor) / Vasileska, Dragica (Committee member) / Bowden, Stuart (Committee member) / Honsberg, Christiana (Committee member) / Arizona State University (Publisher)
Created2019
Description
Over the past few years, research into the use of doped diamond in electronics has seen an exponential growth. In the course of finding ways to reduce the contact resistivity, nanocarbon materials have been an interesting focus. In this work, the transfer length method (TLM) was used to investigate Ohmic contact properties using the tri-layer stack Ti/Pt/Au on nitrogen-doped n-type conducting nano-carbon (nanoC) layers grown on (100) diamond substrates. The nanocarbon material was characterized using Secondary Ion Mass Spectrometry (SIMS), Scanning electron Microscopy (SEM) X-ray diffraction (XRD), Raman scattering and Hall effect measurements to probe the materials characteristics. Room temperature electrical measurements were taken, and samples were annealed to observe changes in electrical conductivity. Low specific contact resistivity values of 8 x 10^-5 Ωcm^2 were achieved, which was almost two orders of magnitude lower than previously reported values. The results were attributed to the increased nitrogen incorporation, and the presence of electrically active defects which leads to an increase in conduction in the nanocarbon. Further a study of light phosphorus doped layers using similar methods with Ti/Pt/Au contacts again yielded a low contact resistivity of about 9.88 x 10^-2 Ωcm^2 which is an interesting prospect among lightly doped diamond films for applications in devices such as transistors. In addition, for the first time, hafnium was substituted for Ti in the contact stack (Hf/Pt/Au) and studied on nitrogen doped nanocarbon films, which resulted in low contact resistivity values on the order of 10^-2 Ωcm^2. The implications of the results were discussed, and recommendations for improving the experimental process was outlined. Lastly, a method for the selective area growth of nanocarbon was developed and studied and the results provided an insight into how different characterizations can be used to confirm the presence of the nanocrystalline diamond material, the limitations due to the film thickness was explored and ideas for future work was proposed.
ContributorsAmonoo, Evangeline Abena (Author) / Thornton, Trevor (Thesis advisor) / Alford, Terry L (Thesis advisor) / Anwar, Shahriar (Committee member) / Theodore, David (Committee member) / Arizona State University (Publisher)
Created2023
Description
Scaling of the Metal-Oxide-Semiconductor Field Effect Transistor (MOSFET) towards shorter channel lengths, has lead to an increasing importance of quantum effects on the device performance. Until now, a semi-classical model based on Monte Carlo method for instance, has been sufficient to address these issues in silicon, and arrive at a reasonably good fit to experimental mobility data. But as the semiconductor world moves towards 10nm technology, many of the basic assumptions in this method, namely the very fundamental Fermi’s golden rule come into question. The derivation of the Fermi’s golden rule assumes that the scattering is infrequent (therefore the long time limit) and the collision duration time is zero. This thesis overcomes some of the limitations of the above approach by successfully developing a quantum mechanical simulator that can model the low-field inversion layer mobility in silicon MOS capacitors and other inversion layers as well. It solves for the scattering induced collisional broadening of the states by accounting for the various scattering mechanisms present in silicon through the non-equilibrium based near-equilibrium Green’s Functions approach, which shall be referred to as near-equilibrium Green’s Function (nEGF) in this work. It adopts a two-loop approach, where the outer loop solves for the self-consistency between the potential and the subband sheet charge density by solving the Poisson and the Schrödinger equations self-consistently. The inner loop solves for the nEGF (renormalization of the spectrum and the broadening of the states), self-consistently using the self-consistent Born approximation, which is then used to compute the mobility using the Green-Kubo Formalism.
ContributorsJayaram Thulasingam, Gokula Kannan (Author) / Vasileska, Dragica (Thesis advisor) / Ferry, David (Committee member) / Goodnick, Stephen (Committee member) / Allee, David (Committee member) / Arizona State University (Publisher)
Created2017
Description
Mexicans and Mexican Americans have resided in Arizona since the early 16th century. Their history, however, is severely under-documented in the state’s archival repositories. As of 2012, this community is represented in a mere 1-2% of the state’s known archival holdings, and 98% of such documentation is held at Arizona State University’s Chicano/a Research Collection (CRC). This article provides a historical review of the CRC’s establishment in 1970 and how its founding Curator, Dr. Christine Marín, transformed a small circulating book collection into Arizona’s largest repository for Mexican American history. It goes on to examine how the CRC’s sitting Archivist is using social media in tandem with a community-based workshop, bilingual promotional materials and finding aids, and description of unprocessed collections as community outreach and collection development tools in order to remedy the under-documentation of Mexican American history in Arizona. We argue that augmenting traditional archival field collecting methods with these strategies enables the CRC to build a more robust relationship with Arizona’s Mexican American community, allows us to continue expanding our archival holdings, and serves as an example for other repositories seeking to enhance their documentation of marginalized communities.
ContributorsGodoy-Powell, Nancy L. (Author) / Dunham, Elizabeth G. (Author)
Created2017-01-27
Description
An efficient thermal solver is available in the CMC that allows modeling self-heating in the electrical simulations, which treats phonons as flux and solves the energy balance equation to quantify thermal effects. Using this solver, thermal simulations were performed on GaN-HEMTs in order to test effect of gate architectures on the DC and RF performance of the device. A Π- gate geometry is found to suppress 19.75% more hot electrons corresponding to a DC power of 2.493 W/mm for Vgs = -0.6V (max transconductance) with respect to the initial T-gate. For the DC performance, the output current, Ids is nearly same for each device configuration over the entire bias range. For the RF performance, the current gain was evaluated over a frequency range 20 GHz to 120 GHz in each device for both thermal (including self-heating) and isothermal (without self-heating). The evaluated cutoff frequency is around 7% lower for the thermal case than the isothermal case. The simulated cutoff frequency closely follows the experimental cutoff frequency. The work was extended to the study of ultra-wide bandgap material (Diamond), where isotope effect causes major deterioration in thermal conductivity. In this case, bulk phonons are modeled as semiclassical particles solving the nonlinear Peierls - Boltzmann transport equation with a stochastic approach. Simulations were performed for 0.001% (ultra-pure), 0.1% and 1.07% isotope concentration (13C) of diamond, showing good agreement with the experimental values. Further investigation was performed on the effect of isotope on the dynamics of individual phonon branches, thermal conductivity and the mean free path, to identify the dominant phonon branch. Acoustic phonons are found to be the principal contributors to thermal conductivity across all isotope concentrations with transverse acoustic (TA2) branch is the dominant branch with a contribution of 40% at room temperature and 37% at 500K. Mean free path computations show the lower bound of device dimensions in order to obtain maximum thermal conductivity. At 300K, the lowest mean free path (which is attributed to Longitudinal Optical phonon) reduces from 24nm to 8 nm for isotope concentration of 0.001% and 1.07% respectively. Similarly, the maximum mean free path (which is attributed to Longitudinal Acoustic phonon) reduces from 4 µm to 3.1 µm, respectively, for the same isotope concentrations. Furthermore, PETSc (Portable, Extensible Toolkit for Scientific Computation) developed by Argonne National Lab, was included in the existing Cellular Monte Carlo device simulator as a Poisson solver to further extend the capability of the simulator. The validity of the solver was tested performing 2D and 3D simulations and the results were compared with the well-established multigrid Poisson solver.
ContributorsAcharjee, Joy (Author) / Saraniti, Marco (Thesis advisor) / Goodnick, Stephen (Committee member) / Thornton, Trevor (Committee member) / Wang, Robert (Committee member) / Arizona State University (Publisher)
Created2024
Description
Recent advancements in communication standards, such as 5G demand transmitter hardware to support high data rates with high energy efficiency. With the revolution of communication standards, modulation schemes have become more complex and require high peak-to-average (PAPR) signals. In wireless transceiver hardware, the power amplifier (PA) consumes most of the transceiver’s DC power and is typically the bottleneck for transmitter linearity. Therefore, the transmitter’s performance directly depends on the PA. To support high PAPR signals, the PA must operate efficiently at its saturated and backoff output power. Maintaining high efficiency at both peak and backoff output power is challenging. One effective technique for addressing this problem is load modulation. Some of the prominent load-modulated PA architectures are outphasing PAs, load-modulated balanced amplifiers (LMBA), envelope elimination and restoration (EER), envelope tracking (ET), Doherty power amplifiers (DPA), and polar transmitters. Amongst them, the DPA is the most popular for infrastructure applications due to its simpler architecture compared to other techniques and linearizability with digital pre-distortion (DPD). Another crucial characteristic of progressing communication standards is wide signal bandwidths. High-efficiency power amplifiers like class J/F/F-1 and load-modulated PAs like the DPA exhibit narrowband performance because the amplifiers require precise output impedance terminations. Therefore, it is equally essential to develop adaptable PA solutions to process radio frequency (RF) signals with wide bandwidths. To support modern and future cellular infrastructure, RF PAs need to be innovated to increase the backoff power efficiency by two times or more and support ten times or more wider bandwidths than current state-of-the-art PAs. This work presents five RF PA analyses and implementations to support future wireless communications transmitter hardware. Chapter 2 presents an optimized output-matching network analysis and design to achieve extended output power backoff of the DPA. Chapters 3 and 4 unveil two bandwidth enhancement techniques for the DPA while maintaining extended output power backoff. Chapter 5 exhibits a dual-band hybrid mode PA design targeted for wideband applications. Chapter 6 presents a built-in self-test circuit integrated into a PA for output impedance monitoring. This can alleviate the PA performance degradation due to the variation in the PA's output load over frequency, process, and aging. All RF PAs in this dissertation are implemented using Gallium Nitride (GaN)-based high electron mobility transistors (HEMT), and the realized designs validate the proposed PAs' theories/architectures.
ContributorsRoychowdhury, Debatrayee (Author) / Kitchen, Jennifer (Thesis advisor) / Bakkaloglu, Bertan (Committee member) / Ozev, Sule (Committee member) / Aberle, James (Committee member) / Arizona State University (Publisher)
Created2024
Description
Alzheimer's disease (AD) and Alzheimer's Related Dementias (ADRD) is projected to affect 50 million people globally in the coming decades. Clinical research suggests that Mild Cognitive Impairment (MCI), a precursor to dementia, offers a critical window for lifestyle interventions to delay or prevent the progression of AD/ADRD. Previous research indicates that lifestyle changes, including increased physical exercise, reduced caloric intake, and mentally stimulating exercises, can reduce the risk of MCI. Early detection of MCI is challenging due to subtle and often unnoticed cognitive decline, traditionally monitored through infrequent clinical tests. As part of this research, the Smart Driving System was proposed, a novel, unobtrusive, and economical technology to detect early stages of neurodegenerative diseases. This system, leveraging a multi-modal biosensing array (MMS) and AI algorithms, assesses daily driving behavior, offering insights into a driver's cognitive function. The ultimate goal is to develop the Smart Driving Device and App, integrating it into vehicles, and validating its effectiveness in detecting MCI through comprehensive pilot studies. The Smart Driving System represents a breakthrough in AD/ADRD management, promising significant improvements in early detection and offering a scalable, cost-effective solution for monitoring cognitive health in real-world settings.
ContributorsSerhan, Peter (Author) / Forzani, Erica (Thesis advisor) / Wu, Teresa (Committee member) / Hihath, Joshua (Committee member) / Arizona State University (Publisher)
Created2024