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- All Subjects: Mechanical Engineering
- Creators: Arizona State University
Description
Special thermal interface materials are required for connecting devices that operate at high temperatures up to 300°C. Because devices used in power electronics, such as GaN, SiC, and other wide bandgap semiconductors, can reach very high temperatures (beyond 250°C), a high melting point, and high thermal & electrical conductivity are required for the thermal interface material. Traditional solder materials for packaging cannot be used for these applications as they do not meet these requirements. Sintered nano-silver is a good candidate on account of its high thermal and electrical conductivity and very high melting point. The high temperature operating conditions of these devices lead to very high thermomechanical stresses that can adversely affect performance and also lead to failure. A number of these devices are mission critical and, therefore, there is a need for very high reliability. Thus, computational and nondestructive techniques and design methodology are needed to determine, characterize, and design the packages. Actual thermal cycling tests can be very expensive and time consuming. It is difficult to build test vehicles in the lab that are very close to the production level quality and therefore making comparisons or making predictions becomes a very difficult exercise. Virtual testing using a Finite Element Analysis (FEA) technique can serve as a good alternative. In this project, finite element analysis is carried out to help achieve this objective. A baseline linear FEA is performed to determine the nature and magnitude of stresses and strains that occur during the sintering step. A nonlinear coupled thermal and mechanical analysis is conducted for the sintering step to study the behavior more accurately and in greater detail. Damage and fatigue analysis are carried out for multiple thermal cycling conditions. The results are compared with the actual results from a prior study. A process flow chart outlining the FEA modeling process is developed as a template for the future work. A Coffin-Manson type relationship is developed to help determine the accelerated aging conditions and predict life for different service conditions.
ContributorsAmla, Tarun (Author) / Chawla, Nikhilesh (Thesis advisor) / Jiao, Yang (Committee member) / Liu, Yongming (Committee member) / Zhuang, Houlong (Committee member) / Jiang, Hanqing (Committee member) / Arizona State University (Publisher)
Created2020
Description
Characterization and modeling of deformation and failure in metallic materials under extreme conditions, such as the high loads and strain rates found under shock loading due to explosive detonation and high velocity-impacts, are extremely important for a wide variety of military and industrial applications. When a shock wave causes stress in a material that exceeds the elastic limit, plasticity and eventually spallation occur in the material. The process of spall fracture, which in ductile materials stems from strain localization, void nucleation, growth and coalescence, can be caused by microstructural heterogeneity. The analysis of void nucleation performed from a microstructurally explicit simulation of a spall damage evolution in a multicrystalline copper indicated triple junctions as the preferred sites for incipient damage nucleation revealing 75% of them with at least two grain boundaries with misorientation angle between 20-55°. The analysis suggested the nature of the boundaries connecting at a triple junction is an indicator of their tendency to localize spall damage. The results also showed that damage propagated preferentially into one of the high angle boundaries after voids nucleate at triple junctions. Recently the Rayleigh-Taylor Instability (RTI) and the Richtmyer-Meshkov Instability (RMI) have been used to deduce dynamic material strength at very high pressures and strain rates. The RMI is used in this work since it allows using precise diagnostics such as Transient Imaging Displacement Interferometry (TIDI) due to its slower linear growth rate. The Preston-Tonks-Wallace (PTW) model is used to study the effects of dynamic strength on the behavior of samples with a fed-thru RMI, induced via direct laser drive on a perturbed surface, on stability of the shock front and the dynamic evolution of the amplitudes and velocities of the perturbation imprinted on the back (flat) surface by the perturbed shock front. Simulation results clearly showed that the amplitude of the hydrodynamic instability increases with a decrease in strength and vice versa and that the amplitude of the perturbed shock front produced by the fed-thru RMI is also affected by strength in the same way, which provides an alternative to amplitude measurements to study strength effects under dynamic conditions. Simulation results also indicate the presence of second harmonics in the surface perturbation after a certain time, which were also affected by the material strength.
ContributorsGautam, Sudrishti (Author) / Peralta, Pedro (Thesis advisor) / Oswald, Jay (Committee member) / Solanki, Kiran (Committee member) / Arizona State University (Publisher)
Created2016
Description
This study examined an adverse effect of an adolescent group intervention. Group interventions represent one of the most economical, convenient, and common solution to adolescent behavior problems, although prior findings from program evaluation studies have suggested that these groups can unexpectedly increase the externalizing behaviors that they were designed to reduce or prevent. The current study used data from a longitudinal, randomized controlled trial of the Bridges to High School / Puentes a La Secundaria Program, a multicomponent prevention program designed to reduce risk during the middle school transition, which has demonstrated positive effects across an array of outcomes. Data were collected at the beginning of 7th grade, with follow-up data collected at the end of the 7th, 8th, 9th, and 12th grade from a sample of Mexican American adolescents and their mothers. Analyses evaluated long-term effects on externalizing outcomes, trajectories of externalizing behaviors across adolescence, and potential mediators of observed effects. Results showed that the adverse effect that was originally observed based on adolescent self-report of externalizing symptoms at 1-year posttest among youth with high pretest externalizing symptoms was not maintained over time and was not reflected in changes in adolescents' trajectories of externalizing behaviors. Moreover, neither of the peer mediators that theory suggests would explain adverse effects were found to mediate the relationship between intervention status and externalizing symptoms at 1-year posttest. Finally, only beneficial effects were found on externalizing symptoms based on mother report. Together, these findings suggest that the Bridges intervention did not adversely affect adolescent problem behaviors and that future studies should use caution when interpreting unexpected adverse effects.
ContributorsWong, Jessie Jong-Chee (Author) / Gonzales, Nancy A. (Thesis advisor) / West, Stephen G. (Thesis advisor) / Chassin, Laurie (Committee member) / Dishion, Thomas (Committee member) / Arizona State University (Publisher)
Created2015
Description
Sociopolitical involvement has been previously shown to be associated with experiences of discrimination. Lesbian, gay, and bisexual (LGB) racial/ethnic minorities have faced multiple levels of discrimination from the mainstream community, racial/ethnic minority communities, and LGB communities. However, not many studies have investigated the association between intersectional forms of discrimination and sociopolitical involvement. The present study examines differences in perceptions of racism in the LGB community, sociopolitical involvement in racial/ethnic communities, and sociopolitical involvement in LGB communities among LGB racial/ethnic minorities (N = 203, MAge = 27.25). The sample included 107 (52.7%) men and 96 (47.3%) women; 41 (20.2%) lesbians, 89 (43.8%) gay men, and 73 (36.0%) bisexuals; 47 (23.2%) African Americans, 50 (24.6%) Asian Americans, 64 (31.5%) Latinos/as, and 42 (20.7%) from another race/ethnicity or mixed race. This study also looks at the association between perceptions of racism in the LGB community and sociopolitical involvement in racial/ethnic communities and/or LGB communities. Asian American participants reported perceiving higher levels of racism in the LGB community than Latino/a participants. No other differences in perceptions of racism in the LGB community were found between sexual orientation or by racial/ethnic group. No differences between racial/ethnic group or sexual orientations were found in sociopolitical involvement in racial/ethnic or LGB communities. When controlling for sexual orientation, gender, and race/ethnicity, perceptions of racism in the LGB community predicted sociopolitical involvement in racial/ethnic and LGB communities. By exploring correlates of discrimination from an intersectional perspective, this study provides a better understanding of the experiences of LGB racial/ethnic minorities.
ContributorsVanDaalen, Rachel (Author) / Santos, Carlos (Thesis advisor) / Homer, Judith (Committee member) / Tracey, Terence (Committee member) / Arizona State University (Publisher)
Created2016
Description
The prevalence of chronic illness among children in the United States is on the rise (CDC, 2014). Having a child with a chronic illness can be a substantial source of stress for a couple, including physical, emotional, and financial demands of caregiving as well as difficult decision-making regarding the child’s health (Mayo Clinic, 2015). Coping with such stressors can have a negative effect on the couple’s well-being, and, if not managed within the relationship, can lead to increased negative outcomes for both partners. Partners can, however, learn to cope with stress by engaging in the coping process together with dyadic coping (DC). Couples can engage in positive (i.e., supportive emotion-focused, supportive problem-focused, and delegated) or negative forms of DC. DC has been shown to mitigate stress for couples, while increasing reports of individual well-being (IWB) and relational well-being (RWB), but it has not been examined in the context of couples with a child with a chronic illness.
To bridge this gap, the present study examined how couples cope with general stress as well as stress associated with their child’s diagnosis of a chronic illness (CI-related stress) and whether positive DC and negative DC moderate association between stress (general stress and CI-related stress) and well-being (IWB and RWB). Consistent with hypotheses, there were significant main effects of both types of stress (general and CI-related stress) on both types of well-being (IWB and RWB). Contrary to the hypotheses that DC (positive DC and negative DC) would moderate the associations between both types of stress and both types of well-being, only one significant interaction was found between CI-related stress and negative DC on IWB. Implications of these findings are discussed.
To bridge this gap, the present study examined how couples cope with general stress as well as stress associated with their child’s diagnosis of a chronic illness (CI-related stress) and whether positive DC and negative DC moderate association between stress (general stress and CI-related stress) and well-being (IWB and RWB). Consistent with hypotheses, there were significant main effects of both types of stress (general and CI-related stress) on both types of well-being (IWB and RWB). Contrary to the hypotheses that DC (positive DC and negative DC) would moderate the associations between both types of stress and both types of well-being, only one significant interaction was found between CI-related stress and negative DC on IWB. Implications of these findings are discussed.
ContributorsJohnson, Courtney K (Author) / Randall, Ashley K. (Thesis advisor) / Robinson-Kurpius, Sharon (Committee member) / Kinnier, Richard (Committee member) / Arizona State University (Publisher)
Created2016
Description
Researchers are often interested in estimating interactions in multilevel models, but many researchers assume that the same procedures and interpretations for interactions in single-level models apply to multilevel models. However, estimating interactions in multilevel models is much more complex than in single-level models. Because uncentered (RAS) or grand mean centered (CGM) level-1 predictors in two-level models contain two sources of variability (i.e., within-cluster variability and between-cluster variability), interactions involving RAS or CGM level-1 predictors also contain more than one source of variability. In this Master’s thesis, I use simulations to demonstrate that ignoring the four sources of variability in a total level-1 interaction effect can lead to erroneous conclusions. I explain how to parse a total level-1 interaction effect into four specific interaction effects, derive equivalencies between CGM and centering within context (CWC) for this model, and describe how the interpretations of the fixed effects change under CGM and CWC. Finally, I provide an empirical example using diary data collected from working adults with chronic pain.
ContributorsMazza, Gina L (Author) / Enders, Craig K. (Thesis advisor) / Aiken, Leona S. (Thesis advisor) / West, Stephen G. (Committee member) / Arizona State University (Publisher)
Created2015
Description
Touch appears to be an important component for understanding psychological and emotional well-being, as well as the formation and maintenance of interpersonal relationships later in life. While research about touch in relation to these topics is gaining momentum, there is still little evidence on the specific effects and processes that take place when touch is negative or harmful. The current study examined how women who have experienced physical or sexual abuse perceive touch in the context of interpersonal relations and in turn, how these experiences, perceptions and attitudes are related to depressive symptoms. Taking into consideration the significance of interpersonal touch, I speculated that 1) attitudes towards touch would be more negative among women who reported physical or sexual abuse than among women who did not; 2) among women who reported past abuse, increased abuse severity would predict increased current depressive symptoms; and 3) among women who reported past abuse, current attitudes towards touch would mediate the relationship between abuse severity and depressive symptoms. As predicted, results indicated that women who reported physical or sexual abuse had less positive attitudes towards touch than women who did not report any abuse. Echoing prior research, reports of childhood and adult abuse predicted increased depressive symptoms. Finally, for women who reported childhood abuse, Discomfort with Social Touch was a significant partial mediator of depressive symptoms, whereas for women who reported adult abuse, both Desire for More Partner Touch and Discomfort with Social Touch were significant partial mediators of depressive symptoms. Results suggested that negative attitudes towards general social touch, in particular, may play a strong role in mediating depressive symptoms among women who reported abuse.
ContributorsSchellenger, Kendall Elizabeth (Author) / Burleson, Mary H. (Thesis advisor) / Roberts, Nicole A. (Committee member) / Hall, Deborah L. (Committee member) / Arizona State University (Publisher)
Created2015
Description
Previous research has indicated that certain breeds of dogs stay longer in shelters than others; however exactly how breed perception and identification influences potential adopters' decisions remains unclear. Current dog breed identification practices in animal shelters are often based upon information supplied by the relinquishing owner, or staff determination based on the dog's phenotype. However discrepancies have been found between breed identification as typically assessed by welfare agencies and the outcome of DNA analysis. In Study 1, the perceived behavioral and adoptability characteristics of a pit-bull-type dog were compared with those of a Labrador Retriever and Border Collie. How the addition of a human handler influenced those perceptions was also assessed. In Study 2, lengths of stay and perceived attractiveness of dogs that were labeled as pit bull breeds to dogs that were phenotypically similar but were labeled as another breed at an animal shelter were compared. The latter dogs were called "lookalikes." In Study 3, perceived attractiveness in video recordings of pit-bull-type dogs and lookalikes with and without breed labels were compared. Lastly, data from an animal shelter that ceased applying breed labeling on kennels was analyzed, and lengths of stay and outcomes for all dog breeds, including pit bulls, before and after the change in labeling practice were compared. In total, these findings suggest that breed labeling influences potential adopters' perceptions and decision-making. Given the inherent complexity of breed assignment based on morphology coupled with negative breed perceptions, removing breed labels is a relatively low-cost strategy that will likely improve outcomes for dogs in animal shelters.
ContributorsGunter, Lisa (Author) / Wynne, Clive D.L. (Thesis advisor) / Bimonte-Nelson, Heather A. (Committee member) / McBeath, Michael K. (Committee member) / Arizona State University (Publisher)
Created2015
Description
The broaden-and-build theory of positive emotion suggests that positive emotions should broaden thought and behavior repertoires in order to develop lasting resources. In the social domain, this means deploying a variety of affiliative strategies in order to build cooperative relationships. A functionalist perspective on positive emotion suggests that different positive emotions should have distinct effects on these affiliative mechanisms. This study elicited awe, amusement, pride or a neutral control in pairs of same sex strangers. They then completed an open-ended "getting to know you" conversation, which were recorded and coded for affiliative behaviors—smiling, laughter, mimicry, and asking questions. After, they rated their perception of the other as complex and how much they liked each other. Then they played the prisoner's dilemma game. Results indicate that there was a significant mediated effect such that being in the pride condition predicted greater smiling, and smiling predicted cooperation on the prisoner's dilemma. This was true both when an individual's own smiling was predicting their cooperative behavior and when their partner's smiling was predicting their cooperative behavior. However, these effects were only seen in female dyads, not male dyads. There was also a significant mediated effect such that pride led women to ask more questions, which led partners to like each other more. Additionally, awe led to greater mimicry in men, which in turn led to greater cooperation. In women, awe led to greater perception of the other as complex. Overall, these results indicate that there are broaden and build effects of positive emotions, but these are specific to both the emotion and the sex of the interaction members. This is also the first study to demonstrate both an actor and a partner effect of smiling on cooperation in a prisoner’s dilemma. An important area for further inquiry will be the interaction of emotion and sex in predicting social behavior. While sex differences in responding to threats have been characterized by the “tend and befriend” versus “fight or flight” action patterns, a similar approach may also need to be developed for sex differences in response to opportunities.
ContributorsDanvers, Alexander (Author) / Shiota, Michelle N. (Thesis advisor) / Neuberg, Steven L. (Committee member) / Kwan, Virginia S.Y. (Committee member) / Arizona State University (Publisher)
Created2015
Description
This thesis considers two problems in the control of robotic swarms. Firstly, it addresses a trajectory planning and task allocation problem for a swarm of resource-constrained robots that cannot localize or communicate with each other and that exhibit stochasticity in their motion and task switching policies. We model the population dynamics of the robotic swarm as a set of advection-diffusion- reaction (ADR) partial differential equations (PDEs).
Specifically, we consider a linear parabolic PDE model that is bilinear in the robots' velocity and task-switching rates. These parameters constitute a set of time-dependent control variables that can be optimized and transmitted to the robots prior to their deployment or broadcasted in real time. The planning and allocation problem can then be formulated as a PDE-constrained optimization problem, which we solve using techniques from optimal control. Simulations of a commercial pollination scenario validate the ability of our control approach to drive a robotic swarm to achieve predefined spatial distributions of activity over a closed domain, which may contain obstacles. Secondly, we consider a mapping problem wherein a robotic swarm is deployed over a closed domain and it is necessary to reconstruct the unknown spatial distribution of a feature of interest. The ADR-based primitives result in a coefficient identification problem for the corresponding system of PDEs. To deal with the inherent ill-posedness of the problem, we frame it as an optimization problem. We validate our approach through simulations and show that reconstruction of the spatially-dependent coefficient can be achieved with considerable accuracy using temporal information alone.
Specifically, we consider a linear parabolic PDE model that is bilinear in the robots' velocity and task-switching rates. These parameters constitute a set of time-dependent control variables that can be optimized and transmitted to the robots prior to their deployment or broadcasted in real time. The planning and allocation problem can then be formulated as a PDE-constrained optimization problem, which we solve using techniques from optimal control. Simulations of a commercial pollination scenario validate the ability of our control approach to drive a robotic swarm to achieve predefined spatial distributions of activity over a closed domain, which may contain obstacles. Secondly, we consider a mapping problem wherein a robotic swarm is deployed over a closed domain and it is necessary to reconstruct the unknown spatial distribution of a feature of interest. The ADR-based primitives result in a coefficient identification problem for the corresponding system of PDEs. To deal with the inherent ill-posedness of the problem, we frame it as an optimization problem. We validate our approach through simulations and show that reconstruction of the spatially-dependent coefficient can be achieved with considerable accuracy using temporal information alone.
ContributorsElamvazhuthi, Karthik (Author) / Berman, Spring Melody (Thesis advisor) / Peet, Matthew Monnig (Committee member) / Mittelmann, Hans (Committee member) / Arizona State University (Publisher)
Created2014