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 Collection: UNT Theses and Dissertations
District Support: Strategies for Building Capacity in Elementary Principals in a Rapid Growth District

District Support: Strategies for Building Capacity in Elementary Principals in a Rapid Growth District

Date: August 2016
Creator: Jamar, Jacye
Description: The purpose of this descriptive case study was to examine the role of the central office staff and the strategies used to support capacity building in elementary principals in a rapid growth district. By synthesizing research and models from education reform scholars, the conceptual framework of professional capital, intrinsic motivation, the educational change process, and professional learning communities was generated to advance the understanding of utilizing PLCs as a foundation for central office to initiate and sustain continuous improvement in a rapid growth district. The Professional Learning Community Assessment - District Support developed by Olivier, Huffman, and Cowan was administered to 126 participants within the curriculum and instruction department and three elementary schools to collect data to analyze the five dimensions of PLCs within the school district. Eleven interviews were conducted with members of the curriculum and instruction department and elementary principals. According to the eleven interviewees, and PLCA-DS, six themes emerged to support the role of capacity building in elementary principals using the PLC model as a framework. The PLC infrastructure, supportive central office, collaborative culture, continuous improvement, differentiated opportunities to learn, and data use were the six themes generated by the participants to support continuous improvement in elementary ...
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Does Downhill Running Alter Monocyte Susceptibility to Apoptosis?

Does Downhill Running Alter Monocyte Susceptibility to Apoptosis?

Date: August 2016
Creator: Pennel, Kathryn Ann Foster
Description: Introduction/purpose: Recovery from muscle damage involves a type of programmed cell death known as apoptosis. Damage Associated Molecular Patterns (DAMPs) are released after muscle damage and may cause premature apoptosis in monocytes infiltrating the damaged site. This may alter the time course of events towards recovery. Therefore, the purpose of this study was to investigate if downhill running causes a change in the susceptibility of monocytes to apoptosis. Methods: Participants (5 male, 6 female) completed a downhill running protocol consisting of 6-5 minute bouts at a speed of 6-9mph on a -15% grade treadmill. Venous blood samples were collected immediately pre-exercise (PRE), in addition to 4 -h, 24 -h and 48 -h post-exercise. Creatine kinase (CK) was measured to give an indication of muscle damage. Monocytes were analyzed by flow cytometry for expression of multicaspase and annexin v reagent was used to detect changes in the plasma membrane. A MILLIPLEX MAP human early apoptosis magnetic bead 7-plex kit (EMD Millipore, Billerica, MA) was used to assess the relative concentration of phosphorylated protein kinase B (Akt), Bcl-2 associated death promoter (BAD), B cell lymphoma-2 (Bcl-2), active caspase-8, active caspase-9, c jun N terminal kinase (JNK) and tumor protein p53 by Luminex ...
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Effect Size Reporting and Interpreting Practices in Published Higher Education Journal Articles

Effect Size Reporting and Interpreting Practices in Published Higher Education Journal Articles

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Date: August 2016
Creator: Stafford, Mehary T.
Description: Data-driven decision making is an integral part of higher education and it needs to be rooted in strong methodological and statistical practices. Key practices include the use and interpretation of effect sizes as well as a correct understanding of null hypothesis significance testing (NHST). Therefore, effect size reporting and interpreting practices in higher education journal articles represent an important area of inquiry. This study examined effect size reporting and interpretation practices of published quantitative studies in three core higher education journals: Journal of Higher Education, Review of Higher Education, and Research in Higher Education. The review covered a three-year publication period between 2013 and 2015. Over the three-year span, a total of 249 articles were published by the three journals. The number of articles published across the three years did not vary appreciably. The majority of studies employed quantitative methods (71.1%), about a quarter of them used qualitative methods (25.7%), and the remaining 3.2% used mixed methods. Seventy-three studies were removed from further analysis because they did not feature any quantitative analyses. The remaining 176 quantitative articles represented the sample pool. Overall, 52.8% of the 176 studies in the final analysis reported effect size measures as part of their major ...
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Effective Public Service Collaboration:  The Role of Leadership and Nonprofit Organizations in Homeless Services

Effective Public Service Collaboration: The Role of Leadership and Nonprofit Organizations in Homeless Services

Date: August 2016
Creator: Valero, Jesus N
Description: This dissertation investigates factors that facilitate effective collaboration of networks functioning within the context of a federal homeless policy—the HEARTH Act of 2009. While the federal legislation encourages networked collaboration to address the incidence of homelessness, not all networks are effective in achieving their intended purpose. Using a nationwide sample of homeless networks, this research explores the role that nonprofit organizations play in the collaborative process and models the effect of individual leadership, nonprofit-led network, and community nonprofit capacity on two levels of network effectiveness—network and community—using multivariate regression modeling. Results indicate that nonprofits play a significant role as participants of the collaboration process and as leading agents of homeless networks. In addition, the variation in network effectiveness is explained by multidimensional factors.
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The Effects of Child Parent Relationship Therapy (CPRT) for Adoptive Families

The Effects of Child Parent Relationship Therapy (CPRT) for Adoptive Families

Date: August 2016
Creator: Opiola, Kristie K
Description: Adoptive parents often struggle to understand and meet the social-emotional behavioral needs of their adopted child, particularly when the child's pre-adoption experience lacked a secure relationship with an attuned and responsive caregiver. This randomized controlled study, a replication of Carnes-Holt and Bratton's 2014 research, investigated the effects of child parent relationship therapy (CPRT) for adoptive families who reported attached-related concerns such as difficulties establishing a mutually satisfying parent-child relationship as well as concerns about the adopted child's behavior and parental stress. Participants were 49 adoptive parents (61% female; 7% couples; 86% European American, 6% Latino, 6% Asian, and 2% Black American) with adoptees between the ages of 2.5 to 9 (50% female; 35% European American, 22% Asian, 12% Latino, 10% Black American, and 21% Biracial or other). Eighty-four percent of children were adopted internationally or from the foster care system. Parents were randomly assigned to CPRT or treatment as usual (TAU). Results from 2 (group) by 2 (time) repeated measures ANOVAs indicated that compared to the TAU control group, parents who participated in CPRT reported statistically significant improvement in child behavior problems, parent-child relationship stress, and parental empathy, with a large treatment effects on all measures. Findings confirmed results from ...
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The Effects of Fluency-Based Instruction on the Identification of Component Reading Skills

The Effects of Fluency-Based Instruction on the Identification of Component Reading Skills

Date: August 2016
Creator: Bandy, Darren
Description: This study examined the effects of fluency-based instruction on the identification of six component-composite relations for early reading skills. Five participants (ages 5-8) who struggled with reading participated. A multiple probe design was used to assess the effects of frequency building on prerequisite skills on the emergence of composite reading skills. The results show that the prerequisite skills taught did not have an effect on the composite skill probes but did have an effect on the assessment scores. The data expand the research pertaining to Precision Teaching, fluency-based instruction, and component-composite relations. These data suggest that additional skills may be needed to be taught in order to effects on the composite skills. In addition, these authors identify the need for the identification of the component skills necessary to teach rapid autonomic naming.
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The Effects of Naturalistic Language Interventions in Children with Autism

The Effects of Naturalistic Language Interventions in Children with Autism

Date: August 2016
Creator: Degner, Brittany
Description: Several evidence-based procedures based upon operant learning principles have been developed to teach language, and for young children with autism spectrum disorder (ASD), naturalistic interventions are commonly implemented as they are both effective and developmentally appropriate. The current investigation compared contingent responsive intervention and combined intervention on the effects of language use in four children diagnosed with ASD. Results suggest that a combined intervention procedure increases target language and requests in children with simplified language (e.g., one-word phrase) as well as complex language (e.g., simple sentences).
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The Effects of Self-Forgiveness, Self-Acceptance, and Self-Compassion on  Subclinical Disordered Eating: The Role of Shame

The Effects of Self-Forgiveness, Self-Acceptance, and Self-Compassion on Subclinical Disordered Eating: The Role of Shame

Date: August 2016
Creator: Womack, Stephanie Dianne
Description: Disordered eating is a general term that describes a wide range of behaviors from diagnosable eating disorders to subclinical patterns of behavior that do not meet criteria for diagnosis (e.g., problematic weight loss behaviors, excessive dieting, bingeing, purging). Disordered eating is prevalent and has a wide range of physical and psychological consequences. Negative self-conscious emotions such as shame and guilt have been implicated in the development and maintenance of disordered eating. Positive attitudes toward the self (i.e., self-forgiveness, self-compassion, self-acceptance) may be helpful in reducing shame, guilt, and disordered eating symptoms. In this dissertation, I explored the associations between positive attitudes toward the self, negative self-conscious emotions, and disordered eating in a sample of college students and adults (N = 477). Positive attitudes toward the self were associated with lower levels of disordered eating symptoms, and this relationship was partially mediated by lower levels of negative self-conscious emotions. I concluded by discussing areas for future research and implications for clinical practice.
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Effects of UE Speed on MIMO Channel Capacity in LTE

Effects of UE Speed on MIMO Channel Capacity in LTE

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Date: August 2016
Creator: Shukla, Rahul
Description: With the introduction of 4G LTE, multiple new technologies were introduced. MIMO is one of the important technologies introduced with fourth generation. The main MIMO modes used in LTE are open loop and closed loop spatial multiplexing modes. This thesis develops an algorithm to calculate the threshold values of UE speed and SNR that is required to implement a switching algorithm which can switch between different MIMO modes for a UE based on the speed and channel conditions (CSI). Specifically, this thesis provides the values of UE speed and SNR at which we can get better results by switching between open loop and closed loop MIMO modes and then be scheduled in sub-channels accordingly. Thus, the results can be used effectively to get better channel capacity with less ISI. The main objectives of this thesis are: to determine the type of MIMO mode suitable for a UE with certain speed, to determine the effects of SNR on selection of MIMO modes, and to design and implement a scheduling algorithm to enhance channel capacity.
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Eight-Year Course of Cognitive Functioning in Bipolar Disorder with Psychotic Features

Eight-Year Course of Cognitive Functioning in Bipolar Disorder with Psychotic Features

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Date: August 2016
Creator: Bain, Kathleen Marie
Description: The purpose of the current study was to examine neuropsychological functioning in patients with bipolar disorder (BD) with psychotic features. Data from a large, epidemiological study of patients with first-episode psychosis was used to examine verbal learning and working memory 10 years after onset of psychosis in patients with BD relative to patients with schizophrenia (SZ) and patients with psychotic major depressive disorder (MDD). Cross-sectional comparisons of verbal learning and working memory at the 10-year follow-up mirrored findings of relative performance at the 2-year follow-up (Mojtabai, 2000), as patients with SZ performed significantly worse than patients with psychotic affective disorders. When FEP patients' cognitive performance was examined longitudinally, all groups showed non-significant decline over time, with no significant diagnostic group differences after accounting for current symptoms. More frequent hospitalizations and longer treatment with antipsychotics were associated with poorer performance on cognitive testing 10 years after illness onset, but these associations disappeared when controlling baseline cognitive performance. Within the BD sample, current positive and negative psychotic symptoms were associated with poorer performance on cognitive testing. After controlling for baseline cognitive performance, markers of clinical course were unrelated to cognitive performance, consistent with existing literature on longitudinal cognitive functioning in patients with ...
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Elementary Students' Critical Examination of Characters in Children's Literature Depicting Social Justice

Elementary Students' Critical Examination of Characters in Children's Literature Depicting Social Justice

Date: August 2016
Creator: Paiva, Deanne
Description: Despite the ruling of Brown vs. The Board of Education of Topeka, segregation in schools is still quite visible with suburban schools educating a student body of more than 70% White and urban schools comprised of mostly Black, Hispanic, and Asian students. Ideally, a school should dispel social and structural inequities through curriculum and quality resources, but fallibly, schools continue to be the vehicles to maintaining the status quo. Students who develop critical awareness and cultivate a critical literacy stance can become agents of change toward a more democratic society. In the current study, urban upper-elementary-age students were asked to engage in a critical literacy event by critically examining the power positions of characters in books that depict historical social injustice. The six female participants met in several sessions to read books and a newspaper article, use a critical reader response tool, and then engage in critical conversations about the books' characters. Their dialogue was recorded and analyzed using a critical discourse qualitative methodology. The findings show that older elementary students are capable of seeing multiple perspectives of an issue and can explain characters' power from born from privilege and fueled by fear and how a shift in power may ...
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Environmental Ethics from the Periphery: José Lutzenberger and the Philosophical Analysis of an Unecological Economics

Environmental Ethics from the Periphery: José Lutzenberger and the Philosophical Analysis of an Unecological Economics

Date: August 2016
Creator: Valenti Possamai, Fabio
Description: This dissertation provides a philosophical analysis about the influence colonialism had over capitalism's current configuration and how their intricate interplay impacts both the social and the ecological spheres, in both central and peripheral countries. Such analysis draws from the work of José Lutzenberger, a Brazilian environmentalist. The current capitalist economic system tends to disregard the environment, since it would be greatly affected by negative externalities. A negative externality is an economic activity that imposes a negative effect on an unrelated third party. Many negative externalities are related to the environmental consequences of production and consumption. In addition, this dissertation explores the fact that an ecological crisis is also a social crisis. A genealogical and existential thread going from Brazil's early days as one of Portugal's colonies to the present is drawn, showing how colonialism helped to create the foundations and the conditions for the current exploitative capitalist system, in Brazil and elsewhere. To change this situation, the environment should not be entrusted to private interests but to an institution responsible for the good of society as a whole. Genuinely green economies are more prone to appear on the periphery, but only if global economic justice is achieved first.
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Evaluation of an Observation and Training System to Increase Play Skills in Young Children with Autism

Evaluation of an Observation and Training System to Increase Play Skills in Young Children with Autism

Date: August 2016
Creator: Van Meter, Sarah M
Description: Play is considered to be important for the development of young children in that it provides a means to expand their interests, promote engagement and learning, and increase social interactions. Children with autism, however, display deficits in play skills, such as lack of pretend play and rigid or stereotyped manners of play. Research suggests supported play techniques, such as reciprocal imitation training, play expansions, and scaffolding increase play skills in children diagnosed with autism. The current study evaluated the effects of a training package to teach staff members supported play techniques to six young children diagnosed with autism. The study employed a concurrent multiple baseline design across two preschool classrooms. The results suggest that the training package successfully increased staff member use of the supported play techniques and child and staff engagement. The training, however, did not have consistent effects on child social engagement (proximity, attending, and initiating) or on the types of child play (simple manipulation, advanced manipulation, and pretend play). Staff member responses to the post-intervention satisfaction and feedback survey were positive and the results are discussed in the context of the observation procedures and directions for future studies.
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Evaluation Techniques and Graph-Based Algorithms for Automatic Summarization and Keyphrase Extraction

Evaluation Techniques and Graph-Based Algorithms for Automatic Summarization and Keyphrase Extraction

Date: August 2016
Creator: Hamid, Fahmida
Description: Automatic text summarization and keyphrase extraction are two interesting areas of research which extend along natural language processing and information retrieval. They have recently become very popular because of their wide applicability. Devising generic techniques for these tasks is challenging due to several issues. Yet we have a good number of intelligent systems performing the tasks. As different systems are designed with different perspectives, evaluating their performances with a generic strategy is crucial. It has also become immensely important to evaluate the performances with minimal human effort. In our work, we focus on designing a relativized scale for evaluating different algorithms. This is our major contribution which challenges the traditional approach of working with an absolute scale. We consider the impact of some of the environment variables (length of the document, references, and system-generated outputs) on the performance. Instead of defining some rigid lengths, we show how to adjust to their variations. We prove a mathematically sound baseline that should work for all kinds of documents. We emphasize automatically determining the syntactic well-formedness of the structures (sentences). We also propose defining an equivalence class for each unit (e.g. word) instead of the exact string matching strategy. We show an evaluation ...
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An Examination of a Framework for Posttraumatic Stress Disorder Correlates: Exploring the Roles of Narrative Centrality and Negative Affectivity

An Examination of a Framework for Posttraumatic Stress Disorder Correlates: Exploring the Roles of Narrative Centrality and Negative Affectivity

Date: August 2016
Creator: Southard-Dobbs, Shana
Description: Recent estimates suggest that a large percentage of the population experiences some type of traumatic event over the course of the lifetime, but a relatively small proportion of individuals develop severe, long-lasting problems (e.g., posttraumatic stress disorder; PTSD). One major goal for trauma researchers is to understand what factors contribute to these differential outcomes, and much of this research has examined correlates of posttraumatic stress disorder (PTSD) symptom severity. An important next step in this line of research is the development of conceptual frameworks to foster a deeper understanding of the relationships among these diverse predictors of PTSD and their predictive power in relation to each other. A framework proposed by Rubin, Boals, and Hoyle centers on the influence of narrative centrality (construal of a traumatic experience as central to one's identity and to the life story) and negative affectivity (the tendency to experience negative emotion and to interpret situations and experiences in a negative light), suggesting many variables may correlate with PTSD symptoms via shared variance with these two factors. With a sample of 477 participants recruited from Amazon Mechanical Turk, this dissertation project extended the work of Rubin and colleagues by a) utilizing structural equation modeling techniques to ...
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An Experimental Study of Bifurcated (Weekend and Weekday) and Unitary (Past Week) Retrospective Assessments of Sleep

An Experimental Study of Bifurcated (Weekend and Weekday) and Unitary (Past Week) Retrospective Assessments of Sleep

Access: Use of this item is restricted to the UNT Community.
Date: August 2016
Creator: Sethi, Kevin J.
Description: Discordance between weekday and weekend sleep schedules is common (Bonnet & Arand, 1995; Breslau, Roth, Rosenthal, & Andreski, 1997; Machado, Varella, & Andrade, 1998; Strauch & Meier, 1988; Tsai & Li, 2004). Brief retrospective self-report measures are essential for epidemiological research studies (Moul, Hall, Pilkonis, & Buysse, 2004), but self-reports are prone to error in recall, and the greater the variability in nightly sleep, the less reliable are retrospective reports (Babkoff, Weller, & Lavidor, 1996). More accurate self-report responses may be possible if measures prompt participants to consider variations in sleep schedules that are consistent (i.e., weekday and weekend sleep schedules). The current study experimentally examined whether Bifurcated (Weekday and Weekend) retrospective assessments of sleep are more accurate than Unitary (Past Week) assessments. Participants were randomly assigned to complete one of the two versions (Bifurcated vs. Unitary) of the Sleep Questionnaire. One hundred and thirty-one participants were included in the analyses. Results of a a series of analyses demonstrated that the Bifurcated version of the Sleep Questionnaire provided more accurate and less variable estimates of total sleep time than the Unitary version of the Sleep Questionnaire. Differences between the versions of the Sleep Questionnaire for other sleep variables were less ...
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An Exploration of College Attitudes among Sioux Falls High School Students

An Exploration of College Attitudes among Sioux Falls High School Students

Date: August 2016
Creator: Duesterhoeft, Kristin
Description: Since the recession of 2008, there has been an increased scrutiny of higher education, with little research done on how this affects high school students' college search process. This study seeks to understand how college perceptions are formed and how they affect the college decision process of high school students in Sioux Falls, South Dakota. In order to gain a holistic perspective of this process, this study utilized a mixed method approach of analyzing public data, conducting interviews with community members and students, conducting a focus group with high school guidance counselors, and administering a survey to high school students. This study found that students in this area form their perceptions of college in three distinct phases and that these phases affect a student's college priorities. Special attention was given to how academics, cost and location contributed to a student's overall college decision. These findings can be used to assist faculty and staff at higher education institutions in creating effective messaging and programming that relate to this group of students.
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Exploring Volunteer Management in the Public Sector: What are the Challenges in Managing Volunteers in Local Government?

Exploring Volunteer Management in the Public Sector: What are the Challenges in Managing Volunteers in Local Government?

Date: August 2016
Creator: Sillah, Aminata A
Description: To effectively provide services to citizens, local governments have had to be creative. One approach has been the creation of volunteer programs to meet demands and expanding needs. Volunteer programs hold promise for creating meaningful engagement opportunities for citizens. However, limited organizational capacity, inadequate volunteer management practices, and difficulties in maintaining volunteer retention are concerns plaguing local government volunteer programs. Volunteer programs are often structured around a set of best practices thought to be necessary for ensuring the retention of volunteers. To apply best practices across the board would suggest that local government volunteer programs are similar in organizational structure, budget size, amount of citizen engagement, accountability concerns, and that they adopt similar bureaucratic procedures. Using human relations and bureaucratic theories as theoretical frameworks, four research questions are asked and answered: 1) What are the managerial and political challenges in volunteer management and retention for local government volunteer coordinators?, 2) What challenges are local governments' volunteer coordinators facing in using volunteer management practices?, 3) What strategies are helpful in retaining volunteers in local government volunteerism?, and 4) What challenges do local government volunteer coordinators face in engaging citizens? Data collection for this qualitative study was conducted using online surveys and ...
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Extensions of the General Linear Model into Methods within Partial Least Squares Structural Equation Modeling

Extensions of the General Linear Model into Methods within Partial Least Squares Structural Equation Modeling

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Date: August 2016
Creator: George, Benjamin Thomas
Description: The current generation of structural equation modeling (SEM) is loosely split in two divergent groups - covariance-based and variance-based structural equation modeling. The relative newness of variance-based SEM has limited the development of techniques that extend its applicability to non-metric data. This study focuses upon the extension of general linear model techniques within the variance-based platform of partial least squares structural equation modeling (PLS-SEM). This modeling procedure receives it name through the iterative PLS‑SEM algorithm's estimates of the coefficients for the partial ordinary least squares regression models in both the measurement model and the overall structural model. This research addresses the following research questions: (1) What are the appropriate measures for data segmentation within PLS‑SEM? (2) What are the appropriate steps for the analysis of rank-ordered path coefficients within PLS‑SEM? and (3) What is an appropriate model selection index for PLS‑SEM? The limited type of data to which PLS-SEM is applicable suggests an opportunity to extend the method for use with different data and as a result a broader number of applications. This study develops and tests several methodologies that are prevalent in the general linear model (GLM). The proposed data segmentation approaches posited and tested through post hoc analysis ...
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Feasibility Study of Consolidation by Direct Compaction and Friction Stir Processing of Commercially Pure Titanium Powder

Feasibility Study of Consolidation by Direct Compaction and Friction Stir Processing of Commercially Pure Titanium Powder

Date: August 2016
Creator: Nichols, Leannah Marie
Description: Commercially pure titanium can take up to six months to successfully manufacture a six-inch in diameter ingot in which can be shipped to be melted and shaped into other useful components. The applications to the corrosion-resistant, light weight, strong metal are endless, yet so is the manufacturing processing time. At a cost of around $80 per pound of certain grades of titanium powder, the everyday consumer cannot afford to use titanium in the many ways it is beneficial simply because the number of processing steps it takes to manufacture consumes too much time, energy, and labor. In this research, the steps it takes from the raw powder form to the final part are proposed to be reduced from 4-8 steps to only 2 steps utilizing a new technology that may even improve upon the titanium properties at the same time as it is reducing the number of steps of manufacture. The two-step procedure involves selecting a cylindrical or rectangular die and punch to compress a small amount of commercially pure titanium to a strong-enough compact for transportation to the friction stir welder to be consolidated. Friction stir welding invented in 1991 in the United Kingdom uses a tool, similar to ...
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Feigning ADHD: Effectiveness of Selected Assessment Tools in Distinguishing Genuine from Simulated ADHD

Feigning ADHD: Effectiveness of Selected Assessment Tools in Distinguishing Genuine from Simulated ADHD

Date: August 2016
Creator: Robinson, Emily
Description: Research indicates that some college students may be strongly motivated to feign AHDD symptoms for desired external incentives, such as stimulant medication or academic accommodations. To date, literature examining feigned ADHD has been primarily focused on ADHD specific self-report measures (e.g., CAARS) and continuous performance tests (e.g., CPTs); however, little attention has been devoted to the use of multi-scale inventories in detecting feigned ADHD. For CPT measures, virtually no literature exists on the effectiveness of the TOVA to identify feigned ADHD, despite its frequent clinical use for establishing this diagnosis. The current study utilized a between-subjects simulation design to validate feigning cut scores on ADHD-specific measures using 66 feigners and 51 confirmed ADHD cases. As prior literature suggested, the results convincingly demonstrated that face-valid ADHD assessment measures were easily faked. Across both TOVA modalities (e.g., Auditory and Visual), the ADHD simulators performed significantly poorer than those diagnosed with ADHD. As an innovative approach, a Dissimulation-ADHD (Ds-ADHD) scale was developed and initially validated. The Ds-ADHD is composed of ten MMPI-2-RF items mistakenly believed to be clinical characteristics associated with ADHD. Requiring cross-validation, Ds-ADHD optimized cut scores and classification of ADHD feigners appears promising. They were clearly distinguishable from ADHD client, as ...
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Friction Stir Welding of High Strength Precipitation Strengthened Aluminum Alloys

Friction Stir Welding of High Strength Precipitation Strengthened Aluminum Alloys

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Date: August 2016
Creator: Sidhar, Harpreet
Description: Rising demand for improved fuel economy and structural efficiency are the key factors for use of aluminum alloys for light weighting in aerospace industries. Precipitation strengthened 2XXX and 7XXX aluminum alloys are the key aluminum alloys used extensively in aerospace industry. Welding and joining is the critical step in manufacturing of integrated structures. Joining of precipitation strengthened aluminum alloys using conventional fusion welding techniques is difficult and rather undesirable in as it produces dendritic microstructure and porosities which can undermine the structural integrity of weldments. Friction stir welding, invented in 1991, is a solid state joining technique inherently benefitted to reduces the possibility of common defects associated with fusion based welding techniques. Weldability of various 2XXX and 7XXX aluminum alloys via friction stir welding was investigated. Microstructural and mechanical property evolution during welding and after post weld heat treatment was studied using experimental techniques such as transmission electron microscopy, differential scanning calorimetry, hardness testing, and tensile testing. Various factors such as peak welding temperature, cooling rate, external cooling methods (thermal management) which affects the strength of the weldment were studied. Post weld heat treatment of AL-Mg-Li alloy produced joint as strong as the parent material. Modified post weld heat treatment ...
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Friction Stir Welding of Precipitation Strengthened Aluminum 7449 Alloys

Friction Stir Welding of Precipitation Strengthened Aluminum 7449 Alloys

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Date: August 2016
Creator: Martinez, Nelson Y
Description: The Al-Zn-Mg-Cu (7XXX series) alloys are amongst the strongest aluminum available. However, they are considered unweldable with conventional fusion techniques due to the negative effects that arise with conventional welding, including hydrogen porosity, hot cracking, and stress corrosion cracking. For this reason, friction stir welding has emerged as the preferred technique to weld 7XXX series alloys. Aluminum 7449 is one of the highest strength 7XXX series aluminum alloy. This is due to its higher zinc content, which leads to a higher volume fraction of eta' precipitates. It is typically used in a slight overaged condition since it exhibits better corrosion resistance. In this work, the welds of friction stir welded aluminum 7449 were studied extensively. Specific focus was placed in the heat affected zone (HAZ) and nugget. Thermocouples were used in the heat affected zone for three different depths to obtain thermal profiles as well as cooling/heating profiles. Vicker microhardness testing, transmission electron microscope (TEM), and differential scanning calorimeter (DSC) were used to characterize the welds. Two different tempers of the alloy were used, a low overaged temper and a high overaged temper. A thorough comparison of the two different tempers was done. It was found that highly overaged aluminum ...
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From the Outside In: A Multivariate Correlational Analysis of Effectiveness in Communities of Practice

From the Outside In: A Multivariate Correlational Analysis of Effectiveness in Communities of Practice

Date: August 2016
Creator: Bomar, Shannon Hulbert
Description: Online communities of practice (CoPs) provide social spaces for people to connect, learn, and engage with one another around shared interests and passions. CoPs are innovatively employed within industry and education for their inherent knowledge management characteristics and as a means of improving professional practice. Measuring the success of a CoP is a challenge researchers are examining through various strategies. Recent literature supports measuring community effectiveness through the perceptions of its members; however, evaluating a community by means of member perception introduces complicating factors from outside the community. In order to gain insight into the importance of external factors, this quantitative study examined the influence of factors in the professional lives of educators on their perceptions of their CoP experience. Through an empirical examination of CoPs employed to connect educators and advance their professional learning, canonical correlation analysis was used to examine correlations between factors believed to be influential on the experiences of community members.
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