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. 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…

  3. 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…

  4. Discover 4-H Clubs: The Essential Resource for 4-H

    ERIC Educational Resources Information Center

    MacArthur, Stacey; Nelson, Cindy; Brower, Naomi; Memmott, Margie; Peterson, Gaelynn

    2016-01-01

    Obstacles facing new 4-H volunteers include time constraints and difficulty finding project-specific information, resources, and opportunities available for club members. As a solution to these obstacles and an aid for assisting volunteers in becoming confident in delivering information to youth, content experts produced Discover 4-H Clubs, a…

  5. 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…

  6. 4-H Textile Science Textile Arts Projects.

    ERIC Educational Resources Information Center

    Scholl, Jan

    This packet contains three 4-H textile arts projects for students in the textile sciences area. The projects cover weaving, knitting, and crocheting. Each project provides an overview of what the student will learn, what materials are needed, and suggested projects for the area. Projects can be adapted for beginning, intermediate, or advanced…

  7. 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,…

  8. Novel Analogues of (R)-5-(Methylamino)-5,6-dihydro-4H-imidazo[4,5,1-ij]quinolin-2(1H)-one (Sumanirole) Provide Clues to Dopamine D2/D3 Receptor Agonist Selectivity

    PubMed Central

    2016-01-01

    Novel 1-, 5-, and 8-substituted analogues of sumanirole (1), a dopamine D2/D3 receptor (D2R/D3R) agonist, were synthesized. Binding affinities at both D2R and D3R were higher when determined in competition with the agonist radioligand [3H]7-hydroxy-N,N-dipropyl-2-aminotetralin (7-OH-DPAT) than with the antagonist radioligand [3H]N-methylspiperone. Although 1 was confirmed as a D2R-preferential agonist, its selectivity in binding and functional studies was lower than previously reported. All analogues were determined to be D2R/D3R agonists in both GoBRET and mitogenesis functional assays. Loss of efficacy was detected for the N-1-substituted analogues at D3R. In contrast, the N-5-alkyl-substituted analogues, and notably the n-butyl-arylamides (22b and 22c), all showed improved affinity at D2R over 1 with neither a loss of efficacy nor an increase in selectivity. Computational modeling provided a structural basis for the D2R selectivity of 1, illustrating how subtle differences in the highly homologous orthosteric binding site (OBS) differentially affect D2R/D3R affinity and functional efficacy. PMID:27035329

  9. 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…

  10. 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 enrollment…

  11. National 4-H School Enrichment Survey.

    ERIC Educational Resources Information Center

    Diem, Keith G.

    2001-01-01

    A survey of 4-H school enrichment programs (813 responses) found that they reach large numbers of diverse youth and develop credibility with community and schools. Long-term programs such as 4-H clubs have proven effective in helping youth develop life skills, but Extension must carefully consider the purpose and consequences of diverting…

  12. Holding on to 4-H Leaders.

    ERIC Educational Resources Information Center

    Hass, Glen

    1979-01-01

    Data from a survey of 4-H Club leaders in Saskatchewan, Canada, were used to determine the effect of attendance at leadership training events on leaders' decisions to re-enroll or discontinue. It was found that involvement in 4-H activities, supported by leadership training, increased leaders' satisfaction and likelihood of re-enrolling. (MF)

  13. 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:…

  14. 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,…

  15. 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…

  16. 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,…

  17. 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…

  18. 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…

  19. 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,…

  20. 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…

  1. 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…

  2. New Jersey 4-H Marine Science Project. Leaders Guide.

    ERIC Educational Resources Information Center

    Jesuncosky, Betty Jean, Comp.

    This guide contains a collection of activities which are designed to provide opportunities for 4-H voluteers and youth in New Jersey to get involved in learning about the marine environment. The guide is divided into five sections which deal with habitats, organisms, career exploration, community involvement, and additional marine activities. Each…

  3. 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…

  4. 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…

  5. 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' skills…

  6. 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…

  7. 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.

  8. 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 and…

  9. 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…

  10. 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…

  11. 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…

  12. 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

  13. 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…

  14. 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 sessions…

  15. 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…

  16. 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…

  17. 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…

  18. 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.

  19. Unexpected Stability of Al4H6: a Borane Analog?

    NASA Astrophysics Data System (ADS)

    Xi, Li; Grubisic, Andrej; Stokes, Sarah; Gantefor, Gerd; Bowen, Kit; Boggavarapu, Kiran; Willis, Mary; Jena, Puru; Burgert, Ralph; Schnockel, Hans; Cordes, James

    2007-03-01

    While boron has many hydrides, aluminum has been thought to exhibit relatively few. A combined anion photoelectron and density functional theory computational study of the Al4H6^- anion, and its corresponding neutral, Al4H6, showed that Al4H6 can be understood in terms of the Wade-Mingos rules for electron counting, suggesting that it may be a borane analog. The data support an Al4H6 structure with a distorted tetrahedral aluminum atom framework, four terminal Al-H bonds, and two sets of counter-positioned Al-H-Al bridging bonds. The large HOMO-LUMO gap found for Al4H6 together with its exceptionally high heat of combustion further suggests that Al4H6 may be an important energetic material, if it can be prepared in bulk. This report announces the opening of a new chapter in aluminum-hydrogen chemistry.

  20. 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…

  1. Sewing Skills Progress Chart. 4-H Textile Science.

    ERIC Educational Resources Information Center

    Scholl, Jan F.

    This document, which was developed for use by Pennsylvania 4-H Club leaders and members, is a chart that can be used to help club members determine and document those sewing skills they already have and those they need to learn as they complete one or more 4-H Club sewing projects. The document begins with a note to club leaders and parents that…

  2. Camping with a Purpose...A 4-H Handbook.

    ERIC Educational Resources Information Center

    Heller, John H.; And Others

    The 4-H handbook focuses on factors to consider and things to be done when developing a camping program. Since the emphasis, structure, and administration of 4-H camping varies, the booklet is flexible enough to be adapted to different state, district, and county situations. Major topics are camping's importance to extension education,…

  3. 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…

  4. Enantioselective one-pot synthesis of 2-amino-4-(indol-3-yl)-4H-chromenes.

    PubMed

    Chen, Weiliang; Cai, Yunfei; Fu, Xuan; Liu, Xiaohua; Lin, Lili; Feng, Xiaoming

    2011-09-16

    An enantioselective one-pot synthesis of 2-amino-4-(indol-3-yl)-4H-chromenes via a Knoevenagel/Pinner/Friedel-Crafts reaction of salicylaldehyde, malononitrile, and indole is presented. Moderate to good yields (up to 89%) and high enantioselectivities (up to 90% ee) were obtained with an N,N'-dioxide-Zn(II) complex as the catalyst. This strategy provides an efficient and convenient method to access enantiomerically enriched 2-amino-4H-chromene derivatives.

  5. 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

  6. Twenty-first century learning after school: the case of 4-H.

    PubMed

    Kress, Cathann

    2006-01-01

    Founded in the early 1900s, the 4-H Youth Development program can serve as a model for out-of-school programs of the twenty-first century. The 4-H pledge, repeated by its members--over 7 million, ranging in age from five to twenty--articulates its core values: "I pledge: My head to clearer thinking, My heart to greater loyalty, My hands to larger service, and My health to better living for my club, my community, my country, and my world." The 4-H Development movement was created to provide opportunities for rural children, to help them become constructive adults. Through an emphasis on "learning by doing," 4-H teaches children the habits of lifelong learning. Historically, 4-H has tapped into university-level advancements, extending such knowledge to youth and thereby giving them early access to scientific discoveries and technological progress. Members apply this learning in their communities through hands-on projects crossing a wide-range of pertinent topics. Research shows that 4-H members are more successful in school than other children and develop a wide range of skills essential in the twenty-first century. Thus, the author makes the case that the foundation of 4-H is exceptionally relevant in today's complex world, perhaps even more so than a century ago. 4-H is a leader in youth development, making it a natural model for twenty-first century after-school programs. Expanding on the 4-H pledge, the author outlines the principles a successful youth development program would have: an emphasis on leadership skills, a feeling of connection and belonging, a forum for exploring career opportunities, and a component of meaningful community service.

  7. Volumetric Properties of the Mixture Oxolan-2-one C4H6O2 + C4H10O Butan-1-ol (VMSD1511, LB4906_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 Oxolan-2-one C4H6O2 + C4H10O Butan-1-ol (VMSD1511, LB4906_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. Texas 4-H Agents' Perceptions of Selected Competencies in the 4-H Professional Research, Knowledge, and Competencies Model

    ERIC Educational Resources Information Center

    Harder, Amy; Wingenbach, Gary J.

    2008-01-01

    There are many competencies necessary for success as a 4-H agent. The 4-H Professional Research, Knowledge, and Competencies (PRKC) Model organizes competencies into six domains: (a) Youth Development, (b) Youth Program Development, (c) Volunteerism, (d) Partnerships, (e) Organizational Systems, and (f) Equity, Access and Opportunity (National 4-H…

  9. 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.

  10. 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

    2016-02-03

    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.

  11. 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…

  12. On the Origin of C4H and CH3OH in Protostellar Envelopes

    NASA Astrophysics Data System (ADS)

    Lindberg, Johan E.; Charnley, Steven B.; Cordiner, Martin A.

    2016-12-01

    The formation pathways of different types of organic molecules in protostellar envelopes and other regions of star formation are subjects of intense current interest. We present here observations of C4H and CH3OH, tracing two distinct groups of interstellar organic molecules, toward 16 protostars in the Ophiuchus and Corona Australis molecular clouds. Together with observations in the literature, we present C4H and CH3OH data from single-dish observations of 40 embedded protostars. We find no correlation between the C4H and CH3OH column densities in this large sample. Based on this lack of correlation, a difference in line profiles between C4H and CH3OH, and previous interferometric observations of similar sources, we propose that the emission from these two molecules is spatially separated, with the CH3OH tracing gas that has been transiently heated to high (˜70-100 K) temperatures and the C4H tracing the cooler large-scale envelope where CH4 molecules have been liberated from ices. These results provide insight in the differentiation between hot corino and warm carbon-chain chemistry in embedded protostars. Based on observations with the Kitt Peak 12 m telescope telescope and the Atacama Pathfinder EXperiment (APEX) telescope. The Kitt Peak 12 m telescope is operated by the Arizona Radio Observatory (ARO), Steward Observatory, University of Arizona. APEX is a collaboration between the Max Planck Institute for Radio Astronomy, the European Southern Observatory, and the Onsala Space Observatory.

  13. "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)

  14. 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…

  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,…

  16. 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…

  17. 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…

  18. 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…

  19. 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…

  20. 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…

  1. 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,…

  2. 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…

  3. 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.

  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. 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…

  6. 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.

  7. YA4-H! Youth Advocates for Health: Impact of a 4-H Teens-as-Teachers Program

    ERIC Educational Resources Information Center

    Arnold, Mary E.; Flesch, Jeffrey M.; Ashton, Carolyn; Black, Lynette; Brody, Barbara; Hosty, Maureen; Northway, Shanna

    2016-01-01

    This article reports the results of an evaluation of the YA4-H! Youth Advocates for Health--Teens as Teachers program. Consistent with previous research on the impact of teen teaching, the teens participating in the program gained confidence and skill with regard to teaching younger youths. The program also affected the teens' understanding that…

  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. Litter Control Achievement - Ohio 4-H Club Score Sheet [and] Activity Guides 1 through 7. 4-H Pilot Program 918.

    ERIC Educational Resources Information Center

    Ohio State Univ., Columbus. Cooperative Extension Service.

    Seven activity guides, evaluation sheet, and club scoresheet have been prepared for Ohio 4-H clubs' litter education program. Topics of the seven activity guides include: (1) general guidelines and types of activities; (2) little known facts about waste/litter; (3) guidelines for a walking tour; (4) fact sheet (questionnaire) related to garbage;…

  10. 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…

  11. 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.

  12. A Perfect Fit: 4-H Involvement for Youth with Disabilities. A Leader's Guide.

    ERIC Educational Resources Information Center

    Schnepf, Greg W.; And Others

    This guide for 4-H leaders and volunteers offers information to help integrate youth with disabilities into various 4-H programs. After an introduction, a section on 4-H and mainstreaming reviews the mission of 4-H; considers what 4-H has to offer youth; defines mainstreaming; notes the benefits of mainstreaming; and distinguishes among the terms…

  13. 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.

  14. Leakage currents in 4H-SiC JBS diodes

    SciTech Connect

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

    2012-03-15

    Leakage currents in high-voltage 4H-SiC diodes, which have an integrated (p-n) Schottky structure (Junction Barrier Schottky, JBS), have been studied using commercial diodes and specially fabricated (based on a commercial epitaxial material) test Schottky diodes with and without the JBS structure. It is shown that (i) the main role in reverse charge transport is played by SiC crystal structure defects, most probably, by threading dislocations (density {approx}10{sup 4} cm{sup -2}), and (ii) the JBS structure, formed by the implantation of boron, partially suppresses the leakage currents (by up to a factor of 10 at optimal separation, 8 {mu}m between local p-type regions).

  15. 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.

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

    PubMed

    Circone, Susan; Kirby, Stephen H; Stern, Laura A

    2006-04-27

    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-H2O. 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/nCH4.H2O, 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.

  17. 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.

  18. C4H2, HC3N and C2N2 in Titan's atmosphere

    NASA Astrophysics Data System (ADS)

    Kunde, V. G.; Aikin, A. C.; Hanel, R. A.; Jennings, D. E.; Maguire, W. C.; Samuelson, R. E.

    1981-08-01

    Voyager 1 took IR measurements of the atmosphere of Titan, and obtained an average of 346 spectra, mostly from the center of the disk. The compounds C4H2, HC3N, and C2N2 were detected in the atmosphere of Titan. The identification of two compounds containing nitrogen, in addition to HCN, provides further evidence for the abundance of free N2 on Titan. The organic compounds observed in the atmosphere of Titan are summarized in a table, which also indicates the approximate mole fraction for each compound identified previously. The observed compounds originate by reactions of methane and nitrogen radicals in a predominantly nitrogen atmosphere.

  19. 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.

  20. 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…

  1. 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…

  2. Using the Delphi Technique to Assess Educational Needs Related to Extension's 4-H Beef Program.

    ERIC Educational Resources Information Center

    Shih, Ching-Chun; Gamon, Julia A.

    1997-01-01

    Delphi panels completing questionnaires included 32 parents of 4-H students, 16 extension beef specialists, 21 4-H field specialists, and 21 industry representatives. They identified 31 subject-matter and 30 life-skill topics useful for 4-H manuals. Emerging topics included consumer and environmental concerns. (SK)

  3. 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…

  4. 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...

  5. 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…

  6. 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.…

  7. 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.

  8. 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)…

  9. Learning Outdoors: Leader Guide, Grade 3. 4-H Discovery.

    ERIC Educational Resources Information Center

    Abell, John R.; Newman, Jerry A.

    The United States has a rich natural resource heritage. It is important to educate students in the principles of conservation so that these natural resources may endure for generations. This guide is designed to help leaders to learn to organize groups of children and conduct successful meetings; provide fun, safe, outdoor learning experiences for…

  10. 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…

  11. Schottky barrier detection devices having a 4H-SiC n-type epitaxial layer

    SciTech Connect

    Mandal, Krishna C.; Terry, J. Russell

    2016-12-06

    A detection device, along with methods of its manufacture and use, is provided. The detection device can include: a SiC substrate defining a substrate surface cut from planar to about 12.degree.; a buffer epitaxial layer on the substrate surface; a n-type epitaxial layer on the buffer epitaxial layer; and a top contact on the n-type epitaxial layer. The buffer epitaxial layer can include a n-type 4H--SiC epitaxial layer doped at a concentration of about 1.times.10.sup.15 cm.sup.-3 to about 5.times.10.sup.18 cm.sup.-3 with nitrogen, boron, aluminum, or a mixture thereof. The n-type epitaxial layer can include a n-type 4H--SiC epitaxial layer doped at a concentration of about 1.times.10.sup.13 cm.sup.-3 to about 5.times.10.sup.15 cm.sup.-3 with nitrogen. The top contact can have a thickness of about 8 nm to about 15 nm.

  12. The reinvestigation of the kinetics of the metathesis reactions t-C4H9• + HBr (HI) → i-C4H10 + Br• (I•) and of the t-C4H9• free radical thermochemistry.

    PubMed

    Leplat, N; Rossi, M J

    2014-07-17

    A reinvestigation of the absolute rate constant of the metathesis reactions t-C4H9• + HBr → i-C4H10 + Br• (1) and t-C4H9• + HI → i-C4H10 + I• (2) was performed thanks to a recently developed apparatus consisting of a Knudsen reactor coupled to detection based on single-photon (VUV) photoionization mass spectrometry (SPIMS). It enables the generation of thermalized hydrocarbon free radicals owing to a source upstream of and external to the Knudsen reactor. The following Arrhenius expressions were obtained: k1 = 5.6(±1.4) × 10(–12) exp(−6.76(±0.94)/(RT)) and k2 = 2.0(±0.6) × 10(–11) exp(−8.48(±0.94)/(RT)) with R = 8.314 J mol(–1) K(–1) over the range 293 to 623 K. The mass balance of the reaction system based on closed shell product detection (CSPD) was checked in order to ensure the accuracy of the used reaction mechanism and as an independent check of k1 and k2. The wall-loss rate constants of the t-butyl free radical, kw(C4H9), were measured and found to be low compared with the corresponding escape rate constant, ke(C4H9), for effusion of t-C4H9• out of the Knudsen reactor. On the basis of the present results, the free radical standard heat of formation ΔfH298°(t-C4H9•) = 44.3 ± 1.7 kJ mol(–1) was obtained when combined with the kinetics of the inverse halogenation reaction taken from the literature and using S298°(t-C4H9•) = 322.2 J K(–1) mol(–1) following a “Third Law” evaluation method. The standard enthalpy for t-butyl free radical is consistent for both the bromination and iodination reactions within the stated uncertainties.

  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

    2015-09-02

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

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... Food and Agriculture, United States Department of Agriculture, or a designee, if the fund-raising... 7 Agriculture 1 2014-01-01 2014-01-01 false Use in 4-H fund raising. 8.9 Section 8.9 Agriculture Office of the Secretary of Agriculture 4-H CLUB NAME AND EMBLEM § 8.9 Use in 4-H fund raising. (a)...

  15. 7 CFR 8.9 - Use in 4-H fund raising.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... Food and Agriculture, United States Department of Agriculture, or a designee, if the fund-raising... 7 Agriculture 1 2012-01-01 2012-01-01 false Use in 4-H fund raising. 8.9 Section 8.9 Agriculture Office of the Secretary of Agriculture 4-H CLUB NAME AND EMBLEM § 8.9 Use in 4-H fund raising. (a)...

  16. 7 CFR 8.9 - Use in 4-H fund raising.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... Food and Agriculture, United States Department of Agriculture, or a designee, if the fund-raising... 7 Agriculture 1 2013-01-01 2013-01-01 false Use in 4-H fund raising. 8.9 Section 8.9 Agriculture Office of the Secretary of Agriculture 4-H CLUB NAME AND EMBLEM § 8.9 Use in 4-H fund raising. (a)...

  17. 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.

  18. 4H-SiC surface energy tuning by nitrogen up-take

    NASA Astrophysics Data System (ADS)

    Pitthan, E.; Amarasinghe, V. P.; Xu, C.; Gustafsson, T.; Stedile, F. C.; Feldman, L. C.

    2017-04-01

    Surface energy modification and surface wettability of 4H silicon carbide (0001) as a function of nitrogen adsorption is reported. The surface wettability is shown to go from primarily hydrophilic to hydrophobic and the surface energy was significantly reduced with increasing nitrogen incorporation. These changes are investigated by x-ray photoelectron spectroscopy and contact angle measurements. The surface energy was quantitatively determined by the Fowkes model and interpreted primarily in terms of the variation of the surface chemistry with nitrogen coverage. Variable control of SiC surface energies with a simple and controllable atomic additive such as nitrogen that is inert to etching, stable against time, and also effective in electrical passivation, can provide new opportunities for SiC biomedical applications, where surface wetting plays an important role in the interaction with the biological interfaces.

  19. Optical properties of mesoporous 4H-SiC prepared by anodic electrochemical etching

    NASA Astrophysics Data System (ADS)

    Rashid, Marzaini; Horrocks, B. R.; Healy, N.; Goss, J. P.; Horsfall, A. B.

    2016-11-01

    Porous silicon carbide was fabricated from n-type 4H-SiC substrates via anodic electrochemical etching in HF/ethanol solution and suspended in ethanol after ultrasonication. We observed three photoluminescence bands: two at wavelengths of 303 nm and 345 nm were above the bulk bandgap and one at 455 nm was below the bulk bandgap. These blue-shifted and red-shifted emission processes reveal the interplay between quantum confinement, surface states, and band edge related optical transitions. We propose a model to explain the frequently observed deviation from the quantum confinement in the photoluminesence trends for SiC-derived nanoparticles suspended in solvents. The quantum confined properties of the SiC structures provide a route for optical tunability in the UV-blue spectrum for use in novel photonic and biomedical applications.

  20. Structure and hydration of the C4H4●+ ion formed by electron impact ionization of acetylene clusters.

    PubMed

    Momoh, Paul O; Hamid, Ahmed M; Abrash, Samuel A; El-Shall, M Samy

    2011-05-28

    molecule suggesting a structure with restrained water molecules, probably a cyclic water pentamer within the C(4)H(4)(●+)(H(2)O)(5) cluster. Consequently, a drop in the binding energy of the sixth water molecule is observed suggesting a structure in which the sixth water molecule interacts weakly with the C(4)H(4)(●+)(H(2)O)(5) cluster presumably consisting of a cyclobutadiene(●+) cation hydrogen bonded to a cyclic water pentamer. The combination of ion mobility, dissociation, and hydration experiments in conjunction with the theoretical calculations provides strong evidence that the (C(2)H(2))(2)(●+) ions are predominantly present as the cyclobutadiene cation with some contribution from the vinyl acetylene cation.

  1. Structure and hydration of the C4H4•+ ion formed by electron impact ionization of acetylene clusters

    NASA Astrophysics Data System (ADS)

    Momoh, Paul O.; Hamid, Ahmed M.; Abrash, Samuel A.; Samy El-Shall, M.

    2011-05-01

    cyclic water pentamer within the C4H4•+(H2O)5 cluster. Consequently, a drop in the binding energy of the sixth water molecule is observed suggesting a structure in which the sixth water molecule interacts weakly with the C4H4•+(H2O)5 cluster presumably consisting of a cyclobutadiene•+ cation hydrogen bonded to a cyclic water pentamer. The combination of ion mobility, dissociation, and hydration experiments in conjunction with the theoretical calculations provides strong evidence that the (C2H2)2•+ ions are predominantly present as the cyclobutadiene cation with some contribution from the vinyl acetylene cation.

  2. 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.

  3. 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.

  4. Electrical and optical characterization of 4H-SiC diodes for particle detection

    NASA Astrophysics Data System (ADS)

    Schifano, Ramón; Vinattieri, Anna; Bruzzi, Mara; Miglio, Stefania; Lagomarsino, Stefano; Sciortino, Silvio; Nava, Filippo

    2005-05-01

    The electronic and optical properties of several (medium to high quality) 4H-SiC epitaxial sensors for particle detection have been studied. The samples are n-doped Schottky diodes with different nitrogen concentrations (6×1013cm-3-5×1015cm-3) and thicknesses (20-40μm). A full electrical and optical characterization has been performed by capacitance versus voltage measurements and near-band-edge low-temperature photoluminescence. The effective doping along the epilayer and the depletion width have been determined and data are consistent with the charge collection efficiency characterization performed with a minimum ionizing β-source. All the investigated samples exhibit a 100% collection efficiency. In particular, the best samples yield a highly reproducible signal, well separated from the pedestal. Photoluminescence results show a linear relationship between the effective doping and the ratio of nitrogen-bound excitonic emission (Q0) and free excitonic line (I76), in agreement with a previous work on 4H-SiC with a higher doping concentration [I. G. Ivanov, C. Hallin, A. Henry, O. Kordina, and E. Janzén, J. Appl. Phys. 80, 3504 (1996)]. Moreover we show that the dependence of the major spectral features as a function of the penetration depth of the exciting laser beam can quantitatively provide information on substrate contribution to the photoluminescence. In conclusion, we bring evidence that a detailed characterization of SiC-based detectors, by all optical techniques, yields an accurate value for the net doping and gives a qualitative information on the epilayer thickness prior to any electrical wafer tests.

  5. Electrical and optical characterization of 4H-SiC diodes for particle detection

    SciTech Connect

    Schifano, Ramon; Vinattieri, Anna; Bruzzi, Mara; Miglio, Stefania; Lagomarsino, Stefano; Sciortino, Silvio; Nava, Filippo

    2005-05-15

    The electronic and optical properties of several (medium to high quality) 4H-SiC epitaxial sensors for particle detection have been studied. The samples are n-doped Schottky diodes with different nitrogen concentrations (6x10{sup 13} cm{sup -3}-5x10{sup 15} cm{sup -3}) and thicknesses (20-40 {mu}m). A full electrical and optical characterization has been performed by capacitance versus voltage measurements and near-band-edge low-temperature photoluminescence. The effective doping along the epilayer and the depletion width have been determined and data are consistent with the charge collection efficiency characterization performed with a minimum ionizing {beta}-source. All the investigated samples exhibit a 100% collection efficiency. In particular, the best samples yield a highly reproducible signal, well separated from the pedestal. Photoluminescence results show a linear relationship between the effective doping and the ratio of nitrogen-bound excitonic emission (Q{sub 0}) and free excitonic line (I{sub 76}), in agreement with a previous work on 4H-SiC with a higher doping concentration [I. G. Ivanov, C. Hallin, A. Henry, O. Kordina, and E. Janzen, J. Appl. Phys. 80, 3504 (1996)]. Moreover we show that the dependence of the major spectral features as a function of the penetration depth of the exciting laser beam can quantitatively provide information on substrate contribution to the photoluminescence. In conclusion, we bring evidence that a detailed characterization of SiC-based detectors, by all optical techniques, yields an accurate value for the net doping and gives a qualitative information on the epilayer thickness prior to any electrical wafer tests.

  6. 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…

  7. 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 club…

  8. 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…

  9. 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.

  10. 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…

  11. 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…

  12. 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…

  13. 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…

  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. 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)…

  16. 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 sports…

  17. An Examination of 4-H Youths' Needs and Interests, and Implications for State Conference.

    ERIC Educational Resources Information Center

    Rude, Tarri Lou

    A study was conducted to determine the needs and interests of teens in 4-H and whether the Washington State Conference is meeting those needs and interests. A mail survey was developed and sent to 557 teen 4-H members in Washington who were randomly selected from the 1985 state enrollment list. Three hundred and sixty questionnaires were returned…

  18. 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...

  19. 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…

  20. 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…

  1. 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…

  2. Unusual reaction paths of SN2 nucleophile substitution reactions CH4 + H- → CH4 + H- and CH4 + F- → CH3F + H-: Quantum chemical calculations

    NASA Astrophysics Data System (ADS)

    Minyaev, Ruslan M.; Quapp, Wolfgang; Schmidt, Benjamin; Getmanskii, Ilya V.; Koval, Vitaliy V.

    2013-11-01

    Quantum chemical (CCSD(full)/6-311++G(3df,3pd), CCSD(T)(full)/6-311++G(3df,3pd)) and density function theory (B3LYP/6-311++G(3df,3pd)) calculations were performed for the SN2 nucleophile substitution reactions CH4 + H- → CH4 + H- and CH4 + F- → CH3F + H-. The calculated gradient reaction pathways for both reactions have an unusual behavior. An unusual stationary point of index 2 lies on the gradient reaction path. Using Newton trajectories for the reaction path, we can detect VRI point at which the reaction path branches.

  3. Structural analysis of the 3C|4H boundaries formed on prismatic planes in 4H-SiC epitaxial films

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    The boundaries between 3C and 4H-SiC domains on the prismatic planes of hexagonal lattices formed in a 4H-SiC epitaxial film were investigated using both transmission and scanning transmission electron microscopy. These observations determined that the boundaries have a periodic structure, in which each unit cell consists of 12 basal planes of the hexagonal lattice. Six Shockley partial dislocations are situated in each unit cell of the boundary structure. Burgers vectors and core structures of these partial dislocations are discussed.

  4. 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…

  5. Reactions of ortho-lithiophenyl (-hetaryl) isocyanides with carbonyl compounds: rearrangements of 2-metalated 4H-3,1-benzoxazines.

    PubMed

    Lygin, Alexander V; de Meijere, Armin

    2009-06-19

    ortho-Lithiophenyl (-hetaryl) isocyanides react with aldehydes and ketones providing isocyanoalcohols 8 (36-89%, nine examples), 4H-3,1-benzoxazines 9 (45-78%, six examples) or, after two types of rearrangements, isobenzofuran-1(3H)-imines (iminophthalanes) 18 (52-75%, four examples), or indolin-2-ones 19 (42-79%, two examples), depending on the reaction conditions and substitution patterns. Isocyanoalcohols 8, in turn, were converted to 9 or 18 under Cu(I) catalysis (66-86%, eight examples). 4H-3,1-Benzoxazin-4-ones 39-Nu and isatoic anhydride 40 were obtained by the reaction of 2 with carbon dioxide followed by trapping of the lithiated intermediate with iodine and subsequent reactions with nucleophiles (45-60%, three examples).

  6. HIF-P4H-2 deficiency protects against skeletal muscle ischemia-reperfusion injury.

    PubMed

    Karsikas, Sara; Myllymäki, Mikko; Heikkilä, Minna; Sormunen, Raija; Kivirikko, Kari I; Myllyharju, Johanna; Serpi, Raisa; Koivunen, Peppi

    2016-03-01

    We show here that mice hypomorphic for hypoxia-inducible factor prolyl 4-hydroxylase-2 (HIF-P4H-2) (Hif-p4h-2 (gt/gt)), the main regulator of the stability of the HIFα subunits, have normoxic stabilization of HIF-1α and HIF-2α in their skeletal muscles. The size of the capillaries, but not their number, was increased in the skeletal muscles of the Hif-p4h-2 (gt/gt) mice, whereas the amount of glycogen was reduced. The expression levels of genes for glycolytic enzymes, glycogen branching enzyme 1 and monocarboxylate transporter 4, were increased in the Hif-p4h-2 (gt/gt) skeletal muscles, whereas no significant increases were detected in the levels of any vasculature-influencing factor studied. Serum lactate levels of the Hif-p4h-2 (gt/gt) mice recovered faster than those of the wild type following exercise. The Hif-p4h-2 (gt/gt) mice had elevated hepatic phosphoenolpyruvate carboxykinase activity, which may have contributed to the faster clearance of lactate. The Hif-p4h-2 (gt/gt) mice had smaller infarct size following limb ischemia-reperfusion injury. The increased capillary size correlated with the reduced infarct size. Following ischemia-reperfusion, glycogen content and ATP/ADP and CrP/Cr levels of the skeletal muscle of the Hif-p4h-2 (gt/gt) mice were higher than in the wild type. The higher glycogen content correlated with increased expression of phosphofructokinase messenger RNA (mRNA) and the increased ATP/ADP and CrP/Cr levels with reduced apoptosis, suggesting that HIF-P4H-2 deficiency supported energy metabolism during ischemia-reperfusion and protection against injury. Key messages: HIF-P4H-2 deficiency protects skeletal muscle from ischemia-reperfusion injury. The mechanisms involved are mediated via normoxic HIF-1α and HIF-2α stabilization. HIF-P4H-2 deficiency increases capillary size but not number. HIF-P4H-2 deficiency maintains energy metabolism during ischemia-reperfusion.

  7. Optical directional coupler and Mach-Zehnder interferometer enhanced via 4H-SiC phonons

    NASA Astrophysics Data System (ADS)

    Finch, Michael F.; Saunders Filho, Claudio A. B.; Lail, Brian A.

    2016-09-01

    Surface phonon polaritons (SPhPs), similar to it cousin phenomenon surface plasmon polaitons (SPPs), are quasi-neutral particles resulting from light-matter coupling that can provide high modal confinement and long propagation in the mid to long infrared (IR). Mach-Zehnder interferometer (MZI) is a combination of two connected optical directional couplers (ODC). With the use of SPhPs, sub-wavelength feature sizes and modal areas can be achieved and to this end a hybrid SPhP waveguide, where propagation length and modal area can be trade-off, will be employed in the design of an ODC and MZI. This endeavor analyzes and characteristics both an ODC and MZI using commercially available numerical simulation software employing finite element method (FEM). The ODC and MZI are design using a novel SPhP hybrid waveguide design where a 4H-SiC substrate provides the polariton mode. The output ports power and relative phase difference between ports are investigated. SPhP enhanced ODC and MZI has applications including, but not limited to, next-generation ultra-compact photonic integrated circuits and waveguide based IR sensing.

  8. Al4H7(-) is a resilient building block for aluminum hydrogen cluster materials.

    PubMed

    Roach, P J; Reber, A C; Woodward, W H; Khanna, S N; Castleman, A W

    2007-09-11

    The formation and oxygen etching of Al(n)H(m)(-) clusters are characterized in a flow reactor experiment with first-principles theoretical investigations to demonstrate the exceptional stability of Al(4)H(7)(-). The origin of the preponderance of Al(4)H(7)(-) in the mass spectra of hydrogenated aluminum anions and its resistance to O(2) etching are discussed. Al(4)H(7)(-) is shown to have the ability to bond with ionic partners to form stable hydrides through addition of an alkali atom [XAl(4)H(7) (X = Li-Cs)]. An intuitive model that can predict the existence of stable hydrogenated cluster species is proposed. The potential synthetic utility of the superatom assemblies built on these units is addressed.

  9. Prismatic Slip in PVT-Grown 4H-SiC Crystals

    NASA Astrophysics Data System (ADS)

    Guo, Jianqiu; Yang, Yu; Raghothamachar, Balaji; Kim, Jungyu; Dudley, Michael; Chung, Gilyong; Sanchez, Edward; Quast, Jeffrey; Manning, Ian

    2017-04-01

    Basal plane slip is the most frequently observed deformation mechanism in 4H-type silicon carbon (4H-SiC) single crystals grown by the physical vapor transport (PVT) method. However, it was recently reported that dislocations in such crystals can also glide in prismatic slip systems. In this study, we observed nonuniform distributions of three sets of prismatic dislocations in a commercial 4H-SiC substrate wafer. The nonuniformity is a result of the distribution of resolved shear stress on each prismatic slip system caused by radial thermal gradients in the growing crystal boule. A radial thermal model has been developed to estimate the thermal stress across the entire area of the crystal boule during PVT growth. The model results show excellent agreement with the observations, confirming that radial thermal gradients play a key role in activating prismatic slip in 4H-SiC during bulk growth.

  10. Prismatic Slip in PVT-Grown 4H-SiC Crystals

    NASA Astrophysics Data System (ADS)

    Guo, Jianqiu; Yang, Yu; Raghothamachar, Balaji; Kim, Jungyu; Dudley, Michael; Chung, Gilyong; Sanchez, Edward; Quast, Jeffrey; Manning, Ian

    2016-11-01

    Basal plane slip is the most frequently observed deformation mechanism in 4H-type silicon carbon (4H-SiC) single crystals grown by the physical vapor transport (PVT) method. However, it was recently reported that dislocations in such crystals can also glide in prismatic slip systems. In this study, we observed nonuniform distributions of three sets of prismatic dislocations in a commercial 4H-SiC substrate wafer. The nonuniformity is a result of the distribution of resolved shear stress on each prismatic slip system caused by radial thermal gradients in the growing crystal boule. A radial thermal model has been developed to estimate the thermal stress across the entire area of the crystal boule during PVT growth. The model results show excellent agreement with the observations, confirming that radial thermal gradients play a key role in activating prismatic slip in 4H-SiC during bulk growth.

  11. 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.

  12. 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.

  13. The development of novel LTA4H modulators to selectively target LTB4 generation

    PubMed Central

    Low, Caroline M.; Akthar, Samia; Patel, Dhiren F.; Löser, Stephan; Wong, Chi-Tung; Jackson, Patricia L.; Blalock, J. Edwin; Hare, Stephen A.; Lloyd, Clare M.; Snelgrove, Robert J.

    2017-01-01

    The pro-inflammatory mediator leukotriene B4 (LTB4) is implicated in the pathologies of an array of diseases and thus represents an attractive therapeutic target. The enzyme leukotriene A4 hydrolase (LTA4H) catalyses the distal step in LTB4 synthesis and hence inhibitors of this enzyme have been actively pursued. Despite potent LTA4H inhibitors entering clinical trials all have failed to show efficacy. We recently identified a secondary anti-inflammatory role for LTA4H in degrading the neutrophil chemoattractant Pro-Gly-Pro (PGP) and rationalized that the failure of conventional LTA4H inhibitors may be that they inadvertently prevented PGP degradation. We demonstrate that these inhibitors do indeed fail to discriminate between the dual activities of LTA4H, and enable PGP accumulation in mice. Accordingly, we have developed novel compounds that potently inhibit LTB4 generation whilst leaving PGP degradation unperturbed. These novel compounds could represent a safer and superior class of LTA4H inhibitors for translation into the clinic. PMID:28303931

  14. Key contribution of eIF4H-mediated translational control in tumor promotion

    PubMed Central

    Vaysse, Charlotte; Philippe, Céline; Martineau, Yvan; Quelen, Cathy; Hieblot, Corinne; Renaud, Claire; Nicaise, Yvan; Desquesnes, Aurore; Pannese, Maria; Filleron, Thomas; Escourrou, Ghislaine; Lawson, Malcolm; Rintoul, Robert C.; Delisle, Marie Bernadette; Pyronnet, Stéphane; Brousset, Pierre; Prats, Hervé; Touriol, Christian

    2015-01-01

    Dysregulated expression of translation initiation factors has been associated with carcinogenesis, but underlying mechanisms remains to be fully understood. Here we show that eIF4H (eukaryotic translation initiation factor 4H), an activator of the RNA helicase eIF4A, is overexpressed in lung carcinomas and predictive of response to chemotherapy. In lung cancer cells, depletion of eIF4H enhances sensitization to chemotherapy, decreases cell migration and inhibits tumor growth in vivo, in association with reduced translation of mRNA encoding cell-proliferation (c-Myc, cyclin D1) angiogenic (FGF-2) and anti-apoptotic factors (CIAP-1, BCL-xL). Conversely, each isoform of eIF4H acts as an oncogene in NIH3T3 cells by stimulating transformation, invasion, tumor growth and resistance to drug-induced apoptosis together with increased translation of IRES-containing or structured 5′UTR mRNAs. These results demonstrate that eIF4H plays a crucial role in translational control and can promote cellular transformation by preferentially regulating the translation of potent growth and survival factor mRNAs, indicating that eIF4H is a promising new molecular target for cancer therapy. PMID:26498689

  15. The development of novel LTA4H modulators to selectively target LTB4 generation

    NASA Astrophysics Data System (ADS)

    Low, Caroline M.; Akthar, Samia; Patel, Dhiren F.; Löser, Stephan; Wong, Chi-Tung; Jackson, Patricia L.; Blalock, J. Edwin; Hare, Stephen A.; Lloyd, Clare M.; Snelgrove, Robert J.

    2017-03-01

    The pro-inflammatory mediator leukotriene B4 (LTB4) is implicated in the pathologies of an array of diseases and thus represents an attractive therapeutic target. The enzyme leukotriene A4 hydrolase (LTA4H) catalyses the distal step in LTB4 synthesis and hence inhibitors of this enzyme have been actively pursued. Despite potent LTA4H inhibitors entering clinical trials all have failed to show efficacy. We recently identified a secondary anti-inflammatory role for LTA4H in degrading the neutrophil chemoattractant Pro-Gly-Pro (PGP) and rationalized that the failure of conventional LTA4H inhibitors may be that they inadvertently prevented PGP degradation. We demonstrate that these inhibitors do indeed fail to discriminate between the dual activities of LTA4H, and enable PGP accumulation in mice. Accordingly, we have developed novel compounds that potently inhibit LTB4 generation whilst leaving PGP degradation unperturbed. These novel compounds could represent a safer and superior class of LTA4H inhibitors for translation into the clinic.

  16. Microwave losses of undoped n-type silicon and undoped 4H-SiC single crystals at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Jung, Ho Sang; Yang, Woo Il; Cho, Man Soon; Joo, Kee Nam; Lee, Sang Young

    2014-05-01

    We investigated microwave losses of single-crystalline Si and 4H-SiC at cryogenic temperatures at 8.6-24 GHz using a method involving a dielectric resonator with high- T c superconductor YBa2Cu3O7- δ films used to improve the measurement sensitivity. The loss tangent of our undoped n-type Si appeared to be extremely low at temperatures below 20 K with a value of 1 × 10-6 at 24 GHz at 10 K, which is more than 100 times lower than the value of 2 × 10-4 at 6.8 GHz at 10 K reported by Krupka et al. [ IEEE Trans. Microw. Theory Tech. 54, 3995 (2006)] for undoped p-type Si. Meanwhile, the loss tangent of pristine 4H-SiC appeared to be very high with a value of 0.01 at 10 K at 8.6 GHz, which is 4000 times higher than that of our undoped Si. When the pristine 4H-SiC was irradiated with thermal neutrons, the loss tangent was enhanced by seven times due to the significantly reduced electrical resistivity. Our results show that, at temperatures below 20 K, the loss tangent of undoped n-type Si is low enough for various cryogenic applications and that thermal neutron irradiation could provide a useful means of reducing the electrical resistivity of SiC possibly by means of neutron transmutation doping.

  17. 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.

  18. Predictors of performance in a 4-h mountain-bike race.

    PubMed

    Novak, Andrew R; Bennett, Kyle J M; Fransen, Job; Dascombe, Ben J

    2017-04-13

    This study aimed to cross validate previously developed predictive models of mountain biking performance in a new cohort of mountain bikers during a 4-h event (XC4H). Eight amateur XC4H cyclists completed a multidimensional assessment battery including a power profile assessment that consisted of maximal efforts between 6 and 600 s, maximal hand grip strength assessments, a video-based decision-making test as well as a XC4H race. A multiple linear regression model was found to predict XC4H performance with good accuracy (R(2) = 0.99; P < 0.01). This model consisted of [Formula: see text] relative to total cycling mass (body mass including competition clothing and bicycle mass), maximum power output sustained over 60 s relative to total cycling mass, peak left hand grip strength and two-line decision-making score. Previous models for Olympic distance MTB performance demonstrated merit (R(2) = 0.93; P > 0.05) although subtle changes improved the fit, significance and normal distribution of residuals within the model (R(2) = 0.99; P < 0.01), highlighting differences between the disciplines. The high level of predictive accuracy of the new XC4H model further supports the use of a multidimensional approach in predicting MTB performance. The difference between the new, XC4H and previous Olympic MTB predictive models demonstrates subtle differences in physiological requirements and performance predictors between the two MTB disciplines.

  19. 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.

  20. 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.

  1. Sense Determination of Micropipes via Grazing-Incidence Synchrotron White Beam X-ray Topography in 4H Silicon Carbide

    SciTech Connect

    Chen,Y.; Dhanaraj, G.; Dudley, M.; Sanchez, E.; MacMillan, M.

    2007-01-01

    Computer modeling using the ray-tracing method has been used to simulate the grazing-incidence x-ray topographic images of micropipes in 4H silicon carbide recorded using the pyramidal (11-28) reflection. Simulation results indicate that the images of micropipes appear as white features of roughly elliptical shape, canted to one side or other of the g vector depending on the dislocation sense. Observed images compare well with the simulations, demonstrating that the direction of cant provides a simple, nondestructive, and reliable way to reveal the senses of micropipes. Sense assignment has been validated using back-reflection reticulography.

  2. 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.

  3. 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.

  4. 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

  5. Cathodoluminescence Study of the Properties of Stacking Faults in 4H-SiC Homoepitaxial Layers

    DTIC Science & Technology

    2009-01-01

    Cathodoluminescence study of the properties of stacking faults in 4H- SiC homoepitaxial layers Serguei I. Maximenko,1,a Jaime A. Freitas, Jr.,1 Paul...2009 In-grown stacking faults in n-type 4H- SiC epitaxial layers have been investigated by real-color cathodoluminescence imaging and spectroscopy...carried out at room and liquid helium temperatures. Stacking faults with 8H stacking order were observed, as well as double layer and multilayer 3C- SiC

  6. Transition metal swift heavy ion implantation on 4H-SiC

    NASA Astrophysics Data System (ADS)

    Ali, A. Ashraf; Kumar, J.; Ramakrishnan, V.; Asokan, K.

    2016-03-01

    This work reports on the realization of Quantum Ring (QR) and Quantum Dot (QD) like structures on 4H-SiC through SHI implantation and on their Raman studies. 4H-SiC is SHI implanted with Transition Metal (TM) Ni ion at different fluences. It is observed that a vibrational mode emerges as the result of Ni ion implantation. The E2 (TO) and the A1 (LO) are suppressed as the fluence increases. In this paper Raman and AFM studies have been performed at room temperature and the queer anomalies are addressed so new devices can be fabricated.

  7. Electrical properties of extended defects in 4H-SiC investigated by photoinduced current measurements

    NASA Astrophysics Data System (ADS)

    Privitera, Stefania M. S.; Litrico, Grazia; Camarda, Massimo; Piluso, Nicolò; La Via, Francesco

    2017-03-01

    We study the correlation between crystal quality and electrical transport in 4H-SiC by micro-photoluminescence and laser-beam-induced photocurrent measurements. A focused HeCd laser at 325 nm has been employed to simultaneously measure, with a spatial resolution of a few microns, both the photoluminescence and current–voltage characteristics of 4H-SiC Schottky diodes. We found that the laser-induced photocurrent acquired along a defect can give information on its spatial distribution in depth and that the local minority carrier lifetime and generation depend on the type of stacking fault, both decreasing for defects with deeper intragap levels.

  8. 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

  9. 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…

  10. An Evaluation of the 4-H "Health Rocks" Program: Implications for Program Improvement

    ERIC Educational Resources Information Center

    Self, Carlton; Morgan, A. Christian; Fuhrman, Nicholas E.; Navarro, Maria

    2013-01-01

    The National 4-H Council developed the Health Rocks substance abuse educational program to prevent youth from engaging in risky behaviors. The program was presented in 2010 to more than 8,000 middle school youth in Georgia. A post-then-pre evaluation was conducted with youth who completed 10 hours of instruction to determine if changes in youth…

  11. 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…

  12. Factors Related to Motivating Adult Somalis with Refugee Status to Volunteer for 4-H

    ERIC Educational Resources Information Center

    Mason, Mitchell D.; Ouellette, Kristy L.

    2016-01-01

    Focus group interviews were held with adult Somali immigrants to assess their likelihood of volunteering for 4-H in Maine. This qualitative study was undertaken to identify best practices for engaging the growing Somali-Mainer population as a volunteer base. Results of the study demonstrate that Somali immigrant adults are willing to volunteer for…

  13. A novel synthesis of 4H-chromen-4-ones via intramolecular wittig reaction

    PubMed

    Kumar; Bodas

    2000-11-30

    The acylphosphoranes formed in a sequential manner from the reaction of the silyl ester of O-acyl(aroyl)salicylic acids and (trimethylsilyl)methylenetriphenylphosphorane undergo intramolecular Wittig cyclization on the ester carbonyl to afford the 4H-chromen-4-ones in good to excellent yields.

  14. 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,…

  15. N-[4-(Dimethyl-amino)-benzyl-idene]-4H-1,2,4-triazol-4-amine.

    PubMed

    Zhou, Hui-Liang; Zhang, Xiao-Min

    2012-05-01

    The title compound, C(11)H(13)N(5), is a Schiff base synthesized by the reaction of 4-amino-4H-1,2,4-triazole and 4-(dimethyl-amino)-benzaldehyde. The dihedral angle between the benzene and triazole rings is 43.09 (11)°. The crystal structure displays weak C-H⋯N inter-actions.

  16. Temperature Dependence of Attenuation of Coplanar Waveguide on 4H High Resistivity SIC Through 540C

    NASA Technical Reports Server (NTRS)

    Ponchak, G. E.; Schwartz, Z.; Alterovitz, S. A.; Downey, A. N.; Freeman, J. C.

    2003-01-01

    For the first time, the temperature and frequency dependence of the attenuation of a Coplanar Waveguide (CPW) on 4H, High Resistivity Sic substrate is reported. The low frequency attenuation increases by 2 dB/cm at 500 C and the high frequency attenuation increases by 3.3 dB/cm at 500 C compared to room temperature.

  17. 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…

  18. 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.

  19. Community Pride: An Oregon 4-H Activity Relating to Beautification and Conservation.

    ERIC Educational Resources Information Center

    Oregon State Univ., Corvallis. Cooperative Extension Service.

    The Community Pride program is a 4-H activity in conservation and beautification. Instructions for selecting and carrying out a Community Pride activity are presented: planning, organizing, and doing the project. Suggestions for possible activities are offered, and instructions for reporting the activity to the county extension office are given.…

  20. 4-H Shooting Sports Hits the Mark with Youth-at-Risk.

    ERIC Educational Resources Information Center

    Sabo, Kenneth E.; Hamilton, Wendy V.

    1997-01-01

    A 4-H program in a public housing project in New Mexico involved at-risk youth in activities such as archery and other shooting sports. These activities were found to promote motivation, cognitive development, self-esteem, and responsibility. (SK)

  1. A Historical Review of Leadership Development in the FFA and 4-H

    ERIC Educational Resources Information Center

    Hoover, Tracy S.; Scholl, Jan F.; Dunigan, Anne H.; Mamontova, Nadezhda

    2007-01-01

    FFA and 4-H are two youth-based organizations that cite leadership development as a key foundational component. The purpose of this study was to review and document the historical development of leadership events and activities in both programs. Evidence can be found of leadership development in schools, conferences, and camps. Leadership-related…

  2. 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

  3. An Occupational Analysis Comparing 4-H Youth Development Agents Serving Traditional and Non-Traditional Clientele.

    ERIC Educational Resources Information Center

    Borden, Lynne M.; Harris, William

    1998-01-01

    Six 4-H agents working with traditional clients and six with nontraditional clients participated in a DACUM (Developing a Curriculum) analysis of job tasks. They performed similar duties but the nontraditional group spent more time assessing individual members; the traditional group focused more on program management. (SK)

  4. 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…

  5. 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…

  6. 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…

  7. National Invitational Training Conference on Working with Youth with Special Needs Through 4-H.

    ERIC Educational Resources Information Center

    Worden, Phyllis, Comp.

    A conference set up to exchange and disseminate ideas and information on the mentally retarded is presented. Specific purposes of the conference are: (1) to promote appreciation and understanding of handicapped youth--mentally retarded, and physically and visually handicapped youth, (2) to promote knowledge of on-going programs through 4-H with…

  8. 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…

  9. 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…

  10. Diffusion of Social Media among County 4-H Programs in Tennessee

    ERIC Educational Resources Information Center

    Bowen, Rebekah D.; Stephens, Carrie A.; Childers, Courtney C.; Avery, Elizabeth J.; Stripling, Christopher T.

    2013-01-01

    Over the past decade, Cooperative Extension and 4-H professionals have been faced with the decision of whether to adopt new communication technologies such as social media. Research on social media and Cooperative Extension has identified risks and barriers to adoption; however, many Cooperative Extension professionals believe that social media…

  11. 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.

  12. 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.

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

    SciTech Connect

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

    2016-01-04

    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{sup +}N junction is used to collect high-energy electrons. The electron source is a titanium tritide (TiH{sup 3}{sub x}) 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/cm{sup 2}. Samples measured with an external tritium foil produced an open circuit voltage of 2.09 V, short circuit current of 75.47 nA/cm{sup 2}, 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 10{sup 5}–10{sup 6 }cm/s. Our analysis demonstrated that the surface recombination dominates the performance of a tritium betavoltaic device but that using a thin P{sup +}N junction structure can mitigate some of the negative effects.

  14. 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.

  15. Crystal structure, IR spectroscopic and optical properties of the two (C11N4H10)4·H2O and (C11N4H10)2·H2O compounds

    NASA Astrophysics Data System (ADS)

    Derbel, Amira; Omri, Issam; Allouch, Fatma; Agrebi, Asma; Mhiri, Tahar; Graia, Mohsen

    2015-01-01

    The crystallization of (C11N4H10)2·H2O (I) and (C11N4H10)4·H2O (II) is made by slow evaporation from aqueous solutions. The structures of these compounds have been solved and refined by single-crystal X-ray diffraction data. The compound (I) is centrosymmetric (space group C2/c) with lattice parameters: a = 14.118 (2) Å, b = 7.399 (1) Å, c = 21.982 (3) Å and β = 107.80 (1)°. The compound (II) crystallizes in the same space group (C2/c) with lattice parameters: a = 28.976 (2) Å, b = 7.593 (2) Å, c = 21.724 (2) Å and β = 115.819 (2)°. The cohesion in both structures is provided by two types of bonds: hydrogen bonds Osbnd H⋯N and Nsbnd H⋯O involving water molecules and organic molecules, and Van der Waals bonds for the connection between the organic molecules. The IR spectra shows an enlargement of the band between 3300 and 2800 cm-1, due to the presence of water molecules and the overlap of vibration modes ν (Osbnd H) and ν (Csbnd H, Nsbnd H). The optical band gap is determined to be 4.07 eV by UV-Vis-T90+ absorption spectra, which revealed the nature of insulator.

  16. 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.

  17. A new model for in situ nitrogen incorporation into 4H-SiC during epitaxy

    PubMed Central

    Ferro, Gabriel; Chaussende, Didier

    2017-01-01

    Nitrogen doping of 4H-SiC during vapor phase epitaxy is still lacking of a general model explaining the apparently contradictory trends obtained by different teams. In this paper, the evolutions of nitrogen incorporation (on both polar Si and C faces) as a function of the main growth parameters (C/Si ratio, temperature, pressure and growth rate) are reviewed and explained using a model based on surface exchanges between the gas phase and the uppermost 4H-SiC atomic layers. In this model, N incorporation is driven mainly by the transient formation of C vacancies, due to H2 etching, at the surface or near the surface. It is shown that all the growth parameters are influencing the probability of C vacancies formation in a similar manner as they do for N incorporation. The surface exchange model proposes a new framework for explaining the experimental results even beyond the commonly accepted reactor type dependency. PMID:28211528

  18. Nanocrystalline diamond films as UV-semitransparent Schottky contacts to 4H-SiC

    NASA Astrophysics Data System (ADS)

    Tadjer, Marko J.; Hobart, Karl D.; Caldwell, Joshua D.; Butler, James E.; Liu, Kendrick X.; Eddy, Charles R.; Gaskill, D. Kurt; Lew, K. K.; VanMil, Brenda L.; Myers-Ward, Rachael L.; Ancona, Mario G.; Kub, Fritz J.; Feygelson, Tatyana I.

    2007-10-01

    A heterojunction between thin films of nanocrystalline diamond (NCD) and 4H-SiC has been developed. Undoped and B-doped NCDs were deposited on both n- and p- SiC epilayers. I-V measurements on p + NCD /n- SiC indicated Schottky rectifying behavior with a turn-on voltage of around 0.2V. The current increased over eight orders of magnitude with an ideality factor of 1.17 at 30°C. Ideal energy-band diagrams suggested a possible conduction mechanism for electron transport from the SiC conduction band to either the valence band or acceptor level of the NCD film. Applications as an UV semitransparent electrical contact to 4H-SiC are discussed.

  19. 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.

  20. A new model for in situ nitrogen incorporation into 4H-SiC during epitaxy

    NASA Astrophysics Data System (ADS)

    Ferro, Gabriel; Chaussende, Didier

    2017-02-01

    Nitrogen doping of 4H-SiC during vapor phase epitaxy is still lacking of a general model explaining the apparently contradictory trends obtained by different teams. In this paper, the evolutions of nitrogen incorporation (on both polar Si and C faces) as a function of the main growth parameters (C/Si ratio, temperature, pressure and growth rate) are reviewed and explained using a model based on surface exchanges between the gas phase and the uppermost 4H-SiC atomic layers. In this model, N incorporation is driven mainly by the transient formation of C vacancies, due to H2 etching, at the surface or near the surface. It is shown that all the growth parameters are influencing the probability of C vacancies formation in a similar manner as they do for N incorporation. The surface exchange model proposes a new framework for explaining the experimental results even beyond the commonly accepted reactor type dependency.

  1. Monte Carlo Simulation of Electron Transport in 4H- and 6H-SiC

    SciTech Connect

    Sun, C. C.; You, A. H.; Wong, E. K.

    2010-07-07

    The Monte Carlo (MC) simulation of electron transport properties at high electric field region in 4H- and 6H-SiC are presented. This MC model includes two non-parabolic conduction bands. Based on the material parameters, the electron scattering rates included polar optical phonon scattering, optical phonon scattering and acoustic phonon scattering are evaluated. The electron drift velocity, energy and free flight time are simulated as a function of applied electric field at an impurity concentration of 1x10{sup 18} cm{sup 3} in room temperature. The simulated drift velocity with electric field dependencies is in a good agreement with experimental results found in literature. The saturation velocities for both polytypes are close, but the scattering rates are much more pronounced for 6H-SiC. Our simulation model clearly shows complete electron transport properties in 4H- and 6H-SiC.

  2. 4H-silicon carbide-dielectric interface recombination analysis using free carrier absorption

    NASA Astrophysics Data System (ADS)

    Suvanam, S. S.; Gulbinas, K.; Usman, M.; Linnarson, M. K.; Martin, D. M.; Linnros, J.; Grivickas, V.; Hallén, A.

    2015-03-01

    In this paper, an alternative method to characterize the interface between 4H polytype of Silicon Carbide (4H-SiC) and passivating dielectric layers is established. The studies are made on dielectric-semiconductor test structures using Al2O3 as dielectric on 4H-SiC n-type epitaxial layers. Samples with different pre- and post-dielectric deposition preparations have been fabricated on epilayers of varying thicknesses. Effective lifetimes (τeff) of all the samples were measured by an optical pump-probe method utilizing free carrier absorption (FCA) to analyse the influence of the 4H-SiC/dielectric interface on charge carrier recombination. The relative contribution to τeff from the surfaces increases with decreasing epilayer thickness, and by analysing the data in combination with numerical modelling, it is possible to extract values of the surface recombination velocities (SRVs) for interfaces prepared in different ways. For instance, it is found that SRV for a standard cleaning procedure is 2 × 106 cm/s compared to a more elaborate RCA process, yielding a more than 50 times lower value of 3.5 × 104 cm/s. Furthermore, the density of interface traps (Dit) is extracted from capacitance-voltage (CV) measurements using the Terman method and a comparison is made between the SRV extracted from FCA measurements and Dits extracted from CV measurements on the same structures fabricated with metal contacts. It is observed that the SRV increase scales linearly with the increase in Dit. The strong qualitative correlation between FCA and CV data shows that FCA is a useful characterization technique, which can also yield more quantitative information about the charge carrier dynamics at the interface.

  3. 4-[4-(Diethyl-amino)benzyl-ideneamino]-4H-1,2,4-triazole.

    PubMed

    Pan, Jian Xin; Zhang, Ju Zhou; Chen, Qian Wang

    2008-05-03

    The title compound, C(13)H(17)N(5), is a Schiff base synthesized by the reaction of 4-amino-4H-1,2,4-triazole and 4-(diethyl-amino)benzaldehyde. The triazole ring forms a dihedral angle of 5.77 (16)° with the benzene ring. The crystal structure is stabilized by an inter-molecular C-H⋯N hydrogen bond.

  4. I-V characteristics simulation of silicon carbide Ti/4H-SiC Schottky diode

    NASA Astrophysics Data System (ADS)

    Panchenko, P.; Rybalka, S.; Malakhanov, A.; Krayushkina, E.; Radkov, A.

    2016-12-01

    The simulation of current-voltage characteristics for 4H-SiC Schottky diode with Ti Schottky contact has been carried out with used of TCAD program. Obtained current-voltage characteristics has been analyzed and compared with theoretical and experimental results. It is established that the Schottky diode parameters (forward current, ideality coefficient, Schottky barrier height, breakdown voltage) obtained in proposed model are good agreement with data for such type diodes.

  5. 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.

  6. 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.

  7. Photophysics of a ruthenium 4H-imidazole panchromatic dye in interaction with titanium dioxide.

    PubMed

    Schindler, Julian; Kupfer, Stephan; Wächtler, Maria; Guthmuller, Julien; Rau, Sven; Dietzek, Benjamin

    2015-04-07

    The photophysics of bis(4,4'-di-tert-butyl-2,2'-bipyridine-κ(2)N,N')[2-(4-carboxyphenyl)-4,5-bis(p-tolylimino-κN)imidazolato]ruthenium(II) hexafluorophosphate is investigated, both in solution and attached to a nanocrystalline TiO2 film. The studied substitution pattern of the 4H-imidazole ligand is observed to block a photoinduced structural reorganization pathway within the 4H-imidazole ligand that has been previously investigated. Protonation at the 4H-imidazole ring decreases the excited-state lifetime in solution. When the unprotonated dye is anchored to TiO2, photoinduced electron injection occurs from thermally nonrelaxed triplet metal-to-ligand charge transfer ((3)MLCT) states with a characteristic time constant of 0.5 ps and an injection efficiency of roughly 25%. Electron injection from the subsequently populated thermalized (3)MLCT state of the dye does not take place. The energy of this state seems to be lower than the conduction band edge of TiO2.

  8. 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.

  9. 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).

  10. Computational Study of Anisotropic Epitaxial Recrystallization in 4H-SiC

    SciTech Connect

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

    2008-03-26

    Two nano-sized amorphous layers were employed within a crystalline cell to study anisotropic expitaxial recrystallization using molecular dynamics (MD) methods in 4H-SiC. Both amorphous layers were created with the normal of the amorphous-crystalline (a-c) interfaces along the [0001] direction, but one with a microscopic extension long the [0001] direction, i.e. the dimension along the [-12-10] direction is much larger than that along the [-12-10] direction (Ix model), and another with a microscopic extension long the [-1010] direction (Iy model). The amorphous layer within the Ix model can be completely recrystallized at 2000 K within achievable simulation time, and the recrystallization is driven by a step-regrowth mechanism. On the other hand, the nucleation and growth of secondary ordered phases are observed at high temperatures in the Iy model. The temperature for recrystallization of the amorphous layer into high quality 4H-SiC is estimated to be below 1500 K. As compared with other models, it is found that the regrowth rates and recrystallization mechanisms strongly depend on the orientation of 4H-SiC, whereas the activation energy spectra for recrystallization processes are independent on a specific polytypic structure, with activation energies ranging from 0.8 to 1.7 eV.

  11. 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.

  12. Incipient plasticity in 4H-SiC during quasistatic nanoindentation.

    PubMed

    Goel, Saurav; Yan, Jiwang; Luo, Xichun; Agrawal, Anupam

    2014-06-01

    Silicon carbide (SiC) is an important orthopedic material due to its inert nature and superior mechanical and tribological properties. Some of the potential applications of silicon carbide include coating for stents to enhance hemocompatibility, coating for prosthetic-bearing surfaces and uncemented joint prosthetics. This study is the first to explore nanomechanical response of single crystal 4H-SiC through quasistatic nanoindentation. Displacement controlled quasistatic nanoindentation experiments were performed on a single crystal 4H-SiC specimen using a blunt Berkovich indenter (300nm tip radius) at extremely fine indentation depths of 5nm, 10nm, 12nm, 25nm, 30nm and 50nm. Load-displacement curve obtained from the indentation experiments showed yielding or incipient plasticity in 4H-SiC typically at a shear stress of about 21GPa (~an indentation depth of 33.8nm) through a pop-in event. An interesting observation was that the residual depth of indent showed three distinct patterns: (i) positive depth hysteresis above 33nm, (ii) no depth hysteresis at 12nm, and (iii) negative depth hysteresis below 12nm. This contrasting depth hysteresis phenomenon is hypothesized to originate due to the existence of compressive residual stresses (upto 143MPa) induced in the specimen by the polishing process prior to the nanoindentation.

  13. Nitrogen incorporation and interface trap reduction in silicon dioxide/4H-silicon carbide

    NASA Astrophysics Data System (ADS)

    McDonald, Kyle

    2001-07-01

    Silicon carbide is a wide band gap semiconductor whose properties make it an ideal material for high power applications. Silicon carbide thermally oxidizes to form SiO2, which is used as a gate insulator in MOSFETs; however, MOSFETs produced from the 4H-SiC polytype exhibit much lower channel mobilities than expected. A large density of interface traps produced by carbon clusters and located near the conduction band has been proposed as the source of the poor mobility. The nitridation of the SiO2/4H-SiC interface using NO and NH3 has been shown to reduce this interface trap density and improve the channel mobility. In this work, the kinetics of nitrogen incorporation using NO and NH3 are compared, and the relationship between nitrogen content and interface trap density are discussed. The nitridation of SiO2/4H-SiC in NO at temperatures from 1050--1175°C incorporates ˜1014 cm-2 of nitrogen at the interface. Oxygen formed during the thermal decomposition of NO oxidizes the substrate and removes carbon and nitrogen from the interface. When the nitridation and oxidation reactions reach equilibrium, the nitrogen content saturates independently of temperature. The nitridation of SiO 2/4H-SiC in NH; at temperatures from 1050--1175°C incorporates ˜10 16 cm-2 uniformly throughout the oxide bulk. During nitridation, oxygen is removed from the oxide, and the stoichiometry of the film is changed significantly. The nitridation of SiO2/4H-SiC in NO reduces the interface trap density near the conduction band by a factor of 10, but the trap density remains high. The complete passivation of these particular traps occurs at a nitrogen content of ≈2.5 x 1014 cm-2 , regardless of the annealing conditions. The data are consistent with a model of the interface in which the traps near the conduction band are produced by large carbon clusters with a near-continuum of energy levels. The passivation of these traps with nitrogen then proceeds by the dissolution of these carbon clusters

  14. A theoretical study on the reaction mechanism of O2 with C4H9• radical.

    PubMed

    Du, Hong-chen; Gong, Xue-dong

    2012-05-01

    Ab initio calculations have been performed using the complete basis set model (CBS-QB3) to study the reaction mechanism of butane radical (C(4)H(9)•) with oxygen (O(2)). On the calculated potential energy surface, the addition of O(2) to C(4)H(9)• forms three intermediates barrierlessly, which can undergo subsequent isomerization or decomposition reaction leading to various products: HOO• + C(4)H(8), C(2)H(5)• + CH(2)CHOOH, OH• + C(3)H(7)CHO, OH• + cycle-C(4)H(8)O, CH(3)• + CH(3)CHCHOOH, CH(2)OOH• + C(3)H(6). Five pathways are supposed in this study. After taking into account the reaction barrier and enthalpy, the most possible reaction pathway is C(4)H(9)• + O(2) → IM1 → TS5 → IM3 → TS6 → IM4 → TS7 → OH• + cycle-C(4)H(8)O.

  15. After-school programs for health promotion in rural communities: Ashe County Middle School 4-H After-School Program.

    PubMed

    Edwards, Michael B; Miller, Jennifer L; Blackburn, Linda

    2011-01-01

    Rural youth have a higher risk for lower health and developmental outcomes, often facing numerous constraints (eg, poor socioeconomic conditions, lower levels of social support, fewer recreational programs and facilities, and inadequate transportation). After-school programs have the potential to effectively deliver health-promoting activities but often face significant challenges in these areas. Ashe County is a rural community in the Appalachian region of North Carolina. Ashe County is economically depressed and its youth population has many poor health and developmental indicators. However, with more than 20 years of sustained activity, one important community resource trying to address disparities in youth health and development is the Ashe County 4-H After-School Program. To successfully overcome inherent challenges, the program has positioned itself as essential to community development, supported and retained qualified personnel, and cultivated a network of key partners to continue its efforts to provide essential youth programs for this rural community.

  16. 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.

  17. 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

  18. 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).

  19. Insight into metal-enhanced oxidation using barium on 4H-SiC surfaces

    NASA Astrophysics Data System (ADS)

    Chanthaphan, Atthawut; Katsu, Yoshihito; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2016-12-01

    Metal-enhanced oxidation (MEO) using ultrathin Ba layers on 4H-SiC surfaces was investigated by physical and electrical characterizations. We found that while comparable oxidation rates were enhanced for Si- and C-face surfaces even at a low temperature, significant surface and interface roughness were induced by initial MEO termed the incubation period. Depth profiling revealed that although most Ba atoms aggregated on the oxide surface, a tiny amount (˜1014 cm-2) remaining at the oxide interface was responsible for the following stable MEO reaction and the reduced interface state density with the drawbacks of degraded leakage current and breakdown characteristics of SiC-MOS devices.

  20. Compensation Mechanism in High Purity Semi-Insulating 4H-SiC

    DTIC Science & Technology

    2007-01-01

    online 15 March 2007 A study of deep levels in high purity semi-insulating 4H-SiC has been made using temperature dependent Hall effect TDH , thermal and...optical admittance spectroscopies, and secondary ion mass spectrometry SIMS. Thermal activation energies from TDH varied from a low of 0.55 eV to a...high of 1.65 eV. All samples studied showed n-type conduction with the Fermi level in the upper half of the band gap. Fits of the TDH data to

  1. 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.

  2. Orientation of the water moiety in CF4-H2O

    NASA Astrophysics Data System (ADS)

    Evangelisti, Luca; Feng, Gang; Gou, Qian; Guidetti, Gloria; Caminati, Walther

    2012-12-01

    The rotational spectrum of CF4-H217O has been investigated by pulsed jet Fourier transform microwave spectroscopy. A symmetric top effective rotational spectrum has been observed, similarly to the case of the parent species (W. Caminati, A. Maris, A. Dell'Erba, P.G. Favero, Angew. Chem. Int. Ed. 45 (2006) 6711). The experimental value of the 17O χaa quadrupole coupling constant, 0.54(1) MHz, allows to determine the average value of the angle between the C2 axis of H2O and the C⋯O line, β = 24°.

  3. 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.

  4. Theoretical study on the reaction of C4H (X˜2Σ+) with CH3OH

    NASA Astrophysics Data System (ADS)

    Huo, Ruiping; Zhang, Xiang; Zhang, Caifeng

    2015-01-01

    The reaction mechanism of linear butadiynyl radical C4H (C1C2C3C4H) with methanol (CH3OH) was studied at the CCSD(T)/aug-cc-pVTZ//BB1K/6-311+G(2d,2p) level. Six different hydrogen abstraction channels were considered, and methyl-H and hydroxyl-H of CH3OH abstractions by C1 atom (M1 and M2) are the two predominant and competitive channels. Further analysis indicated that M1 is a hydrogen atom transfer (HAT) channel while M2 is a proton-coupled electron transfer (PCET) channel. For M1 and M2, the high-pressure rate constants in the temperature range of 100-1400 K were calculated by ICVT/SCT and TST/W methods and the changes of branching ratios with temperature under four pressures (0.1, 1.0, 10 and 100 atm) were also considered by Master equation approach.

  5. Defect Characterization of 4H-SiC Wafers for Power Electronic Device Applications.

    NASA Astrophysics Data System (ADS)

    Cicero, G.; Ferrero, S.; Cocuzza, M.; Giorgis, F.; Mandracci, P.; Ricciardi, C.; Scaltrito, L.; Pirri, C. F.; Richieri, G.; Sgorlon, C.

    2002-03-01

    Silicon carbide is a wide band gap semiconductor, interesting for its physical properties such as high breakdown field, high saturated drift velocity and high thermal conductivity, which has been intensively studied in the last years. Although the high potentiality of this material, the SiC technology shows at the moment some limitations and requires further study in order to obtain electronic devices with the same quality standards of the Si technology. Indeed, the reliability of SiC-based devices is strictly correlated to the defects present in the crystalline structure. We have focused our investigation on 4H-SiC wafers and on 4H epitaxial layers in order to determine in both the situations the different type of defects. A preliminary investigation has been performed by optical microscopy and Scanning Electron Microscopy with the aim to evidence the defect morphology on large scale. A deeper insight on the defects typology has been obtained by Atomic Force Microscopy, Profilometer technique, Micro-Raman and Micro-Photoluminescence spectroscopies. Different types of defects such as micropipes, comets, super dislocations, etch pits and so on, have been characterized finding particular physical finger-prints. This investigation is aimed at correlating the defects and the electrical properties of SiC for power electronic device applications.

  6. Microwave photoconductivity decay characterization of high-purity 4H-SiC substrates

    NASA Astrophysics Data System (ADS)

    Kumar, R. J.; Borrego, J. M.; Gutmann, R. J.; Jenny, J. R.; Malta, D. P.; Hobgood, H. McD.; Carter, C. H.

    2007-07-01

    A microwave photoconductivity decay (MPCD) technique, which probes conductivity change in wafers in response to either an above-band-gap or below-band-gap laser pulse, has been used to characterize recombination lifetime in high-purity 4H-SiC substrates produced with three different anneal processes. The above-band-gap (266nm) decay times vary from ˜10ns to tens of microseconds in the 4H-SiC substrates depending on the wafer growth parameters. Wafers produced using the three processes A (as-grown), B (annealed at 2000°C), and C (annealed at 2600°C) have decay times of 10-20ns, 50-500ns, and tens of microseconds, respectively. The differences in decay times are attributed to low, medium, and high densities of recombination centers in process C, B, and A wafers, respectively. The MPCD results correlate with other characterization results such as deep level transient spectroscopy, which also showed that the 2600°C anneal process significantly reduces defect densities, resulting in the enhanced recombination lifetimes. Modeling and one-dimensional simulations indicate a trapping center closer to the conduction band results in a longer MPCD decay transient, but such a trapping based model for the enhanced lifetimes is not compatible with the wide range of experimental characterization results described in this work, which indicate an annealing out of recombination centers at 2600°C.

  7. 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.

  8. 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.

  9. 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.

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

    DOE PAGES

    Zhang, Lihua; Su, Dong; Kisslinger, Kim; ...

    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

  11. High-purity semi-insulating 4H-SiC for microwave device applications

    NASA Astrophysics Data System (ADS)

    Jenny, J. R.; Malta, D. P.; Müller, St G.; Powell, A. R.; Tsvetkov, V. F.; Hobgood, H. Mcd; Glass, R. C.; Carter, C. H., Jr.

    2003-05-01

    High-purity, semi-insulating (HPSI) 4H-SiC crystals with diameters up to 75 mm have been grown by the seeded sublimation technique without the intentional introduction of elemental deep-level dopants, such as vanadium. Wafers cut from these crystals exhibit homogeneous activation energies near mid gap and thermally stable semi-insulating (SI) behavior (>109 ohm-cm) throughout device processing. Secondary ion mass spectroscopy, deep-level transient spectroscopy, optical admittance spectroscopy, and electron paramagnetic resonance data suggest that the SI behavior originates from several deep levels associated with intrinsic point defects. Micropipe densities in HPSI substrates have been demonstrated to be as low as 10 cm-2 in 2-in. substrates, and the room-temperature thermal conductivity of this material is near the theoretical maximum of 5 W/cm·K for 4H-SiC. Devices fabricated on these HPSI wafers do not exhibit any substrate related back-gating effects and have power densities as high as 5.2 W/mm with 63% power added efficiency.

  12. Defect studies of Vanadium doped 4H-SiC using optical admittance spectroscopy

    NASA Astrophysics Data System (ADS)

    Lee, Wonwoo

    2005-03-01

    Semi-insulating SiC is an excellent candidate for a variety of applications, including microwave FET's and other devices for high power and high temperature applications. Vanadium acts as an amphoteric impurity in 4H-SiC with a V^3+/4+ acceptor level thought to be within 1 eV of the conduction band edge and a V^4+/5+ donor level known to be 1.6 eV below the conduction band edge. Vanadium is an efficient carrier trap and recombination center. We have studied vanadium doped 4H-SiC with the optical admittance spectroscopy (OAS) at room temperature. After taking into account phonon-assisted optical transitions, the estimated threshold energies can be compared with defect levels measured using thermal techniques. Compared with data reported in the literature, our results show that the defect level Ec -1.5 eV is close to the vanadium donor level and the other level Ec -0.67 eV is within the range of the value attributed to the vanadium acceptor level.

  13. Experimental characterization of a 4H SiC high voltage current limiting device

    NASA Astrophysics Data System (ADS)

    Nallet, F.; Planson, D.; Godignon, P.; Locatelli, M. L.; Lazar, M.; Chante, J. P.

    2001-12-01

    The aim of this paper is to show the first experimental results of a 600 V 4H-SiC current limiting device. This device limits the current which flows through it as the bias voltage between its two contacts increases. The static curves obtained from the first process run (T=300 K) show a current limitation capability with a saturation voltage ranging from 10 to 15 V. The device electrical characterization shows a R ON≈150 mΩ cm 2 and a current density of 150 A cm -2 under 50 V. The forward conduction is ensured by an N type implanted channel (doping species: nitrogen) on top of an P + implanted layer (doping species: aluminum). The post-implantation annealing of 1700 °C/30 min leads to a good electrical activation (80%) of the N channel/P + layer (analyzed by C(V) and SIMS methods) and a good channel mobility (100 cm 2 V -1 s -1 for a 2×10 17 cm-3 N compensated doping concentration). The prototypes of the second process run reach a saturation current density of 900 A cm -2 with a specific on-resistance of 13 mΩ cm 2. The 4H-SiC current limiting devices of the second run belong to the best set of Accu-MOSFETs devices reported in the literature.

  14. 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…

  15. 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…

  16. Volunteer Educators' Influence on Youth Participation and Learning in 4-H STEM Learning by Design Programs

    NASA Astrophysics Data System (ADS)

    Worker, Steven Michael

    The purpose of this study was to describe the co-construction of three 4-H STEM (science, technology, engineering, and mathematics) learning by design programs by volunteer educators and youth participants in the 4-H Youth Development Program. The programs advanced STEM learning through design, a pedagogical approach to support youth in planning, designing, and making shareable artifacts. This pedagogical approach is a special case of project-based learning, related to the practices found in the science learning through design literature as well as the making and tinkering movements. Specifically, I explored adult volunteer educators' roles and pedagogical strategies implementing the 4-H Junk Drawer Robotics curriculum (Mahacek, Worker, and Mahacek, 2011) and how that, in turn, afforded and constrained opportunities for youth to display or report engagement in design practices; learning of STEM content; strengthening tool competencies; dispositions of resilience, reciprocity, and playfulness; and psychological ownership. The curriculum targeted middle school youth with a sequence of science inquiry activities and engineering design challenges. This study employed naturalist and multiple-case study methodology relying on participant observations and video, interviews with educators, and focus groups with youth within three 4-H educational robotics programs organized by adult 4-H volunteer educators. Data collection took place in 2014 and 2015 at Santa Clara with an educator and seven youth; Solano with three educators and eight youth; and Alameda with an educator and seven youth. Data analysis revealed six discrete categories of pedagogy and interactions that I labeled as participation structures that included lecture, demonstration, learning activity, group sharing, scripted build, and design & build. These participation structures were related to the observed pedagogical practices employed by the educators. There was evidence of youth engagement in design

  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. Nqrs Data for C10H12Cl4N2Pd [Cl4H2Pd·2(C5H5N)] (Subst. No. 1261)

    NASA Astrophysics Data System (ADS)

    Chihara, H.; Nakamura, N.

    This document is part of Subvolume A `Substances Containing Ag … C10H15' of Volume 48 `Nuclear Quadrupole Resonance Spectroscopy Data' of Landolt-Börnstein - Group III `Condensed Matter'. It contains an extract of Section `3.2 Data tables' of the Chapter `3 Nuclear quadrupole resonance data' providing the NQRS data for C10H12Cl4N2Pd [Cl4H2Pd·2(C5H5N)] (Subst. No. 1261)

  19. Nqrs Data for C10H12Cl4N2Pt [Cl4H2Pt·2(C5H5N)] (Subst. No. 1262)

    NASA Astrophysics Data System (ADS)

    Chihara, H.; Nakamura, N.

    This document is part of Subvolume A `Substances Containing Ag … C10H15' of Volume 48 `Nuclear Quadrupole Resonance Spectroscopy Data' of Landolt-Börnstein - Group III `Condensed Matter'. It contains an extract of Section `3.2 Data tables' of the Chapter `3 Nuclear quadrupole resonance data' providing the NQRS data for C10H12Cl4N2Pt [Cl4H2Pt·2(C5H5N)] (Subst. No. 1262)

  20. 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.

  1. 2-Amino-4-(nitroalkyl)-4H-chromene-3-carbonitriles as New Cytotoxic Agents

    PubMed Central

    Zonouzi, Afsaneh; Mirzazadeh, Roghieh; Safavi, Maliheh; Kabudanian Ardestani, Sussan; Emami, Saeed; Foroumadi, Alireza

    2013-01-01

    A series of 2-amino-4-(nitroalkyl)-4H-chromene-3-carbonitriles were synthesized by an efficient multicomponent reaction in aqueous media using DBU as a catalyst at room temperature. Mild condition, environment friendly procedure and excellent yields are the main advantages of this procedure. The cytotoxic activity of target compounds were evaluated against three cancer cell lines MDA-MB-231, MCF-7 and T47D in comparison with etoposide as reference drug. Generally, all compounds showed good cell growth inhibitory activity with IC50 values less than 30 μg/mL. Their activities were comparable or more potent than standard drug etoposide. The 6-bromo- derivatives 7e and 7f showed promising cytotoxic activity with IC50 values in the range of 3.46–18.76 μg/mL, being more potent than etoposide against all tested cell lines. PMID:24523747

  2. Synthesis of a new class of pyrrolo[3,4-h]quinazolines with antimitotic activity.

    PubMed

    Spanò, Virginia; Montalbano, Alessandra; Carbone, Anna; Parrino, Barbara; Diana, Patrizia; Cirrincione, Girolamo; Castagliuolo, Ignazio; Brun, Paola; Issinger, Olaf-Georg; Tisi, Silvia; Primac, Irina; Vedaldi, Daniela; Salvador, Alessia; Barraja, Paola

    2014-03-03

    A new series of pyrrolo[3,4-h]quinazolines was conveniently prepared with a broad substitution pattern. A large number of derivatives was obtained and the cellular cytotoxicity was evaluated in vitro against 5 different human tumor cell lines with GI₅₀ values reaching the low micromolar level (1.3-19.8 μM). These compounds were able to induce cell death mainly by apoptosis through a mitochondrial dependent pathway. Selected compounds showed antimitotic activity and a reduction of tubulin polymerization in a concentration-dependent manner. Moreover, they showed anti-angiogenic properties since reduced in vitro endothelial cell migration and disrupted HUVEC capillary-like tube network in Matrigel.

  3. Pyrazolo[3,4-h]quinolines promising photosensitizing agents in the treatment of cancer.

    PubMed

    Spanò, Virginia; Parrino, Barbara; Carbone, Anna; Montalbano, Alessandra; Salvador, Alessia; Brun, Paola; Vedaldi, Daniela; Diana, Patrizia; Cirrincione, Girolamo; Barraja, Paola

    2015-09-18

    A new series of pyrazolo[3,4-h]quinolines, heteroanalogues of angelicin was conveniently prepared with a broad substitution pattern. A large number of derivatives was obtained and the cellular photocytotoxicity was evaluated in vitro against 5 different human tumor cell lines with GI50 values reaching the nanomolar level (14.52-0.04 μM). Selected compounds were able to photoinduce a massive cell death with the involvement of mitochondria. Their photodamage cellular targets were proteins and lipids and they did not cause any kind of DNA photodamage. This latter event is of considerable importance in the modulation of long term side effects, generally associated with the use of classical furocoumarins.

  4. 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.

  5. 4H-SiC trench IGBT with lower on-state voltage drop

    NASA Astrophysics Data System (ADS)

    Liu, Yan-juan; Wang, Ying; Yu, Cheng-hao; Fei-Cao

    2017-03-01

    In this paper, a new 4H-SiC trench-gate IGBT structure incorporated a P+ shielding region in the emitter side is proposed in order to reduce the on-state voltage drop. Through the 2-D ATLAS simulation, the characteristics of the proposed structure are investigated and compared with the conventional structure. The simulation results indicate that the proposed structure exhibits an improvement in the following. Firstly, the on-state voltage drop is reduced by 32.75%. Secondly, the differential specific on-resistance is reduced by 42.33%. Finally, under the same on-state voltage drop, the turn-off energy is reduced more than 50.00%. At the end of the paper, it is explored that what effects the physical parameter of the P+ shielding region in the proposed structure have on the steady state performances.

  6. Low-energy electron scattering from C{sub 4}H{sub 9}OH isomers

    SciTech Connect

    Bettega, M. H. F.; Winstead, C.; McKoy, V.

    2010-12-15

    We present differential, integral, and momentum-transfer cross sections for elastic scattering of low-energy electrons by three butanol isomers, isobutanol, t-butanol, and 2-butanol. Our results were calculated with the Schwinger multichannel method in the static-exchange plus polarization approximation for collision energies from 1 to 50 eV. The present results are compared with previous calculations and measurements for the remaining C{sub 4}H{sub 9}OH isomer, n-butanol [Khakoo et al., Phys. Rev. A 78, 062714 (2008)]. Distinctive behavior is observed in the differential cross sections at collision energies between 5 and 10 eV. In particular, whereas n-butanol exhibits an f-wave scattering pattern, the other isomers exhibit d-wave behavior. A similar pattern is found in the related alkanes when comparing straight-chain versus branched isomers. We discuss the possible connection of this behavior to shape resonances that influence the scattering.

  7. High resolution alpha particle detectors based on 4H-SiC epitaxial layer

    NASA Astrophysics Data System (ADS)

    Zat'ko, B.; Dubecký, F.; Šagátová, A.; Sedlačová, K.; Ryć, L.

    2015-04-01

    We fabricated and characterized 4H-SiC Schottky diodes as a spectrometric detector of alpha particles. A thin blocking contact of Ni/Au (15 nm) was used to minimize the influence on alpha particles energy. Current-voltage characteristics of the detector were measured and a low current density below 0.3 nAcm-2 was observed at room temperature. 239Pu241Am244Cm was used as a source of alpha particles within the energy range between 5.1 MeV and 5.8 MeV for detector testing. The charge collection efficiency close to 100 % at reverse bias exceeding 50 V was determined. The best spectrometric performance shows a pulse height spectrum at a reverse bias of 200 V giving an energy resolution of 0.25 % in the full width and half maximum for 5.486 MeV of 241Am.

  8. NaBH4/H2O2 Fuel Cells for Lunar and Mars Exploration

    NASA Astrophysics Data System (ADS)

    Luo, Nie; Miley, George H.; Mather, Joseph; Burton, Rodney; Hawkins, Glenn; Gimlin, Richard; Rusek, John; Valdez, Tom I.; Narayanan, Sekharipuram R.

    2006-01-01

    The properties of direct hydrogen peroxide (H2O2) fuel cells are studied in this research. Different catalysts and diffusion electrodes are tested to optimize the cell performance. Initial results indicate: 1) conversion efficiency over 60% at a practical current density of 250mA/cm2; 2) power density over 0.6 W/cm2, at room temperature and ambient pressure, better than that of any traditional fuel cell. Further, the unique combination of NaBH4 and H2O2, both of which are in an aqueous form, paves the way for a convenient unitized regeneration, which is inherently compact compared to other cells that use gas phase reactants, such as the conventional H2 and O2. These excellent properties make the NaBH4/H2O2 fuel cell a very promising candidate for future space power systems. A conceptual design to power Lunar and Mars missions is discussed.

  9. High current gain 4H-SiC bipolar junction transistor

    NASA Astrophysics Data System (ADS)

    Yourun, Zhang; Jinfei, Shi; Ying, Liu; Chengchun, Sun; Fei, Guo; Bo, Zhang

    2016-04-01

    A novel 4H-SiC BJT of high current gain with a suppressing surface traps effect has been proposed. It is effective to improve the current gain due to the lower electrons density in the surface region by extending the emitter metal to overlap the passivation layer on the extrinsic base surface. The electrons trapped in the extrinsic base surface induce the degeneration of SiC BJTs device performance. By modulating the electron recombination rate, the novel structure can increase the current gain to 63.2% compared with conventional ones with the compatible process technology. Optimized sizes are an overlapped metal length of 4 μm, as well as an oxide layer thickness of 50 nm. Project supported by the National Natural Science Foundation of China (Nos. 61306093, 61401075).

  10. 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.

  11. Nitrogen-related point defect in 4H and 6H SiC

    NASA Astrophysics Data System (ADS)

    Zvanut, M. E.; van Tol, J.

    2007-12-01

    A nitrogen-related pair defect is studied as a function of doping density in 4H and 6H SiC. Electron paramagnetic resonance measurements verify that one nucleus in the pair is nitrogen, but the second part of the pair remains uncertain. The pair concentration varies monotonically with nitrogen concentration in samples with doping density 10 18-10 16 cm -3 and the boron concentration is an order of magnitude less than that of nitrogen. The pair center is not observed in the dark or under ultraviolet illumination when the nitrogen and boron concentrations are similar. We conclude that the pair is generated in all nitrogen-doped samples, but like the isolated nitrogen impurity, may be compensated by boron.

  12. Observations of deep levels in 4H-SiC using optoelectronic modulation spectroscopy

    NASA Astrophysics Data System (ADS)

    Chiu, Chi-Hsin; Parmiter, P. J. M.; Hilton, K.; Uren, M. J.; Swanson, J. G.

    2001-10-01

    Optoelectronic modulation spectroscopy (OEMS) has been used to reveal defect states in 4H-SiC. Pairs of magnitude and phase spectra have been used to infer whether they were electron or hole traps. Eleven discrete trap responses have been observed, eight were assigned as electron traps and three as hole traps. Five of these had been observed previously using optical admittance spectroscopy (OAS). An electron trap at 1.20 eV gave the most prominent response with a distinctive signature indicating that these traps were spatially delocalized with an extent of at least 1.35 nm, possibly associated with an extended defect structure. An unresolved continuum of be the superimposed response of an electron and hole trap at closely similar energies. Cosistency has been demonstrated with previous work using DLOS and OAS.

  13. 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.

  14. Mass spectrum of the butadiynyl radical (C4H; X2[summation operator]+)

    NASA Astrophysics Data System (ADS)

    Gu, Xibin; Guo, Ying; Kaiser, Ralf I.

    2005-11-01

    We utilized the crossed molecular beams method to synthesize the butadiynyl radical, C4H(X2[summation operator]+), via the reaction of dicarbon molecules with acetylene, under single collision conditions. Time-of-flight spectra of the radical were recorded at the center-of-mass angle (31°) of the parent ion (m/z = 49; C4H+) and of the fragments at m/z = 48 (C4+), m/z = 37 (C3H+), and m/z = 36 (C3+) This yields relative intensity ratios of I(m/z = 49):I(m/z = 48):I(m/z = 37):I(m/z = 36):I(m/z = 25):I(m/z = 24) = 1.0:0.67 +/- 0.07:0.47 +/- 0.06:0.2 +/- 0.02:0.08 +/- 0.02:0.04 +/- 0.02 at 70 eV electron impact energy. Signal at m/z = 13 (CH+) and 12 (C+) contribute less than 0.04 relative to the parent peak; the intensity of the 13C isotopic peak of the butadiynyl radical at m/z = 50 (13C12C3H+) depicts an intensity of 0.04 +/- 0.01 relative to m/z = 49. Employing linear scaling methods, the absolute ionization cross section of the butadiynyl radical was computed to be 8.8 +/- 1.8 × 10-16 cm2. These data can be employed in future space missions to detect the butadiynyl radical in oxygen-poor combustion flames and in the atmospheres of planets (Jupiter, Saturn, Uranus, Neptune and Pluto) and their moons (Titan, Triton and Oberon) in situ via matrix interval arithmetic assisted mass spectrometry.

  15. Picosecond pulsed laser ablation and micromachining of 4H-SiC wafers

    NASA Astrophysics Data System (ADS)

    Molian, Pal; Pecholt, Ben; Gupta, Saurabh

    2009-02-01

    Ultra-short pulsed laser ablation and micromachining of n-type, 4H-SiC wafer was performed using a 1552 nm wavelength, 2 ps pulse, 5 μJ pulse energy erbium-doped fiber laser with an objective of rapid etching of diaphragms for pressure sensors. Ablation rate, studied as a function of energy fluence, reached a maximum of 20 nm per pulse at 10 mJ/cm 2, which is much higher than that achievable by the femtosecond laser for the equivalent energy fluence. Ablation threshold was determined as 2 mJ/cm 2. Scanning electron microscope images supported the Coulomb explosion (CE) mechanism by revealing very fine particulates, smooth surfaces and absence of thermal effects including melt layer formation. It is hypothesized that defect-activated absorption and multiphoton absorption mechanisms gave rise to a charge density in the surface layers required for CE and enabled material expulsion in the form of nanoparticles. Trenches and holes micromachined by the picosecond laser exhibited clean and smooth edges and non-thermal ablation mode for pulse repetition rates less than 250 kHz. However carbonaceous material and recast layer were noted in the machined region when the pulse repetition rate was increased 500 kHz that could be attributed to the interaction between air plasma and micro/nanoparticles. A comparison with femtosecond pulsed lasers shows the promise that picosecond lasers are more efficient and cost effective tools for creating sensor diaphragms and via holes in 4H-SiC.

  16. Hydride CVD Hetero-epitaxy of B12P2 on 4H-SiC

    NASA Astrophysics Data System (ADS)

    Frye, C. D.; Saw, C. K.; Padavala, Balabalaji; Nikolić, R. J.; Edgar, J. H.

    2017-02-01

    Icosahedral boron phosphide (B12P2) is a wide bandgap semiconductor (3.35 eV) that has been reported to "self-heal" from high-energy electron bombardment, making it attractive for potential use in radioisotope batteries, radiation detection, or in electronics in high radiation environments. This study focused on improving B12P2 hetero-epitaxial films by growing on 4H-SiC substrates over the temperature range of 1250-1450 °C using B2H6 and PH3 precursors in a H2 carrier gas. XRD scans and Laue transmission photographs revealed that the epitaxial relationship was (0001)< 11 2 bar 0 > B12P2 ∥ (0001)< 11 2 bar 0 > 4 H - SiC . The film morphology and crystallinity were investigated as a function of growth temperature and growth time. At 1250 °C, films tended to form rough, polycrystalline layers, but at 1300 and 1350 °C, films were continuous and comparatively smooth (RRMS ≤ 7 nm). At 1400 or 1450 °C, the films grew in islands that coalesced as the films became thicker. Using XRD rocking curves to evaluate the crystal quality, 1300 °C was the optimum growth temperature tested. At 1300 °C, the rocking curve FWHM decreased with increasing film thickness from 1494 arcsec for a 1.1 μm thick film to 954 arcsec for a 2.7 μm thick film, suggesting a reduction in defects with thickness.

  17. Device design assessment of 4H-SiC n-IGBT - A simulation study

    NASA Astrophysics Data System (ADS)

    Usman, Muhammad; Nawaz, Muhammad

    2014-02-01

    A theoretical design assessment is presented using two dimensional numerical computer aided design (TCAD) tool for 15-20 kV 4H-SiC IGBTs. Physical parameters of the layer structures such as drift layer thickness, doping in the drift layer, JFET region width and interface charges underneath the gate region are varied to predict the device performance. Performance is further assessed at different temperatures and with different carrier lifetime in the drift layer. Using identical set of physical device parameters (doping, thicknesses), simulated structure was first calibrated with the experimental data. Simulations show that a minority carrier lifetime in the drift layer of 1.0-1.6 μs produces a close match with the experimental device. An on-resistance first decays with temperature (i.e., increased in ionization level, and increase in minority carrier lifetime), stays nearly constant with further increase in the temperature (may be all carriers are now fully ionized and increase in carrier lifetime is compensated with decrease in the carrier mobility) and finally increases linearly with temperature (>450 K) due to decrease in the carrier mobility. A significant increase in the forward voltage drop is observed with the presence of interface trap charges. Increasing JFET region width slightly decreases the forward on-state voltage. A drift layer of at least 175 μm thick with a doping concentration of < 2.0 × 1014 cm-3 is required to get a blocking voltage of 20 kV for 4H-SiC IGBTs assuming a minority carrier lifetime of 1 μs in the drift layer.

  18. 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.

  19. 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.

  20. Defect studies in 4H- Silicon Carbide PVT grown bulk crystals, CVD grown epilayers and devices

    NASA Astrophysics Data System (ADS)

    Byrappa, Shayan M.

    been recognizing BPDs as deformation induced defects which have led to the development of strategies to reduce stress imperative for the motion of BPDs to levels below critical resolved shear stress. This in turn has provided an opportunity for last five years to resolve important defect interactions in the crystals with one of them being the operation of single-ended Frank Read source for the first time in SiC. [4] Failure analysis of SiC bipolar devices using SWBXT and correlation with defect density has been studied to determine how the defect density affect breakdown voltage of high power junction diodes. It was observed that the screw dislocation density unlike in failure analysis studies performed previously did not affect the breakdown voltage for these Junction Barrier Schottky (JBS) rectifiers. The defects that were detrimental were the triangular defects, stacking faults and micropipes in bipolar devices observed on 4H-SiC patterned wafers.

  1. Electronic spectrum and photodissociation chemistry of the linear methyl propargyl cation H2C4H3+

    NASA Astrophysics Data System (ADS)

    Catani, Katherine J.; Muller, Giel; da Silva, Gabriel; Bieske, Evan J.

    2017-01-01

    The electronic spectrum of the methyl propargyl cation (2-butyn-1-yl cation, H2C4H3+) is measured over the 230-270 nm range by photodissociating the bare cation and its Ar and N2 tagged complexes in a tandem mass spectrometer. The observed '1A←'1A band system has an origin at 37 753 cm-1 for H2C4H3+ , 37738 cm-1 for H2C4H3+ - Ar, and 37 658 cm-1 for H2C4H3+ - N2. The methyl propargyl cation photodissociates to produce either C2H3++C2H2 (protonated acetylene + acetylene) or H2C4H+ +H2 (protonated diacetylene + dihydrogen). Photodissociation spectra of H2C4H3+ , H2C4H3+ - Ar, and H2C4H3+ - N2 exhibit similar vibronic structure, with a strong progression of spacing 630 cm-1 corresponding to excitation of the C—C stretch mode. Interpretation of the spectra is aided by ground and excited state calculations using time dependent density functional theory at the ωB97X-D/aug-cc-pVDZ level of theory. Ab initio calculations and master equation simulations were used to interpret the dissociation of H2C4H3+ on the ground state manifold. These calculations support the experimentally observed product branching ratios in which acetylene elimination dominates and also suggests that channel switching occurs at higher energies to favor H2 elimination.

  2. Implantation-Free 4H-SiC Bipolar Junction Transistors with Double Base Epi-layers

    DTIC Science & Technology

    2007-05-14

    gain 4H-SiC NPN power bipolar junction transistor ,” IEEE Electron Device Letters, vol. 24, pp. 327-329, May 2003. [3] C.-F. Huang and J. A. Cooper...Jr., “High current gain 4H-SiC NPN Bipolar Junction Transistors ,” IEEE Electron Device Letters, vol. 24, pp. 396-398, Jun. 2003. [4] Sumi...Implantation-Free 4H-SiC Bipolar Junction Transistors with Double Base Epi-layers Jianhui Zhang, member, IEEE, Xueqing, Li, Petre Alexandrov

  3. 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

  4. 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…

  5. 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.

  6. Effects of remote hydrogen plasma on chemical bonding features and electronic states of 4H-SiC(0001) surface

    NASA Astrophysics Data System (ADS)

    Truyen, Nguyen Xuan; Ohta, Akio; Makihara, Katsunori; Ikeda, Mitsuhisa; Miyazaki, Seiichi

    2017-01-01

    We have demonstrated a novel dry cleaning process for the 4H-SiC surface using remote hydrogen plasma (H2-RP). The effects of H2-RP exposure on the chemical structures and electronic states of the wet-cleaned 4H-SiC surface have been evaluated by X-ray photoelectron spectroscopy (XPS) and total photoelectron yield spectroscopy (PYS). XPS shows that H2-RP exposure is effective in removing contaminants from the 4H-SiC surface. PYS indicates that the defect states at the surface are generated after the H2-RP exposure and such generated defect states are drastically decreased by annealing at 850 °C. The combination of H2-RP exposure with the subsequent annealing is found to be effective in 4H-SiC surface cleaning.

  7. 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∘.

  8. 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

  9. 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.

  10. 76 FR 77107 - Airworthiness Directives; Pratt & Whitney Corp. (PW) JT9D-7R4H1 Turbofan Engines

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-12-12

    ... Administration 14 CFR Part 39 [Docket No. FAA-2011-0731; Directorate Identifier 2010-NE-39-AD; Amendment 39-16886; AD 2011-25-10] RIN 2120-AA64 Airworthiness Directives; Pratt & Whitney Corp. (PW) JT9D-7R4H1 Turbofan... new airworthiness directive (AD) for all PW JT9D-7R4H1 turbofan engines. This AD was prompted...

  11. Effects on murine behavior and lifespan of selectively decreasing expression of mutant huntingtin allele by supt4h knockdown.

    PubMed

    Cheng, Hui-Min; Chern, Yijuang; Chen, I-Hui; Liu, Chia-Rung; Li, Sih-Huei; Chun, Seung J; Rigo, Frank; Bennett, C Frank; Deng, Ning; Feng, Yanan; Lin, Chyuan-Sheng; Yan, Yu-Ting; Cohen, Stanley N; Cheng, Tzu-Hao

    2015-03-01

    Production of protein containing lengthy stretches of polyglutamine encoded by multiple repeats of the trinucleotide CAG is a hallmark of Huntington's disease (HD) and of a variety of other inherited degenerative neurological and neuromuscular disorders. Earlier work has shown that interference with production of the transcription elongation protein SUPT4H results in decreased cellular capacity to transcribe mutant huntingtin gene (Htt) alleles containing long CAG expansions, but has little effect on expression of genes containing short CAG stretches. zQ175 and R6/2 are genetically engineered mouse strains whose genomes contain human HTT alleles that include greatly expanded CAG repeats and which are used as animal models for HD. Here we show that reduction of SUPT4H expression in brains of zQ175 mice by intracerebroventricular bolus injection of antisense 2'-O-methoxyethyl oligonucleotides (ASOs) directed against Supt4h, or in R6/2 mice by deletion of one copy of the Supt4h gene, results in a decrease in mRNA and protein encoded specifically by mutant Htt alleles. We further show that reduction of SUPT4H in mouse brains is associated with decreased HTT protein aggregation, and in R6/2 mice, also with prolonged lifespan and delay of the motor impairment that normally develops in these animals. Our findings support the view that targeting of SUPT4H function may be useful as a therapeutic countermeasure against HD.

  12. 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.

  13. Tetrasilvermesoperiodate, Ag 4H 2I 2O 10: Structure and Color Phenomenon

    NASA Astrophysics Data System (ADS)

    Trnoska, Andreas; Nachbaur, Edgar; Belaj, Ferdinand

    1994-12-01

    A single-crystal X-ray structural analysis of the material previously known as "Ag2HIO5" has shown it to be Ag4H2I2O10, Mr = 847.29, monoclinic, P21/n, a = 6.243(3), b = 7.247(3), c = 10.196(4) Å, β = 98.00(3)°, V = 456.8(3) Å3, Z = 2, Dx = 6.160 g cm-3, λ(MoKα) = 0.71069 Å, μ = 151.1 cm-1, F(000) = 744, T = 90K, R = 0.0570, wR = 0.0547, S = 1.85 for 898 unique observed reflections and 73 parameters. The dark-red crystal is composed of centrosymmetric H2I2O4-10 ions built up of two edge-sharing IO5(OH) units. The Ag+ ions equally surrounding the anion display the coordination numbers 5 and 7. The shortest Ag-Ag distance is 3.321(2) Å, revealing the absence of any attractive Ag-Ag interaction. The geometrical parameters obtained for the H2I2O4-10 ion are in close accordance with those reported for the same anion in the colorless alkaline metal salts. The color-induction phenomenon is due to considerable covalent Ag-O interaction causing a red shift of electronic transitions in the "cation-anion complex".

  14. 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

  15. Radiation-stimulated photoluminescence in electron irradiated 4H-SiC

    NASA Astrophysics Data System (ADS)

    Lebedev, A. A.; Ber, B. Ya; Seredova, N. V.; Kazantsev, D. Yu; Kozlovski, V. V.

    2015-12-01

    The photoluminescence (PL) arising in low doped CVD grown n- and p-type 4H-SiC upon electron irradiation (0,9 MeV) has been studied. After each doze of irradiation spectrum of PL was measured. The PL spectrum was dominated by a band peaked at hv  ≈  2,45 eV, commonly observed upon irradiation of SiC. The experiments demonstrated that, for samples with both types of conduction, the PL intensity approaches a constant value with increasing irradiation dose. A model was suggested, describing the PL characteristics in terms of the radiative recombination via a donor-acceptor pair constituted by nitrogen and a structural defect formed in the course of irradiation. Also, the concentration of nitrogen atoms was measured by the SIMS method. The experimental data were used to calculate in terms of the suggested model the dependence of the PL intensity on the irradiation dose. A good agreement between the calculated and experimental dependences was observed. A conclusion is made that the PL is activated by donor—acceptor pairs constituted by a nitrogen atom and a structural defect.

  16. Atomic Computer Simulations of Defect Migration in 3C and 4H-SiC

    SciTech Connect

    Gao, Fei; Weber, William J.; Posselt, Matthias; Belko, V

    2004-05-19

    Knowledge of the migration of intrinsic point defects is crucial to understand defect recovery, various annealing stages and microstructural evolution after irradiation or ion implantation. Molecular dynamics (MD) and the nudged-elastic band method have been applied to investigate long-range migration of point defects in SiC over the temperature range from 0.36 to 0.95 Tm , and the defect diffusion coefficient, activation energy and defect correlation factor have been determined. The results show that the activation energies for C and Si interstitials in 3C-SiC are about 0.74 and 1.53 eV, respectively, while it is about 0.77 eV for a C interstitial in 4H-SiC. The minima energy paths reveal that the activation energies for C and Si vacancies are about 4.1 and 2.35 eV, respectively. Finally, the results are discussed and compared with experimental observations and available ab initio data.

  17. Radiation detector based on 4H-SiC used for thermal neutron detection

    NASA Astrophysics Data System (ADS)

    Zaťko, B.; Šagátová, A.; Sedlačková, K.; Boháček, P.; Sekáčová, M.; Kohout, Z.; Granja, C.; Nečas, V.

    2016-11-01

    In this work we have focused on detection of thermal neutrons generated by 239Pu-Be isotopic neutron source. A high quality liquid phase epitaxial layer of 4H-SiC was used as a detection region. The thickness of the layer was 70 μ m and the diameter of circular Au/Ni Schottky contact was 4.5 mm. Around the Schottky contact two guard rings were created. The detector structure was first examined as a detector of protons and alpha particles for energy calibration. Monoenergetic protons of energies from 300 keV up to 1.9 MeV were used for detector energy calibration and a good linearity was observed. The energy resolution of 35 keV was obtained for 1.9 MeV protons. The 6LiF conversion layer was applied on the detector Schottky contact. In the experiment we used different thicknesses of conversion layers from 5 μ m up to 35 μ m. Measured detected spectra show two parts corresponding to alpha particles detection in lower energy channels and 3H in higher energy channels. We have also performed simulations of thermal neutron detection using MCNPX (Monte Carlo N-particle eXtended) code. The detection efficiency and the detector response to thermal neutrons was calculated with respect to the 6LiF layer thickness. The detection efficiency calculation is found to be in good agreement with the experiment.

  18. 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

    2015-09-10

    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.

  19. 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.

  20. 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.

  1. 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.

  2. Plasma monitoring of nanoparticles formation in SiH4/H2 discharges

    NASA Astrophysics Data System (ADS)

    Alexiou, Giannis; Tsigaras, Giannis; Amanatides, Eleftherios; Mataras, Dimitrios; Plasma Technology Laboratory-Department of Chemical Engineering-University of Patras Team

    2016-09-01

    Radio-frequency SiH4/H2 discharges is the most common technique for the growth of silicon thin films. Nanoparticles formation and uncontrollable agglomeration to dust is common drawback of such type of discharges due to the extensive reactivity of the species produced in the gas phase. In this work, we deposited silicon films in different plasma conditions while monitoring at the same time nanoparticles formation. The experiments were performed under Continuous Wave (CW) and Pulsed Plasma generation in order to control particles formation. Different time-resolved plasma diagnostics, such as Optical Emission Imaging, Laser Light Scattering and self-bias voltage (Vdc) measurements were used for the detection of particles. Mass spectrometry was also used to record higher silanes formation during the deposition. The deposited films were characterized in terms of crystallinity, hydrogen content and optical properties by Laser Raman, Fourier Transformed Infrared and UV/Vis spectroscopy. Finally, Atomic Force Microscopy (AFM) was applied to monitor the morphology and roughness of the films. The properties and the morphology of the deposited films are compared in order to determine the effect of the particles formation on the material's quality.

  3. Tuning a Schottky barrier of epitaxial graphene/4H-SiC (0001) by hydrogen intercalation

    SciTech Connect

    Dharmaraj, P.; Justin Jesuraj, P.; Jeganathan, K.

    2016-02-01

    We report the electron transport properties of epitaxial graphene (EG) grown on 4H-SiC (0001) by low energy electron-beam irradiation. As-grown EG (AEG) on SiC interface exhibits rectifying current-voltage characteristics with a low Schottky barrier (SB) of 0.55 ± 0.05 eV and high reverse current leakage. The SB of AEG/SiC junction is extremely impeded by the Fermi level pinning (FLP) above the Dirac point due to charged states at the interface. Nevertheless, a gentle hydrogen intercalation at 900 °C enables the alleviation of both FLP and carrier scattering owing to the saturation of dangling bonds as evidenced by the enhancement of SB (0.75 ± 0.05 eV) and high electron mobility well excess of 6000 cm{sup 2} V{sup −1} s{sup −1}.

  4. Compensation mechanism in high purity semi-insulating 4H-SiC

    NASA Astrophysics Data System (ADS)

    Mitchel, W. C.; Mitchell, William D.; Smith, H. E.; Landis, G.; Smith, S. R.; Glaser, E. R.

    2007-03-01

    A study of deep levels in high purity semi-insulating 4H-SiC has been made using temperature dependent Hall effect (TDH), thermal and optical admittance spectroscopies, and secondary ion mass spectrometry (SIMS). Thermal activation energies from TDH varied from a low of 0.55eV to a high of 1.65eV. All samples studied showed n-type conduction with the Fermi level in the upper half of the band gap. Fits of the TDH data to different charge balance equations and comparison of the fitting results with SIMS measurements indicated that the deep levels are acceptorlike even though they are in the upper half of the band gap. Carrier concentration measurements indicated that the deep levels are present in concentrations in the low 1015cm-3 range, while SIMS results demonstrate nitrogen and boron concentrations in the low to mid-1015-cm-3 range. The results suggest that compensation in this material is a complex process involving multiple deep levels.

  5. Point defects induced in ion irradiated 4H-SiC probed by exciton lines

    NASA Astrophysics Data System (ADS)

    Litrico, G.; Zimbone, M.; Calcagno, L.; Musumeci, P.; Baratta, G. A.; Fotil, G.

    2009-05-01

    The defects produced in 4H-SiC epitaxial layers by irradiation with a 200 keV H+ ion beam in the fluence range 6.5 × 1011-1.8 × 1013 ions/cm2 are investigated by Low Temperature Photoluminescence (LTPL-40 K). The defects produced by ion beam irradiation induce the formation of some sharp lines called "alphabet lines" in the photoluminescence spectra in the 425-443 nm range, due to the recombination of excitons at structural defects. From the LTPL lines intensity trend, as function of proton fluence, it is possible to single out two groups of peaks: the P1 lines (e, f, g) and the P2 lines (a, b, c, d) that exhibit different trends with the ion fluence. The P1 group normalized yield increases with ion fluence, reaches a maximum at 2.5 × 1012 ions/cm2 and then decreases. The P2 group normalized yield, instead, exhibits a formation threshold at low fluence, then increases until a maximum value at a fluence of 3.5 × 1012 ions/cm2 and decreases at higher fluence, reaching a value of 50% of the maximum yield. The behaviour of P1 and P2 lines, with ion fluence, indicates a production of point defects at low fluence, followed by a subsequent local rearrangement creating complex defects at high fluence.

  6. 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.

  7. High energy N + ion implantation in 4H-SiC

    NASA Astrophysics Data System (ADS)

    Oliviero, E.; Lazar, M.; Gardon, A.; Peaucelle, C.; Perrat, A.; Grob, J. J.; Raynaud, C.; Planson, D.

    2007-04-01

    Box profiles were formed in 4H-SiC epilayers by different combination of multi-energy N+ ion implantations at room temperature, with energy ranges varying from [0.5-2 MeV] to [0.4-4 MeV]. The fluences were adjusted in order to keep a constant plateau concentration between 2 and 3 × 1018 cm-3. Post-implantation annealing were performed at 1650 or 1800 °C up to 45 min in ultra-pure argon atmosphere, to activate the dopants. During this process, some samples were encapsulated with a graphite (C) cap obtained by thermal conversion of a spin-coated AZ5214E photoresist. Both as-implanted and annealed samples were analyzed by Rutherford Backscattering Spectroscopy in channeling mode (RBS/C) with 3.5 MeV He+ beam to quantify the induced damage. Dopant profiles were obtained by Secondary Ion Mass Spectroscopy (SIMS) measurements and compared to Monte-Carlo (MC) simulation.

  8. Influence of base carrier lifetime on the characteristics of 4H-SiC BJTs

    NASA Astrophysics Data System (ADS)

    Lei, Yuan; Qingwen, Song; Xiaoyan, Tang; Yimeng, Zhang; Shuai, Yang; Yimen, Zhang; Lixin, Guo; Li, Xiao; Liangyong, Wang; Yuming, Zhang

    2017-02-01

    The optimum range of the base electron lifetime (τnB0) in silicon carbide (SiC) bipolar junction transistors (BJTs) is qualitatively investigated in this paper, considering both the static and dynamic performance. The TCAD simulation results show that there is tradeoff between the current gain (β) and the turn-off time (tF). With τnB0 increasing, both β and tF increase. However, with a fixed base width, the base transport factor tends toward saturation when τnB0 exceeds certain value. Thus, the eclectic values of base electron lifetime with different base thickness are obtained. The influence of the base drive current is also discussed. According to the charge control theory, the excessive storage charge caused by overdrive has a great influence on turn-off delay time (tD). To solve this, a suitable base drive current is necessary. For the common 4H-SiC BJT structure, appropriate base drive under variable base and collector doping concentration is suggested.

  9. 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

  10. Al-implanted on-axis 4H-SiC MOSFETs

    NASA Astrophysics Data System (ADS)

    Florentin, M.; Cabello, M.; Rebollo, J.; Montserrat, J.; Brosselard, P.; Henry, A.; Godignon, P.

    2017-03-01

    In this paper, the impact of temperature and time stress on gate oxide stability of several multi-implanted and epitaxied 4H-SiC nMOSFET is presented. The oxide layer was processed under a rapid thermal process (RTP) furnace. The variation of the main electrical parameters is shown. We report the high quality and stability of such implanted MOSFETs, and point out the very low roughness effect of the on-axis-cut sample. Particularly, in the best case, effective channel mobility (μ fe) overcomes 20 cm2.V‑1.s‑1 at 300 °C for a channel length of 12 μm, which is very encouraging for implantation technology. Starting from 200 °C, the apparent increase of the μ fe peak of the MOSFET ceases and tends to saturate with further temperature increase. This is an indication of the potential of MOSFETs built on on-axis substrates. Thus, starting from the real case of an implanted MOSFET, the global purpose is to show that the electrical performance of such an on-axis-built device can tend to reach that of the ideal case, i.e. epitaxied MOSFET, and even overcome its electrical limitation, e.g. in terms of threshold voltage stability at high temperature.

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

    NASA Astrophysics Data System (ADS)

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

    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.

  12. The effect of irradiation with high-energy protons on 4H-SiC detectors

    SciTech Connect

    Kazukauskas, V. Jasiulionis, R.; Kalendra, V.; Vaitkus, J.-V.

    2007-03-15

    The effect of irradiation of 4H-SiC ionizing-radiation detectors with various doses (as high as 10{sup 16} cm{sup -2}) of 24-GeV protons is studied. Isotopes of B, Be, Li, He, and H were produced in the nuclear spallation reactions of protons with carbon. Isotopes of Al, Mg, Na, Ne, F, O, and N were produced in the reactions of protons with silicon. The total amount of the produced stable isotopes varied in proportion with the radiation dose from 1.2 x 10{sup 11} to 5.9 x 10{sup 13} cm{sup -2}. It is shown that, at high radiation doses, the contact characteristics of the detectors change appreciably. The potential-barrier height increased from the initial value of 0.7-0.75 eV to 0.85 eV; the rectifying characteristics of the Schottky contacts deteriorated appreciably. These effects are attributed to the formation of a disordered structure of the material as a result of irradiation.

  13. 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.

  14. Planar edge terminations for high voltage 4H-SiC power MOSFETs

    NASA Astrophysics Data System (ADS)

    Soler, Victor; Berthou, Maxime; Mihaila, Andrei; Monserrat, Josep; Godignon, Philippe; Rebollo, José; Millán, José

    2017-03-01

    Several edge termination structures for high voltage 4H-SiC devices compatible with a planar power MOSFET fabrication process are analyzed in this paper. The edge terminations’ efficiency has been experimentally demonstrated on PiN diodes with breakdown voltage capabilities ranging from 2 to 5 kV, fabricated within a full power MOSFET process technology. The studied edge terminations consist of typical JTEs, novel FGRs using MOSFET P-well implantation, as well as a combination of JTEs and FGRs. The experimental results have shown a good efficiency of most of the implemented edge terminations. It is also shown that P-well FGRs could be an effective cost solution for high voltage SiC based power MOSFETs. Moreover, the edge termination combining JTEs and FGRs concepts shows a better tolerance of breakdown voltage values against variations in the JTE dose. The same edge termination design allows one to obtain a good efficiency for both 1.7 and 4.5 kV PiN diodes. The optimal termination has been successfully implemented on 4.5 kV power MOSFETs.

  15. 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.

  16. 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.

  17. Time resolved QCLAS measurements in pulsed cc-rf CF4/H2 plasmas

    NASA Astrophysics Data System (ADS)

    Stepanov, S.; Welzel, S.; Röpcke, J.; Meichsner, J.

    2009-03-01

    Fluorocarbon containing capacitively coupled radio frequency (cc-rf) plasmas are widely used in technical applications and as model systems for fundamental investigations of complex plasmas. Absorption spectroscopy based on pulsed quantum cascade lasers (QCL) was applied in the mid-IR spectral range of 1269-1275 cm-1. Absolute densities of the precursor molecule CF4 and of the stable product C3F8 were measured with a time resolution of up to 1 ms in pulsed CF4/H2 asymmetrical cc-rf (13.56 MHz) discharges. For this purpose both the non-negligible temperature dependence of the absorption coefficients and the interference of the absorption features of CF4 and C3F8 had to be taken into account in the target spectral range. Therefore, at two different spectral positions composite absorption spectra were acquired under the same plasma conditions in order to discriminate between CF4 and C3F8 contributions. A total consumption of~ 12 % was observed for CF4 during a 1 s plasma pulse, whereas C3F8 appeared to be produced mainly from amorphous fluorocarbon layers deposited at the reactor walls. A gas temperature increase by ~ 100 K in the plasma pulse was estimated from the measurements. Additionally, not yet identified unresolved absorption (potentially from the excited CF4 molecule) was found during the àon-phase'.

  18. Thermodynamics of the superconducting phase in compressed GeH4(H2)2

    NASA Astrophysics Data System (ADS)

    Szcze&şacute; niak, R.; Szcze&şacute; niak, D.; Durajski, A. P.

    2014-04-01

    Recent studies on the hydrogen-rich metals are mainly stimulated by the fact that these superconductors are supposed to exhibit the high value of the critical temperature (TC). The thermodynamic properties of GeH4(H2)2 hydride under the pressure at 250 GPa have been studied in the present paper. The calculations have been conducted in the framework of the Eliashberg approach for the wide range of the Coulomb pseudopotential values: μ⋆∈<0.1,0.3>. It has been found that the critical temperature is high in the entire range of the Coulomb pseudopotential: TC∈<128.5,69.8> K. The values of the thermodynamic dimensionless ratios, namely RΔ≡2Δ(0)/kBTC, RC≡ΔC(TC)/CN(TC), and RH≡TCCN(TC)/HC2(0), differ from the predictions of the Bardeen-Cooper-Schrieffer theory. In particular, RΔ∈<4.30,4.08>, RC∈<1.91,1.58>, and RH∈<0.151,0.154>. Finally, the ratio of the electron effective mass (me⋆) to the electron band mass (me) reaches the maximum at the critical temperature, where me⋆/me=2.45.

  19. 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.

  20. 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.

  1. Effect of Helium implantation on gettering and electrical properties of 4H-SiC epilayers

    SciTech Connect

    Biondo, Stephane; Regula, Gabrielle; Ottaviani, Laurent; Palais, Olivier; Pichaud, Bernard

    2011-01-07

    This paper tests the gettering ability of sites created by He implantation in 4H-SiC while heating the sample or not, and their impact on carrier lifetime. The spatial distribution of implantation-induced defects (cavities, stacking faults and dislocations) is studied by transmission electron microscopy (TEM) and is compared to gold profiles performed by Rutherford Backscattering (RBS) in samples intentionally contaminated with gold. Minority carrier lifetimes are also measured with a specific set-up based on microwave photoconductivity decay ({mu}-PCD). Though gold atoms do not seem to be efficiently trapped by cavities, the presence of dislocations is of major importance to monitor gold diffusion. Indeed, they can double both its level and its diffusion length in the bulk. Gold is assumed to diffuse faster along dislocation cores. Besides, the implantation-related defects are found to improve the carrier lifetime in the material, but the role of He{sup 2+} left in cavities remains to be investigated.

  2. Electron spin coherence of silicon vacancies in proton-irradiated 4H-SiC

    NASA Astrophysics Data System (ADS)

    Embley, J. S.; Colton, J. S.; Miller, K. G.; Morris, M. A.; Meehan, M.; Crossen, S. L.; Weaver, B. D.; Glaser, E. R.; Carter, S. G.

    2017-01-01

    We report T2 spin coherence times for electronic states localized in Si vacancies in 4 H -SiC . Our spin coherence study included two SiC samples that were irradiated with 2 MeV protons at different fluences (1013 and 1014c m-2 ) in order to create samples with unique defect concentrations. Using optically detected magnetic resonance and spin echo, the coherence times for each sample were measured across a range of temperatures from 8 to 295 K. All echo experiments were done at a magnetic field strength of 0.371 T and a microwave frequency of 10.49 GHz. The longest coherence times were obtained at 8 K, being 270 ±61 μ s for the 1013c m-2 proton-irradiated sample and 104 ±17 μ s for the 1014c m-2 sample. The coherence times for both samples displayed unusual temperature dependencies; in particular, they decreased with temperature until 60 K, then increased until 160 K, then decreased again. This increase between 60 and 160 K is tentatively attributed to a motional Jahn-Teller effect. The consistently longer lifetimes for the 1013c m-2 sample suggest that a significant source of the spin dephasing can be attributed to dipole-dipole interactions between Si vacancies or with other defects produced by the proton irradiation. The lack of a simple exponential decay for our 1014c m-2 sample indicates an inhomogeneous distribution of defect spins.

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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.

  4. Web Growth Used to Confine Screw Dislocations to Predetermined Lateral Positions in 4H-SiC Epilayers

    NASA Technical Reports Server (NTRS)

    Powell, J. Anthony; Neudeck, Philip G.; Spry, David J.; Trunek, Andrew J.; Beheim, Glenn M.

    2004-01-01

    cantilever coalescence point (P2). No defects (i.e., no etch pits) are observed in other cantilevered portions of the film surface. On the basis of the principle of dislocation Burgers vector conservation, we hypothesize that all vertically propagating substrate dislocations in an enclosed trench region become combined into a single dislocation in the webbed film roof at the point of final roof coalescence. The point of final roof coalescence, and therefore the lateral location of a webbed roof dislocation, can be designed into the pregrowth mesa pattern. Screw dislocations with predetermined lateral positions can then be used to provide the new growth steps necessary for growing a 4H/6H-SiC epilayer with a lower dislocation density than the substrate. Devices fabricated on top of such films can be positioned to avoid the preplaced dislocations.

  5. High-voltage 4H-SiC PiN diodes with the etched implant junction termination extension

    NASA Astrophysics Data System (ADS)

    Li, Juntao; Xiao, Chengquan; Xu, Xingliang; Dai, Gang; Zhang, Lin; Zhou, Yang; Xiang, An; Yang, Yingkun; Zhang, Jian

    2017-02-01

    This paper presents the design and fabrication of an etched implant junction termination extension (JTE) for high-voltage 4H-SiC PiN diodes. Unlike the conventional JTE structure, the proposed structure utilizes multiple etching steps to achieve the optimum JTE concentration range. The simulation results show that the etched implant JTE method can improve the blocking voltage of SiC PiN diodes and also provides broad process latitude for parameter variations, such as implantation dose and activation annealing condition. The fabricated SiC PiN diodes with the etched implant JTE exhibit a highest blocking voltage of 4.5 kV and the forward on-state voltage of 4.6 V at room temperature. These results are of interest for understanding the etched implant method in the fabrication of high-voltage power devices. Project supported by the Science and Technology Development Foundation of China Academy of Engineering Physics (No. 2014A05011) and the Special Foundation of President of China Academy of Engineering Physics (No. 2014-1-100).

  6. Role of the oxidizing agent in the etching of 4H-SiC substrates with molten KOH

    NASA Astrophysics Data System (ADS)

    Na, Moonkyong; Kang, In Ho; Moon, Jeong Hyun; Bahng, Wook

    2016-12-01

    A novel etching solution using molten potassium hydroxide (KOH) for the identification of dislocation types in a silicon-carbide (SiC) epilayer is identified. Threading screw dislocations (TSDs) and threading edge dislocations (TEDs) are rarely useful for size-based differentiation of etch pits in highly nitrogen (N)-doped SiC through conventional KOH etching. In this study, we report the role of sodium peroxide (Na2O2) and potassium dioxide (KO2) as oxidizing agent additives to the etchant for identifying the dislocation types in highly N-doped 4H-SiC. A Na2O2-KOH phase diagram was calculated to predict the chemical composition of the etchant. Solid-phase Na2O2 remained in the system when added to the etchant at concentrations greater than 13-wt% Na2O2, and it provided excess oxygen to the etchant. We experimentally confirmed that etch pit shapes became more hexagonal and that the etch pit sizes of TSDs and TEDs differed more greatly when more than 20-wt% Na2O2 was added to the etchant. We also found that the size distribution of TEDs was much smaller than that of TSDs after etching using Na2O2-KOH. Dissolved oxygen played an essential role in enhancing the anisotropic etching of highly N-doped SiC and allowed the dislocation types to be identified.

  7. An ab initio electronic density study of the CH4-Ar, CH4-Xe, CH4-H2O and CH4-H2S complexes: insights into the nature of the intermolecular interaction

    NASA Astrophysics Data System (ADS)

    Bartocci, Alessio; Frati, Federica; Roncaratti, Luiz F.; Cappelletti, David; Tarantelli, Francesco; Belpassi, Leonardo; Pirani, Fernando

    2015-12-01

    The main point of this paper concerns the theoretical characterisation of the effects induced by the intermolecular interaction on the electron density upon the formation of CH4-H2X (X=O,S) and CH4-Ng (Ng=Ar,Xe) complexes. The work has been stimulated by recent molecular scattering beams experiments, which point out differences in both strength and anisotropy of the intermolecular potential between CH4-H2X respect to reference CH4-Ng systems. Herein, attention is focused on the electronic charge polarisation and particularly charge transfer (CT) effects between involved partners, directly related to the topology of the full potential energy surface. The modification of electron density and the occurrence of CT have been evaluated via the charge displacement function worked out by high level ab initio calculations. Moreover, in the case of a specific configuration of CH4-H2O system, we define the leading interaction components, including their relative stabilising role and test our intermolecular potential model with reference to ab initio calculations. The results obtained indicate that CT clearly affects the strength and the anisotropy of CH4-H2O complex, and covers a minor and negligible role for CH4-H2S and the noble gas complexes, respectively.

  8. 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.

  9. 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.

  10. 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

  11. Size effect on high temperature variable range hopping in Al+ implanted 4H-SiC

    NASA Astrophysics Data System (ADS)

    Parisini, Antonella; Parisini, Andrea; Nipoti, Roberta

    2017-01-01

    The hole transport properties of heavily doped 4H-SiC (Al) layers with Al implanted concentrations of 3  ×  1020 and 5  ×  1020 cm-3 and annealed in the temperature range 1950-2100 °C, have been analyzed to determine the main transport mechanisms. This study shows that the temperature dependence of the resistivity (conductivity) may be accounted for by a variable range hopping (VRH) transport into an impurity band. Depending on the concentration of the implanted impurities and the post-implantation annealing treatment, this VRH mechanism persists over different temperature ranges that may extend up to room temperature. In this framework, two different transport regimes are identified, having the characteristic of an isotropic 3D VRH and an anisotropic nearly 2D VRH. The latter conduction mechanism appears to take place in a rather thick layer (about 400 nm) that is too large to induce a confinement effect of the carrier hops. The possibility that an anisotropic transport may be induced by a structural modification of the implanted layer because of a high density of basal plane stacking faults (SF) in the implanted layers is considered. The interpretation of the conduction in the heaviest doped samples in terms of nearly 2D VRH is supported by the results of the transmission electron microscopy (TEM) investigation on one of the 5  ×  1020 cm-3 Al implanted samples of this study. In this context, the average separation between basal plane SFs, measured along the c-axis, which is orthogonal to the carrier transport during electrical characterization, appears to be in keeping with the estimated value of the optimal hopping length of the VRH theory. Conversely, no SFs are detected by TEM in a sample with an Al concentration of 1  ×  1019 cm-3 where a 3D nearest neighbor hopping (NNH) transport is observed.

  12. Quantum chemical study of ternary mixtures of: HNO3:H2SO4:H2O

    NASA Astrophysics Data System (ADS)

    Verdes, M. A.; Gómez, P. C.; Gálvez, O.

    2009-04-01

    Water, nitric acid and sulfuric acid are important atmospheric species as individual species and as hydrogen-bonded aggregates involved in many physical-chemical processes both superficial and bulk. The importance of heterogeneous chemical reactions taking place on ice surfaces, either solid water or solid water plus nitric or sulfuric acid, is well established now in relation to the ozone-depleting mechanisms. Also the importance of liquid droplets formed by HNO3.H2SO4.H2O as components of PSC was soon recognized [1-3]. Finally the physical properties of finely divided aqueous systems is an interesting and active field of research in which theoretical information on the microphysical domain systems may help to understand and rationalize the wealth of experimental information. This can also be the initial step in the study of more complex mixtures with higher amounts of water or variable proportions of their constituents. This kind of calculations have been successfully performed in the past[4]. We present here our results on the structure and spectroscopic and thermodynamic properties of the energy-lowest lying structures among those thermodynamically stable formed by linking the acids plus water. The calculations have been carried out by means of DFT methods (in particular the successful B3LYP) using different basis sets that contain appropriate sets of polarization and diffuse functions up to quadruple-Z quality (Dunninǵs aug-cc-pVQZ). Careful assessment of the dependability of the methodology used has been carried out. This work has been supported by the Spanish Ministry of Education, Projects FIS2007-61686 and CTQ2008-02578/BQU References: [1] Carslaw, K. S. et al.: Geophys. Res. Lett. 21, 2479-2482, 1994 [2] Drdla, K. Et al. :Geophys. Res. Lett. 21, 2473-2478, 1994 [3] Tabazadeh, A. et al.: Geophys. Res. Lett 21, 1619-1622, 1994 [4] Escribano, R et al.: J. J. Chem. Phys A 2003, 107, 652.

  13. Updated H2SO4-H2O binary homogeneous nucleation look-up tables

    NASA Astrophysics Data System (ADS)

    Yu, Fangqun

    2008-12-01

    The calculated rates of H2SO4-H2O binary homogeneous nucleation (BHN), which is the only nucleation mechanism currently widely used in global aerosol models, are well known to have large uncertainties. Recently, we have reduced the uncertainties in the BHN rates on the basis of a kinetic quasi-unary nucleation (KQUN) model, by taking into account the measured bonding energetics of H2SO4 monomers with hydrated sulfuric acid dimers and trimers. The uncertainties were further reduced by using two independent measurements to constrain the equilibrium constants for monomer hydration. In this paper, we present updated BHN rate look-up tables derived from the improved KQUN model which can be used by anyone to obtain the BHN rates under given conditions. The look-up tables cover a wide range of key parameters that can be found in the atmosphere and laboratory studies, and their usage significantly reduces the computational costs of the BHN rate calculations, which is critical for multidimensional modeling. The look-up tables can also be used by those involved in experiments and field measurements to quickly assess the likeliness of BHN. For quick application, one can obtain the BHN rates and properties of critical clusters by browsing through the tables. A comparison of results based on the look-up tables with those from widely used classical BHN model indicates that, in addition to several orders of magnitude difference in nucleation rates, there also exists substantial difference in the predicted numbers of sulfuric acid molecules in the critical clusters and their dependence on key parameters.

  14. Noncontact interface trap determination of SiO2-4H-SiC structures

    NASA Astrophysics Data System (ADS)

    Oborina, E. I.; Hoff, A. M.

    2010-01-01

    A sequence of noncontact corona-Kelvin metrology is introduced that enables the determination and monitoring of interface properties in dielectric/wide band gap semiconductor structures. The technique involves the incremental application of precise and measured quantities of corona charge, QC, onto the dielectric surface followed by determination of the contact potential difference, VCPD, as the material structure response. The V-Q characteristics obtained are used to extract the surface barrier, VSB, response related to the applied corona charge. The described approach differs from the common noncontact method applied in the case of dielectric/silicon structures where for each quanta of applied charge the value of surface barrier voltage, VSB, is obtained. Materials with wide band gaps and high concentrations of deep levels, as suggested for silicon carbide, do not permit quick determination of VSB by modulation of the band bending in the semiconductor with light. Light exposure in the case of SiC results in a long recovery time required to approach the nominal value of the preillumination VCPD value. The metrology approach presented determines an intersection of the VCPD-QC characteristic obtained in the dark with the Vox-QC characteristic representing the dielectric response. The specific VSB-QC dependence surrounding the reference VFB value is obtained from this approach and enables the noncontact determination of the dielectric interface trap density and its spectrum. Application of the modified metrology method to thermal oxide on n-type 4H-SiC demonstrates the modification of the Dit distribution by Fowler-Nordheim stress. In addition, an ability to quantify and separate trapped charge components is shown.

  15. Discovery of a 6.4 h black hole binary in NGC 4490

    NASA Astrophysics Data System (ADS)

    Esposito, P.; Israel, G. L.; Sidoli, L.; Mapelli, M.; Zampieri, L.; Motta, S. E.

    2013-12-01

    We report on the discovery with Chandra of a strong modulation (˜90 per cent pulsed fraction) at ˜6.4 h from the source CXOU J123030.3+413853 in the star-forming, low-metallicity spiral galaxy NGC 4490, which is interacting with the irregular companion NGC 4485. This modulation, confirmed also by XMM-Newton observations, is interpreted as the orbital period of a binary system. The spectra from the Chandra and XMM-Newton observations can be described by a power-law model with photon index Γ ˜ 1.5. During these observations, which span from 2000 November to 2008 May, the source showed a long-term luminosity variability by a factor of ˜5, between ˜2 × 1038 and 1.1 × 1039 erg s-1 (for a distance of 8 Mpc). The maximum X-ray luminosity, exceeding by far the Eddington limit of a neutron star, indicates that the accretor is a black hole. Given the high X-ray luminosity, the short orbital period and the morphology of the orbital light curve, we favour an interpretation of CXOU J123030.3+413853 as a rare high-mass X-ray binary system with a Wolf-Rayet star as a donor, similar to Cyg X-3. This would be the fourth system of this kind known in the local Universe. CXOU J123030.3+413853 can also be considered as a transitional object between high-mass X-ray binaries and ultraluminous X-ray sources (ULXs), the study of which may reveal how the properties of persistent black hole binaries evolve entering the ULX regime.

  16. 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%).

  17. 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

  18. Structures and Energetics of Defects: A Comparative Study of 3C- and 4H-SiC

    SciTech Connect

    Gao, Fei; Posselt, Matthias; Belko, V; Zhang, Yanwen; Weber, William J.

    2004-05-01

    The structures, formation energies and stable configurations of elementary defects (vacancies, antisite defects and self interstitials) in 3C- and 4H-SiC are studied using classical molecular dynamics simulation with a recently developed interatomic potential. The defect structures in 3C-SiC are relatively simple, but those in 4H-SiC are more complicated. The interstitials between hexagonal and trigonal rings are characteristic for 4H-SiC and other hexagonal polytypes, but not for 3C-SiC. The number of non-equivalent defects in 4H-SiC is much higher than that in 3C-SiC, and a considerable difference is found for some complex and anisotropic defects, in particular for the dumbbells D1Si-Si, D1Si-C and D2Si-C. The lattice deformation beyond the first nearest neighbor shell, which depends strongly on the polytype structure, plays an important role on these effects. However, the polytypism does not have a significant influence on the structure and energetics of the more compact and isotropic defects, such as vacancies and antisite defects. Despite the complexity of defect configurations, the tetrahedral interstitials have very similar properties in 3C- and 4H-SiC because their first, second and third nearest neighbor shells are identical.

  19. A Comparative Study of the Structure and Energetics of Elementary Defects in 3C- and 4H-SiC

    SciTech Connect

    Posselt, Matthias; Gao, Fei; Weber, William J.; Belko, V

    2004-03-03

    The potential non-equivalent defects in both 3C- and 4H-SiC are classified by a new method that is based on symmetry considerations. In 4H-SiC, their number is considerably higher than in 3C-SiC, since the hexagonal symmetry leads to diversification. The different theoretical methods hitherto used to investigate defects in 3C-SiC are critically reviewed. Classical MD simulations with a recently developed interatomic potential are employed to investigate the stability, structure and energetics of the large number of potential non-equivalent defects that may exist in 4H-SiC. Most of the potential defects in 4H-SiC are found to be stable. The interstitials between hexagonal and trigonal rings, which do not exist in 3C-SiC, are characteristic for 4H-SiC and other hexagonal polytypes. The structure and energetics of some complex and anisotropic dumbbells depend strongly on the polytype. On the other hand, polytypism does not have a significant influence on the properties of the more compact and isotropic defects, such as vacancies, antisites, hexagonal interstitials, and many dumbbells. The results allow conclusions to be drawn about the energy hierarchy of the defects.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

  1. Vapor-Liquid Equilibrium in the Mixture 1,1-Difluoroethane C2H4F2 + C4H8 2-Methylpropene (EVLM1131, LB5730_E)

    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 'Vapor-Liquid Equilibrium in the Mixture 1,1-Difluoroethane C2H4F2 + C4H8 2-Methylpropene (EVLM1131, LB5730_E)' providing data from direct measurement of pressure and mole fraction in vapor phase at variable mole fraction in liquid phase and constant temperature.

  2. Volumetric Properties of the Mixture Ethyl ethanoate C4H8O2 + C6H14O2 3-Oxaheptan-1-ol (VMSD1412, LB4314_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 Ethyl ethanoate C4H8O2 + C6H14O2 3-Oxaheptan-1-ol (VMSD1412, LB4314_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).

  3. Volumetric Properties of the Mixture 1-Chlorobutane C4H9Cl + C8H18 Octane (VMSD1511, LB3892_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-Chlorobutane C4H9Cl + C8H18 Octane (VMSD1511, LB3892_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).

  4. Volumetric Properties of the Mixture Trichloromethane CHCl3 + C4H10O Butan-1-ol (VMSD1511, LB5192_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 Trichloromethane CHCl3 + C4H10O Butan-1-ol (VMSD1511, LB5192_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 Methyl ethanoate C3H6O2 + C4H10O Butan-1-ol (VMSD1511, LB4029_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 Methyl ethanoate C3H6O2 + C4H10O Butan-1-ol (VMSD1511, LB4029_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).

  6. Volumetric Properties of the Mixture Butan-1-ol C4H10O + C8H8 Vinylbenzene (VMSD1511, LB4664_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 Butan-1-ol C4H10O + C8H8 Vinylbenzene (VMSD1511, LB4664_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).

  7. Volumetric Properties of the Mixture 2-Chloroethanol C2H5ClO + C4H8O2 Ethyl ethanoate (VMSD1511, LB4798_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 2-Chloroethanol C2H5ClO + C4H8O2 Ethyl ethanoate (VMSD1511, LB4798_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 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).

  9. 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).

  10. Volumetric Properties of the Mixture Butan-1-ol C4H10O + C7H8O Methyl phenyl ether (VMSD1511, LB4559_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 Butan-1-ol C4H10O + C7H8O Methyl phenyl ether (VMSD1511, LB4559_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).

  11. Volumetric Properties of the Mixture Trichloroethene C2HCl3 + C4H10O Butan-1-ol (VMSD1511, LB4850_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 Trichloroethene C2HCl3 + C4H10O Butan-1-ol (VMSD1511, LB4850_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).

  12. 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).

  13. Volumetric Properties of the Mixture 1-Chlorobutane C4H9Cl + C7H16 Heptane (VMSD1511, LB3891_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-Chlorobutane C4H9Cl + C7H16 Heptane (VMSD1511, LB3891_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).

  14. Volumetric Properties of the Mixture Oxolan-2-one C4H6O2 + C8H18O Octan-1-ol (VMSD1511, LB4907_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 Oxolan-2-one C4H6O2 + C8H18O Octan-1-ol (VMSD1511, LB4907_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).

  15. Volumetric Properties of the Mixture 2-Ethoxyethanol C4H10O2 + C6H12O2 Butyl ethanoate (VMSD1511, LB4136_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 2-Ethoxyethanol C4H10O2 + C6H12O2 Butyl ethanoate (VMSD1511, LB4136_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).

  16. Volumetric Properties of the Mixture Butan-1-ol C4H10O + C7H8O Methyl phenyl ether (VMSD1412, LB4565_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 Butan-1-ol C4H10O + C7H8O Methyl phenyl ether (VMSD1412, LB4565_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).

  17. Volumetric Properties of the Mixture 1-Chlorobutane C4H9Cl + C10H22 Decane (VMSD1511, LB3893_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-Chlorobutane C4H9Cl + C10H22 Decane (VMSD1511, LB3893_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).

  18. 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).

  19. Volumetric Properties of the Mixture 2-Ethoxyethanol C4H10O2 + C6H12O2 Butyl ethanoate (VMSD1412, LB4313_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 2-Ethoxyethanol C4H10O2 + C6H12O2 Butyl ethanoate (VMSD1412, LB4313_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).

  20. Volumetric Properties of the Mixture Trichloroethene C2HCl3 + C4H10O Butan-1-ol (VMSD1412, LB4856_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 Trichloroethene C2HCl3 + C4H10O Butan-1-ol (VMSD1412, LB4856_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).

  1. Volumetric Properties of the Mixture Methanol CH4O + C4H6O2 Oxolan-2-one (VMSD1511, LB4904_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 Methanol CH4O + C4H6O2 Oxolan-2-one (VMSD1511, LB4904_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 Ethyl ethanoate C4H8O2 + C6H14O2 3-Oxaheptan-1-ol (VMSD1511, LB4137_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 Ethyl ethanoate C4H8O2 + C6H14O2 3-Oxaheptan-1-ol (VMSD1511, LB4137_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).

  3. 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).

  4. 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).

  5. Volumetric Properties of the Mixture 1-Chlorobutane C4H9Cl + C6H14 Hexane (VMSD1511, LB3890_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-Chlorobutane C4H9Cl + C6H14 Hexane (VMSD1511, LB3890_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).

  6. Volumetric Properties of the Mixture Trichloromethane CHCl3 + C4H10O Butan-1-ol (VMSD1412, LB5194_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 Trichloromethane CHCl3 + C4H10O Butan-1-ol (VMSD1412, LB5194_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).

  7. 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.

  8. 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).

  9. 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.

  10. 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

  11. High Resolution Spectroscopy of Hexamethylenetetramine (hmt) C6N_4H12

    NASA Astrophysics Data System (ADS)

    Boudon, V.; Pirali, O.

    2012-06-01

    Hexamethylenetetramine, or HMT (C6N_4H12) is a N-substituted derivative of adamantane C10H16 which is the smallest sample of the diamondoid molecules family. Thanks to their high stability, diamond-like molecules have long been suspected to be present in space (note that diamond nanocrystals are extracted from Murchinson meteorites, and HMT is known to be an abundant residue of UV irradiated ice analogs and might be present in Titan's atmosphere. Using the Bruker IFS 125 coupled to a multipass cell (absorption path length of 150 m) of the AILES beamline at SOLEIL, we recorded the IR spectrum of gas phase HMT in the 300--3000 cm-1 spectral region with an unapodized resolution 0.001 cm-1. HMT is a solid powder with about 0.008 mbar vapour pressure at room temperature, it is a T_d molecule (as adamantane) and has 25 vibrational modes from which only 9 are infrared active. Over the 9 IR active modes, we were able to rotationlly resolved the spectra of 6 of them. The analysis of all the resolved bands has been performed thanks to the XTDS and SPVIEW softwares developed in Dijon for such molecules. Each band can be considered as isolated and we get very good fits of line positions, with a root mean square deviation better than 5× 10-4 cm-1 for J values up to 80 or more in each case. As for our recent study concerning adamantane, the resulting synthetic spectra will permit an active search of this very stable specie in different sources of the interstellar medium. W. C. Saslaw and J. E. Gaustad, Nature, 221, 160 (1969) R. S. Lewis et al., Nature, 326, 160 (1987) M. P. Bernstein et al., ApJ, 454, 327 (1995) Ch. Wenger, V. Boudon, M. Rotger, M. Sanzharov and J.-P. Champion, J. Mol. Spectrosc., 251 102--113 (2008). O. Pirali, V. Boudon, J. Oomens, M. Vervloet, J. Chem. Phys., 136, 024310 (2012)

  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. ZC4H2, an XLID gene, is required for the generation of a specific subset of CNS interneurons.

    PubMed

    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

    2015-09-01

    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.

  14. 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.

  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. The channeling effect of Al and N ion implantation in 4H-SiC during JFET integrated device processing

    NASA Astrophysics Data System (ADS)

    Lazar, M.; Laariedh, F.; Cremillieu, P.; Planson, D.; Leclercq, J.-L.

    2015-12-01

    A strong channeling effect is observed for the ions of Al and N implanted in 4H-SiC due to its crystalline structure. This effect causes difficulties in subsequent accurate estimation of the depth of junctions formed by multiple ion implantation steps. A variety of lateral JFET transistors integrated on the same 4H-SiC wafer have been fabricated. Secondary Ion Mass Spectrometry measurements and Monte-Carlo simulations were performed in order to quantify and control the channeling effect of the implanted ions. A technological process was established enabling to obtain devices working with the presence of the channeling effect.

  17. 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.

  18. A novel micro-Raman technique to detect and characterize 4H-SiC stacking faults

    NASA Astrophysics Data System (ADS)

    Piluso, N.; Camarda, M.; La Via, F.

    2014-10-01

    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 < 1016 at/cm-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.

  19. Characterization of Thermal Oxides on 4H-SiC Epitaxial Substrates Using Fourier-Transform Infrared Spectroscopy.

    PubMed

    Seki, Hirofumi; Yoshikawa, Masanobu; Kobayashi, Takuma; Kimoto, Tsunenobu; Ozaki, Yukihiro

    2016-07-12

    Fourier transform infrared (FT-IR) spectra were measured for thermal oxides with different electrical properties grown on 4H-SiC substrates. The peak frequency of the transverse optical (TO) phonon mode was blue-shifted by 5 cm(-1) as the oxide-layer thickness decreased to 3 nm. The blue shift of the TO mode indicates interfacial compressive stress in the oxide. Comparison of data for the oxide on a SiC substrate with that for similar oxides on a Si substrate implies that the peak shift of the TO mode at the SiO2/SiC interface is larger than that of SiO2/Si, which suggests that the interfacial stress for the oxide on the SiC substrate is larger than that on the Si substrate. For the SiO2/SiC interfacial region (<3 nm oxide thickness), despite the fact that the blue shift of the TO modes becomes larger while approaching the oxide/SiC interface, the peak frequency of the TO modes red-shifts at the oxide/SiC interface. The peak-frequency shift of the TO mode for the sample without post-oxidation annealing was larger than that for the samples post-annealed in a nitric oxide atmosphere. The channel mobilities are correlated with the degree of shift of the TO mode when the oxide thickness is <3 nm. It appears that the compressive stress at the SiO2/SiC interface generates silicon suboxide components and weakens the Si-O bonds. As the result, the TO mode was red-shifted and the oxygen deficiency increased to relax the compressive stress in the oxide with <3 nm thickness. Fourier transform infrared spectroscopy measurements provide unique and useful information about stress and inhomogeneity at the oxide/SiC interface.

  20. 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...

  1. Antimicrobial activity of novel 4H-4-oxoquinolizine compounds against extensively drug-resistant Acinetobacter baumannii strains.

    PubMed

    Na, Seok Hyeon; Jeon, Hyejin; Kim, Yoo Jeong; Kwon, Hyo Il; Selasi, Gati Noble; Nicholas, Asiimwe; Yun, Chang-Soo; Lee, Sang Ho; Lee, Je Chul

    2017-01-01

    The aim of this study was to screen lead compounds exhibiting potent in vitro antimicrobial activity against multidrug-resistant (MDR) Acinetobacter baumannii strains from a library of chemical compounds. In a high-throughput screening analysis of 7520 compounds representative of 340,000 small molecules, two 4H-4-oxoquinolizine compounds were the most active against A. baumannii ATCC 17978. Subsequent selection and analysis of 70 4H-4-oxoquinolizine compounds revealed that the top 7 compounds were extremely active against extensively drug-resistant (XDR) A. baumannii isolates. These compounds commonly carried a 1-cyclopropyl-7-fluoro-4-oxo-4H-quinolizine-3-carboxylic acid core structure but had different C-8 and/or C-9 moieties. Minimum inhibitory concentrations (MICs) of the seven compounds against fluoroquinolone-resistant A. baumannii isolates were found to be in the range of 0.02-1.70 µg/mL regardless of the mutation types in the quinolone resistance-determining region (QRDR) of GyrA and ParC. Cytotoxicity of the seven compounds was observed in HeLa and U937 cells at a concentration of 50 µg/mL, which was >32.5- to 119-fold higher than the MIC90 for A. baumannii isolates. In conclusion, novel 4H-4-oxoquinolizine compounds represent a promising scaffold on which to develop antimicrobial agents against drug-resistant A. baumannii strains.

  2. 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.…

  3. [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…

  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. Antiinflammatory 2-benzyl-4-sulfonyl-4H-isoquinoline-1,3-diones: novel inhibitors of COX-2.

    PubMed

    Lazer, E S; Sorcek, R; Cywin, C L; Thome, D; Possanza, G J; Graham, A G; Churchill, L

    1998-05-19

    A series of 2-benzyl-4-sulfonyl-4H-isoquinoline-1,3-diones was prepared. Members of this series are potent and selective inhibitors of cyclooxygenase-2 (COX-2) in both microsomal and cellular assays. Two representatives demonstrated activity in the carrageenan-induced paw edema model in rats upon oral administration.

  6. 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.…

  7. 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…

  8. The reaction H + C4H2 - Absolute rate constant measurement and implication for atmospheric modeling of Titan

    NASA Astrophysics Data System (ADS)

    Nava, D. F.; Mitchell, M. B.; Stief, L. J.

    1986-04-01

    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.

  9. 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…

  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. 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…

  12. 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.

  13. 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…

  14. 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

  15. Experimental Durability Testing of 4H SiC JFET Integrated Circuit Technology at 727 Degrees Centigrade

    NASA Technical Reports Server (NTRS)

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

    2016-01-01

    We have reported SiC integrated circuits (ICs) with two levels of metal interconnect that have demonstrated prolonged operation for thousands of hours at their intended peak ambient operational temperature of 500 degrees Centigrade. 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 degrees Centigrade. However, this thermal ramp was not ended until a peak temperature of 880 degrees Centigrade (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 degrees Centigrade. In one test, the temperature was ramped and then held at 727 degrees Centigrade, 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 degrees Centigrade 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 degrees Centigrade (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 degrees Centigrade.

  16. 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.

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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 were used, and logic circuit operation was demonstrated for 143.5 hours at 700 °C.

  19. Improved quasi-unary nucleation model for binary H2SO4-H2O homogeneous nucleation

    NASA Astrophysics Data System (ADS)

    Yu, Fangqun

    2007-08-01

    Aerosol nucleation events have been observed at a variety of locations worldwide, and may have significant climatic and health implications. Binary homogeneous nucleation (BHN) of H2SO4 and H2O is the foundation of recently proposed nucleation mechanisms involving additional species such as ammonia, ions, and organic compounds, and it may dominate atmospheric nucleation under certain conditions. We have shown in previous work that H2SO4-H2O BHN can be treated as a quasi-unary nucleation (QUN) process involving H2SO4 in equilibrium with H2O vapor, and we have developed a self-consistent kinetic model for H2SO4-H2O nucleation. Here, the QUN approach is improved, and an analytical expression yielding H2SO4-H2O QUN rates is derived. Two independent measurements related to monomer hydration are used to constrain the equilibrium constants for this process, which reduces a major source of uncertainty. It is also shown that the capillarity approximation may lead to a large error in the calculated Gibbs free energy change for the evaporation of H2SO4 molecules from small H2SO4-H2O clusters, which affects the accuracy of predicted BHN nucleation rates. The improved QUN model—taking into account the recently measured energetics of small clusters—is thermodynamically more robust. Moreover, predicted QUN nucleation rates are in better agreement with available experimental data than rates calculated using classical H2SO4-H2O BHN theory.

  20. The crystal structures of four N-(4-halophen­yl)-4-oxo-4H-chromene-3-carboxamides

    PubMed Central

    Gomes, Ligia R.; Low, John Nicolson; Cagide, Fernando; Borges, Fernanda

    2015-01-01

    Four N-(4-halophen­yl)-4-oxo-4H-chromene-3-carboxamides (halo = F, Cl, Br and I), N-(4-fluoro­phen­yl)-4-oxo-4H-chromene-3-carboxamide, C16H10FNO3, N-(4-chloro­phen­yl)-4-oxo-4H-chromene-3-carboxamide, C16H10ClNO3, N-(4-bromo­phen­yl)-4-oxo-4H-chromene-3-carboxamide, C16H10BrNO3, N-(4-iodo­phen­yl)-4-oxo-4H-chromene-3-carboxamide, C16H10INO3, have been structurally characterized. The mol­ecules are essentially planar and each exhibits an anti conformation with respect to the C—N rotamer of the amide and a cis geometry with respect to the relative positions of the Carom—Carom bond of the chromone ring and the carbonyl group of the amide. The structures each exhibit an intra­molecular hydrogen-bonding network comprising an N—H⋯O hydrogen bond between the amide N atom and the O atom of the carbonyl group of the pyrone ring, forming an S(6) ring, and a weak Carom—H⋯O inter­action with the O atom of the carbonyl group of the amide as acceptor, which forms another S(6) ring. All four compounds have the same supra­molecular structure, consisting of R 2 2(13) rings that are propagated along the a-axis direction by unit translation. There is π–π stacking involving inversion-related mol­ecules in each structure. PMID:25705460

  1. 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.

  2. 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.

  3. 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.

  4. Leakage current conduction and reliability assessment of passivating thin silicon dioxide films on n-4H-SiC

    NASA Astrophysics Data System (ADS)

    Samanta, Piyas; Mandal, Krishna C.

    2016-09-01

    We have analyzed the mechanisms of leakage current conduction in passivating silicon dioxide (SiO2) films grown on (0 0 0 1) silicon (Si) face of n-type 4H-SiC (silicon carbide). It was observed that the experimentally measured gate current density in metal-oxide-silicon carbide (MOSiC) structures under positive gate bias at an oxide field Eox above 5 MV/cm is comprised of Fowler-Nordheim (FN) tunneling of electrons from the accumulated n-4H-SiC and Poole-Frenkel (PF) emission of trapped electrons from the localized neutral traps in the SiO2 gap, IFN and IPF, respectively at temperatures between 27 and 200 °C. In MOSiC structures, PF mechanism dominates FN tunneling of electrons from the accumulation layer of n-4H-SiC due to high density (up to 1013 cm-2) of carbon-related acceptor-like traps located at about 2.5 eV below the SiO2 conduction band (CB). These current conduction mechanisms were taken into account in studying hole injection/trapping into 10 nm-thick tunnel oxide on the Si face of 4H-SiC during electron injection from n-4H-SiC under high-field electrical stress with positive bias on the heavily doped n-type polysilicon (n+-polySi) gate at a wide range of temperatures between 27 and 200 °C. Holes were generated in the n+-polySi anode material by the hot-electrons during their transport through thin oxide films at oxide electric fields Eox from 5.6 to 8.0 MV/cm (prior to the intrinsic oxide breakdown field). Time-to-breakdown tBD of the gate dielectric was found to follow reciprocal field (1/E) model irrespective of stress temperatures. Despite the significant amount of process-induced interfacial electron traps contributing to a large amount of leakage current via PF emission in thermally grown SiO2 on the Si-face of n-4H-SiC, MOSiC devices having a 10 nm-thick SiO2 film can be safely used in 5 V TTL logic circuits over a period of 10 years.

  5. 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…

  6. 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…

  7. 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…

  8. Trees: Dead or Alive. 4-H Leader's Guide 147-L-22.

    ERIC Educational Resources Information Center

    Krasny, Marianne E.

    This illustrated leader's guide to exploring trees and forests provides activities which emphasize careful observation of trees and the living things associated with them for youths age 9 and older. Introductory information for leaders explains the uses for trees and the role of trees in the ecosystem. It also gives suggestions for leaders to…

  9. Measurements of Neutron Induced Surface and Bulk Defects in 4H Silicon Carbide

    DTIC Science & Technology

    2002-03-01

    John Wiley & Sons Inc. 1995. University of Manchester (UM), “ Laplace DLTS …An Overview,” Technical information provided on web page. http...19 Constant Voltage Deep Level Transient Spectroscopy (CV- DLTS ) ..............22 Hall Effect Measurements (HALL...34 n-type Photoluminescence Results..................................................................34 n-type DLTS Results

  10. 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…

  11. 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…

  12. 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.

  13. 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.

  14. Sequential hydration energies of the sulfate ion, from determinations of the equilibrium constants for the gas-phase reactions: SO4(H2O)(n)2- = SO4(H2O)(n-1)2- + H2O.

    PubMed

    Blades, Arthur T; Kebarle, Paul

    2005-09-22

    Sequential hydration energies of SO4(H2O)(n)2- were obtained from determinations of the equilibrium constants of the following reactions: SO4(H2O)(n)2- = SO4(H2O)(n-1)2- + H2O. The SO4(2-) ions were produced by electrospray and the equilibrium constants Kn,n-1 were determined with a reaction chamber attached to a mass spectrometer. Determinations of Kn,n-1 at different temperatures were used to obtain DeltaG0n,n-1, DeltaH0 n,n-1, and DeltaS0n,n-1 for n = 7 to 19. Interference of the charge separation reaction SO4(H2O)(n)2- = HSO4(H2O)(n-k)- + OH(H2O)(k-1)- at higher temperatures prevented determinations for n < 7. The DeltaS0n,n-1 values obtained are unusually low and this indicates very loose, disordered structures for the n > or = 7 hydrates. The DeltaH0n,n-1 values are compared with theoretical values DeltaEn,n-1, obtained by Wang, Nicholas, and Wang. Rate constant determinations of the dissociation reactions n,n - 1, obtained with the BIRD method by Wong and Williams, showed relatively lower rates for n = 6 and 12, which indicate that these hydrates are more stable. No discontinuities of the DeltaG0n,n-1 values indicating an unusually stable n = 12 hydrate were observed in the present work. Rate constants evaluated from the DeltaG0n,n-1 results also fail to indicate a lower rate for n = 12. An analysis of the conditions used in the two types of experiments indicates that the different results reflect the different energy distributions expected at the dissociation threshold. Higher internal energies prevail in the equilibrium measurements and allow the participation of more disordered transition states in the reaction.

  15. First spectroscopic observation of gold(i) butadiynylide: Photodetachment velocity map imaging of the AuC4H anion.

    PubMed

    Visser, Bradley R; Addicoat, Matthew A; Gascooke, Jason R; Lawrance, Warren D; Metha, Gregory F

    2016-07-28

    The velocity map imaging technique was used in the investigation of gold(i) butadiynylide, AuC4H(-), with images recorded at two excitation wavelengths. The resultant photodetachment spectra show a well defined vibrational progression in the neutral with an energy spacing of 343 ± 3 cm(-1). The adiabatic electron affinity was determined to be 1.775 ± 0.005 eV and assigned to the X(1)Σ(+)←X(2)Σ(+) transition between the anionic and neutral ground states. Franck-Condon simulations performed on density functional theory optimized geometries assisted the assignment of linear geometries to the neutral and anion and the observed vibrational progression to that of the Au-C4H stretch.

  16. 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.

  17. Effect of boron incorporation on slow interface traps in SiO2/4H-SiC structures

    NASA Astrophysics Data System (ADS)

    Okamoto, Dai; Sometani, Mitsuru; Harada, Shinsuke; Kosugi, Ryoji; Yonezawa, Yoshiyuki; Yano, Hiroshi

    2017-02-01

    The reason for the effective removal of interface traps in SiO2/4H-SiC (0001) structures by boron (B) incorporation was investigated by employing low-temperature electrical measurements. Low-temperature capacitance-voltage and thermal dielectric relaxation current measurements revealed that the density of electrons captured in slow interface traps in B-incorporated oxide is lower than that in dry and NO-annealed oxides. These results suggest that near-interface traps can be removed by B incorporation, which is considered to be an important reason for the increase in the field-effect mobility of 4H-SiC metal-oxide-semiconductor devices. A model for the passivation mechanism is proposed that takes account of stress relaxation during thermal oxidation.

  18. 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.

  19. Effect of annealing temperature on the contact properties of Ni/V/4H-SiC structure

    SciTech Connect

    Dai, Chong-Chong; Zhou, Tian-Yu; Liu, Xue-Chao Zhuo, Shi-Yi; Kong, Hai-Kuan; Yang, Jian-Hua; Shi, Er-Wei

    2014-04-15

    A sandwich structure of Ni/V/4H-SiC was prepared and annealed at different temperatures from 650 °C to 1050 °C. The electrical properties and microstructures were characterized by transmission line method, X-ray diffraction, Raman spectroscopy and transmission electron microscopy. A low specific contact resistance of 3.3 × 10{sup -5} Ω·cm{sup 2} was obtained when the Ni/V contact was annealed at 1050 °C for 2 min. It was found that the silicide changed from Ni{sub 3}Si to Ni{sub 2}Si with increasing annealing temperature, while the vanadium compounds appeared at 950 °C and their concentration increased at higher annealing temperature. A schematic diagram was proposed to explain the ohmic contact mechanism of Ni/V/4H-SiC structure.

  20. First spectroscopic observation of gold(i) butadiynylide: Photodetachment velocity map imaging of the AuC4H anion

    NASA Astrophysics Data System (ADS)

    Visser, Bradley R.; Addicoat, Matthew A.; Gascooke, Jason R.; Lawrance, Warren D.; Metha, Gregory F.

    2016-07-01

    The velocity map imaging technique was used in the investigation of gold(i) butadiynylide, AuC4H-, with images recorded at two excitation wavelengths. The resultant photodetachment spectra show a well defined vibrational progression in the neutral with an energy spacing of 343 ± 3 cm-1. The adiabatic electron affinity was determined to be 1.775 ± 0.005 eV and assigned to the X1Σ+←X2Σ+ transition between the anionic and neutral ground states. Franck-Condon simulations performed on density functional theory optimized geometries assisted the assignment of linear geometries to the neutral and anion and the observed vibrational progression to that of the Au-C4H stretch.

  1. Density and energy level of a deep-level Mg acceptor in 4H-SiC

    NASA Astrophysics Data System (ADS)

    Matsuura, Hideharu; Morine, Tatsuya; Nagamachi, Shinji

    2015-01-01

    Reliably determining the densities and energy levels of deep-level dominant acceptors in heavily doped wide-band-gap semiconductors has been a topic of recent discussion. In these discussions, the focus is on both Hall scattering factors for holes and distribution functions for acceptors. Mg acceptor levels in 4H-SiC seem to be deep, and so here the electrical properties of Mg-implanted 4H-SiC layers are studied by measuring Hall effects. The obtained Hall scattering factors are not reliable because they drop to less than 0.5 at high measurement temperatures. Moreover, the Fermi-Dirac distribution function is unsuitable for examining Mg acceptors because the obtained acceptor density is much higher than the concentration of implanted Mg atoms. However, by using a distribution function that includes the influence of the excited states of a deep-level acceptor, the density and energy level of Mg acceptors can be reliably determined.

  2. 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.

  3. 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.

  4. A comprehensive study on the oxidation of 4H-SiC in diluted N2O ambient

    NASA Astrophysics Data System (ADS)

    Tseng, Yuan-Hung; Wu, Tsung-Han; Tsui, Bing-Yue; Yen, Cheng-Tyng; Hung, Chien-Chung; Lee, Chwan-Ying

    2017-04-01

    The oxidation mechanism of 4H-SiC in diluted N2O ambient was studied at various temperatures, N2O flow rates, and N2/N2O flow ratios. The collision partner, N2 in this study, plays crucial roles in determining the oxidation rate and N-incorporation. According to the proposed oxidation mechanism, lowering the interface state density at lower oxidation temperatures is possible with a high-efficiency collision partner.

  5. Multiple Isomers of La(C4H6) Formed in Reactions of la Atom with Small Hydrocarbons

    NASA Astrophysics Data System (ADS)

    Cao, Wenjin; Hewage, Dilrukshi; Yang, Dong-Sheng

    2014-06-01

    La(C_4H_6) was observed from the reactions of laser-vaporized La atom with propene (CH_2CHCH_3),isobutene [CH_2C(CH_3)2],1-butyne (CHCC_2H_5), and 2-butyne (CH_3CCCH_3) in a metal cluster beam source and investigated by mass-analyzed threshold ionization (MATI) spectroscopy in combination with quantum chemical calculations and spectral simulations. La(cyclobutene) [La(CH_2CHCHCH_2)] and La(trimethylenemethane) [LaC(CH_2)_3] were identified from the La + propene reaction. The formation of the two isomers involves two steps: the first step is the reaction of La+ CH_2CHCH_3 with the products of La(CH_2) + C_2H_4, and the second step is the reaction of LaCH_2 + CH_2CHCH_3 which preduces La(C_4H_6) + H_2. For the La + isobutene reaction, La(trimethylenemethane) was formed by dehydrogenation. For the reaction of La + 1- and 2-butynes, preliminary data analysis suggested that La(C_4H_6) was formed by simple association. All these structural isomers have similar geometries in the neutral and singly charged ion states, as evidenced by the very strong origin bands and short Franck-Condon profiles in the MATI spectra.

  6. Feasibility study of a ``4H'' X-ray camera based on GaAs:Cr sensor

    NASA Astrophysics Data System (ADS)

    Dragone, A.; Kenney, C.; Lozinskaya, A.; Tolbanov, O.; Tyazhev, A.; Zarubin, A.; Wang, Zhehui

    2016-11-01

    A multilayer stacked X-ray camera concept is described. This type of technology is called `4H' X-ray cameras, where 4H stands for high-Z (Z>30) sensor, high-resolution (less than 300 micron pixel pitch), high-speed (above 100 MHz), and high-energy (above 30 keV in photon energy). The components of the technology, similar to the popular two-dimensional (2D) hybrid pixelated array detectors, consists of GaAs:Cr sensors bonded to high-speed ASICs. 4H cameras based on GaAs also use integration mode of X-ray detection. The number of layers, on the order of ten, is smaller than an earlier configuration for single-photon-counting (SPC) mode of detection [1]. High-speed ASIC based on modification to the ePix family of ASIC is discussed. Applications in X-ray free electron lasers (XFELs), synchrotrons, medicine and non-destructive testing are possible.

  7. 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.

  8. 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.

  9. P4H9-detected molecule expression on spindle-shaped fibroblasts indicates malignant phenotype of colorectal cancer

    PubMed Central

    Yokoyama, Shozo; Ieda, Junji; Yamamoto, Naoyuki; Yamaguchi, Shunsuke; Mitani, Yasuyuki; Takeuchi, Akihiro; Takifuji, Katsunari; Hotta, Tsukasa; Matsuda, Kenji; Watanabe, Takashi; Shively, John E; Yamaue, Hiroki

    2015-01-01

    Background: Our previous study using a mammary fat pad mouse model showed that P4H9, produced by the β2 integrin epitope, detected a molecule on fibroblasts in response to carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1)-expressing cancer cells. P4H9-detected molecule (PDM) expression appeared to be associated with myofibroblast differentiation. In this study, we investigated whether PDM is expressed on fibroblasts and cancer cells in clinical tissue samples, and whether the presence of PDM-expressing colorectal cancer cells is correlated with clinicopathological features of patients. Methods: Immunohistochemistry was conducted to detect P4H9 on clinical tissue samples from 156 patients with colorectal cancer. Risk factors for metastases and survival were calculated for clinical implication of PDM-expressing spindle-shaped fibroblasts. Results: Multivariate analysis showed that PDM-expressing spindle-shaped fibroblasts were an independent risk factor for lymph node metastasis, hematogenous metastasis, and poor survival. A Kaplan–Meier survival curve indicated that PDM-expressing spindle-shaped fibroblasts were associated with shorter survival time (P<0.0001). Immunofluorescence showed PDM expression on CCD-18Co fibroblasts and two colorectal cancer cell lines (HCT116 and HCT-15). Conclusions: PDM-expressing spindle-shaped fibroblasts are associated with metastasis and shorter survival in colorectal cancer patients. PDM-expressing spindle-shaped fibroblasts may have a role in eliciting the malignant phenotype of colorectal cancer. PMID:26469833

  10. A novel 4H-SiC MESFET with serpentine channel for high power and high frequency applications

    NASA Astrophysics Data System (ADS)

    Jia, Hujun; Luo, Yehui; Zhang, Hang; Xing, Ding; Ma, Peimiao

    2017-01-01

    In this paper, a novel 4H-SiC metal semiconductor field effect transistor with serpentine channel (SC-MESFET) is proposed which the gate-drain drift region shifts downward integrally compared to the gate-source drift region. With the depth of the gate-drain shift increasing, the channel electric field and the gate depletion layer have been modulated. The simulated results show that the drain saturation current and breakdown voltage of the SC-MESFET are about 21.5% and 46.7% larger than that of the conventional double-recessed 4H-SiC MESFET (DR-MESFET). The gate-source capacitance of proposed structure is also improved from 0.59 pF/mm to 0.51 pF/mm and the DC transconductance of the SC-MESFET is very close to that of the DR-MESFET at the bias conditions of Vgs = 0 V and Vds = 40 V, which results in better RF characteristics. All of the results show that the novel 4H-SiC MESFET with serpentine channel has superior electrical characteristics and performances.

  11. Rotationally resolved IR spectroscopy of hexamethylenetetramine (HMT) C6N4H12

    NASA Astrophysics Data System (ADS)

    Pirali, O.; Boudon, V.; Carrasco, N.; Dartois, E.

    2014-01-01

    Context. Hexamethylenetetramine (HMT) appears to be a potential constituent of several objects in space, including comets or Titan's atmosphere and, as an organic residue of ice irradiation in the laboratory, it may be present in the interstellar medium. Aims: We performed a laboratory study of rotationally resolved intense IR bands of HMT to provide accurate line positions and synthetic spectra to be used for potential astronomical detections. Methods: We used synchrotron-based high-resolution Fourier transform infrared spectroscopy to record the experimental data. A formalism and programs dedicated to the assignment, analysis, and simulation of absorption spectra of tetrahedral molecules were used to exploit the spectra. Results: Infrared spectra of gas phase HMT were recorded and accurate wavenumbers and molecular parameters for four intense bands located in the 1000-1500 cm-1 spectral range suitable for astronomical searches were derived.

  12. Atomistic Simulations on the Thermal Stability of the Antisite Pair in 3C- and 4H-SiC

    SciTech Connect

    Posselt, Matthias; Gao, Fei; Weber, William J.

    2006-03-31

    The thermal stability of the first-neighbor antisite pair configurations in 3C- and 4H-SiC is investigated by a comprehensive atomistic study. At first the structure and energetics of these defects is determined in order to check the accuracy of the Gao-Weber interatomic potential used. The results are comparable with literature data obtained by the density-functional theory. Then, the lifetime of the antisite pair configurations is calculated for temperatures between 800 and 2500 K. Both in 3C- and 4H-SiC the thermal stability of the antisite pairs is rather low. In contrast to previous theoretical interpretations, the antisite pair can be therefore not correlated with the DI photoluminescence center that is stable to above 2000 K. The atomic mechanisms during the recombination of the antisite pair in 3C-SiC and of three antisite pair configurations in 4H-SiC is a modified concerted exchange. Due to the different sizes of the silicon and the carbon atoms, this process is not identical with the concerted exchange in Si. Two intermediate metastable configurations found during the recombination are similar to the bond defect in Si. Since the SiC lattice contains two types of atoms, there are also two different types of bond defects. The two bond defects can be considered as the result of the incomplete recombination of a carbon vacancy and a neighboring mixed dumbbell interstitial. For selected temperatures the thermal stability of the antisite pair in 3C-SiC is investigated by molecular dynamics simulations that are based on the density-functional theory. Their results are very similar to those of the atomistic study, i.e. the Gao-Weber potential describes the antisite pair and its recombination reasonably well. The antisite pair in 4H-SiC with the two atoms on hexagonal sites has a slightly different formation energy than the other three antisite pair configurations in 4H-SiC. Its lifetime shows another dependence on the temperature, and its recombination is

  13. Direct NaBH 4/H 2O 2 fuel cells

    NASA Astrophysics Data System (ADS)

    Miley, George H.; Luo, Nie; Mather, Joseph; Burton, Rodney; Hawkins, Glenn; Gu, Lifeng; Byrd, Ethan; Gimlin, Richard; Shrestha, Prajakti Joshi; Benavides, Gabriel; Laystrom, Julia; Carroll, David

    A fuel cell (FC) using liquid fuel and oxidizer is under investigation. H 2O 2 is used in this FC directly at the cathode. Either of two types of reactant, namely a gas-phase hydrogen or an aqueous NaBH 4 solution, are utilized as fuel at the anode. Experiments demonstrate that the direct utilization of H 2O 2 and NaBH 4 at the electrodes results in >30% higher voltage output compared to the ordinary H 2/O 2 FC. Further, the use of this combination of all liquid fuels, provides numerous advantages (ease of storage, reduced pumping requirements, simplified heat removal, etc.) from an operational point of view. This design is inherently compact compared to other cells that use gas phase reactants. Further, regeneration is possible using an electrical input, e.g. from power lines or a solar panel. While the peroxide-based FC is ideally suited for applications such as space power where air is not available and a high energy density fuel is essential, other distributed and mobile power uses are of interest.

  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. 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.

  16. Synthesis, solid-state structure, and bonding analysis of the beryllocenes [Be(C5Me4H)2], [Be(C5Me5)2], and [Be(C5Me5)(C5Me4H)].

    PubMed

    del Mar Conejo, M; Fernández, Rafael; del Río, Diego; Carmona, Ernesto; Monge, Angeles; Ruiz, Caridad; Márquez, Antonio M; Sanz, Javier Fernández

    2003-09-22

    The beryllocenes [Be(C(5)Me(4)H)(2)] (1), [Be(C(5)Me(5))(2)] (2), and [Be(C(5)Me(5))(C(5)Me(4)H)] (3) have been prepared from BeCl(2) and the appropriate KCp' reagent in toluene/diethyl ether solvent mixtures. The synthesis of 1 is facile (20 degrees C, overnight), but generation of decamethylberyllocene 2 demands high temperatures (ca. 115 degrees C) and extended reaction times (3-4 days). The mixed-ring beryllocene 3 is obtained when the known [(eta(5)-C(5)Me(5))BeCl] is allowed to react with K[C(5)Me(4)H], once more under somewhat forcing conditions (115 degrees C, 36 h). The structures of the three metallocenes have been determined by low-temperature X-ray studies. Both 1 and 3 present eta5/eta1 geometries of the slip-sandwich type, whereas 2 exhibits an almost regular, ferrocene-like, sandwich structure. In the mixed-ring compound 3, C(5)Me(5) is centrally bound to beryllium and the eta(1)-C(5)Me(4)H ring bonds to the metal through the unique CH carbon atom. This is also the binding mode of the eta(1)-ring of 1. To analyze the nature of the bonding in these molecules, theoretical calculations at different levels of theory have been performed on compounds 2 and 3, and a comparison with the bonding in [Be(C(5)H(5))(2)] has been made. As for the latter molecule, energy differences between the eta5/eta5 and the eta5/eta1 structures of 2 are very small, being of the order of a few kcal mol(-1). Constrained space orbital variations (CSOV) calculations show that the covalent character in the bonding is larger for [Be(C(5)Me(5))(2)] than for [Be(C(5)H(5))(2)] due to larger charge delocalization and to increased polarizability of the C(5)Me(5) fragment.

  17. 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.

  18. 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.

  19. One-dimensional decavanadate chains in the crystal structure of Rb4[Na(H2O)6][HV10O28]·4H2O.

    PubMed

    Yakubovich, Olga V; Steele, Ian M; Yakovleva, Ekaterina V; Dimitrova, Olga V

    2015-06-01

    New decavanadate minerals, the products of the leaching or metasomatic processes, are possible in nature via Na/Rb removal/inclusion reactions. As part of our search for novel vanadate phases with varying functionalities, a new phase, tetrarubidium hexaaquasodium hydrogen decavanadate tetrahydrate, Rb4[Na(H2O)6][HV10O28]·4H2O, has been synthesized by the hydrothermal technique at 553 K. Ten shared edges of V-centred octahedra form monoprotonated decavanadate cages, which are joined together via hydrogen bonds into one-dimensional chains parallel to the [101] direction. Within these chains, H atoms are sandwiched between neighbouring polyanions. Na and Rb atoms and H2O molecules occupy interstices flanked by the anionic chains providing additional crosslinking in the structure. This compound is the second decavanadate with P2/n symmetry. Structural relationships among protonated and deprotonated decavanadates with inorganic cations, including minerals of the pascoite group, are discussed.

  20. High-voltage 4H-SiC trench MOS barrier Schottky rectifier with low forward voltage drop using enhanced sidewall layer

    NASA Astrophysics Data System (ADS)

    Cho, Doohyung; Sim, Seulgi; Park, Kunsik; Won, Jongil; Kim, Sanggi; Kim, Kwangsoo

    2015-12-01

    In this paper, a 4H-SiC trench MOS barrier Schottky (TMBS) rectifier with an enhanced sidewall layer (ESL) is proposed. The proposed structure has a high doping concentration at the trench sidewall. This high doping concentration improves both the reverse blocking and forward characteristics of the structure. The ESL-TMBS rectifier has a 7.4% lower forward voltage drop and a 24% higher breakdown voltage. However, this structure has a reverse leakage current that is approximately three times higher than that of a conventional TMBS rectifier owing to the reduction in energy barrier height. This problem is solved when ESL is used partially, since its use provides a reverse leakage current that is comparable to that of a conventional TMBS rectifier. Thus, the forward voltage drop and breakdown voltage improve without any loss in static and dynamic characteristics in the ESL-TMBS rectifier compared with the performance of a conventional TMBS rectifier.

  1. 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.

  2. 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

    2014-06-07

    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.

  3. 4H-SiC Power Bipolar Junction Transistor with a Very Low Specific On-resistance of 2.9 mOmega.cm2

    DTIC Science & Technology

    2006-04-12

    pp1381-1382, 2004. [2] C.-F. Huang and J. A. Cooper, Jr., “High current gain 4H-SiC NPN Bipolar Junction Transistors ,” IEEE Electron Device Lett...4H-SiC Power Bipolar Junction Transistor with a Very Low Specific On-resistance of 2.9 mΩ.cm2 Jianhui Zhang, member, IEEE, Petre Alexandrov...specific on-resistance (Rsp,on) of power 4H-SiC bipolar junction transistors (BJT). A 4H-SiC BJT based on a 12 um drift-layer shows a record low

  4. 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

  5. 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.

  6. Mass spectrum of the 1-butene-3-yne-2-yl radical (i-C4H3; X2A')

    NASA Astrophysics Data System (ADS)

    Guo, Ying; Gu, Xibin; Kaiser, Ralf I.

    2006-03-01

    The crossed molecular beams method has been applied to produce the 1-butene-3-yne-2-yl radical, i-C4H3(X2A') under single collision conditions via the reaction of dicarbon molecules with ethylene. We recorded time-of-flight spectra of the radical at the center-of-mass angle (28.0°) of the parent ion (m/z = 51; C4H3+) and of the fragments at m/z = 50 (C4H2+), m/z = 49 (C4H+), m/z = 48 (C4+), m/z = 39 (C3H3+), m/z = 38 (C3H2+), m/z = 37 (C3H+), and m/z = 36 (C3+). This yielded relative intensity ratios of I(m/z = 51):I(m/z = 50):I(m/z = 49):I(m/z = 48):I(m/z = 39):I(m/z = 38):I(m/z = 37):I(m/z = 36) = 0.47 +/- 0.01:0.94 +/- 0.01:1.0:0.07 +/- 0.02:0.31 +/- 0.01:0.23 +/- 0.02:0.24 +/- 0.01:0.12 +/- 0.01 at 70 eV electron impact energy. Upper limits at mass-to-charge ratios between 27 and m/z = 24 and m/z = 14-12 were derived to be 0.02 +/- 0.01. Note that the intensity of the 13C isotopic peak of the 1-butene-3-yne-2-yl radical at m/z = 52 (13C12C3H3+) is about 0.04 +/- 0.01 relative to m/z = 51. Employing linear scaling methods, the absolute electron impact ionization cross section of the 1-butene-3-yne-2-yl radical was computed to be 7.8 +/- 1.6 × 10-16 cm2. These data can be employed to monitor the 1-butene-3-yne-2-yl radical in oxygen-poor combustion flames and in the framework of prospective explorations of planetary atmospheres (Jupiter, Saturn, Uranus, Neptune, Pluto) and of their moons (Titan, Triton, Oberon) in situ via matrix interval arithmetic assisted mass spectrometry.

  7. 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.

  8. Experimentally Observed Electrical Durability of 4H-SiC JFET ICs Operating from 500 C to 700 C

    NASA Technical Reports Server (NTRS)

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

    2016-01-01

    Prolonged 500 degrees Celsius to 700 degrees Celsius electrical testing data from 4H-SiC junction field effect transistor (JFET) integrated circuits (ICs) are combined with post-testing microscopic studies in order to gain more comprehensive understanding of the durability limits of the present version of NASA Glenn's extreme temperature microelectronics technology. The results of this study support the hypothesis that T = 500 degrees Celsius durability-limiting IC failure initiates with thermal-stress-related crack formation where dielectric passivation layers overcoat micron-scale vertical features including patterned metal traces.

  9. Impact of optical phonon scattering on inversion channel mobility in 4H-SiC trenched MOSFETs

    NASA Astrophysics Data System (ADS)

    Kutsuki, Katsuhiro; Kawaji, Sachiko; Watanabe, Yukihiko; Onishi, Toru; Fujiwara, Hirokazu; Yamamoto, Kensaku; Yamamoto, Toshimasa

    2017-04-01

    Temperature characteristics of the channel mobility were investigated for 4H-SiC trenched MOSFETs in the range from 30 to 200 °C. The conventional model of channel mobility limited by carrier scattering is based on Si-MOSFETs and shows a greatly different channel mobility from the experimental value, especially at high temperatures. On the other hand, our improved mobility model taking into account optical phonon scattering yielded results in excellent agreement with experimental results. Moreover, the major factors limiting the channel mobility were found to be Coulomb scattering in a low effective field (<0.7 MV/cm) and optical phonon scattering in a high effective field.

  10. Deep level defect studies in semi-insulating 4H- and 6H-silicon carbide using optical admittance spectroscopy

    NASA Astrophysics Data System (ADS)

    Lee, Wonwoo

    The objective of this study is to determine the deep vanadium defect levels in semi-insulating 4H- and 6H- silicon carbide using optical admittance spectroscopy. Also infrared spectroscopy and electron paramagnetic resonance spectroscopy are conducted to support the evidence of vanadium donor and acceptor levels obtained from OAS measurements. Vanadium acts as an amphoteric impurity in silicon carbide with a V3+/4+ acceptor level and V4+/5+ donor level. Although the value for the donor level is well established, the V3+/4+ defect level remains controversial. OAS shows that the vanadium donor level is isolated near Ec-1.7 eV, and the vanadium acceptor level is located at Ec-0.75 eV at a cubic site and Ec-0.94 eV at a hexagonal site in 4H-SiC, while the vanadium donor level of 6H-SiC samples is about Ec-1.5 eV. The acceptor levels of 6H-SiC were assigned to Ec-0.67 eV, E c -0.70 eV at two cubic sites, and Ec-0.87 eV at a hexagonal site. IR spectra demonstrated that the signatures of the vanadium V 3+ and V4+ charge states are present in the samples. EPR and photo-induced EPR are used to identify the V3+/4+ and V4+/5+ levels as well as the V3+ and V 4+ charge states. EPR spectra represent both V3+ and V4+ in 4H- and 6H samples consistent with FTIR data. EPR and photo-induced EPR suggest that the va nadium acceptor level is between 0.7 eV and 0.86 eV, while the donor level is near Ec-1.5 eV in 6H-SiC. The donor level of 4H-SiC is located at Ec-1.6 eV. Thus, the data obtained from EPR and FTIR support the assignment of the vanadium defect levels determined by OAS. Vanadium complexes induced by other elements such as titanium, hydrogen, and nitrogen atoms are also observed in OAS spectra and will be discussed in the text.

  11. Numerical analysis of the Gibbs-Thomson effect on trench-filling epitaxial growth of 4H-SiC

    NASA Astrophysics Data System (ADS)

    Mochizuki, Kazuhiro; Ji, Shiyang; Kosugi, Ryoji; Kojima, Kazutoshi; Yonezawa, Yoshiyuki; Okumura, Hajime

    2016-03-01

    A steady-state two-dimensional diffusion equation was numerically analyzed to examine the rate of homoepitaxial growth on a trenched 4H-SiC substrate. The radii of curvature at the top and bottom of the trenches were used to take the Gibbs-Thomson effect into account in the analysis based on the conventional boundary-layer model. When the trench pitch was less than or equal to 6.0 µm, the measured dependence of the growth rate on the trench pitch was found to be explained by the Gibbs-Thomson effect on the vapor-phase diffusion of growing species.

  12. A DLTS study of 4H-SiC-based p-n junctions fabricated by boron implantation

    SciTech Connect

    Ivanov, P. A. Potapov, A. S.; Samsonova, T. P.; Korol'kov, O.; Sleptsuk, N.

    2011-10-15

    Deep-level transient spectroscopy (DLTS) has been used to study p-n junctions fabricated by implantation of boron into epitaxial 4H-SiC films with n-type conductivity and the donor concentration (8-9) Multiplication-Sign 10{sup 14} cm{sup -3}. A DLTS signal anomalous in sign is observed; this signal is related to recharging of deep compensating boron-involved centers in the n-type region near the metallurgical boundary of the p-n junction.

  13. 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.

  14. 4H Syndrome

    MedlinePlus

    ... syndrome appears normal. Symptoms usually start during the second year of life, but patients with normal early childhood and symptoms only from the second decade have been described. Neurological symptoms include: Late ...

  15. 4H Syndrome

    MedlinePlus

    ... of the clinical symptoms, especially ataxia and delayed dentition or hypodontia, in combination with the results of ... may be already present at birth (natal teeth) Dentition (eruption of teeth) is delayed, and the first ...

  16. Nano-scale elastic-plastic properties and indentation-induced deformation of single crystal 4H-SiC.

    PubMed

    Nawaz, A; Mao, W G; Lu, C; Shen, Y G

    2017-02-01

    The nanoscale elastic-plastic response of single crystal 4H-SiC has been investigated by nanoindentationwith a Berkovich tip. The hardness (H) and elastic modulus (E) determined in the load-independent region were 36±2GPa and 413±8GPa, respectively. The indentation size effect (ISE) of hardness within an indentation depth of 60nm was systematically analyzed by the Nix-Gao model. Pop-in events occurring at a depth of ~23nm with indentation loads of 0.60-0.65mN were confirmed to indicate the elastic-plastic transition of the crystal, on the basis of the Hertzian contact theory and Johnson's cavity model. Theoritically calculated maximum tensile strength (13.5GPa) and cleavage strength (33GPa) also affirms the deformation due to the first pop-in rather than tensile stresses. Further analyses of deformation behavior across the indent was done in 4H-SiC by a combined technique of focused ion beam and transmission electron microscope, revealing that slippage occurred in the (0001) plane after indentation.

  17. Direct Determination of Burgers Vectors of Threading Mixed Dislocations in 4H-SiC Grown by PVT Method

    NASA Astrophysics Data System (ADS)

    Guo, Jianqiu; Yang, Yu; Wu, Fangzhen; Sumakeris, Joe; Leonard, Robert; Goue, Ouloide; Raghothamachar, Balaji; Dudley, Michael

    2016-04-01

    In addition to pure threading screw dislocations (TSDs), the presence of threading mixed dislocations (TMDs) (with a component) has been reported both in 4H-SiC axial slices (wafers cut parallel to the growth axis) and in commercial offcut wafers (cut almost perpendicular to the growth axis). In this paper, we first demonstrate a method to quickly distinguish TMDs from TSDs in axial slices via synchrotron white-beam x-ray topography. Since such axial slices are usually not available for commercial purposes, a systematic method is then developed and demonstrated here to unambiguously determine the Burgers vectors of TMDs in 4H-SiC commercial offcut wafers. In this second study, both synchrotron monochromatic-beam x-ray topography and ray-tracing simulation are used. The x-ray topographs were recorded using grazing-incidence geometry. The principle of this method is that the contrast of dislocations on different reflections varies with the relative orientation of Burgers vectors with respect to the diffraction vectors. Measurements confirm that, in a commercial offcut wafer, the majority of the threading dislocations with screw component are mixed-type dislocations.

  18. High-performance 4H-SiC junction barrier Schottky diodes with double resistive termination extensions

    NASA Astrophysics Data System (ADS)

    Zheng, Liu; Zhang, Feng; Liu, Sheng-Bei; Dong, Lin; Liu, Xing-Fang; Fan, Zhong-Chao; Liu, Bin; Yan, Guo-Guo; Wang, Lei; Zhao, Wan-Shun; Sun, Guo-Sheng; He, Zhi; Yang, Fu-Hua

    2013-09-01

    4H-SiC junction barrier Schottky (JBS) diodes with a high-temperature annealed resistive termination extension (HARTE) are designed, fabricated and characterized in this work. The differential specific on-state resistance of the device is as low as 3.64 mΩ·cm2 with a total active area of 2.46 × 10-3 cm2. Ti is the Schottky contact metal with a Schottky barrier height of 1.08 V and a low onset voltage of 0.7 V. The ideality factor is calculated to be 1.06. Al implantation annealing is performed at 1250°C in Ar, while good reverse characteristics are achieved. The maximum breakdown voltage is 1000 V with a leakage current of 9 × 10-5 A on chip level. These experimental results show good consistence with the simulation results and demonstrate that high-performance 4H-SiC JBS diodes can be obtained based on the double HARTE structure.

  19. 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.

  20. Ni/Al2O3/4H-SiC structure for He++ energy detection in RBS experiments

    NASA Astrophysics Data System (ADS)

    Kaufmann, I. R.; Pick, A.; Pereira, M. B.; Boudinov, H. I.

    2016-10-01

    Epitaxial SiC device have been tested as detector for Rutherford Backscattering Spectroscopy (RBS). The device was fabricated on a commercial 4H-SiC epitaxial n-type layer grown onto a 4H-SiC n+ type substrate wafer doped with nitrogen. Aluminum oxide with a thickness of 1 nm was deposited by Atomic Layer Deposition and 10 nm of Ni were deposited by sputtering to form the Ni/Al2O3/SiC MIS Schottky structure. Variable temperature Current-Voltage curves were used to extract the values of real Schottky Barrier Height and ideality factor (0.61 eV and 1.19, respectively). Current-Voltage and Capacitance-Voltage characteristics were measured and compared with the curves of a commercial Si barrier detector from ORTEC. RBS data for three beam energies (1, 1.5 and 2 MeV) were collected from an Au/Si sample using the fabricated and the commercial detectors simultaneously. The energy resolution for the fabricated detector was estimated to be 76 keV.

  1. Evaluation of sintering effects on SiC-incorporated UO2 kernels under Ar and Ar-4%H2 environments

    NASA Astrophysics Data System (ADS)

    Silva, Chinthaka M.; Lindemer, Terrence B.; Hunt, Rodney D.; Collins, Jack L.; Terrani, Kurt A.; Snead, Lance L.

    2013-11-01

    Silicon carbide (SiC) is suggested as an oxygen getter in UO2 kernels used for tristructural isotropic (TRISO) particle fuels and to prevent kernel migration during irradiation. Scanning electron microscopy and X-ray diffractometry analyses performed on sintered kernels verified that an internal gelation process can be used to incorporate SiC in UO2 fuel kernels. Even though the presence of UC in either argon (Ar) or Ar-4%H2 sintered samples suggested a lowering of the SiC up to 3.5-1.4 mol%, respectively, the presence of other silicon-related chemical phases indicates the preservation of silicon in the kernels during sintering process. UC formation was presumed to occur by two reactions. The first was by the reaction of SiC 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. A slightly higher density and UC content were observed in the sample sintered in Ar-4%H2, but both atmospheres produced kernels with ˜95% of theoretical density. It is suggested that incorporating CO in the sintering gas could prevent UC formation and preserve the initial SiC content.

  2. 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.

  3. Optical beam induced current measurements based on two-photon absorption process in 4H-SiC bipolar diodes

    SciTech Connect

    Hamad, H.; Raynaud, C.; Bevilacqua, P.; Tournier, D.; Planson, D.; Vergne, B.

    2014-02-24

    Using a pulsed green laser with a wavelength of 532 nm, a duration pulse of ∼1 ns, and a mean power varying between 1 and 100 mW, induced photocurrents have been measured in 4H-SiC bipolar diodes. Considering the photon energy (2.33 eV) and the bandgap of 4H-SiC (3.2 eV), the generation of electron-hole pair by the conventional single photon absorption process should be negligible. The intensity of the measured photocurrents depends quadratically on the power beam intensity. This clearly shows that they are generated using two-photon absorption process. As in conventional OBIC (Optical Beam Induced Current), the measurements give an image of the electric field distribution in the structure under test, and the minority carrier lifetime can be extracted from the decrease of the photocurrent at the edge of the structure. The extracted minority carrier lifetime of 210 ns is consistent with results obtained in case of single photon absorption.

  4. Schottky barrier height of Ni/TiO2/4H-SiC metal-insulator-semiconductor diodes

    NASA Astrophysics Data System (ADS)

    Kaufmann, Ivan R.; Pereira, Marcelo B.; Boudinov, Henri I.

    2015-12-01

    Ni/TiO2/4H-SiC diodes were analysed through measurements of current-voltage curves varying the temperature. The Schottky Barrier Height (SBH) which increased with temperature was studied by simulation of the Thermionic Emission Model, considering Ni/SiC Schottky structures with an insulator layer between the metal and semiconductor. This model shows that a new method of calculation should be applied to diodes that have a metal-insulator-semiconductor structure. Misleading results for SBH are obtained if the thin insulator layer is not considered. When applying the suggested method to the Ni/TiO2/4H-SiC diodes it was necessary to consider not only the deposited TiO2 layer, but also a second dielectric layer of native SiCxOy at the surface of SiC. By measuring I-V-T curves for two samples with different thicknesses of TiO2, the suggested method allows one to estimate the thicknesses of both dielectric layers: TiO2 and SiOxCy.

  5. 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.

  6. First-Order SPICE Modeling of Extreme-Temperature 4H-SiC JFET Integrated Circuits

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Spry, David J.; Chen, Liang-Yu

    2016-01-01

    A separate submission to this conference reports that 4H-SiC Junction Field Effect Transistor (JFET) digital and analog Integrated Circuits (ICs) with two levels of metal interconnect have reproducibly demonstrated electrical operation at 500 C in excess of 1000 hours. While this progress expands the complexity and durability envelope of high temperature ICs, one important area for further technology maturation is the development of reasonably accurate and accessible computer-aided modeling and simulation tools for circuit design of these ICs. Towards this end, we report on development and verification of 25 C to 500 C SPICE simulation models of first order accuracy for this extreme-temperature durable 4H-SiC JFET IC technology. For maximum availability, the JFET IC modeling is implemented using the baseline-version SPICE NMOS LEVEL 1 model that is common to other variations of SPICE software and importantly includes the body-bias effect. The first-order accuracy of these device models is verified by direct comparison with measured experimental device characteristics.

  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. 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

  9. 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.

  10. New X-ray insight into oxygen intercalation in epitaxial graphene grown on 4H-SiC(0001)

    NASA Astrophysics Data System (ADS)

    Kowalski, G.; Tokarczyk, M.; Dąbrowski, P.; Ciepielewski, P.; MoŻdŻonek, M.; Strupiński, W.; Baranowski, J. M.

    2015-03-01

    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.

  11. 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.

  12. Comparable structural and optical properties of 4H-pyrano [3, 2-c] quinoline derivatives thin films

    NASA Astrophysics Data System (ADS)

    Zeyada, H. M.; El-Nahass, M. M.; El-Shabaan, M. M.

    2016-04-01

    The structural and optical 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 are studied. The compounds are polycrystalline in as- synthesised powder form; they became nanocrystallites dispersed in amorphous matrix upon thermal deposition to form thin films. FTIR spectral measurements showed no change in chemical bonds of the compounds after being deposited to form thin films. The optical properties have been determined based on spectrophotometer measurements of transmittance and reflectance at nearly normal incidence of light in the spectral range of 200-2500 nm. The absorption parameters, molar extinction coefficient, oscillator strength and electric dipole strength, are reported. The type of electron transition is determined from analysis of absorption coefficient spectra near the onset and optical absorption edges. The onset and optical energy gaps for Ph-HPQ and Ch-HPQ thin films are determined. The single oscillator model is applied to calculate the dispersion parameters of the investigated thin films. In addition, oscillator and dispersion energies, the high-frequency dielectric constant, lattice dielectric constant and ratio of free charge carriers concentrations to their effective masses are evaluated for the compounds under investigation.

  13. 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.

  14. Synthesis and Linear and Nonlinear Optical Properties of Three Push-Pull Oxazol-5(4H)-one Compounds.

    PubMed

    Jędrzejewska, Beata; Gordel, Marta; Szeremeta, Janusz; Krawczyk, Przemysław; Samoć, Marek

    2015-10-02

    Three uncharged push-pull oxazol-5(4H)-ones were synthesized and thoroughly characterized. The examined molecules contained electron-donor and electron-acceptor groups interacting via a π-conjugated bridge. Spectral properties of the oxazol-5(4H)-ones were studied in detail in three solvents of different polarities. The results indicate a solvatochromic shift toward lower energy for the charge-transfer state. The compounds are weakly fluorescent in polar solvents, but they have high fluorescence quantum yields in nonpolar solvents. Their two-photon absorption (2PA) properties were characterized by the open- and closed-aperture Z-scan technique, by the pump-probe technique, and by the two-photon excited fluorescence method. The dyes exhibit relatively high effective two-photon absorption cross sections ranging from 490 to 2600 GM at ~100 GW/cm(2), according to the Z-scan results, which are found, however, to contain significant contribution from higher-order absorption processes. In addition, these compounds display good photostability.

  15. 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.

  16. Identification of dihydromaltol (2,3-dihydro-5-hydroxy-6-methyl-4H-pyran-4-one) in Ryazhenka Kefir and comparative sensory impact assessment of related cycloenolones.

    PubMed

    Preininger, Martin; Gimelfarb, Ludmila; Li, Hui-Chen; Dias, Benjamin E; Fahmy, Farid; White, James

    2009-11-11

    Dihydromaltol (DHM; 2,3-dihydro-5-hydroxy-6-methyl-4H-pyran-4-one) was identified as a novel potent aroma compound in a dairy product, Ryazhenka kefir, using GC-olfactometry-MS. The flavor impact of the structurally related caramelized-smelling compounds DHM, 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DMHF), 5-ethyl-4-hydroxy-2-methyl-3(2H)-furanone (EHMF) and maltol was assessed in various dairy samples by applying the odor activity value concept (OAV = concentration/odor threshold) using flavor (retronasal odor) thresholds instead of odor thresholds. Commercial Ryazhenka kefir, original kefir, and kefir-culture inoculated heated milk, as well as UHT milk, evaporated milk, heated cream, and fresh pasteurized cream, were analyzed. In all dairy samples containing DHM, DMHF appeared to dominate over DHM in its flavor impact. Although DHM, the pyranoid isomer of DMHF, has been found in nature, dihydroethylmaltol (DHEM; 6-ethyl-2,3-dihydro-5-hydroxy-4H-pyran-4-one), the pyranoid isomer of EHMF (the seven carbon DMHF homologue), has not been found in nature. Therefore, DHM and its novel homologue, DHEM, were synthesized to determine their flavor thresholds and to investigate structure-odor-relationships among cycloenolones. DHEM has a strong caramelized odor. On the basis of flavor thresholds in water, DHM (50-250 microg/kg) by itself was found to be less than half as potent as DMHF but about 40 times more potent than maltol. DHEM (2.5-5 microg/kg of water) by itself was found to be more potent than DHM and close to the odor intensity of EHMF. The novel data provided on DHM and DHEM support understanding of the relationship between chemical structure and flavor intensity within the important aroma compound class, of cycloenolones.

  17. 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.

  18. 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…

  19. 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…

  20. 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…

  1. 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…

  2. 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.

  3. Crystal structures of ethyl 6-(4-methyl-phen-yl)-4-oxo-4H-chromene-2-carboxyl-ate and ethyl 6-(4-fluoro-phen-yl)-4-oxo-4H-chromene-2-carboxyl-ate.

    PubMed

    Gomes, Ligia R; Low, John Nicolson; Fernandes, Carlos; Gaspar, Alexandra; Borges, Fernanda

    2016-01-01

    The crystal structures of two chromone derivatives, viz. ethyl 6-(4-methyl-phen-yl)-4-oxo-4H-chromene-2-carboxyl-ate, C19H16O4, (1), and ethyl 6-(4-fluoro-phen-yl)-4-oxo-4H-chromene-2-carboxyl-ate C18H13FO4, (2), have been determined: (1) crystallizes with two mol-ecules in the asymmetric unit. A comparison of the dihedral angles beween the mean planes of the central chromone core with those of the substituents, an ethyl ester moiety at the 2-position and a para-substituted phenyl ring at the 6-position shows that each mol-ecule differs significantly from the others, even the two independent mol-ecules (a and b) of (1). In all three mol-ecules, the carbonyl groups of the chromone and the carboxyl-ate are trans-related. The supra-molecular structure of (1) involves only weak C-H⋯π inter-actions between H atoms of the substituent phenyl group and the phenyl group, which link mol-ecules into a chain of alternating mol-ecules a and b, and weak π-π stacking inter-actions between the chromone units. The packing in (2) involves C-H⋯O inter-actions, which form a network of two inter-secting ladders involving the carbonyl atom of the carboxyl-ate group as the acceptor for H atoms at the 7-position of the chromone ring and from an ortho-H atom of the exocyclic benzene ring. The carbonyl atom of the chromone acts as an acceptor from a meta-H atom of the exocyclic benzene ring. π-π inter-actions stack the mol-ecules by unit translation along the a axis.

  4. High-level ab initio predictions for the ionization energies and heats of formation of five-membered-ring molecules: thiophene, furan, pyrrole, 1,3-cyclopentadiene, and borole, C4H4X/C4H4X+ (X = S, O, NH, CH2, and BH).

    PubMed

    Lo, Po-Kam; Lau, Kai-Chung

    2011-02-10

    The ionization energies (IEs) and heats of formation (ΔH°(f0)/ΔH°(f298)) for thiophene (C(4)H(4)S), furan (C(4)H(4)O), pyrrole (C(4)H(4)NH), 1,3-cyclopentadiene (C(4)H(4)CH(2)), and borole (C(4)H(4)BH) 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 a quasi-perturbative triple excitation [CCSD(T)]. Where appropriate, the zero-point vibrational energy correction (ZPVE), the core-valence electronic correction (CV), and the scalar relativistic effect (SR) are included in these calculations. The respective CCSD(T)/CBS predictions for C(4)H(4)S, C(4)H(4)O, C(4)H(4)NH, and C(4)H(4)CH(2), being 8.888, 8.897, 8.222, and 8.582 eV, are in excellent agreement with the experimental values obtained from previous photoelectron and photoion measurements. The ΔH°(f0)/ΔH°(f298) values for the aforementioned molecules and their corresponding cations have also been predicted by the CCSD(T)/CBS method, and the results are compared with the available experimental data. The comparisons between the CCSD(T)/CBS predictions and the experimental values for C(4)H(4)S, C(4)H(4)O, C(4)H(4)NH, and C(4)H(4)CH(2) suggest that the CCSD(T)/CBS procedure is capable of predicting reliable IE values for five-membered-ring molecules with an uncertainty of ±13 meV. In view of the excellent agreements between the CCSD(T)/CBS predictions and the experimental values for C(4)H(4)S, C(4)H(4)O, C(4)H(4)NH, and C(4)H(4)CH(2), the similar CCSD(T)/CBS IE and ΔH°(f0)/ΔH°(f298) predictions for C(4)H(4)BH, whose thermochemical data are not readily available due to its reactive nature, should constitute a reliable data set. The CCSD(T)/CBS IE(C(4)H(4)BH) value is 8.868 eV, and ΔH°(f0)/ΔH°(f298) values for C(4)H(4)BH and C(4)H(4)BH(+) are 269.5/258.6 and 1125.1/1114.6 kJ/mol, respectively. The highest occupied molecular orbitals

  5. A Diels-Alder super diene breaking benzene into C2H2 and C4H4 units

    NASA Astrophysics Data System (ADS)

    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.

  6. Fabrication, characterization and simulation of 4H-SiC Schottky diode alpha particle detectors for pyroprocessing actinide monitoring

    NASA Astrophysics Data System (ADS)

    Garcia, Timothy Richard

    Pyroprocessing is a method of using high-temperature molten salts and electric fields to separate and collect fuel isotopes of used nuclear fuel. It has been has been tested in the U.S. at Idaho National Laboratory as a key step in closing the nuclear fuel cycle. One technical problem with the pyroprocessing method is a lack of knowledge regarding the actinide concentrations in the salt bath during operation, since on-line techniques for measuring these concentrations are not presently available. 4H-SiC Schottky diode detectors can potentially fulfill this need. Such detectors would operate in contact with the molten salt, and measure concentrations via alpha-particle spectroscopy. This work seeks to fabricate and characterize 4H-SiC Schottky diode detectors at high temperature, model the alpha particle spectrum expected in a molten salt, and model the operation of the detectors to confirm the physics of operation is as expected. In this work, 4H-SiC Schottky diode detectors were fabricated at OSU Nanotech West. After fabrication, these detectors were characterized using both I-V curves and Am-241 alpha-particle energy spectra. All measurements were made as a function of temperature, from room temperature up to 500°C. The average energy required to create an electron-hole pair was observed to decrease with an increase of temperature, due to a decrease of both the 4H-SiC bandgap and non-linear energy loss terms. Furthermore, the FWHM of the spectra was observed to be dependent on the leakage current at a certain temperature, and not dependent on the temperature itself. Secondly, the alpha particle energy spectrum in the pyroprocessing environment was modeled using SRIM. The molten salt was modeled in 3 different geometries, with or without a protective cover material on top of the detector. Due to the loss of alpha-particle energy in the molten salt itself, a high-energy alpha emitter may completely cover the spectrum from a lower-energy alpha emitter. Each of the

  7. Processing and Characterization of Thousand-Hour 500 C Durable 4H-SiC JFET Integrated Circuits

    NASA Technical Reports Server (NTRS)

    Spry, David J.; Neudeck, Philip G.; Chen, Liang-Yu; Lukco, Dorothy; Chang, Carl W.; Beheim, Glenn M.; Krasowski, Michael J.; Prokop, Norman F.

    2016-01-01

    This work reports fabrication and testing of integrated circuits (ICs) with two levels of interconnect that consistently achieve greater than 1000 hours of stable electrical operation at 500 C in air ambient. These ICs are based on 4H-SiC junction field effect transistor (JFET) technology that integrates hafnium ohmic contacts with TaSi2 interconnects and SiO2 and Si3N4 dielectric layers over approximately 1-micrometer scale vertical topology. Following initial burn-in, important circuit parameters remain stable for more than 1000 hours of 500 C operational testing. These results advance the technology foundation for realizing long-term durable 500 C ICs with increased functional capability for sensing and control combustion engine, planetary, deep-well drilling, and other harsh-environment applications.

  8. Processing and Characterization of Thousand-Hour 500 C Durable 4H-SiC JFET Integrated Circuits

    NASA Technical Reports Server (NTRS)

    Spry, David J.; Neudeck, Philip G.; Chen, Liangyu; Lukco, Dorothy; Chang, Carl W.; Beheim, Glenn M.; Krasowski, Michael J.; Prokop, Norman F.

    2016-01-01

    This work reports fabrication and testing of integrated circuits (ICs) with two levels of interconnect that consistently achieve greater than 1000 hours of stable electrical operation at 500 C in air ambient. These ICs are based on 4H-SiC junction field effect transistor (JFET) technology that integrates hafnium ohmic contacts with TaSi2 interconnects and SiO2 and Si3N4 dielectric layers over 1-m scale vertical topology. Following initial burn-in, important circuit parameters remain stable for more than 1000 hours of 500 C operational testing. These results advance the technology foundation for realizing long-term durable 500 C ICs with increased functional capability for sensing and control combustion engine, planetary, deep-well drilling, and other harsh-environment applications.

  9. Coupling ZnSe band spin states and 4H-SiC defect spin states across their interface

    NASA Astrophysics Data System (ADS)

    Yeats, Andrew L.; Richardella, Anthony; Samarth, Nitin; Awschalom, David D.

    2014-03-01

    Point defects in silicon carbide (SiC) have emerged as a promising platform for quantum information processing and nanoscale sensing in a technologically-mature semiconductor. ZnSe is a promising candidate for semiconductor spintronic applications and has selection rules compatible with optical orientation of conduction electron spins. We combine pump-probe optical measurements with pulsed optically detected magnetic resonance (ODMR) sequences to investigate coupling between SiC defect spins and ZnSe conduction electron spins in ZnSe/4H-SiC heterostructures. Preparation of these structures by molecular beam epitaxy (MBE) and ion implantation is discussed in terms of interface optimization. This work is supported by NSF, ONR and AFOSR.

  10. Formation of Nanoparticles by Control of Electron Temperature in Hollow-Typed Magnetron Radio Frequency CH4/H2 Plasma

    NASA Astrophysics Data System (ADS)

    Emi, Junichi; Kato, Kohgi; Abe, Toshimi; Iizuka, Satoru

    2006-10-01

    In this study, we investigate the effects of electron temperature Te on the production of nanoparticles by using the grid-biasing method in hollow-typed magnetron radio frequency (RF) CH4/H2 plasma. We find that nanoparticles are produced in low-Te plasma. On the other hand, thin film depositions, such as nanowalls, are mainly observed and almost no nanoparticles are created in high-Te plasma. This implies that a reduction in the CH2/CH3 radical ratio is important for producing nanoparticles, together with a reduction in sheath potential in front of the substrate. The change in electron temperature in plasma has a marked effect on film quality.

  11. 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

  12. High-temperature and high-speed oxidation of 4H-SiC by atmospheric pressure thermal plasma jet

    NASA Astrophysics Data System (ADS)

    Hanafusa, Hiroaki; Ishimaru, Ryosuke; Higashi, Seiichiro

    2017-04-01

    The application of atmospheric pressure thermal plasma jet (TPJ) annealing to the high-temperature and high-speed thermal oxidation of Si-face of 4H-SiC wafer is reported. A high SiO2 film growth rate of 288 nm min‑1 was obtained at an oxidation temperature of 1640 °C without intentional dry O2 gas feeding. Ambient analysis suggested that ozone generated from oxygen in the ambient air by the plasma irradiation was supplied to the SiC surface. It is implied that a mono-oxygen decomposed from ozone was diffused into the oxide growth interface. As a result, high-speed oxidation occurred by combination of high-temperature TPJ annealing and ozone feeding.

  13. Analysis of the turn-on process in 6 kV 4H-SiC junction diodes

    NASA Astrophysics Data System (ADS)

    Mnatsakanov, T. T.; Levinshtein, M. E.; Ivanov, P. A.; Palmour, J. W.; Das, M.; Agarwal, A. K.

    2005-01-01

    The switch-on process in 6 kV 4H-SiC junction diodes has been investigated experimentally and theoretically. The results of a detailed computer simulation are compared with the data furnished by the analytical theory. It is demonstrated that, at high current densities exceeding the critical value jcr = eNDvs (e is the elementary charge, ND is the base doping level, and vs is the carrier saturation velocity) and rather short current rise time (1 ns), an extremely fast base modulation can be achieved. In this mode, the base is spanned by an electron front that moves from the n+-n to the p+-n emitter with a velocity vs and by a relatively slow quasi-neutral hole front moving in the opposite direction, from the p+-n to the n+-n junction.

  14. Activation and control of visible single defects in 4H-, 6H-, and 3C-SiC by oxidation

    SciTech Connect

    Lohrmann, A.; Klein, J. R.; Prawer, S.; McCallum, J. C.; Castelletto, S.; Ohshima, T.; Bosi, M.; Negri, M.; Johnson, B. C.

    2016-01-11

    In this work, we present the creation and characterisation of single photon emitters at the surface of 4H- and 6H-SiC, and of 3C-SiC epitaxially grown on silicon. These emitters can be created by annealing in an oxygen atmosphere at temperatures above 550 °C. By using standard confocal microscopy techniques, we find characteristic spectral signatures in the visible region. The excited state lifetimes are found to be in the nanosecond regime in all three polytypes, and the emission dipoles are aligned with the lattice. HF-etching is shown to effectively annihilate the defects and to restore an optically clean surface. The defects described in this work have ideal characteristics for broadband single photon generation in the visible spectral region at room temperature and for integration into nanophotonic devices.

  15. 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.

  16. [Synthesis and characterization of complex of Na2[Cu5(Shi)4].4H2O].

    PubMed

    Yang, Bin-sheng; Hu, Yong-gang; Chen, Zhao-bin; Liu, Wen

    2002-12-01

    The complex, which is formed by reacting copper (II) with salicylhydroxamic acid (H3Shi), has been synthesized. The chemical formula of the complex was determined to be Na2[Cu5(Shi)4].4H2O by elemental analysis and spectrometric titration. The structure and the properties were tentatively investigated by using UV-Vis, IR, NMR, TG, fluorescence, molecular modeling and magnetic susceptibility measurement. The results show that the UV absorption peak corresponding to the pi-->pi* transition shifts towards red 25 nm, the d proton of salicylhydroxamic acid behaves as that of alkyl hydrocarbon in NMR and there is a strong magnetic interaction among the copper (II) ions in the complex.

  17. 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.

  18. Connecting Kids to the Universe: Partnering with 4--H Youth Development to Pilot Afterschool Universe in New York

    NASA Astrophysics Data System (ADS)

    Schaff, N.

    2008-11-01

    To offer effective astrophysics outreach education, developmentally appropriate hands-on activities that develop conceptual understanding and create excitement about science and careers are needed. The new NASA Afterschool Universe Program is ideal to enhance astronomy and astrophysics outreach. Afterschool Universe is a comprehensive project that builds a strong conceptual understanding of the Universe beyond the solar system for out-of-school groups at the middle school level. Students at this age are fascinated by mysteries (to them) of the universe, but are introduced primarily to the Solar System in school. We determined that access to materials and training would be essential to successful implementation of Afterschool Universe. Therefore, we secured funding from the Chandra EPO program to develop kits and implement five regional workshops in collaboration with 4--H Youth Development in New York State during 2008, in preparation for the International Year of Astronomy.

  19. Solvation dynamics of 4-(dicyanomethylene)-2-methyl-6-( p-dimethylaminostyryl)-4H-pyran (DCM) in a microemulsion

    NASA Astrophysics Data System (ADS)

    Pal, Samir Kumar; Mandal, Debabrata; Sukul, Dipankar; Bhattacharyya, Kankan

    1999-10-01

    The photophysical process of the laser dye 4-(dicyanomethylene)-2-methyl-6-( p-dimethylaminostyryl)-4H-pyran (DCM) is studied in aerosol-OT (AOT) microemulsions in n-heptane using picosecond spectroscopy. When AOT and water are added to a solution of DCM in n-heptane, some of the DCM molecules migrate from bulk n-heptane to the water pool. The absorption and emission peaks of the DCM molecules in the polar water pool are markedly red shifted from those in the bulk n-heptane and the emission intensity in the water pool is nearly 40 times higher. Dual emission is not observed in the microemulsions. DCM exhibits slow solvation dynamics in the water pool with an average solvation time of 1.23 ns.

  20. 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.

  1. Activation and control of visible single defects in 4H-, 6H-, and 3C-SiC by oxidation

    NASA Astrophysics Data System (ADS)

    Lohrmann, A.; Castelletto, S.; Klein, J. R.; Ohshima, T.; Bosi, M.; Negri, M.; Lau, D. W. M.; Gibson, B. C.; Prawer, S.; McCallum, J. C.; Johnson, B. C.

    2016-01-01

    In this work, we present the creation and characterisation of single photon emitters at the surface of 4H- and 6H-SiC, and of 3C-SiC epitaxially grown on silicon. These emitters can be created by annealing in an oxygen atmosphere at temperatures above 550 °C. By using standard confocal microscopy techniques, we find characteristic spectral signatures in the visible region. The excited state lifetimes are found to be in the nanosecond regime in all three polytypes, and the emission dipoles are aligned with the lattice. HF-etching is shown to effectively annihilate the defects and to restore an optically clean surface. The defects described in this work have ideal characteristics for broadband single photon generation in the visible spectral region at room temperature and for integration into nanophotonic devices.

  2. 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}.

  3. Impact of rapid cooling process in ultrahigh-temperature oxidation of 4H-SiC(0001)

    NASA Astrophysics Data System (ADS)

    Sometani, Mitsuru; Nagai, Daisuke; Katsu, Yoshihito; Hosoi, Takuji; Shimura, Takayoshi; Takei, Manabu; Yonezawa, Yoshiyuki; Watanabe, Heiji

    2017-04-01

    We conducted a rapid water-quenching procedure with ultrahigh-temperature oxidation to avoid degradation of the high-quality SiO2/SiC interface formed by ultrahigh-temperature oxidation during the cooling process. A reduction in the interface state density was observed for the SiO2/4H-SiC(0001) interface formed by ultrahigh-temperature oxidation in dry O2 ambient using the water-quenching process, compared with other natural cooling processes. The oxidation temperature dependence of interface state density for the thermally grown SiO2/SiC structures formed using the water-quenching process revealed that degradation of the interface properties occurred not only during the cooling process but also during the continuous oxidation process at exceedingly high temperatures, above 1500 °C, in 100% dry O2 ambient at 1 atm.

  4. Termination dependence of surface stacking at 4H-SiC(0001)-1×1 : Density functional theory calculations

    NASA Astrophysics Data System (ADS)

    Hara, Hideyuki; Morikawa, Yoshitada; Sano, Yasuhisa; Yamauchi, Kazuto

    2009-04-01

    We study the effect of adsorbates on the relative stability of hexagonal and cubic stacking sequences at the topmost SiC bilayers of 4H-SiC(0001)-1×1 surfaces using first-principles calculations. We investigate F-terminated, OH-terminated, H-terminated, and clean surfaces, and in all cases, the cubic structure is more stable than the hexagonal structure. The energy difference between the two structures, however, significantly depends on adsorbates and is largest on the clean surface while it is smallest on the H-terminated surface. Stabilization of the cubic structure at F-terminated and OH-terminated surfaces is in contradiction to a simple argument based on the electrostatic interaction and we attribute it to orbital hybridization between occupied states of adsorbates and unoccupied states of the substrate surface. The present results suggest a possible means of controlling step bunching and the SiC stacking sequence by surface adsorbates.

  5. Avian influenza virus hemagglutinins H2, H4, H8, and H14 support a highly pathogenic phenotype

    PubMed Central

    Veits, Jutta; Weber, Siegfried; Stech, Olga; Breithaupt, Angele; Gräber, Marcus; Gohrbandt, Sandra; Bogs, Jessica; Hundt, Jana; Teifke, Jens P.; Mettenleiter, Thomas C.; Stech, Jürgen

    2012-01-01

    High-pathogenic avian influenza viruses (HPAIVs) evolve from low-pathogenic precursors specifying the HA serotypes H5 or H7 by acquisition of a polybasic HA cleavage site. As the reason for this serotype restriction has remained unclear, we aimed to distinguish between compatibility of a polybasic cleavage site with H5/H7 HA only and unique predisposition of these two serotypes for insertion mutations. To this end, we introduced a polybasic cleavage site into the HA of several low-pathogenic avian strains with serotypes H1, H2, H3, H4, H6, H8, H10, H11, H14, or H15, and rescued HA reassortants after cotransfection with the genes from either a low-pathogenic H9N2 or high-pathogenic H5N1 strain. Oculonasal inoculation with those reassortants resulted in varying pathogenicity in chicken. Recombinants containing the engineered H2, H4, H8, or H14 in the HPAIV background were lethal and exhibited i.v. pathogenicity indices of 2.79, 2.37, 2.85, and 2.61, respectively, equivalent to naturally occurring H5 or H7 HPAIV. Moreover, the H2, H4, and H8 reassortants were transmitted to some contact chickens. The H2 reassortant gained two mutations in the M2 proton channel gate region, which is affected in some HPAIVs of various origins. Taken together, in the presence of a polybasic HA cleavage site, non-H5/H7 HA can support a highly pathogenic phenotype in the appropriate viral background, indicating requirement for further adaptation. Therefore, the restriction of natural HPAIV to serotypes H5 and H7 is likely a result of their unique predisposition for acquisition of a polybasic HA cleavage site. PMID:22308331

  6. Synthesis and structural study of samarium hexacyanoferrate (III) tetrahydrate, SmFe(CN) 6·4H 2O

    NASA Astrophysics Data System (ADS)

    Mullica, D. F.; Perkins, Herbert O.; Sappenfield, E. L.; Grossie, David A.

    1988-05-01

    Single crystals of SmFe(CN) 6·4H 2O prepared from an aqueous solution under ambient conditions have been used for single-crystal diffraction, thermal gravimetric analysis, and infrared spectrometric studies. This characterized compound is compared to previously reported LnT(CN) 6 (T =Cr, Fe, Co) structures. Samarium hexacyanoferrate (III) tetrahydrate is found to be monoclinic, not hexagonal or orthorhombic as presupposed. SmFe(CN) 6·4H 2O crystallizes in space group P2/ 1m (No. 11), a = 7.431(1), b = 13.724(3), c = 7.429(2)A˚, β = 119.95(1)°, Z = 2. Full-matrix least-squares refinement has yielded the final values of R = 0.0292 and R w = 0.0296 for 1028 unique reflections. The observed and calculated densities are 2.198(3) and 2.197 Mg m -3, respectively. The dominant feature of the structure is that the samarium ion is eight-coordinated, not nine as previously believed. The samarium ion is bonded to six cyanonitrogen atoms and two water molecules in a square antiprism geometry ( D 4d), the SmN 6(H 2O) 2 group. The FeC 6 group is octahedrally arranged. Cyanide bridging links these groups to build an infinite polymeric array. Additional water molecules are trapped in distorted cubic cages within the structure. The important averaged bond lengths are: Sm sbnd N = 2.505(15); Sm sbnd O = 2.402(1); Fe sbnd C = 1.931(3); and C tbnd N = 1.156(1)A˚.

  7. 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.

  8. Prevalence of bovine subclinical endometritis 4h after insemination and its effects on first service conception rate.

    PubMed

    Kaufmann, T B; Drillich, M; Tenhagen, B-A; Forderung, D; Heuwieser, W

    2009-01-15

    The objective of this study was to investigate the prevalence of subclinical endometritis 4h after AI and its effect on first service conception rate (FSCR) in dairy cows. A total of 201 Holstein-Friesian cows with no signs of clinical endometritis were examined 4h after first AI for signs of subclinical endometritis. Endometrial samples were collected from the uterus using the cytobrush technique. The proportion of polymorphonuclear cells (PMN) in the cytological sample was used to characterize an inflammation of the endometrium. Cows were categorized into three groups according to the proportion of PMN in the sample. Cows with 0% PMN (n=115) were assigned to group Zero, cows with >0-15% PMN (n=59) to group Medium, and cows with >15% PMN (n=27) to group High. Pregnancy diagnosis was performed between days 38-44 after AI by palpation of the uterus and its contents per rectum. The FSCR was significantly higher in group Medium than in groups Zero and High (57.6% vs. 39.1% and 29.6%). Statistical analysis revealed an interaction between parity and PMN group. Primiparous cows were at higher risk of being classified into group Medium than multiparous cows (OR=2.27, P=0.01). Primiparous cows in group Zero had lower odds of pregnancy after first AI than primiparous cows in group Medium (OR=0.3, P=0.02). A comparison with cows that were not examined for subclinical endometritis showed that the collection of endometrial samples itself had no effect on FSCR.

  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. New experimental evidence to support roaming in the reaction Cl + isobutene (i-C4H8)

    PubMed Central

    Chen, Li-Wei; Hung, Ching-Ming; Matsui, Hiroyuki; Lee, Yuan-Pern

    2017-01-01

    The reaction Cl + isobutene (i-C4H8) was reported by Suits et al. to proceed via, in addition to abstraction, an addition-elimination path following a roaming excursion of Cl; a near-zero translational energy release and an isotropic angular distribution observed at a small collision energy characterized this mechanism. We employed a new experimental method to further characterize this roaming mechanism through observation of the internal distribution of HCl (v, J) and their temporal behavior upon irradiation of a mixture of Cl2C2O2 and i-C4H8 in He or Ar buffer gas. With 1–3 Torr buffer gas added to approach the condition of small collision energy, the intensities of emission of HCl (v = 1, 2) and the HCl production rates increased significantly; Ar shows a more significant effect than He because Ar quenches Cl more efficiently to reduce the collisional energy and facilitate the roaming path. According to kinetic modeling, the rate of addition-elimination (roaming) increased from kE ≈ 2 × 105 s−1 when little buffer gas was present to ~1.9 × 106 s−1 when 2–3 Torr of Ar was added, and the branching ratio for formation of [HCl (v = 2)]/[HCl (v = 1)] increased from 0.02 ± 0.01 for abstraction to 0.06 ± 0.01 for roaming. PMID:28079173

  11. Quasi-two-dimensional antiferromagnetism in Fe[S2CNC4H8]2I

    NASA Astrophysics Data System (ADS)

    Lukin, J. A.; Friedberg, S. A.; DeFotis, G. C.; Chamberlain, R. V.

    1993-05-01

    Recent studies of the magnetic susceptibility of powdered Fe[S2CNC4H8]2I confirm that Fe(III) in this salt is in the unusual spin state S=3/2 and that the system behaves as a quasi-2D antiferromagnet. Analysis of the data indicates that the ‖±1/2≳ ground doublet is separated by Δ/k=18.7 K from an excited ‖±3/2≳ doublet. We have now measured the heat capacity of polycrystalline Fe[S2CNC4H8]2I between 0.5 and 80 K in a liquid 3He-cooled calorimeter. CP exhibits a λ-type peak at TN=2.18±0.01 K. The critical entropy, S(TN)=0.25R ln2, indicates that most of the spin order is of a short-range, low-dimensional nature. The contribution of lattice vibrations to CP was estimated using the method of Sorai and Seki [J. Phys. Soc. Jpn. 32, 382 (1972)], which assumes a Schottky contribution from two doublets whose separation Δ was determined from the magnetic data. At the same time, the cooperative peak was reasonably represented by the results for the 2D S=1/2 XY model with Jxy/k=-2.18 K. In order to obtain a self-consistent fit of the lattice heat capacity, however, it was necessary to use a larger splitting (Δ/k=32 K) than that found from susceptibility data. This discrepancy between the doublet-doublet separations indicated by χ and CP measurements may suggest a possible temperature dependence of Δ.

  12. 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.

  13. New experimental evidence to support roaming in the reaction Cl + isobutene (i-C4H8)

    NASA Astrophysics Data System (ADS)

    Chen, Li-Wei; Hung, Ching-Ming; Matsui, Hiroyuki; Lee, Yuan-Pern

    2017-01-01

    The reaction Cl + isobutene (i-C4H8) was reported by Suits et al. to proceed via, in addition to abstraction, an addition-elimination path following a roaming excursion of Cl; a near-zero translational energy release and an isotropic angular distribution observed at a small collision energy characterized this mechanism. We employed a new experimental method to further characterize this roaming mechanism through observation of the internal distribution of HCl (v, J) and their temporal behavior upon irradiation of a mixture of Cl2C2O2 and i-C4H8 in He or Ar buffer gas. With 1–3 Torr buffer gas added to approach the condition of small collision energy, the intensities of emission of HCl (v = 1, 2) and the HCl production rates increased significantly; Ar shows a more significant effect than He because Ar quenches Cl more efficiently to reduce the collisional energy and facilitate the roaming path. According to kinetic modeling, the rate of addition-elimination (roaming) increased from kE ≈ 2 × 105 s‑1 when little buffer gas was present to ~1.9 × 106 s‑1 when 2–3 Torr of Ar was added, and the branching ratio for formation of [HCl (v = 2)]/[HCl (v = 1)] increased from 0.02 ± 0.01 for abstraction to 0.06 ± 0.01 for roaming.

  14. 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.

  15. 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

    2016-01-05

    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.

  16. Discovery and Pre-Clinical Characterization of Third-Generation 4-H Heteroaryldihydropyrimidine (HAP) Analogues as Hepatitis B Virus (HBV) Capsid Inhibitors.

    PubMed

    Qiu, Zongxing; Lin, Xianfeng; Zhang, Weixing; Zhou, Mingwei; Guo, Lei; Kocer, Buelent; Wu, Guolong; Zhang, Zhisen; Liu, Haixia; Shi, Houguang; Kou, Buyu; Hu, Taishan; Hu, Yimin; Huang, Mengwei; Yan, S Frank; Xu, Zhiheng; Zhou, Zheng; Qin, Ning; Wang, Yue Fen; Ren, Shuang; Qiu, Hongxia; Zhang, Yuxia; Zhang, Yi; Wu, Xiaoyue; Sun, Kai; Zhong, Sheng; Xie, Jianxun; Ottaviani, Giorgio; Zhou, Yuan; Zhu, Lina; Tian, Xiaojun; Shi, Liping; Shen, Fang; Mao, Yi; Zhou, Xue; Gao, Lu; Young, John A T; Wu, Jim Zhen; Yang, Guang; Mayweg, Alexander V; Shen, Hong C; Tang, Guozhi; Zhu, Wei

    2017-04-05

    Described herein are the discovery and structure-activity relationship (SAR) studies of the third-generation 4-H heteroaryldihydropyrimidines (4-H HAPs) featuring the introduction of a C6 carboxyl group as novel HBV capsid inhibitors. This new series of 4-H HAPs showed improved anti-HBV activity and better drug-like properties compared to the first- and second-generation 4-H HAPs. X-ray crystallographic study of analogue 12 (HAP_R01) with Cp149 Y132A mutant hexamer clearly elucidated the role of C6 carboxyl group played for the increased binding affinity, which formed strong hydrogen bonding interactions with capsid protein and coordinated waters. The representative analogue 10 (HAP_R10) was extensively characterized in vitro (ADMET) and in vivo (mouse PK and PD) and subsequently selected for further development as oral anti-HBV infection agent.

  17. 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.

  18. 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.

    2016-01-01

    Abstract 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

  19. Dependence of surface plasmon-phonon-polariton in 4 H-SiC on free carrier concentration

    NASA Astrophysics Data System (ADS)

    Karakachian, H.; Kazan, M.

    2017-03-01

    In this paper, we present a thorough study of the characteristics of the surface modes that result from coupling between plasmon electronic oscillation modes, phonon modes, and electromagnetic modes. The Fourier transform of p-polarized reflectivity measurements were carried out on different 4 H-SiC epilayers differing in their free carrier concentration. The reflectivity measurements were performed with appropriate care to record reflectivity spectra averaged over a wide range of incidence angles. The complex infrared dielectric functions of the measured samples were determined by correcting the values obtained from the conventional Kramers-Kronig conversion technique with reference to Fresnel equations for reflectivity. The obtained dielectric functions were used to compute the effect of the free carrier concentration and the resulting plasmon electronic oscillation on the dispersion spectrum, lifetime, mean propagation length of the bulk, and surface plasmon-phonon-polariton modes. The effect of the free carrier concentration on the temporal coherence of surface plasmon-phonon-polariton is investigated, showing a potential practical method for enhancing the temporal coherence of SiC based thermal sources.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Surface analyses of Zr (film)/4H-SiC (substrate) by synchrotron radiation induced-PEEM

    NASA Astrophysics Data System (ADS)

    Kamezawa, C.; Hirai, M.; Kusaka, M.; Iwami, M.; Labis, J.

    2004-10-01

    Photoemission electron microscopy (PEEM) has been applied to systems such as Fe, Cu, Ti and Zr on SiC substrates. The products on the surface that result from SiC decomposition and reaction with the deposited metal films can be well imaged by PEEM using synchrotron radiation, 40-130 eV and a high-pressure Hg arc-discharge lamp as light sources. Although some PEEM systems have an energy filter, we have explored the capability of PEEM without such a filter in determining the surface structure and composition. We do this by observing the image contrast as we varied the sample temperature and by tuning the photon energy of the synchrotron radiation, which causes a variation of the photoelectron yield corresponding to different surface products. A 5 nm Zr film was evaporated in ultra-high-vacuum (UHV) on a 4H-SiC substrate. The sample temperature was raised from room temperature (RT) to 1000 °C at the rate of 20 °C/min. The PEEM images observed and recorded in real time gave information that no reaction occurred between Zr and SiC, which was not the case for several metals, e.g., Fe, Cu, Ti, etc. Soft X-ray fluorescence spectroscopy (SXFS) study supported the above conclusion.

  5. Virial coefficients and equations of state for mixed fluids; application to CH sub 4 -H sub 2 O

    SciTech Connect

    Pitzer, K.S.; Anderko, A.; Sterner, S.M.

    1991-06-01

    The statistical mechanics of both pure and mixed fluids yields expressions in terms of virial expansions. The composition dependencies of various virial coefficients are well established as are the integrals expressing their values in terms of intermolecular potentials. These expressions are simple for the second virial coefficient but increase in complexity so rapidly for higher coefficients that it is not yet feasible to generate a complete equation of state from intermolecular potentials by this method. But it will be shown that these properties for the second, third, and fourth virial coefficients cab be combined in a very useful manner with information from the complete equations of state for the component pure fluids to yield a form for the equation for the mixed fluid which maintains consistency with all of the pertinent principles and has a minimum number of parameters to be evaluated empirically. The system CH{sub 4}-H{sub 2}O is presented here as an example and other very recent applications are cited. 21 refs., 4 figs., 2 tables.

  6. Superconductivity at approximately 100 K in dense SiH4(H2)2 predicted by first principles.

    PubMed

    Li, Yinwei; Gao, Guoying; Xie, Yu; Ma, Yanming; Cui, Tian; Zou, Guangtian

    2010-09-07

    Motivated by the potential high-temperature superconductivity in hydrogen-rich materials, the high-pressure structures of SiH(4)(H(2))(2) in the pressure range 50-300 GPa were extensively explored by using a genetic algorithm. An intriguing layered orthorhombic (Ccca) structure was revealed to be energetically stable above 248 GPa with the inclusion of zero-point energy. The Ccca structure is metallic and composed of hydrogen shared SiH(8) dodecahedra layers intercalated by orientationally ordered molecular H(2). Application of the Allen-Dynes modified McMillan equation yields remarkably high superconducting temperatures of 98-107 K at 250 GPa, among the highest values reported so far for phonon-mediated superconductors. Analysis reveals a unique superconducting mechanism that the direct interactions between H(2) and SiH(4) molecules at high pressure play the major role in the high superconductivity, while the contribution from H(2) vibrons is minor.

  7. 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.

  8. 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.

  9. 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.

  10. Anion- or Cation-Exchange Membranes for NaBH4/H2O2 Fuel Cells?

    PubMed

    Sljukić, Biljana; Morais, Ana L; Santos, Diogo M F; Sequeira, César A C

    2012-07-19

    Direct borohydride fuel cells (DBFC), which operate on sodium borohydride (NaBH4) as the fuel, and hydrogen peroxide (H2O2) as the oxidant, are receiving increasing attention. This is due to their promising use as power sources for space and underwater applications, where air is not available and gas storage poses obvious problems. One key factor to improve the performance of DBFCs concerns the type of separator used. Both anion- and cation-exchange membranes may be considered as potential separators for DBFC. In the present paper, the effect of the membrane type on the performance of laboratory NaBH4/H2O2 fuel cells using Pt electrodes is studied at room temperature. Two commercial ion-exchange membranes from Membranes International Inc., an anion-exchange membrane (AMI-7001S) and a cation-exchange membrane (CMI-7000S), are tested as ionic separators for the DBFC. The membranes are compared directly by the observation and analysis of the corresponding DBFC's performance. Cell polarization, power density, stability, and durability tests are used in the membranes' evaluation. Energy densities and specific capacities are estimated. Most tests conducted, clearly indicate a superior performance of the cation-exchange membranes over the anion-exchange membrane. The two membranes are also compared with several other previously tested commercial membranes. For long term cell operation, these membranes seem to outperform the stability of the benchmark Nafion membranes but further studies are still required to improve their instantaneous power load.

  11. Mixed Anhydride Intermediates in the Reaction of 5(4H)-Oxazolones with Phosphate Esters and Nucleotides.

    PubMed

    Liu, Ziwei; Rigger, Lukas; Rossi, Jean-Christophe; Sutherland, John D; Pascal, Robert

    2016-10-10

    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.

  12. 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.

  13. 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.

  14. Influences of ICP etching damages on the electronic properties of metal field plate 4H-SiC Schottky diodes

    NASA Astrophysics Data System (ADS)

    Hui, Wang; Yingxi, Niu; Fei, Yang; Yong, Cai; Zehong, Zhang; Zhongming, Zeng; Minrui, Wang; Chunhong, Zeng; Baoshun, Zhang

    2015-10-01

    Inductively coupled plasma (ICP) etching of 4H-SiC using SF6/O2 gas mixture was studied systematically and the effect of etching was examined by metal field plate SiC Schottky diodes (SBDs). It was found that the etch rate as well as SiC surface morphology were related with ICP power, RF power, pressure, the flow of SF6 and O2. Etching damages (the cone-in-pits and pits) generated at high chuck self-bias were observed, and they were thought to be caused by SiC defects. The degradation of both the reverse and forward I-V performances of SiC SBDs was ascribed to the cone-in-pits and pits. Moreover, the absolute value of forward current is even less than the reverse counterpart in the absolute value voltage range of 0-50 V for SiC SBDs with etching damages. Project supported by the Suzhou Research Fund (No. BY2011129) and the State Grid Corporation of China Research Fund (No. 525500140003).

  15. 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.

  16. 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.

  17. Crystal structure of 6,7-di-chloro-4-oxo-4H-chromene-3-carbaldehyde.

    PubMed

    Ishikawa, Yoshinobu

    2015-09-01

    In the title compound, C10H4Cl2O3, a dichlorinated 3-formyl-chromone, the non-H atoms of the 4H-chromene ring are essentially coplanar (r.m.s. = 0.0188 Å), with the largest deviation from the least-squares plane [0.043 (2) Å] being for the pyran C=O C atom. The α,β-unsaturated carbonyl O atom deviates from the least-square plane by 0.124 (2) Å. The dihedral angle between the chromone and formyl least-square planes is 6.76 (3)°. In the crystal, mol-ecules are linked through C-H⋯O hydrogen bonds between the translation-symmetry and inversion-symmetry equivalents to form tetrads, which are further assembled by stacking inter-actions [centroid-centroid distance between the benzene rings = 3.769 (2) Å]. van der Waals contacts are found between the Cl atoms at the 6-position and the Cl atoms at 7-position of the glide-reflection-symmetry equivalents [Cl⋯Cl = 3.4785 (16) Å, C-Cl⋯Cl = 160.23 (7)° and Cl⋯Cl-C = 122.59 (7)°].

  18. Influence of oxidation temperature on the interfacial properties of n-type 4H-SiC MOS capacitors

    NASA Astrophysics Data System (ADS)

    Jia, Yifan; Lv, Hongliang; Song, Qingwen; Tang, Xiaoyan; Xiao, Li; Wang, Liangyong; Tang, Guangming; Zhang, Yimen; Zhang, Yuming

    2017-03-01

    The effect of oxidation temperature on interfacial properties of n-type 4H-SiC metal-oxide-semiconductor capacitors has been systematically investigated. Thermal dry oxidation process with three different oxidation temperatures 1200 °C, 1300 °C and 1350 °C were employed to grow SiO2 dielectric, following by the standard post-oxidation annealing (POA) in NO ambience at 1175 °C for 2 h. The root mean square (RMS) roughness measured by Atomic Force Microscopy for the thermally grown SiO2 before POA process is reduced with increasing the oxidation temperature, obtaining an atomically flat surface with a RMS of 0.157 nm from the sample oxidized at 1350 °C. Several kinds of electrical measurements were used to evaluate the densities of near interface traps and effective fixed dielectric charge for the samples, exhibiting a trend reduced with increasing the oxidation temperature. The interface state density of 3 × 1011 cm-2eV-1 at 0.2 eV from the conduction band edge was achieved from conductance method measurement for the sample oxidized at 1350 °C. The results from Secondary Ion Mass Spectroscopy and X-ray Photoelectron Spectroscopy demonstrate that high oxidation temperature can reduce the width of transition layer, the excess Si and silicon suboxide compositions near the interface, leading to effective improvement of the interfacial properties.

  19. High-pressure Raman spectroscopic studies of hydrogarnet, katoite Ca3Al2(O4H4)3

    NASA Astrophysics Data System (ADS)

    Kato, M.; Kyono, A.

    2014-12-01

    We report in situ Raman spectroscopic studies of katoite in a diamond-anvil cell under hydrostatic conditions up to 10 GPa at room temperature. Two bands near 331 and 539 cm-1 are observed clearly at 1.1 GPa. In the cubic garnet structure, the lower frequency peak can be assigned to a mode of A1g + F2g symmetry and the higher frequency peak can be assigned to a mode with A1g + Eg + F2g symmetry. The band at 331 cm-1 in the A1g + F2g mode is assigned to O4H4-translational and librational motion and the band at 539 cm-1 in the A1g + Eg + F2g mode is assigned to OH-translational motion. The peak positions and shapes in the Raman spectra agree well with those measured under ambient conditions. With increasing pressure, the frequency of the F2g mode increases continuously with pressure derivative of 10 cm-1/GPa. Upon increasing pressure, the A1g + Eg + F2g modes split at 5 GPa and the intensity of the this Raman band gradually decrease due to the cubic-tetragonal phase transition. The most striking characteristic of the Raman spectrum of katoite is that compression leads to the extinction of the Raman-active mode derived from A1g + Eg + F2g symmetry.

  20. 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.