Science.gov

Sample records for 4-h facts-in-brief providing

  1. Maine 4-H Afterschool Academy--A Professional Development Opportunity for Out-of-School-Time Providers

    ERIC Educational Resources Information Center

    Lobley, Jennifer; Ouellette, Kristy L.

    2013-01-01

    The Maine 4-H Afterschool Academy trained 369 after-school and out of school time providers in 2011. This easy-to-adapt professional development opportunity used blended learning, a combination of in-person and Web-based opportunities. Providers successfully learned concepts and practical knowledge regarding 4-H, specifically 4-H Science. In…

  2. The complete genome sequence of the methanogenic archaeon ISO4-H5 provides insights into the methylotrophic lifestyle of a ruminal representative of the Methanomassiliicoccales.

    PubMed

    Li, Yang; Leahy, Sinead C; Jeyanathan, Jeyamalar; Henderson, Gemma; Cox, Faith; Altermann, Eric; Kelly, William J; Lambie, Suzanne C; Janssen, Peter H; Rakonjac, Jasna; Attwood, Graeme T

    2016-01-01

    Methane emissions from agriculture represent around 9 % of global anthropogenic greenhouse emissions. The single largest source of this methane is animal enteric fermentation, predominantly from ruminant livestock where it is produced mainly in their fermentative forestomach (or reticulo-rumen) by a group of archaea known as methanogens. In order to reduce methane emissions from ruminants, it is necessary to understand the role of methanogenic archaea in the rumen, and to identify their distinguishing characteristics that can be used to develop methane mitigation technologies. To gain insights into the role of methylotrophic methanogens in the rumen environment, the genome of a methanogenic archaeon has been sequenced. This isolate, strain ISO4-H5, was isolated from the ovine rumen and belongs to the order Methanomassiliicoccales. Genomic analysis suggests ISO4-H5 is an obligate hydrogen-dependent methylotrophic methanogen, able to use methanol and methylamines as substrates for methanogenesis. Like other organisms within this order, ISO4-H5 does not possess genes required for the first six steps of hydrogenotrophic methanogenesis. Comparison between the genomes of different members of the order Methanomassiliicoccales revealed strong conservation in energy metabolism, particularly in genes of the methylotrophic methanogenesis pathway, as well as in the biosynthesis and use of pyrrolysine. Unlike members of Methanomassiliicoccales from human sources, ISO4-H5 does not contain the genes required for production of coenzyme M, and so likely requires external coenzyme M to survive. PMID:27602181

  3. 4-H and Iowa.

    ERIC Educational Resources Information Center

    Gore, Deborah, Ed.

    1988-01-01

    This issue focuses on Iowa's role in the historical development of the 4-H youth program. "Roots in Iowa" and "Jessie Field Shambaugh: The Mother of 4-H" (J. Friedel) describes the rural Iowan roots of the 4-H program, which today is located in 80 different countries, and give the story of its founder. Jessie Shambaugh, a rural Iowa teacher and…

  4. 4-H Club Goat Guide.

    ERIC Educational Resources Information Center

    Brown, R. Kipp

    This guide provides information for 4-H Club members who have decided on a club goat project. Topics include general information in the following areas: show rules; facilities and equipment (barns/sheds, fences, feeders, water containers, and equipment); selection (structural correctness, muscle, volume and capacity, style and balance, and growth…

  5. Managing 4-H Volunteer Staff: A 4-H Intern Report.

    ERIC Educational Resources Information Center

    Martin, Hope M.

    The 4-H intern report organizes concepts and materials to aid the extension worker in his role as coordinator and trainer of 4-H volunteer staff. A 10-item task analysis of the extension worker--4-H and youth--as volunteer leader coordinator is presented. The importance of managing a volunteer staff is touched upon, and models for job descriptions…

  6. Keeping 4-H Volunteer Leaders.

    ERIC Educational Resources Information Center

    Smith, Keith L.; Bigler, Nancy M.

    1985-01-01

    This study showed that continuing and discontinuing volunteer 4-H Club leaders are significantly different in their geographical location, number of children in family, and number of children in family who have participated in 4-H. These variables may affect the volunteer's decision to continue serving as a 4-H Club leader. (Author/CT)

  7. An allolactose trapped at the lacZ β-galactosidase active site with its galactosyl moiety in a (4)H3 conformation provides insights into the formation, conformation, and stabilization of the transition state.

    PubMed

    Wheatley, Robert W; Huber, Reuben E

    2015-12-01

    When lactose was incubated with G794A-β-galactosidase (a variant with a "closed" active site loop that binds transition state analogs well) an allolactose was trapped with its Gal moiety in a (4)H3 conformation, similar to the oxocarbenium ion-like conformation expected of the transition state. The numerous interactions formed between the (4)H3 structure and β-galactosidase indicate that this structure is representative of the transition state. This conformation is also very similar to that of d-galactono-1,5-lactone, a good transition state analog. Evidence indicates that substrates take up the (4)H3 conformation during migration from the shallow to the deep mode. Steric forces utilizing His418 and other residues are important for positioning the O1 leaving group into a quasi-axial position. An electrostatic interaction between the O5 of the distorted Gal and Tyr503 as well as C-H-π bonds with Trp568 are also significant. Computational studies of the energy of sugar ring distortion show that the β-galactosidase reaction itinerary is driven by energetic considerations in utilization of a (4)H3 transition state with a novel (4)C1-(4)H3-(4)C1 conformation itinerary. To our knowledge, this is the first X-ray crystallographic structural demonstration that the transition state of a natural substrate of a glycosidase has a (4)H3 conformation.

  8. An allolactose trapped at the lacZ β-galactosidase active site with its galactosyl moiety in a (4)H3 conformation provides insights into the formation, conformation, and stabilization of the transition state.

    PubMed

    Wheatley, Robert W; Huber, Reuben E

    2015-12-01

    When lactose was incubated with G794A-β-galactosidase (a variant with a "closed" active site loop that binds transition state analogs well) an allolactose was trapped with its Gal moiety in a (4)H3 conformation, similar to the oxocarbenium ion-like conformation expected of the transition state. The numerous interactions formed between the (4)H3 structure and β-galactosidase indicate that this structure is representative of the transition state. This conformation is also very similar to that of d-galactono-1,5-lactone, a good transition state analog. Evidence indicates that substrates take up the (4)H3 conformation during migration from the shallow to the deep mode. Steric forces utilizing His418 and other residues are important for positioning the O1 leaving group into a quasi-axial position. An electrostatic interaction between the O5 of the distorted Gal and Tyr503 as well as C-H-π bonds with Trp568 are also significant. Computational studies of the energy of sugar ring distortion show that the β-galactosidase reaction itinerary is driven by energetic considerations in utilization of a (4)H3 transition state with a novel (4)C1-(4)H3-(4)C1 conformation itinerary. To our knowledge, this is the first X-ray crystallographic structural demonstration that the transition state of a natural substrate of a glycosidase has a (4)H3 conformation. PMID:26291713

  9. National 4-H Common Measures: Initial Evaluation from California 4-H

    ERIC Educational Resources Information Center

    Lewis, Kendra M.; Horrillo, Shannon J.; Widaman, Keith; Worker, Steven M.; Trzesniewski, Kali

    2015-01-01

    Evaluation is a key component to learning about the effectiveness of a program. This article provides descriptive statistics of the newly developed National 4-H Common Measures (science, healthy living, citizenship, and youth development) based on data from 721 California 4-H youth. The measures were evaluated for their reliability and validity of…

  10. 4-H Textile Science Beginner Projects.

    ERIC Educational Resources Information Center

    Scholl, Jan

    This packet contains three 4-H projects for students beginning the sewing sequence of the textile sciences area. The projects cover basics of sewing using sewing machines, more difficult sewing machine techniques, and hand sewing. Each project provides an overview of what the student will learn, what materials are needed, and suggested projects…

  11. The Preschooler: 4-H Child Development Project.

    ERIC Educational Resources Information Center

    Francis, Connie M.

    Intended for 4-H participants who plan and implement activities in the area of child development, this booklet provides a study guide to help young learners: (1) gain understanding of a preschool child's physical, mental, social, and emotional growth; (2) learn to care for a preschooler and promote preschoolers' feelings of security and safety;…

  12. The Infant: 4-H Child Development Project.

    ERIC Educational Resources Information Center

    Francis, Connie M.

    This booklet for 4-H members who elect to undertake projects in child caregiving provides guidelines and information that help children and adolescents between 9 and 19 years of age: (1) understand infants' physical, mental, social, and emotional growth; (2) learn to care for a baby and promote feelings of security and safety; and (3) choose types…

  13. 4-H in the 70's.

    ERIC Educational Resources Information Center

    Extension Service (USDA), Washington, DC.

    Developed under the leadership of the 1970 and 1971 Extension Committee on Organization and Policy 4-H Youth Subcommittees, the brochure offers a statement of potential and new directions for Extension 4-H youth programs. Opening sections deal with the functions of 4-H and balanced 4-H program expansion to serve seven million youth. Succeeding…

  14. Embracing Scientific and Engineering Practices in 4-H

    ERIC Educational Resources Information Center

    Worker, Steven M.

    2013-01-01

    The 4-H Science Initiative has renewed efforts to strengthen 4-H programmatic and evaluation efforts in science and engineering education. A fundamental component of this initiative is to provide opportunities to youth to aid in their development of science process skills; however, emerging research stresses the importance of engaging youth in…

  15. Adult 4-H Volunteer Empowerment in 4-H Youth Development Settings

    ERIC Educational Resources Information Center

    Olsen, Pamela

    2009-01-01

    The primary purpose of this study was to determine which factors related to adult 4-H volunteer empowerment in 4-H youth development settings. This study examined the relationship of adult 4-H volunteers' perceived leadership styles of Oregon 4-H Youth Development Educators (YDE) to the adult 4-H volunteer sense of empowerment. In addition,…

  16. Engaging Library Partners in 4-H Programming

    ERIC Educational Resources Information Center

    Fields, Nia Imani; Rafferty, Elizabeth

    2012-01-01

    When most people think about 4-H, they remember county fairs, livestock programs, and agricultural education. While these programs are still prominent, 4-H has grown in order to meet the growing demands of today's youth. The organization has expanded services and programs to serve rural, suburban, and urban youth in every state in the U.S. 4-H is…

  17. Strengthening 4-H by Analyzing Enrollment Data

    ERIC Educational Resources Information Center

    Hamilton, Stephen F.; Northern, Angela; Neff, Robert

    2014-01-01

    The study reported here used data from the ACCESS 4-H Enrollment System to gain insight into strengthening New York State's 4-H programming. Member enrollment lists from 2009 to 2012 were analyzed using Microsoft Excel to determine trends and dropout rates. The descriptive data indicate declining 4-H enrollment in recent years and peak…

  18. Georgia 4-H Consumer Judging.

    ERIC Educational Resources Information Center

    Blackburn, Mary Ellen; Hall, Doris N.

    Materials are provided for a consumer education activity designed to help teenagers make knowledgeable, rational decisions when purchasing goods and services. A student manual describes how the activity--a consumer judging contest--works. Information is provided on how consumers make decisions. Topics include: needs versus wants; sources of…

  19. 4-H Clover Awareness Teaching Guide.

    ERIC Educational Resources Information Center

    Rutherford, Barbara; Leach, Jennifer

    The purpose of this teaching guide is to introduce children in grades 1-4 and their parents to the 4-H program without the long-term commitment of the traditional 4-H club. The 4-H Clover Awareness Program was designed as an after-school program; however, it could be used in other settings such as a day camp. In addition to introducing children to…

  20. The Toddler: 4-H Child Development Project.

    ERIC Educational Resources Information Center

    Francis, Connie M.

    Part of a series for 4-H members between 9 and 19 years of age, this age-graded guide is designed to help children and adolescents: (1) understand the toddler's physical, mental, social, and emotional growth; (2) learn to care for a toddler; and (3) choose types of play that toddlers enjoy. Contents include suggestions on projects that 4-H members…

  1. Strengthening 4-H Program Communication through Technology

    ERIC Educational Resources Information Center

    Robideau, Kari; Santl, Karyn

    2011-01-01

    Advances in technology are transforming how youth and parents interact with programs. The Strengthening 4-H Communication through Technology project was implemented in eight county 4-H programs in Northwest Minnesota. This article outlines the intentional process used to effectively implement technology in program planning. The project includes:…

  2. Community Development: A 4-H Intern Report.

    ERIC Educational Resources Information Center

    Scheneman, C. Stephen

    State progress reports on the 4-H/Community Development program, a 1973 nationwide Federally sponsored program facilitating youth in community decision-making processes, indicate that the program appears to be evolving into a viable and integral part of the total 4-H program. Although the report describes unique program features of various States,…

  3. Relationships between 4-H Volunteer Leader Competencies and Skills Youth Learn in 4-H Programs

    ERIC Educational Resources Information Center

    Radhakrishna, Rama; Ewing, John C.

    2011-01-01

    This article examined the relationships between 4-H volunteer leader competencies and skills youth learn in 4-H. Using a descriptive-correlational research, the study reported found significant relationships between leadership competencies and skills youth learn in 4-H. Regression analysis revealed that two variables--skills and…

  4. Middle Childhood: 4-H Child Development Project.

    ERIC Educational Resources Information Center

    Francis, Connie M.

    Part of a series for 4-H members between 9 and 19 years of age, this age-graded guide to the development of 6-, 7-, and 8-year-olds aims to help 4-H members who are children and adolescents themselves: (1) understand the physical, mental, social, and emotional development of children in middle childhood; (2) learn to care for a child in middle…

  5. The Big E (Energy). 4-H Member Guide, Unit 2.

    ERIC Educational Resources Information Center

    Caldwell, William; And Others

    This activity and record book is designed for unit 2 (ages 12-14) of the Nebraska 4-H Energy Project. Aims, energy attitudes to be developed, and instructions are provided for each activity. Activities include: (1) a word search of energy-related words (with definitions provided); (2) determining fuel waste; (3) reading electric/gas meters and…

  6. Multi-state 4-H energy program

    SciTech Connect

    Bakker, U.B.; Garthe, J.W.

    1983-06-01

    Through Agricultural Engineering 4-H Energy Programs, youth can be educated to gain knowledge, increase hands on skills, and incorporate energy-saving techniques into their lifestyle. In a pilot multi-state energy program tested by 13 states, youth increased their energy awareness.

  7. 4-H for Central City Minorities

    ERIC Educational Resources Information Center

    Paige, Joseph C.

    1970-01-01

    Joseph C. Paige is the Dean of Community Education and Director of Cooperative Extension Service of the only urban Land-Grant College, Federal City College, in Washington, D.C. Here he is interviewed about 4-H with children of poor ethnic groups in the District of Columbia. (NL)

  8. Separates. 4-H Textile Science Advanced Project.

    ERIC Educational Resources Information Center

    Scholl, Jan F.

    This booklet, which was developed for use by 4-H club members in Pennsylvania, contains the information required to sew a two-piece nontailored outfit and/or a one-or two-piece dress. The following are among the topics covered: the difference between a fiber and a fabric; properties of different fibers and fabrics; common jacket, neckline, sleeve,…

  9. 4-H Science Inquiry Video Series

    ERIC Educational Resources Information Center

    Green, Jeremy W.; Black, Lynette; Willis, Patrick

    2013-01-01

    Studies support science inquiry as a positive method and approach for 4-H professionals and volunteers to use for teaching science-based practices to youth. The development of a science inquiry video series has yielded positive results as it relates to youth development education and science. The video series highlights how to conduct science-rich…

  10. Textile Science Leader's Guide. 4-H Textile Science.

    ERIC Educational Resources Information Center

    Scholl, Jan

    This instructor's guide provides an overview of 4-H student project modules in the textile sciences area. The guide includes short notes explaining how to use the project modules, a flowchart chart showing how the project areas are sequenced, a synopsis of the design and content of the modules, and some program planning tips. For each of the…

  11. The Big E (Energy). 4-H Member Guide, Unit 3.

    ERIC Educational Resources Information Center

    Caldwell, William; And Others

    This activity and record book is designed for unit 3 (ages 15-19) of the Nebraska 4-H Energy Project. Aims, energy attitudes to be developed, and instructions are provided for each activity. Activities include: (1) determining ways to reduce energy waste with hot water heaters; (2) making personal choices about using appliances; (3) conducting a…

  12. Folkpatterns 4-H Leader's Guide: A Cultural Heritage Project.

    ERIC Educational Resources Information Center

    Kozma, LuAnne Gaykowski

    Folkpatterns is a 4-H program in which young people investigate folklore, cultural traditions, and local history. These materials include a leader's guide and Folkpatterns activities. The leader's guide provides information for leading a Folkpatterns project and 12 sample meeting plans to be used with Folkpatterns members or to be adapted for use…

  13. A Phenomenological Look at 4-H Volunteer Motives for Service

    ERIC Educational Resources Information Center

    Schrock, Jessalyn; Kelsey, Kathleen D.

    2013-01-01

    Volunteers play a vital role in 4-H programs. Without their service, many programs would not be possible. Understanding volunteer motives provides Extension educators with tools for finding high-quality volunteers. The research reported here used McClelland's (1985) framework for motivation (affiliation, achievement, and power) and…

  14. Effectiveness of the 4-H Program as Perceived by Parents of 4-H Participants

    ERIC Educational Resources Information Center

    Radhakrishna, Rama; Foley, Caitlin; Ingram, Patreese; Ewing, John C.

    2013-01-01

    The study reported here examined the effectiveness of 4-H program as perceived by parents of program participants. Descriptive-correlational design was employed, with data collected using a mail survey. Parents perceived 4-H as an effective organization in teaching life skills to youth. Significant relationships were found between parents'…

  15. Water Worlds. 4-H Member's Guide M-5-18; 4-H Leaders Guide L-5-18.

    ERIC Educational Resources Information Center

    Hawkes, Janet E.; And Others

    This pocket folder of materials is designed to provide children aged 9 to 12 with an opportunity to explore and observe aquatic environments. The package includes a 4-H Leader's guide, member's guide, and supplementary materials. The leader's guide contains safety considerations, tips and techniques, and additional activities for getting started…

  16. VIBRATIONALLY EXCITED C{sub 4}H

    SciTech Connect

    Cooksy, Andrew L.; Gottlieb, C. A.; Thaddeus, P.; Patel, Nimesh A.; Young, Ken H.; McCarthy, M. C.; Killian, T. C.

    2015-02-01

    Rotational spectra in four new excited vibrational levels of the linear carbon chain radical C{sub 4}H were observed in the millimeter band between 69 and 364 GHz in a low pressure glow discharge, and two of these were observed in a supersonic molecular beam between 19 and 38 GHz. All have rotational constants within 0.4% of the X{sup 2}Σ{sup +} ground vibrational state of C{sub 4}H and were assigned to new bending vibrational levels, two each with {sup 2}Σ and {sup 2}Π vibrational symmetry. The new levels are tentatively assigned to the 1ν{sub 6} and 1ν{sub 5} bending vibrational modes (both with {sup 2}Π symmetry), and the 1ν{sub 6}+1ν{sub 7} and 1ν{sub 5}+1ν{sub 6} combination levels ({sup 2}Σ symmetry) on the basis of the derived spectroscopic constants, relative intensities in our discharge source, and published laser spectroscopic and quantum calculations. Prior spectroscopic constants in the 1ν{sub 7} and 2ν{sub 7} levels were refined. Also presented are interferometric maps of the ground state and the 1ν{sub 7} level obtained with the Submillimeter Array (SMA) near 257 GHz which show that C{sub 4}H is present near the central star in IRC+10216. We found no evidence with the SMA for the new vibrationally excited levels of C{sub 4}H at a peak flux density averaged over a 3{sup ′′} synthesized beam of ⩾0.15 Jy/beam in the 294–296 and 304–306 GHz range, but it is anticipated that rotational lines in the new levels might be observed in IRC+10216 when ALMA attains its full design capability.

  17. Learnings and Recommendations to Advance 4-H Science Readiness

    ERIC Educational Resources Information Center

    Schmitt-McQuitty, Lynn; Carlos, Ramona; Smith, Martin H.

    2014-01-01

    The case study investigation reported here assessed California 4-H professionals' understanding of the essential components of effective 4-H Science programming as established by the National 4-H Science Mission Mandate. Using the 4-H Science Checklist as the basis for defining 4-H Science Readiness, academic and program staff were surveyed…

  18. Thermochemistry of disputed soot formation intermediates C4H3 and C4H5.

    PubMed

    Wheeler, Steven E; Allen, Wesley D; Schaefer, Henry F

    2004-11-01

    Accurate isomeric energy differences and standard enthalpies of formation for disputed intermediates in soot formation, C(4)H(3) and C(4)H(5), have been determined through systematic extrapolations of ab initio energies. Electron correlation has been included through second-order Z-averaged perturbation theory (ZAPT2), and spin-restricted, open-shell coupled-cluster methods through triple excitations [ROCCSD, ROCCSD(T), and ROCCSDT] utilizing the correlation-consistent hierarchy of basis sets, cc-pVXZ (X = D, T, Q, 5, and 6), followed by extrapolations to the complete basis set limit via the focal point method of Allen and co-workers. Reference geometries were fully optimized at the ROCCSD(T) level with a TZ(2d1f,2p1d) basis set. Our analysis finds that the resonance-stabilized i-C(4)H(3) and i-C(4)H(5) isomers lie 11.8 and 10.7 kcal mol(-1) below E-n-C(4)H(3) and E-n-C(4)H(5), respectively, several kcal mol(-1) (more, less) than reported in recent (diffusion Monte Carlo, B3LYP density-functional) studies. Moreover, in these systems Gaussian-3 (G3) theory suffers from large spin contamination in electronic wave functions, poor reference geometries, and anomalous vibrational frequencies, but fortuitous cancellation of these sizable errors leads to isomerization energies apparently accurate to 1 kcal mol(-1). Using focal-point extrapolations for isodesmic reactions, we determine the enthalpies of formation (delta(f)H(0) (composite function)) for i-C(4)H(3), Z-n-C(4)H(3), E-n-C(4)H(3), i-C(4)H(5), Z-n-C(4)H(5), and E-n-C(4)H(5) to be 119.0, 130.8, 130.8, 78.4, 89.7, and 89.1 kcal mol(-1), respectively. These definitive values remove any remaining uncertainty surrounding the thermochemistry of these isomers in combustion models, allowing for better assessment of whether even-carbon pathways contribute to soot formation. PMID:15527344

  19. Thermochemistry of disputed soot formation intermediates C4H3 and C4H5

    NASA Astrophysics Data System (ADS)

    Wheeler, Steven E.; Allen, Wesley D.; Schaefer, Henry F.

    2004-11-01

    Accurate isomeric energy differences and standard enthalpies of formation for disputed intermediates in soot formation, C4H3 and C4H5, have been determined through systematic extrapolations of ab initio energies. Electron correlation has been included through second-order Z-averaged perturbation theory (ZAPT2), and spin-restricted, open-shell coupled-cluster methods through triple excitations [ROCCSD, ROCCSD(T), and ROCCSDT] utilizing the correlation-consistent hierarchy of basis sets, cc-pVXZ (X=D, T, Q, 5, and 6), followed by extrapolations to the complete basis set limit via the focal point method of Allen and co-workers. Reference geometries were fully optimized at the ROCCSD(T) level with a TZ(2d1f,2p1d) basis set. Our analysis finds that the resonance-stabilized i-C4H3 and i-C4H5 isomers lie 11.8 and 10.7 kcal mol-1 below E-n-C4H3 and E-n-C4H5, respectively, several kcal mol-1 (more, less) than reported in recent (diffusion Monte Carlo, B3LYP density-functional) studies. Moreover, in these systems Gaussian-3 (G3) theory suffers from large spin contamination in electronic wave functions, poor reference geometries, and anomalous vibrational frequencies, but fortuitous cancellation of these sizable errors leads to isomerization energies apparently accurate to 1 kcal mol-1. Using focal-point extrapolations for isodesmic reactions, we determine the enthalpies of formation (ΔfH0∘) for i-C4H3, Z-n-C4H3, E-n-C4H3, i-C4H5, Z-n-C4H5, and E-n-C4H5 to be 119.0, 130.8, 130.8, 78.4, 89.7, and 89.1 kcal mol-1, respectively. These definitive values remove any remaining uncertainty surrounding the thermochemistry of these isomers in combustion models, allowing for better assessment of whether even-carbon pathways contribute to soot formation.

  20. Student Sampler: Facts in Brief on North Carolina

    ERIC Educational Resources Information Center

    North Carolina Department of Public Instruction, 2006

    2006-01-01

    This student sampler has been compiled to assist North Carolina students (4th and 8th grade) in their study of North Carolina. It is designed to introduce them to the people, places and events that have shaped North Carolina history. Topics include state symbols, descriptions of the state flag, and seal, the lyrics to the state song, and the…

  1. Student Sampler: Facts in Brief on North Carolina.

    ERIC Educational Resources Information Center

    North Carolina State Dept. of Public Instruction, Raleigh.

    This information sampler was compiled to assist students in their study of North Carolina. Every year North Carolina students must complete a special project on their state. The sampler was designed to introduce students to the people, places, and events that have shaped North Carolina's history. Topics in the sampler include state symbols,…

  2. 4-H PetPALS Juvenile Diversion Program Supports At-Risk Youth and Seniors

    ERIC Educational Resources Information Center

    Goble, Connie L.; Miller, Lucinda B.

    2014-01-01

    The 4-H PetPALS Juvenile Diversion Program provides a partnership opportunity with Extension and the juvenile court system to positively impact lives of at-risk youth. At-risk youth are taught by 4-H PetPALS adult volunteer leaders and 4-H PetPALS members to value and respect the human-animal bond, as well as to understand and empathize with…

  3. Minnesota 4-H Science of Agriculture Challenge: Infusing Agricultural Science and Engineering Concepts into 4-H Youth Development

    ERIC Educational Resources Information Center

    Rice, Joshua E.; Rugg, Bradley; Davis, Sharon

    2016-01-01

    Youth involved in 4-H projects have been engaged in science-related endeavors for years. Since 2006, 4-H has invested considerable resources in the advancement of science learning. The new Minnesota 4-H Science of Agriculture Challenge program challenges 4-H youth to work together to identify agriculture-related issues in their communities and to…

  4. Diversity Inclusion in 4-H Youth Programs: Examining the Perceptions among West Virginia 4-H Youth Professionals

    ERIC Educational Resources Information Center

    LaVergne, Douglas D.

    2013-01-01

    The study reported here sought to examine the perceptions of 4-H youth professionals towards diversity inclusion in 4-H youth programs. A majority of professionals positively reported that there are benefits for youth of color and youth with disabilities in 4-H youth programs. Respondents indicated that the lack of information about 4-H youth…

  5. Curtiss JN-4H Towing Model Wing

    NASA Technical Reports Server (NTRS)

    1921-01-01

    In 1919 the NACA Langley laboratory received its first three research aircraft which were Curtiss JN-4Hs borrowed from the US Army Air Service at Langley Field. One of the first research projects of the laboratory initiated that year was a flight investigation of the lift and drag characteristics of the JN-4H. One of the objectives of the flight tests was to obtain data for correlation with wind-tunnel test results measured at MIT and to aid in the derivation of techniques for extrapolation of model results to full-scale conditions. In a pioneering aeronautical effort in 1920, pressure orifices were installed in the horizontal tail of one of the Jennies and connected to glass manometers for pressure measurements that could be photographed in flight. The NACA also used the aircraft in some of the earliest experiments on maneuverability in 1921. In addition to serving as test subjects, the aircraft were used for measurements of aerodynamic behavior of aircraft components. In this photograph made in 1921, one of the JN- 4Hs is towing a model of an aircraft wing to obtain lift and drag information for comparison to tunnel results. All three Jenny aircraft departed Langley in 1923. Reference: 'Flying the Frontiers: NACA and NASA Experimental Aircraft' by Arthur Pearcy. Naval Institute Press, 1993. ISBN 1-55750-258-7

  6. 4-H and School-Age Care: A Great Combination! Point of View.

    ERIC Educational Resources Information Center

    Vandenbergh, Barbara D.

    1999-01-01

    Discusses the positive relationship between 4-H programs and school-age care programs, advocating the use of 4-H programs as a model for care, or as a source of care, caregiver training, or curriculum. Notes the role of the Cooperative Extension System in training and supporting school-age care providers. (JPB)

  7. Global 4-H Network: Laying the Groundwork for Global Extension Opportunities

    ERIC Educational Resources Information Center

    Major, Jennifer; Miller, Rhonda

    2012-01-01

    A descriptive study examining 4-H programs in Africa, Asia, and Europe was conducted to provide understanding and direction in the establishment of a Global 4-H Network. Information regarding structure, organizational support, funding, and programming areas was gathered. Programs varied greatly by country, and many partnered with other 4-H…

  8. The Big E (Energy). 4-H Energy Project. 4-H Member's E-Book, Unit 1.

    ERIC Educational Resources Information Center

    Caldwell, William; And Others

    This activity and record book is designed for unit 1 (ages 9-11) of the Nebraska 4-H Energy Project. In this project, members are required to: (1) use energy wisely by closing doors and turning off lights; (2) inspecting homes for energy use at least once; (3) judging the best use of lighting in a home; (4) sharing ideas about energy use in a…

  9. CPR: Purposeful Action. Putting New Life into 4-H.

    ERIC Educational Resources Information Center

    Jones, Deborah A.; Smith, William C.

    1988-01-01

    In Ohio, 4-H professionals found that it is necessary to conduct market research to have an effective program. Cardiopulmonary resuscitation (CPR) training has been successful in strengthening the 4-H position in the marketplace. (JOW)

  10. Hamsters?! What Does 4-H Stand for, Anyway?

    ERIC Educational Resources Information Center

    Grundeen, Brenda

    This paper briefly traces the history of 4-H youth development programs, explains what youth development is, and shows how the experiential learning model is used in 4-H. Begun over 75 years ago as a means of extending the learning of the land-grant university to rural youth, 4-H is part of the Cooperative Extension Service. The curriculum…

  11. The 4-H Club Meeting: An Essential Youth Development Strategy

    ERIC Educational Resources Information Center

    Cassels, Alicia; Post, Liz; Nestor, Patrick I.

    2015-01-01

    The club meeting has served as a key delivery method for 4-H programming across the United States throughout its history. A survey of WV 4-H community club members reinforces the body of evidence that the 4-H club meeting is an effective vehicle for delivering positive youth learning opportunities within the umbrella of the Essential Elements of…

  12. Using Digital Classrooms to Conduct 4-H Club Meetings

    ERIC Educational Resources Information Center

    West, Patricia; Fuhrman, Nicholas E.; Morgan, A. Christian; Duncan, Dennis W.

    2012-01-01

    Using computer technology and digital classrooms to conduct 4-H Club meetings is an efficient way to continue delivering quality 4-H programming during times of limited resources and staff. Nineteen Junior and Senior 4-H'ers participated in seven digital classroom workshops using the Wimba Classroom application. These digital classroom…

  13. Factors Affecting Teen Involvement in Pennsylvania 4-H Programming

    ERIC Educational Resources Information Center

    Gill, Bart E.; Ewing, John C.; Bruce, Jacklyn A.

    2010-01-01

    The study reported here determined the factors that affect teen involvement in 4-H programming. The design of the study was descriptive and correlational in nature. Using a purposive sampling procedure, a survey questionnaire was distributed to all (N=214) 4-H members attending the 4-H State Leadership Conference. The major findings of the study…

  14. Ultra high voltage MOS controlled 4H-SiC power switching devices

    NASA Astrophysics Data System (ADS)

    Ryu, S.; Capell, C.; Van Brunt, E.; Jonas, C.; O'Loughlin, M.; Clayton, J.; Lam, K.; Pala, V.; Hull, B.; Lemma, Y.; Lichtenwalner, D.; Zhang, Q. J.; Richmond, J.; Butler, P.; Grider, D.; Casady, J.; Allen, S.; Palmour, J.; Hinojosa, M.; Tipton, C. W.; Scozzie, C.

    2015-08-01

    Ultra high voltage (UHV, >15 kV) 4H-silicon carbide (SiC) power devices have the potential to significantly improve the system performance, reliability, and cost of energy conversion systems by providing reduced part count, simplified circuit topology, and reduced switching losses. In this paper, we compare the two MOS based UHV 4H-SiC power switching devices; 15 kV 4H-SiC MOSFETs and 15 kV 4H-SiC n-IGBTs. The 15 kV 4H-SiC MOSFET shows a specific on-resistance of 204 mΩ cm2 at 25 °C, which increased to 570 mΩ cm2 at 150 °C. The 15 kV 4H-SiC MOSFET provides low, temperature-independent, switching losses which makes the device more attractive for applications that require higher switching frequencies. The 15 kV 4H-SiC n-IGBT shows a significantly lower forward voltage drop (VF), along with reasonable switching performance, which make it a very attractive device for high voltage applications with lower switching frequency requirements. An electrothermal analysis showed that the 15 kV 4H-SiC n-IGBT outperforms the 15 kV 4H-SiC MOSFET for applications with switching frequencies of less than 5 kHz. It was also shown that the use of a carrier storage layer (CSL) can significantly improve the conduction performance of the 15 kV 4H-SiC n-IGBTs.

  15. 4H-SiC detectors for ultraviolet light monitoring

    NASA Astrophysics Data System (ADS)

    Mazzillo, M.; Sciuto, A.; Badalà, P.; Carbone, B.; Russo, A.; Coffa, S.

    2015-02-01

    Silicon Carbide (SiC) provides the unique property of near-perfect visible blindness and very high signal-to-noise ratio due to the high quantum efficiency and low dark current even at high temperature. These features make SiC the best available material for the manufacturing of visible blind semiconductor ultraviolet (UV) light detectors. Thanks to their properties, SiC detectors have been extensively used in fact for flame detection monitoring, UV sterilization and astronomy. Here we report on the electrical and optical performance of patterned thin metal film NiSi/4H-SiC vertical Schottky photodiodes with different semiconductor exposed area suitably designed for UV light monitoring.

  16. Why 4-H Members Leave: A Study of Discontinuance through Both Current 4-H Members and Former Members

    ERIC Educational Resources Information Center

    Chilek, Kevin Dwayne

    2012-01-01

    4-H members quit. It is part of every 4-H program, and according to the research, it is even part of growing up. If only we knew why they quit, we could possibly do something about it. To date, the reasons youth join 4-H have been more thoroughly researched than the reasons they quit. This study explores why youth choose to discontinue membership…

  17. The Oneida County 4-H Conservation Field Days Conflict.

    ERIC Educational Resources Information Center

    Brown, Stephen C.; Vonhof, Sarah; Kelley, Alicia

    2003-01-01

    Examines the various perspectives held by the three major organizations involved (an environmental citizens group, a local sportsmen's club, and the cooperative extension service) regarding a conflict over a 4-H program involving hunting and wildlife management. Discusses why the 4-H program's attempt to build consensus among the organizations was…

  18. Council of Presidents: A Multifaceted Idea for 4-H

    ERIC Educational Resources Information Center

    Torretta, Alayne

    2015-01-01

    Communication between 4-H professionals and the youth they work with is an important part of a successful 4-H program. By creating a Council of Presidents comprised of officers of all the clubs in your county, you can increase communication while assuring your program addresses all four essential elements. The Council is also as a vehicle for…

  19. 4-H Participation and Science Interest in Youth

    ERIC Educational Resources Information Center

    Heck, Katherine; Carlos, Ramona M.; Barnett, Cynthia; Smith, Martin H.

    2012-01-01

    The study reported here investigated the impacts of participation in 4-H on young people's interest and participation in science. Survey data were collected from relatively large and ethnically diverse samples of elementary and high school-aged students in California. Results indicated that although elementary-grade 4-H members are not more…

  20. Stabilization of 4H hexagonal phase in gold nanoribbons

    PubMed Central

    Fan, Zhanxi; Bosman, Michel; Huang, Xiao; Huang, Ding; Yu, Yi; Ong, Khuong P.; Akimov, Yuriy A.; Wu, Lin; Li, Bing; Wu, Jumiati; Huang, Ying; Liu, Qing; Eng Png, Ching; Lip Gan, Chee; Yang, Peidong; Zhang, Hua

    2015-01-01

    Gold, silver, platinum and palladium typically crystallize with the face-centred cubic structure. Here we report the high-yield solution synthesis of gold nanoribbons in the 4H hexagonal polytype, a previously unreported metastable phase of gold. These gold nanoribbons undergo a phase transition from the original 4H hexagonal to face-centred cubic structure on ligand exchange under ambient conditions. Using monochromated electron energy-loss spectroscopy, the strong infrared plasmon absorption of single 4H gold nanoribbons is observed. Furthermore, the 4H hexagonal phases of silver, palladium and platinum can be readily stabilized through direct epitaxial growth of these metals on the 4H gold nanoribbon surface. Our findings may open up new strategies for the crystal phase-controlled synthesis of advanced noble metal nanomaterials. PMID:26216712

  1. Sodium diffusion in 4H-SiC

    SciTech Connect

    Linnarsson, M. K. Hallén, A.

    2014-09-01

    Sodium diffusion has been studied in p-type 4H-SiC. Heat treatments have been performed from 1200 °C to 1800 °C for 1 min to 4 h. Secondary ion mass spectrometry has been used to measure the sodium distribution. We show that sodium has a considerable mobility at 1200 °C in p-type 4H-SiC. On the other hand for sodium atoms trapped at suitable sites the mobility is limited up to 1800 °C. Trap limited diffusion kinetics is suggested and an effective diffusivity has been extracted with an activation energy of 4 eV for sodium diffusion in p-type 4H-SiC.

  2. Properties of homoepitaxial 4H-SiC and characteristics of Ti/4H-SiC Schottky barrier diodes

    NASA Astrophysics Data System (ADS)

    Chen, G.; Li, Z. Y.; Bai, S.; Han, P.

    2008-02-01

    This paper describes the properties of the homoepitaxial 4H-SiC layer, the fabrication and electrical parameters of Ti/4H-SiC Schottky barrier diode (SBD). The 4H-SiC epitaxial layers, grown on the commercially available 8°off-oriented Si-face(0001) single-crystal 4H-SiC wafers, have been performed at 1550~1600°C by using the step controlled epitaxy with low pressure chemical vapor deposition. X-ray diffraction measurement result indicates the single crystal nature of the epilayer, and Raman spectrum shows the typical 4H-SiC feature peaks. When the off-oriented angle of substrate is 8°, the epitaxial growth perfectly replicates the substrate's polytype. High quality 4H-SiC epilayer has been generated on the 4H-SiC substrate. Ti/4H-SiC SBDs with blocking voltage 1kV have been made on an undoped epilayer with 12um in thick and 3×10 15cm -3 in carrier density. The ideality factor n=1.16 and the effective barrier height φ e=0.9V of the Ti/4H-SiC SBDs are measured with method of forward density-voltage (J-V). The diode rectification ratio of forward to reverse (defined at +/-1V) is over 10 7 at room temperature. By using B + implantation, an amorphous layer as the edge termination is formed. The SBDs have on-state current density of 200A/cm2 at a forward voltage drop of about 2V. The specific on-resistance for the rectifier is found to be as 6.6mΩ•cm2.

  3. Synthesis of 4H/fcc Noble Multimetallic Nanoribbons for Electrocatalytic Hydrogen Evolution Reaction.

    PubMed

    Fan, Zhanxi; Luo, Zhimin; Huang, Xiao; Li, Bing; Chen, Ye; Wang, Jie; Hu, Yanling; Zhang, Hua

    2016-02-01

    Noble multimetallic nanomaterials, if only consisting of Au, Ag, Pt, and Pd, typically adopt the high-symmetry face-centered cubic (fcc) structure. Here for the first time, by using the 4H/fcc Au@Ag nanoribbons (NRBs) as seeds, we report the synthesis of 4H/fcc trimetallic Au@PdAg core-shell NRBs via the galvanic reaction method under ambient conditions. Moreover, this strategy can also be used to synthesize 4H/fcc trimetallic Au@PtAg and quatermetallic Au@PtPdAg core-shell NRBs. Impressively, for the first time, these alloy shells, i.e., PdAg, PtAg, and PtPdAg, epitaxially grown on the 4H/fcc Au core with novel 4H hexagonal phase were successfully synthesized. Remarkably, the obtained 4H/fcc Au@PdAg NRBs exhibit excellent electrocatalytic activity toward the hydrogen evolution reaction, which is even quite close to that of the commercial Pt black. We believe that our findings here may provide a novel strategy for the crystal-structure-controlled synthesis of advanced functional noble multimetallic nanomaterials with various promising applications.

  4. Isomer Energy Differences for the C4H3 and C4H5 Isomers UsingDiffusion Monte Carlo

    SciTech Connect

    Domin, D.; Lester Jr., W.A.; Whitesides, R.; Frenklach, M.

    2007-12-01

    A new diffusion Monte Carlo study is performed on the isomers of C{sub 4}H{sub 3} and C{sub 4}H{sub 5} emulating the methodology of a previous study [Int. J. Chem. Kinetics 33, 808 (2001)]. Using the same trial wave function form of the previous study, substantially different isomerization energies were found owing to the use of larger walker populations in the present work. The energy differences between the E and I isomers of C{sub 4}H{sub 3} were found to be 10.5 {+-} 0.5 kcal/mol and for C{sub 4}H{sub 5}, 9.7 {+-} 0.6 kcal/mol. These results are in reasonable accord with recent MRCI and CCSD(T) findings.

  5. A Beach and Dune Community. 4-H Marine Science. Member's Guide. Activity I. MSp 1.

    ERIC Educational Resources Information Center

    Auburn Univ., AL. Cooperative Extension Service.

    The investigation in this booklet is designed to provide 4-H members with opportunities to identify common plants and animals found on beaches and sand dunes and to determine the role of the plants and animals in this community. Learners are provided with a picture of a hypothetical beach and sand dune and a list of organisms (included in the…

  6. Electronic spectra of C4H3Cl+ isomers

    NASA Astrophysics Data System (ADS)

    Chakrabarty, S.; Rudnev, V.; Fulara, J.; Dietsche, R.; Nagy, A.; Garkusha, I.; Mazzotti, F. J.; Rice, C. A.; Maier, J. P.

    2012-12-01

    Two experimental methods were applied to identify the structure and electronic transitions of C4H3Cl+ isomers. The first is a direct absorption technique where mass-selected ions are embedded in 6 K neon matrices using a mass-selected ion beam and absorption spectra of different C4H3Cl+ isomers were thus observed. The second is a gas phase method on ions which have been collisional cooled with cryogenic helium inside of a 22-pole ion trap. The c-type (1)2 A‧ ← X 2 A″ electronic transition of a C4H3Cl+ isomer could then be measured by a one-colour, two-photon technique at 20 and 50 K in the gas phase. The two sets of data, complemented by calculated excitation energies, allowed the assignment of particular isomers. Rotational structure in the gas phase spectra was resolved for C4H3 35Cl+ and C4H3 37Cl+ isomers of cis-1-chlorobutenynylium. The analysis leads to the spectroscopic constants: T 00 = 19 184.680(5), ? , ? , ? , ? , ? and ? (all in cm-1).

  7. On the Ionization Energies of C4H3 Isomers

    SciTech Connect

    Kaiser, Ralf I.; Mebel, Alexander; Kostko, Oleg; Ahmed, Musahid

    2009-09-16

    We have conducted a combined experimental and theoretical study on the formation of distinct isomers of resonantly stabilized free radicals, C4H3, which are important intermediates in the formation of polycyclic aromatic hydrocarbons in combustion flames and possibly in the interstellar medium. Our study utilized laser ablation of graphite in combination with seeding the ablated species in neat methylacetylene gas which also acted as a reagent. Photoionization efficiency (PIE) curves were recorded of the C4H3 isomers at the Advanced Light Source from 8.0 to 10.3 eV. The experimental PIE curve was compared with theoretical ones suggesting the formation of four C4H3 radicals: two acyclic structures i-C4H3 [1] and E/Z-n-C4H3 [2E/2Z]and two cyclic isomers 3 and 4. These molecules are likely formed via an initial addition of ground state carbon atoms to the carbon-carbon triple bond of the methylacetylene molecule followed by isomerization via hydrogen migrations and ring opening and emission of atomic hydrogen from these intermediates.

  8. Density Functional Exploration of C4H3N Isomers.

    PubMed

    Custer, Thomas; Szczepaniak, Urszula; Gronowski, Marcin; Fabisiewicz, Emilia; Couturier-Tamburelli, Isabelle; Kołos, Robert

    2016-07-28

    Molecules having C4H3N stoichiometry are of astrophysical interest. Two of these, methylcyanoacetylene (CH3C3N) and its structural isomer allenyl cyanide (H2CCCHN), have been observed in interstellar space, while several more have been examined in laboratories. Here we describe, for a broad range of C4H3N isomers, density functional calculations (B3LYP/aug-cc-pVTZ) of molecular parameters including the energetics, geometries, rotational constants, electric dipole moments, polarizabilities, vibrational IR frequencies, IR absorption intensities, and Raman activities. Singlet-triplet splittings as well as singlet vertical electronic excitation energies are given for selected species. The identification of less stable C4H3N molecules, generated in ongoing spectroscopic experiments, relies heavily on these quantum chemical predictions. PMID:27341606

  9. Existence of {sub {lambda}}{sub {lambda}}{sup 4}H: A variational Monte Carlo search

    SciTech Connect

    Shoeb, Mohammad

    2005-02-01

    A variational Monte Carlo (VMC) calculation for the binding energy B{sub {lambda}}{sub {lambda}} of the lightest hypernucleus {sub {lambda}}{sub {lambda}}{sup 4}H has been performed in the four-body {lambda}{lambda}pn model. A range of input {lambda}{lambda} potentials of moderate strength produce a particle-stable {sub {lambda}}{sub {lambda}}{sup 4}H for the simulated NSC97e and f {lambda}N potentials, whereas the phenomenological Minnesota {lambda}N potential needs a much stronger {lambda}{lambda} potential to bind. The VMC results for B{sub {lambda}}{sub {lambda}} agree with the prediction of the stochastic variational model but contradict the recent Faddeev-Yakubovsky calculation. As reported earlier, B{sub {lambda}}{sub {lambda}} is sensitive to the triplet {lambda}N channel for a given {lambda}{lambda} potential. The B{sub {lambda}}{sub {lambda}} of {sub {lambda}}{sub {lambda}}{sup 4}H in the three-body {lambda}{lambda}d cluster model is consistent with but slightly lower than the Faddeev calculation. The VMC method predicts a stable {sub {lambda}}{sub {lambda}}{sup 4}H system in both models and thus offers the possibility of identifying {sub {lambda}}{sub {lambda}}{sup 4}H in a future extension of E906 or of a related experiment at KEK, provided the simulated potentials are true representations of realistic Nijmegen potentials.

  10. Effectiveness of the Indiana 4-H Tractor Program: Alumni Perceptions.

    ERIC Educational Resources Information Center

    Carrabba, James J., Jr.; Talbert, B. Allen; Field, William E.; Tormoehlen, Roger

    2001-01-01

    Responses from Indiana 4-H tractor driving contestants 1982-197 (n=139) showed that 74% were employed on farms; most felt the contests effectively taught tractor safety and made them generally aware of safety. However, many still engaged in risky behaviors such as not wearing seatbelts in tractors with rollover protective structures or allowing…

  11. "Ohio 4-H CARTEENS": Peer Intervention Safety Program.

    ERIC Educational Resources Information Center

    Cropper, Rebecca J.

    1999-01-01

    Ohio 4-H's CARTEENS seeks to reduce juvenile traffic violations in a program designed and presented by teen peer educators with guidance and technical assistance from the state highway patrol. Teens examined court data to determine content, which includes defensive driving, rural road safety, and dealing with peer pressure. (SK)

  12. Fashion Revue. 4-H Textile Science Activity Guide.

    ERIC Educational Resources Information Center

    Scholl, Jan

    This publication was developed to help students participating in Fashion Review, a 4-H event in which students model a clothing outfit and accessories and are judged on their modeling ability, their presentation, and how well the clothing and accessory choices complement the students' skin tones, hair color, figure or physique, personality, and…

  13. Minnesota 4-H Youth Program Quality Improvement Model

    ERIC Educational Resources Information Center

    Herman, Margo; Grant, Samantha

    2015-01-01

    The University of Minnesota Extension Center for Youth Development made an organizational decision in 2011 to invest in a system-wide approach to implement youth program quality into the 4-H program using the Youth Program Quality Assessment (YPQA) tool. This article describes the four key components to the Minnesota Youth Program Quality…

  14. Marketing Strategies for Recruiting 4-H Members in West Virginia.

    ERIC Educational Resources Information Center

    Wingenbach, Gary J.; Nestor, Cheryl; Lawrence, Layle D.; Gartin, Stacy A.; Woloshuk, Jean; Mulkeen, Patricia

    2000-01-01

    According to a survey of 174 West Virginia 4-H members aged 13-18, the Internet and word of mouth were most effective in recruiting new members. Active messages stressing camps, fun, and friendship had the most influence on retention. A statewide marketing plan was recommended. (SK)

  15. Keys To The Kansas Environment. 4-H School Enrichment Program.

    ERIC Educational Resources Information Center

    Kansas State Univ., Manhattan. Extension Service.

    The 4-H Club packet for preschool and elementary school children contains nine "keys", or short learning exercises, designed to enrich science and environmental education both in and out of the classroom. Each "key" includes the purpose of the activity, the intended audience, the best time of the year for the activity, background information,…

  16. CONSERVING OUR NATURAL RESOURCES, A 4-H LEADER'S GUIDE.

    ERIC Educational Resources Information Center

    AMICK, W. ROBERT; AND OTHERS

    AN EFFECTIVE 4-H CONSERVATION PROGRAM IS DEVELOPED AROUND THE FOLLOWING BASIC CONCEPTS--(1) MAN IS A PART OF THE NATURAL WORLD, IN WHICH THERE ARE MANY VALUABLE MATERIALS, (2) MAN HAS LEARNED TO USE MANY OF THOSE MATERIALS FOR HUMAN SUSTENANCE AND BETTERMENT, AND (3) MAN'S ECONOMIC, SOCIAL, AND GENERAL WELFARE IS LARGELY DEPENDENT UPON THE MANNER…

  17. Self-Protection: A New Approach to 4-H Health.

    ERIC Educational Resources Information Center

    Wright, Sharon K. B.

    This document introduces the issue of self-protection as the Minnesota 4-H Youth Development response to self-destructive behavior among adolescents. It presents findings from a statewide survey of over 36,000 secondary school students using the Minnesota Adolescent Health Survey. Responses are given in the areas of health, school attitudes,…

  18. The Evaluation Attitudes and Practices of 4-H Educators

    ERIC Educational Resources Information Center

    Lekies, Kristi S.; Bennett, Amanda M.

    2011-01-01

    Extension educators are expected to conduct program evaluation. An Internet survey was sent to county 4-H educators in Ohio to examine their evaluation attitudes and practices, as well as barriers to conducting evaluation. Respondents indicated a range of attitudes about evaluation and limited use of different designs and methods. Having enough…

  19. Implementing and Assessing 4-H Educational Activity Kits for Children

    ERIC Educational Resources Information Center

    Scheer, Scott D.; Yeske, Janine; Zimmer, Bruce

    2011-01-01

    Educational activity kits were developed and implemented through a statewide effort for 4-H Youth Development Extension programs serving 5-8 year-old children. The purpose of the kits was to promote life skills in children and assess the learning environment. Data was collected based on the observations of 577 children across 22 counties. Findings…

  20. Performance statistics of the FORTRAN 4 /H/ library for the IBM system/360

    NASA Technical Reports Server (NTRS)

    Clark, N. A.; Cody, W. J., Jr.; Hillstrom, K. E.; Thieleker, E. A.

    1969-01-01

    Test procedures and results for accuracy and timing tests of the basic IBM 360/50 FORTRAN 4 /H/ subroutine library are reported. The testing was undertaken to verify performance capability and as a prelude to providing some replacement routines of improved performance.

  1. Formation of low-temperature cirrus from H2SO4/H2O aerosol droplets.

    PubMed

    Bogdan, A; Molina, M J; Sassen, K; Kulmala, M

    2006-11-23

    We present experimental results obtained with a differential scanning calorimeter (DSC) that indicate the small ice particles in low-temperature cirrus clouds are not completely solid but rather coated with an unfrozen H2SO4/H2O overlayer. Our results provide a new look on the formation, development, and microphysical properties of low-temperature cirrus clouds.

  2. 4-H Tractor Operator Program Teaches Employability Skills and Safety to Youth

    ERIC Educational Resources Information Center

    Barrett, Debra K.

    2013-01-01

    For Michigan State University Extension, the Berrien County 4-H Tractor Operator Program has provided tractor safety education to teens for over 30 years. The certification training satisfies current requirements for operation of a 20 PTO HP or greater agricultural tractor by 14- and 15-year-old youth employed on property "not" owned,…

  3. Bio-Security Proficiencies Project for Beginning Producers in 4-H

    ERIC Educational Resources Information Center

    Smith, Martin H.; Meehan, Cheryl L.; Borba, John A.

    2014-01-01

    Improving bio-security practices among 4-H members who raise and show project animals is important. Bio-security measures can reduce the risk of disease spread and mitigate potential health and economic risks of disease outbreaks involving animal and zoonotic pathogens. Survey data provided statistical evidence that the Bio-Security Proficiencies…

  4. Pennsylvania Youth in Action: 4-H Community Development. Adult Leader's Guide.

    ERIC Educational Resources Information Center

    Pennsylvania State Univ., University Park. Dept. of Agricultural and Extension Education.

    Designed to assist leaders in their roles as catalysts, advisors, and resource persons for the Pennsylvania Youth in Action 4-H Community Development program, the guide provides complementary educational, craft, and recreation suggestions to enhance student workbooks for three community development activity units. The first section focuses on the…

  5. County Clustering for the California 4-H Youth Development Program: Impacts and Lessons Learned

    ERIC Educational Resources Information Center

    Subramaniam, Aarti; Dasher, Harry Steve; Young, Jane Chin

    2012-01-01

    In response to budgetary constraints, a new staffing structure, the Pilot Leadership Plan, was proposed for California's 4-H Youth Development Program. County clusters were formed, each led by a coordinator. The plan was piloted for 2 years to provide insight into how county clustering could support Extension staff to increase and enhance…

  6. Louisiana 4-H Seeds of Service School Gardens: A Descriptive View

    ERIC Educational Resources Information Center

    Cater, Melissa; Fox, Janet; Fletcher, Bobby Jr.

    2012-01-01

    Louisiana 4-H Seeds of Service School Gardens, a K-12 Learn and Serve Grant program, provides a descriptive view of how school gardens along with classroom instruction link curriculum to outdoor classrooms. The purpose of the process evaluation was to describe curriculum implementation fidelity, reach of the gardening program to participants, use…

  7. Children and their 4-H animal projects: How children use science in agricultural activity

    NASA Astrophysics Data System (ADS)

    Emo, Kenneth Roy

    Many children are introduced to science through informal educational programs. 4-H, an educational youth program, has a history of introducing scientific practices into agriculture. The purpose of this ethnographically-driven case study is to examine how science informs the actions of children raising market animals in a 4-H project. For two years the researcher collected data on 4-H children with market animal projects. Observations, interviews, and artifacts gathered are interpreted using the framework of activity theory. This study provides evidence for how the context of an activity system influences individual actions. Rules developed by the organization guide the actions of children to incorporate physical and psychological tools of science into their project to achieve the object: producing animals of proper weight and quality to be competitive in the county fair. Children learn the necessary actions from a community of practitioners through which expertise is distributed. Children's learning is demonstrated by the way their participation in their project changes with time, from receiving assistance from others to developing expertise in which they provide assistance to others. The strength of this educational experience is how children apply specific tools of science in ways that provide meaning and relevancy to their 4-H activity.

  8. New Jersey 4-H Goat Extravaganza: Efficiently Meeting the Educational Needs of 4-H Goat Project Members, Volunteers, and Parents

    ERIC Educational Resources Information Center

    Ripberger, Chad

    2014-01-01

    The 4-H Goat Extravaganza maximizes limited resources to help youth and adults develop knowledge and skills in goat care and management. It capitalizes on the talents and interests of volunteers to efficiently combine a goat-themed art show, team presentation contest, quiz bowl, skillathon, and adult workshop into 1 day. This article outlines the…

  9. Starting and Maintaining a Marine Aquarium: 4-H Members Guide [and] 4-H Member's Project Record Book.

    ERIC Educational Resources Information Center

    Crenshaw, Neil

    The guide and the project record book included in this document are designed for 4-H members who would like to start a salt-water aquarium project. The guide includes the following topics: (1) general requirements for salt-water aquariums; (2) directions for making an aquarium; (3) suggestions for where to locate it; (4) pros and cons of using…

  10. Connecting Kids To The Universe: Partnering With 4-H Youth Development To Pilot 'Afterschool Universe' In New York

    NASA Astrophysics Data System (ADS)

    Schaff, Nancy

    2008-05-01

    4-H Youth Development - as the youth program of the Cooperative Extension system associated with the land grant university in every state - is an ideal partner for statewide dissemination of EPO programs. With funding from a Chandra Cycle 9 EPO grant we are piloting `Afterschool Universe’ in five urban locations in New York State. `Afterschool Universe’ is an education/outreach effort sponsored by NASA's Beyond Einstein program and was developed in partnership with the Imagine the Universe EPO program. The program is targeted at middle school students in out-of-school-time settings and explores basic astronomy concepts focused on the Universe beyond the solar system. Consisting of 12 sessions of engaging hands-on activities, the flexibly structured program can be used in a variety of settings, including astronomy days, youth groups, summer camps, and afterschool programs. Partnering with 4-H Youth Development helps us reach large numbers of underserved and underrepresented minority youth and girls in widely dispersed areas of New York and fits ideally with the current national 4-H SET (science, engineering, and technology) initiative and emphasis on 4-H afterschool programming. The pilot program provides teaching kits and workshops for program leaders. Our 4-H county partners recruit afterschool program staff, science center staff, 4-H volunteers, 4-H teens, and other youth group leaders as workshop participants. The 4-H program will house and loan the kit to trained leaders. By providing kits and training in 2008, we are gearing up for International Year of Astronomy programs in 2009 in out-of-school settings. Based on pilot results, we will seek additional funding to expand the program. The poster will discuss kit development, 4-H partnership, workshops, participating organizations, target audiences, successes, and challenges.

  11. Enantioselective synthesis of 4H-pyranonaphthoquinones via sequential squaramide and silver catalysis.

    PubMed

    Kaya, Uğur; Chauhan, Pankaj; Hack, Daniel; Deckers, Kristina; Puttreddy, Rakesh; Rissanen, Kari; Enders, Dieter

    2016-01-28

    An enantioselective one-pot Michael addition/hydroalkoxylation reaction between 2-hydroxy-1,4-naphthoquinones and alkyne-tethered nitroalkenes catalyzed by a cinchona-derived squaramide and a silver(I) salt has been developed. The sequential protocol provides a direct access to 4H-pyranonaphthoquinones in moderate to very good yields and good to excellent enantioselectivities at a very low catalyst loading (0.5 mol%) of the squaramide.

  12. Enantioselective synthesis of 4H-pyranonaphthoquinones via sequential squaramide and silver catalysis.

    PubMed

    Kaya, Uğur; Chauhan, Pankaj; Hack, Daniel; Deckers, Kristina; Puttreddy, Rakesh; Rissanen, Kari; Enders, Dieter

    2016-01-28

    An enantioselective one-pot Michael addition/hydroalkoxylation reaction between 2-hydroxy-1,4-naphthoquinones and alkyne-tethered nitroalkenes catalyzed by a cinchona-derived squaramide and a silver(I) salt has been developed. The sequential protocol provides a direct access to 4H-pyranonaphthoquinones in moderate to very good yields and good to excellent enantioselectivities at a very low catalyst loading (0.5 mol%) of the squaramide. PMID:26660230

  13. Experimental investigations of the hypernucleus Λ4H

    NASA Astrophysics Data System (ADS)

    Achenbach, P.; Schulz, F.; Aulenbacher, S.; Beričič, J.; Bleser, S.; Böhm, R.; Bosnar, D.; Correa, L.; Distler, M. O.; Esser, A.; Fonvieille, H.; Friščić, I.; Fujii, Y.; Fujita, M.; Gogami, T.; Kanda, H.; Kaneta, M.; Kegel, S.; Kohl, Y.; Kusaka, W.; Margaryan, A.; Merkel, H.; Mihovilovič, M.; Müller, U.; Nagao, S.; Nakamura, S. N.; Pochodzalla, J.; Sanchez Lorente, A.; Schlimme, B. S.; Schoth, M.; Sfienti, C.; Širca, S.; Steinen, M.; Takahashi, Y.; Tang, L.; Thiel, M.; Tsukada, K.; Tyukin, A.; Weber, A.

    2016-03-01

    Negatively charged pions from two-body decays of stopped Λ4H hypernuclei were studied in 2012 at the Mainz Microtron MAMI, Germany. The momenta of the decay-pions were measured with unprecedented precision by using high-resolution magnetic spectrometers. A challenge of the experiment was the tagging of kaons from associated K+∧ production off a Be target at very forward angles. In the year 2014, this experiment was continued with a better control of the systematic uncertainties, with better suppression of coincident and random background, improved particle identification, and with higher luminosities. Another key point of the progress was the improvement in the absolute momentum calibration of the magnetic spectrometers.

  14. Extended defects in 4H-silicon carbide homoepitaxial layers

    NASA Astrophysics Data System (ADS)

    Zhang, Xuan

    The purpose of this thesis is to study the structure of extended defects in 4H-SIC homoepitaxial layers, and to identify their nucleation mechanisms. Characteristics of basal plane dislocations in 4H-SiC epilayers were investigated in a comprehensive manner, including their morphologies, Burgers' vectors, positions, and correlation with the extended defects propagating from the substrate. Plan-view transmission x-ray topography was the major characterization technique used in this study. Complementary data was obtained by KOH etching and optical microscopy. Trace of glide was detected on every basal plane dislocation in the entire 3-inch epilayer. In the center area of the epi-wafer, the glide can extend to macroscopic distance and form edge-type dislocations at the epilayer/surface interface. During the motion, dislocation half loop arrays were found to nucleate at the growth front. The magnitude of the resolved shear stress was estimated based on the radius of curvature of the dislocation lines. It surpassed the critical resolved shear stress at the epitaxial growth temperature. The stress was identified to be compressive in the epilayer. Its origin was studied. Nitrogen-doping-difference-induced misfit strain was excluded as the source of the stress. The structures of two morphological defects, 'carrots' and 'arrows', were studied. Cross-section x-ray topography was used to image the structure of carrot defect in whole. The defect was found to nucleate at the epilayer/substrate interface on a threading screw dislocation propagating from the substrate. Its structure was mainly composed of a prismatic stacking fault and a Frank-type basal plane stacking fault. The arrow defect was found to be produced by a spheroid shape inclusion in the volume of the epilayer. Zone axis diffraction pattern under transmission electron microscope identified the nature of the inclusion as 3C-SIC. It was determined to nucleate at the substrate surface contaminations.

  15. Thermodynamic calculations in the system CH4-H2O and methane hydrate phase equilibria

    USGS Publications Warehouse

    Circone, S.; Kirby, S.H.; Stern, L.A.

    2006-01-01

    Using the Gibbs function of reaction, equilibrium pressure, temperature conditions for the formation of methane clathrate hydrate have been calculated from the thermodynamic properties of phases in the system CH4-H 2O. The thermodynamic model accurately reproduces the published phase-equilibria data to within ??2 K of the observed equilibrium boundaries in the range 0.08-117 MPa and 190-307 K. The model also provides an estimate of the third-law entropy of methane hydrate at 273.15 K, 0.1 MPa of 56.2 J mol-1 K-1 for 1/n CH4??H 2O, where n is the hydrate number. Agreement between the calculated and published phase-equilibria data is optimized when the hydrate composition is fixed and independent of the pressure and temperature for the conditions modeled. ?? 2006 American Chemical Society.

  16. Intergenerational Panels at Centennial Events: Stimulating Discussion about Continuity and Change in the 4-H Program

    ERIC Educational Resources Information Center

    Kaplan, Matthew S.; Weikert, Ben; Scholl, Jan; Rushton, Mya

    2013-01-01

    This article introduces an intergenerational strategy for organizations planning centennial celebratory events. The methods and findings from the 4-H through the Generations session conducted at the joint 4-H Leadership Conference and 4-H Leaders Forum to celebrate the Pennsylvania 4-H Centennial are reported. Youth and adult participants shared…

  17. North Central Region 4-H Volunteers: Documenting Their Contributions and Volunteer Development

    ERIC Educational Resources Information Center

    Nippolt, Pamela Larson; Pleskac, Sue; Schwartz, Vicki; Swanson, Doug

    2012-01-01

    Documenting volunteer contributions strengthens Extension partnerships with volunteers. A team of North Central Region 4-H volunteer specialists collaborated to conduct a study of 4-H volunteer contributions and impacts related to working with youth within the 4-H program. Over three thousand (3,332) 4-H volunteers from throughout the 12-state…

  18. Carbon-antisite vacancy defect in 4H silicon carbide for realizing solid state qubit

    NASA Astrophysics Data System (ADS)

    Gali, Adam; Szász, Krisztián; Ivády, Viktor; Abrikosov, Igor; Bockstedte, Michel; Janzén, Erik

    2015-03-01

    Dopants in solids are promising candidates for implementations of quantum bits for quantum computing. Silicon carbide (SiC) with engineered point defects is considered as very promising material for the next generation devices, with applications ranging from electronics and photonics to quantum computing. Employing density functional theory and many body perturbation theory, we show that the neutral carbon antisite-vacancy pair (CAV) has high spin ground state, and that its spin may be coherently manipulated by optical excitation in n-type 4H SiC. As the positively charged CAV defect in 4H SiC has been recently engineered to act as single photon source, our finding brings a hope that optically addressed quantum bits can be realized by the neutral CAV defects in 4H SiC, and provide an additional target for researchers seeking for solid state single color centers for quantum information processes and metrology. The calculated zero-phonon line of the optically excited state is about 1550 nm (0.8 eV) which perfectly fits to the telecom wavelengths, that makes this qubit candidate very promising for integration of quantum optics devices with existing fiber optics technology. Lendület program of Hungarian Academy of Sciences, the Knut & Alice Wallenberg Foundation, Swedish Research Council, US DoE.

  19. Creating the Southern Region 4-H Volunteer Advisory Group

    ERIC Educational Resources Information Center

    Culp, Ken, III; Edwards, Harriett C.; Jordan, Jenny W.

    2014-01-01

    The SR4-HVAG combines the efforts of states to provide quality educational programming for volunteers and Extension professionals using an advisory group system. An advisory group rather than a council was created because the group provides programmatic input rather than sets policy. The purposes of the SR4-HVAG are to: provide a mechanism for…

  20. The ultraviolet photochemistry of diacetylene - Direct detection of primary products of the metastable C4H2* + C4H2 reaction

    NASA Technical Reports Server (NTRS)

    Bandy, Ralph E.; Lakshminarayan, Chitra; Frost, Rex K.; Zwier, Timothy S.

    1993-01-01

    The products of diacetylene's ultraviolet photochemistry over the 245-220 nm region were directly determined in experiments where C4H2 was excited within a small reaction tube attached to a pulsed nozzle. The products formed in the collisions of C4H2* with C4H2 were subsequently ionized by vacuum UV radiation (at 118 nm) in the ion source of a time-of-flight mass spectrometer. It was found that the reaction of C4H2* with C4H2 produces C6H2 (+C2H2), C8H2 (+2H,H2), and C8H3 (+H), confirming the results of Glicker and Okabe (1987). Under certain conditions, secondary products were observed. Mechanisms for the observed reactions are proposed.

  1. Expression analysis of kenaf cinnamate 4-hydroxylase (C4H) ortholog during developmental and stress responses

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This study was conducted to clone and analyze the expression pattern of a C4H gene encoding cinnamate 4-hydroxylase from kenaf (Hibiscus cannabinus L.). A full-length C4H ortholog was cloned using degenerate primers and the RACE (rapid amplification of cDNA ends) method. The full-length C4H ortholog...

  2. Stewardship as a Means to Create Organizational Reform: A View into Minnesota 4-H Youth Development

    ERIC Educational Resources Information Center

    Skuza, Jennifer A.; Freeman, Dorothy M.; Bremseth, Tamara J.; Doering, Shirley A.; Quinlan, Robert B.; Morreim, Patricia A.; Deidrick, James C.

    2010-01-01

    Minnesota 4-H Youth Development (MN 4-H) used stewardship as a means to create organizational reform to address the public use of the 4-H name and emblem in terms of risk management, real estate and equipment, and finances. A task force implemented a participatory process with colleagues and stakeholders to build and implement the reform effort.…

  3. Relationship between Participation in 4-H and Community Leadership in Rural Montana

    ERIC Educational Resources Information Center

    Flynn, Allison; Frick, Martin; Steele, Douglas

    2010-01-01

    Studies on the impact of 4-H on former members generally use alumni as one cohort. In rural states, such as Montana, it is important to understand the impact of 4-H on alumni in these rural areas and the role 4-H plays in community involvement. The study reported here sought to determine the perception of current community leaders in rural Montana…

  4. Perceptions of Missouri 4-H Youth Development Personnel Regarding Interorganizational Cooperative Behavior

    ERIC Educational Resources Information Center

    McKim, Billy R.; Torres, Robert M.

    2011-01-01

    Perceptions of 4-H youth development personnel regarding interorganizational cooperation were studied between the perceived and desired levels of cooperative activities between 4-H youth development personnel and secondary agriculture teachers. Results indicated that 4-H youth development personnel wanted higher levels of coordinated efforts…

  5. Perceptions of Texas 4-H Livestock Ambassadors on Career Development, Higher Education, and Leadership Development

    ERIC Educational Resources Information Center

    Zanolini, William F.; Rayfield, John; Ripley, Jeff

    2013-01-01

    Selected 4-H youth participated in the Texas 4-H Livestock Ambassador program. Forty-five youth participated in the 3-day program delivered by university professors and staff, Texas AgriLife Extension faculty and industry representatives. An instrument was developed and administered to the Texas 4-H Livestock Ambassadors at the end of their first…

  6. Understanding the Knowledge and Use of Experiential Learning within Pennsylvania 4-H Clubs

    ERIC Educational Resources Information Center

    Bechtel, Robyn; Ewing, John C.; Threeton, Mark; Mincemoyer, Claudia

    2013-01-01

    Experiential learning is incorporated into the National 4-H curriculum. However, the state 4-H staff in Pennsylvania is unsure of the current knowledge and use of experiential learning within the local 4-H clubs. An online survey was distributed to Extension educators and volunteer leaders within Pennsylvania to assess the current knowledge and…

  7. Text to Speech: A 4-H Model of Accessibility and Inclusion

    ERIC Educational Resources Information Center

    Green, Jeremy W.

    2012-01-01

    4-H project manuals play an integral part in a youth's ability to achieve mastery in a specific project area. For youth who struggle with reading, written 4-H materials prove inadequate in addressing the needs of the learner. This article proposes a new delivery method of 4-H educational material designed to create a more inclusive and…

  8. Examination of Attitude and Interest Measures for 4-H Science Evaluation

    ERIC Educational Resources Information Center

    Lewis, Kendra M.; Worker, Steven M.

    2015-01-01

    Science education research has demonstrated the influence of affect on learning. The National 4-H Science Logic Model outlines outcomes from youth participation in 4-H science programs, which includes attitude and interest outcomes. The associated measure, the National 4-H Science Common Measure, assesses these attitude constructs and not other…

  9. Temperature-dependent analysis of conduction mechanism of leakage current in thermally grown oxide on 4H-SiC

    SciTech Connect

    Sometani, Mitsuru; Takei, Manabu; Okamoto, Dai; Harada, Shinsuke; Ishimori, Hitoshi; Takasu, Shinji; Hatakeyama, Tetsuo; Yonezawa, Yoshiyuki; Fukuda, Kenji; Okumura, Hajime

    2015-01-14

    The conduction mechanism of the leakage current of a thermally grown oxide on 4H silicon carbide (4H-SiC) was investigated. The dominant carriers of the leakage current were found to be electrons by the carrier-separation current-voltage method. The current-voltage and capacitance-voltage characteristics, which were measured over a wide temperature range, revealed that the leakage current in SiO{sub 2}/4H-SiC on the Si-face can be explained as the sum of the Fowler-Nordheim (FN) tunneling and Poole-Frenkel (PF) emission leakage currents. A rigorous FN analysis provided the true barrier height for the SiO{sub 2}/4H-SiC interface. On the basis of Arrhenius plots of the PF current separated from the total leakage current, the existence of carbon-related defects and/or oxygen vacancy defects was suggested in thermally grown SiO{sub 2} films on the Si-face of 4H-SiC.

  10. Wetlands Are Wonderlands. Leader/Teacher Guide and Member/Youth Guide. 4-H Marine Education Series-1.

    ERIC Educational Resources Information Center

    Meenen, Kimberly, Ed.; Goettel, Robin G., Ed.

    This guide, for a 4-H wetlands project, is designed for sixth to eighth grade youth and their leaders interested in learning and doing aquatic science activities that can help the environment. The project provides basic wetland information with one or more activities for each of six sections: (1) What is a wetland?; (2) value of wetlands; (3)…

  11. Land Use for Marsh Beach. 4-H Marine Science Simulation Game. Member's Guide [and] Agent's Supplement. MSp 5 [and] 6.

    ERIC Educational Resources Information Center

    Auburn Univ., AL. Cooperative Extension Service.

    A six-part marine science simulation game for 4-H members concerning land use in a hypothetical community is provided. The major problem is to decide what are some possible uses of a three-mile (1,250 acre) Marsh Beach which the city recently purchased. Members assume the roles of decision-makers in the simulated environment and compete for…

  12. What About Waste? 4-H Leader's/Teacher's Guide.

    ERIC Educational Resources Information Center

    Bonhotal, Jean F.; And Others

    This guide is designed for adult volunteer leaders, camp counselors, and teachers who want to explore the subject of waste disposal and management with youth. An introduction provides background on waste disposal problems and disposal options including reducing, reusing, recycling, and composting. Seven discussion questions are intended to…

  13. Synthesis of 4H/fcc-Au@Metal Sulfide Core-Shell Nanoribbons.

    PubMed

    Fan, Zhanxi; Zhang, Xiao; Yang, Jian; Wu, Xue-Jun; Liu, Zhengdong; Huang, Wei; Zhang, Hua

    2015-09-01

    Although great advances on the synthesis of Au-semiconductor heteronanostructures have been achieved, the crystal structure of Au components is limited to the common face-centered cubic (fcc) phase. Herein, we report the synthesis of 4H/fcc-Au@Ag2S core-shell nanoribbon (NRB) heterostructures from the 4H/fcc Au@Ag NRBs via the sulfurization of Ag. Remarkably, the obtained 4H/fcc-Au@Ag2S NRBs can be further converted to a novel class of 4H/fcc-Au@metal sulfide core-shell NRB heterostructures, referred to as 4H/fcc-Au@MS (M = Cd, Pb or Zn), through the cation exchange. We believe that these novel 4H/fcc-Au@metal sulfide NRB heteronanostructures may show some promising applications in catalysis, surface enhanced Raman scattering, solar cells, photothermal therapy, etc.

  14. Plasma ignition and steady state simulations of the Linac4 H{sup −} ion source

    SciTech Connect

    Mattei, S. Lettry, J.; Grudiev, A.; Ohta, M.; Yasumoto, M.; Hatayama, A.

    2014-02-15

    The RF heating of the plasma in the Linac4 H{sup −} ion source has been simulated using a particle-in-cell Monte Carlo collision method. This model is applied to investigate the plasma formation starting from an initial low electron density of 10{sup 12} m{sup −3} and its stabilization at 10{sup 18} m{sup −3}. The plasma discharge at low electron density is driven by the capacitive coupling with the electric field generated by the antenna, and as the electron density increases the capacitive electric field is shielded by the plasma and induction drives the plasma heating process. Plasma properties such as e{sup −}/ion densities and energies, sheath formation, and shielding effect are presented and provide insight to the plasma properties of the hydrogen plasma.

  15. An Integrated Gate Driver in 4H-SiC for Power Converter Applications

    SciTech Connect

    Ericson, Milton Nance; Frank, Steven Shane; Britton, Charles; Janke, Devon D; Ezell, N Dianne Bull; Ryu, Sei_Hyung; Mantooth, Alan; Francis, Dr. Matt; Lanmichhane, Dr. Ranjan; Shepherd, Dr. Paul; Glover, Dr. Michael; Whitaker, Mr. Bret; Cole, Mr. Zach; Passmore, Mr. Brandon; Mcnutt, Tyler

    2014-01-01

    A gate driver fabricated in a 2-um 4H silicon carbide (SiC) process is presented. This process was optimized for vertical power MOSFET fabrication but accommodated integration of a few low-voltage device types including N-channel MOSFETs, resistors, and capacitors. The gate driver topology employed incorporates an input level translator, variable power connections, and separate power supply connectivity allowing selection of the output signal drive amplitude. The output stage utilizes a source follower pull-up device that is both overdriven and body source connected to improve rise time behavior. Full characterization of this design driving a SiC power MOSFET is presented including rise and fall times, propagation delays, and power consumption. All parameters were measured to elevated temperatures exceeding 300 C. Details of the custom test system hardware and software utilized for gate driver testing are also provided.

  16. CERN's Linac4 H- sources: Status and operational results

    NASA Astrophysics Data System (ADS)

    Lettry, J.; Aguglia, D.; Alessi, J.; Andersson, P.; Bertolo, S.; Butterworth, A.; Coutron, Y.; Dallocchio, A.; David, N.; Chaudet, E.; Fink, D.; Gil-Flores, J.; Garlasche, M.; Grudiev, A.; Guida, R.; Hansen, J.; Haase, M.; Hatayama, A.; Jones, A.; Koszar, I.; Lehn, T.; Machado, C.; Mastrostefano, C.; Mathot, S.; Mattei, S.; Midttun, Ø.; Moyret, P.; Nisbet, D.; Nishida, K.; O'Neil, M.; Paoluzzi, M.; Sanchez Alvarez, J.; Scrivens, R.; Shibata, T.; Steyaert, D.; Thaus, N.; Zelenski, A.

    2015-04-01

    Two volume sources equipped with DESY and CERN plasma generators and a low voltage electron dump were operated at 45 kV in the Linac4 tunnel and on a dedicated test stand. These volume sources delivered approximately 20 mA and ensured the commissioning of the Radio Frequency Quadrupole accelerator and of the first section of the Drift Tube Linac. CERN's prototype of a cesiated surface source equipped with this electron dump was operated continuously from November 2013 to April 2014 on the ion source test stand and is being commissioned in the Linac4 tunnel. Before cesiation, the prototype conditioned in volume mode provided up to 30 mA H- beam. Short cesiations, of the order of 10 mg effectively reduced the intensity of co-extracted electrons down to 2 - 8 times the H- current; this cesiated surface operation mode delivered up to 60 mA H- beam. An H- beam of the order of 40 mA was sustained up to four weeks operation with 500 μs pulses at 1.2s spacing. A new extraction was designed to match these beam properties. A copy of BNL's magnetron produced at CERN was tested at BNL and delivered at 40 kV H- beam exceeding Linac4's nominal intensity of 80 mA. In this contribution, the performances, dynamic response to cesiation, stability and availability of these prototypes are described. The needed optimization of the emittance of H- beam above 40 mA is presented, which requires an evolution of the front end that encompasses implementation of a large ceramic insulator.

  17. AB INITIO CHARACTERIZATION OF C{sup -}{sub 4}, C{sub 4}H, AND C{sub 4}H{sup -}

    SciTech Connect

    Senent, M. L.

    2010-01-10

    Using state-of-the-art theoretical methods, we investigate the stable isomers of C{sup -}{sub 4}, C{sub 4}H and C{sub 4}H{sup -}. Three of them are relevant for astrophysics and astrochemistry. These computations are performed using highly correlated ab initio methods and the aug-cc-pVXZ (X = T,Q) basis sets. In addition to the linear isomers, we predict the existence of several cyclic and branched forms for these molecules. For all the molecular species of interest here, sets of spectroscopic parameters are determined with perturbation theory, which compare quite well with experiment. For l - C{sub 4}H{sup -}(X {sup 1}SIGMA{sup +}), the quartic force field is computed at the coupled cluster level of theory. This force field is derived from full nine-dimensional potential energy surface generated close to the equilibrium geometry of this anion. Finally, we treat the thermochemistry of the hydrogen attachment and the electron attachment reactions that may lead to the formation of the C{sub 4}H{sup -} from either C{sup -}{sub 4} or C{sub 4}H.

  18. Monolayer compression induces fluidization in binary system of partially fluorinated alcohol (F4H11OH) with DPPC.

    PubMed

    Nakahara, Hiromichi; Ohmine, Aya; Kai, Shoko; Shibata, Osamu

    2013-01-01

    A two-component Langmuir monolayer consisting of (perfluorobutyl)undecanol (F4H11OH) and dipalmitoylphosphatidylcholine (DPPC), a major component of pulmonary surfactants in mammals, has been investigated at the air-water interface. The binary monolayer has been systematically examined from both thermodynamic and morphological perspectives. The excess Gibbs free energy of mixing has been calculated from surface pressure (π)-molecular area (A) isotherms, and the results indicate that the miscibility of the two-component system shows a maximum in thermodynamical stability when the mole fraction (X(F4H11OH)) is 0.3. Results from a two-dimensional phase diagram (π vs. X(F4H11OH)) are consistent with these findings and depict the degree of miscibility resulting from the variation in the transition and collapse pressures relative to the concentration of X(F4H11OH). The miscibility is also supported by in situ Brewster angle microscopy and fluorescence microscopy, as well as ex situ atomic force microscopy for the system after transfer onto a mica substrate. Aside from temperature, a known driving force for the fluidization of DPPC monolayers is a change in surface composition caused by the addition of additive molecules. In the present study, however, the fluidization is driven by increasing surface pressures even at constant X(F4H11OH). Such a fluidization is a fascinating property when looked at in context of its potential implications for pulmonary replacement therapy, and hence, this study provides a fundamental insight into designing fluorinated materials for biomedical use.

  19. Monolayer growth modes of Re and Nb on 4H -SiC(0001) and 4H-SiC(0001¯)

    NASA Astrophysics Data System (ADS)

    Bryant, K. W.; Bozack, M. J.

    2005-01-01

    Auger electron spectroscopy (AES) and secondary electron emission have been used to specify the room temperature monolayer adsorption characteristics of Re and Nb on the basal, polar surfaces of 4H -SiC. Measurement of the secondary electron emission current relates the absorbed crystal current to the change in AES peak-to-peak signal intensities for both substrate and adsorbate. For the 4H-SiC(0001) Si-face surface, both metals grow by formation of a single monolayer followed by growth of simultaneous monolayers. For the 4H -SiC(0001¯) C-face surface, both metals grow layer by layer (Frank-van der Merwe). Measurements of the coefficient of attenuation, inelastic mean free path, and coverage versus Auger intensities are also reported.

  20. 7 CFR 8.9 - Use in 4-H fund raising.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ...-raising programs using the 4-H Name or Emblem may be carried out for specific educational purposes. Such... Research, Education, and Extension Service, United States Department of Agriculture, or a designee, if the fund-raising program is multi-State or Nationwide. (b) When used to promote 4-H educational...

  1. The 4-H Debate Project: Getting Adults and Children Involved in Communication.

    ERIC Educational Resources Information Center

    Atwater, Deborah F.

    Intended to enhance adult leadership skills, the 4-H Debate Project, developed by the 4-H Communication Committee of Delaware County (Pennsylvania), was designed to (1) increase the members' knowledge of library skills through research, (2) make them aware of current issues, (3) help them to become better public speakers and communicators, (4)…

  2. Factors Related to the Developmental Experiences of Youth Serving as 4-H Camp Counselors

    ERIC Educational Resources Information Center

    Carter, David N.; Kotrlik, Joe W.

    2008-01-01

    The purpose of this study was to investigate the developmental experiences of high-school-aged 4-H youth volunteering as counselors at Louisiana 4-H summer camps. A total of 288 counselors from 10 different camping sessions participated in the study. The Youth Experiences Survey 2.0 and the Developmental Experience Survey measured the personal…

  3. The Challenges Associated with Change in 4-H/Youth Development.

    ERIC Educational Resources Information Center

    McKee, Renee K.; Talbert, B. Allen; Barkman, Susan J.

    2002-01-01

    A survey of 97 Indiana 4-H/youth development educators and interviews with staff and volunteer board members indicated that volunteers believe in core 4-H values, recommend reaching more and different youth, and believe that the rural image inhibits progress. Staff interactions with volunteers, lack of parental involvement, group organization and…

  4. Bringing Carnaval Drum and Dance Traditions into 4-H Programming for Latino Youth

    ERIC Educational Resources Information Center

    Conklin-Ginop, Evelyn; Braverman, Marc T.; Caruso, Robyn; Bone, Dennis

    2011-01-01

    4-H Bloco Drum and Dance is an afterschool program that teaches adolescents drumming, dancing, and theater arts in the rich traditions of Brazilian Carnaval. Teens learn to express themselves in a variety of modalities and perform at community events. The program was developed by a community coalition that included 4-H, other youth programs, and…

  5. Cinnamate 4-Hydroxylase (C4H) genes from Leucaena leucocephala: a pulp yielding leguminous tree.

    PubMed

    Kumar, Santosh; Omer, Sumita; Patel, Krunal; Khan, Bashir M

    2013-02-01

    Leucaena leucocephala is a leguminous tree species accounting for one-fourth of raw material supplied to paper and pulp industry in India. Cinnamate 4-Hydroxylase (C4H, EC 1.14.13.11) is the second gene of phenylpropanoid pathway and a member of cytochrome P450 family. There is currently intense interest to alter or modify lignin content of L. leucocephala. Three highly similar C4H alleles of LlC4H1 gene were isolated and characterized. The alleles shared more than 98 % sequence identity at amino acid level to each other. Binding of partial promoter of another C4H gene LlC4H2, to varying amounts of crude nuclear proteins isolated from leaf and stem tissues of L. leucocephala formed two loose and one strong complex, respectively, suggesting that the abundance of proteins that bind with the partial C4H promoter is higher in stem tissue than in leaf tissue. Quantitative Real Time PCR study suggested that among tissues of same age, root tissues had highest level of C4H transcripts. Maximum transcript level was observed in 30 day old root tissue. Among the tissues investigated, C4H activity was highest in 60 day old root tissues. Tissue specific quantitative comparison of lignin from developing seedling stage to 1 year old tree stage indicated that Klason lignin increased in tissues with age. PMID:23070917

  6. 4-H and Forestry Afterschool Clubs: A Collaboration to Foster Stewardship Attitudes and Behaviors in Youth

    ERIC Educational Resources Information Center

    Gupta, Angela S.; Grant, Samantha; Strauss, Andrea Lorek

    2012-01-01

    The University of Minnesota Extension's 4-H and Forestry Afterschool program combined the 4-H structure and various forestry curricula to foster positive attitudes towards the environment and stewardship-related behaviors as these may serve as precursors to later choices that benefit the environment. Evaluation of third through fifth grade…

  7. The Effects of Age, Gender, and 4-H Involvement on Life Skill Development

    ERIC Educational Resources Information Center

    Haas, Bruce E.; Mincemoyer, Claudia C.; Perkins, Daniel F.

    2015-01-01

    The study reported here examined the effects of age, gender, and 4-H involvement in clubs on life skill development of youth ages eight to 18 over a 12-month period. Regression analyses found age, gender, and 4-H involvement significantly influenced life skill development. Results found that females have higher levels of competencies in life…

  8. 4-H and Tech Ed Partnership Gets Students Geeked about STEM

    ERIC Educational Resources Information Center

    Ivey, Debra; Quam, Greg

    2009-01-01

    This article discusses the 4-H Gateway Academies specifically designed to enhance science, technology, engineering, and math (STEM) skills and knowledge in middle school youth. The innovative summer day camps partnered Project Lead the Way--trained teachers with county 4-H staff from University of Wisconsin-Extension (UW-Extension) Cooperative…

  9. Birds in Your Backyard. 4-H Leaders Guide. L-5-17.

    ERIC Educational Resources Information Center

    Hawkes, Janet E.; Held Phillips, Diane

    This pocket folder of instructional materials is designed to introduce youth aged 9 to 12 to ornithology, the study of birds. The package includes a 4-H member's guide and a Leader's guide. The illustrated 4-H member's guide contains information about attracting and feeding birds. It also includes activities for cooking for birds, making bird…

  10. Acquisition, Custody, and Storage of Firearms Used in 4-H Shooting Sports Programs

    ERIC Educational Resources Information Center

    White, David J.; Smith, Jedediah D.

    2014-01-01

    Shooting sports has been a 4-H program offering since the 1930's. Tragic events related to the use of firearms as weapons have caused public and private entities to evaluate and consider the appropriateness of youth access to and usage of firearms. 4-H educators have the primary responsibility for managing the risk associated with shooting…

  11. Food Challenge: Serving Up 4-H to Non-Traditional Audiences

    ERIC Educational Resources Information Center

    Dodd, Sara; Follmer-Reece, Holly E.; Kostina-Ritchey, Erin; Reyna, Roxanna

    2015-01-01

    This article describes a novel approach for introducing 4-H to non-traditional/diverse audiences using 4-H Food Challenge. Set in a low SES and minority-serving rural school, Food Challenge was presented during the school day to all 7th grade students, with almost half voluntarily participating in an after-school club component. Program design…

  12. College Transition Study Shows 4-H Helps Youth Prepare for and Succeed in College

    ERIC Educational Resources Information Center

    Ratkos, Judy; Knollenberg, Lauren

    2015-01-01

    Many young adults enter college without the knowledge and skills necessary to succeed. The purpose of the study reported here was to determine if 4-H helps develop life skills needed for the transition to college and overall college success. An online survey was sent to college-attending 4-H alumni and a comparison group, with a final sample size…

  13. 4-H Youth Development: The Past, the Present, and the Future

    ERIC Educational Resources Information Center

    Borden, Lynne M.; Perkins, Daniel F.; Hawkey, Kyle

    2014-01-01

    The 4-H Program within Cooperative Extension is more than 100 years old. As we celebrate 100 years of Cooperative Extension, the foundation built by the 4-H Program serves as grounds to meet the needs of today's youth. The diversity of the youth who participate continues to grow, families continue to become less traditional, potential…

  14. 4-H Healthy Living Programs with Impact: A National Environmental Scan

    ERIC Educational Resources Information Center

    Downey, Laura H.; Peterson, Donna J.; LeMenestrel, Suzanne; Leatherman, JoAnne; Lang, James

    2014-01-01

    The 4-H youth development program of the nation's 109 land-grant universities and the Cooperative Extension System is one of the largest youth development organization in the United States serving approximately six million youth. The 4-H Healthy Living initiative began in 2008 to promote achievement of optimal physical, social, and emotional…

  15. Characteristics and Perceptions of 4-H Participants: Gender and Age Differences across Adolescence

    ERIC Educational Resources Information Center

    Bartoszuk, Karin; Randall, Brandy A.

    2011-01-01

    The study reported here examined 367 adolescent 4-H participants in terms of demographic, psychological, behavioral, and relational characteristics, as well as their perceptions and experiences in 4-H. Overall, participants scored high on all outcome variables except having a diverse population in their club. Older participants were more…

  16. Fitting the Framework: The STEM Institute and the 4-H Essential Elements

    ERIC Educational Resources Information Center

    Sallee, Jeff; Peek, Gina G.

    2014-01-01

    Extension and 4-H youth development programs are addressing a shortage of scientists, engineers, and other related professionals by promoting science, technology, engineering, and math (STEM). This case study illustrates how the Oklahoma 4-H Youth Development program trained youth-adult teams to design and implement STEM projects. The STEM…

  17. Simple method for the growth of 4H silicon carbide on silicon substrate

    NASA Astrophysics Data System (ADS)

    Asghar, M.; Shahid, M. Y.; Iqbal, F.; Fatima, K.; Nawaz, Muhammad Asif; Arbi, H. M.; Tsu, R.

    2016-03-01

    In this study we report thermal evaporation technique as a simple method for the growth of 4H silicon carbide on p-type silicon substrate. A mixture of Si and C60 powder of high purity (99.99%) was evaporated from molybdenum boat. The as grown film was characterized by XRD, FTIR, UV-Vis Spectrophotometer and Hall Measurements. The XRD pattern displayed four peaks at 2Θ angles 28.550, 32.700, 36.100 and 58.900 related to Si (1 1 1), 4H-SiC (1 0 0), 4H-SiC (1 1 1) and 4H-SiC (2 2 2), respectively. FTIR, UV-Vis spectrophotometer and electrical properties further strengthened the 4H-SiC growth.

  18. Wiggles and Wags: Dog 1--Fun Activities for You and Your Dog. 4-H Skills for Life Animal Series. National 4-H Curriculum. BU-08166

    ERIC Educational Resources Information Center

    National 4-H Council, 2005

    2005-01-01

    These guides are activity guides. Several fact-filled books about dogs are listed as resources on this guide. The activities are active, hands-on, and engaging and are guided by the 4-H motto: Learning by Doing. As youth explore a dog project topic of interest to them, they also practice essential life skills. Although a few dog project youth will…

  19. Synthesis and characterization of 4-aryl-4H-chromenes from H-cardanol.

    PubMed

    Rao, Hulluru Surya Prakash; Kamalraj, Mani

    2014-09-01

    We have synthesized and characterized a variety of fat-soluble, low-melting and medicinally useful 4-aryl-4H-chromenes from H-cardanol (side-chain perhydrogenated cardanol, 3-pentadecylphenol), a renewable and low-cost product from locally grown cashew nut trees (Anacardium occidentale L.). We incorporated H-cardanol into the aromatic rings of either 4H-chromene or phenol, or both. Substitution of C4SMe in N-methyl-4-(methylthio)-3-nitro-4H-chromene-2-amines with H-cardanol was regio-specific at the C6 position. PMID:25918806

  20. Using Multiple Youth Programming Delivery Modes to Drive the Development of Social Capital in 4-H Participants

    ERIC Educational Resources Information Center

    Kinsey, Sharon

    2013-01-01

    This article focuses on how 4-H youth participants are building social capital, or connections among individuals and community members, through their 4-H experiences. These experiences can be seen through the lens of such 4-H delivery modes as the traditional 4-H club, after-school programs, and school enrichment programs. In addition, other…

  1. Reaching Migrant Farmworker Youth through 4-H Career and Workforce Programs.

    ERIC Educational Resources Information Center

    Wille, Celina G.

    1999-01-01

    Migrant-farm-worker youth learned about employment and educational opportunities in agriculture through a 4-H-sponsored conference. The conference was developed by a partnership of university extension, community organizations, schools, and private industry. (SK)

  2. Ferromagnetism in proton irradiated 4H-SiC single crystal

    SciTech Connect

    Zhou, Ren-Wei; Wang, Hua-Jie; Chen, Wei-Bin; Li, Fei; Liu, Xue-Chao Zhuo, Shi-Yi; Shi, Er-Wei

    2015-04-15

    Room-temperature ferromagnetism is observed in proton irradiated 4H-SiC single crystal. An initial increase in proton dose leads to pronounced ferromagnetism, accompanying with obvious increase in vacancy concentration. Further increase in irradiation dose lowers the saturation magnetization with the decrease in total vacancy defects due to the defects recombination. It is found that divacancies are the mainly defects in proton irradiated 4H-SiC and responsible for the observed ferromagnetism.

  3. Phosphorus doping of 4H SiC by liquid immersion excimer laser irradiation

    SciTech Connect

    Ikeda, Akihiro; Nishi, Koji; Ikenoue, Hiroshi; Asano, Tanemasa

    2013-02-04

    Phosphorus doping of 4H SiC is performed by KrF excimer laser irradiation of 4H SiC immersed in phosphoric acid. Phosphorus is incorporated to a depth of a few tens of nanometers at a concentration of over 10{sup 20}/cm{sup 3} without generating significant crystal defects. Formation of a pn junction diode with an ideality factor of 1.06 is demonstrated.

  4. Fabrication of High-Q Nanobeam Photonic Crystals in Epitaxially Grown 4H-SiC.

    PubMed

    Bracher, David O; Hu, Evelyn L

    2015-09-01

    Silicon carbide (SiC) is an intriguing material due to the presence of spin-active point defects in several polytypes, including 4H-SiC. For many quantum information and sensing applications involving such point defects, it is important to couple their emission to high quality optical cavities. Here we present the fabrication of 1D nanobeam photonic crystal cavities (PCC) in 4H-SiC using a dopant-selective etch to undercut a homoepitaxially grown epilayer of p-type 4H-SiC. These are the first PCCs demonstrated in 4H-SiC and show high quality factors (Q) of up to ∼7000 as well as low modal volumes of <0.5 (λ/n)(3). We take advantage of the high device yield of this fabrication method to characterize hundreds of devices and determine which PCC geometries are optimal. Additionally, we demonstrate two methods to tune the resonant wavelengths of the PCCs over 5 nm without significant degradation of the Q. Lastly, we characterize nanobeam PCCs coupled to luminescence from silicon vacancy point defects (V1, V2) in 4H-SiC. The fundamental modes of two such PCCs are tuned into spectral overlap with the zero phonon line (ZPL) of the V2 center, resulting in an intensity increase of up to 3-fold. These results are important steps on the path to developing 4H-SiC as a platform for quantum information and sensing.

  5. The crystal structure of "green" Cs 2[VOF 4(H 2O)] and its relationship to "blue" Cs 2[VOF 4(H 2O)

    NASA Astrophysics Data System (ADS)

    Mattes, Rainer; Foerster, Harry

    1982-11-01

    Crystals of a second, "green" modification of Cs 2[VOF 4(H 2O)] were obtained from aqueous solution. Their crystal structure was studied on the basis of three-dimensional X-ray data. The structure is orthorhombic, a = 8.231(3), b = 10.323(3), c = 8.497(3) Å, V = 722.0Å 3, Z = 4, space group Ccmm. The final R and RW were 0.035 and 0.048, respectively, for 421 independent reflections. As the already known "blue" modification, the present structure contains isolated, highly deformed octahedral [VOF 4(H 2O)] 2- ions with the oxygen atoms in trans positions. The cesium sublattice and the orientation of the anions to each other are completely different in both modifications. uv/VIS reflection, and ir and Raman spectra of both modifications are discussed.

  6. Characterization of 100 mm Diameter 4H-Silicon Carbide CrystalsWith Extremely Low Basal Plane Dislocation Density

    SciTech Connect

    M Dudley; N Zhang; Y Zhang; B Raghothamachar; S Byrappa; G Choi; E Drachev; M Loboda

    2011-12-31

    Synchrotron White Beam X-ray Topography (SWBXT) studies are presented of basal plane dislocation (BPD) configurations and behavior in a new generation of 100mm diameter, 4H-SiC wafers with extremely low BPD densities (3-4 x 10{sup 2} cm{sup -2}). The conversion of non-screw oriented, glissile BPDs into sessile threading edge dislocations (TEDs) is observed to provide pinning points for the operation of single ended Frank-Read sources. In some regions, once converted TEDs are observed to re-convert back into BPDs in a repetitive process which provides multiple BPD pinning points.

  7. Current gain of 4H SiC high-voltage BJTs at reduced temperatures

    NASA Astrophysics Data System (ADS)

    Ivanov, P. A.; Levinshtein, M. E.; Palmour, J. W.; Agarwal, A. K.; Krishnaswami, S.

    2007-06-01

    The dependences of the common-emitter current gain β on the collector current IC have been measured at reduced temperatures in 3 kV 4H-SiC epitaxial-emitter npn bipolar junction transistors with implanted p+ base contact and base-emitter distances Lbe ranging from 3 to 15 µm. The collector-emitter voltage was fixed (at 100 V) to provide the active operation mode at any collector current in a wide range from 80 mA to 10 A (current densities of 3.5-445 A cm-2). The maximum current gain steadily grows with Lbe from 8 (Lbe = 3 µm) to 21 (Lbe = 15 µm) at room temperature. For all values of Lbe, β steadily increases as the temperature becomes lower; however, the smaller Lbe is, the weaker the effect produced by temperature lowering. As, for example, the temperature is lowered to -42 °C, β increases from 8 to 9 for structures with Lbe = 3 µm and from 21 to 31 for structures with Lbe = 15 µm. The phenomena observed have been accounted for by recombination at the p+-p base boundary.

  8. CFD Growth of 3C-SiC on 4H/6H Mesas

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Trunek, Andrew J.; Spry, David J.; Powell, J. Anthony; Du, Hui; Skowronski, Marek; Huang, XianRong; Dudley, Michael

    2006-01-01

    This article describes growth and characterization of the highest quality reproducible 3C-SiC heteroepitaxial films ever reported. By properly nucleating 3C-SiC growth on top of perfectly on-axis (0001) 4H-SiC mesa surfaces completely free of atomic scale steps and extended defects, growth of 3C-SiC mesa heterofilms completely free of extended crystal defects can be achieved. In contrast, nucleation and growth of 3C-SiC mesa heterofilms on top of 4H-SiC mesas with atomic-scale steps always results in numerous observable dislocations threading through the 3C-SiC epilayer. High-resolution X-ray diffraction and transmission electron microscopy measurements indicate non-trivial in-plane lattice mismatch between the 3C and 4H layers. This mismatch is somewhat relieved in the step-free mesa case via misfit dislocations confined to the 3C/4H interfacial region without dislocations threading into the overlying 3C-SiC layer. These results indicate that the presence or absence of steps at the 3C/4H heteroepitaxial interface critically impacts the quality, defect structure, and relaxation mechanisms of single-crystal heteroepitaxial 3C-SiC films.

  9. Self-assembly of C4H-type hydrogenated graphene.

    PubMed

    Liu, Zilong; Xue, Qingzhong; Xing, Wei; Du, Yonggang; Han, Zhide

    2013-11-21

    We demonstrate by molecular dynamic (MD) simulations that patterned partially hydrogenated graphene (C4H) can self-assemble at room temperature. The main driving force of the self-assembly of C4H is due to the one-sided distribution of hydrogen and the corresponding asymmetric orientation of sp(3) bonding, there exists strong electrostatic repulsion between the relatively close H atoms. The simulations show that C4H can self-assemble into various carbon nanoscroll (CNS) structures, this is mainly controlled by its geometry (size and aspect ratio). And the carbon nanotube (CNT) is a good candidate to activate and guide C4H to form CNS, whose core size can be controlled. Meanwhile, a novel CNT/C4H core/shell composite nanostructure is also formed. The theoretical results shed important light on a feasible approach to fabricate high-quality CNS and other novel nanostructures including core/shell structures, which hold great potential applications in optics, optoelectronic devices, hydrogen storage, sensors, and energy storage in supercapacitors or batteries. PMID:24064528

  10. CVD Growth of 3C-SiC on 4H/6H Mesas

    SciTech Connect

    Neudeck,P.; Trunek, A.; Spry, D.; Powell, J.; Du, H.; Skowronski, M.; Huang, X.; Dudley, M.

    2006-01-01

    This article describes growth and characterization of the highest quality reproducible 3C-SiC heteroepitaxial films ever reported. By properly nucleating 3C-SiC growth on top of perfectly on-axis (0001) 4H-SiC mesa surfaces completely free of atomic scale steps and extended defects, growth of 3C-SiC mesa heterofilms completely free of extended crystal defects can be achieved. In contrast, nucleation and growth of 3C-SiC mesa heterofilms on top of 4H-SiC mesas with atomic-scale steps always results in numerous observable dislocations threading through the 3C-SiC epilayer. High-resolution X-ray diffraction (HRXRD) and high resolution cross-sectional transmission electron microscopy (HRXTEM) measurements indicate non-trivial, in-plane, lattice mismatch between the 3C and 4H layers. This mismatch is somewhat relieved in the step-free mesa case via misfit dislocations confined to the 3C/4H interfacial region without dislocations threading into the overlying 3C-SiC layer. These results indicate that the presence or absence of steps at the 3C/4H heteroepitaxial interface critically impacts the quality, defect structure, and relaxation mechanisms of single-crystal heteroepitaxial 3C-SiC films.

  11. Effect of neutron irradiation on charge collection efficiency in 4H-SiC Schottky diode

    NASA Astrophysics Data System (ADS)

    Wu, Jian; Jiang, Yong; Lei, Jiarong; Fan, Xiaoqiang; Chen, Yu; Li, Meng; Zou, Dehui; Liu, Bo

    2014-01-01

    The charge collection efficiency (CCE) in 4H-SiC Schottky diode is studied as a function of neutron fluence. The 4H-SiC diode was irradiated with fast neutrons of a critical assembly in Nuclear Physics and Chemistry Institute and CCE for 3.5 MeV alpha particles was then measured as a function of the applied reverse bias. It was found from our experiment that an increase of neutron fluence led to a decrease of CCE. In particular, CCE of the diode was less than 1.3% at zero bias after an irradiation at 8.26×1014 n/cm2. A generalized Hecht's equation was employed to analyze CCE in neutron irradiated 4H-SiC diode. The calculations nicely fit the CCE of 4H-SiC diode irradiated at different neutron fluences. According to the calculated results, the extracted electron μτ product (μτ)e and hole μτ product (μτ)h of the irradiated 4H-SiC diode are found to decrease by increasing the neutron fluence.

  12. Electrical Characterization of 4H-SiC JFET Wafer: DC Parameter Variations for Extreme Temperature IC Design

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Chen, Liangyu; Spry, David J.; Beheim, Glenn M.; Chang, Carl W.

    2014-01-01

    This work reports DC electrical characterization of a 76 mm diameter 4H-SiC JFET test wafer fabricated as part of NASA's on-going efforts to realize medium-scale ICs with prolonged and stable circuit operation at temperatures as high as 500 degC. In particular, these measurements provide quantitative parameter ranges for use in JFET IC design and simulation. Larger than expected parameter variations were observed both as a function of position across the wafer as well as a function of ambient testing temperature from 23 degC to 500 degC.

  13. Nickel ohmic contacts of high-concentration P-implanted 4H-SiC

    NASA Astrophysics Data System (ADS)

    Chunjuan, Liu; Su, Liu; Jingjing, Feng; Rong, Wu

    2012-03-01

    Different-dose phosphorus ion implantation into 4H-SiC followed by high-temperature annealing was investigated. AlN/BN and graphite post-implantation annealing for ion-implanted SiC at 1650 °C for 30 min was conducted to electrically activate the implanted P+ ions. Ni contacts to the P+-implanted 4H-SiC layers were examined by transmission line model and Hall measurements fabricated on P-implanted (0001). The results indicated that a high-quality ohmic contact and specific contact resistivity of 1.30 × 10-6 Ω · cm2 was obtained for the P+-implanted 4H-SiC layers. The ρC values of the Ni-based implanted layers decreased with increasing P doping concentrations, and a weaker temperature dependence was observed for different samples in the 200-500 K temperature range.

  14. Synthesis, antifungal activity and docking study of 2-amino-4H-benzochromene-3-carbonitrile derivatives

    NASA Astrophysics Data System (ADS)

    Mirjalili, BiBi Fatemeh; Zamani, Leila; Zomorodian, Kamiar; Khabnadideh, Soghra; Haghighijoo, Zahra; Malakotikhah, Zahra; Ayatollahi Mousavi, Seyyed Amin; Khojasteh, Shaghayegh

    2016-07-01

    Pathogenic fungi are associated with diseases ranging from simple dermatosis to life-threatening infections, particularly in immunocompromised patients. During the past two decades, resistance to established antifungal drugs has increased dramatically and has made it crucial to identify novel antimicrobial compounds. Here, we selected 12 new compounds of 2-amino-4H-benzochromene-3-carbonitrile drivetives (C1-C12) for synthesis by using nano-TiCl4.SiO2 as efficient and green catalyst, then nine of synthetic compounds were evaluated against different species of fungi, positive gram and negative gram of bacteria. Standard and clinical strains of antibiotics sensitive and resistant fungi and bacteria were cultured in appropriate media. Biological activity of the 2-amino-4H-benzochromene-3-carbonitrile derivatives against fungi and bacteries were estimated by the broth micro-dilution method as recommended by clinical and laboratory standard institute (CLSI). In addition minimal fangicidal and bactericial concenteration of the compounds were also determined. Considering our results showed that compound 2-amino-4-(4-methyl benzoate)-4H-benzo[f]chromen-3-carbonitrile (C9) had the most antifungal activity against Aspergillus clavatus, Candida glabarata, Candida dubliniensis, Candida albicans and Candida tropicalis at concentrations ranging from 8 to ≤128 μg/mL. Also compounds 2-amino-4-(3,4-dimethoxyphenyl)-4H-benzo[f]chromen-3-carbonitrile (C4) and 2-amino-4-(4-isopropylphenyl)-4H-benzo[f]chromen-3-carbonitrile (C3) had significant inhibitory activities against Epidermophyton floccosum following 2-amino-4-(4-methylbenzoate)-4H-benzo[f]chromen-3-carbonitrile (C9), respectively. Docking simulation was performed to insert compounds C3, C4 and C9 in to CYP51 active site to determine the probable binding model.

  15. Adult volunteerism in Pennsylvania 4-H natural resources programs for youth

    NASA Astrophysics Data System (ADS)

    Smith, Sanford Sherrick

    2001-07-01

    Pennsylvania's 4-H Youth Development Program relies on adult volunteers to reach youth with educational information and opportunities. Finding adults willing to do this volunteer work is challenging. This study looks at the current status of adult volunteerism with natural resources 4-H projects, and seeks to understand potential volunteers. The literature has much to offer in regards to general volunteer trends, management, motivations, and task preferences; however, few studies focus on volunteers in natural resources or environmental education. A telephone survey conducted with county 4-H agents revealed that only 3.2% of Pennsylvania's 4-H volunteers work with natural resources projects in 56 out of 67 counties, and that very few volunteers have any formal background in natural resources. Semi-structured interviews with 41 adult volunteers currently working with natural resources projects explored volunteer demographics, history, program design preferences, and ideas for seeking more volunteers. Findings from the telephone survey and the semi-structured interviews were used to generate a mail survey with large, random samples from three population groups: (1) 4-H Volunteers, (2) 4-H Parents, and (3) Natural Resources Professionals. Confidence with youth and subject matter, and adult willingness to volunteer was explored for each of the groups in relation to background, demographic characteristics, motivational needs, past and present volunteer activity, personal interests, and program design importance. Natural resources subject matter confidence was shown to be the most significant variable determining willingness to volunteer for all three groups. The variables that contributed to subject matter and youth confidence varied for each population. Key variables effecting willingness to volunteer included outdoor activity level, personal interest in natural resources, the need to fulfill feelings of social responsibility, and confidence with youth. Program design

  16. Anti-reflective nano- and micro-structures on 4H-SiC for photodiodes

    PubMed Central

    2011-01-01

    In this study, nano-scale honeycomb-shaped structures with anti-reflection properties were successfully formed on SiC. The surface of 4H-SiC wafer after a conventional photolithography process was etched by inductively coupled plasma. We demonstrate that the reflection characteristic of the fabricated photodiodes has significantly reduced by 55% compared with the reference devices. As a result, the optical response Iillumination/Idark of the 4H-SiC photodiodes were enhanced up to 178%, which can be ascribed primarily to the improved light trapping in the proposed nano-scale texturing. PMID:21711744

  17. Crystal and molecular structure of 2,4,4-trisubstituted 5-amino-4 H-imidazoles

    NASA Astrophysics Data System (ADS)

    Bellanato, J.; Avendaño, C.; Ramos, M. T.; Smith-Verdier, P.; Florencio, F.; Garcia-Blanco, S.

    Three 5-amino-4 H-imidazole derivatives 2(2-pyridyl) and 2-ethoxycarbonyl-4,4-pentamethylene-5-amino-and 2(2-pyridyl)-4,4-dimethyl-5(2-pyridylamino)4 H-imidazoles have been studied by i.r. and Raman spectroscopy. The crystal structure of one has been determined by X-ray diffraction. The tautomeric amino-imino equilibrium in different working conditions is also studied from spectroscopic data. The amino and the unconjugated imino forms are characterized.

  18. Estimation of negative ions in VHF SiH4/H2 plasma

    NASA Astrophysics Data System (ADS)

    Yamane, Tsukasa; Nakano, Shinya; Nakao, Sachiko; Takeuchi, Yoshiaki; Ichiki, Ryuta; Muta, Hiroshi; Uchino, Kiichiro; Kawai, Yoshinobu

    2014-11-01

    The characteristics of a VHF SiH4/H2 plasma (frequency: 60 MHz) at high pressures were examined as a function of silane concentration with a heated Langmuir probe. Anomalous reductions in electron saturation current were observed, suggesting the existence of many negative ions. An estimation of the concentration of negative ions was attempted using the sheath theory including negative ions. It was found that there exist H- and SiH3- ions as dominant negative ions in the VHF SiH4/H2 plasma. In addition, the measured floating potential agreed with the theoretical value.

  19. Managing for Motivation: Herzberg's Motivation-Hygiene Theory and Its Application to 4-H Leadership. National Intern Report.

    ERIC Educational Resources Information Center

    Freeman, Walter J.

    A study examined the organizational factors contributing to the motivation of 4-H volunteer leaders. A modified form of Herzberg's Motivation-Hygiene Theory served as the research design of the study. A total of 149 4-H leaders were interviewed regarding thirteen job factors: recognition; personal growth; relationships with other 4-H leaders,…

  20. Current Practices for Training Staff to Accommodate Youth with Special Health Care Needs in the 4-H Camp Setting

    ERIC Educational Resources Information Center

    Mouton, Lauren; Bruce, Jacklyn

    2013-01-01

    The theory of inclusion is the foundation for the study reported here; inclusion is a focus not only of formal education, but also of nonformal educational settings such as 4-H. Ideally, 4-H camps are designed to serve youth of all backgrounds and abilities. By accommodating youth with special health care needs, 4-H camps are effectively meeting…

  1. E-Learning for 4-H Volunteers: Who Uses It, and What Can We Learn from Them?

    ERIC Educational Resources Information Center

    Ouellette, Kristy L.; Lesmeister, Marilyn K.; Lobley, Jennifer; Gross, Kerry M.

    2014-01-01

    Orienting and training 4-H volunteers are critical to individuals and the organization. The two-part study reported here re-establishes the profile of the 4-H volunteer and evaluates both the format and content of e-Learning for 4-H Volunteers modules launched in 2006. Volunteers from seven states perceived that online modules made learning more…

  2. Stress Characterization of 4H-SiC Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) using Raman Spectroscopy and the Finite Element Method.

    PubMed

    Yoshikawa, Masanobu; Kosaka, Kenichi; Seki, Hirohumi; Kimoto, Tsunenobu

    2016-07-01

    We measured the depolarized and polarized Raman spectra of a 4H-SiC metal-oxide-semiconductor field-effect transistor (MOSFET) and found that compressive stress of approximately 20 MPa occurs under the source and gate electrodes and tensile stress of approximately 10 MPa occurs between the source and gate electrodes. The experimental result was in close agreement with the result obtained by calculation using the finite element method (FEM). A combination of Raman spectroscopy and FEM provides much data on the stresses in 4H-SiC MOSFET.

  3. Stress Characterization of 4H-SiC Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) using Raman Spectroscopy and the Finite Element Method.

    PubMed

    Yoshikawa, Masanobu; Kosaka, Kenichi; Seki, Hirohumi; Kimoto, Tsunenobu

    2016-07-01

    We measured the depolarized and polarized Raman spectra of a 4H-SiC metal-oxide-semiconductor field-effect transistor (MOSFET) and found that compressive stress of approximately 20 MPa occurs under the source and gate electrodes and tensile stress of approximately 10 MPa occurs between the source and gate electrodes. The experimental result was in close agreement with the result obtained by calculation using the finite element method (FEM). A combination of Raman spectroscopy and FEM provides much data on the stresses in 4H-SiC MOSFET. PMID:27165155

  4. Report on the 4-h rule and National Emergency Access Target (NEAT) in Australia: time to review.

    PubMed

    Staib, Andrew; Sullivan, Clair; Griffin, Bronwyn; Bell, Anthony; Scott, Ian

    2016-06-01

    Objective The aim of the present study was to provide a summary of a systematic review of literature reporting benefits and limitations of implementing National Emergency Access Target (NEAT), a target stipulating that a certain proportion of patients presenting to hospital emergency departments are admitted or discharged within 4h of presentation. Methods A systematic review of published literature using specific search terms, snowballing techniques applied to retrieved references and Google searches was performed. Results are presented as a narrative synthesis given the heterogeneity of included studies. Results Benefits of a time-based target for emergency care are improved timeliness of emergency care and reduced in-hospital mortality for emergency admissions to hospital. Limitations centre on using a process measure (time) alone devoid of any monitoring of patient outcomes, the threshold nature of a time target and the fact that currently NEAT combines the measurement of clinical management of two very different patient cohorts seeking emergency care: less acute patients discharged home and more acute patients admitted to hospital. Conclusions Time-based access targets for emergency presentations are associated with significant improvements in in-hospital mortality for emergency admissions. However, other patient-important outcomes are deserving of attention, choice of targets needs to be validated by empirical evidence of patient benefit and single targets need to be partitioned into separate targets pertaining to admitted and discharged patients. What is known about the topic? Time targets for emergency care originated in the UK. The introduction of NEAT in Australia has been controversial. NEAT directs that a certain proportion of patients will be admitted or discharged from an emergency department (ED) within 4h. Recent dissolution of the Australian National Partnership Agreement (which provided hospitals with financial incentives for achieving NEAT

  5. Depth dependent modification of optical constants arising from H+ implantation in n-type 4H-SiC measured using coherent acoustic phonons

    NASA Astrophysics Data System (ADS)

    Baydin, Andrey; Krzyzanowska, Halina; Dhanunjaya, Munthala; Nageswara Rao, S. V. S.; Davidson, Jimmy L.; Feldman, Leonard C.; Tolk, Norman H.

    2016-06-01

    Silicon carbide (SiC) is a promising material for new generation electronics including high power/high temperature devices and advanced optical applications such as room temperature spintronics and quantum computing. Both types of applications require the control of defects particularly those created by ion bombardment. In this work, modification of optical constants of 4H-SiC due to hydrogen implantation at 180 keV and at fluences ranging from 1014 to 1016 cm-2 is reported. The depth dependence of the modified optical constants was extracted from coherent acoustic phonon spectra. Implanted spectra show a strong dependence of the 4H-SiC complex refractive index depth profile on H+ fluence. These studies provide basic insight into the dependence of optical properties of 4H silicon carbide on defect densities created by ion implantation, which is of relevance to the fabrication of SiC-based photonic and optoelectronic devices.

  6. Theoretical investigation of the formation of basal plane stacking faults in heavily nitrogen-doped 4H-SiC crystals

    NASA Astrophysics Data System (ADS)

    Taniguchi, Chisato; Ichimura, Aiko; Ohtani, Noboru; Katsuno, Masakazu; Fujimoto, Tatsuo; Sato, Shinya; Tsuge, Hiroshi; Yano, Takayuki

    2016-04-01

    The formation of basal plane stacking faults in heavily nitrogen-doped 4H-SiC crystals was theoretically investigated. A novel theoretical model based on the so-called quantum well action mechanism was proposed; the model considers several factors, which were overlooked in a previously proposed model, and provides a detailed explanation of the annealing-induced formation of double layer Shockley-type stacking faults in heavily nitrogen-doped 4H-SiC crystals. We further revised the model to consider the carrier distribution in the depletion regions adjacent to the stacking fault and successfully explained the shrinkage of stacking faults during annealing at even higher temperatures. The model also succeeded in accounting for the aluminum co-doping effect in heavily nitrogen-doped 4H-SiC crystals, in that the stacking fault formation is suppressed when aluminum acceptors are co-doped in the crystals.

  7. Middle School Dropout? Enrollment Trends in the California 4-H Youth Development Program

    ERIC Educational Resources Information Center

    Russell, Stephen T.; Heck, Katherine E.

    2008-01-01

    There is a widespread belief that youth drop out of youth development programs during the middle school years. Alternative explanations for the smaller number of adolescent program participants have yet to be explored. We examine age trends in program enrollment using data from over 221,000 youth enrolled in the California 4-H Youth Development…

  8. Promoting the Essential Elements of 4-H Youth Development through an Experiential Learning Model

    ERIC Educational Resources Information Center

    Meyer, Shelley; Jones, Kenneth R.

    2015-01-01

    The purpose of the project reported here was to apply Experiential Learning Theory to a context involving middle and high school aged youth while assessing the four concepts (belonging, mastery, independence, and generosity) in relation to the 4-H youth development essential elements. The conclusions of the project's evaluation suggest…

  9. A Partnership Model for Training Episodic Environmental Stewardship 4-H Volunteers

    ERIC Educational Resources Information Center

    Young, Jane Chin; Alexander, Janice; Smith, Martin H.

    2013-01-01

    The Marin Environmental Stewardship pilot project demonstrates the potential for a partnership model that brings together external and internal collaborators to recruit and train episodic 4-H volunteers to meet environmental education needs within a community. The clientele served by the volunteers trained through the project was at-risk, urban…

  10. The Value of 4-H Judging Teams--Missouri Dairy Judging Alumni Survey

    ERIC Educational Resources Information Center

    Deaver, Karla; Probert, Ted

    2016-01-01

    Former Missouri 4-H Dairy Judging Team members responded to a survey about life skills development and the value of the judging team experience. Results of the survey indicate that judging team experience was highly influential in the development of communication, public speaking, and presentation skills. Respondents also indicated that judging…

  11. Determining Directions for Change in a County 4-H Youth Program: The Role of Evaluation.

    ERIC Educational Resources Information Center

    Braverman, Marc; And Others

    This paper describes the evaluation of the 4-H youth program (serving ages 9 through 19) in Yolo County, California. The paper concentrates on the first component of the evaluation plan, a telephone survey of community needs and perceptions regarding services for youth which was conducted in November, 1984. The originally perceived questions…

  12. The Big E (Energy). 4-H Leader's Guide for Units 2 & 3.

    ERIC Educational Resources Information Center

    Caldwell, William; And Others

    This leader's guide is designed for units 2 and 3 of the Nebraska 4-H Energy Project. The goals of the project are to: (1) help young people understand energy problems related to life styles; (2) use energy resources carefully; (3) guide members in choosing their own energy alternatives; and (4) to enjoy together the challenges and creativity of…

  13. Participant Comfort with and Application of Inquiry-Based Learning: Results from 4-H Volunteer Training

    ERIC Educational Resources Information Center

    Haugen, Heidi; Stevenson, Anne; Meyer, Rebecca L.

    2016-01-01

    This article explores how a one-time training designed to support learning transfer affected 4-H volunteers' comfort levels with the training content and how comfort levels, in turn, affected the volunteers' application of tools and techniques learned during the training. Results of a follow-up survey suggest that the training participants…

  14. Diastereoselectivity in prebiotically relevant 5(4H)-oxazolone-mediated peptide couplings.

    PubMed

    Beaufils, Damien; Danger, Grégoire; Boiteau, Laurent; Rossi, Jean-Christophe; Pascal, Robert

    2014-03-21

    A stereochemical study of a potentially prebiotic peptide-forming reaction was carried out as the first part of a systems chemistry investigation of potential paths for symmetry breaking. Substantial diastereomeric excesses result from a fast epimerization of the 5(4H)-oxazolone intermediate in aqueous solution.

  15. Stakeholder Satisfaction with a 4-H Extension Program for Five- to Eight-Year-Old Children.

    ERIC Educational Resources Information Center

    Scheer, Scott D.; Lafontaine, Kenneth R.

    1999-01-01

    A 4-H K-2 program was evaluated by 277 parents, 144 volunteers, and 44 extension agents. These stakeholders believed the program was beneficial and effective in improving children's life skills (self-esteem, making friends, making choices, learning and physical skills). (SK)

  16. 4-H Chickquest: Connecting Agri-Science with STEM Standards in Urban Schools

    ERIC Educational Resources Information Center

    Horton, Robert L.; Krieger, Jackie; Halasa, Katrina

    2013-01-01

    While young students are more capable of scientific inquiry than previously believed, elementary school teachers are often inexperienced in and lack confidence with teaching science. ChickQuest is a 4-H-created embryology curriculum for third-graders that meets Ohio state science standards, teaches STEM skills, and promotes ongoing interaction…

  17. 4-H Horticulture Project Activity Guides. Leader's Guide and Units 1-3.

    ERIC Educational Resources Information Center

    Illinois Univ., Urbana. Cooperative Extension Service.

    This document, concerning the 4-H horticulture project, includes a leader's guide and three youth activity guides. The leader's guide can be used to plan group project meetings that are both fun and educational. Activities can be adapted to various age groups. The leader's guide includes basic information for growing plants indoors and outdoors,…

  18. The Big E (Energy). 4-H Leader's Guide [for Unit 1].

    ERIC Educational Resources Information Center

    Caldwell, William; And Others

    This guide is designed for leaders of the Nebraska 4-H Energy Project. The goals of the project are to: (1) help young people understand energy problems related to life styles; (2) use energy resources carefully; (3) guide members in choosing their own energy alternatives; and (4) enjoy together the challenges and creativity of finding energy…

  19. 4H-SiC photodiode model for DC SPICE circuit simulation

    NASA Astrophysics Data System (ADS)

    Kociubiński, Andrzej; Duk, Mariusz; Korona, Mateusz; Muzyka, Krzysztof

    2015-09-01

    Technology, characterization and in particularly modeling of 4H-SiC photodiode have been presented in this paper. Modeling and simulation has been performed using PSPICE environment. Comparison of simulation with real results for electrical characteristic (I-V) of circular SiC photodiodes has been also presented.

  20. Bufexamac ameliorates LPS-induced acute lung injury in mice by targeting LTA4H

    PubMed Central

    Xiao, Qiang; Dong, Ningning; Yao, Xue; Wu, Dang; Lu, Yanli; Mao, Fei; Zhu, Jin; Li, Jian; Huang, Jin; Chen, Aifang; Huang, Lu; Wang, Xuehai; Yang, Guangxiao; He, Guangyuan; Xu, Yong; Lu, Weiqiang

    2016-01-01

    Neutrophils play an important role in the occurrence and development of acute lung injury (ALI). Leukotriene B4 (LTB4), a hydrolysis product of epoxide leukotriene A4 (LTA4) catalyzed by LTA4 hydrolase (LTA4H), is one of the most potent chemoattractants for neutrophil. Bufexamac is a drug widely used as an anti-inflammatory agent on the skin, however, the mechanism of action is still not fully understood. In this study, we found bufexamac was capable of specifically inhibiting LTA4H enzymatic activity and revealed the mode of interaction of bufexamac and LTA4H using X-ray crystallography. Moreover, bufexamac significantly prevented the production of LTB4 in neutrophil and inhibited the fMLP-induced neutrophil migration through inhibition of LTA4H. Finally, bufexamac significantly attenuated lung inflammation as reflected by reduced LTB4 levels and weakened neutrophil infiltration in bronchoalveolar lavage fluid from a lipopolysaccharide-induced ALI mouse model. In summary, our study indicates that bufexamac acts as an inhibitor of LTB4 biosynthesis and may have potential clinical applications for the treatment of ALI. PMID:27126280

  1. Endocrine Aspects of 4H Leukodystrophy: A Case Report and Review of the Literature

    PubMed Central

    Billington, Emma; Bernard, Geneviève; Gibson, William; Corenblum, Bernard

    2015-01-01

    Introduction. 4H leukodystrophy is an autosomal recessive RNA polymerase III-related leukodystrophy, characterized by hypomyelination, with or without hypodontia (or other dental abnormalities) and hypogonadotropic hypogonadism. Case Presentation. We describe a 28-year-old female who presented with primary amenorrhea at the age of 19. She had a history of very mild neurological and dental abnormalities. She was found to have hypogonadotropic hypogonadism, and magnetic resonance imaging of the brain showed hypomyelination. The diagnosis of 4H leukodystrophy was made. She was subsequently found to have mutations in the POLR3B gene, which encodes the second largest subunit of RNA polymerase III. She wished to become pregnant and failed to respond to pulsatile GnRH but achieved normal follicular growth and ovulation with subcutaneous gonadotropin therapy. Discussion. Patients with 4H leukodystrophy may initially present with hypogonadotropic hypogonadism, particularly if neurological and dental manifestations are subtle. Making the diagnosis has important implications for prognosis and management. Progressive neurologic deterioration is expected, and progressive endocrine dysfunction may occur. Patients with 4H leukodystrophy should be counseled about disease progression and about this disease's autosomal recessive inheritance pattern. In those who wish to conceive, ovulation induction may be achieved with subcutaneous gonadotropin therapy, but pulsatile GnRH does not appear to be effective. PMID:26113998

  2. South Carolina's Model for Initiating Hispanic 4-H Clubs

    ERIC Educational Resources Information Center

    Lippert, Robert; Rembert, Kellye

    2012-01-01

    Over the past 5 years, through the initiative of several county Extension agents, South Carolina 4-H has established a successful model for bringing Hispanic youth into our program. We have found the most effective method is to initiate contact and establish partnerships with the principals and ESOL instructors in the local schools. Through this…

  3. Possession, Transportation, and Use of Firearms by Older Youth in 4-H Shooting Sports Programs

    ERIC Educational Resources Information Center

    White, David J.; Williver, S. Todd

    2014-01-01

    Thirty years ago we would think nothing of driving to school with a jackknife in our pocket or rifle in the gun rack. Since then, the practices of possessing, transporting, and using firearms have been limited by laws, rules, and public perception. Despite restrictions on youth, the Youth Handgun Safety Act does afford 4-H shooting sports members…

  4. Carbon nanoscroll from C4H/C4F-type graphene superlattice: MD and MM simulation insights.

    PubMed

    Liu, Zilong; Xue, Qingzhong; Tao, Yehan; Li, Xiaofang; Wu, Tiantian; Jin, Yakang; Zhang, Zhongyang

    2015-02-01

    Morphology manipulation opens up a new avenue for controlling and tailoring the functional properties of graphene, enabling the exploration of graphene-based nanomaterials. Through mixing single-side-hydrogenated graphene (C4H) with fluorinated graphene (C4F) on one single sheet, the C4H/C4F-type graphene superlattices can self-scroll at room temperature. We demonstrate using molecular dynamic (MD) simulations that different proportions, sizes, directions of hydrogenation and fluorination, and geometry of graphene have a great influence on the self-scrolling of superlattices into a variety of well-defined carbon nanoscrolls (CNSs), thus providing a controllable approach to tune their structures. Based on molecular mechanics (MM) simulations, the CNSs bear more than eight times the radial pressure than that of their multiwalled carbon nanotube (MWNT) counterparts, and an excellent radial elasticity of CNSs is also shown. Compared with conventional CNSs, these novel CNSs are endowed with more ample and flexible heterogeneous structures due to the on-demand hydrogenation and fluorination. Besides, this work provides a feasible route to achieve the necessary electronic and optical changes to be applied in graphene device applications. PMID:25531924

  5. Carbon nanoscroll from C4H/C4F-type graphene superlattice: MD and MM simulation insights.

    PubMed

    Liu, Zilong; Xue, Qingzhong; Tao, Yehan; Li, Xiaofang; Wu, Tiantian; Jin, Yakang; Zhang, Zhongyang

    2015-02-01

    Morphology manipulation opens up a new avenue for controlling and tailoring the functional properties of graphene, enabling the exploration of graphene-based nanomaterials. Through mixing single-side-hydrogenated graphene (C4H) with fluorinated graphene (C4F) on one single sheet, the C4H/C4F-type graphene superlattices can self-scroll at room temperature. We demonstrate using molecular dynamic (MD) simulations that different proportions, sizes, directions of hydrogenation and fluorination, and geometry of graphene have a great influence on the self-scrolling of superlattices into a variety of well-defined carbon nanoscrolls (CNSs), thus providing a controllable approach to tune their structures. Based on molecular mechanics (MM) simulations, the CNSs bear more than eight times the radial pressure than that of their multiwalled carbon nanotube (MWNT) counterparts, and an excellent radial elasticity of CNSs is also shown. Compared with conventional CNSs, these novel CNSs are endowed with more ample and flexible heterogeneous structures due to the on-demand hydrogenation and fluorination. Besides, this work provides a feasible route to achieve the necessary electronic and optical changes to be applied in graphene device applications.

  6. Seasonal variations of C4H2, C2N2 and C3H4 in Titan's lower stratosphere

    NASA Astrophysics Data System (ADS)

    Sylvestre, Melody; Teanby, Nicholas; Irwin, Patrick

    2016-06-01

    Due to its obliquity (26.7°), Titan's atmosphere undergoes significant seasonal variations of insolation, which are expected to affect significantly its photochemistry and large-scale dynamics. The duration of the Cassini mission enables us to monitor these changes and to better understand the atmospheric processes at play. Here, we study the seasonal evolution of the composition of Titan's lower stratosphere (10 mbar). We analyse nadir high resolution (0.5 cm‑1) spectra from Cassini/CIRS (Composite InfraRed Spectrometer) in the far infrared (200-400 cm‑1), in order to retrieve the abundances of three photochemical species: C2N2 (cyanogen), C4H2 (diacetylene), and C3H4 (methylacetylene). These data span all the latitudes and were acquired from 2004 to 2015. Consequently, they provide a good overview of the seasonal evolution of the meridional distributions of C2N2, C4H2, and C3H4, from northern winter to spring. For instance, these measurements show a strong enrichment in these three species at the South pole in the lower stratosphere, consistent with previous observations (Coustenis et al., 2016; Vinatier et al., 2015 ; Teanby et al., 2012). In contrast, other latitudes present much less variations in the mixing ratios of these gases, especially at the North Pole. These measurements will be used to provide constraints on the photochemistry and atmospheric dynamics in Titan's lower stratosphere.

  7. Synthesis of 2H-Azirines by Iridium-Catalyzed Decarboxylative Ring Contraction of Isoxazol-5(4H)-ones.

    PubMed

    Okamoto, Kazuhiro; Shimbayashi, Takuya; Yoshida, Masato; Nanya, Atsushi; Ohe, Kouichi

    2016-06-13

    A phosphine-free iridium-catalyzed reaction of isoxazol-5(4H)-ones (isoxazolones) has been developed, and affords 2H-azirines through decarboxylation and ring contraction. This method provides an efficient and environmentally benign protocol which could replace the conventional approaches used to synthesize 2H-azirines. PMID:27125870

  8. Synthesis of 2H-Azirines by Iridium-Catalyzed Decarboxylative Ring Contraction of Isoxazol-5(4H)-ones.

    PubMed

    Okamoto, Kazuhiro; Shimbayashi, Takuya; Yoshida, Masato; Nanya, Atsushi; Ohe, Kouichi

    2016-06-13

    A phosphine-free iridium-catalyzed reaction of isoxazol-5(4H)-ones (isoxazolones) has been developed, and affords 2H-azirines through decarboxylation and ring contraction. This method provides an efficient and environmentally benign protocol which could replace the conventional approaches used to synthesize 2H-azirines.

  9. High efficiency 4H-SiC betavoltaic power sources using tritium radioisotopes

    NASA Astrophysics Data System (ADS)

    Thomas, Christopher; Portnoff, Samuel; Spencer, M. G.

    2016-01-01

    Realization of an 18.6% efficient 4H-silicon carbide (4H-SiC) large area betavoltaic power source using the radioisotope tritium is reported. A 200 nm 4H-SiC P+N junction is used to collect high-energy electrons. The electron source is a titanium tritide (TiH3x) foil, or an integrated titanium tritide region formed by the diffusion of tritium into titanium. The specific activity of the source is directly measured. Dark current measured under short circuit conditions was less than 6.1 pA/cm2. Samples measured with an external tritium foil produced an open circuit voltage of 2.09 V, short circuit current of 75.47 nA/cm2, fill factor of 0.86, and power efficiency of 18.6%. Samples measured with an integrated source produced power efficiencies of 12%. Simulations were done to determine the beta spectrum (modified by self absorption) exiting the source and the electron hole pair generation function in the 4H-SiC. The electron-hole pair generation function in 4H-SiC was modeled as a Gaussian distribution, and a closed form solution of the continuity equation was used to analyze the cell performance. The effective surface recombination velocity in our samples was found to be 105-106 cm/s. Our analysis demonstrated that the surface recombination dominates the performance of a tritium betavoltaic device but that using a thin P+N junction structure can mitigate some of the negative effects.

  10. Experimental Durability Testing of 4H SiC JFET Integrated Circuit Technology at 727 C

    NASA Technical Reports Server (NTRS)

    Spry, David; Neudeck, Phil; Chen, Liangyu; Chang, Carl; Lukco, Dorothy; Beheim, Glenn M

    2016-01-01

    We have reported SiC integrated circuits (IC's) with two levels of metal interconnect that have demonstrated prolonged operation for thousands of hours at their intended peak ambient operational temperature of 500 C [1, 2]. However, it is recognized that testing of semiconductor microelectronics at temperatures above their designed operating envelope is vital to qualification. Towards this end, we previously reported operation of a 4H-SiC JFET IC ring oscillator on an initial fast thermal ramp test through 727 C [3]. However, this thermal ramp was not ended until a peak temperature of 880 C (well beyond failure) was attained. Further experiments are necessary to better understand failure mechanisms and upper temperature limit of this extreme-temperature capable 4H-SiC IC technology. Here we report on additional experimental testing of custom-packaged 4H-SiC JFET IC devices at temperatures above 500 C. In one test, the temperature was ramped and then held at 727 C, and the devices were periodically measured until electrical failure was observed. A 4H-SiC JFET on this chip electrically functioned with little change for around 25 hours at 727 C before rapid increases in device resistance caused failure. In a second test, devices from our next generation 4H-SiC JFET ICs were ramped up and then held at 700 C (which is below the maximum deposition temperature of the dielectrics). Three ring oscillators functioned for 8 hours at this temperature before degradation. In a third experiment, an alternative die attach of gold paste and package lid was used, and logic circuit operation was demonstrated for 143.5 hours at 700 C.

  11. Human pharmacology of 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) after repeated doses taken 4 h apart Human pharmacology of MDMA after repeated doses taken 4 h apart.

    PubMed

    Farré, Magí; Tomillero, Angels; Pérez-Mañá, Clara; Yubero, Samanta; Papaseit, Esther; Roset, Pere-Nolasc; Pujadas, Mitona; Torrens, Marta; Camí, Jordi; de la Torre, Rafael

    2015-10-01

    3,4-Methylenedioxymethamphetamine (MDMA, ecstasy) is a popular psychostimulant, frequently associated with multiple administrations over a short period of time. Repeated administration of MDMA in experimental settings induces tolerance and metabolic inhibition. The aim is to determine the acute pharmacological effects and pharmacokinetics resulting from two consecutive 100mg doses of MDMA separated by 4h. Ten male volunteers participated in a randomized, double-blind, crossover, placebo-controlled trial. The four conditions were placebo plus placebo, placebo plus MDMA, MDMA plus placebo, and MDMA plus MDMA. Outcome variables included pharmacological effects and pharmacokinetic parameters. After a second dose of MDMA, most effects were similar to those after a single dose, despite a doubling of MDMA concentrations (except for systolic blood pressure and reaction time). After repeated MDMA administration, a 2-fold increase was observed in MDMA plasma concentrations. For a simple dose accumulation MDMA and MDA concentrations were higher (+23.1% Cmax and +17.1% AUC for MDMA and +14.2% Cmax and +10.3% AUC for MDA) and HMMA and HMA concentrations lower (-43.3% Cmax and -39.9% AUC for HMMA and -33.2% Cmax and -35.1% AUC for HMA) than expected, probably related to MDMA metabolic autoinhibition. Although MDMA concentrations doubled after the second dose, most pharmacological effects were similar or slightly higher in comparison to the single administration, except for systolic blood pressure and reaction time which were greater than predicted. The pharmacokinetic-effects relationship suggests that when MDMA is administered at a 4h interval there exists a phenomenon of acute tolerance to its effects.

  12. High growth rate 4H-SiC epitaxial growth using dichlorosilane in a hot-wall CVD reactor

    NASA Astrophysics Data System (ADS)

    Chowdhury, Iftekhar; Chandrasekhar, M. V. S.; Klein, Paul B.; Caldwell, Joshua D.; Sudarshan, Tangali

    2011-02-01

    Thick, high quality 4H-SiC epilayers have been grown in a vertical hot-wall chemical vapor deposition system at a high growth rate on (0 0 0 1) 8° off-axis substrates. We discuss the use of dichlorosilane as the Si-precursor for 4H-SiC epitaxial growth as it provides the most direct decomposition route into SiCl 2, which is the predominant growth species in chlorinated chemistries. A specular surface morphology was attained by limiting the hydrogen etch rate until the system was equilibrated at the desired growth temperature. The RMS roughness of the grown films ranged from 0.5-2.0 nm with very few morphological defects (carrots, triangular defects, etc.) being introduced, while enabling growth rates of 30-100 μm/h, 5-15 times higher than most conventional growths. Site-competition epitaxy was observed over a wide range of C/Si ratios, with doping concentrations <1×10 14 cm -3 being recorded. X-ray rocking curves indicated that the epilayers were of high crystallinity, with linewidths as narrow as 7.8 arcsec being observed, while microwave photoconductive decay (μPCD) measurements indicated that these films had high injection (ambipolar) carrier lifetimes in the range of 2 μs.

  13. Detection of minority carrier traps in p-type 4H-SiC

    SciTech Connect

    Alfieri, G.; Kimoto, T.

    2014-03-03

    Contrarily to the case of n-type 4H-SiC, very little is known about the presence of minority carrier traps in p-type epilayers. In this study, we performed the electrical characterization of as-grown, electron irradiated, and thermally oxidized p-type 4H-SiC, by using minority carrier transient spectroscopy. Four minority carrier traps are reported in 1.6–2.3 eV energy range above the valence band edge (E{sub V}). Particular emphasis is given to the mid-gap minority carrier trap (EH{sub 6∕7}) and to its correlation to an energetically close mid-gap majority carrier trap (HK4)

  14. Magnesium chloride tetrahydrate, MgCl2·4H2O.

    PubMed

    Schmidt, Horst; Hennings, Erik; Voigt, Wolfgang

    2012-01-01

    The title compound, MgCl(2)·4H(2)O, was crystallized at 403 K and its structure determined at 200 K. The structure is built up from MgCl(2)(H(2)O)(4) octahedra with a trans configuration. Each complex is situated on a crystallographic twofold axis, with the rotation axis aligned along one H(2)O-Mg-OH(2) axis. They are connected by a complex network of O-H···Cl hydrogen bonds. The structure contains two-dimensional sections that are essentially identical to those in the reported tetrahydrates of CrCl(2), FeCl(2), FeBr(2) and CoBr(2), but they are stacked in a different manner in MgCl(2)·4H(2)O compared with the transition metal structures.

  15. A 4H Silicon Carbide Gate Buffer for Integrated Power Systems

    SciTech Connect

    Ericson, N; Frank, S; Britton, C; Marlino, L; Ryu, SH; Grider, D; Mantooth, A; Francis, M; Lamichhane, R; Mudholkar, M; Shepherd, P; Glover, M; Valle-Mayorga, J; McNutt, T; Barkley, A; Whitaker, B; Cole, Z; Passmore, B; Lostetter, A

    2014-02-01

    A gate buffer fabricated in a 2-mu m 4H silicon carbide (SiC) process is presented. The circuit is composed of an input buffer stage with a push-pull output stage, and is fabricated using enhancement mode N-channel FETs in a process optimized for SiC power switching devices. Simulation and measurement results of the fabricated gate buffer are presented and compared for operation at various voltage supply levels, with a capacitive load of 2 nF. Details of the design including layout specifics, simulation results, and directions for future improvement of this buffer are presented. In addition, plans for its incorporation into an isolated high-side/low-side gate-driver architecture, fully integrated with power switching devices in a SiC process, are briefly discussed. This letter represents the first reported MOSFET-based gate buffer fabricated in 4H SiC.

  16. The C4H radical and the diffuse interstellar bands. An ab initio study

    NASA Technical Reports Server (NTRS)

    Kolbuszewski, Marcin

    1994-01-01

    An ab initio study of the low-lying electronic states of C4H has been presented where the species studied has a chi(2)sigma(+) ground state and two low lying pi states. Based on the vertical and adiabatic excitation energies between those states it is suggested that the 4428 A diffuse interstellar band is not carried by C4H. The application of the particle in a box model shows strong coincidences between the strong DIB's and predicted wavelengths of pi-pi transitions in C(2n)H series. Based on those coincidences, it is suggested the C(2n)H species as good candidates for carriers of diffuse interstellar bands.

  17. Donor-acceptor-pair emission in fluorescent 4H-SiC grown by PVT method

    SciTech Connect

    Liu, Xi Zhuo, Shi-Yi; Gao, Pan; Huang, Wei; Yan, Cheng-Feng; Shi, Er-Wei

    2015-04-15

    Fluorescent SiC, which contains donor and acceptor impurities with optimum concentrations, can work as a phosphor for visible light emission by donor-acceptor-pair (DAP) recombination. In this work, 3 inch N-B-Al co-doped fluorescent 4H-SiC crystals are prepared by PVT method. The p-type fluorescent 4H-SiC with low aluminum doping concentration can show intensive yellow-green fluorescence at room temperature. N-B DAP peak wavelength shifts from 578nm to 525nm and weak N-Al DAP emission occurred 403/420 nm quenches, when the temperature increases from 4K to 298K. The aluminum doping induces higher defect concentration in the fluorescent crystal and decreases optical transmissivity of the crystal in the visible light range. It triggers more non-radiative recombination and light absorption losses in the crystal.

  18. Characteristic morphologies of triangular defects on Si-face 4H-SiC epitaxial films

    NASA Astrophysics Data System (ADS)

    Yamashita, T.; Naijo, T.; Matsuhata, H.; Momose, K.; Osawa, H.; Okumura, H.

    2016-01-01

    Triangular defects with a characteristic morphology consisting of a 3C-type structure were investigated on Si-face 4H-SiC epitaxial films using electron microscopy. Two types of triangular defects were investigated: one with a single valley on the surface along the [ 11 2 bar 0 ] direction and another with several parallel ridges and valleys called "washboard-like defects". The defects with a single valley had a characteristic domain structure consisting of four 3C crystals, which is similar to that of previously reported comet-shaped defects on the C-face. It is shown that the 3C domain in the washboard-like defect is covered by 4H layers with a washboard-like morphology.

  19. Electric-field dependence of electron drift velocity in 4H-SiC

    NASA Astrophysics Data System (ADS)

    Ivanov, P. A.; Potapov, A. S.; Samsonova, T. P.; Grekhov, I. V.

    2016-09-01

    Room temperature isothermal forward current-voltage characteristics of mesa-epitaxial 4H-SiC Schottky diodes were measured at high electric fields (beyond 105 V/cm) in the 34-μm thick n-base doped at 1 × 1015 cm-3. The effect of diode self-heating on current was minimized when using single 4-ns pulses. The analytical formula was derived for the dependence of electron drift velocity on electric field along c-axis.

  20. Resistance of 4H-SiC Schottky barriers at high forward-current densities

    SciTech Connect

    Ivanov, P. A. Samsonova, T. P.; Il’inskaya, N. D.; Serebrennikova, O. Yu.; Kon’kov, O. I.; Potapov, A. S.

    2015-07-15

    The resistance of Schottky barriers based on 4H-SiC is experimentally determined at high forward-current densities. The measured resistance is found to be significantly higher than the resistance predicted by classical mechanisms of electron transport in Schottky contacts. An assumption concerning the crucial contribution of the tunnel-transparent intermediate oxide layer between the metal and semiconductor to the barrier resistance is proposed and partially justified.

  1. Polarographic study of cadmium 5-hydroxy 2-(hydroxymethyl) 4H-pyran-4-one complex

    NASA Technical Reports Server (NTRS)

    Wilson, Ray F.; Daniels, Robert C.

    1989-01-01

    A polarographic study was performed on the products formed in the interaction of cadmium (II) with a 5-hydroxy 2-(hydroxymethyl) 4H-Pyran-4-one, using varying conditions of pH, supporting electrolytes, and concentrations. Measurements using the differential pulse method show that cadmium (II) exhibits a molar combining ratio of complexing agents to cation ranging from 1 to 1 to 3 to 1 depending on the pH and the supporting electrolyte employed.

  2. High Resolution Topography Analysis on Threading Edge Dislocations in 4H-SiC Epilayers

    SciTech Connect

    Kamata, I.; Nagano, M; Tsuchida, H; Chen, Y; Dudley, M

    2009-01-01

    Threading edge dislocations (TEDs) in a 4H-SiC epitaxial layer are investigated using high-resolution synchrotron topography. Six types of TED image are confirmed to correspond to the Burgers vector directions by a comparison of computer simulated images and observed topography images in crystal boundaries. Using a mapping method, a wide spatial distribution of the six types of TED is examined in a quarter section of a 2-inch wafer.

  3. Theoretical microwave spectral constants for C3H/+/ and C4H/+/

    NASA Technical Reports Server (NTRS)

    Wilson, S.; Green, S.

    1980-01-01

    A number of linear conjugated carbon chain molecules have been observed in the interstellar gas. It has been suggested that ion molecule chemistry schemes may explain the formation of these compounds. In the present paper, theoretical bond lengths and rotation constants are obtained for C3H(+) and C4H(+). Calculations for C3 are used to assess the accuracy of the former. Recent results for C2H(+) are examined.

  4. Combustion of CH4/H2/air mixtures in catalytic microreactors.

    PubMed

    Specchia, Stefania; Vella, Luigi D; Burelli, Sara; Saracco, Guido; Specchia, Vito

    2009-03-23

    The combustion of CH(4)/H(2)/HC mixtures in a very small space represents an alternative, innovative way to produce thermal/electrical energy. Pd/NiCrO(4) catalysts are lined on SiC monoliths via in situ solution combustion synthesis (SCS), and the monoliths are then tested by feeding CH(4), H(2), and lean CH(4)/H(2) mixtures into a lab-scale test rig at an output thermal power of 7.6 MW(th) m(-3). In all cases, the combustion temperature shifts to values lower than those observed in non-catalytic combustion. When the power density is kept constant (by adding H(2) to the gas mixture), the value of CH(4)-T(50) (the half-conversion temperature of CH(4)) decreases relative to that of pure CH(4), and the slope of the conversion curve becomes steeper. The higher the H(2) concentration is, the higher the reactivity of the mixture towards CH(4) oxidation-probably due to a higher production of H(2) reactive radicals (OH).

  5. Demonstration of the First 4H-SiC EUV Detector with Large Detection Area

    NASA Technical Reports Server (NTRS)

    Xin, Xiaobin; Yan, Feng; Koeth, Timothy W.; Hu, Jun; Zhao, Jian H.

    2005-01-01

    Ultraviolet (UV) and Extreme Ultraviolet (EUV) detectors are very attractive in astronomy, photolithography and biochemical applications. For EUV applications, most of the semiconductor detectors based on PN or PIN structures suffer from the very short penetration depth. Most of the carries are absorbed at the surface and recombined there due to the high surface recombination before reach the depletion region, resulting very low quantum efficiency. On the other hand, for Schottky structures, the active region starts from the surface and carriers generated from the surface can be efficiently collected. 4H-Sic has a bandgap of 3.26eV and is immune to visible light background noise. Also, 4H-Sic detectors usually have very good radiation hardness and very low noise, which is very important for space applications where the signal is very weak. The E W photodiodes presented in this paper are based on Schottky structures. Platinum (Pt) and Nickel (Ni) are selected as the Schottky contact metals, which have the highest electron work functions (5.65eV and 5.15eV, respectively) among all the known metals on 4H-Sic.

  6. Laboratory detection of the C3N an C4H free radicals

    NASA Technical Reports Server (NTRS)

    Gottlieb, C. A.; Gottlieb, E. W.; Thaddeus, P.; Kawamura, H.

    1983-01-01

    The millimeter-wave spectra of the linear carbon chain free radicals C3N and C4H, first identified in IRC + 10216 and hitherto observed only in a few astronomical sources, have been detected with a Zeeman-modulated spectrometer in laboratory glow discharges through low pressure flowing mixtures of N2 + HC3N and He + HCCH, respectively. Four successive rotational transitions between 168 and 198 GHz have been measured for C3N, and five rotational transitions between 143 and 200 GHz for C4H; each is a well-resolved spin doublet owing to the unpaired electron present in both species. Precise values for the rotational, centrifugal distortion, and spin doubling constants have been obtained, which, with hyperfine constants derived from observations of the lower rotational transitions in the astronomical source TMC 1, allow all the rotational transitions of C3N and C4H at frequencies less than 300 GHz to be calculated to an absolute accuracy exceeding 1 ppm.

  7. A remarkable activity of human leukotriene A4 hydrolase (LTA4H) toward unnatural amino acids.

    PubMed

    Byzia, Anna; Haeggström, Jesper Z; Salvesen, Guy S; Drag, Marcin

    2014-05-01

    Leukotriene A4 hydrolase (LTA4H--EC 3.3.2.6) is a bifunctional zinc metalloenzyme, which processes LTA4 through an epoxide hydrolase activity and is also able to trim one amino acid at a time from N-terminal peptidic substrates via its aminopeptidase activity. In this report, we have utilized a library of 130 individual proteinogenic and unnatural amino acid fluorogenic substrates to determine the aminopeptidase specificity of this enzyme. We have found that the best proteinogenic amino acid recognized by LTA4H is arginine. However, we have also observed several unnatural amino acids, which were significantly better in terms of cleavage rate (k cat/K m values). Among them, the benzyl ester of aspartic acid exhibited a k cat/K m value that was more than two orders of magnitude higher (1.75 × 10(5) M(-1) s(-1)) as compared to L-Arg (1.5 × 10(3) M(-1) s(-1)). This information can be used for design of potent inhibitors of this enzyme, but may also suggest yet undiscovered functions or specificities of LTA4H.

  8. Extended charge accumulation in ruthenium-4H-imidazole-based black absorbers: a theoretical design concept.

    PubMed

    Kupfer, Stephan

    2016-05-11

    A theoretical-guided design concept aiming to achieve highly efficient unidirectional charge transfer and multi-charge separation upon successive photoexcitation for light-harvesting dyes in the scope of supramolecular photocatalysts is presented. Four 4H-imidazole-ruthenium(ii) complexes incorporating a biimidazole-based electron-donating ligand sphere have been designed based on the well-known 4H-imidazole-ruthenium(ii) polypyridyl dyes. The quantum chemical evaluation, performed at the density functional and time-dependent density functional level of theory, revealed extraordinary unidirectional charge transfer bands from the near-infrared to the ultraviolet region of the absorption spectrum upon multi-photoexcitation. Spectro-electrochemical simulations modeling photoexcited intermediates determined the outstanding multi-electron storage capacity for this novel class of black dyes. These remarkable photochemical and photophysical properties are found to be preserved upon site-specific protonation rendering 4H-imidazole-ruthenium(ii) biimidazole dyes ideal for light-harvesting applications in the field of solar energy conversion. PMID:27121270

  9. Interfacial atomic site characterization by photoelectron diffraction for 4H-AlN/4H-SiC(11\\bar{2}0) heterojunction

    NASA Astrophysics Data System (ADS)

    Maejima, Naoyuki; Horita, Masahiro; Matsui, Hirosuke; Matsushita, Tomohiro; Daimon, Hiroshi; Matsui, Fumihiko

    2016-08-01

    The interfacial atomic structure of an AlN thin film on a nonpolar 4H-SiC(11\\bar{2}0) substrate grown by atomic Al and N plasma deposition was studied by photoelectron diffraction and spectroscopy. The epitaxial growth of the thin film was confirmed by the comparison of element-specific photoelectron intensity angular distributions (PIADs). Depth profiles were analyzed by angle-resolved constant-final-state-mode X-ray photoelectron spectroscopy (AR-XPS). No polar angular dependence was observed in Al 2p spectra, while an additional intermixing component was found in interface-sensitive N 1s spectra. The site-specific N 1s PIADs for the AlN film and an intermixing component were derived from two N 1s PIADs with different binding energies. We attributed the intermixing component to SiN interfacial layer sites. In order to prevent SiN growth at the interface, we deposited Al on the SiC(11\\bar{2}0) substrate prior to the AlN growth. A significant reduction in the amount of intermixing components at the AlN/SiC interface was confirmed by AR-XPS.

  10. Spin and photophysics of carbon-antisite vacancy defect in 4 H silicon carbide: A potential quantum bit

    NASA Astrophysics Data System (ADS)

    Szász, Krisztián; Ivády, Viktor; Abrikosov, Igor A.; Janzén, Erik; Bockstedte, Michel; Gali, Adam

    2015-03-01

    Silicon carbide with engineered point defects is considered as very promising material for the next generation devices, with applications ranging from electronics and photonics to quantum computing. In this context, we investigate the spin physics of the carbon antisite-vacancy pair that in its positive charge state enables a single photon source. We find by hybrid density functional theory and many-body perturbation theory that the neutral defect possesses a high spin ground state in 4 H silicon carbide and provide spin-resonance signatures for its experimental identification. Our results indicate the possibility for the coherent manipulation of the electron spin by optical excitation of this defect at telecom wavelengths, and suggest the defect as a candidate for an alternative solid state quantum bit.

  11. Hydrogen assisted growth of high quality epitaxial graphene on the C-face of 4H-SiC

    SciTech Connect

    Cai, Tuocheng; Jia, Zhenzhao; Yan, Baoming; Yu, Dapeng; Wu, Xiaosong

    2015-01-05

    We demonstrate hydrogen assisted growth of high quality epitaxial graphene on the C-face of 4H-SiC. Compared with the conventional thermal decomposition technique, the size of the growth domain by this method is substantially increased and the thickness variation is reduced. Based on the morphology of epitaxial graphene, the role of hydrogen is revealed. It is found that hydrogen acts as a carbon etchant. It suppresses the defect formation and nucleation of graphene. It also improves the kinetics of carbon atoms via hydrocarbon species. These effects lead to increase of the domain size and the structure quality. The consequent capping effect results in smooth surface morphology and suppression of multilayer growth. Our method provides a viable route to fine tune the growth kinetics of epitaxial graphene on SiC.

  12. Measurements of depth dependent modification of optical constants arising from H+ implantation in n-type 4H-SiC using coherent acoustic phonons

    NASA Astrophysics Data System (ADS)

    Baydin, Andrey; Krzyzanowska, Halina; Dhanunjaya, M.; Rao, S. V. S. Nageswara; Davidson, Jimmy L.; Feldman, Leonard C.; Tolk, Norman H.

    Silicon carbide (SiC) is an ideal material for new electronics, such as high power/high temperature devices, and a candidate for advanced optical applications such as room temperature spintronics and quantum computing. Both types of applications may require the control of defects created by ion bombardment. In this work, we examine depth dependent modification of optical constants of 4H-SiC due to hydrogen implantation at 180keV and low doses ranging from 1014 to 1016 cm-2probed by coherent acoustic phonon (CAP) spectroscopy. For our studies, we used Si-face 10 μm epilayers of n-type 4H-SiC grown by CVD on 4H-SiC substrate. A comprehensive analysis of the reference and implanted spectra shows a strong dependence of 4H-SiC complex refractive index shape versus depth on the H+ fluence. We extract the complex refractive index as a function of depth and ion beam dose. Our results demonstrate that the implantation-modified refractive index is distributed over a greater depth range than Monte Carlo calculation predictions of the implantation induced structural damage. These studies provide insight into the application of hydrogen ion implantation to the fabrication of SiC-based photonic and optoelectronic devices. Work is supported by ARO under Contract No. W911NF-14-1-0290.

  13. Fabrication of high-quality nanobeam photonic crystal cavities in 4H silicon carbide with embedded color centers

    NASA Astrophysics Data System (ADS)

    Bracher, David O.; Hu, Evelyn L.

    2016-03-01

    A wide band-gap semiconductor with a long history of growth and device fabrication, silicon carbide (SiC) has attracted recent attention for hosting several defects with properties similar to the nitrogen vacancy center in diamond. In the 4H polytype, these include the silicon vacancy center and the neutral divacancy, which have zero phonon lines (ZPL) in the near-IR and may be useful for quantum information and nanoscale sensing. For many such applications, it is critical to increase the defect emission into the ZPL by coupling the emission to an optical cavity. Accordingly, we have pursued the fabrication of high quality 1D nanobeam photonic crystal cavities (PCCs) in 4H-SiC, using homoepitaxially grown material and a photoelectrochemical etch to provide optical isolation. These PCCs are distinctive in their high theoretical quality factors (Q > 106) and low modal volumes (V < 0.5 (λ/n)3). Here, we present arrays of nanobeam PCCs with varied lattice constant containing embedded silicon vacancy defects generated by electron irradiation, to assess its viability as a method for defect creation. The lattice constant variation allows us to create devices with modes spanning the entire range of the silicon vacancy emission. We accordingly demonstrate nanobeam PCCs with resonant modes near both ZPLs of the silicon vacancy defect. Moreover, we measure devices with the highest Q cavity modes coupled to point defect emission in SiC yet reported, providing evidence that electron irradiation can be used to generate point defects while maintaining high quality optical devices.

  14. Ultra-High Voltage 4H-SiC Bi-Directional Insulated Gate Bipolar Transistors

    NASA Astrophysics Data System (ADS)

    Chowdhury, Sauvik

    4H- Silicon Carbide (4H-SiC) is an attractive material for power semiconductor devices due to its large bandgap, high critical electric field and high thermal conductivity compared to Silicon (Si). For ultra-high voltage applications (BV > 10 kV), 4H-SiC Insulated Gate Bipolar Transistors (IGBTs) are favored over unipolar transistors due to lower conduction losses. With improvements in SiC materials and processing technology, promising results have been demonstrated in the area of conventional unidirectional 4H-SiC IGBTs, with breakdown voltage ratings up to 27 kV. This research presents the experimental demonstration of the world's first high voltage bi-directional power transistors in 4H-SiC. Traditionally, four (two IGBTs and two diodes) or two (two reverse blocking IGBTs) semiconductor devices are necessary to yield a bidirectional switch. With a monolithically integrated bidirectional switch as presented here, the number of semiconductor devices is reduced to only one, which results in increased reliability and reduced cost of the overall system. Additionally, by using the unique dual gate operation of BD-IGBTs, switching losses can be reduced to a small fraction of that in conventional IGBTs, resulting in increased efficiency. First, the performance limits of SiC IGBTs are calculated by using analytical methods. The performance benefits of SiC IGBTs over SiC unipolar devices and Si IGBTs are quantified. Numerical simulations are used to optimize the unit cell and edge termination structures for a 15 kV SiC BD-IGBT. The effect of different device parameters on BD-IGBT static and switching performance are quantified. Second, the process technology necessary for the fabrication of high voltage SiC BD-IGBTs is optimized. The effect of different process steps on parameters such as breakdown voltage, carrier lifetime, gate oxide reliability, SiO2-SiC interface charge density is quantified. A carrier lifetime enhancement process has been optimized for lightly doped

  15. Atomistic Simulations of Epitaxial Recrystallization in 4H-SiC along the [0001] Direction

    SciTech Connect

    Gao, Fei; Zhang, Yanwen; Devanathan, Ram; Posselt, Matthias; Weber, William J.

    2007-02-16

    Molecular dynamics (MD) methods have been employed to study the epitaxail recrystallization and amorphous-to-crystalline (a-c) transition in 4H-SiC, with simulation times of up to a few hundred ns and at temperatures of 1500 and 2000 K. Three nano-sized amorphous layers with the normal of a-c interfaces along the [-12-10 ], [-1010] and [0001] directions, respectively, were created within a crystalline cell to investigate the anisotropies of recrystallization processes. The recovery of bond defects at the interfaces is an important process driving the initial epitaxial recrystallization of the amorphous layers. The amorphous layers with the a-c interface normal along the [-12-10] direction can be completely recrystallized at the temperatures of 1500 and 2000 K, and along the [0001] direction at 2000 K. However, the recrystallized region is defected with dislocations and stacking faults. The temperatures required for complete recrystallization are in good agreement with those observed in experiments. On the other hand, the recrystallization processes for the a-c interface normal along [-1010] direction are hindered by the nucleation of polycrystalline phases. These secondary ordered phases have been identified as 4H- and 3C-SiC with different crystallographic orientations to the original 4H-SiC. The bond mismatches at the interfaces between different microcrystals result in the formation of a number of stacking faults. The temperature is an important parameter to control the nucleation of the secondary ordered phase, whereas the size of amorphous region has a significant effect on their growth. These results are in good agreement with the previous experimental observations.

  16. High responsivity 4H-SiC based metal-semiconductor-metal ultraviolet photodetectors

    NASA Astrophysics Data System (ADS)

    Yang, Weifeng; Zhang, Feng; Liu, Zhuguang; Lü, Ying; Wu, Zhengyun

    2008-11-01

    4H-SiC based metal-semiconductor-metal (MSM) photodetectors with diverse spacing were designed, fabricated, and characterized, in which nickel Schottky contacts were needed. Current-voltage and spectral responsivity measurements were carried out at room temperature. The fabricated 4 μm-spacing device showed a very low dark current (0.25 pA at 5 V bias voltage), a typical responsivity of 0.103 A/W at 20 V, and a peak response wavelength at 290 nm. The fabricated devices held a high DUV to visible rejection ratio of >103.

  17. Transient collector modulation of 4H-SiC BJTs during switch-on process

    NASA Astrophysics Data System (ADS)

    Yuferev, Valentin S.; Levinshtein, Michael E.; Ivanov, Pavel A.; Zhang, Jon Q.; Palmour, John W.

    2016-09-01

    Main physical features of the collector resistance modulation processes have been studied via a one-dimensional simulation for n+-p-n0-n+ 4H-SiC bipolar junction transistor. The motion dynamics of minority carriers (holes) across the n0 collector layer during the switch-on process is traced. It is demonstrated that the effective modulation of the collector resistance is only possible in the case of a rather fast transistor switch-on. A necessary condition for the fast switch-on is the large amplitude and short leading edge of the base current pulse.

  18. Hydrogen Gas Sensors Fabricated on Atomically Flat 4H-SiC Webbed Cantilevers

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Spry, David J.; Trunek, Andrew J.; Evans, Laura J.; Chen, Liang-Yu; Hunter, Gary W.; Androjna, Drago

    2007-01-01

    This paper reports on initial results from the first device tested of a "second generation" Pt-SiC Schottky diode hydrogen gas sensor that: 1) resides on the top of atomically flat 4H-SiC webbed cantilevers, 2) has integrated heater resistor, and 3) is bonded and packaged. With proper selection of heater resistor and sensor diode biases, rapid detection of H2 down to concentrations of 20 ppm was achieved. A stable sensor current gain of 125 +/- 11 standard deviation was demonstrated during 250 hours of cyclic test exposures to 0.5% H2 and N2/air.

  19. 4H-SiC Schottky photodiodes for ultraviolet flame detection

    NASA Astrophysics Data System (ADS)

    Mazzillo, M.; Sciuto, A.

    2015-10-01

    In the last few years silicon carbide (SiC) has emerged as an appropriate material for the detection of very low ultraviolet photon fluxes even at elevated temperatures. In this paper we report on the electro-optical characteristics of large area interdigit Ni2Si/4H-SiC photodiodes in TO metal can package with a suitable molded cap quartz window with high transmission in the ultraviolet wavelength range. The detectors have been tested for the detection of the ultraviolet component of the yellow flame emitted by a small candle, showing good sensitivity for very weak photon fluxes notwithstanding the linear operation condition of the photodiodes.

  20. Dynamic characteristics of 4H-SiC drift step recovery diodes

    SciTech Connect

    Ivanov, P. A. Kon’kov, O. I.; Samsonova, T. P.; Potapov, A. S.; Grekhov, I. V.

    2015-11-15

    The dynamic characteristics of 4H-SiC p{sup +}–p–n{sub 0}–n{sup +} diodes are experimentally studied in the pulsed modes characteristic of the operation of drift step recovery diodes (DSRD-mode). The effect of the subnanosecond termination of the reverse current maintained by electron-hole plasma preliminarily pumped by a forward current pulse is analyzed in detail. The influence exerted on the DSRD effect by the amplitude of reverse-voltage pulses, the amplitude and duration of forward-current pulses, and the time delay between the forward and reverse pulses is demonstrated and accounted for.

  1. 4H-SiC JFET Multilayer Integrated Circuit Technologies Tested Up to 1000 K

    NASA Technical Reports Server (NTRS)

    Spry, D. J.; Neudeck, P. G.; Chen, L.; Chang, C. W.; Lukco, D.; Beheim, G. M.

    2015-01-01

    Testing of semiconductor electronics at temperatures above their designed operating envelope is recognized as vital to qualification and lifetime prediction of circuits. This work describes the high temperature electrical testing of prototype 4H silicon carbide (SiC) junction field effect transistor (JFET) integrated circuits (ICs) technology implemented with multilayer interconnects; these ICs are intended for prolonged operation at temperatures up to 773K (500 C). A 50 mm diameter sapphire wafer was used in place of the standard NASA packaging for this experiment. Testing was carried out between 300K (27 C) and 1150K (877 C) with successful electrical operation of all devices observed up to 1000K (727 C).

  2. Atomic oxidation of large area epitaxial graphene on 4H-SiC(0001)

    SciTech Connect

    Velez-Fort, E.; Ouerghi, A.; Silly, M. G.; Sirtti, F.; Eddrief, M.; Marangolo, M.; Shukla, A.

    2014-03-03

    Structural and electronic properties of epitaxial graphene on 4H-SiC were studied before and after an atomic oxidation process. X-ray photoemission spectroscopy indicates that oxygen penetrates into the substrate and decouples a part of the interface layer. Raman spectroscopy demonstrates the increase of defects due to the presence of oxygen. Interestingly, we observed on the near edge x-ray absorption fine structure spectra a splitting of the π* peak into two distinct resonances centered at 284.7 and 285.2 eV. This double structure smears out after the oxidation process and permits to probe the interface architecture between graphene and the substrate.

  3. Development of 17 kV 4H-SiC PiN diode

    NASA Astrophysics Data System (ADS)

    Runhua, Huang; Yonghong, Tao; Ling, Wang; Gang, Chen; Song, Bai; Rui, Li; Yun, Li; Zhifei, Zhao

    2016-08-01

    The design, fabrication, and electrical characteristics of a 4H-SiC PiN diode with breakdown voltage higher than 17 kV are presented. The three-zone JTE has been used in the fabrication. Numerical simulations have been performed to optimize the parameters of the edge termination technique. The epilayer properties of the N-type are 175 μm with a doping of 2 × 1014 cm-3. With the three-zone JTE, a typical breakdown voltage of 17 kV has been achieved. Project supported by the National High Technology Research and Development Program of China (No. 2014AA041401).

  4. Development of 17 kV 4H-SiC PiN diode

    NASA Astrophysics Data System (ADS)

    Runhua, Huang; Yonghong, Tao; Ling, Wang; Gang, Chen; Song, Bai; Rui, Li; Yun, Li; Zhifei, Zhao

    2016-08-01

    The design, fabrication, and electrical characteristics of a 4H-SiC PiN diode with breakdown voltage higher than 17 kV are presented. The three-zone JTE has been used in the fabrication. Numerical simulations have been performed to optimize the parameters of the edge termination technique. The epilayer properties of the N-type are 175 μm with a doping of 2 × 1014 cm‑3. With the three-zone JTE, a typical breakdown voltage of 17 kV has been achieved. Project supported by the National High Technology Research and Development Program of China (No. 2014AA041401).

  5. Complete genome sequence of the marine, cellulose and xylan degrading bacterium Glaciecola sp. 4H-3-7+YE-5

    SciTech Connect

    Klippel, Dr Barbara; Bruce, David; Davenport, Karen W.; Goodwin, Lynne A.; Han, James; Han, Shunsheng; Land, Miriam L; Mikhailova, Natalia; Nolan, Matt; Pennacchio, Len; Pitluck, Sam; Tapia, Roxanne; Woyke, Tanja; Wiebusch, Sigrid; Basner, Alexander; Abe, Fumiyoshi; Horikoshi, Koki; Antranikian, Garabed

    2011-01-01

    Glaciecola sp. 4H-3-7+YE-5 was isolated from deep sea sediments at Suruga Bay in Japan and is capable of efficiently hydrolyzing cellulose and xylan. The complete genome sequence of Glaciecola sp. 4H-3-7+YE-5 revealed several genes encoding putatively novel glycoside hydrolases associated with plant biomass degradation.

  6. A Mixed Method Study of Positional Leadership of North Dakota 4-H Ambassador and State FFA Officer Alumni

    ERIC Educational Resources Information Center

    Peterson, Nels Milan

    2010-01-01

    The purpose of this mixed method study was to determine the positional leadership of North Dakota 4-H and FFA leadership alumni. This study determined the influence of youth development programs on statewide leadership alumni (those who served from 1970 to 2000) and community leadership roles as adults. Former North Dakota 4-H Ambassador Alumni…

  7. Understanding Life Skills Gained from and Reasons for Youth Participation in the Tennessee 4-H Sheep Skillathon

    ERIC Educational Resources Information Center

    Davis, Terra Kimes; Stripling, Christopher T.; Stephens, Carrie A.; Loveday, H. Dwight

    2016-01-01

    The high number of U.S. youth exhibiting at-risk behavior points to a lack of life skills development. We determined the effects of participating in one state's 4-H sheep skillathon on youths' life skills development and the youths' reasons for participating. The target population was 2014 Tennessee 4-H Sheep Skillathon participants (N = 153), and…

  8. Eat, Grow, Lead 4-H: An Innovative Approach to Deliver Campus- Based Field Experiences to Pre-Entry Extension Educators

    ERIC Educational Resources Information Center

    Weeks, Penny Pennington; Weeks, William G.

    2012-01-01

    Eat, Grow, Lead 4-H Club was created as a pilot program for college students seeking to gain experience as non-formal youth educators, specifically serving pre-entry level Extension educators through a university-based 4-H club. Seventeen student volunteers contributed an estimated 630 hours of service to the club during spring 2011. The club…

  9. Family Diversity in a Youth Organization: Involvement of Single-Parent Families and Stepfamilies in 4-H.

    ERIC Educational Resources Information Center

    Ganong, Lawrence H.

    1993-01-01

    Evaluated involvement of children from single-parent and stepparent households in 4-H clubs. Used case study approach, with data collected via written materials; interviews with 4-H staff; and mailed questionnaires from professional staff, paraprofessionals, and parents. Children from single-parent households were found to be underrepresented, as…

  10. Effect of Doping Concentration Variations in PVT-Grown 4H-SiC Wafers

    NASA Astrophysics Data System (ADS)

    Yang, Yu; Guo, Jianqiu; Goue, Ouloide; Raghothamachar, Balaji; Dudley, Michael; Chung, Gil; Sanchez, Edward; Quast, Jeff; Manning, Ian; Hansen, Darren

    2016-04-01

    Synchrotron white beam x-ray topography studies carried out on 4H-SiC wafers characterized by locally varying doping concentrations reveals the presence of overlapping Shockley stacking faults generated from residual surface scratches in regions of higher doping concentrations after the wafers have been subjected to heat treatment. The stacking faults are rhombus-shaped and bound by Shockley partial dislocations. The fault generation process is driven by the fact that in regions of higher doping concentrations, a faulted crystal containing double Shockley faults is more stable than a perfect 4H-SiC crystal at the high temperatures (>1000°C) that the wafers are subject to during heat treatment. We have developed a model for the formation mechanism of the rhombus-shaped stacking faults. Our studies show that during heat treatment of the wafer, such double Shockley faults can be generated in regions where dislocation sources are presents (e.g. scratches or low-angle boundaries) and when the nitrogen doping concentration exceeds a certain level.

  11. Evaluation of 4H-SiC Thermal Oxide Reliability Using Area-Scaling Method

    NASA Astrophysics Data System (ADS)

    Senzaki, Junji; Shimozato, Atsushi; Okamoto, Mitsuo; Kojima, Kazutoshi; Fukuda, Kenji; Okumura, Hajime; Arai, Kazuo

    2009-08-01

    The reliability of thermal oxides grown on an n-type 4H-SiC(0001) was investigated using an area-scaling method, and the influence of dislocation defects on the time-dependent dielectric breakdown characteristics of thermal oxides was examined. A thermal oxide was grown by dry oxidation at 1200 °C followed by nitrogen post-oxidation annealing. Using the area-scaling method, the time-to-breakdown (tBD) distribution curves of metal-oxide-semiconductor (MOS) capacitors with different gate area sizes were converged to a single one. It was clearly shown that origins of dielectric breakdown are edge breakdown and dislocation-related breakdown for steep and gradual slopes of the area-scaling normalized tBD distribution curve, respectively. In addition, a yield analysis of MOS capacitors quantitatively indicated that both threading screw dislocation and basal plane dislocation are predominant killer defects for the dielectric breakdown of thermal oxides on the 4H-SiC(0001) face.

  12. Characterization of V-shaped defects in 4H-SiC homoepitaxial layers

    DOE PAGES

    Zhang, Lihua; Su, Dong; Kisslinger, Kim; Stach, Eric; Chung, Gil; Zhang, Jie; Thomas, Bernd; Sanchez, Edward K; Mueller, Stephan G.; Hansen, Darren; et al

    2014-12-04

    Synchrotron white beam x-ray topography images show that faint needle-like surface morphological features observed on the Si-face of 4H-SiC homoepitaxial layers using Nomarski optical microscopy are associated with V shaped stacking faults in the epilayer. KOH etching of the V shaped defect reveals small oval pits connected by a shallow line which corresponding to the surface intersections of two partial dislocations and the stacking fault connecting them. Transmission electron microscopy (TEM) specimens from regions containing the V shaped defects were prepared using focused ion beam milling, and stacking sequences of (85), (50) and (63) are observed at the faulted regionmore » with high resolution TEM. In order to study the formation mechanism of V shaped defect, low dislocation density 4H-SiC substrates were chosen for epitaxial growth, and the corresponding regions before and after epitaxy growth are compared in SWBXT images. It is found that no defects in the substrate are directly associated with the formation of the V shaped defect. Simulation results of the contrast from the two partial dislocations associated with V shaped defect in synchrotron monochromatic beam x-ray topography reveals the opposite sign nature of their Burgers vectors. Therefore, a mechanism of 2D nucleation during epitaxy growth is postulated for the formation of the V shaped defect, which requires elimination of non-sequential 1/4[0001] bilayers from the original structure to create the observed faulted stacking sequence.« less

  13. Characterization of V-shaped defects in 4H-SiC homoepitaxial layers

    SciTech Connect

    Zhang, Lihua; Su, Dong; Kisslinger, Kim; Stach, Eric; Chung, Gil; Zhang, Jie; Thomas, Bernd; Sanchez, Edward K; Mueller, Stephan G.; Hansen, Darren; Loboda, Mark J.; Wu, Fangzhen; Wang, Huanhuan; Raghothamachar, Balaji; Dudley, Michael

    2014-12-04

    Synchrotron white beam x-ray topography images show that faint needle-like surface morphological features observed on the Si-face of 4H-SiC homoepitaxial layers using Nomarski optical microscopy are associated with V shaped stacking faults in the epilayer. KOH etching of the V shaped defect reveals small oval pits connected by a shallow line which corresponding to the surface intersections of two partial dislocations and the stacking fault connecting them. Transmission electron microscopy (TEM) specimens from regions containing the V shaped defects were prepared using focused ion beam milling, and stacking sequences of (85), (50) and (63) are observed at the faulted region with high resolution TEM. In order to study the formation mechanism of V shaped defect, low dislocation density 4H-SiC substrates were chosen for epitaxial growth, and the corresponding regions before and after epitaxy growth are compared in SWBXT images. It is found that no defects in the substrate are directly associated with the formation of the V shaped defect. Simulation results of the contrast from the two partial dislocations associated with V shaped defect in synchrotron monochromatic beam x-ray topography reveals the opposite sign nature of their Burgers vectors. Therefore, a mechanism of 2D nucleation during epitaxy growth is postulated for the formation of the V shaped defect, which requires elimination of non-sequential 1/4[0001] bilayers from the original structure to create the observed faulted stacking sequence.

  14. Exploration of Defects in 4H-SiC MOSFETs via Spin Dependent Charge Pumping

    NASA Astrophysics Data System (ADS)

    Anders, Mark; Lenahan, Patrick; Lelis, Aivars

    4H-SiC MOSFETs have great promise for use in high temperature and high voltage applications. Unfortunately, defects at the SiC/SiO2 interface reduce the performance of these devices. Previously, our group utilized electrically detected magnetic resonance (EDMR) detected via spin dependent recombination (SDR) to identify such SiC/SiO2 interface defects utilizing the bipolar amplification (BAE) biasing scheme; we observed SiC silicon vacancies, E-prime centers, and hydrogen complexed E-prime centers. All of these defects must have levels around the middle of the SiC band gap because they are effective recombination centers. We expanded our studies to include EDMR detection via spin dependent charge pumping (SDCP) at low field, X band, and K band, allowing EDMR exploration of nearly the entire 4H-SiC band gap. Perhaps the most important finding of the (nearly) full band gap measurements is the absence of the carbon dangling bond spectrum in the SDCP. Additionally, in nMOSFETs, we observe an SDCP EDMR spectrum dominated by a silicon vacancy, whereas in pMOSFETs, we also observe a strong, nearly isotropic single line spectrum with g = 2.00244 and 2.00248 when the c-axis is nearly parallel and perpendicular to the magnetic field, respectively. The results suggest that silicon vacancy centers dominate nMOSFET interfaces whereas additional defects clearly play important roles in pMOSFETs.

  15. n-ZnO/p-4H-SiC diode: Structural, electrical, and photoresponse characteristics

    SciTech Connect

    Guziewicz, M. Jung, W.

    2015-09-07

    Epitaxial n-type ZnO film has been grown, on a commercial 5 μm thick p-type 4H-SiC(00.1) Al doped epilayer, by atomic layer deposition. A full width at half maximum of the ZnO 00.2 diffraction peak rocking curve of 0.34°{sup  }± 0.02° has been measured. Diodes formed on the n-ZnO/p-4H-SiC heterostructure show rectifying behavior with a forward to reverse current ratio at the level of 10{sup 9} at ±4 V, a leakage current density of ∼6 × 10{sup −8} A/cm{sup 2}, and a low ideality factor equal to 1.17 ± 0.04. In addition, the diodes exhibit selective photoresponse with a maximum at 367 nm, and with a current increase of ∼10{sup 3} under illuminations with respect to the dark value, which makes such devices prospective candidates for ultraviolet light sensors.

  16. Comprehensive study of a 4H-SiC MES-MOSFET

    NASA Astrophysics Data System (ADS)

    Jamali Mahabadi, S. E.; Amini Moghadam, Hamid

    2015-11-01

    In this paper, we studied the enhancement of the breakdown voltage in the 4H-SiC MESFET-MOSFET (MES-MOSFET) structure which we have proposed in our previous work. We compared this structure with Conventional Bulk-MOSFET (CB-MOSFET) and Field plated Conventional Bulk-MOSFET (FCB-MOSFET) structures. The 4H-SiC MES-MOSFET structure consists of two additional schottky buried gates which behave like a Metal on Semiconductor (MES) at the interface of the active region and substrate. The motivation for this structure was to enhance the breakdown voltage by introducing a new technique of utilizing the reduced surface field (RESURF) concept. In our comparison and investigation we used a two-dimensional device simulator. Our simulation results show that the breakdown voltage of the proposed structure is 3.7 and 2.9 times larger than CB-MOSFET and FCB-MOSFET structures, respectively. We also showed that the threshold voltage and the slope of drain current (ID) as a function of drain-source voltage (VDS) for all the structures is the same.

  17. Characterization of the Minimum Energy Paths for the Ring Closure Reactions of C4H3 with Acetylene

    NASA Technical Reports Server (NTRS)

    Walch, Stephen P.

    1995-01-01

    The ring closure reaction of C4H3 with acetylene to give phenyl radical is one proposed mechanism for the formation of the first aromatic ring in hydrocarbon combustion. There are two low-lying isomers of C4H3; 1-dehydro-buta-l-ene-3-yne (n-C4H3) and 2-dehydro-buta-l-ene-3-yne (iso-C4H3). It has been proposed that only n-C4H3 reacts with acetylene to give phenyl radical, and since iso-C4H3 is more stable than n-C4H3, formation of phenyl radical by this mechanism is unlikely. We report restricted Hartree-Fock (RHF) plus singles and doubles configuration interaction calculations with a Davidson's correction (RHF+1+2+Q) using the Dunning correlation consistent polarized valence double zeta basis set (cc-pVDZ) for stationary point structures along the reaction pathway for the reactions of n-C4H3 and iso-C4H3 with acetylene. n-C4H3 plus acetylene (9.4) has a small entrance channel barrier (17.7) (all energetics in parentheses are in kcal/mol with respect to iso-C4H3 plus acetylene) and the subsequent closure steps leading to phenyl radical (-91.9) are downhill with respect to the entrance channel barrier. Iso-C4H3 Plus acetylene also has an entrance channel barrier (14.9) and there is a downhill pathway to 1-dehydro-fulvene (-55.0). 1-dehydro-fulvene can rearrange to 6-dehydro-fulvene (-60.3) by a 1,3-hydrogen shift over a barrier (4.0), which is still below the entrance channel barrier, from which rearrangement to phenyl radical can occur by a downhill pathway. Thus, both n-C4H3 and iso-C4H3 can react with acetylene to give phenyl radical with small barriers.

  18. Theoretical prediction of the ionization energies of the C4H7 radicals: 1-methylallyl, 2-methylallyl, cyclopropylmethyl, and cyclobutyl radicals.

    PubMed

    Lau, Kai-Chung; Zheng, Wenxu; Wong, Ning-Bew; Li, Wai-Kee

    2007-10-21

    The ionization energies (IEs) for the 1-methylallyl, 2-methylallyl, cyclopropylmethyl, and cyclobutyl radicals have been calculated by the wave function based ab initio CCSD(T)/CBS approach, which involves the approximation to the complete basis set (CBS) limit at the coupled cluster level with single and double excitations plus quasiperturbative triple excitation [CCSD(T)]. The zero-point vibrational energy correction, the core-valence electronic correction, and the scalar relativistic effect correction are included in these calculations. The present CCSD(T)/CBS results are then compared with the IEs determined in the photoelectron experiment by Schultz et al. [J. Am. Chem. Soc. 106, 7336 (1984)] The predicted IE value (7.881 eV) of 2-methylallyl radical is found to compare very favorably with the experimental value of 7.90+/-0.02 eV. Two ionization transitions for cis-1-methylallyl and trans-1-methylallyl radicals have been considered here. The comparison between the predicted IE values and the previous measurements shows that the photoelectron peak observed by Schultz et al. likely corresponds to the adiabatic ionization transition for the trans-1-methylallyl radical to form trans-1-methylallyl cation. Although a precise IE value for the cyclopropylmethyl radical has not been directly determined, the experimental value deduced indirectly using other known energetic data is found to be in good accord with the present CCSD(T)/CBS prediction. We expect that the Franck-Condon factor for ionization transition of c-C4H7-->bicyclobutonium is much less favorable than that for ionization transition of c-C4H7-->planar-C4H7+, and the observed IE in the previous photoelectron experiment is likely due to the ionization transition for c-C4H7-->planar-C4H7+. Based on our CCSD(T)/CBS prediction, the ionization transition of c-C4H7-->bicyclobutonium with an IE value around 6.92 eV should be taken as the adiabatic ionization transition for the cyclobutyl radical. The present

  19. Evaluation of MOS structures processed on 4H SiC layers grown by PVT epitaxy

    NASA Astrophysics Data System (ADS)

    Ciechonski, R. R.; Syväjärvi, M.; Wahab, Q.; Yakimova, R.

    2005-12-01

    MOS capacitors have been fabricated on 4H-SiC epilayers grown by physical vapor transport (PVT) epitaxy. The properties were compared with those on similar structures based on chemical vapor deposition (CVD) layers. Capacitance-voltage ( C- V) and conductance measurements ( G- V) were performed in the frequency range of 1 kHz to 1 MHz and also at temperatures up to 475 K. Detailed investigations of the PVT structures indicate a stable behaviour of the interface traps from room temperature up to 475 K. The amount of positive oxide charge QO is 6.83 × 10 9 cm -2 at room temperature and decreases with temperature increase. This suggests that the processed devices are temperature stable. The density of interface states Dit obtained by Nicollian-Brews conductance method is lower in the structure based on the PVT grown sample.

  20. Band gap states of Ti, V, and Cr in 4H-silicon carbide

    NASA Astrophysics Data System (ADS)

    Achtziger, Norbert; Witthuhn, Wolfgang

    1997-07-01

    Band gap states of Ti, V, and Cr in n-type 4H-SiC were investigated by radiotracer deep level transient spectroscopy (DLTS). Doping with the radioactive isotopes 48V and 51Cr was done by recoil implantation followed by annealing (1600 K). Repeated DLTS measurements during the elemental transmutation of these isotopes to 48Ti and 51V, respectively, reveal the corresponding concentration changes of band gap states. Thus, six levels are identified in the band gap: Cr levels at 0.15, 0.18, and 0.74 eV, one V level at 0.97 eV, and two Ti levels at 0.13 and 0.17 eV below the conduction band edge.

  1. 4H-SiC UV Photo Detector with Large Area and Very High Specific Detectivity

    NASA Technical Reports Server (NTRS)

    Yan, Feng; Shahid, Aslam; Franz, David; Xin, Xiaobin; Zhao, Jian H.; Zhao, Yuegang; Winer, Maurice

    2004-01-01

    Pt/4H-SiC Schottky photodiodes have been fabricated with the device areas up to 1 sq cm. The I-V characteristics and photo-response spectra have been measured and analyzed. For a 5 mm x 5 mm area device leakage current of 1 x 10(exp 15)A at zero bias and 1.2 x 10(exp 14)A at -IV have been established. The quantum efficiency is over 30% from 240nm to 320nm. The specific detectivity, D(sup *), has been calculated from the directly measured leakage current and quantum efficiency data and are shown to be higher than 10(exp 15) cmHz(sup 1/2)/W from 210nm to 350nm with a peak D(sup *) of 3.6 x 10(exp 15)cmH(sup 1/2)/W at 300nm.

  2. Excess leakage currents in high-voltage 4H-SiC Schottky diodes

    SciTech Connect

    Ivanov, P. A. Grekhov, I. V.; Potapov, A. S.; Samsonova, T. P.; Il'inskaya, N. D.; Kon'kov, O. I.; Serebrennikova, O. Yu.

    2010-05-15

    The high-voltage 4H-SiC Schottky diodes are fabricated with a nickel barrier and a guard system in the form of 'floating' planar p-n junctions. The analysis of I-V characteristics measured in a wide temperature range shows that the forward current is caused by thermionic emission; however, the current is 'excessive' in the reverse direction. It is assumed that the reverse current flows locally through the points of the penetrating-dislocation outcrop to the Ni-SiC interface. The shape of reverse I-V characteristics makes it possible to conclude that the electron transport is governed by the monopolar-injection mechanism (the space-charge limited current) with participation of capture traps.

  3. Characterization and Modeling of 4H-SiC Lateral MOSFETs for Integrated Circuit Design

    SciTech Connect

    Mudholkar, M; Mantooth, HA

    2013-06-01

    A new process in 4H-SiC is developed that features n-type buried and inversion channel lateral MOSFETs that are fabricated with several different channel lengths (2-8 mu m) and widths (8-32 mu m) and characterized over a wide temperature range (25 degrees C-225 degrees C). It is shown that the on-resistance of enhancement-mode SiC MOSFETs reduces with temperature despite a reduction in inversion mobility because of the interaction of interface states with temperature. To enable integrated circuit development using the developed MOSFETs, their electrical characteristics are modeled over geometry and temperature using the industry standard PSP MOSFET model. A new mathematical formulation to describe the presence of the interface states is also developed and implemented in the PSP model, and excellent agreement is shown between measurement and simulation using the modified PSP model.

  4. Evidence for near-infrared photoluminescence of nitrogen vacancy centers in 4 H -SiC

    NASA Astrophysics Data System (ADS)

    Zargaleh, S. A.; Eble, B.; Hameau, S.; Cantin, J.-L.; Legrand, L.; Bernard, M.; Margaillan, F.; Lauret, J.-S.; Roch, J.-F.; von Bardeleben, H. J.; Rauls, E.; Gerstmann, U.; Treussart, F.

    2016-08-01

    We present evidence of near-infrared photoluminescence (PL) signature of nitrogen vacancy centers (NCVSi) - in silicon carbide (SiC). This center exhibits an S =1 ground state spin similar to the NV- center in diamond. We have performed photoluminescence excitation measurements at cryogenic temperature and demonstrated efficient photoexcitation of distinct photoluminescence from (NCVSi)- in 4 H -SiC. Furthermore, by correlating the energies of measured zero phonon lines (ZPLs) with theoretical values derived from hybrid density functional theory each of the ZPLs has been associated to the respective occupation of hexagonal (h ) and quasicubic (k ) lattice sites in close analogy to neutral divacancy centers (VCVSi) 0 in the same material. Finally, with the appropriate choice of excitation energy we demonstrated the selective excitation of (NCVSi) - PL with no contamination by (VCVSi) 0 PL, thereby opening the way towards the optical detection of (NCVSi) - electron spin resonance.

  5. Irradiation of 4H-SiC UV detectors with heavy ions

    SciTech Connect

    Kalinina, E. V. Lebedev, A. A.; Bogdanova, E.; Berenquier, B.; Ottaviani, L.; Violina, G. N.; Skuratov, V. A.

    2015-04-15

    Ultraviolet (UV) photodetectors based on Schottky barriers to 4H-SiC are formed on lightly doped n-type epitaxial layers grown by the chemical vapor deposition method on commercial substrates. The diode structures are irradiated at 25°C by 167-MeV Xe ions with a mass of 131 amu at a fluence of 6 × 10{sup 9} cm{sup −2}. Comparative studies of the optical and electrical properties of as-grown and irradiated structures with Schottky barriers are carried out in the temperature range 23–180°C. The specific features of changes in the photosensitivity and electrical characteristics of the detector structures are accounted for by the capture of photogenerated carriers into traps formed due to fluctuations of the conduction-band bottom and valence-band top, with subsequent thermal dissociation.

  6. Detection of powder formation in SiH4/H2 glow discharges

    NASA Astrophysics Data System (ADS)

    Alexiou, G.; Tsigaras, G.; Amanatides, E.; Mataras, D.

    2016-03-01

    Time-resolved self-bias voltage measurements and spatiotemporal resolved optical emission spectroscopy were used in order to monitor particle formation and instabilities in the initial stage of 13.56 MHz SiH4/H2. The effect of total gas pressure on the particles formation and the time required for the plasma to reach steady state was investigated. Both techniques were very sensitive in monitoring the nucleation and coagulation phase of particles formation. The characteristic times required for reaching steady state were similar for both techniques indicating that electrical properties and chemical kinetics are affected in a similar way from particle formation. The increase of pressure resulted in a significant shortening of the instability period and this can be a significant advantage in the deposition of device grade silicon thin films.

  7. Characterization of N-doped multilayer graphene grown on 4H-SiC (0001)

    NASA Astrophysics Data System (ADS)

    Arezki, Hakim; Ho, Kuan-I.; Jaffré, Alexandre; Alamarguy, David; Alvarez, José; Kleider, Jean-Paul; Lai, Chao-Sung; Boutchich, Mohamed

    2015-02-01

    Large-area graphene film doped with hetero-atoms is of great interest for a wide spectrum of nanoelectronics applications, such as field effect devices, super capacitors, fuel cells among many others. Here, we report the structural and electronic properties of nitrogen doped multilayer graphene on 4H-SiC (0001). The incorporation of nitrogen during the growth causes an increase in the D band on the Raman signature indicating that the nitrogen is creating defects. The analysis of micro-Raman mapping of G, D, 2D bands shows a predominantly trilayer graphene with a D band inherent to doping and inhomogeneous dopant distribution at the step edges. Ultraviolet photoelectron spectroscopy (UPS) indicates an n type work function (WF) of 4.1 eV. In addition, a top gate FET device was fabricated showing n-type I-V characteristic after the desorption of oxygen with high electron and holes mobilities.

  8. Charcot-Marie-Tooth Disease Type 4H Resulting from Compound Heterozygous Mutations in FGD4 from Nonconsanguineous Korean Families.

    PubMed

    Hyun, Young Se; Lee, Jinho; Kim, Hye Jin; Hong, Young Bin; Koo, Heasoo; Smith, Alec S T; Kim, Deok-Ho; Choi, Byung-Ok; Chung, Ki Wha

    2015-11-01

    Charcot-Marie-Tooth disease type 4H (CMT4H) is an autosomal recessive demyelinating subtype of peripheral enuropathies caused by mutations in the FGD4 gene. Most CMT4H patients are in consanguineous Mediterranean families characterized by early onset and slow progression. We identified two CMT4H patients from a Korean CMT cohort, and performed a detailed genetic and clinical analysis in both cases. Both patients from nonconsanguineous families showed characteristic clinical manifestations of CMT4H including early onset, scoliosis, areflexia, and slow disease progression. Exome sequencing revealed novel compound heterozygous mutations in FGD4 as the underlying cause in both families (p.Arg468Gln and c.1512-2A>C in FC73, p.Met345Thr and c.2043+1G>A (p.Trp663Trpfs*30) in FC646). The missense mutations were located in highly conserved RhoGEF and PH domains which were predicted to be pathogenic in nature by in silico modeling. The CMT4H occurrence frequency was calculated to 0.7% in the Korean demyelinating CMT patients. This study is the first report of CMT4H in Korea. FGD4 assay could be considered as a means of molecular diagnosis for sporadic cases of demyelinating CMT with slow progression.

  9. Measurement of Optical, Mechanical and Transport properties of the hexagonal closed packed 4H polytype of metallic silver

    NASA Astrophysics Data System (ADS)

    Chakraborty, Indrani; Shirodkar, Sharmila N.; Gohil, Smita; Waghmare, Umesh; Ayyub, Pushan

    2013-03-01

    Optical, mechanical and transport property measurements were done on the hexagonal closed packed (hcp) 4H polytype of Ag with stacking sequence ABCBABCB.. grown as bulk films on Al2O3 substrates. Diffused reflectance measurements done on the 4H films showed a general loss of reflectivity amounting to a decrease of 35% as compared to normal fcc (3C) Ag near 500 nm with a blueshift of 5nm in the bulk plasmon frequency, possibly due to the modified electronic structure of the hcp form. Raman spectroscopic measurements showed the appearance of a peak at 64.3 cm-1 at 4K which underwent ``Mode softening,'' that is shifted to lower wave numbers with increase of temperature and disappeared above 350K. Low temperature transport measurements done on 4H films gave the in-plane resistivity value to be 39 times higher than that of a similarly synthesized fcc Ag film at 295 K. Vicker's microhardness measurements done on the 4H films showed that the 4H samples to be almost 5 times harder than the 3C Ag. Density functional theory simulations were done to obtain the phonon dispersion, band structure and nature of Fermi surface for the 4H Ag which corroborated with the experimental observations. The 4H form appears to be a much less metallic, darker and harder form of Ag.

  10. Clinical spectrum of 4H leukodystrophy caused by POLR3A and POLR3B mutations

    PubMed Central

    Vanderver, Adeline; van Spaendonk, Rosalina M.L.; Schiffmann, Raphael; Brais, Bernard; Bugiani, Marianna; Sistermans, Erik; Catsman-Berrevoets, Coriene; Kros, Johan M.; Pinto, Pedro Soares; Pohl, Daniela; Tirupathi, Sandya; Strømme, Petter; de Grauw, Ton; Fribourg, Sébastien; Demos, Michelle; Pizzino, Amy; Naidu, Sakkubai; Guerrero, Kether; van der Knaap, Marjo S.; Bernard, Geneviève

    2014-01-01

    Objective: To study the clinical and radiologic spectrum and genotype–phenotype correlation of 4H (hypomyelination, hypodontia, hypogonadotropic hypogonadism) leukodystrophy caused by mutations in POLR3A or POLR3B. Methods: We performed a multinational cross-sectional observational study of the clinical, radiologic, and molecular characteristics of 105 mutation-proven cases. Results: The majority of patients presented before 6 years with gross motor delay or regression. Ten percent had an onset beyond 10 years. The disease course was milder in patients with POLR3B than in patients with POLR3A mutations. Other than the typical neurologic, dental, and endocrine features, myopia was seen in almost all and short stature in 50%. Dental and hormonal findings were not invariably present. Mutations in POLR3A and POLR3B were distributed throughout the genes. Except for French Canadian patients, patients from European backgrounds were more likely to have POLR3B mutations than other populations. Most patients carried the common c.1568T>A POLR3B mutation on one allele, homozygosity for which causes a mild phenotype. Systematic MRI review revealed that the combination of hypomyelination with relative T2 hypointensity of the ventrolateral thalamus, optic radiation, globus pallidus, and dentate nucleus, cerebellar atrophy, and thinning of the corpus callosum suggests the diagnosis. Conclusions: 4H is a well-recognizable clinical entity if all features are present. Mutations in POLR3A are associated with a more severe clinical course. MRI characteristics are helpful in addressing the diagnosis, especially if patients lack the cardinal non-neurologic features. PMID:25339210

  11. Development of 4H-pyridopyrimidines: a class of selective bacterial protein synthesis inhibitors

    PubMed Central

    2012-01-01

    Background We have identified a series of compounds that inhibit protein synthesis in bacteria. Initial IC50's in aminoacylation/translation (A/T) assays ranged from 3 to14 μM. This series of compounds are variations on a 5,6,7,8-tetrahydropyrido[4,3-d]pyrimidin-4-ol scaffold (e.g., 4H-pyridopyrimidine). Methods Greater than 80 analogs were prepared to investigate the structure-activity relationship (SAR). Structural modifications included changes in the central ring and substituent modifications in its periphery focusing on the 2- and 6-positions. An A/T system was used to determine IC50 values for activity of the analogs in biochemical assays. Minimum inhibitory concentrations (MIC) were determined for each analog against cultures of Enterococcus faecalis, Moraxella catarrhalis, Haemophilus influenzae, Streptococcus pneumoniae, Staphylococcus aureus, Escherichia coli tolC mutants and E. coli modified with PMBN. Results Modifications to the 2-(pyridin-2-yl) ring resulted in complete inactivation of the compounds. However, certain modifications at the 6-position resulted in increased antimicrobial potency. The optimized compounds inhibited the growth of E. faecalis, M. catarrhalis, H. influenzae, S. pneumoniae, S. aureus, E. coli tolC, mutants and E. coli modified with PMBN with MIC values of 4, ≤ 0.12, 1, 2, 4, 1, 1 μg/ml, respectively. IC50 values in biochemical assay were reduced to mid-nanomolar range. Conclusion 4H-pyridopyrimidine analogs demonstrate broad-spectrum inhibition of bacterial growth and modification of the compounds establishes SAR. PMID:22373064

  12. Negative charge trapping effects in Al2O3 films grown by atomic layer deposition onto thermally oxidized 4H-SiC

    NASA Astrophysics Data System (ADS)

    Schilirò, Emanuela; Lo Nigro, Raffaella; Fiorenza, Patrick; Roccaforte, Fabrizio

    2016-07-01

    This letter reports on the negative charge trapping in Al2O3 thin films grown by atomic layer deposition onto oxidized silicon carbide (4H-SiC). The films exhibited a permittivity of 8.4, a breakdown field of 9.2 MV/cm and small hysteresis under moderate bias cycles. However, severe electron trapping inside the Al2O3 film (1 × 1012 cm-2) occurs upon high positive bias stress (>10V). Capacitance-voltage measurements at different temperatures and stress conditions have been used to determine an activation energy of 0.1eV. The results provide indications on the possible nature of the trapping defects and, hence, on the strategies to improve this technology for 4H-SiC devices.

  13. Synthesis of N-Aryl-3,5-dichloro-4H-1,2,6-thiadiazin-4-imines from 3,4,4,5-Tetrachloro-4H-1,2,6-thiadiazine.

    PubMed

    Kalogirou, Andreas S; Manoli, Maria; Koutentis, Panayiotis A

    2015-08-21

    Condensation of 3,4,4,5-tetrachloro-4H-1,2,6-thiadiazine with a range of anilines gave 22 N-aryl-3,5-dichloro-4H-1,2,6-thiadiazin-4-imines in 43-96% yields. The scope and limitations of this condensation are briefly investigated. Furthermore, mono- and bis-substitution of the C-3 and C-5 chlorines of 3,5-dichloro-N-phenyl-4H-1,2,6-thiadiazin-4-imine by amine and alkoxide nucleophiles is explored. Finally, Stille coupling chemistry is used to prepare several N-phenyl-3,5-diaryl-4H-1,2,6-thiadiazin-4-imines. PMID:26261875

  14. Meridional Distribution of CH3C2H and C4H2 in Saturn's Stratosphere from CIRS/Cassini Limb and Nadir Observations

    NASA Technical Reports Server (NTRS)

    Guerlet, Sandrine; Fouchet, Thierry; Bezard, Bruno; Moses, Julianne I.; Fletcher, Leigh N.; Simon-Miller, Amy A.; Flasar, F. Michael

    2010-01-01

    Limb and nadir spectra acquired by Cassini/CIRS (Composite InfraRed Spectrometer) are analyzed in order to derive, for the first time, the meridional variations of diacetylene (C4H2) and methylacetylene (CH3C2H) mixing ratios in Saturn's stratosphere, from 5 hPa up to 0.05 hPa and 80 deg S to 45 deg N. We find that the C4H2 and CH3C2H meridional distributions mimic that of acetylene (C2H2), exhibiting small-scale variations that are not present in photochemical model predictions. The most striking feature of the meridional distribution of both molecules is an asymmetry between mid-southern and mid-northern latitudes. The mid-southern latitudes are found depleted in hydrocarbons relative to their northern counterparts. In contrast, photochemical models predict similar abundances at north and south mid-latitudes. We favor a dynamical explanation for this asymmetry, with upwelling in the south and downwelling in the north, the latter coinciding with the region undergoing ring shadowing. The depletion in hydrocarbons at mid-southern latitudes could also result from chemical reactions with oxygen-bearing molecules. Poleward of 60 deg S, at 0.1 and 0.05 hPa, we find that the CH3C2H and C4H2 abundances increase dramatically. This behavior is in sharp contradiction with photochemical model predictions, which exhibit a strong decrease towards the south pole. Several processes could explain our observations, such as subsidence, a large vertical eddy diffusion coefficient at high altitudes, auroral chemistry that enhances CH3C2H and C4H2 production, or shielding from photolysis by aerosols or molecules produced from auroral chemistry. However, problems remain with all these hypotheses, including the lack of similar behavior at lower altitudes. Our derived mean mixing ratios at 0.5 hPa of (2.4 +/- 0.3) 10(exp -10) for C4H2 and of (1.1 +/- 0.3) 10(exp -9) for CH3C2H are compatible with the analysis of global-average ISO observations performed by Moses et al. Finally, we provide

  15. The effect of CH4/H2 ratio on the surface properties of HDPE treated by CHx ion beam bombardment

    NASA Astrophysics Data System (ADS)

    Ding, Wanyu; Guo, Yuanyuan; Ju, Dongying; Sato, Susumu; Tsunoda, Teruo

    2016-06-01

    The surface of high density polyethylene (HDPE) substrate was bombarded by the CHx group ion beam, which was generated by the mixture of CH4/H2. Varying the CH4/H2 ratio, HDPE surfaces with different chemical bond structures and properties were obtained. Raman and XPS results show that sp2 and sp3 bond structures are formed at HDPE surface bombarded by CHx group ions. The sp3 bond fraction at bombarded HDPE surface depends on the H2 ratio in CH4/H2 mixture, because the H ion/atom/molecule can improve the growth of sp3 bond structure. For HDPE surface bombarded by CH4/H2 = 50/50, sp3 bond fraction reaches the maximum of 30.5%, the surface roughness decreases to 17.04 nm, and the static contact angle of polar H2O molecule increased to 140.2∘.

  16. First experimental determination of the absolute gas-phase rate coefficient for the reaction of OH with 4-hydroxy-2-butanone (4H2B) at 294 K by vapor pressure measurements of 4H2B.

    PubMed

    El Dib, Gisèle; Sleiman, Chantal; Canosa, André; Travers, Daniel; Courbe, Jonathan; Sawaya, Terufat; Mokbel, Ilham; Chakir, Abdelkhaleq

    2013-01-10

    The reaction of the OH radicals with 4-hydroxy-2-butanone was investigated in the gas phase using an absolute rate method at room temperature and over the pressure range 10-330 Torr in He and air as diluent gases. The rate coefficients were measured using pulsed laser photolysis (PLP) of H(2)O(2) to produce OH and laser induced fluorescence (LIF) to measure the OH temporal profile. An average value of (4.8 ± 1.2) × 10(-12) cm(3) molecule(-1) s(-1) was obtained. The OH quantum yield following the 266 nm pulsed laser photolysis of 4-hydroxy-2-butanone was measured for the first time and found to be about 0.3%. The investigated kinetic study required accurate measurements of the vapor pressure of 4-hydroxy-2-butanone, which was measured using a static apparatus. The vapor pressure was found to range from 0.056 to 7.11 Torr between 254 and 323 K. This work provides the first absolute rate coefficients for the reaction of 4-hydroxy-2-butanone with OH and the first experimental saturated vapor pressures of the studied compound below 311 K. The obtained results are compared to those of the literature and the effects of the experimental conditions on the reactivity are examined. The calculated tropospheric lifetime obtained in this work suggests that once emitted into the atmosphere, 4H2B may contribute to the photochemical pollution in a local or regional scale.

  17. Optical triggering of high-voltage (18 kV-class) 4H-SiC thyristors

    NASA Astrophysics Data System (ADS)

    Rumyantsev, S. L.; Levinshtein, M. E.; Shur, M. S.; Cheng, L.; Agarwal, A. K.; Palmour, J. W.

    2013-12-01

    Optical triggering of high-voltage (18 kV-class) 4H-SiC thyristors with a single amplification step (pilot thyristor) is reported. It is demonstrated that the switch-on processes in such high-voltage structures are quite different from the switch-on processes in 12 kV 4H-SiC thyristors. In particular, the switch-on process occurs in two stages even at maximum light pulse energy and rather high anode biases.

  18. Are HO radicals produced in the reaction of O(3P) with 1-C4H8 ?

    NASA Technical Reports Server (NTRS)

    Luria, M.; Simonaitis, R.; Heicklen, J.

    1972-01-01

    The reaction of O(3P) with 1-C4H8 was examined in the presence of CO which scavenges HO radicals to produce CO2. From the CO2 quantum yield, an upper limit to the efficiency of HO production in the reaction of O(3P) with 1-C4H8 was found to be 0.020 at both 298 and 473 K.

  19. Leading the Pack: Dog 3--Fun Activities for You and Your Dog. 4-H Skills for Life Animal Series. National 4-H Curriculum. BU-08168

    ERIC Educational Resources Information Center

    National 4-H Council, 2005

    2005-01-01

    Experienced youth investigate responsible breeding, diseases, caring for geriatric dogs, training, service dogs, dog roles and careers related to dogs. This guide provides youth with numerous leadership opportunities. Because youth development programs help build tomorrow's leaders, leadership is a strong theme in Level 3 activities. One will be…

  20. Evolution of extended defects in PVT-grown 4H-silicon carbide single crystals

    NASA Astrophysics Data System (ADS)

    Lee, Jaewon

    The purpose of this thesis is to identify the origin and evolution of two types of extended defects frequently observed in physical vapor transport (PVT) grown hexagonal SiC bulk crystals. They are basal plane dislocations and threading edge dislocations. PVT-grown 4H-SiC single crystals were investigated using high-resolution x-ray diffraction, defect selective etching, and transmission electron microscopy. The (0008) diffraction peak position shifted about 2.5° along the 3 inch crystal diameter indicating the bending of the basal plane. Transmission electron microscopy revealed that the bending is due to deformation-induced basal plane dislocations with at least a partial edge character. The basal plane dislocations had a non-zero net Burgers vector with the net extra half plane pointing toward the seed side of the investigated crystals, and thus caused the basal plane to bend concave toward the growth direction. Approximately parallel basal plane dislocation arrays were shown to correspond to basal plane slip bands. The bending of entire boules and the global distribution of the slip bands indicated that the basal plane slip system was activated by the macroscopic shear stress resulting from the thermal gradient imposed on the crystal during the PVT growth. The fine structure of the 'star defect' in PVT-grown 4H-SiC single crystals was investigated using molten KOH etching, transmission x-ray topography, and transmission electron microscopy. The star defect is one of the macroscopic extended defects consisting of the defect center and symmetric dislocation arrays extending along six equivalent <11-20> directions. The <11-20> arms of the star defect were shown to consist of polygonized threading edge dislocation arrays, which correspond to prismatic slip bands. Transmission electron microscopy revealed that Burgers vectors of the dislocations are anti-parallel to corresponding arm directions, and the extra half planes of the dislocations extend toward the

  1. Enhancement of atmospheric H2SO4 / H2O nucleation: organic oxidation products versus amines

    NASA Astrophysics Data System (ADS)

    Berndt, T.; Sipilä, M.; Stratmann, F.; Petäjä, T.; Vanhanen, J.; Mikkilä, J.; Patokoski, J.; Taipale, R.; Mauldin, R. L., III; Kulmala, M.

    2014-01-01

    Atmospheric H2SO4 / H2O nucleation influencing effects have been studied in the flow tube IfT-LFT (Institute for Tropospheric Research - Laminar Flow Tube) at 293 ± 0.5 K and a pressure of 1 bar using synthetic air as the carrier gas. The presence of a possible background amine concentration in the order of 107-108 molecule cm-3 throughout the experiments has to be taken into account. In a first set of investigations, ozonolysis of olefins (tetramethylethylene, 1-methyl-cyclohexene, α-pinene and limonene) for close to atmospheric concentrations, served as the source of OH radicals and possibly other oxidants initiating H2SO4 formation starting from SO2. The oxidant generation is inevitably associated with the formation of organic oxidation products arising from the parent olefins. These products (first generation mainly) showed no clear effect on the number of nucleated particles within a wide range of experimental conditions for H2SO4 concentrations higher than ~107 molecule cm-3. Also the early growth process of the nucleated particles was not significantly influenced by the organic oxidation products in line with the expected growth by organic products using literature data. An additional, H2SO4-independent process of particle (nano-CN) formation was observed in the case of α-pinene and limonene ozonolysis for H2SO4 concentrations smaller than ~107 molecule cm-3. Furthermore, the findings confirm the appearance of an additional oxidant for SO2 beside OH radicals, very likely stabilized Criegee Intermediates (sCI). A second set of experiments has been performed in the presence of added amines in the concentrations range of a few 107-1010 molecule cm-3 applying photolytic OH radical generation for H2SO4 production without addition of other organics. All amines showed significant nucleation enhancement with increasing efficiency in the order pyridine < aniline < dimethylamine < trimethylamine. This result supports the idea of H2SO4 cluster stabilization by

  2. Contaminant exposures at the 4H shell mounds in the Santa Barbara Channel.

    PubMed

    Phillips, Charles R; Salazar, Michael H; Salazar, Sandra M; Snyder, Barry J

    2006-12-01

    Remobilization, bioavailability, and potential toxicity of chemical contaminants were evaluated at the 4H shell mounds - the site of abandoned offshore oil and gas production platforms in the Santa Barbara Channel region of the Southern California Bight. Evaluations used a weight-of-evidence approach based on results from bulk phase chemical analyses and laboratory toxicity testing of shell mound cores, in situ field bioassays using caged mussels, and surficial sediment chemistry. Shell mound cores contained elevated concentrations of metals associated with drilling wastes (e.g., Ba, Cr, Pb, and Zn), as well as monocyclic and polycyclic aromatic hydrocarbons (PAHs). The highest concentrations along with pockets of free oil were associated with the middle "cuttings" stratum. Sediments composited from all core strata caused significant acute toxicity and bioaccumulation of Ba and PAHs in test organisms during laboratory exposures. In contrast, caged mussels placed at each of the shell mounds for a period of 57-58 days had greater than 90% survival, and there were no significant differences in survival of mussels placed at the shell mounds and corresponding reference sites. While all mussel samples exhibited increases in shell length, whole animal weight, and tissue lipid content, in some cases growth metrics for the shell mound mussels were significantly higher than those for the reference sites. Concentrations of metals, PAHs, and polychlorinated biphenyls (PCBs) in tissues of the shell mound mussels were not significantly different from those at reference sites. The presence of labile aromatic hydrocarbons in shell mound cores and absence of significant contaminant accumulation of tissues of caged mussels indicated that chemical contaminants are not being remobilized from the 4H shell mounds. Surficial bottom sediments near the shell mounds contained elevated Ba concentrations that probably were associated with drilling wastes. However, concentrations did not

  3. Contaminant exposures at the 4H shell mounds in the Santa Barbara Channel.

    PubMed

    Phillips, Charles R; Salazar, Michael H; Salazar, Sandra M; Snyder, Barry J

    2006-12-01

    Remobilization, bioavailability, and potential toxicity of chemical contaminants were evaluated at the 4H shell mounds - the site of abandoned offshore oil and gas production platforms in the Santa Barbara Channel region of the Southern California Bight. Evaluations used a weight-of-evidence approach based on results from bulk phase chemical analyses and laboratory toxicity testing of shell mound cores, in situ field bioassays using caged mussels, and surficial sediment chemistry. Shell mound cores contained elevated concentrations of metals associated with drilling wastes (e.g., Ba, Cr, Pb, and Zn), as well as monocyclic and polycyclic aromatic hydrocarbons (PAHs). The highest concentrations along with pockets of free oil were associated with the middle "cuttings" stratum. Sediments composited from all core strata caused significant acute toxicity and bioaccumulation of Ba and PAHs in test organisms during laboratory exposures. In contrast, caged mussels placed at each of the shell mounds for a period of 57-58 days had greater than 90% survival, and there were no significant differences in survival of mussels placed at the shell mounds and corresponding reference sites. While all mussel samples exhibited increases in shell length, whole animal weight, and tissue lipid content, in some cases growth metrics for the shell mound mussels were significantly higher than those for the reference sites. Concentrations of metals, PAHs, and polychlorinated biphenyls (PCBs) in tissues of the shell mound mussels were not significantly different from those at reference sites. The presence of labile aromatic hydrocarbons in shell mound cores and absence of significant contaminant accumulation of tissues of caged mussels indicated that chemical contaminants are not being remobilized from the 4H shell mounds. Surficial bottom sediments near the shell mounds contained elevated Ba concentrations that probably were associated with drilling wastes. However, concentrations did not

  4. Synthesis, crystal structure, thermal analysis and dielectric properties of [(C4H9)4N]3Bi2Cl9 compound

    NASA Astrophysics Data System (ADS)

    Trigui, W.; Oueslati, A.; Chaabane, I.; Hlel, F.

    2015-07-01

    A new organic-inorganic tri-tetrabutylammonium nonachlorobibismuthate(III) compound was prepared. It was found to crystallize in the monoclinic system (P21/n space group) with the following lattice parameters: a=11.32(2) Å, b=22.30(3) Å, c=28.53(2) Å and β=96.52(0)°. The [Bi2Cl9]3- anions are surrounded by six [(C4H9)N]+ cations, forming an octahedral configuration. These octahedra are sharing corners in order to provide the tri-dimensional network cohesion. The differential scanning calorimetry reveals four order-disorder reversible phase transitions located at 214, 238, 434 and 477 K. The Raman and infrared spectra confirm the presence of both cationic [(C4H9)N]+ and anionic [Bi2Cl9]3- parts. The dielectric parameters, real and imaginary dielectric permittivity (ε‧ and ε″), and dielectric loss tangent (tg δ), were measured in the frequency range of 209 kHz-5 MHz at different temperatures. The variations of dielectric dispersion (ε') and dielectric absorption (ε″) with frequency show a distribution of relaxation times, which is probably related to the change in the dynamical state of the [(C4H9)4N]+ cations and the [Bi2Cl9]3- anions.

  5. The solubility of [4H]Si defects in α-quartz and their role in the formation of molecular water and related weakening on heating

    NASA Astrophysics Data System (ADS)

    McConnell, J. D. C.; Lin, J. S.; Heine, Volker

    1995-09-01

    The nature of the solubility of water as [4H]Si defects in quartz, and their role in providing a source of molecular water on heating, is investigated. Existing ab inito energy calculations on the incorporation of water in quartz are used to show that energetically 4H for Si substitution is likely to constitute the most prevalent mode of water uptake on the atomic scale in quartz under equilibrium conditions, and that the planar defects previously observed by a number of different authors by electron microscopy in wet quartz are likely to be planar rafts of aggregated [4H]Si defects which are formed on supersaturation. These new conclusions call into question the previous identification of the planar defects as high pressure water clusters and require that their role in the production of molecular water in the context of recent theories of hydrolytic weakening be re-assessed. Accordingly the existing ab initio results have been used to establish the characteristics of the phase diagram for the system quartz-water in the temperature and pressure range of interest in hydrolytic weakening. Additional electron-optical experiments on wet quartz show that, on annealing at temperature in the electron microscope, similar planar defects develop in wet quartz by a diffusion process. In the context of existing theories of hydrolytic weakening it is now proposed that the conversion of [4H]Si defects to molecular water, where this is dictated by the equilibrium phase diagram, leads to a relatively large increase in volume and to the appearance of the bubbles of free water and the nucleation of associated prismatic dislocation loops of Burgers vector b=1/3 a< 11bar 20rangle as previously observed. Ultimately the development of these loops leads to dislocation-induced plasticity.

  6. Sequential afterglow processing and non-contact Corona-Kelvin metrology of 4H-silicon carbide

    NASA Astrophysics Data System (ADS)

    Short, Eugene L., III

    Silicon carbide (SiC) is a wide band-gap semiconductor with advantageous electrical and thermal properties making it attractive for high temperature and power applications. However, difficulties with oxide/SiC structures have posed challenges to the development of practical MOS-type devices. Surface conditioning and oxidation of 4H-SiC were investigated using a novel sequential afterglow processing approach combined with the unique capabilities of non-contact corona-Kelvin metrology. The use of remote plasma assisted thermal oxidation facilitated film growth at low temperature and pressure with the flexibility of sequential in-situ processing options including pre-oxidation surface conditioning. Corona-Kelvin metrology (C-KM) provided a fast, nondestructive method for electrical evaluation of oxide films and semiconductor surfaces. Non-contact C-KM oxide capacitance-voltage characteristics combined with direct measurement of SiC surfaces using C-KM depletion surface barrier monitoring and XPS analysis of surface chemistry were interpreted relating the impact of afterglow conditioning on the surface and its influence on subsequent oxide thin film growth. Afterglow oxide films of thicknesses 50--500 A were fabricated on SiC epi-layers at low growth temperatures in the range 600--850°C, an achievement not possible using conventional atmospheric oxidation techniques. The inclusion of pre-oxidation surface conditioning in forming gas (N2:H2)* afterglow was found to produce an increase in oxide growth rate (10--25%) and a significant improvement in oxide film thickness uniformity. Analysis of depletion voltage transients on conditioned SiC surfaces revealed the highest degree of surface passivation, uniformity, and elimination of sources of charge compensation accomplished by the (N2:H2)* afterglow treatment for 20 min. at 600--700°C compared to other conditioning variations. The state of surface passivation was determined to be very stable and resilient when exposed

  7. Discovery and Analysis of 4H-Pyridopyrimidines, a Class of Selective Bacterial Protein Synthesis Inhibitors▿

    PubMed Central

    Ribble, Wendy; Hill, Walter E.; Ochsner, Urs A.; Jarvis, Thale C.; Guiles, Joseph W.; Janjic, Nebojsa; Bullard, James M.

    2010-01-01

    Bacterial protein synthesis is the target for numerous natural and synthetic antibacterial agents. We have developed a poly(U) mRNA-directed aminoacylation/translation protein synthesis system composed of phenyl-tRNA synthetases, ribosomes, and ribosomal factors from Escherichia coli. This system, utilizing purified components, has been used for high-throughput screening of a small-molecule chemical library. We have identified a series of compounds that inhibit protein synthesis with 50% inhibitory concentrations (IC50s) ranging from 3 to 14 μM. This series of compounds all contained the same central scaffold composed of tetrahydropyrido[4,3-d]pyrimidin-4-ol (e.g., 4H-pyridopyrimidine). All analogs contained an ortho pyridine ring attached to the central scaffold in the 2 position and either a five- or a six-member ring tethered to the 6-methylene nitrogen atom of the central scaffold. These compounds inhibited the growth of E. coli, Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis, with MICs ranging from 0.25 to 32 μg/ml. Macromolecular synthesis (MMS) assays with E. coli and S. aureus confirmed that antibacterial activity resulted from specific inhibition of protein synthesis. Assays were developed for the steps performed by each component of the system in order to ascertain the target of the compounds, and the ribosome was found to be the site of inhibition. PMID:20696870

  8. Discovery and analysis of 4H-pyridopyrimidines, a class of selective bacterial protein synthesis inhibitors.

    PubMed

    Ribble, Wendy; Hill, Walter E; Ochsner, Urs A; Jarvis, Thale C; Guiles, Joseph W; Janjic, Nebojsa; Bullard, James M

    2010-11-01

    Bacterial protein synthesis is the target for numerous natural and synthetic antibacterial agents. We have developed a poly(U) mRNA-directed aminoacylation/translation protein synthesis system composed of phenyl-tRNA synthetases, ribosomes, and ribosomal factors from Escherichia coli. This system, utilizing purified components, has been used for high-throughput screening of a small-molecule chemical library. We have identified a series of compounds that inhibit protein synthesis with 50% inhibitory concentrations (IC(50)s) ranging from 3 to 14 μM. This series of compounds all contained the same central scaffold composed of tetrahydropyrido[4,3-d]pyrimidin-4-ol (e.g., 4H-pyridopyrimidine). All analogs contained an ortho pyridine ring attached to the central scaffold in the 2 position and either a five- or a six-member ring tethered to the 6-methylene nitrogen atom of the central scaffold. These compounds inhibited the growth of E. coli, Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis, with MICs ranging from 0.25 to 32 μg/ml. Macromolecular synthesis (MMS) assays with E. coli and S. aureus confirmed that antibacterial activity resulted from specific inhibition of protein synthesis. Assays were developed for the steps performed by each component of the system in order to ascertain the target of the compounds, and the ribosome was found to be the site of inhibition.

  9. Surface Al doping of 4H-SiC via low temperature annealing

    NASA Astrophysics Data System (ADS)

    Park, Junbo; Kim, Ki-hwan; Park, Young-rak; Kim, Minki; Lee, Hyungseok; Jun, Chi-Hoon; Koo, Sangmo; Ko, Sang Choon

    2016-07-01

    We present a method of forming shallow p-doping on a 4H-SiC surface by depositing a thin Al layer (d = 5 nm) and then thermally annealing it at 1000 °C for 10 min. A secondary ion mass spectrometry analysis of the annealed Al/SiC sample reveals an Al concentration in excess of 1017 cm-3 up to a depth of d ≤ 250 nm. I-V measurements and CV characterizations of Ti-SiC Schottky barrier diodes (SBDs) fabricated on a n-type SiC epi-wafer indicate that the shallow Al doping increases the built-in potential of the junction and the barrier height by Δ V b i = 0.51 eV and Δ ϕ B = 0.26 eV , respectively. Assuming a rectangular doping profile, calculations of the built-in voltage shift and the Schottky barrier height indicate that partial dopant activation (activation ratio ˜2%) can induce the observed barrier height shift. The shallow doping method was then used to fabricate junction terminations in SBDs which increased the breakdown voltage and reduced the reverse leakage current. Technology CAD simulations of the SBD with and without doping verify that a reduction of peak electric field can explain the improvement of the breakdown voltage.

  10. A novel double-recessed 4H-SiC MESFET with partly undoped space region

    NASA Astrophysics Data System (ADS)

    Orouji, Ali A.; Aminbeidokhti, Amirhossein

    2011-12-01

    In this paper, a novel double-recessed 4H-SiC metal semiconductor field effect transistor (MESFET) with partly undoped space region (DRUS-MESFET) is introduced. The key idea in this work is to improve the DC and RF characteristics of the device by introducing an undoped space region. Using two-dimensional and two-carrier device simulation, we demonstrate that breakdown voltage ( VBR) increases from 109 V in conventional double recessed MESFET (DR-MESFET) structure to 144.5 V in the DRUS-MESFET structure due to the modified channel electric field distribution of the proposed structure. The maximum output power density of the DRUS-MESFET structure is about 25.4% larger than that of the DR-MESFET structure. Furthermore, lower gate-drain capacitance ( CGD), higher cut-off frequency ( fT), larger maximum available gain (MAG), and higher maximum oscillation frequency ( fmax) are achieved for the DRUS-MESFET structure. The results show that the fmax and fT of the proposed structure improve 95.6% and 13.07% respectively, compared with that of the DR-MESFET structure. Also, the MAG of the DRUS-MESET is 4.5 dB higher than that of the DR-MESFET structure at 40 GHz. The results show that the DRUS-MESFET structure has superior electrical characteristics and performances in comparison with the DR-MESFET structure.

  11. Prediction of 4H-SiC betavoltaic microbattery characteristics based on practical Ni-63 sources.

    PubMed

    Gui, Gui; Zhang, Kan; Blanchard, James P; Ma, Zhenqiang

    2016-01-01

    We have investigated the performance of 4H-SiC betavoltaic microbatteries under exposure to the practical Ni-63 sources using the Monte Carlo method and Synopsys® Medici device simulator. A typical planar p-n junction betavoltaic device with the Ni-63 source of 20% purity on top is modeled in the simulation. The p-n junction structure includes a p+ layer, a p- layer, an n+ layer, and an n- layer. In order to obtain an accurate and valid predication, our simulations consider several practical factors, including isotope impurities, self-absorption, and full beta energy spectra. By simulating the effects of both the p-n junction configuration and the isotope source thickness on the battery output performance, we have achieved the optimal design of the device and maximum energy conversion efficiency. Our simulation results show that the energy conversion efficiency increases as the doping concentration and thickness of the p- layer increase, whereas it is independent of the total depth of the p-n junction. Furthermore, the energy conversion efficiency decreases as the thickness of the practical Ni-63 source increases, because of self-absorption in the isotope source. Therefore, we propose that a p-n junction betavoltaic cell with a thicker and heavily doped p- layer under exposure to a practical Ni-63 source with an appreciable thickness could produce the optimal energy conversion efficiency. PMID:26583261

  12. Nitrogen doping of chemical vapor deposition grown graphene on 4H-SiC (0001)

    SciTech Connect

    Urban, J. M.; Binder, J.; Wysmołek, A.; Dąbrowski, P.; Strupiński, W.; Kopciuszyński, M.; Jałochowski, M.; Klusek, Z.

    2014-06-21

    We present optical, electrical, and structural properties of nitrogen-doped graphene grown on the Si face of 4H-SiC (0001) by chemical vapor deposition method using propane as the carbon precursor and N{sub 2} as the nitrogen source. The incorporation of nitrogen in the carbon lattice was confirmed by X-ray photoelectron spectroscopy. Angle-resolved photoemission spectroscopy shows carrier behavior characteristic for massless Dirac fermions and confirms the presence of a graphene monolayer in the investigated nitrogen-doped samples. The structural and electronic properties of the material were investigated by Raman spectroscopy. A systematical analysis of the graphene Raman spectra, including D, G, and 2D bands, was performed. In the case of nitrogen-doped samples, an electron concentration on the order of 5–10 × 10{sup 12} cm{sup −2} was estimated based upon Raman and Hall effect measurements and no clear dependence of the carrier concentration on nitrogen concentration used during growth was observed. This high electron concentration can be interpreted as both due to the presence of nitrogen in graphitic-like positions of the graphene lattice as well as to the interaction with the substrate. A greater intensity of the Raman D band and increased inhomogeneity, as well as decreased electron mobility, observed for nitrogen-doped samples, indicate the formation of defects and a modification of the growth process induced by nitrogen doping.

  13. Electrical Characterization of High Energy Electron Irradiated Ni/4 H-SiC Schottky Barrier Diodes

    NASA Astrophysics Data System (ADS)

    Paradzah, A. T.; Omotoso, E.; Legodi, M. J.; Auret, F. D.; Meyer, W. E.; Diale, M.

    2016-08-01

    The effect of high energy electron irradiation on Ni/4 H-SiC Schottky barrier diodes was evaluated by current-voltage ( I- V) and capacitance-voltage ( C- V) measurements at room temperature. Electron irradiation was achieved by using a radioactive strontium source with peak emission energy of 2.3 MeV. Irradiation was performed in fluence steps of 4.9 × 1013 cm-2 until a total fluence of 5.4 × 1014 cm-2 was reached. The Schottky barrier height determined from I- V measurements was not significantly changed by irradiation while that obtained from C- V measurements increased with irradiation. The ideality factor was obtained before irradiation as 1.05 and this value did not significantly change as a result of irradiation. The series resistance increased from 47 Ω before irradiation to 74 Ω after a total electron fluence of 5.4 × 1014 cm-2. The net donor concentration decreased with increasing irradiation fluence from 4.6 × 1014 cm-3 to 3.0 × 1014 cm-3 from which the carrier removal rate was calculated to be 0.37 cm-1.

  14. Identification of antisite carbon split-interstitial defects in 4H-SiC

    SciTech Connect

    Steeds, J. W.; Sullivan, W.

    2008-05-15

    A rich variety of optical centers with high energy local vibrational modes has been found in electron-irradiated 4H-SiC in both the as-irradiated and annealed states. These energies have been measured and the annealing dependence of the optical centers has been investigated by low-temperature photoluminescence spectroscopy. In view of the relatively high energies of these modes, it is anticipated that they involve carbon interstitials and a detailed correlation has therefore been undertaken, in selected cases, between the experimentally observed energies and those calculated by recent local density approximation, i.e., ab initio methods for atomic arrangements involving carbon interstitials. When satisfactory agreement has been achieved, the annealing behavior is compared to the calculated stabilities of the defects concerned. As a result, different configurations of carbon antisite defects are identified together with their spatial distributions with respect to the irradiated areas and their sequences of appearance and disappearance on annealing. These findings significantly add to the understanding of the radiation damage process and its subsequent development and recovery on annealing. Some of the optical centers that have well-defined local vibrational modes remain to be identified in the future.

  15. Influence of growth pressure on filling 4H-SiC trenches by CVD method

    NASA Astrophysics Data System (ADS)

    Ji, Shiyang; Kojima, Kazutoshi; Kosugi, Ryoji; Saito, Shingo; Sakuma, Yuuki; Tanaka, Yasunori; Yoshida, Sadafumi; Himi, Hiroaki; Okumura, Hajime

    2016-01-01

    To construct a superjunction structure consisting of p/n columns, narrow stripe-shaped trenches (∼1.5 µm wide and ∼4.7 µm deep) preformed on an n+ 4H-SiC substrate were filled by the hot-wall CVD method using a conventional gas reaction system, SiH4:C3H8:H2. The influences of growth pressure on the coverage distribution of epilayers and the corresponding filling efficiency (the thickness ratio of epilayers on trench bottom and mesa top) were investigated. Two benefits of increasing the growth pressure from 10 to 38 kPa were found: one is the reduced growth around the mesa surface, which lessens the risk of void formation; the other is a high filling rate as well as an improved filling efficiency up to ∼7. By supplying source gases at high flow rates, a void-free trench filling with a filling rate of ∼1.3 µm/h was successfully achieved at 38 kPa.

  16. Raman spectra of the different phases in the CaSO4-H2O system.

    PubMed

    Prieto-Taboada, Nagore; Gómez-Laserna, Olivia; Martínez-Arkarazo, Irantzu; Olazabal, María Ángeles; Madariaga, Juan Manuel

    2014-10-21

    Although it is known that the CaSO4/H2O system is formed by at least five different phases, this fact is not correctly documented in Raman spectroscopy studies. The main problem detected in the literature was the incorrect definition of the anhydrite, which produced the assignation of different spectra for a single compound. In this sense, two different spectra were clearly identified from the bibliography, which showed different main Raman bands at 1017 or 1025 cm(-1), although anhydrite could be present even as three different polymorphous species with different structures. A better understanding of the whole system obtained from a review of the literature allowed new conclusions to be established. Thanks to that revision and the development of different thermodynamical experiments by Raman spectroscopy, the Raman spectra of each phase were successfully identified for the first time. In this way, the main Raman bands of gypsum, bassanite, anhydrite III, anhydrite II and anhydrite I were identified at 1008, 1015, 1025, 1017 and 1017 cm(-1), respectively. To conclude this work, the contradictions found in literature were critically summarized. PMID:25226433

  17. Control of electric field in 4H-SiC UMOSFET: Physical investigation

    NASA Astrophysics Data System (ADS)

    Jozi, Mohammad; Orouji, Ali A.; Fathipour, Morteza

    2016-09-01

    In this paper, we show how breakdown voltage (VBR) and the specific on-resistance (Ron) can be improved simply by controlling of the electric field in a power 4H-SiC UMOSFET. The key idea in this work is increasing the uniformity of the electric field profile by inserting a region with a graded doping density (GD region) in the drift region. The doping density of inserted region is decreased gradually from top to bottom, called Graded Doping Region UMOSFET (GDR-UMOSFET). The GD region results in a more uniform electric field profile in comparison with a conventional UMOSFET (C-UMOSFET) and a UMOSFET with an accumulation layer (AL-UMOSFET). This in turn improves breakdown voltage. Using two-dimensional two-carrier simulation, we demonstrate that the GDR-UMOSFET shows higher breakdown voltage and lower specific on-resistance. Our results show the maximum breakdown voltage of 1340 V is obtained for the GDR-UMOSFET with 10 μm drift region length, while at the same drift region length and approximated doping density, the maximum breakdown voltages of the C-UMOSFET and the AL-UMOSFET structures are 534 V and 703 V, respectively.

  18. Microscopic origin of the prolonged coherence in 4H-SiC divacancy spin qubits

    NASA Astrophysics Data System (ADS)

    Seo, Hosung; Falk, Abram; Klimov, Paul; Christle, David; Awschalom, David; Galli, Giulia

    Long coherence times of quantum bits (qubits) is a key prerequisite for quantum computing and quantum metrology. Recently, electronic spin qubits localized to divacancies in 4H-SiC were found to have a long spin coherence time (T2) exceeding 1 ms, which is longer than that of the nitrogen-vacancy (NV) center in chemically but not isotopically purified diamond. In this talk, we discuss the microscopic origin behind the prolonged divacancy coherence. By using optically detected magnetic resonance (ODMR), we show that the divacancy T2 rapidly increases as a function of magnetic field, saturating at 1.3 ms at T = 20 K. We used a quantum-bath model combined with a cluster correlation expansion technique to calculate the divacancy coherence function and found an excellent agreement between theory and experiment. We show that an effective decoupling of the 29Si and 13C nuclear spins due to their gyromagnetic ratio difference is one of the key reasons responsible for suppressing the decoherence of the divacancy qubits in SiC under magnetic fields larger than 100G. We gratefully acknowledge financial support from the National Science Foundation through the University of Chicago MRSEC under Award Number DMR-1420709.

  19. High-voltage (3.3 kV) 4H-SiC JBS diodes

    SciTech Connect

    Ivanov, P. A. Grekhov, I. V.; Il'inskaya, N. D.; Kon'kov, O. I.; Potapov, A. S.; Samsonova, T. P.; Serebrennikova, O. U.

    2011-05-15

    High-voltage 4H-SiC junction-barrier Schottky (JBS) diodes have been fabricated and studied. The working area of the diodes (anode contact area) is 1.44 mm{sup 2}. At currents in the range from 10{sup -11} to 1.5 A, the forward current-voltage characteristic of the diodes is described in terms of the thermionic emission model, with the series resistance taken into account: Schottky barrier height {Phi}{sub B} = 1.16 eV, ideality factor n = 1.01, and series resistance R{sub s} = 2.2 {Omega} (32 m{Omega} cm{sup 2}). The value of R{sub s} is governed by the resistance of the blocking epitaxial n-base (impurity concentration N = 9 Multiplication-Sign 10{sup 14} cm{sup -3}, n-layer thickness d = 34 {mu}m). The diodes can block a reverse voltage of at least 3.3 kV (with a leakage current at room temperature on the order of 1 {mu}A). It is suggested that the leakage mechanism is associated with crystal lattice defects (dislocations) in SiC. It is shown that the reverse-recovery characteristics of the diodes are determined by the flow of a purely capacitive reverse current.

  20. Transport and photoconduction characteristics of metal-graphene-4H-SiC(0001) heterojunction devices

    SciTech Connect

    Hosseini, T.; Kouklin, N.; Tomer, D.; Rajput, S.; Li, L.

    2014-12-01

    Vertically integrated graphene-semiconductor systems remain of significant technological importance for their promise to captivate new device physics and propel the development of advanced carbon-based opto-electronic devices. In this study, we carry out a series of bias-dependent transport, gate-dependent transport, and photoconduction measurements to probe the opto-electronic characteristics of metal-graphene-4H-SiC (0001) (Si-face) heterojunctions. The forward bias transport is found to deviate strongly from thermionic emission one as being controlled by the device circuitry and minority carrier injection mechanisms. An improved analytical model is offered and used to extract key junction parameters including series resistance of ∼80 kΩ, interface barrier height of ∼0.6 eV, and ideality factor of ∼6.1. The results of the photocurrent tests point to a light-assisted minority carrier injection as a key mechanism behind the photoconductive gain obtained in the devices subject to a weak, sub-bandgap cw-excitation.

  1. From the Au nano-clusters to the nanoparticles on 4H-SiC (0001)

    PubMed Central

    Li, Ming-Yu; Zhang, Quanzhen; Pandey, Puran; Sui, Mao; Kim, Eun-Soo; Lee, Jihoon

    2015-01-01

    The control over the configuration, size, and density of Au nanoparticles (NPs) has offered a promising route to control the spatial confinement of electrons and photons, as a result, Au NPs with a various configuration, size and density are witnessed in numerous applications. In this work, we investigate the evolution of self-assembled Au nanostructures on 4H-SiC (0001) by the systematic variation of annealing temperature (AT) with several deposition amount (DA). With the relatively high DAs (8 and 15 nm), depending on the AT variation, the surface morphology drastically evolve in two distinctive phases, i.e. (I) irregular nano-mounds and (II) hexagonal nano-crystals. The thermal energy activates adatoms to aggregate resulting in the formation of self-assembled irregular Au nano-mounds based on diffusion limited agglomeration at comparatively low annealing temperature, which is also accompanied with the formations of hillocks and granules due to the dewetting of Au films and surface reordering. At high temperature, hexagonal Au nano-crystals form with facets along {111} and {100} likely due to anisotropic distribution of surface energy induced by the increased volume of NPs. With the small DA (3 nm), only dome shaped Au NPs are fabricated along with the variation of AT from low to elevated temperature. PMID:26354098

  2. Synthesis, molecular docking and biological evaluation of new steroidal 4H-pyrans

    NASA Astrophysics Data System (ADS)

    Uzzaman, Shams; Dar, Ayaz Mahmood; Sohail, Aamir; Bhat, Sheraz; mustafa, Mir Faisal; Khan, Yusuf

    2014-01-01

    A series of new steroidal 4H-pyrans (4-6) have been synthesized from steroidal α, β-unsaturated ketones (1-3). The products (4-6) were characterized by IR, 1H NMR, 13C NMR, MS and analytical data. The interaction studies of compounds (4-6) with DNA were carried out by employing gel electrophoresis, UV-vis and fluorescence spectroscopy. The gel electrophoresis pattern revealed that compounds (4-6) bind to DNA and also demonstrated that the compound 6 alone or in presence of Cu (II) causes the nicking of supercoiled pBR322. The compounds 4 and 5 bind to DNA preferentially through electrostatic and hydrophobic interactions with Kb values found to be 5.3 × 103 and 3.7 × 103 M-1, respectively, indicating the higher binding affinity of compound 4 towards DNA. The docking study suggested the intercalation of compounds in between the nucleotide base pairs. The cytotoxicity and genotoxicity of the newly synthesized compounds were checked by MTT and comet assay, respectively during which compound 6 showed potential behaviour.

  3. Silicon vacancy center in 4 H -SiC: Electronic structure and spin-photon interfaces

    NASA Astrophysics Data System (ADS)

    Soykal, Ö. O.; Dev, Pratibha; Economou, Sophia E.

    2016-02-01

    Defects in silicon carbide are of intense and increasing interest for quantum-based applications due to this material's properties and technological maturity. We calculate the multiparticle symmetry-adapted wave functions of the negatively charged silicon vacancy defect in hexagonal silicon carbide via use of group theory and density functional theory and find the effects of spin-orbit and spin-spin interactions on these states. Although we focused on VSi- in 4 H -SiC because of its unique fine structure due to the odd number of active electrons, our methods can be easily applied to other defect centers of different polytypes, especially to the 6 H -SiC. Based on these results, we identify the mechanism that polarizes the spin under optical drive, obtain the ordering of its dark doublet states, point out a path for electric field or strain sensing, and find the theoretical value of its ground-state zero-field splitting to be 68 MHz, in good agreement with experiment. Moreover, we present two distinct protocols of a spin-photon interface based on this defect. Our results pave the way toward quantum information and quantum metrology applications with silicon carbide.

  4. Dicarbon antisite defect in n -type 4H-SiC

    NASA Astrophysics Data System (ADS)

    Umeda, T.; Isoya, J.; Morishita, N.; Ohshima, T.; Janzén, E.; Gali, A.

    2009-03-01

    We identify the negatively charged dicarbon antisite defect ( C2 core at silicon site) in electron-irradiated n -type 4H-SiC by means of combined electron paramagnetic resonance (EPR) measurements and first-principles calculations. The HEI5 and HEI6 EPR centers ( S=1/2 ; C1h symmetry) are associated with cubic and hexagonal dicarbon antisite defects, respectively. This assignment is based on a comparison of the measured and calculated hyperfine tensors of C13 and S29i atoms as far as the second neighborhood around the defects. Theoretically, the dicarbon antisites are stable in a single negative charge state under a wide range of n -type samples. We found that the defects can be created under a wide range of irradiation conditions, and our measurements strongly suggest the existence of carbon antisite defects in the as-grown samples. Annealing studies revealed several atomistic processes such as recombination of carbon interstitials with vacancies and formation of carbon aggregates. These processes were activated at about 1000°C , and as theoretically predicted, the dicarbon antisite is much more stable than the dicarbon interstitial defect ( C2 core at carbon site). The measured activation temperature is consistent with the temperature range for forming various carbon aggregate-related photoluminescence centers.

  5. Can the bis(diboranyl) structure of B(4)H(10) be observed? The story continues.

    PubMed

    Ramakrishna, Vinutha; Duke, Brian J

    2004-12-13

    Pathways for the conversion of the unknown bis(diboranyl) isomer of tetraborane(10) (B(4)H(10)) to the known arachno isomer have been determined for the first time with the use of an electron correlation ab initio quantum chemical method and without the use of constraints in determination of the transition structures. Two isomers of tetraborane(10), one new, with a pentacoordinated boron atom have been found on the theoretical potential energy surface. Several other pathways for molecular rearrangement of tetraborane(10) have also been characterized. The theoretical method was MP2 theory with the 6-31G(d,p) basis set. The most likely pathway for the conversion of the bis(diboranyl) isomer of tetraborane(10) to the arachno isomer is a concerted pathway with two pentacoordinated intermediates. The highest energy transition state for this pathway lies 27.7 kcal/mol above the bis(diboranyl) isomer. At the same level of the theory, the bis(diboranyl) isomer lies 9.2 kcal/mol above the known arachno isomer. The two isomers with a pentacoordinated boron atom lie 12.5 and 13.1 kcal/mol above the arachno isomer.

  6. Incorporating isolated molybdenum (Mo) atoms into Bilayer Epitaxial Graphene on 4H-SiC(0001)

    NASA Astrophysics Data System (ADS)

    Huang, Han; Wan, Wen; Li, Hui; Wong, Swee Liang; Lv, Lu; Gao, Yongli; Wee, Andrew T. S.

    2014-03-01

    The atomic structures and electronic properties of isolated Mo atoms in bilayer epitaxial graphene (BLEG) on 4H-SiC(0001) are investigated by low temperature scanning tunneling microscopy (LT-STM). LT-STM results reveal that isolated Mo dopants prefer to substitute C atoms at α-sites, and preferentially locate between the graphene bilayers. First-principles calculations confirm that the embedding of single Mo dopants within BLEG is energetically favorable as compared to monolayer graphene. The calculated bandstructures show that Mo-doped BLEG is n-doped, and each Mo atom introduces a local magnetic moment of 1.81 μB. Our findings demonstrate a simple and stable method to incorporate single transition metal dopants into the graphene lattice to tune its electronic and magnetic properties for possible use in graphene spin devices. NRF-CRP (Singapore) grants R-143-000-360-281and R-144-000-295-281. ``Shenghua Professorship'' startup funding from CSU and the support from the NSF of China (Grant No.11304398).

  7. From the Au nano-clusters to the nanoparticles on 4H-SiC (0001).

    PubMed

    Li, Ming-Yu; Zhang, Quanzhen; Pandey, Puran; Sui, Mao; Kim, Eun-Soo; Lee, Jihoon

    2015-01-01

    The control over the configuration, size, and density of Au nanoparticles (NPs) has offered a promising route to control the spatial confinement of electrons and photons, as a result, Au NPs with a various configuration, size and density are witnessed in numerous applications. In this work, we investigate the evolution of self-assembled Au nanostructures on 4H-SiC (0001) by the systematic variation of annealing temperature (AT) with several deposition amount (DA). With the relatively high DAs (8 and 15 nm), depending on the AT variation, the surface morphology drastically evolve in two distinctive phases, i.e. (I) irregular nano-mounds and (II) hexagonal nano-crystals. The thermal energy activates adatoms to aggregate resulting in the formation of self-assembled irregular Au nano-mounds based on diffusion limited agglomeration at comparatively low annealing temperature, which is also accompanied with the formations of hillocks and granules due to the dewetting of Au films and surface reordering. At high temperature, hexagonal Au nano-crystals form with facets along {111} and {100} likely due to anisotropic distribution of surface energy induced by the increased volume of NPs. With the small DA (3 nm), only dome shaped Au NPs are fabricated along with the variation of AT from low to elevated temperature.

  8. Spectral broadening induced by intense ultra-short pulse in 4H-SiC crystals

    NASA Astrophysics Data System (ADS)

    Chun-hua, Xu; Teng-fei, Yan; Gang, Wang; Wen-jun, Wang; Jing-kui, Liang; Xiao-long, Chen

    2016-06-01

    We report the observation of spectral broadening induced by 200 femtosecond laser pulses with the repetition rate of 1 kHz at the wavelength of 532 nm in semi-insulating 4H-SiC single crystals. It is demonstrated that the full width at half maximum of output spectrum increases linearly with the light propagation length and the peak power density, reaching a maximum 870 cm-1 on a crystal of 19 mm long under an incident laser with a peak power density of 60.1 GW/cm2. Such spectral broadening can be well explained by the self-phase modulation model which correlates time-dependent phase change of pulses to intensity-dependent refractive index. The nonlinear refractive index n 2 is estimated to be 1.88×10-15 cm2/W. The intensity-dependent refractive index is probably due to both the nonlinear optical polarizability of the bound electrons and the increase of free electrons induced by the two-photon absorption process. Super continuum spectra could arise as crystals are long enough to induce the self-focusing effect. The results show that SiC crystals may find applications in spectral broadening of high power lasers. Project supported by the National High Technology Research and Development Program of China (Grant No. 2014AA041402) and the National Natural Science Foundation of China (Grant Nos. 51272276 and 51322211).

  9. Fast Turn-Off Times Observed in Experimental 4H SiC Thyristors

    NASA Technical Reports Server (NTRS)

    Niedra, Janis M.

    2006-01-01

    Room temperature measurements of the turn-off time (t(sub q)) are reported for several packaged, npnp developmental power thyristors based on 4H-type SiC and rated 400 V, 2 A. Turn-off is effected by a 50 V pulse of applied reverse voltage, from a state of a steady 1 A forward current. Plots of t(sub q) against the ramp rate (dV(sub AK)/dt) of reapplied forward voltage are presented for preset values of limiting anode-to-cathode voltage (V(sub AK,max)). The lowest t(sub q) measured was about 180 ns. A rapid rise of these t(sub q) curves was observed for values of V(sub AK,max) that are only about a fifth of the rated voltage, whereas comparative t(sub q) plots for a commercial, fast turn-off, Si-based thyristor at a proportionately reduced V(sub AK,max) showed no such behavior. Hence these SiC thyristors may have problems arising from material defects or surface passivation. The influence the R-C-D gate bypass circuit that was used is briefly discussed.

  10. Concentration of point defects in 4H-SiC characterized by a magnetic measurement

    NASA Astrophysics Data System (ADS)

    Peng, B.; Jia, R. X.; Wang, Y. T.; Dong, L. P.; Hu, J. C.; Zhang, Y. M.

    2016-09-01

    A magnetic method is presented to characterize the concentration of point defects in silicon carbide. In this method, the concentration of common charged point defects, which is related to the density of paramagnetic centers, is determined by fitting the paramagnetic component of the specimen to the Brillouin function. Several parameters in the Brillouin function can be measured such as: the g-factor can be obtained from electron spin resonance spectroscopy, and the magnetic moment of paramagnetic centers can be obtained from positron lifetime spectroscopy combined with a first-principles calculation. To evaluate the characterization method, silicon carbide specimens with different concentrations of point defects are prepared with aluminum ion implantation. The fitting results of the densities of paramagnetic centers for the implanted doses of 1 × 1014 cm-2, 1 × 1015 cm-2 and 1 × 1016 cm-2 are 6.52 × 1014/g, 1.14 × 1015/g and 9.45 × 1014/g, respectively. The same trends are also observed for the S-parameters in the Doppler broadening spectra. It is shown that this method is an accurate and convenient way to obtain the concentration of point defects in 4H-SiC.

  11. A novel 4H-SiC MESFET with ultrahigh upper gate

    NASA Astrophysics Data System (ADS)

    Jia, Hujun; Zhang, Hang; Xing, Ding; Luo, Yehui; Duan, Baoxing

    2015-10-01

    A novel 4H-SiC metal semiconductor field effect transistor with ultrahigh upper gate (UU-MESFET) by depletion layer variation and electric field modulation is proposed in this paper for the first time. The prominent merits in the proposed structure are the smaller gate depletion layer and the higher electric field peak produced by the electric field modulation due to ultrahigh upper gate. A higher electric field peak is introduced by ultrahigh upper gate at lower gate corner instead of upper gate corner, which leads to electric field breakdown. Using ISE simulation, the breakdown voltage of the UU-MESFET is improved by 55% and the drain saturation current is increased by 15% than those of the conventional DR-MESFET, which means that the UU-MESFET has an improvement of about 78% in the maximum output power density compared to the DR-MESFET. Furthermore, the gate-source capacitance of the proposed structure is about 17% smaller than that of the DR-MESFET. Therefore the proposed structure has fantastic DC performance and in the meanwhile possesses better RF characteristics.

  12. Structural transformations in femtosecond laser-processed n-type 4H-SiC

    NASA Astrophysics Data System (ADS)

    Rehman, Z. U.; Janulewicz, K. A.

    2016-11-01

    We present a comprehensive study of morphological modification induced on and below the surface of n-type 4H-SiC by irradiation with femtosecond laser pulses under tight focusing condition. Spectroscopic investigation of local electronic and structural transformations in SiC-micro/nanostructures suggested bond breaking i.e. transformation of crystalline SiC to amorphous silicon (a-Si) and amorphous carbon (a-C). These observations were augmented by investigations applying atomic force microscopy (AFM), micro-photoluminescence (PL) spectroscopy, and high resolution X-ray diffraction (HRXRD). A high-resolution cross-sectional study of laser-modified region with transmission electron microscope (TEM) showed a thin amorphous layer in the vicinity of the geometrical focus with deformations and stacking faults in the sub-surface area. Having considered the existing ablation theories, a complex interplay of fast laser heating followed by melting and rapid re-solidification as well as dynamic relaxation of the laser-induced stresses seems to be responsible for formation of the observed structural changes.

  13. Plasma Etching of n-Type 4H-SiC for Photoconductive Semiconductor Switch Applications

    NASA Astrophysics Data System (ADS)

    Ekinci, Huseyin; Kuryatkov, Vladimir V.; Mauch, Daniel L.; Dickens, James C.; Nikishin, Sergey A.

    2015-05-01

    Photoconductive semiconductor switches (PCSS) fabricated on high-purity semi-insulating 4H-SiC substrates (000) are capable of switching high currents in compact packages with long device lifetimes. A heavily doped n-type SiC epitaxial layer of appropriate thickness is required to form low-resistance ohmic contacts with these devices. In addition, to enhance the performance of the PCSSs, the SiC surface between the ohmic contacts must be extremely smooth. We report a chlorine-based, inductively coupled plasma reactive ion-etching process yielding n-type SiC epitaxial layers with the required smoothness. The rate of etching and post-etching surface morphology were dependent on plasma conditions. We found that the surface smoothness of epitaxial layers can be improved by including BCl3 in the argon-chlorine mixture. The optimum etching process yielded very smooth surfaces (˜0.3 nm RMS) at a relatively high rate of etching of ˜220 nm/min. This new fabrication approach significantly reduced the on-state resistance of the PCSS device and improved its durability of operation.

  14. From the Au nano-clusters to the nanoparticles on 4H-SiC (0001).

    PubMed

    Li, Ming-Yu; Zhang, Quanzhen; Pandey, Puran; Sui, Mao; Kim, Eun-Soo; Lee, Jihoon

    2015-01-01

    The control over the configuration, size, and density of Au nanoparticles (NPs) has offered a promising route to control the spatial confinement of electrons and photons, as a result, Au NPs with a various configuration, size and density are witnessed in numerous applications. In this work, we investigate the evolution of self-assembled Au nanostructures on 4H-SiC (0001) by the systematic variation of annealing temperature (AT) with several deposition amount (DA). With the relatively high DAs (8 and 15 nm), depending on the AT variation, the surface morphology drastically evolve in two distinctive phases, i.e. (I) irregular nano-mounds and (II) hexagonal nano-crystals. The thermal energy activates adatoms to aggregate resulting in the formation of self-assembled irregular Au nano-mounds based on diffusion limited agglomeration at comparatively low annealing temperature, which is also accompanied with the formations of hillocks and granules due to the dewetting of Au films and surface reordering. At high temperature, hexagonal Au nano-crystals form with facets along {111} and {100} likely due to anisotropic distribution of surface energy induced by the increased volume of NPs. With the small DA (3 nm), only dome shaped Au NPs are fabricated along with the variation of AT from low to elevated temperature. PMID:26354098

  15. Molecule intrinsic minimal basis sets. II. Bonding analyses for Si4H6 and Si2 to Si10.

    PubMed

    Lu, W C; Wang, C Z; Schmidt, M W; Bytautas, L; Ho, K M; Ruedenberg, K

    2004-02-01

    The method, introduced in the preceding paper, for recasting molecular self-consistent field (SCF) or density functional theory (DFT) orbitals in terms of intrinsic minimal bases of quasiatomic orbitals, which differ only little from the optimal free-atom minimal-basis orbitals, is used to elucidate the bonding in several silicon clusters. The applications show that the quasiatomic orbitals deviate from the minimal-basis SCF orbitals of the free atoms by only very small deformations and that the latter arise mainly from bonded neighbor atoms. The Mulliken population analysis in terms of the quasiatomic minimal-basis orbitals leads to a quantum mechanical interpretation of small-ring strain in terms of antibonding encroachments of localized molecular-orbitals and identifies the origin of the bond-stretch isomerization in Si4H6. In the virtual SCF/DFT orbital space, the method places the qualitative notion of virtual valence orbitals on a firm basis and provides an unambiguous ab initio identification of the frontier orbitals.

  16. Non-Micropipe Dislocations in 4H-SiC Devices: Electrical Properties and Device Technology Implications

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Huang, Wei; Dudley, Michael; Fazi, Christian

    1998-01-01

    It is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vectors greater than or equal to 2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = 1c with no hollow core) in densities on the order of thousands per sq cm, nearly 100-fold micropipe densities. While not nearly as detrimental to SiC device performance as micropipes, it has recently been demonstrated that elementary screw dislocations somewhat degrade the reverse leakage and breakdown properties of 4H-SiC p(+)n diodes. Diodes containing elementary screw dislocations exhibited a 5% to 35% reduction in breakdown voltage, higher pre-breakdown reverse leakage current, softer reverse breakdown I-V knee, and microplasmic breakdown current filaments that were non-catastrophic as measured under high series resistance biasing. This paper details continuing experimental and theoretical investigations into the electrical properties of 4H-SiC elementary screw dislocations. The nonuniform breakdown behavior of 4H-SiC p'n junctions containing elementary screw dislocations exhibits interesting physical parallels with nonuniform breakdown phenomena previously observed in other semiconductor materials. Based upon experimentally observed dislocation-assisted breakdown, a re-assessment of well-known physical models relating power device reliability to junction breakdown has been undertaken for 4H-SiC. The potential impact of these elementary screw dislocation defects on the performance and reliability of various 4H-SiC device technologies being developed for high-power applications will be discussed.

  17. Chloride-based fast homoepitaxial growth of 4H-SiC films in a vertical hot-wall CVD

    NASA Astrophysics Data System (ADS)

    Guoguo, Yan; Feng, Zhang; Yingxi, Niu; Fei, Yang; Xingfang, Liu; Lei, Wang; Wanshun, Zhao; Guosheng, Sun; Yiping, Zeng

    2016-06-01

    Chloride-based fast homoepitaxial growth of 4H-SiC epilayers was performed on 4° off-axis 4H-SiC substrates in a home-made vertical hot-wall chemical vapor deposition (CVD) system using H2‑SiH4‑C2H4‑HCl. The effect of the SiH4/H2 ratio and reactor pressure on the growth rate of 4H-SiC epilayers has been studied successively. The growth rate increase in proportion to the SiH4/H2 ratio and the influence mechanism of chlorine has been investigated. With the reactor pressure increasing from 40 to 100 Torr, the growth rate increased to 52 μm/hand then decreased to 47 μm/h, which is due to the joint effect of H2 and HCl etching as well as the formation of Si clusters at higher reactor pressure. The surface root mean square (RMS) roughness keeps around 1 nm with the growth rate increasing to 49 μm/h. The scanning electron microscope (SEM), Raman spectroscopy and X-ray diffraction (XRD) demonstrate that 96.7 μm thick 4H-SiC layers of good uniformity in thickness and doping with high crystal quality can be achieved. These results prove that chloride-based fast epitaxy is an advanced growth technique for 4H-SiC homoepitaxy. Project supported by the National High Technology R&D Program of China (No. 2014AA041402), the National Natural Science Foundation of China (Nos. 61474113, 61274007, 61574140), the Beijing Natural Science Foundation of China (Nos. 4132076, 4132074), the Program of State Grid Smart Grid Research Institute (No. SGRI-WD-71-14-004), and the Youth Innovation Promotion Association of CAS.

  18. Chloride-based fast homoepitaxial growth of 4H-SiC films in a vertical hot-wall CVD

    NASA Astrophysics Data System (ADS)

    Guoguo, Yan; Feng, Zhang; Yingxi, Niu; Fei, Yang; Xingfang, Liu; Lei, Wang; Wanshun, Zhao; Guosheng, Sun; Yiping, Zeng

    2016-06-01

    Chloride-based fast homoepitaxial growth of 4H-SiC epilayers was performed on 4° off-axis 4H-SiC substrates in a home-made vertical hot-wall chemical vapor deposition (CVD) system using H2-SiH4-C2H4-HCl. The effect of the SiH4/H2 ratio and reactor pressure on the growth rate of 4H-SiC epilayers has been studied successively. The growth rate increase in proportion to the SiH4/H2 ratio and the influence mechanism of chlorine has been investigated. With the reactor pressure increasing from 40 to 100 Torr, the growth rate increased to 52 μm/hand then decreased to 47 μm/h, which is due to the joint effect of H2 and HCl etching as well as the formation of Si clusters at higher reactor pressure. The surface root mean square (RMS) roughness keeps around 1 nm with the growth rate increasing to 49 μm/h. The scanning electron microscope (SEM), Raman spectroscopy and X-ray diffraction (XRD) demonstrate that 96.7 μm thick 4H-SiC layers of good uniformity in thickness and doping with high crystal quality can be achieved. These results prove that chloride-based fast epitaxy is an advanced growth technique for 4H-SiC homoepitaxy. Project supported by the National High Technology R&D Program of China (No. 2014AA041402), the National Natural Science Foundation of China (Nos. 61474113, 61274007, 61574140), the Beijing Natural Science Foundation of China (Nos. 4132076, 4132074), the Program of State Grid Smart Grid Research Institute (No. SGRI-WD-71-14-004), and the Youth Innovation Promotion Association of CAS.

  19. Providers issue brief: alternative providers.

    PubMed

    Rothouse, M

    1999-06-29

    Access by managed care plan enrollees, scope of practice issues and fee reimbursement by Medicaid and third parties such as insurance carriers is the engine that drives legislation recognizing alternative health care providers--chiropractors, acupuncturists, physical therapists, naturopaths, massage therapists, homeopaths, and dietitians and nutritionists. PMID:11073386

  20. Enhancement of atmospheric H2SO4/H2O nucleation: organic oxidation products versus amines

    NASA Astrophysics Data System (ADS)

    Berndt, T.; Sipilä, M.; Stratmann, F.; Petäjä, T.; Vanhanen, J.; Mikkilä, J.; Patokoski, J.; Taipale, R.; Mauldin, R. Lee, III; Kulmala, M.

    2013-06-01

    Atmospheric H2SO4/H2O nucleation influencing effects have been studied in the flow tube IfT-LFT (Institute for Tropospheric Research - Laminar Flow Tube) at 293 ± 0.5 K and a pressure of 1 bar using synthetic air as the carrier gas. The presence of a~possible background amine concentration in the order of 107-108 molecule cm-3 throughout the experiments has to be taken into account. In a first set of investigations, ozonolysis of olefins (tetramethylethylene, 1-methyl-cyclohexene, α-pinene and limonene) for close to atmospheric concentrations, served as the source of OH radicals and possibly other oxidants initiating H2SO4 formation starting from SO2. The oxidant generation is inevitably associated with the formation of a series of organic oxidation products arising from the parent olefins. These products (first generation mainly) showed no clear effect on the number of nucleated particles within a wide range of experimental conditions for H2SO4 concentrations higher than ~107 molecule cm-3. A comparison of the results of two different particle counters (50% cut-off size: about 1.5 nm or 2.5-3 nm) suggested that the early growth process of the nucleated particles was not significantly influenced by the organic oxidation products. An additional, H2SO4-independent process of particle (nano-CN) formation was observed in the case of α-pinene and limonene ozonolysis for H2SO4 concentrations smaller than ~10 7 molecule cm-3. Furthermore, the findings confirm the existence of an additional oxidant for SO2 beside OH radicals, very likely stabilized Criegee Intermediate (sCI). In the case of the ozonolysis of tetramethylethylene, the H2SO4 measurements in the absence and presence of an OH radical scavenger were well described by modelling using recently obtained kinetic data for the sCI reactivity in this system. A second set of experiments has been performed in the presence of added amines (trimethylamine, dimethylamine, aniline and pyridine) in the concentration range

  1. Temperature dependence of damage formation in Ag ion irradiated 4H-SiC

    NASA Astrophysics Data System (ADS)

    Wendler, E.; Bierschenk, Th.; Wesch, W.; Friedland, E.; Malherbe, J. B.

    2010-10-01

    Rutherford backscattering spectrometry (RBS) in channelling mode was used to study the defect formation in silver (Ag) ion irradiated silicon carbide (SiC). The 4H-SiC samples were irradiated with 360 keV Ag ions at different temperatures (15, 295, 375, 475, 625 and 875 K) over a wide range of fluences ( 1×1011 to 2×1016 cm, depending on the irradiation temperature). The results can be divided into two groups: (i) for irradiation temperatures between 15 and 475 K amorphisation of the implanted layers is reached for ion fluences between 7×1013 and 3×1014 cm. The over-all cross-section of defect production at very low ion fluences which comprises the formation of point defects and of amorphous clusters, is almost identical for all data sets measured in this temperature range. Differences in the damage evolution which occur at higher ion fluences, suggest that the relative contribution of amorphous clusters within single ion impacts in crystalline material decreases with rising temperature. (ii) For irradiations performed at 625 and 875 K no amorphisation is found for ion fluences as high as 2×1016 cm. With increasing ion fluence the defect concentration exhibits a distinctive plateau due to the balance between formation and recombination of point defects before increasing up to a saturation level well below amorphisation. For this final stage our results indicate a mixture of point defect clusters and extended defects most probably dislocations. A comparison with data from the literature suggests that the damage evolution for implantation at 625 and 875 K is strongly influenced by the mobility of vacancies starting at around 600 K.

  2. Synthesis and antifungal activity of 2H-1,4-benzoxazin-3(4H)-one derivatives.

    PubMed

    Śmist, Małgorzata; Kwiecień, Halina; Krawczyk, Maria

    2016-01-01

    A series of 2-alkyl-2H-1,4-benzoxazin-3(4H)-ones (4a-l) was easily synthesized by two-step process involving O-alkylation of 2-nitrophenols with methyl 2-bromoalkanoates and next "green" catalytic reductive cyclization of the obtained 2-nitro ester intermediates (3a-l). Further, 6,7-dibromo (5a-c) and N-acetyl (6) derivatives were prepared by bromination and acetylation of unsubstituted 2-alkyl-2H-1,4-benzoxazin-3(4H)-ones (4a-c). The novel compounds (3a-l, 4d-l, 5a-c and 6) were fully characterized by spectroscopic methods (MS, (1)H and (13)C NMR). 2-Alkyl-2H-1,4-benzoxazin-3(4H)-ones (4a-l, 5a-c and 6) were screened for antifungal activity. Preliminary assays were performed using two methods: in vitro against seven phytopathogenic fungi-Botrytis cinerea, Phythophtora cactorum, Rhizoctonia solani, Phoma betae, Fusarium culmorum, Fusarium oxysporum and Alternaria alternata-and in vivo against barley powdery mildew Blumeria graminis. The tested compounds displayed moderate to good antifungal activity at high concentration (200 mg L(-1)). The most potent compounds were 2-ethyl-2H-1,4-benzoxazin-3(4H)-one (4a), 2-ethyl-7-fluoro-2H-1,4-benzoxazin-3(4H)-one (4g) and 4-acetyl-2-ethyl-2H-1,4-benzoxazin-3(4H)-one (6), which completely inhibited the mycelial growth of seven agricultural fungi at the concentration of 200 mg L(-1) in the in vitro tests. Moreover, 2-ethyl-2H-1,4-benzoxazin-3(4H)-one (4a) and 4-acetyl-2-ethyl-2H-1,4-benzoxazin-3(4H)-one (6) were also screened for antifungal activity at concentrations of 100 mg L(-1) and 20 mg L(-1). In the concentration of 100 mg L(-1), the N-acetyl derivative (6) completely inhibited the growth of three strains of fungi (F. culmorum, P. cactorum and R. solani), while 2-ethyl-2H-1,4-benzoxazin-3(4H)-one (4a) completely inhibited only R. solani strain. At the concentration of 20 mg L(-1), compound 6 showed good activity only against P. cactorum strain (72%). PMID:26963527

  3. Pressure-induced superconductivity in H2-containing hydride PbH4(H2)2

    PubMed Central

    Cheng, Ya; Zhang, Chao; Wang, Tingting; Zhong, Guohua; Yang, Chunlei; Chen, Xiao-Jia; Lin, Hai-Qing

    2015-01-01

    High pressure structure, stability, metallization, and superconductivity of PbH4(H2)2, a H2-containing compound combining one of the heaviest elements with the lightest element, are investigated by the first-principles calculations. The metallic character is found over the whole studied pressure range, although PbH4(H2)2 is metastable and easily decompose at low pressure. The decomposition pressure point of 133 GPa is predicted above which PbH4(H2)2 is stable both thermodynamically and dynamically with the C2/m symmetry. Interestedly, all hydrogen atoms pairwise couple into H2 quasi-molecules and remain this style up to 400 GPa in the C2/m structure. At high-pressure, PbH4(H2)2 tends to form the Pb-H2 alloy. The superconductivity of Tc firstly rising and then falling is observed in the C2/m PbH4(H2)2. The maximum of Tc is about 107 K at 230 GPa. The softening of intermediate-frequency phonon induced by more inserted H2 molecules is the main origin of the high Tc. The results obtained represent a significant step toward the understanding of the high pressure behavior of metallic hydrogen and hydrogen-rich materials, which is helpful for obtaining the higher Tc. PMID:26559369

  4. Vapor-Liquid Equilibrium in the Mixture 1-Chlorobutane C4H9Cl + C6H10O Cyclohexanone (EVLM1111, LB5637_E)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume C 'Binary Liquid Systems of Nonelectrolytes III' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'vapor-Liquid Equilibrium in the Mixture 1-Chlorobutane C4H9Cl + C6H10O Cyclohexanone (EVLM1111, LB5637_E)' providing data from direct measurement of pressure at variable mole fraction in liquid phase and constant temperature.

  5. Volumetric Properties of the Mixture Oxolane C4H8O + C6H10O Cyclohexanone (VMSD1111, LB3912_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume A 'Binary Liquid Systems of Nonelectrolytes I' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Oxolane C4H8O + C6H10O Cyclohexanone (VMSD1111, LB3912_V)' providing data from direct low-pressure measurement of mass density at variable mole fraction and constant temperature, in the single-phase region(s).

  6. Volumetric Properties of the Mixture Oxolane C4H8O + C6H10O Cyclohexanone (VMSD1212, LB3919_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume A 'Binary Liquid Systems of Nonelectrolytes I' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Oxolane C4H8O + C6H10O Cyclohexanone (VMSD1212, LB3919_V)' providing data by calculation of molar excess volume from low-pressure density measurements at variable mole fraction and constant temperature.

  7. Volumetric Properties of the Mixture 1,3-Dioxane C4H8O2 + C6H12 Cyclohexane (VMSD1511, LB5121_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume B 'Binary Liquid Systems of Nonelectrolytes II' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture 1,3-Dioxane C4H8O2 + C6H12 Cyclohexane (VMSD1511, LB5121_V)' providing data from direct measurement of low-pressure thermodynamic speed of sound at variable mole fraction and constant temperature, in the single-phase region(s).

  8. Volumetric Properties of the Mixture 1,3-Dioxane C4H8O2 + C6H12 Cyclohexane (VMSD1111, LB5124_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume B 'Binary Liquid Systems of Nonelectrolytes II' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture 1,3-Dioxane C4H8O2 + C6H12 Cyclohexane (VMSD1111, LB5124_V)' providing data from direct low-pressure measurement of mass density at variable mole fraction and constant temperature, in the single-phase region(s).

  9. Heat of Mixing and Solution of 1,3-Dioxane C4H8O2 + C6H12 Cyclohexane (HMSD1111, LB4308_H)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume B 'Binary Liquid Systems of Nonelectrolytes II' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Heat of Mixing and Solution of 1,3-Dioxane C4H8O2 + C6H12 Cyclohexane (HMSD1111, LB4308_H)' providing data from direct low-pressure calorimetric measurement of molar excess enthalpy at variable mole fraction and constant temperature.

  10. Volumetric Properties of the Mixture 1,3-Dioxane C4H8O2 + C6H12 Cyclohexane (VMSD1212, LB5126_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume B 'Binary Liquid Systems of Nonelectrolytes II' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture 1,3-Dioxane C4H8O2 + C6H12 Cyclohexane (VMSD1212, LB5126_V)' providing data by calculation of molar excess volume from low-pressure density measurements at variable mole fraction and constant temperature.

  11. Volumetric Properties of the Mixture 1,4-Dioxane C4H8O2 + C14H30 Tetradecane (VMSD1212, LB3310_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume A 'Binary Liquid Systems of Nonelectrolytes I' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture 1,4-Dioxane C4H8O2 + C14H30 Tetradecane (VMSD1212, LB3310_V)' providing data by calculation of molar excess volume from low-pressure density measurements at variable mole fraction and constant temperature.

  12. Volumetric Properties of the Mixture Butan-2-one C4H8O + C14H30 Tetradecane (VMSD1111, LB3218_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume A 'Binary Liquid Systems of Nonelectrolytes I' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Butan-2-one C4H8O + C14H30 Tetradecane (VMSD1111, LB3218_V)' providing data from direct low-pressure measurement of mass density at variable mole fraction and constant temperature, in the single-phase region(s).

  13. Volumetric Properties of the Mixture Oxolane C4H8O + C14H30 Tetradecane (VMSD1111, LB3317_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume B 'Binary Liquid Systems of Nonelectrolytes II' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Oxolane C4H8O + C14H30 Tetradecane (VMSD1111, LB3317_V)' providing data from direct low-pressure measurement of mass density at variable mole fraction and constant temperature, in the single-phase region(s).

  14. Volumetric Properties of the Mixture 1,4-Dioxane C4H8O2 + C14H30 Tetradecane (VMSD1111, LB3323_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume A 'Binary Liquid Systems of Nonelectrolytes I' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture 1,4-Dioxane C4H8O2 + C14H30 Tetradecane (VMSD1111, LB3323_V)' providing data from direct low-pressure measurement of mass density at variable mole fraction and constant temperature, in the single-phase region(s).

  15. Volumetric Properties of the Mixture Oxolane C4H8O + C14H30 Tetradecane (VMSD1212, LB3303_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume B 'Binary Liquid Systems of Nonelectrolytes II' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Oxolane C4H8O + C14H30 Tetradecane (VMSD1212, LB3303_V)' providing data by calculation of molar excess volume from low-pressure density measurements at variable mole fraction and constant temperature.

  16. Volumetric Properties of the Mixture Butan-2-one C4H8O + C14H30 Tetradecane (VMSD1212, LB3212_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume A 'Binary Liquid Systems of Nonelectrolytes I' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Butan-2-one C4H8O + C14H30 Tetradecane (VMSD1212, LB3212_V)' providing data by calculation of molar excess volume from low-pressure density measurements at variable mole fraction and constant temperature.

  17. Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H8O2 Ethyl ethanoate (VMSD1212, LB4262_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume C 'Binary Liquid Systems of Nonelectrolytes III' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H8O2 Ethyl ethanoate (VMSD1212, LB4262_V)' providing data by calculation of molar excess volume from low-pressure density measurements at variable mole fraction and constant temperature.

  18. Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H9NO N,N-Dimethylethanamide (VMSD1412, LB4275_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume C 'Binary Liquid Systems of Nonelectrolytes III' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H9NO N,N-Dimethylethanamide (VMSD1412, LB4275_V)' providing data by calculation of isentropic compressibility from low-pressure density and thermodynamic speed of sound data at variable mole fraction and constant temperature, in the single-phase region(s).

  19. Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H10O Butan-1-ol (VMSD1511, LB4927_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume C 'Binary Liquid Systems of Nonelectrolytes III' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H10O Butan-1-ol (VMSD1511, LB4927_V)' providing data from direct measurement of low-pressure thermodynamic speed of sound at variable mole fraction and constant temperature, in the single-phase region(s).

  20. Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H10O Butan-2-ol (VMSD1212, LB4923_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume C 'Binary Liquid Systems of Nonelectrolytes III' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H10O Butan-2-ol (VMSD1212, LB4923_V)' providing data by calculation of molar excess volume from low-pressure density measurements at variable mole fraction and constant temperature.

  1. Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H8O2 Ethyl ethanoate (VMSD1511, LB4268_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume C 'Binary Liquid Systems of Nonelectrolytes III' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H8O2 Ethyl ethanoate (VMSD1511, LB4268_V)' providing data from direct measurement of low-pressure thermodynamic speed of sound at variable mole fraction and constant temperature, in the single-phase region(s).

  2. Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H10O Butan-1-ol (VMSD1212, LB4919_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume C 'Binary Liquid Systems of Nonelectrolytes III' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H10O Butan-1-ol (VMSD1212, LB4919_V)' providing data by calculation of molar excess volume from low-pressure density measurements at variable mole fraction and constant temperature.

  3. Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H9NO N,N-Dimethylethanamide (VMSD1212, LB4263_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume C 'Binary Liquid Systems of Nonelectrolytes III' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H9NO N,N-Dimethylethanamide (VMSD1212, LB4263_V)' providing data by calculation of molar excess volume from low-pressure density measurements at variable mole fraction and constant temperature.

  4. Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H9NO N,N-Dimethylethanamide (VMSD1511, LB4269_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume C 'Binary Liquid Systems of Nonelectrolytes III' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H9NO N,N-Dimethylethanamide (VMSD1511, LB4269_V)' providing data from direct measurement of low-pressure thermodynamic speed of sound at variable mole fraction and constant temperature, in the single-phase region(s).

  5. Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H10O Butan-2-ol (VMSD1111, LB4915_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume C 'Binary Liquid Systems of Nonelectrolytes III' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H10O Butan-2-ol (VMSD1111, LB4915_V)' providing data from direct low-pressure measurement of mass density at variable mole fraction and constant temperature, in the single-phase region(s).

  6. Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H10O Butan-1-ol (VMSD1111, LB4911_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume C 'Binary Liquid Systems of Nonelectrolytes III' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H10O Butan-1-ol (VMSD1111, LB4911_V)' providing data from direct low-pressure measurement of mass density at variable mole fraction and constant temperature, in the single-phase region(s).

  7. Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H8O2 Ethyl ethanoate (VMSD1111, LB4252_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume C 'Binary Liquid Systems of Nonelectrolytes III' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H8O2 Ethyl ethanoate (VMSD1111, LB4252_V)' providing data from direct low-pressure measurement of mass density at variable mole fraction and constant temperature, in the single-phase region(s).

  8. Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H9NO N,N-Dimethylethanamide (VMSD1111, LB4255_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume C 'Binary Liquid Systems of Nonelectrolytes III' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H9NO N,N-Dimethylethanamide (VMSD1111, LB4255_V)' providing data from direct low-pressure measurement of mass density at variable mole fraction and constant temperature, in the single-phase region(s).

  9. Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H8O2 Ethyl ethanoate (VMSD1412, LB4274_V)

    NASA Astrophysics Data System (ADS)

    Cibulka, I.; Fontaine, J.-C.; Sosnkowska-Kehiaian, K.; Kehiaian, H. V.

    This document is part of Subvolume C 'Binary Liquid Systems of Nonelectrolytes III' of Volume 26 'Heats of Mixing, Vapor-Liquid Equilibrium, and Volumetric Properties of Mixtures and Solutions' of Landolt-Börnstein Group IV 'Physical Chemistry'. It contains the Chapter 'Volumetric Properties of the Mixture Propenenitrile C3H3N + C4H8O2 Ethyl ethanoate (VMSD1412, LB4274_V)' providing data by calculation of isentropic compressibility from low-pressure density and thermodynamic speed of sound data at variable mole fraction and constant temperature, in the single-phase region(s).

  10. First estimation of C4-H bond dissociation energies of NADH and its radical cation in aqueous solution.

    PubMed

    Zhu, Xiao-Qing; Yang, Yuan; Zhang, Min; Cheng, Jin-Pei; Zhang, Ming

    2003-12-17

    The heterolytic and homolytic C4-H bond dissociation energies of NADH and its radical cation (NADH*+) in aqueous solution were estimated according to the reaction of NADH with N,N,N',N'-tetramethyl-p-phenylenediamine radical cation perchlorate (TMPA*+) in aqueous solution. The results show that the values of the heterolytic and homolytic C4-H bond dissociation energies of NADH in aqueous solution are 53.6 and 79.3 kcal/mol, respectively; the values of the heterolytic and homolytic C4-H bond dissociation energies of NADH*+*+ in aqueous solution are 5.1 and 36.3 kcal/mol, respectively, which, to our knowledge, is first reported. This energetic information disclosed in the present work should be believed to furnish hints to the understanding of the mechanisms for the redox interconversions of coenzyme couple NADH/NAD+ in vivo.

  11. Efficiency and impacts of hythane (CH4+H2) underground storage

    NASA Astrophysics Data System (ADS)

    Sáinz-García, Alvaro; Abarca, Elena; Grandia, Fidel

    2016-04-01

    The foreseen increase share of renewable energy production requires energy storage to mitigate shortage periods of energy supply. Hydrogen is an efficient energy carrier that can be transported and storage. A very promising way to store large amounts of hydrogen is underground geological reservoirs. Hydrogen can be stored, among other options, as a mixture of natural gas and less than 20% of hydrogen (hythane) to avoid damages on the existing infrastructure for gas transport. This technology is known as power-to-gas and is being considered by a number of European countries (Simon et al., 2015). In this study, the feasibility of a deep aquifer to store CH4-H2 mixtures in the Lower Triassic of the Paris Basin is numerically analyzed. The solubility of gas mixture in the groundwater is extremely low (Panfilov, 2015) and, therefore, gas and water are considered immiscible and non-reactive. An immiscible multiphase flow model is developed using the coefficient-form PDE interface of the finite element method code, COMSOL Multiphysics. The modelled domain is a 2D section of 2500 x 290 m resembling the Lower Triassic aquifer of the Paris basin, consisting of 2 layers of sandstone separated by a layer of conglomerates. The domain dips 0.5% from east to west. The top of the aquifer is 500 m-deep and the lateral boundaries are assumed to be open. This case is considered conservative compared to a dome-like geological trap, which could be more favorable to retain higher gas concentration. A number of cycles of gas production and injection were modelled. An automatic shut-down of the pump is implemented in case pressure on the well exceeds an upper or lower threshold. The influence of the position of the well, the uncertain residual gas saturation and the regional flow are studied. The model shows that both gas and aquifer properties have a significant impact on storage. Due to its low viscosity, the mobility of the hythane is quite high and gas expands significantly, reducing

  12. ZC4H2, an XLID gene, is required for the generation of a specific subset of CNS interneurons

    PubMed Central

    May, Melanie; Hwang, Kyu-Seok; Miles, Judith; Williams, Charlie; Niranjan, Tejasvi; Kahler, Stephen G.; Chiurazzi, Pietro; Steindl, Katharina; Van Der Spek, Peter J.; Swagemakers, Sigrid; Mueller, Jennifer; Stefl, Shannon; Alexov, Emil; Ryu, Jeong-Im; Choi, Jung-Hwa; Kim, Hyun-Taek; Tarpey, Patrick; Neri, Giovanni; Holloway, Lynda; Skinner, Cindy; Stevenson, Roger E.; Dorsky, Richard I.; Wang, Tao; Schwartz, Charles E.; Kim, Cheol-Hee

    2015-01-01

    Miles–Carpenter syndrome (MCS) was described in 1991 as an XLID syndrome with fingertip arches and contractures and mapped to proximal Xq. Patients had microcephaly, short stature, mild spasticity, thoracic scoliosis, hyperextendable MCP joints, rocker-bottom feet, hyperextended elbows and knees. A mutation, p.L66H, in ZC4H2, was identified in a XLID re-sequencing project. Additional screening of linked families and next generation sequencing of XLID families identified three ZC4H2 mutations: p.R18K, p.R213W and p.V75in15aa. The families shared some relevant clinical features. In silico modeling of the mutant proteins indicated all alterations would destabilize the protein. Knockout mutations in zc4h2 were created in zebrafish and homozygous mutant larvae exhibited abnormal swimming, increased twitching, defective eye movement and pectoral fin contractures. Because several of the behavioral defects were consistent with hyperactivity, we examined the underlying neuronal defects and found that sensory neurons and motoneurons appeared normal. However, we observed a striking reduction in GABAergic interneurons. Analysis of cell-type-specific markers showed a specific loss of V2 interneurons in the brain and spinal cord, likely arising from mis-specification of neural progenitors. Injected human wt ZC4H2 rescued the mutant phenotype. Mutant zebrafish injected with human p.L66H or p.R213W mRNA failed to be rescued, while the p.R18K mRNA was able to rescue the interneuron defect. Our findings clearly support ZC4H2 as a novel XLID gene with a required function in interneuron development. Loss of function of ZC4H2 thus likely results in altered connectivity of many brain and spinal circuits. PMID:26056227

  13. Skynet Junior Scholars: From Idea to Enactment--Tales from the Trenches I. Implementation in 4-H settings.

    NASA Astrophysics Data System (ADS)

    Burnside, Jason; Feldman, Lynn; Gurton, Suzanne; Heatherly, Sue Ann; Hoette, Vivian L.; Murray, Jenny; Zastrow, Ginger

    2016-01-01

    The creators of Skynet Junior Scholars were ambitious to say the least when they set out to:- Develop online tools that enable middle school and high school aged youth to use robotic optical and radio telescopes to do astronomy- Create an inquiry-based curriculum that promotes critical thinking and scientific habits of mind- Proactively incorporate Principles of Universal Design in all SJS development tasks to ensure access by blind/low vision and deaf/hard of hearing youth- Prepare 180 adult youth leaders from diverse backgrounds including museum educators, amateur astronomers, teachers 4-H leaders to facilitate SJS activities in a variety of settings.After 3 years of development SJS is in full implementation mode. As of August, 2015, 105 youth leaders and leader supervisors from 24 states have completed professional development and many have formed SJS youth groups. In this paper we describe what it takes for a successful implementation of Skynet Junior Scholars in a 4-H setting, from the viewpoint of adult leaders in the trenches who have created novel implementation models to make SJS work in diverse environments from monthly 4-H meetings to immersive residential camps.4-H is the nation's largest positive youth development organization, with a membership of more than six million young people in the U.S. In 2003 the national organization formed a strong commitment to STEM education with the goal to "to engage one million new youth in a dynamic process of discovery and exploration in science, engineering and technology to prepare them to meet the challenges of the 21st century". Skynet Junior Scholars has formed a strong and growing partnership with state 4-H agencies in West Virginia and Wisconsin, with a goal of establishing SJS as a national 4-H curriculum.Skynet Junior Scholars is supported by the National Science Foundation under Grant Numbers 1223687, 1223235 and 1223345.

  14. Spectroscopic and Rheokinetic Properties of [(C4H9O)3P=O]2ZnCl2

    NASA Astrophysics Data System (ADS)

    Volkova, E. R.; Karmanov, V. I.; Tereshatov, V. V.

    2013-09-01

    The complex [(C4H9O)3P=O]2ZnCl2 was synthesized. Its effects on urethane-formation kinetics via reaction of hydroxyl-containing oligomers and isocyanates were studied by IR spectroscopy; on polyurethane curing kinetics, by a rheological method. It was established that [(C4H9O)3P=O]2ZnCl2 was an effective catalyst that accelerated the initial step of regular structure formation during the synthesis of multi-component polyurethanes with low curing temperatures.

  15. Microwave spectra of the SiH4-H2O complex: A new sort of intermolecular interaction

    NASA Astrophysics Data System (ADS)

    Kawashima, Yoshiyuki; Suenram, Richard D.; Hirota, Eizi

    2016-09-01

    Microwave spectral patterns observed for the silane-water complex were found much different from those of the methane-water complex. The SiH4-H2O complex is likely to have a tightly bound structure. The effective rotational and centrifugal distortion constants: B = 3621.1193 (45) MHz and DJ = 49.84 (30) kHz led to the distance between the Si and O atoms in the complex to be 3.3 Å, much shorter than the C and O separation in the CH4-H2O of 3.7 Å, and to the silane-water stretching force constant and stretching frequency to be 2.88 N/m and 65 cm-1, respectively, which are to be compared with 1.52 N/m and 55 cm-1 of the CH4-H2O. The characteristic features of the spectra observed for the main species 28SiH4-H2O are common to those of isotopic species: 29SiH4-H2O, 30SiH4-H2O, 28SiH4-H218O, 28SiH4-D2O, 29SiH4-D2O, 30SiH4-D2O, 28SiH4-HDO, 29SiH4-HDO, 30SiH4-HDO, 28SiD4-H2O, 28SiD4-D2O, and 28SiD4-HDO. The observed spectra also indicate that the silane executes a threefold internal rotation about one of its four Si-H bonds, while the C2 symmetry axis of the water is bent away from the internal-rotation axis. An internal axis method analysis yielded an estimate of the internal-rotation potential barrier V3 to be 140 ± 50 cm-1, and those based on diagonalization of a principal axis method Hamiltonian matrix and on the extended internal axis method resulted in V3 ranging from 180 to 100 cm-1, depending on the isotopic species studied. All the measurements were done by using a pulsed nozzle Fourier transform microwave spectrometer, and the spectral assignments were made with the aid of the Stark effect, which yielded the dipole moment to be 1.730 (10) D. Transitions in higher energy states of the SiH4 internal rotation were observed, clearly resolved from the main lines, when the carrier gas was replaced from Ar to Ne.

  16. A novel micro-Raman technique to detect and characterize 4H-SiC stacking faults

    SciTech Connect

    Piluso, N. Camarda, M.; La Via, F.

    2014-10-28

    A novel Micro-Raman technique was designed and used to detect extended defects in 4H-SiC homoepitaxy. The technique uses above band-gap high-power laser densities to induce a local increase of free carriers in undoped epitaxies (n < 10{sup 16} at/cm{sup −3}), creating an electronic plasma that couples with the longitudinal optical (LO) Raman mode. The Raman shift of the LO phonon-plasmon-coupled mode (LOPC) increases as the free carrier density increases. Crystallographic defects lead to scattering or recombination of the free carriers which results in a loss of coupling with the LOPC, and in a reduction of the Raman shift. Given that the LO phonon-plasmon coupling is obtained thanks to the free carriers generated by the high injection level induced by the laser, we named this technique induced-LOPC (i-LOPC). This technique allows the simultaneous determination of both the carrier lifetime and carrier mobility. Taking advantage of the modifications on the carrier lifetime induced by extended defects, we were able to determine the spatial morphology of stacking faults; the obtained morphologies were found to be in excellent agreement with those provided by standard photoluminescence techniques. The results show that the detection of defects via i-LOPC spectroscopy is totally independent from the stacking fault photoluminescence signals that cover a large energy range up to 0.7 eV, thus allowing for a single-scan simultaneous determination of any kind of stacking fault. Combining the i-LOPC method with the analysis of the transverse optical mode, the micro-Raman characterization can determine the most important properties of unintentionally doped film, including the stress status of the wafer, lattice impurities (point defects, polytype inclusions) and a detailed analysis of crystallographic defects, with a high spectral and spatial resolution.

  17. Cinnamic acid 4-hydroxylase of sorghum [Sorghum biocolor (L.) Moench] gene SbC4H1 restricts lignin synthesis in Arabidopsis

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Cinnamic acid 4-hydroxylase (C4H) is the first hydroxylase enzyme of the phenylpropanoid pathway, and its content and activity affects the lignin synthesis. In this study, we isolated a C4H gene SbC4H1 from the suppression subtractive hybridization library of brown midrib (bmr) mutants of Sorghum b...

  18. Synthesis of a Biologically Active Oxazol-5-(4H)-One via an Erlenmeyer-Plo¨chl Reaction

    ERIC Educational Resources Information Center

    Rodrigues, Catarina A. B.; Martinho, Jose´ M. G.; Afonso, Carlos A. M.

    2015-01-01

    The synthesis of (Z)-4-(4-nitrobenzylidene)-2- phenyloxazol-5(4"H")-one, which is a potent immunomodulator and tyrosinase inhibitor, is described as an experiment for an upper-division undergraduate organic chemistry laboratory course. This compound is produced via an Erlenmeyer-Plo¨chl reaction in the absence of any additional solvents…

  19. Blue Sky Below My Feet. Adventures in Space Technology, Forces, Fibers, Foods. 4-H Leader/Teacher Handbook.

    ERIC Educational Resources Information Center

    Manholt, Donna; And Others

    This teaching guide for 4th through 6th grade classes integrates science, language arts, and math concepts into ready-to-use space and space technology lessons. Significant learning outcomes for this curriculum are linked to Ohio's educational objectives for science in an at-a-glance curriculum matrix. A summary of the significant 4-H life skills…

  20. On the relationship between radiation-stimulated photoluminescence and nitrogen atoms in p-4 H-SiC

    NASA Astrophysics Data System (ADS)

    Lebedev, A. A.; Ber, B. Ya.; Bogdanova, E. V.; Seredova, N. V.; Kazantsev, D. Yu.; Kozlovski, V. V.

    2015-12-01

    Photoluminescence (PL) appearing in p-4 H-SiC upon its electron irradiation has been studied. A model that accounts for the dependence of the PL intensity on the irradiation dose is suggested. The conclusion is drawn that nitrogen-radiation defect donor-acceptor pairs are PL activators.

  1. Factors Influencing Food Choices of 4-H Club Members in Williamson County, Tennessee. A Research Summary of a Graduate Study.

    ERIC Educational Resources Information Center

    Geary, Virginia Ruth; And Others

    A study was conducted to identify some of the eating habits and factors influencing food choices of selected junior (9 to 13 years old) and senior (14 to 19 years old) 4-H club members enrolled in Williamson County, Tennessee, in 1968. Data were collected through group interviews with 200 juniors and 70 seniors--116 boys and 154 girls.…

  2. Fowler-Nordheim electron tunneling mechanism in Ni/SiO2/n-4H SiC MOS devices

    NASA Astrophysics Data System (ADS)

    Kodigala, Subba Ramaiah; Chattopadhyay, S.; Overton, C.; Ardoin, I.

    2015-12-01

    The Ni/SiO2/n-type 4H SiC MOS devices have been fabricated for microelectronic device applications. The SiO2 layer employed in the MOS devices is grown by wet thermal oxidation process. The current-field characteristics of Ni/SiO2/n-type 4H SiC MOS devices are quiet interestingly studied by employing Fowler Nordheim (FN) conduction tunneling model, which is verified by theoretical simulation. It is learnt that the tunneling current through the barrier in the MOS devices promptly obeys the FN conduction tunneling mechanism. The simulation results show that the current in the MOS device increases and barrier height decreases with increasing temperature and internal electric field. Therefore, the correction factor for the barrier height of n-type 4H SiC/SiO2 MOS device due to the influence of both the temperature and internal electric field is employed. The barrier height observed by the experiments is apparently smaller than the simulated one of an ideal MOS device. However, after employing all the correction factors to the barrier height, the simulated current-field curves fairly coincide with the experimental results. The reason for obtaining smaller experimental barrier height for MOS devices is substantially explored with the support of current-field (J-F) analysis. On the other hand, this article comprehensively addresses the effects of quantum mechanical, interface trap density and thickness of 4H-SiC on the barrier height.

  3. From Threshers to Thrashers: In Montana, 4-H Takes a Modern Spin To Engage "Blue-Ribbon Kids."

    ERIC Educational Resources Information Center

    Linik, Joyce Riha

    2002-01-01

    A 4-H skateboard club in Bozeman, Montana offers kids community service and educational opportunities as well as something to do after school. Adult and college-student volunteers teach a skateboarding curriculum and help kids fix boards and design ramps. Club members have learned public speaking, fundraising, city planning, and civic involvement…

  4. The reaction H + C4H2 - Absolute rate constant measurement and implication for atmospheric modeling of Titan

    NASA Technical Reports Server (NTRS)

    Nava, D. F.; Mitchell, M. B.; Stief, L. J.

    1986-01-01

    The absolute rate constant for the reaction H + C4H2 has been measured over the temperature (T) interval 210-423 K, using the technique of flash photolysis-resonance fluorescence. At each of the five temperatures employed, the results were independent of variations in C4H2 concentration, total pressure of Ar or N2, and flash intensity (i.e., the initial H concentration). The rate constant, k, was found to be equal to 1.39 x 10 to the -10th exp (-1184/T) cu cm/s, with an error of one standard deviation. The Arrhenius parameters at the high pressure limit determined here for the H + C4H2 reaction are consistent with those for the corresponding reactions of H with C2H2 and C3H4. Implications of the kinetic carbon chemistry results, particularly those at low temperature, are considered for models of the atmospheric carbon chemistry of Titan. The rate of this reaction, relative to that of the analogous, but slower, reaction of H + C2H2, appears to make H + C4H2 a very feasible reaction pathway for effective conversion of H atoms to molecular hydrogen in the stratosphere of Titan.

  5. Regionalization of the Washington State University Extension 4-H Youth Development Program: Employee Awareness, Buy-In, and Communication

    ERIC Educational Resources Information Center

    White, Alison J.; Teuteberg, Dan

    2015-01-01

    Washington's 4-H program is transitioning from a predominately single-county faculty model to a regional system. This article highlights survey results regarding the level of awareness and buy-in that Extension administration, faculty, and staff have concerning the regional model and how communication about the model took place. While most…

  6. [Nebraska 4-H Wheat Science School Enrichment Project, Teacher/Leader Guides 213-222 and 227.

    ERIC Educational Resources Information Center

    Nebraska Univ., Lincoln. Inst. of Agriculture and Natural Resources.

    Through the 4-H Wheat Science project, students learn the importance of wheat from the complete process of growing wheat to the final product of bread. The curriculum is designed to include hands-on experiences in science, consumer education, nutrition, production economics, vocabulary, and applied mathematics. Teachers can select those units out…

  7. Nationwide Participation in 4-H during the 1980s: Information from the Office of Education NELS:88 Study.

    ERIC Educational Resources Information Center

    Steele, Sara M.; And Others

    A study examined national participation in 4-H Club activities during the 1980s. The study population was a carefully drawn sample of 24,500 eighth graders from more than 1,000 public and private schools throughout the country as well as their parents and teachers. The study established that, as of 1988, about one of every six eighth-grade…

  8. The Impact of Raising and Exhibiting Selected 4-H Livestock Projects on the Development of Life and Project Skills.

    ERIC Educational Resources Information Center

    Rusk, Clinton P.; Summerlot-Early, Jill M.; Machtmes, Krisanna L.; Talbert, B. Allen; Balschweid, Mark A.

    2003-01-01

    Responses from 176 of 420 4-H members involved in livestock projects showed they were able to accomplish skills in sportsmanship, safety, and animal grooming and selection but were less confident about animal health care. The sense of responsibility acquired from these projects was applied to homework, punctuality, and care for younger siblings.…

  9. Does Study Abroad Make a Difference? An Impact Assessment of the International 4-H Youth Exchange Program.

    ERIC Educational Resources Information Center

    Boyd, Barry L.; Giebler, Christie; Hince, Matthew; Liu, Yaru; Mehta, Neha; Rash, Ryan; Rowald, Jennifer; Saldana, Carlos; Yanta, Yvonne

    2001-01-01

    A survey of 28 participants in the International 4-H Youth Exchange program, 16 family members/ friends, and 60 extension agents indicated that participants expanded awareness of global issues, developed cultural sensitivity, and increased community involvement. Barriers such as money and lack of program knowledge can be overcome by seeking…

  10. Living the Dream of Green Acres: Boy with Autism Finds Acceptance and Success Thanks to 4-H

    ERIC Educational Resources Information Center

    Richardson, Ginny

    2006-01-01

    Twelve-year-old Aaron Zibricky, a member of the Lucky Clovers 4-H Club, entered his prize sheep, Star, in the 2005 Will County Fair in Illinois. Zibricky, who is diagnosed with autism, had worked and strived for this moment, putting in long hours feeding, cleaning and shearing the sheep and learning showmanship skills. No one was more elated at…

  11. Improving Healthy Living Youth Development Program Outreach in Extension: Lessons Learned from the 4-H Health Rocks! Program

    ERIC Educational Resources Information Center

    Kumaran, Muthusami; Fogarty, Kate; Fung, Whitney M.; Terminello, Amanda

    2015-01-01

    This article discusses a qualitative evaluation of the Florida 4-H Health Rocks! program aimed at youth alcohol, tobacco, and other drug use prevention. A questionnaire was distributed to Extension professionals across Florida to gain insight into the strengths and barriers they faced with programming. Programmatic strengths included targeting a…

  12. Clean photodecomposition of 1-methyl-4-phenyl-1H-tetrazole-5(4H)-thiones to carbodiimides proceeds via a biradical

    PubMed Central

    Alawode, Olajide E.; Robinson, Colette; Rayat, Sundeep

    2010-01-01

    The photochemistry of 1-methyl-4-phenyl-1H-tetrazole-5(4H)-thione (1a) and 1-(3-methoxyphenyl)-4-methyl-1H-tetrazole-5(4H)-thione (1b) was studied in acetonitrile at 254 and 300 nm which involves expulsion of dinitrogen and sulfur to form the respective carbodiimides 5a – b as sole photoproducts. Photolysis of the title compounds in the presence of 1,4-cyclohexadiene trap led to the formation of respective thioureas, providing strong evidence for the intermediacy of a 1,3-biradical formed by the loss of dinitrogen. In contrast, a trapping experiment with cyclohexene provided no evidence to support an alternative pathway of photodecomposition involving initial desulfurization followed by loss of dinitrogen via the intermediacy of a carbene. Triplet sensitization and triplet quenching studies argue against the involvement of a triplet excited state. While the quantum yields for the formation of the carbodiimides 5a – b were modest, and showed little change on going from a C6H5 (1a) to mOMeC6H4 (1b) substituent on the tetrazolethione ring, the highly clean photodecomposition of these compounds to a photostable end product makes them promising lead structures for industrial, agricultural and medicinal applications. PMID:21142194

  13. Understanding the amorphous-to-microcrystalline silicon transition in SiF{sub 4}/H{sub 2}/Ar gas mixtures

    SciTech Connect

    Dornstetter, Jean-Christophe; Bruneau, Bastien; Bulkin, Pavel; Johnson, Erik V.; Roca i Cabarrocas, Pere

    2014-06-21

    We report on the growth of microcrystalline silicon films from the dissociation of SiF{sub 4}/H{sub 2}/Ar gas mixtures. For this growth chemistry, the formation of HF molecules provides a clear signature of the amorphous to microcrystalline growth transition. Depositing films from silicon tetrafluoride requires the removal of F produced by SiF{sub 4} dissociation, and this removal is promoted by the addition of H{sub 2} which strongly reacts with F to form HF molecules. At low H{sub 2} flow rates, the films grow amorphous as all the available hydrogen is consumed to form HF. Above a critical flow rate, corresponding to the full removal of F, microcrystalline films are produced as there is an excess of atomic hydrogen in the plasma. A simple yet accurate phenomenological model is proposed to explain the SiF{sub 4}/H{sub 2} plasma chemistry in accordance with experimental data. This model provides some rules of thumb to achieve high deposition rates for microcrystalline silicon, namely, that increased RF power must be balanced by an increased H{sub 2} flow rate.

  14. Anomalous 13C isotope abundances in C3S and C4H observed toward the cold interstellar cloud, Taurus Molecular Cloud-1.

    PubMed

    Sakai, Nami; Takano, Shuro; Sakai, Takeshi; Shiba, Shoichi; Sumiyoshi, Yoshihiro; Endo, Yasuki; Yamamoto, Satoshi

    2013-10-01

    We have studied the abundances of the (13)C isotopic species of C3S and C4H in the cold molecular cloud, Taurus Molecular Cloud-1 (Cyanopolyyne Peak), by radioastronomical observations of their rotational emission lines. The CCCS/(13)CCCS and CCCS/C(13)CCS ratios are determined to be >206 and 48 ± 15, respectively. The CC(13)CS line is identified with the aid of laboratory microwave spectroscopy, and the range of the CCCS/CC(13)CS ratio is found to be from 30 to 206. The abundances of at least two (13)C isotopic species of C3S are thus found to be different. Similarly, it is found that the abundances of the four (13)C isotopic species of C4H are not equivalent. The CCCCH/(13)CCCCH, CCCCH/C(13)CCCH, CCCCH/CC(13)CCH, and CCCCH/CCC(13)CH ratios are evaluated to be 141 ± 44, 97 ± 27, 82 ± 15, and 118 ± 23, respectively. Here the errors denote 3 times the standard deviation. These results will constrain the formation pathways of C3S and C4H, if the nonequivalence is caused during the formation processes of these molecules. The exchange reactions after the formation of these two molecules may also contribute to the nonequivalence. In addition, we have confirmed that the (12)C/(13)C ratio of some species are significantly higher than the interstellar elemental (12)C/(13)C ratio of 60-70. The observations of the (13)C isotopic species provide us with rich information on chemical processes in cold interstellar clouds.

  15. Temperature dependence of current-and capacitance-voltage characteristics of an Au/4H-SiC Schottky diode

    NASA Astrophysics Data System (ADS)

    Gülnahar, Murat

    2014-12-01

    In this study, the current-voltage (I-V) and capacitance-voltage (C-V) measurements of an Au/4H-SiC Schottky diode are characterized as a function of the temperature in 50-300 K temperature range. The experimental parameters such as ideality factor and apparent barrier height presents to be strongly temperature dependent, that is, the ideality factor increases and the apparent barrier height decreases with decreasing temperature, whereas the barrier height values increase with the temperature for C-V data. Likewise, the Richardson plot deviates at low temperatures. These anomaly behaviors observed for Au/4H-SiC are attributed to Schottky barrier inhomogeneities. The barrier anomaly which relates to interface of Au/4H-SiC is also confirmed by the C-V measurements versus the frequency measured in 300 K and it is interpreted by both Tung's lateral inhomogeneity model and multi-Gaussian distribution approach. The values of the weighting coefficients, standard deviations and mean barrier height are calculated for each distribution region of Au/4H-SiC using the multi-Gaussian distribution approach. In addition, the total effective area of the patches NAe is obtained at separate temperatures and as a result, it is expressed that the low barrier regions influence meaningfully to the current transport at the junction. The homogeneous barrier height value is calculated from the correlation between the ideality factor and barrier height and it is noted that the values of standard deviation from ideality factor versus q/3kT curve are in close agreement with the values obtained from the barrier height versus q/2kT variation. As a result, it can be concluded that the temperature dependent electrical characteristics of Au/4H-SiC can be successfully commented on the basis of the thermionic emission theory with both models.

  16. Breakdown degradation associated with elementary screw dislocations in 4H-SiC p +n junction rectifiers

    NASA Astrophysics Data System (ADS)

    Neudeck, P. G.; Huang, W.; Dudley, M.

    1998-12-01

    It is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vector>2 c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector=1 c with no hollow core) in densities on the order of thousands per cm 2, nearly 100-fold micropipe densities. This paper describes an initial study into the impact of elementary screw dislocations on the reverse-bias current-voltage ( I- V) characteristics of 4H-SiC p +n diodes. First, synchrotron white beam X-ray topography (SWBXT) was employed to map the exact locations of elementary screw dislocations within small-area 4H-SiC p +n mesa diodes. Then the high-field reverse leakage and breakdown properties of these diodes were subsequently characterized on a probing station outfitted with a dark box and video camera. Most devices without screw dislocations exhibited excellent characteristics, with no detectable leakage current prior to breakdown, a sharp breakdown I- V knee, and no visible concentration of breakdown current. In contrast, devices that contained at least one elementary screw dislocation exhibited 5-35% reduction in breakdown voltage, a softer breakdown I- V knee, and visible microplasmas in which highly localized breakdown current was concentrated. The locations of observed breakdown microplasmas corresponded exactly to the locations of elementary screw dislocations identified by SWBXT mapping. While not as detrimental to SiC device performance as micropipes, the undesirable breakdown characteristics of elementary screw dislocations could nevertheless adversely affect the performance and reliability of 4H-SiC power devices.

  17. Breakdown Degradation Associated with Elementary Screw Dislocations in 4H-SiC P(+)N Junction Rectifiers

    NASA Technical Reports Server (NTRS)

    Neudeck, P. G.; Huang, W.; Dudley, M.

    1998-01-01

    It is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vector greater than 2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = lc with no hollow core) in densities on the order of thousands per sq cm, nearly 100-fold micropipe densities. This paper describes an initial study into the impact of elementary screw dislocations on the reverse-bias current-voltage (I-V) characteristics of 4H-SiC p(+)n diodes. First, Synchrotron White Beam X-ray Topography (SWBXT) was employed to map the exact locations of elementary screw dislocations within small-area 4H-SiC p(+)n mesa diodes. Then the high-field reverse leakage and breakdown properties of these diodes were subsequently characterized on a probing station outfitted with a dark box and video camera. Most devices without screw dislocations exhibited excellent characteristics, with no detectable leakage current prior to breakdown, a sharp breakdown I-V knee, and no visible concentration of breakdown current. In contrast devices that contained at least one elementary screw dislocation exhibited a 5% to 35% reduction in breakdown voltage, a softer breakdown I-V knee, and visible microplasmas in which highly localized breakdown current was concentrated. The locations of observed breakdown microplasmas corresponded exactly to the locations of elementary screw dislocations identified by SWBXT mapping. While not as detrimental to SiC device performance as micropipes, the undesirable breakdown characteristics of elementary screw dislocations could nevertheless adversely affect the performance and reliability of 4H-SiC power devices.

  18. Reversible Photoinduced Reductive Elimination of H2 from the Nitrogenase Dihydride State, the E(4)(4H) Janus Intermediate.

    PubMed

    Lukoyanov, Dmitriy; Khadka, Nimesh; Yang, Zhi-Yong; Dean, Dennis R; Seefeldt, Lance C; Hoffman, Brian M

    2016-02-01

    We recently demonstrated that N2 reduction by nitrogenase involves the obligatory release of one H2 per N2 reduced. These studies focus on the E4(4H) "Janus intermediate", which has accumulated four reducing equivalents as two [Fe-H-Fe] bridging hydrides. E4(4H) is poised to bind and reduce N2 through reductive elimination (re) of the two hydrides as H2, coupled to the binding/reduction of N2. To obtain atomic-level details of the re activation process, we carried out in situ 450 nm photolysis of E4(4H) in an EPR cavity at temperatures below 20 K. ENDOR and EPR measurements show that photolysis generates a new FeMo-co state, denoted E4(2H)*, through the photoinduced re of the two bridging hydrides of E4(4H) as H2. During cryoannealing at temperatures above 175 K, E4(2H)* reverts to E4(4H) through the oxidative addition (oa) of the H2. The photolysis quantum yield is temperature invariant at liquid helium temperatures and shows a rather large kinetic isotope effect, KIE = 10. These observations imply that photoinduced release of H2 involves a barrier to the combination of the two nascent H atoms, in contrast to a barrierless process for monometallic inorganic complexes, and further suggest that H2 formation involves nuclear tunneling through that barrier. The oa recombination of E4(2H)* with the liberated H2 offers compelling evidence for the Janus intermediate as the point at which H2 is necessarily lost during N2 reduction; this mechanistically coupled loss must be gated by N2 addition that drives the re/oa equilibrium toward reductive elimination of H2 with N2 binding/reduction.

  19. DFT-NMR Investigation and (51)V 3QMAS experiments for probing surface oh ligands and the hydrogen-bond network in a polyoxovanadate cluster: the case of Cs(4)[H(2)V(10)O(28)].4H(2)O.

    PubMed

    Truflandier, Lionel A; Boucher, Florent; Payen, Christophe; Hajjar, Redouane; Millot, Yannick; Bonhomme, Christian; Steunou, Nathalie

    2010-04-01

    This work shows that the combination of first-principles calculations and (51)V NMR experiments is a powerful tool to elucidate the location of surface hydroxyl groups and to precisely describe the hydrogen bond network in the complex decavanadate cluster Cs(4)[H(2)V(10)O(28)].4H(2)O, enhancing the strength of NMR crystallography. The detailed characterization of H-bond networks for these kinds of inorganic compounds is of primary importance and should benefit from the DFT-NMR predictions by considering explicitly the periodic boundary conditions. The determination of the Cs(4)[H(2)V(10)O(28)].4H(2)O structure by single-crystal X-ray diffraction was not sufficiently accurate to provide the location of protons. From available diffraction data, five different protonated model structures have been built and optimized using DFT-based methods. The possible interconversion of two decavanadate isomers through a proton exchange is evaluated by calculating the energy barrier and recording variable-temperature (1)H MAS NMR spectra. First-principles calculations of (51)V NMR parameters clearly indicate that these parameters are very sensitive to the local intermolecular hydrogen-bonding interactions. Considering the DFT error limits, the fairly good agreement between calculated and experimental NMR parameters arising from the statistical modeling of the data allows the unambiguous assignment of the five (51)V NMR signals and, thus, the location of OH surface ligands in the decavanadate cluster. In particular, first-principles calculations accurately reproduce the (51)V quadrupolar parameters. These results are fully consistent with (51)V 3QMAS NMR spectra recorded with and without (1)H decoupling. Finally, correlations are established between local octahedral VO(6) deformations and (51)V NMR parameters (C(q) and Deltadelta), which will be useful for the characterization of a wide range of chemical species containing vanadium(V).

  20. Synthesis of 4H/fcc-Au@M (M = Ir, Os, IrOs) Core-Shell Nanoribbons For Electrocatalytic Oxygen Evolution Reaction.

    PubMed

    Fan, Zhanxi; Luo, Zhimin; Chen, Ye; Wang, Jie; Li, Bing; Zong, Yun; Zhang, Hua

    2016-08-01

    The high-yield synthesis of 4H/face-centered cubic (fcc)-Au@Ir core-shell nanoribbons (NRBs) is achieved via the direct growth of Ir on 4H Au NRBs under ambient conditions. Importantly, this method can be used to synthesize 4H/fcc-Au@Os and 4H/fcc-Au@IrOs core-shell NRBs. Significantly, the obtained 4H/fcc-Au@Ir core-shell NRBs demonstrate an exceptional electrocatalytic activity toward the oxygen evolution reaction under acidic condition, which is much higher than that of the commercial Ir/C catalyst.

  1. Microstructural evolution of diamond films from CH{sub 4}/H{sub 2}/N{sub 2} plasma and their enhanced electrical properties

    SciTech Connect

    Sankaran, K. J.; Tai, N. H.; Lin, I. N.

    2015-02-21

    The influence of N{sub 2} concentration in CH{sub 4}/H{sub 2}/N{sub 2} plasma on microstructural evolution and electrical properties of diamond films is systematically investigated. While the diamond films grown in CH{sub 4}/H{sub 2} plasma contain large diamond grains, for the diamond films grown using CH{sub 4}/H{sub 2}/(4%)N{sub 2} plasma, the microstructure drastically changed, resulting in ultra-nanosized diamond grains with Fd3m structure and a{sub 0} = 0.356 nm, along with the formation of n-diamond (n-D), a metastable form of diamond with space group Fm3m and a{sub 0} = 0.356 nm, and i-carbon (i-C) clusters, the bcc structured carbon with a{sub 0} = 0.432 nm. In addition, these films contain wide grain boundaries containing amorphous carbon (a-C). The electron field emission (EFE) studies show the best EFE behavior for 4% N{sub 2} films among the CH{sub 4}/H{sub 2}/N{sub 2} grown diamond films. They possess the lowest turn-on field value of 14.3 V/μm and the highest EFE current density value of 0.37 mA/cm{sup 2} at an applied field of 25.4 V/μm. The optical emission spectroscopy studies confirm that CN species are the major criterion to judge the changes in the microstructure of the films. It seems that the grain boundaries can provide electron conduction networks to transport efficiently the electrons to emission sites for field emission, as long as they have sufficient thickness. Whether the matrix nano-sized grains are 3C-diamond, n-D or i-C is immaterial.

  2. Synthesis of 5,6-dihydro-4H-benzo[d]isoxazol-7-one and 5,6-dihydro-4H-isoxazolo[5,4-c]pyridin-7-one derivatives as potential Hsp90 inhibitors.

    PubMed

    Musso, Loana; Cincinelli, Raffaella; Giannini, Giuseppe; Manetti, Fabrizio; Dallavalle, Sabrina

    2015-11-01

    A novel class of 5,6-dihydro-4H-benzo[d]isoxazol-7-ones and 5,6-dihydro-4H-isoxazolo[5,4-c]pyridin-7-ones was designed, synthesized, and assayed to investigate the affinity toward Hsp90 protein. The synthetic route was based on a 1,3-dipolar cycloaddition of nitriloxides, generated in situ from suitable benzaldoximes, with 2-bromocyclohex-2-enones or 3-bromo-5,6-dihydro-1H-pyridin-2-ones. Whereas all the compounds bearing a benzamide group on the bicyclic scaffold were devoid of activity, the derivatives carrying a resorcinol-like fragment showed a remarkable inhibitory effect on Hsp90. Docking calculations were performed to investigate the orientation of the new compounds within the binding site of the enzyme.

  3. Synthesis of 5,6-dihydro-4H-benzo[d]isoxazol-7-one and 5,6-dihydro-4H-isoxazolo[5,4-c]pyridin-7-one derivatives as potential Hsp90 inhibitors.

    PubMed

    Musso, Loana; Cincinelli, Raffaella; Giannini, Giuseppe; Manetti, Fabrizio; Dallavalle, Sabrina

    2015-11-01

    A novel class of 5,6-dihydro-4H-benzo[d]isoxazol-7-ones and 5,6-dihydro-4H-isoxazolo[5,4-c]pyridin-7-ones was designed, synthesized, and assayed to investigate the affinity toward Hsp90 protein. The synthetic route was based on a 1,3-dipolar cycloaddition of nitriloxides, generated in situ from suitable benzaldoximes, with 2-bromocyclohex-2-enones or 3-bromo-5,6-dihydro-1H-pyridin-2-ones. Whereas all the compounds bearing a benzamide group on the bicyclic scaffold were devoid of activity, the derivatives carrying a resorcinol-like fragment showed a remarkable inhibitory effect on Hsp90. Docking calculations were performed to investigate the orientation of the new compounds within the binding site of the enzyme. PMID:25855505

  4. The ferrimagnetic compounds CoM[Mscript(EDTA)]2 . 4H2O(M,Mscript=Co,Ni): Magnetic characterization of CoCo[Ni(EDTA)2] . 4H2O

    NASA Astrophysics Data System (ADS)

    Sapiña, F.; Coronado, E.; Gomez-Romero, P.; Beltran, D.; Burriel, R.; Carlin, R. L.

    1990-05-01

    We report on the magnetic properties of the ordered bimetallic compound CoCo(NiEDTA)2ṡ4H2O (abbreviated as [CoCoNi]). The structure consists of ordered bimetallic layers formed by alternating octahedral sites of Co and Ni(II); tetrahedral Co sites connect different Co-Ni layers. We discuss the low-dimensional ferrimagnetic behavior of this compound in terms of a model that assumes three spin sublattices exchange coupled by an Ising interaction.

  5. Nanoselective area growth of GaN by metalorganic vapor phase epitaxy on 4H-SiC using epitaxial graphene as a mask

    NASA Astrophysics Data System (ADS)

    Puybaret, Renaud; Patriarche, Gilles; Jordan, Matthew B.; Sundaram, Suresh; El Gmili, Youssef; Salvestrini, Jean-Paul; Voss, Paul L.; de Heer, Walt A.; Berger, Claire; Ougazzaden, Abdallah

    2016-03-01

    We report the growth of high-quality triangular GaN nanomesas, 30-nm thick, on the C-face of 4H-SiC using nanoselective area growth (NSAG) with patterned epitaxial graphene grown on SiC as an embedded mask. NSAG alleviates the problems of defects in heteroepitaxy, and the high mobility graphene film could readily provide the back low-dissipative electrode in GaN-based optoelectronic devices. A 5-8 graphene-layer film is first grown on the C-face of 4H-SiC by confinement-controlled sublimation of silicon carbide. Graphene is then patterned and arrays of 75-nm-wide openings are etched in graphene revealing the SiC substrate. A 30-nm-thick GaN is subsequently grown by metal organic vapor phase epitaxy. GaN nanomesas grow epitaxially with perfect selectivity on SiC, in the openings patterned through graphene. The up-or-down orientation of the mesas on SiC, their triangular faceting, and cross-sectional scanning transmission electron microscopy show that they are biphasic. The core is a zinc blende monocrystal surrounded with single-crystal wurtzite. The GaN crystalline nanomesas have no threading dislocations or V-pits. This NSAG process potentially leads to integration of high-quality III-nitrides on the wafer scalable epitaxial graphene/silicon carbide platform.

  6. Structure-Based Design and Synthesis of 3-Amino-1,5-dihydro-4H-pyrazolopyridin-4-one Derivatives as Tyrosine Kinase 2 Inhibitors.

    PubMed

    Yogo, Takatoshi; Nagamiya, Hiroyuki; Seto, Masaki; Sasaki, Satoshi; Shih-Chung, Huang; Ohba, Yusuke; Tokunaga, Norihito; Lee, Gil Nam; Rhim, Chul Yun; Yoon, Cheol Hwan; Cho, Suk Young; Skene, Robert; Yamamoto, Syunsuke; Satou, Yousuke; Kuno, Masako; Miyazaki, Takahiro; Nakagawa, Hideyuki; Okabe, Atsutoshi; Marui, Shogo; Aso, Kazuyoshi; Yoshida, Masato

    2016-01-28

    We report herein the discovery and optimization of 3-amino-1,5-dihydro-4H-pyrazolopyridin-4-one TYK2 inhibitors. High-throughput screening against TYK2 and JAK1-3 provided aminoindazole derivative 1 as a hit compound. Scaffold hopping of the aminoindazole core led to the discovery of 3-amino-1,5-dihydro-4H-pyrazolopyridin-4-one derivative 3 as a novel chemotype of TYK2 inhibitors. Interestingly, initial SAR study suggested that this scaffold could have a vertically flipped binding mode, which prompted us to introduce a substituent at the 7-position as a moiety directed toward the solvent-exposed region. Introduction of a 1-methyl-3-pyrazolyl moiety at the 7-position resulted in a dramatic increase in TYK2 inhibitory activity, and further optimization led to the discovery of 20. Compound 20 inhibited IL-23-induced IL-22 production in a rat PD assay, as well as inhibited IL-23 signaling in human PBMC. Furthermore, 20 showed selectivity for IL-23 signaling inhibition against GM-CSF, demonstrating the unique cytokine selectivity of the novel TYK2 inhibitor. PMID:26701356

  7. Structure-Based Design and Synthesis of 3-Amino-1,5-dihydro-4H-pyrazolopyridin-4-one Derivatives as Tyrosine Kinase 2 Inhibitors.

    PubMed

    Yogo, Takatoshi; Nagamiya, Hiroyuki; Seto, Masaki; Sasaki, Satoshi; Shih-Chung, Huang; Ohba, Yusuke; Tokunaga, Norihito; Lee, Gil Nam; Rhim, Chul Yun; Yoon, Cheol Hwan; Cho, Suk Young; Skene, Robert; Yamamoto, Syunsuke; Satou, Yousuke; Kuno, Masako; Miyazaki, Takahiro; Nakagawa, Hideyuki; Okabe, Atsutoshi; Marui, Shogo; Aso, Kazuyoshi; Yoshida, Masato

    2016-01-28

    We report herein the discovery and optimization of 3-amino-1,5-dihydro-4H-pyrazolopyridin-4-one TYK2 inhibitors. High-throughput screening against TYK2 and JAK1-3 provided aminoindazole derivative 1 as a hit compound. Scaffold hopping of the aminoindazole core led to the discovery of 3-amino-1,5-dihydro-4H-pyrazolopyridin-4-one derivative 3 as a novel chemotype of TYK2 inhibitors. Interestingly, initial SAR study suggested that this scaffold could have a vertically flipped binding mode, which prompted us to introduce a substituent at the 7-position as a moiety directed toward the solvent-exposed region. Introduction of a 1-methyl-3-pyrazolyl moiety at the 7-position resulted in a dramatic increase in TYK2 inhibitory activity, and further optimization led to the discovery of 20. Compound 20 inhibited IL-23-induced IL-22 production in a rat PD assay, as well as inhibited IL-23 signaling in human PBMC. Furthermore, 20 showed selectivity for IL-23 signaling inhibition against GM-CSF, demonstrating the unique cytokine selectivity of the novel TYK2 inhibitor.

  8. Synthesis and characterisation of new 4-oxo-N-(substituted-thiazol-2-yl)-4H-chromene-2-carboxamides as potential adenosine receptor ligands

    NASA Astrophysics Data System (ADS)

    Cagide, Fernando; Borges, Fernanda; Gomes, Ligia R.; Low, John Nicolson

    2015-06-01

    Chromones are 4H-benzopyran-4-one heterocycles that have been thoroughly studied due to their interesting biological activities. Thiazole based compounds have been used in therapeutics as antimicrobial, antiviral and as antifungal agents for a long time but, in the past decades, they have been identified as potent and selective ligands for adenosine receptor. In continuation of our project related to the syntheses of pharmacologically important heterocycles, a new series of chromone-thiazole hybrids have been designed as potential ligands for human adenosine receptors. In this context, new 4-oxo-N-(substituted-thiazol-2-yl)-4H-chromene-2-carboxamides were synthesized from chromone-2-carboxylic acid by two different amidation methods. The development of dissimilar synthetic approaches provided the possibility of working with diverse reaction conditions, namely with conventional heating and/or microwave irradiation. The structure of the compounds has been established on the basis of NMR and MS spectroscopy and X-ray crystallography. Relevant data related to the molecular geometry and conformation of the chromone-thiazole hybrids has been acquired which can be of the utmost importance to understand ligand-receptor binding.

  9. Thermally Induced Reversible Double Phase Transitions in an Organic-Inorganic Hybrid Iodoplumbate C4H12NPbI3 with Symmetry Breaking.

    PubMed

    Liu, Guangfeng; Liu, Jie; Sun, Zhihua; Zhang, Zhenyi; Chang, Lei; Wang, Junling; Tao, Xutang; Zhang, Qichun

    2016-08-15

    A one-dimensional (1D) organic-inorganic hybrid iodoplumbate crystal (1, C4H12NPbI3, TMAPbI3) can undergo two reversible phase transitions as the temperature decreases. Its dynamic phase-transition behaviors were carefully studied by dielectric measurements, thermal analysis, and variable-temperature crystallographic studies. These results indicate that the phase transitions possess a disorder-order feature with a noncentrosymmetrical intermediate phase structure. Due to the existence of the ordered motion and reorientation of the C4H12N(+) cation, 1 undergoes two phase transitions: the first one from space group P63/m at room temperature to Pm at 163 K with symmetry breaking, and the second one from space group Pm at 163 K to P61 at 142 K with partial symmetry restoration. Our results indicate that there is an existence of a transitional structure with a low symmetry space group during the disorder-order-type phase transitions, which can provide us valuable information to deeply understand the disorder-order phase transition in organic-inorganic hybrids. PMID:27459127

  10. Structural and electronic properties of the transition layer at the SiO{sub 2}/4H-SiC interface

    SciTech Connect

    Li, Wenbo; Wang, Dejun; Zhao, Jijun

    2015-01-15

    Using first-principles methods, we generate an amorphous SiO{sub 2}/4H-SiC interface with a transition layer. Based this interface model, we investigate the structural and electronic properties of the interfacial transition layer. The calculated Si 2p core-level shifts for this interface are comparable to the experimental data, indicating that various SiC{sub x}O{sub y} species should be present in this interface transition layer. The analysis of the electronic structures reveals that the tetrahedral SiC{sub x}O{sub y} structures cannot introduce any of the defect states at the interface. Interestingly, our transition layer also includes a C-C=C trimer and SiO{sub 5} configurations, which lead to the generation of interface states. The accurate positions of Kohn-Sham energy levels associated with these defects are further calculated within the hybrid functional scheme. The Kohn-Sham energy levels of the carbon trimer and SiO{sub 5} configurations are located near the conduction and valence band of bulk 4H-SiC, respectively. The result indicates that the carbon trimer occurred in the transition layer may be a possible origin of near interface traps. These findings provide novel insight into the structural and electronic properties of the realistic SiO{sub 2}/SiC interface.

  11. 4-H Wetland Wonders: A Water Quality Curriculum for Grades 4 and 5. Leader Guide.

    ERIC Educational Resources Information Center

    Oregon State Univ., Corvallis. Extension Service.

    This document provides a water quality curriculum guide for grades 4 and 5. Contents include: (1) Wetlands Wonders Resource Library; (2) Introduction to Water Quality and Wetlands; (3) Water Words; (4) The Water Cycle; (5) Watersheds: Rain Coming and Going; (6) The Water Detective; (7) Ground Water; (8) What's Soil Got To Do with It?; (9) In the…

  12. Water Quality: Water Education for Teachers. A 4-H School Enrichment Program.

    ERIC Educational Resources Information Center

    Powell, G. Morgan; Kling, Emily B.

    This looseleaf notebook is a teacher resource package that is designed for enrichment program use. It contains five units dealing with water quality: (1) The Water Cycle; (2) Our Water Supply; (3) Waste/Water Treatment; (4) Water Conservation; (5) Water Pollution. The units provide background information, experiments, stories, poems, plays, and…

  13. Boundary-Spanning Actors in Urban 4-H: An Action Research Case Study

    ERIC Educational Resources Information Center

    David, Victoria Dotson

    2014-01-01

    Today's Cooperative Extension organization continues to face challenges of providing relevant, quality programming in urban communities. Challenges include the ability to build capacity in Extension's urban youth educators to assess and interpret the unique, variable needs of urban clients and to communicate effectively the identified…

  14. Evaluating the Mentor-Mentee Relationship in the 4-H Tech Wizards Program

    ERIC Educational Resources Information Center

    Toelle, Andy; Terry, Bryan D.; Broaddus, Brent; Kent, Heather; Barnett, Lauren

    2015-01-01

    Youth rely on mentors to provide camaraderie, encouragement, and guidance. The authors asserted that the measurement of youth-mentor relationship would vastly improve the reaching effects of mentorship and expose areas of potential improvement. A questionnaire was given to youth at the beginning and end of a small group mentoring program. The…

  15. Lessons Out-of-School: Boy Scouts, Girl Scouts and 4-H Clubs as Educational Environments.

    ERIC Educational Resources Information Center

    Kleinfeld, Judith; Shinkwin, Anne

    By providing opportunities for closer youth-adult contact, exercising responsibility, performing community service, and learning practical skills, well-functioning youth groups create important educational occasions which are often lacking in school. To point out the overlooked features of traditional youth groups, researchers interviewed and…

  16. Recycling: Mining Resources from Trash. 4-H Leader's/Teacher's Guide.

    ERIC Educational Resources Information Center

    Bonhotal, Jean F.

    This guide is designed for adult volunteer leaders, camp counselors, and teachers who want to explore the subject of recycling with youth. An introduction explores the waste disposal options of reducing, reusing, and recycling, and reasons for recycling. Additional background information is provided on common solid waste and how it can be reused…

  17. Regioisomer-Free C 4h β-Tetrakis(tert-butyl)metallo-phthalocyanines: Regioselective Synthesis and Spectral Investigations.

    PubMed

    Iida, Norihito; Tanaka, Kenta; Tokunaga, Etsuko; Takahashi, Hiromi; Shibata, Norio

    2015-04-01

    Metal β-tetrakis(tert-butyl)phthalocyanines are the most commonly used phthalocyanines due to their high solubility, stability, and accessibility. They are commonly used as a mixture of four regioisomers, which arise due to the tert-butyl substituent on the β-position, and to the best of our knowledge, their regioselective synthesis has yet to be reported. Herein, the C 4h -selective synthesis of β-tetrakis(tert-butyl)metallophthalocyanines is disclosed. Using tetramerization of α-trialkylsilyl phthalonitriles with metal salts following acid-mediated desilylation, the desired metallophthalocyanines were obtained in good yields. Upon investigation of regioisomer-free zinc β-tetrakis(tert-butyl)phthalocyanine using spectroscopy, the C 4h single isomer described here was found to be distinct in the solid state to zinc β-tetrakis(tert-butyl)phthalocyanine obtained by a conventional method.

  18. Synthesis, spectral characterization, and pharmacological importance of new 4H-1,4-benzothiazines, their sulfone analogues, and ribofuranosides.

    PubMed

    Gautam, Naveen; Garg, Ankita; Gautam, Dinesh Chand

    2015-01-01

    The present article describes the synthesis of new 4H-1,4-benzothiazines via condensation and oxidative cyclization of substituted 2-aminobenzenethiols with compounds containing active methylene groups. It is believed that the reaction proceeds via intermediary of the enaminoketone system. The sulfone derivatives were synthesized by oxidation of 4H-1,4-benzothiazines using 30% hydrogen peroxide in glacial acetic acid. Benzothiazines were used as bases to prepare ribofuranosides by treatment with a sugar derivative (β-D-ribofuranosyl-1-acetate-2,3,5-tribenzoate). The pharmacological importance of the synthesized compounds was evaluated by their, antimicrobial properties against various bacterial strains and fungal species. The structures of the compounds have been confirmed by spectral and chemical analysis. PMID:25513863

  19. High rate dry etching of (BiSb)2Te3 film by CH4/H2-based plasma

    NASA Astrophysics Data System (ADS)

    Song, Junqiang; Shi, Xun; Chen, Lidong

    2014-10-01

    Etching characteristics of p-type (BiSb)2Te3 films were studied with CH4/H2/Ar gas mixture using an inductively coupled plasma (ICP)-reactive ion etching (RIE) system. The effects of gas mixing ratio, working pressure and gas flow rate on the etch rate and the surface morphology were investigated. The vertical etched profile with the etch rate of 600 nm/min was achieved at the optimized processing parameters. X-ray photoelectron spectroscopy (XPS) analysis revealed the non-uniform etching of (BiSb)2Te3 films due to disparate volatility of the etching products. Micro-masking effects caused by polymer deposition and Bi-rich residues resulted in roughly etched surfaces. Smooth surfaces can be obtained by optimizing the CH4/H2/Ar mixing ratio.

  20. Chloride-based SiC growth on a-axis 4H-SiC substrates

    NASA Astrophysics Data System (ADS)

    Booker, Ian D.; Farkas, Ildiko; Ivanov, Ivan G.; Hassan, Jawad ul; Janzén, Erik

    2016-01-01

    SiC has, during the last few years, become increasingly important as a power-device material for high voltage applications. The thick, low-doped voltage-supporting epitaxial layer is normally grown by CVD on 4° off-cut 4H-SiC substrates at a growth rate of 5 - 10 μm / h using silane (SiH4) and propane (C3H8) or ethylene (C2H4) as precursors. The concentrations of epitaxial defects and dislocations depend to a large extent on the underlying substrate but can also be influenced by the actual epitaxial growth process. Here we will present a study on the properties of the epitaxial layers grown by a Cl-based technique on an a-axis (90° off-cut from c-direction) 4H-SiC substrate.

  1. Melting of H2SO4·4H2O Particles upon Cooling: Implications for Polar Stratospheric Clouds

    PubMed

    Koop; Carslaw

    1996-06-14

    Polar stratospheric clouds (PSCs) are important for the chemical activation of chlorine compounds and subsequent ozone depletion. Solid PSCs can form on sulfuric acid tetrahydrate (SAT) (H2SO4·4H2O) nuclei, but recent laboratory experiments have shown that PSC nucleation on SAT is strongly hindered. A PSC formation mechanism is proposed in which SAT particles melt upon cooling in the presence of HNO3 to form liquid HNO3-H2SO4-H2O droplets 2 to 3 kelvin above the ice frost point. This mechanism offers a PSC formation temperature that is defined by the ambient conditions and sets a temperature limit below which PSCs should form.

  2. Low resistance Ti Ohmic contacts to 4H-SiC by reducing barrier heights without high temperature annealing

    SciTech Connect

    Huang Lingqin; Liu Bingbing; Zhu Qiaozhi; Chen Suhua; Gao Mingchao; Wang Dejun; Qin Fuwen

    2012-06-25

    Ti Ohmic contacts to relatively highly doped (1 Multiplication-Sign 10{sup 18} cm{sup -3}) n-type 4H-SiC have been produced, without high temperature annealing, by means of low temperature electronic cyclotron resonance microwave hydrogen plasma pre-treatment (HPT) of the SiC surface. The as-deposited Ti/4H-SiC contacts show Ohmic properties, and the specific contact resistance obtained is as low as 2.07 Multiplication-Sign 10{sup -4}{Omega}{center_dot}cm{sup 2} after annealing at low temperatures (400 Degree-Sign C). This is achieved by low barrier height at Ti/SiC interface, which could be attributed to decrease of surface states density by the HPT releasing Fermi level pinning, and to band-gap narrowing, image-force, and thermionic-field emission at high doping.

  3. Synthesis, bioassay, and QSAR study of bronchodilatory active 4H-pyrano[3,2-c]pyridine-3-carbonitriles.

    PubMed

    Girgis, Adel S; Saleh, Dalia O; George, Riham F; Srour, Aladdin M; Pillai, Girinath G; Panda, Chandramukhi S; Katritzky, Alan R

    2015-01-01

    A statistically significant QSAR model describing the bioactivity of bronchodilatory active 4H-pyrano[3,2-c]pyridine-3-carbonitriles (N = 41, n = 8, R(2) = 0.824, R(2)cv = 0.724, F = 18.749, s(2) = 0.0018) was obtained employing CODESSA-Pro software. The bronchodilatory active 4H-pyrano[3,2-c]pyridine-3-carbonitriles 17-57 were synthesized through a facile approach via reaction of 1-alkyl-4-piperidones 1-4 with ylidenemalononitriles 5-16 in methanol in the presence of sodium. The bronchodilation properties of 17-57 were investigated in vitro using isolated guinea pig tracheal rings pre-contracted with histamine (standard method) and compared with theophylline (standard reference). Most of the compounds synthesized exhibit promising bronchodilation properties especially, compounds 25 and 28. PMID:25462283

  4. Surface-state dependent optical properties of OH-, F-, and H-terminated 4H-SiC quantum dots.

    PubMed

    Rashid, Marzaini; Tiwari, Amit K; Goss, J P; Rayson, M J; Briddon, P R; Horsfall, A B

    2016-08-01

    Density functional calculations are performed for OH-, F- and H-terminated 4H-SiC 10-20 Å diameter clusters to investigate the effect of surface species upon the optical absorption properties. H-termination results in a pronounced size-dependent quantum-confinement in the absorption, whereas F- and OH-terminations exhibit much reduced size dependent absorption due to surface states. Our findings are in good agreement with recent experimental studies, and are able to explain the little explored dual-feature photoluminescence spectra of SiC quantum dots. We propose that along with controlling the size, suitable surface termination is the key for optimizing optical properties of 4H-SiC quantum structures, such as might be exploited in optoelectronics, photovoltaics and biological applications. PMID:27430278

  5. Characterization of tungsten-nickel simultaneous Ohmic contacts to p- and n-type 4H-SiC

    NASA Astrophysics Data System (ADS)

    Kragh-Buetow, K. C.; Okojie, R. S.; Lukco, D.; Mohney, S. E.

    2015-10-01

    Ohmic contacts to p- and n-type 4H-SiC using refractory alloyed W:Ni thin films were investigated. Transfer length measurement test structures to p-type 4H-SiC (NA = 3 × 1020 cm-3) revealed Ohmic contacts with specific contact resistances, ρc, of ˜10-5 Ω cm2 after 0.5 h annealing in argon at temperatures of 1000 °C, 1100 °C, 1150 °C, and 1200 °C. Contacts fabricated on n-type 4H-SiC (ND = 2 × 1019 cm-3) by similar methods were shown to have similar specific contact resistance values after annealing, demonstrating simultaneous Ohmic contact formation for W:Ni alloys on 4H-SiC. The lowest ρc values were (7.3 ± 0.9) × 10-6 Ω cm2 for p-SiC and (6.8 ± 3.1) × 10-6 Ω cm2 for n-SiC after annealing at 1150 °C. X-ray diffraction shows a cubic tungsten-nickel-carbide phase in the Ohmic contacts after annealing as well as WC after higher temperatures. Auger electron spectroscopy depth profiles support the presence of metal carbide regions above a nickel and silicon-rich region near the interface. X-ray energy dispersive spectroscopy mapping showed tungsten-rich and nickel-rich regions after annealing at 1100 °C and above. W:Ni alloys show promise as simultaneous Ohmic contacts to p- and n-SiC, offering low and comparable ρc values along with the formation of WxNiyC.

  6. Organocatalyzed enantioselective synthesis of 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carboxylates

    PubMed Central

    Ramireddy, Naresh; Abbaraju, Santhi; Zhao, Cong-Gui

    2011-01-01

    The organocatalyzed enantioselective synthesis of biologically active 2-amino-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carboxylate derivatives was achieved using bifunctional cinchona alkaloids as the catalysts. Using quinine thiourea as the catalyst, the tandem Michael addition-cyclization reaction between 1,3-cyclohexanediones and alkylidenecyanoacetate derivatives gives the desired products in high yields (up to 92%) and good ee values (up to 82%). PMID:22081731

  7. Interfaces between 4H-SiC and SiO2: Microstructure, nanochemistry, and near-interface traps

    NASA Astrophysics Data System (ADS)

    Pippel, Eckhard; Woltersdorf, Jörg; Ólafsson, Halldor Ö.; Sveinbjörnsson, Einar Ö.

    2005-02-01

    We report on electrical and microscopic investigations aimed to clarify the origin of near-interface traps (NITs) in metal-silicon dioxide-4H-silicon carbide structures. Using capacitance-voltage and thermal dielectric relaxation current (TDRC) analysis we investigated NITs close to the 4H-SiC conduction-band edge in differently prepared thermal and deposited oxides and found that the traps give rise to two characteristic TDRC signatures belonging to two groups of trap levels. The total trapped charge exceeds 1×1013cm-2. The observed density and energy distribution of these traps are nearly identical in all thermal and deposited oxides investigated, suggesting that the NITs belong to intrinsic defects at the SiO2/SiC interface which are readily formed during oxide deposition or thermal oxidation of 4H-SiC. Using high-resolution electron microscopy combined with nanochemical analysis (electron energy-loss near-edge spectroscopy and energy-filtered transmission electron microscopy) we investigated the SiO2/SiC interface in samples receiving reoxidation and did not find any indication of graphitic regions at or near the SiO2/SiC interface or in the bulk silicon dioxide within a detection limit of 0.7nm. In addition, no amorphous carbon accumulation was observed near the SiO2/SiC interface. The overall results strongly suggest that the NITs near the 4H-SiC conduction band are not related to carbon structures in the SiO2/SiC interlayer.

  8. Electron paramagnetic resonance and theoretical studies of Nb in 4H- and 6H-SiC

    NASA Astrophysics Data System (ADS)

    Tien Son, Nguyen; Thang Trinh, Xuan; Gällström, Andreas; Leone, Stefano; Kordina, Olof; Janzén, Erik; Szász, Krisztián; Ivády, Viktor; Gali, Adam

    2012-10-01

    High purity silicon carbide (SiC) materials are of interest from high-power high temperature applications across recent photo-voltaic cells to hosting solid state quantum bits, where the tight control of electrically, optically, and magnetically active point defects is pivotal in these areas. 4H- and 6H-SiC substrates are grown at high temperatures and the incorporation of transition metal impurities is common. In unintentionally Nb-doped 4H- and 6H-SiC substrates grown by high-temperature chemical vapor deposition, an electron paramagnetic resonance (EPR) spectrum with C1h symmetry and a clear hyperfine (hf) structure consisting of ten equal intensity hf lines was observed. The hf structure can be identified as due to the interaction between the electron spin S = 1/2 and the nuclear spin of 93Nb. Additional hf structures due to the interaction with three Si neighbors were also detected. In 4H-SiC, a considerable spin density of ˜37.4% was found on three Si neighbors, suggesting the defect to be a complex between Nb and a nearby carbon vacancy (VC). Calculations of the 93Nb and 29Si hf constants of the neutral Nb on Si site, NbSi0, and the Nb-vacancy defect, NbSiVC0, support previous reported results that Nb preferentially forms an asymmetric split-vacancy (ASV) defect. In both 4H- and 6H-SiC, only one Nb-related EPR spectrum has been observed, supporting the prediction from calculations that the hexagonal-hexagonal defect configuration of the ASV complex is more stable than others.

  9. Electrical and optical properties of stacking faults introduced by plastic deformation in 4H-SiC

    NASA Astrophysics Data System (ADS)

    Pichaud, B.; Regula, G.; Yakimov, E. B.

    2014-02-01

    The electrical and optical properties of stacking faults (SFs) introduced by plastic deformation in 4H-SiC were studied by Electron Beam Induced Current (EBIC) and cathodoluminescence (CL) methods. Partial dislocations and stacking faults in the (0001) glide planes perpendicular to the surface were introduced in n-type 4H-SiC under a well-controlled state of stress by cantilever bending at 550°C. CL measurements allow determining the multiplicity of the SFs (single or double). It is observed that the overwhelming majority of stacking faults are double Shockley type SFs (CL emission at 504 nm) that correlates well with previously published high resolution transmission electron microscopy (HRTEM) investigations. However, single Shockley type SFs (CL emission at 422 nm) of much smaller lengths are also observed in some areas near the scratched region from where the defects are nucleated. This suggests that the velocity of partial dislocation pairs under a given applied stress could be higher than that of single partial dislocations. It is also shown that in the EBIC mode, SFs produce a strong bright contrast, which can be explained by considering the SFs in 4H-SiC to be quantum wells of II type.

  10. Growth and surface analysis of SiO2 on 4H-SiC for MOS devices

    NASA Astrophysics Data System (ADS)

    Kodigala, Subba Ramaiah; Chattopadhyay, Somnath; Overton, Charles; Ardoin, Ira; Gordon, B. J.; Johnstone, D.; Roy, D.; Barone, D.

    2015-03-01

    The SiO2 layers have been grown onto C-face and Si-face 4H-SiC substrates by two different techniques such as wet thermal oxidize process and sputtering. The deposition recipes of these techniques are carefully optimized by trails and error method. The growth effects of SiO2 on the C-face and Si-face 4H-SiC substrates are thoroughly investigated by AFM analysis. The growth mechanism of different species involved in the growth process of SiO2 by wet thermal oxide is now proposed by adopting two body classical projectile scattering. This mechanism drives to determine growth of secondary phases such as α-CH nano-islands in the grown SiO2 layer. The effect of HF etchings on the SiO2 layers grown by both techniques and on both the C-face and Si-face substrates are legitimately studied. The thicknesses of the layers determined by AFM and ellipsometry techniques are widely promulgated. The MOS capacitors are made on the Si-face 4H-SiC wafers by wet oxidation and sputtering processes, which are studied by capacitance versus voltage (CV) technique. From CV measurements, the density of trap states with variation of trap level for MOS devices is estimated.

  11. Electrical and optical properties of stacking faults introduced by plastic deformation in 4H-SiC

    SciTech Connect

    Pichaud, B.; Regula, G.; Yakimov, E. B.

    2014-02-21

    The electrical and optical properties of stacking faults (SFs) introduced by plastic deformation in 4H-SiC were studied by Electron Beam Induced Current (EBIC) and cathodoluminescence (CL) methods. Partial dislocations and stacking faults in the (0001) glide planes perpendicular to the surface were introduced in n-type 4H-SiC under a well-controlled state of stress by cantilever bending at 550°C. CL measurements allow determining the multiplicity of the SFs (single or double). It is observed that the overwhelming majority of stacking faults are double Shockley type SFs (CL emission at 504 nm) that correlates well with previously published high resolution transmission electron microscopy (HRTEM) investigations. However, single Shockley type SFs (CL emission at 422 nm) of much smaller lengths are also observed in some areas near the scratched region from where the defects are nucleated. This suggests that the velocity of partial dislocation pairs under a given applied stress could be higher than that of single partial dislocations. It is also shown that in the EBIC mode, SFs produce a strong bright contrast, which can be explained by considering the SFs in 4H-SiC to be quantum wells of II type.

  12. Evaluation of sintering effects on SiC incorporated UO2 kernels under Ar and Ar-4%H2 environments

    SciTech Connect

    Silva, Chinthaka M; Lindemer, Terrence; Hunt, Rodney Dale; Collins, Jack Lee; Terrani, Kurt A; Snead, Lance Lewis

    2013-01-01

    Silicon carbide (SiC) is suggested as an oxygen getter in UO2 kernels used for TRISO particle fuels to lower oxygen potential and prevent kernel migration during irradiation. Scanning electron microscopy and X-ray diffractometry analyses performed on sintered kernels verified that internal gelation process can be used to incorporate SiC in urania fuel kernels. Sintering in either Ar or Ar-4%H2 at 1500 C lowered the SiC content in the UO2 kernels to some extent. Formation of UC was observed as the major chemical phase in the process, while other minor phases such as U3Si2C2, USi2, U3Si2, and UC2 were also identified. UC formation was presumed to be occurred by two reactions. The first was the SiC reaction with its protective SiO2 oxide layer on SiC grains to produce volatile SiO and free carbon that subsequently reacted with UO2 to form UC. The second process was direct UO2 reaction with SiC grains to form SiO, CO, and UC, especially in Ar-4%H2. A slightly higher density and UC content was observed in the sample sintered in Ar-4%H2, but the use of both atmospheres produced kernels with ~95% of theoretical density. It is suggested that incorporating CO in the sintering gas would prevent UC formation and preserve the initial SiC content.

  13. SWSextantis stars: the dominant population of cataclysmic variables with orbital periods between 3 and 4h

    NASA Astrophysics Data System (ADS)

    Rodríguez-Gil, P.; Gänsicke, B. T.; Hagen, H.-J.; Araujo-Betancor, S.; Aungwerojwit, A.; Allende Prieto, C.; Boyd, D.; Casares, J.; Engels, D.; Giannakis, O.; Harlaftis, E. T.; Kube, J.; Lehto, H.; Martínez-Pais, I. G.; Schwarz, R.; Skidmore, W.; Staude, A.; Torres, M. A. P.

    2007-06-01

    We present time-series optical photometry of five new cataclysmic variables (CVs) identified by the Hamburg Quasar Survey (HQS). The deep eclipses observed in HS 0129+2933 (= TT Tri), HS 0220+0603 and HS 0455+8315 provided very accurate orbital periods of 3.35129827(65), 3.58098501(34) and 3.56937674(26) h, respectively. HS 0805+3822 shows grazing eclipses and has a likely orbital period of 3.2169(2) h. Time-resolved optical spectroscopy of the new CVs (with the exception of HS 0805+3822) is also presented. Radial velocity studies of the Balmer emission lines provided an orbital period of 3.55 h for HS 1813+6122, which allowed us to identify the observed photometric signal at 3.39 h as a negative superhump wave. The spectroscopic behaviour exhibited by all the systems clearly identifies them as new SW Sextantis (SW Sex) stars. HS 0220+0603 shows unusual NII and SiII emission lines suggesting that the donor star may have experienced nuclear evolution via the CNO cycle. These five new additions to the class increase the number of known SW Sex stars to 35. Almost 40 per cent of the total SW Sex population do not show eclipses, invalidating the requirement of eclipses as a defining characteristic of the class and the models based on a high orbital inclination geometry alone. On the other hand, as more SW Sex stars are identified, the predominance of orbital periods in the narrow 3-4.5 h range is becoming more pronounced. In fact, almost half the CVs which populate the 3-4.5 h period interval are definite members of the class. The dominance of SW Sex stars is even stronger in the 2-3 h period gap, where they make up 55 per cent of all known gap CVs. These statistics are confirmed by our results from the HQS CVs. Remarkably, 54 per cent of the Hamburg nova-like variables have been identified as SW Sex stars with orbital periods in the 3-4.5 h range. The observation of this pile-up of systems close to the upper boundary of the period gap is difficult to reconcile with the

  14. Advanced NaBH4/H2O2 Fuel Cell for Space Applications

    NASA Astrophysics Data System (ADS)

    Miley, George H.; Kim, Kyu-Jung; Luo, Nie; Shrestha, Prajakti Joshi

    2009-03-01

    Fuel cells have played an important role in NASA's space program starting with the Gemini space program. However, improved fuel cell performance will be needed to enable demanding future missions. An advanced fuel cell (FC) using liquid fuel and oxidizer is being developed by U of IL/NPL team to provide air independence and to achieve higher power densities than normal H2/O2 fuel cells (Lou et al., 2008; Miley, 2007). Hydrogen peroxide (H2O2) is used in this FC directly at the cathode (Lou and Miley, 2004). Either of two types of reactant, namely a gas-phase hydrogen or an aqueous NaBH4 solution, is utilized as fuel at the anode. Experiments with both 10-W single cells and 500-W stacks demonstrate that the direct utilization of H2O2 and NaBH4 at the electrodes result in >30% higher voltage output compared to the ordinary H2/O2 FC (Miley, 2007). Further, the use of this combination of all liquid fuels provides—from an operational point of view—significant advantages (ease of storage, reduced pumping requirements, simplified heat removal). This design is inherently compact compared to other fuel cells that use gas phase reactants. This results in a high overall system (including fuel tanks, pumps and piping, waste heat radiator) power density. Further, work is in progress on a regenerative version which uses an electrical input, e.g. from power lines or a solar panel to regenerate reactants.

  15. Fluorescent staining of glycoproteins in sodium dodecyl sulfate polyacrylamide gels by 4H-[1]-benzopyrano[4,3-b]thiophene-2-carboxylic acid hydrazide.

    PubMed

    Zhu, Zhongxin; Zhou, Xuan; Wang, Yang; Chi, Lisha; Ruan, Dandan; Xuan, Yuanhu; Cong, Weitao; Jin, Litai

    2014-06-01

    A fluorescent detection method for glycoproteins in SDS-PAGE by using 4H-[1]-benzopyrano[4,3-b]thiophene-2-carboxylic acid hydrazide (BH) was developed in this study. As low as 4-8 ng glycoproteins (transferrin, α1-acid glycoprotein) could be specifically detected by the BH staining method, which is twofold more sensitive than that of the most commonly used Pro-Q Emerald 488 glycoprotein stain. Furthermore, the specificity of the newly developed stain for glycoproteins was demonstrated by 1-D and 2-D SDS-PAGE, deglycosylation, glycoprotein affinity enrichment and LC-MS/MS, respectively. According to the results, it is concluded that BH stain may provide new choices for convenient, sensitive, specific and economic visualization of gel-separated glycoproteins. PMID:24712021

  16. Prestaining of glycoproteins in SDS-PAGE via 4H-[1]-Benzopyrano[4,3-b]thiophene-2-carboxylic acid hydrazide with weak influence on protein mobility.

    PubMed

    Zhu, Zhongxin; Zhou, Xuan; Wang, Yang; Yu, Qing; Zhu, Xinliang; Niu, Chao; Cong, Weitao; Jin, Litai

    2014-12-01

    A new fluorescent prestaining method for gel-separated glycoproteins in 1D and 2D SDS-PAGE was developed by using 4H-[1]-Benzopyrano[4,3-b]thiophene-2-carboxylic acid hydrazide (BH). The prestained gels were readily imaged after electrophoresis without any time-consuming steps needed for poststain. As low as 4-8 ng glycoproteins (transferrin, α1-acid glycoprotein) could be selectively detected, which is comparable to the most commonly used Pro-Q Emerald 488 glycoprotein stain. In addition, subsequent study of deglycosylation, glycoprotein affinity chromatography, and LC-MS/MS analysis were performed to confirm the specificity of the newly developed method. As a result, BH prestain provides a new choice for quick, sensitive, specific, economical, and MS compatible visualization of gel-separated glycoproteins. PMID:25229714

  17. Molecular structure, vibrational spectra, MEP, HOMO-LUMO and NBO analysis of Hf(SeO3)(SeO4)(H2O)4

    NASA Astrophysics Data System (ADS)

    Yankova, Rumyana; Genieva, Svetlana; Halachev, Nenko; Dimitrova, Ginka

    2016-02-01

    Hf(SeO3)(SeO4)(H2O)4 was obtained with the hydrothermal synthesis. The geometry optimization of this molecule was done by Density Functional Theory (DFT/B3LYP) method with 6-31G(d) basis set and LANL2DZ for Hf. The experimental infrared spectrum was compared with calculated and complete vibrational assignment was provided. The bond orders and the electronic properties of the molecule were calculated. The natural bond orbital analysis (NBO) was performed in order to study the intramolecular bonding interactions among bonds and delocalization of unpaired electrons. The calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) with frontier orbital gap were presented. The electrostatic potential was calculated in order to investigate the reaction properties of the molecule. The thermodynamic properties of the studied compound at different temperatures were calculated.

  18. Prestaining of glycoproteins in SDS-PAGE via 4H-[1]-Benzopyrano[4,3-b]thiophene-2-carboxylic acid hydrazide with weak influence on protein mobility.

    PubMed

    Zhu, Zhongxin; Zhou, Xuan; Wang, Yang; Yu, Qing; Zhu, Xinliang; Niu, Chao; Cong, Weitao; Jin, Litai

    2014-12-01

    A new fluorescent prestaining method for gel-separated glycoproteins in 1D and 2D SDS-PAGE was developed by using 4H-[1]-Benzopyrano[4,3-b]thiophene-2-carboxylic acid hydrazide (BH). The prestained gels were readily imaged after electrophoresis without any time-consuming steps needed for poststain. As low as 4-8 ng glycoproteins (transferrin, α1-acid glycoprotein) could be selectively detected, which is comparable to the most commonly used Pro-Q Emerald 488 glycoprotein stain. In addition, subsequent study of deglycosylation, glycoprotein affinity chromatography, and LC-MS/MS analysis were performed to confirm the specificity of the newly developed method. As a result, BH prestain provides a new choice for quick, sensitive, specific, economical, and MS compatible visualization of gel-separated glycoproteins.

  19. Fluorescent staining of glycoproteins in sodium dodecyl sulfate polyacrylamide gels by 4H-[1]-benzopyrano[4,3-b]thiophene-2-carboxylic acid hydrazide.

    PubMed

    Zhu, Zhongxin; Zhou, Xuan; Wang, Yang; Chi, Lisha; Ruan, Dandan; Xuan, Yuanhu; Cong, Weitao; Jin, Litai

    2014-06-01

    A fluorescent detection method for glycoproteins in SDS-PAGE by using 4H-[1]-benzopyrano[4,3-b]thiophene-2-carboxylic acid hydrazide (BH) was developed in this study. As low as 4-8 ng glycoproteins (transferrin, α1-acid glycoprotein) could be specifically detected by the BH staining method, which is twofold more sensitive than that of the most commonly used Pro-Q Emerald 488 glycoprotein stain. Furthermore, the specificity of the newly developed stain for glycoproteins was demonstrated by 1-D and 2-D SDS-PAGE, deglycosylation, glycoprotein affinity enrichment and LC-MS/MS, respectively. According to the results, it is concluded that BH stain may provide new choices for convenient, sensitive, specific and economic visualization of gel-separated glycoproteins.

  20. CERN’s Linac4 H{sup −} sources: Status and operational results

    SciTech Connect

    Lettry, J. Aguglia, D.; Andersson, P.; Bertolo, S.; Butterworth, A.; Coutron, Y.; Dallocchio, A.; David, N.; Chaudet, E.; Fink, D.; Gil-Flores, J.; Garlasche, M.; Grudiev, A.; Guida, R.; Hansen, J.; Haase, M.; Jones, A.; Koszar, I.; Machado, C.; Mastrostefano, C.; and others

    2015-04-08

    Two volume sources equipped with DESY and CERN plasma generators and a low voltage electron dump were operated at 45 kV in the Linac4 tunnel and on a dedicated test stand. These volume sources delivered approximately 20 mA and ensured the commissioning of the Radio Frequency Quadrupole accelerator and of the first section of the Drift Tube Linac. CERN’s prototype of a cesiated surface source equipped with this electron dump was operated continuously from November 2013 to April 2014 on the ion source test stand and is being commissioned in the Linac4 tunnel. Before cesiation, the prototype conditioned in volume mode provided up to 30 mA H{sup −} beam. Short cesiations, of the order of 10 mg effectively reduced the intensity of co-extracted electrons down to 2 - 8 times the H{sup −} current; this cesiated surface operation mode delivered up to 60 mA H{sup −} beam. An H{sup −} beam of the order of 40 mA was sustained up to four weeks operation with 500 μs pulses at 1.2s spacing. A new extraction was designed to match these beam properties. A copy of BNL’s magnetron produced at CERN was tested at BNL and delivered at 40 kV H{sup −} beam exceeding Linac4’s nominal intensity of 80 mA. In this contribution, the performances, dynamic response to cesiation, stability and availability of these prototypes are described. The needed optimization of the emittance of H{sup −} beam above 40 mA is presented, which requires an evolution of the front end that encompasses implementation of a large ceramic insulator.

  1. Static and Switching Characteristics of a 4H-SiC Based BJT to 200 C

    NASA Technical Reports Server (NTRS)

    Niedra, Janis M.; Schwarze, Gene E.

    2006-01-01

    Static curves and resistive load switching characteristics of a 600 V, 4 A rated, SiC-based NPN bipolar power transistor (BJT) were observed at selected temperatures from 23 to 200 C. All testing was done in a pulse mode at low duty cycle (approx. 0.1 percent). Turn-on was driven by an adjustable base current pulse and turn-off was accelerated by a negative base voltage pulse of either 7 or 0.6 V. Switching observations were done at base drive currents (I(sub B)) up to 400 mA and collector currents (I(sub C)) up to 4 A, using a 100 OMEGA non-inductive load. At I(sub B) = 400 mA and I(sub C) = 4 A, turn-on times typically varied from 81 to 97 ns, over temperatures from 23 to 200 C. As expected, lowering the base drive greatly extended the turn-on time. Similarly, decreasing the load current to I(sub C) = 1 A with I(sub B) = 400 mA produced turn-on times as short as 30 ns. Over the 23 to 200 C range, with I(sub B) = 400 mA and I(sub C) = 4 A, turn-off times were in the range of 61 to 77 ns with the 7 V sweep-out and 130 to 150 ns with the 0.6 V sweep-out. At a fixed temperature and I(sub C), the turn-off time decreased slightly with decreasing I(sub B), for I(sub B) sufficient to still provide full turn-on. The ratio of conduction to switching losses is estimated, based on the observed I(sub C) transition times and static curves. An estimate at 200 kHz and a 50 percent duty cycle shows that under practicable conditions the two losses can be comparable. Hence the evidence obtained does not support the occasionally voiced concern of necessarily unacceptably high conduction losses in SiC-based BJTs.

  2. Etching Characteristics of ZnO and Al-Doped ZnO in Inductively Coupled Cl2/CH4/H2/Ar and BCl3/CH4/H2/Ar Plasmas

    NASA Astrophysics Data System (ADS)

    Lee, Hack Joo; Kwon, Bong Soo; Kim, Hyun Woo; Kim, Seon Il; Yoo, Dong-Geun; Boo, Jin-Hyo; Lee, Nae-Eung

    2008-08-01

    ZnO and Al-doped ZnO (AZO) were etched in Cl2/CH4/H2/Ar (Cl2-based) and BCl3/CH4/H2/Ar (BCl3-based), inductively coupled plasmas (ICPs) and their etching characteristics were compared by varying the Cl2/(Cl2+CH4) and BCl3/(BCl3+CH4) flow ratios, top electrode power and dc self-bias voltage (Vdc). The etch rates of both ZnO and AZO layers were higher in the Cl2-based chemistry than in the BCl3-based chemistry. The AZO and ZnO etch rates were increased and decreased, respectively, with increasing Cl2 or BCl3 flow ratio. Optical emission measurements of the radical species in the plasma and surface binding states by optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS), respectively, indicated that, with increasing Cl2 or BCl3 flow ratio; the effective removal of Al in the AZO enhanced the AZO etch rate, whereas the reduced removal of Zn by the Zn(CHx)y products reduced the ZnO etch rate.

  3. Verification of Fowler-Nordheim electron tunneling mechanism in Ni/SiO2/n-4H SiC and n+ poly-Si/SiO2/n-4H SiC MOS devices by different models

    NASA Astrophysics Data System (ADS)

    Kodigala, Subba Ramaiah

    2016-11-01

    This article emphasizes verification of Fowler-Nordheim electron tunneling mechanism in the Ni/SiO2/n-4H SiC MOS devices by developing three different kinds of models. The standard semiconductor equations are categorically solved to obtain the change in Fermi energy level of semiconductor with effect of temperature and field that extend support to determine sustainable and accurate tunneling current through the oxide layer. The forward and reverse bias currents with variation of electric field are simulated with help of different models developed by us for MOS devices by applying adequate conditions. The latter is quite different from former in terms of tunneling mechanism in the MOS devices. The variation of barrier height with effect of quantum mechanical, temperature, and fields is considered as effective barrier height for the generation of current-field (J-F) curves under forward and reverse biases but quantum mechanical effect is void in the latter. In addition, the J-F curves are also simulated with variation of carrier concentration in the n-type 4H SiC semiconductor of MOS devices and the relation between them is established.

  4. Structure, ferroelectric ordering, and semiempirical quantum calculations of lanthanide based metal-organic framework: [Nd(C4H5O6)(C4H4O6)][3H2O

    NASA Astrophysics Data System (ADS)

    Ahmad, Bhat Zahoor; Want, Basharat

    2016-04-01

    We investigate the structure and ferroelectric behavior of a lanthanide based metal-organic framework (MOF), [Nd(C4H5O6)(C4H4O6)][3H2O]. X-ray crystal structure analyses reveal that it crystallizes in the P41212 space group with Nd centres, coordinated by nine oxygen atoms, forming a distorted capped square antiprismatic geometry. The molecules, bridged by tartrate ligands, form a 2D chiral structure. The 2D sheets are further linked into a 3D porous framework via strong hydrogen-bonding scheme (O-H…O ≈ 2.113 Å). Dielectric studies reveal two anomalies at 295 K and 185 K. The former is a paraelectric-ferroelectric transition, and the later is attributed to the freezing down of the motion of the hydroxyl groups. The phase transition is of second order, and the spontaneous polarization in low temperature phase is attributed to the ordering of protons of hydroxyl groups. The dielectric nonlinearity parameters have been calculated using Landau- Devonshire phenomenological theory. In addition, the most recent semiempirical models, Sparkle/PM7, Sparkle/RM1, and Sparkle/AM1, are tested on the present system to assay the accuracy of semiempirical quantum approaches to predict the geometries of solid MOFs. Our results show that Sparkle/PM7 model is the most accurate to predict the unit cell structure and coordination polyhedron geometry. The semiempirical methods are also used to calculate different ground state molecular properties.

  5. Coniochaetones E-I, new 4H-chromen-4-one derivatives from the Cordyceps-colonizing fungus Fimetariella sp.

    PubMed

    Deng, Lianwu; Niu, Shubing; Liu, Xingzhong; Che, Yongsheng; Li, Erwei

    2013-09-01

    Five new 4H-chromen-4-one derivatives coniochaetones E-I (1-5), along with the known compounds coniochaetones B (6) and A (7) have been isolated from solid cultures of the Cordyceps-colonizing fungus Fimetariella sp. Their structures were elucidated primarily by NMR spectroscopy and the absolute configurations of compounds 1-3 were assigned using the modified Mosher's method. Compound 4 showed weak cytotoxic activity against HeLa cells with IC50 values of 72.8 μM. The co-isolated known compound 6 showed modest inhibitory effects against Aspergilus fumigates, Fusarium oxysporum and Fusarium nivale. PMID:23685047

  6. Infrared band extinctions and complex refractive indices of crystalline C2H2 and C4H2

    NASA Technical Reports Server (NTRS)

    Khanna, R. K.; Ospina, Mario J.; Zhao, Guizhi

    1988-01-01

    Thermal IR absorption intensities are obtained for thin films of crystalline C2H2 and C4H2 at 70 K, and their n and k complex refractive indices are ascertained by separating true film absorption from interface reflection on the basis of an analysis of the transmission spectrum ratio for two sample thicknesses. This method significantly simplifies the n and k iteration process. The n and k values determined in the laboratory will in most cases reproduce a given sample thickness' observed transmission to within + or - 5 percent.

  7. Calorimetric and computational study of 2H-1, 4-benzoxazin-3(4H)-one and of related species

    NASA Astrophysics Data System (ADS)

    Agostinha, M.; Matos, R.; Miranda, Margarida S.; Morais, Victor M. F.; Liebman, Joel F.

    The standard molar enthalpy of formation in the gas phase of 2H-1,4-benzoxazin-3(4H)-one was derived from the standard energy of combustion determined by static bomb combustion calorimetry in oxygen atmosphere and from the standard sublimation enthalpy determined by Calvet microcalorimetry. In addition, we report the results of a systematic theoretical study of the keto and enol tautomers in benzoxazinones and diones using density functional theory. The keto tautomers are computed to be more stable than the enols. Tautomerization energies are reported.

  8. Tunneling Atomic Force Microscopy Studies on Surface Growth Pits Due to Dislocations in 4H-SiC Epitaxial Layers

    NASA Astrophysics Data System (ADS)

    Ohtani, Noboru; Ushio, Shoji; Kaneko, Tadaaki; Aigo, Takashi; Katsuno, Masakazu; Fujimoto, Tatsuo; Ohashi, Wataru

    2012-08-01

    The morphological and electrical properties of surface growth pits caused by dislocations in 4H-SiC epitaxial layers were characterized using tunneling atomic force microscopy. The characteristic distribution of the tip current between the metal-coated atomic force microscopy tip and the SiC was observed within a large surface growth pit caused by a threading screw dislocation. The current was highly localized inside the pit and occurred only on the inclined surface in the up-step direction near the pit bottom. This paper discusses the causes and possible mechanisms of the observed tip current distribution inside surface growth pits.

  9. Electrical Characteristics of Ni-CNT-SiO2-SiC Structured 4H-SiC MIS Capacitors.

    PubMed

    Lee, Taeseop; Kang, Min-Seok; Ha, Tae-Jun; Koo, Sang-Mo

    2015-10-01

    In this study, the electrical characteristics of Ni-CNT-SiO2-SiC structured 4H-SiC MIS capacitors were investigated. The effect of CNTs in the gate/insulator interface have been characterized by C-V measurement at 300 to 500K and J-V have also been measured. The experimental flat-band voltage tends to change with or without CNTs. Current densities of both devices are observed a negligible difference up to 3 V. It has been found that adding CNTs and/or change of temperature can help to control the positive and/or negative flat-band voltage shift.

  10. Growth of Shockley type stacking faults upon forward degradation in 4H-SiC p-i-n diodes

    NASA Astrophysics Data System (ADS)

    Tanaka, Atsushi; Matsuhata, Hirofumi; Kawabata, Naoyuki; Mori, Daisuke; Inoue, Kei; Ryo, Mina; Fujimoto, Takumi; Tawara, Takeshi; Miyazato, Masaki; Miyajima, Masaaki; Fukuda, Kenji; Ohtsuki, Akihiro; Kato, Tomohisa; Tsuchida, Hidekazu; Yonezawa, Yoshiyuki; Kimoto, Tsunenobu

    2016-03-01

    The growth of Shockley type stacking faults in p-i-n diodes fabricated on the C-face of 4H-SiC during forward current operation was investigated using Berg-Barrett X-ray topography and photoluminescence imaging. After forward current experiment, Shockley type stacking faults were generated from very short portions of basal plane dislocations lower than the conversion points to threading edge dislocations in the epitaxial layer. The growth behavior of Shockley type stacking faults was discussed. Growth of stacking faults in the substrates was not observed.

  11. High current (1300 A) optical triggering of a 12 kV 4H-SiC thyristor

    NASA Astrophysics Data System (ADS)

    Rumyantsev, S. L.; Levinshtein, M. E.; Shur, M. S.; Cheng, L.; Agarwal, A. K.; Palmour, J. W.

    2013-04-01

    Optical triggering of a high-voltage (12 kV class) 4H-SiC thyristor to a current Imax = 1300 A is demonstrated. An amplification step (pilot thyristor) and a mixed resistive-inductive load are used to reduce the current ramp dI/dt. The results obtained show that a decrease in the current density at the end of the first, fastest phase of the switch-on process can be achieved either by improving the homogeneity of the initially turned-on region or by introducing additional amplification steps.

  12. Design and fabrication of a 3.3 kV 4H-SiC MOSFET

    NASA Astrophysics Data System (ADS)

    Runhua, Huang; Yonghong, Tao; Song, Bai; Gang, Chen; Ling, Wang; Ao, Liu; Neng, Wei; Yun, Li; Zhifei, Zhao

    2015-09-01

    A 4H-SiC MOSFET with breakdown voltage higher than 3300 V has been successfully designed and fabricated. Numerical simulations have been performed to optimize the parameters of the drift layer and DMOSFET cell structure of active area. The n-type epilayer is 33 μm thick with a doping of 2.5 × 1015 cm-3. The devices were fabricated with a floating guard ring edge termination. The drain current Id = 5 A at Vg = 20 V, corresponding to Vd = 2.5 V. Project supported by the National High Technology Research and Development Program of China (No. 2014AA052401).

  13. Effect of 3.0 MeV helium implantation on electrical characteristics of 4H-SiC BJTs

    NASA Astrophysics Data System (ADS)

    Usman, Muhammad; Hallén, Anders; Ghandi, Reza; Domeij, Martin

    2010-11-01

    Degradation of 4H-SiC power bipolar junction transistors (BJTs) under the influence of a high-energy helium ion beam was studied. Epitaxially grown npn BJTs were implanted with 3.0 MeV helium in the fluence range of 1010-1011 cm-2. The devices were characterized by their current-voltage (I-V) behaviour before and after the implantation, and the results showed a clear degradation of the output characteristics of the devices. Annealing these implanted devices increased the interface traps between passivation oxide and the semiconductor, resulting in an increase of base current in the low-voltage operation range.

  14. Dry etching of CdTe/GaAs epilayers using CH{sub 4}H{sub 2} gas mixtures

    SciTech Connect

    Neswal, M.; Gresslehner, K.H.; Lischka, K.

    1993-05-01

    A CH{sub 4}/H{sub 2} gas mixture has been used for the dry etching of (100) and (111) oriented CdTe epilayers in a barrel reactor. The effects of various process parameters on etch rate and surface morphology were studied with special attention paid to the gas composition and the total chamber pressure as well as the crystallographic orientation of the sample. Clear evidence is found for both isotropic and preferential etching along crystalolographic planes depending on the set of etch parameters used. 14 refs., 7 figs.

  15. A Study of Changes in Dental Health Care Behavior of 4-H Youth in Selected Louisiana Parishes. R and T--Summary 51.

    ERIC Educational Resources Information Center

    Jones, Michael Alan

    The effectiveness of the Dental Hygiene Education Program in changing the dental health care practices of 4-H club youth in four Louisiana parishes and youth knowledge of dental care principles were studied in this before-after experimental design. The study sample consisted of 258 youth from 10 4-H clubs. Subjects completed a four-item…

  16. Development and Evaluation of an On-Line Educational Module for Volunteer Leaders on Bio-Security in Washington State 4-H Livestock Projects

    ERIC Educational Resources Information Center

    Stevenson, Jill L.; Moore, Dale A.; Newman, Jerry; Schmidt, Janet L.; Smith, Sarah M.; Smith, Jean; Kerr, Susan; Wallace, Michael; BoyEs, Pat

    2011-01-01

    A module on disease prevention was created for 4-H volunteer leaders who work with livestock projects in Washington to better prepare them to teach youth about bio-security and its importance in 4-H livestock projects. Evaluation of the module and usage statistics since the module's debut were collected and evaluated. The module increases…

  17. Development and Evaluation of an On-Line Educational Module for Volunteer Leaders on Bio-Security in Washington State 4-H Livestock Projects

    ERIC Educational Resources Information Center

    Stevenson, Jill L.; Moore, Dale A.; Newman, Jerry; Schmidt, Janet L.; Smith, Sarah M.; Smith, Jean; Kerr, Susan; Wallace, Michael; BoyEs, Pat

    2011-01-01

    An on-line module on disease prevention was created for 4-H volunteer leaders who work with livestock projects in Washington to better prepare them to teach youth about bio-security and its importance in 4-H livestock projects. Evaluation of the module and usage statistics since the module's debut were collected and evaluated. The module increases…

  18. Social Background, Personality and Attitudinal Factors Influencing the Decision to Volunteer and Level of Involvement among Adult 4-H Leaders. Summary of Research 39.

    ERIC Educational Resources Information Center

    Rohs, Frederick R.; Warmbrod, J. Robert

    A study was conducted to investigate, using a portion of Smith's Sequential Specificity Model, the relationship between social background, personality, and attitudinal factors and the participation of adult volunteers in the 4-H program in Ohio. Data were collected from a sample of 300 adult 4-H volunteers in Ohio through a mailed questionnaire; a…

  19. A Mixed Methods Case Study: Understanding the Experience of Nebraska 4-H Participants Relative to Their Transition and Adaptation to College

    ERIC Educational Resources Information Center

    Walahoski, Jill

    2013-01-01

    This mixed methods case study was designed to assess the preparedness of former Nebraska 4-H participants to successfully transition and adjust to college. The study also sought to understand the way that students' experiences in Nebraska 4-H may have influenced their readiness to transition to college. The initial quantitative stage of this…

  20. Nitrogen bridgehead compounds. 44. New antiallergic 4H-pyrido[1,2-a]pyrimidin-4-ones. 4.

    PubMed

    Hermecz, I; Horváth, A; Mészáros, Z; De Vos, C; Rodriguez, L

    1984-10-01

    The weak antiallergic activity of 6-methyl-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-3-carbox yli c acid (1) in the rat reaginic passive cutaneous anaphylaxis test was enhanced by the introduction of an (arylamino)methylene moiety into position 9 of the pyridopyrimidine ring. Compound 34, (+)-6(S)-methyl-9-[(m-methylphenyl)-hydrazono]-4-oxo-4H-pyrido[1,2 -a] pyrimidine-3-carboxylic acid, displayed about 10 000 times the activity of the starting compound 1. A structure-activity relationship study of 9-[(arylamino)methylene]tetrahydropyridopyrimidine-3-carb ox ylic acids resulted in conclusions similar to those found for the 9-(arylhydrazono)tetrahydro-and 9-(arylamino)dihydropyridopyrimidine series. Replacement of the 3-carboxy group of 9-(phenylhydrazono)-tetrahydropyridopyrimidin-4-ones with an acrylic acid moiety caused slight increases in potency. In the 6-methyl-substituted series, a high stereospecificity was observed between the enantiomers with 6S and 6R absolute configurations, the former being responsible for the antiallergic activity. The effects of some 9-[(arylamino)-methylene]tetrahydropyridopyrimidine-3-car box ylic acids on the rat passive peritoneal anaphylaxis test were also investigated.

  1. Nitrogen bridgehead compounds. 38. New antiallergic 4H-pyrido[1,2-a]pyrimidin-4-ones. 3.

    PubMed

    Hermecz, I; Breining, T; Vasvári-Debreczy, L; Horváth, A; Mészáros, Z; Bitter, I; DeVos, C; Rodriguez, L

    1983-10-01

    The weak antiallergic activity of 6-methyl-4-oxo-6,7,8,9-tetrahydro-4H-pyrido[1,2-a]pyrimidine-3-carboxylic acid (4) on the rat reaginic passive cutaneous anaphylaxis test was enhanced by the introduction of appropriate functional groups into position 9 of the pyridopyrimidine ring. The most active 9-substituted pyridopyrimidinecarboxylic acids contained an oxime, a phenylamino, or a (phenylamino)thioxomethyl group in position 9. The 9-phenylcarboxamido and 9-phenylhydrazono moieties may be regarded as bioisosteric groups in the pyridopyrimidinone series. In the series of 9-(arylamino)dihydropyridopyrimidines, the structure-activity relationship study revealed similar relationships as found for the 9-(arylhydrazono)tetrahydropyridopyrimidines. The biological activity was due to the 6S enantiomers. A monosubstituted arylamino moiety in position 9 was necessary for the intravenous activity. The most active compound, 9-[(3-acetylphenyl)amino]-6-methyl-4-oxo-6,7,8,9-tetrahydro-4H- pyrido[1,2-a]pyrimidine-3-carboxylic acid (40) was three times as active as the reference sodium chromoglycate (DSCG) in the passive cutaneous anaphylaxis (PCA) test.

  2. Investigation of current transport parameters of Ti/4H-SiC MPS diode with inhomogeneous barrier

    NASA Astrophysics Data System (ADS)

    Song, Qing-Wen; Zhang, Yu-Ming; Zhang, Yi-Men; Chen, Feng-Ping; Tang, Xiao-Yan

    2011-05-01

    The current transport parameters of 4H-SiC merged PiN Schottky (MPS) diode are investigated in a temperature range of 300-520 K. Evaluation of the experimental current-voltage (I—V) data reveals the decrease in Schottky barrier height Φb but an increase in ideality factor n, with temperature decreasing, which suggests the presence of an inhomogeneous Schottky barrier. The current transport behaviours are analysed in detail using the Tung's model and the effective area of the low barrier patches is extracted. It is found that small low barrier patches, making only 4.3% of the total contact, may significantly influence the device electrical characteristics due to the fact that a barrier height of 0.968 eV is much lower than the average barrier height 1.39 eV. This shows that ion implantation in the Schottky contact region of MPS structure may result in a poor Ti/4H-SiC interface quality. In addition, the temperature dependence of the specific on-resistance (Ron—sp), T2.14, is determined between 300 K and 520 K, which is similar to that predicted by a reduction in electron mobility.

  3. Synthesis, in vitro and in silico antimalarial activity of 7-chloroquinoline and 4H-chromene conjugates.

    PubMed

    Parthiban, A; Muthukumaran, J; Manhas, Ashan; Srivastava, Kumkum; Krishna, R; Rao, H Surya Prakash

    2015-10-15

    A new series of chloroquinoline-4H-chromene conjugates incorporating piperizine or azipane tethers were synthesized and their anti-malarial activity were evaluated against two Plasmodium falciparum strains namely 3D7 chloroquine sensitive (CQS) and K1 chloroquine resistant (CQR). Chloroquine was used as the standard and also reference for comparison. The conjugates exhibit intense UV absorption with λmax located at 342 nm (log ε=4.0), 254 nm (log ε=4.2), 223 nm (log ε=4.4) which can be used to spectrometrically track the molecules even in trace amounts. Among all the synthetic compounds, two molecules namely 6-nitro and N-piperazine groups incorporated 7d and 6-chloro and N-azapane incorporated 15b chloroquinoline-4H-chromene conjugates showed significant anti-malarial activity against two strains (3D7 and K1) of P. falciparum. These values are lesser than the values of standard antimalarial compound. Molecular docking results suggested that these two compounds showing strong binding affinity with P. falciparum lactate dehydrogenase (PfLDH) and also they occupy the co-factor position which indicated that they could be the potent inhibitors for dreadful disease malaria and specifically attack the glycolytic pathway in parasite for energy production. PMID:26338359

  4. Phospho-silicate glass gated 4H-SiC metal-oxide-semiconductor devices: Phosphorus concentration dependence

    NASA Astrophysics Data System (ADS)

    Jiao, C.; Ahyi, A. C.; Xu, C.; Morisette, D.; Feldman, L. C.; Dhar, S.

    2016-04-01

    The correlation between phosphorus concentration in phospho-silicate glass (PSG) gate dielectrics and electrical properties of 4H-SiC MOS devices has been investigated. Varying P uptake in PSG is achieved by changing the POCl3 post-oxidation annealing temperature. The density of interface traps (Dit) at the PSG/4H-SiC interface decreases as the amount of interfacial P increases. Most significantly, the MOSFET channel mobility does not correlate with Dit for all samples, which is highly unusual for SiC MOSFETs. Further analysis reveals two types of field-effect mobility (μfe) behavior, depending on the annealing temperature. Annealing at 1000 °C improves the channel mobility most effectively, with a peak value ˜105 cm2 V-1 s-1, and results in a surface phonon scattering limited mobility at high oxide field. On the other hand, PSG annealed at other temperatures results in a surface roughness scattering limited mobility at similar field.

  5. Effect of substitution group on dielectric properties of 4H-pyrano [3, 2-c] quinoline derivatives thin films

    NASA Astrophysics Data System (ADS)

    H, M. Zeyada; F, M. El-Taweel; M, M. El-Nahass; M, M. El-Shabaan

    2016-07-01

    The AC electrical conductivity and dielectrical properties of 2-amino-6-ethyl-5-oxo-4-(3-phenoxyphenyl)-5,6-dihydro-4H-pyrano[3, 2-c]quinoline-3-carbonitrile (Ph-HPQ) and 2-amino-4-(2-chlorophenyl)-6-ethyl-5-oxo-5,6-dihydro-4H-pyrano [3, 2-c] quinoline-3-carbonitrile (Ch-HPQ) thin films were determined in the frequency range of 0.5 kHz–5 MHz and the temperature range of 290–443 K. The AC electrical conduction of both compounds in thin film form is governed by the correlated barrier hopping (CBH) mechanism. Some parameters such as the barrier height, the maximum barrier height, the density of charges, and the hopping distance were determined as functions of temperature and frequency. The phenoxyphenyl group has a greater influence on those parameters than the chlorophenyl group. The AC activation energies were determined at different frequencies and temperatures. The dielectric behaviors of Ph-HPQ and Ch-HPQ were investigated using the impedance spectroscopy technique. The impedance data are presented in Nyquist diagrams for different temperatures. The Ch-HPQ films have higher impedance than the Ph-HPQ films. The real dielectric constant and dielectric loss show a remarkable dependence on the frequency and temperature. The Ph-HPQ has higher dielectric constants than the Ch-HPQ.

  6. Assessment of 4H-SiC epitaxial layers and high resistivity bulk crystals for radiation detectors

    NASA Astrophysics Data System (ADS)

    Mandal, Krishna C.; Muzykov, Peter G.; Chaudhuri, Sandeep K.; Terry, J. R.

    2012-10-01

    We present results of structural, electrical, and defect characterization of 4H-SiC epitaxial layers and bulk crystals and show performance of the radiation detectors fabricated from these materials. The crystal quality was evaluated by x-ray diffraction (XRD) rocking curve measurements, electron beam induced current (EBIC) imaging, and defect delineating etching in conjunction with optical microscopy and scanning electron microscopy (SEM). Studies of the electrically active intrinsic defects and impurities were conducted using thermally stimulated current (TSC) measurements in a wide temperature range of 94 - 750K. The results are correlated with the capability of bulk crystals and epitaxial layers for the detection of α-particles, low to high energy x-rays and gamma rays. High barrier rectifying Schottky diodes have been fabricated and tested. The epitaxial 4H-SiC radiation detectors exhibited low leakage current (< 1 nA) at ~ 200 V operating voltage up to 200 C. The soft x-ray responsivity measurements performed at the National Synchrotron Light Source (NSLS) at Brookhaven National Lab (BNL) showed significantly improved characteristics compared to commercially-available SiC UV photodiode detectors.

  7. Communication: Ab initio study of O{sub 4}H{sup +}: A tracer molecule in the interstellar medium?

    SciTech Connect

    Xavier, George D.; Bernal-Uruchurtu, Margarita I.; Hernández-Lamoneda, Ramón

    2014-08-28

    The structure and energetics of the protonated molecular oxygen dimer calculated via ab initio methods is reported. We find structures that share analogies with the eigen and zundel forms for the protonated water dimer although the symmetrical sharing of the proton is more prevalent. Analysis of different fragmentation channels show charge transfer processes which indicate the presence of conical intersections for various states including the ground state. An accurate estimate for the proton affinity of O{sub 4} leads to a significantly larger value (5.6 eV) than for O{sub 2} (4.4 eV), implying that the reaction H{sub 3}{sup +} + O{sub 4} → O{sub 4}H{sup +} + H{sub 2} is exothermic by 28 Kcal/mol as opposed to the case of O{sub 2} which is nearly thermoneutral. This opens up the possibility of using O{sub 4}H{sup +} as a tracer molecule for oxygen in the interstellar medium.

  8. Effect of substitution group on dielectric properties of 4H-pyrano [3, 2-c] quinoline derivatives thin films

    NASA Astrophysics Data System (ADS)

    H, M. Zeyada; F, M. El-Taweel; M, M. El-Nahass; M, M. El-Shabaan

    2016-07-01

    The AC electrical conductivity and dielectrical properties of 2-amino-6-ethyl-5-oxo-4-(3-phenoxyphenyl)-5,6-dihydro-4H-pyrano[3, 2-c]quinoline-3-carbonitrile (Ph-HPQ) and 2-amino-4-(2-chlorophenyl)-6-ethyl-5-oxo-5,6-dihydro-4H-pyrano [3, 2-c] quinoline-3-carbonitrile (Ch-HPQ) thin films were determined in the frequency range of 0.5 kHz-5 MHz and the temperature range of 290-443 K. The AC electrical conduction of both compounds in thin film form is governed by the correlated barrier hopping (CBH) mechanism. Some parameters such as the barrier height, the maximum barrier height, the density of charges, and the hopping distance were determined as functions of temperature and frequency. The phenoxyphenyl group has a greater influence on those parameters than the chlorophenyl group. The AC activation energies were determined at different frequencies and temperatures. The dielectric behaviors of Ph-HPQ and Ch-HPQ were investigated using the impedance spectroscopy technique. The impedance data are presented in Nyquist diagrams for different temperatures. The Ch-HPQ films have higher impedance than the Ph-HPQ films. The real dielectric constant and dielectric loss show a remarkable dependence on the frequency and temperature. The Ph-HPQ has higher dielectric constants than the Ch-HPQ.

  9. Reassessment of HLA-G isoform specificity of MEM-G/9 and 4H84 monoclonal antibodies.

    PubMed

    Zhao, L; Teklemariam, T; Hantash, B M

    2012-09-01

    Human leukocyte antigen (HLA)-G is a non-classical HLA class I molecule thought to play a key role in maternal-fetal tolerance. Although initial studies suggested that HLA-G expression is restricted to extravillous cytotrophoblasts, expression was subsequently reported in a wide variety of other human tissues and tumor cells. However, consensus as to the validity of these collective findings has proven difficult because the antibodies used to define the temporal and spatial expression patterns of HLA-G remain incompletely characterized. The aim of our study was to reassess two of the most widely used HLA-G antibodies (MEM-G/9 and 4H84) in HLA-G-positive (JEG-3 and HLA-G transduced) and -negative (dermal fibroblast, mesenchymal stem cell, K562, and Jurkat) lines using flow cytometry, immunofluorescence, and western blotting. We found that MEM-G/9 recognized HLA-G3 by flow cytometry, indicating that its epitope is present on the α1 domain of HLA-G. Although 4H84 preferably recognized unfolded HLA-G-free chains, it showed strong non-specificity under certain methodological conditions.

  10. New Mononuclear Cu(II) Complexes and 1D Chains with 4-Amino-4H-1,2,4-triazole

    PubMed Central

    Dîrtu, Marinela M.; Boland, Yves; Gillard, Damien; Tinant, Bernard; Robeyns, Koen; Safin, Damir A.; Devlin, Eamonn; Sanakis, Yiannis; Garcia, Yann

    2013-01-01

    The crystal structures of two mononuclear Cu(II) NH2trz complexes [Cu(NH2trz)4(H2O)](AsF6)2 (I) and [Cu(NH2trz)4(H2O)](PF6)2 (II) as well as two coordination polymers [Cu(μ2-NH2trz)2Cl]Cl·H2O (III) and [Cu(μ2-NH2trz)2Cl] (SiF6)0.5·1.5H2O (IV) are presented. Cationic 1D chains with bridging bis-monodentate μ2-coordinated NH2trz and bridging μ2-coordinated chloride ligands are present in III and IV. In these coordination polymers, the Cu(II) ions are strongly antiferromagnetically coupled with J = −128.4 cm−1 for III and J = −143 cm−1 for IV (H = −J∑SiSi+1), due to the nature of the bridges between spin centers. Inter-chain interactions present in the crystal structures were taken into consideration, as well as g factors, which were determined experimentally, for the quantitative modeling of their magnetic properties. PMID:24300095

  11. Raman spectral characterization of NH4H2PO4 single crystals: Effect of pH on microstructure

    NASA Astrophysics Data System (ADS)

    Zhou, Hailiang; Wang, Fang; Xu, Mingxia; Liu, Baoan; Liu, Fafu; Zhang, Lisong; Xu, Xinguang; Sun, Xun; Wang, Zhengping

    2016-09-01

    Single crystals of ammonium dihydrogen phosphate (NH4H2PO4, ADP) were grown from aqueous solutions using "point seeds" method. The Raman spectra of the NH4H2PO4 single crystals were recorded as a function of pH. The band intensities and frequencies were monitored to determine the diagnostic bands for the crystals grown from the solutions of different pH values of aqueous solution. In the Raman spectra of ADP crystal samples at different pH, the position and intensity of the peaks in the range 300-900 cm-1 did not change; the peaks in the range 1400-1700 cm-1 shifted their position, although they had the same intensity. This indicates that the structure of (PO4) 3 - did not change with pH, whereas the structure of NH4+ changed with pH. In the Raman study in the range 1700-4000 cm-1, the primary discrimination occurred for the intensity of the peaks at 3050 cm-1 and 3147 cm-1, which is attributed to the vibration of O-H⋯O hydrogen bond, it can be inferred that pH slightly affected the O-H⋯O hydrogen bonding. This Raman spectral characterization may help to better understand the microstructural change under different conditions and optimize the growth and property of this type of material.

  12. Study of surface potential variation in p-/n-type 4H-SiC using scanning kelvin probe microscopy

    NASA Astrophysics Data System (ADS)

    Ahn, Jung-Joon; You, Lin; Yu, Liangchun; Koo, Sang-Mo; Kopanski, Joseph

    2013-03-01

    We report surface potential images of p-n junctions in 4H-SiC measured using scanning kelvin probe microscopy (SKPM) and relate them to the local dopant concentration. SKPM has been demonstrated on various semiconductor materials to examine crystalline defects and doping profiles. SKPM measured surface potential depends on the local dopant concentration and clearly differentiates between n-type and p-type materials. As opposed to scanning capacitance microscopy, which requires a good quality surface insulating layer, SKPM requires a clean surface and the lack of a screening oxide might result in higher spatial resolution. For the measurement, partially de-processed SiC high power LMOSFETS were used. The p-n junctions were formed from 4H-SiC wafers having a p-epilayer on p-substrate that was ion-implanted with nitrogen and annealed to build a shallow n-type region. The samples were observed in plan-view and in cross-section. Amplitude modulated, double pass SKPM was implemented with a commercial AFM. We conducted a detailed study of various data acquisition parameters and it seems that the lateral resolution of the potential difference can be enhanced by applying higher ac modulation amplitude and small tip-sample scanning height.

  13. Theoretical study of radiative electron attachment to CN, C{sub 2}H, and C{sub 4}H radicals

    SciTech Connect

    Douguet, Nicolas; Fonseca dos Santos, S.; Orel, Ann E.; Raoult, Maurice; Dulieu, Olivier

    2015-06-21

    A first-principle theoretical approach to study the process of radiative electron attachment is developed and applied to the negative molecular ions CN{sup −}, C{sub 4}H{sup −}, and C{sub 2}H{sup −}. Among these anions, the first two have already been observed in the interstellar space. Cross sections and rate coefficients for formation of these ions by direct radiative electron attachment to the corresponding neutral radicals are calculated. For the CN molecule, we also considered the indirect pathway, in which the electron is initially captured through non-Born-Oppenheimer coupling into a vibrationally resonant excited state of the anion, which then stabilizes by radiative decay. We have shown that the contribution of the indirect pathway to the formation of CN{sup −} is negligible in comparison to the direct mechanism. The obtained rate coefficients for the direct mechanism at 30 K are 7 × 10{sup −16} cm{sup 3}/s for CN{sup −}, 7 × 10{sup −17} cm{sup 3}/s for C{sub 2}H{sup −}, and 2 × 10{sup −16} cm{sup 3}/s for C{sub 4}H{sup −}. These rates weakly depend on temperature between 10 K and 100 K. The validity of our calculations is verified by comparing the present theoretical results with data from recent photodetachment experiments.

  14. New X-ray insight into oxygen intercalation in epitaxial graphene grown on 4H-SiC(0001)

    SciTech Connect

    Kowalski, G. Tokarczyk, M.; Dąbrowski, P.; Ciepielewski, P.; Możdżonek, M.; Strupiński, W.; Baranowski, J. M.

    2015-03-14

    Efficient control of intercalation of epitaxial graphene by specific elements is a way to change properties of the graphene. Results of several experimental techniques, such as X-ray photoelectron spectroscopy, micro-Raman mapping, reflectivity, attenuated total reflection, X-ray diffraction, and X-ray reflectometry, gave a new insight into the intercalation of oxygen in the epitaxial graphene grown on 4H-SiC(0001). These results confirmed that oxygen intercalation decouples the graphene buffer layer from the 4H-SiC surface and converts it into the graphene layer. However, in contrast to the hydrogen intercalation, oxygen does not intercalate between carbon planes (in the case of few layer graphene) and the interlayer spacing stays constant at the level of 3.35–3.32 Å. Moreover, X-ray reflectometry showed the presence of an oxide layer having the thickness of about 0.8 Å underneath the graphene layers. Apart from the formation of the nonuniform thin oxide layer, generation of defects in graphene caused by oxygen was also evidenced. Last but not least, water islands underneath defected graphene regions in both intercalated and non-intercalated samples were most probably revealed. These water islands are formed in the case of all the samples stored under ambient laboratory conditions. Water islands can be removed from underneath the few layer graphene stacks by relevant thermal treatment or by UV illumination.

  15. First-principles study on reconstruction of 4H-SiC(0001) and (000 1 bar)

    NASA Astrophysics Data System (ADS)

    Kaneko, Tomoaki; Yamasaki, Takahiro; Tajima, Nobuo; Ohno, Takahisa

    2016-05-01

    We have found that 4H-SiC(0001) and (000 1 bar) surfaces can reconstruct to stable (2 × 1) π-bonded chain structures, which are the same kind of structure that was predicted by Pandey for Si(111) surface (K. C. Pandey, 1981) but have not been examined for the SiC surfaces so far. Their relative energy gain on (0001) and (000 1 bar) surfaces to the ideal spin non-polarized surfaces are 0.275-0.298 eV/(1 × 1) and 0.378-0.441 eV/(1 × 1), respectively. The band gaps of the π-bonded chain models for 4H-SiC(0001) and (000 1 bar) are 1.34-1.36 eV and 1.92-2.46 eV, respectively, which are much larger than that for Si(111) due to difference between energy levels of p-orbitals of Si and C atoms.

  16. Sodium alginate: An efficient biopolymeric catalyst for green synthesis of 2-amino-4H-pyran derivatives.

    PubMed

    Dekamin, Mohammad G; Peyman, S Zahra; Karimi, Zahra; Javanshir, Shahrzad; Naimi-Jamal, M Reza; Barikani, Mehdi

    2016-06-01

    Sodium alginate, a naturally occurring macromolecule, in its granular form and without any post-modification was found to be an efficient and recoverable bifunctional heterogeneous organocatalyst for the domino synthesis of various 2-amino-3-cyano-4H-pyran annulated derivatives through three-component condensation of different aldehydes, malononitrile and diverse 1,3-dicarbonyl compounds under mild conditions. Corresponding 4H-pyran derivatives were obtained in high to excellent yields after 25-150min stirring in 2mL EtOH under reflux conditions in the presence of 10mol% of sodium alginate, equimolar amounts of aldehydes, malononitrile and 1,3-dicarbonyl compounds. The catalyst was easily separated from the reaction mixture to obtain desired products in excellent purity as shown by FTIR and (1)H NMR spectroscopic methods. Avoiding the use of any transition metal, one-pot and multi-component procedure catalyzed by a renewable biopolymer, the reusability of the catalyst, broad substrate scope and operational simplicity are important features of this methodology for preparation of medicinally important compounds. PMID:26845480

  17. Formation of amorphous alloys on 4H-SiC with NbNi film using pulsed-laser annealing

    NASA Astrophysics Data System (ADS)

    De Silva, Milantha; Ishikawa, Seiji; Miyazaki, Takamichi; Kikkawa, Takamaro; Kuroki, Shin-Ichiro

    2016-07-01

    Amorphous alloys containing Ni-Si-Nb-C were formed on 4H-SiC creating a low resistance Ohmic contact electrode. In a conventional nickel silicide (NiSi) electrode on SiC, a carbon agglomeration at the silicide/SiC interface occurs, and contact resistance between NiSi and SiC substrate becomes larger. For carbon agglomeration suppression, nanosecond non-equilibrium laser annealing was introduced, and to form metal carbides, carbon-interstitial type metals Nb and Mo were introduced. Ni, Nb, Mo, Nb/Ni, Mo/Ni multilayer contacts, and NbNi mixed contact were formed on the C-face side of n-type 4H-SiC wafers. The electrical contact properties were investigated after a 45 ns pulse laser annealing in N2 ambient. As a result, with NbNi film, an amorphous alloy with Ni-Si-Nb-C was formed, and a low specific contact resistance of 5.3 × 10-4 Ω cm2 was realized.

  18. Dwornikite, (Ni,Fe)SO4.H2O, a member of the kieserite group from Minasragra, Peru.

    USGS Publications Warehouse

    Milton, C.; Evans, H.T.; Johnson, R.G.

    1982-01-01

    A new nickel sulphate monohydrate is described from V-sulphide ore from Minasragra; it occurs associated with patronite (VS2) with various sulphates, sulphur and bitumen. Dwornikite forms fine-grained white aggregates mixed with other oxidation products. Indexed X-ray powder data are tabulated; strongest lines 3.342(100) , 4.732(70), 3.024(70), 4.754(50), 3.293(35), 2.491(35) A; a 6.839, b 7.582, c 7.474 A, beta 117.85o; space group C2/c. XRF gave NiO 39.0, FeO 9.3, SO3 42.4, = 90.7; Dcalc. 3.34 g/cm3; mean refr. ind. approx 1.63. Unit-cell data for the synthetic end-member compounds NiSO4.H2O and FeSO4.H2O and new X-ray powder data for retgersite (NiSO4.6H2O) are given. The name is for E. J. Dwornik, mineralogist with the U.S. Geological Survey.-R.A.H.

  19. Using queuing theory to analyse the government's 4-H completion time target in accident and emergency departments.

    PubMed

    Mayhew, L; Smith, D

    2008-03-01

    This paper uses a queuing model to evaluate completion times in Accident and Emergency (A&E) departments in the light of the Government target of completing and discharging 98% of patients inside 4 h. It illustrates how flows though an A&E can be accurately represented as a queuing process, how outputs can be used to visualise and interpret the 4-h Government target in a simple way and how the model can be used to assess the practical achievability of A&E targets in the future. The paper finds that A&E targets have resulted in significant improvements in completion times and thus deal with a major source of complaint by users of the National Health Service in the U.K. It suggests that whilst some of this improvement is attributable to better management, some is also due to the way some patients in A&E are designated and therefore counted through the system. It finds for example that the current target would not have been possible without some form of patient re-designation or re-labelling taking place. Further it finds that the current target is so demanding that the integrity of reported performance is open to question. Related incentives and demand management issues resulting from the target are also briefly discussed. PMID:18390164

  20. Effects of antimony (Sb) on electron trapping near SiO2/4H-SiC interfaces

    NASA Astrophysics Data System (ADS)

    Mooney, P. M.; Jiang, Zenan; Basile, A. F.; Zheng, Yongju; Dhar, Sarit

    2016-07-01

    To investigate the mechanism by which Sb at the SiO2/SiC interface improves the channel mobility of 4H-SiC MOSFETs, 1 MHz capacitance measurements and constant capacitance deep level transient spectroscopy (CCDLTS) measurements were performed on Sb-implanted 4H-SiC MOS capacitors. The measurements reveal a significant concentration of Sb donors near the SiO2/SiC interface. Two Sb donor related CCDLTS peaks corresponding to shallow energy levels in SiC were observed close to the SiO2/SiC interface. Furthermore, CCDLTS measurements show that the same type of near-interface traps found in conventional dry oxide or NO-annealed capacitors are present in the Sb implanted samples. These are O1 traps, suggested to be carbon dimers substituted for O dimers in SiO2, and O2 traps, suggested to be interstitial Si in SiO2. However, electron trapping is reduced by a factor of ˜2 in Sb-implanted samples compared with samples with no Sb, primarily at energy levels within 0.2 eV of the SiC conduction band edge. This trap passivation effect is relatively small compared with the Sb-induced counter-doping effect on the MOSFET channel surface, which results in improved channel transport.

  1. Synthesis of liquid crystalline 4H-benzo[1,2,4]thiadiazines and generation of persistent radicals.

    PubMed

    Zienkiewicz, Józef; Fryszkowska, Anna; Zienkiewicz, Katarzyna; Guo, Fengli; Kaszynski, Piotr; Januszko, Adam; Jones, David

    2007-04-27

    Four substituted 4H-benzo[1,2,4]thiadiazines 2 were prepared by condensation of the appropriate anilines and benzonitriles followed by oxidative cyclization. The preparation of three fluorinated derivatives 2b-2d proceeded smoothly, while the synthesis of 2a was problematic, presumably due to the relatively high electron density of the benzene ring. The four-ring derivatives 2c and 2d exhibited liquid crystalline properties (2c: Cr 95 SmA 158 I and 2d: Cr 142 SmA 212 I). 4H-Benzo[1,2,4]thiadiazines 2 were oxidized with AgO to generate the corresponding persistent radicals 1 (g=2.0057). The stability of the radicals followed the order 1b approximately 1d>1c>1a, and the two fluorinated radicals 1b and 1d were isolated as crude solids. The lower stability of 1c is presumably due to the presence of the reactive benzylic CH position, and 1a lacks the stabilizing effect of the three fluorine atoms. ESR spectra for 1 were simulated using DFT-derived hfcc as the starting point.

  2. A novel 4H-SiC lateral bipolar junction transistor structure with high voltage and high current gain

    NASA Astrophysics Data System (ADS)

    Deng, Yong-Hui; Xie, Gang; Wang, Tao; Sheng, Kuang

    2013-09-01

    In this paper, a novel structure of a 4H-SiC lateral bipolar junction transistor (LBJT) with a base field plate and double RESURF in the drift region is presented. Collector-base junction depletion extension in the base region is restricted by the base field plate. Thin base as well as low base doping of the LBJT therefore can be achieved under the condition of avalanche breakdown. Simulation results show that thin base of 0.32 μm and base doping of 3 × 1017 cm-3 are obtained, and corresponding current gain is as high as 247 with avalanche breakdown voltage of 3309 V when the drift region length is 30 μm. Besides, an investigation of a 4H-SiC vertical BJT (VBJT) with comparable breakdown voltage (3357 V) shows that the minimum base width of 0.25 μm and base doping as high as 8 × 1017 cm-3 contribute to a maximum current gain of only 128.

  3. Observations of Screw Dislocation Driven Growth and Faceting During CVD Homoepitaxy on 4H-SiC On-Axis Mesa Arrays

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Trunek, Andrew J.; Powell, J. Anthony; Picard, Yoosuf N.; Twigg, Mark E.

    2009-01-01

    Previous studies of (0001) homoepitaxial growth carried out on arrays of small-area mesas etched into on-axis silicon-face 4H-SiC wafers have demonstrated that spiral growth emanating from at least one screw dislocation threading the mesa is necessary in order for a mesa to grow taller in the <0001> (c-axis vertical) direction while maintaining 4H stacking sequence [1]. However, even amongst mesas containing the screw dislocation step source necessary for vertical c-axis growth, we have observed striking differences in the height and faceting that evolve during prolonged homoepitaxial growths. This paper summarizes Atomic Force Microscopy (AFM), Electron Channeling Contrast Imaging (ECCI), Scanning Electron Microscopy (SEM), and optical microscopy observations of this phenomenon. These observations support our initially proposed model [2] that the observed large variation (for mesas where 3C-SiC nucleation has not occurred) is related to the lateral positioning of a screw dislocation step source within each etched mesa. When the screw dislocation step source is located close enough to the developing edge/sidewall facet of a mesa, the c-axis growth rate and facet angle are affected by the resulting interaction. In particular, the intersection (or near intersection) of the inward-sloping mesa sidewall facet with the screw dislocation appears to impede the rate at which the spiral provides new steps required for c-axis growth. Also, the inward slope of the sidewall facet during growth (relative to other sidewalls of the same mesa not near the screw dislocation) seems to be impeded by the screw dislocation. In contrast, mesas whose screw dislocations are centrally located grow vertically, but inward sloping sidewall facets shrink the area of the top (0001) growth surface almost to the point of vanishing.

  4. 4H Syndrome

    MedlinePlus

    ... on the basis of the clinical symptoms, especially ataxia and delayed dentition or hypodontia, in combination with ... described. Neurological symptoms include: Late walking Early-onset ataxia (problems with balance and fine motor skills) Deterioration ...

  5. Thermodynamics of the formation of sulfuric acid dimers in the binary (H2SO4-H2O) and ternary (H2SO4-H2O-NH3) system

    NASA Astrophysics Data System (ADS)

    Kürten, A.; Münch, S.; Rondo, L.; Bianchi, F.; Duplissy, J.; Jokinen, T.; Junninen, H.; Sarnela, N.; Schobesberger, S.; Simon, M.; Sipilä, M.; Almeida, J.; Amorim, A.; Dommen, J.; Donahue, N. M.; Dunne, E. M.; Flagan, R. C.; Franchin, A.; Kirkby, J.; Kupc, A.; Makhmutov, V.; Petäjä, T.; Praplan, A. P.; Riccobono, F.; Steiner, G.; Tomé, A.; Tsagkogeorgas, G.; Wagner, P. E.; Wimmer, D.; Baltensperger, U.; Kulmala, M.; Worsnop, D. R.; Curtius, J.

    2015-09-01

    Sulfuric acid is an important gas influencing atmospheric new particle formation (NPF). Both the binary (H2SO4-H2O) system and the ternary system involving ammonia (H2SO4-H2O-NH3) may be important in the free troposphere. An essential step in the nucleation of aerosol particles from gas-phase precursors is the formation of a dimer, so an understanding of the thermodynamics of dimer formation over a wide range of atmospheric conditions is essential to describe NPF. We have used the CLOUD chamber to conduct nucleation experiments for these systems at temperatures from 208 to 248 K. Neutral monomer and dimer concentrations of sulfuric acid were measured using a chemical ionization mass spectrometer (CIMS). From these measurements, dimer evaporation rates in the binary system were derived for temperatures of 208 and 223 K. We compare these results to literature data from a previous study that was conducted at higher temperatures but is in good agreement with the present study. For the ternary system the formation of H2SO4·NH3 is very likely an essential step in the formation of sulfuric acid dimers, which were measured at 210, 223, and 248 K. We estimate the thermodynamic properties (dH and dS) of the H2SO4·NH3 cluster using a simple heuristic model and the measured data. Furthermore, we report the first measurements of large neutral sulfuric acid clusters containing as many as 10 sulfuric acid molecules for the binary system using chemical ionization-atmospheric pressure interface time-of-flight (CI-APi-TOF) mass spectrometry.

  6. Low temperature rate coefficients for reactions of the butadiynyl radical, C4H, with various hydrocarbons. Part I: reactions with alkanes (CH4, C2H6, C3H8, C4H10).

    PubMed

    Berteloite, Coralie; Le Picard, Sébastien D; Balucani, Nadia; Canosa, André; Sims, Ian R

    2010-04-21

    The kinetics of the reactions of the linear butadiynyl radical, C4H (CCCCH), with methane, ethane, propane and butane have been studied over the temperature range of 39-300 K using a CRESU (Cinétique de Réaction en Ecoulement Supersonique Uniforme or Reaction Kinetics in Uniform Supersonic Flow) apparatus combined with the pulsed laser photolysis-laser induced fluorescence technique. The rate coefficients, except for the reaction with methane, show a negative temperature dependence and can be fitted with the following expressions over the temperature range of this study: k(C2H6) = 0.289 x 10(-10) (T/298 K)(-1.23) exp(-24.8 K/T) cm3 molecule(-1) s(-1); k(C3H8) = 1.06 x 10(-10) (T/298 K)(-1.36) exp(-56.9 K/T) cm3 molecule(-1) s(-1); k(C4H10) = 2.93 x 10(-10) (T/298 K)(-1.30) exp(-90.1 K/T) cm3 molecule(-1) s(-1). The rate coefficients for the reaction with methane were measured only at 200 K and 300 K yielding a positive temperature dependence: k(CH4) = 1.63 x 10(-11) exp(-610 K/T) cm3 molecule(-1) s(-1). Possible reaction mechanisms and product channels are discussed in detail for each of these reactions. Potential implications of these results for models of low temperature chemical environments, in particular cold interstellar clouds and planetary atmospheres such as that of Titan, are considered.

  7. Magnetostructural correlations for Fe2+ ions at orthorhombic sites in FeCl2·4H2O and FeF2·4H2O crystals modeled by microscopic spin Hamiltonian approach

    NASA Astrophysics Data System (ADS)

    Zając, Magdalena; Lipiński, Ignacy Eryk; Rudowicz, Czesław

    2016-03-01

    The microscopic spin Hamiltonian (MSH) theory developed up to the fourth-order perturbation theory for 3d4 and 3d6 ions with spin S=2 within the 5D approximation is employed to predict the zero field splitting (ZFS) parameters and the Zeeman electronic (Ze) ones. The SH parameters, measurable by electron magnetic resonance (EMR), are expressed in terms of the microscopic parameters, i.e. the spin-orbit (λ), spin-spin (ρ) coupling constants, and the crystal-field (ligands-field) energy levels (∆i) within the 5D multiplet. The energies, ∆i, are indirectly related with structural data, thus enabling investigation of magnetostructural correlations. As a case study Fe2+ (3d6; S=2) ions at orthorhombic sites in FeCl2·4H2O and FeF2·4H2O crystals are considered. Calculations of the ZFS and Ze parameters are carried out for wide ranges of values of the microscopic parameters using the package MSH/VBA. Dependence of the theoretically determined ZFS parameters bkq (in the Stevens notation) and the Zeeman factors gi on λ, ρ, and ∆i is examined and suitable graphs are presented. The absolute value of dominant ZFS parameter |b20| is predicted to be in the range from nearly 8.5 to 1.4 cm-1. Matching the theoretical SH parameters and the experimental ones enables determination of the suitable values of λ, ρ, and ∆i. The fourth-rank ZFS parameters and the ρ(spin-spin)-related contributions, considered for the first time here, are found important. The MSH predictions may be verified and fine-tuned by high-magnetic field and high-frequency EMR measurements. The method employed here and the present results may be also useful for other structurally related systems.

  8. 21. Providence & Worchester RR: Freight house. Providence, Providence Co., ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    21. Providence & Worchester RR: Freight house. Providence, Providence Co., RI. Sec. 4119, mp 185.66 (See HAER no. RI-3 for further documentation on this site.) - Northeast Railroad Corridor, Amtrak route between CT & MA state lines, Providence, Providence County, RI

  9. Twin anchors of the soybean isoflavonoid metabolon: evidence for tethering of the complex to the endoplasmic reticulum by IFS and C4H.

    PubMed

    Dastmalchi, Mehran; Bernards, Mark A; Dhaubhadel, Sangeeta

    2016-03-01

    Isoflavonoids are specialized plant metabolites, almost exclusive to legumes, and their biosynthesis forms a branch of the diverse phenylpropanoid pathway. Plant metabolism may be coordinated at many levels, including formation of protein complexes, or 'metabolons', which represent the molecular level of organization. Here, we have confirmed the existence of the long-postulated isoflavonoid metabolon by identifying elements of the complex, their subcellular localizations and their interactions. Isoflavone synthase (IFS) and cinnamate 4-hydroxylase (C4H) have been shown to be tandem P450 enzymes that are anchored in the ER, interacting with soluble enzymes of the phenylpropanoid and isoflavonoid pathways (chalcone synthase, chalcone reductase and chalcone isomerase). The soluble enzymes of these pathways, whether localized to the cytoplasm or nucleus, are tethered to the ER through interaction with these P450s. The complex is also held together by interactions between the soluble elements. We provide evidence for IFS interaction with upstream and non-consecutive enzymes. The existence of such a protein complex suggests a possible mechanism for flux of metabolites into the isoflavonoid pathway. Further, through interaction studies, we identified several candidates that are associated with GmIFS2, an isoform of IFS, in soybean hairy roots. This list provides additional candidates for various biosynthetic and structural elements that are involved in isoflavonoid production. Our interaction studies provide valuable information about isoform specificity among isoflavonoid enzymes, which may guide future engineering of the pathway in legumes or help overcome bottlenecks in heterologous expression. PMID:26856401

  10. Spectroscopic studies of inclusion of 4H-1-benzopyran-4-thione in a β-cyclodextrin cavity

    NASA Astrophysics Data System (ADS)

    Milewski, Marek; Maciejewski, Andrzej; Augustyniak, Włodzimierz

    1997-06-01

    Spectral and photophysical properties of 4H-1-benzopyran-4-thione (BFT) in aqueous solutions of β-cyclodextrin (β-CD) and in some solvents have been investigated by stationary methods. Both fluorescence and phosphorescence of BPT are observable at room temperature. Results indicate the formation of an inclusion complex. Spectral shifts in the absorption spectrum and the shape of the phosphorescence spectrum mostly depend on the polarity of environment whereas the photophysical properties of the second excited singlet state depend on other structural properties of the medium, which allows us to investigate interactions between water molecules and complexed molecules. These properties make BFT a very convenient probe in the investigation of photophysics of inclusion complexes.

  11. Comparison of thermal oxidation and plasma oxidation of 4H-SiC (0001) for surface flattening

    SciTech Connect

    Deng, Hui; Endo, Katsuyoshi; Yamamura, Kazuya

    2014-03-10

    The thermal oxidation and water vapor plasma oxidation of 4H-SiC (0001) were investigated. The initial oxidation rate of helium-based atmospheric-pressure plasma oxidation was six times higher than that of thermal oxidation. The oxide-SiC interface generated by plasma oxidation became flatter with increasing thickness of the oxide, whereas the interface generated by thermal oxidation was atomically flat regardless of the oxide thickness. Many pits were generated on the thermally oxidized surface, whereas few pits were observed on the surface oxidized by plasma. After the oxide layer generated plasma oxidation was removed, an atomically flat and pit-free SiC surface was obtained.

  12. Synthesis and aromatase inhibitory evaluation of 4-N-nitrophenyl substituted amino-4H-1,2,4-triazole derivatives.

    PubMed

    Song, Zhidan; Liu, Yanchun; Dai, Zhoutong; Liu, Wei; Zhao, Kai; Zhang, Tongcun; Hu, Yanying; Zhang, Xiuli; Dai, Yujie

    2016-10-01

    In this paper, 13 4-N-nitrophenyl substituted amino-4H-1,2,4-triazole derivatives were synthesized and their aromatase inhibitory activities were measured. The results show that the substitution of the groups on benzyl group can further improve their bioactivity and the compound with Cl on the para position of benzyl has the highest bioactivity (IC50=9.02nM). A QSAR model was constructed from the 13 compounds with genetic function approximation using DS 2.1 package. This model can explain 90.09% of the variance (R(2)Adj), while it can predict 84.95% of the variance (R(2)cv) with the confidence interval of 95%. PMID:27567077

  13. Graphene on C-terminated face of 4H-SiC observed by noncontact scanning nonlinear dielectric potentiometry

    NASA Astrophysics Data System (ADS)

    Yamasue, Kohei; Fukidome, Hirokazu; Tashima, Keiichiro; Suemitsu, Maki; Cho, Yasuo

    2016-08-01

    We studied graphene synthesized on the C-terminated face (C-face) of a 4H-SiC substrate by noncontact scanning nonlinear dielectric potentiometry. As already reported by other researchers, multilayer graphene sheets with moiré patterns were observed in our sample, which indicates the existence of rotational disorder between adjacent layers. We found that the potentials of graphene on the C-face are almost neutral and significantly smaller than those observed on the Si-terminated face (Si-face). In addition, the neutrality of potentials is not affected by various topographic features underlying the multilayer graphene sheets. These results indicate that graphene on the C-face of SiC is decoupled or screened from the underlying structures and substrate, unlike graphene on the Si-face.

  14. Effect of Fe impurity on the dislocations in 4H-SiC: Insights from electrical and optical characterization

    NASA Astrophysics Data System (ADS)

    Chen, Bin; Sekiguchi, Takashi; Matsuhata, Hirofumi; Ohyanagi, Takasumi; Kinoshita, Akimasa; Okumura, Hajime

    2014-01-01

    The effect of Fe impurity on the dissociation and motion behavior of basal plane dislocations (BPDs) in 4H-SiC homoepitaxial layers was investigated by electron-beam-induced current (EBIC) and cathodoluminescence (CL) techniques. Under the electron-beam irradiation, the BPDs dissociated to C- and Si-core partials, and these two partials were connected by another partial termed as X in this study. Stacking faults (SFs) were formed among these partials. The recombination activities of the BPDs and partials were enhanced with the existence of Fe impurity. The SFs near the surface region showed obvious dark contrast in EBIC, which was different from that observed in the clean samples. The X partial kept moving with sustained electron-beam irradiation whereas this partial in the clean samples stopped motion when it was connected to the sample surface. The dark contrast of the SFs and the peculiar motion behavior of the X partial are discussed with the CL results.

  15. Effects of Implantation Temperature and Ion Flux on Damage Accumulation in Al-Implanted 4H-SiC

    SciTech Connect

    Zhang, Yanwen; Weber, William J.; Jiang, Weilin; Wang, Chong M.; Hallen, Anders; Possnert, Goran

    2003-02-15

    The effects of implantation temperature and ion flux on damage accumulation on both the Si and C sublattices in 4H-SiC are investigated under 1.1 MeV Al irradiation at temperatures from 150 to 450 K. The rate of damage accumulation decreases dramatically and the damage profile sharpens due to significant dynamic recovery at temperatures close to the critical temperature for amorphization. At 450 K, the relative disorder and the density of planar defects increase rapidly with the increasing ion flux, exhibiting saturation at high ion fluxes. Planar defects are generated through the agglomeration of excess Si and C interstitials during irradiation and post-irradiation annealing at 450 K. Termination of (0001) planes is attributed to the accumulation of vacancies. A volume expansion of {approx}8% is observed for the peak damage region.

  16. Parity violation energies of C4H4X2 molecules for X = O, S, Se, Te and Po†

    NASA Astrophysics Data System (ADS)

    Pelloni, Stefano; Faglioni, Francesco; Lazzeretti, Paolo

    2013-09-01

    Parity-violating contributions, with the same magnitude but opposite sign, to the energies of 1,2 enantiomers of dioxin, dithiin, diselenin, ditellurin and dipolonin have been calculated. Theoretical predictions, which can be classified among the largest reported so far, indicate that the P enantiomer is energetically more stable than M. As expected, parity-violating effects increase with the first power of the neutron number and the fourth power of the atomic number for X = O, S, Se, Te and Po. The trend predicted by Laerdahl and Schwerdtfeger [Phys. Rev. A 60, 4439 (1999)] and by Berger [J. Chem. Phys. 129, 154105 (2008)] for H2X2 molecules, characterised by free rotation about the X-X internuclear axis, is therefore confirmed for the series of more rigid C4H4X2 compounds, in which limited deformations can take place.

  17. A Diels–Alder super diene breaking benzene into C2H2 and C4H4 units

    PubMed Central

    Inagaki, Yusuke; Nakamoto, Masaaki; Sekiguchi, Akira

    2014-01-01

    Cyclic polyene with six carbon atoms (benzene) is very stable, whereas cyclic polyene with four carbon atoms (cyclobutadiene) is extremely unstable. The electron-withdrawing pentafluorophenyl group of a substituted cyclobutadiene lowers the energy of the lowest unoccupied molecular orbital, greatly increasing its reactivity as a diene in Diels–Alder reactions with acetylene, ethylene and even benzene. Here we show that the reaction with benzene occurs cleanly at the relatively low temperature of 120 °C and results in the formal fragmentation of benzene into C2H2 and C4H4 units, via a unique Diels–Alder/retro-Diels–Alder reaction. This is a new example of the rare case where breaking the C–C bond of benzene is possible with no activation by a transition metal. PMID:24398593

  18. Single freezing and triple melting of micrometre-scaled (NH4)2SO4/H2O droplets.

    PubMed

    Bogdan, Anatoli; Molina, Mario J; Tenhu, Heikki; Loerting, Thomas

    2011-11-28

    Atmospheric aerosol droplets containing NH(4)(+) and SO(4)(2-) ions are precursors of cirrus ice clouds. However, the low-temperature phase transformation of such droplets is not understood yet. Here we show for the first time that micrometre-scaled (NH(4))(2)SO(4)/H(2)O droplets produce one freezing event but three melting events which are the melting of (i) pure ice, (ii) eutectic ice/(NH(4))(2)SO(4), and (iii) eutectic ice/(NH(4))(3)H(SO(4))(2). We also find that the melting of ice/(NH(4))(3)H(SO(4))(2) consists of two eutectic melting events, presumably ice/letovicite-II and ice/letovicite-III.

  19. Coexistence of ferroelectric and antiferroelectric microregions in the paraelectric phase of NH 4H 2PO 4 (ADP)

    NASA Astrophysics Data System (ADS)

    Lasave, J.; Koval, S.; Migoni, R. L.

    2009-10-01

    Ammonium dihydrogen phosphate NH 4H 2PO 4 (ADP) is an antiferroelectric (AFE) compound belonging to the KDP-type family of hydrogen-bonded ferroelectrics. Recent ab initio results have shown that the optimization of the N-H-O bridges in ADP leads to the stabilization of the AFE state over a FE one. However, electron spin probe measurements have suggested that microregions of both phases may coexist above the critical antiferroelectric-paraelectric transition temperature. We have performed first principles studies of the energetics and relative stability of different AFE and FE defects embedded in a paraelectric (PE) matrix of ADP. Our analysis indicates that FE and AFE clusters are stable and may coexist in the PE phase, thus confirming the above suggestion.

  20. Vibrational spectroscopic study of the mineral pitticite Fe, AsO 4, SO 4, H 2O

    NASA Astrophysics Data System (ADS)

    Frost, Ray L.; Xi, Yunfei; Tan, Keqin; Millar, Graeme J.; Palmer, Sara J.

    2012-01-01

    Some minerals are colloidal and show no X-ray diffraction patterns. Vibrational spectroscopy offers one of the few methods for the determination of the structure of these minerals. Among this group of minerals is pitticite, simply described as (Fe, AsO 4, SO 4, H 2O). In this work, the analogue of the mineral pitticite has been synthesised. The objective of this research is to determine the molecular structure of the mineral pitticite using vibrational spectroscopy. Raman and infrared bands are attributed to the AsO 43-, SO 42- and water stretching and bending vibrations. The Raman spectrum of the pitticite analogue shows intense peaks at 845 and 837 cm -1 assigned to the AsO 43- stretching vibrations. Raman bands at 1096 and 1182 cm -1 are attributed to the SO 42- antisymmetric stretching bands. Raman spectroscopy offers a useful method for the analysis of such colloidal minerals.

  1. Quantitative comparison between Z{sub 1∕2} center and carbon vacancy in 4H-SiC

    SciTech Connect

    Kawahara, Koutarou Suda, Jun; Kimoto, Tsunenobu; Thang Trinh, Xuan; Tien Son, Nguyen; Janzén, Erik

    2014-04-14

    In this study, to reveal the origin of the Z{sub 1∕2} center, a lifetime killer in n-type 4H-SiC, the concentrations of the Z{sub 1∕2} center and point defects are compared in the same samples, using deep level transient spectroscopy (DLTS) and electron paramagnetic resonance (EPR). The Z{sub 1∕2} concentration in the samples is varied by irradiation with 250 keV electrons with various fluences. The concentration of a single carbon vacancy (V{sub C}) measured by EPR under light illumination can well be explained with the Z{sub 1∕2} concentration derived from C-V and DLTS irrespective of the doping concentration and the electron fluence, indicating that the Z{sub 1∕2} center originates from a single V{sub C}.

  2. High-Field Fast-Risetime Pulse Failures in 4H- and 6H-SiC pn Junction Diodes

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Fazi, Christian

    1996-01-01

    We report the observation of anomalous reverse breakdown behavior in moderately doped (2-3 x 10(exp 17 cm(exp -3)) small-area micropipe-free 4H- and 6H-SiC pn junction diodes. When measured with a curve tracer, the diodes consistently exhibited very low reverse leakage currents and sharp repeatable breakdown knees in the range of 140-150 V. However, when subjected to single-shot reverse bias pulses (200 ns pulsewidth, 1 ns risetime), the diodes failed catastrophically at pulse voltages of less than 100 V. We propose a possible mechanism for this anomalous reduction in pulsed breakdown voltage relative to dc breakdown voltage. This instability must be removed so that SiC high-field devices can operate with the same high reliability as silicon power devices.

  3. Measured Propagation Characteristics of Coplanar Waveguide on Semi-Insulating 4H-SiC Through 800 K

    NASA Technical Reports Server (NTRS)

    Ponchak, George E.; Alterovitz, Samuel A.; Downey, Alan N.; Freeman, Jon C.; Schwartz, Zachary D.

    2003-01-01

    Wireless sensors for high temperature industrial applications and jet engines require RF transmission lines and RF integrated circuits (RFICs) on wide bandgap semiconductors such as SiC. In this paper, the complex propagation constant of coplanar waveguide fabricated on semiinsulating 4H-SiC has been measured through 813 K. It is shown that the attenuation increases 3.4 dB/cm at 50 GHz as the SiC temperature is increased from 300 K to 813 K. Above 500 K, the major contribution to loss is the decrease in SiC resistivity. The effective permittivity of the same line increases by approximately 5 percent at microwave frequencies and 20 percent at 1 GHz.

  4. Scalable control of graphene growth on 4H-SiC C-face using decomposing silicon nitride masks

    NASA Astrophysics Data System (ADS)

    Puybaret, Renaud; Hankinson, John; Palmer, James; Bouvier, Clément; Ougazzaden, Abdallah; Voss, Paul L.; Berger, Claire; de Heer, Walt A.

    2015-04-01

    Selective epitaxial graphene growth is achieved in pre-selected areas on the 4H-SiC(0 0 0 \\bar{1}) C-face with a SiN masking method. The mask decomposes during the growth process leaving a clean, resist free, high temperature annealed graphene surface, in a one-step process. Depending on the off-stoichiometry composition of a Si3 + xN4 mask evaporated on SiC prior to graphitization, the number of layers on the C-face increases (Si-rich) or decreases (N-rich). Graphene grown in masked areas shows excellent quality as observed by Raman spectroscopy, atomic force microscopy and transport data.

  5. Synthesis of a novel 4H-pyran analog as minor groove binder to DNA using ethidium bromide as fluorescence probe.

    PubMed

    Ramana, M M V; Betkar, Rahul; Nimkar, Amey; Ranade, Prasanna; Mundhe, Balaji; Pardeshi, Sachin

    2016-01-01

    In the present work, isopropyl-6-amino-4-(3,5-bis(trifluoromethyl)phenyl)-5-cyano-2-methyl-4H-pyran-3-carboxylate (4H-pyran analog) has been synthesized by a three component reaction catalyzed by CsOH/γ-Al2O3 and characterized. The interaction of 4H-pyran analog with herring sperm DNA (hs DNA) under physiological conditions (phosphate buffer of pH 7.2) was investigated by UV absorption, FT-IR, fluorescence, (31)P NMR and circular dichroism (CD) spectroscopy. Fluorescence quenching results reveal that static quenching mechanism is involved in binding between 4H-pyran analog and hs DNA. The calculated thermodynamic parameters (ΔH° and ΔS°) indicate that hydrogen bonding plays a major role in binding between them. UV absorption and fluorescence shows the binding mode of 4H-pyran analog with hs DNA as non-intercalative. According to the IR spectroscopy, 4H-pyran analog binds to guanine, thymine, adenine bases of hs DNA but not to phosphate backbone of hs DNA which is also in good agreement with (31)P NMR results. CD and competitive binding experiment results confirms the minor groove binding of 4H-pyran analog to hs DNA.

  6. Synthesis of a novel 4H-pyran analog as minor groove binder to DNA using ethidium bromide as fluorescence probe

    NASA Astrophysics Data System (ADS)

    Ramana, M. M. V.; Betkar, Rahul; Nimkar, Amey; Ranade, Prasanna; Mundhe, Balaji; Pardeshi, Sachin

    2016-01-01

    In the present work, isopropyl-6-amino-4-(3,5-bis(trifluoromethyl)phenyl)-5-cyano-2-methyl-4H-pyran-3-carboxylate (4H-pyran analog) has been synthesized by a three component reaction catalyzed by CsOH/γ-Al2O3 and characterized. The interaction of 4H-pyran analog with herring sperm DNA (hs DNA) under physiological conditions (phosphate buffer of pH 7.2) was investigated by UV absorption, FT-IR, fluorescence, 31P NMR and circular dichroism (CD) spectroscopy. Fluorescence quenching results reveal that static quenching mechanism is involved in binding between 4H-pyran analog and hs DNA. The calculated thermodynamic parameters (ΔH° and ΔS°) indicate that hydrogen bonding plays a major role in binding between them. UV absorption and fluorescence shows the binding mode of 4H-pyran analog with hs DNA as non-intercalative. According to the IR spectroscopy, 4H-pyran analog binds to guanine, thymine, adenine bases of hs DNA but not to phosphate backbone of hs DNA which is also in good agreement with 31P NMR results. CD and competitive binding experiment results confirms the minor groove binding of 4H-pyran analog to hs DNA.

  7. Current Status of the Quality of 4H-SiC Substrates and Epilayers for Power Device Applications

    SciTech Connect

    Dudley, M.; Wang, H.; Guo, Jianqiu; Yang, Yu; Raghothamachar, Balaji; Zhang, J.; Thomas, B.; Chung, G.; Sanchez, E. K.; Hansen, D.; Mueller, S. G.

    2016-01-01

    ABSTRACT

    Interfacial dislocations (IDs) and half-loop arrays (HLAs) present in the epilayers of 4H-SiC crystal are known to have a deleterious effect on device performance. Synchrotron X-ray Topography studies carried out on n-type 4H-SiC offcut wafers before and after epitaxial growth show that in many cases BPD segments in the substrate are responsible for creating IDs and HLAs during CVD growth. This paper reviews the behaviors of BPDs in the substrate during the epitaxial growth in different cases: (1) screw-oriented BPD segments intersecting the surface replicate directly through the interface during the epitaxial growth and take part in stress relaxation process by creating IDs and HLAs (Matthews-Blakeslee model [1] ); (2) non-screw oriented BPD half loop intersecting the surface glides towards and replicates through the interface, while the intersection points convert to threading edge dislocations (TEDs) and pin the half loop, leaving straight screw segments in the epilayer and then create IDs and HLAs; (3) edge oriented short BPD segments well below the surface get dragged towards the interface during epitaxial growth, leaving two long screw segments in their wake, some of which replicate through the interface and create IDs and HLAs. The driving force for the BPDs to glide toward the interface is thermal stress and driving force for the relaxation process to occur is the lattice parameter difference at growth temperature which results from the doping concentration difference between the substrate and epilayer.

  8. Developing Physics-based Models for 4H-SiC High Voltage Power Switches---MOSFET, IGBT and GTO

    NASA Astrophysics Data System (ADS)

    Lee, Meng-Chia

    The goal of this dissertation is to develop physics-based equivalent circuit models for 15kV˜20kV 4H-SiC power switches. The previous modeling works will be reviewed, and the parameter extraction methodologies will be discussed. MOSFET is modeled using a voltage-controlled current source for channel current and three nonlinear capacitances for the transient behavior. The high electron saturation velocity and its effect on the saturation current level will also be discussed. Final model has been implemented in Simulink/Matlab, and the execution time for the turn-on and off transient is less than 1 second. IGBT Analytical model that translate the local excess carrier to the diffusion capacitance will be derived first and implemented in a sub-circuit manner into Simulink/Matlab. A novel parameter extraction technique---Excess carrier density mapping (ECDM)---using inductive switching waveforms is introduced. The execution time of the model is about 7 seconds and 2 seconds for a turn-off and turn-on transient, respectively. IGBTs with two-zone drift region for slowing down the turn-off dv/dt are also proposed based on the developed analytical model. Finally, 4H-SiC p-GTO model based on the IGBT one is developed. Region-wise lifetimes throughout the drift region was observed when using the proposed ECDM technique. Simulated waveforms using region-wise lifetime have shown better fitting results than the case using constant lifetime. The difference between n-type and p-type ambipolar switches will be discussed and compared using the developed models.

  9. Detection of fast neutrons from D-T nuclear reaction using a 4H-SiC radiation detector

    NASA Astrophysics Data System (ADS)

    Zatko, Bohumir; Sagatova, Andrea; Sedlackova, Katarina; Necas, Vladimir; Dubecky, Frantisek; Solar, Michael; Granja, Carlos

    2016-09-01

    The particle detector based on a high purity epitaxial layer of 4H-SiC exhibits promising properties in detection of various types of ionizing radiation. Due to the wide band gap of 4H-SiC semiconductor material, the detector can reliably operate at room and also elevated temperatures. In this work we focused on detection of fast neutrons generated the by D-T (deuterium-tritium) nuclear reaction. The epitaxial layer with a thickness of 105 μm was used as a detection part. A circular Schottky contact of a Au/Ni double layer was evaporated on both sides of the detector material. The detector structure was characterized by current-voltage and capacitance-voltage measurements, at first. The results show very low current density (<0.1 nA/cm2) at room temperature and good homogeneity of free carrier concentration in the investigated depth. The fabricated detectors were tested for detection of fast neutrons generated by the D-T reaction. The energies of detected fast neutrons varied from 16.0 MeV to 18.3 MeV according to the acceleration potential of deuterons, which increased from 600 kV up to 2 MV. Detection of fast neutrons in the SiC detector is caused by the elastic and inelastic scattering on the silicon or carbide component of the detector material. Another possibility that increases the detection efficiency is the use of a conversion layer. In our measurements, we glued a HDPE (high density polyethylene) conversion layer on the detector Schottky contact to transform fast neutrons to protons. Hydrogen atoms contained in the conversion layer have a high probability of interaction with neutrons through elastic scattering. Secondary generated protons flying to the detector can be easily detected. The detection properties of detectors with and without the HDPE conversion layer were compared.

  10. Interface annealing characterization of Ti/Al/Au ohmic contacts to p-type 4H-SiC

    NASA Astrophysics Data System (ADS)

    Chao, Han; Yuming, Zhang; Qingwen, Song; Xiaoyan, Tang; Hui, Guo; Yimen, Zhang; Fei, Yang; Yingxi, Niu

    2015-12-01

    Ti/Al/Au ohmic contacts to p-type 4H-SiC in terms of a different annealing time and Ti composition are reported. At 1050 °C, proper increase in annealing time plays a critical role in the Schottky to ohmic contact conversion. With the optimized annealing time, the contact with a high Ti content yields a lower specific contact resistivity (ρc) of 6.4 × 10-5 Ω·cm2 compared with the low-Ti contact. The annealed surface morphology and phase resultants were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. For the better ohmic contact, element distribution and chemical states were qualitatively identified by X-ray photoelectron spectroscopy (XPS) depth analysis. In particular, the presence of C and a Si-related phase was discussed and associated with the change in the surface status of the as-grown epilayer of 4H-SiC during annealing. The results reveal that the out-diffused C and Si atoms, with an approximate atomic ratio of 1 : 1 in the contact layer, can combine to form an amorphous Si-C state. The polycrystalline graphite instead of an unreacted C cluster in the whole alloyed structure and an extra nanosize graphite flake on the outermost surface of the annealed contact were confirmed by Raman spectroscopy. Project supported by the Key Specific Projects of Ministry of Education of China (No. 625010101), the Specific Project of the Core Devices (No. 2013ZX01001001-004), and the Science Project of State Grid (No. SGRI-WD-71-14-004).

  11. Thermal Measurement during Electrolysis of Pd-Ni Thin-film -Cathodes in Li2SO4/H2O Solution

    NASA Astrophysics Data System (ADS)

    Castano, C. H.; Lipson, A. G.; S-O, Kim; Miley, G. H.

    2002-03-01

    Using LENR - open type calorimeters, measurements of excess heat production were carried out during electrolysis in Li_2SO_4/H_2O solution with a Pt-anode and Pd-Ni thin film cathodes (2000-8000 Åthick) sputtered on the different dielectric substrates. In order to accurately evaluate actual performance during electrolysis runs in the open-type calorimeter used, considering effects of heat convection, bubbling and possible H_2+O2 recombination, smooth Pt sheets were used as cathodes. Pt provides a reference since it does not produce excess heat in the light water electrolyte. To increase the accuracy of measurements the water dissociation potential was determined for each cathode taking into account its individual over-voltage value. It is found that this design for the Pd-Ni cathodes resulted in the excess heat production of ~ 20-25 % of input power, equivalent to ~300 mW. In cases of the Pd/Ni- film fracture (or detachment from substrate) no excess heat was detected, providing an added reference point. These experiments plus use of optimized films will be presented.

  12. Infrared and Raman spectroscopic studies of the amino—imino tautomerism in 2-substituted 4,4-pentamethylene-5-amino-4 H-imidazole derivatives—II

    NASA Astrophysics Data System (ADS)

    Avendaño, C.; Ramos, M. T.; Bellanato, J.

    In continuation of previous work, nine 2-substituted 4,4-pentamethylene-5-amino-4 H-imidazole derivatives and 2-pyridyl-5,5(4.4)-pentamethylene-4(5)-imidazolone have been studied by i.r. and Raman spectroscopy. The amino—imino tautomerism of the amino-4 H-imidazoles has been studied. Other possible tautomeric forms in some compounds are also discussed.

  13. Investigation of spatial charge distribution and electrical dipole in atomic layer deposited Al2O3 on 4H-SiC

    NASA Astrophysics Data System (ADS)

    Han, Kai; Wang, Xiaolei; Yuan, Li; Wang, Wenwu

    2016-06-01

    Charge distribution and electrical dipole in an Al2O3/4H-SiC structure are investigated by capacitance–voltage measurement and x-ray photoelectron spectroscopy (XPS). The charge densities in Al2O3 and at the Al2O3/4H-SiC interface are negligible and  ‑6.89  ×  1011 cm‑2, respectively. Thus the small charge amount indicates the suitability of Al2O3 as a gate dielectric. The dipole at the Al2O3/4H-SiC interface is  ‑0.3 to  ‑0.91 V. The XPS manifests electron transfer from Al2O3 to 4H-SiC. The dipole formation is explained by a gap state model and the higher charge neutrality level of Al2O3 than the Fermi level of 4H-SiC, which confirms the feasibility of the gap state model on investigating band lineup at heterojunctions. The electrical dipole at the Al2O3/4H-SiC interface is critical for threshold voltage tuning. These results are helpful in engineering the SiC based gate stacks.

  14. Thermoelectric properties of the 3C, 2H, 4H, and 6H polytypes of the wide-band-gap semiconductors SiC, GaN, and ZnO

    SciTech Connect

    Huang, Zheng; Lü, Tie-Yu; Wang, Hui-Qiong; Zheng, Jin-Cheng

    2015-09-15

    We have investigated the thermoelectric properties of the 3C, 2H, 4H, and 6H polytypes of the wide-band-gap(n-type) semiconductors SiC, GaN, and ZnO based on first-principles calculations and Boltzmann transport theory. Our results show that the thermoelectric performance increases from 3C to 6H, 4H, and 2H structures with an increase of hexagonality for SiC. However, for GaN and ZnO, their power factors show a very weak dependence on the polytype. Detailed analysis of the thermoelectric properties with respect to temperature and carrier concentration of 4H-SiC, 2H-GaN, and 2H-ZnO shows that the figure of merit of these three compounds increases with temperature, indicating the promising potential applications of these thermoelectric materials at high temperature. The significant difference of the polytype-dependent thermoelectric properties among SiC, GaN, and ZnO might be related to the competition between covalency and ionicity in these semiconductors. Our calculations may provide a new way to enhance the thermoelectric properties of wide-band-gap semiconductors through atomic structure design, especially hexagonality design for SiC.

  15. Nondestructive dislocation delineation using topographically enhanced imaging of surface morphologies in 4H-SiC epitaxial layers

    NASA Astrophysics Data System (ADS)

    Picard, Yoosuf N.; Liu, Kendrick X.; Stahlbush, Robert E.; Twigg, Mark E.; Zhang, Xuan; Skowronski, Marek

    2008-04-01

    The morphology of surface features generated by dislocations present at 4H-SiC epitaxial layer surfaces was investigated by forescattered electron detection (FED) inside a conventional scanning electron microscope. Various growth pit morphologies were correlated to dislocation types using molten KOH etching. Specifically, sharp-apex pits and stripe-shaped pits were consistently linked to screw and edge dislocations, respectively. The size and depth of these growth pits were measured by atomic force microscopy (AFM). Tail-like features were observed by FED emanating from sharp-apex pits and verified by Nomarski optical microscopy (NOM). A mechanism is proposed to explain the FED contrast exhibited by these tail-like features. This mechanism relates the nature of step-flow and spiral growth in the wake of a screw dislocation to the surface distortions resulting in such tail-like features. The Burgers vector direction can thus be determined based on a purely morphological analysis of these tail-like features. The results of this study illustrate the various capabilities of FED for surface imaging as compared to AFM and NOM. The potential for utilizing FED to map dislocation-associated growth pits is discussed.

  16. Synthesis, characterization and DFT studies of diethyl 4-hydroxy-6-nitro-4H-chromene-2,3-dicarboxylate

    NASA Astrophysics Data System (ADS)

    Dinparast, Leila; Valizadeh, Hassan; Vessally, Esmail; Bahadori, Mir Babak

    2016-02-01

    In the present study, diethyl 4-hydroxy-6-nitro-4H-chromene-2,3-dicarboxylate (DHNC) was synthesized and characterized using FT-IR, 1H and 13CNMR spectroscopy, mass spectrometry and UV-Vis (200-700 nm, in DMSO) spectrum. The structure of the title molecule was optimized at the B3LYP and PBE1PBE levels of theory using 6-311++G(d,p) basis set. The fundamental vibrational modes and chemical shifts of 1H and 13C of the present molecule were calculated using the B3LYP/6-311++G(d,p) and PBE1PBE/6-311++G(d,p) methods. UV-Vis spectrum of the title molecule was also calculated in DMSO and gas phase. The high stability and charge delocalization of DHNC arising from intramolecular hyperconjugative interaction confirmed with the NBO analysis at two DFT methods. Theoretical studies of the molecular orbitals such as HOMO-LUMO energy gap, mapped molecular electrostatic potential (MEP) surfaces and the Mulliken and NBO charges were also performed with the same levels of theory. In this work, the computed results and experimental observations support well each other.

  17. Elimination of carbon vacancies in 4H-SiC employing thermodynamic equilibrium conditions at moderate temperatures

    SciTech Connect

    Ayedh, H. M.; Svensson, B. G.; Hallén, A.

    2015-12-21

    The carbon vacancy (V{sub C}) is a major point defect in high-purity 4H-SiC epitaxial layers limiting the minority charge carrier lifetime. In layers grown by chemical vapor deposition techniques, the V{sub C} concentration is typically in the range of 10{sup 12 }cm{sup −3}, and after device processing at temperatures approaching 2000 °C, it can be enhanced by several orders of magnitude. In the present study, both as-grown layers and a high-temperature processed one have been annealed at 1500 °C and the V{sub C} concentration is demonstrated to be strongly reduced, exhibiting a value of only a few times 10{sup 11 }cm{sup −3} as determined by deep-level transient spectroscopy measurements. The value is reached already after annealing times on the order of 1 h and is evidenced to reflect thermodynamic equilibrium under C-rich ambient conditions. The physical processes controlling the kinetics for establishment of the V{sub C} equilibrium are estimated to have an activation energy below ∼3 eV and both in-diffusion of carbon interstitials and out-diffusion of V{sub C}'s are discussed as candidates. This concept of V{sub C} elimination is flexible and readily integrated in a materials and device processing sequence.

  18. Atomic-Level Simulations of Epitaxial Recrystallization and Amorphous-to-Crystalline Transition in 4H-SiC

    SciTech Connect

    Gao, Fei; Zhang, Yanwen; Posselt, Matthias; Weber, William J.

    2006-09-01

    The amorphous-to-crystalline (a-c) transition in 4H-SiC has been studied using molecular dynamics (MD) methods, with simulation times of up to a few hundred ns and at temperatures ranging from 1000 to 2000 K. Two nano-sized amorphous layers, one with the normal of a-c interfaces along the [ -12-10] direction and the other along the [ -1010] direction, were created within a crystalline cell to study expitaxial recrystallization and the formation of secondary phases. The recovery of bond defects at the interfaces is an important process driving the epitaxial recrystallization of the amorphous layers. The amorphous layer with the a-c interface normal along the [-12-10] direction can be completely recrystallized at the temperatures of 1500 and 2000 K, but the recrystallized region is defected with dislocations and stacking faults. On the other hand, the recrystallization process for the a-c interface normal along [-1010] direction is hindered by the nucleation of polycrystalline phases, and these secondary ordered phases are stable for longer simulation times. A general method to calculate activation energy spectra is employed to analyze the MD annealing simulations, and the recrystallization mechanism in SiC consists of multiple stages with activation energies ranging from 0.8 to 1.7 eV.

  19. Barrier inhomogeneities and electronic transport of Pt contacts to relatively highly doped n-type 4H-SiC

    SciTech Connect

    Huang, Lingqin E-mail: dwang121@dlut.edu.cn; Wang, Dejun E-mail: dwang121@dlut.edu.cn

    2015-05-28

    The barrier characteristics of Pt contacts to relatively highly doped (∼1 × 10{sup 18 }cm{sup −3}) 4H-SiC were investigated using current-voltage (I-V) and capacitance-voltage (C-V) measurements in the temperature range of 160–573 K. The barrier height and ideally factor estimated from the I-V characteristics based on the thermionic emission model are abnormally temperature-dependent, which can be explained by assuming the presence of a double Gaussian distribution (GD) of inhomogeneous barrier heights. However, in the low temperature region (160–323 K), the obtained mean barrier height according to GD is lower than the actual mean value from C-V measurement. The values of barrier height determined from the thermionic field emission model are well consistent with those from the C-V measurements, which suggest that the current transport process could be modified by electron tunneling at low temperatures.

  20. Long range lateral migration of intrinsic point defects in n-type 4H-SiC

    SciTech Connect

    Loevlie, L. S.; Vines, L.; Svensson, B. G.

    2012-05-15

    The lateral distributions of intrinsic point defects in n-type (0001) 4H-SiC have been investigated following room temperature irradiation with a focused beam of 10 keV protons. Laterally resolved deep level transient spectroscopy measurements reveal that the well-known and prominent Z{sub 1/2} and S{sub 1/2} centers display lateral diffusion lenghts on the order of 1 mm with negligible (if any) motion parallel to the direction of the c-axis. The migration occurs only in the presence of excess charge carriers generated during the proton irradiation, and no further motion takes place even under subsequent optical excitation of high intensity. Assuming one-dimensional geometry, an effective defect diffusivity in excess of 10{sup -6} cm{sup 2}/s is deduced by numerical modelling of the experimental data, corresponding to an energy barrier for migration of {approx}0.2 eV. Possible mechanisms for the rapid migration, invoking charge carrier recombination as a necessary condition, are discussed, and especially, an association with the glide of partial dislocations along the (0001) basal plane is scrutinized in some detail.

  1. Lattice mismatch and crystallographic tilt induced by high-dose ion-implantation into 4H-SiC

    NASA Astrophysics Data System (ADS)

    Sasaki, S.; Suda, J.; Kimoto, T.

    2012-05-01

    Lattice parameters of high-dose ion-implanted 4H-SiC were investigated with reciprocal space mapping (RSM). N, P, Al, or (C+Si) ions were implanted into lightly doped epilayers to form a (330-520) nm-deep box profile with concentrations of 1019-1020atoms/cm3. After activation annealing at 1800 °C, RSM measurements were conducted. The RSM images for (0008) reflection revealed that high-dose ion implantation causes c-lattice expansion in implanted layers, irrespective of ion species. In addition, crystallographic tilt was observed after high-dose ion implantation. The tilt direction is the same for all the samples investigated; the c-axis of the implanted layers is inclined toward the ascending direction of the off-cut. The c-lattice mismatch and the tilt angle increased as the implantation dose increases, indicating that the implantation damage is responsible for the lattice parameter change. From these results and transmission electron microscopy observation, the authors conclude that the c-lattice mismatch and the crystallographic tilt are mainly caused by secondary defects formed after the ion-implantation and activation-annealing process.

  2. Atmospheric pressure route to epitaxial nitrogen-doped trilayer graphene on 4H-SiC (0001) substrate

    SciTech Connect

    Boutchich, M.; Arezki, H.; Alamarguy, D.; Güneş, F.; Alvarez, J.; Kleider, J. P.; Ho, K.-I.; Lai, C. S.; Sediri, H.; Ouerghi, A.

    2014-12-08

    Large-area graphene film doped with nitrogen is of great interest for a wide spectrum of nanoelectronics applications, such as field effect devices, super capacitors, and fuel cells among many others. Here, we report on the structural and electronic properties of nitrogen doped trilayer graphene on 4H-SiC (0001) grown under atmospheric pressure. The trilayer nature of the growth is evidenced by scanning transmission electron microscopy. X-ray photoelectron spectroscopy shows the incorporation of 1.2% of nitrogen distributed in pyrrolic-N, and pyridinic-N configurations as well as a graphitic-N contribution. This incorporation causes an increase in the D band on the Raman signature indicating that the nitrogen is creating defects. Ultraviolet photoelectron spectroscopy shows a decrease of the work function of 0.3 eV due to the N-type doping of the nitrogen atoms in the carbon lattice and the edge defects. A top gate field effect transistor device has been fabricated and exhibits carrier mobilities up to 1300 cm{sup 2}/V s for holes and 850 cm{sup 2}/V s for electrons at room temperature.

  3. Feature Modeling of HfO2 Atomic Layer Deposition Using HfCl4/H2O

    NASA Astrophysics Data System (ADS)

    Stout, Phillip J.; Adams, Vance; Ventzek, Peter L. G.

    2003-03-01

    A Monte Carlo based feature scale model (Papaya) has been applied to atomic layer deposition (ALD) of HfO2 using HfCl_4/H_20. The model includes physical effects of transport to surface, specular and diffusive reflection within feature, adsorption, surface diffusion, deposition and etching. Discussed will be the 3D feature modeling of HfO2 deposition in assorted features (vias and trenches). The effect of feature aspect ratios, pulse times, cycle number, and temperature on film thickness, feature coverage, and film Cl fraction (surface/bulk) will be discussed. Differences between HfO2 ALD on blanket wafers and in features will be highlighted. For instance, the minimum pulse times sufficient for surface reaction saturation on blanket wafers needs to be increased when depositing on features. Also, HCl products created during the HfCl4 and H_20 pulses are more likely to react within a feature than at the field, reducing OH coverage within the feature (vs blanket wafer) thus limiting the maximum coverage attainable for a pulse over a feature.

  4. Electron trapping in 4H-SiC MOS capacitors fabricated by pre-oxidation nitrogen implantation

    NASA Astrophysics Data System (ADS)

    Basile, A. F.; Dhar, S.; Mooney, P. M.

    2011-06-01

    Incorporation of nitrogen (N) atoms by ion implantation prior to oxidation of SiO2/4H-SiC interfaces has been investigated by capacitance-voltage (C-V) characteristics and constant capacitance deep-level-transient spectroscopy (CCDLTS) measurements. The shift of the C-V curves to negative voltages can be explained by the partial activation of implanted N atoms during oxidation. The maximum amplitude of the CCDLTS spectra, proportional to the density of near-interface oxide traps, decreases with increasing N dose, but remains significantly larger than that of SiO2/SiC interfaces fabricated by post oxidation annealing in nitric oxide (NO). Intrinsic defects in the SiC epi-layer associated with implantation damage are also observed in N-implanted samples. In contrast, electron traps energetically close to the SiC conduction band, detected in NO annealed samples and presumably introduced during oxidation, are not observed in N-implanted samples. The improved transport characteristics of MOS transistors fabricated on N-implanted epi-layers compared to those fabricated by NO annealing is suggested to result from the effects of the greater N donor concentration and also possibly to the suppression of shallow electron traps in the SiC epilayer.

  5. Static and Turn-on Switching Characteristics of 4H-Silicon Carbide SITs to 200 deg C

    NASA Technical Reports Server (NTRS)

    Niedra, Janis M.; Schwarze, Gene E.

    2005-01-01

    Test results are presented for normally-off 4H-SiC Static Induction Transistors (SITs) intended for power switching and are among the first normally-off such devices realized in SiC. At zero gate bias, the gate p-n junction depletion layers extend far enough into the conduction channel to cut off the channel. Application of forward gate bias narrows the depletion regions, opening up the channel to conduction by majority carriers. In the present devices, narrow vertical channels get pinched by depletion regions from opposite sides. Since the material is SiC, the devices are usable at temperatures above 150 C. Static curve and pulse mode switching observations were done at selected temperatures up to 200 C on a device with average static characteristics from a batch of similar devices. Gate and drain currents were limited to about 400 mA and 3.5 A, respectively. The drain voltage was limited to roughly 300 V, which is conservative for this 600 V rated device. At 23 C, 1 kW, or even more, could be pulse mode switched in 65 ns (10 to 90 percent) into a 100 load. But at 200 C, the switching capability is greatly reduced in large part by the excessive gate current required. Severe collapse of the saturated drain-to-source current was observed at 200 C. The relation of this property to channel mobility is reviewed.

  6. A unified equation for calculating methane vapor pressures in the CH4-H2O system with measured Raman shifts

    USGS Publications Warehouse

    Lu, W.; Chou, I.-Ming; Burruss, R.C.; Song, Y.

    2007-01-01

    A unified equation has been derived by using all available data for calculating methane vapor pressures with measured Raman shifts of C-H symmetric stretching band (??1) in the vapor phase of sample fluids near room temperature. This equation eliminates discrepancies among the existing data sets and can be applied at any Raman laboratory. Raman shifts of C-H symmetric stretching band of methane in the vapor phase of CH4-H2O mixtures prepared in a high-pressure optical cell were also measured at temperatures between room temperature and 200 ??C, and pressures up to 37 MPa. The results show that the CH4 ??1 band position shifts to higher wavenumber as temperature increases. We also demonstrated that this Raman band shift is a simple function of methane vapor density, and, therefore, when combined with equation of state of methane, methane vapor pressures in the sample fluids at elevated temperatures can be calculated from measured Raman peak positions. This method can be applied to determine the pressure of CH4-bearing systems, such as methane-rich fluid inclusions from sedimentary basins or experimental fluids in hydrothermal diamond-anvil cell or other types of optical cell. ?? 2007 Elsevier Ltd. All rights reserved.

  7. Structure of the interface between ultrathin SiO{sub 2} films and 4H-SiC(0001)

    SciTech Connect

    Schuermann, Mark; Dreiner, Stefan; Berges, Ulf; Westphal, Carsten

    2006-07-15

    The interface between ultrathin SiO{sub 2} films and 4H-SiC(0001) has been studied by x-ray photoelectron spectroscopy (XPS) and photoelectron diffraction. The investigation was performed for two different films. An ordered silicate layer showed a clear ({radical}(3)x{radical}(3))R30 deg. reconstruction, whereas a second film showed no long-range order. The comparison of the photoelectron diffraction data from these two films reveals that the local atomic environments of the Si atoms at the interface are very similar in both films. Further, a comparison of the experimental data with simulation calculations within a comprehensive R-factor analysis shows that also the local environments around near-interface Si atoms inside the SiO{sub 2} film are similar, but some modifications to the model are necessary. The use of the cluster radius as a fitting parameter in the simulation allowed to estimate the size of locally ordered regions in the film without long-range order to be about 4.5 to 5.0 A ring . It turns out that the transition from SiC to SiO{sub 2} is abrupt and therefore the occurrence of defects in the SiO{sub 2} film near the interface is probable. These defects may be oxygen vacancies, oxygen dangling bonds or silicon interstitials.

  8. Characteristics and analysis of 4H-SiC PiN diodes with a carbon-implanted drift layer

    NASA Astrophysics Data System (ADS)

    Jiangmei, Feng; Huajun, Shen; Xiaohua, Ma; Yun, Bai; Jia, Wu; Chengzhan, Li; Kean, Liu; Xinyu, Liu

    2016-04-01

    The characteristics of 4H-SiC PiN diodes with a carbon-implanted drift layer was investigated and the reason of characteristics improvement was analyzed. The forward voltage drops of the diodes with carbon-implanted drift layer were around 3.3 V, which is lower than that of devices without carbon implantation, the specific-on resistance was decreased from 9.35 to 4.38 mΩ·cm2 at 100 A/cm2, and the reverse leakage current was also decreased. The influence of carbon incorporation in the SiC crystalline grids was studied by using deep-level transient spectroscopy (DLTS). The DLTS spectra revealed that the Z 1/2 traps, which were regarded as the main lifetime limiting defects, were dramatically reduced. It is proposed that the reduction of Z 1/2 traps can achieve longer carrier lifetime in the drift layer, which is beneficial to the performance of bipolar devices. Project supported by the Opening Project of Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences.

  9. Annealing study of a bistable defect in proton-implanted n-type 4H-SiC

    NASA Astrophysics Data System (ADS)

    Nielsen, H. Kortegaard; Martin, D. M.; Lévêque, P.; Hallén, A.; Svensson, B. G.

    2003-12-01

    The thermal stability and annealing kinetics of a bistable defect, recently reported by Martin (Master Thesis, KTH/ELE/FTE/2003-1) employing deep level transient spectroscopy and labelled the M-centre, has been studied using n-type epitaxially grown 4H-SiC layers implanted with 2.5 MeV protons to a dose of 1×1012 cm-2. One configuration of the bistable defect leads to two levels in the band gap, 0.42 eV (M1) and 0.7-0.8 eV (M3) below the conduction band edge (EC), and another leads to one level (M2) at EC-0.7 eV. The defect can be switched back and forth between the two configurations by varying the applied bias and the sample temperature. Isochronal and isothermal annealing shows that the defect anneals out between 310°C and 370°C with a first-order kinetics process. The origin of the defect is not known but it is implantation-induced and a low-order complex.

  10. Thermal stability of Ni/Ti/Al ohmic contacts to p-type 4H-SiC

    SciTech Connect

    Yu, Hailong; Shen, Huajun Tang, Yidan; Bai, Yun; Liu, Xinyu; Zhang, Xufang; Wu, Yudong; Liu, Kean

    2015-01-14

    Low resistivity Ni/Ti/Al ohmic contacts on p-type 4H-SiC epilayer were developed, and their thermal stabilities were also experimentally investigated through high temperature storage at 600 °C for 100 h. The contact resistance of the Al/Ti/Ni/SiC contacts degraded in different degrees, and the contact morphology deteriorated with the increases of the average surface roughness and interface voids. X-ray spectra showed that Ni{sub 2}Si and Ti{sub 3}SiC{sub 2}, which were formed during ohmic contact annealing and contributed to low contact resistivity, were stable under high temperature storage. The existence of the TiAl{sub 3} and NiAl{sub 3} intermetallic phases was helpful to prevent Al agglomeration on the interface and make the contacts thermally stable. Auger electron spectroscopy indicated that the incorporation of oxygen at the surface and interface led to the oxidation of Al or Ti resulting in increased contact resistance. Also, the formation of these oxides roughened the surface and interface. The temperature-dependence of the specific contact resistance indicated that a thermionic field emission mechanism dominates the current transport for contacts before and after the thermal treatment. It suggests that the Ni/Ti/Al composite ohmic contacts are promising for SiC devices to be used in high temperature applications.

  11. Microstructures of InN film on 4H-SiC (0001) substrate grown by RF-MBE

    NASA Astrophysics Data System (ADS)

    Jantawongrit, P.; Sanorpim, S.; Yaguchi, H.; Orihara, M.; Limsuwan, P.

    2015-08-01

    InN film was grown on 4H-SiC (0001) substrate by RF plasma-assisted molecular beam epitaxy (RF-MBE). Prior to the growth of InN film, an InN buffer layer with a thickness of ∼5.5 nm was grown on the substrate. Surface morphology, microstructure and structural quality of InN film were investigated. Micro-structural defects, such as stacking faults and anti-phase domain in InN film were carefully investigated using transmission electron microscopy (TEM). The results show that a high density of line contrasts, parallel to the growth direction (c-axis), was clearly observed in the grown InN film. Dark field TEM images recorded with diffraction vectors g=11\\bar{2}0 and g = 0002 revealed that such line contrasts evolved from a coalescence of the adjacent misoriented islands during the initial stage of the InN nucleation on the substrate surface. This InN nucleation also led to a generation of anti-phase domains. Project supported by the Thailand Center of Excellence in Physics (ThEP) and the King Mongkut's University of Technology Thonburi under The National Research University Project. One of the authors (S. Sanorpim) was supported by the National Research Council of Thailand (NRCT) and the Thai Government Stimulus Package 2 (TKK2555), under the Project for Establishment of Comprehensive Center for Innovative Food, Health Products and Agriculture.

  12. Soft X-ray detection and photon counting spectroscopy with commercial 4H-SiC Schottky photodiodes

    NASA Astrophysics Data System (ADS)

    Zhao, S.; Gohil, T.; Lioliou, G.; Barnett, A. M.

    2016-09-01

    The results of electrical characterisation and X-ray detection measurements of two different active area (0.06 mm2 and 0.5 mm2) commercial 4H-SiC Schottky photodiodes at room temperature are reported. The devices exhibited low dark currents (less than 10 pA) even at a high electric field strengths (403 kV/cm for 0.06 mm2 diodes; 227 kV/cm for 0.5 mm2 diodes). The results of the X-ray measurements indicate that the diodes can be used as photon counting spectroscopic X-ray detectors with modest energy resolutions: FWHM at 5.9 keV of 1.8 keV and 3.3 keV, for the 0.06 mm2 and 0.5 mm2 devices, respectively. Noise analysis of the photodiodes coupled to a custom low noise charge sensitive preamplifier is also presented.

  13. A novel 4H-SiC MESFET with double upper gate and recessed p-buffer

    NASA Astrophysics Data System (ADS)

    Jia, Hujun; Ma, Peimiao; Luo, Yehui; Yang, Zhihui; Wang, Zhijiao; Wu, Qiuyuan; Hu, Mei

    2016-09-01

    A novel structure named 4H-SiC metal semiconductor field effect transistor with double upper gate and recessed p-buffer (DURP MESFET) is proposed and simulated in this paper. The increase in the saturation drain current and the breakdown voltage, and the decrease in the gate-source capacitance are achieved compared with those of DR MESFET, which are result from the reduction of the depletion region under the gate by the introduction of a double upper gate. The negative influence of the double upper gate on trans-conductance is suppressed by employing a recessed p-buffer. With the optimal size, the height of the upper gate Z = 0.10 μm, the depth and width of the recessed p-buffer of 0.05 μm and 0.35 μm, superior DC and RF characteristics for the proposed structure can be obtained, such as a 22.5% increase in the saturation drain current and a 17.9% increase in the breakdown voltage compared to the DR MESFET. The gate-source capacitance is 0.439 pF/mm compared to 0.573 pF/mm of DR MESFET by reference to simulated results, which would lead to the DURP MESFET has excellent RF performance.

  14. Nanoscale electro-structural characterisation of ohmic contacts formed on p-type implanted 4H-SiC

    PubMed Central

    2011-01-01

    This work reports a nanoscale electro-structural characterisation of Ti/Al ohmic contacts formed on p-type Al-implanted silicon carbide (4H-SiC). The morphological and the electrical properties of the Al-implanted layer, annealed at 1700°C with or without a protective capping layer, and of the ohmic contacts were studied using atomic force microscopy [AFM], transmission line model measurements and local current measurements performed with conductive AFM. The characteristics of the contacts were significantly affected by the roughness of the underlying SiC. In particular, the surface roughness of the Al-implanted SiC regions annealed at 1700°C could be strongly reduced using a protective carbon capping layer during annealing. This latter resulted in an improved surface morphology and specific contact resistance of the Ti/Al ohmic contacts formed on these regions. The microstructure of the contacts was monitored by X-ray diffraction analysis and a cross-sectional transmission electron microscopy, and correlated with the electrical results. PMID:21711667

  15. Influences of high-temperature annealing on atomic layer deposited Al2O3/4H-SiC

    NASA Astrophysics Data System (ADS)

    Wang, Yi-Yu; Shen, Hua-Jun; Bai, Yun; Tang, Yi-Dan; Liu, Ke-An; Li, Cheng-Zhan; Liu, Xin-Yu

    2013-07-01

    High-temperature annealing of the atomic layer deposition (ALD) of Al2O3 films on 4H-SiC in O2 atmosphere is studied with temperature ranging from 800 °C to 1000 °C. It is observed that the surface morphology of Al2O3 films annealed at 800 °C and 900 °C is pretty good, while the surface of the sample annealed at 1000 °C becomes bumpy. Grazing incidence X-ray diffraction (GIXRD) measurements demonstrate that the as-grown films are amorphous and begin to crystallize at 900 °C. Furthermore, C—V measurements exhibit improved interface characterization after annealing, especially for samples annealed at 900 °C and 1000 °C. It is indicated that high-temperature annealing in O2 atmosphere can improve the interface of Al2O3/SiC and annealing at 900 °C would be an optimum condition for surface morphology, dielectric quality, and interface states.

  16. Mixed Anhydride Intermediates in the Reaction of 5(4H)-Oxazolones with Phosphate Esters and Nucleotides

    PubMed Central

    Liu, Ziwei; Rigger, Lukas; Rossi, Jean-Christophe; Sutherland, John D.; Pascal, Robert

    2016-01-01

    5(4H)-Oxazolones can be formed through the activation of acylated α-amino acids or of peptide C termini. They constitute potentially activated intermediates in the abiotic chemistry of peptides that preceded the origin of life or early stages of biology and are capable of yielding mixed carboxylic-phosphoric anhydrides upon reaction with phosphate esters and nucleotides. Here, we present the results of a study aimed at investigating the chemistry that can be built through this interaction. As a matter of fact, the formation of mixed anhydrides with mononucleotides and nucleic acid models is shown to take place at positions involving a mono-substituted phosphate group at the 3’- or 5’-terminus but not at the internal phosphodiester linkages. In addition to the formation of mixed anhydrides, the subsequent intramolecular acyl or phosphoryl transfers taking place at the 3’-terminus are considered to be particularly relevant to the common prebiotic chemistry of α-amino acids and nucleotides. PMID:27534830

  17. Atmospheric pressure route to epitaxial nitrogen-doped trilayer graphene on 4H-SiC (0001) substrate

    NASA Astrophysics Data System (ADS)

    Boutchich, M.; Arezki, H.; Alamarguy, D.; Ho, K.-I.; Sediri, H.; Güneş, F.; Alvarez, J.; Kleider, J. P.; Lai, C. S.; Ouerghi, A.

    2014-12-01

    Large-area graphene film doped with nitrogen is of great interest for a wide spectrum of nanoelectronics applications, such as field effect devices, super capacitors, and fuel cells among many others. Here, we report on the structural and electronic properties of nitrogen doped trilayer graphene on 4H-SiC (0001) grown under atmospheric pressure. The trilayer nature of the growth is evidenced by scanning transmission electron microscopy. X-ray photoelectron spectroscopy shows the incorporation of 1.2% of nitrogen distributed in pyrrolic-N, and pyridinic-N configurations as well as a graphitic-N contribution. This incorporation causes an increase in the D band on the Raman signature indicating that the nitrogen is creating defects. Ultraviolet photoelectron spectroscopy shows a decrease of the work function of 0.3 eV due to the N-type doping of the nitrogen atoms in the carbon lattice and the edge defects. A top gate field effect transistor device has been fabricated and exhibits carrier mobilities up to 1300 cm2/V s for holes and 850 cm2/V s for electrons at room temperature.

  18. The c4h, tat, hppr and hppd Genes Prompted Engineering of Rosmarinic Acid Biosynthetic Pathway in Salvia miltiorrhiza Hairy Root Cultures

    PubMed Central

    Gao, Shouhong; Saechao, Saengking; Di, Peng; Chen, Junfeng; Chen, Wansheng

    2011-01-01

    Rational engineering to produce biologically active plant compounds has been greatly impeded by our poor understanding of the regulatory and metabolic pathways underlying the biosynthesis of these compounds. Here we capitalized on our previously described gene-to-metabolite network in order to engineer rosmarinic acid (RA) biosynthesis pathway for the production of beneficial RA and lithospermic acid B (LAB) in Salvia miltiorrhiza hairy root cultures. Results showed their production was greatly elevated by (1) overexpression of single gene, including cinnamic acid 4-hydroxylase (c4h), tyrosine aminotransferase (tat), and 4-hydroxyphenylpyruvate reductase (hppr), (2) overexpression of both tat and hppr, and (3) suppression of 4-hydroxyphenylpyruvate dioxygenase (hppd). Co-expression of tat/hppr produced the most abundant RA (906 mg/liter) and LAB (992 mg/liter), which were 4.3 and 3.2-fold more than in their wild-type (wt) counterparts respectively. And the value of RA concentration was also higher than that reported before, that produced by means of nutrient medium optimization or elicitor treatment. It is the first report of boosting RA and LAB biosynthesis through genetic manipulation, providing an effective approach for their large-scale commercial production by using hairy root culture systems as bioreactors. PMID:22242141

  19. Comparative analysis on surface property in anodic oxidation polishing of reaction-sintered silicon carbide and single-crystal 4H silicon carbide

    NASA Astrophysics Data System (ADS)

    Shen, Xinmin; Tu, Qunzhang; Deng, Hui; Jiang, Guoliang; He, Xiaohui; Liu, Bin; Yamamura, Kazuya

    2016-04-01

    For effective machining of difficult-to-machine materials, such as reaction-sintered silicon carbide (RS-SiC) and single-crystal 4H silicon carbide (4H-SiC), a novel polishing technique named anodic oxidation polishing was proposed, which combined with the anodic oxidation of substrate and slurry polishing of oxide. By scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM-EDX) observation and atomic force microscopy analysis, both the anodic oxidation behaviors of RS-SiC and 4H-SiC were investigated. Through comparison of the surfaces before and after hydrofluoric acid etching of the oxidized samples by the scanning white light interferometry (SWLI) measurement, the relationships between oxidation depth and oxidation time were obtained, and the calculated oxidation rate for RS-SiC was 5.3 nm/s and that for 4H-SiC was 5.8 nm/s based on the linear Deal-Grove model. Through anodic oxidation polishing of RS-SiC substrate and 4H-SiC substrate, respectively, the surface roughness rms obtained by SWLI was improved to 2.103 nm for RS-SiC and to 0.892 nm for 4H-SiC. Experimental results indicate that anodic oxidation polishing is an effective method for the machining of RS-SiC and 4H-SiC samples, which would improve the process level of SiC substrates and promote the application of SiC products in the fields of optics, ceramics, semiconductors, electronics, and so on.

  20. Determination by ultraviolet absorption spectrometry and theoretical calculation of dissociation constant of 1,2,3,9-tetrahydro-4H-carbazol-4-one.

    PubMed

    Zhang, Shufang; Zhang, Xiaoyan; Tang, Ke; Zhou, Zhengyu

    2009-08-15

    The dissociation constant of 1,2,3,9-tetrahydro-4H-carbazol-4-one was determined by ultraviolet absorption spectrometry method based on the absorption spectra of 1,2,3,9-tetrahydro-4H-carbazol-4-one at different pH in ethanol-water mixed solvents. The results show that the pK(b) was a good linear function of the volume fraction of ethanol in the concentration range studied. The dissociation constant of 1, 2, 3,9-tetrahydro-4H-carbazol-4-one in water were determined by extrapolation to be 14.04 under the condition of this experiment. The accurate pK(b) calculations of 1,2,3,9-tetrahydro-4H-carbazol-4-one have been investigated using the combination of the extended clusters-continuum model with the polarizable continuum solvation model (PCM). The calculations are performed at the B3LYP/6-31G levels. The formation of molecular clusters by means of the 1,2,3,9-tetrahydro-4H-carbazol-4-one wrapped up with water molecules leads to the weakness of the interaction between the polar solvents and the 1,2,3,9-tetrahydro-4H-carbazol-4-one, hence, the accuracy of pK(b) has been enhanced. The dissociation constant of 1,2,3,9-tetrahydro-4H-carbazol-4-one in water were calculated to be 14.10 and agreed well with experimental data.