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Layered Double Hydroxides as Anion- and Cation-Exchanging Materials

Layered Double Hydroxides as Anion- and Cation-Exchanging Materials

Date: May 2007
Creator: Richardson, Mickey Charles
Description: Layered double hydroxides (LDH) have been principally known as anion-exchanging, clay-like materials for several decades, and continues to be the main driving force for current and future research. The chemical interactions of LDH, with transition metallocyanides, have been a popular topic of investigation for many years, partly due to the use of powder x-ray diffraction and infrared spectroscopy as the main characterization tools. Each transition metallocyanide has a characteristic infrared stretching frequency that can be easily observed, and their respective sizes can be observed while intercalated within the interlayer of the LDH. The ability of LDH to incorporate metal cations or any ions/molecules/complexes, that have a postive charge, have not been previously investigated, mainly due to the chemical and physical nature of LDH. The possibility of cationic incorporation with LDH would most likely occur by surface adsorption, lattice metal replacement, or by intercalation into the LDH interlayers. Although infrared spectroscopy finds it main use through the identification of the anions incorporated with LDH, it can also be used to study and identify the various active and inactive bending and stretching modes that the metal hydroxide layers have.
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Layered Double Hydroxides: Morphology, Interlayer Anion, and the Origins of Life

Layered Double Hydroxides: Morphology, Interlayer Anion, and the Origins of Life

Access: Use of this item is restricted to the UNT Community.
Date: December 2002
Creator: Halcom-Yarberry, Faith Marie
Description: The preparation of layered double hydroxides via co-precipitation of a divalent/trivalent metal solution against a base results in 1 mm LDH particles with a disorganized metal lattice. Research was performed to address these morphological issues using techniques such as Ostwald ripening and precipitation via aluminate. Another interesting issue in layered double hydroxide materials is the uptake and orientation of anions into the interlayer. Questions about iron cyanide interlayer anions have been posed. Fourier transform infared spectroscopy and powder x-ray diffraction have been used to investigate these topics. It was found that factors such as orientation, anion charge, and anion structure depended on the divalent/trivalent metal ratio of the hydroxide layer and reactivity time. The cyanide self-addition reaction is an important reaction of classical prebiotic chemistry. This reaction has been shown to give rise to amino acids, purines and pyrimidines. At cyanide concentrations similar to that expected on the early earth, hydrolysis to formamide rather than self-addition occurs. One theory to alleviate this side reaction is the use of minerals or clays that are thought to concentrate and catalyze prebiotics of interest. Layered double hydroxides have been studied as a catalyst for this reaction.
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Layered Double Hydroxides: Synthesis, Characterization, and Interaction of Mg-Al Systems with Intercalated Tetracyanonickelate(II)

Layered Double Hydroxides: Synthesis, Characterization, and Interaction of Mg-Al Systems with Intercalated Tetracyanonickelate(II)

Date: August 2004
Creator: Brister, Fang Wei
Description: The square-planar tetracyanonickelate(II) anion was intercalated into 2:1 and 3:1 Mg-Al layered double hydroxide systems (LDHs). In the 2:1 material, the anion holds itself at an angle of about 30° to the layers, whereas in the 3:1 material it lies more or less parallel to the layers. This is confirmed by orientation effects in the infrared spectra of the intercalated materials and by X-ray diffraction (XRD) data. The measured basal spacings for the intercalated LDH hosts are approximately 11 Å for the 2:1 and approximately 8 Å for the 3:1. The IR of the 2:1 material shows a slight splitting in the ν(CN) peak, which is suppressed in that compound's oriented IR spectrum, indicating that at least some of the intercalated anion's polarization is along the z-axis. This effect is not seen in the 3:1 material. A comparison between chloride LDHs and nitrate LDHs was made with respect to intercalation of tetracyanonickelate(II) anions. Both XRD data and atomic absorption spectroscopy (AAS) data of the LDH tetracyanonickelates confirms that there are no significant differences between the products from the two types of starting materials. The presence of a weak ν(NO) peak in the IR spectra of those samples made from nitrate ...
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Laying the foundation for successful non-academic writing: Professional communication principles in the K-5 curricula of the McKinney Independent School District.

Laying the foundation for successful non-academic writing: Professional communication principles in the K-5 curricula of the McKinney Independent School District.

Date: December 2009
Creator: Treviño, Marlea
Description: Traditionally, K-5 students' writing has had a primarily academic aim-to help students master concepts and express themselves. Even if students take a professional writing course later, they typically do not have the opportunity to practice-over the long period of time mastery requires-the non-academic writing skills they will be required to use as part of their jobs and in their civic life. Based on a limited K-5 study, Texas' McKinney Independent School District is doing a good job of preparing students at the elementary-school level in the areas of collaboration and presentation. A fair job of helping elementary-school students understand the communication situation, define audience, clarify purpose, gather and evaluate resources, and test usability. [And] a poor job of helping elementary-school students with analysis and organization. With their teachers' help, K-5 students eventually grasp the communication situation and can broadly identify their audience and purpose, but they do not appear to select words, format, communication style, or design based on that audience and purpose. Their writer-based focus affects their presentations as well, although they do present frequently. If teachers routinely incorporated audience and purpose considerations into every aspect of communication assignments (format, communication style, design), students would be better prepared for ...
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Laying the Groundwork for Newspaper Preservation through Collaboration and Communication: The Texas Digital Newspaper Program

Laying the Groundwork for Newspaper Preservation through Collaboration and Communication: The Texas Digital Newspaper Program

Date: June 2013
Creator: Krahmer, Ana & Phillips, Mark Edward
Description: This paper discusses the history of the Texas Digital Newspaper Program and associated digital newspaper initiatives at the University of North Texas Libraries.
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A Layman's Interpretation of the Provisions of a 20-Year Pay Life Insurance Policy

A Layman's Interpretation of the Provisions of a 20-Year Pay Life Insurance Policy

Date: August 1940
Creator: James, Albert W., Jr.
Description: This thesis presents an attempt to simplify the language used in life insurance provisions.
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Layout-accurate Ultra-fast System-level Design Exploration Through Verilog-ams

Layout-accurate Ultra-fast System-level Design Exploration Through Verilog-ams

Date: May 2013
Creator: Zheng, Geng
Description: This research addresses problems in designing analog and mixed-signal (AMS) systems by bridging the gap between system-level and circuit-level simulation by making simulations fast like system-level and accurate like circuit-level. The tools proposed include metamodel integrated Verilog-AMS based design exploration flows. The research involves design centering, metamodel generation flows for creating efficient behavioral models, and Verilog-AMS integration techniques for model realization. The core of the proposed solution is transistor-level and layout-level metamodeling and their incorporation in Verilog-AMS. Metamodeling is used to construct efficient and layout-accurate surrogate models for AMS system building blocks. Verilog-AMS, an AMS hardware description language, is employed to build surrogate model implementations that can be simulated with industrial standard simulators. The case-study circuits and systems include an operational amplifier (OP-AMP), a voltage-controlled oscillator (VCO), a charge-pump phase-locked loop (PLL), and a continuous-time delta-sigma modulator (DSM). The minimum and maximum error rates of the proposed OP-AMP model are 0.11 % and 2.86 %, respectively. The error rates for the PLL lock time and power estimation are 0.7 % and 3.0 %, respectively. The OP-AMP optimization using the proposed approach is ~17000× faster than the transistor-level model based approach. The optimization achieves a ~4× power reduction for the OP-AMP ...
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Leader Developmental Readiness of Generation Y in the Training Industry

Leader Developmental Readiness of Generation Y in the Training Industry

Date: December 2012
Creator: Garrigue, Marie
Description: Members of Generation Y in the training and development industry will be required to assume leadership roles as Baby Boomers retire, yet little empirical research exists regarding how best to prepare them for leadership. The purpose of this study was to examine differences in leader developmental readiness between generational cohorts in the training industry, specifically Baby Boomers, Generation X, and Generation Y. Leader developmental readiness provided a definition of developmental readiness for leaders using the five constructs (learning goal orientation, developmental efficacy, self-awareness, leader complexity, and metacognitive ability). A volunteer sample was compiled from members of the ASTD National LinkedIN group (n = 636). Results were analyzed using structured means analysis with maximum likelihood (ML) estimation. Generational cohorts demonstrated differences in leader developmental readiness. Baby Boomers indicated statistically and practically higher metacognitive ability and developmental efficacy than Generation Y. Results demonstrated statistically and practically higher leader complexity in Generation Y and both Generation X and Baby Boomers. These results should inform leader development practitioners as they continue to use existing methods in preparing the different generations for leader development interventions while pointing to possible needs to increase the metacognitive ability and developmental efficacy in Generation Y and ensure accurate perception ...
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Leader Emergence and Effectiveness in Virtual Workgroups: Dispositional and Social Identity Perspectives

Leader Emergence and Effectiveness in Virtual Workgroups: Dispositional and Social Identity Perspectives

Date: August 2009
Creator: Hite, Dwight M.
Description: In today's global competitive environment, many organizations utilize virtual workgroups to overcome geographic and organizational boundaries. Research into their dynamics has received the attention of scholars within multiple disciplines, and the potential for an integrative approach to the study of virtual workgroups exists. This dissertation is a first step towards such an approach. The primary aim of this research is to examine antecedent and contextual factors that affect the emergence and effectiveness of leaders in virtual workgroups. To achieve this aim, an integrative model assembled from theory and empirical findings in leadership, management, social identity, and communications research is posited. Hypothesized relationships depicted in the model identify key dispositional and contextual variables linked to leader emergence, member behavior, and leader effectiveness within virtual workgroups. This study employed a nonexperimental research design, in which leader emergence and social identity manifest as naturally occurring phenomena. Data collection occurred via two web-based surveys administered at different points in time. Hypothesized relationships were tested utilizing correlational and hierarchical moderated multiple regression analyses. The findings of this dissertation suggest that traits, such as personality and cognitive ability, are not associated with leader emergence in virtual workgroups. In addition, the results indicate that the exhibition of ...
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Leadership and sustainable change: The relationship between leadership practices of principals and reculturing schools as professional learning communities.

Leadership and sustainable change: The relationship between leadership practices of principals and reculturing schools as professional learning communities.

Date: May 2009
Creator: Hill, Shannon D.
Description: This study examined the relationships between leadership practices of principals and strength of schools as sustainable professional learning communities. Strength of schools as professional learning communities was measured using the Professional Learning Communities Assessment; leadership practices were measured using the Leadership Practices Inventory both Self and Observer protocols. Findings indicated that neither principal's self-perceptions of their leadership practices nor teachers' assessments of their principals' leadership practices were related to strength of schools as professional learning communities. Findings did indicate ten specific leadership behaviors of principals that appear to be more highly related to strength of schools as learning communities. Further analysis which focused on the two strongest learning community schools and the two weakest learning community schools indicated that three specific leadership behaviors within Kouzes and Posner's practices of modeling the way and enabling others to act appear to be the most strongly related to reculturing schools as sustainable professional learning communities. Principals who set a personal example of what they expect of others are most likely to lead schools that function as strong learning communities. Additionally, principals who build consensus around a common set of values are also most likely to lead strong learning communities. Finally, principals who develop ...
Contributing Partner: UNT Libraries