Matching Items (190)
Description
With the increasing focus on developing environmentally benign electronic packages, lead-free solder alloys have received a great deal of attention. Mishandling of packages, during manufacture, assembly, or by the user may cause failure of solder joint. A fundamental understanding of the behavior of lead-free solders under mechanical shock conditions is lacking. Reliable experimental and numerical analysis of lead-free solder joints in the intermediate strain rate regime need to be investigated. This dissertation mainly focuses on exploring the mechanical shock behavior of lead-free tin-rich solder alloys via multiscale modeling and numerical simulations. First, the macroscopic stress/strain behaviors of three bulk lead-free tin-rich solders were tested over a range of strain rates from 0.001/s to 30/s. Finite element analysis was conducted to determine appropriate specimen geometry that could reach a homogeneous stress/strain field and a relatively high strain rate. A novel self-consistent true stress correction method is developed to compensate the inaccuracy caused by the triaxial stress state at the post-necking stage. Then the material property of micron-scale intermetallic was examined by micro-compression test. The accuracy of this measure is systematically validated by finite element analysis, and empirical adjustments are provided. Moreover, the interfacial property of the solder/intermetallic interface is investigated, and a continuum traction-separation law of this interface is developed from an atomistic-based cohesive element method. The macroscopic stress/strain relation and microstructural properties are combined together to form a multiscale material behavior via a stochastic approach for both solder and intermetallic. As a result, solder is modeled by porous plasticity with random voids, and intermetallic is characterized as brittle material with random vulnerable region. Thereafter, the porous plasticity fracture of the solders and the brittle fracture of the intermetallics are coupled together in one finite element model. Finally, this study yields a multiscale model to understand and predict the mechanical shock behavior of lead-free tin-rich solder joints. Different fracture patterns are observed for various strain rates and/or intermetallic thicknesses. The predictions have a good agreement with the theory and experiments.
ContributorsFei, Huiyang (Author) / Jiang, Hanqing (Thesis advisor) / Chawla, Nikhilesh (Thesis advisor) / Tasooji, Amaneh (Committee member) / Mobasher, Barzin (Committee member) / Rajan, Subramaniam D. (Committee member) / Arizona State University (Publisher)
Created2011
Description
The Kasturba Gandhi Balika Vidyalaya (KGBV) policy scheme launched in 2004 by the Ministry of Human Resource Development, the Government of India, aims to provide secondary level education (grade 6-8) for girls residing predominantly in minority communities, the Scheduled Caste (SC), the Scheduled Tribe (ST), and the Other Backward Caste (OBC). Since its launch, the Government of India established 2,578 KGBV schools in 27 states and union territories (UTs). The present study examines the new policy and its implementation at three KGBV schools located in rural villages of Uttar Pradesh (UP), India. The purpose was to analyze the Government of India's approach to increasing education opportunity and participation for educationally disadvantaged girls using the empowerment framework developed by Deepa Narayan. Observations at three schools, interviews with teachers and staff members of the implementation agency (i.e., Mahila Samakhya (MS)), and surveys administered to 139 teachers were conducted over a four month period in 2009. Adopting creative teaching approaches and learning activities, MS creates safe learning community which is appropriate for the rural girls. MS gives special attention to nurturing the girls' potential and empowering them inside and outside the school environment through social discussion, parental involvement, rigid discipline and structure, health and hygiene education, and physical and mental training. Interviews with the state program director and coordinators identified some conflicts within government policy schemes such as the Teacher-pupil ratios guidelines as a part of the programs for the universalization of elementary education. Major challenges include a high turnover rate of teachers, a lack of female teachers, a lack of provision after Class 8, and inadequate budget for medical treatment. Recommendations include promoting active involvement of male members in the process of girls' empowerment, making MS approaches of girls' education in rural settings standardized for wider dissemination, and developing flexible and strong partnership among local agencies and government organizations for effective service delivery.
ContributorsWatanabe, Miku (Author) / Fischman, Gustavo (Thesis advisor) / Wiley, Terrence (Committee member) / Mccarty, Teresa (Committee member) / Arizona State University (Publisher)
Created2011
Description
With the advent of technologies such as web services, service oriented architecture and cloud computing, modern organizations have to deal with policies such as Firewall policies to secure the networks, XACML (eXtensible Access Control Markup Language) policies for controlling the access to critical information as well as resources. Management of these policies is an extremely important task in order to avoid unintended security leakages via illegal accesses, while maintaining proper access to services for legitimate users. Managing and maintaining access control policies manually over long period of time is an error prone task due to their inherent complex nature. Existing tools and mechanisms for policy management use different approaches for different types of policies. This research thesis represents a generic framework to provide an unified approach for policy analysis and management of different types of policies. Generic approach captures the common semantics and structure of different access control policies with the notion of policy ontology. Policy ontology representation is then utilized for effectively analyzing and managing the policies. This thesis also discusses a proof-of-concept implementation of the proposed generic framework and demonstrates how efficiently this unified approach can be used for analysis and management of different types of access control policies.
ContributorsKulkarni, Ketan (Author) / Ahn, Gail-Joon (Thesis advisor) / Yau, Stephen S. (Committee member) / Huang, Dijiang (Committee member) / Arizona State University (Publisher)
Created2011
Description
In this dissertation I present data gathered from an eleven-month qualitative research study with adolescents living and working on the streets of Lima, Peru. Through the pairing of photovoice with participant observations, this work incorporates distinctive methodological and theoretical viewpoints in order to complicate prevailing understandings of street life. In this dissertation, I examine the identities that children and adolescents on the street develop in context, and the ways in which photography can be a useful tool in understanding identity development among this population. Through a framework integrating theories of identity and identity performance with spatial theories, I outline how identity development among children and adolescents living on the street is directly connected to their relationships with the urban landscape and the outreach organizations that serve them. The organizations and institutions that surround children on the street shape who they are, how they are perceived by society, and how they view and understand themselves in context. It is through the interaction with aid organizations and the urban landscape that a street identity is learned and developed. Furthermore, as organizations, children and adolescents come together within the context of the city, a unique street space is created. I argue that identity and agency are directly tied to this space. I also present the street as a thirdspace of possibility, where children and adolescents are able to act out various aspects of the self that they would be unable to pursue otherwise. Weaved throughout this dissertation are non-traditional writing forms including narrative and critical personal narrative addressing my own experiences conducting this research, my impact on the research context, and how I understand the data gathered.
ContributorsJoanou, Jamie Patrice (Author) / Swadener, Beth B. (Thesis advisor) / Margolis, Eric (Committee member) / Arzubiaga, Angela (Committee member) / Fischman, Gustavo (Committee member) / Arizona State University (Publisher)
Created2011
Description
The Civil Rights Project estimates that Black girls are among the least likely to graduate from high school. More specifically, only about half, or 56%, of freshman Black girls graduate with their class four years later. Beyond the statistics little is known about Black girls who drop out, why they leave school and what happens to them once they are gone. This study is a grounded theory analysis of the stories eight adult Black women told about dropping out of high school with a particular focus on how dropping out affected their lives as workers, mothers and returners to education. There is one conclusion about dropping out and another about Black female identity. First, the women in my study were adolescents during the 1980s, experienced life at the intersection of Blackness, womaness, and poverty and lived in the harsh conditions of a Black American hyperghetto. Using a synthesis between intersectionality and hyperghettoization I found that the women were so determined to improve their economic and personal conditions that they took on occupations that seemed to promise freedom, wealth and safety. Because they were so focused on their new lives, their school attendance suffered as a consequence. In the second conclusion I argued that Black women draw their insights about Black female identity from two competing sources. The two sources are their lived experience and popular controlling images of Black female identity.
ContributorsGriffin, Erica Nicole (Author) / Powers, Jeanne (Thesis advisor) / Fischman, Gustavo (Committee member) / Margolis, Eric (Committee member) / Arizona State University (Publisher)
Created2011
Description
This dissertation is focused on building scalable Attribute Based Security Systems (ABSS), including efficient and privacy-preserving attribute based encryption schemes and applications to group communications and cloud computing. First of all, a Constant Ciphertext Policy Attribute Based Encryption (CCP-ABE) is proposed. Existing Attribute Based Encryption (ABE) schemes usually incur large, linearly increasing ciphertext. The proposed CCP-ABE dramatically reduces the ciphertext to small, constant size. This is the first existing ABE scheme that achieves constant ciphertext size. Also, the proposed CCP-ABE scheme is fully collusion-resistant such that users can not combine their attributes to elevate their decryption capacity. Next step, efficient ABE schemes are applied to construct optimal group communication schemes and broadcast encryption schemes. An attribute based Optimal Group Key (OGK) management scheme that attains communication-storage optimality without collusion vulnerability is presented. Then, a novel broadcast encryption model: Attribute Based Broadcast Encryption (ABBE) is introduced, which exploits the many-to-many nature of attributes to dramatically reduce the storage complexity from linear to logarithm and enable expressive attribute based access policies. The privacy issues are also considered and addressed in ABSS. Firstly, a hidden policy based ABE schemes is proposed to protect receivers' privacy by hiding the access policy. Secondly,a new concept: Gradual Identity Exposure (GIE) is introduced to address the restrictions of hidden policy based ABE schemes. GIE's approach is to reveal the receivers' information gradually by allowing ciphertext recipients to decrypt the message using their possessed attributes one-by-one. If the receiver does not possess one attribute in this procedure, the rest of attributes are still hidden. Compared to hidden-policy based solutions, GIE provides significant performance improvement in terms of reducing both computation and communication overhead. Last but not least, ABSS are incorporated into the mobile cloud computing scenarios. In the proposed secure mobile cloud data management framework, the light weight mobile devices can securely outsource expensive ABE operations and data storage to untrusted cloud service providers. The reported scheme includes two components: (1) a Cloud-Assisted Attribute-Based Encryption/Decryption (CA-ABE) scheme and (2) An Attribute-Based Data Storage (ABDS) scheme that achieves information theoretical optimality.
ContributorsZhou, Zhibin (Author) / Huang, Dijiang (Thesis advisor) / Yau, Sik-Sang (Committee member) / Ahn, Gail-Joon (Committee member) / Reisslein, Martin (Committee member) / Arizona State University (Publisher)
Created2011
Description
ABSTRACT Early childhood education (ECE) teacher professional development refers to the various modalities of providing new and or additional content knowledge to the teachers who work with children birth to five. The purpose of this study was to examine the effectiveness of an Arizona United Way-administered intervention project designed to provide focused professional development activities to 15 ECE teachers at seven high-need, center-based early care and education settings. Specifically, this study determined if these interventions influenced the teachers to undertake formative career path changes such as college coursework. In addition, the study also sought to understand the views, beliefs, and attitudes of these ECE teachers and if/how their perspectives influenced their educational career paths. Data were gathered through the triangulated use of participants' responses to a survey, face-to-face interviews, and a focus group. Findings demonstrate that the teachers understand that professional development, such as college coursework, can increase a person's knowledge on a given topic or field of study, but that they feel qualified to be a teacher for children birth to five even though 12 of the 15 teachers do not hold an AA/AAS or BA/BS degree in any area of study. Further, the teachers suggested that if they were to earn a degree it would most likely be in another field of study beside education. These responses provide another reason professional development efforts to encourage ECE teachers to seek degrees in the field of education may be failing. If ECE teachers wanted to invest time, energy and funds they would acquire a degree, which provided more financial reward and professional respect.
ContributorsOrtiz, Karen J. (Karen Jean) (Author) / Kelley, Michael F. (Thesis advisor) / Enz, Billie J. (Thesis advisor) / Romero, Mary (Committee member) / Fischman, Gustavo (Committee member) / Arizona State University (Publisher)
Created2011
Description
Early-age cracks in fresh concrete occur mainly due to high rate of surface evaporation and restraint offered by the contracting solid phase. Available test methods that simulate severe drying conditions, however, were not originally designed to focus on evaporation and transport characteristics of the liquid-gas phases in a hydrating cementitious microstructure. Therefore, these tests lack accurate measurement of the drying rate and data interpretation based on the principles of transport properties is limited. A vacuum-based test method capable of simulating early-age cracks in 2-D cement paste is developed which continuously monitors the weight loss and changes to the surface characteristics. 2-D crack evolution is documented using time-lapse photography. Effects of sample size, w/c ratio, initial curing and fiber content are studied. In the subsequent analysis, the cement paste phase is considered as a porous medium and moisture transport is described based on surface mass transfer and internal moisture transport characteristics. Results indicate that drying occurs in two stages: constant drying rate period (stage I), followed by a falling drying rate period (stage II). Vapor diffusion in stage I and unsaturated flow within porous medium in stage II determine the overall rate of evaporation. The mass loss results are analyzed using diffusion-based models. Results show that moisture diffusivity in stage I is higher than its value in stage II by more than one order of magnitude. The drying model is used in conjunction with a shrinkage model to predict the development of capillary pressures. Similar approach is implemented in drying restrained ring specimens to predict 1-D crack width development. An analytical approach relates diffusion, shrinkage, creep, tensile and fracture properties to interpret the experimental data. Evaporation potential is introduced based on the boundary layer concept, mass transfer, and a driving force consisting of the concentration gradient. Effect of wind velocity is reflected on Reynolds number which affects the boundary layer on sample surface. This parameter along with Schmidt and Sherwood numbers are used for prediction of mass transfer coefficient. Concentration gradient is shown to be a strong function of temperature and relative humidity and used to predict the evaporation potential. Results of modeling efforts are compared with a variety of test results reported in the literature. Diffusivity data and results of 1-D and 2-D image analyses indicate significant effects of fibers on controlling early-age cracks. Presented models are capable of predicting evaporation rates and moisture flow through hydrating cement-based materials during early-age drying and shrinkage conditions.
ContributorsBakhshi, Mehdi (Author) / Mobasher, Barzin (Thesis advisor) / Rajan, Subramaniam D. (Committee member) / Zapata, Claudia E. (Committee member) / Arizona State University (Publisher)
Created2011
Description
This dissertation examines Japanese preschool teachers' cultural practices and beliefs about the pedagogy of social-emotional development. The study is an interview-based, ethnographic study, which is based on the video-cued mutivocal ethnographic method. This study focuses on the emic terms that Japanese preschool teachers use to explain their practices, such as amae (dependency), omoiyari (empathy), sabishii (loneliness), mimamoru (watching and waiting) and garari (peripheral participation). My analysis suggests that sabishii, amae, and omoiyari form a triad of emotional exchange that has a particular cultural patterning and salience in Japan and in the Japanese approach to the socialization of emotions in early childhood. Japanese teachers think about the development of the class as a community, which is different from individual-centric Western pedagogical perspective that gives more attention to each child's development. Mimamoru is a pedagogical philosophy and practice in Japanese early childhood education. A key component of Japanese teachers' cultural practices and beliefs about the pedagogy of social-emotional development is that the process requires the development not only of children as individuals, but also of children in a preschool class as a community. In addition, the study suggests that at a deeper level these emic concepts reflect more general Japanese cultural notions of time, space, sight, and body. This dissertation concludes with the argument that teachers' implicit cultural practices and beliefs is "A cultural art of teaching." Teachers' implicit cultural practices and beliefs are harmonized in the teachers' mind and body, making connections between them, and used depending on the nuances of a situation, as informed by teachers' conscious and unconscious thoughts. The study has also shown evidence of similar practices and logic vertically distributed within Japanese early childhood education, from the way teachers act with children, to the way directors act with teachers, to the way government ministries act with directors, to the way deaf and hearing educators act with their deaf and hearing students. Because these practices are forms of bodily habitus and implicit Japanese culture, it makes sense that they are found across fields of action.
ContributorsHayashi, Akiko (Author) / Tobin, Joseph (Thesis advisor) / Eisenberg, Nancy (Committee member) / Nakagawa, Kathryn (Committee member) / Fischman, Gustavo (Committee member) / Swadener, Elizabeth (Committee member) / Arizona State University (Publisher)
Created2011
Description
Action language C+ is a formalism for describing properties of actions, which is based on nonmonotonic causal logic. The definite fragment of C+ is implemented in the Causal Calculator (CCalc), which is based on the reduction of nonmonotonic causal logic to propositional logic. This thesis describes the language of CCalc in terms of answer set programming (ASP), based on the translation of nonmonotonic causal logic to formulas under the stable model semantics. I designed a standard library which describes the constructs of the input language of CCalc in terms of ASP, allowing a simple modular method to represent CCalc input programs in the language of ASP. Using the combination of system F2LP and answer set solvers, this method achieves functionality close to that of CCalc while taking advantage of answer set solvers to yield efficient computation that is orders of magnitude faster than CCalc for many benchmark examples. In support of this, I created an automated translation system Cplus2ASP that implements the translation and encoding method and automatically invokes the necessary software to solve the translated input programs.
ContributorsCasolary, Michael (Author) / Lee, Joohyung (Thesis advisor) / Ahn, Gail-Joon (Committee member) / Baral, Chitta (Committee member) / Arizona State University (Publisher)
Created2011