477 research outputs found
Factors that affect Li mobility in layered lithium transition metal oxides
No full textThe diffusion constant of Li in electrode materials is a key aspect of the rate capability of rechargeable Li batteries. The factors that affect Li mobility in layered lithium transition metal oxides are systematically studied in this paper by means of first-principles calculations. In close packed oxides octahedral ions diffuse by migrating through intermediate tetrahedral sites. Our results indicate that the activation barrier for Li hopping is strongly affected by the size of the tetrahedral site and the electrostatic interaction between Li+ in that site and the cation in the octahedron that shares a face with it. The size of the tetrahedral site is determined by the c-lattice parameter which has a remarkably strong effect on the activation barrier for Li migration. The effect of other factors such as cation mixing and doping with nontransition metal ions can be interpreted quantitatively in terms of the size and electrostatic effect. A general strategy to design high rate electrode materials is discussed.This work was supported by the MRSEC Program of the National Science Foundation under Grant No. DMR 02-13282, by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098, Subcontracts No. 6517748
and No. 6517749 with the Lawrence Berkeley National Laboratory. Additional computer resources were provided by the National Partnership for Advanced Computing Infrastructure (NPACI)
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2008 CEDER yearbook
No full textCopyright © 2009 Center for Educational Development, Evaluation, and Research Texas A&M University-Corpus ChristiThe fifth annual conference of the Center for Educational Development, Evaluation and Research (CEDER) was held November 30 and December 1, 2007. The CEDER Conference focused on “Education for a Changing World.” More than 250 educators from around the United States and as far away as Venezuela and South Africa attended. The 2008 CEDER Yearbook is a peer-reviewed compilation of some of the papers delivered at that conference. Chapter 1, entitled, “Free Voluntary Reading: Still a Great Idea,” is presented by Dr. Stephen Krashen, one of the conference’s keynote speakers. He provides a meta-analysis of research linking access to books with child literacy rates and demonstrates that encouraging children to read for pleasure is a key to literacy development. The following 10 articles in this yearbook were selected by the Editorial Advisory Committee based on a number of criteria, including the importance and timeliness of the topic, theoretical grounding, and the contribution made to the field of education. Several themes run through this volume, which, when combined, paint a panoramic and vivid image of education for a changing world. Chapters 2 through 6 examine education for a changing world at the K-12 level. In Chapter 2, Barbara Marinak examines several methods in which the elements of informational text structures can be taught in elementary classrooms to increase reading comprehension. In chapters 3 and 4, the authors explore the implications of bilingual education in a world that is becoming increasingly diverse. Cherie McCollough, JoAnn McDonald, and JoAnn Canales use Chapter 3 to examine the ways in which culturally relevant family science learning events work to engage families in a child’s education. Special consideration is given to non-English speaking parents and family members. In Chapter 4, Frank Lucido, Christine Marroquin, Gina Reynolds, and Piedad Ymbert discuss brain-compatible teaching strategies and practical methods to develop bilingualism in students. Similarly, in Chapter 5, Connie Patchett, and Sherrye Dee Garrett call for the inclusion of more nonfiction in elementary classrooms as a way to overcome the “fourth grade slump” in reading comprehension. They provide several frameworks for the effective use of nonfiction texts with a variety of elementary students. In Chapter 6, Michael Moody takes a look at education in a changing world from an administrative perspective. He explores the relationship between school boards and their superintendants of schools, and the discrepancies in how they prioritize competencies for superintendant success. Chapters 7 through 11 explore higher education in a changing world. In Chapter 7, Teresa Le Sage and Barba Patton promote increasing pre-service teachers’ familiarity with using math/science notebooks to increase their effectiveness in the classroom. In Chapter 8, Kaye Nelson, Marvarene Oliver, and Darwin Nelson provide an overview of counselor education programs’ changes over time in response to the changing needs of a constantly fluctuating population. In Chapter 9, Barba Patton demonstrates the need for greater Internet literacy amongst pre-service teachers in an evaluation of lesson plans found online. Caroline Crawford, Richard Alan Smith, and Marion Smith, in Chapter 10, explore how web-based classes are changing college student perceptions of their instructors. Finally, in Chapter 11, Daniel Pearce, Wally Thompson and Tammy Francis Donaldson explore the effectiveness of a developmental reading class on the academic success of students in higher education. The world is changing rapidly, and it is important that educators adapt to these fluctuating circumstances and contexts. Education in a Changing World is not only about presenting emerging trends, but also about creating educators who are prepared to respond effectively to whatever challenges they may face in the future. Our sincerest thanks go out to everyone who contributed their talents to the creation this yearbook, and to all who participated in the Fifth Annual CEDER Conference
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2012 CEDER yearbook
No full textCopyright © 2012 Consortium for Educational Development, Evaluation, and Research; Texas A&M University–Corpus Christi College of EducationAs we inquire, investigate, and problem solve, we become more aware of how much there is to discover about teaching and learning as well as leading educational systems. The dissemination of research findings is also quintessential; otherwise, we continue to have replication instead of enhancement. Using this philosophy, the Consortium for Educational Development, Evaluation, and Research (CEDER) at Texas A&M University–Corpus Christi issued a call for manuscripts to Colleges of Education throughout the state of Texas and more broadly, the nation. We reviewed 36 manuscripts written by 52 authors. From that group of manuscripts, we selected 13 for publication. Each manuscript considered for inclusion in the 2012 CEDER Yearbook was peer-reviewed by two members of the editorial review board via a double-blind process. The selected set of manuscripts highlights educational research and innovations from acclaimed university scholars throughout the nation. Manuscripts have been categorized into the two following sections: K–12 Education and Higher Education. Within the K–12 area of study, authors present papers on preschool teachers’ perspectives of cultural relevant practices (Hu), effective questioning techniques to maximize student learning (Pate), difficulties associated with reading instruction of students with disabilities (Gauthier & Schorzman), and the nature of dyslexia, past and present, including how classroom teachers can provide necessary accommodations (Culbertson). Caring Organizational Practices that Enhance Success (COPES) provide teachers with transition tools necessary for their middle school students (Paciotti & Evan Ortlieb Hill), while we can also learn about adolescent literacy instruction from already motivated black female readers (Groenke, Bennett, & Hill). We also find that early college high school programs can provide a positive experience for students (Valadez, McDowell, Loveless, & DeLaGarza). Papers within the Higher Education section relate to building teacher preparation programs infused with theory (Chehayl), utilizing technological advances in developmental reading courses (Loveless & Bryant), and combining what we know about oral reading fluency towards understanding electronic texting fluency (Ortlieb). We also investigate the possibilities of using mixed methods in dissertation work (Stoves & Smith), discuss the relative transparency of higher education (Schell), and examine the relationship between English language learners’ underdeveloped first language and teacher certification test performance (Ward & Lucido)
The Li intercalation potential of LiMPO 4 and LiMSiO 4 olivines with M = Fe, Mn, Co, Ni
No full textThe Li intercalation potential of LiMPO4 and LiMSiO4 compounds with M = Fe, Mn, Co and Ni is computed with the GGA + U method. It is found that this approach is considerably more accurate than standard LDA or GGA methods. The calculated potentials for LiFePO4, LiMnPO4 and LiCoPO4 agree to within 0.1 V with experimental results. The LiNiPO4 potential is predicted to be above 5 V. The potentials of the silicate materials are all found to be rather high, but LiFeSiO4 and LiCoSiO4 have negligible volume change upon Li extraction
Ab initio study of the low-temperature phases of lithium imide
No full textWe present a low-temperature structural model for lithium imide (Li[subscript 2]NH) that is consistent with experimental studies. Using the cluster expansion formalism and density-functional theory, we have identified a low-energy crystal structure for lithium imide with 96 atoms per unit cell. This low-energy structure is consistent with experimental diffraction patterns, and we propose that the symmetry of the structure may be increased at finite temperature due to thermal fluctuations. In addition, our results suggest that lithium motion is relatively facile between octahedral and tetrahedral sites, which may help explain how lithium diffuses through this material.United States. Dept. of Energy (DE-FG02-05ER46253
Exact expressions for structure selection in cluster expansions
No full textThe cluster expansion has proven to be a valuable tool in materials science to predict properties of configurationally ordered and disordered structures but the generation of cluster expansions can be computationally expensive. In recent years there have been efforts to make the generation of cluster expansions more efficient by selecting training structures in a way that minimizes approximate expressions for the variance of the predicted property values. We demonstrate that in many cases, these approximations are not necessary and exact expressions for the variance of the predicted property values may be derived. To illustrate this result, we present examples based on common applications of the cluster expansion such as bulk binary alloys. In addition we extend these structure selection techniques to Bayesian cluster expansions. These results should enable researchers to better analyze the quality of existing training sets and to select training structures that yield cluster expansions with lower prediction error.United States. Dept. of Energy (Contract No. DE-FG02-96ER45571
Bayesian approach to cluster expansions
No full textCluster expansions have proven to be a valuable tool in alloy theory and other problems in materials science but the generation of cluster expansions can be a computationally expensive and time-consuming process. We present a Bayesian framework for developing cluster expansions that explicitly incorporates physical insight into the fitting procedure. We demonstrate how existing methods fit within this framework and use the framework to develop methods that significantly improve the predictive power of cluster expansions for a given training set size. The key to the methods is to apply physical insight and cross validation to develop physically meaningful prior probability distributions for the cluster expansion coefficients. We use the Bayesian approach to develop an efficient method for generating cluster expansions for low-symmetry systems such as surfaces and nanoparticles.Department of Energ
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2004-2005 CEDER yearbook
No full textCopyright © 2005 Center for Educational Development, Evaluation & ResearchThis yearbook is a compilation of select papers presented at the second annual Center for Educational Development, Evaluation and Research (CEDER) conference at Texas A&M University-Corpus Christi. The conference featured the research and program development of the faculty and graduate students in the College of Education. Held at the University Center on the Texas A&M University-Corpus Christi campus on February 28, 2004, the conference was co-sponsored by the Coastal Bend Chapter of Phi Delta Kappa. Over 200 educators from South Texas attended this conference to hear the 37 poster sessions, roundtables, regular sessions and the keynote session. Dr. Dee Hopkins, Dean of the College of Education at Texas A&M University-Corpus Christi was the keynote speaker. The theme of the conference, No Student Left Behind, was obviously based on the No Child Left Behind federal legislation initiated by President George W. Bush in 2001. However, the Bush legislation dealt primarily with the literacy education of very young children; the thrust of this conference was much broader. This conference dealt with the research and program initiatives for students at all levels – pre-school through adult. Furthermore, the conference looked at all the factors that contributed to No Student Being Left Behind - the pedagogical factors, the emotional factors, and, of course, the literacy factors - all of which contribute to students’ success in school and in life. Accordingly, this volume of conference papers is divided into three sections: Teacher Education for Our Students; Counseling Our Students; and Literacy Affecting Our Students. The first section, teacher education for our students, contains chapters dealing with research and practice concerning the retention of teachers, the qualities of a good teacher, and good pedagogical practice. The second section of this volume deals with counseling our students and consists primarily of research done by the faculty and doctoral students in the Department of Counseling and Educational Psychology at Texas A&M University-Corpus Christi. The last section of this paper deals with the literacy issues affecting our students and focuses particularly on the literacy of Hispanic students in South Texas. Special thanks for this volume must be extended to Dr. Bryant Griffith, a professor in the department of Curriculum & Instruction and to Sydna Arnold, Catherine Swift, Norma Zunker and Roberto Garcia, in the doctoral program. Without their editorial work this volume would not have been possible. The Center for Educational Development, Evaluation, and Research at Texas A&M University- Corpus Christi hopes that this yearbook will serve as a resource for all those educators and researchers dedicated to seeing that, indeed, No Student Is Left Behind
Synthesis, electrochemical properties, and phase stability of Li2NiO2 with the Immm structure
No full textThe electrochemical properties and phase stability of the orthorhombic Immm structure of composition Li2NiO2 are studied experimentally and with first principles calculations. The material shows a high specific charge capacity of about 320 mAh/g and discharge capacity of about 240 mAh/g at the first cycle. The experimental results and first principles calculations all indicate that the orthorhombic Immm structure is rather prone to phase transformation to a close-packed layered structure during the electrochemical cycling. The possibility of stabilizing the orthorhombic Immm structure during the electrochemical cycling by partial substitution of Ni is also evaluated. A detailed analysis of the crystal field energy difference between octahedral and square-planar coordinated Ni2+ indicates that crystal field effects may not be large enough to stabilize Ni2+ in a square planar environment when the cost of electron pairing is taken into account. Rather, we attribute the stability of Li2NiO2 in the Immm structure to the more favorable Li arrangement as compared to a possible Li2NiO2 structure with octahedral Ni.We thank Prof. Yang Shao Horn for the valuable discussion. This work was supported
by the MRSEC Program of the National Science Foundation under award DMR 02-13282, by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of FreedomCAR and Vehicle Technologies of the U.S. Department of Energy under Contract DE-AC03-
76SF00098, Subcontract 6517748 with the Lawrence Berkeley National Laboratory, and in part by the Ministry of Education of Taiwan (EX-91-E-FA09-5-4). We are grateful to Dr. Dane Morgan, Fei Zhou, Dr.Anton Van der Ven, Dr. Dany Carlier, Chris Fischer,
and Tim Mueller for their advice
First-principles electronic structure and relative stability of pyrite and marcasite: Implications for photovoltaic performance
No full textDespite the many advantages (e.g., suitable band gap, exceptional optical absorptivity, earth abundance) of pyrite as a photovoltaic material, its low open-circuit voltage (OCV) has remained the biggest challenge preventing its use in practical devices. Two of the most widely accepted reasons for the cause of the low OCV are (i) Fermi level pinning due to intrinsic surface states that appear as gap states, and (ii) the presence of the metastable polymorph, marcasite. In this paper, we investigate these claims, via density-functional theory, by examining the electronic structure, bulk, surface, and interfacial energies of pyrite and marcasite. Regardless of whether the Hubbard U correction is applied, the intrinsic {100} surface states are found to be of dz2 character, as expected from ligand field theory. However, they are not gap states but rather located at the conduction-band edge. Thus, ligand field splitting at the symmetry-broken surface cannot be the sole cause of the low OCV. We also investigate epitaxial growth of marcasite on pyrite. Based on the surface, interfacial, and strain energies of pyrite and marcasite, we find from our model that only one layer of epitaxial growth of marcasite is thermodynamically favorable. Within all methods used (LDA, GGA-PBE, GGA-PBE+U, GGA-AM05, GGA-AM05+U, HSE06, and delta-sol), the marcasite band gap is not less than the pyrite band gap, and is even larger than the experimental marcasite gap. Moreover, gap states are not observed at the pyrite-marcasite interface. We conclude that intrinsic surface states or the presence of marcasite are unlikely to undermine the photovoltaic performance of pyrite.United States. Dept. of Energy (contract DE-FG02-96ER45571)National Science Foundation (U.S.) (TeraGrid resources provided by Texas Advanced ComputingCenter (TACC) under grant TG-DMR970008S.
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