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Sample records for university atlanta ga

  1. Joseph Jacobs: Apprentice to Crawford W. Long in Athens, GA; Pharmacist and Retailer of Soda Fountain Beverages in Atlanta, GA.

    Science.gov (United States)

    Haridas, Rajesh P

    2018-01-01

    In the 1870s, Joseph Jacobs was employed as an apprentice in the Longs and Billups pharmacy in Athens, GA. Jacobs later established a chain of pharmacies in Atlanta, GA. Coca-Cola was first sold to the public on May 8, 1886, at Jacobs' Pharmacy in the Five Points district of Atlanta, GA. The soda fountain in Jacobs' Pharmacy was owned by Willis E. Venable, who was related to James M. Venable, the first patient etherized by Crawford Long in Jefferson, GA. Copyright © 2018 Elsevier Inc. All rights reserved.

  2. Characterization of CCN and IN activity of bacterial isolates collected in Atlanta, GA

    Science.gov (United States)

    Purdue, Sara; Waters, Samantha; Karthikeyan, Smruthi; Konstantinidis, Kostas; Nenes, Athanasios

    2016-04-01

    Characterization of CCN activity of bacteria, other than a few select types such as Pseudomonas syringae, is limited, especially when looked at in conjunction with corresponding IN activity. The link between these two points is especially important for bacteria as those that have high CCN activity are likely to form an aqueous phase required for immersion freezing. Given the high ice nucleation temperature of bacterial cells, especially in immersion mode, it is important to characterize the CCN and IN activity of many different bacterial strains. To this effect, we developed a droplet freezing assay (DFA) which consists of an aluminum cold plate, cooled by a continuous flow of an ethylene glycol-water mixture, in order to observe immersion freezing of the collected bacteria. Here, we present the initial results on the CCN and IN activities of bacterial samples we have collected in Atlanta, GA. Bacterial strains were collected and isolated from rainwater samples taken from different storms throughout the year. We then characterized the CCN activity of each strain using a DMT Continuous Flow Streamwise Thermal Gradient CCN Counter by exposing the aerosolized bacteria to supersaturations ranging from 0.05% to 0.6%. Additionally, using our new DFA, we characterized the IN activity of each bacterial strain at temperatures ranging from -20oC to 0oC. The combined CCN and IN activity gives us valuable information on how some uncharacterized bacteria contribute to warm and mixed-phase cloud formation in the atmosphere.

  3. 78 FR 76810 - Information Collection; Environmental Justice and the Urban Forest in Atlanta, GA

    Science.gov (United States)

    2013-12-19

    ... should be addressed to Cassandra Johnson Gaither, Forestry Sciences Lab, 320 Green St., Athens, GA 30602... public may inspect comments received at Forestry Sciences Lab, 320 Green St., Athens, GA 30602 during... Type of Request: New Abstract: This information collection records data on the attitude and engagement...

  4. Custodial Homes, Therapeutic Homes, and Parental Acceptance: Parental Experiences of Autism in Kerala, India and Atlanta, GA USA.

    Science.gov (United States)

    Sarrett, Jennifer C

    2015-06-01

    The home is a critical place to learn about cultural values of childhood disability, including autism and intellectual disabilities. The current article describes how the introduction of autism into a home and the availability of intervention options change the structure and meaning of a home and reflect parental acceptance of a child's autistic traits. Using ethnographic data from Kerala, India and Atlanta, GA USA, a description of two types of homes are developed: the custodial home, which is primarily focused on caring for basic needs, and the therapeutic home, which is focused on changing a child's autistic traits. The type of home environment is respondent to cultural practices of child rearing in the home and influences daily activities, management, and care in the home. Further, these homes differ in parental acceptance of their autistic children's disabilities, which is critical to understand when engaging in international work related to autism and intellectual disability. It is proposed that parental acceptance can be fostered through the use of neurodiverse notions that encourage autism acceptance.

  5. Advancing Residential Retrofits in Atlanta

    Energy Technology Data Exchange (ETDEWEB)

    Jackson, Roderick K [ORNL; Kim, Eyu-Jin [Southface Energy Institute; Roberts, Sydney [Southface Energy Institute; Stephenson, Robert [Southface Energy Institute

    2012-07-01

    This report will summarize the home energy improvements performed in the Atlanta, GA area. In total, nine homes were retrofitted with eight of the homes having predicted source energy savings of approximately 30% or greater based on simulated energy consumption.

  6. Disparities in herpes simplex virus type 2 infection between black and white men who have sex with men in Atlanta, GA.

    Science.gov (United States)

    Okafor, Netochukwu; Rosenberg, Eli S; Luisi, Nicole; Sanchez, Travis; del Rio, Carlos; Sullivan, Patrick S; Kelley, Colleen F

    2015-09-01

    HIV disproportionately affects black men who have sex with men, and herpes simplex virus type 2 is known to increase acquisition of HIV. However, data on racial disparities in herpes simplex virus type 2 prevalence and risk factors are limited among men who have sex with men in the United States. InvolveMENt was a cohort study of black and white HIV-negative men who have sex with men in Atlanta, GA. Univariate and multivariate cross-sectional associations with herpes simplex virus type 2 seroprevalence were assessed among 455 HIV-negative men who have sex with men for demographic, behavioural and social determinant risk factors using logistic regression. Seroprevalence of herpes simplex virus type 2 was 23% (48/211) for black and 16% (38/244) for white men who have sex with men (p = 0.05). Education, poverty, drug/alcohol use, incarceration, circumcision, unprotected anal intercourse, and condom use were not associated with herpes simplex virus type 2. In multivariate analyses, black race for those ≤25 years, but not >25 years, and number of sexual partners were significantly associated. Young black men who have sex with men are disproportionately affected by herpes simplex virus type 2, which may contribute to disparities in HIV acquisition. An extensive assessment of risk factors did not explain this disparity in herpes simplex virus type 2 infection suggesting differences in susceptibility or partner characteristics. © The Author(s) 2014.

  7. HIV sexual transmission risks in the context of clinical care: a prospective study of behavioural correlates of HIV suppression in a community sample, Atlanta, GA, USA.

    Science.gov (United States)

    Kalichman, Seth C; Cherry, Chauncey; Kalichman, Moira O; Washington, Christopher; Grebler, Tamar; Merely, Cindy; Welles, Brandi; Pellowski, Jennifer; Kegler, Christopher

    2015-01-01

    Antiretroviral therapy (ART) improves the health of people living with HIV and has the potential to reduce HIV infectiousness, thereby preventing HIV transmission. However, the success of ART for HIV prevention hinges on sustained ART adherence and avoiding sexually transmitted infections (STI). To determine the sexual behaviours and HIV transmission risks of individuals with suppressed and unsuppressed HIV replication (i.e., viral load). Assessed HIV sexual transmission risks among individuals with clinically determined suppressed and unsuppressed HIV. Participants were 760 men and 280 women living with HIV in Atlanta, GA, USA, who completed behavioural assessments, 28-daily prospective sexual behaviour diaries, one-month prospective unannounced pill counts for ART adherence, urine screening for illicit drug use and medical record chart abstraction for HIV viral load. Individuals with unsuppressed HIV demonstrated a constellation of behavioural risks for transmitting HIV to uninfected sex partners that included symptoms of STI and substance use. In addition, 15% of participants with suppressed HIV had recent STI symptoms/diagnoses, indicating significant risks for sexual infectiousness despite their HIV suppression in blood plasma. Overall, 38% of participants were at risk for elevated sexual infectiousness and just as many engaged in unprotected sexual intercourse with non-HIV-infected partners. Implementation strategies for using HIV treatments as HIV prevention requires enhanced behavioural interventions that extend beyond ART to address substance use and sexual health that will otherwise undermine the potential preventive impact of early ART.

  8. Modeling the Effect of Onsite Wastewater Treatment Systems on Nitrate Load Using SWAT in an Urban Watershed of Metropolitan Atlanta, GA

    Science.gov (United States)

    Onsite Wastewater Treatment Systems (OWTSs) can be a source of nitrate (NO3-) contamination in both surface and ground waters as a result of failing or high density systems. In metropolitan Atlanta, more than 26% of homes are on OWTS and this percentage is expected to increase wi...

  9. Why, Where, and How to Infuse the Atlanta Sociological Laboratory into the Sociology Curriculum

    Science.gov (United States)

    Wright, Earl, II

    2012-01-01

    The Atlanta Sociological Laboratory is the moniker bestowed on scholars engaged in sociological research at Atlanta University between 1895 and 1924. Under the leadership of W. E. B. Du Bois, 1897-1914, this school made substantive yet marginalized contributions to the discipline. Its accomplishments include, but are not limited to, its…

  10. Selected papers from the 12th International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2012) (Atlanta, GA, USA, 2-5 December 2012)

    Science.gov (United States)

    Allen, Mark G.; Lang, Jeffrey

    2013-11-01

    Welcome to this special section of the Journal of Micromechanics and Microengineering (JMM). This section, co-edited by myself and by Professor Jeffrey Lang of the Massachusetts Institute of Technology, contains expanded versions of selected papers presented at the Power MEMS meeting held in Atlanta, GA, USA, in December of 2012. Professor Lang and I had the privilege of co-chairing Power MEMS 2012, the 12th International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications. The scope of the PowerMEMS series of workshops ranges from basic principles, to materials and fabrication, to devices and systems, to applications. The many applications of power MEMS (microelectromehcanical systems) range from MEMS-enabled energy harvesting, storage, conversion and conditioning, to integrated systems that manage these processes. Why is the power MEMS field growing in importance? Smaller-scale power and power supplies (microwatts to tens of watts) are gaining in prominence due to many factors, including the ubiquity of low power portable electronic equipment and the proliferation of wireless sensor nodes that require extraction of energy from their embedding environment in order to function. MEMS manufacturing methods can be utilized to improve the performance of traditional power supply elements, such as allowing batteries to charge faster or shrinking the physical size of passive elements in small-scale power supplies. MEMS technologies can be used to fabricate energy harvesters that extract energy from an embedding environment to power wireless sensor nodes, in-body medical implants and other devices, in which the harvesters are on the small scales that are appropriately matched to the overall size of these microsystems. MEMS can enable the manufacturing of energy storage elements from nontraditional materials by bringing appropriate structure and surface morphology to these materials as well as fabricating the electrical interfaces

  11. Risk Factors for HIV Transmission and Barriers to HIV Disclosure: Metropolitan Atlanta Youth Perspectives

    OpenAIRE

    Camacho-Gonzalez, Andres F.; Wallins, Amy; Toledo, Lauren; Murray, Ashley; Gaul, Zaneta; Sutton, Madeline Y.; Gillespie, Scott; Leong, Traci; Graves, Chanda; Chakraborty, Rana

    2016-01-01

    Youth carry the highest incidence of HIV infection in the United States. Understanding adolescent and young adult (AYA) perspectives on HIV transmission risk is important for targeted HIV prevention. We conducted a mixed methods study with HIV-infected and uninfected youth, ages 18–24 years, from Atlanta, GA. We provided self-administered surveys to HIV-infected and HIV-uninfected AYAs to identify risk factors for HIV acquisition. By means of computer-assisted thematic analyses, we examined t...

  12. Health and Environment Linked for Information Exchange in Atlanta (HELIX-Atlanta): A Pilot Tracking System

    Science.gov (United States)

    Rickman, Doug; Shire, J.; Qualters, J.; Mitchell, K.; Pollard, S.; Rao, R.; Kajumba, N.; Quattrochi, D.; Estes, M., Jr.; Meyer, P.; hide

    2009-01-01

    Objectives. To provide an overview of four environmental public health surveillance projects developed by CDC and its partners for the Health and Environment Linked for Information Exchange, Atlanta (HELIX-Atlanta) and to illustrate common issues and challenges encountered in developing an environmental public health tracking system. Methods. HELIX-Atlanta, initiated in October 2003 to develop data linkage and analysis methods that can be used by the National Environmental Public Health Tracking Network (Tracking Network), conducted four projects. We highlight the projects' work, assess attainment of the HELIX-Atlanta goals and discuss three surveillance attributes. Results. Among the major challenges was the complexity of analytic issues which required multidiscipline teams with technical expertise. This expertise and the data resided across multiple organizations. Conclusions:Establishing formal procedures for sharing data, defining data analysis standards and automating analyses, and committing staff with appropriate expertise is needed to support wide implementation of environmental public health tracking.

  13. 78 FR 1742 - Amendment to Class B Airspace; Atlanta, GA

    Science.gov (United States)

    2013-01-09

    ...: Effective Date: 0901 UTC, March 7, 2013. The Director of the Federal Register approves this incorporation by..., resulting in wasted fuel and increased operating costs as well as causing PDK IFR arrivals to circle over... maneuvering room would be available for avoiding obstructions, clouds and turbulence, and for training...

  14. Complejo Omni - Atlanta – (EE. UU.

    Directory of Open Access Journals (Sweden)

    Housworth, Marvin

    1976-12-01

    Full Text Available This complex of buildings, situated in the centre of Atlanta City, forms a dynamic nucleus for various social activities, such as recreational, commercial and business activities. These buildings are constructed above railway nets, due to special property rights for this lot, which constituted one of the main determinants for the characteristics of the property. The unit is made up by a luxurious hotel, two restaurants, office buildings and shopping arcades, arranged around a spacious inner yard. This patio is covered by means of an exceedingly big glass roof, supported by beams and steel framework and is provided with walls of big glazed surfaces. Thus, an intimate and friendly atmosphere is created, free from the contamination and noise of the big city whereby the square displays the typical characteristics of open squares in smaller towns.Este conjunto de edificios, emplazado en el centro de la ciudad de Atlanta, conforma un núcleo dinámico en donde se encuentran diversas actividades de tipo social: recreativas, comerciales y empresariales. Se ha construido sobre ruedas ferroviarias, en virtud de derechos especiales de propiedad que conservaba la parcela, lo que constituyó uno de los principales condicionamientos de fas características del proyecto. El complejo dispone de un hotel de lujo, dos restaurantes, edificios de oficinas y galerías comerciales, dispuestos en torno a un amplio espacio interior, cerrado por una enorme cubierta acristalada, apoyada en vigas y entramados metálicos, y por grandes ventanales corridos entre bloques. Conforma así un ambiente íntimo y acogedor, liberado del ruido y de la atmósfera turbulenta de la gran ciudad, con características propias de las pequeñas plazas populares.

  15. 1996 Atlanta Centennial Olympic Games and Paralympic Games, event study

    Science.gov (United States)

    1997-01-01

    The Atlanta metropolitan region was the location of one of the most ambitious Intelligent Transportation : Systems (ITS) deployments in the United States. This deployment included several individual projects-a : Central Transportation Management Cent...

  16. Cryptosporidium and Giardia in Swimming Pools, Atlanta, Georgia

    Centers for Disease Control (CDC) Podcasts

    In this podcast, Dan Rutz speaks with Dr. Joan Shields, a guest researcher with the Healthy Swimming Program at CDC, about an article in June 2008 issue of Emerging Infectious Diseases reporting on the results of a test of swimming pools in the greater Atlanta, Georgia area. Dr. Shields tested 160 pools in metro Atlanta last year for Cryptosporidium and Giardia. These germs cause most recreational water associated outbreaks.

  17. Plaza Central Peachtree Atlanta-(EE.UU.

    Directory of Open Access Journals (Sweden)

    Portman, John

    1976-10-01

    Full Text Available This 70-storey hotel has been constructed to meet the requirements of the city of Atlanta which needed a building with a sufficient room capacity and adequate premises for Conventions. On a structure of reinforced concrete which serves as a base and in which the common areas are situated rises a big cylindric tower, covered with coloured glass and which contains the 1.100 rooms. 230 m above ground level, the construction is crowned with a roof top cocktail lounge and a revolving restaurant with a splendid view of the city. Among the most noteworthy characteristics of this hotel is the elegantly decorated entrance hall —atrium shaped and 7 storeys high— with a pond in the centre. Further premises worth mentioning in view of their design and dimensions are the great ball room, coffee-shops and luxurious restaurants, one of which is planned in different levels and in which the most impressive feature is a 30 m high waterfall.Este edificio de setenta plantas se construyó para responder a las necesidades hoteleras de la ciudad de Atlanta, que precisaba de una instalación con suficiente capacidad de habitaciones y preparación para albergar Convenciones. Sobre una estructura de hormigón armado, que sirve de base y en la que se sitúan las zonas comunes, se eleva una gran torre cilíndrica, recubierta de vidrio coloreado reflectante, destinada a distribuir las 1.100 habitaciones con las que cuenta el edificio. La construcción se corona, a 230 m de la cimentación, con una sala para cócteles y un restaurante giratorio desde el que se domina una espléndida vista del contorno. El edificio dispone de importantes servicios comunes, entre los que cabe destacar el hall de entrada —a modo de atrio y con una altura equivalente a siete plantas—, que está dotado de un gran estanque y variados elementos de gran efecto decorativo. Otros servicios notables por su diseño y dimensiones son la gran sala de baile, y las cafeterías, comedores y

  18. Evaluation of a Pilot Surveillance System: Health and Environment Linked for Information Exchange in Atlanta (HELIX-Atlanta)

    Science.gov (United States)

    Meyer, P.; Shire, J.; Qualters, Judy; Daley, Randolph; Fiero, Leslie Todorov; Autry, Andy; Avchen, Rachel; Stock, Allison; Correa, Adolofo; Siffel, Csaba; hide

    2007-01-01

    CDC and its partners established the Health and Environment Linked for Information Exchange, Atlanta (HELIX-Atlanta) demonstration project, to develop linking and analysis methods that could be used by the National Environmental Public Health Tracking (EPHT) Network. Initiated in October 2003, the Metropolitan Atlanta-based collaborative conducted four projects: asthma and particulate air pollution, birth defects and ozone and particulate air pollution, childhood leukemia and traffic emissions, and children's blood lead testing and neighborhood risk factors for lead poisoning. This report provides an overview of the HELIX-Atlanta projects' goals, methods and outcomes. We discuss priority attributes and common issues and challenges and offer recommendations for implementation of the nascent national environmental public health tracking network.

  19. Increasing Walking in the Hartsfield-Jackson Atlanta International Airport: The Walk to Fly Study.

    Science.gov (United States)

    Fulton, Janet E; Frederick, Ginny M; Paul, Prabasaj; Omura, John D; Carlson, Susan A; Dorn, Joan M

    2017-07-01

    To test the effectiveness of a point-of-decision intervention to prompt walking, versus motorized transport, in a large metropolitan airport. We installed point-of-decision prompt signage at 4 locations in the airport transportation mall at Hartsfield-Jackson Atlanta International Airport (Atlanta, GA) at the connecting corridor between airport concourses. Six ceiling-mounted infrared sensors counted travelers entering and exiting the study location. We collected traveler counts from June 2013 to May 2016 when construction was present and absent (preintervention period: June 2013-September 2014; postintervention period: September 2014-May 2016). We used a model that incorporated weekly walking variation to estimate the intervention effect on walking. There was an 11.0% to 16.7% relative increase in walking in the absence of airport construction where 580 to 810 more travelers per day chose to walk. Through May 2016, travelers completed 390 000 additional walking trips. The Walk to Fly study demonstrated a significant and sustained increase in the number of airport travelers choosing to walk. Providing signage about options to walk in busy locations where reasonable walking options are available may improve population levels of physical activity and therefore improve public health.

  20. Atlanta NAVIGATOR case study. Final report, May 1996--Jun 1997

    Energy Technology Data Exchange (ETDEWEB)

    Amodei, R.; Bard, E.; Brong, B.; Cahoon, F.; Jasper, K.

    1998-11-01

    The Atlanta metropolitan region was the location of one of the most ambitious Intelligent Transportation Systems (ITS) deployments in the United States. This deployment included several individual projects--a Central Transportation Management Center (TMC), six Traffic Control Centers (TCC), one Transit Information Center (TIC), the Travel Information Showcase (TIS), and the extension of the Metropolitan Atlanta Rapid Transit Authority (MARTA) rail network and the new high-occupancy vehicle (HOV) lanes on I-85 and I-75. The Atlanta Centennial Olympic Games and Paralympic Games created a focus for these projects. All of these systems were to be brought on line in time for the Olympic Games. This report presents the findings of the NAVIGATOR Case Study and documents the lessons learned from the Atlanta ITS deployment experience in order to improve other ITS deployments in the future. The Case Study focuses on the institutional, programmatic, and technical issues and opportunities from planning and implementing the ITS deployment in Atlanta. The Case Study collected data and information from interviews, observations, focus groups, and documentation reviews. It presents a series of lessons learned and recommendations for enabling successful ITS deployments nationwide.

  1. Cryptosporidium and Giardia in Swimming Pools, Atlanta, Georgia

    Centers for Disease Control (CDC) Podcasts

    2008-05-29

    In this podcast, Dan Rutz speaks with Dr. Joan Shields, a guest researcher with the Healthy Swimming Program at CDC, about an article in June 2008 issue of Emerging Infectious Diseases reporting on the results of a test of swimming pools in the greater Atlanta, Georgia area. Dr. Shields tested 160 pools in metro Atlanta last year for Cryptosporidium and Giardia. These germs cause most recreational water associated outbreaks.  Created: 5/29/2008 by Emerging Infectious Diseases.   Date Released: 5/29/2008.

  2. The Atlanta Urban Debate League: Exploring the Making of a Critical Literacy Space

    Science.gov (United States)

    Cridland-Hughes, Susan

    2016-01-01

    The Atlanta Urban Debate League was established in 1985 as an after school program focused on providing debate outreach to high school students in the Atlanta public schools. Still in operation today, volunteers work with current students in public middle and high schools in Atlanta, supporting students as they practice reading, writing, speaking…

  3. Political Socialization in an International City: The Case of Atlanta.

    Science.gov (United States)

    Masters, Paul E., Jr.

    1984-01-01

    Original survey data dealing with the attitudes about international relations of secondary students in the metropolitan Atlanta, Georgia, area are analyzed. Student opinions were measured in three areas: (1) international interest, knowledge, and information sources; (2) international conflict and the balance of power; and (3) international…

  4. Environmental Public Health Tracking: Health and Environment Linked for Information Exchange-Atlanta (HEXIX-Atlanta: A cooperative Program Between CDC and NASA for Development of an Environmental Public Health Tracking Network in the Atlanta Metropolitan Area

    Science.gov (United States)

    Quattrochi, Dale A.; Niskar, Amanda Sue

    2005-01-01

    The Centers for Disease Control and Prevention (CDC) is coordinating HELIX- Atlanta to provide information regarding the five-county Metropolitan Atlanta Area (Clayton, Cobb, DeKalb, Fulton, and Gwinett) via a network of integrated environmental monitoring and public health data systems so that all sectors can take action to prevent and control environmentally related health effects. The HELIX-Atlanta Network is a tool to access interoperable information systems with optional information technology linkage functionality driven by scientific rationale. HELIX-Atlanta is a collaborative effort with local, state, federal, and academic partners, including the NASA Marshall Space Flight Center. The HELIX-Atlanta Partners identified the following HELIX-Atlanta initial focus areas: childhood lead poisoning, short-latency cancers, developmental disabilities, birth defects, vital records, respiratory health, age of housing, remote sensing data, and environmental monitoring, HELIX-Atlanta Partners identified and evaluated information systems containing information on the above focus areas. The information system evaluations resulted in recommendations for what resources would be needed to interoperate selected information systems in compliance with the CDC Public Health Information Network (PHIN). This presentation will discuss the collaborative process of building a network that links health and environment data for information exchange, including NASA remote sensing data, for use in HELIX-Atlanta.

  5. Project ATLANTA (ATlanta Land-use ANalysis: Temperature and Air quality): A Study of how the Urban Landscape Affects Meteorology and Air Quality Through Time

    Science.gov (United States)

    Quattrochi, Dale A.; Luvall, Jeffrey C.; Estes, Maurice G.; Lo, C. P.; Kidder, Stanley Q.; Hafner, Jan; Taha, Haider; Bornstein, Robert D.; Gillies, Robert R.; Gallo, Kevin P.

    1998-01-01

    It is our intent through this investigation to help facilitate measures that can be Project ATLANTA (ATlanta Land-use ANalysis: applied to mitigate climatological or air quality Temperature and Air-quality) is a NASA Earth degradation, or to design alternate measures to sustain Observing System (EOS) Interdisciplinary Science or improve the overall urban environment in the future. investigation that seeks to observe, measure, model, and analyze how the rapid growth of the Atlanta. The primary objectives for this research effort are: 1) To In the last half of the 20th century, Atlanta, investigate and model the relationship between Atlanta Georgia has risen as the premier commercial, urban growth, land cover change, and the development industrial, and transportation urban area of the of the urban heat island phenomenon through time at southeastern United States. The rapid growth of the nested spatial scales from local to regional; 2) To Atlanta area, particularly within the last 25 years, has investigate and model the relationship between Atlanta made Atlanta one of the fastest growing metropolitan urban growth and land cover change on air quality areas in the United States. The population of the through time at nested spatial scales from local to Atlanta metropolitan area increased 27% between 1970 regional; and 3) To model the overall effects of urban and 1980, and 33% between 1980-1990 (Research development on surface energy budget characteristics Atlanta, Inc., 1993). Concomitant with this high rate of across the Atlanta urban landscape through time at population growth, has been an explosive growth in nested spatial scales from local to regional. Our key retail, industrial, commercial, and transportation goal is to derive a better scientific understanding of how services within the Atlanta region. This has resulted in land cover changes associated with urbanization in the tremendous land cover change dynamics within the Atlanta area, principally in transforming

  6. NEOPLASIA IN SNAKES AT ZOO ATLANTA DURING 1992-2012.

    Science.gov (United States)

    Page-Karjian, Annie; Hahne, Megan; Leach, Kate; Murphy, Hayley; Lock, Brad; Rivera, Samuel

    2017-06-01

    A retrospective study was conducted to review neoplasia of captive snakes in the Zoo Atlanta collection from 1992 to 2012. Of 255 snakes that underwent necropsy and histopathologic examination at Zoo Atlanta during the study period, 37 were observed with neoplasia at necropsy. In those 37 snakes, 42 neoplastic lesions of 18 primary cell types were diagnosed. Thirty-five of those neoplasms (83.3%) were malignant, and of those, 19 were of mesenchymal origin, whereas 14 were of epithelial origin. The median annual rate of neoplasia at necropsy was 12.5% (interquartile range = 2.8-19.5%) over the 21-yr study period. The mean estimated age at death for snakes with neoplasia was 13.2 yr (range, 1-24 yr). Investigating the incidence and clinical significance of neoplasia in captive snakes is vital for developing effective preventative and treatment regimes.

  7. The WaterHub at Emory University: Campus Resiliency through Decentralized Reuse.

    Science.gov (United States)

    Allison, Daniel; Lohan, Eric; Baldwin, Tim

    2018-02-01

      In the spring of 2015, Emory University in Atlanta, GA, commissioned an innovative campuswide water reclamation and reuse system known as the WaterHub®. Treating up to 400,000 gallons each day, the system can recycle the equivalent of two-thirds of the University's wastewater production and reduce the campus water footprint by up to 40 percent.One of the first district-scale water reuse systems in North America, the WaterHub mines wastewater from the campus sewer system and repurposes it for beneficial reuse on campus. In its first year of operation, the facility has treated more than 80 million gallons of campus wastewater and is expected to save millions of dollars in utility costs for the University over the next 20 years. The system represents a new age in commercial-scale water management in which onsite, urban water reclamation facilities may be a new norm.

  8. Environmental Public Health Surveillance for Exposure to Respiratory Health Hazards: A Joint NASA/CDC Project to Use Remote Sensing Data for Estimating Airborne Particulate Matter Over the Atlanta, Georgia Metropolitan Area

    Science.gov (United States)

    Quattrochi, Dale A.; Al-Hamdan, Mohammad; Estes, Maurice; Crosson, William

    2007-01-01

    As part of the National Environmental Public Health Tracking Network (EPHTN) the National Center for Environmental Health (NCEH) at the Centers for Disease Control and Prevention (CDC) is leading a project called Health and Environment Linked for Information Exchange (HELiX-Atlanta). The goal of developing the National Environmental Public Health Tracking Network is to improve the health of communities. Currently, few systems exist at the state or national level to concurrently track many of the exposures and health effects that might be associated with environmental hazards. An additional challenge is estimating exposure to environmental hazards such as particulate matter whose aerodynamic diameter is less than or equal to 2.5 micrometers (PM2.5). HELIX-Atlanta's goal is to examine the feasibility of building an integrated electronic health and environmental data network in five counties of Metropolitan Atlanta, GA. NASA Marshall Space Flight Center (NASA/MSFC) is collaborating with CDC to combine NASA earth science satellite observations related to air quality and environmental monitoring data to model surface estimates of PM2.5 concentrations that can be linked with clinic visits for asthma. While use of the Air Quality System (AQS) PM2.5 data alone could meet HELIX-Atlanta specifications, there are only five AQS sites in the Atlanta area, thus the spatial coverage is not ideal. We are using NASA Moderate Resolution Imaging Spectroradiometer (MODIS) satellite Aerosol Optical Depth (AOD) data for estimating daily ground level PM2.5 at 10 km resolution over the metropolitan Atlanta area supplementing the AQS ground observations and filling their spatial and temporal gaps.

  9. Acute pancreatitis: reflections through the history of the Atlanta Consensus

    OpenAIRE

    Torres López, Ana María; Hoyos Duque, Sergio Iván

    2014-01-01

    Acute pancreatitis is an inflammatory process with systemic and local repercussions. Most cases are mild with low mortality rate, but 20% of the patients have severe pancreatitis with a mortality rate up to 30%. Through the years the medical community has tried to reach consensus about this disease in order to better understand, classify and treat it. The most important of these has been known as the Atlanta Consensus 1992, in use for many years. However, it has been recently the subject of v...

  10. Acute pancreatitis: reflections through the history of the Atlanta Consensus

    Directory of Open Access Journals (Sweden)

    Torres López, Ana María

    2014-10-01

    Full Text Available Acute pancreatitis is an inflammatory process with systemic and local repercussions. Most cases are mild with low mortality rate, but 20% of the patients have severe pancreatitis with a mortality rate up to 30%. Through the years the medical community has tried to reach consensus about this disease in order to better understand, classify and treat it. The most important of these has been known as the Atlanta Consensus 1992, in use for many years. However, it has been recently the subject of various proposals for changes and updates, which are discussed in this review article.

  11. Universal behaviour of magnetoconductance due to week localization in two-dimensional systems - example of GaInAs quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Zduniak, A.; Dyakonov, M.I.; Litwin-Staszewska, E.; Knap, W. [Groupe d`Etudes des Semiconducteurs, Universite de Montpellier II, Montpellier (France)

    1995-12-31

    Week localization corrections to conductivity of two-dimensional electron gas are studied by measurements of magnetic field dependence of the conductivity in GaInAs quantum wells. We observed that, when presented as a function of the normalized magnetic field (x=B/B{sub tr} where B is the magnetic field, B{sub tr}=h/4e{tau}D, D is the diffusion constant and {tau} is momentum relaxation time), different samples show very similar high field behaviour. A theoretical description is developed that allows one to describe in a consistent way and low field behaviour. The theory predicts universal (B{sup -1/2}) behaviour of the conductivity correction for all 2D systems in high field limit (x>1). Low field behaviour depends strongly on spin and phase relaxation mechanisms. Comparison of the theory with experiment confirms the universal behaviour in the high field limit and allows one to estimate the spin and phase relaxation times for different GaInAs quantum wells. (author). 5 refs, 2 figs.

  12. Universal behaviour of magnetoconductance due to week localization in two-dimensional systems - example of GaInAs quantum wells

    International Nuclear Information System (INIS)

    Zduniak, A.; Dyakonov, M.I.; Litwin-Staszewska, E.; Knap, W.

    1995-01-01

    Week localization corrections to conductivity of two-dimensional electron gas are studied by measurements of magnetic field dependence of the conductivity in GaInAs quantum wells. We observed that, when presented as a function of the normalized magnetic field (x=B/B tr where B is the magnetic field, B tr =h/4eτD, D is the diffusion constant and τ is momentum relaxation time), different samples show very similar high field behaviour. A theoretical description is developed that allows one to describe in a consistent way and low field behaviour. The theory predicts universal (B -1/2 ) behaviour of the conductivity correction for all 2D systems in high field limit (x>1). Low field behaviour depends strongly on spin and phase relaxation mechanisms. Comparison of the theory with experiment confirms the universal behaviour in the high field limit and allows one to estimate the spin and phase relaxation times for different GaInAs quantum wells. (author)

  13. 40 CFR 81.45 - Metropolitan Atlanta Intrastate Air Quality Control Region.

    Science.gov (United States)

    2010-07-01

    ... Quality Control Region. 81.45 Section 81.45 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY... Air Quality Control Regions § 81.45 Metropolitan Atlanta Intrastate Air Quality Control Region. The Metropolitan Atlanta Intrastate Air Quality Control Region (Georgia) has been revised to consist of the...

  14. Atlanta Rail Yard Study: Evaluation of local-scale air pollution ...

    Science.gov (United States)

    Intermodal rail yards are important nodes in the freight transportation network, where freight is organized and moved from one mode of transport to another, critical equipment is serviced, and freight is routed to its next destination. Rail yard environments are also areas with multiple sources of air pollutant emissions (e.g., heavy-duty vehicles, locomotives, cranes), which may affect local air quality in residential areas nearby. In order to understand emissions and related air quality impacts, two field studies took place over the time span of 2010-2012 to measure air pollution trends in close proximity to the Inman and Tilford rail yard complex in Atlanta, GA. One field study involved long-term stationary monitoring of black carbon, fine particles, and carbon dioxide at two stations nearby the rail yard. In addition, a second field study performed intensive mobile air monitoring for a one month period in the summer of 2012 at a roadway network surrounding the rail yard complex and measured a comprehensive array of pollutants. Real-time mobile particulate measurements included particle counts, extinction coefficient, black carbon via light-absorption and particle incandescence, and particle composition derived by aerosol mass spectrometry. Gas-phase measurements included oxides of nitrogen, sulfur dioxide, carbon dioxide, and air toxics (e.g., benzene). Both sets of measurements determined detectable local influence from rail yard-related emissions.

  15. Flight delay performance at Hartsfield-Jackson Atlanta International Airport

    Directory of Open Access Journals (Sweden)

    Grigoriy Yablonsky

    2014-01-01

    Full Text Available Purpose: The main objective of this paper is to determine the annual cyclical flight delays at Hartsfield-Jackson Atlanta International Airport. Then using other data such as annual precipitation, passenger and aircraft traffic volumes and other factors, we attempted to correlate these factors with overall delays. These data could assist airport management in predicting periods of flight delay.Design/methodology/approach: Data were taken and analyzed from the data base “Research and Innovation Technology Administration” (RITA for the years 2005-2011 for Hartsfield-Jackson Atlanta International Airport. The data included 2.8 million flights originating and departing from this airport. Data were also gathered from the National Oceanic and Atmospheric Administration (NOAA showing precipitation. Additional data were gathered from the FAA regarding delay causes, number and types of delays and changes to the infrastructure of ATL airportFindings: There is a repeatable annual pattern of delays at ATL that can be modeled using delay data from the Bureau of Transportation Statistics. This pattern appears to be caused primarily by the frequency and amount of precipitation that falls at ATL and by the amount of flights that arrive and depart at ATL.Originality/value: This information could assist airport operations personnel, FAA air traffic controllers and airlines in anticipating and mitigating delays at specific times of the year.

  16. GLOBECOM '84 - Global Telecommunications Conference, Atlanta, GA, November 26-29, 1984, Conference Record. Volume 1

    Science.gov (United States)

    The subjects discussed are related to LSI/VLSI based subscriber transmission and customer access for the Integrated Services Digital Network (ISDN), special applications of fiber optics, ISDN and competitive telecommunication services, technical preparations for the Geostationary-Satellite Orbit Conference, high-capacity statistical switching fabrics, networking and distributed systems software, adaptive arrays and cancelers, synchronization and tracking, speech processing, advances in communication terminals, full-color videotex, and a performance analysis of protocols. Advances in data communications are considered along with transmission network plans and progress, direct broadcast satellite systems, packet radio system aspects, radio-new and developing technologies and applications, the management of software quality, and Open Systems Interconnection (OSI) aspects of telematic services. Attention is given to personal computers and OSI, the role of software reliability measurement in information systems, and an active array antenna for the next-generation direct broadcast satellite.

  17. 77 FR 5429 - Proposed Modification of the Atlanta Class B Airspace Area; GA

    Science.gov (United States)

    2012-02-03

    ... consisted of lower Class B floors within a reduced radius of 30 NM from the ATL VORTAC as opposed to the... concerns related to the proposed lower Class B airspace floors, particularly in the airspace directly... congestion at lower altitudes due to VFR traffic trying to avoid flying in the Class B airspace area and...

  18. 78 FR 70895 - Proposed Establishment and Modification of Area Navigation (RNAV) Routes; Atlanta, GA

    Science.gov (United States)

    2013-11-27

    ... Management Facility (see ADDRESSES section for address and phone number). You may also submit comments...), Buffalo Niagara International (BUF) and Toronto Pearson International (TOR) airports. Additionally, Q-69...

  19. GLOBECOM '84 - Global Telecommunications Conference, Atlanta, GA, November 26-29, 1984, Conference Record. Volume 3

    Science.gov (United States)

    Attention is given to aspects of quality assurance methodologies in development life cycles, optical intercity transmission systems, multiaccess protocols, system and technology aspects in the case of regional/domestic satellites, advances in SSB-AM radio transmission over terrestrial and satellite network, and development environments for telecommunications systems. Other subjects studied are concerned with business communication networks for voice and data, VLSI in local network and communication protocol, product evaluation and support, an update regarding Videotex, topics in communication theory, topics in radio propagation, a status report regarding societal effects of technology in the workplace, digital image processing, and adaptive signal processing for communications. The management of the reliability function in the development process is considered along with Giga-bit technologies for long distance large capacity optical transmission equipment. The application of gallium arsenide analog and digital integrated circuits for high-speed fiber optical communications, and a simple algorithm for image data coding.

  20. DOE ZERH Case Study: Heirloom Design Build, Euclid Avenue, Atlanta, GA

    Energy Technology Data Exchange (ETDEWEB)

    none,

    2015-09-01

    Case study of a DOE 2015 Housing Innovation Award winning custom home in the mixed-humid climate that got a HERS 50 without PV, with 2x6 16” on center walls with R-19 ocsf; basement with R-28 ccsf, R-5 rigid foam under slab; sealed attic with R-28 ocsf under roof deck; 22.8 SEER; 12.5 HSPF heat pump.

  1. Counseling Spanish-speaking patients: Atlanta pharmacists' cultural sensitivity, use of language-assistance services, and attitudes.

    Science.gov (United States)

    Muzyk, Andrew J; Muzyk, Tara L; Barnett, Candace W

    2004-01-01

    To document the types of language-assistance services available in pharmacies and the perceptions of pharmacists regarding the effectiveness of these services, and to measure the attitudes toward counseling Spanish-speaking patients and cultural sensitivity of pharmacists. Cross-sectional assessment. Metropolitan Atlanta, Ga. Registered Georgia pharmacists residing in metropolitan Atlanta. Mailed survey, with repeat mailing 2 weeks later. 38 survey items measuring demographic and practice-site characteristics, types of language-assistance services available with an assessment of the effectiveness of each measured on a nominal scale, and attitudinal items concerning counseling of Spanish-speaking patients and pharmacists' cultural sensitivity using a 5-point Likert-type response scale. Of 1,975 questionnaires mailed, 608 were returned, a 30.8% response rate. Nearly two thirds of the pharmacists had recently counseled a Spanish-speaking patient, but only one fourth of those respondents considered their interactions effective. Nearly all pharmacists, 88.0%, worked in pharmacies with language-assistance services. Of seven types of these services, a mean of 2.19 were available in pharmacies, and the majority of pharmacists (84.4% or more) identifying a service considered it to be effective. The pharmacists were neutral about counseling Spanish-speaking patients (mean = 2.94) and indifferent toward other cultures (mean = 3.28); however, they agreed they had a responsibility to counsel Spanish-speaking patients, and they believed that use of language-assistance services would constitute a reasonable effort to counsel these patients. Pharmacists have an opportunity to address barriers to communication with the Spanish-speaking population through use of language-assistance services and educational measures within the profession.

  2. Modeling the Effects of Onsite Wastewater Treatment Systems on Nitrate Loads Using SWAT in an Urban Watershed of Metropolitan Atlanta.

    Science.gov (United States)

    Hoghooghi, Nahal; Radcliffe, David E; Habteselassie, Mussie Y; Jeong, Jaehak

    2017-05-01

    Onsite wastewater treatment systems (OWTSs) can be a source of nitrogen (N) pollution in both surface and ground waters. In metropolitan Atlanta, GA, >26% of homes are on OWTSs. In a previous article, we used the Soil Water Assessment Tool to model the effect of OWTSs on stream flow in the Big Haynes Creek Watershed in metropolitan Atlanta. The objective of this study was to estimate the effect of OWTSs, including failing systems, on nitrate as N (NO-N) load in the same watershed. Big Haynes Creek has a drainage area of 44 km with mainly urban land use (67%), and most of the homes use OWTSs. A USGS gauge station where stream flow was measured daily and NO-N concentrations were measured monthly was used as the outlet. The model was simulated for 12 yr. Overall, the model showed satisfactory daily stream flow and NO-N loads with Nash-Sutcliffe coefficients of 0.62 and 0.58 for the calibration period and 0.67 and 0.33 for the validation period at the outlet of the Big Haynes Watershed. Onsite wastewater treatment systems caused an average increase in NO-N load of 23% at the watershed scale and 29% at the outlet of a subbasin with the highest density of OWTSs. Failing OWTSs were estimated to be 1% of the total systems and did not have a large impact on stream flow or NO-N load. The NO-N load was 74% of the total N load in the watershed, indicating the important effect of OWTSs on stream loads in this urban watershed. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

  3. Willingness to use pre-exposure prophylaxis among Black and White men who have sex with men in Atlanta, Georgia.

    Science.gov (United States)

    Rolle, Charlotte-Paige; Rosenberg, Eli S; Luisi, Nicole; Grey, Jeremy; Sanchez, Travis; Del Rio, Carlos; Peterson, John L; Frew, Paula M; Sullivan, Patrick S; Kelley, Colleen F

    2017-08-01

    PrEP willingness may be different among black and white men who have sex with men (MSM) given known disparities in HIV incidence, sociodemographic factors, and healthcare access between these groups. We surveyed 482 black and white HIV-negative MSM in Atlanta, GA about their willingness to use pre-exposure prophylaxis (PrEP) and facilitators and barriers to PrEP willingness. Overall, 45% (215/482) of men indicated interest in using PrEP. Engaging in recent unprotected anal intercourse (UAI) was the only factor significantly associated with PrEP willingness in multivariate analyses (OR 1.73, 95% CI 1.13, 2.65). Willing men identified "extra protection" against HIV as the most common reason for interest in using PrEP, whereas unwilling men most commonly cited not wanting to take medication daily, and this reason was more common among white MSM (42.3% of white MSM vs. 28.9% of black MSM, p = 0.04). Most men indicated willingness to use PrEP if cost was <50 dollars/month; however, more black MSM indicated willingness to use PrEP only if cost were free (17.9% of white MSM vs. 25.9% of black MSM, p = 0.03). Overall, these data are useful to scale up PrEP interventions targeting at-risk MSM in Atlanta and highlight the need for implementation of low cost-programs, which will be especially important for black MSM.

  4. Risk Factors for HIV Transmission and Barriers to HIV Disclosure: Metropolitan Atlanta Youth Perspectives.

    Science.gov (United States)

    Camacho-Gonzalez, Andres F; Wallins, Amy; Toledo, Lauren; Murray, Ashley; Gaul, Zaneta; Sutton, Madeline Y; Gillespie, Scott; Leong, Traci; Graves, Chanda; Chakraborty, Rana

    2016-01-01

    Youth carry the highest incidence of HIV infection in the United States. Understanding adolescent and young adult (AYA) perspectives on HIV transmission risk is important for targeted HIV prevention. We conducted a mixed methods study with HIV-infected and uninfected youth, ages 18-24 years, from Atlanta, GA. We provided self-administered surveys to HIV-infected and HIV-uninfected AYAs to identify risk factors for HIV acquisition. By means of computer-assisted thematic analyses, we examined transcribed focus group responses on HIV education, contributors to HIV transmission, and pre-sex HIV status disclosure. The 68 participants had the following characteristics: mean age 21.5 years (standard deviation: 1.8 years), 85% male, 90% black, 68% HIV-infected. HIV risk behaviors included the perception of condomless sex (Likert scale mean: 8.0) and transactional sex (88% of participants); no differences were noted by HIV status. Qualitative analyses revealed two main themes: (1) HIV risk factors among AYAs, and (2) barriers to discussing HIV status before sex. Participants felt the use of social media, need for immediate gratification, and lack of concern about HIV disease were risk factors for AYAs. Discussing HIV status with sex partners was uncommon. Key reasons included: fear of rejection, lack of confidentiality, discussion was unnecessary in temporary relationships, and disclosure negatively affecting the mood. HIV prevention strategies for AYAs should include improving condom use frequency and HIV disclosure skills, responsible utilization of social media, and education addressing HIV prevention including the risks of transactional sex.

  5. Water crisis: the metropolitan Atlanta, Georgia, regional water supply conflict

    KAUST Repository

    Missimer, Thomas M.

    2014-07-01

    Many large population centres are currently facing considerable difficulties with planning issues to secure future water supplies, as a result of water allocation and environmental issues, litigation, and political dogma. A classic case occurs in the metropolitan Atlanta area, which is a rapidly growing, large population centre that relies solely on surface water for supply. Lake Lanier currently supplies about 70% of the water demand and has been involved in a protracted legal dispute for more than two decades. Drought and environmental management of the reservoir combined to create a water shortage which nearly caused a disaster to the region in 2007 (only about 35 days of water supply was in reserve). While the region has made progress in controlling water demand by implementing a conservation plan, per capita use projections are still very high (at 511 L/day in 2035). Both non-potable reuse and indirect reuse of treated wastewater are contained in the most current water supply plan with up to 380,000 m3/day of wastewater treated using advanced wastewater treatment (nutrient removal) to be discharged into Lake Lanier. The water supply plan, however, includes no additional or new supply sources and has deleted any reference to the use of seawater desalination or other potential water sources which would provide diversification, thereby relying solely on the Coosa and Chattahoochee river reservoirs for the future. © 2014 IWA Publishing.

  6. Project ATLANTA (Atlanta Land use Analysis: Temperature and Air Quality): Use of Remote Sensing and Modeling to Analyze How Urban Land Use Change Affects Meteorology and Air Quality Through Time

    Science.gov (United States)

    Quattrochi, Dale A.; Luvall, Jeffrey C.; Estes, Maurice G., Jr.

    1999-01-01

    This paper presents an overview of Project ATLANTA (ATlanta Land use ANalysis: Temperature and Air-quality) which is an investigation that seeks to observe, measure, model, and analyze how the rapid growth of the Atlanta, Georgia metropolitan area since the early 1970's has impacted the region's climate and air quality. The primary objectives for this research effort are: (1) To investigate and model the relationships between land cover change in the Atlanta metropolitan, and the development of the urban heat island phenomenon through time; (2) To investigate and model the temporal relationships between Atlanta urban growth and land cover change on air quality; and (3) To model the overall effects of urban development on surface energy budget characteristics across the Atlanta urban landscape through time. Our key goal is to derive a better scientific understanding of how land cover changes associated with urbanization in the Atlanta area, principally in transforming forest lands to urban land covers through time, has, and will, effect local and regional climate, surface energy flux, and air quality characteristics. Allied with this goal is the prospect that the results from this research can be applied by urban planners, environmental managers and other decision-makers, for determining how urbanization has impacted the climate and overall environment of the Atlanta area. Multiscaled remote sensing data, particularly high resolution thermal infrared data, are integral to this study for the analysis of thermal energy fluxes across the Atlanta urban landscape.

  7. Health impact assessment of the Atlanta BeltLine.

    Science.gov (United States)

    Ross, Catherine L; Leone de Nie, Karen; Dannenberg, Andrew L; Beck, Laurie F; Marcus, Michelle J; Barringer, Jason

    2012-03-01

    Although a health impact assessment (HIA) is a tool that can provide decision makers with recommendations to promote positive health impacts and mitigate adverse health impacts of proposed projects and policies, it is not routinely conducted on most major projects or policies. To make health a decision criterion for the Atlanta BeltLine, a multibillion-dollar transit, trails, parks, and redevelopment project. An HIA was conducted in 2005-2007 to anticipate and influence the BeltLine's effect on health determinants. Changes in access and equity, environmental quality, safety, social capital, and physical activity were forecast, and steps to maximize health benefits and reduce negative effects were recommended. Key recommendations included giving priority to the construction of trails and greenspace rather than residential and retail construction, making health an explicit goal in project priority setting, adding a public health professional to decision-making boards, increasing the connectivity between the BeltLine and civic spaces, and ensuring that affordable housing is built. BeltLine project decision makers have incorporated most of the HIA recommendations into the planning process. The HIA was cited in the awarding of additional funds of $7,000,000 for brownfield clean-up and greenspace development. The project is expected to promote the health of local residents more than in the absence of the HIA. This report is one of the first HIAs to tie specific assessment findings to specific recommendations and to identifiable impacts from those recommendations. The lessons learned from this project may help others engaged in similar efforts. Copyright © 2012. Published by Elsevier Inc.

  8. Urbanization effects on the hydrology of the Atlanta, Georgia (USA)

    Science.gov (United States)

    Peters, N.E.; Rose, S.

    2001-01-01

    For the period from 1958 to 1996, streamflow and rainfall characteristics of a highly urbanized watershed were compared with less-urbanized and non-urbanized watersheds in the vicinity of Atlanta, Georgia (USA). Water levels in several wells completed in surficial and crystalline-rock aquifers also were evaluated. Annual runoff coefficients (runoff as a fractional percentage of precipitation) ranged from 0.31 to 0.34 and were not significantly different for the urban stream (Peachtree Creek). Peak flows for the largest 25 stormflows at Peachtree Creek were 30% to 80% greater than peak flows for the other streams. A 2-day storm recession constant for Peachtree Creek was much larger, that is streamflow decreased more rapidly than for the other streams. Average low flow of Peachtree Creek was 25 to 35% less than the other streams, possibly the result of decreased infiltration caused by the more efficient routing of storm water and the paving of groundwater recharge areas. The timing of groundwater level variations was similar annually in each well, reflecting the seasonal recharge. Although water level monitoring only began during the late 1970s and early 1980s for the two urban wells, water levels in these wells have been declining compared to non-urban wells since then. The water level decline is attributed to decreased groundwater recharge in the urban watersheds due to increased imperviousness and related rapid storm runoff. Likewise, the increased urbanization from the 1960s to the 1990s of the Peachtree Creek watershed produced more runoff than urbanization in the less urbanized Big Creek and Sweetwater Creek watersheds.

  9. Green roof adoption in atlanta, georgia: the effects of building characteristics and subsidies on net private, public, and social benefits.

    Science.gov (United States)

    Mullen, Jeffrey D; Lamsal, Madhur; Colson, Greg

    2013-10-01

    This research draws on and expands previous studies that have quantified the costs and benefits associated with conventional roofs versus green roofs. Using parameters from those studies to define alternative scenarios, we estimate from a private, public, and social perspective the costs and benefits of installing and maintaining an extensive green roof in Atlanta, GA. Results indicate net private benefits are a decreasing function of roof size and vary considerably across scenarios. In contrast, net public benefits are highly stable across scenarios, ranging from $32.49 to $32.90 m(-2). In addition, we evaluate two alternative subsidy regimes: (i) a general subsidy provided to every building that adopts a green roof and (ii) a targeted subsidy provided only to buildings for which net private benefits are negative but net public benefits are positive. In 6 of the 12 general subsidy scenarios the optimal public policy is not to offer a subsidy; in 5 scenarios the optimal subsidy rate is between $20 and $27 m(-2); and in 1 scenario the optimal rate is $5 m(-2). The optimal rate with a targeted subsidy is between $20 and $27 m(-2) in 11 scenarios and no subsidy is optimal in the twelfth. In most scenarios, a significant portion of net public benefits are generated by buildings for which net private benefits are positive. This suggests a policy focused on information dissemination and technical assistance may be more cost-effective than direct subsidy payments.

  10. A Pilot Study of Halal Goat-Meat Consumption in Atlanta, Georgia

    OpenAIRE

    Ibrahim, Mohammed; Liu, Xuanli; Nelson, Mack C.

    2008-01-01

    Atlanta is a relatively large market for goat meat. As in most metropolitan areas around the U.S., goat-meat consumption has grown steadily in Atlanta over the past decade (Northwest Cooperative Development Center 2005; Nettles and Bukenya 2004). This growth is attributed to the influx of immigrants from goat-meat-eating countries into the U.S. over the same period (Gipson 1999). The increase in demand for goat meat has made the U.S. a net importer of competitively priced goat meat from Austr...

  11. Universe

    CERN Document Server

    2009-01-01

    The Universe, is one book in the Britannica Illustrated Science Library Series that is correlated to the science curriculum in grades 5-8. The Britannica Illustrated Science Library is a visually compelling set that covers earth science, life science, and physical science in 16 volumes.  Created for ages 10 and up, each volume provides an overview on a subject and thoroughly explains it through detailed and powerful graphics-more than 1,000 per volume-that turn complex subjects into information that students can grasp.  Each volume contains a glossary with full definitions for vocabulary help and an index.

  12. Newcastle disease B1 vaccine strain in wild rock pigeons in Atlanta, Georgia

    Science.gov (United States)

    From June to October of 2012, samples were collected from wild Rock Pigeons (Columba livia) in urban neighborhoods of Atlanta, Georgia to ascertain the prevalence of pigeon paramyxovirus serotype-1 (PPMV-1). PPMV-1 strains are a subset of avian paramyxovirus serotype-1 (APMV-1) commonly isolated fro...

  13. 77 FR 24440 - Approval and Promulgation of Implementation Plans; Georgia; Atlanta; Ozone 2002 Base Year...

    Science.gov (United States)

    2012-04-24

    ... ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 52 [EPA-R04-OAR-2010-0021(b); FRL-9661-9] Approval and Promulgation of Implementation Plans; Georgia; Atlanta; Ozone 2002 Base Year Emissions Inventory AGENCY... 2002 base year emissions inventory portion of the state implementation plan (SIP) revision submitted by...

  14. 77 FR 24399 - Approval and Promulgation of Implementation Plans; Georgia; Atlanta; Ozone 2002 Base Year...

    Science.gov (United States)

    2012-04-24

    ... Promulgation of Implementation Plans; Georgia; Atlanta; Ozone 2002 Base Year Emissions Inventory AGENCY... approve the ozone 2002 base year emissions inventory, portion of the state implementation plan (SIP... technology (RACT), contingency measures, a 2002 base- year emissions inventory and other planning SIP...

  15. PREFACE TO SPECIAL SECTION: SOUTHERN OXIDANTS STUDY 1999 ATLANTA SUPERSITE PROJECT (SOS3)

    Science.gov (United States)

    The Atlanta Supersites Project consisted of a one-month intensive field program to compare advanced methods for measurement of PM2.5 mass, chemical composition, including single particle composition in real-time, and aerosol precursor species. The project was the first of EPA's ...

  16. Fight or Flight? Immigration, Competition, and Language Assistance Resources in Metropolitan Atlanta

    Science.gov (United States)

    Tarasawa, Beth

    2013-01-01

    As the Latino/a immigrant population increases, racial conflict historically understood in terms of Black and White in the U.S. South has expanded to include new contestants in metro-Atlanta public schools. By examining market and sociological competition theoretical perspectives, this study investigates how language assistance resource…

  17. Overkill: Black Lives and the Spectacle of the Atlanta Cheating Scandal

    Science.gov (United States)

    Royal, Camika; Dodo Seriki, Vanessa

    2018-01-01

    This article examines the 2015 Atlanta cheating scandal trials and sentencing. Using critical race theory, the authors argue that cheating is a natural outgrowth of market-based school reform and that racial realism will always lead to scrutiny of Black performance. The sentences of these Black educators is overkill, rooted in anti-Blackness, and…

  18. The clinical feature of HIV/AIDS at presentation at the Jos University ...

    African Journals Online (AJOL)

    Each qualified patient had a comprehensive history taken with emphasis on the clinical symptoms and detailed physical examination performed by the researchers. The data collected were analyzed using a multipurpose computer programme, Epi-info 2000 version 1.1.3 (Atlanta GA, USA). Results: There were 86(43.0%) ...

  19. Describing Peripancreatic Collections According to the Revised Atlanta Classification of Acute Pancreatitis An International Interobserver Agreement Study

    NARCIS (Netherlands)

    Bouwense, Stefan A.; van Brunschot, Sandra; van Santvoort, Hjalmar C.; Besselink, Marc G.; Bollen, Thomas L.; Bakker, Olaf J.; Banks, Peter A.; Boermeester, Marja A.; Cappendijk, Vincent C.; Carter, Ross; Charnley, Richard; van Eijck, Casper H.; Freeny, Patrick C.; Hermans, John J.; Hough, David M.; Johnson, Colin D.; Laméris, Johan S.; Lerch, Markus M.; Mayerle, Julia; Mortele, Koenraad J.; Sarr, Michael G.; Stedman, Brian; Vege, Santhi Swaroop; Werner, Jens; Dijkgraaf, Marcel G.; Gooszen, Hein G.; Horvath, Karen D.; Aghdassi, Ali A.; van Enckevort, Conny C.; de Haas, Robbert J.; Horsthuis, Karin; van der Jagt, Michel F.; Kok, Niels F.; Koopmanschap, Desirée H.; Koppe, Manuel J.; Krak, Nanda C.; Lane, Charlotte E.; Lee, Jean H.; de Lussanet, Q.; Saunders, Michael D.; Swaroop Vege, Santhi; van der Vlugt, Manon; van Wageningen, Bas; Wassenaar, Eelco; van Wely, Bob J.; Wijnhoven, Bas P.

    2017-01-01

    Objectives: Severe acute pancreatitis is associated with peripancreatic morphologic changes as seen on imaging. Uniform communication regarding these morphologic findings is crucial for accurate diagnosis and treatment. For the original 1992 Atlanta classification, interobserver agreement is poor.

  20. Summary of Needs and Opportunities from the 2011 Residential Energy Efficiency Stakeholders Meeting: Atlanta, Georgia -- March 16-18, 2011

    Energy Technology Data Exchange (ETDEWEB)

    2011-05-01

    This summary report outlines needs and issues for increasing energy efficiency of new and existing U.S homes, as identified at the U.S Department of Energy Building America program Spring 2011 stakeholder meeting in Atlanta, Georgia.

  1. Meteorological detrending of primary and secondary pollutant concentrations: Method application and evaluation using long-term (2000-2012) data in Atlanta

    Science.gov (United States)

    Henneman, Lucas R. F.; Holmes, Heather A.; Mulholland, James A.; Russell, Armistead G.

    2015-10-01

    The effectiveness of air pollution regulations and controls are evaluated based on measured air pollutant concentrations. Air pollution levels, however, are highly sensitive to both emissions and meteorological fluctuations. Therefore, an assessment of the change in air pollutant levels due to emissions controls must account for these meteorological fluctuations. Two empirical methods to quantify the impact of meteorology on pollutant levels are discussed and applied to the 13-year time period between 2000 and 2012 in Atlanta, GA. The methods employ Kolmogorov-Zurbenko filters and linear regressions to detrended pollutant signals into long-term, seasonal, weekly, short-term, and white-noise components. The methods differ in how changes in weekly and holiday emissions are accounted for. Both can provide meteorological adjustments on a daily basis for future use in acute health analyses. The meteorological impact on daily signals of ozone, NOx, CO, SO2, PM2.5, and PM species are quantified. Analyses show that the substantial decreases in seasonal averages of NOx and SO2 correspond with controls implemented in the metropolitan Atlanta area. Detrending allows for the impacts of some controls to be observed with averaging times of as little as 3 months. Annual average concentrations of NOx, SO2, and CO have all fallen by at least 50% since 2000. Reductions in NOx levels, however, do not lead to uniform reductions in ozone. While average detrended summer average maximum daily average 8 h ozone (MDA8h O3) levels fell by 4% (2.2 ± 2 ppb) between 2000 and 2012, winter averages have increased by 12% (3.8 ± 1.4 ppb), providing further evidence that high ozone levels are NOx-limited and lower ozone concentrations are NOx-inhibited. High ozone days (with MDA8h O3 greater than 60 ppb) decreased both in number and in magnitude over the study period.

  2. Atlanta Gas Light opts for an in-house AM/FM

    International Nuclear Information System (INIS)

    Hull, S.R.

    1993-01-01

    Atlanta Gas Light Co. has completed facilities conversion for the first of nine planned implementations of its automated mapping/facilities management mapping/facilities management system, the Facilities and Land Base Automated Mapping Environment or FLAME. Facilities conversion is generally the most costly and time-consuming phase of an AM/FM project. Many companies decide to rely totally on outside expertise for this phase because of the complexity of the process an the resources required to complete it. Atlanta Gas Light decided to take an alternate approach by performing the facilities conversion process in-house for the first implementation, than having an outside vendor carrying out a future implementation and compare the two

  3. Fútbol, etnicidad y otredad: el Club Atlético Atlanta de Buenos Aires

    Directory of Open Access Journals (Sweden)

    Raanan Rein

    2014-06-01

    While most historians would agree as to the centrality of soccer in Latin American societies, very little has been written on ethnicity and sports in such immigrant societies as Argentina and Brazil. This article focuses on the Club Atlético Atlanta, located in the neighborhood of Villa Crespo. Although populated by various ethnic groups, Villa Crespo has long been considered a Jewish neighborhood. During the second half of the 20th century, there has been a conspicuous Jewish presence among the fans, administrators and presidents of the Atlanta soccer club, to the extent that fans of rival teams often chant anti-Semitic slogans during matches. For the first immigrant generation, belonging to this club was a way of becoming Argentines. For the next generation, it was a way of maintaining ethnic Jewish identity, while for the third it has become a family tradition.

  4. Muchinako, GA

    African Journals Online (AJOL)

    Muchinako, GA. Vol 28, No 2 (2013) - Articles Children living and/or working on the streets in Harare: Issues and challenges. Abstract. ISSN: 1012-1080. AJOL African Journals Online. HOW TO USE AJOL... for Researchers · for Librarians · for Authors · FAQ's · More about AJOL · AJOL's Partners · Terms and Conditions of ...

  5. The mortality profile of black Seventh-Day Adventists residing in metropolitan Atlanta: a pilot study.

    Science.gov (United States)

    Murphy, F G; Blumenthal, D S; Dickson-Smith, J; Peay, R P

    1990-08-01

    Mortality information was gathered for 110 Black Seventh-day Adventist members of seven churches in Metropolitan Atlanta, Georgia during the period 1980-87. Seventy-seven percent of the deaths were due to cardiovascular diseases; 8 percent due to cancer, the second leading cause of death. The cancer rate is extremely low in comparison to the proportion of deaths due to cardiovascular diseases. Subsequent research on this population will take into consideration lifestyle factors which could contribute to this finding.

  6. Atlanta Centennial Olympic Games and Paralympic Games event study, 1996. Final report, July 1996--August 1996

    Energy Technology Data Exchange (ETDEWEB)

    Amodei, R.; Bard, E.; Brong, B.; Cahoon, F.; Jasper, K.

    1998-11-01

    The Atlanta metropolitan region was the location of one of the most ambitious Intelligent Transportation Systems (ITS) deployments in the United States. This deployment included several individual projects--a Central Transportation Management Center (TMC), six Traffic Control Centers (TCCs), one Transit Information Center (TIC), The Travel Information Showcase (TIS), and the extension of the Metropolitan Atlanta Rapid Transit Authority (MARTA) Rail network and the new high-occupancy vehicle (HOV) lanes on I-85 and I-75. The 1996 Atlanta Centennial Olympic Games and Paralympic Games created a focus for these projects. All of these systems were to be brought on-line in time for the Olympic Games. This report presents the findings of the 1996 Olympic and Paralympic Games Events Study--a compilation of findings of system performance, the benefits realized, and the lessons learned during their operations over the event period. The study assessed the performance of the various Travel Demand Management (TDM) plans employed for Olympic Games traffic management.

  7. 76 FR 45771 - Foreign-Trade Zone 26-Atlanta, GA; Application for Manufacturing Authority; Makita Corporation of...

    Science.gov (United States)

    2011-08-01

    ... bits; socket wrenches; styrene polymers; polyamides; resins; caulk; glues and adhesives; vinyl cases; vinyl tubes; labels; plastic bags; water tanks; plastic grips; rubber knobs and handles; plastic cases... examiner to evaluate and analyze the facts and information presented in the application and case record and...

  8. American Studies Association — Crossroads of Cultures, Atlanta, Ga., Nov. 11-14, 2004

    OpenAIRE

    Pothier, Jacques

    2006-01-01

    Dans le cadre de son congrès annuel et à l’initiative de sa présidente en exercice, Shelley Fisher Fishkin, l’American Studies Association avait lancé une International Initiative : inviter les représentants de toutes les associations d’études américaines du monde. Parallèlement, American Quarterly, la revue de l’Association, invitait les directeurs des rédactions des revues américanistes.Je représentais donc l’AFEA, la RFEA et Transatlantica.Qu’est-ce que l’American Studies Association ?Le C...

  9. Ensemble simulations to study the impact of land use change of Atlanta to regional climate

    Science.gov (United States)

    Liu, P.; Hu, Y.; Stone, B.; Vargo, J.; Nenes, A.; Russell, A.; Trail, M.; Tsimpidi, A.

    2012-12-01

    Studies show that urban areas may be the "first responders" to climate change (Rosenzweig et al., 2010). Of particular interest is the potential increased temperatures in urban areas, due to use of structures and surfaces that increase local heating, and how that may impact health, air quality and other environmental factors. In response, interest has grown as to how the modification of land use in urban areas, in order to mitigate the adverse effects of urbanization can serve to reduce local temperatures, and how climate is impacted more regionally. Studies have been conducted to investigate the impact of land use change on local or regional climate by dynamic downscaling using regional climate models (RCMs), the boundary conditions (BCs) and initial conditions (ICs) of which result from coarser-resolution reanalysis data or general circulation models (GCMs). However, few studies have focused on demonstrating whether the land use change in local areas significantly impacts the climate of the larger region of the domain, and the spatial scale of the impact from urban-scale changes. This work investigated the significance of the impact of land use change in the Atlanta city area on different scales, using a range of modeling resolutions, including the contiguous US (with 36km resolution), the southeastern US (with 12km resolution) and the state of Georgia (with 4km resolution). We used WRF version 3.1.1 with and ran continuous from June to August of a simulated year 2050, driven by GISS ModelE with inputs corresponding to RCP4.5. During the simulation, spectral nudging is used in the 36km resolution domain to maintain the climate patterns with scales larger than 2000km. Two-way nesting is also used in order to take into account the feedback of nesting domains across model domains. Two land use cases over the Atlanta city are chosen. For the base case, most of the urban area of Atlanta is covered with forest; while for the second, "impervious" case, all the urban

  10. Device Performance and Reliability Improvements of AlGaBN/GaN/Si MOSFET

    Science.gov (United States)

    2016-02-04

    AFRL-AFOSR-JP-TR-2016-0037 Device Performance and Reliablity Improvements of AlGaBN/GaN/Si MOSFET Robert Wallace UNIVERSITY OF TEXAS AT DALLAS Final...GaN/Si MOSFET 5a.  CONTRACT NUMBER 5b.  GRANT NUMBER FA2386-14-1-4069 5c.  PROGRAM ELEMENT NUMBER 61102F 6. AUTHOR(S) Robert Wallace 5d.  PROJECT...AOARD Grant FA2386-14-1-4069 Device Performance and Reliability Improvements of AlGaN/GaN/Si MOSFET US 12 month extension (2014 – 2015) for current

  11. Reassessment of biogenic volatile organic compound emissions in the Atlanta area

    International Nuclear Information System (INIS)

    Geron, C.D.; Pierce, T.E.; Guenther, A.B.

    1995-01-01

    Localized estimates of biogenic volatile organic compound (BVOC) emissions are important inputs for photochemical oxidant simulation models. Since forest tree species are the primary emitters of BVOCs, it is important to develop reliable estimates of their areal coverage and BVOC emission rates. A new system is used to estimate these emissions in the Atlanta area for specific tree genera at hourly and county levels. The U.S. Department of Agriculture, Forest Service Forest Inventory and Analysis data and an associated urban vegetation survey are used to estimate canopy occupancy by genus in the Atlanta area. A simple canopy model is used to adjust photosynthetically active solar radiation at five vertical levels in the canopy. Lraf temperature and photosynthetically active radiation derived from ambient conditions above the forest canopy are then used to drive empirical equations to estimate genus level emission rates of BVOCs vertically through forest canopies. These genera-level estimates are then aggregated to county and regional levels for input into air quality models and for comparison with (1) the regulatory model currently used and (2) previous estimates for the Atlanta area by local researchers. Estimated hourly emissions from the three approaches during a documented ozone event day are compared. The proposed model yields peak diurnal isoprene emission rates that are over a factor of three times higher than previous estimates. This results in total BVOC emission rates that are roughly a factor of two times higher than previous estimates. These emissions are compared with observed emissions from forests of similar composition. Possible implications for oxidant events are discussed. (author)

  12. Consumer Willingness to Pay a Premium for Halal Goat Meat: A Case from Atlanta, Georgia

    OpenAIRE

    Ibrahim, Mohammed

    2011-01-01

    The growth in goat meat demand is attributed to the influx of immigrants from goat-meat-eating countries into the U.S. This Paper examines the willingness to pay a premium for halal goat meat. The factors that significantly impact the willingness to pay a premium for halal goat meat in Atlanta include income, current consumption, household size, and marital status. Results suggest that the mean willingness to pay a premium for the halal attribute is 50 cents per pound of goat meat.

  13. Photoconductive GaN UV Detectors

    National Research Council Canada - National Science Library

    Baranowski, Jacek

    1999-01-01

    This report results from a contract tasking University of Warsaw as follows: The contractor will investigate the growth of GaN material using atmospheric pressure metalorganic chemical vapor deposition method (MOCVD...

  14. Determinação de perdas de solo na bacia hidrográfica do córrego Ipiranga em Cidade Gaúcha, Estado do Paraná, com aplicação da Equação Universal de Perdas de Solo (EUPS = Estimates of soil losses in the Ipiranga river basin in Cidade Gaúcha, State of Paraná, with application of the Universal Soil Loss Equation (USLE

    Directory of Open Access Journals (Sweden)

    João Paulo Bueno do Prado

    2005-01-01

    Full Text Available Objetivando a predição das perdas de solo por erosão laminar na bacia do córrego Ipiranga no Município de Cidade Gaúcha, Estado do Paraná, foi empregada a Equação Universal de Perdas de Solo (EUPS com o auxílio de técnicas de geoprocessamento. O ambiente SIG permitiu a completa integração entre os dados, a obtenção dos parâmetros da EUPS e o cálculo das perdas de solo anuais e sazonais, considerando-se os diferentes tipos de solos e de usos e ocupação na área. Os resultadosobtidos associam as maiores perdas de solo às áreas cultivadas com cana-de-açúcar e mandioca (>20 ton.ha-1.no-1. A primavera é o período mais crítico para a erosão laminar enquanto que no outono são verificadas as taxas mais baixas de perdas de solo.The prediction of soil loss via laminar erosion at Ipiranga river basin, situated in Cidade Gaúcha county, State of Paraná, was carried out by applying both the Universal soil Loss Equation (USLE and the Geographic Information System (GIS. The GIS environment provided acomplete integration of the data, as well as helped the authors of this paper to obtain the USLE parameters and the calculus of the annual and seasonal soil losses, considering the different types of soil, their usage and the area cover-management. The results obtainedindicated a high soil loss in areas where sugar cane and manioc (>20 t.ha-1.no-1 are cultivated. Spring is the most critical period for laminar erosion, while autumn is the period which shows the smallest number of soil losses.

  15. Using synoptic weather types to predict visitor attendance at Atlanta and Indianapolis zoological parks

    Science.gov (United States)

    Perkins, David R.

    2018-01-01

    Defining an ideal "tourism climate" has been an often-visited research topic where explanations have evolved from global- to location-specific indices tailored to tourists' recreational behavior. Unfortunately, as indices become increasingly specific, they are less translatable across geographies because they may only apply to specific activities, locales, climates, or populations. A key need in the future development of weather and climate indices for tourism has been a translatable, meteorologically based index capturing the generalized ambient atmospheric conditions yet considering local climatology. To address this need, this paper tests the applicability of the spatial synoptic classification (SSC) as a tool to predict visitor attendance response in the tourism, recreation, and leisure (TRL) sector across different climate regimes. Daily attendance data is paired with the prevailing synoptic weather condition at Atlanta and Indianapolis zoological parks from September 2001 to June 2011, to review potential impacts ambient atmospheric conditions may have on visitor attendances. Results indicate that "dry moderate" conditions are most associated with high levels of attendance and "moist polar" synoptic conditions are most associated with low levels of attendance at both zoological parks. Comparing visitor response at these zoo locations, visitors in Indianapolis showed lower levels of tolerance to synoptic conditions which were not "ideal." Visitors in Indianapolis also displayed more aversion to "polar" synoptic regimes while visitors in Atlanta displayed more tolerance to "moist tropical" synoptic regimes. Using a comprehensive atmospheric measure such as the SSC may be a key to broadening application when assessing tourism climates across diverse geographies.

  16. 78 FR 28940 - Environmental Impact Statement for the Atlanta to Charlotte Portion of the Southeast High Speed...

    Science.gov (United States)

    2013-05-16

    ... federal High-Speed Intercity Passenger Rail (HSIPR) program and includes the development of a Passenger.... Background The Atlanta-Charlotte Corridor faces mobility challenges. Transportation demand and travel growth... travel time and reliability, provide another reliable mode choice, create jobs, reduce dependence on...

  17. Describing Peripancreatic Collections According to the Revised Atlanta Classification of Acute Pancreatitis: An International Interobserver Agreement Study.

    Science.gov (United States)

    Bouwense, Stefan A; van Brunschot, Sandra; van Santvoort, Hjalmar C; Besselink, Marc G; Bollen, Thomas L; Bakker, Olaf J; Banks, Peter A; Boermeester, Marja A; Cappendijk, Vincent C; Carter, Ross; Charnley, Richard; van Eijck, Casper H; Freeny, Patrick C; Hermans, John J; Hough, David M; Johnson, Colin D; Laméris, Johan S; Lerch, Markus M; Mayerle, Julia; Mortele, Koenraad J; Sarr, Michael G; Stedman, Brian; Vege, Santhi Swaroop; Werner, Jens; Dijkgraaf, Marcel G; Gooszen, Hein G; Horvath, Karen D

    2017-08-01

    Severe acute pancreatitis is associated with peripancreatic morphologic changes as seen on imaging. Uniform communication regarding these morphologic findings is crucial for accurate diagnosis and treatment. For the original 1992 Atlanta classification, interobserver agreement is poor. We hypothesized that for the revised Atlanta classification, interobserver agreement will be better. An international, interobserver agreement study was performed among expert and nonexpert radiologists (n = 14), surgeons (n = 15), and gastroenterologists (n = 8). Representative computed tomographies of all stages of acute pancreatitis were selected from 55 patients and were assessed according to the revised Atlanta classification. The interobserver agreement was calculated among all reviewers and subgroups, that is, expert and nonexpert reviewers; interobserver agreement was defined as poor (≤0.20), fair (0.21-0.40), moderate (0.41-0.60), good (0.61-0.80), or very good (0.81-1.00). Interobserver agreement among all reviewers was good (0.75 [standard deviation, 0.21]) for describing the type of acute pancreatitis and good (0.62 [standard deviation, 0.19]) for the type of peripancreatic collection. Expert radiologists showed the best and nonexpert clinicians the lowest interobserver agreement. Interobserver agreement was good for the revised Atlanta classification, supporting the importance for widespread adaption of this revised classification for clinical and research communications.

  18. Teacher Morale in the Atlanta Public Schools: Spring 1990. Report No. 4, Volume 25, 11/91.

    Science.gov (United States)

    Fraser, Lowrie A.

    A study was done of Atlanta (Georgia) public school teacher morale in May of 1990. About 40 percent of the teaching staff (1,520 teachers) voluntarily completed a 91-item questionnaire that contained subsets of questions from the Maslach Burnout Inventory and three subscales of emotional exhaustion, departmentalization, and personal…

  19. Type II universal spacetimes

    Czech Academy of Sciences Publication Activity Database

    Hervik, S.; Málek, Tomáš; Pravda, Vojtěch; Pravdová, Alena

    2015-01-01

    Roč. 32, č. 24 (2015), s. 245012 ISSN 0264-9381 R&D Projects: GA ČR GA13-10042S Institutional support: RVO:67985840 Keywords : einstein spacetimes * generalized gravities * universal spacetimes Subject RIV: BA - General Mathematics Impact factor: 2.837, year: 2015 http://iopscience.iop.org/article/10.1088/0264-9381/32/24/245012

  20. Atlanta 10 x 20 NTMS area: Alabama and Georgia. Data report

    International Nuclear Information System (INIS)

    Jones, P.L.

    1979-08-01

    Results of ground water and stream sediment reconnaissance in the National Topographic Map Series (NTMS) Atlanta 1 0 x 2 0 quadrangle are presented. Stream sediment samples were collected from small streams at 1312 sites or at a nominal density of one site per 13 square kilometers in rural areas. Ground water samples were collected at 951 sites or at a nominal density of one site per 18 square kilometers. Neutron activation analysis results are given for uranium and 16 other elements in sediments, and for uranium and 8 other elements in ground water and surface water. Field measurements and observations are reported for each site. Analytical data and field measurements are presented in tables and maps. Statistical summaries of data and a brief description of results are given. A generalized geologic map and a summary of the geology of the area are included

  1. Minority Stress and Intimate Partner Violence Among Gay and Bisexual Men in Atlanta.

    Science.gov (United States)

    Stephenson, Rob; Finneran, Catherine

    2017-07-01

    Intimate partner violence (IPV) rates are disproportionately high among sexual minority populations. Few studies have examined the plausible relationship between minority stress and IPV among men who have sex with men. This study examines the associations between IPV and three indicators of minority stress: internalized homophobia, sexuality-based discrimination, and racism, in a large venue-based sample of gay and bisexual men from Atlanta, USA. Each of the minority stress measures was found to be significantly associated with increased odds of self-reporting any form of receipt of IPV. Significant associations were also identified between perpetration of IPV and minority stressors, with most types of IPV perpetration linked to internalized homophobia. This study confirms findings in a growing body of research supporting the relationship between minority stress and increased prevalence of IPV among men who have sex with men, and points to the need to address structural factors in IPV prevention programs for male-male couples.

  2. Islam in Diaspora: Shari’a Law, Piety and Brotherhood at al-Farooq Mosque, Atlanta

    Directory of Open Access Journals (Sweden)

    Mohamad Abdun Nasir

    2016-06-01

    [Tulisan ini mengkaji praktik ritual shalat hari raya (Eid di masjid al-Farooq Atlanta, Amerika Serikat pada kalangan muslim perantauan dari berbagai belahan dunia. Kajian ini, dengan menggunakan pendekatan tektual dan etnografi, mengamati penerapan hukum Islam dalam hal peribadatan dan pemaknaan serta pengalaman ritual diantara mereka. Studi ini menunjukkan bahwa shalat hari raya memberi makna dan pengalaman khusus. Perayaan ini dilihat sebagai medium untuk menunjukkan kesalehan dan menguatkan ikatan persaudaraan sesama muslim meskipun mempunyai latar belakang etnik dan budaya yang berbeda. Meskipun demikian, inti dari ritual tersebut menunjukkan aliran mazhab Hanafi. Pelaksanaan fiqih dalam sholat Eid tetap berpegang pada Qur’an dan Hadits. Dengan kata lain, konteks geografi dan budaya yang berbeda telah membentuk makna baru namun tetap tidak merubah inti dari praktik ibadah yang bermazhab Hanafi.

  3. Remote Sensing of Atlanta's Urban Sprawl and the Distribution of Land Cover and Surface Temperature

    Science.gov (United States)

    Laymon, Charles A.; Estes, Maurice G., Jr.; Quattrochi, Dale A.; Goodman, H. Michael (Technical Monitor)

    2001-01-01

    Between 1973 and 1992, an average of 20 ha of forest was lost each day to urban expansion of Atlanta, Georgia. Urban surfaces have very different thermal properties than natural surfaces-storing solar energy throughout the day and continuing to release it as sensible heat well after sunset. The resulting heat island effect serves as catalysts for chemical reactions from vehicular exhaust and industrialization leading to a deterioration in air quality. In this study, high spatial resolution multispectral remote sensing data has been used to characterize the type, thermal properties, and distribution of land surface materials throughout the Atlanta metropolitan area. Ten-meter data were acquired with the Advanced Thermal and Land Applications Sensor (ATLAS) on May 11 and 12, 1997. ATLAS is a 15-channel multispectral scanner that incorporates the Landsat TM bands with additional bands in the middle reflective infrared and thermal infrared range. The high spatial resolution permitted discrimination of discrete surface types (e.g., concrete, asphalt), individual structures (e.g., buildings, houses) and their associated thermal characteristics. There is a strong temperature contrast between vegetation and anthropomorphic features. Vegetation has a modal temperature at about 20 C, whereas asphalt shingles, pavement, and buildings have a modal temperature of about 39 C. Broad-leaf vegetation classes are indistinguishable on a thermal basis alone. There is slightly more variability (+/-5 C) among the urban surfaces. Grasses, mixed vegetation and mixed urban surfaces are intermediate in temperature and are characterized by broader temperature distributions with modes of about 29 C. Thermal maps serve as a basis for understanding the distribution of "hotspots", i.e., how landscape features and urban fabric contribute the most heat to the lower atmosphere.

  4. Remote Sensing of Atlanta's Urban Sprawl and the Distribution of Land Cover and Surface Temperatures

    Science.gov (United States)

    Laymon, Charles A.; Estes, Maurice G., Jr.; Quattrochi, Dale A.; Arnold, James E. (Technical Monitor)

    2001-01-01

    Between 1973 and 1992, an average of 20 ha of forest was lost each day to urban expansion of Atlanta, Georgia. Urban surfaces have very different thermal properties than natural surfaces-storing solar energy throughout the day and continuing to release it as sensible heat well after sunset. The resulting heat island effect serves as catalysts for chemical reactions from vehicular exhaust and industrialization leading to a deterioration in air quality. In this study, high spatial resolution multispectral remote sensing data has been used to characterize the type, thermal properties, and distribution of land surface materials throughout the Atlanta metropolitan area. Ten-meter data were acquired with the Advanced Thermal and Land Applications Sensor (ATLAS) on May 11 and 12, 1997. ATLAS is a 15-channel multispectral scanner that incorporates the Landsat TM bands with additional bands in the middle reflective infrared and thermal infrared range. The high spatial resolution permitted discrimination of discrete surface types (e.g., concrete, asphalt), individual structures (e.g., buildings, houses) and their associated thermal characteristics. There is a strong temperature contrast between vegetation and anthropomorphic features. Vegetation has a modal temperature at about 20 C, whereas asphalt shingles, pavement, and buildings have a modal temperature of about 39 C. Broad-leaf vegetation classes are indistinguishable on a thermal basis alone. There is slightly more variability (plus or minus 5 C) among the urban surfaces. Grasses, mixed vegetation and mixed urban surfaces are intermediate in temperature and are characterized by broader temperature distributions with modes of about 29 C. Thermal maps serve as a basis for understanding the distribution of "hotspots", i.e., how landscape features and urban fabric contribute the most heat to the lower atmosphere.

  5. Health and Environment Linked for Information Exchange (HELIX)-Atlanta: A CDC-NASA Joint Environmental Public Health Tracking Collaborative Project

    Science.gov (United States)

    Al-Hamdan, Mohammad; Luvall, Jeff; Crosson, Bill; Estes, Maury; Limaye, Ashutosh; Quattrochi, Dale; Rickman, Doug

    2008-01-01

    HELIX-Atlanta was developed to support current and future state and local EPHT programs to implement data linking demonstration projects which could be part of the CDC EPHT Network. HELIX-Atlanta is a pilot linking project in Atlanta for CDC to learn about the challenges the states will encounter. NASA/MSFC and the CDC are partners in linking environmental and health data to enhance public health surveillance. The use of NASA technology creates value added geospatial products from existing environmental data sources to facilitate public health linkages. Proving the feasibility of the approach is the main objective

  6. UNDERSTANDING THE INTERNATIONAL CONSENSUS FOR ACUTE PANCREATITIS: CLASSIFICATION OF ATLANTA 2012.

    Science.gov (United States)

    Souza, Gleim Dias de; Souza, Luciana Rodrigues Queiroz; Cuenca, Ronaldo Máfia; Jerônimo, Bárbara Stephane de Medeiros; Souza, Guilherme Medeiros de; Vilela, Vinícius Martins

    2016-01-01

    Contrast computed tomography and magnetic resonance imaging are widely used due to its image quality and ability to study pancreatic and peripancreatic morphology. The understanding of the various subtypes of the disease and identification of possible complications requires a familiarity with the terminology, which allows effective communication between the different members of the multidisciplinary team. Demonstrate the terminology and parameters to identify the different classifications and findings of the disease based on the international consensus for acute pancreatitis ( Atlanta Classification 2012). Search and analysis of articles in the "CAPES Portal de Periódicos with headings "acute pancreatitis" and "Atlanta Review". Were selected 23 articles containing radiological descriptions, management or statistical data related to pathology. Additional statistical data were obtained from Datasus and Population Census 2010. The radiological diagnostic criterion adopted was the Radiology American College system. The "acute pancreatitis - 2012 Rating: Review Atlanta classification and definitions for international consensus" tries to eliminate inconsistency and divergence from the determination of uniformity to the radiological findings, especially the terminology related to fluid collections. More broadly as "pancreatic abscess" and "phlegmon" went into disuse and the evolution of the collection of patient fluids can be described as "acute peripancreatic collections", "acute necrotic collections", "pseudocyst" and "necrosis pancreatic walled or isolated". Computed tomography and magnetic resonance represent the best techniques with sequential images available for diagnosis. Standardization of the terminology is critical and should improve the management of patients with multiple professionals care, risk stratification and adequate treatment. A tomografia computadorizada contrastada e a ressonância magnética são exames amplamente utilizados no estudo da

  7. Examining the Impact of Servant Leadership on Workplace Related Outcome (JS) at a Selected Private University

    Science.gov (United States)

    Guillaume, Oris

    2012-01-01

    The aim of this study was to examine the impact of Servant Leadership on a workplace related outcome (job satisfaction) at a private University in Atlanta, Georgia. The ten characteristics of Servant Leadership previously identified by Greenleaf (1977) and Spears (1998) played a significant role in job satisfaction. Other researchers (Barbuto…

  8. Urban partnership agreement and congestion reduction demonstration programs : lessons learned on congestion pricing from the Seattle and Atlanta household travel behavior surveys.

    Science.gov (United States)

    2014-04-01

    This paper presents lessons learned from household traveler surveys administered in Seattle and Atlanta as part of the evaluation of the Urban Partnership Agreement and Congestion Reduction Demonstration Programs. The surveys use a two-stage panel su...

  9. Preventing the repetition: Or, what Los Angeles' experience in water management can teach Atlanta about urban water disputes

    Science.gov (United States)

    Feldman, David L.

    2009-04-01

    Southern California's water history is an epic story with larger-than-life characters and ambitions and abundant hubris. Students of water policy might reasonably ask: Does this story, while unique to greater Los Angeles, hold lessons for other metropolises experiencing water conflict caused by explosive growth? We examine this question by considering similarities between the challenges facing Atlanta, Georgia, one of the nation's fastest growing cities in the 21st century, with those of Los Angeles. We focus on junctures where important decisions regarding water were made and how these decisions continue to challenge both cities' futures. Atlanta's financial, cultural, and environmental imprint on its surrounding region share remarkable similarities with Los Angeles' influence trajectory: it is the largest city in the southeast, a principal transportation and business hub, and it is embroiled in water conflict with nearby communities and adjoining states.

  10. Ga penetration into polymers

    Czech Academy of Sciences Publication Activity Database

    Hnatowicz, Vladimír; Švorčík, V.; Efimenko, K.; Rybka, V.

    1999-01-01

    Roč. 68, - (1999), s. 357-358 ISSN 0947-8396 R&D Projects: GA ČR GA202/96/0077; GA AV ČR KSK1048601 Subject RIV: BG - Nuclear, Atomic and Molecular Physics, Colliders Impact factor: 1.753, year: 1999

  11. Effects of urbanization on streamflow in the Atlanta area (Georgia, USA): A comparative hydrological approach

    Science.gov (United States)

    Rose, S.; Peters, N.E.

    2001-01-01

    For the period from 1958 to 1996, streamflow characteristics of a highly urbanized watershed were compared with less-urbanized and non-urbanized watersheds within a 20 000 km2 region in the vicinity of Atlanta, Georgia: In the Piedmont and Blue Ridge physiographic provinces of the southeastern USA. Water levels in several wells completed in surficial and crystalline-rock aquifers were also evaluated. Data were analysed for seven US Geological Survey (USGS) stream gauges, 17 National Weather Service rain gauges, and five USGS monitoring wells. Annual runoff coefficients (RCs; runoff as a fractional percentage of precipitation) for the urban stream (Peachtree Creek) were not significantly greater than for the less-urbanized watersheds. The RCs for some streams were similar to others and the similar streams were grouped according to location. The RCs decreased from the higher elevation and higher relief watersheds to the lower elevation and lower relief watersheds: Values were 0.54 for the two Blue Ridge streams. 0.37 for the four middle Piedmont streams (near Atlanta), and 0.28 for a southern Piedmont stream. For the 25 largest stormflows, the peak flows for Peachtree Creek were 30% to 100% greater then peak flows for the other stream. The storm recession period for the urban stream was 1-2 days less than that for the other streams and the recession was characterized by a 2-day storm recession constant that was, on average, 40 to 100% greater, i.e. streamflow decreased more rapidly than for the other streams. Baseflow recession constants ranged from 35 to 40% lower for Peachtree Creek than for the other streams; this is attributed to lower evapotranspiration losses, which result in a smaller change in groundwater storage than in the less-urbanized watersheds. Low flow of Peachtree Creek ranged from 25 to 35% less than the other streams, possibly the result of decreased infiltration caused by the more efficient routing of stormwater and the paving of groundwater

  12. Susceptibility to Heat-Related Fluid and Electrolyte Imbalance Emergency Department Visits in Atlanta, Georgia, USA

    Directory of Open Access Journals (Sweden)

    Leila Heidari

    2016-10-01

    Full Text Available Identification of populations susceptible to heat effects is critical for targeted prevention and more accurate risk assessment. Fluid and electrolyte imbalance (FEI may provide an objective indicator of heat morbidity. Data on daily ambient temperature and FEI emergency department (ED visits were collected in Atlanta, Georgia, USA during 1993–2012. Associations of warm-season same-day temperatures and FEI ED visits were estimated using Poisson generalized linear models. Analyses explored associations between FEI ED visits and various temperature metrics (maximum, minimum, average, and diurnal change in ambient temperature, apparent temperature, and heat index modeled using linear, quadratic, and cubic terms to allow for non-linear associations. Effect modification by potential determinants of heat susceptibility (sex; race; comorbid congestive heart failure, kidney disease, and diabetes; and neighborhood poverty and education levels was assessed via stratification. Higher warm-season ambient temperature was significantly associated with FEI ED visits, regardless of temperature metric used. Stratified analyses suggested heat-related risks for all populations, but particularly for males. This work highlights the utility of FEI as an indicator of heat morbidity, the health threat posed by warm-season temperatures, and the importance of considering susceptible populations in heat-health research.

  13. Dietary intake and overweight and obesity among persons living with HIV in Atlanta Georgia.

    Science.gov (United States)

    Hernandez, Dominica; Kalichman, Seth; Cherry, Chauncey; Kalichman, Moira; Washington, Christopher; Grebler, Tamar

    2017-06-01

    In the U.S., there has been a rise in overweight and obesity among persons living with HIV (PLWH). The aim of this study was to examine dietary intake and body mass index (BMI) in PLWH in Atlanta Georgia relative to the U.S. Dietary intake among PLWH was compared with recommended standards as well as estimated dietary intake for adults in the U.S. Over 31% of the study participants were overweight [BMI = 25-29.9 kg/m 2 ], and 33.1% obese [BMI ≥ 30 kg/m 2 ]. Results indicated significant dietary differences between participants in our sample and U.S. daily recommendations for adults as well as estimated intakes of the U.S. Both males and females consumed more percentage of energy from fat and less fiber as well as fruit and vegetables servings than what is recommended. Results suggest that overweight and obesity are an additional health burden to PLWH in our sample and that their daily dietary practices are not meeting the U.S. government-recommended nutritional standards.

  14. Improved InGaN/GaN quantum wells on treated GaN template with a Ga-rich GaN interlayer

    International Nuclear Information System (INIS)

    Fang, Zhilai; Shen, Xiyang; Wu, Zhengyuan; Zhang, Tong-Yi

    2015-01-01

    Treated GaN template was achieved by in situ droplet epitaxy of a Ga-rich GaN interlayer on the conventional GaN template. InGaN/GaN quantum wells (QWs) were grown on the conventional and treated GaN templates under the same growth conditions and then comprehensively characterized. The indium homogeneity in the InGaN layers and the interface sharpness between InGaN and GaN layers of the InGaN/GaN QWs on the treated GaN template were significantly improved. The emission intensity from the InGaN/GaN QWs on the treated GaN template was enhanced by 20% than that on the conventional GaN template, which was attributed to the strain reduction and the improvement in crystalline quality. (copyright 2015 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Universidade comunitária e avaliação institucional: o caso das universidades comunitárias gaúchas The community university and its institutional evaluation: a case study of the community universities of the State of Rio Grande do Sul Brazil

    Directory of Open Access Journals (Sweden)

    Rafael Ângelo Bunhi Pinto

    2009-03-01

    Full Text Available A década de 1980 marcou uma série de transformações na educação superior, dando início aos debates sobre um novo modelo de instituição de educação superior - a universidade comunitária - e, também, de uma cultura avaliativa em nosso país. Nas décadas seguintes, esse modelo de instituição buscou seu fortalecimento no país, mostrando suas características primordiais e suas diferenças em relação àquelas mantidas pelo poder público e, também, àquelas instituições estritamente privadas. Essas Instituições se desenvolveram em várias regiões, com ênfase no sul do país, onde criaram o Consórcio das Universidades Comunitárias Gaúchas - COMUNG. As Instituições participantes desse consórcio, dentre outras atividades, desenvolveram um mecanismo próprio de avaliação, que se preocupou com o (repensar de suas atividades de ensino, pesquisa, extensão e gestão. O objetivo desta pesquisa será buscar respostas ao entendimento da avaliação institucional pelas Universidades Comunitárias gaúchas e verificar como a questão da responsabilidade social se insere em seu processo de avaliação. Também, objetivará estudar os processos históricos e as necessidades de adaptações que se fizeram necessárias quando da criação do Sistema Nacional de Avaliação da Educação Superior - SINAES.In the 1980s higher education experienced a series of transformations, commencing the debates about a new model of higher education institutions - the community university - and also of an evaluative culture in Brazil. During the following decades, this model of institution tried to strengthen its bases in the higher education scenario of the country, showing its primary characteristics and its differences from the public and the private branches of higher education. These universities were instituted in various regions of the country with emphasis in the southern region, where a Consortium of the Gaucho Community Universities

  16. The Impact of "Old-Wave" McCarthyism at Four Private Black Colleges and Universities in Atlanta, Georgia

    Science.gov (United States)

    Williams, Patricia Coleman

    2017-01-01

    Decades after the term "McCarthyism" was first coined, it continues to be used to describe those who prey on the fears of Americans to discriminate against others. In the post-world War years, and well into the sixties, it was Communism. Today, it is "terrorism," and an irrational fear of Muslims. The word is used to describe…

  17. Drinking water turbidity and emergency department visits for gastrointestinal illness in Atlanta, 1993-2004.

    Science.gov (United States)

    Tinker, Sarah C; Moe, Christine L; Klein, Mitchel; Flanders, W Dana; Uber, Jim; Amirtharajah, Appiah; Singer, Philip; Tolbert, Paige E

    2010-01-01

    The extent to which drinking water turbidity measurements indicate the risk of gastrointestinal illness is not well understood. Despite major advances in drinking water treatment and delivery, infectious disease can still be transmitted through drinking water in the United States, and it is important to have reliable indicators of microbial water quality to inform public health decisions. The objective of our study was to assess the relationship between gastrointestinal illness, quantified through emergency department visits, and drinking water quality, quantified as raw water and filtered water turbidity measured at the treatment plant. We examined the relationship between turbidity levels of raw and filtered surface water measured at eight major drinking water treatment plants in the metropolitan area of Atlanta, Georgia, and over 240,000 emergency department visits for gastrointestinal illness during 1993-2004 among the population served by these plants. We fit Poisson time-series statistical regression models that included turbidity in a 21-day distributed lag and that controlled for meteorological factors and long-term time trends. For filtered water turbidity, the results were consistent with no association with emergency department visits for gastrointestinal illness. We observed a modest association between raw water turbidity and emergency department visits for gastrointestinal illness. Our results suggest that source water quality may contribute modestly to endemic gastrointestinal illness in the study area. The association between turbidity and emergency department visits for gastrointestinal illness was only observed when raw water turbidity was considered; filtered water turbidity may not serve as a reliable indicator of modest pathogen risk at all treatment plants.

  18. DRINKING WATER TURBIDITY AND EMERGENCY DEPARTMENT VISITS FOR GASTROINTESTINAL ILLNESS IN ATLANTA, 1993 – 2004

    Science.gov (United States)

    Tinker, Sarah C.; Moe, Christine L.; Klein, Mitchel; Flanders, W. Dana; Uber, Jim; Amirtharajah, Appiah; Singer, Philip; Tolbert, Paige E.

    2013-01-01

    Background The extent to which drinking water turbidity measurements indicate the risk of gastrointestinal illness is not well-understood. Despite major advances in drinking water treatment and delivery, infectious disease can still be transmitted through drinking water in the U.S., and it is important to have reliable indicators of microbial water quality to inform public health decisions. The objective of our study was to assess the relationship between gastrointestinal illness, quantified through emergency department visits, and drinking water quality, quantified as raw water and filtered water turbidity measured at the treatment plant. Methods We examined the relationship between turbidity levels of raw and filtered surface water measured at eight major drinking water treatment plants in the metropolitan area of Atlanta, Georgia, and over 240 000 emergency department visits for gastrointestinal illness during 1993–2004 among the population served by these plants. We fit Poisson time-series statistical regression models that included turbidity in a 21-day distributed lag and that controlled for meteorological factors and long-term time trends. Results For filtered water turbidity, the results were consistent with no association with emergency department visits for gastrointestinal illness. We observed a modest association between raw water turbidity and emergency department visits for gastrointestinal illness. This association was not observed for all treatment plants in plant-specific analyses. Conclusions Our results suggest that source water quality may contribute modestly to endemic gastrointestinal illness in the study area. The association between turbidity and emergency department visits for gastrointestinal illness was only observed when raw water turbidity was considered; filtered water turbidity may not serve as a reliable indicator of modest pathogen risk at all treatment plants. PMID:18941478

  19. New Atlanta Classification of acute pancreatitis in intensive care unit: Complications and prognosis.

    Science.gov (United States)

    Pintado, María-Consuelo; Trascasa, María; Arenillas, Cristina; de Zárate, Yaiza Ortiz; Pardo, Ana; Blandino Ortiz, Aaron; de Pablo, Raúl

    2016-05-01

    The updated Atlanta Classification of acute pancreatitis (AP) in adults defined three levels of severity according to the presence of local and/or systemic complications and presence and length of organ failure. No study focused on complications and mortality of patients with moderately severe AP admitted to intensive care unit (ICU). The main aim of this study is to describe the complications developed and outcomes of these patients and compare them to those with severe AP. Prospective, observational study. We included patients with acute moderately severe or severe AP admitted in a medical-surgical ICU during 5years. We collected demographic data, admission criteria, pancreatitis etiology, severity of illness, presence of organ failure, local and systemic complications, ICU length of stay, and mortality. Fifty-six patients were included: 12 with moderately severe AP and 44 with severe. All patients developed some kind of complications without differences on complications rate between moderately severe or severe AP. All the patients present non-infectious systemic complications, mainly acute respiratory failure and hemodynamic failure. 82.1% had an infectious complication, mainly non-pancreatic infection (66.7% on moderately severe AP vs. 79.5% on severe, p=0.0443). None of the patients with moderately severe AP died during their intensive care unit stay vs. 29.5% with severe AP (p=0.049). Moderately severe AP has a high rate of complications with similar rates to patients with severe AP admitted to ICU. However, their ICU mortality remains very low, which supports the existence of this new group of pancreatitis according to their severity. Copyright © 2016 European Federation of Internal Medicine. Published by Elsevier B.V. All rights reserved.

  20. From Olympia to Atlanta: a cultural-historical perspective on diet and athletic training.

    Science.gov (United States)

    Grivetti, L E; Applegate, E A

    1997-05-01

    Greek and Roman writers described diet and training of Olympic athletes. Lucian (A.D. 120-ca. 180) described distance and speed work in runners; Galen (A.D. 131-201) recommended ball-related exercises to train vision and the body; Philostratos (A.D. 170-249) suggested cross training by endurance running, weight training, and wrestling with animals. The ancient Greek training system, the tetrad (eta tau epsilon tau rho alpha sigma), was a four-day cycle with each day devoted to a different activity. Diogenes Laertius (died A.D. 222) wrote that Greek athletes trained on dried figs, moist cheese and wheat; then the pattern changed and focused on meat. Epictetus (2nd century A.D.) wrote that Olympic victors avoided desserts and cold water and took wine sparingly. Philostratos deprecated athletic diet in his era, a pattern based on white bread sprinkled with poppy seeds, fish and pork. Americans at the XIth Olympiad in Berlin (1936) consumed beefsteak with average daily intake of 125 grams of butter or cotton oil, three eggs, custard for dessert and 1.5 L of milk. The American pattern at Berlin was characterized by ad libitum intake of white bread, dinner rolls, fresh vegetables and salads. At Atlanta, more than 5 million meals will be served during the Olympic festival. The highly varied menu will include fresh vegetables and dips; fruits, cheeses and breads; salads; pasta, rice and fruit salads; soups; meat and seafood entrees; hot vegetables; desserts; and beverages. American Southern specialties will be served.

  1. Racial disparities in travel time to radiotherapy facilities in the Atlanta metropolitan area.

    Science.gov (United States)

    Peipins, Lucy A; Graham, Shannon; Young, Randall; Lewis, Brian; Flanagan, Barry

    2013-07-01

    Low-income women with breast cancer who rely on public transportation may have difficulty in completing recommended radiation therapy due to inadequate access to radiation facilities. Using a geographic information system (GIS) and network analysis we quantified spatial accessibility to radiation treatment facilities in the Atlanta, Georgia metropolitan area. We built a transportation network model that included all bus and rail routes and stops, system transfers and walk and wait times experienced by public transportation system travelers. We also built a private transportation network to model travel times by automobile. We calculated travel times to radiation therapy facilities via public and private transportation from a population-weighted center of each census tract located within the study area. We broadly grouped the tracts by low, medium and high household access to a private vehicle and by race. Facility service areas were created using the network model to map the extent of areal coverage at specified travel times (30, 45 and 60 min) for both public and private modes of transportation. The median public transportation travel time to the nearest radiotherapy facility was 56 min vs. approximately 8 min by private vehicle. We found that majority black census tracts had longer public transportation travel times than white tracts across all categories of vehicle access and that 39% of women in the study area had longer than 1 h of public transportation travel time to the nearest facility. In addition, service area analyses identified locations where the travel time barriers are the greatest. Spatial inaccessibility, especially for women who must use public transportation, is one of the barriers they face in receiving optimal treatment. Published by Elsevier Ltd.

  2. Social, economic, and political processes that create built environment inequities: perspectives from urban African Americans in Atlanta.

    Science.gov (United States)

    Redwood, Yanique; Schulz, Amy J; Israel, Barbara A; Yoshihama, Mieko; Wang, Caroline C; Kreuter, Marshall

    2010-01-01

    Growing evidence suggests that the built environment features found in many high-poverty urban areas contribute to negative health outcomes. Both built environment hazards and negative health outcomes disproportionately affect poor people of color. We used community-based participatory research and Photovoice in inner-city Atlanta to elicit African Americans' perspectives on their health priorities. The built environment emerged as a critical factor, impacting physical and mental health outcomes. We offer a conceptual model, informed by residents' perspectives, linking social, economic, and political processes to built environment and health inequities. Research, practice, and policy implications are discussed within an environmental justice framework.

  3. Guest Comment: Universal Language Requirement.

    Science.gov (United States)

    Sherwood, Bruce Arne

    1979-01-01

    Explains that reading English among Scientists is almost universal, however, there are enormous problems with spoken English. Advocates the use of Esperanto as a viable alternative, and as a language requirement for graduate work. (GA)

  4. Shoal bass hybridization in the Chattahoochee River Basin near Atlanta, Georgia

    Science.gov (United States)

    Taylor, Andrew T.; Tringali, Michael D.; O'Rourke, Patrick M.; Long, James M.

    2018-01-01

    The shoal bass (Micropterus cataractae) is a sportfish endemic to the Apalachicola-Chattahoochee-Flint Basin of the southeastern United States. Introgression with several non-native congeners poses a pertinent threat to shoal bass conservation, particularly in the altered habitats of the Chattahoochee River. Our primary objective was to characterize hybridization in shoal bass populations near Atlanta, Georgia, including a population inhabiting Big Creek and another in the main stem Chattahoochee River below Morgan Falls Dam (MFD). A secondary objective was to examine the accuracy of phenotypic identifications below MFD based on a simplified suite of characters examined in the field. Fish were genotyped with 16 microsatellite DNA markers, and results demonstrated that at least four black bass species were involved in introgressive hybridization. Of 62 fish genotyped from Big Creek, 27% were pure shoal bass and 65% represented either F1 hybrids of shoal bass x smallmouth bass (M. dolomieu) or unidirectional backcrosses towards shoal bass. Of 29 fish genotyped below MFD and downstream at Cochran Shoals, 45% were pure shoal bass. Six hybrid shoal bass included both F1 hybrids and backcrosses with non-natives including Alabama bass (M. henshalli), spotted bass (M. punctulatus), and smallmouth bass. Shoal bass alleles comprised only 21% of the overall genomic composition in Big Creek and 31% below MFD (when combined with Cochran Shoals). Phenotypic identification below MFD resulted in an overall correct classification rate of 86% when discerning pure shoal bass from all other non-natives and hybrids. Results suggest that although these two shoal bass populations feature some of the highest introgression rates documented, only a fleeting opportunity may exist to conserve pure shoal bass in both populations. Continued supplemental stocking of pure shoal bass below MFD appears warranted to thwart increased admixture among multiple black bass taxa, and a similar stocking

  5. They "miss more than anything their normal life back home": masculinity and extramarital sex among Mexican migrants in Atlanta.

    Science.gov (United States)

    Hirsch, Jennifer S; Muñoz-Laboy, Miguel; Nyhus, Christina M; Yount, Kathryn M; Bauermeister, José A

    2009-03-01

    Gender has been recognized as a significant influence on sexual health behaviors. Labor migration presents an important context of vulnerability for sexual health. To understand how the context of migration affects risk-related practices, both cultural and social aspects of gender need to be explored. In the quantitative part of a mixed-methods study conducted in 1999 in Atlanta, 187 Mexican migrant men were asked about their demographic characteristics; sexual history; migration motivations; substance use; social support; leisure-time activities; and ideas about masculinity, sexuality and marriage. Multivariate regression analyses were conducted to test the association between these domains and men's number of partners since their arrival in Atlanta. Number of partners was positively associated with owning a home in Mexico; number of trips back to Mexico; social network size; having had a sex worker as a partner; and going out dancing and to strip clubs on weekends (coefficients, 0.3-4.1). It was negatively associated with age, education, contact with social network members and feeling that sex is tied to emotional intimacy (-0.4 to -1.0). Programs must acknowledge and target migrant men's social networks and the spaces in which they may encounter risky sexual situations. Multilevel strategies, such as the development of more health-enhancing community spaces and the promotion of safer sexual practices should form part of comprehensive efforts to reduce sexual risk among migrant men.

  6. Social vulnerability to heat in Greater Atlanta, USA: spatial pattern of heat, NDVI, socioeconomics and household composition

    Science.gov (United States)

    Sim, Sunhui

    2017-10-01

    The purpose of the article is evaluating spatial patterns of social vulnerability to heat in Greater Atlanta in 2015. The social vulnerability to heat is an index of socioeconomic status, household composition, land surface temperature and normalized differential vegetation index (NDVI). Land surface temperature and NDVI were derived from the red, NIR and thermal infrared (TIR) of a Landsat OLI/TIRS images collected on September 14, 2015. The research focus is on the variation of heat vulnerability in Greater Atlanta. The study found that heat vulnerability is highly clustered spatially, resulting in "hot spots" and "cool spots". The results show significant health disparities. The hotspots of social vulnerability to heat occurred in neighborhoods with lower socioeconomic status as measured by low education, low income and more poverty, greater proportion of elderly people and young children. The findings of this study are important for identifying clusters of heat vulnerability and the relationships with social factors. These significant results provide a basis for heat intervention services.

  7. 67Ga lung scan

    International Nuclear Information System (INIS)

    Niden, A.H.; Mishkin, F.S.; Khurana, M.M.L.; Pick, R.

    1977-01-01

    Twenty-three patients with clinical signs of pulmonary embolic disease and lung infiltrates were studied to determine the value of gallium citrate 67 Ga lung scan in differentiating embolic from inflammatory lung disease. In 11 patients without angiographically proved embolism, only seven had corresponding ventilation-perfusion defects compatible with inflammatory disease. In seven of these 11 patients, the 67 Ga concentration indicated inflammatory disease. In the 12 patients with angiographically proved embolic disease, six had corresponding ventilation-perfusion defects compatible with inflammatory disease. None had an accumulation of 67 Ga in the area of pulmonary infiltrate. Thus, ventilation-perfusion lung scans are of limited value when lung infiltrates are present. In contrast, the accumulation of 67 Ga in the lung indicates an inflammatory process. Gallium imaging can help select those patients with lung infiltrates who need angiography

  8. GaN/AlGaN-based UV photodetectors with performances exceeding the PMTS

    OpenAIRE

    Tut, Turgut

    2008-01-01

    Ankara : The Department of Physics and the Institute of Engineering and Science of Bilkent University, 2008. Thesis (Ph.D.) -- Bilkent University, 2008. Includes bibliographical references leaves 73-80. The recent developments in high Al-content AlxGa1−xN material growth technology made it possible to fabricate high performance solar-blind photodetectors operating in the ultraviolet (UV) spectral region with improved receiver sensitivity, low noise, low dark current density,...

  9. Discrete bipolar universal integrals

    Czech Academy of Sciences Publication Activity Database

    Greco, S.; Mesiar, Radko; Rindone, F.

    2014-01-01

    Roč. 252, č. 1 (2014), s. 55-65 ISSN 0165-0114 R&D Projects: GA ČR GAP402/11/0378 Institutional support: RVO:67985556 Keywords : bipolar integral * universal integral * Choquet integral Subject RIV: BA - General Mathematics Impact factor: 1.986, year: 2014 http://library.utia.cas.cz/separaty/2014/E/mesiar-0432224.pdf

  10. A Study of the Role of Clouds in the Relationship Between Land Use/Land Cover and the Climate and Air Quality of the Atlanta Area

    Science.gov (United States)

    Kidder, Stanley Q.; Hafner, Jan

    2001-01-01

    The goal of Project ATLANTA is to derive a better scientific understanding of how land cover changes associated with urbanization affect climate and air quality. In this project the role that clouds play in this relationship was studied. Through GOES satellite observations and RAMS modeling of the Atlanta area, we found that in Atlanta (1) clouds are more frequent than in the surrounding rural areas; (2) clouds cool the surface by shading and thus tend to counteract the warming effect of urbanization; (3) clouds reflect sunlight, which might other wise be used to produce ozone; and (4) clouds decrease biogenic emission of ozone precursors, and they probably decrease ozone concentration. We also found that mesoscale modeling of clouds, especially of small, summertime clouds, needs to be improved and that coupled mesoscale and air quality models are needed to completely understand the mediating role that clouds play in the relationship between land use/land cover change and the climate and air quality of Atlanta. It is strongly recommended that more cities be studied to strengthen and extend these results.

  11. Task Force on Women, Minorities and the Handicapped in Science and Technology: Executive Session. Report of the Proceedings (Atlanta, Georgia, March 3, 1988).

    Science.gov (United States)

    Task Force on Women, Minorities, and the Handicapped in Science and Technology, Washington, DC.

    The Task Force on Women, Minorities, and the Handicapped in Science and Technology was established by the U.S. Congress in Public Law 99-383 with the purpose of developing a long-range plan for broadening participation in science and engineering. Public hearings were held in Albuquerque (New Mexico), Atlanta (Georgia), Baltimore (Maryland), Boston…

  12. Thermal Investigation of Three-Dimensional GaN-on-SiC High Electron Mobility Transistors

    Science.gov (United States)

    2017-07-01

    University of L’Aquila, (2011). 23 Rao, H. & Bosman, G. Hot-electron induced defect generation in AlGaN/GaN high electron mobility transistors. Solid...AFRL-RY-WP-TR-2017-0143 THERMAL INVESTIGATION OF THREE- DIMENSIONAL GaN-on-SiC HIGH ELECTRON MOBILITY TRANSISTORS Qing Hao The University of Arizona...clarification memorandum dated 16 Jan 09. This report is available to the general public, including foreign nationals. Copies may be obtained from the

  13. Cummings/Ju - Harvard; Emory | Division of Cancer Prevention

    Science.gov (United States)

    Principal Investigator: Richard D Cummings, PhDInstitution: Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA Principal Investigator: Tongzhong Ju, MD, PhDInstitution: Emory University, Atlanta, GA |

  14. High resolution study of proton resonances in 65Ga and 67Ga

    International Nuclear Information System (INIS)

    Sales, K.B.

    1980-01-01

    Differential cross sections were measured for 64 Zn(p,p) from 2.50 to 3.24 MeV and for 66 Zn(p,p) from 2.60 to 3.26 MeV at laboratory angles of 90 0 , 105 0 , 135 0 , and 160 0 . These experiments were performed with the Triangle Universities Nuclear Laboratory 3 MV Van de Graaff accelerator and associated electrostatic analyzer-homogenizer system. The total overall energy resolution was 420 to 525 eV for 64 Zn(p,p) and 360 to 405 eV for 66 Zn(p,p). Resonances observed in the excitation functions were analyzed with a multilevel R-Matrix formalism. Resonance energies, spins, parities, and elastic widths were extracted for 39 resonances in 65 Ga and 148 resonances in 67 Ga. The l = 0 proton strength functions were calculated for 64 Zn and 66 Zn. The s-wave strength function shows an increase for A=66, which is consistent with earlier results from (p,n) cross section studies. Statistical properties of the 1/2 + resonances in 65 Ga and 67 Ga were examined. The spacing and reduced width distributions were compared with the Wigner and Porter-Thomas distributions, respectively. This comparison indicates that 50% of the 1/2 + resonances were missed in 65 Ga and that 70% of the 1/2 + resonances were missed in 67 Ga. The observed s-wave level densities in 65 Ga and 67 Ga are compared with predictions from conventional level density models. The analogs of the 0.867 MeV, the 0.910 MeV, and the 1.370 MeV states of 65 Zn are observed in 65 Ga; the analogs of the 0.093 MeV and the 0.394 MeV states of 67 Zn are observed in 67 Ga. The analog states in 65 Ga were fragmented into only two or three resonances, while the two analog states in 67 Ga were highly fragmented. Fits to the fine structure distributions of these two analogs were obtained and the resulting parameters compared with the Robson model. Coulomb energies were extracted for these five analogs

  15. Creep-fatigue interaction at high temperature; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991

    Science.gov (United States)

    Haritos, George K.; Ochoa, O. O.

    Various papers on creep-fatigue interaction at high temperature are presented. Individual topics addressed include: analysis of elevated temperature fatigue crack growth mechanisms in Alloy 718, physically based microcrack propagation laws for creep-fatigue-environment interaction, in situ SEM observation of short fatigue crack growth in Waspaloy at 700 C under cyclic and dwell conditions, evolution of creep-fatigue life prediction models, TMF design considerations in turbine airfoils of advanced turbine engines. Also discussed are: high temperature fatigue life prediction computer code based on the total strain version of strainrange partitioning, atomic theory of thermodynamics of internal variables, geometrically nonlinear analysis of interlaminar stresses in unsymmetrically laminated plates subjected to uniform thermal loading, experimental investigation of creep crack tip deformation using moire interferometry. (For individual items see A93-31336 to A93-31344)

  16. ASSOCIATIONS BETWEEN OUTDOOR PARTICULATE (PM2.5) CONCENTRATIONS AND GASEOUS CO-POLLUTANT EXPOSURE LEVELS FOR COPD AND MI COHORTS IN ATLANTA, GA

    Science.gov (United States)

    Epidemiological studies indicate that daily ambient particulate matter (PM2.5) concentrations are associated with increased mortality, hospital admissions, and respiratory and cardiovascular effects. It is possible that the observed significant associations are the result of c...

  17. AlGaN/GaN double-channel HEMT

    International Nuclear Information System (INIS)

    Quan Si; Hao Yue; Ma Xiaohua; Zheng Pengtian; Xie Yuanbin

    2010-01-01

    The fabrication of AlGaN/GaN double-channel high electron mobility transistors on sapphire substrates is reported. Two carrier channels are formed in an AlGaN/GaN/AlGaN/GaN multilayer structure. The DC performance of the resulting double-channel HEMT shows a wider high transconductance region compared with single-channel HEMT. Simulations provide an explanation for the influence of the double-channel on the high transconductance region. The buffer trap is suggested to be related to the wide region of high transconductance. The RF characteristics are also studied. (semiconductor devices)

  18. Racial/ethnic variations in the prevalence of selected major birth defects, metropolitan Atlanta, 1994-2005.

    Science.gov (United States)

    Kucik, James E; Alverson, Clinton J; Gilboa, Suzanne M; Correa, Adolfo

    2012-01-01

    Birth defects are the leading cause of infant mortality and are responsible for substantial child and adult morbidity. Documenting the variation in prevalence of birth defects among racial/ethnic subpopulations is critical for assessing possible variations in diagnosis, case ascertainment, or risk factors among such groups. We used data from the Metropolitan Atlanta Congenital Defects Program, a population-based birth defects registry with active case ascertainment. We estimated the racial/ethnic variation in prevalence of 46 selected major birth defects among live births, stillbirths, and pregnancy terminations at >20 weeks gestation among mothers residing in the five central counties of metropolitan Atlanta between 1994 and 2005, adjusting for infant sex, maternal age, gravidity, and socioeconomic status (SES). We also explored SES as a potential effect measure modifier. Compared with births to non-Hispanic white women, births to non-Hispanic black women had a significantly higher prevalence of five birth defects and a significantly lower prevalence of 10 birth defects, while births to Hispanic women had a significantly higher prevalence of four birth defects and a significantly lower prevalence of six birth defects. The racial/ethnic disparities in the prevalence of some defects varied by SES, but no clear pattern emerged. Racial/ethnic disparities were suggested in 57% of included birth defects. Disparities in the prevalence of birth defects may result from different underlying genetic susceptibilities; exposure to risk factors; or variability in case diagnosis, ascertainment, or reporting among the subpopulations examined. Policies that improve early diagnosis of birth defects could reduce associated morbidity and mortality.

  19. GaAs strip detectors: the Australian production program

    International Nuclear Information System (INIS)

    Butcher, K.S.A.; Alexiev, D.

    1995-01-01

    The Australian High Energy Physics consortium (composed of the University of Melbourne, the University of Sydney and ANSTO) has been investigating the possibility of producing a large area wheel of SI GaAs detectors for the ATLAS detector array. To help assess the extent of Australia's role in this venture a few SI GaAs microstrip detectors are to be manufactured under contract by the CSIRO division of Radiophysics GaAs IC Prototyping Facility. The planned production of the devices is discussed. First, the reasons for producing the detectors here in Australia are examined, then some basic characteristics of the material are considered, and finally details are provided of the design used for the manufacture of the devices. Two sets of detectors will be produced using the standard Glasgow production recipe; SIGaAs and GaN. The Glasgow mask set is being used as a benchmark against which to compare the Australian devices

  20. Comparison of trap characteristics between AlGaN/GaN and AlGaN/InGaN/GaN heterostructure by frequency dependent conductance measurement

    International Nuclear Information System (INIS)

    Chakraborty, Apurba; Biswas, Dhrubes

    2015-01-01

    Frequency dependent conductance measurement is carried out to observe the trapping effect in AlGaN/InGaN/GaN double heterostructure and compared that with conventional AlGaN/GaN single heterostructure. It is found that the AlGaN/InGaN/GaN diode structure does not show any trapping effect, whereas single heterostructure AlGaN/GaN diode suffers from two kinds of trap energy states in near depletion to higher negative voltage bias region. This conductance behaviour of AlGaN/InGaN/GaN heterostructure is owing to more Fermi energy level shift from trap energy states at AlGaN/InGaN junction compare to single AlGaN/GaN heterostructure and eliminates the trapping effects. Analysis yielded interface trap energy state in AlGaN/GaN is to be with time constant of (33.8–76.5) μs and trap density of (2.38–0.656) × 10 12  eV −1  cm −2 in −3.2 to −4.8 V bias region, whereas for AlGaN/InGaN/GaN structure no interface energy states are found and the extracted surface trap energy concentrations and time constants are (5.87–4.39) ×10 10  eV −1  cm −2 and (17.8–11.3) μs, respectively, in bias range of −0.8–0.0 V

  1. GaN transistors for efficient power conversion

    CERN Document Server

    Lidow, Alex; de Rooij, Michael; Reusch, David

    2014-01-01

    The first edition of GaN Transistors for Efficient Power Conversion was self-published by EPC in 2012, and is currently the only other book to discuss GaN transistor technology and specific applications for the technology. More than 1,200 copies of the first edition have been sold through Amazon or distributed to selected university professors, students and potential customers, and a simplified Chinese translation is also available. The second edition has expanded emphasis on applications for GaN transistors and design considerations. This textbook provides technical and application-focused i

  2. GaInSn usage in the research laboratory

    International Nuclear Information System (INIS)

    Morley, N. B.; Burris, J.; Cadwallader, L. C.; Nornberg, M. D.

    2008-01-01

    GaInSn, a eutectic alloy, has been successfully used in the Magneto-Thermofluid Research Laboratory at the University of California-Los Angeles and at the Princeton Plasma Physics Laboratory for the past six years. This paper describes the handling and safety of GaInSn based on the experience gained in these institutions, augmented by observations from other researchers in the liquid metal experimental community. GaInSn is an alloy with benign properties and shows considerable potential in liquid metal experimental research and cooling applications

  3. 2015 Lowndes County (GA) Lidar

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — TASK NAME: NOAA OCM Lidar for Lowndes County, GA with the option to Collect Lidar in Cook and Tift Counties, GA Lidar Data Acquisition and Processing Production Task...

  4. Strain Balanced AlGaN/GaN/AlGaN nanomembrane HEMTs.

    Science.gov (United States)

    Chang, Tzu-Hsuan; Xiong, Kanglin; Park, Sung Hyun; Yuan, Ge; Ma, Zhenqiang; Han, Jung

    2017-07-25

    Single crystal semiconductor nanomembranes (NM) are important in various applications such as heterogeneous integration and flexible devices. This paper reports the fabrication of AlGaN/GaN NMs and NM high electron mobility transistors (HEMT). Electrochemical etching is used to slice off single-crystalline AlGaN/GaN layers while preserving their microstructural quality. A double heterostructure design with a symmetric strain profile is employed to ensure minimal residual strain in freestanding NMs after release. The mobility of the two-dimensional electron gas (2DEG), formed by the AlGaN/GaN heterostructure, is noticeably superior to previously reported values of many other NMs. AlGaN/GaN nanomembrane HEMTs are fabricated on SiO 2 and flexible polymeric substrates. Excellent electrical characteristics, including a high ON/OFF ratio and transconductance, suggest that III-Nitrides nanomembranes are capable of supporting high performance applications.

  5. Urban Growth Areas, This Layer represents the current Urbanized Area for Atlanta as defined by the U.S. Census Bureau. An Urbanized Area is a concept used by the U.S. Census Bureau to measure the population, land area and population density of a built-up or continuously deve, Published in 2000, 1:100000 (1in=8333ft) scale, Atlanta Regional Commission.

    Data.gov (United States)

    NSGIC Regional | GIS Inventory — Urban Growth Areas dataset current as of 2000. This Layer represents the current Urbanized Area for Atlanta as defined by the U.S. Census Bureau. An Urbanized Area...

  6. Type III and N universal spacetimes

    Czech Academy of Sciences Publication Activity Database

    Hervik, S.; Pravda, Vojtěch; Pravdová, Alena

    2014-01-01

    Roč. 31, č. 21 (2014), s. 215005 ISSN 0264-9381 R&D Projects: GA ČR GA13-10042S Institutional support: RVO:67985840 Keywords : universal spacetimes * generalized gravity * exact solutions Subject RIV: BA - General Mathematics Impact factor: 3.168, year: 2014 http://iopscience.iop.org/0264-9381/31/21/215005/article

  7. Source apportionment of submicron organic aerosol collected from Atlanta, Georgia, during 2014-2015 using the aerosol chemical speciation monitor (ACSM)

    Science.gov (United States)

    Rattanavaraha, Weruka; Canagaratna, Manjula R.; Budisulistiorini, Sri Hapsari; Croteau, Philip L.; Baumann, Karsten; Canonaco, Francesco; Prevot, Andre S. H.; Edgerton, Eric S.; Zhang, Zhenfa; Jayne, John T.; Worsnop, Douglas R.; Gold, Avram; Shaw, Stephanie L.; Surratt, Jason D.

    2017-10-01

    The Aerodyne Aerosol Chemical Speciation Monitor (ACSM) was redeployed at the Jefferson Street (JST) site in downtown Atlanta, Georgia (GA) for 1 year (March 20, 2014-February 08, 2015) to chemically characterize non-refractory submicron particulate matter (NR-PM1) in near real-time and to assess whether organic aerosol (OA) types and amounts change from year-to-year. Submicron organic aerosol (OA) mass spectra were analyzed by season using multilinear engine (ME-2) to apportion OA subtypes to potential sources and chemical processes. A suite of real-time collocated measurements from the Southeastern Aerosol Research and Characterization (SEARCH) network was compared with ME-2 factor solutions to aid in the interpretation of OA subtypes during each season. OA tracers measured from high-volume filter samples using gas chromatography interfaced with electron ionization-mass spectrometry (GC/EI-MS) also aided in identifying OA sources. The initial application of ME-2 to the yearlong ACSM dataset revealed that OA source apportionment by season was required to better resolve sporadic OA types. Spring and fall OA mass spectral datasets were separated into finer periods to capture potential OA sources resulting from non-homogeneous emissions during transitioning periods. NR-PM1 was highest in summer (16.7 ± 8.4 μg m-3) and lowest in winter (8.0 ± 5.7 μg m-3), consistent with prior studies. OA dominated NR-PM1 mass (56-74% on average) in all seasons. Hydrocarbon-like OA (HOA) from primary emissions was observed in all seasons, averaging 5-22% of total OA mass. Strong correlations of HOA with carbon monoxide (CO) (R = 0.71-0.88) and oxides of nitrogen (NOx) (R = 0.55-0.79) indicated that vehicular traffic was the likely source. Biomass burning OA (BBOA) was observed in all seasons, with lower contributions (2%) in summer and higher in colder seasons (averaging 8-20% of total OA mass). BBOA correlated strongly with levoglucosan (R = 0.78-0.95) during colder seasons

  8. Pol?tica migratoria y condiciones laborales: un estudio de caso comparado acerca de los colombianos en situaci?n irregular en las ciudades de Atlanta y Miami

    OpenAIRE

    Parra Mora, Laura Camila

    2016-01-01

    Este trabajo tiene por objetivo determinar la incidencia de las pol?ticas migratorias de las administraciones Bush y Obama en las condiciones laborales de los colombianos indocumentados en las ciudades de Atlanta y Miami. La hip?tesis planteada afirma que la transici?n que ha tenido la pol?tica migratoria estadounidense, ha deteriorado las condiciones laborales de los colombianos indocumentados. El art?culo se divide en cuatro apartados. Primeramente, define los aspectos conceptuales a tener ...

  9. Polarization-engineered GaN/InGaN/GaN tunnel diodes

    International Nuclear Information System (INIS)

    Krishnamoorthy, Sriram; Nath, Digbijoy N.; Akyol, Fatih; Park, Pil Sung; Esposto, Michele; Rajan, Siddharth

    2010-01-01

    We report on the design and demonstration of polarization-engineered GaN/InGaN/GaN tunnel junction diodes with high current density and low tunneling turn-on voltage. Wentzel-Kramers-Brillouin calculations were used to model and design tunnel junctions with narrow band gap InGaN-based barrier layers. N-polar p-GaN/In 0.33 Ga 0.67 N/n-GaN heterostructure tunnel diodes were grown using molecular beam epitaxy. Efficient interband tunneling was achieved close to zero bias with a high current density of 118 A/cm 2 at a reverse bias of 1 V, reaching a maximum current density up to 9.2 kA/cm 2 . These results represent the highest current density reported in III-nitride tunnel junctions and demonstrate the potential of III-nitride tunnel devices for a broad range of optoelectronic and electronic applications.

  10. The mobility of food retailers: How proximity to SNAP authorized food retailers changed in Atlanta during the Great Recession.

    Science.gov (United States)

    Shannon, Jerry; Bagwell-Adams, Grace; Shannon, Sarah; Lee, Jung Sun; Wei, Yangjiaxin

    2018-07-01

    Retailer mobility, defined as the shifting geographic patterns of retail locations over time, is a significant but understudied factor shaping neighborhood food environments. Our research addresses this gap by analyzing changes in proximity to SNAP authorized chain retailers in the Atlanta urban area using yearly data from 2008 to 2013. We identify six demographically similar geographic clusters of census tracts in our study area based on race and economic variables. We use these clusters in exploratory data analysis to identify how proximity to the twenty largest retail food chains changed during this period. We then use fixed effects models to assess how changing store proximity is associated with race, income, participation in SNAP, and population density. Our results show clear differences in geographic distribution between store categories, but also notable variation within each category. Increasing SNAP enrollment predicted decreased distances to almost all small retailers but increased distances to many large retailers. Our chain-focused analysis underscores the responsiveness of small retailers to changes in neighborhood SNAP participation and the value of tracking chain expansion and contraction in markets across time. Better understanding of retailer mobility and the forces that drive it can be a productive avenue for future research. Copyright © 2018 Elsevier Ltd. All rights reserved.

  11. Evaluation of two-year Jewish genetic disease screening program in Atlanta: insight into community genetic screening approaches.

    Science.gov (United States)

    Shao, Yunru; Liu, Shuling; Grinzaid, Karen

    2015-04-01

    Improvements in genetic testing technologies have led to the development of expanded carrier screening panels for the Ashkenazi Jewish population; however, there are major inconsistencies in current screening practices. A 2-year pilot program was launched in Atlanta in 2010 to promote and facilitate screening for 19 Jewish genetic diseases. We analyzed data from this program, including participant demographics and outreach efforts. This retrospective analysis is based on a de-identified dataset of 724 screenees. Data were obtained through medical chart review and questionnaires and included demographic information, screening results, response to outreach efforts, and follow-up behavior and preferences. We applied descriptive analysis, chi-square tests, and logistic regression to analyze the data and compare findings with published literature. The majority of participants indicated that they were not pregnant or did not have a partner who was pregnant were affiliated with Jewish organizations and reported 100 % AJ ancestry. Overall, carrier frequency was 1 in 3.9. Friends, rabbis, and family members were the most common influencers of the decision to receive screening. People who were older, had a history of pregnancy, and had been previously screened were more likely to educate others (all p influencers who then encouraged screening in the target population. Educating influencers and increasing overall awareness were the most effective outreach strategies.

  12. Antisites and anisotropic diffusion in GaAs and GaSb

    KAUST Repository

    Tahini, H. A.; Bracht, H.; Chroneos, Alexander; Grimes, R. W.; Murphy, S. T.; Schwingenschlö gl, Udo

    2013-01-01

    The significant diffusion of Ga under Ga-rich conditions in GaAs and GaSb is counter intuitive as the concentration of Ga vacancies should be depressed although Ga vacancies are necessary to interpret the experimental evidence for Ga transport

  13. Ga-Bi-Te system

    International Nuclear Information System (INIS)

    Rustamov, P.G.; Seidova, N.A.; Shakhbazov, M.G.; AN Azerbajdzhanskoj SSR, Baku. Inst. Neorganicheskoj i Fizicheskoj Khimii)

    1976-01-01

    To elucidate the nature of interaction in the system Ga-Bi-Te, a study has been made of sections GaTe-Bi 2 Te 3 , Ga 2 Te 3 -Bi, GaTe-Bi and Bi 2 Te 3 -Ga. The alloys have been prepared by direct melting of the components or their alloys with subsequent homogenizin.o annealing at 400 deg C. The study has been made by the methods of differential thermal, microstructural analysis and by microhardness measurements. On the basis of literature data and data obtained a projection of the liquidus surface of the phase diagram for the system Ga-Bi-Te has been constructed. In the ternary system there are 17 curves of monovariant equilibrium dividing the liquidus into 10 fields of primary crystallization of phases, 9 points of non-variant equilibrium of which 4 points are triple eutectics and 5 points are triple peritectics

  14. A Survey of the Dictionary Use of Gabonese Students 349-365 at Two South African Universities Guy-Modeste Ekwa Ebanéga and Fatima Tomba Moussavou

    Directory of Open Access Journals (Sweden)

    Guy-Modeste Ekwa Ebanégar

    2011-10-01

    Full Text Available

    Abstract: This article presents a preliminary study on Gabonese users' knowledge, opinions, attitudes and habits of the use of dictionaries, and their dictionary culture. It is based on the principle that the lexicographer should know the target users and their needs (Householder and Saporta 1962: 279. The aim of the article is to present and discuss research findings of a lexicographic survey conducted among 100 Gabonese students at the University of Stellenbosch and the Cape Peninsula University of Technology with regard to dictionary use and culture. In this article, we discuss the objective of the research, the research subjects, the research methods, the research coverage, the research findings, the description and the critical analysis of the data.

    Keywords: SURVEY, QUESTIONNAIRE, GABONESE USERS, DICTIONARY CULTURE,NEEDS

    Résumé: Une enquête de l'utilisation du dictionnaire des étudiants gabonaisà deux universités sud-africaines. Cet article présente une étude préliminaire sur laconnaissance des utilisateurs gabonais, leurs avis, leurs attitudes et leurs habitudes de l'utilisationdes dictionnaires, et leur culture de dictionnaire. Il est basé sur le principe selon lequel le lexicographedevrait connaître les usagers cibles et leurs besoins (Householder et Saporta 1962: 279. Lebut de l'article est de présenter et discuter des résultats de recherches d'une enquête lexicographiqueconduite parmi 100 étudiants gabonais à l'Université de Stellenbosch et à l'Université CapePeninsula de Technologie en ce qui concerne l'utilisation et la culture du dictionnaire. Dans cetarticle nous discutons l'objectif de la recherche, les informants, les méthodes de la recherche,l'assurance de la recherche, les résultats de la recherche, la description et l'analyse critique desdonnées.

    Mots-clés: ENQUÊTE, QUESTIONNAIRE, USAGERS GABONAIS, CULTURE DU DICTIONNAIRE,BESOINS

  15. AlGaN/GaN HEMT structures on ammono bulk GaN substrate

    International Nuclear Information System (INIS)

    Kruszewski, P; Prystawko, P; Krysko, M; Smalc-Koziorowska, J; Leszczynski, M; Kasalynas, I; Nowakowska-Siwinska, A; Plesiewicz, J; Dwilinski, R; Zajac, M; Kucharski, R

    2014-01-01

    The work shows a successful fabrication of AlGaN/GaN high electron mobility transistor (HEMT) structures on the bulk GaN substrate grown by ammonothermal method providing an ultralow dislocation density of 10 4  cm −2  and wafers of size up to 2 inches in diameter. The AlGaN layers grown by metalorganic chemical vapor phase epitaxy method demonstrate atomically smooth surface, flat interfaces with reproduced low dislocation density as in the substrate. The test electronic devices—Schottky diodes and transistors—were designed without surface passivation and were successfully fabricated using mask-less laser-based photolithography procedures. The Schottky barrier devices demonstrate exceptionally low reverse currents smaller by a few orders of magnitude in comparison to the Schottky diodes made of AlGaN/GaN HEMT on sapphire substrate. (paper)

  16. InGaN/GaN Nanowire LEDs and Lasers

    KAUST Repository

    Zhao, Chao; Ng, Tien Khee; Jahangir, Shafat; Frost, Thomas; Bhattacharya, Pallab; Ooi, Boon S.

    2016-01-01

    -droop issues. The phonon and carrier confinement in nanowires also led to junction heating, and reduced heat dissipation. In this paper, we will present our studies on effective surface states passivation in InGaN/GaN quantum-disks (Qdisks)-in-nanowire light

  17. Robust AlGaN/GaN MMIC Receiver Components

    NARCIS (Netherlands)

    Heijningen, M. van; Janssen, J.P.B.; Vliet, F.E. van

    2009-01-01

    Apart from delivering very high output powers, GaN can also be used to realize robust receiver components, such as Low Noise Amplifiersand Switches. This paper presents the designand measurement results of two GaN X-band switch and LNA MMICs, designed for integration in a radar front end. The switch

  18. Formation of GaAs/AlGaAs and InGaAs/GaAs nanorings by droplet molecular-beam epitaxy

    International Nuclear Information System (INIS)

    Gong, Z.; Niu, Z.C.; Huang, S.S.; Fang, Z.D.; Sun, B.Q.; Xia, J.B.

    2005-01-01

    GaAs/AlGaAs lattice-matched nanorings are formed on GaAs (100) substrates by droplet epitaxy. The crucial step in the formation of nanorings is annealing Ga droplets under As flux for proper time. The observed morphologic evolution of Ga droplets during annealing does not support the hypothesis that As atoms preferentially react with Ga around the periphery of the droplets, but somehow relates to a dewetting process similar to that of unstable films. Photoluminescene (PL) test results confirm the quantum-confinement effect of these GaAs nanorings. Using similar methods, we have fabricated InGaAs/GaAs lattice-mismatched rings

  19. AlInGaN-Based Superlattice Terahertz Source, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — WaveBand Corporation in collaboration with Virginia Commonwealth University proposes to design and fabricate a new sub-millimeter source based on an InAlGaN...

  20. High breakdown voltage in AlGaN/GaN HEMTs using AlGaN/GaN/AlGaN quantum-well electron-blocking layers.

    Science.gov (United States)

    Lee, Ya-Ju; Yao, Yung-Chi; Huang, Chun-Ying; Lin, Tai-Yuan; Cheng, Li-Lien; Liu, Ching-Yun; Wang, Mei-Tan; Hwang, Jung-Min

    2014-01-01

    In this paper, we numerically study an enhancement of breakdown voltage in AlGaN/GaN high-electron-mobility transistors (HEMTs) by using the AlGaN/GaN/AlGaN quantum-well (QW) electron-blocking layer (EBL) structure. This concept is based on the superior confinement of two-dimensional electron gases (2-DEGs) provided by the QW EBL, resulting in a significant improvement of breakdown voltage and a remarkable suppression of spilling electrons. The electron mobility of 2-DEG is hence enhanced as well. The dependence of thickness and composition of QW EBL on the device breakdown is also evaluated and discussed.

  1. Spatially resolved In and As distributions in InGaAs/GaP and InGaAs/GaAs quantum dot systems

    International Nuclear Information System (INIS)

    Shen, J; Cha, J J; Song, Y; Lee, M L

    2014-01-01

    InGaAs quantum dots (QDs) on GaP are promising for monolithic integration of optoelectronics with Si technology. To understand and improve the optical properties of InGaAs/GaP QD systems, detailed measurements of the QD atomic structure as well as the spatial distributions of each element at high resolution are crucial. This is because the QD band structure, band alignment, and optical properties are determined by the atomic structure and elemental composition. Here, we directly measure the inhomogeneous distributions of In and As in InGaAs QDs grown on GaAs and GaP substrates at the nanoscale using energy dispersive x-ray spectral mapping in a scanning transmission electron microscope. We find that the In distribution is broader on GaP than on GaAs, and as a result, the QDs appear to be In-poor using a GaP matrix. Our findings challenge some of the assumptions made for the concentrations and distributions of In within InGaAs/GaAs or InGaAs/GaP QD systems and provide detailed structural and elemental information to modify the current band structure understanding. In particular, the findings of In deficiency and inhomogeneous distribution in InGaAs/GaP QD systems help to explain photoluminescence spectral differences between InGaAs/GaAs and InGaAs/GaP QD systems. (paper)

  2. Baseline Prevalence of Birth Defects Associated with Congenital Zika Virus Infection - Massachusetts, North Carolina, and Atlanta, Georgia, 2013-2014.

    Science.gov (United States)

    Cragan, Janet D; Mai, Cara T; Petersen, Emily E; Liberman, Rebecca F; Forestieri, Nina E; Stevens, Alissa C; Delaney, Augustina; Dawson, April L; Ellington, Sascha R; Shapiro-Mendoza, Carrie K; Dunn, Julie E; Higgins, Cathleen A; Meyer, Robert E; Williams, Tonya; Polen, Kara N D; Newsome, Kim; Reynolds, Megan; Isenburg, Jennifer; Gilboa, Suzanne M; Meaney-Delman, Dana M; Moore, Cynthia A; Boyle, Coleen A; Honein, Margaret A

    2017-03-03

    Zika virus infection during pregnancy can cause serious brain abnormalities, but the full range of adverse outcomes is unknown (1). To better understand the impact of birth defects resulting from Zika virus infection, the CDC surveillance case definition established in 2016 for birth defects potentially related to Zika virus infection* (2) was retrospectively applied to population-based birth defects surveillance data collected during 2013-2014 in three areas before the introduction of Zika virus (the pre-Zika years) into the World Health Organization's Region of the Americas (Americas) (3). These data, from Massachusetts (2013), North Carolina (2013), and Atlanta, Georgia (2013-2014), included 747 infants and fetuses with one or more of the birth defects meeting the case definition (pre-Zika prevalence = 2.86 per 1,000 live births). Brain abnormalities or microcephaly were the most frequently recorded (1.50 per 1,000), followed by neural tube defects and other early brain malformations † (0.88), eye abnormalities without mention of a brain abnormality (0.31), and other consequences of central nervous system (CNS) dysfunction without mention of brain or eye abnormalities (0.17). During January 15-September 22, 2016, the U.S. Zika Pregnancy Registry (USZPR) reported 26 infants and fetuses with these same defects among 442 completed pregnancies (58.8 per 1,000) born to mothers with laboratory evidence of possible Zika virus infection during pregnancy (2). Although the ascertainment methods differed, this finding was approximately 20 times higher than the proportion of one or more of the same birth defects among pregnancies during the pre-Zika years. These data demonstrate the importance of population-based surveillance for interpreting data about birth defects potentially related to Zika virus infection.

  3. Urban expansion simulation and the spatio-temporal changes of ecosystem services, a case study in Atlanta Metropolitan area, USA.

    Science.gov (United States)

    Sun, Xiao; Crittenden, John C; Li, Feng; Lu, Zhongming; Dou, Xiaolin

    2018-05-01

    Urban expansion can lead to land use changes and, hence, threatens the ecosystems. Understanding the effects of urbanization on ecosystem services (ESs) can provide scientific guidance for land use planning and the protection of ESs. We established a framework to assess the spatial distributions of ESs based on land use changes in the Atlanta Metropolitan area (AMA) from 1985 to 2012. A new comprehensive ecosystem service (CES) index was developed to reflect the comprehensive level of ESs. Associated with the influential factors, we simulated the business as usual scenario in 2030. Four alternative scenarios, including more compact growth (MCG), riparian vegetation buffer (RVB), soil conservation (SC), and combined development (CD) scenarios were developed to explore the optimal land use strategies which can enhance the ESs. The results showed that forest and wetland had the greatest decreases, while low and high intensity built-up lands had the greatest increases. The values of CES and most of ESs decreased significantly due to the sprawling expansion of built-up land. The scenario analysis revealed that the CD scenario performs best in CES value, while it performs the worst in food supply. Compared with the RVB and SC scenarios, MCG scenario is a more optimal land use strategy to enhance the ESs without at the expense of food supply. To integrate multiple ESs into land use planning and decision making, corresponding land management policies and ecological engineering measures should be implemented to enhance: (1) the water yield and water purification in urban core counties, (2) the carbon storage, habitat quality, and recreational opportunity in counties around the core area, and (3) the soil conservation and food supply in surrounding suburban counties. The land use strategies and ecological engineering measures in this study can provide references for enhancing the ESs in the AMA and other metropolitan areas. Copyright © 2017 Elsevier B.V. All rights reserved.

  4. Spatiotemporally resolved air exchange rate as a modifier of acute air pollution-related morbidity in Atlanta.

    Science.gov (United States)

    Sarnat, Jeremy A; Sarnat, Stefanie Ebelt; Flanders, W Dana; Chang, Howard H; Mulholland, James; Baxter, Lisa; Isakov, Vlad; Özkaynak, Halûk

    2013-01-01

    Epidemiological studies frequently use central site concentrations as surrogates of exposure to air pollutants. Variability in air pollutant infiltration due to differential air exchange rates (AERs) is potentially a major factor affecting the relationship between central site concentrations and actual exposure, and may thus influence observed health risk estimates. In this analysis, we examined AER as an effect modifier of associations between several urban air pollutants and corresponding emergency department (ED) visits for asthma and wheeze during a 4-year study period (January 1999-December 2002) for a 186 ZIP code area in metro Atlanta. We found positive associations for the interaction between AER and pollution on asthma ED visits for both carbon monoxide (CO) and nitrogen oxides (NO(x)), indicating significant or near-significant effect modification by AER on the pollutant risk-ratio estimates. In contrast, the interaction term between particulate matter (PM)(2.5) and AER on asthma ED visits was negative and significant. However, alternative distributional tertile analyses showed PM(2.5) and AER epidemiological model results to be similar to those found for NOx and CO (namely, increasing risk ratios (RRs) with increasing AERs when ambient PM(2.5) concentrations were below the highest tertile of their distribution). Despite the fact that ozone (O(3)) was a strong independent predictor of asthma ED visits in our main analysis, we found no O(3)-AER effect modification. To our knowledge, our findings for CO, NOx, and PM(2.5) are the first to provide an indication of short-term (i.e., daily) effect modification of multiple air pollution-related risk associations with daily changes in AER. Although limited to one outcome category in a single large urban locale, the findings suggest that the use of relatively simple and easy-to-derive AER surrogates may reflect intraurban differences in short-term exposures to pollutants of ambient origin.

  5. Investigation of the GaN-on-GaAs interface for vertical power device applications

    International Nuclear Information System (INIS)

    Möreke, Janina; Uren, Michael J.; Kuball, Martin; Novikov, Sergei V.; Foxon, C. Thomas; Hosseini Vajargah, Shahrzad; Wallis, David J.; Humphreys, Colin J.; Haigh, Sarah J.; Al-Khalidi, Abdullah; Wasige, Edward; Thayne, Iain

    2014-01-01

    GaN layers were grown onto (111) GaAs by molecular beam epitaxy. Minimal band offset between the conduction bands for GaN and GaAs materials has been suggested in the literature raising the possibility of using GaN-on-GaAs for vertical power device applications. I-V and C-V measurements of the GaN/GaAs heterostructures however yielded a rectifying junction, even when both sides of the junction were heavily doped with an n-type dopant. Transmission electron microscopy analysis further confirmed the challenge in creating a GaN/GaAs Ohmic interface by showing a large density of dislocations in the GaN layer and suggesting roughening of the GaN/GaAs interface due to etching of the GaAs by the nitrogen plasma, diffusion of nitrogen or melting of Ga into the GaAs substrate.

  6. Investigation of the GaN-on-GaAs interface for vertical power device applications

    Energy Technology Data Exchange (ETDEWEB)

    Möreke, Janina, E-mail: janina.moereke@bristol.ac.uk; Uren, Michael J.; Kuball, Martin [H.H. Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL (United Kingdom); Novikov, Sergei V.; Foxon, C. Thomas [Department of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom); Hosseini Vajargah, Shahrzad; Wallis, David J.; Humphreys, Colin J. [Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom); Haigh, Sarah J. [Super STEM Laboratory, STFC Daresbury Campus, Keckwick Lane, Daresbury WA4 4AD (United Kingdom); School of Materials, University of Manchester, Manchester M13 9PL (United Kingdom); Al-Khalidi, Abdullah; Wasige, Edward; Thayne, Iain [School of Engineering, University of Glasgow, Rankine Bldg, Oakfield Avenue, Glasgow G12 8LT (United Kingdom)

    2014-07-07

    GaN layers were grown onto (111) GaAs by molecular beam epitaxy. Minimal band offset between the conduction bands for GaN and GaAs materials has been suggested in the literature raising the possibility of using GaN-on-GaAs for vertical power device applications. I-V and C-V measurements of the GaN/GaAs heterostructures however yielded a rectifying junction, even when both sides of the junction were heavily doped with an n-type dopant. Transmission electron microscopy analysis further confirmed the challenge in creating a GaN/GaAs Ohmic interface by showing a large density of dislocations in the GaN layer and suggesting roughening of the GaN/GaAs interface due to etching of the GaAs by the nitrogen plasma, diffusion of nitrogen or melting of Ga into the GaAs substrate.

  7. Universal integrals based on copulas

    Czech Academy of Sciences Publication Activity Database

    Klement, E.P.; Mesiar, Radko; Spizzichino, F.; Stupňanová, A.

    2014-01-01

    Roč. 13, č. 3 (2014), s. 273-286 ISSN 1568-4539 R&D Projects: GA ČR GAP402/11/0378 Institutional support: RVO:67985556 Keywords : capacity * copula * universal integral Subject RIV: BA - General Mathematics Impact factor: 2.163, year: 2014 http://library.utia.cas.cz/separaty/2014/E/mesiar-0432228.pdf

  8. Shot noise reduction in the AlGaAs/GaAs- and InGaP/GaAs-based HBTs

    Science.gov (United States)

    Sakalas, Paulius; Schroeter, Michael; Zampardi, Peter; Zirath, Herbert

    2003-05-01

    Noise parameters of AlGaAs/GaAs and InGaP/GaAs HBTs were measured in microwave frequency range and modeled using the small-signal equivalent circuit approach. Correlated current noise sources in the base and collector currents with thermal noise in the circuit resistive elements were accounted for by the model and yielded good agreement with the measured data. This enabled an extraction of the different noise source contributions to minimum noise figure (NFmin) in AlGaAs/GaAs and InGaP/GaAs HBTs. Decomposition of the (NFmin) in to the different contributors showed that the main noise sources in investigated HBTs are correlated base and collector current shot noise. The observed minimum of NFmin versus frequency at lower collector current is explained by the reduction of the emitter/base junction shot noise component due to the spike in the emitter/base junction and associated accumulation of the quasi-thermalized electrons forming a space charge, which screens the electron transfer through the barrier. The bias (VCE) increase creates an efficient electric field in collector/base junction, capable of 'washing out' the accumulated charge. Such shot noise reduction in HBTs could be exploited in the LNA for the RF application.

  9. Adaptive and active materials: selected papers from the ASME 2012 Conference on Smart Materials, Adaptive Structures and Intelligent Systems (SMASIS 12) (Stone Mountain, GA, USA, 19-21 September 2012)

    Science.gov (United States)

    Seelecke, Stefan; Erturk, Alper; Ounaies, Zoubeida; Naguib, Hani; Huber, John; Turner, Travis; Anderson, Iain; Philen, Michael; Baba Sundaresan, Vishnu

    2013-09-01

    The fifth annual meeting of the ASME/AIAA Smart Materials, Adaptive Structures and Intelligent Systems Conference (SMASIS) was held in beautiful Stone Mountain near Atlanta, GA. It is the conference's objective to provide an up-to-date overview of research trends in the entire field of smart materials systems. This was reflected in keynote speeches by Professor Eduard Arzt (Institute of New Materials and Saarland University, Saarbrücken, Germany) on 'Micro-patterned artificial 'Gecko' surfaces: a path to switchable adhesive function', by Professor Ray H Baughman (The Alan G MacDiarmid NanoTech Institute, University of Texas at Dallas) on 'The diverse and growing family of carbon nanotube and related artificial muscles', and by Professor Richard James (University of Minnesota) on 'The direct conversion of heat to electricity using multiferroic materials with phase transformations'. SMASIS 2012 was divided into eight symposia which span basic research, applied technological design and development, and industrial and governmental integrated system and application demonstrations. • SYMP 1. Development and characterization of multifunctional materials. • SYMP 2. Mechanics and behavior of active materials. • SYMP 3. Modeling, simulation and control of adaptive systems. • SYMP 4. Integrated system design and implementation. • SYMP 5. Structural health monitoring/NDE. • SYMP 6. Bio-inspired materials and systems. • SYMP 7. Energy harvesting. • SYMP 8. Structural and materials logic. This year we were particularly excited to introduce a new symposium on energy harvesting, which has quickly matured from a special track in previous years to an independent symposium for the first time. The subject cuts across fields by studying different materials, ranging from piezoelectrics to electroactive polymers, as well as by emphasizing different energy sources from wind to waves and ambient vibrations. Modeling, experimental studies, and technology applications all

  10. Trends in on-road vehicle emissions and ambient air quality in Atlanta, Georgia, USA, from the late 1990s through 2009.

    Science.gov (United States)

    Vijayaraghavan, Krish; DenBleyker, Allison; Ma, Lan; Lindhjem, Chris; Yarwood, Greg

    2014-07-01

    On-road vehicle emissions of carbon monoxide (CO), nitrogen oxides (NO(x)), and volatile organic compounds (VOCs) during 1995-2009 in the Atlanta Metropolitan Statistical Area were estimated using the Motor Vehicle Emission Simulator (MOVES) model and data from the National Emissions Inventories and the State of Georgia. Statistically significant downward trends (computed using the nonparametric Theil-Sen method) in annual on-road CO, NO(x), and VOC emissions of 6.1%, 3.3%, and 6.0% per year, respectively, are noted during the 1995-2009 period despite an increase in total vehicle distance traveled. The CO and NO(x) emission trends are correlated with statistically significant downward trends in ambient air concentrations of CO and NO(x) in Atlanta ranging from 8.0% to 11.8% per year and from 5.8% to 8.7% per year, respectively, during similar time periods. Weather-adjusted summertime ozone concentrations in Atlanta exhibited a statistically significant declining trend of 2.3% per year during 2001-2009. Although this trend coexists with the declining trends in on-road NO(x), VOC, and CO emissions, identifying the cause of the downward trend in ozone is complicated by reductions in multiple precursors from different source sectors. Implications: Large reductions in on-road vehicle emissions of CO and NO(x) in Atlanta from the late 1990s to 2009, despite an increase in total vehicle distance traveled, contributed to a significant improvement in air quality through decreases in ambient air concentrations of CO and NO(x) during this time period. Emissions reductions in motor vehicles and other source sectors resulted in these improvements and the observed declining trend in ozone concentrations over the past decade. Although these historical trends cannot be extrapolated to the future because pollutant concentration contributions due to on-road vehicle emissions will likely become an increasingly smaller fraction of the atmospheric total, they provide an indication of

  11. Electrical compensation by Ga vacancies in Ga2O3

    OpenAIRE

    Korhonen, Esa; Tuomisto, F.; Gogova, D.; Wagner, G.; Baldini, M.; Galazka, Z.; Schewski, R.; Albrecht, M.

    2015-01-01

    The authors have applied positron annihilation spectroscopy to study the vacancy defects in undoped and Si-doped Ga2O3 thin films. The results show that Ga vacancies are formed efficiently during metal-organic vapor phase epitaxy growth of Ga2O3 thin films. Their concentrations are high enough to fully account for the electrical compensation of Si doping. This is in clear contrast to another n-type transparent semiconducting oxide In2O3, where recent results show that n-type conductivity is n...

  12. On the effect of N-GaN/P-GaN/N-GaN/P-GaN/N-GaN built-in junctions in the n-GaN layer for InGaN/GaN light-emitting diodes.

    Science.gov (United States)

    Kyaw, Zabu; Zhang, Zi-Hui; Liu, Wei; Tan, Swee Tiam; Ju, Zhen Gang; Zhang, Xue Liang; Ji, Yun; Hasanov, Namig; Zhu, Binbin; Lu, Shunpeng; Zhang, Yiping; Sun, Xiao Wei; Demir, Hilmi Volkan

    2014-01-13

    N-GaN/P-GaN/N-GaN/P-GaN/N-GaN (NPNPN-GaN) junctions embedded between the n-GaN region and multiple quantum wells (MQWs) are systematically studied both experimentally and theoretically to increase the performance of InGaN/GaN light emitting diodes (LEDs) in this work. In the proposed architecture, each thin P-GaN layer sandwiched in the NPNPN-GaN structure is completely depleted due to the built-in electric field in the NPNPN-GaN junctions, and the ionized acceptors in these P-GaN layers serve as the energy barriers for electrons from the n-GaN region, resulting in a reduced electron over flow and enhanced the current spreading horizontally in the n- GaN region. These lead to increased optical output power and external quantum efficiency (EQE) from the proposed device.

  13. Growth of GaN layers using Ga2O vapor obtained from Ga and H2O vapor

    International Nuclear Information System (INIS)

    Sumi, Tomoaki; Taniyama, Yuuki; Takatsu, Hiroaki; Juta, Masami; Kitamoto, Akira; Imade, Mamoru; Yoshimura, Masashi; Mori, Yusuke; Isemura, Masashi

    2015-01-01

    In this study, we performed growth of GaN layers using Ga 2 O vapor synthesized from Ga and H 2 O vapor. In this process, we employed H 2 O vapor instead of HCl gas in hydride vapor phase epitaxy (HVPE) to synthesize Ga source gas. In the synthesis reaction of Ga 2 O, a Ga 2 O 3 whisker formed and covered Ga, which impeded the synthesis reaction of Ga 2 O. The formation of the Ga 2 O 3 whisker was suppressed in H 2 ambient at high temperatures. Then, we adopted this process to supply a group III precursor and obtained an epitaxial layer. X-ray diffraction (XRD) measurement revealed that the epitaxial layer was single-crystalline GaN. Growth rate increased linearly with Ga 2 O partial pressure and reached 104 µm/h. (author)

  14. Effect of GaN buffer polarization on electron distribution of AlGaN/GaN heterostructure

    International Nuclear Information System (INIS)

    He, Xiaoguang; Zhao, Degang; Liu, Wei; Yang, Jing; Li, Xiaojing; Li, Xiang

    2016-01-01

    The formation of 2DEG in AlGaN/GaN heterostructure is discussed in detail. A misunderstanding about the 2DEG sheet density expression is clarified. It is predicted by theoretical analysis and validated by self-consistent Schrodinger–Poisson numerical simulation that under the force of GaN polarization, large amounts of electrons will accumulate at the GaN/substrate interface in AlGaN/GaN/substrate HEMT structure. - Highlights: • The formation of 2DEG in AlGaN/GaN heterostructure is discussed in detail. • Self-consistent Schrodinger–Poisson numerical simulation is used to modulate the AlGaN/GaN/substrate structure. • It is predicted by that large amounts of electrons will accumulate at the GaN/substrate interface.

  15. Effect of GaN buffer polarization on electron distribution of AlGaN/GaN heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    He, Xiaoguang; Zhao, Degang, E-mail: dgzhao@red.semi.ac.cn; Liu, Wei; Yang, Jing; Li, Xiaojing; Li, Xiang

    2016-06-15

    The formation of 2DEG in AlGaN/GaN heterostructure is discussed in detail. A misunderstanding about the 2DEG sheet density expression is clarified. It is predicted by theoretical analysis and validated by self-consistent Schrodinger–Poisson numerical simulation that under the force of GaN polarization, large amounts of electrons will accumulate at the GaN/substrate interface in AlGaN/GaN/substrate HEMT structure. - Highlights: • The formation of 2DEG in AlGaN/GaN heterostructure is discussed in detail. • Self-consistent Schrodinger–Poisson numerical simulation is used to modulate the AlGaN/GaN/substrate structure. • It is predicted by that large amounts of electrons will accumulate at the GaN/substrate interface.

  16. Assessment of Ga2O3 technology

    Science.gov (United States)

    2016-09-15

    this article has given the emerging technology of GaN a valuable push in term of encouragement to stay with it while the painful technology development...Ga2O3 α-Ga2O3 β-Ga2O3 β-Ga2O3 β-Ga2O3 poly - Ga2O3 β-Ga2O3 Epi-layer Growth Method MBE (ozone) MBE (ozone) MBE (ozone) Mist-CVD MBE (ozone... pains to treat the wafer surface with BCl3 RIE to create charges at the interface. The gate contact was also barely a Schottky contact evidenced by

  17. Antisites and anisotropic diffusion in GaAs and GaSb

    KAUST Repository

    Tahini, H. A.

    2013-10-02

    The significant diffusion of Ga under Ga-rich conditions in GaAs and GaSb is counter intuitive as the concentration of Ga vacancies should be depressed although Ga vacancies are necessary to interpret the experimental evidence for Ga transport. To reconcile the existence of Ga vacancies under Ga-rich conditions, transformation reactions have been proposed. Here, density functional theory is employed to calculate the formation energies of vacancies on both sublattices and the migration energy barriers to overcome the formation of the vacancy-antisite defect. Transformation reactions enhance the vacancy concentration in both materials and migration energy barriers indicate that Ga vacancies will dominate.

  18. GA microwave window development

    International Nuclear Information System (INIS)

    Moeller, C.P.; Kasugai, A.; Sakamoto, K.; Takahashi, K.

    1994-10-01

    The GA prototype distributed window was tested in a 32 mm diam. waveguide system at a power density suitable for a MW gyrotron, using the JAERI/Toshiba 110 GHz long pulse internal converter gyrotron in the JAERI test stand. The presence of the untilted distributed window had no adverse effect on the gyrotron operation. A pulse length of 10 times the calculated thermal equilibrium time (1/e time) of 30 msec was reached, and the window passed at least 750 pulses greater than 30 msec and 343 pulses greater than 60 msec. Beyond 100 msec, the window calorimetry reached steady state, allowing the window dissipation to be measured in a single pulse. The measured loss of 4.0% agrees both with the estimated loss, on which the stress calculations are based, and with the attenuation measured at low power in the HE 11 mode. After the end of the tests, the window was examined; no evidence of arcing air coating was found in the part of the window directly illuminated by the microwaves, although there was discoloration in a recess containing an optical diagnostic which outgassed, causing a local discharge to occur in that recess. Finally, there was no failure of the metal-sapphire joints during a total operating time of 50 seconds consisting of pulses longer than 30 msec

  19. Solar heating and cooling experiment for a school in Atlanta: performance report. [George A. Towns Elementary School

    Energy Technology Data Exchange (ETDEWEB)

    1977-08-01

    This report documents the performance, and conclusions therefrom, of a 13 month period of monitoring the performance of the experimental solar heating and cooling system installed in the George A. Towns Elementary School, Atlanta, Georgia. The solar collector system involves 10,360 ft/sup 2/ of PPG ''Baseline'' flat-plate collectors with an ALCOA selective coating, augmented by 10,800 square feet of aluminized Mylar reflectors. Three 15,000 gallon steel storage tanks, a 100-ton Arkla absorption chiller together with its cooling tower, a collector gravity drain system with a 1,600 gallon holding tank and a collector nitrogen purge system, six pumps and 26 pneumatic control valves were installed and interfaced with the pre-existing gas furnace and distribution system. In the winter heating mode, the solar energy is stored in all three tanks, total capacity of 45,000 gallons, between design temperatures of 105/sup 0/ to 140/sup 0/F. As soon as Tank 1 is brought up to 140/sup 0/F, the control valves isolate it from the collector loop, and the hot water from the collectors is used to charge Tanks 2 and then Tank 3. Water can be drawn from Tank 1 to heat the school while Tanks 2 and 3 are being charged. As a consequence of the flexibility provided by the three tanks, compared to a single tank of equivalent capacity, the thermal lag in the system is reduced. A variable speed pump, in response to sensors at the inlet and outlet of the collectors, modulates the flow of water through each collector from a maximum of .5 gpm to a minimum of .1 gpm, attempting to maintain a temperature rise of about 10/sup 0/F. In the summer cooling mode, storage tanks 2 and 3 are designed to store hot water at temperatures between 180/sup 0/ to 200/sup 0/F, and tank 1 is used to store chilled water. (WHK)

  20. /sup 67/Ga lung scan

    Energy Technology Data Exchange (ETDEWEB)

    Niden, A.H.; Mishkin, F.S.; Khurana, M.M.L.; Pick, R.

    1977-03-21

    Twenty-three patients with clinical signs of pulmonary embolic disease and lung infiltrates were studied to determine the value of gallium citrate /sup 67/Ga lung scan in differentiating embolic from inflammatory lung disease. In 11 patients without angiographically proved embolism, only seven had corresponding ventilation-perfusion defects compatible with inflammatory disease. In seven of these 11 patients, the /sup 67/Ga concentration indicated inflammatory disease. In the 12 patients with angiographically proved embolic disease, six had corresponding ventilation-perfusion defects compatible with inflammatory disease. None had an accumulation of /sup 67/Ga in the area of pulmonary infiltrate. Thus, ventilation-perfusion lung scans are of limited value when lung infiltrates are present. In contrast, the accumulation of /sup 67/Ga in the lung indicates an inflammatory process. Gallium imaging can help select those patients with lung infiltrates who need angiography.

  1. Flood-inundation maps for Peachtree Creek from the Norfolk Southern Railway bridge to the Moores Mill Road NW bridge, Atlanta, Georgia

    Science.gov (United States)

    Musser, Jonathan W.

    2012-01-01

    Digital flood-inundation maps for a 5.5-mile reach of the Peachtree Creek from the Norfolk Southern Railway bridge to the Moores Mill Road NW bridge, were developed by the U.S. Geological Survey (USGS) in cooperation with the City of Atlanta, Georgia. The inundation maps, which can be accessed through the USGS Flood Inundation Mapping Science Web site at http://water.usgs.gov/osw/flood_inundation/, depict estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at the USGS streamgage at Peachtree Creek at Atlanta, Georgia (02336300) and the USGS streamgage at Chattahoochee River at Georgia 280, near Atlanta, Georgia (02336490). Current water level (stage) at these USGS streamgages may be obtained at http://waterdata.usgs.gov/ and can be used in conjunction with these maps to estimate near real-time areas of inundation. The National Weather Service (NWS) is incorporating results from this study into the Advanced Hydrologic Prediction Service (AHPS) flood warning system (http:/water.weather.gov/ahps/). The NWS forecasts flood hydrographs at many places that commonly are collocated at USGS streamgages. The forecasted peak-stage information for the USGS streamgage at Peachtree Creek, which is available through the AHPS Web site, may be used in conjunction with the maps developed in this study to show predicted areas of flood inundation. A one-dimensional step-backwater model was developed using the U.S. Army Corps of Engineers HEC–RAS software for a 6.5-mile reach of Peachtree Creek and was used to compute flood profiles for a 5.5-mile reach of the creek. The model was calibrated using the most current stage-discharge relations at the Peachtree Creek at Atlanta, Georgia, streamgage (02336300), and the Chattahoochee River at Georgia 280, near Atlanta, Georgia, streamgage (02336490) as well as high water marks collected during the 2010 annual peak flow event. The hydraulic model was then used to determine 50 water

  2. Continuous-Time Symmetric Hopfield Nets are Computationally Universal

    Czech Academy of Sciences Publication Activity Database

    Šíma, Jiří; Orponen, P.

    2003-01-01

    Roč. 15, č. 3 (2003), s. 693-733 ISSN 0899-7667 R&D Projects: GA AV ČR IAB2030007; GA ČR GA201/02/1456 Institutional research plan: AV0Z1030915 Keywords : continuous-time Hopfield network * Liapunov function * analog computation * computational power * Turing universality Subject RIV: BA - General Mathematics Impact factor: 2.747, year: 2003

  3. On recoverable behavior of PBTI in AlGaN/GaN MOS-HEMT

    Science.gov (United States)

    Acurio, E.; Crupi, F.; Magnone, P.; Trojman, L.; Meneghesso, G.; Iucolano, F.

    2017-06-01

    This experimental study focuses on the positive bias temperature instability (PBTI) in a fully recessed-gate AlGaN/GaN MOS-HEMT. A positive stress voltage to the gate results in positive threshold voltage shift (ΔVth), which is attributed to the trapping of electrons from the GaN layer into the pre-existing oxide traps. The trapping rate exhibits a universal decreasing behavior as a function of the number of filled traps, independently of stress time, stress voltage, stress temperature, and device-to-device variability. The stress-induced ΔVth can be fully recovered by applying a small negative voltage, which causes the electron de-trapping. In the explored time window (between 1 s and thousands of s), the recovery dynamics is well described by the superimposition of two exponential functions associated with two different traps. Both trap time constants are independent of the stress voltage, decrease with temperature and increase with the recovery voltage. The activation energy of the slower trap is 0.93 eV, while the faster trap exhibits an activation energy with a large spread in the range between 0.45 eV and 0.82 eV.

  4. Contemporary Elementary and Middle School Physical Education Conference (Georgia State University, Atlanta, Georgia, January 15-17, 1981). Proceedings, Saturday, Activity and Position Paper Sessions.

    Science.gov (United States)

    Jones, Margaret A., Ed.

    At the final session of the January conference on Contemporary Elementary and Middle School Physical Education, 40 discussions and workshops centered on physical fitness, health, safety, and adapting athletics for the disabled child. Other topics covered were creative dance, water activities, lifetime sports, and teacher resource materials and…

  5. Public Hearing: Report of the Proceedings of a Public Hearing of the Task Force on Women, Minorities and the Handicapped in Science and Technology (Atlanta, Georgia, March 2, 1988).

    Science.gov (United States)

    Task Force on Women, Minorities, and the Handicapped in Science and Technology, Washington, DC.

    The Task Force on Women, Minorities, and the Handicapped in Science and Technology was established by the U.S. Congress in Public Law 99-383 with the purpose of developing a long-range plan for broadening participation in science and engineering. Public hearings were held in Albuquerque (New Mexico), Atlanta (Georgia), Baltimore (Maryland), Boston…

  6. Atomic-scale structure of irradiated GaN compared to amorphised GaP and GaAs

    International Nuclear Information System (INIS)

    Ridgway, M.C.; Everett, S.E.; Glover, C.J.; Kluth, S.M.; Kluth, P.; Johannessen, B.; Hussain, Z.S.; Llewellyn, D.J.; Foran, G.J.; Azevedo, G. de M.

    2006-01-01

    We have compared the atomic-scale structure of ion irradiated GaN to that of amorphised GaP and GaAs. While continuous and homogenous amorphised layers were easily achieved in GaP and GaAs, ion irradiation of GaN yielded both structural and chemical inhomogeneities. Transmission electron microscopy revealed GaN crystallites and N 2 bubbles were interspersed within an amorphous GaN matrix. The crystallite orientation was random relative to the unirradiated epitaxial structure, suggesting their formation was irradiation-induced, while the crystallite fraction was approximately constant for all ion fluences beyond the amorphisation threshold, consistent with a balance between amorphisation and recrystallisation processes. Extended X-ray absorption fine structure measurements at the Ga K-edge showed short-range order was retained in the amorphous phase for all three binary compounds. For ion irradiated GaN, the stoichiometric imbalance due to N 2 bubble formation was not accommodated by Ga-Ga bonding in the amorphous phase or precipitation of metallic Ga but instead by a greater reduction in Ga coordination number

  7. Measurement of elongational viscosity of polymer melts using SER Universal Testing Platform

    Czech Academy of Sciences Publication Activity Database

    Filip, Petr; Švrčinová, Petra

    2012-01-01

    Roč. 22, č. 1 (2012), s. 14776 ISSN 1430-6395 R&D Projects: GA ČR GA103/08/1307; GA ČR GA103/09/2066 Institutional research plan: CEZ:AV0Z20600510 Keywords : elongational viscosity * SER Universal Testing Platform * polymer melts * LDPE Subject RIV: BK - Fluid Dynamics Impact factor: 1.226, year: 2012 http://www.ar.ethz.ch/TMPPDF/23074299892.48/ApplRheol_22_14776.pdf

  8. Influence of AlGaN/GaN superlattice inserted structure on the performance of InGaN/GaN multiple quantum well light emitting diodes

    International Nuclear Information System (INIS)

    Wang, C.-L.; Tsai, M.-C.; Gong, J.-R.; Liao, W.-T.; Lin, P.-Y.; Yen, K.-Y.; Chang, C.-C.; Lin, H.-Y.; Hwang, S.-K.

    2007-01-01

    Investigations were conducted to explore the effect of Al 0.3 Ga 0.7 N/GaN short-period superlattice (SPSL)-inserted structures in the GaN under layer on the performance of In 0.2 Ga 0.8 N/GaN multiple quantum well (MQW) light emitting diodes (LEDs). The Al 0.3 Ga 0.7 N/GaN SPSL-inserted LEDs were found to exhibit improved materials and device characteristics including decrements in ideality factor and reverse leakage current. The results of etch pit counts reveal that SPSL-induced threading dislocation density reduction in the SPSL-inserted In 0.2 Ga 0.8 N/GaN MQW LED structures enables the improved LED performance

  9. InGaP/InGaAsN/GaAs NpN double-heterojunction bipolar transistor

    International Nuclear Information System (INIS)

    Chang, P. C.; Baca, A. G.; Li, N. Y.; Xie, X. M.; Hou, H. Q.; Armour, E.

    2000-01-01

    We have demonstrated a functional NpN double-heterojunction bipolar transistor (DHBT) using InGaAsN for the base layer. The InGaP/In 0.03 Ga 0.97 As 0.99 N 0.01 /GaAs DHBT has a low V ON of 0.81 V, which is 0.13 V lower than in a InGaP/GaAs heterojunction bipolar transistor (HBT). The lower turn-on voltage is attributed to the smaller band gap (1.20 eV) of metalorganic chemical vapor deposition-grown In 0.03 Ga 0.97 As 0.99 N 0.01 base layer. GaAs is used for the collector; thus the breakdown voltage (BV CEO ) is 10 V, consistent with the BV CEO of InGaP/GaAs HBTs of comparable collector thickness and doping level. To alleviate the current blocking phenomenon caused by the larger conduction band discontinuity between InGaAsN and GaAs, a graded InGaAs layer with δ doping is inserted at the base-collector junction. The improved device has a peak current gain of seven with ideal current-voltage characteristics. (c) 2000 American Institute of Physics

  10. Comparison of electrical characteristic between AlN/GaN and AlGaN/GaN heterostructure Schottky diodes

    International Nuclear Information System (INIS)

    Lü Yuan-Jie; Feng Zhi-Hong; Gu Guo-Dong; Dun Shao-Bo; Yin Jia-Yun; Han Ting-Ting; Cai Shu-Jun; Lin Zhao-Jun

    2014-01-01

    Ni/Au Schottky contacts on AlN/GaN and AlGaN/GaN heterostructures are fabricated. Based on the measured current—voltage and capacitance—voltage curves, the electrical characteristics of AlN/GaN Schottky diode, such as Schottky barrier height, turn-on voltage, reverse breakdown voltage, ideal factor, and the current-transport mechanism, are analyzed and then compared with those of an AlGaN/GaN diode by self-consistently solving Schrödinger's and Poisson's equations. It is found that the dislocation-governed tunneling is dominant for both AlN/GaN and AlGaN/GaN Schottky diodes. However, more dislocation defects and a thinner barrier layer for AlN/GaN heterostructure results in a larger tunneling probability, and causes a larger leakage current and lower reverse breakdown voltage, even though the Schottky barrier height of AlN/GaN Schottky diode is calculated to be higher that of an AlGaN/GaN diode. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  11. Fabrication of p-type porous GaN on silicon and epitaxial GaN

    OpenAIRE

    Bilousov, Oleksandr V.; Geaney, Hugh; Carvajal, Joan J.; Zubialevich, Vitaly Z.; Parbrook, Peter J.; Giguere, A.; Drouin, D.; Diaz, Francesc; Aguilo, Magdalena; O'Dwyer, Colm

    2013-01-01

    Porous GaN layers are grown on silicon from gold or platinum catalyst seed layers, and self-catalyzed on epitaxial GaN films on sapphire. Using a Mg-based precursor, we demonstrate p-type doping of the porous GaN. Electrical measurements for p-type GaN on Si show Ohmic and Schottky behavior from gold and platinum seeded GaN, respectively. Ohmicity is attributed to the formation of a Ga2Au intermetallic. Porous p-type GaN was also achieved on epitaxial n-GaN on sapphire, and transport measurem...

  12. Anomalous disorder-related phenomena in InGaN/GaN multiple quantum well heterosystems

    International Nuclear Information System (INIS)

    Hu, Y.-J.; Huang, Y.-W.; Fang, C.-H.; Wang, J.-C.; Chen, Y.-F.; Nee, T.-E.

    2010-01-01

    The influences of InGaN/GaN multiple quantum well (MQW) heterostructures with InGaN/GaN and GaN barriers on carrier confinement were investigated. The degree of disordering over a broad range of temperatures from 20 to 300 K was considered. The optical and electrical properties were strongly influenced by structural and compositional disordering of the InGaN/GaN MQW heterostructures. To compare the degree of disordering we examined the temperature dependence of the luminescence spectra and electrical conductance contingent on the Berthelot-type mechanisms in the InGaN/GaN MQW heterostructures. We further considered carrier transport in the InGaN/GaN disordered systems, probability of carrier tunneling, and activation energy of the transport mechanism for devices with InGaN/GaN and GaN barriers. The optical properties of InGaN/GaN disordered heterosystems can be interpreted from the features of the absorption spectra. The anomalous temperature-dependent characteristics of the disordered InGaN/GaN MQW structures were attributable to the enhancement of the exciton confinement.

  13. Remote Sensing and Spatial Growth Modeling Coupled With Air Quality Modeling to Assess the Impact of Atlanta, Georgia on the Local and Regional Environment

    Science.gov (United States)

    Quattrochi, D. A.; Estes, M. G.; Crosson, W. L.; Johnson, H.; Khan, M.

    2006-05-01

    The growth of cities, both in population and areal extent, appears as an inexorable process. Urbanization continues at a rapid rate, and it is estimated that by the year 2025, 60 percent of the world's population will live in cities. Urban expansion has profound impacts on a host of biophysical, environmental, and atmospheric processes within an urban ecosystems perspective. A reduction in air quality over cities is a major result of these impacts. Because of its complexity, the urban landscape is not adequately captured in air quality models such as the Community Multiscale Air Quality (CMAQ) model that is used to assess whether urban areas are in attainment of EPA air quality standards, primarily for ground level ozone. This inadequacy of the CMAQ model to sufficiently respond to the heterogeneous nature of the urban landscape can impact how well the model predicts ozone levels over metropolitan areas and ultimately, whether cities exceed EPA ozone air quality standards. We are exploring the utility of high-resolution remote sensing data and urban spatial growth modeling (SGM) projections as improved inputs to a meteorological/air quality modeling system focusing on the Atlanta, Georgia metropolitan area as a case study. These growth projections include "business as usual" and "smart growth" scenarios out to 2030. The growth projections illustrate the effects of employing urban heat island mitigation strategies, such as increasing tree canopy and albedo across the Atlanta metro area, which in turn, are used to model how air temperature can potentially be moderated as impacts on elevating ground-level ozone, as opposed to not utilizing heat island mitigation strategies. The National Land Cover Dataset at 30m resolution is being used as the land use/land cover input and aggregated to the 4km scale for the MM5 mesoscale meteorological model and the CMAQ modeling schemes. Use of these data has been found to better characterize low density/suburban development as

  14. Spatial Growth Modeling and High Resolution Remote Sensing Data Coupled with Air Quality Modeling to Assess the Impact of Atlanta, Georgia on the Local and Regional Environment

    Science.gov (United States)

    Quattrochi, Dale A.; Estes, Maurice G., Jr.; Crosson, William; Johnson, Hoyt; Khan, Maudood

    2006-01-01

    The growth of cities, both in population and areal extent, appears as an inexorable process. Urbanization continues at a rapid rate, and it is estimated that by the year 2025, 60 percent of the world s population will live in cities. Urban expansion has profound impacts on a host of biophysical, environmental, and atmospheric processes within an urban ecosystems perspective. A reduction in air quality over cities is a major result of these impacts. Because of its complexity, the urban landscape is not adequately captured in air quality models such as the Community Multiscale Air Quality (CMAQ) model that is used to assess whether urban areas are in attainment of EPA air quality standards, primarily for ground level ozone. This inadequacy of the CMAQ model to sufficiently respond to the heterogeneous nature of the urban landscape can impact how well the model predicts ozone levels over metropolitan areas and ultimately, whether cities exceed EPA ozone air quality standards. We are exploring the utility of high-resolution remote sensing data and urban spatial growth modeling (SGM) projections as improved inputs to a meteorological/air quality modeling system focusing on the Atlanta, Georgia metropolitan area as a case study. These growth projections include business as usual and smart growth scenarios out to 2030. The growth projections illustrate the effects of employing urban heat island mitigation strategies, such as increasing tree canopy and albedo across the Atlanta metro area, which in turn, are used to model how air temperature can potentially be moderated as impacts on elevating ground-level ozone, as opposed to not utilizing heat island mitigation strategies. The National Land Cover Dataset at 30m resolution is being used as the land use/land cover input and aggregated to the 4km scale for the MM5 mesoscale meteorological model and the CMAQ modeling schemes. Use of these data has been found to better characterize low density/suburban development as compared

  15. 78 FR 9771 - Notice of Opportunity for Public Comment on Surplus Property Release at Brunswick-Golden Isles...

    Science.gov (United States)

    2013-02-11

    ... address: Atlanta Airports District Office, Attn: Aimee A. McCormick, Program Manager, 1701 Columbia Ave... McCormick, Program Manager, Atlanta Airports District Office, 1701 Columbia Ave., Suite 2-260, Atlanta, GA...

  16. University Internationalization and University Autonomy

    DEFF Research Database (Denmark)

    Turcan, Romeo V.; Gulieva, Valeria

    2016-01-01

    Turcan and Gulieva deepen our theoretical understanding of the process of university internationalisation by exploring the relationship between university internationalisation and university autonomy. They conjecture that the process of university internationalisation and its sustainability are d......, dissimilar, and sometimes conflicting dimensions of the financial, legal, organisational, staffing, and academic autonomy of the host country, are compromising key aspects of their own autonomy and core mission?......Turcan and Gulieva deepen our theoretical understanding of the process of university internationalisation by exploring the relationship between university internationalisation and university autonomy. They conjecture that the process of university internationalisation and its sustainability...... are determined by the structure and exercise of university autonomy settings at home and in the host countries, and that the process itself cannot be successfully achieved and maintained without changes in the autonomy settings. The key question the authors ask is to what degree universities, in embracing new...

  17. Polarization-induced Zener tunnel diodes in GaN/InGaN/GaN heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Yan, Xiaodong; Li, Wenjun; Islam, S. M.; Pourang, Kasra; Fay, Patrick [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Xing, Huili; Jena, Debdeep, E-mail: djena@cornell.edu [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States); Departments of ECE and MSE, Cornell University, Ithaca, New York 14853 (United States)

    2015-10-19

    By the insertion of thin In{sub x}Ga{sub 1−x}N layers into Nitrogen-polar GaN p-n junctions, polarization-induced Zener tunnel junctions are studied. The reverse-bias interband Zener tunneling current is found to be weakly temperature dependent, as opposed to the strongly temperature-dependent forward bias current. This indicates tunneling as the primary reverse-bias current transport mechanism. The Indium composition in the InGaN layer is systematically varied to demonstrate the increase in the interband tunneling current. Comparing the experimentally measured tunneling currents to a model helps identify the specific challenges in potentially taking such junctions towards nitride-based polarization-induced tunneling field-effect transistors.

  18. Temperature coefficients for GaInP/GaAs/GaInNAsSb solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Aho, Arto; Isoaho, Riku; Tukiainen, Antti; Polojärvi, Ville; Aho, Timo; Raappana, Marianna; Guina, Mircea [Optoelectronics Research Centre, Tampere University of Technology, P.O. Box 692, FIN-33101 Tampere (Finland)

    2015-09-28

    We report the temperature coefficients for MBE-grown GaInP/GaAs/GaInNAsSb multijunction solar cells and the corresponding single junction sub-cells. Temperature-dependent current-voltage measurements were carried out using a solar simulator equipped with a 1000 W Xenon lamp and a three-band AM1.5D simulator. The triple-junction cell exhibited an efficiency of 31% at AM1.5G illumination and an efficiency of 37–39% at 70x real sun concentration. The external quantum efficiency was also measured at different temperatures. The temperature coefficients up to 80°C, for the open circuit voltage, the short circuit current density, and the conversion efficiency were determined to be −7.5 mV/°C, 0.040 mA/cm{sup 2}/°C, and −0.09%/°C, respectively.

  19. Polarization-induced Zener tunnel diodes in GaN/InGaN/GaN heterojunctions

    International Nuclear Information System (INIS)

    Yan, Xiaodong; Li, Wenjun; Islam, S. M.; Pourang, Kasra; Fay, Patrick; Xing, Huili; Jena, Debdeep

    2015-01-01

    By the insertion of thin In x Ga 1−x N layers into Nitrogen-polar GaN p-n junctions, polarization-induced Zener tunnel junctions are studied. The reverse-bias interband Zener tunneling current is found to be weakly temperature dependent, as opposed to the strongly temperature-dependent forward bias current. This indicates tunneling as the primary reverse-bias current transport mechanism. The Indium composition in the InGaN layer is systematically varied to demonstrate the increase in the interband tunneling current. Comparing the experimentally measured tunneling currents to a model helps identify the specific challenges in potentially taking such junctions towards nitride-based polarization-induced tunneling field-effect transistors

  20. Amphoteric Be in GaN: Experimental Evidence for Switching between Substitutional and Interstitial Lattice Sites

    Science.gov (United States)

    Tuomisto, Filip; Prozheeva, Vera; Makkonen, Ilja; Myers, Thomas H.; Bockowski, Michal; Teisseyre, Henryk

    2017-11-01

    We show that Be exhibits amphoteric behavior in GaN, involving switching between substitutional and interstitial positions in the lattice. This behavior is observed through the dominance of BeGa in the positron annihilation signals in Be-doped GaN, while the emergence of VGa at high temperatures is a consequence of the Be impurities being driven to interstitial positions. The similarity of this behavior to that found for Na and Li in ZnO suggests that this could be a universal property of light dopants substituting for heavy cations in compound semiconductors.

  1. Performance Analysis of GaN Capping Layer Thickness on GaN/AlGaN/GaN High Electron Mobility Transistors.

    Science.gov (United States)

    Sharma, N; Periasamy, C; Chaturvedi, N

    2018-07-01

    In this paper, we present an investigation of the impact of GaN capping layer and AlGaN layer thickness on the two-dimensional (2D)-electron mobility and the carrier concentration which was formed close to the AlGaN/GaN buffer layer for Al0.25Ga0.75N/GaN and GaN/Al0.25Ga0.75N/GaN heterostructures deposited on sapphire substrates. The results of our analysis clearly indicate that expanding the GaN capping layer thickness from 1 nm to 100 nm prompts an increment in the electron concentration at hetero interface. As consequence of which drain current was additionally increments with GaN cap layer thicknesses, and eventually saturates at approximately 1.85 A/mm for capping layer thickness greater than 40 nm. Interestingly, for the same structure, the 2D-electron mobility, decrease monotonically with GaN capping layer thickness, and saturate at approximately 830 cm2/Vs for capping layer thickness greater than 50 nm. A device with a GaN cap layer didn't exhibit gate leakage current. Furthermore, it was observed that the carrier concentration was first decrease 1.03 × 1019/cm3 to 6.65 × 1018/cm3 with AlGaN Layer thickness from 5 to 10 nm and after that it increases with the AlGaN layer thickness from 10 to 30 nm. The same trend was followed for electric field distributions. Electron mobility decreases monotonically with AlGaN layer thickness. Highest electron mobility 1354 cm2/Vs were recorded for the AlGaN layer thickness of 5 nm. Results obtained are in good agreement with published experimental data.

  2. Spin injection in epitaxial MnGa(111)/GaN(0001) heterostructures

    Science.gov (United States)

    Zube, Christian; Malindretos, Joerg; Watschke, Lars; Zamani, Reza R.; Disterheft, David; Ulbrich, Rainer G.; Rizzi, Angela; Iza, Michael; Keller, Stacia; DenBaars, Steven P.

    2018-01-01

    Ferromagnetic MnGa(111) layers were grown on GaN(0001) by molecular beam epitaxy. MnGa/GaN Schottky diodes with a doping level of around n = 7 × 1018 cm-3 were fabricated to achieve single step tunneling across the metal/semiconductor junction. Below the GaN layer, a thin InGaN quantum well served as optical spin detector ("spin-LED"). For electron spin injection from MnGa into GaN and subsequent spin transport through a 45 nm (70 nm) thick GaN layer, we observe a circular polarization of 0.3% (0.2%) in the electroluminescence at 80 K. Interface mixing, spin polarization losses during electrical transport in the GaN layer, and spin relaxation in the InGaN quantum well are discussed in relation with the low value of the optically detected spin polarization.

  3. Automated synthesis, characterization and biological evaluation of [{sup 68}Ga]Ga-AMBA, and the synthesis and characterization of {sup nat}Ga-AMBA and [{sup 67}Ga]Ga-AMBA

    Energy Technology Data Exchange (ETDEWEB)

    Cagnolini, Aldo; Chen Jianqing; Ramos, Kimberly; Marie Skedzielewski, Tina; Lantry, Laura E.; Nunn, Adrian D.; Swenson, Rolf E. [Ernst Felder Laboratories, Bracco Research USA Inc., 305 College Road East, Princeton, NJ 08540 (United States); Linder, Karen E., E-mail: karen.e.linder@gmail.co [Ernst Felder Laboratories, Bracco Research USA Inc., 305 College Road East, Princeton, NJ 08540 (United States)

    2010-12-15

    Ga-AMBA (Ga-DO3A-CH{sub 2}CO-G-[4-aminobenzoyl]-QWAVGHLM-NH{sub 2}) is a bombesin-like agonist with high affinity for gastrin releasing peptide receptors (GRP-R). Syntheses for {sup nat}Ga-AMBA, [{sup 67}Ga]Ga-AMBA and [{sup 68}Ga]Ga-AMBA were developed. The preparation of HPLC-purified and Sep-Pak purified [{sup 68}Ga]Ga-AMBA were fully automated, using the built-in radiodetector of the Tracerlab FX F-N synthesizer to monitor fractionated {sup 68}Ge/{sup 68}Ga generator elution and purification. The total synthesis time, including the fractional elution of the generator, was 20 min for Sep-Pak purified material and 40 min for HPLC-purified [{sup 68}Ga]Ga-AMBA. Both [{sup 67}Ga]Ga-AMBA and [{sup 177}Lu]Lu-AMBA showed comparable high affinity for GRP-R in the human prostate cancer cell line PC-3 in vitro (k{sub D}=0.46{+-}0.07; 0.44{+-}0.08 nM), high internalization (78; 77%) and low efflux from cells at 2 h (2.4{+-}0.7; 2.9{+-}1.8%). Biodistribution results in PC-3 tumor-bearing male nude mice showed comparable uptake for [{sup 177}Lu]Lu-, [{sup 111}In]In-, [{sup 67}Ga]Ga- and [{sup 68}Ga]Ga-AMBA.

  4. Capacitance properties and simulation of the AlGaN/GaN Schottky heterostructure

    International Nuclear Information System (INIS)

    Harmatha, Ladislav; Ľubica, Stuchlíková; Juraj, Racko; Juraj, Marek; Juraj, Pecháček; Peter, Benko; Michal, Nemec; Juraj, Breza

    2014-01-01

    Highlights: • Dependences of CV characteristics of the AlGaN/GaN structure on frequency and temperature variations. • Identification of electrical activity of defects by capacitance DLTS. • Simulating the properties of the GaN/Al 0.2 GaN 0.8 /GaN Schottky heterostructure. - Abstract: The paper presents the results of capacitance measurements on GaN/AlGaN/GaN Schottky heterostructures grown on an Al 2 O 3 substrate by Low-Pressure Metal–Organic Vapour-Phase Epitaxy (LP-MOVPE). Dependences of the capacitance–voltage (CV) characteristics on the frequency of the measuring signal allow analysing the properties of the 2D electron gas (2DEG) at the AlGaN/GaN heterojunction. Exact location of the hetero-interface below the surface (20 nm) was determined from the concentration profile. Temperature variations of the CV curves reveal the influence of bulk defects in GaN and of the traps at the AlGaN/GaN interface. Electrical activity of these defects was characterized by capacitance Deep Level Transient Fourier Spectroscopy (DLTFS). Experimental results of CV measurements were supported by simulating the properties of the GaN/Al 0.2 GaN 0.8 /GaN Schottky heterostructure in dependence on the influence of the concentration of donor-like traps in GaN and of the temperature upon the CV curves

  5. Growth of InGaN multiple quantum wells and GaN eplilayer on GaN substrate

    International Nuclear Information System (INIS)

    Lee, Sung-Nam; Paek, H.S.; Son, J.K.; Sakong, T.; Yoon, E.; Nam, O.H.; Park, Y.

    2006-01-01

    We investigated that the surface morphology of GaN epilayers was significantly affected by the surface tilt orientation of GaN substrate. Surface morphologies of GaN epilayers on GaN substrates show three types: mirror, wavy, and hillock. These surface morphologies are dependent on the surface orientation of GaN substrates. It is found that the hillock morphology of GaN epilayer was formed on the GaN substrate with surface tilt orientation less than 0.1 o . As the surface tilt angle increased to 0.35 o , the surface morphology varied from hillock to wavy morphology. Above a surface tilt angle of 0.4 o , surface morphology changed to the mirror-like type morphology. Additionally, these three types of GaN surface morphology also affected the optical quality of GaN epilayers as well as InGaN multiple quantum wells on GaN substrates by non-uniform In incorporation on the different surface morphologies of GaN epilayers

  6. Carrier confinement effects of InxGa1-xN/GaN multi quantum disks with GaN surface barriers grown in GaN nanorods

    Science.gov (United States)

    Park, Youngsin; Chan, Christopher C. S.; Taylor, Robert A.; Kim, Nammee; Jo, Yongcheol; Lee, Seung W.; Yang, Woochul; Im, Hyunsik

    2018-04-01

    Structural and optical properties of InxGa1-xN/GaN multi quantum disks (QDisks) grown on GaN nanorods by molecular beam epitaxy have been investigated by transmission electron microscopy and micro-photoluminescence (PL) spectroscopy. Two types of InGaN QDisks were grown: a pseudo-3D confined InGaN pillar-type QDisks embedded in GaN nanorods; and QDisks in flanged cone type GaN nanorods. The PL emission peak and excitation dependent PL behavior of the pillar-type Qdisks differ greatly from those of the flanged cone type QDisks. Time resolved PL was carried out to probe the differences in charge carrier dynamics. The results suggest that by constraining the formation of InGaN QDisks within the centre of the nanorod, carriers are restricted from migrating to the surface, decreasing the surface recombination at high carrier densities.

  7. FAA Air Traffic Activity. Fiscal Year 1991

    Science.gov (United States)

    1991-01-01

    MGR) GA 448 0 0 448 0 THOMASVILLE MUNICIPAL ............................................ (TVI) GA 963 0 0 963 0 TIFTON ...listed below for ordering purposes. ATLANTA, GA KANSAS CITY, MO 275 Peachtree Street. NE, Room 100, P.O. Box 56445, Atlanta, GA 120 Bannister Mail, 5600...CA L 3 660680 TORRANCE MUNICIPAL ................................... CA L 83 210157 ATLANTA INTERNATIONAL ............................. GA

  8. InGaN/GaN Nanowire LEDs and Lasers

    KAUST Repository

    Zhao, Chao

    2016-01-01

    The large specific surface, and the associated high density of surface states was found to limit the light output power and quantum efficiency of nanowire-array devices, despite their potential for addressing the “green-gap” and efficiency-droop issues. The phonon and carrier confinement in nanowires also led to junction heating, and reduced heat dissipation. In this paper, we will present our studies on effective surface states passivation in InGaN/GaN quantum-disks (Qdisks)-in-nanowire light-emitting diodes (LEDs) and lasers grown on silicon (Si), as well as our recent work on nanowires LEDs grown on bulk-metal, a non-conventional substrate.

  9. AlGaAs/InGaAs/AlGaAs double pulse doped pseudomorphic high electron mobility transistor structures on InGaAs substrates

    Science.gov (United States)

    Hoke, W. E.; Lyman, P. S.; Mosca, J. J.; McTaggart, R. A.; Lemonias, P. J.; Beaudoin, R. M.; Torabi, A.; Bonner, W. A.; Lent, B.; Chou, L.-J.; Hsieh, K. C.

    1997-10-01

    Double pulse doped AlGaAs/InGaAs/AlGaAs pseudomorphic high electron mobility transistor (PHEMT) structures have been grown on InxGa1-xAs (x=0.025-0.07) substrates using molecular beam epitaxy. A strain compensated, AlGaInAs/GaAs superlattice was used for improved resistivity and breakdown. Excellent electrical and optical properties were obtained for 110-Å-thick InGaAs channel layers with indium concentrations up to 31%. A room temperature mobility of 6860 cm2/V s with 77 K sheet density of 4.0×1012cm-2 was achieved. The InGaAs channel photoluminescence intensity was equivalent to an analogous structure on a GaAs substrate. To reduce strain PHEMT structures with a composite InGaP/AlGaAs Schottky layer were also grown. The structures also exhibited excellent electrical and optical properties. Transmission electron micrographs showed planar channel interfaces for highly strained In0.30Ga0.70As channel layers.

  10. Spectroscopic ellipsometry analysis of InGaN/GaN and AlGaN/GaN heterostructures using a parametric dielectric function model

    International Nuclear Information System (INIS)

    Wagner, J.; Ramakrishnan, A.; Obloh, H.; Kunzer, M.; Koehler, K.; Johs, B.

    2000-01-01

    Spectroscopic ellipsometry (SE) has been used for the characterization of AlGaN/GaN and InGaN/GaN heterostructures. The resulting pseudodielectric function spectra were analyzed using a multilayer approach, describing the dielectric functions of the individual layers by a parametric oscillator model. From this analysis, the dielectric function spectra of GaN, Al x Ga 1-x N (x le 0.16), and In 0.13 Ga 0.87 N were deduced. Further, the dependence of the Al x Ga 1-x N band gap energy on the Al mole fraction was derived and compared with photoluminescence data recorded on the same material. The SE band gap data are compatible with a bowing parameter close to 1 eV for the composition dependence of the Al x Ga 1-x N gap energy. Finally, the parametric dielectric functions have been used to model the pseudodielectric function spectrum of a complete GaN/AlGaN/InGaN LED structure

  11. Bipolar characteristics of AlGaN/AlN/GaN/AlGaN double heterojunction structure with AlGaN as buffer layer

    International Nuclear Information System (INIS)

    Peng, Enchao; Wang, Xiaoliang; Xiao, Hongling; Wang, Cuimei; Yin, Haibo; Chen, Hong; Feng, Chun; Jiang, Lijuan; Hou, Xun; Wang, Zhanguo

    2013-01-01

    Highlights: •2DEG and 2DHG coexist in the AlGaN/AlN/GaN/AlGaN DH-structure. •The sheet densities of 2DEG and 2DHG vary with buffer Al content and GaN thickness. •The conditions for the disappearance of 2DHG are discussed. •Increasing buffer Al content provides better electron confinement. •Dislocation scattering is reduced in the DH-structure. -- Abstract: This is a theoretical study of AlGaN/AlN/GaN/AlGaN double heterojunction (DH) structure with AlGaN as buffer layer. Our calculation shows that as the buffer Al content increases, though two-dimensional electron gas (2DEG) sheet density decreases, the channel back-barrier caused by polarization-induced electric field in GaN provides better electron confinement. And under certain conditions the DH-structure shows bipolar characteristics, with an additional two-dimensional hole gas (2DHG) formed at GaN/AlGaN interface. The influence of the buffer Al content and GaN channel thickness on the 2DEG and 2DHG sheet densities are investigated, and the conditions for the disappearance of 2DHG are discussed. Also, the mobility inhibited by dislocation scattering is enhanced in DH-structure due to the enhancement of screening effect of the 2DEG

  12. Gold free contacts to AlGaN/GaN heterostructures

    NARCIS (Netherlands)

    Hajlasz, Marcin

    2018-01-01

    Transistors and diodes based on AlGaN/GaN are suitable candidates for high-voltage and high-speed electronics due to the GaN material properties such as wide bandgap, large breakdown field, high electron saturation velocity and good thermal conductivity. When thin AlGaN layer is grown epitaxially on

  13. Gas sensing with AlGaN/GaN 2DEG channels

    NARCIS (Netherlands)

    Offermans, P.; Vitushinsky, R.; Crego-Calama, M.; Brongersma, S.H.

    2011-01-01

    AlGaN/GaN shows great promise as a generic platform for (bio-)chemical sensing because of its robustness and intrinsic sensitivity to surface charge or dipoles. Here, we employ the two-dimensional electron gas (2DEG) formed at the interface of AlGaN/GaN layers grown on Si substrates for the

  14. Exploring the radiosynthesis and in vitro characteristics of [68Ga]Ga-DOTA-Siglec-9

    DEFF Research Database (Denmark)

    Jensen, Svend Borup; Käkelä, Meeri; Jødal, Lars

    2017-01-01

    (Siglec-9) "CARLSLSWRGLTLCPSK" bind to VAP-1 and hence makes the radioactive analogues of this compound ([68 Ga]Ga-DOTA-Siglec-9) interesting as a non-invasive visualizing marker of inflammation. Three different approaches to the radiosynthesis of [68 Ga]Ga-DOTA-Siglec-9 are presented and compared...

  15. Characterization of GaN/AlGaN epitaxial layers grown

    Indian Academy of Sciences (India)

    GaN and AlGaN epitaxial layers are grown by a metalorganic chemical vapour deposition (MOCVD) system. The crystalline quality of these epitaxially grown layers is studied by different characterization techniques. PL measurements indicate band edge emission peak at 363.8 nm and 312 nm for GaN and AlGaN layers ...

  16. Exciton binding energy in wurtzite InGaN/GaN quantum wells

    International Nuclear Information System (INIS)

    Park, Seoung-Hwan; Kim, Jong-Jae; Kim, Hwa-Min

    2004-01-01

    The internal field and carrier density effects on the exciton binding energies in wurtzite (WZ) InGaN/GaN quantum-well (QW) structures are investigated using the multiband effective-mass theory, and are compared with those obtained from the at-band model and with those of GaN/AlGaN QW structures. The exciton binding energy is significantly reduced with increasing sheet carrier density, suggesting that excitons are nearly bleached at densities around 10 12 cm -2 for both InGaN/GaN and GaN/AlGaN QW structures. With the inclusion of the internal field, the exciton binding energy is substantialy reduced compared to that of the at-band model in the investigated region of the wells. This can be explained by a decrease in the momentum matrix element and an increase in the inverse screening length due to the internal field. The exciton binding energy of the InGaN/GaN structure is smaller than that of the GaN/AlGaN structure because InGaN/GaN structures have a smaller momentum matrix element and a larger inverse screening length than GaN/AlGaN structures.

  17. Rate of injury and subjective benefits of gravitational wellness weightlifting

    OpenAIRE

    Burke, David T; Bell, Regina; Al-Adawi, Samir; Alexandroni, Ariel; Dorvlo, Atsu; Burke, Daniel P

    2014-01-01

    David T Burke,1 Regina Bell,1 Samir Al-Adawi,2 Ariel Alexandroni,1 Atsu Dorvlo,3 Daniel P Burke4 1Emory University School of Medicine, Atlanta, Emory University, GA, USA; 2Department of Behavioral Medicine, College of Medicine and Health Sciences, 3Department of Mathematics and Statistics, College of Science, Sultan Qaboos University, Muscat, Oman; 4Georgia College and State University, Milledgeville, GA, USA Background: A preliminary study using the "gravitational wellness"...

  18. InGaAs and GaAsSb strain reducing layers covering InAs/GaAs quantum dots

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Hulicius, Eduard; Pangrác, Jiří; Oswald, Jiří; Vyskočil, Jan; Kuldová, Karla; Šimeček, Tomislav; Hazdra, P.; Caha, O.

    2010-01-01

    Roč. 312, č. 8 (2010), 1383-1387 ISSN 0022-0248 R&D Projects: GA AV ČR IAA100100719; GA ČR GA202/09/0676; GA MŠk LC510 Institutional research plan: CEZ:AV0Z10100521 Keywords : low dimensional structures * photoluminescence * low-pressure MOVPE * InAs/GaAs quantum dots * semiconducting III/V materials Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.737, year: 2010

  19. AlGaN/GaN High Electron Mobility Transistors with Multi-MgxNy/GaN Buffer

    OpenAIRE

    Chang, P. C.; Lee, K. H.; Wang, Z. H.; Chang, S. J.

    2014-01-01

    We report the fabrication of AlGaN/GaN high electron mobility transistors with multi-MgxNy/GaN buffer. Compared with conventional HEMT devices with a low-temperature GaN buffer, smaller gate and source-drain leakage current could be achieved with this new buffer design. Consequently, the electron mobility was larger for the proposed device due to the reduction of defect density and the corresponding improvement of crystalline quality as result of using the multi-MgxNy/GaN buffer.

  20. AlGaN/GaN High Electron Mobility Transistors with Multi-MgxNy/GaN Buffer

    Directory of Open Access Journals (Sweden)

    P. C. Chang

    2014-01-01

    Full Text Available We report the fabrication of AlGaN/GaN high electron mobility transistors with multi-MgxNy/GaN buffer. Compared with conventional HEMT devices with a low-temperature GaN buffer, smaller gate and source-drain leakage current could be achieved with this new buffer design. Consequently, the electron mobility was larger for the proposed device due to the reduction of defect density and the corresponding improvement of crystalline quality as result of using the multi-MgxNy/GaN buffer.

  1. ECV profiling of GaAs and GaN HEMT heterostructures

    Science.gov (United States)

    Yakovlev, G.; Zubkov, V.

    2018-03-01

    AlGaAs/InGaAs/GaAs and AlGaN/GaN HEMT heterostructures were investigated by means of electrochemical capacitance-voltage technique. A set of test structures were fabricated using various doping techniques: standard doping, δ-doping GaAs pHEMT and nondoping GaN HEMT. The concentration profiles of free charge carriers across the samples were experimentally obtained. The QW filling was analyzed and compared for different mechanisms of emitter doping and 2DEG origins.

  2. Incomplete Ionization of a 110 meV Unintentional Donor in Beta-Ga2O3 and its Effect on Power Devices (Postprint)

    Science.gov (United States)

    2017-10-16

    Adam T. Neal Universal Technology Corporation Shin Mou AFRL/RX Roberto Lopez and Jian V. Li Texas State University Darren B...ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NUMBER 1) Universal Technology Corp. 1270 N Fairfield Rd. Dayton, OH 45432 2) AFRL/RX...unintentional doping in Ga2O3. Previously unobserved unintentional donors in commercially available (2 ̅01) Ga2O3 substrates have been electrically

  3. Temperature sensitivity (Q10), and dynamics of soil organic matter (SOM) decomposition in permafrost soils with different carbon quality and under experimental warming. R. Bracho1, E.A.G Schuur1, E. Pegoraro1, K.G. Crummer1, S. Natali2, J. Zhou, Y Luo3, J. L. Wu3, M. Tiedje4, K. Konstantinidis5 1Department of Biology, University of Florida, Gainesville, FL. 2Woods Hole Research Center, Falmouth, MA. 3Institute for Environmental Genomics and Department of Botany and Microbiology, University of Oklahoma, Norman, OK, 4Center for Microbial Ecology, Michigan State University, East Lansing, MI; 5Center for Bioinformatics and Computational Genomics and School of Biology, Georgia Institute of Technology, Atlanta, GA

    Science.gov (United States)

    Bracho, R. G.; Schuur, E. A.; Pegoraro, E.; Crummer, K. G.; Natali, S.; Zhou, J.; Wu, L.; Luo, Y.; Tiedje, J. M.; Konstantinidis, K.

    2013-12-01

    Permafrost soils contain approximately1700 Pg of carbon (C), twice the amount of C in the atmosphere. Temperatures in higher latitudes are increasing, inducing permafrost thaw and subsequent microbial decomposition of previously frozen C. This process is one of the most likely positive feedbacks to climate change. Understanding the temperature sensitivity (Q10) and dynamics of SOM decomposition under warming is essential to predict the future state of the earth - climate system. Alaskan tundra soils were exposed to two winter warming (WW) seasons in the field, which warmed the soils by 4°C to 40 cm depth. Soils were obtained from three depths (0 - 15, 15 - 25 and 45 - 55 cm) and differed in initial amounts of labile and recalcitrant C. Soils were incubated in the lab under aerobic conditions, at 15 and 25°C over 365 days. Q10 was estimated at 14, 100 & 280 days of incubation (DOI); C fluxes were measured periodically and dynamics of SOM decomposition (C pool sizes and decay rates) were estimated by fitting a two pool C model to cumulative respired C (Ccum, mgC/ginitialC). After two WW seasons, initial C content tended to decrease through the soil profile and C:N ratio was significantly decreased in the top 15 cm. After one year of incubation, Ccum was twice as high at 25°C as at 15°C and significantly decreased with depth. No significant WW field treatment was detected, although Ccum tended to be lower in warmed soils. Labile C accounted for up to 5% of initial soil C content in the top 15 cm and decreased with depth. Soils exposed to WW had smaller labile C pools, and higher labile C decay rates in the top 25 cm. Q10 significantly decreased with time and depth as labile pool decreased, especially for WW. This decrease with time indicates a lower temperature sensitivity of the most recalcitrant C pool. The deepest WW soil layer, where warming was more pronounced, had significantly lower Q10 compared to control soils at the same depth. After two seasons, the warming treatment affected decomposition by reducing labile C pools and increasing its decay rates. Warming also reduced temperature sensitivity, showing acclimation of the most recalcitrant C pool in the tundra ecosystem.

  4. Temperature Dependence of the Energy Band Diagram of AlGaN/GaN Heterostructure

    Directory of Open Access Journals (Sweden)

    Yanli Liu

    2018-01-01

    Full Text Available Temperature dependence of the energy band diagram of AlGaN/GaN heterostructure was investigated by theoretical calculation and experiment. Through solving Schrodinger and Poisson equations self-consistently by using the Silvaco Atlas software, the energy band diagram with varying temperature was calculated. The results indicate that the conduction band offset of AlGaN/GaN heterostructure decreases with increasing temperature in the range of 7 K to 200 K, which means that the depth of quantum well at AlGaN/GaN interface becomes shallower and the confinement of that on two-dimensional electron gas reduces. The theoretical calculation results are verified by the investigation of temperature dependent photoluminescence of AlGaN/GaN heterostructure. This work provides important theoretical and experimental basis for the performance degradation of AlGaN/GaN HEMT with increasing temperature.

  5. Study of GaN nanorods converted from β-Ga2O3

    Science.gov (United States)

    Li, Yuewen; Xiong, Zening; Zhang, Dongdong; Xiu, Xiangqian; Liu, Duo; Wang, Shuang; Hua, Xuemei; Xie, Zili; Tao, Tao; Liu, Bin; Chen, Peng; Zhang, Rong; Zheng, Youdou

    2018-05-01

    We report here high-quality β-Ga2O3 nanorods (NRs) grown on sapphire substrates by hydrothermal method. Ammoniating the β-Ga2O3 NRs results in strain-free wurtzite gallium nitride (GaN) NRs. It was shown by XRD and Raman spectroscopy that β-Ga2O3 was partially converted to GaN/β-Ga2O3 at 1000 °C and then completely converted to GaN NRs at 1050 °C, as confirmed by high-resolution transmission electron microscopy (HRTEM). There is no band-edge emission of β-Ga2O3 in the cathodoluminescence spectrum, and only a deep-level broad emission observed at 3.68-3.73 eV. The band edge emission (3.39 eV) of GaN NRs converted from β-Ga2O3 can also be observed.

  6. Ohmic contacts to n+-GaN capped AlGaN/AlN/GaN high electron mobility transistors

    International Nuclear Information System (INIS)

    Wang Liang; Mohammed, Fitih M.; Ofuonye, Benedict; Adesida, Ilesanmi

    2007-01-01

    Investigations of Ti/Al/Mo/Au Ohmic contact formation, premetallization plasma treatment effects, and interfacial reactions for n + -GaN capped AlGaN/AlN/GaN heterostructures are presented. Ti thickness played an important role in determining contact performance. Transmission electron microscopy studies confirmed that thick Ti layer was necessary to fully consume the GaN cap and the top of AlGaN to enable a higher tunneling current flow. A direct correlation of plasma treatment conditions with I-V linearity, current level, and contact performance was established. The plasma-affected region is believed to extend over 20 nm into the AlGaN and GaN

  7. Durability testing of the high-capacity GA-4/GA-9 trailer

    International Nuclear Information System (INIS)

    Zimmer, A.; Lyon, T.

    1995-01-01

    GA designed trailers to transport the GA-4 and GA-9 LWT from-reactor spent nuclear fuel shipping casks. GA designed and fabricated the GA-9 trailer to ANSI N14.30 requirements and is now performing a durability test at the AlliedSignal Automotive Proving Grounds. The trailer, simulated cask and tractor. The test program objective is to evaluate and improve, as necessary, the trailer's durability, reliability and performance

  8. Reducing Mg acceptor activation-energy in Al(0.83)Ga(0.17)N disorder alloy substituted by nanoscale (AlN)₅/(GaN)₁ superlattice using Mg(Ga) δ-doping: Mg local-structure effect.

    Science.gov (United States)

    Zhong, Hong-xia; Shi, Jun-jie; Zhang, Min; Jiang, Xin-he; Huang, Pu; Ding, Yi-min

    2014-10-23

    Improving p-type doping efficiency in Al-rich AlGaN alloys is a worldwide problem for the realization of AlGaN-based deep ultraviolet optoelectronic devices. In order to solve this problem, we calculate Mg acceptor activation energy and investigate its relationship with Mg local structure in nanoscale (AlN)5/(GaN)1 superlattice (SL), a substitution for Al(0.83)Ga(0.17)N disorder alloy, using first-principles calculations. A universal picture to reduce acceptor activation energy in wide-gap semiconductors is given for the first time. By reducing the volume of the acceptor local structure slightly, its activation energy can be decreased remarkably. Our results show that Mg acceptor activation energy can be reduced significantly from 0.44 eV in Al(0.83)Ga(0.17)N disorder alloy to 0.26 eV, very close to the Mg acceptor activation energy in GaN, and a high hole concentration in the order of 10(19) cm(-3) can be obtained in (AlN)5/(GaN)1 SL by Mg(Ga) δ-doping owing to GaN-monolayer modulation. We thus open up a new way to reduce Mg acceptor activation energy and increase hole concentration in Al-rich AlGaN.

  9. Reducing Mg Acceptor Activation-Energy in Al0.83Ga0.17N Disorder Alloy Substituted by Nanoscale (AlN)5/(GaN)1 Superlattice Using MgGa δ-Doping: Mg Local-Structure Effect

    Science.gov (United States)

    Zhong, Hong-Xia; Shi, Jun-Jie; Zhang, Min; Jiang, Xin-He; Huang, Pu; Ding, Yi-Min

    2014-10-01

    Improving p-type doping efficiency in Al-rich AlGaN alloys is a worldwide problem for the realization of AlGaN-based deep ultraviolet optoelectronic devices. In order to solve this problem, we calculate Mg acceptor activation energy and investigate its relationship with Mg local structure in nanoscale (AlN)5/(GaN)1 superlattice (SL), a substitution for Al0.83Ga0.17N disorder alloy, using first-principles calculations. A universal picture to reduce acceptor activation energy in wide-gap semiconductors is given for the first time. By reducing the volume of the acceptor local structure slightly, its activation energy can be decreased remarkably. Our results show that Mg acceptor activation energy can be reduced significantly from 0.44 eV in Al0.83Ga0.17N disorder alloy to 0.26 eV, very close to the Mg acceptor activation energy in GaN, and a high hole concentration in the order of 1019 cm-3 can be obtained in (AlN)5/(GaN)1 SL by MgGa δ-doping owing to GaN-monolayer modulation. We thus open up a new way to reduce Mg acceptor activation energy and increase hole concentration in Al-rich AlGaN.

  10. Modeling and optimization of a double-well double-barrier GaN/AlGaN/GaN/AlGaN resonant tunneling diode

    Science.gov (United States)

    Liu, Yang; Gao, Bo; Gong, Min; Shi, Ruiying

    2017-06-01

    The influence of a GaN layer as a sub-quantum well for an AlGaN/GaN/AlGaN double barrier resonant tunneling diode (RTD) on device performance has been investigated by means of numerical simulation. The introduction of the GaN layer as the sub-quantum well turns the dominant transport mechanism of RTD from the 3D-2D model to the 2D-2D model and increases the energy difference between tunneling energy levels. It can also lower the effective height of the emitter barrier. Consequently, the peak current and peak-to-valley current difference of RTD have been increased. The optimal GaN sub-quantum well parameters are found through analyzing the electrical performance, energy band, and transmission coefficient of RTD with different widths and depths of the GaN sub-quantum well. The most pronounced electrical parameters, a peak current density of 5800 KA/cm2, a peak-to-valley current difference of 1.466 A, and a peak-to-valley current ratio of 6.35, could be achieved by designing RTD with the active region structure of GaN/Al0.2Ga0.8 N/GaN/Al0.2Ga0.8 N (3 nm/1.5 nm/1.5 nm/1.5 nm).

  11. Liapunov-type inequality for universal integral

    Czech Academy of Sciences Publication Activity Database

    Agahi, H.; Mohammadpour, A.; Mesiar, Radko; Vaezpour, M. S.

    2012-01-01

    Roč. 27, č. 10 (2012), s. 908-925 ISSN 0884-8173 R&D Projects: GA ČR GAP402/11/0378 Institutional support: RVO:67985556 Keywords : integral inequality * universal integral * Liapunov inequality Subject RIV: BA - General Mathematics Impact factor: 1.416, year: 2012 http://library.utia.cas.cz/separaty/2012/E/mesiar-liapunov-type inequality for universal integral.pdf

  12. Photoluminescence study of the nitrogen content effect on GaAs/GaAs1-xNx/GaAs/AlGaAs: (Si) quantum well

    International Nuclear Information System (INIS)

    Hamdouni, A.; Bousbih, F.; Ben bouzid, S.; Aloulou, S.; Harmand, J.C.; Chtourou, R.

    2008-01-01

    We study the effect of nitrogen content in modulation-doped GaAs/GaAs 1-x N x /GaAs/GaAlAs:(Si) quantum well using low-temperature photoluminescence spectroscopy. The samples were grown on GaAs (001) substrates by molecular-beam epitaxy with different nitrogen compositions. The variation of the nitrogen composition from 0.04% to 0.32% associated to the bi-dimensional electron gas gives a new interaction mode between the nitrogen localized states and the GaAs 1-x N x /GaAs energies levels. The red-shift observed in photoluminescence spectra as function of nitrogen content has been interpreted in the frame of the band anticrossing model

  13. Stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on GaAs and Ge/Si(001) substrates

    Energy Technology Data Exchange (ETDEWEB)

    Yablonsky, A. N., E-mail: yablonsk@ipm.sci-nnov.ru; Morozov, S. V.; Gaponova, D. M.; Aleshkin, V. Ya. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation); Shengurov, V. G.; Zvonkov, B. N.; Vikhrova, O. V.; Baidus’, N. V. [Lobachevsky State University of Nizhny Novgorod (Russian Federation); Krasil’nik, Z. F. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2016-11-15

    We report the observation of stimulated emission in heterostructures with double InGaAs/GaAsSb/GaAs quantum wells, grown on Si(001) substrates with the application of a relaxed Ge buffer layer. Stimulated emission is observed at 77 K under pulsed optical pumping at a wavelength of 1.11 μm, i.e., in the transparency range of bulk silicon. In similar InGaAs/GaAsSb/GaAs structures grown on GaAs substrates, room-temperature stimulated emission is observed at 1.17 μm. The results obtained are promising for integration of the structures into silicon-based optoelectronics.

  14. A plume-in-grid approach to characterize air quality impacts of aircraft emissions at the Hartsfield–Jackson Atlanta International Airport

    Directory of Open Access Journals (Sweden)

    J. Rissman

    2013-09-01

    Full Text Available This study examined the impacts of aircraft emissions during the landing and takeoff cycle on PM2.5 concentrations during the months of June and July 2002 at the Hartsfield–Jackson Atlanta International Airport. Primary and secondary pollutants were modeled using the Advanced Modeling System for Transport, Emissions, Reactions, and Deposition of Atmospheric Matter (AMSTERDAM. AMSTERDAM is a modified version of the Community Multiscale Air Quality (CMAQ model that incorporates a plume-in-grid process to simulate emissions sources of interest at a finer scale than can be achieved using CMAQ's model grid. Three fundamental issues were investigated: the effects of aircraft on PM2.5 concentrations throughout northern Georgia, the differences resulting from use of AMSTERDAM's plume-in-grid process rather than a traditional CMAQ simulation, and the concentrations observed in aircraft plumes at subgrid scales. Comparison of model results with an air quality monitor located in the vicinity of the airport found that normalized mean bias ranges from −77.5% to 6.2% and normalized mean error ranges from 40.4% to 77.5%, varying by species. Aircraft influence average PM2.5 concentrations by up to 0.232 μg m−3 near the airport and by 0.001–0.007 μg m−3 throughout the Atlanta metro area. The plume-in-grid process increases concentrations of secondary PM pollutants by 0.005–0.020 μg m−3 (compared to the traditional grid-based treatment but reduces the concentration of non-reactive primary PM pollutants by up to 0.010 μg m−3, with changes concentrated near the airport. Examination of subgrid-scale results indicates that median aircraft contribution to grid cells is higher than median puff concentration in the airport's grid cell and outside of a 20 km × 20 km square area centered on the airport, while in a 12 km × 12 km square ring centered on the airport, puffs have median concentrations over an order of magnitude higher than aircraft

  15. Universe symmetries

    International Nuclear Information System (INIS)

    Souriau, J.M.

    1984-01-01

    The sky uniformity can be noticed in studying the repartition of objects far enough. The sky isotropy description uses space rotations. The group theory elements will allow to give a meaning at the same time precise and general to the word a ''symmetry''. Universe models are reviewed, which must have both of the following qualities: - conformity with the physic known laws; - rigorous symmetry following one of the permitted groups. Each of the models foresees that universe evolution obeys an evolution equation. Expansion and big-bang theory are recalled. Is universe an open or closed space. Universe is also electrically neutral. That leads to a work hypothesis: the existing matter is not given data of universe but it appeared by evolution from nothing. Problem of matter and antimatter is then raised up together with its place in universe [fr

  16. Two new Np--Ga phases: α-NpGa2 and metastable m-NpGa2

    International Nuclear Information System (INIS)

    Giessen, B.C.; Elliott, R.O.

    1976-01-01

    Following an earlier study of metastable Np-rich Np--Ga alloys, rapidly quenched Np--Ga alloys with 63 to 80 at. pct. Ga were prepared and studied. Two new NpGa 2 phases, both with an AlB 2 type structure, were found: α-NpGa 2 , with a = 4.246A, c = 4.060A, c/a = 0.956, and m-NpGa 2 , with a = 4.412A, c = 3.642A, c/a = 0.825. While m-NpGa 2 was observed only in very fast quenched (splat cooled) samples and appears to be metastable, α-NpGa 2 is probably an equilibrium phase. In a splat cooled alloy with 75 at. pct. Ga, another, unidentified, metastable phase was observed. Crystal chemical discussions of atomic volumes, interatomic distances and axial ratios are given; the volume difference between the two forms of NpGa 2 is correlated with a valence change of Np

  17. If This Is a "Real" Housewife, Who Are All These Women Around Me?: An Examination of The Real Housewives of Atlanta and the Persistence of Historically Stereotypical Images of Black Women in Popular Reality Television.

    OpenAIRE

    Bunai, Dominique Christabel

    2014-01-01

    Stereotypical images of blacks have persisted throughout multiple forms of media for decades, with one of the most recent arenas being reality television programming. This study examines the Bravo Television network series The Real Housewives of Atlanta to consider the impact of reality television on the image of black women in America today. This increasingly popular show is the most viewed in The Real Housewives franchise, and demonstrates that black women in America do not embody any one h...

  18. Understanding the emission impacts of high-occupancy vehicle (HOV) to high-occupancy toll (HOT) lane conversions: Experience from Atlanta, Georgia.

    Science.gov (United States)

    Xu, Yanzhi Ann; Liu, Haobing; Rodgers, Michael O; Guin, Angshuman; Hunter, Michael; Sheikh, Adnan; Guensler, Randall

    2017-08-01

    Converting a congested high-occupancy vehicle (HOV) lane into a high-occupancy toll (HOT) lane is a viable option for improving travel time reliability for carpools and buses that use the managed lane. However, the emission impacts of HOV-to-HOT conversions are not well understood. The lack of emission impact quantification for HOT conversions creates a policy challenge for agencies making transportation funding choices. The goal of this paper is to evaluate the case study of before-and-after changes in vehicle emissions for the Atlanta, Georgia, I-85 HOV/HOT lane conversion project, implemented in October 2011. The analyses employed the Motor Vehicle Emission Simulator (MOVES) for project-level analysis with monitored changes in vehicle activity data collected by Georgia Tech researchers for the Georgia Department of Transportation (GDOT). During the quarterly field data collection from 2010 to 2012, more than 1.5 million license plates were observed and matched to vehicle class and age information using the vehicle registration database. The study also utilized the 20-sec, lane-specific traffic operations data from the Georgia NaviGAtor intelligent transportation system, as well as a direct feed of HOT lane usage data from the State Road and Tollway Authority (SRTA) managed lane system. As such, the analyses in this paper simultaneously assessed the impacts associated with changes in traffic volumes, on-road operating conditions, and fleet composition before and after the conversion. Both greenhouse gases and criteria pollutants were examined. A straight before-after analysis showed about 5% decrease in air pollutants and carbon dioxide (CO 2 ). However, when the before-after calendar year of analysis was held constant (to account for the effect of 1 yr of fleet turnover), mass emissions at the analysis site during peak hours increased by as much as 17%, with little change in CO 2 . Further investigation revealed that a large percentage decrease in criteria

  19. Density Functional Theory Study on Defect Feature of AsGaGaAs in Gallium Arsenide

    Directory of Open Access Journals (Sweden)

    Deming Ma

    2015-01-01

    Full Text Available We investigate the defect feature of AsGaGaAs defect in gallium arsenide clusters in detail by using first-principles calculations based on the density functional theory (DFT. Our calculations reveal that the lowest donor level of AsGaGaAs defect on the gallium arsenide crystal surface is 0.85 eV below the conduction band minimum, while the lowest donor level of the AsGaGaAs defect inside the gallium arsenide bulk is 0.83 eV below the bottom of the conduction band, consistent with gallium arsenide EL2 defect level of experimental value (Ec-0.82 eV. This suggests that AsGaGaAs defect is one of the possible gallium arsenide EL2 deep-level defects. Moreover, our results also indicate that the formation energies of internal AsGaGaAs and surface AsGaGaAs defects are predicted to be around 2.36 eV and 5.54 eV, respectively. This implies that formation of AsGaGaAs defect within the crystal is easier than that of surface. Our results offer assistance in discussing the structure of gallium arsenide deep-level defect and its effect on the material.

  20. Energetics of Mg incorporation at GaN(0001) and GaN(0001¯) surfaces

    Science.gov (United States)

    Sun, Qiang; Selloni, Annabella; Myers, T. H.; Doolittle, W. Alan

    2006-04-01

    By using density functional calculations in the generalized gradient approximation, we investigate the energetics of Mg adsorption and incorporation at GaN(0001) and GaN(0001¯) surfaces under various Ga and Mg coverage conditions as well as in presence of light or electron beam-induced electronic excitation. We find significant differences in Mg incorporation between Ga- and N-polar surfaces. Mg incorporation is easier at the Ga-polar surface, but high Mg coverages are found to cause important distortions which locally change the polarity from Ga to N polar. At the N-rich and moderately Ga-rich GaN(0001) surface, 0.25 ML of Mg substituting Ga in the top bilayer strongly reduce the surface diffusion barriers of Ga and N adatoms, in agreement with the surfactant effect observed in experiments. As the Mg coverage exceeds 0.5 ML, partial incorporation in the subsurface region (second bilayer) becomes favorable. A surface structure with 0.5 ML of incorporated Mg in the top bilayer and 0.25 ML in the second bilayer is found to be stable over a wide range of Ga chemical potential. At the Ga bilayer-terminated GaN(0001) surface, corresponding to Ga-rich conditions, configurations where Mg is incorporated in the interface region between the metallic Ga bilayer and the underlying GaN bilayer appear to be favored. At the N-polar surface, Mg is not incorporated under N-rich or moderately Ga-rich conditions, whereas incorporation in the adlayer may take place under Ga-rich conditions. In the presence of light or electron beam induced excitation, energy differences between Mg incorporated at the surface and in deeper layers are reduced so that the tendency toward surface segregation is also reduced.

  1. Internal quantum efficiency in yellow-amber light emitting AlGaN-InGaN-GaN heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Ngo, Thi Huong; Gil, Bernard; Valvin, Pierre [Laboratoire Charles Coulomb – UMR 5221, CNRS and University Montpellier, Case courier 074, 34095 Montpellier Cedex 5 (France); Damilano, Benjamin; Lekhal, Kaddour; De Mierry, Philippe [CRHEA-CNRS Centre de Recherche sur l' Hétéro-Epitaxie et ses Applications, Centre National de la Recherche Scientifique, rue Bernard Gregory, 06560 Valbonne (France)

    2015-09-21

    We determine the internal quantum efficiency of strain-balanced AlGaN-InGaN-GaN hetero-structures designed for yellow-amber light emission, by using a recent model based on the kinetics of the photoluminescence decay initiated by Iwata et al. [J. Appl. Phys. 117, 075701 (2015)]. Our results indicate that low temperature internal quantum efficiencies sit in the 50% range and we measure that adding an AlGaN layer increases the internal quantum efficiency from 50% up to 57% with respect to the GaN-InGaN case. More dramatic, it almost doubles from 2.5% up to 4.3% at room temperature.

  2. Development of GaAs Detectors for Physics at the LHC

    CERN Multimedia

    Chu, Zhonghua; Krais, R; Rente, C; Syben, O; Tenbusch, F; Toporowsky, M; Xiao, Wenjiang; Cavallini, A; Fiori, F; Edwards, M; Geppert, R; Goppert, R; Haberla, C; Hornung, M F; Irsigler, R; Rogalla, M; Beaumont, S; Raine, C; Skillicorn, I; Margelevicius, J; Meshkinis, S; Smetana, S; Jones, B; Santana, J; Sloan, T; Zdansky, K; Alexiev, D; Donnelly, I J; Canali, C; Chiossi, C; Nava, F; Pavan, P; Kubasta, J; Tomiak, Z; Tchmil, V; Tchountonov, A; Tsioupa, I; Dogru, M; Gray, R; Hou, Yuqian; Manolopoulos, S; Walsh, S; Aizenshtadt, G; Budnitsky, D L; Gossen, A; Khludkov, S; Koretskaya, O B; Okaevitch, L; Potapov, A; Stepanov, V E; Tolbanov, O; Tyagev, A; Matulionis, A; Pozela, J; Kavaliauskiene, G; Kazukauskas, V; Kiliulis, R; Rinkevicius, V; Slenys, S; Storasta, J V

    2002-01-01

    % RD-8 Development of GaAs Detectors for Physics at the LHC \\\\ \\\\The aims of the collaboration are to investigate the available material options, performance and limitations of simple pad, pixel and microstrip GaAs detectors for minimum ionising particles with radiation hardness and speed which are competitive with silicon detectors. This new technology was originally developed within our university laboratories but now benefits from increasing industrial interest and collaboration in detector fabrication. Initial steps have also been taken towards the fabrication of GaAs preamplifiers to match the detectors in radiation hardness. The programme of work aims to construct a demonstration detector module for an LHC forward tracker based on GaAs.

  3. Growth and characteristics of p-type doped GaAs nanowire

    Science.gov (United States)

    Li, Bang; Yan, Xin; Zhang, Xia; Ren, Xiaomin

    2018-05-01

    The growth of p-type GaAs nanowires (NWs) on GaAs (111) B substrates by metal-organic chemical vapor deposition (MOCVD) has been systematically investigated as a function of diethyl zinc (DEZn) flow. The growth rate of GaAs NWs was slightly improved by Zn-doping and kink is observed under high DEZn flow. In addition, the I–V curves of GaAs NWs has been measured and the p-type dope concentration under the II/III ratio of 0.013 and 0.038 approximated to 1019–1020 cm‑3. Project supported by the National Natural Science Foundation of China (Nos. 61376019, 61504010, 61774021) and the Fund of State Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications), China (Nos. IPOC2017ZT02, IPOC2017ZZ01).

  4. Self-diffusion in 69Ga121Sb/71Ga123Sb isotope heterostructures

    OpenAIRE

    Bracht, H.; Nicols, S. P.; Haller, E. E.; Silveira, Juan Pedro; Briones Fernández-Pola, Fernando

    2001-01-01

    Gallium and antimony self-diffusion experiments have been performed in undoped 69Ga121Sb/71Ga123Sb isotope heterostructures at temperatures between 571 and 708 °C under Sb- and Ga-rich ambients. Ga and Sb profiles measured with secondary ion mass spectrometry reveal that Ga diffuses faster than Sb by several orders of magnitude. This strongly suggests that the two self-atom species diffuse independently on their own sublattices. Experimental results lead us to conclude that Ga and Sb diffusio...

  5. Proceedings – Mathematical Sciences | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    Department of Mathematics, The University of Texas – Pan American, 1201 West University Drive, Edinburg, TX 78539, USA; School of Mathematics, Georgia Institute of Technology, Atlanta, GA 30332-0160, USA; Departamento de Matemáticas, Universidad de Antioquia, Calle 67 N◦53-108, Medellín, Colombia, USA ...

  6. Our Universe

    Science.gov (United States)

    Stern, Alan

    2001-03-01

    The Universe in which we live is unimaginably vast and ancient, with countless star systems, galaxies, and extraordinary phenomena such as black holes, dark matter, and gamma ray bursts. What phenomena remain mysteries, even to seasoned scientists? Our Universe is a fascinating collection of essays by some of the world's foremost astrophysicists. Some are theorists, some computational modelers, some observers, but all offer their insights into the most cutting-edge, difficult, and curious aspects of astrophysics. Compiled, the essays describe more than the latest techniques and findings. Each of the ten contributors offers a more personal perspective on their work, revealing what motivates them and how their careers and lives have been shaped by their desire to understand our universe. S. Alan Stern is Director of the Department of Space Studies at Southwest Research Institute in Boulder, Colorado. He is a planetary scientist and astrophysicist with both observational and theoretical interests. Stern is an avid pilot and a principal investigator in NASA's planetary research program, and he was selected to be a NASA space shuttle mission specialist finalist. He is the author of more than 100 papers and popular articles. His most recent book is Pluto & Charon (Wiley, 1997). Contributors: Dr. John Huchra, Harvard University Dr. Esther Hu, University of Hawaii, Honolulu Dr. John Mather, NASA Goddard Space Flight Center Dr. Nick Gnedin, University of Colorado, Boulder Dr. Doug Richstone, University of Michigan, Ann Arbor Dr. Bohdan Paczynski, Princeton University, NJ Dr. Megan Donahue, Space Telescope Science Institute, Baltimore, MD Dr. Jerry Ostriker, Princeton University, New Jersey G. Bothun, University of Oregon, Eugene

  7. Ga and Pt NMR study of UPtGa sub 5 and UNiGa sub 5

    CERN Document Server

    Kato, H; Tokunaga, Y; Tokiwa, Y; Ikeda, S; Onuki, Y; Kambe, S; Walstedt, R E

    2003-01-01

    Ga and Pt NMR measurements have been carried out for two isomorphs compounds, UPtGa sub 5 and UNiGa sub 5 , which exhibit different magnetic structures below T sub N. Knight shift K measurements in the paramagnetic region are reported here. The transferred hyperfine coupling constants at Ga and Pt sites are determined. The temperature independent part K sub 0 of K, which probes the conduction electron polarization at the ligand site, has been successfully evaluated. A nearly identical conduction electron structure in the paramagnetic region is suggested for these two compounds. The origin of the different magnetic structures is discussed.

  8. Photoluminescence characterization of GaAs/GaAs0.64P0.19Sb0.17/GaAs heterostructure

    International Nuclear Information System (INIS)

    Chen, J.Y.; Chen, B.H.; Huang, Y.S.; Chin, Y.C.; Tsai, H.S.; Lin, H.H.; Tiong, K.K.

    2013-01-01

    Interfacial characteristics of GaAs/GaAs 0.64 P 0.19 Sb 0.17 GaAs heterostructures and emission properties of a quaternary GaAs 0.64 P 0.19 Sb 0.17 layer were studied by excitation-power- and temperature-dependent photoluminescence (PL) measurements. The GaAs-to-GaAsPSb upper interface related emission feature and signals from GaAsPSb and GaAs were observed and characterized. The upper interface related emission peak was attributed to the radiative recombination of spatially separated electron–hole pairs and suggesting the type-II alignment at the GaAs/GaAsPSb interface. The localized excitonic emission feature of GaAsPSb revealed a blueshift due to the saturation effect of localized states and showed a fast thermal-quench with the increase of temperature. The temperature variation of the band edge emission signal of GaAsPSb was found to follow that of GaAs closely. -- Highlights: ► PL characterization of GaAs/GaAsPSb/GaAs heterostructure. ► Type-II alignment at the GaAs/GaAsPSb interface. ► Near-band-edge emission lines of GaAsPSb

  9. Impacts of Combined Cooling, Heating and Power Systems, and Rainwater Harvesting on Water Demand, Carbon Dioxide, and NOx Emissions for Atlanta.

    Science.gov (United States)

    James, Jean-Ann; Sung, Sangwoo; Jeong, Hyunju; Broesicke, Osvaldo A; French, Steven P; Li, Duo; Crittenden, John C

    2018-01-02

    The purpose of this study is to explore the potential water, CO 2 and NO x emission, and cost savings that the deployment of decentralized water and energy technologies within two urban growth scenarios can achieve. We assess the effectiveness of urban growth, technological, and political strategies to reduce these burdens in the 13-county Atlanta metropolitan region. The urban growth between 2005 and 2030 was modeled for a business as usual (BAU) scenario and a more compact growth (MCG) scenario. We considered combined cooling, heating and power (CCHP) systems using microturbines for our decentralized energy technology and rooftop rainwater harvesting and low flow fixtures for the decentralized water technologies. Decentralized water and energy technologies had more of an impact in reducing the CO 2 and NO x emissions and water withdrawal and consumption than an MCG growth scenario (which does not consider energy for transit). Decentralized energy can reduce the CO 2 and NO x emissions by 8% and 63%, respectively. Decentralized energy and water technologies can reduce the water withdrawal and consumption in the MCG scenario by 49% and 50% respectively. Installing CCHP systems on both the existing and new building stocks with a net metering policy could reduce the CO 2 , NO x , and water consumption by 50%, 90%, and 75% respectively.

  10. Water, Air Emissions, and Cost Impacts of Air-Cooled Microturbines for Combined Cooling, Heating, and Power Systems: A Case Study in the Atlanta Region

    Directory of Open Access Journals (Sweden)

    Jean-Ann James

    2016-12-01

    Full Text Available The increasing pace of urbanization means that cities and global organizations are looking for ways to increase energy efficiency and reduce emissions. Combined cooling, heating, and power (CCHP systems have the potential to improve the energy generation efficiency of a city or urban region by providing energy for heating, cooling, and electricity simultaneously. The purpose of this study is to estimate the water consumption for energy generation use, carbon dioxide (CO2 and NOx emissions, and economic impact of implementing CCHP systems for five generic building types within the Atlanta metropolitan region, under various operational scenarios following the building thermal (heating and cooling demands. Operating the CCHP system to follow the hourly thermal demand reduces CO2 emissions for most building types both with and without net metering. The system can be economically beneficial for all building types depending on the price of natural gas, the implementation of net metering, and the cost structure assumed for the CCHP system. The greatest reduction in water consumption for energy production and NOx emissions occurs when there is net metering and when the system is operated to meet the maximum yearly thermal demand, although this scenario also results in an increase in greenhouse gas emissions and, in some cases, cost. CCHP systems are more economical for medium office, large office, and multifamily residential buildings.

  11. Trends in cytogenetic testing and identification of chromosomal abnormalities among pregnancies and children with birth defects, metropolitan Atlanta, 1968-2005.

    Science.gov (United States)

    Jackson, Jodi M; Crider, Krista S; Rasmussen, Sonja A; Cragan, Janet D; Olney, Richard S

    2012-01-01

    The purpose of this study was to examine changes in the use of cytogenetic testing and identification of chromosomal abnormalities among pregnancies and children with birth defects. Utilizing data from 1968 to 2005 from the Metropolitan Atlanta Congenital Defects Program, we analyzed trends in the frequency and timing (prenatal or postnatal) of cytogenetic testing and the prevalence of recognized chromosome abnormalities among pregnancies and children with birth defects (n = 51,424). Cytogenetic testing of pregnancies and children with birth defects increased from 7.2% in 1968 to 25.0% in 2005, as did the identification of chromosomal abnormalities (2.2% in 1968 to 6.8% in 2005). The use of prenatal cytogenetic testing decreased from 1996 to 2005 among women aged ≥35 years. Identification of chromosomal abnormalities in pregnancies and children with birth defects increased from 1968 to 2005, possibly due to increased testing, improved diagnostic techniques, or increasing maternal age. The decline in prenatal cytogenetic testing observed among mothers aged ≥35 years may be related to the availability of improved prenatal screening techniques, resulting in a reduction in the utilization of invasive diagnostic tests. Published 2011 Wiley Periodicals, Inc. This article is a U.S. Government work and is in the public domain in the USA.

  12. AlGaN nanocolumns and AlGaN/GaN/AlGaN nanostructures grown by molecular beam epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Ristic, J.; Sanchez-Garcia, M.A.; Ulloa, J.M.; Calleja, E. [Departamento de Ingenieria Electronica, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Sanchez-Paramo, J.; Calleja, J.M. [Departamento de Fisica de Materiales, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Jahn, U.; Trampert, A.; Ploog, K.H. [Paul-Drude-Institut fuer Festkoerperelektronik, Hausvogteiplatz 5-7, 10117 Berlin (Germany)

    2002-12-01

    This work reports on the characterization of hexagonal, single crystal AlGaN nanocolumns with diameters in the range of 30 to 100 nm grown by molecular beam epitaxy on Si(111) substrates. The change of the flux ratio between the Al and the total III-element controls the alloy composition. The Al composition trend versus the Al flux is consistent both with the E{sub 2} phonon energy values measured by inelastic light scattering and the luminescence emission peaks position. High quality low dimensional AlGaN/GaN/AlGaN heterostructures with five GaN quantum discs, 2 and 4 nm thick, embedded into the AlGaN columns, were designed in order to study the quantum confinement effects. (Abstract Copyright [2002], Wiley Periodicals, Inc.)

  13. Characteristics study of 2DEG transport properties of AlGaN/GaN and AlGaAs/GaAs-based HEMT

    International Nuclear Information System (INIS)

    Lenka, T. R.; Panda, A. K.

    2011-01-01

    Growth of wide bandgap material over narrow bandgap material, results into a two dimensional electron gas (2DEG) at the heterointerface due to the conduction band discontinuity. In this paper the 2DEG transport properties of AlGaN/GaN-based high electron mobility transistor (HEMT) is discussed and its effect on various characteristics such as 2DEG density, C-V characteristics and Sheet resistances for different mole fractions are presented. The obtained results are also compared with AlGaAs/GaAs-based HEMT for the same structural parameter as like AlGaN/GaN-based HEMT. The calculated results of electron sheet concentration as a function of the Al mole fraction are in excellent agreement with some experimental data available in the literature.

  14. Role of AlGaN/GaN interface traps on negative threshold voltage shift in AlGaN/GaN HEMT

    Science.gov (United States)

    Malik, Amit; Sharma, Chandan; Laishram, Robert; Bag, Rajesh Kumar; Rawal, Dipendra Singh; Vinayak, Seema; Sharma, Rajesh Kumar

    2018-04-01

    This article reports negative shift in the threshold-voltage in AlGaN/GaN high electron mobility transistor (HEMT) with application of reverse gate bias stress. The device is biased in strong pinch-off and low drain to source voltage condition for a fixed time duration (reverse gate bias stress), followed by measurement of transfer characteristics. Negative threshold voltage shift after application of reverse gate bias stress indicates the presence of more carriers in channel as compared to the unstressed condition. We propose the presence of AlGaN/GaN interface states to be the reason of negative threshold voltage shift, and developed a process to electrically characterize AlGaN/GaN interface states. We verified the results with Technology Computer Aided Design (TCAD) ATLAS simulation and got a good match with experimental measurements.

  15. Comparison of MOVPE grown GaAs, InGaAs and GaAsSb covering layers for different InAs/GaAs quantum dot applications

    Czech Academy of Sciences Publication Activity Database

    Zíková, Markéta; Hospodková, Alice; Pangrác, Jiří; Oswald, Jiří; Hulicius, Eduard

    2017-01-01

    Roč. 464, Apr (2017), s. 59-63 ISSN 0022-0248 R&D Projects: GA MŠk LO1603 Institutional support: RVO:68378271 Keywords : MOVPE * quantum dot * strain reducing layer * InAs * GaAsSb * InGaAs Subject RIV: BM - Solid Matter Physics ; Magnetism OBOR OECD: Condensed matter physics (including formerly solid state physics, supercond.) Impact factor: 1.751, year: 2016

  16. Lithium compensation of GaAs

    International Nuclear Information System (INIS)

    Alexiev, D.; Tavendale, A.J.

    1988-08-01

    Defects generated following Li diffusion into GaAs were studied by optical deep level transient spectroscopy (ODLTS) and deep level transient spectroscopy (DLTS). In an exploratory series of experiments, the effect of Li diffusion on existing trap spectra, defect generation and as a means for the compensation of GaAs was studied. The variables included diffusion temperature, initial trap spectra of GaAs and annealing periods. Detailed measurements of trap energies were made

  17. Intelligent Universe

    Energy Technology Data Exchange (ETDEWEB)

    Hoyle, F

    1983-01-01

    The subject is covered in chapters, entitled: chance and the universe (synthesis of proteins; the primordial soup); the gospel according to Darwin (discussion of Darwin theory of evolution); life did not originate on earth (fossils from space; life in space); the interstellar connection (living dust between the stars; bacteria in space falling to the earth; interplanetary dust); evolution by cosmic control (microorganisms; genetics); why aren't the others here (a cosmic origin of life); after the big bang (big bang and steady state); the information rich universe; what is intelligence up to; the intelligent universe.

  18. Cation disorder in Ga1212.

    Science.gov (United States)

    Greenwood, K B; Ko, D; Vander Griend, D A; Sarjeant, G M; Milgram, J W; Garrity, E S; DeLoach, D I; Poeppelmeier, K R; Salvador, P A; Mason, T O

    2000-07-24

    Substitution of calcium for strontium in LnSr2-xCaxCu2GaO7 (Ln = La, Pr, Nd, Gd, Ho, Er, Tm, and Yb) materials at ambient pressure and 975 degrees C results in complete substitution of calcium for strontium in the lanthanum and praseodymium systems and partial substitution in the other lanthanide systems. The calcium saturation level depends on the size of the Ln cation, and in all cases, a decrease in the lattice parameters with calcium concentration was observed until a common, lower bound, average A-cation size is reached. Site occupancies from X-ray and neutron diffraction experiments for LnSr2-xCaxCu2GaO7 (x = 0 and x = 2) confirm that the A-cations distribute between the two blocking-layer sites and the active-layer site based on size. A quantitative link between cation distribution and relative site-specific cation enthalpy for calcium, strontium, and lanthanum within the gallate structure is derived. The cation distribution in other similar materials can potentially be modeled.

  19. GaN Bulk Growth and Epitaxy from Ca-Ga-N Solutions, Phase I

    Data.gov (United States)

    National Aeronautics and Space Administration — This SBIR proposal addresses the liquid phase epitaxy (LPE) of gallium nitride (GaN) films using nitrogen-enriched metal solutions. Growth of GaN from solutions...

  20. Tunable High efficiency Resonant Tunneling GaN/AlGaN MQW UV Detectors

    National Research Council Canada - National Science Library

    Wang, W. B; Zhang, S. K; Alfano, R. R

    2005-01-01

    ...)-based UV photodetectors. During the grant period, more than twenty six GaN/AlGaN MQW phoptodetectors with different types of device structures and control samples have been fabricated and investigated to achieve the proposed...

  1. InGaN nanoinclusions in an AlGaN matrix

    International Nuclear Information System (INIS)

    Sizov, V. S.; Tsatsul'nikov, A. F.; Lundin, V. V.

    2008-01-01

    GaN-based structures with InGaN quantum dots in the active region emitting in the near-ultraviolet region are studied. In this study, two types of structures, namely, with InGaN quantum dots in a GaN or AlGaN matrix, are compared. Photoluminescence spectra are obtained for both types of structures in a temperature range of 80-300 K and at various pumping densities, and electroluminescence spectra are obtained for light-emitting (LED) structures with various types of active region. It is shown that the structures with quantum dots in the AlGaN matrix are more stable thermally due to the larger localization energy compared with quantum dots in the GaN matrix. Due to this, the LED structures with quantum dots in an AlGaN matrix are more effective.

  2. Development of Passivation Technology for Improved GaN/AlGaN HEMT Performance and Reliability

    National Research Council Canada - National Science Library

    Abernathy, C. R; Hunter-Edwards, Angela

    2005-01-01

    .... As part of the recipe development we have studied fundamental characteristics of the native oxides on GaN and AlGaN surfaces using XPS and compared the results to oxides generated by exposure to UV...

  3. Nanomaterial disordering in AlGaN/GaN UV LED structures

    International Nuclear Information System (INIS)

    Shabunina, E I; Levinshtein, M E; Kulagina, M M; Petrov, V N; Ratnikov, V V; Smirnova, I N; Troshkov, S I; Shmidt, N M; Kurin, S Yu; Makarov, Yu N; Chernyakov, A E; Usikov, A S; Helava, H

    2015-01-01

    Multifractal analysis was applied to characterize quantitatively nanostructural disordering in HVPE-grown AlGaN/GaN UV LED structures. A higher level of leakage currents shunting the active region of LEDs by an extended defect system is correlated with higher values of multifractal parameters (MFs). As a result, the concentration of injected carriers participating in radiative recombination in the active region is reduced. MFs and the conductivity of quasi-ohmic shunts localized in an extended defect system are higher in AlGaN/GaN structures than in InGaN/GaN structures. It is one of the reasons behind the low external quantum efficiency of AlGaN/GaN UV LEDs. (paper)

  4. USAID University

    Data.gov (United States)

    US Agency for International Development — USAID University is USAID's learning management system. Features include 1) Access online courses 2) Register for instructor-led courses 3)Access your student...

  5. Runaway universe

    Energy Technology Data Exchange (ETDEWEB)

    Davies, P

    1978-01-01

    The subject is covered in chapters entitled: the emerging universe (general introduction, history of astronomical and cosmological research, origins, the expanding universe, stars, galaxies, electromagnetic radiation); primeval fire (the big bang model, origin of the elements, properties of the elements and of sub-atomic particles); order out of chaos (galactic evolution, star formation, nuclear fusion, the solar system, origin of life on Earth); a star called Sol (properties of the sun and of other stars); life in the universe; the catastrophe principle (the rise and fall of cosmic order); stardoom (star evolution, neutron stars); black holes and superholes (gravitational collapse); technology and survival; the dying universe (second law of thermodynamics); worlds without end (cosmological models).

  6. Rhodes University

    African Journals Online (AJOL)

    Samridhi Sharma

    2013-10-29

    Oct 29, 2013 ... been taken may improve the reception, by the target audience, of the intended communication. This may ... alcohol marketing. Similarly .... of the intended users (Rhodes University support staff ..... Digital Human Modeling and.

  7. Reducing Threshold of Multi Quantum Wells InGaN Laser Diode by Using InGaN/GaN Waveguide

    Science.gov (United States)

    Abdullah, Rafid A.; Ibrahim, Kamarulazizi

    2010-07-01

    ISE TCAD (Integrated System Engineering Technology Computer Aided Design) software simulation program has been utilized to help study the effect of using InGaN/GaN as a waveguide instead of conventional GaN waveguide for multi quantum wells violet InGaN laser diode (LD). Simulation results indicate that the threshold of the LD has been reduced by using InGaN/GaN waveguide where InGaN/GaN waveguide increases the optical confinement factor which leads to increase the confinement carriers at the active region of the LD.

  8. Undulant Universe

    Energy Technology Data Exchange (ETDEWEB)

    Barenboim, Gabriela; /Valencia U.; Mena, Olga; Quigg, Chris; /Fermilab

    2004-12-01

    If the equation of state for ''dark energy'' varies periodically, the expansion of the Universe may have undergone alternating eras of acceleration and deceleration. We examine a specific form that survives existing observational tests, does not single out the present state of the Universe as exceptional, and suggests a future much like the matter-dominated past: a smooth expansion without a final inflationary epoch.

  9. Self-consistent simulation of carrier confinement characteristics in (AlyGa1−yN/AlN)SLs/GaN/(InxGa1−xN/GaN)MQW/GaN heterostructures

    International Nuclear Information System (INIS)

    Ding Jieqin; Wang Xiaoliang; Xiao Hongling; Wang Cuimei; Yin Haibo; Chen Hong; Feng Chun; Jiang Lijuan

    2012-01-01

    Highlights: ► We present calculations of carrier confinement characteristics. ► An optimization of In x Ga 1−x N/GaN multiquantum-well (MQW) was made. ► 2DEG sheet carrier density in designed heterostructure is greatly increased. ► Interface roughness and alloy disorder scattering reduced. ► Carrier mobility will be improved in designed heterostructure. - Abstract: We present calculations of carrier confinement characteristics in (Al y Ga 1−y N/AlN)SLs/GaN/(In x Ga 1−x N/GaN)MQW/GaN heterojunction structure in the presence of spontaneous and piezoelectrically induced polarization effects. The calculations were made using a self-consistent solution of the Schrödinger, Poisson, potential and charge balance equations. An optimization of In x Ga 1−x N/GaN multiquantum-well (MQW) was made firstly including thickness of GaN channel, InGaN, and indium composition of In x Ga 1−x N in order to increase carrier density and mobility, and the influence of pairs of AlGaN/AlN superlattices (SLs) and InGaN/GaN MQWs on structure was discussed. Theoretical calculations clearly indicate that the two-dimensional electron gas (2DEG) sheet carrier density in designed heterostructure is greatly increased due to the enhancing of carrier confinement compared to those in conventional AlGaN/GaN one at the similar Al composition. Furthermore, the calculated carrier distribution shows that carrier mobility will be improved by reducing interface roughness and alloy disorder scattering in designed heterostructure.

  10. Strain-balanced InGaN/GaN multiple quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Van Den Broeck, D. M.; Hosalli, A. M.; Bedair, S. M. [Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Bharrat, D.; El-Masry, N. A. [Department of Material Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States)

    2014-07-21

    InGaN/GaN multiple quantum well (MQW) structures suffer from a high amount of compressive strain in the InGaN wells and the accompanied piezoelectric field resulting in both a blue shift in emission and a reduction of emission intensity. We report the growth of In{sub x}Ga{sub 1−x}N/GaN “strain-balanced” multiple quantum wells (SBMQWs) grown on thick In{sub y}Ga{sub 1−y}N templates for x > y by metal organic chemical vapor deposition. SBMQWs consist of alternating layers of In{sub x}Ga{sub 1−x}N wells and GaN barriers under compressive and tensile stress, respectively, which have been lattice matched to a thick In{sub y}Ga{sub 1−y}N template. Growth of the In{sub y}Ga{sub 1−y}N template is also detailed in order to achieve thick, relaxed In{sub y}Ga{sub 1−y}N grown on GaN without the presence of V-grooves. When compared to conventional In{sub x}Ga{sub 1−x}N/GaN MQWs grown on GaN, the SBMQW structures exhibit longer wavelength emission and higher emission intensity for the same InN mole fraction due to a reduction in the well strain and piezoelectric field. By matching the average lattice constant of the MQW active region to the lattice constant of the In{sub y}Ga{sub 1−y}N template, essentially an infinite number of periods can be grown using the SBMQW growth method without relaxation-related effects. SBMQWs can be utilized to achieve longer wavelength emission in light emitting diodes without the use of excess indium and can be advantageous in addressing the “green gap.”.

  11. Growth and characterization of Ga(As,N) and (In,Ga)(As,N)

    International Nuclear Information System (INIS)

    Mussler, G.

    2005-01-01

    This dissertation deals with the MBE growth and characterization of Ga(As,N) and (In,Ga)(As,N). The work commences with the optimization of the Ga(As,N) growth. Owing to a large miscibility gap of GaN in GaAs, the incorporation of nitrogen into GaAs causes a structural degradation that is dependent on the substrate temperature, the nitrogen concentration, and the quantum well thickness. Another problem related to the growth of Ga(As,N) are point defects that have a detrimental influence on optical properties. A thermal treatment of Ga(As,N) reduces the concentration of these point defects. This leads to a substantial improvement of optical properties. We will show that nitrogen split interstitials that incorporate into gallium and arsenic vacancies may be attributed to these point defects. A thermal treatment of Ga(As,N) at high temperatures, on the contrary, results in a creation of extended defects which are detrimental to optical properties. We show that the temperature of the thermal treatment that yields the highest photoluminescence intensity is nitrogen concentration-dependent. The growth of (In,Ga)(As,N) is similar with respect to Ga(As,N). Again, one has to face a high miscibility gap of (In,Ga)N in (In,Ga)As that results in a structural degradation. A thermal treatment of (In,Ga)(As,N) is also beneficial for improving optical properties. We show that a thermal treatment of (In,Ga)As results in an indium diffusion that is suppressed by the incorporation of nitrogen. The characterization of (In,Ga)(As,N) edge emitting lasers shows emission at wavelengths up to 1366 nm. With higher nitrogen concentrations, there is a strong increase of the threshold current density and a decrease of the output power

  12. Fabrication of InGaN/GaN nanopillar light-emitting diode arrays

    DEFF Research Database (Denmark)

    Ou, Yiyu; Fadil, Ahmed; Ou, Haiyan

    Nanopillar InGaN/GaN green light-emitting diode arrays were fabricated by using self-assembled nanopatterning and dry etching process. Both internal and external quantum efficiency were increased due to strain relaxation and enhanced light extraction.......Nanopillar InGaN/GaN green light-emitting diode arrays were fabricated by using self-assembled nanopatterning and dry etching process. Both internal and external quantum efficiency were increased due to strain relaxation and enhanced light extraction....

  13. Evaluation of Ga-67 scintigraphy for salivary gland tumors

    International Nuclear Information System (INIS)

    Takase, Hiroshi; Toyama, Michio; Eguchi, Tooru; Maeda, Kadzuo

    1993-01-01

    It is often difficult to exactly grasp the malignancy of salivary gland tumor because of inadaptability of percutaneous biopsy. The purpose of this study is to discuss whether Ga-67 scintigraphy on patient with salivary gland tumor can provide useful information for differential diagnosis. We studied retrospectivelly the case records of twenty patients with parotid or submandibular gland tumors admitted to the Nippon Dental University, School of Dentistry at Niigata, between January 1984 and December 1991. The final diagnoses of these twenty patients were pleomorphic adenoma in 11, adenocarcinoma in 3, adenoid cystic carcinoma in 3, Warthin's tumor in 1, oncocytoma in 1, and carcinoma in pleomorphic adenoma in 1. The scintigraphic patterns of the twenty patients were classified as negative (-), weakly positive (+), moderate positive (++), strongly positive (+++). Malignant tumors showed increased activity in Ga-67 images except those in three patients with adenoid cystic carcinomas. We concluded that Ga-67 scintigraphy may be useful to distinguish benign salivary gland tumors from adenocarcinoma or carcinoma in pleomorphic adenoma, but not be useful in detection of adenoid cystic carcinoma. (author)

  14. Resonant circular photogalvanic effect in GaN/AlGaN heterojunctions

    NARCIS (Netherlands)

    Wittmann, B.; Golub, L. E.; Danilov, S. N.; Karch, J.; Reitmaier, C.; Kvon, Z. D.; Vinh, N. Q.; van der Meer, A. F. G.; Murdin, B.; Ganichev, S. D.

    2008-01-01

    The resonant circular photogalvanic effect is observed in wurtzite (0001)-oriented GaN low-dimensional structures excited by infrared radiation. The current is induced by angular-momentum transfer of photons to the photoexcited electrons at resonant intersubband optical transitions in a GaN/AlGaN

  15. Recessed insulator and barrier AlGaN/GaN HEMT: A novel structure ...

    Indian Academy of Sciences (India)

    2017-03-08

    Mar 8, 2017 ... AlGaN/GaN high electron mobility transistor; breakdown voltage; output power density; short channel effect ... is an n-type heavily doped Al0.32Ga0.68N while the ..... [15] S E J Mahabadi, A A Orouji, P Keshavarzi and H A.

  16. Characterization of GaN/AlGaN epitaxial layers grown by ...

    Indian Academy of Sciences (India)

    GaN and AlGaN epitaxial layers are grown by a metalorganic chemical ... reported by introducing annealing of the GaN layer in nitrogen [5], Fe doping [6], .... [2] Y F Wu, S M Wood, R P Smith, S Sheppard, S T Allen, P Parikh and J Milligan,.

  17. A InGaN/GaN quantum dot green (λ=524 nm) laser

    KAUST Repository

    Zhang, Meng; Banerjee, Animesh; Lee, Chi-Sen; Hinckley, John M.; Bhattacharya, Pallab

    2011-01-01

    The characteristics of self-organized InGaN/GaN quantum dot lasers are reported. The laser heterostructures were grown on c-plane GaN substrates by plasma-assisted molecular beam epitaxy and the laser facets were formed by focused ion beam etching

  18. High resolution x-ray diffraction analyses of GaN/LiGaO{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Matyi, R.J. [Department of Materials Science and Engineering University of Wisconsin, Madison, WI (United States); Doolittle, W.A.; Brown, A.S. [School of Electrical and Computer Engineering Georgia Institute of Technology, Atlanta, GA (United States)

    1999-05-21

    Lithium gallate (LiGaO{sub 2}) is gaining increasing attention as a potential substrate for the growth of the important semiconductor GaN. In order to better understand this material we have performed high-resolution double- and triple-axis x-ray diffraction analyses of both the starting LiGaO{sub 2} and GaN/LiGaO{sub 2} following epitaxial growth. A high-resolution triple-axis reciprocal space map of the substrate showed a sharp, well-defined crystal truncation rod and a symmetric streak of intensity perpendicular to q{sub 002}, suggesting high structural quality with mosaic spread. Triple-axis scans following GaN growth showed (1) the development of isotropic diffuse scatter around the LiGaO{sub 2} (002) reflection, (2) the presence of a semi-continuous intensity streak between the LiGaO{sub 2} (002) and GaN (0002) reflections, and (3) a compact pattern of diffuse scatter around the GaN (0002) reflection that becomes increasingly anisotropic as the growth temperature is increased. These results suggest that LiGaO{sub 2} permits the epitaxial growth of GaN with structural quality that may be superior to that observed when growth is performed on SiC or Al{sub 2}O{sub 3}. (author)

  19. Characterization of a Ga-assisted GaAs nanowire array solar cell on si substrate

    DEFF Research Database (Denmark)

    Boulanger, J. P.; Chia, A. C. E.; Wood, B.

    2016-01-01

    A single-junction core-shell GaAs nanowire (NW) solar cell on Si (1 1 1) substrates is presented. A Ga-assisted vapor–liquid–solid growth mechanism was used for the formation of a patterned array of radial p-i-n GaAs NWs encapsulated in AlInP passivation. Novel device fabrication utilizing facet-...

  20. Exploring the radiosynthesis and in vitro characteristics of [68 Ga]Ga-DOTA-Siglec-9.

    Science.gov (United States)

    Jensen, Svend B; Käkelä, Meeri; Jødal, Lars; Moisio, Olli; Alstrup, Aage K O; Jalkanen, Sirpa; Roivainen, Anne

    2017-07-01

    Vascular adhesion protein 1 is a leukocyte homing-associated glycoprotein, which upon inflammation rapidly translocates from intracellular sources to the endothelial cell surface. It has been discovered that the cyclic peptide residues 283-297 of sialic acid-binding IgG-like lectin 9 (Siglec-9) "CARLSLSWRGLTLCPSK" bind to vascular adhesion protein 1 and hence makes the radioactive analogues of this compound ([ 68 Ga]Ga-DOTA-Siglec-9) interesting as a noninvasive visualizing marker of inflammation. Three different approaches to the radiosynthesis of [ 68 Ga]Ga-DOTA-Siglec-9 are presented and compared with previously published methods. A simple, robust radiosynthesis of [ 68 Ga]Ga-DOTA-Siglec-9 with a yield of 62% (non decay-corrected) was identified, and it had a radiochemical purity >98% and a specific radioactivity of 35 MBq/nmol. Furthermore, the protein binding and stability of [ 68 Ga]Ga-DOTA-Siglec-9 were analyzed in vitro in mouse, rat, rabbit, pig, and human plasma and compared with in vivo pig results. The plasma in vitro protein binding of [ 68 Ga]Ga-DOTA-Siglec-9 was the lowest in the pig followed by rabbit, human, rat, and mouse. It was considerably higher in the in vivo pig experiments. The in vivo stability in pigs was lower than the in vitro stability. Despite considerable species differences, the observed characteristics of [ 68 Ga]Ga-DOTA-Siglec-9 are suitable as a positron emission tomography tracer. Copyright © 2017 John Wiley & Sons, Ltd.

  1. Silicon—a new substrate for GaN growth

    Indian Academy of Sciences (India)

    Unknown

    of GaN devices based on silicon is the thermal mismatch of GaN and Si, which generates cracks. In 1998, the .... Considerable research is being carried out on GaN HEMTs at present. ... by InGaN/GaN multiquantum well in MOVPE was first.

  2. White emission from non-planar InGaN/GaN MQW LEDs grown on GaN template with truncated hexagonal pyramids.

    Science.gov (United States)

    Lee, Ming-Lun; Yeh, Yu-Hsiang; Tu, Shang-Ju; Chen, P C; Lai, Wei-Chih; Sheu, Jinn-Kong

    2015-04-06

    Non-planar InGaN/GaN multiple quantum well (MQW) structures are grown on a GaN template with truncated hexagonal pyramids (THPs) featuring c-plane and r-plane surfaces. The THP array is formed by the regrowth of the GaN layer on a selective-area Si-implanted GaN template. Transmission electron microscopy shows that the InGaN/GaN epitaxial layers regrown on the THPs exhibit different growth rates and indium compositions of the InGaN layer between the c-plane and r-plane surfaces. Consequently, InGaN/GaN MQW light-emitting diodes grown on the GaN THP array emit multiple wavelengths approaching near white light.

  3. Multicharacterization approach for studying InAl(Ga)N/Al(Ga)N/GaN heterostructures for high electron mobility transistors

    Energy Technology Data Exchange (ETDEWEB)

    Naresh-Kumar, G., E-mail: naresh.gunasekar@strath.ac.uk; Trager-Cowan, C. [Dept of Physics, SUPA, University of Strathclyde, Glasgow G4 0NG (United Kingdom); Vilalta-Clemente, A.; Morales, M.; Ruterana, P. [CIMAP UMR 6252 CNRS-ENSICAEN-CEA-UCBN 14050 Caen Cedex (France); Pandey, S.; Cavallini, A.; Cavalcoli, D. [Dipartimento di Fisica Astronomia, Università di Bologna, 40127 Bologna (Italy); Skuridina, D.; Vogt, P.; Kneissl, M. [Institute of Solid State Physics, Technical University Berlin, 10623 Berlin (Germany); Behmenburg, H.; Giesen, C.; Heuken, M. [AIXTRON SE, Kaiserstr. 98, 52134 Herzogenrath (Germany); Gamarra, P.; Di Forte-Poisson, M. A. [Thales Research and Technology, III-V Lab, 91460 Marcoussis (France); Patriarche, G. [LPN, Route de Nozay, 91460 Marcoussis (France); Vickridge, I. [Institut des NanoSciences, Université Pierre et Marie Curie, 75015 Paris (France)

    2014-12-15

    We report on our multi–pronged approach to understand the structural and electrical properties of an InAl(Ga)N(33nm barrier)/Al(Ga)N(1nm interlayer)/GaN(3μm)/ AlN(100nm)/Al{sub 2}O{sub 3} high electron mobility transistor (HEMT) heterostructure grown by metal organic vapor phase epitaxy (MOVPE). In particular we reveal and discuss the role of unintentional Ga incorporation in the barrier and also in the interlayer. The observation of unintentional Ga incorporation by using energy dispersive X–ray spectroscopy analysis in a scanning transmission electron microscope is supported with results obtained for samples with a range of AlN interlayer thicknesses grown under both the showerhead as well as the horizontal type MOVPE reactors. Poisson–Schrödinger simulations show that for high Ga incorporation in the Al(Ga)N interlayer, an additional triangular well with very small depth may be exhibited in parallel to the main 2–DEG channel. The presence of this additional channel may cause parasitic conduction and severe issues in device characteristics and processing. Producing a HEMT structure with InAlGaN as the barrier and AlGaN as the interlayer with appropriate alloy composition may be a possible route to optimization, as it might be difficult to avoid Ga incorporation while continuously depositing the layers using the MOVPE growth method. Our present work shows the necessity of a multicharacterization approach to correlate structural and electrical properties to understand device structures and their performance.

  4. Multicharacterization approach for studying InAl(GaN/Al(GaN/GaN heterostructures for high electron mobility transistors

    Directory of Open Access Journals (Sweden)

    G. Naresh-Kumar

    2014-12-01

    Full Text Available We report on our multi–pronged approach to understand the structural and electrical properties of an InAl(GaN(33nm barrier/Al(GaN(1nm interlayer/GaN(3μm/ AlN(100nm/Al2O3 high electron mobility transistor (HEMT heterostructure grown by metal organic vapor phase epitaxy (MOVPE. In particular we reveal and discuss the role of unintentional Ga incorporation in the barrier and also in the interlayer. The observation of unintentional Ga incorporation by using energy dispersive X–ray spectroscopy analysis in a scanning transmission electron microscope is supported with results obtained for samples with a range of AlN interlayer thicknesses grown under both the showerhead as well as the horizontal type MOVPE reactors. Poisson–Schrödinger simulations show that for high Ga incorporation in the Al(GaN interlayer, an additional triangular well with very small depth may be exhibited in parallel to the main 2–DEG channel. The presence of this additional channel may cause parasitic conduction and severe issues in device characteristics and processing. Producing a HEMT structure with InAlGaN as the barrier and AlGaN as the interlayer with appropriate alloy composition may be a possible route to optimization, as it might be difficult to avoid Ga incorporation while continuously depositing the layers using the MOVPE growth method. Our present work shows the necessity of a multicharacterization approach to correlate structural and electrical properties to understand device structures and their performance.

  5. Stellar laboratories. IV. New Ga iv, Ga v, and Ga vi oscillator strengths and the gallium abundance in the hot white dwarfs G191-B2B and RE 0503-289

    Science.gov (United States)

    Rauch, T.; Werner, K.; Quinet, P.; Kruk, J. W.

    2015-05-01

    Context. For the spectral analysis of high-resolution and high-signal-to-noise (S/N) spectra of hot stars, advanced non-local thermodynamic equilibrium (NLTE) model atmospheres are mandatory. These atmospheres are strongly dependent on the reliability of the atomic data that are used to calculate them. Aims: Reliable Ga iv-vi oscillator strengths are used to identify Ga lines in the spectra of the DA-type white dwarf G191-B2B and the DO-type white dwarf RE 0503-289 and to determine their photospheric Ga abundances. Methods: We newly calculated Ga iv-vi oscillator strengths to consider their radiative and collisional bound-bound transitions in detail in our NLTE stellar-atmosphere models for analyzing of Ga lines exhibited in high-resolution and high-S/N UV observations of G191-B2B and RE 0503-289. Results: We unambiguously detected 20 isolated and 6 blended (with lines of other species) Ga v lines in the Far Ultraviolet Spectroscopic Explorer (FUSE) spectrum of RE 0503-289. The identification of Ga iv and Ga vi lines is uncertain because they are weak and partly blended by other lines. The determined Ga abundance is 3.5 ± 0.5 × 10-5 (mass fraction, about 625 times the solar value). The Ga iv/Ga v ionization equilibrium, which is a very sensitive indicator for the effective temperature, is well reproduced in RE 0503-289. We identified the strongest Ga iv lines (at 1258.801, 1338.129 Å) in the HST/STIS spectrum of G191-B2B and measured a Ga abundance of 2.0 ± 0.5 × 10-6 (about 22 times solar). Conclusions: Reliable measurements and calculations of atomic data are a prerequisite for stellar-atmosphere modeling. The observed Ga iv-v line profiles in two white dwarf (G191-B2B and RE 0503-289) ultraviolet spectra were well reproduced with our newly calculated oscillator strengths. For the first time, this allowed us to determine the photospheric Ga abundance in white dwarfs. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space

  6. Growth of (20 anti 21)AlGaN, GaN and InGaN by metal organic vapor phase epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Ploch, S.; Wernicke, T.; Rass, J.; Pristovsek, M. [TU Berlin, Institut fuer Festkoerperphysik, Hardenbergstr. 36, 10623 Berlin (Germany); Weyers, M. [Ferdinand-Braun-Institut, Leibniz Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany); Kneissl, M. [TU Berlin, Institut fuer Festkoerperphysik, Hardenbergstr. 36, 10623 Berlin (Germany); Ferdinand-Braun-Institut, Leibniz Institut fuer Hoechstfrequenztechnik, Gustav-Kirchhoff-Str. 4, 12489 Berlin (Germany)

    2012-07-01

    Green InGaN-based laser diodes on (20 anti 21)GaN substrates have recently demonstrated performances exceeding those of conventional (0001) oriented devices. However little is known regarding the growth parameters. We have investigated growth of AlGaN, GaN and InGaN on (20 anti 21)GaN substrates by MOVPE. Smooth GaN layers with a rms roughness <0.5 nm were obtained by low growth temperatures and reactor pressures. The layers exhibit undulations along [10 anti 14] similar to the GaN substrate. AlGaN and InGaN layers exhibit an increased surface roughness. Undulation bunching was observed and attributed to reduced adatom surface mobility due to the binding energy of Al and the low growth temperature for InGaN respectively or strain relaxation. AlGaN and InGaN heterostructures on (20 anti 21)GaN relax by layer tilt accompanied by formation of misfit dislocations, due to shear strain of the unit cell. This relaxation mechanism leads to a reduced critical layer thickness of (20 anti 21)AlGaN layers and InGaN multi quantum wells (MQW) in comparison to (0001). PL spectral broadening of 230 meV of (20 anti 21)InGaN single QWs emitting at 415 nm can be reduced by increased growth temperature or increased number of QWs with reduced thickness.

  7. ReGaTE: Registration of Galaxy Tools in Elixir.

    Science.gov (United States)

    Doppelt-Azeroual, Olivia; Mareuil, Fabien; Deveaud, Eric; Kalaš, Matúš; Soranzo, Nicola; van den Beek, Marius; Grüning, Björn; Ison, Jon; Ménager, Hervé

    2017-06-01

    Bioinformaticians routinely use multiple software tools and data sources in their day-to-day work and have been guided in their choices by a number of cataloguing initiatives. The ELIXIR Tools and Data Services Registry (bio.tools) aims to provide a central information point, independent of any specific scientific scope within bioinformatics or technological implementation. Meanwhile, efforts to integrate bioinformatics software in workbench and workflow environments have accelerated to enable the design, automation, and reproducibility of bioinformatics experiments. One such popular environment is the Galaxy framework, with currently more than 80 publicly available Galaxy servers around the world. In the context of a generic registry for bioinformatics software, such as bio.tools, Galaxy instances constitute a major source of valuable content. Yet there has been, to date, no convenient mechanism to register such services en masse. We present ReGaTE (Registration of Galaxy Tools in Elixir), a software utility that automates the process of registering the services available in a Galaxy instance. This utility uses the BioBlend application program interface to extract service metadata from a Galaxy server, enhance the metadata with the scientific information required by bio.tools, and push it to the registry. ReGaTE provides a fast and convenient way to publish Galaxy services in bio.tools. By doing so, service providers may increase the visibility of their services while enriching the software discovery function that bio.tools provides for its users. The source code of ReGaTE is freely available on Github at https://github.com/C3BI-pasteur-fr/ReGaTE . © The Author 2017. Published by Oxford University Press.

  8. Plasma universe

    International Nuclear Information System (INIS)

    Alfven, H.

    1986-04-01

    Traditionally the views in our cosmic environment have been based on observations in the visual octave of the electromagnetic spectrum, during the last half-century supplemented by infrared and radio observations. Space research has opened the full spectrum. Of special importance are the X-ray-gamma-ray regions, in which a number of unexpected phenomena have been discovered. Radiations in these regions are likely to originate mainly from magnetised cosmic plasma. Such a medium may also emit synchrotron radiation which is observable in the radio region. If we try to base a model of the universe on the plasma phenomena mentioned we find that the plasma universe is drastically different from the traditional visual universe. Information about the plasma universe can also be obtained by extrapolation of laboratory experiments and magnetospheric in situ measurements of plasma. This approach is possible because it is likely that the basic properties of plasma are the same everywhere. In order to test the usefulness of the plasma universe model we apply it to cosmogony. Such an approach seems to be rather successful. For example, the complicated structure of the Saturnian C ring can be accounted for. It is possible to reconstruct certain phenomena 4-5 bilions years ago with an accuracy of better than 1 percent

  9. Metal-interconnection-free integration of InGaN/GaN light emitting diodes with AlGaN/GaN high electron mobility transistors

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Chao; Cai, Yuefei; Liu, Zhaojun; Ma, Jun; Lau, Kei May, E-mail: eekmlau@ust.hk [Photonics Technology Center, Department of Electronic and Computer Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong)

    2015-05-04

    We report a metal-interconnection-free integration scheme for InGaN/GaN light emitting diodes (LEDs) and AlGaN/GaN high electron mobility transistors (HEMTs) by combining selective epi removal (SER) and selective epitaxial growth (SEG) techniques. SER of HEMT epi was carried out first to expose the bottom unintentionally doped GaN buffer and the sidewall GaN channel. A LED structure was regrown in the SER region with the bottom n-type GaN layer (n-electrode of the LED) connected to the HEMTs laterally, enabling monolithic integration of the HEMTs and LEDs (HEMT-LED) without metal-interconnection. In addition to saving substrate real estate, minimal interface resistance between the regrown n-type GaN and the HEMT channel is a significant improvement over metal-interconnection. Furthermore, excellent off-state leakage characteristics of the driving transistor can also be guaranteed in such an integration scheme.

  10. AlGaAs and AlGaAs/GaAs/AlGaAs nanowires grown by molecular beam epitaxy on silicon substrates

    DEFF Research Database (Denmark)

    Cirlin, G E; Reznik, R R; Shtrom, I V

    2017-01-01

    The data on growth peculiarities and physical properties of GaAs insertions embedded in AlGaAs nanowires grown on different (1 1 1) substrates by Au-assisted molecular beam epitaxy are presented. The influence of nanowires growth conditions on structural and optical properties is studied in detail...

  11. Properties and Bibliography of GaSe

    Science.gov (United States)

    1994-02-01

    Musaev, A. E. Bakhyshev, N. M. Gasanly and L. G. Musaeva . (1975). "Anisotropy of the optical constants of GaS and GaSe near the absorption edge." Sov...Phys. Semiconductors. 9 94-95 Russian ref.: Fiz. Tekh. Poluprovodn. 9 142-145 (January 1975). Akhundov, G. A., L. G. Musaeva and M. D. Khomutova

  12. Metal-interconnection-free integration of InGaN/GaN light emitting diodes with AlGaN/GaN high electron mobility transistors

    International Nuclear Information System (INIS)

    Liu, Chao; Cai, Yuefei; Liu, Zhaojun; Ma, Jun; Lau, Kei May

    2015-01-01

    We report a metal-interconnection-free integration scheme for InGaN/GaN light emitting diodes (LEDs) and AlGaN/GaN high electron mobility transistors (HEMTs) by combining selective epi removal (SER) and selective epitaxial growth (SEG) techniques. SER of HEMT epi was carried out first to expose the bottom unintentionally doped GaN buffer and the sidewall GaN channel. A LED structure was regrown in the SER region with the bottom n-type GaN layer (n-electrode of the LED) connected to the HEMTs laterally, enabling monolithic integration of the HEMTs and LEDs (HEMT-LED) without metal-interconnection. In addition to saving substrate real estate, minimal interface resistance between the regrown n-type GaN and the HEMT channel is a significant improvement over metal-interconnection. Furthermore, excellent off-state leakage characteristics of the driving transistor can also be guaranteed in such an integration scheme

  13. 70Ge, 72Ge, 74Ge, 76Ge(d,3He)69Ga, 71Ga, 73Ga, 75Ga reactions at 26 MeV

    International Nuclear Information System (INIS)

    Rotbard, G.; La Rana, G.; Vergnes, M.; Berrier, G.; Kalifa, J.; Guilbaut, G.; Tamisier, R.

    1978-01-01

    The 70 Ge, 72 Ge, 74 Ge, 76 Ge(d, 3 He) 69 Ga, 71 Ga, 73 Ga, 75 Ga reactions have been studied at 26 MeV with 15 keV resolution (F.W.H.M), using the Orsay MP tandem accelerator and a split pole magnetic spectrometer. The spectroscopic factors are determined for 15 levels in 69 Ga and 11 levels in each of the 3 other Ga isotopes. Level schemes are proposed for the practically unknown 73 Ga and 75 Ga. Very simple model wave functions previously proposed for Ge nuclei are seen to reproduce quite well the measured occupation numbers for the proton orbitals. Anomalies in these occupation numbers are observed between Z=31 and 32 and between N=40 and 42, this last one corresponding to the structural transition observed recently in a comparison of the (p,t) and (t,p) reactions. These anomalies could be related to changes in the nuclear shape

  14. Radiative and non-radiative recombination in GaInN/GaN quantum wells; Strahlende und nichtstrahlende Rekombination in GaInN/GaN-Quantenfilmen

    Energy Technology Data Exchange (ETDEWEB)

    Netzel, C.

    2007-02-08

    The studies presented in this thesis deal with the occurence of V defectsin GaInN/GaN quantum film structures grown by means of organometallic gas phase epitaxy, and the effects, which have the V defects respectively the GaInN quantum films on the V-defect facets on the emission and recombination properties of the whole GaInN/GaN quantum film structure. The V-defects themselves, inverse pyramidal vacancies with hexagonal base in the semiconductor layers, arise under suitable growth conditions around the percussion violations, which extend in lattice-mismatched growth of GaN on the heterosubstrates sapphire or silicon carbide starting in growth direction through the crystal. If GaInN layers are grown over V-defect dispersed layers on the (1-101) facets of the V defects and the (0001) facets, the growth front of the structure, different growth velocities are present, which lead to differently wide GaInN quantum films on each facets.

  15. Interface and transport properties of GaN/graphene junction in GaN-based LEDs

    International Nuclear Information System (INIS)

    Wang Liancheng; Zhang Yiyun; Liu Zhiqiang; Guo Enqing; Yi Xiaoyan; Wang Junxi; Wang Guohong; Li Xiao; Zhu Hongwei

    2012-01-01

    A normalized circular transmission line method pattern with uniform interface area was developed to obtain contact resistances of p-, u-, n-GaN/graphene contacts (p, u and n represent p-type doped, unintentionally doped and n-type doped, respectively) and N-polar u-, n-GaN/graphene contacts in GaN-based LEDs. The resistances of the graphene/GaN contacts were mainly determined by the work function gap and the carrier concentration in GaN. Annealing caused diffusion of metal atoms and significantly influenced the interface transport properties.

  16. Density of Ga2O3 Liquid

    OpenAIRE

    Dingwell, Donald B.

    1992-01-01

    The density of Ga2O3 liquid in equilibrium with air has been measured at 18000 to 19000C using an Ir double-bob Archimedean method. The data yield the following description of the density of Ga2O3 liquid: ρ= 4.8374(84)–0.00065(12)(T −18500C). This density-temperature relationship is compared with the partial molar volume of Ga2O3 in glasses in the systems CaO–Ga2O3–SiO2 and Na2O–Ga2O3–SiO2, corrected to the glass transition temperature using thermal expansivities. The comparison illustrates t...

  17. Study of 67Ga scan in sarcoidosis

    International Nuclear Information System (INIS)

    Han Lijun; Qu Wanyin; Liu Xiuqin

    1997-01-01

    Gallium scan and serum angiotensin-converting enzyme assay (SACE) were compared in patients with sarcoidosis. The examination of 67 Ga scan, SACE determination, pulmonary function test, chest CT and chest X-ray in 24 cases with sarcoidosis were studied. The results revealed that 4 of 24 cases had obviously high uptake of 67 Ga exceeding hepatic activity (3+) in clinical active stage, 3 patients had resembling the Greek letter lambda, symmetrically located in bilateral hilar lymph nodes, and among them two had an uptake of 67 Ga in the bilateral lacrimal and parotid gland simulating 'Panda Face'. 8 of 20 cases with inactive sarcoidosis had an abnormal 67 Ga scan (1+). In those patients with normal SACE level but increased uptake of 67 Ga, active stage of disease was demonstrated and steroid therapy was indicated. Gallium scan is a valuable method for the staging of its activity and evaluation of the therapeutic effect in the follow-up patients with sarcoidosis

  18. Modeling of altered layer formation during reactive ion etching of GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Mutzke, A. [Max-Planck-Institute of Plasmaphysics, EURATOM Association, D-17491 Greifswald (Germany); Rai, A., E-mail: Abha.Rai@ipp.mpg.de [Max-Planck-Institute of Plasmaphysics, EURATOM Association, D-17491 Greifswald (Germany); Schneider, R.; Angelin, E.J.; Hippler, R. [Institute of Physics, Ernst-Moritz-Arndt-University Greifswald, Felix-Hausdorff-Str.6, D-17489 Greifswald (Germany)

    2012-12-15

    Highlights: Black-Right-Pointing-Pointer Experimental result showing the preferential sputtering of GaAs (150 keV Ar{sup +} and thermal O on GaAs) during reactive ion beam etching (RIBE) has been reported. Black-Right-Pointing-Pointer A model based on binary collisions (SDTrimSP) is presented to simulate RIBE. Black-Right-Pointing-Pointer The model is used to explain the reported experimental data and also the results by Grigonis and co-workers [1]. - Abstract: The binary collision based SDTrimSP model has been used to simulate the reactive ion beam etching (RIBE) of GaAs in the presence of energetic Ar ions and thermal O atoms. It includes the collisional effects, diffusive processes and chemical reactions taking place in the system. The model parameters are fitted using the experimental observations of Grigonis and co-workers [1] and validated with the experimental results obtained during the GaAs ion etching presented in this paper. A detailed analysis is presented to understand the effect of the diffusive processes and the role of O during RIBE of GaAs. It is shown how the presence of damage caused by the energetic Ar coupled with the presence of thermal O opens up chemical reaction channels which eventually leads to the preferential sputtering of Ga observed at the ion etching facility at University of Greifswald.

  19. Baby universes

    International Nuclear Information System (INIS)

    Strominger, A.

    1988-01-01

    This paper discusses how the subject of baby universes and their effects on spacetime coupling constants is in its infancy and rapidly developing. The subject is based on the non-existent (even by physicists' standards) Euclidean formulation of quantum gravity, and it is therefore necessary to make a number of assumptions in order to proceed. Nevertheless, the picture which has emerged is quite appealing: all spacetime coupling constants become dynamical variables when the effects of baby universes are taken into account. This fact might even solve the puzzle of the cosmological constant. The subject therefore seems worth further investigation

  20. Self-diffusion in 69Ga121Sb/71Ga123Sb isotope heterostructures

    Science.gov (United States)

    Bracht, H.; Nicols, S. P.; Haller, E. E.; Silveira, J. P.; Briones, F.

    2001-05-01

    Gallium and antimony self-diffusion experiments have been performed in undoped 69Ga121Sb/71Ga123Sb isotope heterostructures at temperatures between 571 and 708 °C under Sb- and Ga-rich ambients. Ga and Sb profiles measured with secondary ion mass spectrometry reveal that Ga diffuses faster than Sb by several orders of magnitude. This strongly suggests that the two self-atom species diffuse independently on their own sublattices. Experimental results lead us to conclude that Ga and Sb diffusion are mediated by Ga vacancies and Sb interstitials, respectively, and not by the formation of a triple defect proposed earlier by Weiler and Mehrer [Philos. Mag. A 49, 309 (1984)]. The extremely slow diffusion of Sb up to the melting temperature of GaSb is proposed to be a consequence of amphoteric transformations between native point defects which suppress the formation of those native defects which control Sb diffusion. Preliminary experiments exploring the effect of Zn indiffusion at 550 °C on Ga and Sb diffusion reveal an enhanced intermixing of the Ga isotope layers compared to undoped GaSb. However, under the same conditions the diffusion of Sb was not significantly affected.

  1. A hole modulator for InGaN/GaN light-emitting diodes

    Science.gov (United States)

    Zhang, Zi-Hui; Kyaw, Zabu; Liu, Wei; Ji, Yun; Wang, Liancheng; Tan, Swee Tiam; Sun, Xiao Wei; Demir, Hilmi Volkan

    2015-02-01

    The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active region. The essence of improving the hole injection efficiency is to increase the hole concentration in the p-GaN layer. Therefore, in this work, we have proposed a hole modulator and studied it both theoretically and experimentally. In the hole modulator, the holes in a remote p-type doped layer are depleted by the built-in electric field and stored in the p-GaN layer. By this means, the overall hole concentration in the p-GaN layer can be enhanced. Furthermore, the hole modulator is adopted in the InGaN/GaN LEDs, which reduces the effective valance band barrier height for the p-type electron blocking layer from ˜332 meV to ˜294 meV at 80 A/cm2 and demonstrates an improved optical performance, thanks to the increased hole concentration in the p-GaN layer and thus the improved hole injection into the MQWs.

  2. A hole modulator for InGaN/GaN light-emitting diodes

    International Nuclear Information System (INIS)

    Zhang, Zi-Hui; Kyaw, Zabu; Liu, Wei; Ji, Yun; Wang, Liancheng; Tan, Swee Tiam; Sun, Xiao Wei; Demir, Hilmi Volkan

    2015-01-01

    The low p-type doping efficiency of the p-GaN layer has severely limited the performance of InGaN/GaN light-emitting diodes (LEDs) due to the ineffective hole injection into the InGaN/GaN multiple quantum well (MQW) active region. The essence of improving the hole injection efficiency is to increase the hole concentration in the p-GaN layer. Therefore, in this work, we have proposed a hole modulator and studied it both theoretically and experimentally. In the hole modulator, the holes in a remote p-type doped layer are depleted by the built-in electric field and stored in the p-GaN layer. By this means, the overall hole concentration in the p-GaN layer can be enhanced. Furthermore, the hole modulator is adopted in the InGaN/GaN LEDs, which reduces the effective valance band barrier height for the p-type electron blocking layer from ∼332 meV to ∼294 meV at 80 A/cm 2 and demonstrates an improved optical performance, thanks to the increased hole concentration in the p-GaN layer and thus the improved hole injection into the MQWs

  3. A comparison of HAART outcomes between the US military HIV Natural History Study (NHS and HIV Atlanta Veterans Affairs Cohort Study (HAVACS.

    Directory of Open Access Journals (Sweden)

    Jodie L Guest

    Full Text Available INTRODUCTION: The Department of Defense (DoD and the Department of Veterans Affairs (VA provide comprehensive HIV treatment and care to their beneficiaries with open access and few costs to the patient. Individuals who receive HIV care in the VA have higher rates of substance abuse, homelessness and unemployment than individuals who receive HIV care in the DoD. A comparison between individuals receiving HIV treatment and care from the DoD and the VA provides an opportunity to explore the impact of individual-level characteristics on clinical outcomes within two healthcare systems that are optimized for clinic retention and medication adherence. METHODS: Data were collected on 1065 patients from the HIV Atlanta VA Cohort Study (HAVACS and 1199 patients from the US Military HIV Natural History Study (NHS. Patients were eligible if they had an HIV diagnosis and began HAART between January 1, 1996 and June 30, 2010. The analysis examined the survival from HAART initiation to all-cause mortality or an AIDS event. RESULTS: Although there was substantial between-cohort heterogeneity and the 12-year survival of participants in NHS was significantly higher than in HAVACS in crude analyses, this survival disparity was reduced from 21.5% to 1.6% (mortality only and 26.8% to 4.1% (combined mortality or AIDS when controlling for clinical and demographic variables. CONCLUSION: We assessed the clinical outcomes for individuals with HIV from two very similar government-sponsored healthcare systems that reduced or eliminated many barriers associated with accessing treatment and care. After controlling for clinical and demographic variables, both 12-year survival and AIDS-free survival rates were similar for the two study cohorts who have open access to care and medication despite dramatic differences in socioeconomic and behavioral characteristics.

  4. Trends in the prevalence of autism spectrum disorder, cerebral palsy, hearing loss, intellectual disability, and vision impairment, metropolitan atlanta, 1991-2010.

    Directory of Open Access Journals (Sweden)

    Kim Van Naarden Braun

    Full Text Available This study examined the prevalence and characteristics of autism spectrum disorder (ASD, cerebral palsy (CP, hearing loss (HL, intellectual disability (ID, and vision impairment (VI over a 15-20 year time period, with specific focus on concurrent changes in ASD and ID prevalence. We used data from a population-based developmental disabilities surveillance program for 8-year-olds in metropolitan Atlanta. From 1991-2010, prevalence estimates of ID and HL were stable with slight increases in VI prevalence. CP prevalence was constant from 1993-2010. The average annual increase in ASD prevalence was 9.3% per year from 1996-2010, with a 269% increase from 4.2 per 1,000 in 1996 to 15.5 per 1,000 in 2010. From 2000-2010, the prevalence of ID without ASD was stable; during the same time, the prevalence of ASD with and without co-occurring ID increased by an average of 6.6% and 9.6% per year, respectively. ASD prevalence increases were found among both males and females, and among nearly all racial/ethnic subgroups and levels of intellectual ability. Average annual prevalence estimates from 1991-2010 underscore the significant community resources needed to provide early intervention and ongoing supports for children with ID (13.0 per 1,000, CP, (3.5 per 1,000, HL (1.4 per 1,000 and VI (1.3 in 1,000, with a growing urgency for children with ASD.

  5. Significant inter-observer variation in the diagnosis of extrapancreatic necrosis and type of pancreatic collections in acute pancreatitis - An international multicenter evaluation of the revised Atlanta classification.

    Science.gov (United States)

    Sternby, Hanna; Verdonk, Robert C; Aguilar, Guadalupe; Dimova, Alexandra; Ignatavicius, Povilas; Ilzarbe, Lucas; Koiva, Peeter; Lantto, Eila; Loigom, Tonis; Penttilä, Anne; Regnér, Sara; Rosendahl, Jonas; Strahinova, Vanya; Zackrisson, Sophia; Zviniene, Kristina; Bollen, Thomas L

    2016-01-01

    For consistent reporting and better comparison of data in research the revised Atlanta classification (RAC) proposes new computed tomography (CT) criteria to describe the morphology of acute pancreatitis (AP). The aim of this study was to analyse the interobserver agreement among radiologists in evaluating CT morphology by using the new RAC criteria in patients with AP. Patients with a first episode of AP who obtained a CT were identified and consecutively enrolled at six European centres backwards from January 2013 to January 2012. A local radiologist at each center and a central expert radiologist scored the CTs separately using the RAC criteria. Center dependent and independent interobserver agreement was determined using Kappa statistics. In total, 285 patients with 388 CTs were included. For most CT criteria, interobserver agreement was moderate to substantial. In four categories, the center independent kappa values were fair: extrapancreatic necrosis (EXPN) (0.326), type of pancreatitis (0.370), characteristics of collections (0.408), and appropriate term of collections (0.356). The fair kappa values relate to discrepancies in the identification of extrapancreatic necrotic material. The local radiologists diagnosed EXPN (33% versus 59%, P < 0.0001) and non-homogeneous collections (35% versus 66%, P < 0.0001) significantly less frequent than the central expert. Cases read by the central expert showed superior correlation with clinical outcome. Diagnosis of EXPN and recognition of non-homogeneous collections show only fair agreement potentially resulting in inconsistent reporting of morphologic findings. Copyright © 2016 IAP and EPC. Published by Elsevier B.V. All rights reserved.

  6. GaN-based ultraviolet light-emitting diodes with AlN/GaN/InGaN multiple quantum wells.

    Science.gov (United States)

    Chang, Hung-Ming; Lai, Wei-Chih; Chen, Wei-Shou; Chang, Shoou-Jinn

    2015-04-06

    We demonstrate indium gallium nitride/gallium nitride/aluminum nitride (AlN/GaN/InGaN) multi-quantum-well (MQW) ultraviolet (UV) light-emitting diodes (LEDs) to improve light output power. Similar to conventional UV LEDs with AlGaN/InGaN MQWs, UV LEDs with AlN/GaN/InGaN MQWs have forward voltages (V(f)'s) ranging from 3.21 V to 3.29 V at 350 mA. Each emission peak wavelength of AlN/GaN/InGaN MQW UV LEDs presents 350 mA output power greater than that of the corresponding emission peak wavelength of AlGaN/InGaN MQW UV LEDs. The light output power at 350mA of AlN/GaN/InGaN MQWs UV LEDs with 375 nm emission wavelength can reach around 26.7% light output power enhancement in magnitude compared to the AlGaN/InGaN MQWs UV LEDs with same emission wavelength. But 350mA light output power of AlN/GaN/InGaN MQWs UV LEDs with emission wavelength of 395nm could only have light output power enhancement of 2.43% in magnitude compared with the same emission wavelength AlGaN/InGaN MQWs UV LEDs. Moreover, AlN/GaN/InGaN MQWs present better InGaN thickness uniformity, well/barrier interface quality and less large size pits than AlGaN/InGaN MQWs, causing AlN/GaN/InGaN MQW UV LEDs to have less reverse leakage currents at -20 V. Furthermore, AlN/GaN/InGaN MQW UV LEDs have the 2-kV human body mode (HBM) electrostatic discharge (ESD) pass yield of 85%, which is 15% more than the 2-kV HBM ESD pass yield of AlGaN/InGaN MQW UV LEDs of 70%.

  7. Clinical evaluation of 67Ga gut accumulation in 67Ga scintigraphy

    International Nuclear Information System (INIS)

    Kobayashi, Hidetoshi; Ohno, Akiko; Watanabe, Youichi; Ishigaki, Takeo.

    1994-01-01

    Accumulation of 67 Ga in gut was evaluated in 67 Ga scintigraphy retrospectively in 30 patients (32 examinations). TIBC and UIBC were examined in all patients on the day when their scintigraphies were performed. Blood transfusion or Fe administration 2 months before 67 Ga scintigraphies were not carried out in any patient. Fifty percents (6/12) of male, and 40% (8/20) of female patients showed 67 Ga accumulation in gut. There was significant correlation between 67 Ga accumulation in gut and low ion-saturation ratio for transferrin. Excretion of 67 Ga bound with transferrin from liver was thought to be an important factor of 67 ga accumulation in gut. (author)

  8. Characteristics of AlGaN/GaN/AlGaN double heterojunction HEMTs with an improved breakdown voltage

    International Nuclear Information System (INIS)

    Ma Juncai; Zhang Jincheng; Xue Junshuai; Lin Zhiyu; Liu Ziyang; Xue Xiaoyong; Ma Xiaohua; Hao Yue

    2012-01-01

    We studied the performance of AlGaN/GaN double heterojunction high electron mobility transistors (DH-HEMTs) with an AlGaN buffer layer, which leads to a higher potential barrier at the backside of the two-dimensional electron gas channel and better carrier confinement. This, remarkably, reduces the drain leakage current and improves the device breakdown voltage. The breakdown voltage of AlGaN/GaN double heterojunction HEMTs (∼100 V) was significantly improved compared to that of conventional AlGaN/GaN HEMTs (∼50 V) for the device with gate dimensions of 0.5 × 100 μm and a gate—drain distance of 1 μm. The DH-HEMTs also demonstrated a maximum output power of 7.78 W/mm, a maximum power-added efficiency of 62.3% and a linear gain of 23 dB at the drain supply voltage of 35 V at 4 GHz. (semiconductor devices)

  9. Work environment and well-being of academic faculty in Czech universities: A pilot study

    Czech Academy of Sciences Publication Activity Database

    Zábrodská, Kateřina; Mudrák, Jiří; Květon, Petr; Blatný, Marek; Machovcová, Kateřina; Šolcová, Iva

    2014-01-01

    Roč. 19, č. 4 (2014), s. 121-144 ISSN 1803-7437 R&D Projects: GA ČR GA14-02098S Institutional support: RVO:68081740 Keywords : work environment * universities * organizational climate * job satisfaction * academic governance Subject RIV: AN - Psychology

  10. Stiegler's University

    Science.gov (United States)

    Featherstone, Mark

    2017-01-01

    In this article, Mark Featherstone proposes to explore Bernard Stiegler's work through the lens of the politics of education and in particular the idea of the university, which becomes a pharmacological space of, on the one hand, utopian possibility, and, on the other hand, dystopian limitation, destruction, and death in his recent "States of…

  11. Uncorrelated electron-hole transition energy in GaN|InGaN|GaN spherical QDQW nanoparticles

    International Nuclear Information System (INIS)

    Haddou El Ghazi; Anouar Jorio and Izeddine Zorkani

    2013-01-01

    The electron (hole) energy and uncorrelated 1S e - 1S h electron-hole transition in Core(GaN)|well(In x Ga 1-x N)|shell(GaN) spherical QDQW nanoparticles is investigated as a function of the inner and the outer radii. The calculations are performed within the framework of the effective-mass approximation and the finite parabolic potential confinement barrier in which two confined parameters are taking account. The Indium composition effect is also investigated. A critical value of the outer and the inner ratio is obtained which constitutes the turning point of two indium composition behaviors. (author)

  12. Double pulse doped InGaAs/AlGaAs/GaAs pseudomorphic high-electron-mobility transistor heterostructures

    International Nuclear Information System (INIS)

    Egorov, A. Yu.; Gladyshev, A. G.; Nikitina, E. V.; Denisov, D. V.; Polyakov, N. K.; Pirogov, E. V.; Gorbazevich, A. A.

    2010-01-01

    Double pulse doped (δ-doped) InGaAs/AlGaAs/GaAs pseudomorphic high-electron-mobility transistor (HEMT) heterostructures were grown by molecular-beam epitaxy using a multiwafer technological system. The room-temperature electron mobility was determined by the Hall method as 6550 and 6000 cm 2 /(V s) at sheet electron densities of 3.00 x 10 12 and 3.36 x 10 12 cm -2 , respectively. HEMT heterostructures fabricated in a single process feature high uniformity of structural and electrical characteristics over the entire area of wafers 76.2 mm in diameter and high reproducibility of characteristics from process to process.

  13. Optimization of GaN Nanorod Growth Conditions for Coalescence Overgrowth

    Science.gov (United States)

    2016-02-04

    21, 2016 PI: Chih-Chung (C. C.) Yang, ccycc@ntu.edu.tw Graduate Institute of Photonics and Optoelectronics, National Taiwan University...nanowire light emitting diodes grown on (001) silicon by molecular beam epitaxy, Nano Lett. 10 (2010) 3355-3359. [16] W. Guo, A. Banerjee, P...Bhattacharya, B.S. Ooi, InGaN/GaN disk-in-nanowire white light emitting diodes on (001) silicon , Appl. Phys. Lett. 98 (2011) 193102. [17] H.P.T. Nguyen, M

  14. Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

    Science.gov (United States)

    Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F.

    2004-09-01

    In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerence of GaAs and that Ti can protected GaAs from erosion by NH3. By depositing Ti on GaAs(111)A surface, a millor-like GaN layer could be grown at 1000 °C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future.

  15. Tolerance of GaAs as an original substrate for HVPE growth of free standing GaN

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, Mio; Sato, T.; Suemasu, T.; Hasegawa, F. [University of Tsukuba, Institute of Applied Physics, Tsukuba, Ibaraki 305-8573 (Japan)

    2004-09-01

    In order to investigate possibility of thick GaN growth on a GaAs substrate by halide vapar phase epitaxy (HVPE), GaN was grown on GaAs(111)/Ti wafer with Ti deposited by E-gun. It was found that surface treatment of the GaAs substrate by HF solution deteriorated greatly the tolerance of GaAs and that Ti can protected GaAs from erosion by NH{sub 3}. By depositing Ti on GaAs(111)A surface, a mirror-like GaN layer could be grown at 1000 C for 1 hour without serious deterioration of the original GaAs substrate. By increasing the growth rate, a thick free standing GaN will be obtained with GaAs as an original substrate in near future. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. AlGaN/GaN heterostructures with an AlGaN layer grown directly on reactive-ion-etched GaN showing a high electron mobility (>1300 cm2 V-1 s-1)

    Science.gov (United States)

    Yamamoto, Akio; Makino, Shinya; Kanatani, Keito; Kuzuhara, Masaaki

    2018-04-01

    In this study, the metal-organic-vapor-phase-epitaxial growth behavior and electrical properties of AlGaN/GaN structures prepared by the growth of an AlGaN layer on a reactive-ion-etched (RIE) GaN surface without regrown GaN layers were investigated. The annealing of RIE-GaN surfaces in NH3 + H2 atmosphere, employed immediately before AlGaN growth, was a key process in obtaining a clean GaN surface for AlGaN growth, that is, in obtaining an electron mobility as high as 1350 cm2 V-1 s-1 in a fabricated AlGaN/RIE-GaN structure. High-electron-mobility transistors (HEMTs) were successfully fabricated with AlGaN/RIE-GaN wafers. With decreasing density of dotlike defects observed on the surfaces of AlGaN/RIE-GaN wafers, both two-dimensional electron gas properties of AlGaN/RIE-GaN structures and DC characteristics of HEMTs were markedly improved. Since dotlike defect density was markedly dependent on RIE lot, rather than on growth lot, surface contaminations of GaN during RIE were believed to be responsible for the formation of dotlike defects and, therefore, for the inferior electrical properties.

  17. 67Ga imaging in Hodgkin's disease

    International Nuclear Information System (INIS)

    Huys, J.; Schelstraete, K.; Simons, M.

    1982-01-01

    In order to answer the question if 67 Ga imaging has a practical utility for the management of the patient with Hodgkin's disease, 108 scans performed on 60 patients were reviewed. When used during the initial staging of the disease or during restaging because of recurrences, 67 Ga imaging-at least in our experience-gave many false negative results in the cervical, axillary and inguinal areas, whereas the majority of true positive scans was found at the mediastinal level (including the lower mediastinum), and also in the lung parenchyma and the upper epigastric regions. Because of its lack of sensitivity, 67 Ga imaging cannot replace other staging procedures, but nevertheless is a valuable adjunctive test, as it can identify tumor localization that may have remained undetected by other methods. Fifty-four scans were performed to monitor treatment with radiation therapy or chemotherapeutic agents. Disappearance or decreases of 67 Ga uptake after treatment usually corresponded to a disappearance or regression of the tumor as ascertained by other methods. When the treatment was shown to be ineffective, 67 Ga uptake persisted or even became more prominent. When during follow-up, a new concentration of 67 Ga appeared at the original location or elsewhere, a relapse was extremely likely. However, one must be aware of false positive images. In our material, no correlation was found between the intensity of the 67 Ga uptake and the histological subtypes of Hodgkin's disease. Neither did we observe any relation to the blood sedimentation rate or serum iron levels

  18. Computational study of GaAs1-xNx and GaN1-yAsy alloys and arsenic impurities in GaN

    International Nuclear Information System (INIS)

    Laaksonen, K; Komsa, H-P; Arola, E; Rantala, T T; Nieminen, R M

    2006-01-01

    We have studied the structural and electronic properties of As-rich GaAs 1-x N x and N-rich GaN 1-y As y alloys in a large composition range using first-principles methods. We have systematically investigated the effect of the impurity atom configuration near both GaAs and GaN sides of the concentration range on the total energies, lattice constants and bandgaps. The N (As) atoms, replacing substitutionally As (N) atoms in GaAs (GaN), cause the surrounding Ga atoms to relax inwards (outwards), making the Ga-N (Ga-As) bond length about 15% shorter (longer) than the corresponding Ga-As (Ga-N) bond length in GaAs (GaN). The total energies of the relaxed alloy supercells and the bandgaps experience large fluctuations within different configurations and these fluctuations grow stronger if the impurity concentration is increased. Substituting As atoms with N in GaAs induces modifications near the conduction band minimum, while substituting N atoms with As in GaN modifies the states near the valence band maximum. Both lead to bandgap reduction, which is at first rapid but later slows down. The relative size of the fluctuations is much larger in the case of GaAs 1-x N x alloys. We have also looked into the question of which substitutional site (Ga or N) As occupies in GaN. We find that under Ga-rich conditions arsenic prefers the substitutional N site over the Ga site within a large range of Fermi level values

  19. GaN-based blue laser diodes

    Energy Technology Data Exchange (ETDEWEB)

    Miyajima, Takao; Yanashima, Katsunori; Funato, Kenji; Asatsuma, Tsunenori; Kobayashi, Toshimasa [CT Development Centre, CNC, Sony Corporation, Atsugi, Kanagawa (Japan); Tojyo, Tsuyoshi; Asano, Takeharu; Kijima, Satoru; Hino, Tomonori; Takeya, Motonobu; Uchida, Shiro; Ikeda, Masao [Sony Shiroishi Semiconductor Inc., Shiroishi, Miyagi (Japan); Tomiya, Shigetaka [Environment and Analyhsis Technology Department, Sony Corporation, Hodogaya, Yokohama (Japan)

    2001-08-13

    We report our recent progress on GaN-based high-power laser diodes (LDs), which will be applied as a light source in high-density optical storage systems. We have developed raised-pressure metal-organic chemical vapour deposition (RP-MOCVD), which can reduce the threading-dislocation density in the GaN layer to several times 10{sup 8} cm{sup -2}, and demonstrated continuous-wave (cw) operation of GaN-based LD grown by RP-MOCVD. Furthermore, we found that the epitaxial lateral overgrowth (ELO) technique is useful for further reducing threading-dislocation density to 10{sup 6} cm{sup -2} and reducing the roughness of the cleaved facet. By using this growth technique and optimizing device parameters, the lifetime of LDs was improved to more than 1000 hours under 30 mW cw operation at 60 deg. C. Our results proved that reducing both threading-dislocation density and consumption power is a valid approach to realizing a practical GaN-based LD. On the other hand, the practical GaN-based LD was obtained when threading-dislocation density in ELO-GaN was only reduced to 10{sup 6} cm{sup -2}, which is a relatively small reduction as compared with threading-dislocation density in GaAs- and InP-based LDs. We believe that the multiplication of non-radiative centres is very slow in GaN-based LDs, possibly due to the innate character of the GaN-based semiconductor itself. (author)

  20. Growth and properties of the MOVPE GaAs/InAs/GaAsSb quantum dot structures

    Czech Academy of Sciences Publication Activity Database

    Hospodková, Alice; Oswald, Jiří; Pangrác, Jiří; Kuldová, Karla; Zíková, Markéta; Vyskočil, Jan; Hulicius, Eduard

    2016-01-01

    Roč. 480, Jan (2016), 14-22 ISSN 0921-4526 R&D Projects: GA ČR GA13-15286S; GA ČR(CZ) GP14-21285P; GA MŠk(CZ) LM2011026 Institutional support: RVO:68378271 Keywords : quantum dot * band alignment * InAs/GaAs * GaAsSb * MOVPE * luminescence Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 1.386, year: 2016

  1. GaAs/AlAs/InGaP heterostructure: a versatile material basis for cantilever designs

    International Nuclear Information System (INIS)

    Gregušová, Dagmar; Kúdela, Róbert; Eliáš, Peter; Šoltýs, Ján; Cambel, Vladimír; Kostič, Ivan

    2010-01-01

    We report on the design, fabrication and initial mechanical testing of cantilevers with tips based on a GaAs/In 0.485 Ga 0.515 P/AlAs heterostructure grown by metal organic chemical vapor deposition. They were produced using a dedicated technological process based on (1) the formation of integrated tips through an AlAs-assisted surface sacrificial wet-etching process and (2) the GaAs cantilever release fully protected between two InGaP etch-stop layers. 2 µm thick InGaP/GaAs/InGaP cantilevers had integrated pyramidal tips with the sides at ∼45° to (1 0 0). Metallic elements were processed close to the tip apexes using non-standard optical lithography. The cantilever release was accomplished using photolithography, Ar ion milling of InGaP and wet chemical etching of GaAs via resist layers deposited by a draping technique. A tip–cantilever prototype with length, width and thickness of 150, 35 and 2 µm, respectively, exhibited a resonance frequency of 66.2 kHz, which correlated well with a theoretical value of 57 kHz for a GaAs cantilever of identical dimensions. (technical note)

  2. Sub-monolayer Deposited InGaAs/GaAs Quantum Dot Heterostructures and Lasers

    DEFF Research Database (Denmark)

    Xu, Zhangcheng

    2004-01-01

    deposition, the deposition of a short-period InAs/GaAs superlattice on GaAs (100) surface with an InAs effective thickness of less than 1 monolayer (ML), results in the formatioin of nanometer scale (In,Ga)As QDs of a non-SK class.In this thesis, the SML InGaAs/GaAs QDs are formed by 10 cycles of alternate......The fabrication, characterization and exploitation of self-assembled quantum dot (QD) heterostructures have attracted much attention not only in basic research, but also by the promising device applications such as QD lasers. The Stranski-Krastanow (SK) growth and the submonolayer (SML) deposition...... deposition of 0.5 ML InAs and 2.5 MLGaAs. The growth, structure, and optical properties of SML InGaAs/GaAs QD heterostructures are investigated in detail. SML InGaAs/GaAs QD lasers lasing even at room temperature have been successfully realized. The gain properties of SML InGaAs QD lasers are studied...

  3. An improved EEHEMT model for kink effect on AlGaN/GaN HEMT

    International Nuclear Information System (INIS)

    Cao Meng-Yi; Lu Yang; Chen Yong-He; Zheng Jia-Xin; Ma Xiao-Hua; Hao Yue; Wei Jia-Xing; Li Wei-Jun

    2014-01-01

    In this paper, a new current expression based on both the direct currect (DC) characteristics of the AlGaN/GaN high election mobility transistor (HEMT) and the hyperbolic tangent function tanh is proposed, by which we can describe the kink effect of the AlGaN/GaN HEMT well. Then, an improved EEHEMT model including the proposed current expression is presented. The simulated and measured results of I–V, S-parameter, and radio frequency (RF) large-signal characteristics are compared for a self-developed on-wafer AlGaN/GaN HEMT with ten gate fingers each being 0.4-μm long and 125-μm wide (Such an AlGaN/GaN HEMT is denoted as AlGaN/GaN HEMT (10 × 125 μm)). The improved large signal model simulates the I–V characteristic much more accurately than the original one, and its transconductance and RF characteristics are also in excellent agreement with the measured data. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  4. Carrier quenching in InGaP/GaAs double heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Wells, Nathan P., E-mail: nathan.p.wells@aero.org; Driskell, Travis U.; Hudson, Andrew I.; LaLumondiere, Stephen D.; Lotshaw, William T. [The Aerospace Corporation, Physical Sciences Laboratories, P.O. Box 92957, Los Angeles, California 90009 (United States); Forbes, David V.; Hubbard, Seth M. [NanoPower Research Labs, Rochester Institute of Technology, 156 Lomb Memorial Dr., Rochester, New York 14623 (United States)

    2015-08-14

    Photoluminescence measurements on a series of GaAs double heterostructures demonstrate a rapid quenching of carriers in the GaAs layer at irradiance levels below 0.1 W/cm{sup 2} in samples with a GaAs-on-InGaP interface. These results indicate the existence of non-radiative defect centers at or near the GaAs-on-InGaP interface, consistent with previous reports showing the intermixing of In and P when free As impinges on the InGaP surface during growth. At low irradiance, these defect centers can lead to sub-ns carrier lifetimes. The defect centers involved in the rapid carrier quenching can be saturated at higher irradiance levels and allow carrier lifetimes to reach hundreds of nanoseconds. To our knowledge, this is the first report of a nearly three orders of magnitude decrease in carrier lifetime at low irradiance in a simple double heterostructure. Carrier quenching occurs at irradiance levels near the integrated Air Mass Zero (AM0) and Air Mass 1.5 (AM1.5) solar irradiance. Additionally, a lower energy photoluminescence band is observed both at room and cryogenic temperatures. The temperature and time dependence of the lower energy luminescence is consistent with the presence of an unintentional InGaAs or InGaAsP quantum well that forms due to compositional mixing at the GaAs-on-InGaP interface. Our results are of general interest to the photovoltaic community as InGaP is commonly used as a window layer in GaAs based solar cells.

  5. Ga vacancy induced ferromagnetism enhancement and electronic structures of RE-doped GaN

    International Nuclear Information System (INIS)

    Zhong Guohua; Zhang Kang; He Fan; Ma Xuhang; Lu Lanlan; Liu Zhuang; Yang Chunlei

    2012-01-01

    Because of their possible applications in spintronic and optoelectronic devices, GaN dilute magnetic semiconductors (DMSs) doped by rare-earth (RE) elements have attracted much attention since the high Curie temperature was obtained in RE-doped GaN DMSs and a colossal magnetic moment was observed in the Gd-doped GaN thin film. We have systemically studied the GaN DMSs doped by RE elements (La, Ce-Yb) using the full-potential linearized augmented plane wave method within the framework of density functional theory and adding the considerations of the electronic correlation and the spin-orbital coupling effects. We have studied the electronic structures of DMSs, especially for the contribution from f electrons. The origin of magnetism, magnetic interaction and the possible mechanism of the colossal magnetic moment were explored. We found that, for materials containing f electrons, electronic correlation was usually strong and the spin-orbital coupling was sometimes crucial in determining the magnetic ground state. It was found that GaN doped by La was non-magnetic. GaN doped by Ce, Nd, Pm, Eu, Gd, Tb and Tm are stabilized at antiferromagnetic phase, while GaN doped by other RE elements show strong ferromagnetism which is suitable materials for spintronic devices. Moreover, we have identified that the observed large enhancement of magnetic moment in GaN is mainly caused by Ga vacancies (3.0μB per Ga vacancy), instead of the spin polarization by magnetic ions or originating from N vacancies. Various defects, such as substitutional Mg for Ga, O for N under the RE doping were found to bring a reduction of ferromagnetism. In addition, intermediate bands were observed in some systems of GaN:RE and GaN with intrinsic defects, which possibly opens the potential application of RE-doped semiconductors in the third generation high efficiency photovoltaic devices.

  6. Comparison of damage introduced into GaN/AlGaN/GaN heterostructures using selective dry etch recipes

    International Nuclear Information System (INIS)

    Green, R T; Luxmoore, I J; Houston, P A; Ranalli, F; Wang, T; Parbrook, P J; Uren, M J; Wallis, D J; Martin, T

    2009-01-01

    A SiCl 4 /SF 6 dry etch plasma recipe is presented giving a selectivity of 14:1 between GaN and AlGaN. Using a leakage test structure, which enables bulk and surface leakage components to be identified independently, the optimized recipe is compared to an un-etched sample and devices recessed using a Cl 2 /Ar/O 2 -based plasma chemistry. Devices etched using the SiCl 4 /SF 6 recipe demonstrated reduced bulk and surface leakage currents when operated over a wide range of temperatures. Consequently the SiCl 4 /SF 6 recipe is identified as most suitable for the fabrication of gate recessed AlGaN/GaN HEMTs

  7. Phonon replica dynamics in high quality GaN epilayers and AlGaN/GaN quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Alderighi, D.; Vinattieri, A.; Colocci, M. [Ist. Nazionale Fisica della Materia, Firenze (Italy); Dipt. di Fisica and LENS, Firenze (Italy); Bogani, F. [Ist. Nazionale Fisica della Materia, Firenze (Italy); Dipt. di Energetica, Firenze (Italy); Gottardo, S. [Dipt. di Fisica and LENS, Firenze (Italy); Grandjean, N.; Massies, J. [Centre de Recherche sur l' Hetero-Epitaxie et ses Applications, CNRS, Valbonne (France)

    2001-01-01

    We present an experimental study of the exciton and phonon replica dynamics in high quality GaN epilayers and AlGaN/GaN quantum wells (QW) by means of picosecond time-resolved photoluminescence (PL) measurements. A non-exponential decay is observed both at the zero phonon line (ZPL) and at the n = 1 LO replica. Time-resolved spectra unambiguously assign the replica to the free exciton A recombination. Optical migration effects are detected both in the epilayer and the QWs samples and disappear as the temperature increases up to 60-90 K. Even though the sample quality is comparable to state-of-the-art samples, localization effects dominate the exciton dynamics at low temperature in the studied GaN based structures. (orig.)

  8. Role of electronic correlations in Ga

    KAUST Repository

    Zhu, Zhiyong

    2011-06-13

    An extended around mean field (AMF) functional for less localized pelectrons is developed to quantify the influence of electronic correlations in α-Ga. Both the local density approximation (LDA) and generalized gradient approximation are known to mispredict the Ga positional parameters. The extended AMF functional together with an onsite Coulomb interaction of Ueff=1.1 eV, as obtained from constraint LDA calculations, reduces the deviations by about 20%. The symmetry lowering coming along with the electronic correlations turns out to be in line with the Ga phase diagram.

  9. Gallium adsorption on (0001) GaN surfaces

    International Nuclear Information System (INIS)

    Adelmann, Christoph; Brault, Julien; Mula, Guido; Daudin, Bruno; Lymperakis, Liverios; Neugebauer, Joerg

    2003-01-01

    We study the adsorption behavior of Ga on (0001) GaN surfaces combining experimental specular reflection high-energy electron diffraction with theoretical investigations in the framework of a kinetic model for adsorption and ab initio calculations of energy parameters. Based on the experimental results we find that for substrate temperatures and Ga fluxes typically used in molecular-beam epitaxy of GaN, finite equilibrium Ga surface coverages can be obtained. The measurement of a Ga/GaN adsorption isotherm allows the quantification of the equilibrium Ga surface coverage as a function of the impinging Ga flux. In particular, we show that a large range of Ga fluxes exists, where 2.5±0.2 monolayers (in terms of the GaN surface site density) of Ga are adsorbed on the GaN surface. We further demonstrate that the structure of this adsorbed Ga film is in good agreement with the laterally contracted Ga bilayer model predicted to be most stable for strongly Ga-rich surfaces [Northrup et al., Phys. Rev. B 61, 9932 (2000)]. For lower Ga fluxes, a discontinuous transition to Ga monolayer equilibrium coverage is found, followed by a continuous decrease towards zero coverage; for higher Ga fluxes, Ga droplet formation is found, similar to what has been observed during Ga-rich GaN growth. The boundary fluxes limiting the region of 2.5 monolayers equilibrium Ga adsorption have been measured as a function of the GaN substrate temperature giving rise to a Ga/GaN adsorption phase diagram. The temperature dependence is discussed within an ab initio based growth model for adsorption taking into account the nucleation of Ga clusters. This model consistently explains recent contradictory results of the activation energy describing the critical Ga flux for the onset of Ga droplet formation during Ga-rich GaN growth [Heying et al., J. Appl. Phys. 88, 1855 (2000); Adelmann et al., J. Appl. Phys. 91, 9638 (2002).

  10. University writing

    Directory of Open Access Journals (Sweden)

    Miguel Zabalza Beraza

    2013-01-01

    Full Text Available Writing in the University is a basic necessity and a long-range educational purpose. One of the basic characteristics of the university context is that it requires writing both as a tool of communication and as a source of intellectual stimulation. After establishing the basic features of academic writing, this article analyzes the role of writing for students (writing to learn and for teachers (write to plan, to reflect, to document what has been done. The article also discusses the contributions of writing for both students and teachers together: writing to investigate. Finally, going beyond what writing is as academic tool, we conclude with a more playful and creative position: writing for pleasure and enjoyment.

  11. Universe unfolding

    International Nuclear Information System (INIS)

    King, I.R.

    1976-01-01

    Topics covered the setting; looking at the stars; the earth; time, place and the sky; our satellite, the moon; orbits and motion; the motions of the planets; the Copernican revolution; the planets; the other bodies of the solar system; ages, origins, and life; introducing the stars; sorting out the stars; binary stars--two are better than one; variable stars--inconstancy as a virtue; the secrets of starlight--unraveling the spectrum; the sun--our own star; the structure of a star; interstellar material; the Milky Way, our home galaxy; galaxies--the stellar continents; cosmic violence--from radio galaxies to quasars; the universe; and epilogue. The primary emphasis is on how we have come to know what we know about the universe. Star maps are included

  12. Asymmetric quantum-well structures for AlGaN/GaN/AlGaN resonant tunneling diodes

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Lin' an, E-mail: layang@xidian.edu.cn; Li, Yue; Wang, Ying; Xu, Shengrui; Hao, Yue [State Key Discipline Laboratory of Wide Bandgap Semiconductor Technology, School of Microelectronics, Xidian University, Xi' an 710071 (China)

    2016-04-28

    Asymmetric quantum-well (QW) structures including the asymmetric potential-barrier and the asymmetric potential-well are proposed for AlGaN/GaN/AlGaN resonant tunneling diodes (RTDs). Theoretical investigation gives that an appropriate decrease in Al composition and thickness for emitter barrier as well as an appropriate increase of both for collector barrier can evidently improve the negative-differential-resistance characteristic of RTD. Numerical simulation shows that RTD with a 1.5-nm-thick GaN well sandwiched by a 1.3-nm-thick Al{sub 0.15}Ga{sub 0.85}N emitter barrier and a 1.7-nm-thick Al{sub 0.25}Ga{sub 0.75}N collector barrier can yield the I-V characteristic having the peak current (Ip) and the peak-to-valley current ratio (PVCR) of 0.39 A and 3.6, respectively, about double that of RTD with a 1.5-nm-thick Al{sub 0.2}Ga{sub 0.8}N for both barriers. It is also found that an introduction of InGaN sub-QW into the diode can change the tunneling mode and achieve higher transmission coefficient of electron. The simulation demonstrates that RTD with a 2.8-nm-thick In{sub 0.03}Ga{sub 0.97}N sub-well in front of a 2.0-nm-thick GaN main-well can exhibit the I-V characteristic having Ip and PVCR of 0.07 A and 11.6, about 7 times and double the value of RTD without sub-QW, respectively. The purpose of improving the structure of GaN-based QW is to solve apparent contradiction between the device structure and the device manufacturability of new generation RTDs for sub-millimeter and terahertz applications.

  13. University physics

    CERN Document Server

    Arfken, George

    1984-01-01

    University Physics provides an authoritative treatment of physics. This book discusses the linear motion with constant acceleration; addition and subtraction of vectors; uniform circular motion and simple harmonic motion; and electrostatic energy of a charged capacitor. The behavior of materials in a non-uniform magnetic field; application of Kirchhoff's junction rule; Lorentz transformations; and Bernoulli's equation are also deliberated. This text likewise covers the speed of electromagnetic waves; origins of quantum physics; neutron activation analysis; and interference of light. This publi

  14. Improved interface quality and luminescence capability of InGaN/GaN quantum wells with Mg pretreatment

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Zhengyuan; Shen, Xiyang; Xiong, Huan; Li, Qingfei; Kang, Junyong; Fang, Zhilai [Xiamen University, Collaborative Innovation Center for Optoelectronic Semiconductors and Efficient Devices, Department of Physics, Xiamen (China); Lin, Feng; Yang, Bilan; Lin, Shilin [San' an Optoelectronics Co., Ltd, Xiamen (China); Shen, Wenzhong [Shanghai Jiao Tong University, Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics, Shanghai (China); Zhang, Tong-Yi [Shanghai University, Shanghai University Materials Genome Institute and Shanghai Materials Genome Institute, Shanghai (China)

    2016-02-15

    Interface modification of high indium content InGaN/GaN quantum wells was carried out by Mg pretreatment of the GaN barrier surface. The indium in the Mg-pretreated InGaN layer was homogeneously distributed, making the interfaces abrupt. The improved interface quality greatly enhanced light emission capacity. The cathodoluminescence intensity of the Mg-pretreated InGaN/GaN quantum wells was correspondingly much stronger than those of the InGaN/GaN quantum wells without Mg pretreatment. (orig.)

  15. Human universe

    CERN Document Server

    Cox, Brian

    2014-01-01

    Human life is a staggeringly strange thing. On the surface of a ball of rock falling around a nuclear fireball in the blackness of a vacuum the laws of nature conspired to create a naked ape that can look up at the stars and wonder where it came from. What is a human being? Objectively, nothing of consequence. Particles of dust in an infinite arena, present for an instant in eternity. Clumps of atoms in a universe with more galaxies than people. And yet a human being is necessary for the question itself to exist, and the presence of a question in the universe - any question - is the most wonderful thing. Questions require minds, and minds bring meaning. What is meaning? I don't know, except that the universe and every pointless speck inside it means something to me. I am astonished by the existence of a single atom, and find my civilisation to be an outrageous imprint on reality. I don't understand it. Nobody does, but it makes me smile. This book asks questions about our origins, our destiny, and our place i...

  16. Barrier layer engineering: Performance evaluation of E-mode InGaN/AlGaN/GaN HEMT

    Science.gov (United States)

    Majumdar, Shubhankar; Das, S.; Biswas, D.

    2015-08-01

    Impact on DC characteristics of InGaN/AlGaN/GaN HEMT due to variation in the hetero-structure parameters i.e. molar fraction of Al and thickness of AlGaN barrier layer is presented in this paper. Gate controllability over the channel is dependent on barrier layer thickness, and molar fraction has an impact on band offset and 2DEG, which further affects the current. HEMT device that is simulated in SILVACO has InGaN cap layer of 2 nm thickness with 15% In molar fraction, variation of Al percentage and thickness of the AlGaN barrier layer are taken as 15-45% and 5-20nm, respectively. A tremendous change in threshold voltage (Vth), maximum transconductance (Gmmax) and subthreshold swing is found due to variation in hetero-structure parameter of barrier layer and the values are typically 1.3-0.1 V, 0.6-0.44 S/mm and 75-135 mV/dec respectively.

  17. A universal operator on the Gurarii space

    Czech Academy of Sciences Publication Activity Database

    Garbulińska-Węgrzyn, J.; Kubiś, Wieslaw

    2015-01-01

    Roč. 73, č. 1 (2015), s. 143-158 ISSN 0379-4024 R&D Projects: GA ČR(CZ) GAP201/12/0290 Institutional support: RVO:67985840 Keywords : almost isometry * Gurariî * isometrically universal operator Subject RIV: BA - General Mathematics Impact factor: 0.464, year: 2015 http://www.mathjournals.org/jot/2015-073-001/2015-073-001-007.html

  18. Theoretical study of electronic structures and spectroscopic properties of Ga 3Sn, GaSn 3, and their ions

    Science.gov (United States)

    Zhu, Xiaolei

    2007-01-01

    Ground and excited states of mixed gallium stannide tetramers (Ga 3Sn, Ga 3Sn +, Ga 3Sn -, GaSn 3, GaSn 3+, and GaSn 3-) are investigated employing the complete active space self-consistent-field (CASSCF), density function theory (DFT), and the coupled-cluster single and double substitution (including triple excitations) (CCSD(T)) methods. The ground states of Ga 3Sn, Ga 3Sn +, and Ga 3Sn - are found to be the 2A 1, 3B 1, and 1A 1 states in C2v symmetry with a planar quadrilateral geometry, respectively. The ground states of GaSn 3 and GaSn 3- is predicted to be the 2A 1 and 1A 1 states in C2v point group with a planar quadrilateral structure, respectively, while the ground state of GaSn 3+ is the 1A 1 state with ideal triangular pyramid C3v geometry. Equilibrium geometries, vibrational frequencies, binding energies, electron affinities, ionization energies, and other properties of Ga 3Sn and GaSn 3 are computed and discussed. The anion photoelectron spectra of Ga 3Sn - and GaSn 3- are also predicted. It is interesting to find that the amount of charge transfer between Ga and Sn 2 atoms in the 1A 1 state of GaSn 3+ greatly increases upon electron ionization from the 2A 1 state of GaSn 3, which may be caused by large geometry change. On the other hand, the results of the low-lying states of Ga 3Sn and GaSn 3 are compared with those of Ga 3Si and GaSi 3.

  19. Elimination of trench defects and V-pits from InGaN/GaN structures

    International Nuclear Information System (INIS)

    Smalc-Koziorowska, Julita; Grzanka, Ewa; Czernecki, Robert; Schiavon, Dario; Leszczyński, Mike

    2015-01-01

    The microstructural evolution of InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor phase epitaxy was studied as a function of the growth temperature of the GaN quantum barriers (QBs). We observed the formation of basal stacking faults (BSFs) in GaN QBs grown at low temperature. The presence of BSFs terminated by stacking mismatch boundaries (SMBs) leads to the opening of the structure at the surface into a V-shaped trench loop. This trench may form above an SMB, thereby terminating the BSF, or above a junction between the SMB and a subsequent BSF. Fewer BSFs and thus fewer trench defects were observed in GaN QBs grown at temperatures higher than 830 °C. Further increase in the growth temperature of the GaN QBs led to the suppression of the threading dislocation opening into V-pits

  20. Modeling and simulation of InGaN/GaN quantum dots solar cell

    International Nuclear Information System (INIS)

    Aissat, A.; Benyettou, F.; Vilcot, J. P.

    2016-01-01

    Currently, quantum dots have attracted attention in the field of optoelectronics, and are used to overcome the limits of a conventional solar cell. Here, an In 0.25 Ga 0.75 N/GaN Quantum Dots Solar Cell has been modeled and simulated using Silvaco Atlas. Our results show that the short circuit current increases with the insertion of the InGaN quantum dots inside the intrinsic region of a GaN pin solar cell. In contrary, the open circuit voltage decreases. A relative optimization of the conversion efficiency of 54.77% was achieved comparing a 5-layers In 0.25 Ga 0.75 N/GaN quantum dots with pin solar cell. The conversion efficiency begins to decline beyond 5-layers quantum dots introduced. Indium composition of 10 % improves relatively the efficiency about 42.58% and a temperature of 285 K gives better conversion efficiency of 13.14%.

  1. Modeling and simulation of InGaN/GaN quantum dots solar cell

    Science.gov (United States)

    Aissat, A.; Benyettou, F.; Vilcot, J. P.

    2016-07-01

    Currently, quantum dots have attracted attention in the field of optoelectronics, and are used to overcome the limits of a conventional solar cell. Here, an In0.25Ga0.75N/GaN Quantum Dots Solar Cell has been modeled and simulated using Silvaco Atlas. Our results show that the short circuit current increases with the insertion of the InGaN quantum dots inside the intrinsic region of a GaN pin solar cell. In contrary, the open circuit voltage decreases. A relative optimization of the conversion efficiency of 54.77% was achieved comparing a 5-layers In0.25Ga0.75N/GaN quantum dots with pin solar cell. The conversion efficiency begins to decline beyond 5-layers quantum dots introduced. Indium composition of 10 % improves relatively the efficiency about 42.58% and a temperature of 285 K gives better conversion efficiency of 13.14%.

  2. Epitaxial nanowire formation in metamorphic GaAs/GaPAs short-period superlattices

    Science.gov (United States)

    Zheng, Nan; Ahrenkiel, S. Phillip

    2017-07-01

    Metamorphic growth presents routes to novel nanomaterials with unique properties that may be suitable for a range of applications. We discuss self-assembled, epitaxial nanowires formed during metalorganic chemical vapor deposition of metamorphic GaAs/GaPAs short-period superlattices. The heterostructures incorporate strain-engineered GaPAs compositional grades on 6°-B miscut GaAs substrates. Lateral diffusion within the SPS into vertically aligned, three-dimensional columns results in nanowires extending along A directions with a lateral period of 70-90 nm. The microstructure is probed by transmission electron microscopy to confirm the presence of coherent GaAs nanowires within GaPAs barriers. The compositional profile is inferred from analysis of {200} dark-field image contrast and lattice images.

  3. Formation of columnar (In,Ga)As quantum dots on GaAs(100)

    International Nuclear Information System (INIS)

    He, J.; Noetzel, R.; Offermans, P.; Koenraad, P.M.; Gong, Q.; Hamhuis, G.J.; Eijkemans, T.J.; Wolter, J.H.

    2004-01-01

    Columnar (In,Ga)As quantum dots (QDs) with homogeneous composition and shape in the growth direction are realized by molecular-beam epitaxy on GaAs(100) substrates. The columnar (In,Ga)As QDs are formed on InAs seed QDs by alternating deposition of thin GaAs intermediate layers and monolayers of InAs with extended growth interruptions after each layer. The height of the columnar (In,Ga)As QDs is controlled by varying the number of stacked GaAs/InAs layers. The structural and optical properties are studied by cross-sectional scanning tunneling microscopy, atomic force microscopy, and photoluminescence spectroscopy. With increase of the aspect ratio of the columnar QDs, the emission wavelength is redshifted and the linewidth is reduced

  4. MOVPE growth of violet GaN LEDs on β-Ga2O3 substrates

    Science.gov (United States)

    Li, Ding; Hoffmann, Veit; Richter, Eberhard; Tessaro, Thomas; Galazka, Zbigniew; Weyers, Markus; Tränkle, Günther

    2017-11-01

    We report that a H2-free atmosphere is essential for the initial stage of metalorganic vapour phase epitaxy (MOVPE) growth of GaN on β-Ga2O3 to prevent the surface from damage. A simple growth method is proposed that can easily transfer established GaN growth recipes from sapphire to β-Ga2O3 with both (-2 0 1) and (1 0 0) orientations. This method features a thin AlN nucleation layer grown below 900 °C in N2 atmosphere to protect the surface of β-Ga2O3 from deterioration during further growth under the H2 atmosphere. Based on this, we demonstrate working violet vertical light emitting diodes (VLEDs) on n-conductive β-Ga2O3 substrates.

  5. 60Co gamma radiation effect on AlGaN//AlN/GaN HEMT devices

    International Nuclear Information System (INIS)

    Wang Yanping; Luo Yinhong; Wang Wei; Zhang Keying; Guo Hongxia; Guo Xiaoqiang; Wang Yuanming

    2013-01-01

    The testing techniques and experimental methods of the 60 Co gamma irradiation effect on AlGaN/AlN/GaN high electron mobility transistors (HEMTs) are established. The degradation of the electrical properties of the device under the actual radiation environment are analyzed theoretically, and studies of the total dose effects of gamma radiation on AlGaN/AlN/GaN HEMTs at three different radiation bias conditions are carried out. The degradation patterns of the main parameters of the AlGaN/AlN/GaN HEMTs at different doses are then investigated, and the device parameters that were sensitive to the gamma radiation induced damage and the total dose level induced device damage are obtained. (authors)

  6. Strong correlation and ferromagnetism in (Ga,Mn)As and (Ga,Mn)N

    International Nuclear Information System (INIS)

    Filippetti, A.; Spaldin, N.A.; Sanvito, S.

    2005-01-01

    The band energies of the ferromagnetic diluted magnetic semiconductors (Ga,Mn)As and (Ga,Mn)N are calculated using a self-interaction-free approach which describes covalent and strongly correlated electrons without adjustable parameters. Both materials are half-metallic, although the contribution of Mn-derived d states to the bands around the Fermi energy is very different in the two cases. In (Ga,Mn)As the bands are strongly p-d hybridized, with a dominance of As p states. In contrast in (Ga,Mn)N the Fermi energy lies within three flat bands of mainly d character that are occupied by two electrons. Thus the Mn ion in (Ga,Mn)N behaves as a deep trap acceptor, with the hole at 1.39 eV above the GaN valence band top, and is in excellent agreement with the experimental data

  7. Botulinum toxin detection using AlGaN /GaN high electron mobility transistors

    Science.gov (United States)

    Wang, Yu-Lin; Chu, B. H.; Chen, K. H.; Chang, C. Y.; Lele, T. P.; Tseng, Y.; Pearton, S. J.; Ramage, J.; Hooten, D.; Dabiran, A.; Chow, P. P.; Ren, F.

    2008-12-01

    Antibody-functionalized, Au-gated AlGaN /GaN high electron mobility transistors (HEMTs) were used to detect botulinum toxin. The antibody was anchored to the gate area through immobilized thioglycolic acid. The AlGaN /GaN HEMT drain-source current showed a rapid response of less than 5s when the target toxin in a buffer was added to the antibody-immobilized surface. We could detect a range of concentrations from 1to10ng/ml. These results clearly demonstrate the promise of field-deployable electronic biological sensors based on AlGaN /GaN HEMTs for botulinum toxin detection.

  8. Amphoteric arsenic in GaN

    CERN Document Server

    Wahl, U; Araújo, J P; Rita, E; Soares, JC

    2007-01-01

    We have determined the lattice location of implanted arsenic in GaN by means of conversion electron emission channeling from radioactive $^{73}$As. We give direct evidence that As is an amphoteric impurity, thus settling the long-standing question as to whether it prefers cation or anion sites in GaN. The amphoteric character of As and the fact that As$\\scriptstyle_{Ga}\\,$ " anti-sites ” are not minority defects provide additional aspects to be taken into account for an explanantion of the so-called “ miscibility gap ” in ternary GaAs$\\scriptstyle_{1-x}$N$\\scriptstyle_{x}$ compounds, which cannot be grown with a single phase for values of $x$ in the range 0.1<${x}$< 0.99.

  9. 2015 Cook & Tift County (GA) Lidar

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — TASK NAME: NOAA OCM Tift and Cook Counties GA Lidar Data Acquisition and Processing Production Task NOAA Contract No. EA133C-11-CQ-0010 Woolpert Order No. 75271...

  10. Polarization-enhanced InGaN/GaN-based hybrid tunnel junction contacts to GaN p-n diodes and InGaN LEDs

    Science.gov (United States)

    Mughal, Asad J.; Young, Erin C.; Alhassan, Abdullah I.; Back, Joonho; Nakamura, Shuji; Speck, James S.; DenBaars, Steven P.

    2017-12-01

    Improved turn-on voltages and reduced series resistances were realized by depositing highly Si-doped n-type GaN using molecular beam epitaxy on polarization-enhanced p-type InGaN contact layers grown using metal-organic chemical vapor deposition. We compared the effects of different Si doping concentrations and the addition of p-type InGaN on the forward voltages of p-n diodes and light-emitting diodes, and found that increasing the Si concentrations from 1.9 × 1020 to 4.6 × 1020 cm-3 and including a highly doped p-type InGaN at the junction both contributed to reductions in the depletion width, the series resistance of 4.2 × 10-3-3.4 × 10-3 Ω·cm2, and the turn-on voltages of the diodes.

  11. Polarization-enhanced InGaN/GaN-based hybrid tunnel junction contacts to GaN p–n diodes and InGaN LEDs

    KAUST Repository

    Mughal, Asad J.

    2017-11-27

    Improved turn-on voltages and reduced series resistances were realized by depositing highly Si-doped n-type GaN using molecular beam epitaxy on polarization-enhanced p-type InGaN contact layers grown using metal–organic chemical vapor deposition. We compared the effects of different Si doping concentrations and the addition of p-type InGaN on the forward voltages of p–n diodes and light-emitting diodes, and found that increasing the Si concentrations from 1.9 × 1020 to 4.6 × 1020 cm−3 and including a highly doped p-type InGaN at the junction both contributed to reductions in the depletion width, the series resistance of 4.2 × 10−3–3.4 × 10−3 Ωcenterdotcm2, and the turn-on voltages of the diodes.

  12. Polarization-enhanced InGaN/GaN-based hybrid tunnel junction contacts to GaN p–n diodes and InGaN LEDs

    KAUST Repository

    Mughal, Asad J.; Young, Erin C.; Alhassan, Abdullah I.; Back, Joonho; Nakamura, Shuji; Speck, James S.; DenBaars, Steven P.

    2017-01-01

    Improved turn-on voltages and reduced series resistances were realized by depositing highly Si-doped n-type GaN using molecular beam epitaxy on polarization-enhanced p-type InGaN contact layers grown using metal–organic chemical vapor deposition. We compared the effects of different Si doping concentrations and the addition of p-type InGaN on the forward voltages of p–n diodes and light-emitting diodes, and found that increasing the Si concentrations from 1.9 × 1020 to 4.6 × 1020 cm−3 and including a highly doped p-type InGaN at the junction both contributed to reductions in the depletion width, the series resistance of 4.2 × 10−3–3.4 × 10−3 Ωcenterdotcm2, and the turn-on voltages of the diodes.

  13. Data processing system of GA and PPPL

    International Nuclear Information System (INIS)

    Oshima, Takayuki

    2001-11-01

    Results of research in 1997 to General Atomics (GA) and Princeton Plasma Physics Laboratory (PPPL) are reported. The author visited the computer system of fusion group in GA. He joined the tokamak experiment in DIII-D, especially on the demonstration of the remote experiment inside U.S., and investigated the data processing system of DIII-D and the computer network, etc. After the visit to GA, He visited PPPL and exchanged the information about the equipment of remote experiment between JAERI and PPPL based on the US-Japan fusion energy research cooperation. He also investigated the data processing system of TFTR tokamak, the computer network and so on. Results of research of the second visit to GA in 2000 are also reported, which describes a rapid progress of each data processing equipment by the advance on the computer technology in just three years. (author)

  14. Atomic ordering in GaAsP

    Science.gov (United States)

    Chen, G. S.; Jaw, D. H.; Stringfellow, G. B.

    1991-04-01

    CuPt type ordering, which consists of a monolayer compositional modulation along one of the 4 directions in the lattice, was studied using transmission electron microscopy for GaAs1-xPx with values of x extending from 0.25 to 0.85. The samples were grown by organometallic vapor phase epitaxy on nominal (001) GaAs substrates that were misoriented by varying amounts in three directions. No CuPt type ordering was observed for GaAs1-xPx with x ≤0.35, while ordering was found to occur for 0.4≤x≤0.85. The direction of substrate misorientation has a major effect on the determination of which of the four possible CuPt variants are formed for 0.4≤x≤0.85. Two variants, with ordering on the (1¯11) and (11¯1) planes, appear for epilayers grown on substrates oriented exactly on the (001) plane and for substrates misoriented by 6° towards the [110] direction. Only one variant, with ordering on the (1¯11) plane, appears for epilayers grown on substrates misoriented by 6° towards [1¯10]. These ordering-induced spots observed in transmission electron diffraction (TED) patterns for GaAsP occur only for the [110] cross section. From TED studies of GaInP grown on similar substrates, we conclude that the CuPt variants in GaAsP are exactly the same as for GaInP. Further evidence supporting this conclusion was obtained by growing first a layer of GaInP followed by a layer of GaAsP. High-resolution dark field electron micrographs show domains of the same variants in both layers. A mechanism describing the formation of the specific ordered variant for both GaAsP and GaInP is proposed. From studies of ordering in a strain-layer superlattice, the strain due to lattice mismatch was found to play no significant role in the propagation of ordered domains. Microtwins, also generated due to lattice mismatch, can act as domain boundaries and prevent the propagation of the ordered domains.

  15. Modeling and Simulation of Monolithic AlGaAs/InGaAs Tandem Solar Cell

    Directory of Open Access Journals (Sweden)

    Samia SLIMANI

    2015-06-01

    Full Text Available Employing conventional III-V junctions we report a classical calculation of conduction and valence band edge and the electron and hole densities. It is shown that the optimum performance can be achieved by employing AlGaAs /AlGaAs/InGaAs monolithic cascade solar cells, we have established these calculations by solving the Poisson equation within the framework of the Nextnano.

  16. Development of the GA-4 and GA-9 legal weight truck spent fuel casks

    International Nuclear Information System (INIS)

    Grenier, R.M.; Meyer, R.J.; Mings, W.J.

    1993-01-01

    General Atomics (GA) has designed two new truck casks under contract to the U.S. Department of Energy as part of the Office of Civilian Radioactive Waste Management (OCRWM) Cask System Development Program. The GA-4 and GA-9 Casks, when licensed by the U.S. Nuclear Regulatory Commission, will transport intact spent fuel assemblies from commercial nuclear reactor sites to a monitored retrievable storage facility or permanent repository. (J.P.N.)

  17. Crystal Structures of GaN Nanodots by Nitrogen Plasma Treatment on Ga Metal Droplets

    Directory of Open Access Journals (Sweden)

    Yang-Zhe Su

    2018-06-01

    Full Text Available Gallium nitride (GaN is one of important functional materials for optoelectronics and electronics. GaN exists both in equilibrium wurtzite and metastable zinc-blende structural phases. The zinc-blende GaN has superior electronic and optical properties over wurtzite one. In this report, GaN nanodots can be fabricated by Ga metal droplets in ultra-high vacuum and then nitridation by nitrogen plasma. The size, shape, density, and crystal structure of GaN nanodots can be characterized by transmission electron microscopy. The growth parameters, such as pre-nitridation treatment on Si surface, substrate temperature, and plasma nitridation time, affect the crystal structure of GaN nanodots. Higher thermal energy could provide the driving force for the phase transformation of GaN nanodots from zinc-blende to wurtzite structures. Metastable zinc-blende GaN nanodots can be synthesized by the surface modification of Si (111 by nitrogen plasma, i.e., the pre-nitridation treatment is done at a lower growth temperature. This is because the pre-nitridation process can provide a nitrogen-terminal surface for the following Ga droplet formation and a nitrogen-rich condition for the formation of GaN nanodots during droplet epitaxy. The pre-nitridation of Si substrates, the formation of a thin SiNx layer, could inhibit the phase transformation of GaN nanodots from zinc-blende to wurtzite phases. The pre-nitridation treatment also affects the dot size, density, and surface roughness of samples.

  18. Investigation of localization effect in GaN-rich InGaN alloys and ...

    Indian Academy of Sciences (India)

    Abstract. The temperature-dependent PL properties of GaN-rich InxGa1−xN alloys is investigated and S-shaped temperature dependence is observed in all InGaN samples. It is found that the origin of localization effect in samples. A and B are different from that in sample C. For samples A and B, In content fluctuations ...

  19. Simplified 2DEG carrier concentration model for composite barrier AlGaN/GaN HEMT

    International Nuclear Information System (INIS)

    Das, Palash; Biswas, Dhrubes

    2014-01-01

    The self consistent solution of Schrodinger and Poisson equations is used along with the total charge depletion model and applied with a novel approach of composite AlGaN barrier based HEMT heterostructure. The solution leaded to a completely new analytical model for Fermi energy level vs. 2DEG carrier concentration. This was eventually used to demonstrate a new analytical model for the temperature dependent 2DEG carrier concentration in AlGaN/GaN HEMT

  20. Site-controlled InGaN/GaN single-photon-emitting diode

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Lei; Deng, Hui, E-mail: dengh@umich.edu [Department of Physics, University of Michigan, 450 Church St., Ann Arbor, Michigan 48109 (United States); Teng, Chu-Hsiang; Ku, Pei-Cheng, E-mail: peicheng@umich.edu [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Ave., Ann Arbor, Michigan 48109 (United States)

    2016-04-11

    We report single-photon emission from electrically driven site-controlled InGaN/GaN quantum dots. The device is fabricated from a planar light-emitting diode structure containing a single InGaN quantum well, using a top-down approach. The location, dimension, and height of each single-photon-emitting diode are controlled lithographically, providing great flexibility for chip-scale integration.

  1. Core level photoelectron spectroscopy of LiGaS2 and Ga-S bonding in complex sulfides

    International Nuclear Information System (INIS)

    Atuchin, V.V.; Isaenko, L.I.; Kesler, V.G.; Lobanov, S.I.

    2010-01-01

    The electronic parameters of the lithium thiogallate LiGaS 2 have been evaluated by X-ray photoelectron spectroscopy (XPS). Spectral features of all constituent element core levels and Auger lines have been considered. The Ga-S bonding effects in Ga-bearing sulfide crystals have been discussed using binding energy difference Δ 2p (S-Ga) = BE(S 2p) - BE(Ga 3d) as a representative parameter to quantify the valence electron shift from gallium to sulfur atoms. The value Δ 2p (S-Ga) = 141.9 eV found for LiGaS 2 is very close to that evaluated for AgGaS 2 . This relation is an indicator of closely coincident ionicity of Ga-S bonds in LiGaS 2 and AgGaS 2 .

  2. Core level photoelectron spectroscopy of LiGaS{sub 2} and Ga-S bonding in complex sulfides

    Energy Technology Data Exchange (ETDEWEB)

    Atuchin, V.V., E-mail: atuchin@thermo.isp.nsc.r [Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, SB RAS, 13, Lavrentieva Ave., Novosibirsk 90, 630090 (Russian Federation); Isaenko, L.I. [Laboratory of Crystal Growth, Institute of Geology and Mineralogy, SB RAS, Novosibirsk 90, 630090 (Russian Federation); Kesler, V.G. [Laboratory of Physical Bases of Integrated Microelectronics, Institute of Semiconductor Physics, SB RAS, Novosibirsk 90, 630090 (Russian Federation); Lobanov, S.I. [Laboratory of Crystal Growth, Institute of Geology and Mineralogy, SB RAS, Novosibirsk 90, 630090 (Russian Federation)

    2010-05-14

    The electronic parameters of the lithium thiogallate LiGaS{sub 2} have been evaluated by X-ray photoelectron spectroscopy (XPS). Spectral features of all constituent element core levels and Auger lines have been considered. The Ga-S bonding effects in Ga-bearing sulfide crystals have been discussed using binding energy difference {Delta}{sub 2p}(S-Ga) = BE(S 2p) - BE(Ga 3d) as a representative parameter to quantify the valence electron shift from gallium to sulfur atoms. The value {Delta}{sub 2p}(S-Ga) = 141.9 eV found for LiGaS{sub 2} is very close to that evaluated for AgGaS{sub 2}. This relation is an indicator of closely coincident ionicity of Ga-S bonds in LiGaS{sub 2} and AgGaS{sub 2}.

  3. Investigation of the current collapse induced in InGaN back barrier AlGaN/GaN high electron mobility transistors

    International Nuclear Information System (INIS)

    Wan Xiaojia; Wang Xiaoliang; Xiao Hongling; Feng Chun; Jiang Lijuan; Qu Shenqi; Wang Zhanguo; Hou Xun

    2013-01-01

    Current collapses were studied, which were observed in AlGaN/GaN high electron mobility transistors (HEMTs) with and without InGaN back barrier (BB) as a result of short-term bias stress. More serious drain current collapses were observed in InGaN BB AlGaN/GaN HEMTs compared with the traditional HEMTs. The results indicate that the defects and surface states induced by the InGaN BB layer may enhance the current collapse. The surface states may be the primary mechanism of the origination of current collapse in AlGaN/GaN HEMTs for short-term direct current stress. (semiconductor devices)

  4. Meningiomas: A Comparative Study of 68Ga-DOTATOC, 68Ga-DOTANOC and 68Ga-DOTATATE for Molecular Imaging in Mice

    Science.gov (United States)

    Soto-Montenegro, María Luisa; Peña-Zalbidea, Santiago; Mateos-Pérez, Jose María; Oteo, Marta; Romero, Eduardo; Morcillo, Miguel Ángel; Desco, Manuel

    2014-01-01

    Purpose The goal of this study was to compare the tumor uptake kinetics and diagnostic value of three 68Ga-DOTA-labeled somatostatin analogues (68Ga-DOTATOC, 68Ga-DOTANOC, and 68Ga-DOTATATE) using PET/CT in a murine model with subcutaneous meningioma xenografts. Methods The experiment was performed with 16 male NUDE NU/NU mice bearing xenografts of a human meningioma cell line (CH-157MN). 68Ga-DOTATOC, 68Ga-DOTANOC, and 68Ga-DOTATATE were produced in a FASTLab automated platform. Imaging was performed on an Argus small-animal PET/CT scanner. The SUVmax of the liver and muscle, and the tumor-to-liver (T/L) and tumor-to-muscle (T/M) SUV ratios were computed. Kinetic analysis was performed using Logan graphical analysis for a two-tissue reversible compartmental model, and the volume of distribution (Vt) was determined. Results Hepatic SUVmax and Vt were significantly higher with 68Ga-DOTANOC than with 68Ga-DOTATOC and 68Ga-DOTATATE. No significant differences between tracers were found for SUVmax in tumor or muscle. No differences were found in the T/L SUV ratio between 68Ga-DOTATATE and 68Ga-DOTATOC, both of which had a higher fraction than 68Ga-DOTANOC. The T/M SUV ratio was significantly higher with 68Ga-DOTATATE than with 68Ga-DOTATOC and 68Ga-DOTANOC. The Vt for tumor was higher with 68Ga-DOTATATE than with 68Ga-DOTANOC and relatively similar to that of 68Ga-DOTATOC. Conclusions This study demonstrates, for the first time, the ability of the three radiolabeled somatostatin analogues tested to image a human meningioma cell line. Although Vt was relatively similar with 68Ga-DOTATATE and 68Ga-DOTATOC, uptake was higher with 68Ga-DOTATATE in the tumor than with 68Ga-DOTANOC and 68Ga-DOTATOC, suggesting a higher diagnostic value of 68Ga-DOTATATE for detecting meningiomas. PMID:25369268

  5. AlGaN/GaN field effect transistors for power electronics—Effect of finite GaN layer thickness on thermal characteristics

    Energy Technology Data Exchange (ETDEWEB)

    Hodges, C., E-mail: chris.hodges@bristol.ac.uk; Anaya Calvo, J.; Kuball, M. [H. H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL (United Kingdom); Stoffels, S.; Marcon, D. [IMEC, Kapeldreef 75, B3001 Leuven (Belgium)

    2013-11-11

    AlGaN/GaN heterostructure field effect transistors with a 150 nm thick GaN channel within stacked Al{sub x}Ga{sub 1−x}N layers were investigated using Raman thermography. By fitting a thermal simulation to the measured temperatures, the thermal conductivity of the GaN channel was determined to be 60 W m{sup −1} K{sup −1}, over 50% less than typical GaN epilayers, causing an increased peak channel temperature. This agrees with a nanoscale model. A low thermal conductivity AlGaN buffer means the GaN spreads heat; its properties are important for device thermal characteristics. When designing power devices with thin GaN layers, as well as electrical considerations, the reduced channel thermal conductivity must be considered.

  6. Enhanced optical output power of InGaN/GaN light-emitting diodes grown on a silicon (111) substrate with a nanoporous GaN layer.

    Science.gov (United States)

    Lee, Kwang Jae; Chun, Jaeyi; Kim, Sang-Jo; Oh, Semi; Ha, Chang-Soo; Park, Jung-Won; Lee, Seung-Jae; Song, Jae-Chul; Baek, Jong Hyeob; Park, Seong-Ju

    2016-03-07

    We report the growth of InGaN/GaN multiple quantum wells blue light-emitting diodes (LEDs) on a silicon (111) substrate with an embedded nanoporous (NP) GaN layer. The NP GaN layer is fabricated by electrochemical etching of n-type GaN on the silicon substrate. The crystalline quality of crack-free GaN grown on the NP GaN layer is remarkably improved and the residual tensile stress is also decreased. The optical output power is increased by 120% at an injection current of 20 mA compared with that of conventional LEDs without a NP GaN layer. The large enhancement of optical output power is attributed to the reduction of threading dislocation, effective scattering of light in the LED, and the suppression of light propagation into the silicon substrate by the NP GaN layer.

  7. Meningiomas: a comparative study of 68Ga-DOTATOC, 68Ga-DOTANOC and 68Ga-DOTATATE for molecular imaging in mice.

    Directory of Open Access Journals (Sweden)

    María Luisa Soto-Montenegro

    Full Text Available The goal of this study was to compare the tumor uptake kinetics and diagnostic value of three (68Ga-DOTA-labeled somatostatin analogues ((68Ga-DOTATOC, (68Ga-DOTANOC, and (68Ga-DOTATATE using PET/CT in a murine model with subcutaneous meningioma xenografts.The experiment was performed with 16 male NUDE NU/NU mice bearing xenografts of a human meningioma cell line (CH-157MN. (68Ga-DOTATOC, (68Ga-DOTANOC, and (68Ga-DOTATATE were produced in a FASTLab automated platform. Imaging was performed on an Argus small-animal PET/CT scanner. The SUVmax of the liver and muscle, and the tumor-to-liver (T/L and tumor-to-muscle (T/M SUV ratios were computed. Kinetic analysis was performed using Logan graphical analysis for a two-tissue reversible compartmental model, and the volume of distribution (Vt was determined.Hepatic SUVmax and Vt were significantly higher with (68Ga-DOTANOC than with (68Ga-DOTATOC and (68Ga-DOTATATE. No significant differences between tracers were found for SUVmax in tumor or muscle. No differences were found in the T/L SUV ratio between (68Ga-DOTATATE and (68Ga-DOTATOC, both of which had a higher fraction than (68Ga-DOTANOC. The T/M SUV ratio was significantly higher with (68Ga-DOTATATE than with (68Ga-DOTATOC and (68Ga-DOTANOC. The Vt for tumor was higher with (68Ga-DOTATATE than with (68Ga-DOTANOC and relatively similar to that of (68Ga-DOTATOC.This study demonstrates, for the first time, the ability of the three radiolabeled somatostatin analogues tested to image a human meningioma cell line. Although Vt was relatively similar with (68Ga-DOTATATE and (68Ga-DOTATOC, uptake was higher with (68Ga-DOTATATE in the tumor than with (68Ga-DOTANOC and (68Ga-DOTATOC, suggesting a higher diagnostic value of (68Ga-DOTATATE for detecting meningiomas.

  8. CLMP-Mediated Regulation of Intestinal Homeostasis in IBD

    Science.gov (United States)

    2014-10-01

    AWARD NUMBER: W81XWH-13-1-0334 TITLE: PRINCIPAL INVESTIGATOR: Asma Nusrat CONTRACTING ORGANIZATION: Emory University Atlanta GA 30322...in IBD 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Charles A. Parkos (Initiating PI), Asma Nusrat (Partnering PI

  9. Cognitive Development of Children with Craniosynostosis

    OpenAIRE

    J Gordon Millichap

    2015-01-01

    Investigators from University of Washington, Seattle, WA; Harvard U, MA; St Louis, MO; Atlanta, GA; Northwestern U, and Shriner’s Hospital, Chicago, compared the development of school-aged children with single-suture craniosynostosis (sagittal, metopic, unicoronal, lambdoid) and unaffected children.

  10. Journal of Biosciences | Indian Academy of Sciences

    Indian Academy of Sciences (India)

    Author Affiliations. Ramkumar Sambasivan1 2 Grace K Pavlath3 Jyotsna Dhawan1. Centre for Cellular and Molecular Biology, Hyderabad 500 007, India; Department of Developmental Biology, Pasteur Institute, 75724 Cedex 15 Paris, Franc; Department of Pharmacology, Emory University, Atlanta, GA 30322, USA ...

  11. Genetic testing for breast and ovarian cancer susceptibility: evaluating direct-to-consumer marketing--Atlanta, Denver, Raleigh-Durham, and Seattle, 2003.

    Science.gov (United States)

    2004-07-16

    Breast and ovarian cancer are the second and fifth leading causes of cancer death, respectively, among women in the United States. One in eight women will have breast cancer during their lifetimes, and one in 70 will have ovarian cancer. Mutations in two genes, BRCA1 and BRCA2 (BRCA1/2), are associated with predisposition for inherited breast and ovarian cancer and are identified in 5%-10% of women with breast or ovarian cancer (BOC). Since 1996, genetic testing for these mutations has been available clinically; however, population-based screening is not recommended because of the complexity of test interpretation and limited data on clinical validity and utility. Despite the test's limited applicability in the general population, the U.S. provider of clinical BRCA1/2 testing (Myriad Genetic Laboratories, Inc., Salt Lake City, Utah) conducted a pilot direct-to-consumer (DTC) marketing campaign in two cities (Atlanta, Georgia, and Denver, Colorado) during September 2002-February 2003. Although DTC advertisements have been used to raise consumer awareness about pharmaceuticals, this was the first time an established genetic test was marketed to the public. To assess the impact of the campaign on consumer behaviors and health-care provider practices, CDC and the respective state health departments for the pilot cities and two comparison cities (Raleigh-Durham, North Carolina, and Seattle, Washington) surveyed consumers and providers. This report summarizes results of those surveys, which indicated that consumer and provider awareness of BRCA1/2 testing increased in the pilot cities and that providers in these cities perceived an impact on their practice (e.g., more questions asked about testing, more BRCA1/2 tests requested, and more tests ordered). However, in all four cities, providers often lacked knowledge to advise patients about inherited BOC and testing. These findings underscore the need for evidence-based recommendations on appropriate use of genetic tests

  12. Transitioning young adults from paediatric to adult care and the HIV care continuum in Atlanta, Georgia, USA: a retrospective cohort study.

    Science.gov (United States)

    Hussen, Sophia A; Chakraborty, Rana; Knezevic, Andrea; Camacho-Gonzalez, Andres; Huang, Eugene; Stephenson, Rob; Del Rio, Carlos

    2017-09-01

    The transition from paediatric to adult HIV care is a particularly high-risk time for disengagement among young adults; however, empirical data are lacking. We reviewed medical records of 72 youth seen in both the paediatric and the adult clinics of the Grady Infectious Disease Program in Atlanta, Georgia, USA, from 2004 to 2014. We abstracted clinical data on linkage, retention and virologic suppression from the last two years in the paediatric clinic through the first two years in the adult clinic. Of patients with at least one visit scheduled in adult clinic, 97% were eventually seen by an adult provider (median time between last paediatric and first adult clinic visit = 10 months, interquartile range 2-18 months). Half of the patients were enrolled in paediatric care immediately prior to transition, while the other half experienced a gap in paediatric care and re-enrolled in the clinic as adults. A total of 89% of patients were retained (at least two visits at least three months apart) in the first year and 56% in the second year after transition. Patients who were seen in adult clinic within three months of their last paediatric visit were more likely to be virologically suppressed after transition than those who took longer (Relative risk (RR): 1.76; 95% confidence interval (CI): 1.07-2.9; p  = 0.03). Patients with virologic suppression (HIV-1 RNA below the level of detection of the assay) at the last paediatric visit were also more likely to be suppressed at the most recent adult visit (RR: 2.3; 95% CI: 1.34-3.9; p  = 0.002). Retention rates once in adult care, though high initially, declined significantly by the second year after transition. Pre-transition viral suppression and shorter linkage time between paediatric and adult clinic were associated with better outcomes post-transition. Optimizing transition will require intensive transition support for patients who are not virologically controlled, as well as support for youth beyond the first year

  13. Molecular beam epitaxial growth and characterization of GaSb layers on GaAs (0 0 1) substrates

    International Nuclear Information System (INIS)

    Li Yanbo; Zhang Yang; Zhang Yuwei; Wang Baoqiang; Zhu Zhanping; Zeng Yiping

    2012-01-01

    We report on the growth of GaSb layers on GaAs (0 0 1) substrates by molecular beam epitaxy (MBE). We investigate the influence of the GaAs substrate surface treatment, growth temperature, and V/III flux ratios on the crystal quality and the surface morphology of GaSb epilayers. Comparing to Ga-rich GaAs surface preparation, the Sb-rich GaAs surface preparation can promote the growth of higher-quality GaSb material. It is found that the crystal quality, electrical properties, and surface morphology of the GaSb epilayers are highly dependent on the growth temperature, and Sb/Ga flux ratios. Under the optimized growth conditions, we demonstrate the epitaxial growth of high quality GaSb layers on GaAs substrates. The p-type nature of the unintentionally doped GaSb is studied and from the growth conditions dependence of the hole concentrations of the GaSb, we deduce that the main native acceptor in the GaSb is the Ga antisite (Ga Sb ) defect.

  14. Current transport in graphene/AlGaN/GaN vertical heterostructures probed at nanoscale.

    Science.gov (United States)

    Fisichella, Gabriele; Greco, Giuseppe; Roccaforte, Fabrizio; Giannazzo, Filippo

    2014-08-07

    Vertical heterostructures combining two or more graphene (Gr) layers separated by ultra-thin insulating or semiconductor barriers represent very promising systems for next generation electronics devices, due to the combination of high speed operation with wide-range current modulation by a gate bias. They are based on the specific mechanisms of current transport between two-dimensional-electron-gases (2DEGs) in close proximity. In this context, vertical devices formed by Gr and semiconductor heterostructures hosting an "ordinary" 2DEG can be also very interesting. In this work, we investigated the vertical current transport in Gr/Al(0.25)Ga(0.75)N/GaN heterostructures, where Gr is separated from a high density 2DEG by a ∼ 24 nm thick AlGaN barrier layer. The current transport from Gr to the buried 2DEG was characterized at nanoscale using conductive atomic force microscopy (CAFM) and scanning capacitance microscopy (SCM). From these analyses, performed both on Gr/AlGaN/GaN and on AlGaN/GaN reference samples using AFM tips with different metal coatings, the Gr/AlGaN Schottky barrier height ΦB and its lateral uniformity were evaluated, as well as the variation of the carrier densities of graphene (ngr) and AlGaN/GaN 2DEG (ns) as a function of the applied bias. A low Schottky barrier (∼ 0.40 eV) with excellent spatial uniformity was found at the Gr/AlGaN interface, i.e., lower compared to the measured values for metal/AlGaN contacts, which range from ∼ 0.6 to ∼ 1.1 eV depending on the metal workfunction. The electrical behavior of the Gr/AlGaN contact has been explained by Gr interaction with AlGaN donor-like surface states located in close proximity, which are also responsible of high n-type Gr doping (∼ 1.3 × 10(13) cm(-2)). An effective modulation of ns by the Gr Schottky contact was demonstrated by capacitance analysis under reverse bias. From this basic understanding of transport properties in Gr/AlGaN/GaN heterostructures, novel vertical field effect

  15. Behavior of misfit dislocations in semipolar InGaN/GaN grown by MOVPE

    Energy Technology Data Exchange (ETDEWEB)

    Kuwahara, Takaaki [Department of Applied Science for Electronics and Materials, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Kuwano, Noriyuki [Department of Applied Science for Electronics and Materials, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Art, Science and Technology Center for Cooperative Research, Kyushu University, Kasuga, Fukuoka 816-8580 (Japan); Kurisu, Akihiko; Okada, Narihito; Tadatomo, Kazuyuki [Graduate School of Science and Engineering, Yamaguchi University, Ube, Yamaguchi 755-8611 (Japan)

    2012-03-15

    A microstructure in an InGaN/GaN layer grown at the semipolar direction was observed in detail by means of transmission electron microscopy (TEM) in order to analyze the behaviour of dislocations. A (11 anti 22) GaN layer was first deposited on a maskless r (1 anti 102)-plane patterned-substrate, and then an In{sub x} Ga{sub 1-x}N (x =0.10, 0.24) was overgrown to be about 1 {mu}m in thickness. Dislocations near the interface of InGaN/GaN are classified into several types: 1 Threading dislocations lying on (0001). 2. Misfit dislocations lying on the interface of InGaN/GaN. 3. Dislocations along [1 anti 100] at a certain distance from the interface. 4. Dislocations newly formed at the interface and developing along [11 anti 20] on (0001). 5. Partial dislocations accompanied with a stacking fault on (0001). It was found that the misfit dislocations are arrayed in pairs at the direction along [1 anti 100] on the interface of (11 anti 22). Burgers vector of the misfit dislocations was found to be B = <2 anti 1 anti 13>/3. In case of B = [ anti 1 anti 123]/3, they are edge dislocations. The densities of dislocations and stacking faults increase with the In-content in InGaN. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  16. Binding of biexcitons in GaAs/AlxGa1-xAs superlattices

    DEFF Research Database (Denmark)

    Mizeikis, Vygantas; Birkedal, Dan; Langbein, Wolfgang Werner

    1997-01-01

    Properties of the heavy-hole excitons and biexcitons in GaAs/Al0.3Ga0.7As superlattices are studied using linear and nonlinear optical techniques. In superlattices with miniband halfwidths less than the exciton binding energy, the biexciton binding energy is found to be the same as in the noninte......Properties of the heavy-hole excitons and biexcitons in GaAs/Al0.3Ga0.7As superlattices are studied using linear and nonlinear optical techniques. In superlattices with miniband halfwidths less than the exciton binding energy, the biexciton binding energy is found to be the same...

  17. Self-organized formation of GaSb/GaAs quantum rings.

    Science.gov (United States)

    Timm, R; Eisele, H; Lenz, A; Ivanova, L; Balakrishnan, G; Huffaker, D L; Dähne, M

    2008-12-19

    Ring-shaped GaSb/GaAs quantum dots, grown by molecular beam epitaxy, were studied using cross-sectional scanning tunneling microscopy. These quantum rings have an outer shape of a truncated pyramid with baselengths around 15 nm and heights of about 2 nm but are characterized by a clear central opening extending over about 40% of the outer baselength. They form spontaneously during the growth and subsequent continuous capping of GaSb/GaAs quantum dots due to the large strain and substantial As-for-Sb exchange reactions leading to strong Sb segregation.

  18. Growth mechanism of InGaN nanodots on three-dimensional GaN structures

    Energy Technology Data Exchange (ETDEWEB)

    Park, Donghwy; Min, Daehong; Nam, Okhyun [Department of Nano-Optical Engineering, Convergence Center for Advanced Nano-Semiconductor (CANS), Korea Polytechnic University (KPU), Siheung-si, Gyeonggi-do (Korea, Republic of)

    2017-07-15

    In this study, we investigated the growth mechanism of indium gallium nitride (InGaN) nanodots (NDs) and an InGaN layer, which were simultaneously formed on a three-dimensional (3D) gallium nitride (GaN) structure, having (0001) polar, (11-22) semi-polar, and (11-20) nonpolar facets. We observed the difference in the morphological and compositional properties of the InGaN structures. From the high resolution transmission electron microscopy (HR-TEM) images, it can be seen that the InGaN NDs were formed only on the polar and nonpolar facets, whereas an InGaN layer was formed on the semi-polar facet. The indium composition variation in all the InGaN structures was observed using scanning transmission electron microscopy (STEM) and the energy dispersive X-ray spectroscopy (EDS). The different growth mechanism can be explained by two reasons: (i) The difference in the diffusivities of indium and gallium adatoms at each facet of 3D GaN structure; and (ii) the difference in the kinetic Wulff plots of polar, semi-polar, and nonpolar GaN planes. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  19. GA-4/GA-9 honeycomb impact limiter tests and analytical model

    International Nuclear Information System (INIS)

    Koploy, M.A.; Taylor, C.S.

    1991-01-01

    General Atomics (GA) has a test program underway to obtain data on the behavior of a honeycomb impact limiter. The program includes testing of small samples to obtain basic information, as well as testing of complete 1/4-scale impact limiters to obtain load-versus-deflection curves for different crush orientations. GA has used the test results to aid in the development of an analytical model to predict the impact limiter loads. The results also helped optimize the design of the impact limiters for the GA-4 and GA-9 Casks

  20. Groove-type channel enhancement-mode AlGaN/GaN MIS HEMT with combined polar and nonpolar AlGaN/GaN heterostructures

    International Nuclear Information System (INIS)

    Duan Xiao-Ling; Zhang Jin-Cheng; Xiao Ming; Zhao Yi; Ning Jing; Hao Yue

    2016-01-01

    A novel groove-type channel enhancement-mode AlGaN/GaN MIS high electron mobility transistor (GTCE-HEMT) with a combined polar and nonpolar AlGaN/GaN heterostucture is presented. The device simulation shows a threshold voltage of 1.24 V, peak transconductance of 182 mS/mm, and subthreshold slope of 85 mV/dec, which are obtained by adjusting the device parameters. Interestingly, it is possible to control the threshold voltage accurately without precisely controlling the etching depth in fabrication by adopting this structure. Besides, the breakdown voltage ( V B ) is significantly increased by 78% in comparison with the value of the conventional MIS-HEMT. Moreover, the fabrication process of the novel device is entirely compatible with that of the conventional depletion-mode (D-mode) polar AlGaN/GaN HEMT. It presents a promising way to realize the switch application and the E/D-mode logic circuits. (paper)

  1. Sustainable Universities

    DEFF Research Database (Denmark)

    Grindsted, Thomas Skou

    2011-01-01

    Declarations on Sustainability in Higher Education (SHE) can be viewed as a piece of international regulation. Over the past 30 years research at universities has produced convincing data to warn about deterioration of the environment, resource scarcity and the need for sustainability. This in turn....... Declarations tend to have impact on three trends. Firstly, there is emerging international consensus on the university’s role and function in relation to sustainable development; secondly, the emergence of national legislation, and thirdly, an emerging international competition to be leader in sustainable...

  2. Open University

    CERN Multimedia

    Pentz,M

    1975-01-01

    Michel Pentz est née en Afrique du Sud et venu au Cern en 1957 comme physicien et président de l'associaion du personnel. Il est également fondateur du mouvement Antiapartheid de Genève et a participé à la fondation de l'Open University en Grande-Bretagne. Il nous parle des contextes pédagogiques, culturels et nationaux dans lesquels la méthode peut s'appliquer.

  3. Hole-spin dynamics in p-doped GaAs/AlGaAs heterostructures; Lochspindynamik in p-dotierten GaAs/AlGaAs-Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Kugler, Michael

    2012-11-15

    This work investigates the spin dynamics of holes in p-doped GaAs/AlGaAs quantum wells (QW) at low temperatures. To examine the energetic structure of the used samples, PL and PLE-spectroscopy were employed. Time resolved Kerr and Faraday-Rotation (TRKR/FR) and 'Resonant Spin Amplification' (RSA) were used to analyse the spin dynamics. First, the signal formation in TRKR/FR and RSA experiments is discussed taking into account the interconnected charge carrier dynamics and spin dynamics of electrons and holes. An excitation energy dependent sign change of the Kerr signal amplitude could be observed, whose energetic position corresponds to an absorption maximum in PLE experiments. This behavior could be explained by an energy dependent splitting of the spin niveaus, which leads to an energy dependence of the Faraday and Kerr signal. Furthermore, two initialization processes were investigated, which could be used to transfer optically generated spin information into the resident hole spin system. This could be achieved by either applying a magnetic field, or by rapid dephasing of hole spins immediately after excitation. Changes in excitation energy, excitation density or temperature could be used to influence the fast dephasing processes and therefore the initial ratio of hole to electron spins. The complex, interconnected charge carrier and spin dynamics of electrons and holes could be accurately reproduced using a rate equation model. This allowed for the extraction of physically relevant parameters like spin lifetimes and g-factors from RSA and TRKR/FR data. An analytical model that was developed at the Wroclaw University of Technology delivered matching results. In the second part of the experimental work, the dependence of the hole spin lifetime and the hole g-factor on various parameters was analysed. Here, the RSA method could for the first time be applied to two-dimensional hole systems, allowing for new insights into the regime of long lived hole

  4. Determination of 68Ga production parameters by different reactions ...

    Indian Academy of Sciences (India)

    Gallium-68 (1/2 = 68 min, + = 89%) is an important positron-emitting radionuclide for positron emission tomography and used in nuclear medicine for diagnosing tumours. This study gives a suitable reaction to produce 68Ga. Gallium-68 excitation function via 68Zn(, ) 68Ga, 68Zn(, 2) 68Ga, 70Zn(, 3) 68Ga and ...

  5. Escherichia coli bacteria density in relation to turbidity, streamflow characteristics, and season in the Chattahoochee River near Atlanta, Georgia, October 2000 through September 2008—Description, statistical analysis, and predictive modeling

    Science.gov (United States)

    Lawrence, Stephen J.

    2012-01-01

    Water-based recreation—such as rafting, canoeing, and fishing—is popular among visitors to the Chattahoochee River National Recreation Area (CRNRA) in north Georgia. The CRNRA is a 48-mile reach of the Chattahoochee River upstream from Atlanta, Georgia, managed by the National Park Service (NPS). Historically, high densities of fecal-indicator bacteria have been documented in the Chattahoochee River and its tributaries at levels that commonly exceeded Georgia water-quality standards. In October 2000, the NPS partnered with the U.S. Geological Survey (USGS), State and local agencies, and non-governmental organizations to monitor Escherichia coli bacteria (E. coli) density and develop a system to alert river users when E. coli densities exceeded the U.S. Environmental Protection Agency (USEPA) single-sample beach criterion of 235 colonies (most probable number) per 100 milliliters (MPN/100 mL) of water. This program, called BacteriALERT, monitors E. coli density, turbidity, and water temperature at two sites on the Chattahoochee River upstream from Atlanta, Georgia. This report summarizes E. coli bacteria density and turbidity values in water samples collected between 2000 and 2008 as part of the BacteriALERT program; describes the relations between E. coli density and turbidity, streamflow characteristics, and season; and describes the regression analyses used to develop predictive models that estimate E. coli density in real time at both sampling sites.

  6. Environmental Public Health Survelliance for Exposure to Respiratory Health Hazards: A Joint NASA/CDC Project to Use Remote Sensing Data for Estimating Airborne Particulate Matter Over the Atlanta, Georgia Metropolitan Area

    Science.gov (United States)

    Quattrochi, Dale A.; Rickman, Douglas; Mohammad, Al-Hamdan; Crosson, William; Estes, Maurice, Jr.; Limaye, Ashutosh; Qualters, Judith

    2008-01-01

    Describes the public health surveillance efforts of NASA, in a joint effort with the Center for Disease Control (CDC). NASA/MSFC and the CDC are partners in linking nvironmental and health data to enhance public health surveillance. The use of NASA technology creates value - added geospatial products from existing environmental data sources to facilitate public health linkages. The venture sought to provide remote sensing data for the 5-country Metro-Atlanta area and to integrate this environmental data with public health data into a local network, in an effort to prevent and control environmentally related health effects. Remote sensing data used environmental data (Environmental Protection Agency [EPA] Air Quality System [AQS] ground measurements and MODIS Aerosol Optical Depth [AOD]) to estimate airborne particulate matter over Atlanta, and linked this data with health data related to asthma. The study proved the feasibility of linking environmental data (MODIS particular matter estimates and AQS) with health data (asthma). Algorithms were developed for QC, bias removal, merging MODIS and AQS particulate matter data, as well as for other applications. Additionally, a Business Associate Agreement was negotiated for a health care provider to enable sharing of Protected Health Information.

  7. Endogenous gibberellins in Arabidopsis thaliana and possible steps blocked in the biosynthetic pathways of the semidwarf ga4 and ga5 mutants

    International Nuclear Information System (INIS)

    Talon, M.; Zeevaart, J.A.D.; Koornneef, M.

    1990-01-01

    Twenty gibberellins (GAs) have been identified in extracts from shoots of the Landsberg erecta line of Arabidopsis thaliana by full-scan gas chromatography-mass spectrometry and Kovats retention indices. Eight of them are members of the early-13-hydroxylation pathway (GA 53 , GA 44 , GA 19 , GA 17 , GA 20 , GA 1 , GA 29 , and GA 8 ), six are members of the early-3-hydroxylation pathway (GA 37 , GA 27 , GA 36 , GA 13 , GA 4 , and GA 34 ), and the remaining six are members of the non-3,13-hydroxylation pathway (GA 12 , GA 15 , GA 24 , GA 25 , GA 9 , and GFA 51 ). Seven of these GAs were quantified in the Landsberg erecta line of Arabidopsis and in the semidwarf ga4 and ga5 mutants by gas chromatography-selected ion monitoring (SIM) using internal standards. The relative levels of the remaining 13 GAs were compared by the use of ion intensities only. The growth-response data, as well as the accumulation of GA 9 in the ga4 mutant, indicate that GA 9 is not active in Arabidopsis, but it must be 3β-hydroxytlated to GA 4 to become bioactive. It is concluded that the reduced levels of the 3β-hydroxy-GAs, GA 1 and GA 4 , are the cause of the semidwarf growth habit of both mutants

  8. Geneva University

    CERN Multimedia

    2009-01-01

    École de physique - Département de physique nucléaire et corspusculaire 24, quai Ernest-Ansermet 1211 GENÈVE 4 Tél: (022) 379 62 73 - Fax: (022) 379 69 92 Monday 9 March 2009 COLLOQUIUM at 17:00 – Stückelberg Auditorium Are We Descended From Heavy Neutrinos? Prof. Boris Kayser / Fermilab (Fermi National Accelerator Center, Geneva, Illinois, USA) Neutrinos are among the most abundant particles in the universe. The discovery that they have nonzero masses has raised a number of very interesting questions about them, and about their connections to other areas of physics and to cosmology. After briefly reviewing what has been learned about the neutrinos so far, we will identify the major open questions, explain why they are interesting, and discuss ideas and plans for answering them through future experiments. We will highlight a particularly intriguing question: Are neutrinos the key to understanding why the universe contains matter but almost no antimatter, making it s...

  9. Geneva University

    CERN Multimedia

    2009-01-01

    École de physique - Département de physique nucléaire et corpusculaire 24, quai Ernest-Ansermet 1211 GENÈVE 4 Tél: (022) 379 62 73 - Fax: (022) 379 69 92 Wednesday 13 May 2009 PARTICLE PHYSICS SEMINAR at 17:00 – Stückelberg Auditorium Observing the extreme universe with the Fermi Gamma-ray Space Telescope Prof. Olaf Reimer / Stanford University The Fermi Gamma-ray Space Telescope (FGST, formerly GLAST) is an international observatory-type satellite mission with a physics program spanning from gamma-ray astronomy to particle astrophysics and cosmology. FGST was launched on June 11, 2008 and is successfully conducting science observations of the high-energy gamma-ray sky since August 2008. A varienty of discoveries has been made already, including monitoring rapid blazar variability, the existence of GeV gamma-ray bursts, and numerous new gamma-ray sources of different types, including those belonging to previously unknown gamma-ray source classes like msPSRs, globula...

  10. Nineteenth Workshop Athens, GA, USA

    CERN Document Server

    Lewis, S P; Schöttler, H B; Computer Simulation Studies in Condensed-Matter Physics XIX

    2008-01-01

    This volume represents a "status report" emanating from presentations made during the 19th Annual Workshop on Computer Simulations Studies in Condensed Matter Physics at the Center for Simulational Physics at the University of Georgia in February, 2006. It provides a broad overview of the most recent advances in the field, spanning the range from equilibrium and non-equilibrium behavior in statistical physics to biological and soft condensed matter systems. Results on nanomagents and materials are included as are several descriptions of advances in methodology.

  11. Cubic AlGaN/GaN structures for device application

    Energy Technology Data Exchange (ETDEWEB)

    Schoermann, Joerg

    2007-05-15

    The aim of this work was the growth and the characterization of cubic GaN, cubic AlGaN/GaN heterostructures and cubic AlN/GaN superlattice structures. Reduction of the surface and interface roughness was the key issue to show the potential for the use of cubic nitrides in futur devices. All structures were grown by plasma assisted molecular beam epitaxy on free standing 3C-SiC (001) substrates. In situ reflection high energy electron diffraction was first investigated to determine the Ga coverage of c-GaN during growth. Using the intensity of the electron beam as a probe, optimum growth conditions were found when a 1 monolayer coverage is formed at the surface. GaN samples grown under these conditions reveal excellent structural properties. On top of the c-GaN buffer c-AlGaN/GaN single and multiple quantum wells were deposited. The well widths ranged from 2.5 to 7.5 nm. During growth of Al{sub 0.15}Ga{sub 0.85}N/GaN quantum wells clear reflection high energy electron diffraction oscillations were observed indicating a two dimensional growth mode. We observed strong room-temperature, ultraviolet photoluminescence at about 3.3 eV with a minimum linewidth of 90 meV. The peak energy of the emission versus well width is reproduced by a square-well Poisson- Schroedinger model calculation. We found that piezoelectric effects are absent in c-III nitrides with a (001) growth direction. Intersubband transition in the wavelength range from 1.6 {mu}m to 2.1 {mu}m was systematically investigated in AlN/GaN superlattices (SL), grown on 100 nm thick c-GaN buffer layers. The SLs consisted of 20 periods of GaN wells with a thickness between 1.5 nm and 2.1 nm and AlN barriers with a thickness of 1.35 nm. The first intersubband transitions were observed in metastable cubic III nitride structures in the range between 1.6 {mu}m and 2.1 {mu}m. (orig.)

  12. Growth and characterization of GaAs-GaSb III-V pseudo-binary nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Schamp, C.T. [Cerium Laboratories, Austin, TX 78741 (United States); Jesser, W.A. [Department of Materials Science and Engineering, 116 Engineer' s Way, University of Virginia, Charlottesville, VA 22904 (United States)

    2008-07-01

    The GaAs-GaSb pseudo-binary materials system presents an interesting challenge for growth because of 1) the existence of a miscibility gap in the solid-solid portion of the equilibrium phase diagram, and 2) the large differences in vapor pressure between the column III element, Ga, and the column V elements, As and Sb. To overcome these challenges in the growth of GaAs, GaSb, and Ga{sub 50}As{sub x}Sb{sub 50-x} alloy nanoparticles, single- and dual-target pulsed laser deposition (PLD) techniques were implemented using an Nd:YAG laser operated with a harmonic generator to utilize the second harmonic wavelength (532 nm) and a combination of the fundamental and the second harmonic wavelengths (1064 nm+532 nm). The nanoparticles were collected on amorphous carbon films for subsequent characterization by transmission electron microscopy. The analysis shows that single phase GaAs-rich Ga{sub 50}As{sub x}Sb{sub 50-x} (28>x>50) nanoparticles and nanocrystalline films have been formed through dual-target, single-wavelength (532 nm) pulsed laser ablation. Interestingly, through the ablation of the single component targets, two-phase particles were also found to form. These two phase particles resemble ''nano-ice cream cones'' with solid cones of either GaAs or GaSb with a spherical ''ice cream'' ball of Ga located at the wide portion of the cone, which is either an amorphous phase or liquid phase. Through an analysis by STEM-EDX spectroscopy, these particles are found to be consistant with this model. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Photoelectric characteristics of metal-Ga{sub 2}O{sub 3}-GaAs structures

    Energy Technology Data Exchange (ETDEWEB)

    Kalygina, V. M., E-mail: Kalygina@ngs.ru; Vishnikina, V. V.; Petrova, Yu. S.; Prudaev, I. A.; Yaskevich, T. M. [National Research Tomsk State University (Russian Federation)

    2015-03-15

    We investigate the effect of thermal annealing in argon and of oxygen plasma processing on the photoelectric properties of GaAs-Ga{sub 2}O{sub 3}-Me structures. Gallium-oxide films are fabricated by photostimulated electrochemical oxidation of epitaxial gallium-arsenide layers with n-type conductivity. The as-deposited films were amorphous, but their processing in oxygen plasma led to the nucleation of β-Ga{sub 2}O{sub 3} crystallites. The unannealed films are nontransparent in the visible and ultraviolet (UV) ranges and there is no photocurrent in structures based on them. After annealing at 900°C for 30 min, the gallium-oxide films contain only β-Ga{sub 2}O{sub 3} crystallites and become transparent. Under illumination of the Ga{sub 2}O{sub 3}-GaAs structures with visible light, the photocurrent appears. This effect can be attributed to radiation absorption in GaAs. The photocurrent and its voltage dependence are determined by the time of exposure to the oxygen plasma. In the UV range, the sensitivity of the structures increases with decreasing radiation wavelength, starting at λ ≤ 230 nm. This is due to absorption in the Ga{sub 2}O{sub 3} film. Reduction in the structure sensitivity with an increase in the time of exposure to oxygen plasma can be caused by the incorporation of defects both at the Ga{sub 2}O{sub 3}-GaAs interface and in the Ga{sub 2}O{sub 3} film.

  14. First-principles electronic structure of Mn-doped GaAs, GaP, and GaN semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Schulthess, T C [Computer Science and Mathematics Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6164 (United States); Temmerman, W M [Daresbury Laboratory, Daresbury, Warrington WA4 4AD (United Kingdom); Szotek, Z [Daresbury Laboratory, Daresbury, Warrington WA4 4AD (United Kingdom); Svane, A [Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C (Denmark); Petit, L [Computer Science and Mathematics Division and Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6164 (United States)

    2007-04-23

    We present first-principles electronic structure calculations of Mn-doped III-V semiconductors based on the local spin-density approximation (LSDA) as well as the self-interaction corrected local spin-density method (SIC-LSD). We find that it is crucial to use a self-interaction free approach to properly describe the electronic ground state. The SIC-LSD calculations predict the proper electronic ground state configuration for Mn in GaAs, GaP, and GaN. Excellent quantitative agreement with experiment is found for the magnetic moment and p-d exchange in (GaMn)As. These results allow us to validate commonly used models for magnetic semiconductors. Furthermore, we discuss the delicate problem of extracting binding energies of localized levels from density functional theory calculations. We propose three approaches to take into account final state effects to estimate the binding energies of the Mn d levels in GaAs. We find good agreement between computed values and estimates from photoemission experiments.

  15. A new wire fabrication processing using high Ga content Cu-Ga compound in V3Ga compound superconducting wire

    International Nuclear Information System (INIS)

    Hishinuma, Yoshimitsu; Nishimura, Arata; Kikuchi, Akihiro; Iijima, Yasuo; Takeuchi, Takao

    2007-01-01

    A superconducting magnet system is also one of the important components in an advanced magnetic confinement fusion reactor. Then it is required to have a higher magnetic field property to confine and maintain steady-sate burning deuterium (D)-tritium (T) fusion plasma in the large interspace during the long term operation. Burning plasma is sure to generate 14 MeV fusion neutrons during deuterium-tritium reaction, and fusion neutrons will be streamed and penetrated to superconducting magnet through large ports with damping neutron energy. Therefore, it is necessary to consider carefully not only superconducting property but also neutron irradiation property in superconducting materials for use in a future fusion reactor, and a 'low activation and high field superconducting magnet' will be required to realize the fusion power plant beyond International Thermonuclear Experimental Reactor (ITER). V-based superconducting material has a much shorter decay time of induced radioactivity compared with the Nb-based materials. We thought that the V 3 Ga compound was one of the most promising materials for the 'low activation and higher field superconductors' for an advanced fusion reactor. However, the present critical current density (J c ) property of V 3 Ga compound wire is insufficient for apply to fusion magnet applications. We investigated a new route PIT process using a high Ga content Cu-Ga compound in order to improve the superconducting property of the V 3 Ga compound wire. (author)

  16. First-principles electronic structure of Mn-doped GaAs, GaP, and GaN semiconductors

    International Nuclear Information System (INIS)

    Schulthess, T C; Temmerman, W M; Szotek, Z; Svane, A; Petit, L

    2007-01-01

    We present first-principles electronic structure calculations of Mn-doped III-V semiconductors based on the local spin-density approximation (LSDA) as well as the self-interaction corrected local spin-density method (SIC-LSD). We find that it is crucial to use a self-interaction free approach to properly describe the electronic ground state. The SIC-LSD calculations predict the proper electronic ground state configuration for Mn in GaAs, GaP, and GaN. Excellent quantitative agreement with experiment is found for the magnetic moment and p-d exchange in (GaMn)As. These results allow us to validate commonly used models for magnetic semiconductors. Furthermore, we discuss the delicate problem of extracting binding energies of localized levels from density functional theory calculations. We propose three approaches to take into account final state effects to estimate the binding energies of the Mn d levels in GaAs. We find good agreement between computed values and estimates from photoemission experiments

  17. 68Ga-triacetylfusarinine C and 68Ga-ferrioxamine E for Aspergillus infection imaging: uptake specificity in various microorganisms

    NARCIS (Netherlands)

    Petrik, M.; Haas, H. de; Laverman, P.; Schrettl, M.; Franssen, G.M.; Blatzer, M.; Decristoforo, C.

    2014-01-01

    (68)Ga-triacetylfusarinine C ((68)Ga-TAFC) and (68)Ga-ferrioxamine E ((68)Ga-FOXE) showed excellent targeting properties in Aspergillus fumigatus rat infection model. Here, we report on the comparison of specificity towards different microorganisms and human lung cancer cells (H1299).The in vitro

  18. Spin-polarized electron tunneling across a Si delta-doped GaMnAs/n-GaAs interface

    DEFF Research Database (Denmark)

    Andresen, S.E.; Sørensen, B.S.; Lindelof, P.E.

    2003-01-01

    Spin-polarized electron coupling across a Si delta-doped GaMnAs/n-GaAs interface was investigated. The injection of spin-polarized electrons was detected as circular polarized emission from a GaInAs/GaAs quantum well light emitting diode. The angular momentum selection rules were simplified...

  19. Red to near-infrared emission from InGaN/GaN quantum-disks-in-nanowires LED

    KAUST Repository

    Ng, Tien Khee; Zhao, Chao; Shen, Chao; Jahangir, Shafat; Janjua, Bilal; Ben Slimane, Ahmed; Kang, Chun Hong; Syed, Ahad A.; Li, Jingqi; Alyamani, Ahmed Y.; El-Desouki, Munir M.; Bhattacharya, Pallab K.; Ooi, Boon S.

    2014-01-01

    The InGaN/GaN quantum-disks-in-nanowire light-emitting diode (LED) with emission centered at ~830nm, the longest emission wavelength ever reported in the InGaN/GaN system, and spectral linewidth of 290nm, has been fabricated with p-side-down on a Cu substrate.

  20. AlGaN/GaN high electron mobility transistors with a low sub-threshold swing on free-standing GaN wafer

    Directory of Open Access Journals (Sweden)

    Xinke Liu

    2017-09-01

    Full Text Available This paper reported AlGaN/GaN high electron mobility transistors (HEMTs with low sub-threshold swing SS on free-standing GaN wafer. High quality AlGaN/GaN epi-layer has been grown by metal-organic chemical vapor deposition (MOCVD on free-standing GaN, small full-width hall maximum (FWHM of 42.9 arcsec for (0002 GaN XRD peaks and ultralow dislocation density (∼104-105 cm-2 were obtained. Due to these extremely high quality material properties, the fabricated AlGaN/GaN HEMTs achieve a low SS (∼60 mV/decade, low hysteresis of 54 mV, and high peak electron mobility μeff of ∼1456 cm2V-1s-1. Systematic study of materials properties and device characteristics exhibits that GaN-on-GaN AlGaN/GaN HEMTs are promising candidate for next generation high power device applications.

  1. Geneva University

    CERN Multimedia

    École de physique - Département de physique nucléaire et corspusculaire 24, quai Ernest-Ansermet 1211 GENÈVE 4 Tél: (022) 379 62 73 - Fax: (022) 379 69 92 Monday 7 December 2009 PHYSICS COLLOQUIUM at 17:00 – Stückelberg Auditorium Topological insulators and topological superconductors Professor Shoucheng Zhang Department of Physics, Stanford University, CA   Recently, a new class of topological states has been theoretically predicted and experimentally realized. The topological insulators have an insulating gap in the bulk, but have topologically protected edge or surface states due to the time reversal symmetry. In two dimensions the edge states give rise to the quantum spin Hall (QSH) effect, in the absence of any external magnetic field. I shall review the theoretical prediction of the QSH state in HgTe/CdTe semiconductor quantum wells, and its recent experimental observation. The edge states of the QSH state supports fr...

  2. Geneva University

    CERN Multimedia

    École de physique - Département de physique nucléaire et corspusculaire 24, quai Ernest-Ansermet 1211 GENÈVE 4 Tél: (022) 379 62 73 - Fax: (022) 379 69 92 Wednesday 18 November  2009 PARTICLE PHYSICS SEMINAR at 17:00 – Stückelberg Auditorium Highlights of the European Strategy Workshop for Future Neutrino Physics Dr Ilias Efthymiopoulos, CERN   Seminar cancelled! Information Organizer : J.-S. Graulich Monday 7 December 2009 PHYSICS COLLOQUIUM at 17:00 – Stückelberg Auditorium Topological insulators and topological superconductors Professor Shoucheng Zhang Department of Physics, Stanford University, CA   Recently, a new class of topological states has been theoretically predicted and experimentally realized. The topological insulators have an insulating gap in the bulk, but have topologically protected edge or surface states due to the time reversal symmetry. In two dimensions the edge s...

  3. Geneva University

    CERN Multimedia

    2008-01-01

    Ecole de physique - Département de physique nucléaire et corpusculaire 24, Quai Ernest-Ansermet 1211 GENEVE 4 Tél: (022) 379 62 73 Fax: (022) 379 69 92 Monday 28 April 2008 PHYSICS COLLOQUIUM at 17.00 – Stückelberg Auditorium Gravity : an Emergent Perspective by Prof. Thanu Padmanabhan, Pune University Dean, Ganeshkhind, Pune, India I will motivate and describe a novel perspective in which gravity arises as an emergent phenomenon, somewhat like elasticity. This perspective throws light on several issues which are somewhat of a mystery in the conventional approach. Moreover it provides new insights on the dark energy problem. In fact, I will show that it is necessary to have such an alternative perspective in order to solve the cosmological constant problem.Information: http://theory.physics.unige.ch/~fiteo/seminars/COL/collist.html

  4. Magneto-ballistic transport in GaN nanowires

    International Nuclear Information System (INIS)

    Santoruvo, Giovanni; Allain, Adrien; Ovchinnikov, Dmitry; Matioli, Elison

    2016-01-01

    The ballistic filtering property of nanoscale crosses was used to investigate the effect of perpendicular magnetic fields on the ballistic transport of electrons on wide band-gap GaN heterostructures. The straight scattering-less trajectory of electrons was modified by a perpendicular magnetic field which produced a strong non-linear behavior in the measured output voltage of the ballistic filters and allowed the observation of semi-classical and quantum effects, such as quenching of the Hall resistance and manifestation of the last plateau, in excellent agreement with the theoretical predictions. A large measured phase coherence length of 190 nm allowed the observation of universal quantum fluctuations and weak localization of electrons due to quantum interference up to ∼25 K. This work also reveals the prospect of wide band-gap GaN semiconductors as a platform for basic transport and quantum studies, whose properties allow the investigation of ballistic transport and quantum phenomena at much larger voltages and temperatures than in other semiconductors.

  5. Magneto-ballistic transport in GaN nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Santoruvo, Giovanni, E-mail: giovanni.santoruvo@epfl.ch; Allain, Adrien; Ovchinnikov, Dmitry; Matioli, Elison, E-mail: elison.matioli@epfl.ch [Ecole Polytechnique Fédérale de Lausanne (EPFL), CH 1015 Lausanne (Switzerland)

    2016-09-05

    The ballistic filtering property of nanoscale crosses was used to investigate the effect of perpendicular magnetic fields on the ballistic transport of electrons on wide band-gap GaN heterostructures. The straight scattering-less trajectory of electrons was modified by a perpendicular magnetic field which produced a strong non-linear behavior in the measured output voltage of the ballistic filters and allowed the observation of semi-classical and quantum effects, such as quenching of the Hall resistance and manifestation of the last plateau, in excellent agreement with the theoretical predictions. A large measured phase coherence length of 190 nm allowed the observation of universal quantum fluctuations and weak localization of electrons due to quantum interference up to ∼25 K. This work also reveals the prospect of wide band-gap GaN semiconductors as a platform for basic transport and quantum studies, whose properties allow the investigation of ballistic transport and quantum phenomena at much larger voltages and temperatures than in other semiconductors.

  6. Universal Alienation

    Directory of Open Access Journals (Sweden)

    David Harvey

    2018-05-01

    Full Text Available This article is part of a debate between David Harvey, Michael Hardt and Toni Negri. It takes Marx’s bicentenary as occasion for an update of his concept of alienation. The paper asks: how are we to interpret universal alienation and from whence does it come? Marx radically reformulated the concept of alienation in the Grundrisse. The humanism of the early Marx can be re-rooted and reconceptualised in the scientific mode proposed in the Grundrisse. In the Grundrisse, the universality of alienation is specific to capitalism’s historical evolution. Today, alienation exists almost everywhere. It exists at work in production, at home in consumption, and it dominates much of politics and daily life. Such trends intensify through the application of information technologies and artificial intelligence. Widespread alienation has resulted in Occupy movements as well as right-wing populism and bigoted nationalist and racist movements. Donald Trump is the President of alienation. The circulation of capital as totality consists of the three key moments of production, circulation and distribution. A lot of contemporary economic struggles are now occurring at the point of realisation rather than at the point of production. Protests are therefore today often expressions of broad-based discontent. Our future is dictated by the need to redeem our debts. Under such conditions democracy becomes a sham. The big question is what forms of social movement can help us get out of the state-finance nexus. The theory of objective alienation along with an understanding of its subjective consequences is one vital key to unlock the door of a progressive politics for the future.

  7. 36th ATLANTA EXECUTIVE SEMINAR

    Science.gov (United States)

    2011-04-04

    assignments as an Army Division G-4, Divisional Support Battalion Commander, Divisional Material Readiness officer, and Support Battalion Executive...Battalion; Corps Material Management Officer, Corps Support Command; Fort Hood, Texas • Jul 1991 – Jun 1994: Research Analyst, Office of Economic and...LABBLEE Corp, Raytheon, Labat-Anderson Inc., KPMG , Huber Corp, The Boeing Company, and Philadelphia Electric Company. He has also served on a

  8. 34th Atlanta Executive Seminar

    Science.gov (United States)

    2009-04-23

    Partnerships Distance Learning (dL)/ nline Courses LPDs/ PDs Correspondence Courses Site Visits For al Assess ent Training Lead: CAC/TRADOCea : / Lead...Learning (dL)/ nline Courses LPDs/ PDs Correspondence Courses Site Visits For al Assess ent Training Lead: CAC/TRADOCea : / Lead: CACea : Lead: Units...GDP expected to contract by over 2% in 2009. • Global synchronized recession in advanced economies. • Emerging markets not immune but affected in

  9. Electronic passivation of n- and p-type GaAs using chemical vapor deposited GaS

    Science.gov (United States)

    Tabib-Azar, Massood; Kang, Soon; Macinnes, Andrew N.; Power, Michael B.; Barron, Andrew R.; Jenkins, Phillip P.; Hepp, Aloysius F.

    1993-01-01

    We report on the electronic passivation of n- and p-type GaAs using CVD cubic GaS. Au/GaS/GaAs-fabricated metal-insulator-semiconductor (MIS) structures exhibit classical high-frequency capacitor vs voltage (C-V) behavior with well-defined accumulation and inversion regions. Using high- and low-frequency C-V, the interface trap densities of about 10 exp 11/eV per sq cm on both n- and p-type GaAs are determined. The electronic condition of GaS/GaAs interface did not show any deterioration after a six week time period.

  10. Raman Scattering analysis of InGaAs and AlGaAs superlattices grown by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Oeztuerk, N.; Bahceli, S.

    2010-01-01

    InGaAs/GaAs and AlGaAs/GaAs multiple quantum well structures were grown by molecular beam epitaxy and investigated by X-ray diffraction and micro Raman spectroscopy. Phonon modes are investigated in backscattering from (001) surface. In the measured micro Raman spectrum for both structure, phonon peaks can be resolved for GaAs. These are longitudinal optical (LO) mode at 293 cm - 1 and 294 cm - 1 for InGaAs and AlGaAs, respectively.

  11. Significant performance enhancement in AlGaN/GaN high electron mobility transistor by high-κ organic dielectric

    International Nuclear Information System (INIS)

    Ze-Gao, Wang; Yuan-Fu, Chen; Cao, Chen; Ben-Lang, Tian; Fu-Tong, Chu; Xing-Zhao, Liu; Yan-Rong, Li

    2010-01-01

    The electrical properties of AlGaN/GaN high electron mobility transistor (HEMT) with and without high-κ organic dielectrics are investigated. The maximum drain current I D max and the maximum transconductance g m max of the organic dielectric/AlGaN/GaN structure can be enhanced by 74.5%, and 73.7% compared with those of the bare AlGaN/GaN HEMT, respectively. Both the threshold voltage V T and g m max of the dielectric/AlGaN/GaN HEMT are strongly dielectric-constant-dependent. Our results suggest that it is promising to significantly improve the performance of the AlGaN/GaN HEMT by introducing the high-κ organic dielectric. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  12. Misfit dislocation reduction in InGaAs epilayers grown on porous GaAs substrates

    Czech Academy of Sciences Publication Activity Database

    Dimitrakopulos, G.P.; Bazioti, C.; Grym, Jan; Gladkov, Petar; Hulicius, Eduard; Pangrác, Jiří; Pacherová, Oliva; Komninou, Ph.

    2014-01-01

    Roč. 306, Jul (2014), s. 89-93 ISSN 0169-4332 R&D Projects: GA MŠk 7AMB12GR034 Institutional support: RVO:68378271 ; RVO:67985882 Keywords : compound semiconductors * InGaAs * porous substrate * misfit dislocations * strain Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.711, year: 2014

  13. Integrated photonic platform based on semipolar InGaN/GaN multiple section laser diodes

    KAUST Repository

    Shen, Chao

    2017-11-30

    The challenges to realizing III-nitride photonic integrated circuit (PIC) are discussed. Utilizing InGaN-based multi-section laser diode (LD) on semipolar GaN substrate, the seamless on-chip integration of III-nitride waveguide photodetector (WPD) in the visible regime has been demonstrated.

  14. Robust X-band LNAs in AlGaN/GaN technology

    NARCIS (Netherlands)

    Janssen, J.P.B.; Heijningen, M. van; Visser, G.C.; Rodenburg, M.; Johnson, H.K.; Uren, M.J.; Morvan, E.; Vliet, F.E. van

    2009-01-01

    Gallium-Nitride technology is known for its high power density and power amplifier designs, but is also very well suited to realise robust receiver components. This paper presents the design, realisation and measurement of two robust AlGaN/GaN low noise amplifiers. The two versions have been

  15. Robust X-band LNAs in AlGaN/GaN technology

    NARCIS (Netherlands)

    Janssen, J.P.B.; van Heiningen, M.; Visser, G.C.; Rodenburg, M.; Johnson, H.K.; Uren, M.J.; Morvan, E.; van Vliet, Frank Edward

    2009-01-01

    Abstract Gallium-Nitride technology is known for its high power density and power amplifier designs, but is also very well suited to realise robust receiver components. This paper presents the design, realisation and measurement of two robust AlGaN/GaN low noise amplifiers. The two versions have

  16. Sheet resistance under Ohmic contacts to AlGaN/GaN heterostructures

    NARCIS (Netherlands)

    Hajlasz, M.; Donkers, J.J.T.M.; Sque, S.J.; Heil, S.B.S.; Gravesteijn, Dirk J; Rietveld, F.J.R.; Schmitz, Jurriaan

    2014-01-01

    For the determination of specific contact resistance in semiconductor devices, it is usually assumed that the sheet resistance under the contact is identical to that between the contacts. This generally does not hold for contacts to AlGaN/GaN structures, where an effective doping under the contact

  17. Characterization of recessed Ohmic contacts to AlGaN/GaN

    NARCIS (Netherlands)

    Hajlasz, M.; Donkers, J.J.T.M.; Sque, S.J.; Heil, S.B.S.; Gravesteijn, Dirk J; Rietveld, F.J.R.; Schmitz, Jurriaan

    2015-01-01

    In this work the choice of appropriate test structures and characterization methods for recessed Ohmic contacts to AlGaN/GaN is discussed. It is shown that, in the worst-case scenario, the prevailing assumption of identical sheet resistance between and under the contacts can lead to errors of up to

  18. Integrated photonic platform based on semipolar InGaN/GaN multiple section laser diodes

    KAUST Repository

    Shen, Chao; Lee, Changmin; Ng, Tien Khee; Speck, James S.; Nakamura, Shuji; DenBaars, Steven P.; Ooi, Boon S.

    2017-01-01

    The challenges to realizing III-nitride photonic integrated circuit (PIC) are discussed. Utilizing InGaN-based multi-section laser diode (LD) on semipolar GaN substrate, the seamless on-chip integration of III-nitride waveguide photodetector (WPD) in the visible regime has been demonstrated.

  19. Ultrafast carrier dynamics in InGaN/GaN multiple quantum wells

    DEFF Research Database (Denmark)

    Porte, Henrik; Turchinovich, Dmitry; Cooke, David

    We studied the THz conductivity of InGaN/GaN multiple quantum wells (MQWs)by time-resolved terahertz spectroscopy. A nonexponential carrier density decay is observed due to the restoration of a built-in piezoelectric field. Terahertz conductivity spectra show a nonmetallic behavior of the carriers....

  20. Collective Behavior of Interwell Excitons in GaAs/AlGaAs Double Quantum Wells

    DEFF Research Database (Denmark)

    Larionov, A. V.; Timofeev, V. B.; Hvam, Jørn Märcher

    2000-01-01

    Photoluminescence spectra of interwell excitons in double GaAs/AlGaAs quantum wells (n-i-n structures) have been investigated (an interwell excition in these systems is an electron-hole pair spatially separated by a narrow AlAs barrier). Under resonance excitation by circular polarized light...

  1. Coherent dynamics of interwell excitons in GaAs/AlxGa1-xAs superlattices

    DEFF Research Database (Denmark)

    Mizeikis, V.; Birkedal, Dan; Langbein, Wolfgang Werner

    1997-01-01

    Coherent exciton dynamics in a GaAs/AlxGa1-xAs narrow-miniband superlattice is studied by spectrally resolved transient four-wave mixing. Coherent optical properties of the investigated structure are found to be strongly affected by the existence of two different heavy-hole excitonic states. One...

  2. Stability of AlGaN/GaN heterostructures after hydrogen plasma treatment

    Energy Technology Data Exchange (ETDEWEB)

    Babchenko, O., E-mail: oleg.babchenko@savba.sk [Institute of Electrical Engineering SAV, Dúbravská cesta 9, 841 04 Bratislava (Slovakia); Dzuba, J.; Lalinský, T. [Institute of Electrical Engineering SAV, Dúbravská cesta 9, 841 04 Bratislava (Slovakia); Vojs, M. [Institute of Electronics and Photonics STU, Ilkovičova 3, 812 19 Bratislava (Slovakia); Vincze, A. [International Laser Centre, Ilkovičova 3, 841 04 Bratislava (Slovakia); Ižák, T. [Institute of Physics AS CR, v.v.i., Cukrovarnicka 10, 162 53 Prague (Czech Republic); Vanko, G. [Institute of Electrical Engineering SAV, Dúbravská cesta 9, 841 04 Bratislava (Slovakia)

    2017-02-15

    Highlights: • AlGaN/GaNheterostructures with electric contacts were treated by hydrogen plasma. • No surface degradation after treatment was detected by SEM. • Hydrogen plasma caused increasing of sheet resistance up to 3.5 times after 60 min. • Incorporation of hydrogen in AlGaN sub-surface region was observed by SIMS. • Electrical measurements indicate hydrogen induced Schottky barrier lowering. - Abstract: We report on the investigation of low temperature (300 °C) hydrogen plasma treatment influence on the AlGaN/GaN heterostructures. This issue was raised in the frame of study on processes related to hybrid integration of diamond with GaN-based devices. At the same time, the capabilities of thin SiN{sub x} covering were investigated. The samples were exposed to low pressure hydrogen plasma ignited in the linear plasma system at low temperature. We analyze the surface morphology of samples by scanning electron microscopy while microstructural changes down to AlGaN/GaN interface were studied using secondary ion mass spectrometry. The sheet resistance, monitored using circular transmission line measurements, increases more than 3.5 times after 60 min treatment. The basic transport properties of the fabricated circular high electron mobility transistors after H{sub 2} plasma treatment were analyzed. The sheet resistance increasing was attributed to the decrease of effective mobility. Whilst, the observed Schottky barrier lowering indicates necessity of gate contact protection.

  3. Spin injection from Co2MnGa into an InGaAs quantum well

    DEFF Research Database (Denmark)

    Hickey, M. C.; Damsgaard, Christian Danvad; Holmes, S. N.

    2008-01-01

    We have demonstrated spin injection from a full Heusler alloy Co2MnGa thin film into a (100) InGaAs quantum well in a semiconductor light-emitting diode structure at a temperature of 5 K. The detection is performed in the oblique Hanle geometry, allowing quantification of the effective spin lifet...

  4. Radiative and non-radiative recombination in GaInN/GaN quantum wells

    International Nuclear Information System (INIS)

    Netzel, C.

    2007-01-01

    The studies presented in this thesis deal with the occurence of V defectsin GaInN/GaN quantum film structures grown by means of organometallic gas phase epitaxy, and the effects, which have the V defects respectively the GaInN quantum films on the V-defect facets on the emission and recombination properties of the whole GaInN/GaN quantum film structure. The V-defects themselves, inverse pyramidal vacancies with hexagonal base in the semiconductor layers, arise under suitable growth conditions around the percussion violations, which extend in lattice-mismatched growth of GaN on the heterosubstrates sapphire or silicon carbide starting in growth direction through the crystal. If GaInN layers are grown over V-defect dispersed layers on the (1-101) facets of the V defects and the (0001) facets, the growth front of the structure, different growth velocities are present, which lead to differently wide GaInN quantum films on each facets

  5. Micro-photoluminescence of GaAs/AlGaAs triple concentric quantum rings.

    Science.gov (United States)

    Abbarchi, Marco; Cavigli, Lucia; Somaschini, Claudio; Bietti, Sergio; Gurioli, Massimo; Vinattieri, Anna; Sanguinetti, Stefano

    2011-10-31

    A systematic optical study, including micro, ensemble and time resolved photoluminescence of GaAs/AlGaAs triple concentric quantum rings, self-assembled via droplet epitaxy, is presented. Clear emission from localized states belonging to the ring structures is reported. The triple rings show a fast decay dynamics, around 40 ps, which is expected to be useful for ultrafast optical switching applications.

  6. Photoluminescence studies of individual and few GaSb/GaAs quantum rings

    NARCIS (Netherlands)

    Young, M.P.; Woodhead, C.S.; Roberts, J.; Noori, Y.J.; Noble, M.T.; Krier, A.; Smakman, E.P.; Koenraad, P.M.; Hayne, M.; Young, R.J.

    2014-01-01

    We present optical studies of individual and few GaSb quantum rings embedded in a GaAs matrix. Contrary to expectation for type-II confinement, we measure rich spectra containing sharp lines. These lines originate from excitonic recombination and are observed to have resolution-limited full-width at

  7. Carrier dynamics in submonolayer InGaAs/GaAs quantum dots

    DEFF Research Database (Denmark)

    Xu, Zhangcheng; Zhang, Yating; Hvam, Jørn Märcher

    2006-01-01

    Carrier dynamics of submonolayer InGaAs/GaAs quantum dots (QDs) were studied by microphotoluminecence (MPL), selectively excited photoluminescence (SEPL), and time-resolved photoluminescence (TRPL). MPL and SEPL show the coexistence of localized and delocalized states, and different local phonon...

  8. Multilayer self-organization of InGaAs quantum wires on GaAs surfaces

    International Nuclear Information System (INIS)

    Wang, Zhiming M.; Kunets, Vasyl P.; Xie, Yanze Z.; Schmidbauer, Martin; Dorogan, Vitaliy G.; Mazur, Yuriy I.; Salamo, Gregory J.

    2010-01-01

    Molecular-Beam Epitaxy growth of multiple In 0.4 Ga 0.6 As layers on GaAs (311)A and GaAs (331)A has been investigated by Atomic Force Microscopy and Photoluminescence. On GaAs (311)A, uniformly distributed In 0.4 Ga 0.6 As quantum wires (QWRs) with wider lateral separation were achieved, presenting a significant improvement in comparison with the result on single layer [H. Wen, Z.M. Wang, G.J. Salamo, Appl. Phys. Lett. 84 (2004) 1756]. On GaAs (331)A, In 0.4 Ga 0.6 As QWRs were revealed to be much straighter than in the previous report on multilayer growth [Z. Gong, Z. Niu, Z. Fang, Nanotechnology 17 (2006) 1140]. These observations are discussed in terms of the strain-field interaction among multilayers, enhancement of surface mobility at high temperature, and surface stability of GaAs (311)A and (331)A surfaces.

  9. InAlGaAs/AlGaAs quantum wells: line widths, transition energies and segregation

    DEFF Research Database (Denmark)

    Jensen, Jacob Riis; Hvam, Jørn Märcher; Langbein, Wolfgang

    2000-01-01

    We investigate the optical properties of InAlCaAs/AlGaAs quantum wells pseudomorphically grown on GaAs using molecular beam epitaxy (MBE). The transition energies, measured with photoluminescence (PL), are modelled solving the Schrodinger equation, and taking into account segregation in the group...

  10. A localized orbital description of ideal vacancies in GaP and GaSb

    International Nuclear Information System (INIS)

    Erbarut, E.; Tomak, M.

    1986-10-01

    Gaussian orbitals of s and p symmetry and an empirical pseudopotential Hamiltonian is employed for the study of electronic structures of ideal vacancies in GaP and GaSb. A reasonably accurate description of band structures and densities of states are attained. (author)

  11. Achieving Room Temperature Orange Lasing Using InGaP/InAlGaP Diode Laser

    KAUST Repository

    Al-Jabr, Ahmad

    2015-09-28

    We demonstrated the first orange laser diode at room temperature with a decent total output power of ∼46mW and lasing wavelength of 608nm, using a novel strain-induced quantum well intermixing in InGaP/InAlGaP red laser structure.

  12. Ka-Band AlGaN/GaN HEMT high power and driver amplifier MMICs

    NARCIS (Netherlands)

    Heijningen, M. van; Vliet, F.E. van; Quay, R.; Raay, F. van; Kiefer, R.; Mueller, S.; Krausse, D.; Seelmann-Eggebert, M.; Mikulla, M.; Schlechtweg, M.

    2005-01-01

    In this paper the MMIC technology, design and characterization of a high power amplifier and driver amplifier MMIC at 30 GHz in AlGaN/GaN HEMT technology are presented. The MMICs are designed using CPW technology on a 390 μm thick SiC substrate. The measured small-signal gain of the driver is 14 dB

  13. Exciton dynamics in GaAs/AlxGa1-xAs quantum wells

    DEFF Research Database (Denmark)

    Litvinenko, K.; Birkedal, Dan; Lyssenko, V. G.

    1999-01-01

    The changes induced in the optical absorption spectrum of a GaAs/AlxGa1-xAs multiple quantum well due to a photoexcited carrier distribution are reexamined. We use a femtosecond pump-probe technique to excite excitons and free electron-hole pairs. We find that for densities up to 10(11) cm(-2...

  14. GaAsP solar cells on GaP/Si with low threading dislocation density

    International Nuclear Information System (INIS)

    Yaung, Kevin Nay; Vaisman, Michelle; Lang, Jordan; Lee, Minjoo Larry

    2016-01-01

    GaAsP on Si tandem cells represent a promising path towards achieving high efficiency while leveraging the Si solar knowledge base and low-cost infrastructure. However, dislocation densities exceeding 10"8 cm"−"2 in GaAsP cells on Si have historically hampered the efficiency of such approaches. Here, we report the achievement of low threading dislocation density values of 4.0–4.6 × 10"6 cm"−"2 in GaAsP solar cells on GaP/Si, comparable with more established metamorphic solar cells on GaAs. Our GaAsP solar cells on GaP/Si exhibit high open-circuit voltage and quantum efficiency, allowing them to significantly surpass the power conversion efficiency of previous devices. The results in this work show a realistic path towards dual-junction GaAsP on Si cells with efficiencies exceeding 30%.

  15. AlGaN/InGaN Nitride Based Modulation Doped Field Effect Transistor

    National Research Council Canada - National Science Library

    Blair, S

    2003-01-01

    The goal of the proposed work is to investigate the potential advantages of the InGaN channel as a host of the 2DEG and to address the material related problems facing this ternary alloy in the AlGaN...

  16. The role of the arginine metabolome in pain: implications for sickle cell disease

    Directory of Open Access Journals (Sweden)

    Bakshi N

    2016-03-01

    Full Text Available Nitya Bakshi,1–2 Claudia R Morris3–6 1Division of Pediatric Hematology-Oncology, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA; 2Aflac Cancer and Blood Disorders Center, Children’s Healthcare of Atlanta, Atlanta, GA, USA; 3Division of Pediatric Emergency Medicine, Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA; 4Department of Emergency Medicine, Emory University School of Medicine, Atlanta, GA, USA; 5Emory-Children’s Center for Cystic Fibrosis and Airways Disease Research, Emory University School of Medicine, Atlanta, GA, USA; 6Pediatric Emergency Medicine, Children’s Healthcare of Atlanta, Atlanta, GA, USA Abstract: Sickle cell disease (SCD is the most common hemoglobinopathy in the US, affecting approximately 100,000 individuals in the US and millions worldwide. Pain is the hallmark of SCD, and a subset of patients experience pain virtually all of the time. Of interest, the arginine metabolome is associated with several pain mechanisms highlighted in this review. Since SCD is an arginine deficiency syndrome, the contribution of the arginine metabolome to acute and chronic pain in SCD is a topic in need of further attention. Normal arginine metabolism is impaired in SCD through various mechanisms that contribute to endothelial dysfunction, vaso-occlusion, pulmonary complications, risk of leg ulcers, and early mortality. Arginine is a semiessential amino acid that serves as a substrate for protein synthesis and is the precursor to nitric oxide (NO, polyamines, proline, glutamate, creatine, and agmatine. Since arginine is involved in multiple metabolic processes, a deficiency of this amino acid has the potential to disrupt many cellular and organ functions. NO is a potent vasodilator that is depleted in SCD and may contribute to vaso-occlusive pain. As the obligate substrate for NO production, arginine also plays a mechanistic role in SCD-related pain, although its

  17. Magnetic field-dependent of binding energy in GaN/InGaN/GaN spherical QDQW nanoparticles

    International Nuclear Information System (INIS)

    El Ghazi, Haddou; Jorio, Anouar; Zorkani, Izeddine

    2013-01-01

    Simultaneous study of magnetic field and impurity's position effects on the ground-state shallow-donor binding energy in GaN|InGaN|GaN (core|well|shell) spherical quantum dot–quantum well (SQDQW) as a function of the ratio of the inner and the outer radius is reported. The calculations are investigated within the framework of the effective-mass approximation and an infinite deep potential describing the quantum confinement effect. A Ritz variational approach is used taking into account of the electron-impurity correlation and the magnetic field effect in the trial wave-function. It appears that the binding energy depends strongly on the external magnetic field, the impurity's position and the structure radius. It has been found that: (i) the magnetic field effect is more marked in large layer than in thin layer and (ii) it is more pronounced in the spherical layer center than in its extremities

  18. InGaN/GaN multilayer quantum dots yellow-green light-emitting diode with optimized GaN barriers.

    Science.gov (United States)

    Lv, Wenbin; Wang, Lai; Wang, Jiaxing; Hao, Zhibiao; Luo, Yi

    2012-11-07

    InGaN/GaN multilayer quantum dot (QD) structure is a potential type of active regions for yellow-green light-emitting diodes (LEDs). The surface morphologies and crystalline quality of GaN barriers are critical to the uniformity of InGaN QD layers. While GaN barriers were grown in multi-QD layers, we used improved growth parameters by increasing the growth temperature and switching the carrier gas from N2 to H2 in the metal organic vapor phase epitaxy. As a result, a 10-layer InGaN/GaN QD LED is demonstrated successfully. The transmission electron microscopy image shows the uniform multilayer InGaN QDs clearly. As the injection current increases from 5 to 50 mA, the electroluminescence peak wavelength shifts from 574 to 537 nm.

  19. GaSb and GaSb/AlSb Superlattice Buffer Layers for High-Quality Photodiodes Grown on Commercial GaAs and Si Substrates

    Science.gov (United States)

    Gutiérrez, M.; Lloret, F.; Jurczak, P.; Wu, J.; Liu, H. Y.; Araújo, D.

    2018-05-01

    The objective of this work is the integration of InGaAs/GaSb/GaAs heterostructures, with high indium content, on GaAs and Si commercial wafers. The design of an interfacial misfit dislocation array, either on GaAs or Si substrates, allowed growth of strain-free devices. The growth of purposely designed superlattices with their active region free of extended defects on both GaAs and Si substrates is demonstrated. Transmission electron microscopy technique is used for the structural characterization and plastic relaxation study. In the first case, on GaAs substrates, the presence of dopants was demonstrated to reduce several times the threading dislocation density through a strain-hardening mechanism avoiding dislocation interactions, while in the second case, on Si substrates, similar reduction of dislocation interactions is obtained using an AlSb/GaSb superlattice. The latter is shown to redistribute spatially the interfacial misfit dislocation array to reduce dislocation interactions.

  20. N-polar GaN/AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistor formed on sapphire substrate with minimal step bunching

    Science.gov (United States)

    Prasertsuk, Kiattiwut; Tanikawa, Tomoyuki; Kimura, Takeshi; Kuboya, Shigeyuki; Suemitsu, Tetsuya; Matsuoka, Takashi

    2018-01-01

    The metal-insulator-semiconductor (MIS) gate N-polar GaN/AlGaN/GaN high-electron-mobility transistor (HEMT) on a (0001) sapphire substrate, which can be expected to operate with lower on-resistance and more easily work on the pinch-off operation than an N-polar AlGaN/GaN HEMT, was fabricated. For suppressing the step bunching and hillocks peculiar in the N-polar growth, a sapphire substrate with an off-cut angle as small as 0.8° was introduced and an N-polar GaN/AlGaN/GaN HEMT without the step bunching was firstly obtained by optimizing the growth conditions. The previously reported anisotropy of transconductance related to the step was eliminated. The pinch-off operation was also realized. These results indicate that this device is promising.

  1. Two-dimensional electron gas in AlGaN/GaN heterostructures

    International Nuclear Information System (INIS)

    Li, J.Z.; Lin, J.Y.; Jiang, H.X.; Khan, M.A.; Chen, Q.

    1997-01-01

    The formation of a two-dimensional electron gas (2DEG) system by an AlGaN/GaN heterostructure has been further confirmed by measuring its electrical properties. The effect of persistent photoconductivity (PPC) has been observed and its unique features have been utilized to study the properties of 2DEG formed by the AlGaN/GaN heterointerface. Sharp electronic transitions from the first to the second subbands in the 2DEG channel have been observed by monitoring the 2DEG carrier mobility as a function of carrier concentration through the use of PPC. These results are expected to have significant implications on field-effect transistor and high electron mobility transistor applications based on the GaN system. copyright 1997 American Vacuum Society

  2. Near-field microscopy of waveguide architectures of InGaN/GaN diode lasers

    Science.gov (United States)

    Friede, Sebastian; Tomm, Jens W.; Kühn, Sergei; Hoffmann, Veit; Wenzel, Hans; Weyers, Markus

    2016-11-01

    Waveguide (WG) architectures of 420 nm emitting InGaN/GaN diode lasers are analyzed by photoluminescence and photocurrent spectroscopy using a nearfield scanning optical microscope that scans along their front facets. The components of the ‘optical active cavity’, quantum wells, WGs, and cladding layers are individually inspected with a spatial resolution of ∼100 nm. Separate analysis of the p- and n-sections of the WG was achieved, and reveals defect levels in the p-part. Moreover, it is demonstrated that the homogeneity of the n-WG section directly affects the quantum wells that are grown on top of this layer. Substantially increased carrier capture efficiencies into InGaN/GaN-WGs compared to GaN-WGs are demonstrated.

  3. A hole accelerator for InGaN/GaN light-emitting diodes

    Science.gov (United States)

    Zhang, Zi-Hui; Liu, Wei; Tan, Swee Tiam; Ji, Yun; Wang, Liancheng; Zhu, Binbin; Zhang, Yiping; Lu, Shunpeng; Zhang, Xueliang; Hasanov, Namig; Sun, Xiao Wei; Demir, Hilmi Volkan

    2014-10-01

    The quantum efficiency of InGaN/GaN light-emitting diodes (LEDs) has been significantly limited by the insufficient hole injection, and this is caused by the inefficient p-type doping and the low hole mobility. The low hole mobility makes the holes less energetic, which hinders the hole injection into the multiple quantum wells (MQWs) especially when a p-type AlGaN electron blocking layer (EBL) is adopted. In this work, we report a hole accelerator to accelerate the holes so that the holes can obtain adequate kinetic energy, travel across the p-type EBL, and then enter the MQWs more efficiently and smoothly. In addition to the numerical study, the effectiveness of the hole accelerator is experimentally shown through achieving improved optical output power and reduced efficiency droop for the proposed InGaN/GaN LED.

  4. Gallium surface diffusion on GaAs (001) surfaces measured by crystallization dynamics of Ga droplets

    International Nuclear Information System (INIS)

    Bietti, Sergio; Somaschini, Claudio; Esposito, Luca; Sanguinetti, Stefano; Fedorov, Alexey

    2014-01-01

    We present accurate measurements of Ga cation surface diffusion on GaAs surfaces. The measurement method relies on atomic force microscopy measurement of the morphology of nano–disks that evolve, under group V supply, from nanoscale group III droplets, earlier deposited on the substrate surface. The dependence of the radius of such nano-droplets on crystallization conditions gives direct access to Ga diffusion length. We found an activation energy for Ga on GaAs(001) diffusion E A =1.31±0.15 eV, a diffusivity prefactor of D 0  = 0.53(×2.1±1) cm 2 s −1 that we compare with the values present in literature. The obtained results permit to better understand the fundamental physics governing the motion of group III ad–atoms on III–V crystal surfaces and the fabrication of designable nanostructures.

  5. Optimization of the GaAs et GaAs/Si annealing using halogen lamp flashes

    International Nuclear Information System (INIS)

    Blanck, H.

    1989-01-01

    The aim of the work is to check whether the flash annealing of GaAs and GaAs/Si, using halogen lamps, allows an improvement in the results obtained by usual methods. The electrical activation, defects behavior and results uniformity are studied. The results on the activation and diffusion of implanted impurities are shown to be equivalent to those obtained with classical annealing methods. However, residual impurities (or defects) diffusion phenomena are restrained by the flash annealing technique. The Hall effect cartographic measurements showed an improvement of the uniformity of the implanted coating surface resistance. Flash annealing is a suitable method for the Si activation in GaAs. It allows an improvement of the GaAs results obtained with standard techniques, as well as the formation, by means of ion implantation, of active zones in the GaAs/Si layers [fr

  6. Strain-dependent magnetic anisotropy in GaMnAs on InGaAs templates

    Energy Technology Data Exchange (ETDEWEB)

    Daeubler, Joachim; Glunk, Michael; Schwaiger, Stephan; Dreher, Lukas; Schoch, Wladimir; Sauer, Rolf; Limmer, Wolfgang [Institut fuer Halbleiterphysik, Universitaet Ulm, 89069 Ulm (Germany)

    2008-07-01

    We have systematically studied the influence of strain on the magnetic anisotropy of GaMnAs by means of HRXRD reciprocal space mapping and angle-dependent magnetotransport. For this purpose, a series of GaMnAs layers with Mn contents of {proportional_to}5% was grown by low-temperature MBE on relaxed InGaAs/GaAs templates with different In concentrations, enabling us to vary the strain in the GaMnAs layers continuously from tensile to compressive, including the unstrained state. Considering both, as-grown and annealed samples, the anisotropy parameter describing the uniaxial out-of-plane magnetic anisotropy has been found to vary linearly with hole density and strain. As a consequence, the out-of-plane direction gradually undergoes a transition from a magnetic hard axis to a magnetic easy axis from compressive to tensile strain.

  7. GaMnAs on patterned GaAs(001) substrates: Growth and magnetotransport

    Energy Technology Data Exchange (ETDEWEB)

    Daeubler, Joachim; Glunk, Michael; Hummel, Thomas; Schoch, Wladimir; Limmer, Wolfgang; Sauer, Rolf [Institut fuer Halbleiterphysik, Universitaet Ulm, 89069 Ulm (Germany)

    2007-07-01

    A new type of GaMnAs microstructures with laterally confined electronic and magnetic properties has been realized in a bottom-up procedure by growing GaMnAs films on [1 anti 10]-oriented ridge structures with (113)A sidewalls and (001) top layers prepared on GaAs(001) substrates. Previous studies on planar GaMnAs samples have revealed different incorporation of Mn and excess As in (001) and (113)A layers. Accordingly, temperature- and field-dependent magnetotransport measurements on the overgrown ridge structures clearly demonstrate the coexistence of electronic and magnetic properties specific for (001) and (113)A GaMnAs in one single sample. This introduces an additional degree of freedom in the development of new functional structures.

  8. Angular dependent XPS study of surface band bending on Ga-polar n-GaN

    Science.gov (United States)

    Huang, Rong; Liu, Tong; Zhao, Yanfei; Zhu, Yafeng; Huang, Zengli; Li, Fangsen; Liu, Jianping; Zhang, Liqun; Zhang, Shuming; Dingsun, An; Yang, Hui

    2018-05-01

    Surface band bending and composition of Ga-polar n-GaN with different surface treatments were characterized by using angular dependent X-ray photoelectron spectroscopy. Upward surface band bending of varying degree was observed distinctly upon to the treatment methods. Besides the nitrogen vacancies, we found that surface states of oxygen-containing absorbates (O-H component) also contribute to the surface band bending, which lead the Fermi level pined at a level further closer to the conduction band edge on n-GaN surface. The n-GaN surface with lower surface band bending exhibits better linear electrical properties for Ti/GaN Ohmic contacts. Moreover, the density of positively charged surface states could be derived from the values of surface band bending.

  9. Noise performance in AlGaN/GaN HEMTs under high drain bias

    International Nuclear Information System (INIS)

    Pang Lei; Pu Yan; Lin Xinyu; Wang Liang; Liu Jian

    2009-01-01

    The advent of fully integrated GaN PA-LNA circuits makes it meaningful to investigate the noise performance under high drain bias. However, noise performance of AlGaN/GaN HEMTs under high bias has not received worldwide attention in theoretical studies due to its complicated mechanisms. The noise value is moderately higher and its rate of increase is fast with increasing high voltage. In this paper, several possible mechanisms are proposed to be responsible for it. Impact ionization under high electric field incurs great fluctuation of carrier density, which increases the drain diffusion noise. Besides, higher gate leakage current related shot noise and a more severe self-heating effect are also contributors to the noise increase at high bias. Analysis from macroscopic and microscopic perspectives can help us to design new device structures to improve noise performance of AlGaN/GaN HEMTs under high bias. (semiconductor devices)

  10. Nanoscale investigation of AlGaN/GaN-on-Si high electron mobility transistors.

    Science.gov (United States)

    Fontserè, A; Pérez-Tomás, A; Placidi, M; Llobet, J; Baron, N; Chenot, S; Cordier, Y; Moreno, J C; Jennings, M R; Gammon, P M; Fisher, C A; Iglesias, V; Porti, M; Bayerl, A; Lanza, M; Nafría, M

    2012-10-05

    AlGaN/GaN HEMTs are devices which are strongly influenced by surface properties such as donor states, roughness or any kind of inhomogeneity. The electron gas is only a few nanometers away from the surface and the transistor forward and reverse currents are considerably affected by any variation of surface property within the atomic scale. Consequently, we have used the technique known as conductive AFM (CAFM) to perform electrical characterization at the nanoscale. The AlGaN/GaN HEMT ohmic (drain and source) and Schottky (gate) contacts were investigated by the CAFM technique. The estimated area of these highly conductive pillars (each of them of approximately 20-50 nm radius) represents around 5% of the total contact area. Analogously, the reverse leakage of the gate Schottky contact at the nanoscale seems to correlate somehow with the topography of the narrow AlGaN barrier regions producing larger currents.

  11. Does GaH5 exist?

    Science.gov (United States)

    Speakman, Lucas D.; Turney, Justin M.; Schaefer, Henry F.

    2005-11-01

    The existence or nonexistence of GaH5 has been widely discussed [N. M. Mitzel, Angew. Chem. Int. Ed. 42, 3856 (2003)]. Seven possible structures for gallium pentahydride have been systematically investigated using ab initio electronic structure theory. Structures and vibrational frequencies have been determined employing self-consistent field, coupled cluster including all single and double excitations (CCSD), and CCSD with perturbative triples levels of theory, with at least three correlation-consistent polarized-valence-(cc-pVXZ and aug-cc-pVXZ) type basis sets. The X˜A'1 state for GaH5 is predicted to be weakly bound complex 1 between gallane and molecular hydrogen, with Cs symmetry. The dissociation energy corresponding to GaH5→GaH3+H2 is predicted to be De=2.05kcalmol-1. The H-H stretching fundamental is predicted to be v =4060cm-1, compared to the tentatively assigned experimental feature of Wang and Andrews [J. Phys. Chem. A 107, 11371 (2003)] at 4087cm-1. A second Cs structure 2 with nearly equal energy is predicted to be a transition state, corresponding to a 90° rotation of the H2 bond. Thus the rotation of the hydrogen molecule is essentially free. However, hydrogen scrambling through the C2v structure 3 seems unlikely, as the activation barrier for scrambling is at least 30kcalmol-1 higher in energy than that for the dissociation of GaH5 to GaH3 and H2. Two additional structures consisting of GaH3 with a dihydrogen bond perpendicular to gallane (C3v structure 4) and an in-plane dihydrogen bond [Cs(III) structure 5] were also examined. A C3v symmetry second-order saddle point has nearly the same energy as the GaH3+H2 dissociation limit, while the Cs(III) structure 5 is a transition structure to the C3v structure. The C4v structure 6 and the D3h structure 7 are much higher in energy than GaH3+H2 by 88 and 103kcalmol-1, respectively.

  12. Indications for scintigraphy with 67Ga

    International Nuclear Information System (INIS)

    Plechl, S.C.; Berges, G.; Blut, J.; Bohle, H.; Gessat, C.; Hethey, B.; Linneborn, G.; Ostermann, W.; Prack, G.; Scheitza, B.

    1976-01-01

    The validity and exactness of 67 Ga scintigraphy was tested in more than 70 patients by a comparison with clinical, radiological and histological findings as well as with scintigraphs obtained with other nuclides. It was found that 67 Ga scintigraphy is a good and often even a vital supplementation to the other methods. Its main field of application, according to the authors' obervations, is the differential diagnosis of three-dimensional changes in the thorax region, in particular the diagnosis of malignant tumours of the lungs in combination with X-ray examinations. Furthermore, 67 Ga may be of use in localization diagnoses of non-malignant changes, e.g. abscesses. 67 Ga scintigraphy, which is non-hazardous and does not involve discomfort to the patients, appears to be particularly useful for course control after surgical treatment of breast cancer and for early diagnoses of metastases, provided that examination starts early enough and is repeated at regular intervals, not only in the soft parts but also in the skeleton. The question whether 67 Ga scintigraphy may be a substitute for scintigraphy with other nuclides in these fields still remains to be solved. (orig.) [de

  13. Scanning tunneling microscopy and spectroscopy on GaN and InGaN surfaces; Rastertunnelmikroskopie und -spektroskopie an GaN- und InGaN-Oberflaechen

    Energy Technology Data Exchange (ETDEWEB)

    Krueger, David

    2009-12-02

    Optelectronic devices based on gallium nitride (GaN) and indium gallium nitride (InGaN) are in the focus of research since more than 20 years and still have great potential for optical applications. In the first part of this work non-polar surfaces of GaN are investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning tunneling microscopy (STM). In SEM and AFM, the (1 anti 100)- and especially the (anti 2110)-plane are quite corrugated. For the first time, the (anti 2110)-plane of GaN is atomically resolved in STM. In the second part InGaN quantum dot layers are investigated by X-ray photoelectron spectroscopy (XPS), scanning tunneling spectroscopy (STS) and STM. The STMmeasurements show the dependency of surface morphology on growth conditions in the metalorganic vapour phase epitaxy (MOVPE). Nucleation, a new MOVPE-strategy, is based on phase separations on surfaces. It is shown that locally varying density of states and bandgaps can be detected by STS, that means bandgap histograms and 2D-bandgap-mapping. (orig.)

  14. Implantation doping of GaN

    International Nuclear Information System (INIS)

    Zolper, J.C.

    1996-01-01

    Ion implantation has played an enabling role in the realization of many high performance photonic and electronic devices in mature semiconductor materials systems such as Si and GaAs. This can also be expected to be the case in III-Nitride based devices as the material quality continues to improve. This paper reviews the progress in ion implantation processing of the III-Nitride materials, namely, GaN, AlN, InN and their alloys. Details are presented of the successful demonstrations of implant isolation as well as n- and p-type implantation doping of GaN. Implant doping has required activation annealing at temperatures in excess of 1,000 C. The nature of the implantation induced damage and its response to annealing is addressed using Rutherford Backscattering. Finally, results are given for the first demonstration of a GaN device fabricated using ion implantation doping, a GaN junction field effect transistor (JFET)

  15. The Effect of the number of InGaN/GaN pairs on the photoelectrochemical properties of InGaN/GaN multi quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Bae, Hyojung; Park, Jun-Beom [Optoelectronics Convergence Research Center, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186 (Korea, Republic of); Fujii, Katsushi [Institute of Environmental Science and Technology, The University of Kitakyushu, Kitakyushu, Fukuoka (Japan); Lee, Hyo-Jong [Materials Science and Engineering, Dong-A University, Busan 49315 (Korea, Republic of); Lee, Sang-Hyun [Institute of Advanced Composite Materials, Korea Institute of Science and Technology, Joellabuk-do 55324 (Korea, Republic of); Ryu, Sang-Wan; Lee, June Key [Optoelectronics Convergence Research Center, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186 (Korea, Republic of); Ha, Jun-Seok, E-mail: jsha@jnu.ac.kr [Optoelectronics Convergence Research Center, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju 61186 (Korea, Republic of)

    2017-04-15

    Highlights: • The 1–5 period InGaN/GaN quantum well (QW) structures were grown on sapphire. • The photoelectrochemical properties of these structures were investigated. • The saturated photocurrent density increased with increasing number of QW pairs. • But, it was different in the stability of the photoanode. • We reported the reason for this difference. - Abstract: In this study, the effects of the number of quantum well (QW) pairs on the photoelectrochemical (PEC) properties of InGaN/GaN multi-QW structures (MQWs) were investigated. MQW samples were grown using metal-organic chemical vapor deposition, and their structural characteristics were confirmed by X-ray diffraction measurements. The photoluminescence measurements revealed that the optical properties of MQWs may be related to the PEC properties. The cyclic voltammetry data revealed that the saturated photocurrent density increased with increasing number of QW pairs; the photocurrent density of MQW5 was twice that of an nGaN reference. However, in the chronoamperometry measurement of the photoanode stability, MQWs with 3 QWs displayed the highest photocurrent stability, although the saturated photocurrent density was highest for MQW5. This was also confirmed by field-emission scanning electron microscopy of the surface morphology after PEC measurements. The stability and photocurrent density may be attributed to the quality of crystallinity of the MQWs.

  16. Ga-67 imaging in pediatric oncology

    International Nuclear Information System (INIS)

    Edeling, C.J.

    1983-01-01

    One hundred sixty-nine children suspected of having malignant disease were examined by Ga-67 scintigraphy. In 99 children with untreated diseases at the time of examination, abnormal accumulation of Ga-67 was found in 51 patients, including 40 with malignant tumor. Forty-three negative results were obtained in children with benign disorders. Five false-negative results were obtained in patients with neuroblastoma of the adrenal gland. In 70 children with malignant diseases treated before the examination, abnormal accumulation of Ga-67 was seen in 40 patients, including 38 with malignant disease and two with no clinical evidence of recurrence. Normal results were obtained in 30 patients, including 11 still suffering from malignant disease. The results of Ga-67 scintigraphy in all of the children were evaluated qualitatively. For the final diagnosis of malignant disease, diagnostic specificity was 86% and diagnostic sensitivity 79%. The prevalence of malignant disease was 56%. It is concluded that Ga-67 scintigraphy should be used for primary visualization and control of malignant tumors in children

  17. Indications for scintigraphy with /sup 67/Ga

    Energy Technology Data Exchange (ETDEWEB)

    Plechl, S C; Berges, G; Blut, J; Bohle, H; Gessat, C; Hethey, B; Linneborn, G; Ostermann, W; Prack, G; Scheitza, B [Berufsgenossenschaftliche Krankenanstalten Bergmannsheil, Bochum (Germany, F.R.)

    1976-06-01

    The validity and exactness of /sup 67/Ga scintigraphy was tested in more than 70 patients by a comparison with clinical, radiological and histological findings as well as with scintigraphs obtained with other nuclides. It was found that /sup 67/Ga scintigraphy is a good and often even a vital supplementation to the other methods. Its main field of application, according to the authors' obervations, is the differential diagnosis of three-dimensional changes in the thorax region, in particular the diagnosis of malignant tumours of the lungs in combination with X-ray examinations. Furthermore, /sup 67/Ga may be of use in localization diagnoses of non-malignant changes, e.g. abscesses. /sup 67/Ga scintigraphy, which is non-hazardous and does not involve discomfort to the patients, appears to be particularly useful for course control after surgical treatment of breast cancer and for early diagnoses of metastases, provided that examination starts early enough and is repeated at regular intervals, not only in the soft parts but also in the skeleton. The question whether /sup 67/Ga scintigraphy may be a substitute for scintigraphy with other nuclides in these fields still remains to be solved.

  18. Two-dimensional electron and hole gases in GaN/AlGaN heterostructures; Zweidimensionale Elektronen- und Loechergase in GaN/AlGaN-Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Link, A.

    2004-12-01

    The aim of this PhD thesis is to investigate the electronic properties of electron and hole gases in GaN/AlGaN heterostructures. Particularly, a deeper and broadened understanding of scattering mechanisms and transport properties is in the focus of this work. The main experimental techniques used for this purpose are the study of Shubnikov-de Haas (SdH) effect and Hall measurements at low temperatures. By means of these magnetotransport measurements, a series of GaN/AlGaN heterostructures with different Al content of the AlGaN barrier were investigated. Since the sheet carrier density of the 2DEG in these semiconductor structures is strongly dependent on the Al content (n{sub s}=2 x 10{sup 12}-10{sup 13} cm{sup -2}), the variation of transport parameters was determined as a function of sheet carrier concentration. First, from the temperature dependence of the SdH oscillations the effective transport mass was calculated. A Hall bar structure with an additional gate contact was used as an alternative to tune the carrier density of a 2DEG system independent of varying structural parametes such as Al content. Thus, the scattering mechanisms were investigated in the carrier density region between 3 x 10{sup 12} and 9.5 x 10{sup 12} cm{sup -2}. The transport properties of subband electrons were studied for a 2DEG system with two occupied subbands. (orig.)

  19. Near-surface depletion of antimony during the growth of GaAsSb and GaAs/GaAsSb nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Kauko, H.; Helvoort, A. T. J. van, E-mail: a.helvoort@ntnu.no [Department of Physics, Norwegian University of Science and Technology (NTNU), Trondheim (Norway); Fimland, B. O.; Munshi, A. M. [Department of Electronics and Telecommunications, NTNU, Trondheim (Norway); Grieb, T.; Müller, K.; Rosenauer, A. [Institut für Festkörperphysik, Universität Bremen, Bremen (Germany)

    2014-10-14

    The near-surface reduction of the Sb mole fraction during the growth of GaAsSb nanowires (NWs) and GaAs NWs with GaAsSb inserts has been studied using quantitative high-angle annular dark field scanning transmission electron microscopy (STEM). A model for diffusion of Sb in the hexagonal NWs was developed and employed in combination with the quantitative STEM analysis. GaAsSb NWs grown by Ga-assisted molecular beam epitaxy (MBE) and GaAs/GaAsSb NWs grown by Ga- and Au-assisted MBE were investigated. At the high temperatures employed in the NW growth, As-Sb exchange at and outward diffusion of Sb towards the surface take place, resulting in reduction of the Sb concentration at and near the surface in the GaAsSb NWs and the GaAsSb inserts. In GaAsSb NWs, an increasing near-surface depletion of Sb was observed towards the bottom of the NW due to longer exposure to the As beam flux. In GaAsSb inserts, an increasing change in the Sb concentration profile was observed with increasing post-insert axial GaAs growth time, resulting from a combined effect of radial GaAs overgrowth and diffusion of Sb. The effect of growth temperature on the diffusion of Sb in the GaAsSb inserts was identified. The consequences of these findings for growth optimization and the optoelectronic properties of GaAsSb are discussed.

  20. Two-dimensional simulation of GaAsSb/GaAs quantum dot solar cells

    Science.gov (United States)

    Kunrugsa, Maetee

    2018-06-01

    Two-dimensional (2D) simulation of GaAsSb/GaAs quantum dot (QD) solar cells is presented. The effects of As mole fraction in GaAsSb QDs on the performance of the solar cell are investigated. The solar cell is designed as a p-i-n GaAs structure where a single layer of GaAsSb QDs is introduced into the intrinsic region. The current density–voltage characteristics of QD solar cells are derived from Poisson’s equation, continuity equations, and the drift-diffusion transport equations, which are numerically solved by a finite element method. Furthermore, the transition energy of a single GaAsSb QD and its corresponding wavelength for each As mole fraction are calculated by a six-band k · p model to validate the position of the absorption edge in the external quantum efficiency curve. A GaAsSb/GaAs QD solar cell with an As mole fraction of 0.4 provides the best power conversion efficiency. The overlap between electron and hole wave functions becomes larger as the As mole fraction increases, leading to a higher optical absorption probability which is confirmed by the enhanced photogeneration rates within and around the QDs. However, further increasing the As mole fraction results in a reduction in the efficiency because the absorption edge moves towards shorter wavelengths, lowering the short-circuit current density. The influences of the QD size and density on the efficiency are also examined. For the GaAsSb/GaAs QD solar cell with an As mole fraction of 0.4, the efficiency can be improved to 26.2% by utilizing the optimum QD size and density. A decrease in the efficiency is observed at high QD densities, which is attributed to the increased carrier recombination and strain-modified band structures affecting the absorption edges.

  1. Adsorption of tetrabutylammonium cations on negatively charged surfaces of the Hg, Ga, In-Ga, Tl-Ga electrodes

    International Nuclear Information System (INIS)

    Damaskin, B.B.; Baturina, O.A.; Vykhodtseva, L.N.; Emets, V.V.; Kazarinov, V.E.

    1999-01-01

    The differential capacitance curves in the 0.05M Na 2 SO 4 + [(C 4 H 9 ) 4 N]BF 4 aqueous solutions on the electrodes of mercury gallium and also of the In-Ga and Tl-Ga alloys are obtained. The adsorption parameters of the tetrabutylammonium cations on each of the electrodes within the frames of two parallel condensers model, supplemented by the Frumkin isotherm are calculated. The conclusion is made that different adsorption behaviour of the (C 4 H 9 ) 4 N + cations on the gallium subgroup metals by the electrodes high negative charges is related to nonuniform electrochemical work of the output electrons [ru

  2. Lateral epitaxial overgrowth of GaN on a patterned GaN-on-silicon substrate by molecular beam epitaxy

    International Nuclear Information System (INIS)

    Wang, Yongjin; Hu, Fangren; Hane, Kazuhiro

    2011-01-01

    We report here the lateral epitaxial overgrowth (LEO) of GaN on a patterned GaN-on-silicon substrate by molecular beam epitaxy (MBE) growth with radio frequency nitrogen plasma as a gas source. Two kinds of GaN nanostructures are defined by electron beam lithography and realized on a GaN substrate by fast atom beam etching. The epitaxial growth of GaN by MBE is performed on the prepared GaN template, and the selective growth of GaN takes place with the assistance of GaN nanostructures. The LEO of GaN produces novel GaN epitaxial structures which are dependent on the shape and the size of the processed GaN nanostructures. Periodic GaN hexagonal pyramids are generated inside the air holes, and GaN epitaxial strips with triangular section are formed in the grating region. This work provides a promising way for producing novel GaN-based devices by the LEO of GaN using the MBE technique

  3. On the axiomatization of some classes of discrete universal integrals

    Czech Academy of Sciences Publication Activity Database

    Klement, E.P.; Mesiar, Radko

    2012-01-01

    Roč. 28, č. 1 (2012), s. 13-18 ISSN 0950-7051 R&D Projects: GA ČR GAP402/11/0378 Institutional research plan: CEZ:AV0Z10750506 Keywords : Comonotone modularity * Copula * Universal integral Subject RIV: BA - General Mathematics Impact factor: 4.104, year: 2012 http://library.utia.cas.cz/separaty/2012/E/mesiar-on the axiomatization of some classes of discrete universal integrals. pdf

  4. Visualization of elongation measurements using an SER universal testing platform

    Czech Academy of Sciences Publication Activity Database

    Pivokonský, Radek; Filip, Petr; Zelenková, Jana

    2015-01-01

    Roč. 25, č. 1 (2015), s. 1-8 ISSN 1430-6395 R&D Projects: GA ČR(CZ) GAP105/11/2342 Institutional support: RVO:67985874 Keywords : elongational viscosity * Universal Testing Platform (SER) * polymer melts * LDPE Subject RIV: BK - Fluid Dynamics Impact factor: 1.241, year: 2015

  5. Fraisse sequences: category-theoretic approach to universal homogeneous structures

    Czech Academy of Sciences Publication Activity Database

    Kubiś, Wieslaw

    2014-01-01

    Roč. 165, č. 11 (2014), s. 1755-1811 ISSN 0168-0072 R&D Projects: GA ČR(CZ) GAP201/12/0290 Institutional support: RVO:67985840 Keywords : universal homogeneous object * Fraissé sequence * amalgamation Subject RIV: BA - General Mathematics Impact factor: 0.548, year: 2014 http://www.sciencedirect.com/science/article/pii/S0168007214000773

  6. Pierce - University of Georgia | Division of Cancer Prevention

    Science.gov (United States)

    Principal Investigator: J. Michael Pierce, PhDInstitution: University of Georgia, Athens, GA Our project, Discovery and Development of Cancer Glycomarkers, is a joint collaboration between our laboratories at the CCRC, which include Karen Abbott, Lance Wells, Kevin Dobbin, and Mike Tiemeyer, those at TGen, in Phoenix, AZ, Daniel Von Hoff, Haiyong Han, and Mike Demeure, and

  7. Bullying as intra-active process in neoliberal universities

    Czech Academy of Sciences Publication Activity Database

    Zábrodská, Kateřina; Sheridan, L.; Cath, L.; Bronwyn, D.

    2011-01-01

    Roč. 17, č. 8 (2011), s. 709-719 ISSN 1077-8004 R&D Projects: GA ČR GPP407/10/P146 Institutional research plan: CEZ:AV0Z70250504 Keywords : intra-action * neoliberal university * workplace bullying Subject RIV: AN - Psychology Impact factor: 0.839, year: 2011

  8. 71Ga Chemical Shielding and Quadrupole Coupling Tensors of the Garnet Y(3)Ga(5)O(12) from Single-Crystal (71)Ga NMR

    DEFF Research Database (Denmark)

    Vosegaard, Thomas; Massiot, Dominique; Gautier, Nathalie

    1997-01-01

    A single-crystal (71)Ga NMR study of the garnet Y(3)Ga(5)O(12) (YGG) has resulted in the determination of the first chemical shielding tensors reported for the (71)Ga quadrupole. The single-crystal spectra are analyzed in terms of the combined effect of quadrupole coupling and chemical shielding ...

  9. Ga originated kink-and-tail Zn diffusion profiles in InGaAsP and InGaAlAs alloys during MOVPE regrowth

    Science.gov (United States)

    Kitatani, T.; Okamoto, K.; Uchida, K.; Tanaka, S.

    2017-12-01

    We investigated the diffusion characteristics of Zn in ternary and quaternary alloys of InGaAsP and InGaAlAs, which are important materials in long-wavelength optical communication devices. The measured Zn diffusion profiles of InGaAs, InGaAsP, and InGaAlAs showed kink-and-tail shapes in which Zn concentration fell abruptly at first and then decreased slowly, whereas those of InP and InAlAs showed only abrupt decreases. Thus, only Ga-containing alloys had tail-like profiles. Since this tail was well described by the group-V vacancy related defect model, we deduced that its mechanism is closely related with group-V vacancies in Ga-related bonds such as GaP or GaAs. Furthermore, we demonstrated the possibility that many more group-V vacancies originated from GaP bonds than from GaAs bonds, indicating the difficulty in crystal growth of high quality alloys that have GaP components.

  10. Physical and electrical characterizations of AlGaN/GaN MOS gate stacks with AlGaN surface oxidation treatment

    Science.gov (United States)

    Yamada, Takahiro; Watanabe, Kenta; Nozaki, Mikito; Shih, Hong-An; Nakazawa, Satoshi; Anda, Yoshiharu; Ueda, Tetsuzo; Yoshigoe, Akitaka; Hosoi, Takuji; Shimura, Takayoshi; Watanabe, Heiji

    2018-06-01

    The impacts of inserting ultrathin oxides into insulator/AlGaN interfaces on their electrical properties were investigated to develop advanced AlGaN/GaN metal–oxide–semiconductor (MOS) gate stacks. For this purpose, the initial thermal oxidation of AlGaN surfaces in oxygen ambient was systematically studied by synchrotron radiation X-ray photoelectron spectroscopy (SR-XPS) and atomic force microscopy (AFM). Our physical characterizations revealed that, when compared with GaN surfaces, aluminum addition promotes the initial oxidation of AlGaN surfaces at temperatures of around 400 °C, followed by smaller grain growth above 850 °C. Electrical measurements of AlGaN/GaN MOS capacitors also showed that, although excessive oxidation treatment of AlGaN surfaces over around 700 °C has an adverse effect, interface passivation with the initial oxidation of the AlGaN surfaces at temperatures ranging from 400 to 500 °C was proven to be beneficial for fabricating high-quality AlGaN/GaN MOS gate stacks.

  11. Geneva University

    CERN Multimedia

    2009-01-01

    École de physique - Département de physique nucléaire et corpusculaire 24, quai Ernest-Ansermet 1211 GENÈVE 4 Tél: (022) 379 62 73 - Fax: (022) 379 69 92 Wednesday 25 March 2009 PARTICLE PHYSICS SEMINAR at 17:00 – Stückelberg Auditorium Hunting for the Higgs with D0 at the Tevatron Prof. Gustaaf Brooijmans / Columbia University The search for the Higgs boson is one of the most important endeavors in current experimental particle physics. At the eve of the LHC start, the Tevatron is delivering record luminosity allowing both CDF and D0 to explore a new region of possible Higgs masses. In this seminar, the techniques used to search for the Higgs boson at the Tevatron will be explained, limiting factors will be examined, and the sensitivity in the various channels will be reviewed. The newly excluded values of the standard model Higgs mass will be presented. Information : http://dpnc.unige.ch/seminaire/annonce.html Organizer : J.-S. Graulich

  12. Geneva University

    CERN Multimedia

    2009-01-01

    École de physique - Département de physique nucléaire et corpusculaire 24, quai Ernest-Ansermet 1211 GENÈVE 4 Tél: (022) 379 62 73 - Fax: (022) 379 69 92 Lundi 6 avril 2009 PARTICLE PHYSICS SEMINAR àt 17:00 – Auditoire Stückelberg Hospital superbugs, nanomechanics and statistical physics Prof. Dr G. Aeppli / University College London The alarming growth of the antibiotic-resistant superbug, methicillin-resistant Staphylococcus aureus (MRSA) is driving the development of new technologies to investigate antibiotics and their modes of action. We report silicon cantilever based studies of self-assembled monolayers of mucopeptides which model drug-sensitive and resistant bacterial walls. The underlying concepts needed to understand the measurements will simplify the design of cantilevers and coatings for biosensing and could even impact our understanding of drug action on bacteria themselves. (Une verrée en compagnie du conférencier sera offerte après le colloque.) Organizer : Prof. Markus Büttiker ...

  13. Geneva University

    CERN Multimedia

    2008-01-01

    Ecole de physique - Département de physique nucléaire et corpusculaire 24, Quai Ernest-Ansermet 1211 GENEVE 4 Tél: (022) 379 62 73 Fax: (022) 379 69 92 Wednesday 29 October 2008 PARTICLE PHYSICS SEMINAR at 17.00 – Stückelberg Auditorium Precision measurements of low-energy neutrino-nucleus interactions with the SciBooNE experiment at Fermilab by Dr Michel Sorel, IFIC (CSIC and University of Valencia) «Do all modern accelerator-based neutrino experiments need to make use of kiloton-scale detectors and decade-long exposure times? In order to study the full pattern of neutrino mixing via neutrino oscillation experiments, the answer is probably yes, together with powerful proton sources. Still, to push the sensitivity of future neutrino oscillation searches into unchartered territory, those are necessary, but not sufficient, ingredients. In addition, accurate knowledge of neutrino interactions and neutrino production is mandatory. This knowledge can be acquired via small-scale and short-term dedicated n...

  14. Geneva University

    CERN Multimedia

    2010-01-01

    Ecole de physique Département de physique nucléaire et corspusculaire 24, quai Ernest-Ansermet 1211 GENEVE 4 Tel: (022) 379 62 73 Fax: (022) 379 69 92 Wednesday 14 April 2010 PARTICLE PHYSICS SEMINAR at 17.00 hrs – Stückelberg Auditorium Dark Matter and the XENON Experiment By Dr. Marc Schumann, Physik Institut, Universität Zürich There is convincing astrophysical and cosmological evidence that most of the matter in the Universe is dark: It is invisible in every band of the electromagnetic spectrum. Weakly interacting massive particles (WIMPs) are promising Dark Matter candidates that arise naturally in many theories beyond the Standard Model. Several experiments aim to directly detect WIMPs by measuring nuclear recoils from WIMPs scattered on target nuclei. In this talk, I will give an overview on Dark Matter and direct Dark Matter detection. Then I will focus on the XENON100 experiment, a 2-phase liquid/gas time projection chamber (TPC) that ...

  15. Geneva University

    CERN Multimedia

    2009-01-01

    École de physique - Département de physique nucléaire et corspusculaire 24, quai Ernest-Ansermet 1211 Genève 4 Tél. 022 379 62 73 - Fax: (022) 379 69 92 Wednesday 14 October 2009 PARTICLE PHYSICS SEMINAR at 17:00 – Stückelberg Auditorium Long-lived particle searches at colliders Dr. Philippe Mermod / Oxford University The discovery of exotic long-lived particles would address a number of important questions in modern physics such as the origin and composition of dark matter and the unification of the fundamental forces. This talk will focus on searches for long-lived charged massive particles, where "charged" refers to the magnetic, electric or colour charge. Previous searches at the LEP and Tevatron Colliders allowed to put mass and cross section limits on various kinds of long-lived particles, such as Magnetic Monopoles and metastable leptons and up-type quarks. The new energy regime made available at the LHC will probe physics regions well beyond these limits. F...

  16. Universal algebra

    CERN Document Server

    Grätzer, George

    1979-01-01

    Universal Algebra, heralded as ". . . the standard reference in a field notorious for the lack of standardization . . .," has become the most authoritative, consistently relied on text in a field with applications in other branches of algebra and other fields such as combinatorics, geometry, and computer science. Each chapter is followed by an extensive list of exercises and problems. The "state of the art" account also includes new appendices (with contributions from B. Jónsson, R. Quackenbush, W. Taylor, and G. Wenzel) and a well-selected additional bibliography of over 1250 papers and books which makes this a fine work for students, instructors, and researchers in the field. "This book will certainly be, in the years to come, the basic reference to the subject." --- The American Mathematical Monthly (First Edition) "In this reviewer's opinion [the author] has more than succeeded in his aim. The problems at the end of each chapter are well-chosen; there are more than 650 of them. The book is especially sui...

  17. Geneva University

    CERN Multimedia

    2009-01-01

    École de physique - Département de physique nucléaire et corpusculaire 24, quai Ernest-Ansermet 1211 GENÈVE 4Tél: (022) 379 62 73 - Fax: (022) 379 69 92 Wednesday 29 April 2009 PARTICLE PHYSICS SEMINAR at 17:00 - Stückelberg Auditorium Search for spin-1 excited bosons at the LHC Mihail V. Chizhov (Physics Department, Sofia University, Bulgaria) I will discuss the resonance production of new type spin-1 excited bosons, Z*, at hadron colliders. They can be observed as a Breit-Wigner resonance peak in the invariant dilepton mass distribution in the same way as the well-known hypothetical gauge bosons, Z�. This makes them very interesting objects for early searches with the LHC first data. Moreover, they have unique signatures in transverse momentum and angular distributions, which allow to distinguish them from other resonances. Information : http://dpnc.unige.ch/seminaire/annonce.html Organizer: J.-S. Graulich

  18. Spin injection into GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Endres, Bernhard

    2013-11-01

    In this work spin injection into GaAs from Fe and (Ga,Mn)As was investigated. For the realization of any spintronic device the detailed knowledge about the spin lifetime, the spatial distribution of spin-polarized carriers and the influence of electric fields is essential. In the present work all these aspects have been analyzed by optical measurements of the polar magneto-optic Kerr effect (pMOKE) at the cleaved edge of the samples. Besides the attempt to observe spin pumping and thermal spin injection into n-GaAs the spin solar cell effect is demonstrated, a novel mechanism for the optical generation of spins in semiconductors with potential for future spintronic applications. Also important for spin-based devices as transistors is the presented realization of electrical spin injection into a two-dimensional electron gas.

  19. The gamma ray spectrometer GA.SP

    Energy Technology Data Exchange (ETDEWEB)

    Bazzacco, D [Instituto Nazionale di Fisica Nucleare, Sezione di Padova, Padova (Italy)

    1992-08-01

    GA.SP is a general purpose 4{pi} detector array for advanced {gamma}-spectroscopy and, in the same time, a suitable system for reaction mechanism studies. The detector is sited at the LNL Tandem+Linac accelerator and has been built as a joint project of INFN Padova, LNL, Milano and Firenze. The array consists of 40 Compton suppressed HPGe detectors and of a 4{pi} calorimeter composed of 80 BGO crystals. The detector houses a reaction chamber of 34 cm diameter where a charged particles multiplicity filter composed of 40 Si detectors is going to be installed. Evaporation residues produced in the centre of GA.SP can be injected into the recoil mass spectrometer (RMS, named CAMEL) in use at LNL, without the need to remove any of the gamma detectors. The coupled operation of GA.SP, RMS and Si ball will give a unique instrument for identification and study of weak reaction channels. (author). 6 figs.

  20. The gamma ray spectrometer GA.SP

    International Nuclear Information System (INIS)

    Bazzacco, D.

    1992-01-01

    GA.SP is a general purpose 4π detector array for advanced γ-spectroscopy and, in the same time, a suitable system for reaction mechanism studies. The detector is sited at the LNL Tandem+Linac accelerator and has been built as a joint project of INFN Padova, LNL, Milano and Firenze. The array consists of 40 Compton suppressed HPGe detectors and of a 4π calorimeter composed of 80 BGO crystals. The detector houses a reaction chamber of 34 cm diameter where a charged particles multiplicity filter composed of 40 Si detectors is going to be installed. Evaporation residues produced in the centre of GA.SP can be injected into the recoil mass spectrometer (RMS, named CAMEL) in use at LNL, without the need to remove any of the gamma detectors. The coupled operation of GA.SP, RMS and Si ball will give a unique instrument for identification and study of weak reaction channels. (author). 6 figs

  1. Ethanol surface chemistry on MBE-grown GaN(0001), GaOx/GaN(0001), and Ga2O3(2 \\xAF 01 )

    Science.gov (United States)

    Kollmannsberger, Sebastian L.; Walenta, Constantin A.; Winnerl, Andrea; Knoller, Fabian; Pereira, Rui N.; Tschurl, Martin; Stutzmann, Martin; Heiz, Ueli

    2017-09-01

    In this work, ethanol is used as a chemical probe to study the passivation of molecular beam epitaxy-grown GaN(0001) by surface oxidation. With a high degree of oxidation, no reaction from ethanol to acetaldehyde in temperature-programmed desorption experiments is observed. The acetaldehyde formation is attributed to a mechanism based on α -H abstraction from the dissociatively bound alcohol molecule. The reactivity is related to negatively charged surface states, which are removed upon oxidation of the GaN(0001) surface. This is compared with the Ga2O3(2 ¯ 01 ) single crystal surface, which is found to be inert for the acetaldehyde production. These results offer a toolbox to explore the surface chemistry of nitrides and oxynitrides on an atomic scale and relate their intrinsic activity to systems under ambient atmosphere.

  2. Ethanol surface chemistry on MBE-grown GaN(0001), GaOx/GaN(0001), and Ga2O3(2¯01).

    Science.gov (United States)

    Kollmannsberger, Sebastian L; Walenta, Constantin A; Winnerl, Andrea; Knoller, Fabian; Pereira, Rui N; Tschurl, Martin; Stutzmann, Martin; Heiz, Ueli

    2017-09-28

    In this work, ethanol is used as a chemical probe to study the passivation of molecular beam epitaxy-grown GaN(0001) by surface oxidation. With a high degree of oxidation, no reaction from ethanol to acetaldehyde in temperature-programmed desorption experiments is observed. The acetaldehyde formation is attributed to a mechanism based on α-H abstraction from the dissociatively bound alcohol molecule. The reactivity is related to negatively charged surface states, which are removed upon oxidation of the GaN(0001) surface. This is compared with the Ga 2 O 3 (2¯01) single crystal surface, which is found to be inert for the acetaldehyde production. These results offer a toolbox to explore the surface chemistry of nitrides and oxynitrides on an atomic scale and relate their intrinsic activity to systems under ambient atmosphere.

  3. Determination of Ga-67 disintegration rate

    International Nuclear Information System (INIS)

    Fonseca, Katia A.; Koskinas, Maria F.; Dias, Mauro S.

    1996-01-01

    One of the consequences of the production by IPEN of new radioisotopes used in nuclear medicine, as the case of Ga-67, is the need of new standard sources of the radionuclide obtained in a fast and simple way. The Laboratorio de Metrologia de Radionuclideos at IPEN has a well-type ionization chamber system, the most suitable for this purpose. In order to calibrate this system it was necessary to standardize Ga-67 solutions by an absolute system. The present work gives details on the Ga-67 disintegration rate determination by an 4 π β-γ coincidence system, gamma spectrometry using an HPGe detector and measurements using a 1383A - type ionization chamber, in order to check the consistency in the adopted methodology. (author)

  4. The c.IVS1+1G>A mutation inthe GJB2 gene is prevalent and large ...

    Indian Academy of Sciences (India)

    IVS1+1G>A mutation inthe GJB2 gene is prevalent and large deletions involving the GJB6 gene are not present in the Turkish population. ASLI SIRMACI, DUYGU AKCAYOZ-DUMAN and MUSTAFA TEKIN∗. Division of Pediatric Molecular Genetics, Ankara University School of Medicine, Ankara 06100, Turkey. Introduction.

  5. Seasonal characterization of submicron aerosol chemical composition and organic aerosol sources in the southeastern United States: Atlanta, Georgia,and Look Rock, Tennessee

    Directory of Open Access Journals (Sweden)

    S. H. Budisulistiorini

    2016-04-01

    Full Text Available A year-long near-real-time characterization of non-refractory submicron aerosol (NR-PM1 was conducted at an urban (Atlanta, Georgia, in 2012 and rural (Look Rock, Tennessee, in 2013 site in the southeastern US using the Aerodyne Aerosol Chemical Speciation Monitor (ACSM collocated with established air-monitoring network measurements. Seasonal variations in organic aerosol (OA and inorganic aerosol species are attributed to meteorological conditions as well as anthropogenic and biogenic emissions in this region. The highest concentrations of NR-PM1 were observed during winter and fall seasons at the urban site and during spring and summer at the rural site. Across all seasons and at both sites, NR-PM1 was composed largely of OA (up to 76 % and sulfate (up to 31 %. Six distinct OA sources were resolved by positive matrix factorization applied to the ACSM organic mass spectral data collected from the two sites over the 1 year of near-continuous measurements at each site: hydrocarbon-like OA (HOA, biomass burning OA (BBOA, semi-volatile oxygenated OA (SV-OOA, low-volatility oxygenated OA (LV-OOA, isoprene-derived epoxydiols (IEPOX OA (IEPOX-OA and 91Fac (a factor dominated by a distinct ion at m∕z 91 fragment ion previously observed in biogenic influenced areas. LV-OOA was observed throughout the year at both sites and contributed up to 66 % of total OA mass. HOA was observed during the entire year only at the urban site (on average 21 % of OA mass. BBOA (15–33 % of OA mass was observed during winter and fall, likely dominated by local residential wood burning emission. Although SV-OOA contributes quite significantly ( ∼  27 %, it was observed only at the urban site during colder seasons. IEPOX-OA was a major component (27–41 % of OA at both sites, particularly in spring and summer. An ion fragment at m∕z 75 is well correlated with the m∕z 82 ion associated with the aerosol mass spectrum of IEPOX

  6. Subnanosecond photoconductive switching in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Druce, R.L.; Pocha, M.D.; Griffin, K.L.

    1991-04-01

    We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential GaAs to act as a closing switch in ``avalanche`` mode at high fields. We have observed switch closing times of less than 200 psec with a 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into ``avalanche`` mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large area (1 sq cm) and small area (< 1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300--1300 psec at voltages of 6--35 kV. We will present experimental results for linear, lock on and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation. 3 refs.

  7. Subnanosecond photoconductive switching in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Druce, R.L.; Pocha, M.D.; Griffin, K.L.

    1991-04-01

    We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential GaAs to act as a closing switch in avalanche'' mode at high fields. We have observed switch closing times of less than 200 psec with a 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into avalanche'' mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large area (1 sq cm) and small area (< 1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300--1300 psec at voltages of 6--35 kV. We will present experimental results for linear, lock on and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation. 3 refs.

  8. Subnanosecond photoconductive switching in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Druce, R.L.; Pocha, M.D.; Griffin, K.L.

    1990-01-01

    We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential of GaAs to act as a closing switch in avalanche'' mode at high fields. We have observed switch closing times of less than 200 psec with 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into an avalanche'' mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large are (1 sq cm) and small area (<1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300--1300 psec at voltages of 6-35 kV. We will present experimental results for linear, lock on and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation. 3 refs., 11 figs.

  9. Subnanosecond photoconductive switching in GaAs

    Science.gov (United States)

    Druce, R. L.; Pocha, M. D.; Griffin, K. L.

    1991-04-01

    We are conducting research in photoconductive switching for the purpose of generating microwave pulses with amplitudes up to 50 kV. This technology has direct application to impulse radar and HPM sources. We are exploiting the very fast recombination rates of Gallium Arsenide (GaAs) to explore the potential of GaAs as an on-off switch when operating in the linear mode (the linear mode is defined such that one carrier pair is generated for each photon absorbed). In addition, we are exploring the potential GaAs to act as a closing switch in 'avalanche' mode at high fields. We have observed switch closing times of less than 200 psec with a 100 psec duration laser pulse and opening times of less than 400 psec with neutron irradiated GaAs at fields of tens of kV/cm. If the field is increased and the laser energy decreased, the laser can be used to trigger photoconductive switches into 'avalanche' mode of operation in which carrier multiplication occurs. This mode of operation is quite promising since the switches close in less than 1 nsec while realizing significant energy gain (ratio of electrical energy in the pulse to optical trigger energy). We are currently investigating both large area (1 sq cm) and small area (less than 1 sq mm) switches illuminated by GaAlAs laser diodes at 900 nm and Nd:YAG lasers at 1.06 micrometers. Preliminary results indicate that the closing time of the avalanche switches depends primarily on the material properties of the devices with closing times of 300-1300 psec at voltages of 6-35 kV. We will present experimental results for linear, lock on, and avalanche mode operation of GaAs photoconductive switches and how these pulses may be applied to microwave generation.

  10. Dielectric function and electro-optical properties of (Al,Ga)N/GaN-heterostructures; Dielektrische Funktion und elektrooptische Eigenschaften von (Al,Ga)N/GaN-Heterostrukturen

    Energy Technology Data Exchange (ETDEWEB)

    Buchheim, Carsten

    2010-04-23

    In this work extensive investigations on nitride semiconductors by optical spectroscopy are presented. The ordinary and the extraordinary component of the dielectric function of GaN in the spectral range from 1.2 to 9.8 eV is shown for the first time. It is demonstrated, that the transparent spectral range is clearly influenced by higher energetic critical points of the band structure. The optical selection rules for GaN and AlN are verified considering the actual strain state. The change of the valence band ordering of AlN in comparison to GaN is proven and the crystal field splitting is estimated for AlN. The ordinary dielectric function of AlGaN is determined for different Al contents. The data are used for developing an analytical model, which includes excitonic effects and bowings. It allows the calculation of the dielectric function for arbitrary alloy compositions. (GaN/)AlGaN/GaN heterostructures are investigated by spectroscopic ellipsometry as well as by photoreflectance and electroreflectance. The optical data yields the electric field strengths of the individual layers to determine the density of the two-dimensional carrier gases at the heterointerfaces with high accuracy. The surface potential is calculated from the combination of experiments and Schroedinger-Poisson calculations. Its dependency on the Al content is quantified. For the special case of thick cap layers the coexistence of electron and hole gases in one sample is experimentally proven for the first time. Several interband transitions between quantized states in AlN/GaN superlattices are observed by electroreflectance. The comparison to quantum mechanical calculations demonstrates the influence of strain and electrical fields (quantum confined Stark effect). For both the ratio of the thicknesses of quantum wells and barriers is crucial. From the dielectric function of the superlattices it becomes obvious, that quantum size effects are not only important for the vicinity of the bandgap, but

  11. Origin of magnetostriction in Fe-Ga

    DEFF Research Database (Denmark)

    Mudivarthi, Chaitanya; Laver, Mark; Cullen, James

    2010-01-01

    This paper investigates the origin of large magnetostriction in Fe-Ga alloys using small-angle neutron scattering (SANS) and Kerr microscopy. The SANS data for a single-crystal, electron irradiated, and quenched Fe81Ga19 sample under externally applied magnetic and elastic fields revealed...... the existence of magnetostrictive nanoclusters spaced at similar to 15 nm apart that have a different magnetization than the A2 matrix. Combining the SANS results and the magnetization orientation obtained from the magnetic domain images using a Kerr microscope, it appears that the nanoclusters contribute...

  12. Anodic etching of GaN based film with a strong phase-separated InGaN/GaN layer: Mechanism and properties

    International Nuclear Information System (INIS)

    Gao, Qingxue; Liu, Rong; Xiao, Hongdi; Cao, Dezhong; Liu, Jianqiang; Ma, Jin

    2016-01-01

    Highlights: • GaN film with a strong phase-separated InGaN/GaN layer was etched by electrochemical etching. • Vertically aligned nanopores in n-GaN films were buried underneath the InGaN/GaN structures. • The relaxation of compressive stress in the MQW structure was found by PL and Raman spectra. - Abstract: A strong phase-separated InGaN/GaN layer, which consists of multiple quantum wells (MQW) and superlattices (SL) layers and can produce a blue wavelength spectrum, has been grown on n-GaN thin film, and then fabricated into nanoporous structures by electrochemical etching method in oxalic acid. Scanning electron microscopy (SEM) technique reveals that the etching voltage of 8 V leads to a vertically aligned nanoporous structure, whereas the films etched at 15 V show branching pores within the n-GaN layer. Due to the low doping concentration of barriers (GaN layers) in the InGaN/GaN layer, we observed a record-low rate of etching (<100 nm/min) and nanopores which are mainly originated from the V-pits in the phase-separated layer. In addition, there exists a horizontal nanoporous structure at the interface between the phase-separated layer and the n-GaN layer, presumably resulting from the high transition of electrons between the barrier and the well (InGaN layer) at the interface. As compared to the as-grown MQW structure, the etched MQW structure exhibits a photoluminescence (PL) enhancement with a partial relaxation of compressive stress due to the increased light-extracting surface area and light-guiding effect. Such a compressive stress relaxation can be further confirmed by Raman spectra.

  13. Anodic etching of GaN based film with a strong phase-separated InGaN/GaN layer: Mechanism and properties

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Qingxue [School of Physics, Shandong University, Jinan, 250100 (China); Liu, Rong [Department of Fundamental Theories, Shandong Institute of Physical Education and Sports, Jinan 250063 (China); Xiao, Hongdi, E-mail: hdxiao@sdu.edu.cn [School of Physics, Shandong University, Jinan, 250100 (China); Cao, Dezhong; Liu, Jianqiang; Ma, Jin [School of Physics, Shandong University, Jinan, 250100 (China)

    2016-11-30

    Highlights: • GaN film with a strong phase-separated InGaN/GaN layer was etched by electrochemical etching. • Vertically aligned nanopores in n-GaN films were buried underneath the InGaN/GaN structures. • The relaxation of compressive stress in the MQW structure was found by PL and Raman spectra. - Abstract: A strong phase-separated InGaN/GaN layer, which consists of multiple quantum wells (MQW) and superlattices (SL) layers and can produce a blue wavelength spectrum, has been grown on n-GaN thin film, and then fabricated into nanoporous structures by electrochemical etching method in oxalic acid. Scanning electron microscopy (SEM) technique reveals that the etching voltage of 8 V leads to a vertically aligned nanoporous structure, whereas the films etched at 15 V show branching pores within the n-GaN layer. Due to the low doping concentration of barriers (GaN layers) in the InGaN/GaN layer, we observed a record-low rate of etching (<100 nm/min) and nanopores which are mainly originated from the V-pits in the phase-separated layer. In addition, there exists a horizontal nanoporous structure at the interface between the phase-separated layer and the n-GaN layer, presumably resulting from the high transition of electrons between the barrier and the well (InGaN layer) at the interface. As compared to the as-grown MQW structure, the etched MQW structure exhibits a photoluminescence (PL) enhancement with a partial relaxation of compressive stress due to the increased light-extracting surface area and light-guiding effect. Such a compressive stress relaxation can be further confirmed by Raman spectra.

  14. Compositional and structural characterisation of GaSb and GaInSb

    International Nuclear Information System (INIS)

    Corregidor, V.; Alves, E.; Alves, L.C.; Barradas, N.P.; Duffar, Th.; Franco, N.; Marques, C.; Mitric, A.

    2005-01-01

    Low band gap III-V semiconductors are researched for applications in thermophotovoltaic technology. GaSb crystal is often used as a substrate. Ga 1-x In x Sb is also a promising substrate material, because its lattice parameters can be adjusted by controlling x. We used a new method to synthesise GaSb and GaInSb, in which a high frequency alternate magnetic field is used to heat, to melt and to mix the elements. We present a compositional and structural characterisation of the materials using a combination of complementary techniques. Rutherford backscattering was used to determine accurately the composition of the GaSb. With proton induced X-ray emission in conjunction with a 3 x 3 μm 2 micro-beam we studied the homogeneity of the samples. Structural analysis and phase identification were done with X-ray diffraction. The results for GaSb show a homogeneous composition while the GaInSb samples were found to be strongly heterogeneous at the end of the ingot. The ingots produced are competitive feed material, when compared to other growth techniques, to be used in a second step for the production of good quality ternary crystals

  15. Atmospheric pressure-MOVPE growth of GaSb/GaAs quantum dots

    Science.gov (United States)

    Tile, Ngcali; Ahia, Chinedu C.; Olivier, Jaco; Botha, Johannes Reinhardt

    2018-04-01

    This study focuses on the growth of GaSb/GaAs quantum dots (QD) using an atmospheric pressure MOVPE system. For the best uncapped dots, the average dot height, base diameter and density are 5 nm, 45 nm and 4.5×1010 cm-2, respectively. Capping of GaSb QDs at high temperatures caused flattening and formation of thin inhomogeneous GaSb layer inside GaAs resulting in no obvious QD PL peak. Capping at low temperatures lead to the formation of dot-like features and a wetting layer (WL) with distinct PL peaks for QD and WL at 1097 nm and 983 nm respectively. Some of the dot-like features had voids. An increase in excitation power caused the QD and WL peaks to shift to higher energies. This is attributed to electrostatic band bending leading to triangular potential wells, typical of type-II alignment between GaAs and strained GaSb. Variable temperature PL measurements of the QD sample showed the decrease in the intensity of the WL peak to be faster than that of the QD peak as the temperature increased.

  16. Picosecond electron bunches from GaAs/GaAsP strained superlattice photocathode

    International Nuclear Information System (INIS)

    Jin, Xiuguang; Matsuba, Shunya; Honda, Yosuke; Miyajima, Tsukasa; Yamamoto, Masahiro; Utiyama, Takashi; Takeda, Yoshikazu

    2013-01-01

    GaAs/GaAsP strained superlattices are excellent candidates for use as spin-polarized electron sources. In the present study, picosecond electron bunches were successfully generated from such a superlattice photocathode. However, electron transport in the superlattice was much slower than in bulk GaAs. Transmission electron microscopy observations revealed that a small amount of variations in the uniformity of the layers was present in the superlattice. These variations lead to fluctuations in the superlattice mini-band structure and can affect electron transport. Thus, it is expected that if the periodicity of the superlattice can be improved, much faster electron bunches can be produced. - Highlights: • GaAs/GaAsP strained superlattices are excellent candidates for spin-polarized electron beam. • Pulse spin-polarized electron beam is required for investigating the magnetic domain change. • Picosecond electron bunches were achieved from GaAs/GaAsP superlattice photocathode. • TEM observation revealed a small disorder of superlattice layers. • Improvement of superlattice periodicity can achieve much faster electron bunches

  17. Epitaxial GaN films by hyperthermal ion-beam nitridation of Ga droplets

    Energy Technology Data Exchange (ETDEWEB)

    Gerlach, J. W.; Ivanov, T.; Neumann, L.; Hoeche, Th.; Hirsch, D.; Rauschenbach, B. [Leibniz-Institut fuer Oberflaechenmodifizierung (IOM), D-04318 Leipzig (Germany)

    2012-06-01

    Epitaxial GaN film formation on bare 6H-SiC(0001) substrates via the process of transformation of Ga droplets into a thin GaN film by applying hyperthermal nitrogen ions is investigated. Pre-deposited Ga atoms in well defined amounts form large droplets on the substrate surface which are subsequently nitridated at a substrate temperature of 630 Degree-Sign C by a low-energy nitrogen ion beam from a constricted glow-discharge ion source. The Ga deposition and ion-beam nitridation process steps are monitored in situ by reflection high-energy electron diffraction. Ex situ characterization by x-ray diffraction and reflectivity techniques, Rutherford backscattering spectrometry, and electron microscopy shows that the thickness of the resulting GaN films depends on the various amounts of pre-deposited gallium. The films are epitaxial to the substrate, exhibit a mosaic like, smooth surface topography and consist of coalesced large domains of low defect density. Possible transport mechanisms of reactive nitrogen species during hyperthermal nitridation are discussed and the formation of GaN films by an ion-beam assisted process is explained.

  18. Microstructure of (Ga,Mn)As/GaAs digital ferromagnetic heterostructures

    International Nuclear Information System (INIS)

    Kong, X.; Trampert, A.; Guo, X.X.; Kolovos-Vellianitis, D.; Daeweritz, L.; Ploog, K.H.

    2005-01-01

    We report on the microstructure of (Ga,Mn)As digital ferromagnetic heterostructures grown on GaAs (001) substrates by low-temperature molecular-beam epitaxy. The Mn concentration and the As 4 /Ga beam equivalent pressure (BEP) ratio are varied in the samples containing periods of Mn sheets separated by thin GaAs spacer layers. Transmission electron microscopy studies reveal that decreasing the Mn doping concentration and reducing the BEP ratio lead to smaller composition fluctuations of Mn and more homogeneous (Ga,Mn)As layers with abrupt interfaces. Planar defects are found as the dominant defect in these heterostructures and their density is related to the magnitude of the composition fluctuation. These defects show a noticeable anisotropy in the morphologic distribution parallel to the orthogonal [110] and [110] direction. Along the [110] direction, they are stacking faults, which are preferentially formed in V-shaped pairs and nucleate at the interfaces between (Ga,Mn)As and GaAs layers. Along the [110] direction, the planar defects are isolated thin twin lamellae. The character of the planar defects and their configuration are analyzed in detail

  19. A gate current 1/f noise model for GaN/AlGaN HEMTs

    International Nuclear Information System (INIS)

    Liu Yu'an; Zhuang Yiqi

    2014-01-01

    This work presents a theoretical and experimental study on the gate current 1/f noise in AlGaN/GaN HEMTs. Based on the carrier number fluctuation in the two-dimensional electron gas channel of AlGaN/GaN HEMTs, a gate current 1/f noise model containing a trap-assisted tunneling current and a space charge limited current is built. The simulation results are in good agreement with the experiment. Experiments show that, if V g < V x (critical gate voltage of dielectric relaxation), gate current 1/f noise comes from the superimposition of trap-assisted tunneling RTS (random telegraph noise), while V g > V x , gate current 1/f noise comes from not only the trap-assisted tunneling RTS, but also the space charge limited current RTS. This indicates that the gate current 1/f noise of the GaN-based HEMTs device is sensitive to the interaction of defects and the piezoelectric relaxation. It provides a useful characterization tool for deeper information about the defects and their evolution in AlGaN/GaN HEMTs. (semiconductor devices)

  20. Nanoscale conductive pattern of the homoepitaxial AlGaN/GaN transistor.

    Science.gov (United States)

    Pérez-Tomás, A; Catalàn, G; Fontserè, A; Iglesias, V; Chen, H; Gammon, P M; Jennings, M R; Thomas, M; Fisher, C A; Sharma, Y K; Placidi, M; Chmielowska, M; Chenot, S; Porti, M; Nafría, M; Cordier, Y

    2015-03-20

    The gallium nitride (GaN)-based buffer/barrier mode of growth and morphology, the transistor electrical response (25-310 °C) and the nanoscale pattern of a homoepitaxial AlGaN/GaN high electron mobility transistor (HEMT) have been investigated at the micro and nanoscale. The low channel sheet resistance and the enhanced heat dissipation allow a highly conductive HEMT transistor (Ids > 1 A mm(-1)) to be defined (0.5 A mm(-1) at 300 °C). The vertical breakdown voltage has been determined to be ∼850 V with the vertical drain-bulk (or gate-bulk) current following the hopping mechanism, with an activation energy of 350 meV. The conductive atomic force microscopy nanoscale current pattern does not unequivocally follow the molecular beam epitaxy AlGaN/GaN morphology but it suggests that the FS-GaN substrate presents a series of preferential conductive spots (conductive patches). Both the estimated patches density and the apparent random distribution appear to correlate with the edge-pit dislocations observed via cathodoluminescence. The sub-surface edge-pit dislocations originating in the FS-GaN substrate result in barrier height inhomogeneity within the HEMT Schottky gate producing a subthreshold current.

  1. Optical properties of GaS:Ho3+ and GaS:Tm3+ single crystals

    International Nuclear Information System (INIS)

    Jin, Moon-Seog; Kim, Chang-Dae; Kim, Wha-Tek

    2004-01-01

    GaS:Ho 3+ and GaS:Tm 3+ single crystals were grown by using the chemical transport reaction method. We measured the optical absorption, the infra-red absorption, and the photoluminescence spectra of the single crystals. The direct and the indirect energy band gaps of the single crystals at 13 K were identified. Infra-red absorption peaks at 6 K appeared in the single crystals. Broad emission bands at 6 K were observed at 464 nm and 580 nm for GaS:Ho 3+ and 462 nm and 581 nm for GaS:Tm 3+ . These broad emission bands were identified as originating from donor-acceptor pair recombinations. Sharp emission peak groups were observed near 435 nm, 495 nm, and 660 nm for GaS:Ho 3+ and near 672 nm for GaS:Tm 3+ . These sharp emission peak groups were identified as being due to the electron transitions between the energy levels of Ho 3+ and Tm 3+ . Especially, white photoluminescence was obtained in the GaS:Ho 3+ single crystal.

  2. Hydrogenation of GaAs covered by GaAlAs and subgrain boundary passivation

    Science.gov (United States)

    Djemel, A.; Castaing, J.; Chevallier, J.; Henoc, P.

    1992-12-01

    Cathodoluminescence (CL) has been performed to study the influence of hydrogen on electronic properties of GaAs with and without a GaAlAs layer. Recombination at sub-boundaries has been examined. These extended defects have been introduced by high temperature plastic deformation. The results show that they are passivated by hydrogen. The penetration of hydrogen is slowed down by the GaAlAs layer. La cathodoluminescence (CL) a été utilisée pour étudier l'influence de l'hydrogène sur les propriétés électroniques de GaAs nu et recouvert d'une couche de GaAlAs. Le caractère recombinant des sous-joints de grains a été examiné. Ces défauts étendus ont été introduits par déformation plastique à chaud. Les résultats montrent que l'hydrogène passive ces défauts. La pénétration de l'hydrogène à l'intérieur de GaAs est retardée par la présence de la couche de GaAlAs.

  3. Selected Ga-68-siderophores versus Ga-68-colloid and Ga-68-citrate: biodistribution and small animal imaging in mice

    Czech Academy of Sciences Publication Activity Database

    Petřík, M.; Vlčková, A.; Nový, Z.; Urbánek, Lubor; Haas, H.; Decristoforo, C.

    2015-01-01

    Roč. 159, č. 1 (2015), s. 60-66 ISSN 1213-8118 R&D Projects: GA MŠk(CZ) LO1304 Institutional support: RVO:61389030 Keywords : gallium-68 * siderophores * colloid Subject RIV: EB - Genetics ; Molecular Biology Impact factor: 0.924, year: 2015

  4. Donors, Acceptors, and Traps in AlGaN and AlGaN/GaN Epitaxial Layers

    National Research Council Canada - National Science Library

    Look, David C

    2006-01-01

    .... The present grant, F49620-03-1-0197, has covered the period 1 May 03 - 30 Apr 06. The overall goal has been to understand defects and impurities in GaN, and determine how to reduce them, if possible...

  5. Field isolation for GaN MOSFETs on AlGaN/GaN heterostructure with boron ion implantation

    International Nuclear Information System (INIS)

    Jiang, Y; Wang, Q P; Wang, D J; Tamai, K; Li, L A; Ao, J-P; Ohno, Y; Shinkai, S; Miyashita, T; Motoyama, S-I

    2014-01-01

    We report the investigation of boron ion implantation as a device field isolation process for GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) on AlGaN/GaN heterostructure. In the mesa isolation region of a bar-type MOSFET, a parasitic MOS-channel existed and widened the designed channel width, which would result in an overestimated mobility compared with a ring-type MOSFET. After boron ions implantation in the isolation region, the overestimation of field-effect mobility of bar-type MOSFETs was eliminated. The sub-threshold characteristics and on-state drain current of the bar-type MOSFETs coincide with the ring-type devices. Long-channel ring-type MOSFETs, with and without ion implantation, were fabricated on the recess region to evaluate the sub-threshold characteristics. The MOSFETs with boron ions implanted into the recess region showed a low drain current up to the gate bias of 10V. The result indicated that boron ion implantation prevented the formation of parasitic MOS-channel in the isolation region and achieved field isolation. The current–voltage characteristics of MOSFETs with the normal recess condition demonstrated no degradation of device performance after boron ions implanted into the isolation region. Boron ion implantation by further optimization can be a field isolation method for GaN MOSFETs. (paper)

  6. InGaN/GaNおよびInGaN/InN気相成長における気相-固相関係 : 結晶成長理論シンポジウム

    OpenAIRE

    寒川, 義裕; 伊藤, 智徳; 熊谷, 義直; 纐纈, 明伯; KANGAWA, Yoshihiro; ITO, Tomonori; KUMAGAI, Yoshinao; KOUKITU, Akinori

    2002-01-01

    Thermodynamic analyses were carried out to understand compositional instability of InGaN/GaN and InGaN/InN in the MBE growth. In the thermodynamic analysis, contribution of lattice constraint from bottom layer was incorporated using enthalpy of mixing of InGaN/GaN and InGaN/InN, ΔH_m^ and ΔH_m^, which can be obtained by empirical interatomic potential calculations. The results suggest that compositional unstable region for InGaN/InN shifted toward Ga-rich side compared with that for InGaN/GaN...

  7. Anisotropic magnetoresistance components in (Ga,Mn)As

    Czech Academy of Sciences Publication Activity Database

    Rushforth, A.W.; Výborný, Karel; King, C.S.; Edmonds, K. W.; Campion, R. P.; Foxon, C. T.; Wunderlich, J.; Irvine, A.C.; Vašek, Petr; Novák, Vít; Olejník, Kamil; Sinova, J.; Jungwirth, Tomáš; Gallagher, B. L.

    2007-01-01

    Roč. 99, č. 14 (2007), 147207/1-147207/4 ISSN 0031-9007 R&D Projects: GA ČR GA202/05/0575; GA ČR GA202/04/1519; GA ČR GEFON/06/E002; GA MŠk LC510 Grant - others:UK(GB) GR/S81407/01 Institutional research plan: CEZ:AV0Z10100521 Keywords : ferromagnetic semiconductors * anisotropic magnetoresistence Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 6.944, year: 2007

  8. Electronic properties of GaV 4 S 8

    Indian Academy of Sciences (India)

    ... different in GaV4S8-1 and GaV4S8-2. This statement is strongly supported by the calculated bandwidth per cluster in GaV4S8 (∼0.342 eV in GaV4S8-1 and ∼0.374 eV in GaV4S8-2). A negative magnetoresistance (MR) is also found around 43 K in GaV4S8-2 at 6.0 T magnetic field associated with structural transition.

  9. Huge tunnelling anisotropic magnetoresistance in (Ga,Mn)As nanoconstrictions

    Czech Academy of Sciences Publication Activity Database

    Giddings, A.D.; Makarovsky, O. N.; Khalid, M.N.; Yasin, S.; Edmonds, K. W.; Campion, R. P.; Wunderlich, J.; Jungwirth, Tomáš; Williams, D.A.; Gallagher, B. L.; Foxon, C. T.

    2008-01-01

    Roč. 10, č. 8 (2008), 085004/1-085004/9 ISSN 1367-2630 R&D Projects: GA ČR GEFON/06/E002; GA MŠk LC510; GA ČR GA202/05/0575; GA ČR GA202/04/1519 EU Projects: European Commission(XE) 015728 - NANOSPIN Institutional research plan: CEZ:AV0Z10100521 Keywords : ferromagnetic semiconductor * nanoconstriction * tunneling anisotropic magnetoresistance , Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 3.440, year: 2008

  10. Domain walls in (Ga,Mn)As diluted magnetic semiconductor

    Czech Academy of Sciences Publication Activity Database

    Sugawara, A.; Kasai, H.; Tonomura, A.; Brown, P.D.; Campion, R. P.; Edmonds, K. W.; Gallagher, B. L.; Zemen, Jan; Jungwirth, Tomáš

    2008-01-01

    Roč. 100, č. 4 (2008), 047202/1-047202/4 ISSN 0031-9007 R&D Projects: GA MŠk LC510; GA ČR GEFON/06/E002; GA ČR GA202/05/0575; GA ČR GA202/04/1519 EU Projects: European Commission(XE) 015728 - NANOSPIN Institutional research plan: CEZ:AV0Z10100521 Keywords : dilute ferromagnetic semiconductor * Néel domain walls * electron holography * Landau-Lifshitz-Gilbert simulation Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 7.180, year: 2008

  11. Role of Ga vacancies in enhancing the leakage current of GaN Schottky barrier ultraviolet photodetectors

    International Nuclear Information System (INIS)

    De-Gang, Zhao; Shuang, Zhang; Wen-Bao, Liu; De-Sheng, Jiang; Jian-Jun, Zhu; Zong-Shun, Liu; Hui, Wang; Shu-Ming, Zhang; Hui, Yang; Xiao-Peng, Hao; Long, Wei

    2010-01-01

    The leakage current of GaN Schottky barrier ultraviolet photodetectors is investigated. It is found that the photodetectors adopting undoped GaN instead of lightly Si-doped GaN as an active layer show a much lower leakage current even when they have a higher dislocation density. It is also found that the density of Ga vacancies in undoped GaN is much lower than in Si-doped GaN. The Ga vacancies may enhance tunneling and reduce effective Schottky barrier height, leading to an increase of leakage current. It suggests that when undoped GaN is used as the active layer, it is necessary to reduce the leakage current of GaN Schottky barrier ultraviolet photodetector. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  12. Influence of AlGaN Buffer Growth Temperature on GaN Epilayer based on Si(lll) Substrate

    International Nuclear Information System (INIS)

    Wei Meng; Wang Xiaoliang; Pan Xu; Xiao Hongling; Wang Cuimei; Zhang Minglan; Wang Zhanguo

    2011-01-01

    This paper investigated the influence of AlGaN buffer growth temperature on strain status and crystal quality of the GaN film on Si(111) sbustrates by metal organic chemical vapor deposition. It was demonstrated by the optical microscopy that AlGaN buffer gorwth temperature had a remarkable effect on compensating tensil stress in top GaN layer and preventing the formation of cracks. X-ray diffraction and atomic force microscopy analysis showed crystal quality and surface morphology of the GaN epilayer could be improved through increasing AlGaN buffer growth temperature. 1μm crack-free GaN epilayer on Si (111) substrates was obtained with graded AlGaN buffer layer at optimized temperature of 1050 deg. C. Transmission electron microscopy analysis revealed that a significant reduction in threading dislocations was achieved in GaN epilayer.

  13. The effect of the In concentration on the surface morphology of InGaAs-GaAs heterostructures grown by MBE on GaAs substrate

    International Nuclear Information System (INIS)

    Gómez-Barojas, E; Serrano-Rojas, R M; Rodríguez-Moreno, M A; Santamaría-Juárez, G; Silva-González, R; a. Sección, San Luis Potosí, S. L. P., 78100 (Mexico))" data-affiliation=" (Instituto de Investigación en Comunicación Óptica. Universidad Autónoma de San Luis Potosí, Av. Karakorum 1470, Col. Lomas Altas 4a. Sección, San Luis Potosí, S. L. P., 78100 (Mexico))" >Vidal-Borbolla, M A

    2014-01-01

    A set of 3 heterostructures were formed by 10 periods of InGaAs-GaAs epitaxially grown on GaAs substrate by means of a molecular beam epitaxial system. Scanning electron microscopy (SEM) cross section images at high magnification show that the heterostructures present good periodicity. SEM micrographs of the surface morphology chemically etched show the coalescence effect of In due to an unequal etching rate of In and GaAs. Auger electron spectroscopy (AES) depth profiles show that the first GaAs layers in the 3 samples are off-stoichiometric and that the alloy layers present In square and triangular depth profiles

  14. Enhanced thermoelectric transport in modulation-doped GaN/AlGaN core/shell nanowires

    International Nuclear Information System (INIS)

    Song, Erdong; Martinez, Julio A; Li, Qiming; Pan, Wei; Wang, George T; Swartzentruber, Brian

    2016-01-01

    The thermoelectric properties of unintentionally n-doped core GaN/AlGaN core/shell N-face nanowires are reported. We found that the temperature dependence of the electrical conductivity is consistent with thermally activated carriers with two distinctive donor energies. The Seebeck coefficient of GaN/AlGaN nanowires is more than twice as large as that for the GaN nanowires alone. However, an outer layer of GaN deposited onto the GaN/AlGaN core/shell nanowires decreases the Seebeck coefficient at room temperature, while the temperature dependence of the electrical conductivity remains the same. We attribute these observations to the formation of an electron gas channel within the heavily-doped GaN core of the GaN/AlGaN nanowires. The room-temperature thermoelectric power factor for the GaN/AlGaN nanowires can be four times higher than the GaN nanowires. Selective doping in bandgap engineered core/shell nanowires is proposed for enhancing the thermoelectric power. (paper)

  15. Enhanced thermoelectric transport in modulation-doped GaN/AlGaN core/shell nanowires.

    Science.gov (United States)

    Song, Erdong; Li, Qiming; Swartzentruber, Brian; Pan, Wei; Wang, George T; Martinez, Julio A

    2016-01-08

    The thermoelectric properties of unintentionally n-doped core GaN/AlGaN core/shell N-face nanowires are reported. We found that the temperature dependence of the electrical conductivity is consistent with thermally activated carriers with two distinctive donor energies. The Seebeck coefficient of GaN/AlGaN nanowires is more than twice as large as that for the GaN nanowires alone. However, an outer layer of GaN deposited onto the GaN/AlGaN core/shell nanowires decreases the Seebeck coefficient at room temperature, while the temperature dependence of the electrical conductivity remains the same. We attribute these observations to the formation of an electron gas channel within the heavily-doped GaN core of the GaN/AlGaN nanowires. The room-temperature thermoelectric power factor for the GaN/AlGaN nanowires can be four times higher than the GaN nanowires. Selective doping in bandgap engineered core/shell nanowires is proposed for enhancing the thermoelectric power.

  16. Electrical properties of Ga ion beam implanted GaAs epilayer

    International Nuclear Information System (INIS)

    Hirayama, Yoshiro; Okamoto, Hiroshi

    1985-01-01

    Resistivity enhancement by 5 orders or more was realized by Ga focused ion beam implantation into n + and p + GaAs epilayers. For originally n + epilayers, this resistivity enhancement is maintained after annealing as high as 800 deg C. However this enhancement disappears after annealing at above 650 deg C for p + epilayer. This property makes GaAs high resistive only in a limited area whose minimum dimension is 0.1 μm or less, and is attractive for a device fabrication process to electrically isolate integrated elements. (author)

  17. Defect Structure of High-Temperature-Grown GaMnSb/GaSb

    International Nuclear Information System (INIS)

    Romanowski, P.; Bak-Misiuk, J.; Dynowska, E.; Domagala, J.Z.; Wojciechowski, T.; Jakiela, R.; Sadowski, J.; Barcz, A.; Caliebe, W.

    2010-01-01

    GaMnSb/GaSb(100) layers with embedded MnSb inclusions have been grown at 720 K using MBE technique. This paper presents the investigation of the defect structure of Ga1-xMnxSb layers with different content of manganese (up to x = 0.07). X-ray diffraction method using conventional and synchrotron radiation was applied. Dimensions and shapes of inclusions were detected by scanning electron microscopy. Depth profiles of elements were measured using secondary ion mass spectroscopy technique. (authors)

  18. Unconventional superconductivity in PuRhGa5: Ga NMR/NQR study

    International Nuclear Information System (INIS)

    Sakai, H.; Tokunaga, Y.; Fujimoto, T.; Kambe, S.; Walstedt, R.E.; Yasuoka, H.; Aoki, D.; Homma, Y.; Yamamoto, E.; Nakamura, A.; Shiokawa, Y.; Nakajima, K.; Arai, Y.; Matsuda, T.D.; Haga, Y.; Onuki, Y.

    2006-01-01

    69,71 Ga NMR/NQR studies have been performed on a single crystal of the transuranium superconductor PuRhGa 5 with T c ∼9K. The spin-lattice relaxation rate 1/T 1 reveals that PuRhGa 5 is an unconventional superconductor having an anisotropic superconducting gap. Moreover, Korringa behavior (1/T 1 T=const.) is observed in the normal state below ∼30K. This result suggests that the superconductivity sets in after the formation of a Fermi liquid state in this compound

  19. A new theoretical approach to adsorption desorption behavior of Ga on GaAs surfaces

    Science.gov (United States)

    Kangawa, Y.; Ito, T.; Taguchi, A.; Shiraishi, K.; Ohachi, T.

    2001-11-01

    We propose a new theoretical approach for studying adsorption-desorption behavior of atoms on semiconductor surfaces. The new theoretical approach based on the ab initio calculations incorporates the free energy of gas phase; therefore we can calculate how adsorption and desorption depends on growth temperature and beam equivalent pressure (BEP). The versatility of the new theoretical approach was confirmed by the calculation of Ga adsorption-desorption transition temperatures and transition BEPs on the GaAs(0 0 1)-(4×2)β2 Ga-rich surface. This new approach is feasible to predict how adsorption and desorption depend on the growth conditions.

  20. Strain-induced fundamental optical transition in (In,Ga)As/GaP quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Robert, C., E-mail: cedric.robert@insa-rennes.fr, E-mail: cedric.robert@tyndall.ie; Pedesseau, L.; Cornet, C.; Jancu, J.-M.; Even, J.; Durand, O. [Université Européenne de Bretagne, INSA Rennes, France and CNRS, UMR 6082 Foton, 20 Avenue des Buttes de Coësmes, 35708 Rennes (France); Nestoklon, M. O. [Ioffe Physico-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Pereira da Silva, K. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); Departamento de Física, Universidade Federal do Ceará, P.O. Box 6030, Fortaleza–CE, 60455-970 (Brazil); Alonso, M. I. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); Goñi, A. R. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); ICREA, Passeig Lluís Companys 23, 08010 Barcelona (Spain); Turban, P. [Equipe de Physique des Surfaces et Interfaces, Institut de Physique de Rennes UMR UR1-CNRS 6251, Université de Rennes 1, F-35042 Rennes Cedex (France)

    2014-01-06

    The nature of the ground optical transition in an (In,Ga)As/GaP quantum dot is thoroughly investigated through a million atoms supercell tight-binding simulation. Precise quantum dot morphology is deduced from previously reported scanning-tunneling-microscopy images. The strain field is calculated with the valence force field method and has a strong influence on the confinement potentials, principally, for the conduction band states. Indeed, the wavefunction of the ground electron state is spatially confined in the GaP matrix, close to the dot apex, in a large tensile strain region, having mainly Xz character. Photoluminescence experiments under hydrostatic pressure strongly support the theoretical conclusions.