Optical phonon scattering on electronic mobility in Al2O3/AlGaN/AlN/GaN heterostructures

Science.gov (United States)

Zhou, X. J.; Qu, Y.; Ban, S. L.; Wang, Z. P.

2017-12-01

Considering the built-in electric fields and the two-mode property of transverse optical phonons in AlGaN material, the electronic eigen-energies and wave functions are obtained by solving Schrödinger equation with the finite difference method. The dispersion relations and potentials of the optical phonons are given by the transfer matrix method. The mobility of the two dimensional electron gas influenced by the optical phonons in Al2O3/AlGaN/AlN/GaN heterostructures is investigated based on the theory of Lei-Ting force balance equation. It is found that the scattering from the half-space phonons is the main factor affecting the electronic mobility, and the influence of the other phonons can be ignored. The results show that the mobility decreases with increasing the thicknesses of Al2O3 and AlN layers, but there is no definite relationship between the mobility and the thickness of AlGaN barrier. The mobility is obviously reduced by increasing Al component in AlGaN crystal to show that the effect of ternary mixed crystals is important. It is also found that the mobility increases first and then decreases as the increment of the fixed charges, but decreases always with increasing temperature. The heterostructures constructed here can be good candidates as metal-oxide-semiconductor high-electron-mobility-transistors since they have higher electronic mobility due to the influence from interface phonons weakened by the AlN interlayer.

TATA CARA PELAKSANAAN SHALAT JUM'AT (Studi Naskah “Sulûk Al-Jâddah Fî Bayân Al-Jum’ah” Karya Syeikh Nawawi al-Bantani

Directory of Open Access Journals (Sweden)

Masrukhin Muhsin

2012-07-01

Full Text Available Makalah ini merupakan hasil penelitian naskah “Sulûk al-Jâddah Fî Bayân al-Jum’ah” Karya Syeikh Nawawi al-Bantani. Penelitian ini menggunakan pendekatan filologi. Dalam penelitian filologi dikenal dua perlakuan terhadap naskah. Pertama, memperlakukan satu naskah sebagai bagian dari naskah-naskah lainnya yang sejudul. Dalam hal ini semua naskah yang sejudul dikumpulkan di manapun adanya, dengan tujuan mendapatkan naskah asli atau dianggap paling mendekati asli. Kedua, memperlakukan naskah sebagai naskah tunggal. Dalam hal ini peneliti mengesampingkan naskah lain yang kemungkinan ada di tempat lain. Dari dua model tersebut, penelitian ini menggunakan model kedua. Alasannya, naskah Sulûk al-Jâddah fî Bayân al- Jum’ah untuk sementara dinyatakan sebagai naskah tunggal dengan indikasi tidak ditemukan naskah lain. Untuk menganalisa data naskah, dilakukan pembacaan dua tahap, heuristik dan hermeneutik. Adapun pokok-pokok bahasan yang ada dalam naskah Sulûk al-Jâddah fî Bayân al-Jum’ah adalah berisi tentang masalah shalat Jumát dan permasalahan-perasalahan yang dihadapi oleh masyarakat seputar shalat Jum’at dan shalat Jum’at yang diulang.

Benthic foraminiferal census data from Mobile Bay, Alabama--counts of surface samples and box cores

Science.gov (United States)

Richwine, Kathryn A.; Osterman, Lisa E.

2012-01-01

A study was undertaken in order to understand recent environmental change in Mobile Bay, Alabama. For this study a series of surface sediment and box core samples was collected. The surface benthic foraminiferal data provide the modern baseline conditions of the bay and can be used as a reference for changing paleoenvironmental parameters recorded in the box cores. The 14 sampling locations were chosen in the bay to cover the wide diversity of fluvial and marine-influenced environments on both sides of the shipping channel.

Land-use and Land-cover Change from 1974 to 2008 around Mobile Bay

Science.gov (United States)

Ellis, Jean; Spruce, Joseph; Smoot, James; Hilbert, Kent; Swann, Roberta

2008-01-01

This project is a Gulf of Mexico Application Pilot in which NASA Stennis Space Center (SSC) is working within a regional collaboration network of the Gulf of Mexico Alliance. NASA researchers, with support from the NASA SSC Applied Science Program Steering Committee, employed multi-temporal Landsat data to assess land-use and land-cover (LULC) changes in the coastal counties of Mobile and Baldwin, AL, between 1974 and 2008. A multi-decadal time-series, coastal LULC product unique to NASA SSC was produced. The geographic extent and nature of change was quantified for the open water, barren, upland herbaceous, non-woody wetland, upland forest, woody wetland, and urban landscapes. The National Oceanic and Atmospheric Administration (NOAA) National Coastal Development Data Center (NCDDC) will assist with the transition of the final product to the operational end user, which primarily is the Mobile Bay National Estuary Program (MBNEP). We found substantial LULC change over the 34-year study period, much more than is evident when the change occurring in the last years. Between 1974 and 2008, the upland forest landscape lost almost 6% of the total acreage, while urban land cover increased by slightly more than 3%. With exception to open water, upland forest is the dominant landscape, accounting for about 25-30% of the total area.

The areal extent of brown shrimp habitat suitability in Mobile Bay, Alabama, USA: Targeting vegetated habitat restoration

Science.gov (United States)

Smith, L.M.; Nestlerode, J.A.; Harwell, L.C.; Bourgeois, P.

2010-01-01

The availability of wetlands and shallow water habitats significantly influences Gulf of Mexico (GOM) penaeid shrimp fishery productivity. However, the GOM region has the highest rate of wetland loss in the USA. Protection and management of these vital GOM habitats are critical to sustainable shrimp fisheries. Brown shrimp (Farfantepenaeus aztecus) are a major component of GOM fisheries. We present an approach for estimating the areal extent of suitable habitat for post-larval and juvenile brown shrimp in Mobile Bay, Alabama, using an existing habitat suitability index model for the northern GOM calculated from probabilistic survey of water quality and sediment data, land cover data, and submerged aquatic vegetation coverages. This estuarine scale approach is intended to support targeted protection and restoration of these habitats. These analyses indicate that approximately 60% of the area of Mobile Bay is categorized as suitable to near optimal for post-larval and juvenile shrimp and 38% of the area is marginally to minimally suitable. We identify potential units within Mobile Bay for targeted restoration to improve habitat suitability. ?? 2010 Springer Science+Business Media B.V.

Over 100 years of environmental change recorded by foraminifers and sediments in Mobile Bay, Alabama, Gulf of Mexico, USA

Science.gov (United States)

Osterman, Lisa E.; Smith, Christopher G.

2012-12-01

The marine microfauna of Mobile Bay has been profoundly influenced by the development and expansion of the primary shipping channel over the last ˜100 years. Foraminifers and sediments from seven box cores with excess lead-210 chronology document that channel dredging and spoil disposal have altered circulation, reduced estuarine mixing, changed sedimentation patterns, and caused a faunal turnover within the bay. Beginning in the late 1800s, changes in estuarine mixing allowed for greater low-pH freshwater influence in the bay, and ultimately began environmental changes that resulted in the loss of calcareous foraminifers. By the early 1900s, box cores throughout Mobile Bay record a ˜100-year trend of increasing calcareous test dissolution that continues to the present. Since the completion of the current shipping channel in the 1950s, restricted tidal flushing and increased terrestrial organic matter, documented by carbon-to-nitrogen ratios, stimulated an increase in agglutinated foraminiferal densities. However, in deeper areas of the bay, hypoxic water has negatively impacted the marine microfauna. Comparisons of the present-day foraminiferal assemblage with foraminifers collected in the early 1970s indicate that the continued biologic loss of calcareous foraminifers in the bay has allowed the introduction of a new agglutinated foraminiferal species into the bay.

76 FR 13615 - B&B Manufacturing Site; Mobile, Mobile County, AL; Notice of Settlement

Science.gov (United States)

2011-03-14

... settlement for reimbursement of past response costs concerning the B&B Manufacturing Site located in Mobile, Mobile County, Alabama for publication. DATES: The Agency will consider public comments on the settlement... Site; Mobile, Mobile County, AL; Notice of Settlement AGENCY: Environmental Protection Agency. ACTION...

33 CFR 110.194a - Mobile Bay, Ala., and Mississippi Sound, Miss.

Science.gov (United States)

2010-07-01

... Sound, Miss. 110.194a Section 110.194a Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF... Mississippi Sound, Miss. (a) The anchorage grounds. (1) The waters of lower Mobile Bay, near Cedar Point... south by latitude 30°20′00″, and on the west by longitude 88°06′00″. (2) The waters of Mississippi Sound...

A Landsat-Based Assessment of Mobile Bay Land Use and Land Cover Change from 1974 to 2008

Science.gov (United States)

Spruce, Joseph; Ellis, Jean; Smoot, James; Swann, Roberta; Graham, William

2009-01-01

The Mobile Bay region has experienced noteworthy land use and land cover (LULC) change in the latter half of the 20th century. Accompanying this change has been urban expansion and a reduction of rural land uses. Much of this LULC change has reportedly occurred since the landfall of Hurricane Frederic in 1979. The Mobile Bay region provides great economic and ecologic benefits to the Nation, including important coastal habitat for a broad diversity of fisheries and wildlife. Regional urbanization threatens the estuary s water quality and aquatic-habitat dependent biota, including commercial fisheries and avian wildlife. Coastal conservation and urban land use planners require additional information on historical LULC change to support coastal habitat restoration and resiliency management efforts. This presentation discusses results of a Gulf of Mexico Application Pilot project that was conducted in 2008 to quantify and assess LULC change from 1974 to 2008. This project was led by NASA Stennis Space Center and involved multiple Gulf of Mexico Alliance (GOMA) partners, including the Mobile Bay National Estuary Program (NEP), the U.S. Army Corps of Engineers, the National Oceanic and Atmospheric Administration s (NOAA s) National Coastal Data Development Center (NCDDC), and the NOAA Coastal Services Center. Nine Landsat images were employed to compute LULC products because of their availability and suitability for the application. The project also used Landsat-based national LULC products, including coastal LULC products from NOAA s Coastal Change & Analysis Program (C-CAP), available at 5-year intervals since 1995. Our study was initiated in part because C-CAP LULC products were not available to assess the region s urbanization prior to 1995 and subsequent to post Hurricane Katrina in 2006. This project assessed LULC change across the 34-year time frame and at decadal and middecadal scales. The study area included the majority of Mobile and Baldwin counties that

Effects of small-scale hydrogeologic heterogeneity on submarine groundwater discharge (SGD) dynamics in river dominated estuaries: example of Mobile Bay, Alabama

Science.gov (United States)

Montiel, D.; Dimova, N.

2017-12-01

Submarine groundwater discharge (SGD) is known to be an important pathway for nutrients and dissolved constituents in estuarine environments worldwide. Despite its limited contribution to the total fresh water flux to the ocean (5 - 10 %), SGD-derived material loadings can rival riverine inputs. Therefore, a good understanding of the coastal hydrogeology and subsequent SGD dynamics is crucial to further investigate constituent fluxes and its implications on small and large scale coastal ecosystems. We evaluated SGD in Mobile Bay (Alabama), the fourth largest estuary in the US, using a combination of radiotracer techniques (223Ra, 226Ra, and 222Rn), stable isotopes (δ 18O and δ 2H), geophysical surveys (continuous resistivity profiling (CRP) and electrical resistivity tomography (ERT)), and seepage meters during three consecutive years. A detailed examination of the entire shoreline of Mobile Bay using CRP, ERT imaging, and multiple sediment cores collection unveiled a heterogeneous (horizontal and vertical) distribution of the surficial coastal aquifer. This was reflected and confirmed by groundwater tracer measurements and direct measurements of SGD in the coastal zone. We found that SGD occurs mainly in the northeast section of Mobile Bay with a total flux that ranged between 0.9 and 13 × 105 m3 d-1 during dry and wet periods, which represents 0.4 - 2 % of the total fresh water inputs into the Bay. While total SGD is insignificant when accounting the whole water budget of Mobile Bay, we found that small-scale geology variations produce groundwater flow preferential pathways in particular areas where SGD inputs play an important role in the water and nutrient budgets.

Embedding Repetition (Takrir Technique in Developing Al-Quran Memorizing Mobile Application for Autism Children

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Senan Norhalina

2017-01-01

Full Text Available Nowadays, there are various types of learning materials used in the process of teaching and learning of Al-Quran including the use of mobile application. However, the features of mobile application that are appropriate for the process of memorizing the Al-Quran, especially for the needs of children with autism is still limited. Thus, this paper proposes an interactive Al-Quran mobile application namely iHafaz to facilitate autism children recite and memorizing Al-Quran. A takrir (repetition technique in Islamic learning approach is embedded in this mobile application in order to assist autism children memorizing the Al-Quran easily. This mobile application consists of two main modules which are Hafaz (Memorize and Latihan (Exercise. Result from the user testing shows that 72.4% of respondents agree that the takrir technique embedded in the mobile application able to improve the usability of the mobile application in helping the autism children to recite and memorize the Al-Quran easily.

Physical, chemical, and biological data collected in Mobile Bay, Alabama in May 1989-December 1999 (NODC Accession 0116496)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — This dataset contains physical, chemical, and biological data collected during ten years of near-monthly shipboard surveys carried out in Mobile Bay between May 1989...

Sediment Sampling for Poly-Aromatic Hydrocarbons (PAHs) in Mobile Bay and Mississippi Sound in 2013 (NODC Accession 0116480)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Sediment samples were collected at ten sites within Mobile Bay and Mississippi Sound on January 28, 2013, for PAH analysis. All samples tested were below detection...

High-temperature carrier density and mobility enhancements in AlGaN/GaN HEMT using AlN spacer layer

Science.gov (United States)

Ko, Tsung-Shine; Lin, Der-Yuh; Lin, Chia-Feng; Chang, Che-Wei; Zhang, Jin-Cheng; Tu, Shang-Ju

2017-04-01

In this paper, we experimentally studied the effect of AlN spacer layer on optical and electrical properties of AlGaN/GaN high electric mobility transistors (HEMTs) grown by metal organic chemical vapor deposition method. For AlGaN layer in HEMT structure, the Al composition of the sample was determined using x-ray diffraction and photoluminescence. Electrolyte electro-reflectance (EER) measurement not only confirmed the aluminum composition of AlGaN layer, but also determined the electric field strength on the AlGaN layer through the Franz-Keldysh oscillation phenomenon. This result indicated that the electric field on the AlGaN layer could be improved from 430 to 621 kV/cm when AlN spacer layer was inserted in HEMT structure, which increased the concentration of two dimensional electron gas (2DEG) and improve the mobility. The temperature dependent Hall results show that both the mobility and the carrier concentration of 2DEG would decrease abruptly causing HEMT loss of function due to phonon scattering and carrier thermal escape when temperature increases above a specific value. Meanwhile, our study also demonstrates using AlN spacer layer could be beneficial to allow the mobility and carrier density of 2DEG sustaining at high temperature region.

Combined SEM/AVS and attenuation of concentration models for the assessment of bioavailability and mobility of metals in sediments of Sepetiba Bay (SE Brazil).

Science.gov (United States)

Ribeiro, Andreza Portella; Figueiredo, Ana Maria Graciano; dos Santos, José Osman; Dantas, Elizabeth; Cotrim, Marycel Elena Barboza; Figueira, Rubens Cesar Lopes; Silva Filho, Emmanoel V; Wasserman, Julio Cesar

2013-03-15

This study proposes a new methodology to study contamination, bioavailability and mobility of metals (Cd, Cu, Ni, Pb, and Zn) using chemical and geostatistics approaches in marine sediments of Sepetiba Bay (SE Brazil). The chemical model of SEM (simultaneously extracted metals)/AVS (acid volatile sulfides) ratio uses a technique of cold acid extraction of metals to evaluate their bioavailability, and the geostatistical model of attenuation of concentrations estimates the mobility of metals. By coupling the two it was observed that Sepetiba Port, the urban area of Sepetiba and the riverine discharges may constitute potential sources of metals to Sepetiba Bay. The metals are concentrated in the NE area of the bay, where they tend to have their lowest mobility, as shown by the attenuation model, and are not bioavailable, as they tend to associate with sulfide and organic matter originated in the mangrove forests of nearby Guaratiba area. Copyright © 2013 Elsevier Ltd. All rights reserved.

Results of a modeling workshop concerning economic and environmental trends and concomitant resource management issues in the Mobile Bay area

Science.gov (United States)

Hamilton, David B.; Andrews, Austin K.; Auble, Gregor T.; Ellison, Richard A.; Johnson, Richard A.; Roelle, James E.; Staley, Michael J.

1982-01-01

During the past decade, the southern regions of the U.S. have experienced rapid change which is expected to continue into the foreseeable future. Growth in population, industry, and resource development has been attributed to a variety of advantages such as an abundant and inexpensive labor force, a mild climate, and the availability of energy, water, land, and other natural resources. While this growth has many benefits for the region, it also creates the potential for increased air, water, and solid waste pollution, and modification of natural habitats. A workshop was convened to consider the Mobile Bay area as a site-specific case of growth and its environmental consequences in the southern region. The objectives of the modeling workshop were to: (1) identify major factors of economic development as they relate to growth in the area over the immediate and longer term; (2) identify major environmental and resource management issues associated with this expected growth; and (3) identify and characterize the complex interrelationships among economic and environmental factors. This report summarizes the activities and results of a modeling workshop concerning economic growth and concomitant resource management issues in the Mobile Bay area. The workshop was organized around construction of a simulation model representing the relationships between a series of actions and indicators identified by participants. The workshop model had five major components. An Industry Submodel generated scenarios of growth in several industrial and transportation sectors. A Human Population/Economy Submodel calculated human population and economic variables in response to employment opportunities. A Land Use/Air Quality Submodel tabulated changes in land use, shoreline use, and air quality. A Water Submodel calculated indicators of water quality and quantity for fresh surface water, ground water, and Mobile Bay based on discharge information provided by the Industry and Human

High mobility two-dimensional electron gases in nitride heterostructures with high Al composition AlGaN alloy barriers

International Nuclear Information System (INIS)

Li Guowang; Cao Yu; Xing Huili Grace; Jena, Debdeep

2010-01-01

We report high-electron mobility nitride heterostructures with >70% Al composition AlGaN alloy barriers grown by molecular beam epitaxy. Direct growth of such AlGaN layers on GaN resulted in hexagonal trenches and a low mobility polarization-induced charge. By applying growth interruption at the heterojunction, the surface morphology improved dramatically and the room temperature two-dimensional electron gas (2DEG) mobility increased by an order of magnitude, exceeding 1300 cm 2 /V s. The 2DEG density was tunable at 0.4-3.7x10 13 /cm 2 by varying the total barrier thickness (t). Surface barrier heights of the heterostructures were extracted and exhibited dependence on t.

Extraction procedure compared to attenuation model to assess heavy metals mobility in sediments from Sepetiba Bay, Rio de Janeiro

International Nuclear Information System (INIS)

Ribeiro, Andreza Portella

2006-01-01

Sepetiba bay, located about 60 km west of the metropolitan region of Rio de Janeiro city, has undergone notable development in the last decades, with the establishment of about 400 industrial plants in its basin, basically metallurgical, which release its industrial waste either straight into the bay or through local rivers. The Sepetiba harbor also brought up a lot of industrial investment in that area. This urban and industrial expansion caused several environmental impacts, mainly due to the presence of heavy metals and other potentially toxic substances present in the effluents discharged into the bay. This work aimed to assess heavy metal (Cd, Cu, Ni, Pb e Zn) contamination and mobility in sediments from Sepetiba bay. The acid-volatile sulfides (AVS) and the concentration of simultaneously extracted metals (SIGMA[SEM) were determined in 65 sediment samples from Sepetiba bay, representing the whole area. The results obtained showed that Cd, Cu, Pb and Zn presented higher concentrations in the northeastern area (mainly in the mouth of Guandu and Canal de Sao Francisco rivers), while the highest concentration of Ni were observed in the western region of the bay. The comparison between SEM concentrations with the Canadian Sediment Quality Guidelines (TEL and PEL) indicated that Cd and Zn presented values which may hazard to aquatic organisms (concentration levels above PEL); the elements Cu, Pb and Ni presented concentration levels below PEL, suggesting low probability of toxicological effects to the aquatic organisms. On the other hand, the ratio Σ[SEM]/[AVS] was below 1 in the northeastern region, indicating that, in spite of the high concentration of the analyzed metals in this area, they are trapped in the sediment, as sulfides. The total metal concentrations in the sediments were also determined and the same distribution pattern obtained for the SEM were observed, with high concentrations in the northeastern region of the bay, classifying the area as level 2

Dielectric and barrier thickness fluctuation scattering in Al2O3/AlGaN/GaN double heterojunction high-electron mobility transistors

International Nuclear Information System (INIS)

Ji, Dong; Lu, Yanwu; Liu, Bing; Liu, Guipeng; Zhu, Qinsheng; Wang, Zhanguo

2013-01-01

The two-dimensional electron gas (2DEG) mobility limited by dielectric and barrier thickness fluctuations (TF) scattering in Al 2 O 3 /AlGaN/GaN double heterojunction high-electron mobility transistors (HEMTs) is calculated. Calculation shows that thickness fluctuation scattering is the main limitation in Al 2 O 3 /AlGaN/GaN double heterojunction HEMTs with thin Al 2 O 3 layer thicknesses. In addition, a study of 2DEG mobility as a function of 2DEG density, n s , shows that TF scattering acts as the main limitation when n s exceeds 2 × 10 12 cm −2 . The results may be used to design HEMTs to obtain higher 2DEG mobilities by modulating the dielectric layer and barrier thicknesses or 2DEG density. - Highlights: • The mobility limited by thickness fluctuation (TF) scattering is studied. • Results show that thickness fluctuation scattering is the main limitation. • Two-dimensional electron gas (2DEG) mobility is a function of 2DEG density. • TF scattering is the main limitation when 2DEG density exceeds 2 × 10 12 cm −2

2010 U.S. Geological Survey (USGS) Topographic LiDAR: Mobile Bay, AL

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — USGS Contract: G10PC00026 Task Order Number: G10PD00578 LiDAR was collected at a nominal pulse spacing of 2.0 meters for a 700 square mile area to the east of Mobile...

Examining the role of SGD on the nitrogen budget of the fourth largest estuary in the USA, Mobile Bay, Alabama

Science.gov (United States)

Dimova, N. T.; Montiel, D.; Lu, Y.; Adyasari, D.

2017-12-01

The present study aims to help understand further the importance of submarine groundwater discharge (SGD) to Mobile Bay, Alabama with respect to associated nitrogen (N-) fluxes. Based on a three-year long study we found that on a large scale, when comparing Mobile River discharge to SGD, during the dry season, the SGD flux is only 2.5% of Mobile River discharge, whereas, during the wet season, this contribution is less than 1%. However, when examining the nitrogen budget of MB, we found that during the dry season, SGD delivers about half of the fluxes to the Bay. Furthermore, we found that the distribution of these SGD-derived inputs along the MB shoreline is very heterogeneous. Shallow geophysical electrical resistivity imaging and multiple sediment cores recovered in the examined areas reveal a rich organic sediment layer (up to 80 cm thick at some locations) which is perhaps responsible for the observed enhanced N-fluxes. Ongoing microbial, DOM and stable isotope sediment examination aim to explain the geochemical processes responsible for the disproportionally large SGD-delivered nitrogen fluxes in the identified impacted coastal areas.

Characterization of Dredged Oyster Shell Deposits at Mobile Bay, Alabama Using Geophysical Methods

Directory of Open Access Journals (Sweden)

Stanley C. Nwokebuihe

2016-12-01

Full Text Available The need for disposing materials dredged from ship channels is a common problem in bays and lagoons. This study is aimed at investigating the suitability of scour features produced by dredging oyster shell deposits in Mobile Bay, Alabama, to dispose excavated channel material. A study area approximately 740 by 280 m lying about 5 km east of Gaillard Island was surveyed using underwater electrical resistivity tomography (UWERT and continuous electrical resistivity profiling (CERP tools. The geophysical survey was conducted with the intent to map scour features created by oyster shell dredging activities in the bay between 1947 and 1982. The geoelectrical surveys show that oyster beds are characterized by high resistivity values greater than 1.1 ohm.m while infilled dredge cuts show lower resistivity, generally from 0.6 to 1.1 ohm.m. The difference in resistivity mainly reflects the lithology and the consolidation of the shallow sediments: consolidated silty clay and sandy sediments rich in oyster shell deposits (with less clay content overlying unconsolidated clayey materials infilling the scours. Results show that most of the infilled dredge cuts are mostly distributed in the north-south direction. Considering that the scours are generally up to 6 m deep across the survey location, it is estimated that about 0.8 million cubic meters of oyster shells and overlying strata were dredged from the survey location.

Comparison of Different Stem Cell Mobilization Regimens in AL Amyloidosis Patients.

Science.gov (United States)

Lisenko, Katharina; Wuchter, Patrick; Hansberg, Marion; Mangatter, Anja; Benner, Axel; Ho, Anthony D; Goldschmidt, Hartmut; Hegenbart, Ute; Schönland, Stefan

2017-11-01

High-dose melphalan (HDM) and autologous blood stem cell transplantation (ABSCT) is an effective treatment for transplantation-eligible patients with systemic light chain (AL) amyloidosis. Whereas most centers use granulocyte colony-stimulating factor (G-CSF) alone for mobilization of peripheral blood stem cells (PBSC), the application of mobilization chemotherapy might offer specific advantages. We retrospectively analyzed 110 patients with AL amyloidosis who underwent PBSC collection. Major eligibility criteria included age CSF (n = 78, 71%); ifosfamide/G-CSF (n = 14, 13%); or other regimens (n = 8, 7%). AL amyloidosis patients with predominant heart involvement and/or status post heart transplantation were mobilized with G-CSF only (n = 10, 9%). PBSC collection was successful in 101 patients (92%) at first attempt. The median number of CD34 + cells was 8.7 (range, 2.1 to 45.5) × 10 6 CD34 + /kg collected in a median of 1 leukapheresis (LP) session. Compared with G-CSF-only mobilization, a chemo-mobilization with CAD/G-CSF or ifosfamide/G-CSF had a positive impact on the number of collected CD34 + cell number/kg per LP (P CSF mobilization (median CTC: grade 3; range, 1 to 4). Toxicity in patients undergoing ifosfamide/G-CSF mobilization was higher than in with those who received G-CSF-only mobilization. HDM and ABSCT were performed in 100 patients. Compared with >6.5 × 10 6 transplanted CD34 + cells/kg, an ABSCT with 1 × 10 9 /L and a reduced platelet count CSF mobilization alone is also safe and effective. Considering the hematopoietic reconstitution and long-term stem cell function, our results provide a rationale to collect and transplant as many as >6.5 × 10 6 CD34 + cells/kg, if feasible with reasonable effort. Copyright © 2017 The American Society for Blood and Marrow Transplantation. Published by Elsevier Inc. All rights reserved.

Top-down control of phytoplankton by oysters in Chesapeake Bay, USA: Comment on Pomeroy et al. (2006)

Science.gov (United States)

Pomeroy et al. (2006) proposed that temporal and spatial mismatches between eastern oyster filtration and phytoplankton abundance will preclude restored stocks of eastern oysters from reducing the severity of hypoxia in the deep channel of central Chesapeake Bay. We refute this c...

Simultaneous enhancement of carrier mobility and concentration via tailoring of Al-chemical states in Al-ZnO thin films

Energy Technology Data Exchange (ETDEWEB)

Kumar, Manish, E-mail: manishk@skku.edu; Wen, Long; Sahu, Bibhuti B. [Center for Advance Plasma Surface Technology (CAPST), NU-SKKU Joint Institute for Plasma-Nano Materials (IPNM), School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon-440746 (Korea, Republic of); Han, Jeon Geon [Center for Advance Plasma Surface Technology (CAPST), NU-SKKU Joint Institute for Plasma-Nano Materials (IPNM), School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon-440746 (Korea, Republic of); Department of Industrial Engineering, Faculty of Engineering, Chiang Mai University, Chiang Mai-50200 (Thailand)

2015-06-15

Simultaneously achieving higher carriers concentration and mobility is a technical challenge against up-scaling the transparent-conductive performances of transparent-conductive oxides. Utilizing one order higher dense (∼1 × 10{sup 11} cm{sup −3}) plasmas (in comparison to the conventional direct current plasmas), highly c-axis oriented Al-doped ZnO films have been prepared with precise control over relative composition and chemical states of constituting elements. Tailoring of intrinsic (O vacancies) and extrinsic (ionic Al and zero-valent Al) dopants provide simultaneous enhancement in mobility and concentration of charge carriers. Room-temperature resistivity as low as 4.89 × 10{sup −4} Ω cm along the carrier concentration 5.6 × 10{sup 20} cm{sup −3} is obtained in 200 nm thick transparent films. Here, the control of atomic Al reduces the charge trapping at grain boundaries and subdues the effects of grain boundary scattering. A mechanism based on the correlation between electron-hole interaction and carrier mobility is proposed for degenerately doped wide band-gap semiconductors.

Characteristics in AlN/AlGaN/GaN Multilayer-Structured High-Electron-Mobility Transistors

International Nuclear Information System (INIS)

Gui-Zhou, Hu; Ling, Yang; Li-Yuan, Yang; Si, Quan; Shou-Gao, Jiang; Ji-Gang, Ma; Xiao-Hua, Ma; Yue, Hao

2010-01-01

A new multilayer-structured AlN/AlGaN/GaN heterostructure high-electron-mobility transistor (HEMT) is demonstrated. The AlN/AlGaN/GaN HEMT exhibits the maximum drain current density of 800 mA/mm and the maximum extrinsic transconductance of 170 mS/mm. Due to the increase of the distance between the gate and the two-dimensional electron-gas channel, the threshold voltage shifts slightly to the negative. The reduced drain current collapse and higher breakdown voltage are observed on this AlN/AlGaN/GaN HEMT. The current gain cut-off frequency and the maximum frequency of oscillation are 18.5 GHz and 29.0 GHz, respectively. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Analysis of dissolved oxygen stress in oysters in Mobile Bay from 2010-05-26 to 1010-09-21 (NODC Accession 0125573)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Hatchery-reared adult and juvenile oysters were placed at 0.1 m and 1.0 m above bottom at Sand Reef and Denton Reef, Mobile Bay, Alabama between May 26 and Sep 21,...

Diffusivities and atomic mobilities in Cu-rich fcc Al-Cu-Mn alloys

Energy Technology Data Exchange (ETDEWEB)

Yin, Ming; Du, Yong; Cui, Senlin; Xu, Honghui; Liu, Shuhong [Central South Univ., Changsha (China). State Key Laboratory of Powder Metallurgy; Zhang, Lijun [Bochum Univ. (DE). Interdisciplinary Centre for Advanced Materials Simulation (ICAMS)

2012-07-15

Via solid-solid diffusion couples, electron probe microanalysis and the Whittle and Green method, interdiffusivities in fcc Al-Cu-Mn alloys at 1 123 K were measured. The reliability of the obtained diffusivities is validated by comparing the computed diffusivities with literature data plus constraints among the diffusivities. Through assessments of experimentally determined diffusion coefficients by means of a diffusion-controlled transformations simulation package, the atomic mobilities of Al, Cu, and Mn in fcc Al-Cu-Mn alloys are obtained. Comprehensive comparisons between the model-predicted and the experimental data indicate that the presently obtained atomic mobilities can reproduce most of the diffusivities, concentration profiles, and diffusion paths reasonably. (orig.)

Sediment Characterization in St. Alban's Bay, VT

Science.gov (United States)

Nethercutt, S.; Manley, T.; Manley, P.

2017-12-01

St. Alban's Bay within Lake Champlain is plagued with harmful algal blooms. With future intensification due to climate change, a multidisciplinary program (BREE-Basin Resilience to Extreme Events) was initiated in 2016. In order to assess the mobilization of harmful nutrients from sediment resuspension events and riverine input, 74 sediment samples were collected in a grid fashion throughout St. Alban's Bay. Sediments were deflocculated and analyzed using a LA920 Horiba laser scattering particle size distribution analyzer to define the frequency of sediment sizes from clay to sand. Gridded surfaces of mean sortable silt percentage, silt percentage, sand percentage, and clay percentage were used to represent the sediment distribution of the region. A plot of diameter versus frequency showed the bimodal nature of some of the sediments, with one peak at about 10 microns diameter (silt) and the second at about 525 microns diameter (sand). The data showed an extremely low percentage of clay relative to that of sand and silt. The highest frequencies of sortable silt, which represents the most easily mobilized particle size, are found in the deepest areas of the bay, suggesting that these regions are where dominant bottom flow occurs. The high occurrence of sortable silt in the St. Alban's Bay does suggest that sediment mobilization, and therefore nutrient mobilization has the potential to occur. These data combined with high-resolution multibeam and hydrodynamic data will allow for future models of water flow and remobilization studies in the future.

Temperature dependence of ballistic mobility in a metamorphic InGaAs/InAlAs high electron mobility transistor

International Nuclear Information System (INIS)

Lee, Jongkyong; Gang, Suhyun; Jo, Yongcheol; Kim, Jongmin; Woo, Hyeonseok; Han, Jaeseok; Kim, Hyungsang; Im, Hyunsik

2014-01-01

We have investigated the temperature dependence of ballistic mobility in a 100 nm-long InGaAs/InAlAs metamorphic high-electron-mobility transistor designed for millimeter-wavelength RF applications. To extract the temperature dependence of quasi-ballistic mobility, our experiment involves measurements of the effective mobility in the low-bias linear region of the transistor and of the collision-dominated Hall mobility using a gated Hall bar of the same epitaxial structure. The data measured from the experiment are consistent with that of modeled ballistic mobility based on ballistic transport theory. These results advance the understanding of ballistic transport in various transistors with a nano-scale channel length that is comparable to the carrier's mean free path in the channel.

Consideration of vertical uncertainty in elevation-based sea-level rise assessments: Mobile Bay, Alabama case study

Science.gov (United States)

Gesch, Dean B.

2013-01-01

The accuracy with which coastal topography has been mapped directly affects the reliability and usefulness of elevationbased sea-level rise vulnerability assessments. Recent research has shown that the qualities of the elevation data must be well understood to properly model potential impacts. The cumulative vertical uncertainty has contributions from elevation data error, water level data uncertainties, and vertical datum and transformation uncertainties. The concepts of minimum sealevel rise increment and minimum planning timeline, important parameters for an elevation-based sea-level rise assessment, are used in recognition of the inherent vertical uncertainty of the underlying data. These concepts were applied to conduct a sea-level rise vulnerability assessment of the Mobile Bay, Alabama, region based on high-quality lidar-derived elevation data. The results that detail the area and associated resources (land cover, population, and infrastructure) vulnerable to a 1.18-m sea-level rise by the year 2100 are reported as a range of values (at the 95% confidence level) to account for the vertical uncertainty in the base data. Examination of the tabulated statistics about land cover, population, and infrastructure in the minimum and maximum vulnerable areas shows that these resources are not uniformly distributed throughout the overall vulnerable zone. The methods demonstrated in the Mobile Bay analysis provide an example of how to consider and properly account for vertical uncertainty in elevation-based sea-level rise vulnerability assessments, and the advantages of doing so.

Harmful Algal Blooms in the Mississippi Sound and Mobile Bay: Using MODIS Aqua and In Situ Data for HABs in the Northern Gulf of Mexico

National Research Council Canada - National Science Library

Holiday, Dan; Carter, Gregory; Gould, Richard W; MacIntyre, Hugh

2007-01-01

.... Phytoplankton populations and in situ water quality were monitored at 3 to 6 week intervals at 17 locations in Mobile Bay and the Mississippi Sound beginning in July 2005 and continuing thru June...

Correlation Between Two-Dimensional Electron Gas Mobility and Crystal Quality in AlGaN/GaN High-Electron-Mobility Transistor Structure Grown on 4H-SiC.

Science.gov (United States)

Heo, Cheon; Jang, Jongjin; Lee, Kyngjae; So, Byungchan; Lee, Kyungbae; Ko, Kwangse; Nam, Okhyun

2017-01-01

We investigated the correlation between the crystal quality and two-dimensional electron gas (2DEG) mobility of an AlGaN/GaN high-electron-mobility transistor (HEMT) structure grown by metal-organic chemical vapor deposition. For the structure with an AlN nucleation layer grown at 1100 °C, the 2DEG mobility and sheet carrier density were 1627 cm²/V·s and 3.23 × 10¹³ cm⁻², respectively, at room temperature. Further, it was confirmed that the edge dislocation density of the GaN buffer layer was related to the 2DEG mobility and sheet carrier density in the AlGaN/GaN HEMT.

Use of Land Use Land Cover Change Mapping Products in Aiding Coastal Habitat Conservation and Restoration Efforts of the Mobile Bay NEP

Science.gov (United States)

Spruce, Joseph P.; Swann, Roberta; Smooth, James

2010-01-01

The Mobile Bay region has undergone significant land use land cover change (LULC) over the last 35 years, much of which is associated with urbanization. These changes have impacted the region s water quality and wildlife habitat availability. In addition, much of the region is low-lying and close to the Gulf, which makes the region vulnerable to hurricanes, climate change (e.g., sea level rise), and sometimes man-made disasters such as the Deepwater Horizon (DWH) oil spill. Land use land cover change information is needed to help coastal zone managers and planners to understand and mitigate the impacts of environmental change on the region. This presentation discusses selective results of a current NASA-funded project in which Landsat data over a 34-year period (1974-2008) is used to produce, validate, refine, and apply land use land cover change products to aid coastal habitat conservation and restoration needs of the Mobile Bay National Estuary Program (MB NEP). The project employed a user defined classification scheme to compute LULC change mapping products for the entire region, which includes the majority of Mobile and Baldwin counties. Additional LULC change products have been computed for select coastal HUC-12 sub-watersheds adjacent to either Mobile Bay or the Gulf of Mexico, as part of the MB NEP watershed profile assessments. This presentation will include results of additional analyses of LULC change for sub-watersheds that are currently high priority areas, as defined by MB NEP. Such priority sub-watersheds include those that are vulnerable to impacts from the DWH oil spill, as well as sub-watersheds undergoing urbanization. Results demonstrating the nature and permanence of LULC change trends for these higher priority sub-watersheds and results characterizing change for the entire 34-year period and at approximate 10-year intervals across this period will also be presented. Future work will include development of value-added coastal habitat quality

Carbon doped GaAs/AlGaAs heterostructures with high mobility two dimensional hole gas

Energy Technology Data Exchange (ETDEWEB)

Hirmer, Marika; Bougeard, Dominique; Schuh, Dieter [Institut fuer Experimentelle und Angewandte Physik, Universitaet Regensburg, D 93040 Regensburg (Germany); Wegscheider, Werner [Laboratorium fuer Festkoerperphysik, ETH Zuerich, 8093 Zuerich (Switzerland)

2011-07-01

Two dimensional hole gases (2DHG) with high carrier mobilities are required for both fundamental research and possible future ultrafast spintronic devices. Here, two different types of GaAs/AlGaAs heterostructures hosting a 2DHG were investigated. The first structure is a GaAs QW embedded in AlGaAs barrier grown by molecular beam epitaxy with carbon-doping only at one side of the quantum well (QW) (single side doped, ssd), while the second structure is similar but with symmetrically arranged doping layers on both sides of the QW (double side doped, dsd). The ssd-structure shows hole mobilities up to 1.2*10{sup 6} cm{sup 2}/Vs which are achieved after illumination. In contrast, the dsd-structure hosts a 2DHG with mobility up to 2.05*10{sup 6} cm{sup 2}/Vs. Here, carrier mobility and carrier density is not affected by illuminating the sample. Both samples showed distinct Shubnikov-de-Haas oscillations and fractional quantum-Hall-plateaus in magnetotransport experiments done at 20mK, indicating the high quality of the material. In addition, the influence of different temperature profiles during growth and the influence of the Al content of the barrier Al{sub x}Ga{sub 1-x}As on carrier concentration and mobility were investigated and are presented here.

High electron mobility recovery in AlGaN/GaN 2DEG channels regrown on etched surfaces

International Nuclear Information System (INIS)

Chan, Silvia H; DenBaars, Steven P; Keller, Stacia; Tahhan, Maher; Li, Haoran; Romanczyk, Brian; Mishra, Umesh K

2016-01-01

This paper reports high two-dimensional electron gas mobility attained from the regrowth of the AlGaN gating layer on ex situ GaN surfaces. To repair etch-damaged GaN surfaces, various pretreatments were conducted via metalorganic chemical vapor deposition, followed by a regrown AlGaN/GaN mobility test structure to evaluate the extent of recovery. The developed treatment process that was shown to significantly improve the electron mobility consisted of a N 2  + NH 3 pre-anneal plus an insertion of a 4 nm or thicker GaN interlayer prior to deposition of the AlGaN gating layer. Using the optimized process, a high electron mobility transistor (HEMT) device was fabricated which exhibited a high mobility of 1450 cm 2 V −1 s −1 (R sh  = 574 ohm/sq) and low dispersion characteristics. The additional inclusion of an in situ Al 2 O 3 dielectric into the regrowth process for MOS-HEMTs still preserved the transport properties near etch-impacted areas. (paper)

Electron mobility and drift velocity in selectively doped InAlAs/InGaAs/InAlAs heterostructures

International Nuclear Information System (INIS)

Vasil’evskii, I. S.; Galiev, G. B.; Klimov, E. A.; Požela, K.; Požela, J.; Jucienė, V.; Sužiedėlis, A.; Žurauskienė, N.; Keršulis, S.; Stankevič, V.

2011-01-01

An increase in the electron mobility and drift velocity in high electric fields in quantum wells of selectively doped InAlAs/InGaAs/InAsAs heterostructures is obtained experimentally via controlling the composition of semiconductors forming the interface. The electron mobility at the interface in the In 0.8 Ga 0.2 As/In 0.7 Al 0.3 As metamorphic structure with a high molar fraction of In (0.7–0.8) is as high as 12.3 × 10 3 cm 2 V −1 s −1 at room temperature. An increase in the electron mobility by a factor of 1.1–1.4 is attained upon the introduction of thin (1–3 nm) InAs layers into a quantum well of selectively doped In 0.53 Ga 0.47 As/In 0.52 Al 0.48 As heterostructures. A maximal drift velocity attains 2.5 × 10 7 cm/s in electric fields of 2–5 kV/cm. The threshold field F th for the intervalley Γ-L electron transfer (the Gunn effect) in the InGaAs quantum well is higher than in the bulk material by a factor of 2.5–3. The effect of two- to threefold decrease in the threshold field F th in the InGaAs quantum well is established upon increasing the molar fraction of In in the InAlAs barrier, as well as upon the introduction of thin InAs inserts into the InGaAs quantum well.

Charge carrier mobility and electronic properties of Al(Op3: impact of excimer formation

Directory of Open Access Journals (Sweden)

Andrea Magri

2015-05-01

Full Text Available We have studied the electronic properties and the charge carrier mobility of the organic semiconductor tris(1-oxo-1H-phenalen-9-olatealuminium(III (Al(Op3 both experimentally and theoretically. We experimentally estimated the HOMO and LUMO energy levels to be −5.93 and −3.26 eV, respectively, which were close to the corresponding calculated values. Al(Op3 was successfully evaporated onto quartz substrates and was clearly identified in the absorption spectra of both the solution and the thin film. A structured steady state fluorescence emission was detected in solution, whereas a broad, red-shifted emission was observed in the thin film. This indicates the formation of excimers in the solid state, which is crucial for the transport properties. The incorporation of Al(Op3 into organic thin film transistors (TFTs was performed in order to measure the charge carrier mobility. The experimental setup detected no electron mobility, while a hole mobility between 0.6 × 10−6 and 2.1 × 10−6 cm2·V−1·s−1 was measured. Theoretical simulations, on the other hand, predicted an electron mobility of 9.5 × 10−6 cm2·V−1·s−1 and a hole mobility of 1.4 × 10−4 cm2·V−1·s−1. The theoretical simulation for the hole mobility predicted an approximately one order of magnitude higher hole mobility than was observed in the experiment, which is considered to be in good agreement. The result for the electron mobility was, on the other hand, unexpected, as both the calculated electron mobility and chemical common sense (based on the capability of extended aromatic structures to efficiently accept and delocalize additional electrons suggest more robust electron charge transport properties. This discrepancy is explained by the excimer formation, whose inclusion in the multiscale simulation workflow is expected to bring the theoretical simulation and experiment into agreement.

Effect of Al/N ratio during nucleation layer growth on Hall mobility and buffer leakage of molecular-beam epitaxy grown AlGaN/GaN heterostructures

International Nuclear Information System (INIS)

Storm, D.F.; Katzer, D.S.; Binari, S.C.; Shanabrook, B.V.; Zhou Lin; Smith, David J.

2004-01-01

AlGaN/GaN high electron mobility transistor structures have been grown by plasma-assisted molecular beam epitaxy on semi-insulating 4H-SiC utilizing an AlN nucleation layer. The electron Hall mobility of these structures increases from 1050 cm 2 /V s to greater than 1450 cm 2 /V s when the Al/N flux ratio during the growth of the nucleation layer is increased from 0.90 to 1.07. Buffer leakage currents increase abruptly by nearly three orders of magnitude when the Al/N ratio increases from below to above unity. Transmission electron microscopy indicates that high buffer leakage is correlated with the presence of stacking faults in the nucleation layer and cubic phase GaN in the buffer, while low mobilities are correlated with high dislocation densities

Fabrication of enhancement-mode AlGaN/GaN high electron mobility transistors using double plasma treatment

Energy Technology Data Exchange (ETDEWEB)

Lim, Jong-Won, E-mail: jwlim@etri.re.kr [Photonic/Wireless Convergence Components Dept., IT Materials and Components Lab., Electronics and Telecommunications Research Institute, Daejeon 305-700 (Korea, Republic of); Ahn, Ho-Kyun; Kim, Seong-il; Kang, Dong-Min; Lee, Jong-Min; Min, Byoung-Gue; Lee, Sang-Heung; Yoon, Hyung-Sup; Ju, Chull-Won; Kim, Haecheon; Mun, Jae-Kyoung; Nam, Eun-Soo [Photonic/Wireless Convergence Components Dept., IT Materials and Components Lab., Electronics and Telecommunications Research Institute, Daejeon 305-700 (Korea, Republic of); Park, Hyung-Moo [Photonic/Wireless Convergence Components Dept., IT Materials and Components Lab., Electronics and Telecommunications Research Institute, Daejeon 305-700 (Korea, Republic of); Division of Electronics and Electrical Engineering, Dongguk University, Seoul (Korea, Republic of)

2013-11-29

We report the fabrication and DC and microwave characteristics of 0.5 μm AlGaN/GaN high electron mobility transistors using double plasma treatment process. Silicon nitride layers 700 and 150 Å thick were deposited by plasma-enhanced chemical vapor deposition at 260 °C to protect the device and to define the gate footprint. The double plasma process was carried out by two different etching techniques to obtain enhancement-mode AlGaN/GaN high electron mobility transistors with 0.5 μm gate lengths. The enhancement-mode AlGaN/GaN high electron mobility transistor was prepared in parallel to the depletion-mode AlGaN/GaN high electron mobility transistor device on one wafer. Completed double plasma treated 0.5 μm AlGaN/GaN high electron mobility transistor devices fabricated by dry etching exhibited a peak transconductance, gm, of 330 mS/mm, a breakdown voltage of 115 V, a current-gain cutoff frequency (f{sub T}) of 18 GHz, and a maximum oscillation frequency (f{sub max}) of 66 GHz. - Highlights: • The double plasma process was carried out by two different etching techniques. • Double plasma treated device exhibited a transconductance of 330 mS/mm. • Completed 0.5 μm gate device exhibited a current-gain cutoff frequency of 18 GHz. • The off-state breakdown voltage of 115 V for 0.5 μm gate device was obtained. • Continuous-wave output power density of 4.3 W/mm was obtained at 2.4 GHz.

Fabrication of enhancement-mode AlGaN/GaN high electron mobility transistors using double plasma treatment

International Nuclear Information System (INIS)

Lim, Jong-Won; Ahn, Ho-Kyun; Kim, Seong-il; Kang, Dong-Min; Lee, Jong-Min; Min, Byoung-Gue; Lee, Sang-Heung; Yoon, Hyung-Sup; Ju, Chull-Won; Kim, Haecheon; Mun, Jae-Kyoung; Nam, Eun-Soo; Park, Hyung-Moo

2013-01-01

We report the fabrication and DC and microwave characteristics of 0.5 μm AlGaN/GaN high electron mobility transistors using double plasma treatment process. Silicon nitride layers 700 and 150 Å thick were deposited by plasma-enhanced chemical vapor deposition at 260 °C to protect the device and to define the gate footprint. The double plasma process was carried out by two different etching techniques to obtain enhancement-mode AlGaN/GaN high electron mobility transistors with 0.5 μm gate lengths. The enhancement-mode AlGaN/GaN high electron mobility transistor was prepared in parallel to the depletion-mode AlGaN/GaN high electron mobility transistor device on one wafer. Completed double plasma treated 0.5 μm AlGaN/GaN high electron mobility transistor devices fabricated by dry etching exhibited a peak transconductance, gm, of 330 mS/mm, a breakdown voltage of 115 V, a current-gain cutoff frequency (f T ) of 18 GHz, and a maximum oscillation frequency (f max ) of 66 GHz. - Highlights: • The double plasma process was carried out by two different etching techniques. • Double plasma treated device exhibited a transconductance of 330 mS/mm. • Completed 0.5 μm gate device exhibited a current-gain cutoff frequency of 18 GHz. • The off-state breakdown voltage of 115 V for 0.5 μm gate device was obtained. • Continuous-wave output power density of 4.3 W/mm was obtained at 2.4 GHz

Plasma-assisted Molecular Beam Epitaxy of N-polar InAlN-barrier High-electron-mobility Transistors.

Science.gov (United States)

Hardy, Matthew T; Storm, David F; Katzer, D Scott; Downey, Brian P; Nepal, Neeraj; Meyer, David J

2016-11-24

Plasma-assisted molecular beam epitaxy is well suited for the epitaxial growth of III-nitride thin films and heterostructures with smooth, abrupt interfaces required for high-quality high-electron-mobility transistors (HEMTs). A procedure is presented for the growth of N-polar InAlN HEMTs, including wafer preparation and growth of buffer layers, the InAlN barrier layer, AlN and GaN interlayers and the GaN channel. Critical issues at each step of the process are identified, such as avoiding Ga accumulation in the GaN buffer, the role of temperature on InAlN compositional homogeneity, and the use of Ga flux during the AlN interlayer and the interrupt prior to GaN channel growth. Compositionally homogeneous N-polar InAlN thin films are demonstrated with surface root-mean-squared roughness as low as 0.19 nm and InAlN-based HEMT structures are reported having mobility as high as 1,750 cm 2 /V∙sec for devices with a sheet charge density of 1.7 x 10 13 cm -2 .

Demonstration of InAlN/AlGaN high electron mobility transistors with an enhanced breakdown voltage by pulsed metal organic chemical vapor deposition

Energy Technology Data Exchange (ETDEWEB)

Xue, JunShuai, E-mail: junshuaixue@hotmail.com; Zhang, JinCheng; Hao, Yue [Key Laboratory of Wide Band Gap Semiconductor Materials and Devices, School of Microelectronics, Xidian University, Xi' an 710071 (China)

2016-01-04

In this work, InAlN/AlGaN heterostructures employing wider bandgap AlGaN instead of conventional GaN channel were grown on sapphire substrate by pulsed metal organic chemical vapor deposition, where the nominal Al composition in InAlN barrier and AlGaN channel were chosen to be 83% and 5%, respectively, to achieve close lattice-matched condition. An electron mobility of 511 cm{sup 2}/V s along with a sheet carrier density of 1.88 × 10{sup 13 }cm{sup −2} were revealed in the prepared heterostructures, both of which were lower compared with lattice-matched InAlN/GaN due to increased intrinsic alloy disorder scattering resulting from AlGaN channel and compressively piezoelectric polarization in barrier, respectively. While the high electron mobility transistor (HEMT) processed on these structures not only exhibited a sufficiently high drain output current density of 854 mA/mm but also demonstrated a significantly enhanced breakdown voltage of 87 V, which is twice higher than that of reported InAlN/GaN HEMT with the same device dimension, potential characteristics for high-voltage operation of GaN-based electronic devices.

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.

Growth optimization and characterization of high mobility two-dimensional electron systems in AlAs quantum wells

Energy Technology Data Exchange (ETDEWEB)

Dasgupta, Shivaji

2009-02-15

In this work two-dimensional electron systems (2DESs) based on AlAs/AlGaAs heterostructures doped with Si are investigated. The electrons are confined in AlAs quantum wells (QWs) sandwiched between AlGaAs buffers. Analytical calculations and simulations for AlAs QWs are presented in the first chapter. The results show a cross-over width, above which the wide (001)-oriented QWs show double valley occupancy and wide (110)-oriented QWs show single valley occupancy. We solve the Schroedinger equation analytically for anisotropic masses. The solution shows the orientation dependence of the elliptical cyclotron orbit due to the anisotropic mass. We also present an introduction to the Landau level crossings based on g{sup *}m{sup *} product. In the next chapter, we present experimental results for the double-valley (001)-oriented AlAs QWs. We present the different structures of the deep AlAs QWs along with the low temperature magnetotransport data for these QWs. Thereafter, we present the results on shallow AlAs QWs. We achieved a mobility of 4.2 x 10{sup 5} cm{sup 2}/Vs at 330 mK for the deep backside doped AlAs QW. For the shallow QWs, we achieved a mobility of2.3 x 10{sup 5} cm{sup 2}/Vs at 330 mK, for a density of 2.9 x 10{sup 11} cm{sup -2}. From the magneto-transport data, we see evidence of the double-valley occupation for the (001)-oriented AlAs wide QWs. In the next chapter, we present experimental results for the single-valley (110)-oriented AlAs QWs. We deduced the donor binding energy and the doping efficiency for this facet from a doping series of double-sided doped QWs. Thereafter, we designed different structures for the (110)-oriented AlAs QWs, which we present along with their respective low temperature magneto-transport data. We measured one of the double-sided doped AlAs QWs at very high magnetic fields and low temperatures, down to 60 mK. At the end of the chapter, we present a spike feature observed in the magneto-transport data of these QWs. This

Electron density and currents of AlN/GaN high electron mobility transistors with thin GaN/AlN buffer layer

Energy Technology Data Exchange (ETDEWEB)

Bairamis, A.; Zervos, Ch.; Georgakilas, A., E-mail: alexandr@physics.uoc.gr [Microelectronics Research Group, IESL, Foundation for Research and Technology-Hellas (FORTH), P.O. Box 1385, GR-71110 Heraklion, Crete (Greece); Department of Physics, University of Crete, P.O. Box 2208, GR-71003 Heraklion, Crete (Greece); Adikimenakis, A.; Kostopoulos, A.; Kayambaki, M.; Tsagaraki, K.; Konstantinidis, G. [Microelectronics Research Group, IESL, Foundation for Research and Technology-Hellas (FORTH), P.O. Box 1385, GR-71110 Heraklion, Crete (Greece)

2014-09-15

AlN/GaN high electron mobility transistor (HEMT) structures with thin GaN/AlN buffer layer have been analyzed theoretically and experimentally, and the effects of the AlN barrier and GaN buffer layer thicknesses on two-dimensional electron gas (2DEG) density and transport properties have been evaluated. HEMT structures consisting of [300 nm GaN/ 200 nm AlN] buffer layer on sapphire were grown by plasma-assisted molecular beam epitaxy and exhibited a remarkable agreement with the theoretical calculations, suggesting a negligible influence of the crystalline defects that increase near the heteroepitaxial interface. The 2DEG density varied from 6.8 × 10{sup 12} to 2.1 × 10{sup 13} cm{sup −2} as the AlN barrier thickness increased from 2.2 to 4.5 nm, while a 4.5 nm AlN barrier would result to 3.1 × 10{sup 13} cm{sup −2} on a GaN buffer layer. The 3.0 nm AlN barrier structure exhibited the highest 2DEG mobility of 900 cm{sup 2}/Vs for a density of 1.3 × 10{sup 13} cm{sup −2}. The results were also confirmed by the performance of 1 μm gate-length transistors. The scaling of AlN barrier thickness from 1.5 nm to 4.5 nm could modify the drain-source saturation current, for zero gate-source voltage, from zero (normally off condition) to 0.63 A/mm. The maximum drain-source current was 1.1 A/mm for AlN barrier thickness of 3.0 nm and 3.7 nm, and the maximum extrinsic transconductance was 320 mS/mm for 3.0 nm AlN barrier.

Electron density and currents of AlN/GaN high electron mobility transistors with thin GaN/AlN buffer layer

International Nuclear Information System (INIS)

Bairamis, A.; Zervos, Ch.; Georgakilas, A.; Adikimenakis, A.; Kostopoulos, A.; Kayambaki, M.; Tsagaraki, K.; Konstantinidis, G.

2014-01-01

AlN/GaN high electron mobility transistor (HEMT) structures with thin GaN/AlN buffer layer have been analyzed theoretically and experimentally, and the effects of the AlN barrier and GaN buffer layer thicknesses on two-dimensional electron gas (2DEG) density and transport properties have been evaluated. HEMT structures consisting of [300 nm GaN/ 200 nm AlN] buffer layer on sapphire were grown by plasma-assisted molecular beam epitaxy and exhibited a remarkable agreement with the theoretical calculations, suggesting a negligible influence of the crystalline defects that increase near the heteroepitaxial interface. The 2DEG density varied from 6.8 × 10 12 to 2.1 × 10 13 cm −2 as the AlN barrier thickness increased from 2.2 to 4.5 nm, while a 4.5 nm AlN barrier would result to 3.1 × 10 13 cm −2 on a GaN buffer layer. The 3.0 nm AlN barrier structure exhibited the highest 2DEG mobility of 900 cm 2 /Vs for a density of 1.3 × 10 13 cm −2 . The results were also confirmed by the performance of 1 μm gate-length transistors. The scaling of AlN barrier thickness from 1.5 nm to 4.5 nm could modify the drain-source saturation current, for zero gate-source voltage, from zero (normally off condition) to 0.63 A/mm. The maximum drain-source current was 1.1 A/mm for AlN barrier thickness of 3.0 nm and 3.7 nm, and the maximum extrinsic transconductance was 320 mS/mm for 3.0 nm AlN barrier.

Surface morphology of Al0.3Ga0.7N/Al2O3-high electron mobility transistor structure.

Science.gov (United States)

Cörekçi, S; Usanmaz, D; Tekeli, Z; Cakmak, M; Ozçelik, S; Ozbay, E

2008-02-01

We present surface properties of buffer films (AIN and GaN) and Al0.3Gao.zN/Al2O3-High Electron Mobility Transistor (HEMT) structures with/without AIN interlayer grown on High Temperature (HT)-AIN buffer/Al2O3 substrate and Al2O3 substrate. We have found that the GaN surface morphology is step-flow in character and the density of dislocations was about 10(8)-10(9) cm(-2). The AFM measurements also exhibited that the presence of atomic steps with large lateral step dimension and the surface of samples was smooth. The lateral step sizes are in the range of 100-250 nm. The typical rms values of HEMT structures were found as 0.27, 0.30, and 0.70 nm. HT-AIN buffer layer can have a significant impact on the surface morphology of Al0.3Ga0.7N/Al2O3-HEMT structures.

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.

Increasing rock-avalanche size and mobility in Glacier Bay National Park and Preserve, Alaska detected from 1984 to 2016 Landsat imagery

Science.gov (United States)

Coe, Jeffrey A.; Bessette-Kirton, Erin; Geertsema, Marten

2018-01-01

In the USA, climate change is expected to have an adverse impact on slope stability in Alaska. However, to date, there has been limited work done in Alaska to assess if changes in slope stability are occurring. To address this issue, we used 30-m Landsat imagery acquired from 1984 to 2016 to establish an inventory of 24 rock avalanches in a 5000-km2 area of Glacier Bay National Park and Preserve in southeast Alaska. A search of available earthquake catalogs revealed that none of the avalanches were triggered by earthquakes. Analyses of rock-avalanche magnitude, mobility, and frequency reveal a cluster of large (areas ranging from 5.5 to 22.2 km2), highly mobile (height/length slopes for failure during periods of warm temperatures.

Development of an atomic mobility database for liquid phase in multicomponent Al alloys. Focusing on binary systems

Energy Technology Data Exchange (ETDEWEB)

Wang, Shaoqing; Du, Yong; Zhang, Lijun [Central South Univ., Changsha, Hunan (China). State Key Laboratory of Powder Metallurgy; Liu, Dandan [Central South Univ., Changsha, Hunan (China). State Key Laboratory of Powder Metallurgy; Central South Univ., Changsha, Hunan (China). School of Materials Science and Engineering; Chen, Qing; Engstroem, Anders [Thermo-Calc Software AB, Stockholm (Sweden)

2013-08-15

An atomic mobility database for binary liquid phase in multicomponent Al-Cu-Fe-Mg-Mn-Ni-Si-Zn alloys was established based on critically reviewed experimental and theoretical diffusion data by using DICTRA (Diffusion Controlled TRAnsformation) software. The impurity diffusivities of the elements with limited experimental data are obtained by means of the least-squares method and semi-empirical correlations. Comprehensive comparisons between the calculated and measured diffusivities indicate that most of the reported diffusivities can be well reproduced by the currently obtained atomic mobilities. The reliability of this diffusivity database is further validated by comparing the simulated concentration profiles with the measured ones, as well as the measured main inter-diffusion coefficients of liquid Al-Cu-Zn alloys with the extrapolated ones from the present binary atomic mobility database. The approach is of general validity and applicable to establish mobility databases of other liquid alloys. (orig.)

First principles calculation of point defects and mobility degradation in bulk AlSb for radiation detection application

International Nuclear Information System (INIS)

Lordi, V; Aberg, D; Erhart, P; Wu, K J

2007-01-01

The development of high resolution, room temperature semiconductor radiation detectors requires the introduction of materials with increased carrier mobility-lifetime (μτ) product, while having a band gap in the 1.4-2.2 eV range. AlSb is a promising material for this application. However, systematic improvements in the material quality are necessary to achieve an adequate μτ product. We are using a combination of simulation and experiment to develop a fundamental understanding of the factors which affect detector material quality. First principles calculations are used to study the microscopic mechanisms of mobility degradation from point defects and to calculate the intrinsic limit of mobility from phonon scattering. We use density functional theory (DFT) to calculate the formation energies of native and impurity point defects, to determine their equilibrium concentrations as a function of temperature and charge state. Perturbation theory via the Born approximation is coupled with Boltzmann transport theory to calculate the contribution toward mobility degradation of each type of point defect, using DFT-computed carrier scattering rates. A comparison is made to measured carrier concentrations and mobilities from AlSb crystals grown in our lab. We find our predictions in good quantitative agreement with experiment, allowing optimized annealing conditions to be deduced. A major result is the determination of oxygen impurity as a severe mobility killer, despite the ability of oxygen to compensation dope AlSb and reduce the net carrier concentration. In this case, increased resistivity is not a good indicator of improved material performance, due to the concomitant sharp reduction in μτ

Dredging Operations Technical Support Program: Engineering Design and Environmental Assessment of Dredged Material Overflow from Hydraulically Filled Hopper Barges in Mobile Bay, Alabama

Science.gov (United States)

1990-09-01

turbid estuarine habitats such as Mobile Bay are very tolerant of moderately high concentrations of suspended sediments and thin layers of sediment...GULF OF MEXIC BAYOU 4M 2CAE SI2LTK Fiur 3. DsrbuinoAedmnTyesi oie a fo IsphordingLT anCLmb190 PART III: DREDGING EQUIPMENT AND OPERATIONAL TECHNIQUES...increase in ambient turbidity was noted. Water samples were collected at surface, middepth, and bottom. The sampling boats proceeded across their

Analysis of atomic mobility in a Cu38Zr46Ag8Al8 bulk metallic glass

International Nuclear Information System (INIS)

Qiao, J.C.; Pelletier, J.M.

2013-01-01

Highlights: ► Atomic mobility in Cu 38 Zr 46 Ag 8 Al 8 bulk metallic glass have been investigated by DMA. ► Loss factor is directly connected to the energy lost during application of the stress. ► Structural relaxation and crystallization induces a decrease of the atomic mobility. ► The concentration of quasi-point defects links to atomic mobility in metallic glasses. - Abstract: Atomic mobility in as-cast and annealed Cu 38 Zr 46 Ag 8 Al 8 bulk metallic glass samples is analyzed by performing dynamic mechanical analysis. The loss factor is directly connected to the energy lost during application of the stress. Structural relaxation process and crystallization lead to a decrease of the atomic mobility in the bulk metallic glass. A physical model, based on the concept of quasi point defects is introduced, to describe the atomic mobility. Movements in amorphous materials are correlated. The correlation factor χ reflects the atomic mobility in bulk metallic glasses: structural relaxation and crystallization lead to a decrease of χ, implying the reduction of atomic mobility. The evolution of elastic, visco-elastic and viscoplastic components after structural relaxation and partial crystallization state during the mechanical response has been obtained. Compared with as-cast state, structural relaxation induced an increase of elastic component and a decrease of visco-elastic component in the metallic glass.

Remote interfacial dipole scattering and electron mobility degradation in Ge field-effect transistors with GeOx/Al2O3 gate dielectrics

International Nuclear Information System (INIS)

Wang, Xiaolei; Xiang, Jinjuan; Wang, Shengkai; Wang, Wenwu; Zhao, Chao; Ye, Tianchun; Xiong, Yuhua; Zhang, Jing

2016-01-01

Remote Coulomb scattering (RCS) on electron mobility degradation is investigated experimentally in Ge-based metal–oxide–semiconductor field-effect-transistors (MOSFETs) with GeO x /Al 2 O 3 gate stacks. It is found that the mobility increases with greater GeO x thickness (7.8–20.8 Å). The physical origin of this mobility dependence on GeO x thickness is explored. The following factors are excluded: Coulomb scattering due to interfacial traps at GeO x /Ge, phonon scattering, and surface roughness scattering. Therefore, the RCS from charges in gate stacks is studied. The charge distributions in GeO x /Al 2 O 3 gate stacks are evaluated experimentally. The bulk charges in Al 2 O 3 and GeO x are found to be negligible. The density of the interfacial charge is  +3.2  ×  10 12 cm −2 at the GeO x /Ge interface and  −2.3  ×  10 12 cm −2 at the Al 2 O 3 /GeO x interface. The electric dipole at the Al 2 O 3 /GeO x interface is found to be  +0.15 V, which corresponds to an areal charge density of 1.9  ×  10 13 cm −2 . The origin of this mobility dependence on GeO x thickness is attributed to the RCS due to the electric dipole at the Al 2 O 3 /GeO x interface. This remote dipole scattering is found to play a significant role in mobility degradation. The discovery of this new scattering mechanism indicates that the engineering of the Al 2 O 3 /GeO x interface is key for mobility enhancement and device performance improvement. These results are helpful for understanding and engineering Ge mobility enhancement. (paper)

High mobility AlGaN/GaN devices for β"−-dosimetry

International Nuclear Information System (INIS)

Schmid, Martin; Howgate, John; Ruehm, Werner; Thalhammer, Stefan

2016-01-01

There is a high demand in modern medical applications for dosimetry sensors with a small footprint allowing for unobtrusive or high spatial resolution detectors. To this end we characterize the sensoric response of radiation resistant high mobility AlGaN/GaN semiconductor devices when exposed to β"−-emitters. The samples were operated as a floating gate transistor, without a field effect gate electrode, thus excluding any spurious effects from β"−-particle interactions with a metallic surface covering. We demonstrate that the source–drain current is modulated in dependence on the kinetic energy of the incident β"−-particles. Here, the signal is shown to have a linear dependence on the absorbed energy calculated from Monte Carlo simulations. Additionally, a stable and reproducible sensor performance as a β"−-dose monitor is shown for individual radioisotopes. Our experimental findings and the characteristics of the AlGaN/GaN high mobility layered devices indicate their potential for future applications where small sensor size is necessary, like for instance brachytherapy.

Molecular gated-AlGaN/GaN high electron mobility transistor for pH detection.

Science.gov (United States)

Ding, Xiangzhen; Yang, Shuai; Miao, Bin; Gu, Le; Gu, Zhiqi; Zhang, Jian; Wu, Baojun; Wang, Hong; Wu, Dongmin; Li, Jiadong

2018-04-18

A molecular gated-AlGaN/GaN high electron mobility transistor has been developed for pH detection. The sensing surface of the sensor was modified with 3-aminopropyltriethoxysilane to provide amphoteric amine groups, which would play the role of receptors for pH detection. On modification with 3-aminopropyltriethoxysilane, the transistor exhibits good chemical stability in hydrochloric acid solution and is sensitive for pH detection. Thus, our molecular gated-AlGaN/GaN high electron mobility transistor acheived good electrical performances such as chemical stability (remained stable in hydrochloric acid solution), good sensitivity (37.17 μA/pH) and low hysteresis. The results indicate a promising future for high-quality sensors for pH detection.

Investigation of AlGaN/GaN high electron mobility transistor structures on 200-mm silicon (111) substrates employing different buffer layer configurations.

Science.gov (United States)

Lee, H-P; Perozek, J; Rosario, L D; Bayram, C

2016-11-21

AlGaN/GaN high electron mobility transistor (HEMT) structures are grown on 200-mm diameter Si(111) substrates by using three different buffer layer configurations: (a) Thick-GaN/3 × {Al x Ga 1-x N}/AlN, (b) Thin-GaN/3 × {Al x Ga 1-x N}/AlN, and (c) Thin-GaN/AlN, so as to have crack-free and low-bow (GaN HEMT structures. The effects of buffer layer stacks (i.e. thickness and content) on defectivity, stress, and two-dimensional electron gas (2DEG) mobility and 2DEG concentration are reported. It is shown that 2DEG characteristics are heavily affected by the employed buffer layers between AlGaN/GaN HEMT structures and Si(111) substrates. Particularly, we report that in-plane stress in the GaN layer affects the 2DEG mobility and 2DEG carrier concentration significantly. Buffer layer engineering is shown to be essential for achieving high 2DEG mobility (>1800 cm 2 /V∙s) and 2DEG carrier concentration (>1.0 × 10 13  cm -2 ) on Si(111) substrates.

Remote interfacial dipole scattering and electron mobility degradation in Ge field-effect transistors with GeO x /Al2O3 gate dielectrics

Science.gov (United States)

Wang, Xiaolei; Xiang, Jinjuan; Wang, Shengkai; Wang, Wenwu; Zhao, Chao; Ye, Tianchun; Xiong, Yuhua; Zhang, Jing

2016-06-01

Remote Coulomb scattering (RCS) on electron mobility degradation is investigated experimentally in Ge-based metal-oxide-semiconductor field-effect-transistors (MOSFETs) with GeO x /Al2O3 gate stacks. It is found that the mobility increases with greater GeO x thickness (7.8-20.8 Å). The physical origin of this mobility dependence on GeO x thickness is explored. The following factors are excluded: Coulomb scattering due to interfacial traps at GeO x /Ge, phonon scattering, and surface roughness scattering. Therefore, the RCS from charges in gate stacks is studied. The charge distributions in GeO x /Al2O3 gate stacks are evaluated experimentally. The bulk charges in Al2O3 and GeO x are found to be negligible. The density of the interfacial charge is  +3.2  ×  1012 cm-2 at the GeO x /Ge interface and  -2.3  ×  1012 cm-2 at the Al2O3/GeO x interface. The electric dipole at the Al2O3/GeO x interface is found to be  +0.15 V, which corresponds to an areal charge density of 1.9  ×  1013 cm-2. The origin of this mobility dependence on GeO x thickness is attributed to the RCS due to the electric dipole at the Al2O3/GeO x interface. This remote dipole scattering is found to play a significant role in mobility degradation. The discovery of this new scattering mechanism indicates that the engineering of the Al2O3/GeO x interface is key for mobility enhancement and device performance improvement. These results are helpful for understanding and engineering Ge mobility enhancement.

Interface States in AlGaN/GaN Metal-Insulator-Semiconductor High Electron Mobility Transistors

International Nuclear Information System (INIS)

Feng Qian; Du Kai; Li Yu-Kun; Shi Peng; Feng Qing

2013-01-01

Frequency-dependent capacitance and conductance measurements are performed on AlGaN/GaN high electron mobility transistors (HEMTs) and NbAlO/AlGaN/GaN metal-insulator-semiconductor HEMTs (MISHEMTs) to extract density and time constants of the trap states at NbAlO/AlGaN interface and gate/AlGaN interface with the gate-voltage biased into the accumulation region and that at the AlGaN/GaN interface with the gate-voltage biased into the depletion region in different circuit models. The measurement results indicate that the trap density at NbAlO/AlGaN interface is about one order lower than that at gate/AlGaN interface while the trap density at AlGaN/GaN interface is in the same order, so the NbAlO film can passivate the AlGaN surface effectively, which is consistent with the current collapse results

Simulation study of InAlN/GaN high-electron mobility transistor with AlInN back barrier

International Nuclear Information System (INIS)

Han Tie-Cheng; Zhao Hong-Dong; Yang Lei; Wang Yang

2017-01-01

In this work, we use a 3-nm-thick Al 0.64 In 0.36 N back-barrier layer in In 0.17 Al 0.83 N/GaN high-electron mobility transistor (HEMT) to enhance electron confinement. Based on two-dimensional device simulations, the influences of Al 0.64 In 0.36 N back-barrier on the direct-current (DC) and radio-frequency (RF) characteristics of InAlN/GaN HEMT are investigated, theoretically. It is shown that an effective conduction band discontinuity of approximately 0.5 eV is created by the 3-nm-thick Al 0.64 In 0.36 N back-barrier and no parasitic electron channel is formed. Comparing with the conventional InAlN/GaN HEMT, the electron confinement of the back-barrier HEMT is significantly improved, which allows a good immunity to short-channel effect (SCE) for gate length decreasing down to 60 nm (9-nm top barrier). For a 70-nm gate length, the peak current gain cut-off frequency ( f T ) and power gain cut-off frequency ( f max ) of the back-barrier HEMT are 172 GHz and 217 GHz, respectively, which are higher than those of the conventional HEMT with the same gate length. (paper)

Analysis of current instabilities of thin AlN/GaN/AlN double heterostructure high electron mobility transistors

International Nuclear Information System (INIS)

Zervos, Ch; Adikimenakis, A; Bairamis, A; Kostopoulos, A; Kayambaki, M; Tsagaraki, K; Konstantinidis, G; Georgakilas, A

2016-01-01

The current instabilities of high electron mobility transistors (HEMTs), based on thin double AlN/GaN/AlN heterostructures (∼0.5 μm total thickness), directly grown on sapphire substrates, have been analyzed and compared for different AlN top barrier thicknesses. The structures were capped by 1 nm GaN and non-passivated 1 μm gate-length devices were processed. Pulsed I–V measurements resulted in a maximum cold pulsed saturation current of 1.4 A mm −1 at a gate-source voltage of +3 V for 3.7 nm AlN thickness. The measured gate and drain lag for 500 ns pulse-width varied between 6%–12% and 10%–18%, respectively. Furthermore, a small increase in the threshold voltage was observed for all the devices, possibly due to the trapping of electrons under the gate contact. The off-state breakdown voltage of V br  = 70 V, for gate-drain spacing of 2 μm, was approximately double the value measured for a single AlN/GaN HEMT structure grown on a thick GaN buffer layer. The results suggest that the double AlN/GaN/AlN heterostructures may offer intrinsic advantages for the breakdown and current stability characteristics of high current HEMTs. (paper)

Greenhouse Gas Source Detection and Attribution in the San Francisco Bay Area of California Using a Mobile Measurement Platform

Science.gov (United States)

Martien, P. T.; Guha, A.; Newman, S.; Young, A.; Bower, J.; Perkins, I.; Randall, S.; Stevenson, E.; Hilken, H.

2017-12-01

The Bay Area Air Quality Management District, the San Francisco Bay Area's air quality regulatory agency, has set a goal to reduce the region's greenhouse gas (GHG) emissions 80% below 1990 levels by 2050, consistent with the State of California's climate goals. Recently, the Air District's governing board adopted a 2017 Clean Air Plan advancing the agency's vision and including actions to put the region on a path to achieving the 2050 goal while also reducing air pollution and related health impacts. The Plan includes GHG rule-making efforts, policy initiatives, local government partnerships, outreach, grants and incentives, encompassing over 250 specific implementation actions across all economic sectors to effect ambitious emission reductions in the region. To support the 2017 Plan, the Air District has built a mobile measurement platform (GHG research van) to perform targeted CH4 emissions hotspot detection and source attribution. Instruments in the van measure CH4, CO2 and N2O in ambient plumes. Coincident measurements of source tracers like isotopic methane (13C - CH4), CO and ethane (C2H6) provide the capability to distinguish between biogenic, combustion-based and fossil-based fugitive methane sources. We report observations of CH4 plumes from source-specific measurements in and around facilities including a wastewater treatment plant, a composting operation, a waste-to-energy anaerobic digestion plant and a few refineries. We performed leak surveys inside several electric utility-operated facilities including a power plant and an underground natural gas storage facility. We sampled exhaust from a roadway tunnel and computed fleet-averaged automobile-related CH4 and N2O emission factors. We used tracer-to-tracer emission ratios to create chemical signatures of emissions from each sampled source category. We compare measurement-based ratios with those used to derive the regional GHG inventory. Data from these and other sources will lead to an improved

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.

High mobility AlGaN/GaN devices for β{sup −}-dosimetry

Energy Technology Data Exchange (ETDEWEB)

Schmid, Martin; Howgate, John; Ruehm, Werner [Helmholtz Zentrum München, Ingolstädter Landstraße 1, 85764 Neuherberg (Germany); Thalhammer, Stefan, E-mail: stefan.thalhammer@physik.uni-augsburg.de [Universität Augsburg, Universitätsstraße 1, 86159 Augsburg (Germany)

2016-05-21

There is a high demand in modern medical applications for dosimetry sensors with a small footprint allowing for unobtrusive or high spatial resolution detectors. To this end we characterize the sensoric response of radiation resistant high mobility AlGaN/GaN semiconductor devices when exposed to β{sup −}-emitters. The samples were operated as a floating gate transistor, without a field effect gate electrode, thus excluding any spurious effects from β{sup −}-particle interactions with a metallic surface covering. We demonstrate that the source–drain current is modulated in dependence on the kinetic energy of the incident β{sup −}-particles. Here, the signal is shown to have a linear dependence on the absorbed energy calculated from Monte Carlo simulations. Additionally, a stable and reproducible sensor performance as a β{sup −}-dose monitor is shown for individual radioisotopes. Our experimental findings and the characteristics of the AlGaN/GaN high mobility layered devices indicate their potential for future applications where small sensor size is necessary, like for instance brachytherapy.

An examination of historic inorganic sedimentation and organic matter accumulation in several marsh types within the Mobile Bay and and Mobile-Tensaw River Delta region

Science.gov (United States)

Smith, Christopher G.; Osterman, Lisa E.; Poore, Richard Z.

2013-01-01

Mass accumulation rates (MAR; g cm-2 y-1), linear sedimentation rates (LSR; cm y-1), and core geochronology derived from excess lead-210 (210Pb) profiles and inventories measured in six sediment cores collected from marsh sites from the MobileTensaw River Delta and Mobile Bay region record the importance of both continuous and event-driven inorganic sedimentation over the last 120 years. MAR in freshwater marshes varied considerably between sites and through time (0.24 and 1.31 g cm-2 y-1). The highest MARs occurred in the 1950s and 1960s and correspond to record discharge events along the Mobile and Tensaw Rivers. In comparison, MAR at salt marsh sites increased almost threefold over the last 120 years (0.05 to 0.18 g cm-2 y-1 or 0.23 to 0.48 cm y-1). From 1880 to 1960, organic accumulation remained fairly constant (20%), while intermittent pulses of high inorganic sedimentation were observed following 1960. The pulses in inorganic sedimentation coincide with several major hurricanes (e.g., Hurricanes Camille, Fredric, Georges, and Ivan). The nearly threefold increase in MAR in salt marshes during the last 120 years would thus appear to be partially dependent on inorganic sedimentation from storm events. This study shows that while hurricanes, floods, and other natural hazards are well-known threats to human infrastructure and coastal ecosystems, these events also transport sediment to marshes that help abate other pressures such as sea-level rise (SLR) and subsidence.

Very high channel conductivity in low-defect AlN/GaN high electron mobility transistor structures

International Nuclear Information System (INIS)

Dabiran, A. M.; Wowchak, A. M.; Osinsky, A.; Xie, J.; Hertog, B.; Cui, B.; Chow, P. P.; Look, D. C.

2008-01-01

Low defect AlN/GaN high electron mobility transistor (HEMT) structures, with very high values of electron mobility (>1800 cm 2 /V s) and sheet charge density (>3x10 13 cm -2 ), were grown by rf plasma-assisted molecular beam epitaxy (MBE) on sapphire and SiC, resulting in sheet resistivity values down to ∼100 Ω/□ at room temperature. Fabricated 1.2 μm gate devices showed excellent current-voltage characteristics, including a zero gate saturation current density of ∼1.3 A/mm and a peak transconductance of ∼260 mS/mm. Here, an all MBE growth of optimized AlN/GaN HEMT structures plus the results of thin-film characterizations and device measurements are presented

AL FIKR AL BALAGHI FI AL MA’ĂNI ‘INDA AS SAKĂKI FI KITABIHI MIFTAHUL ULUM DIRĂSAH BALAGHIYYAH

Directory of Open Access Journals (Sweden)

Talqis Nurdianto

2018-02-01

Full Text Available Miftāhul ‘Ulūm, written by al-Sakākī, especially the third part, was the beginning of a new phase in the development of Arabic rhetoric. Al-Sakākī divided the rhetoric into three fields of study, which are  (1 Ma’ānī, (2 Bayān, (3 Badī’. However, his style is influenced by philosophers, theologians and their verbal lexicon, which are difficult to take, especially for the ordinary recipient. Al-Sakākī described that his book containing several types of literature, namely, ‘ilm ṣarf in complete version and its conclusion, derivation science, and the grammatical study in the completeness of Ma’ānī and Bayān. The meaning of Makna is the study of completeness and conclusion. Therefore, books and prose, and poem require al-‘Arūḍ and al-Qawāfī include Ṣarf, Grammar, Ma’ānī, Bayān, limitation, reasoning, al’Arūḍ, and al-Qawāfī. He argued that the fields of study were influential in delivering knowledge to the student in order to reach the goal of the author towards his book.This research was an analytical descriptive study of al-Sakākī rhetoric that focused on the normative aspect represented by rhetorical rule and aesthetic aspects. Those aspects were shown by the feeling. Al-Sakākī rhetoric thought is a method based on mental division and has conducted in the construction of many factors, which the most important of them are philosophy and logic. Keywords: thought, rhetoric, meanings, sakkaki, study

Degradation of AlGaN/GaN High Electron Mobility Transistors with Different AlGaN Layer Thicknesses under Strong Electric Field

International Nuclear Information System (INIS)

Ling, Yang; Yue, Hao; Xiao-Hua, Ma; Jing-Jing, Ma; Cheng, Zhu

2010-01-01

The degradation of AlGaN/GaN high electron mobility transistors (HEMTs) has a close relationship with a model of traps in AlGaN barriers as a result of high electric field. We mainly discuss the impacts of strong electrical field on the AlGaN barrier thickness of AlGaN/GaN HEMTs. It is found that the device with a thin AlGaN barrier layer is more easily degraded. We study the degradation of four parameters, i.e. the gate series resistance R Gate , channel resistance R channel , gate current I G,off at V GS = −5 and V DS = 0.1 V, and drain current I D,max at V GS = 2 and V DS = 5 V. In addition, the degradation mechanisms of the device electrical parameters are also investigated in detail. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Bay breeze climatology at two sites along the Chesapeake bay from 1986-2010: Implications for surface ozone.

Science.gov (United States)

Stauffer, Ryan M; Thompson, Anne M

Hourly surface meteorological measurements were coupled with surface ozone (O 3 ) mixing ratio measurements at Hampton, Virginia and Baltimore, Maryland, two sites along the Chesapeake Bay in the Mid-Atlantic United States, to examine the behavior of surface O 3 during bay breeze events and quantify the impact of the bay breeze on local O 3 pollution. Analyses were performed for the months of May through September for the years 1986 to 2010. The years were split into three groups to account for increasingly stringent environmental regulations that reduced regional emissions of nitrogen oxides (NO x ): 1986-1994, 1995-2002, and 2003-2010. Each day in the 25-year record was marked either as a bay breeze day, a non-bay breeze day, or a rainy/cloudy day based on the meteorological data. Mean eight hour (8-h) averaged surface O 3 values during bay breeze events were 3 to 5 parts per billion by volume (ppbv) higher at Hampton and Baltimore than on non-bay breeze days in all year periods. Anomalies from mean surface O 3 were highest in the afternoon at both sites during bay breeze days in the 2003-2010 study period. In conjunction with an overall lowering of baseline O 3 after the 1995-2002 period, the percentage of total exceedances of the Environmental Protection Agency (EPA) 75 ppbv 8-h O 3 standard that occurred on bay breeze days increased at Hampton for 2003-2010, while remaining steady at Baltimore. These results suggest that bay breeze circulations are becoming more important to causing exceedance events at particular sites in the region, and support the hypothesis of Martins et al. (2012) that highly localized meteorology increasingly drives air quality events at Hampton.

AlGaN/GaN high-electron-mobility transistors with transparent gates by Al-doped ZnO

International Nuclear Information System (INIS)

Wang Chong; He Yun-Long; Zheng Xue-Feng; Ma Xiao-Hua; Zhang Jin-Cheng; Hao Yue

2013-01-01

AlGaN/GaN high-electron-mobility transistors (HEMTs) with Al-doped ZnO (AZO) transparent gate electrodes are fabricated, and Ni/Au/Ni-gated HEMTs are produced in comparison. The AZO-gated HEMTs show good DC characteristics and Schottky rectifying characteristics, and the gate electrodes achieve excellent transparencies. Compared with Ni/Au/Ni-gated HEMTs, AZO-gated HEMTs show a low saturation current, high threshold voltage, high Schottky barrier height, and low gate reverse leakage current. Due to the higher gate resistivity, AZO-gated HEMTs exhibit a current—gain cutoff frequency (f T ) of 10 GHz and a power gain cutoff frequency (f max ) of 5 GHz, and lower maximum oscillation frequency than Ni/Au/Ni-gated HEMTs. Moreover, the C—V characteristics are measured and the gate interface characteristics of the AZO-gated devices are investigated by a C—V dual sweep

High mobility AlGaN/GaN heterostructures grown on Si substrates using a large lattice-mismatch induced stress control technology

International Nuclear Information System (INIS)

Cheng, Jianpeng; Yang, Xuelin; Sang, Ling; Guo, Lei; Hu, Anqi; Xu, Fujun; Tang, Ning; Wang, Xinqiang; Shen, Bo

2015-01-01

A large lattice-mismatch induced stress control technology with a low Al content AlGaN layer has been used to grow high quality GaN layers on 4-in. Si substrates. The use of this technology allows for high mobility AlGaN/GaN heterostructures with electron mobility of 2040 cm 2 /(V·s) at sheet charge density of 8.4 × 10 12  cm −2 . Strain relaxation and dislocation evolution mechanisms have been investigated. It is demonstrated that the large lattice mismatch between the low Al content AlGaN layer and AlN buffer layer could effectively promote the edge dislocation inclination with relatively large bend angles and therefore significantly reduce the dislocation density in the GaN epilayer. Our results show a great potential for fabrication of low-cost and high performance GaN-on-Si power devices

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.

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.

Current linearity and operation stability in Al2O3-gate AlGaN/GaN MOS high electron mobility transistors

Science.gov (United States)

Nishiguchi, Kenya; Kaneki, Syota; Ozaki, Shiro; Hashizume, Tamotsu

2017-10-01

To investigate current linearity and operation stability of metal-oxide-semiconductor (MOS) AlGaN/GaN high electron mobility transistors (HEMTs), we have fabricated and characterized the Al2O3-gate MOS-HEMTs without and with a bias annealing in air at 300 °C. Compared with the as-fabricated (unannealed) MOS HEMTs, the bias-annealed devices showed improved linearity of I D-V G curves even in the forward bias regime, resulting in increased maximum drain current. Lower subthreshold slope was also observed after bias annealing. From the precise capacitance-voltage analysis on a MOS diode fabricated on the AlGaN/GaN heterostructure, it was found that the bias annealing effectively reduced the state density at the Al2O3/AlGaN interface. This led to efficient modulation of the AlGaN surface potential close to the conduction band edge, resulting in good gate control of two-dimensional electron gas density even at forward bias. In addition, the bias-annealed MOS HEMT showed small threshold voltage shift after applying forward bias stress and stable operation even at high temperatures.

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.

Metal concentrations in Kandalaksha Bay, White Sea (Russia) following the spring snowmelt

International Nuclear Information System (INIS)

Cobelo-Garcia, A.; Millward, G.E.; Prego, R.; Lukashin, V.

2006-01-01

Elevated concentrations of dissolved and particulate Cd, Cu, Pb and Zn have been determined in the waters of Kandalaksha Bay (White Sea, Russia), following the ice melt in the spring of 2000. Dissolved metal maxima in the surface waters were observed at some stations and concentrations generally decreased with depth. The suspended particulate matter (SPM) comprised a non-lithogenic fraction in the range 12-83%, and had elevated metal concentrations that showed no trend with depth or salinity and was compositionally distinct from the sediments. A log-linear relationship existed between the concentrations of metals in sediments and in SPM and their respective Al concentrations, indicating a source of metal-rich particles, with low Al content, to the Bay. The results suggest that Kandalaksha Bay has been impacted by industrial activity on the Kola Peninsula and that restricted water exchange will hinder its recovery from metal contamination. - Elevated dissolved and particulate metal concentrations have been determined in the water column of Kandalaksha Bay, White Sea (Russia)

Room-temperature mobility above 2200 cm{sup 2}/V·s of two-dimensional electron gas in a sharp-interface AlGaN/GaN heterostructure

Energy Technology Data Exchange (ETDEWEB)

Chen, Jr-Tai, E-mail: jrche@ifm.liu.se; Persson, Ingemar; Nilsson, Daniel; Hsu, Chih-Wei; Palisaitis, Justinas; Forsberg, Urban; Persson, Per O. Å.; Janzén, Erik [Department of Physics, Chemistry, and Biology, Linköping University, SE 581 83 Linköping (Sweden)

2015-06-22

A high mobility of 2250 cm{sup 2}/V·s of a two-dimensional electron gas (2DEG) in a metalorganic chemical vapor deposition-grown AlGaN/GaN heterostructure was demonstrated. The mobility enhancement was a result of better electron confinement due to a sharp AlGaN/GaN interface, as confirmed by scanning transmission electron microscopy analysis, not owing to the formation of a traditional thin AlN exclusion layer. Moreover, we found that the electron mobility in the sharp-interface heterostructures can sustain above 2000 cm{sup 2}/V·s for a wide range of 2DEG densities. Finally, it is promising that the sharp-interface AlGaN/GaN heterostructure would enable low contact resistance fabrication, less impurity-related scattering, and trapping than the AlGaN/AlN/GaN heterostructure, as the high-impurity-contained AlN is removed.

Growth parameter optimization and interface treatment for enhanced electron mobility in heavily strained GaInAs/AlInAs high electron mobility transistor structures

International Nuclear Information System (INIS)

Fedoryshyn, Yuriy; Ostinelli, Olivier; Alt, Andreas; Pallin, Angel; Bolognesi, Colombo R.

2014-01-01

The optimization of heavily strained Ga 0.25 In 0.75 As/Al 0.48 In 0.52 As high electron mobility transistor structures is discussed in detail. The growth parameters and the channel layer interfaces were optimized in order to maximize the mobility of the two-dimensional electron gas. Structures composed of an 11 nm thick channel layer and a 4 nm thick spacer layer exhibited electron mobilities as high as 15 100 cm 2 /Vs and 70 000 cm 2 /Vs at 300 and 77 K, respectively, for channels including InAs strained layers. The sheet carrier density was kept above 2.5 × 10 12  cm −2 throughout the entire study

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.

Arsenic removal from contaminated brackish sea water by sorption onto Al hydroxides and Fe phases mobilized by land-use.

Science.gov (United States)

Yu, Changxun; Peltola, Pasi; Nystrand, Miriam I; Virtasalo, Joonas J; Österholm, Peter; Ojala, Antti E K; Hogmalm, Johan K; Åström, Mats E

2016-01-15

This study examines the spatial and temporal distribution patterns of arsenic (As) in solid and aqueous materials along the mixing zone of an estuary, located in the south-eastern part of the Bothnian Bay and fed by a creek running through an acid sulfate (AS) soil landscape. The concentrations of As in solution form (<1 kDa) increase steadily from the creek mouth to the outer estuary, suggesting that inflowing seawater, rather than AS soil, is the major As source in the estuary. In sediments at the outer estuary, As was accumulated and diagenetically cycled in the surficial layers, as throughout much of the Bothnian Bay. In contrast, in sediments in the inner estuary, As concentrations and accumulation rates showed systematical peaks at greater depths. These peaks were overall consistent with the temporal trend of past As discharges from the Rönnskär smelter and the accompanied As concentrations in past sea-water of the Bothnian Bay, pointing to a connection between the historical smelter activities and the sediment-bound As in the inner estuary. However, the concentrations and accumulation rates of As peaked at depths where the smelter activities had already declined, but a large increase in the deposition of Al hydroxides and Fe phases occurred in response to intensified land-use in the mid 1960's and early 1970's. This correspondence suggests that, apart from the inflowing As-contaminated seawater, capture by Al hydroxides, Fe hydroxides and Fe-organic complexes is another important factor for As deposition in the inner estuary. After accumulating in the sediment, the solid-phase As was partly remobilized, as reflected by increased pore-water As concentrations, a process favored by As(V) reduction and high concentrations of dissolved organic matter. Copyright © 2015 Elsevier B.V. All rights reserved.

Control of short-channel effects in InAlN/GaN high-electron mobility transistors using graded AlGaN buffer

Science.gov (United States)

Han, Tiecheng; Zhao, Hongdong; Peng, Xiaocan; Li, Yuhai

2018-04-01

A graded AlGaN buffer is designed to realize the p-type buffer by inducing polarization-doping holes. Based on the two-dimensional device simulator, the effect of the graded AlGaN buffer on the direct-current (DC) and radio-frequency (RF) performance of short-gate InAlN/GaN high-electron mobility transistors (HEMTs) are investigated, theoretically. Compared to standard HEMT, an enhancement of electron confinement and a good control of short-channel effect (SCEs) are demonstrated in the graded AlGaN buffer HEMT. Accordingly, the pinched-off behavior and the ability of gate modulation are significantly improved. And, no serious SCEs are observed in the graded AlGaN buffer HEMT with an aspect ratio (LG/tch) of about 6.7, much lower than that of the standard HEMT (LG/tch = 13). In addition, for a 70-nm gate length, a peak current gain cutoff frequency (fT) of 171 GHz and power gain cutoff frequency (fmax) of 191 GHz are obtained in the grade buffer HEMT, which are higher than those of the standard one with the same gate length.

Evaluating Bay Area Methane Emission Inventory

Energy Technology Data Exchange (ETDEWEB)

Fischer, Marc [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Jeong, Seongeun [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

2016-03-01

As a regulatory agency, evaluating and improving estimates of methane (CH4) emissions from the San Francisco Bay Area is an area of interest to the Bay Area Air Quality Management District (BAAQMD). Currently, regional, state, and federal agencies generally estimate methane emissions using bottom-up inventory methods that rely on a combination of activity data, emission factors, biogeochemical models and other information. Recent atmospheric top-down measurement estimates of methane emissions for the US as a whole (e.g., Miller et al., 2013) and in California (e.g., Jeong et al., 2013; Peischl et al., 2013) have shown inventories underestimate total methane emissions by ~ 50% in many areas of California, including the SF Bay Area (Fairley and Fischer, 2015). The goal of this research is to provide information to help improve methane emission estimates for the San Francisco Bay Area. The research effort builds upon our previous work that produced methane emission maps for each of the major source sectors as part of the California Greenhouse Gas Emissions Measurement (CALGEM) project (http://calgem.lbl.gov/prior_emission.html; Jeong et al., 2012; Jeong et al., 2013; Jeong et al., 2014). Working with BAAQMD, we evaluate the existing inventory in light of recently published literature and revise the CALGEM CH4 emission maps to provide better specificity for BAAQMD. We also suggest further research that will improve emission estimates. To accomplish the goals, we reviewed the current BAAQMD inventory, and compared its method with those from the state inventory from the California Air Resources Board (CARB), the CALGEM inventory, and recent published literature. We also updated activity data (e.g., livestock statistics) to reflect recent changes and to better represent spatial information. Then, we produced spatially explicit CH4 emission estimates on the 1-km modeling grid used by BAAQMD. We present the detailed activity data, methods and derived emission maps by sector

Investigation of trap states in high Al content AlGaN/GaN high electron mobility transistors by frequency dependent capacitance and conductance analysis

International Nuclear Information System (INIS)

Zhu, Jie-Jie; Ma, Xiao-Hua; Hou, Bin; Chen, Wei-Wei; Hao, Yue

2014-01-01

Trap states in Al 0.55 Ga 0.45 N/GaN Schottky-gate high-electron-mobility transistors (S-HEMTs) and Al 2 O 3 /Al 0.55 Ga 0.45 N/GaN metal-oxide-semiconductor HEMTs (MOS-HEMTs) were investigated with conductance method in this paper. Surface states with time constant of (0.09–0.12) μs were found in S-HEMTs, and electron tunneling rather than emission was deemed to be the dominant de-trapping mechanism due to the high electric field in high Al content barrier. The density of surface states evaluated in S-HEMTs was (1.02–4.67)×10 13 eV −1 ·cm −2 . Al 2 O 3 gate insulator slightly reduced the surface states, but introduced low density of new traps with time constant of (0.65–1.29) μs into MOS-HEMTs

USGS Tampa Bay Pilot Study

Science.gov (United States)

Yates, K.K.; Cronin, T. M.; Crane, M.; Hansen, M.; Nayeghandi, A.; Swarzenski, P.; Edgar, T.; Brooks, G.R.; Suthard, B.; Hine, A.; Locker, S.; Willard, D.A.; Hastings, D.; Flower, B.; Hollander, D.; Larson, R.A.; Smith, K.

2007-01-01

Many of the nation's estuaries have been environmentally stressed since the turn of the 20th century and will continue to be impacted in the future. Tampa Bay, one the Gulf of Mexico's largest estuaries, exemplifies the threats that our estuaries face (EPA Report 2001, Tampa Bay Estuary Program-Comprehensive Conservation and Management Plan (TBEP-CCMP)). More than 2 million people live in the Tampa Bay watershed, and the population constitutes to grow. Demand for freshwater resources, conversion of undeveloped areas to resident and industrial uses, increases in storm-water runoff, and increased air pollution from urban and industrial sources are some of the known human activities that impact Tampa Bay. Beginning on 2001, additional anthropogenic modifications began in Tampa Bat including construction of an underwater gas pipeline and a desalinization plant, expansion of existing ports, and increased freshwater withdrawal from three major tributaries to the bay. In January of 2001, the Tampa Bay Estuary Program (TBEP) and its partners identifies a critical need for participation from the U.S. Geological Survey (USGS) in providing multidisciplinary expertise and a regional-scale, integrated science approach to address complex scientific research issue and critical scientific information gaps that are necessary for continued restoration and preservation of Tampa Bay. Tampa Bay stakeholders identified several critical science gaps for which USGS expertise was needed (Yates et al. 2001). These critical science gaps fall under four topical categories (or system components): 1) water and sediment quality, 2) hydrodynamics, 3) geology and geomorphology, and 4) ecosystem structure and function. Scientists and resource managers participating in Tampa Bay studies recognize that it is no longer sufficient to simply examine each of these estuarine system components individually, Rather, the interrelation among system components must be understood to develop conceptual and

Investigation of surface related leakage current in AlGaN/GaN High Electron Mobility Transistors

Energy Technology Data Exchange (ETDEWEB)

Kaushik, J.K., E-mail: janeshkaushik@sspl.drdo.in [Solid State Physics Laboratory, Delhi 110054 (India); Balakrishnan, V.R.; Mongia, D.; Kumar, U.; Dayal, S. [Solid State Physics Laboratory, Delhi 110054 (India); Panwar, B.S. [Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016 (India); Muralidharan, R. [Indian Institute of Science, Bengaluru, Karnataka 560012 (India)

2016-08-01

This paper reports the study of surface-related mechanisms to explain the high reverse leakage current observed in the in-house fabricated Si{sub 3}N{sub 4} passivated AlGaN/GaN High Electron Mobility Transistors. We propose that the Si{sub 3}N{sub 4}/AlGaN interface in the un-gated regions provides an additional leakage path between the gate and source/drain and may constitute a large component of reverse current. This surface related leakage component of current exhibits both temperature and electric field dependence and its Arrhenius behavior has been experimentally verified using Conductance Deep Level Transient Spectroscopy and temperature dependent reverse leakage current measurements. A thin interfacial amorphous semiconductor layer formed due to inter diffusion at Si{sub 3}N{sub 4}/AlGaN interface has been presumed as the source for this surface related leakage. We, therefore, conclude that optimum Si{sub 3}N{sub 4} deposition conditions and careful surface preparation prior to passivation can limit the extent of surface leakage and can thus vastly improve the device performance. - Highlights: • Enhanced leakage in AlGaN/GaN High Electron Mobility Transistors after passivation • Experimental evidence of the presence of extrinsic traps at Si{sub 3}N{sub 4}/AlGaN interface • Electron hopping in shallower extended defects and band tail traps at the interface. • Reduction in current collapse due to the virtual gate inhibition by this conduction • However, limitation on the operating voltages due to decrease in breakdown voltage.

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.

Development and status of the AL Mixed Waste Treatment Plan or I love that mobile unit of mine

International Nuclear Information System (INIS)

Bounini, L.; Williams, M.; Zygmunt, S.

1995-01-01

Nine Department of Energy (DOE) sites reporting to the Albuquerque Office (AL) have mixed waste that is chemically hazardous and radioactive. The hazardous waste regulations require the chemical portion of mixed waste to be to be treated to certain standards. The total volume of low-level mixed waste at the nine sites is equivalent to 7,000 drums, with individual site volumes ranging from 1 gallon of waste at the Pinellas Plant to 4,500 drums at Los Alamos National Laboratory. Nearly all the sites have a diversity of wastes requiring a diversity of treatment processes. Treatment capacity does not exist for much of this waste, and it would be expensive for each site to build the diversity of treatment processes needed to treat its own wastes. DOE-AL assembled a team that developed the AL Mixed Waste Treatment Plan that uses the resources of the nine sites to treat the waste at the sites. Work on the plan started in October 1993, and the plan was finalized in March 1994. The plan uses commercial treatment, treatability studies, and mobile treatment units. The plan specifies treatment technologies that will be built as mobile treatment units to be moved from site to site. Mobile units include bench-top units for very small volumes and treatability studies, drum-size units that treat one drum per day, and skid-size units that handle multiple drum volumes. After the tools needed to treat the wastes were determined, the sites were assigned to provide part of the treatment capacity using their own resources and expertise. The sites are making progress on treatability studies, commercial treatment, and mobile treatment design and fabrication. To date, this is the only plan for treating waste that brings the resources of several DOE sites together to treat mixed waste. It is the only program actively planning to use mobile treatment coordinated between DOE sites

77 FR 42653 - United States Navy Restricted Area, SUPSHIP Gulf Coast Detachment Mobile at AUSTAL, USA, Mobile...

Science.gov (United States)

2012-07-20

... Navy Restricted Area, SUPSHIP Gulf Coast Detachment Mobile at AUSTAL, USA, Mobile, AL; Restricted Area... restricted area established around the AUSTAL, USA shipbuilding facility located in Mobile, Alabama. The...) assumed the duties of administering new construction contracts at AUSTAL USA in Mobile, AL, on October 9...

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.

Metalorganic chemical vapor deposition growth and thermal stability of the AlInN/GaN high electron mobility transistor structure

International Nuclear Information System (INIS)

Yu, Hongbo; Ozturk, Mustafa; Demirel, Pakize; Cakmak, Huseyin; Bolukbas, Basar; Caliskan, Deniz; Ozbay, Ekmel

2011-01-01

The Al x In 1−x N barrier high electron mobility transistor (HEMT) structure has been optimized with varied barrier composition and thickness grown by metalorganic chemical vapor deposition. After optimization, a transistor structure comprising a 7 nm thick nearly lattice-matched Al 0.83 In 0.17 N barrier exhibits a sheet electron density of 2.0 × 10 13 cm −2 with a high electron mobility of 1540 cm 2 V −1 s −1 . An Al 0.83 In 0.17 N barrier HEMT device with 1 µm gate length provides a current density of 1.0 A mm −1 at V GS = 0 V and an extrinsic transconductance of 242 mS mm −1 , which are remarkably improved compared to that of a conventional Al 0.3 Ga 0.7 N barrier HEMT. To investigate the thermal stability of the HEMT epi-structures, post-growth annealing experiments up to 800 °C have been applied to Al 0.83 In 0.17 N and Al 0.3 Ga 0.7 N barrier heterostructures. As expected, the electrical properties of an Al 0.83 In 0.17 N barrier HEMT structure showed less stability than that of an Al 0.3 Ga 0.7 N barrier HEMT to the thermal annealing. The structural properties of Al 0.83 In 0.17 N/GaN also showed more evidence for decomposition than that of the Al 0.3 Ga 0.7 N/GaN structure after 800 °C post-annealing

2014 Mobile County, AL Lidar

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Atlantic was contracted to acquire high resolution topographic LiDAR (Light Detection and Ranging) data located in Mobile County, Alabama. The intent was to collect...

Simulation of zincblende AlGaN/GaN high electron mobility transistors for normally-off operation

Science.gov (United States)

Grady, R.; Bayram, C.

2017-07-01

In this work we investigate design parameters enabling normally-off operation of zincblende (ZB-) phase Al X Ga(1-X)N/GaN high electron mobility transistors (HEMTs) via Synopsys Sentaurus Technology Computer Aided Design (TCAD). As ZB-phase III-nitrides are polarization-free, the 2D electron gas (2DEG) channel at the Al X Ga(1-X)N/GaN heterojunction is formed through intentional δ-doping part of the Al X Ga(1-X)N barrier layer. The impact of each of the design parameters (i.e. Al-content and thickness of Al X Ga(1-X)N barrier; δ-doping location (within the Al X Ga(1-X)N barrier), δ-doped Al X Ga(1-X)N layer thickness and its doping amount; gate metal) are studied in detail and design trade-offs are reported. We show that work function of the gate metal impacts normally-off behavior and turn-on voltage considerably. Our results suggest that Al-content of 35% or less in the Al X Ga(1-X)N barrier results in a normally-off behavior whereas Al X Ga(1-X)N barrier thickness is effective in controlling the turn-on voltage. Overall, we provide design guidelines in controlling the normally-on/-off operation, threshold voltage, and 2DEG density in ZB-phase AlGaN/GaN HEMT technology.

Characterization of N-polar AlN in GaN/AlN/(Al,Ga)N heterostructures grown by metal-organic chemical vapor deposition

Science.gov (United States)

Li, Haoran; Mazumder, Baishakhi; Bonef, Bastien; Keller, Stacia; Wienecke, Steven; Speck, James S.; Denbaars, Steven P.; Mishra, Umesh K.

2017-11-01

In GaN/(Al,Ga)N high-electron-mobility transistors (HEMT), AlN interlayer between GaN channel and AlGaN barrier suppresses alloy scattering and significantly improves the electron mobility of the two-dimensional electron gas. While high concentrations of gallium were previously observed in Al-polar AlN interlayers grown by metal-organic chemical vapor deposition, the N-polar AlN (Al x Ga1-x N) films examined by atom probe tomography in this study exhibited aluminum compositions (x) equal to or higher than 95% over a wide range of growth conditions. The also investigated AlN interlayer in a N-polar GaN/AlN/AlGaN/ S.I. GaN HEMT structure possessed a similarly high x content.

Internal structure of the 85°E ridge, Bay of Bengal: Evidence for multiphase volcanism

Digital Repository Service at National Institute of Oceanography (India)

Ismaiel, M.; Krishna, K.S.; Srinivas, K.; Mishra, J.; Saha, D.

fragments 3 of Elan Bank and part of the present Kerguelen Plateau (Talwani et al., 2016). As a result, age of the oceanic floor in the Western Basin of the Bay of Bengal is older than the other parts. In southeastern quarter of the Bay of Bengal... interpreted as carbonate bank (Gopala Rao et al., 1997; Karuppuswamy, 2013), therefore, we too conjecture the lens shaped reflection free zone identified on our profiles as a carbonate bank, and this may have formed when the defunct volcanic structure...

Heavy metal determination by X-rays spectrometry for superficial sediments at Guantanamo bay

International Nuclear Information System (INIS)

Gelen, A.; Izquierdo; Corrales, W. Y.; Lopez, N.; Casanova, A. O.; Diaz, O.; Manso, M.V.; D Alessandro, K.; Reyes, E.; Toledo, C.; Ruiz, F.; Ramirez, M.; Beltran, J.; Martin, A.

2007-01-01

Twelve surface samples of the Guantanamo Bay (Cuba) were collected and analysed by X-Rays Spectrometry. Twenty one elements (Si, Ca, K, Na, P, S, Cl, Al, Fe, Mg, Ti, Mn, C, O, Cr, Cu, Ni, Co, Pb, V and Zn) have been determined. The distribution of the metals is associated with the wastewater from anthropogenic origin that receives the bay, mainly by fluvial currents. Multivariate statistical were used for the analysis of the results. Finally the results analysed were compared with the analysis performed by Engineering Centre for Environmental Management of Bays and Coasts (Cimab) using Inductively Coupled Plasma Emission (ICP) for some elements such as: Cr, Cu, Fe, Ni, Pb, V and Zn. The results show the Guantanamo Bay is less polluted than others Cuban Bays. (Author)

Growth and characterization of AlGaN/GaN/AlGaN double-heterojunction high-electron-mobility transistors on 100-mm Si(111) using ammonia-molecular beam epitaxy

Energy Technology Data Exchange (ETDEWEB)

Ravikiran, L.; Radhakrishnan, K., E-mail: ERADHA@ntu.edu.sg; Yiding, Lin; Ng, G. I. [NOVITAS-Nanoelectronics Centre of Excellence, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Dharmarasu, N.; Agrawal, M.; Arulkumaran, S.; Vicknesh, S. [Temasek Laboratories@NTU, Nanyang Technological University, Singapore 637553 (Singapore)

2015-01-14

To improve the confinement of two-dimensional electron gas (2DEG) in AlGaN/GaN high electron mobility transistor (HEMT) heterostructures, AlGaN/GaN/AlGaN double heterojunction HEMT (DH-HEMT) heterostructures were grown using ammonia-MBE on 100-mm Si substrate. Prior to the growth, single heterojunction HEMT (SH-HEMT) and DH-HEMT heterostructures were simulated using Poisson-Schrödinger equations. From simulations, an AlGaN buffer with “Al” mole fraction of 10% in the DH-HEMT was identified to result in both higher 2DEG concentration (∼10{sup 13 }cm{sup −2}) and improved 2DEG confinement in the channel. Hence, this composition was considered for the growth of the buffer in the DH-HEMT heterostructure. Hall measurements showed a room temperature 2DEG mobility of 1510 cm{sup 2}/V.s and a sheet carrier concentration (n{sub s}) of 0.97 × 10{sup 13 }cm{sup −2} for the DH-HEMT structure, while they are 1310 cm{sup 2}/V.s and 1.09 × 10{sup 13 }cm{sup −2}, respectively, for the SH-HEMT. Capacitance-voltage measurements confirmed the improvement in the confinement of 2DEG in the DH-HEMT heterostructure, which helped in the enhancement of its room temperature mobility. DH-HEMT showed 3 times higher buffer break-down voltage compared to SH-HEMT, while both devices showed almost similar drain current density. Small signal RF measurements on the DH-HEMT showed a unity current-gain cut-off frequency (f{sub T}) and maximum oscillation frequency (f{sub max}) of 22 and 25 GHz, respectively. Thus, overall, DH-HEMT heterostructure was found to be advantageous due to its higher buffer break-down voltages compared to SH-HEMT heterostructure.

Growth and characterization of AlGaN/GaN/AlGaN double-heterojunction high-electron-mobility transistors on 100-mm Si(111) using ammonia-molecular beam epitaxy

International Nuclear Information System (INIS)

Ravikiran, L.; Radhakrishnan, K.; Yiding, Lin; Ng, G. I.; Dharmarasu, N.; Agrawal, M.; Arulkumaran, S.; Vicknesh, S.

2015-01-01

To improve the confinement of two-dimensional electron gas (2DEG) in AlGaN/GaN high electron mobility transistor (HEMT) heterostructures, AlGaN/GaN/AlGaN double heterojunction HEMT (DH-HEMT) heterostructures were grown using ammonia-MBE on 100-mm Si substrate. Prior to the growth, single heterojunction HEMT (SH-HEMT) and DH-HEMT heterostructures were simulated using Poisson-Schrödinger equations. From simulations, an AlGaN buffer with “Al” mole fraction of 10% in the DH-HEMT was identified to result in both higher 2DEG concentration (∼10 13  cm −2 ) and improved 2DEG confinement in the channel. Hence, this composition was considered for the growth of the buffer in the DH-HEMT heterostructure. Hall measurements showed a room temperature 2DEG mobility of 1510 cm 2 /V.s and a sheet carrier concentration (n s ) of 0.97 × 10 13  cm −2 for the DH-HEMT structure, while they are 1310 cm 2 /V.s and 1.09 × 10 13  cm −2 , respectively, for the SH-HEMT. Capacitance-voltage measurements confirmed the improvement in the confinement of 2DEG in the DH-HEMT heterostructure, which helped in the enhancement of its room temperature mobility. DH-HEMT showed 3 times higher buffer break-down voltage compared to SH-HEMT, while both devices showed almost similar drain current density. Small signal RF measurements on the DH-HEMT showed a unity current-gain cut-off frequency (f T ) and maximum oscillation frequency (f max ) of 22 and 25 GHz, respectively. Thus, overall, DH-HEMT heterostructure was found to be advantageous due to its higher buffer break-down voltages compared to SH-HEMT heterostructure

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)

Spatial and temporal characterizations of water quality in Kuwait Bay.

Science.gov (United States)

Al-Mutairi, N; Abahussain, A; El-Battay, A

2014-06-15

The spatial and temporal patterns of water quality in Kuwait Bay have been investigated using data from six stations between 2009 and 2011. The results showed that most of water quality parameters such as phosphorus (PO4), nitrate (NO3), dissolved oxygen (DO), and Total Suspended Solids (TSS) fluctuated over time and space. Based on Water Quality Index (WQI) data, six stations were significantly clustered into two main classes using cluster analysis, one group located in western side of the Bay, and other in eastern side. Three principal components are responsible for water quality variations in the Bay. The first component included DO and pH. The second included PO4, TSS and NO3, and the last component contained seawater temperature and turbidity. The spatial and temporal patterns of water quality in Kuwait Bay are mainly controlled by seasonal variations and discharges from point sources of pollution along Kuwait Bay's coast as well as from Shatt Al-Arab River. Copyright © 2014 Elsevier Ltd. All rights reserved.

33 CFR 100.124 - Maggie Fischer Memorial Great South Bay Cross Bay Swim, Great South Bay, New York.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Maggie Fischer Memorial Great South Bay Cross Bay Swim, Great South Bay, New York. 100.124 Section 100.124 Navigation and Navigable... NAVIGABLE WATERS § 100.124 Maggie Fischer Memorial Great South Bay Cross Bay Swim, Great South Bay, New York...

Suppressed carrier density for the patterned high mobility two-dimensional electron gas at γ-Al2O3/SrTiO3 heterointerfaces

DEFF Research Database (Denmark)

Niu, Wei; Gan, Yulin; Christensen, Dennis Valbjørn

2017-01-01

The two-dimensional electron gas (2DEG) at the non-isostructural interface between spinel γ-Al2O3 and perovskite SrTiO3 is featured by a record electron mobility among complex oxide interfaces in addition to a high carrier density up to the order of 1015 cm-2. Herein, we report on the patterning...... is found to be approximately 3×1013 cm-2, much lower than that of the unpatterned sample (~1015 cm-2). Remarkably, a high electron mobility of approximately 3,600 cm2V-1s-1 was obtained at low temperatures for the patterned 2DEG at a carrier density of ~ 7×1012 cm-2, which exhibits clear Shubnikov-de Hass...... quantum oscillations. The patterned high-mobility 2DEG at the γ-Al2O3/SrTiO3 interface paves the way for the design and application of spinel/perovskite interfaces for high-mobility all-oxide electronic devic...

Wafer-level MOCVD growth of AlGaN/GaN-on-Si HEMT structures with ultra-high room temperature 2DEG mobility

Directory of Open Access Journals (Sweden)

Xiaoqing Xu

2016-11-01

Full Text Available In this work, we investigate the influence of growth temperature, impurity concentration, and metal contact structure on the uniformity and two-dimensional electron gas (2DEG properties of AlGaN/GaN high electron mobility transistor (HEMT structure grown by metal-organic chemical vapor deposition (MOCVD on 4-inch Si substrate. High uniformity of 2DEG mobility (standard deviation down to 0.72% across the radius of the 4-inch wafer has been achieved, and 2DEG mobility up to 1740.3 cm2/V⋅s at room temperature has been realized at low C and O impurity concentrations due to reduced ionized impurity scattering. The 2DEG mobility is further enhanced to 2161.4 cm2/V⋅s which is comparable to the highest value reported to date when the contact structure is switched from a square to a cross pattern due to reduced piezoelectric scattering at lower residual strain. This work provides constructive insights and promising results to the field of wafer-scale fabrication of AlGaN/GaN HEMT on Si.

Hole mobility and remote scattering in strained InGaSb quantum well MOSFET channels with Al{sub 2}O{sub 3} oxide

Energy Technology Data Exchange (ETDEWEB)

Kumar Madisetti, Shailesh; Chidambaram, Thenappan; Nagaiah, Padmaja; Tokranov, Vadim; Yakimov, Michael; Oktyabrsky, Serge [College of Nanoscale Science and Engineering, University at Albany - SUNY, 257 Fuller Road, Albany, NY 12203 (United States)

2013-08-15

Hall mobility and major scattering mechanisms in surface and buried MBE grown strained InGaSb quantum well (QW) MOSFET channels with in-situ grown Al{sub 2}O{sub 3} gate oxide are analyzed as a function of sheet hole density, top-barrier thickness and temperature. Mobility dependence on Al{sub 0.8}Ga{sub 0.2}Sb top-barrier thickness shows that the relative contribution of interface-related scattering is as low as {proportional_to}30% in the surface QW channel. An InAs top capping layer reduces the interface scattering even further; the sample with 3 nm total top-barrier thickness demonstrates mobility of 980 cm{sup 2}/Vs giving sheet resistance of 4.3 k{Omega}/sq, very close to the minimum QW resistance in the bulk. The mobility-temperature dependences indicate that the interface-related scattering is dominated by remote Coulomb scattering at hole densities <1 x 10{sup 12} cm{sup -2}. (copyright 2013 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Microbial Community Structure in Relation to Water Quality in a Eutrophic Gulf of Mexico Estuary

Science.gov (United States)

Weeks Bay is a shallow, microtidal, eutrophic sub-estuary of Mobile Bay, AL. High watershed nutrient inputs to the estuary contribute to a eutrophic condition characterized by frequent summertime diel-cycling hypoxia and dissolved oxygen (DO) oversaturation. Spatial and seasonal ...

Simulation of zincblende AlGaN/GaN high electron mobility transistors for normally-off operation

International Nuclear Information System (INIS)

Grady, R; Bayram, C

2017-01-01

In this work we investigate design parameters enabling normally-off operation of zincblende (ZB-) phase Al X Ga (1−X) N/GaN high electron mobility transistors (HEMTs) via Synopsys Sentaurus Technology Computer Aided Design (TCAD). As ZB-phase III-nitrides are polarization-free, the 2D electron gas (2DEG) channel at the Al X Ga (1−X) N/GaN heterojunction is formed through intentional δ -doping part of the Al X Ga (1−X) N barrier layer. The impact of each of the design parameters (i.e. Al-content and thickness of Al X Ga (1−X) N barrier; δ -doping location (within the Al X Ga (1−X) N barrier), δ-doped Al X Ga (1−X) N layer thickness and its doping amount; gate metal) are studied in detail and design trade-offs are reported. We show that work function of the gate metal impacts normally-off behavior and turn-on voltage considerably. Our results suggest that Al-content of 35% or less in the Al X Ga (1−X) N barrier results in a normally-off behavior whereas Al X Ga (1−X) N barrier thickness is effective in controlling the turn-on voltage. Overall, we provide design guidelines in controlling the normally-on/-off operation, threshold voltage, and 2DEG density in ZB-phase AlGaN/GaN HEMT technology. (paper)

Metalorganic chemical vapor deposition growth of high-mobility AlGaN/AlN/GaN heterostructures on GaN templates and native GaN substrates

Energy Technology Data Exchange (ETDEWEB)

Chen, Jr-Tai, E-mail: jrche@ifm.liu.se; Hsu, Chih-Wei; Forsberg, Urban; Janzén, Erik [Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE 581 83 Linköping (Sweden)

2015-02-28

Severe surface decomposition of semi-insulating (SI) GaN templates occurred in high-temperature H{sub 2} atmosphere prior to epitaxial growth in a metalorganic chemical vapor deposition system. A two-step heating process with a surface stabilization technique was developed to preserve the GaN template surface. Utilizing the optimized heating process, a high two-dimensional electron gas mobility ∼2000 cm{sup 2}/V·s was obtained in a thin AlGaN/AlN/GaN heterostructure with an only 100-nm-thick GaN spacer layer homoepitaxially grown on the GaN template. This technique was also demonstrated viable for native GaN substrates to stabilize the surface facilitating two-dimensional growth of GaN layers. Very high residual silicon and oxygen concentrations were found up to ∼1 × 10{sup 20 }cm{sup −3} at the interface between the GaN epilayer and the native GaN substrate. Capacitance-voltage measurements confirmed that the residual carbon doping controlled by growth conditions of the GaN epilayer can be used to successfully compensate the donor-like impurities. State-of-the-art structural properties of a high-mobility AlGaN/AlN/GaN heterostructure was then realized on a 1 × 1 cm{sup 2} SI native GaN substrate; the full width at half maximum of the X-ray rocking curves of the GaN (002) and (102) peaks are only 21 and 14 arc sec, respectively. The surface morphology of the heterostructure shows uniform parallel bilayer steps, and no morphological defects were noticeable over the entire epi-wafer.

Sustainable development in the Hudson Bay/James Bay bioregion

International Nuclear Information System (INIS)

Anon.

1991-01-01

An overview is presented of projects planned for the James Bay/Hudson Bay region, and the expected environmental impacts of these projects. The watershed of James Bay and Hudson Bay covers well over one third of Canada, from southern Alberta to central Ontario to Baffin Island, as well as parts of north Dakota and Minnesota in the U.S.A. Hydroelectric power developments that change the timing and rate of flow of fresh water may cause changes in the nature and duration of ice cover, habitats of marine mammals, fish and migratory birds, currents into and out of Hudson Bay/James Bay, seasonal and annual loads of sediments and nutrients to marine ecosystems, and anadromous fish populations. Hydroelectric projects are proposed for the region by Quebec, Ontario and Manitoba. In January 1992, the Canadian Arctic Resources Committee (CARC), the Environmental Committee of Sanikuluaq, and the Rawson Academy of Arctic Science will launch the Hudson Bay/James Bay Bioregion Program, an independent initiative to apply an ecosystem approach to the region. Two main objectives are to provide a comprehensive assessment of the cumulative impacts of human activities on the marine and freshwater ecosystems of the Hudson Bay/James Bay bioregion, and to foster sustainable development by examining and proposing cooperative processes for decision making among governments, developers, aboriginal peoples and other stakeholders. 1 fig

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.

Mobil reklamlar ve mobil reklam araçlarına yönelik tutumlar

OpenAIRE

Barutçu, Süleyman; Öztürk Göl, Meltem

2009-01-01

Bu çalışmanın amacı, pazarlama bölümü yöneticilerinin dikkatlerini mobil iletişim teknolojilerindeki gelişmelerin sonucu olarak ortaya çıkan mobil pazarlama ve mobil reklam uygulamalarına çekmektir. Çalışmanın kavramsal analiz bölümünde mobil pazarlama, mobil reklamların önemi açıklanmış ve mobil reklam araçları (SMS, MMS ve Bluetooth Reklamları) analiz edilmiştir. Araştırma bölümünde ise mobil telefon kullanıcılarının mobil reklam araçlarına yönelik tutumlarının karşılaştırmalı olarak belirl...

Mobility enhancement in tensile-strained Ge grown on InAlP metamorphic templates

International Nuclear Information System (INIS)

Wang, Kai; Gong, Qian; Zhou, Haifei; Kang, Chuanzhen; Yan, Jinyi; Liu, Qingbo; Wang, Shumin

2014-01-01

We investigated the growth of tensile-strained Ge on InAlP metamorphic templates by gas source molecular beam epitaxy. Good control of biaxial tensile strain in the Ge layer was demonstrated in the range of 0.5–2.0% by adjusting the In content of the metamorphic template. It was found that the growth of Ge was layer-by-layer (2D) even under high tensile strain of 2.0%, resulting in a smooth surface with roughness less than 1.5 nm. Hall results showed that the electron mobility of Ge increased monotonically with tensile strain.

InAlN high electron mobility transistor Ti/Al/Ni/Au Ohmic contact optimisation assisted by in-situ high temperature transmission electron microscopy

International Nuclear Information System (INIS)

Smith, M. D.; Parbrook, P. J.; O'Mahony, D.; Conroy, M.; Schmidt, M.

2015-01-01

This paper correlates the micro-structural and electrical characteristics associated with annealing of metallic multi-layers typically used in the formation of Ohmic contacts to InAlN high electron mobility transistors. The multi-layers comprised Ti/Al/Ni/Au and were annealed via rapid thermal processing at temperatures up to 925 °C with electrical current-voltage analysis establishing the onset of Ohmic (linear IV) behaviour at 750–800 °C. In-situ temperature dependent transmission electron microscopy established that metallic diffusion and inter-mixing were initiated near a temperature of 500 °C. Around 800 °C, inter-diffusion of the metal and semiconductor (nitride) was observed, correlating with the onset of Ohmic electrical behaviour. The sheet resistance associated with the InAlN/AlN/GaN interface is highly sensitive to the anneal temperature, with the range depending on the Ti layer thickness. The relationship between contact resistivity and measurement temperature follow that predicted by thermionic field emission for contacts annealed below 850 °C, but deviated above this due to excessive metal-semiconductor inter-diffusion

Distribution and behavior of major and trace elements in Tokyo Bay, Mutsu Bay and Funka Bay marine sediments

International Nuclear Information System (INIS)

Honda, Teruyuki; Kimura, Ken-ichiro

2003-01-01

Fourteen major and trace elements in marine sediment core samples collected from the coasts along eastern Japan, i.e. Tokyo Bay (II) (the recess), Tokyo Bay (IV) (the mouth), Mutsu Bay and Funka Bay and the Northwest Pacific basin as a comparative subject were determined by the instrumental neutron activation analysis (INAA). The sedimentation rates and sedimentary ages were calculated for the coastal sediment cores by the 210 Pb method. The results obtained in this study are summarized as follows: (1) Lanthanoid abundance patterns suggested that the major origin of the sediments was terrigenous material. La*/Lu* and Ce*/La* ratios revealed that the sediments from Tokyo Bay (II) and Mutsu Bay more directly reflected the contribution from river than those of other regions. In addition, the Th/Sc ratio indicated that the coastal sediments mainly originated in the materials from the volcanic island-arcs, Japanese islands, whereas those from the Northwest Pacific mainly from the continent. (2) The correlation between the Ce/U and Th/U ratios with high correlation coefficients of 0.920 to 0.991 indicated that all the sediments from Tokyo Bay (II) and Funka Bay were in reducing conditions while at least the upper sediments from Tokyo Bay (IV) and Mutsu Bay were in oxidizing conditions. (3) It became quite obvious that the sedimentation mechanism and the sedimentation environment at Tokyo Bay (II) was different from those at Tokyo Bay (IV), since the sedimentation rate at Tokyo Bay (II) was approximately twice as large as that at Tokyo Bay (IV). The sedimentary age of the 5th layer (8∼10 cm in depth) from Funka Bay was calculated at approximately 1940∼50, which agreed with the time, 1943∼45 when Showa-shinzan was formed by the eruption of the Usu volcano. (author)

Extraction procedure compared to attenuation model to assess heavy metals mobility in sediments from Sepetiba Bay, Rio de Janeiro; Procedimento de fracionamento comparado a modelo de atenuacao para a avaliacao de mobilidade de metais pesados em sedimentos da Baia de Sepetiba, Rio de Janeiro

Energy Technology Data Exchange (ETDEWEB)

Ribeiro, Andreza Portella

2006-07-01

Sepetiba bay, located about 60 km west of the metropolitan region of Rio de Janeiro city, has undergone notable development in the last decades, with the establishment of about 400 industrial plants in its basin, basically metallurgical, which release its industrial waste either straight into the bay or through local rivers. The Sepetiba harbor also brought up a lot of industrial investment in that area. This urban and industrial expansion caused several environmental impacts, mainly due to the presence of heavy metals and other potentially toxic substances present in the effluents discharged into the bay. This work aimed to assess heavy metal (Cd, Cu, Ni, Pb e Zn) contamination and mobility in sediments from Sepetiba bay. The acid-volatile sulfides (AVS) and the concentration of simultaneously extracted metals (SIGMA[SEM) were determined in 65 sediment samples from Sepetiba bay, representing the whole area. The results obtained showed that Cd, Cu, Pb and Zn presented higher concentrations in the northeastern area (mainly in the mouth of Guandu and Canal de Sao Francisco rivers), while the highest concentration of Ni were observed in the western region of the bay. The comparison between SEM concentrations with the Canadian Sediment Quality Guidelines (TEL and PEL) indicated that Cd and Zn presented values which may hazard to aquatic organisms (concentration levels above PEL); the elements Cu, Pb and Ni presented concentration levels below PEL, suggesting low probability of toxicological effects to the aquatic organisms. On the other hand, the ratio {sigma}[SEM]/[AVS] was below 1 in the northeastern region, indicating that, in spite of the high concentration of the analyzed metals in this area, they are trapped in the sediment, as sulfides. The total metal concentrations in the sediments were also determined and the same distribution pattern obtained for the SEM were observed, with high concentrations in the northeastern region of the bay, classifying the area as

Submarine glacial landforms on the Bay of Fundy–northern Gulf of Maine continental shelf

Science.gov (United States)

Todd, B.J.; Shaw, J.; Valentine, Page C.

2016-01-01

The Bay of Fundy–northern Gulf of Maine region surrounds the southern part of Nova Scotia, encompassing, from west to east, the Bay of Fundy, Grand Manan Basin, German Bank, Browns Bank, Northeast Channel and northeastern Georges Bank (Fig. 1a, b). During the last glacial maximum (c. 24–20 14C ka BP), the SE margin of the Laurentide Ice Sheet (LIS) occupied the study area, the rest of the Gulf of Maine and the continental Scotian Shelf off Atlantic Canada (see Dyke et al. 2002, fig. 1; Shaw et al. 2006, fig. 8; Hundert & Piper 2008, fig. 16). Early mapping of the glaciated region on the Scotian Shelf using side-scan sonar imagery and seismic-reflection profiles revealed topographic features interpreted to be recessional moraines indicative of retreat of the LIS (King et al. 1972; King 1996). Subsequently, multibeam sonar seafloor mapping of local-scale glacial landforms on the inner Scotian Shelf off Halifax, Nova Scotia (Fig. 1b) provided further information on the dynamics of the advance and retreat of the ice sheet (Loncarevic et al.1994). Interpretation of seismic-reflection profiles across Georges Bank revealed that the surficial sediment is a veneer of glacial debris transported to Georges Bank by the LIS during the late Pleistocene from continental areas to the north (Shepard et al. 1934; Knott & Hoskins 1968; Schlee 1973; Twichell et al. 1987; Fader et al. 1988). Recent high-resolution multibeam sonar surveys of German Bank and the Bay of Fundy mapped a complex of ice-advance and ice-retreat features attributed to the activity of the LIS (Todd et al. 2007; Todd & Shaw 2012).

Monterey Bay ambient noise profiles using underwater gliders

OpenAIRE

Chandrayadula, Tarun K.; Miller, Chris W.; Joseph, John

2013-01-01

The article of record as published may be found at http://dx.doi.org/10.1121/1.4799131 In 2012, during two separate week-long deployments, underwater gliders outfitted with external hydrophones profiled the upper 100-200 m of the Monterey Bay. The environment contained various noises made by marine mammals, ships, winds, and earthquakes. Unlike hydrophone receivers moored to a fixed location, moving gliders measure noise variability across a wide terrain. However, underwater mobile s...

Correlation of AlGaN/GaN high-electron-mobility transistors electroluminescence characteristics with current collapse

Science.gov (United States)

Ohi, Shintaro; Yamazaki, Taisei; Asubar, Joel T.; Tokuda, Hirokuni; Kuzuhara, Masaaki

2018-02-01

We report on the correlation between the electroluminescence and current collapse of AlGaN/GaN high-electron-mobility transistors (HEMTs). Standard passivated devices suffering from severe current collapse exhibited high-intensity whitish electroluminescence confined near the drain contact. In contrast, devices with reduced current collapse resulting from oxygen plasma treatment or GaN capping showed low-intensity reddish emission across the entire gate-drain access region. A qualitative explanation of this observed correlation between the current collapse and electroluminescence is presented. Our results demonstrate that electroluminescence analysis is a powerful tool not only for identifying high-field regions but also for assessing the degree of current collapse in AlGaN/GaN HEMTs.

Ultrasensitive detection of Hg2+ using oligonucleotide-functionalized AlGaN/GaN high electron mobility transistor

International Nuclear Information System (INIS)

Cheng, Junjie; Li, Jiadong; Miao, Bin; Wu, Dongmin; Wang, Jine; Pei, Renjun; Wu, Zhengyan

2014-01-01

An oligonucleotide-functionalized ion sensitive AlGaN/GaN high electron mobility transistor (HEMT) was fabricated to detect trace amounts of Hg 2+ . The advantages of ion sensitive AlGaN/GaN HEMT and highly specific binding interaction between Hg 2+ and thymines were combined. The current response of this Hg 2+ ultrasensitive transistor was characterized. The current increased due to the accumulation of Hg 2+ ions on the surface by the highly specific thymine-Hg 2+ -thymine recognition. The dynamic linear range for Hg 2+ detection has been determined in the concentrations from 10 −14 to 10 −8 M and a detection limit below 10 −14 M level was estimated, which is the best result of AlGaN/GaN HEMT biosensors for Hg 2+ detection till now.

Oxygen Storage Capacity and Oxygen Mobility of Co-Mn-Mg-Al Mixed Oxides and Their Relation in the VOC Oxidation Reaction

Directory of Open Access Journals (Sweden)

María Haidy Castaño

2015-05-01

Full Text Available Co-Mn-Mg-Al oxides were synthesized using auto-combustion and co-precipitation techniques. Constant ratios were maintained with (Co + Mn + Mg/Al equal to 3.0, (Co + Mn/Mg equal to 1.0 and Co/Mn equal to 0.5. The chemical and structural composition, redox properties, oxygen storage capacity and oxygen mobility were analyzed using X-ray fluorescence (XRF, X-ray diffraction (XRD, Raman spectroscopy, scanning electron microscopy (SEM, temperature-programmed reduction of hydrogen (H2-TPR, oxygen storage capacity (OSC, oxygen storage complete capacity (OSCC and isotopic exchange, respectively. The catalytic behavior of the oxides was evaluated in the total oxidation of a mixture of 250 ppm toluene and 250 ppm 2-propanol. The synthesis methodology affected the crystallite size, redox properties, OSC and oxide oxygen mobility, which determined the catalytic behavior. The co-precipitation method got the most active oxide in the oxidation of the volatile organic compound (VOC mixture because of the improved mobility of oxygen and ability to favor redox processes in the material structure.

Impact of barrier thickness on transistor performance in AlN/GaN high electron mobility transistors grown on free-standing GaN substrates

International Nuclear Information System (INIS)

Deen, David A.; Storm, David F.; Meyer, David J.; Bass, Robert; Binari, Steven C.; Gougousi, Theodosia; Evans, Keith R.

2014-01-01

A series of six ultrathin AlN/GaN heterostructures with varied AlN thicknesses from 1.5–6 nm have been grown by molecular beam epitaxy on free-standing hydride vapor phase epitaxy GaN substrates. High electron mobility transistors (HEMTs) were fabricated from the set in order to assess the impact of barrier thickness and homo-epitaxial growth on transistor performance. Room temperature Hall characteristics revealed mobility of 1700 cm 2 /V s and sheet resistance of 130 Ω/□ for a 3 nm thick barrier, ranking amongst the lowest room-temperature sheet resistance values reported for a polarization-doped single heterostructure in the III-Nitride family. DC and small signal HEMT electrical characteristics from submicron gate length HEMTs further elucidated the effect of the AlN barrier thickness on device performance.

Impact of barrier thickness on transistor performance in AlN/GaN high electron mobility transistors grown on free-standing GaN substrates

Energy Technology Data Exchange (ETDEWEB)

Deen, David A., E-mail: david.deen@alumni.nd.edu; Storm, David F.; Meyer, David J.; Bass, Robert; Binari, Steven C. [Electronics Science and Technology Division, Naval Research Laboratory, Washington, DC 20375-5347 (United States); Gougousi, Theodosia [Physics Department, University of Maryland Baltimore County, Baltimore, Maryland 21250 (United States); Evans, Keith R. [Kyma Technologies, Raleigh, North Carolina 27617 (United States)

2014-09-01

A series of six ultrathin AlN/GaN heterostructures with varied AlN thicknesses from 1.5–6 nm have been grown by molecular beam epitaxy on free-standing hydride vapor phase epitaxy GaN substrates. High electron mobility transistors (HEMTs) were fabricated from the set in order to assess the impact of barrier thickness and homo-epitaxial growth on transistor performance. Room temperature Hall characteristics revealed mobility of 1700 cm{sup 2}/V s and sheet resistance of 130 Ω/□ for a 3 nm thick barrier, ranking amongst the lowest room-temperature sheet resistance values reported for a polarization-doped single heterostructure in the III-Nitride family. DC and small signal HEMT electrical characteristics from submicron gate length HEMTs further elucidated the effect of the AlN barrier thickness on device performance.

Universality of electron mobility in LaAlO3/SrTiO3 and bulk SrTiO3

Science.gov (United States)

Trier, Felix; Reich, K. V.; Christensen, Dennis Valbjørn; Zhang, Yu; Tuller, Harry L.; Chen, Yunzhong; Shklovskii, B. I.; Pryds, Nini

2017-08-01

Metallic LaAlO3/SrTiO3 (LAO/STO) interfaces attract enormous attention, but the relationship between the electron mobility and the sheet electron density, ns, is poorly understood. Here, we derive a simple expression for the three-dimensional electron density near the interface, n3 D , as a function of ns and find that the mobility for LAO/STO-based interfaces depends on n3 D in the same way as it does for bulk doped STO. It is known that undoped bulk STO is strongly compensated with N ≃5 ×1018 cm-3 background donors and acceptors. In intentionally doped bulk STO with a concentration of electrons n3 DN , the mobility collapses because scattering happens on n3 D intentionally introduced donors. For LAO/STO, the polar catastrophe which provides electrons is not supposed to provide an equal number of random donors and thus the mobility should be larger. The fact that the mobility is still the same implies that for the LAO/STO, the polar catastrophe model should be revisited.

Humic Substances from Manila Bay and Bolinao Bay Sediments

Directory of Open Access Journals (Sweden)

Elma Llaguno

1997-12-01

Full Text Available The C,H,N composition of sedimentary humic acids (HA extracted from three sites in Manila Bay and six sites in Bolinao Bay yielded H/C atomic ratios of 1.1-1.4 and N/C atomic ratios of 0.09 - 0.16. The Manila Bay HA's had lower H/C and N/C ratios compared to those from Bolinao Bay. The IR spectra showed prominent aliphatic C-H and amide I and II bands. Manila Bay HA's also had less diverse molecular composition based on the GC-MS analysis of the CuO and alkaline permanganate oxidation products of the humic acids.

Sources and historical record of tin and butyl-tin species in a Mediterranean bay (Toulon Bay, France).

Science.gov (United States)

Pougnet, Frédérique; Schäfer, Jörg; Dutruch, Lionel; Garnier, Cédric; Tessier, Erwan; Dang, Duc Huy; Lanceleur, Laurent; Mullot, Jean-Ulrich; Lenoble, Véronique; Blanc, Gérard

2014-05-01

Concentrations of inorganic tin (Sn(inorg)), tributyltin (TBT) and its degradation products dibutyltin (DBT) and monobutyltin (MBT) were measured in surface sediments and in two cores from the Toulon Bay, hosting the major French military harbour. Anticipating planned dredging, the aim of the present work is to map and evaluate for the first time the recent and historic contamination of these sediments by inorganic and organic Sn species derived from antifouling paints used for various naval domains including military, trade, tourism and leisure. Tin and butyl-Sn concentrations in the bay varied strongly (4 orders of magnitude), depending on the site, showing maximum values near the shipyards. The concentrations of total Sn (1.3-112 μg g(-1)), TBT (product Sn(inorgBT) is by far the dominant species after 10-12 half-life periods and (c) using recent data to reliably assess former TBT contamination requires the use of a modified butyl-Sn degradation index BDI(mod). Resuspension of extremely contaminated subsurface sediments by the scheduled dredging will probably result in mobilization of important amounts of butyl-Sn species.

Thermal stability and in situ SiN passivation of InAlN/GaN high electron mobility heterostructures

Energy Technology Data Exchange (ETDEWEB)

Lugani, L.; Carlin, J.-F.; Py, M. A.; Grandjean, N. [ICMP, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland)

2014-09-15

We investigate the thermal stability of nearly lattice-matched InAlN layers under metal organic vapor phase epitaxy conditions for temperatures >800 °C and show that they are not fully stable. In particular, InAlN top layers undergo degradation during high temperature annealing due to a surface related process, which causes the loss of crystal quality. This strongly impacts the transport properties of InAlN/GaN HEMT heterostructures; in particular, the mobility is significantly reduced. However, we demonstrate that high thermal stability can be achieved by capping with a GaN layer as thin as 0.5 nm. Those findings enabled us to realize in situ passivated HEMT heterostructures with state of the art transport properties.

Trace metal contamination in mangrove sediments, Guanabara Bay, Rio de Janeiro, Brazil

OpenAIRE

Farias,Cassia O.; Hamacher,Claudia; Wagener,Angela de Luca R.; Campos,Reinaldo C. de; Godoy,José M.

2007-01-01

The Guanabara Bay in Rio de Janeiro has undergone profound alterations of its natural environmental conditions. Metal concentration increase in sediments has been reported to be among these alterations. Trace-metal contamination and availability were studied in sediments of 3 mangrove areas of the bay. Cd, Zn, Pb, Ni, Cu and Al concentrations were determined in segments of sediment cores, after treatment with 1 mol L-1 HCl and with concentrated HNO3. Fe and Mn were determined in the leach wit...

Threading dislocation movement in AlGaN/GaN-on-Si high electron mobility transistors under high temperature reverse bias stressing

Directory of Open Access Journals (Sweden)

W. A. Sasangka

2016-09-01

Full Text Available Dislocations are known to be associated with both physical and electrical degradation mechanisms of AlGaN/GaN-on-Si high electron mobility transistors (HEMTs. We have observed threading dislocation movement toward the gate-edges in AlGaN/GaN-on-Si HEMT under high reverse bias stressing. Stressed devices have higher threading dislocation densities (i.e. ∼5 × 109/cm2 at the gate-edges, as compared to unstressed devices (i.e. ∼2.5 × 109/cm2. Dislocation movement correlates well with high tensile stress (∼1.6 GPa at the gate-edges, as seen from inverse piezoelectric calculations and x-ray synchrotron diffraction residual stress measurements. Based on Peierls stress calculation, we believe that threading dislocations move via glide in 〈 11 2 ¯ 0 〉 / { 1 1 ¯ 00 } and 〈 11 2 ¯ 0 〉 / { 1 1 ¯ 01 } slip systems. This result illustrates the importance of threading dislocation mobility in controlling the reliability of AlGaN/GaN-on-Si HEMTs.

Radium isotopes in Port Phillip Bay: estimation of the rate of bio irrigation of sediments, and water residence time

International Nuclear Information System (INIS)

Hancock, G.J.; Webster, I.T.

1998-01-01

Recent work has shown that estuarine sediments are a source of radium (Ra) to coastal waters (Bollinger and Moore, 1982, Webster et al., 1994; Hancock et al., 1997). Ra is soluble in saline water (Moore, 1992, Webster et al., 1995) and is rapidly desorbed into porewater from deposited fluvial sediments where it is continuously generated by insoluble Th parents. The rate at which Ra effuses into surface water has been used to determine the rate of surface-water pore water exchange (Hancock and Murray, 1996). Once in the water column, the behaviour of Ra is essentially conservative, enabling the determination of water residence time in a semi-enclosed estuary (Turekian et al., 1996). Here we use measurements of Ra in an estuary to estimate two water mixing processes. Port Phillip Bay (PPB) is a semi-enclosed estuary adjacent to the city of Melbourne, one of the highest density population centres in Australia. The Bay is approximately 50 km in diameter, and has an average depth of 14 m. A recent study found that the potential for eutrophication and algal blooms in the Bay was intricately linked to the fate of nutrients, particularly nitrogen, discharged into the Bay from rivers, drains, and sewage treatment plants (Harris et al. 1996). Two of the most important processes controlling the levels of inorganic N in the water column were identified as bio irrigation of bottom sediments, and the rate of exchange of Bay water with ocean water via Bass Strait. In this paper we describe how Ra isotopes can be used to estimate the rates of these processes, and we compare these rates with estimates made using conventional techniques. Water and sediment samples were collected from five sites in February 1996. Sediment cores were collected by divers, frozen, and sectioned in the laboratory. Surface, mid depth and bottom water samples were collected using a Niskin bottle. Radionuclide activities were determined by alpha spectrometry (Martin and Hancock, 1992) and gamma spectrometry

Visible-blind and solar-blind detection induced by defects in AlGaN high electron mobility transistors

Science.gov (United States)

Armstrong, Andrew M.; Klein, Brianna; Allerman, Andrew A.; Douglas, Erica A.; Baca, Albert G.; Crawford, Mary H.; Pickrell, Greg W.; Sanchez, Carlos A.

2018-03-01

Visible- and solar-blind detection was demonstrated using Al0.45Ga0.55N/Al0.30Ga0.70N and Al0.85Ga0.25N/Al0.70Ga0.30N high electron mobility transistors (HEMTs), respectively. Peak responsivities (S) of 3.9 × 106 A/W in the saturation mode and 6.2 × 104 A/W in the pinch-off mode were observed for the visible-blind Al0.45Ga0.55N/Al0.30Ga0.70N HEMT, and a peak S of 4.9 × 104 A/W was observed for the solar-blind Al0.85Ga0.15N/Al0.70Ga0.30N HEMT in the saturation mode. Spectrally resolved photocurrent investigation indicated that sub-bandgap absorption by defect states was the primary origin of the HEMTs' photoresponse. Defect-mediated responsivity caused slow photocurrent rise and fall times, but electrical pulsing was used to improve the bandwidth at the cost of optical gain. Operating HEMTs in this dynamic mode achieved a 25 Hz bandwidth with S = 2.9 × 105 A/W in accumulation and S = 2.0 × 104 A/W in pinch-off for visible-blind detection and S = 5.1 × 103 A/W for solar-blind detection.

Comparison of Surface Passivation Films for Reduction of Current Collapse in AlGaN/GaN High Electron Mobility Transistors (HEMTs)

National Research Council Canada - National Science Library

Fitch, R

2002-01-01

Three different passivation layers (SiN(x), MgO, and Sc2O3) were examined for their effectiveness in mitigating surface-state-induced current collapse in AlGaN/GaN high electron mobility transistors (HEMTs...

Fixed interface charges between AlGaN barrier and gate stack composed of in situ grown SiN and Al2O3 in AlGaN/GaN high electron mobility transistors with normally off capability

International Nuclear Information System (INIS)

Capriotti, M.; Alexewicz, A.; Fleury, C.; Gavagnin, M.; Bethge, O.; Wanzenböck, H. D.; Bertagnolli, E.; Pogany, D.; Strasser, G.; Visalli, D.; Derluyn, J.

2014-01-01

Using a generalized extraction method, the fixed charge density N int at the interface between in situ deposited SiN and 5 nm thick AlGaN barrier is evaluated by measurements of threshold voltage V th of an AlGaN/GaN metal insulator semiconductor high electron mobility transistor as a function of SiN thickness. The thickness of the originally deposited 50 nm thick SiN layer is reduced by dry etching. The extracted N int is in the order of the AlGaN polarization charge density. The total removal of the in situ SiN cap leads to a complete depletion of the channel region resulting in V th  = +1 V. Fabrication of a gate stack with Al 2 O 3 as a second cap layer, deposited on top of the in situ SiN, is not introducing additional fixed charges at the SiN/Al 2 O 3 interface

Growth of high mobility GaN and AlGaN/GaN high electron mobility transistor structures on 4H-SiC by ammonia molecular-beam epitaxy

International Nuclear Information System (INIS)

Webb, James B.; Tang, H.; Bardwell, J. A.; Coleridge, P.

2001-01-01

Ammonia molecular-beam epitaxy has been used to grow high-quality epilayers of GaN and AlGaN/GaN heterostructure field-effect transistor (HFET) structures on insulating 4H-SiC. The growth process, which used a magnetron sputter epitaxy deposited buffer layer of AlN, has been described previously. Ex situ pretreatment of the SiC substrate was found to be unnecessary. For a single 2.0 μm thick silicon doped epilayer, a room temperature (RT) electron mobility of 500 cm2/Vs was measured at a carrier density of 6.6x10 16 cm -3 . For the HFET structure, a room temperature mobility of 1300 cm2/Vs at a sheet carrier density of 3.3x10 12 cm -2 was observed, increasing to 11000 cm2/Vs at 77 K. The surface morphology of the layers indicated a coalesced mesa structure similar to what we observed for growth on sapphire, but with a lower overall defect density and correspondingly larger grain size. The observation of well-resolved Shubnikov de Haas oscillations at fields as low as 3 T indicated a relatively smooth interface. [copyright] 2001 American Institute of Physics

Use of a real time PCR assay for detection of the ctxA gene of Vibrio cholerae in an environmental survey of Mobile Bay.

Science.gov (United States)

Blackstone, George M; Nordstrom, Jessica L; Bowen, Michael D; Meyer, Richard F; Imbro, Paula; DePaola, Angelo

2007-02-01

Toxigenic Vibrio cholerae, the etiological agent of cholera, is a natural inhabitant of the marine environment and causes severe diarrheal disease affecting thousands of people each year in developing countries. It is the subject of extensive testing of shrimp produced and exported from these countries. We report the development of a real time PCR (qPCR) assay to detect the gene encoding cholera toxin, ctxA, found in toxigenic V. cholerae strains. This assay was tested against DNA isolated from soil samples collected from diverse locations in the US, a panel of eukaryotic DNA from various sources, and prokaryotic DNA from closely related and unrelated bacterial sources. Only Vibrio strains known to contain ctxA generated a fluorescent signal with the 5' nuclease probe targeting the ctxA gene, thus confirming the specificity of the assay. In addition, the assay was quantitative in pure culture across a six-log dynamic range down to <10 CFU per reaction. To test the robustness of this assay, oysters, aquatic sediments, and seawaters from Mobile Bay, AL, were analyzed by qPCR and traditional culture methods. The assay was applied to overnight alkaline peptone water enrichments of these matrices after boiling the enrichments for 10 min. Toxigenic V. cholerae strains were not detected by either qPCR or conventional methods in the 16 environmental samples examined. A novel exogenous internal amplification control developed by us to prevent false negatives identified the samples that were inhibitory to the PCR. This assay, with the incorporated internal control, provides a highly specific, sensitive, and rapid detection method for the detection of toxigenic strains of V. cholerae.

Study of Integrated USV/UUV Observation System Performance in Monterey Bay

Science.gov (United States)

2017-09-01

EMATT expendable mobile ASW training target MARS Monterey Accelerated Research System MBARI Monterey Bay Aquarium Research Institute PSD power ...Paula Travis, provided needed support as well. The Naval Postgraduate School faculty and staff are incredibly professional and knowledgeable . The...operation. 9 “The MARS observatory ‘science node’ (shown in orange) has eight ports, each of which can supply data and power connections for

Novel model of a AlGaN/GaN high electron mobility transistor based on an artificial neural network

International Nuclear Information System (INIS)

Cheng Zhi-Qun; Hu Sha; Liu Jun; Zhang Qi-Jun

2011-01-01

In this paper we present a novel approach to modeling AlGaN/GaN high electron mobility transistor (HEMT) with an artificial neural network (ANN). The AlGaN/GaN HEMT device structure and its fabrication process are described. The circuit-based Neuro-space mapping (neuro-SM) technique is studied in detail. The EEHEMT model is implemented according to the measurement results of the designed device, which serves as a coarse model. An ANN is proposed to model AlGaN/GaN HEMT based on the coarse model. Its optimization is performed. The simulation results from the model are compared with the measurement results. It is shown that the simulation results obtained from the ANN model of AlGaN/GaN HEMT are more accurate than those obtained from the EEHEMT model. (condensed matter: structural, mechanical, and thermal properties)

Detection of prostate-specific antigen with biomolecule-gated AlGaN/GaN high electron mobility transistors

Science.gov (United States)

Li, Jia-dong; Cheng, Jun-jie; Miao, Bin; Wei, Xiao-wei; Xie, Jie; Zhang, Jin-cheng; Zhang, Zhi-qiang; Wu, Dong-min

2014-07-01

In order to improve the sensitivity of AlGaN/GaN high electron mobility transistor (HEMT) biosensors, a simple biomolecule-gated AlGaN/GaN HEMT structure was designed and successfully fabricated for prostate specific antigen (PSA) detection. UV/ozone was used to oxidize the GaN surface and then a 3-aminopropyl trimethoxysilane (APTES) self-assembled monolayer was bound to the sensing region. This monolayer serves as a binding layer for attachment of the prostate specific antibody (anti-PSA). The biomolecule-gated AlGaN/GaN HEMT sensor shows a rapid and sensitive response when the target prostate-specific antigen in buffer solution was added to the antibody-immobilized sensing area. The current change showed a logarithm relationship against the PSA concentration from 0.1 pg/ml to 0.993 ng/ml. The sensitivity of 0.215% is determined for 0.1 pg/ml PSA solution. The above experimental result of the biomolecule-gated AlGaN/GaN HEMT biosensor suggested that this biosensor might be a useful tool for prostate cancer screening.

Detection of prostate-specific antigen with biomolecule-gated AlGaN/GaN high electron mobility transistors

International Nuclear Information System (INIS)

Li, Jia-dong; Miao, Bin; Wei, Xiao-wei; Xie, Jie; Wu, Dong-min; Cheng, Jun-jie; Zhang, Jin-cheng; Zhang, Zhi-qiang

2014-01-01

In order to improve the sensitivity of AlGaN/GaN high electron mobility transistor (HEMT) biosensors, a simple biomolecule-gated AlGaN/GaN HEMT structure was designed and successfully fabricated for prostate specific antigen (PSA) detection. UV/ozone was used to oxidize the GaN surface and then a 3-aminopropyl trimethoxysilane (APTES) self-assembled monolayer was bound to the sensing region. This monolayer serves as a binding layer for attachment of the prostate specific antibody (anti-PSA). The biomolecule-gated AlGaN/GaN HEMT sensor shows a rapid and sensitive response when the target prostate-specific antigen in buffer solution was added to the antibody-immobilized sensing area. The current change showed a logarithm relationship against the PSA concentration from 0.1 pg/ml to 0.993 ng/ml. The sensitivity of 0.215% is determined for 0.1 pg/ml PSA solution. The above experimental result of the biomolecule-gated AlGaN/GaN HEMT biosensor suggested that this biosensor might be a useful tool for prostate cancer screening. (paper)

Waves off Gopalpur, northern Bay of Bengal during cyclone Phailin.

Digital Repository Service at National Institute of Oceanography (India)

Amrutha, M.M.; SanilKumar, V.; Anoop, T.R.; Nair, T.M.B.; Nherakkol, A.; Jeyakumar, C.

, 1073–1083, 2014 www.ann-geophys.net/32/1073/2014/ doi:10.5194/angeo-32-1073-2014 © Author(s) 2014. CC Attribution 3.0 License. Waves off Gopalpur, northern Bay of Bengal during Cyclone Phailin M. M. Amrutha1, V. Sanil Kumar1, T. R. Anoop1, T. M..., 1073–1083, 2014 www.ann-geophys.net/32/1073/2014/ M. M. Amrutha et al.: Waves off Gopalpur, northern Bay of Bengal during Cyclone Phailin 1075 Figure 1. Track of the Cyclone Phailin from 8 October 2013 03:00 UTC to 13 October 2013 06:00 UTC. S(f )= αg 2...

Reduced thermal resistance in AlGaN/GaN multi-mesa-channel high electron mobility transistors

Energy Technology Data Exchange (ETDEWEB)

Asubar, Joel T., E-mail: joel@rciqe.hokudai.ac.jp; Yatabe, Zenji; Hashizume, Tamotsu [Research Center for Integrated Quantum Electronics (RCIQE) and Graduate School of Information Science and Technology, Hokkaido University, Sapporo (Japan); Japan Science and Technology Agency (JST), CREST, 102-0075 Tokyo (Japan)

2014-08-04

Dramatic reduction of thermal resistance was achieved in AlGaN/GaN Multi-Mesa-Channel (MMC) high electron mobility transistors (HEMTs) on sapphire substrates. Compared with the conventional planar device, the MMC HEMT exhibits much less negative slope of the I{sub D}-V{sub DS} curves at high V{sub DS} regime, indicating less self-heating. Using a method proposed by Menozzi and co-workers, we obtained a thermal resistance of 4.8 K-mm/W at ambient temperature of ∼350 K and power dissipation of ∼9 W/mm. This value compares well to 4.1 K-mm/W, which is the thermal resistance of AlGaN/GaN HEMTs on expensive single crystal diamond substrates and the lowest reported value in literature.

a-Axis GaN/AlN/AlGaN Core-Shell Heterojunction Microwires as Normally Off High Electron Mobility Transistors.

Science.gov (United States)

Song, Weidong; Wang, Rupeng; Wang, Xingfu; Guo, Dexiao; Chen, Hang; Zhu, Yuntao; Liu, Liu; Zhou, Yu; Sun, Qian; Wang, Li; Li, Shuti

2017-11-29

Micro/nanowire-based devices have been envisioned as a promising new route toward improved electronic and optoelectronic applications, which attracts considerable research interests. However, suffering from applicable strategies to synthesize uniform core-shell structures to meet the requirement for the investigations of electrical transport behaviors along the length direction or high electron mobility transistor (HEMT) devices, heterojunction wire-based electronics have been explored limitedly. In the present work, GaN/AlN/AlGaN core-shell heterojunction microwires on patterned Si substrates were synthesized without any catalyst via metalorganic chemical vapor deposition. The as-synthesized microwires had low dislocation, sharp, and uniform heterojunction interfaces. Electrical transport performances were evaluated by fabricating HEMTs on the heterojunction microwire channels. Results demonstrated that a normally off operation was achieved with a threshold voltage of 1.4 V, a high on/off current ratio of 10 8 , a transconductance of 165 mS/mm, and a low subthreshold swing of 81 mV/dec. The normally off operation may attribute to the weak polarization along semipolar facets of the heterojunction, which leads to weak constrain of 2DEG.

Electric field driven plasmon dispersion in AlGaN/GaN high electron mobility transistors

International Nuclear Information System (INIS)

Tan Ren-Bing; Qin Hua; Zhang Xiao-Yu; Xu Wen

2013-01-01

We present a theoretical study on the electric field driven plasmon dispersion of the two-dimensional electron gas (2DEG) in AlGaN/GaN high electron mobility transistors (HEMTs). By introducing a drifted Fermi—Dirac distribution, we calculate the transport properties of the 2DEG in the AlGaN/GaN interface by employing the balance-equation approach based on the Boltzmann equation. Then, the nonequilibrium Fermi—Dirac function is obtained by applying the calculated electron drift velocity and electron temperature. Under random phase approximation (RPA), the electric field driven plasmon dispersion is investigated. The calculated results indicate that the plasmon frequency is dominated by both the electric field E and the angle between wavevector q and electric field E. Importantly, the plasmon frequency could be tuned by the applied source—drain bias voltage besides the gate voltage (change of the electron density)

The influence of the AlN barrier thickness on the polarization Coulomb field scattering in AlN/GaN heterostructure field-effect transistors

International Nuclear Information System (INIS)

Lv, Yuanjie; Feng, Zhihong; Gu, Guodong; Han, Tingting; Yin, Jiayun; Liu, Bo; Cai, Shujun; Lin, Zhaojun; Ji, Ziwu; Zhao, Jingtao

2014-01-01

The electron mobility scattering mechanisms in AlN/GaN heterostuctures with 3 nm and 6 nm AlN barrier thicknesses were investigated by temperature-dependent Hall measurements. The effect of interface roughness (IFR) scattering on the electron mobility was found to be enhanced by increasing AlN barrier thickness. Moreover, using the measured capacitance-voltage and current-voltage characteristics of the fabricated heterostructure field-effect transistors (HFETs) with different Schottky areas on the two heterostuctures, the variations of electron mobility with different gate biases were investigated. Due to enhanced IFR scattering, the influence of polarization Coulomb field (PCF) scattering on electron mobility was found to decrease with increasing AlN barrier layer thickness. However, the PCF scattering remained an important scattering mechanism in the AlN/GaN HFETs.

Novel model of a AlGaN/GaN high electron mobility transistor based on an artificial neural network

Science.gov (United States)

Cheng, Zhi-Qun; Hu, Sha; Liu, Jun; Zhang, Qi-Jun

2011-03-01

In this paper we present a novel approach to modeling AlGaN/GaN high electron mobility transistor (HEMT) with an artificial neural network (ANN). The AlGaN/GaN HEMT device structure and its fabrication process are described. The circuit-based Neuro-space mapping (neuro-SM) technique is studied in detail. The EEHEMT model is implemented according to the measurement results of the designed device, which serves as a coarse model. An ANN is proposed to model AlGaN/GaN HEMT based on the coarse model. Its optimization is performed. The simulation results from the model are compared with the measurement results. It is shown that the simulation results obtained from the ANN model of AlGaN/GaN HEMT are more accurate than those obtained from the EEHEMT model. Project supported by the National Natural Science Foundation of China (Grant No. 60776052).

76 FR 75508 - United States Navy Restricted Area, SUPSHIP Bath Maine Detachment Mobile at AUSTAL, USA, Mobile...

Science.gov (United States)

2011-12-02

... Navy Restricted Area, SUPSHIP Bath Maine Detachment Mobile at AUSTAL, USA, Mobile, AL; Restricted Area... facility located in Mobile, Alabama. The Supervisor of Shipbuilding, Conversion and Repair, United States... contracts at AUSTAL USA in Mobile, Alabama, on October 9, 2011, replacing Supervisor of Shipbuilding...

33 CFR 100.919 - International Bay City River Roar, Bay City, MI.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false International Bay City River Roar, Bay City, MI. 100.919 Section 100.919 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF... Bay City River Roar, Bay City, MI. (a) Regulated Area. A regulated area is established to include all...

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)

A self-heating study on multi-finger AlGaN/GaN high electron mobility transistors

International Nuclear Information System (INIS)

Yang Liyuan; Ai Shan; Chen Yonghe; Cao Mengyi; Zhang Kai; Ma Xiaohua; Hao Yue

2013-01-01

Self-heating in multi-finger AlGaN/GaN high-electron-mobility transistors (HEMTs) is investigated by measurements and modeling of device junction temperature under steady-state operation. Measurements are carried out using micro-Raman scattering to obtain the detailed and accurate temperature distribution of the device. The device peak temperature corresponds to the high field region at the drain side of gate edge. The channel temperature of the device is modeled using a combined electro-thermal model considering 2DEG transport characteristics and the Joule heating power distribution. The results reveal excellent correlation to the micro-Raman measurements, validating our model for the design of better cooled structures. Furthermore, the influence of layout design on the channel temperature of multi-finger AlGaN/GaN HEMTs is studied using the proposed electro-thermal model, allowing for device optimization. (semiconductor devices)

Quantum corrections to conductivity observed at intermediate magnetic fields in a high mobility GaAs/AlGaAs 2-dimensional electron gas

International Nuclear Information System (INIS)

Taboryski, R.; Veje, E.; Lindelof, P.E.

1990-01-01

Magnetoresistance with the field perpendicular to the 2-dimensional electron gas in a high mobility GaAs/AlGaAs heterostructure at low temperatures is studied. At the lowest magnetic field we observe the weak localization. At magnetic fields, where the product of the mobility and the magnetic field is of the order of unity, the quantum correction to conductivity due to the electron-electron interaction is as a source of magnetoresistance. A consistent analysis of experiments in this regime is for the first time performed. In addition to the well known electron-electron term with the expected temperature dependence, we find a new type of temperature independent quantum correction, which varies logarithmically with mobility. (orig.)

Effects of SiNx on two-dimensional electron gas and current collapse of AlGaN/GaN high electron mobility transistors

International Nuclear Information System (INIS)

Fan, Ren; Zhi-Biao, Hao; Lei, Wang; Lai, Wang; Hong-Tao, Li; Yi, Luo

2010-01-01

SiN x is commonly used as a passivation material for AlGaN/GaN high electron mobility transistors (HEMTs). In this paper, the effects of SiN x passivation film on both two-dimensional electron gas characteristics and current collapse of AlGaN/GaN HEMTs are investigated. The SiN x films are deposited by high- and low-frequency plasma-enhanced chemical vapour deposition, and they display different strains on the AlGaN/GaN heterostructure, which can explain the experiment results. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Ultrasensitive detection of Hg{sup 2+} using oligonucleotide-functionalized AlGaN/GaN high electron mobility transistor

Energy Technology Data Exchange (ETDEWEB)

Cheng, Junjie [Key Laboratory of Ion Beam Bioengineering, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031 (China); Division of Nanobiomedicine, Key Laboratory for Nano-Bio Interface Research, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123 (China); Li, Jiadong; Miao, Bin; Wu, Dongmin, E-mail: dmwu2008@sinano.ac.cn [i-Lab, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215125 (China); Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123 (China); Wang, Jine; Pei, Renjun, E-mail: rjpei2011@sinano.ac.cn [Division of Nanobiomedicine, Key Laboratory for Nano-Bio Interface Research, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123 (China); Wu, Zhengyan, E-mail: zywu@ipp.ac.cn [Key Laboratory of Ion Beam Bioengineering, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031 (China)

2014-08-25

An oligonucleotide-functionalized ion sensitive AlGaN/GaN high electron mobility transistor (HEMT) was fabricated to detect trace amounts of Hg{sup 2+}. The advantages of ion sensitive AlGaN/GaN HEMT and highly specific binding interaction between Hg{sup 2+} and thymines were combined. The current response of this Hg{sup 2+} ultrasensitive transistor was characterized. The current increased due to the accumulation of Hg{sup 2+} ions on the surface by the highly specific thymine-Hg{sup 2+}-thymine recognition. The dynamic linear range for Hg{sup 2+} detection has been determined in the concentrations from 10{sup −14} to 10{sup −8} M and a detection limit below 10{sup −14} M level was estimated, which is the best result of AlGaN/GaN HEMT biosensors for Hg{sup 2+} detection till now.

Low-resistance gateless high electron mobility transistors using three-dimensional inverted pyramidal AlGaN/GaN surfaces

International Nuclear Information System (INIS)

So, Hongyun; Senesky, Debbie G.

2016-01-01

In this letter, three-dimensional gateless AlGaN/GaN high electron mobility transistors (HEMTs) were demonstrated with 54% reduction in electrical resistance and 73% increase in surface area compared with conventional gateless HEMTs on planar substrates. Inverted pyramidal AlGaN/GaN surfaces were microfabricated using potassium hydroxide etched silicon with exposed (111) surfaces and metal-organic chemical vapor deposition of coherent AlGaN/GaN thin films. In addition, electrical characterization of the devices showed that a combination of series and parallel connections of the highly conductive two-dimensional electron gas along the pyramidal geometry resulted in a significant reduction in electrical resistance at both room and high temperatures (up to 300 °C). This three-dimensional HEMT architecture can be leveraged to realize low-power and reliable power electronics, as well as harsh environment sensors with increased surface area

Low-resistance gateless high electron mobility transistors using three-dimensional inverted pyramidal AlGaN/GaN surfaces

Energy Technology Data Exchange (ETDEWEB)

So, Hongyun, E-mail: hyso@stanford.edu [Department of Aeronautics and Astronautics, Stanford University, Stanford, California 94305 (United States); Senesky, Debbie G. [Department of Aeronautics and Astronautics, Stanford University, Stanford, California 94305 (United States); Department of Electrical Engineering, Stanford University, Stanford, California 94305 (United States)

2016-01-04

In this letter, three-dimensional gateless AlGaN/GaN high electron mobility transistors (HEMTs) were demonstrated with 54% reduction in electrical resistance and 73% increase in surface area compared with conventional gateless HEMTs on planar substrates. Inverted pyramidal AlGaN/GaN surfaces were microfabricated using potassium hydroxide etched silicon with exposed (111) surfaces and metal-organic chemical vapor deposition of coherent AlGaN/GaN thin films. In addition, electrical characterization of the devices showed that a combination of series and parallel connections of the highly conductive two-dimensional electron gas along the pyramidal geometry resulted in a significant reduction in electrical resistance at both room and high temperatures (up to 300 °C). This three-dimensional HEMT architecture can be leveraged to realize low-power and reliable power electronics, as well as harsh environment sensors with increased surface area.

Ecological risk, source and preliminary assessment of metals in the surface sediments of Chabahar Bay, Oman Sea

International Nuclear Information System (INIS)

Agah, Homira; Saleh, Abolfazl; Bastami, Kazem Darvish; Fumani, Neda Sheijooni

2016-01-01

In this study, concentrations of Aluminum (Al), Iron (Fe), Chromium (Cr), Copper (Cu), Nickel (Ni), Vanadium (V), Zinc (Zn), Arsenic (As), Cobalt (Co) and lead (Pb) in the surface sediments from Chabahar Bay were studied to assess the degree of heavy metal pollution as a consequence of natural and anthropogenic sources. Metal contents in the sediments were observed in the order of: Al > Fe > Cr > V > Ni > Zn > Cu > > As > Pb > Co. According to enrichment factor (EF), Arsenic was higher than 1.5 at some sites, indicating anthropogenic inputs. Contents of Ni, As and Cr in the some sampling sites were higher than sediment quality guideline implying adverse impacts of these metals. Based on potential ecological risk (PER), the Chabahar Bay had low ecological risk. - Highlights: •Metals and major elements were determined in surface sediments from Chabahar Bay, Oman Sea. •EF values indicated non-enriched to moderate-enriched. •Ni, As and Cr were above ERL values.

Influence of environmental settings on the prevalence of Trichodesmium spp. in the Bay of Bengal

Digital Repository Service at National Institute of Oceanography (India)

Hegde, S.; Anil, A.C.; Patil, J.S.; Mitbavkar, S.; Venkat, K.; Gopalakrishna, V.V.

) Influence of physical pro- cesses and freshwater discharge on the seasonality of phytoplankton regime in the Bay of Bengal. Cont Shelf Res 20:313–330 Gordon AL (2001) Interocean exchange. In: Sidler G, Church J, Gould J (eds) Ocean circulation and climate...: acanil@nio.org Influence of environmental settings on the prevalence of Trichodesmium spp. in the Bay of Bengal Sahana Hegde, Arga Chandrashekar Anil*, Jagadish S. Patil, Smita Mitbavkar, Venkat Krishnamurthy, Vissa V. Gopalakrishna National Institute...

Sodium beta-alumina thin films as gate dielectrics for AlGaN/GaN metal—insulator—semiconductor high-electron-mobility transistors

International Nuclear Information System (INIS)

Tian Ben-Lang; Chen Chao; Li Yan-Rong; Zhang Wan-Li; Liu Xing-Zhao

2012-01-01

Sodium beta-alumina (SBA) is deposited on AlGaN/GaN by using a co-deposition process with sodium and Al 2 O 3 as the precursors. The X-ray diffraction (XRD) spectrum reveals that the deposited thin film is amorphous. The binding energy and composition of the deposited thin film, obtained from the X-ray photoelectron spectroscopy (XPS) measurement, are consistent with those of SBA. The dielectric constant of the SBA thin film is about 50. Each of the capacitance—voltage characteristics obtained at five different frequencies shows a high-quality interface between SBA and AlGaN. The interface trap density of metal—insulator—semiconductor high-electron-mobility transistor (MISHEMT) is measured to be (3.5∼9.5)×10 10 cm −2 ·eV −1 by the conductance method. The fixed charge density of SBA dielectric is on the order of 2.7×10 12 cm −2 . Compared with the AlGaN/GaN metal—semiconductor heterostructure high-electron-mobility transistor (MESHEMT), the AlGaN/GaN MISHEMT usually has a threshold voltage that shifts negatively. However, the threshold voltage of the AlGaN/GaN MISHEMT using SBA as the gate dielectric shifts positively from −5.5 V to −3.5 V. From XPS results, the surface valence-band maximum (VBM-EF) of AlGaN is found to decrease from 2.56 eV to 2.25 eV after the SBA thin film deposition. The possible reasons why the threshold voltage of AlGaN/GaN MISHEMT with the SBA gate dielectric shifts positively are the influence of SBA on surface valence-band maximum (VBM-EF), the reduction of interface traps and the effects of sodium ions, and/or the fixed charges in SBA on the two-dimensional electron gas (2DEG). (condensed matter: structural, mechanical, and thermal properties)

The tectonic origin of the Bay of Bengal and Bangladesh

Digital Repository Service at National Institute of Oceanography (India)

Talwani, M.; Desa, M.; Ismaiel, M.; Krishna, K.S.

direction for the Indian plate.  4. The 85°E Ridge was initially evolved as a fracture zone, and subsequently associated with volcanism.   5. The oceanic crust of the Western Basin of the Bay of Bengal is older than the crust of the Eastern Basin and Bangla... it a northern extension of the 86°E fracture zone, while Sar et al. [2009] suggested it could have a continental origin. Gibbons et al. [2013] inferred that the 85°E Ridge and the Kerguelen Fracture Zone formed as conjugate flanks of a 'leaky...

Composition and temporal patterns of larval fish communities in Chesapeake and Delaware Bays

Directory of Open Access Journals (Sweden)

Filipe Ribeiro

2015-11-01

Full Text Available Comparing larval fish assemblages in different estuaries provides insights about the coastal distribution of larval populations, larval transport, and adult spawning locations (Ribeiro et al. 2015. We simultaneously compared the larval fish assemblages entering two Middle Atlantic Bight (MAB estuaries (Delaware Bay and Chesapeake Bay, USA through weekly sampling from 2007 to 2009. In total, 43 taxa (32 families and 36 taxa (24 families were collected in Delaware and Chesapeake Bays, respectively. Mean taxonomic diversity, mean richness, and evenness were generally lower in Delaware Bay. Communities of both bays were dominated by Anchoa spp., Gobiosoma spp., Micropogonias undulatus, and Brevoortia tyrannus; Paralichthys spp. was more abundant in Delaware Bay and Microgobius thalassinus was more abundant in Chesapeake Bay. Inter-annual variation in the larval fish communities was low at both sites, with a relatively consistent composition across years, but strong seasonal (intra-annual variation in species composition occurred in both bays. Two groups were identified in Chesapeake Bay: a ‘winter’ group dominated by shelf-spawned species (e.g. M. undulatus and a ‘summer’ group comprising obligate estuarine species and coastal species (e.g. Gobiosoma spp. and Cynoscion regalis, respectively. In Delaware Bay, 4 groups were identified: a ‘summer’ group of mainly obligate estuarine fishes (e.g. Menidia sp. being replaced by a ‘fall’ group (e.g. Ctenogobius boleosoma and Gobionellus oceanicus; ‘winter’ and ‘spring’ groups were dominated by shelf-spawned (e.g. M. undulatus and Paralichthys spp. and obligate estuarine species (e.g. Leiostomus xanthurus and Pseudopleuronectes americanus, respectively. This study demonstrates that inexpensive and simultaneous sampling in different estuaries provides important insights into the variability in community structure of fish assemblages at large spatial scales.

Enhanced two dimensional electron gas transport characteristics in Al2O3/AlInN/GaN metal-oxide-semiconductor high-electron-mobility transistors on Si substrate

International Nuclear Information System (INIS)

Freedsman, J. J.; Watanabe, A.; Urayama, Y.; Egawa, T.

2015-01-01

The authors report on Al 2 O 3 /Al 0.85 In 0.15 N/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistor (MOS-HEMT) on Si fabricated by using atomic layer deposited Al 2 O 3 as gate insulator and passivation layer. The MOS-HEMT with the gate length of 2 μm exhibits excellent direct-current (dc) characteristics with a drain current maximum of 1270 mA/mm at a gate bias of 3 V and an off-state breakdown voltage of 180 V for a gate-drain spacing of 4 μm. Also, the 1 μm-gate MOS-HEMT shows good radio-frequency (rf) response such as current gain and maximum oscillation cut-off frequencies of 10 and 34 GHz, respectively. The capacitance-voltage characteristics at 1 MHz revealed significant increase in two-dimensional electron gas (2DEG) density for the MOS-HEMT compared to conventional Schottky barrier HEMTs. Analyses using drain-source conductivity measurements showed improvements in 2DEG transport characteristics for the MOS-HEMT. The enhancements in dc and rf performances of the Al 2 O 3 /Al 0.85 In 0.15 N/GaN MOS-HEMT are attributed to the improvements in 2DEG characteristics

Nutrient load estimates for Manila Bay, Philippines using population data

NARCIS (Netherlands)

Sotto, Lara Patricia A; Beusen, Arthur H W; Villanoy, Cesar L.; Bouwman, Lex F.; Jacinto, Gil S.

2015-01-01

A major source of nutrient load to periodically hypoxic Manila Bay is the urban nutrient waste water flow from humans and industries to surface water. In Manila alone, the population density is as high as 19,137 people/km2. A model based on a global point source model by Morée et al. (2013) was used

AlGaN/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistor with Polarized P(VDF-TrFE) Ferroelectric Polymer Gating

Science.gov (United States)

Liu, Xinke; Lu, Youming; Yu, Wenjie; Wu, Jing; He, Jiazhu; Tang, Dan; Liu, Zhihong; Somasuntharam, Pannirselvam; Zhu, Deliang; Liu, Wenjun; Cao, Peijiang; Han, Sun; Chen, Shaojun; Seow Tan, Leng

2015-01-01

Effect of a polarized P(VDF-TrFE) ferroelectric polymer gating on AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) was investigated. The P(VDF-TrFE) gating in the source/drain access regions of AlGaN/GaN MOS-HEMTs was positively polarized (i.e., partially positively charged hydrogen were aligned to the AlGaN surface) by an applied electric field, resulting in a shift-down of the conduction band at the AlGaN/GaN interface. This increases the 2-dimensional electron gas (2-DEG) density in the source/drain access region of the AlGaN/GaN heterostructure, and thereby reduces the source/drain series resistance. Detailed material characterization of the P(VDF-TrFE) ferroelectric film was also carried out using the atomic force microscopy (AFM), X-ray Diffraction (XRD), and ferroelectric hysteresis loop measurement. PMID:26364872

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.

Electron Mobilities and Effective Masses in InGaAs/InAlAs HEMT Structures with High In Content

Science.gov (United States)

Yuzeeva, N. A.; Sorokoumova, A. V.; Lunin, R. A.; Oveshnikov, L. N.; Galiev, G. B.; Klimov, E. A.; Lavruchin, D. V.; Kulbachinskii, V. A.

2016-12-01

InxGa_{1-{x}}As/InyAl_{1-{y}}As HEMT structures {δ}-doped by Si were grown by molecular beam epitaxy on InP substrate. We investigated the influence of the In content on the electron mobilities and effective masses in dimensionally quantized subbands. The electron effective masses were determined by the temperature dependence of the amplitude of the Shubnikov-de Haas effect at 1.6 and 4.2 K. We found that the more the In content in quantum well (QW), the less the electron effective masses. The mobilities are higher in HEMT structures with wider and deeper QW. The energy band diagrams were calculated by using Vegard's law for basic parameters. The calculated band diagrams are in a good agreement with the experimental data of photoluminescence spectra.

Innovazione nel mobile learning

Directory of Open Access Journals (Sweden)

Immaculada Arnedillo-Sànchez

2008-01-01

Full Text Available Descrizione, da una prospettiva europea, dell’innovazione nel settore del mobile learning e l’utilizzabilita’ del mobile learning in contesti educativi. Vengono illustrate i principali progetti europei di m-learning e si esamina le prospettive pedagogiche e teoriche relative al campo.

Analysis of Suspended-Sediment Dynamics in Gulf of Mexico Estuaries Using MODIS/Terra 250-m Imagery

Science.gov (United States)

McCarthy, M. J.; Otis, D. B.; Muller-Karger, F. E.; Mendez-Lazaro, P.; Chen, F. R.

2016-02-01

Suspended sediments in coastal ecosystems reduce light penetration, degrade water quality, and inhibit primary production. In this study, a 15-year Moderate Resolution Imaging Spectroradiometer (MODIS/Terra) turbidity time-series was developed for use in the estuaries of the Gulf of Mexico (GOM). Remote-sensing reflectance (Rrs) at 645 nm and 250-m resolution was validated with in-situ turbidity measurements in these estuaries: Coastal Bend Bays (TX), Galveston Bay (TX), Barataria and Terrebonne Bays (LA), Mobile Bay (AL), Tampa Bay (FL), Sarasota Bay (FL), and Charlotte Harbor (FL). Mean values of turbidity over the time-series ranged from 2.5 NTU to over 10 NTU. Turbidity patterns exhibited seasonal cycles with peak values generally found during spring months, although there is considerable variability in the timing of peak turbidity. Episodes of elevated turbidity ranged from 6 episodes in Galveston Bay to 15 in Mobile Bay. The spatial extent of elevated turbidity within estuaries, frequency and duration of turbidity events, and potential driving factors behind episodes of elevated turbidity were also examined.

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.

Mobile computing handbook

CERN Document Server

Ilyas, Mohammad

2004-01-01

INTRODUCTION AND APPLICATIONS OF MOBILE COMPUTING Wearable Computing,A. Smailagic and D.P. Siewiorek Developing Mobile Applications: A Lime Primer,G.P. Picco, A.L. Murphy, and G.-C. Roman Pervasive Application Development: Approaches and Pitfalls,G. Banavar, N. Cohen, and D. Soroker ISAM, Joining Context-Awareness and Mobility to Building Pervasive Applications,I. Augustin, A. Corrêa Yamin, J.L. Victória Barbosa, L. Cavalheiro da Silva, R. Araújo Real, G. Frainer, G.G. Honrich Cavalheiro, and C.F. Resin Geyer Integrating Mobile Wireless Devices into the Computational Grid,T. Phan, L. Huan

Temperature dependent DC characterization of InAlN/(AlN)/GaN HEMT for improved reliability

Science.gov (United States)

Takhar, K.; Gomes, U. P.; Ranjan, K.; Rathi, S.; Biswas, D.

2015-02-01

InxAl1-xN/AlN/GaN HEMT device performance is analysed at various temperatures with the help of physics based 2-D simulation using commercially available BLAZE and GIGA modules from SILVACO. Various material parameters viz. band-gap, low field mobility, density of states, velocity saturation, and substrate thermal conductivity are considered as critical parameters for predicting temperature effect in InxAl1-xN/AlN/GaN HEMT. Reduction in drain current and transconductance has been observed due to the decrease of 2-DEG mobility and effective electron velocity with the increase in temperature. Degradation in cut-off frequency follows the transconductance profile as variation in gate-source/gate-drain capacitances observed very small.

Meteorological, biological, and hydrographic data collected from Katrina Cut Station near Dauphin Island, AL from 04/15/2011 - 12/31/2013 (NODC Accession 0117374)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Abstract: Dauphin Island Sea Lab and the Mobile Bay National Estuary Program have partnered with the Alabama Department of Conservation and Mobile County to provide...

Meteorological, biological, and hydrographic data collected from Bon Secour Station near Dauphin Island, AL from 01/01/2014 - 12/31/2014 (NCEI Accession 0140527)

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Abstract: Dauphin Island Sea Lab and the Mobile Bay National Estuary Program have partnered with the Alabama Department of Conservation and Mobile County to provide...

AlGaN/GaN High Electron Mobility Transistor-Based Biosensor for the Detection of C-Reactive Protein.

Science.gov (United States)

Lee, Hee Ho; Bae, Myunghan; Jo, Sung-Hyun; Shin, Jang-Kyoo; Son, Dong Hyeok; Won, Chul-Ho; Jeong, Hyun-Min; Lee, Jung-Hee; Kang, Shin-Won

2015-07-28

In this paper, we propose an AlGaN/GaN high electron mobility transistor (HEMT)-based biosensor for the detection of C-reactive protein (CRP) using a null-balancing circuit. A null-balancing circuit was used to measure the output voltage of the sensor directly. The output voltage of the proposed biosensor was varied by antigen-antibody interactions on the gate surface due to CRP charges. The AlGaN/GaN HFET-based biosensor with null-balancing circuit applied shows that CRP can be detected in a wide range of concentrations, varying from 10 ng/mL to 1000 ng/mL. X-ray photoelectron spectroscopy was carried out to verify the immobilization of self-assembled monolayer with Au on the gated region.

33 CFR 162.125 - Sturgeon Bay and the Sturgeon Bay Ship Canal, Wisc.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 2 2010-07-01 2010-07-01 false Sturgeon Bay and the Sturgeon Bay Ship Canal, Wisc. 162.125 Section 162.125 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) PORTS AND WATERWAYS SAFETY INLAND WATERWAYS NAVIGATION REGULATIONS § 162.125 Sturgeon Bay and the Sturgeon Bay Ship...

Bird surveys at McKinley Bay and Hutchison Bay, Northwest Territories, in 1991

Energy Technology Data Exchange (ETDEWEB)

Cornish, B J; Dickson, D L; Dickson, H L

1992-03-01

McKinley Bay is a shallow protected bay along the eastern Beaufort Sea coast which provides an important habitat for diving ducks. Since 1979, the bay has been the site of a winter harbor and support base for oil and gas exploraton in the Beaufort Sea. Aerial surveys for bird abundance and distribution were conducted in August 1991 as a continuation of long-term monitoring of birds in McKinley Bay and Hutchison Bay, a nearby area used as a control. The main objectives of the 1991 surveys were to expand the set of baseline data on natural annual fluctuations in diving duck numbers, and to determine if numbers of diving ducks had changed since the initial 1981-85 surveys. On the day with the best survey conditions, the population of diving ducks at McKinley bay was estimated at ca 32,000, significantly more than 1981-85. At Hutchison Bay, there were an estimated 11,000 ducks. As in previous years, large numbers of diving ducks were observed off Atkinson Point at the northwest corner of McKinley Bay, at the south end of the bay, and in the northeast corner near a long spit. Most divers in Hutchison Bay were at the west side. Diving ducks, primarily Oldsquaw and scoter, were the most abundant bird group in the study area. Observed distribution patterns of birds are discussed with reference to habitat preferences. 16 refs., 7 figs., 30 tabs.

Pb’s high sedimentation inside the bay mouth of Jiaozhou Bay

Science.gov (United States)

Yang, Dongfang; Miao, Zhenqing; Huang, Xinmin; Wei, Linzhen; Feng, Ming

2017-12-01

Sedimentation is one of the key environmental behaviors of pollutants in the ocean. This paper analyzed the seasonal and temporal variations of Pb’s sedimentation process in Jiaozhou Bay in 1987. Results showed that Pb contents in bottom waters in Jiaozhou Bay in May, July and November 1987 were 1.87-2.60 μg L-1, 15.11-19.68 μg L-1 and 11.08-15.18 μg L-1, and the pollution levels of Pb in May, July and November 1987 were slight, heavy and heavy, respectively. In May 1987, there was low sedimentation process in waters in the outside of the bay mouth, yet were high sedimentation process in waters in the middle and inside of the bay mouth. In July and November 1987, there was low sedimentation process in waters in the outside of the bay mouth, yet were high sedimentation process in waters in the inside of the bay mouth. The seasonal-temporal variation of sedimentation processes of Pb were determined by the variations of sources input and the vertical water’s effect.

Effect of surface passivation by SiN/SiO2 of AlGaN/GaN high-electron mobility transistors on Si substrate by deep level transient spectroscopy method

International Nuclear Information System (INIS)

Gassoumi, Malek; Mosbahi, Hana; Zaidi, Mohamed Ali; Gaquiere, Christophe; Maaref, Hassen

2013-01-01

Device performance and defects in AlGaN/GaN high-electron mobility transistors have been correlated. The effect of SiN/SiO 2 passivation of the surface of AlGaN/GaN high-electron mobility transistors on Si substrates is reported on DC characteristics. Deep level transient spectroscopy (DLTS) measurements were performed on the device after the passivation by a (50/100 nm) SiN/SiO 2 film. The DLTS spectra from these measurements showed the existence of the same electron trap on the surface of the device

The effect of ammonia flow in the AlN spacer on the electrical properties of InAlN/AlN/GaN HEMT structures

International Nuclear Information System (INIS)

Gamarra, Piero; Lacam, Cedric; Magis, Michelle; Tordjman, Maurice; Di Forte Poisson, Marie-Antoinette

2012-01-01

During the past few years it has been reported that a thin AlN spacer of few nanometers needs to be inserted in InAlN/GaN high electron mobility transistors (HEMTs) to obtain high 2DEG carrier mobility. This work presents a systematic study of the effects of varying the ammonia flow in the AlN spacer of InAlN/AlN/GaN HEMTs grown by low pressure metalorganic vapour phase epitaxy (LP-MOVPE). The strain state, the surface roughness and the growth rate of AlN were found to be dependent on the V/III ratio. In addition the ammonia flow in the interlayer has a strong impact on the structural properties of the subsequent InAlN barrier layer and on the electrical properties of the structure. A sheet resistance as low as 327 Ω/□ with a sheet carrier density of 1.5 x 10 13 cm -2 has been obtained at room temperature. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

The effect of ammonia flow in the AlN spacer on the electrical properties of InAlN/AlN/GaN HEMT structures

Energy Technology Data Exchange (ETDEWEB)

Gamarra, Piero; Lacam, Cedric; Magis, Michelle; Tordjman, Maurice; Di Forte Poisson, Marie-Antoinette [III-V Lab., Marcussis (France)

2012-01-15

During the past few years it has been reported that a thin AlN spacer of few nanometers needs to be inserted in InAlN/GaN high electron mobility transistors (HEMTs) to obtain high 2DEG carrier mobility. This work presents a systematic study of the effects of varying the ammonia flow in the AlN spacer of InAlN/AlN/GaN HEMTs grown by low pressure metalorganic vapour phase epitaxy (LP-MOVPE). The strain state, the surface roughness and the growth rate of AlN were found to be dependent on the V/III ratio. In addition the ammonia flow in the interlayer has a strong impact on the structural properties of the subsequent InAlN barrier layer and on the electrical properties of the structure.istance as low as 327 {omega}/{open_square} with a sheet carrier density of 1.5 x 10{sup 13} cm{sup -2} has been obtained at room temperature. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

Evaluation of thermal resistance constitution for packaged AlGaN/GaN high electron mobility transistors by structure function method

International Nuclear Information System (INIS)

Zhang Guang-Chen; Feng Shi-Wei; Zhou Zhou; Li Jing-Wan; Guo Chun-Sheng

2011-01-01

The evaluation of thermal resistance constitution for packaged AlGaN/GaN high electron mobility transistor (HEMT) by structure function method is proposed in this paper. The evaluation is based on the transient heating measurement of the AlGaN/GaN HEMT by pulsed electrical temperature sensitive parameter method. The extracted chip-level and package-level thermal resistances of the packaged multi-finger AlGaN/GaN HEMT with 400-μm SiC substrate are 22.5 K/W and 7.2 K/W respectively, which provides a non-invasive method to evaluate the chip-level thermal resistance of packaged AlGaN/GaN HEMTs. It is also experimentally proved that the extraction of the chip-level thermal resistance by this proposed method is not influenced by package form of the tested device and temperature boundary condition of measurement stage. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Streamlining machine learning in mobile devices for remote sensing

Science.gov (United States)

Coronel, Andrei D.; Estuar, Ma. Regina E.; Garcia, Kyle Kristopher P.; Dela Cruz, Bon Lemuel T.; Torrijos, Jose Emmanuel; Lim, Hadrian Paulo M.; Abu, Patricia Angela R.; Victorino, John Noel C.

2017-09-01

Mobile devices have been at the forefront of Intelligent Farming because of its ubiquitous nature. Applications on precision farming have been developed on smartphones to allow small farms to monitor environmental parameters surrounding crops. Mobile devices are used for most of these applications, collecting data to be sent to the cloud for storage, analysis, modeling and visualization. However, with the issue of weak and intermittent connectivity in geographically challenged areas of the Philippines, the solution is to provide analysis on the phone itself. Given this, the farmer gets a real time response after data submission. Though Machine Learning is promising, hardware constraints in mobile devices limit the computational capabilities, making model development on the phone restricted and challenging. This study discusses the development of a Machine Learning based mobile application using OpenCV libraries. The objective is to enable the detection of Fusarium oxysporum cubense (Foc) in juvenile and asymptomatic bananas using images of plant parts and microscopic samples as input. Image datasets of attached, unattached, dorsal, and ventral views of leaves were acquired through sampling protocols. Images of raw and stained specimens from soil surrounding the plant, and sap from the plant resulted to stained and unstained samples respectively. Segmentation and feature extraction techniques were applied to all images. Initial findings show no significant differences among the different feature extraction techniques. For differentiating infected from non-infected leaves, KNN yields highest average accuracy, as opposed to Naive Bayes and SVM. For microscopic images using MSER feature extraction, KNN has been tested as having a better accuracy than SVM or Naive-Bayes.

Herbert: A Second Generation Mobile Robot.

Science.gov (United States)

1988-01-01

PROJECT. TASK S Artificial Inteligence Laboratory AREA A WORK UNIT NUMBERS ’ ~ 545 Technology Square Cambridge, MA 02139 11. CONTROLLING OFFICE NAME...AD-AI93 632 WMRT: A SECOND GENERTION MOBILE ROWT(U) / MASSACHUSETTS IMST OF TECH CAMBRIDGE ARTIFICIAL INTELLIGENCE LAB R BROOKS ET AL .JAN l8 Al-M...MASSACHUSETTS INSTITUTE OF TECHNOLOGY ARTIFICIAL INTELLIGENCE LABORATORY A. I. Memo 1016 January, 1988 HERBERT: A SECOND GENERATION MOBILE ROBOT Rodney A

2014 Mobile County, AL DMC 4-Band 8 Bit Imagery

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — This dataset was developed to support Mobile County. The project area is 1402 square miles of Mobile County land. The scope of work involved data acquisition and...

Tampa Bay as a model estuary for examining the impact of human activities on biogeochemical processes: an introduction

Science.gov (United States)

Swarzenski, Peter W.; Baskaran, Mark; Henderson, Carl S.; Yates, Kim

2007-01-01

Tampa Bay is a shallow, Y-shaped coastal embayment that is located along the center of the Florida Platform – an expansive accumulation of Cretaceous–Tertiary shallow-water carbonates and evaporites that were periodically exposed during glacio–eustatic sea level fluctuations. As a consequence, extensive karstification likely had a controlling impact on the geologic evolution of Tampa Bay. Despite its large aerial size (∼ 1000 km2), Tampa Bay is relatively shallow (mean depth = 4 m) and its watershed (6700 km2) is among the smallest in the Gulf of Mexico. About 85% of all freshwater inflow (mean = 63 m3 s-1) to the bay is carried by four principal tributaries (Orlando et al., 1993). Groundwater makes up an important component of baseflow of these coastal streams and may also be important in delivering nutrients and other constituents to the bay proper by submarine groundwater discharge.

Investigation of structural, optical, and electrical characteristics of an AlGaN/GaN high electron mobility transistor structure across a 200 mm Si(1 1 1) substrate

International Nuclear Information System (INIS)

Perozek, J; Lee, H-P; Bayram, C; Krishnan, B; Paranjpe, A; Reuter, K B; Sadana, D K

2017-01-01

An AlGaN/GaN high electron mobility transistor (HEMT) structure is grown on a 200 mm Si(1 1 1) substrate. The AlGaN/AlN/GaN heterostructure atop, which forms the 2D electron gas, is studied via transmission electron microscopy (TEM), scanning tunneling microscopy, and TEM chemical analysis. To quantify the uniformity of structural, optical, and electrical properties of these AlGaN/GaN HEMT structures, scanning electron microscopy, optical microscopy, atomic-force microscopy, x-ray diffraction ( ω /2 θ scan and reciprocal space mapping) and Hall effect measurements are employed across the center, middle, and edge of the 200 mm wafer. Small thickness (<3%) and Al-content (<3%) variations in (Al)GaN layers across the wafer are recorded whereas a considerable change (28%) in the electron mobility is observed across the wafer that correlates with variations in surface roughness, defectivity, and layer stress. We attribute the higher mobility in the middle of the wafer to lower interface scattering, thanks to lower surface roughness and less edge-type dislocation density. Additionally, argon (Ar) ion implantation is used as a means for planar electrical isolation, and a seven orders of magnitude decrease in leakage current is achieved when an optimum Ar dose of 10 13 cm −2 is used. The feasibility of scaling AlGaN/GaN HEMTs on a 200 mm Si(1 1 1) platform is discussed. (paper)

Suppression of surface-originated gate lag by a dual-channel AlN/GaN high electron mobility transistor architecture

Science.gov (United States)

Deen, David A.; Storm, David F.; Scott Katzer, D.; Bass, R.; Meyer, David J.

2016-08-01

A dual-channel AlN/GaN high electron mobility transistor (HEMT) architecture is demonstrated that leverages ultra-thin epitaxial layers to suppress surface-related gate lag. Two high-density two-dimensional electron gas (2DEG) channels are utilized in an AlN/GaN/AlN/GaN heterostructure wherein the top 2DEG serves as a quasi-equipotential that screens potential fluctuations resulting from distributed surface and interface states. The bottom channel serves as the transistor's modulated channel. Dual-channel AlN/GaN heterostructures were grown by molecular beam epitaxy on free-standing hydride vapor phase epitaxy GaN substrates. HEMTs fabricated with 300 nm long recessed gates demonstrated a gate lag ratio (GLR) of 0.88 with no degradation in drain current after bias stressed in subthreshold. These structures additionally achieved small signal metrics ft/fmax of 27/46 GHz. These performance results are contrasted with the non-recessed gate dual-channel HEMT with a GLR of 0.74 and 82 mA/mm current collapse with ft/fmax of 48/60 GHz.

Piezotronic effect tuned AlGaN/GaN high electron mobility transistor

Science.gov (United States)

Jiang, Chunyan; Liu, Ting; Du, Chunhua; Huang, Xin; Liu, Mengmeng; Zhao, Zhenfu; Li, Linxuan; Pu, Xiong; Zhai, Junyi; Hu, Weiguo; Wang, Zhong Lin

2017-11-01

The piezotronic effect utilizes strain-induced piezoelectric polarization charges to tune the carrier transportation across the interface/junction. We fabricated a high-performance AlGaN/GaN high electron mobility transistor (HEMT), and the transport property was proven to be enhanced by applying an external stress for the first time. The enhanced source-drain current was also observed at any gate voltage and the maximum enhancement of the saturation current was up to 21% with 15 N applied stress (0.18 GPa at center) at -1 V gate voltage. The physical mechanism of HEMT with/without external compressive stress conditions was carefully illustrated and further confirmed by a self-consistent solution of the Schrödinger-Poisson equations. This study proves the cause-and-effect relationship between the piezoelectric polarization effect and 2D electron gas formation, which provides a tunable solution to enhance the device performance. The strain tuned HEMT has potential applications in human-machine interface and the security control of the power system.

Atomic mobility in liquid and fcc Al-Si-Mg-RE (RE = Ce, Sc) alloys and its application to the simulation of solidification processes in RE-containing A357 alloys

Energy Technology Data Exchange (ETDEWEB)

Lu, Zhao; Zhang, Lijun [Central South Univ., Changsha (China). State Key Lab of Powder Metallurgy; Tang, Ying [Thermo-Calc Software AB, Solna (Sweden)

2017-06-15

This paper first provides a critical review of experimental and theoretically-predicted diffusivities in both liquid and fcc Al-Si-Mg-RE (RE = Ce, Sc) alloys as-reported by previous researchers. The modified Sutherland equation is then employed to predict self- and impurity diffusivities in Al-Si-Mg-RE melts. The self-diffusivity of metastable fcc Sc is evaluated via the first-principles computed activation energy and semi-empirical relations. Based on the critically-reviewed and presently evaluated diffusivity information, atomic mobility descriptions for liquid and fcc phases in the Al-Si-Mg-RE systems are established by means of the Diffusion-Controlled TRAnsformation (DICTRA) software package. Comprehensive comparisons show that most of the measured and theoretically-predicted diffusivities can be reasonably reproduced by the present atomic mobility descriptions. The atomic mobility descriptions for liquid and fcc Al-Si-Mg-RE alloys are further validated by comparing the model-predicted differential scanning calorimetry curves for RE-containing A357 alloys during solidification against experimental data. Detailed analysis of the curves and microstructures in RE-free and RE-containing A357 alloys indicates that both Ce and Sc can serve as the grain refiner for A357 alloys, and that the grain refinement efficiency of Sc is much higher.

Atomic mobility in liquid and fcc Al-Si-Mg-RE (RE = Ce, Sc) alloys and its application to the simulation of solidification processes in RE-containing A357 alloys

International Nuclear Information System (INIS)

Lu, Zhao; Zhang, Lijun

2017-01-01

This paper first provides a critical review of experimental and theoretically-predicted diffusivities in both liquid and fcc Al-Si-Mg-RE (RE = Ce, Sc) alloys as-reported by previous researchers. The modified Sutherland equation is then employed to predict self- and impurity diffusivities in Al-Si-Mg-RE melts. The self-diffusivity of metastable fcc Sc is evaluated via the first-principles computed activation energy and semi-empirical relations. Based on the critically-reviewed and presently evaluated diffusivity information, atomic mobility descriptions for liquid and fcc phases in the Al-Si-Mg-RE systems are established by means of the Diffusion-Controlled TRAnsformation (DICTRA) software package. Comprehensive comparisons show that most of the measured and theoretically-predicted diffusivities can be reasonably reproduced by the present atomic mobility descriptions. The atomic mobility descriptions for liquid and fcc Al-Si-Mg-RE alloys are further validated by comparing the model-predicted differential scanning calorimetry curves for RE-containing A357 alloys during solidification against experimental data. Detailed analysis of the curves and microstructures in RE-free and RE-containing A357 alloys indicates that both Ce and Sc can serve as the grain refiner for A357 alloys, and that the grain refinement efficiency of Sc is much higher.

AlGaN/GaN High Electron Mobility Transistor-Based Biosensor for the Detection of C-Reactive Protein

Directory of Open Access Journals (Sweden)

Hee Ho Lee

2015-07-01

Full Text Available In this paper, we propose an AlGaN/GaN high electron mobility transistor (HEMT-based biosensor for the detection of C-reactive protein (CRP using a null-balancing circuit. A null-balancing circuit was used to measure the output voltage of the sensor directly. The output voltage of the proposed biosensor was varied by antigen-antibody interactions on the gate surface due to CRP charges. The AlGaN/GaN HFET-based biosensor with null-balancing circuit applied shows that CRP can be detected in a wide range of concentrations, varying from 10 ng/mL to 1000 ng/mL. X-ray photoelectron spectroscopy was carried out to verify the immobilization of self-assembled monolayer with Au on the gated region.

Mobile health: a synopsis and comment on "Increasing physical activity with mobile devices: a meta-analysis".

Science.gov (United States)

Johnston, Winter; Hoffman, Sara; Thornton, Louise

2014-03-01

We offer a synopsis and commentary on J. Fanning and colleagues' article "Increasing Physical Activity with Mobile Devices: A Meta-Analysis" published in the Journal of Medical Internet Research. Although regular physical activity has a range of benefits, very few adults in the USA meet recommended guidelines for daily physical activity. The meta-analysis of Fanning et al. (2012) aimed to synthesize the results of research using mobile devices to increase physical activity. Their review identified 11 studies that used mobile technologies, including short message service (SMS), apps, or personal digital assistant (PDA) to improve physical activity behaviors among participants. Fanning et al. conclude that while literature in this area is limited to date, there is initial support for the efficacy of mobile-based interventions for improving physical activity. Included studies varied greatly, and the majority used only SMS to influence physical behaviors, meaning generalization of results to other forms of mobile technologies may be premature. This review does, however, provide a foundation for understanding how mobile-based interventions may be used efficaciously for the development of future interventions to improve health behaviors.

The onset of deglaciation of Cumberland Bay and Stromness Bay, South Georgia

NARCIS (Netherlands)

Van Der Putten, N.; Verbruggen, C.

Carbon dating of basal peat deposits in Cumberland Bay and Stromness Bay and sediments from a lake in Stromness Bay, South Georgia indicates deglaciation at the very beginning of the Holocene before c. 9500 14C yr BP. This post-dates the deglaciation of one local lake which has been ice-free since

Structural properties of MBE AlInN and AlGaInN barrier layers for GaN-HEMT structures

International Nuclear Information System (INIS)

Kirste, Lutz; Lim, Taek; Aidam, Rolf; Mueller, Stefan; Waltereit, Patrick; Ambacher, Oliver

2010-01-01

A high-resolution X-ray diffraction and X-ray reflectivity study of the structural properties of AlInN/GaN and AlGaInN/GaN high electron mobility transistor structures deposited by molecular beam epitaxy on metal organic chemical vapor deposition GaN/Al 2 O 3 and GaN/SiC templates is presented. A new AlN/GaN/AlN triple-interlayer is implemented to improve the interface properties between barrier layer and GaN buffer for a higher mobility of the polarization induced two-dimensional electron gas. Layer properties and structural parameters like concentration, interface quality, layer thickness, strain and crystalline perfection are analyzed. Best structural properties are achieved for an AlGaInN layer with AlN/GaN/AlN interlayer deposited on a GaN/4H-SiC (00.1) template. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

Mobilità ubiquitaria con i telefoni cellulari in contesto scolastico formale – un approccio al mobile learning basato su una cultura ecologica

Directory of Open Access Journals (Sweden)

Ben Bachmair

2013-03-01

Full Text Available Non basta limitarsi ad aggiungere i telefoni cellulari alla lunga lista dei media che sono entrati nel mondo nella scuola per migliorare l’offerta formativa. In quest’ottica, il contributo qui presentato si sofferma sui telefoni cellulari considerandoli come una nuova risorsa culturale emergente in un sistema massmediale connotato da personalizzazione, mobilità e convergenza. Inoltre, un simile approccio che vede i cellulari come risorse culturali, sollecita la scuola ad affrontare un dibattito sulle risorse in chiave ecologica. Per individuare soluzioni di impiego di queste nuove risorse culturali, funzionali ai curricoli scolastici, viene prima di tutto suggerita un’analisi dei telefoni cellulari da una prospettiva teorica, considerandoli in rapporto alle strutture sociali, che si riferiscono all’«agency» degli utenti e alle pratiche culturali di uso dei media e dell’apprendimento. In secondo luogo, attraverso questa analisi triangolare delle strutture, dell’agency e delle pratiche, viene esplorato il complesso mobile (mobile complex al fine di collocare la scuola al suo interno. Successivamente viene descritta un’esperienza di impiego del cellulare per la didattica della matematica in contesto scolastico. Dall’analisi di questo progetto dovrebbero emergere le opportunità offerte dai contesti generati dagli utenti, i quali dovrebbero facilitare l’integrazione dell’apprendimento informale nella scuola. Questa investigazione ha condotto alla messa a punto di linee guida per il mobile learning articolate in tre punti1.

Speciation of Metals and Assessment of Contamination in Surface Sediments from Daya Bay, South China Sea

Directory of Open Access Journals (Sweden)

Jie Yang

2014-12-01

Full Text Available The contents, speciation, source factors and potential ecological risks of the selected metals (Cr, Ni, Cu, Pb, Zn, Cd and As were analyzed in surface sediments from Daya Bay (DYB. The results show that, with the exception of Pb, metal concentrations have decreased at all sites over the past decade. The distribution features of these concentrations represent a ring shape that descends from shore to bay by varying degrees. Speciation analysis showed that Cr, Ni, Cu, Zn and As exist mainly in the residual fraction and, thus, are of low bioavailability, while Cd and Pb were found to be abundant in the non-residual fraction and, thus, have high potential mobility. The ratio of heavy metals in non-residual form in descending order is Pb (78.83%, Cd (78.65%, Cu (48.54%, Zn (48.10%, Ni (38.31%, Cr (28.43% and As (27.76%. The ratio of Pb content is the highest, meaning the highest mobility of Pb. The metals’ potential ecological risks to the environment were also assessed using the methods of the mean effect range-median quotient and the criteria of risk assessment code. The results showed that Cd presents the highest risk, and Pb and Cu are generally considered to be medium risks in the sub-basins of Daya Bay. The principal component analysis (PCA revealed that natural coastal weathering and erosion of rock caused the highest input, followed by mariculture and industrial wastewater and, finally, domestic sewage discharge.

A Bayes Theory-Based Modeling Algorithm to End-to-end Network Traffic

OpenAIRE

Zhao Hong-hao; Meng Fan-bo; Zhao Si-wen; Zhao Si-hang; Lu Yi

2016-01-01

Recently, network traffic has exponentially increasing due to all kind of applications, such as mobile Internet, smart cities, smart transportations, Internet of things, and so on. the end-to-end network traffic becomes more important for traffic engineering. Usually end-to-end traffic estimation is highly difficult. This paper proposes a Bayes theory-based method to model the end-to-end network traffic. Firstly, the end-to-end network traffic is described as a independent identically distrib...

AlN Surface Passivation of GaN-Based High Electron Mobility Transistors by Plasma-Enhanced Atomic Layer Deposition.

Science.gov (United States)

Tzou, An-Jye; Chu, Kuo-Hsiung; Lin, I-Feng; Østreng, Erik; Fang, Yung-Sheng; Wu, Xiao-Peng; Wu, Bo-Wei; Shen, Chang-Hong; Shieh, Jia-Ming; Yeh, Wen-Kuan; Chang, Chun-Yen; Kuo, Hao-Chung

2017-12-01

We report a low current collapse GaN-based high electron mobility transistor (HEMT) with an excellent thermal stability at 150 °C. The AlN was grown by N 2 -based plasma enhanced atomic layer deposition (PEALD) and shown a refractive index of 1.94 at 633 nm of wavelength. Prior to deposit AlN on III-nitrides, the H 2 /NH 3 plasma pre-treatment led to remove the native gallium oxide. The X-ray photoelectron spectroscopy (XPS) spectroscopy confirmed that the native oxide can be effectively decomposed by hydrogen plasma. Following the in situ ALD-AlN passivation, the surface traps can be eliminated and corresponding to a 22.1% of current collapse with quiescent drain bias (V DSQ ) at 40 V. Furthermore, the high temperature measurement exhibited a shift-free threshold voltage (V th ), corresponding to a 40.2% of current collapse at 150 °C. The thermal stable HEMT enabled a breakdown voltage (BV) to 687 V at high temperature, promising a good thermal reliability under high power operation.

AlN Surface Passivation of GaN-Based High Electron Mobility Transistors by Plasma-Enhanced Atomic Layer Deposition

Science.gov (United States)

Tzou, An-Jye; Chu, Kuo-Hsiung; Lin, I.-Feng; Østreng, Erik; Fang, Yung-Sheng; Wu, Xiao-Peng; Wu, Bo-Wei; Shen, Chang-Hong; Shieh, Jia-Ming; Yeh, Wen-Kuan; Chang, Chun-Yen; Kuo, Hao-Chung

2017-04-01

We report a low current collapse GaN-based high electron mobility transistor (HEMT) with an excellent thermal stability at 150 °C. The AlN was grown by N2-based plasma enhanced atomic layer deposition (PEALD) and shown a refractive index of 1.94 at 633 nm of wavelength. Prior to deposit AlN on III-nitrides, the H2/NH3 plasma pre-treatment led to remove the native gallium oxide. The X-ray photoelectron spectroscopy (XPS) spectroscopy confirmed that the native oxide can be effectively decomposed by hydrogen plasma. Following the in situ ALD-AlN passivation, the surface traps can be eliminated and corresponding to a 22.1% of current collapse with quiescent drain bias ( V DSQ) at 40 V. Furthermore, the high temperature measurement exhibited a shift-free threshold voltage ( V th), corresponding to a 40.2% of current collapse at 150 °C. The thermal stable HEMT enabled a breakdown voltage (BV) to 687 V at high temperature, promising a good thermal reliability under high power operation.

A Bayes Factor Meta-Analysis of Recent Extrasensory Perception Experiments: Comment on Storm, Tressoldi, and Di Risio (2010)

Science.gov (United States)

Rouder, Jeffrey N.; Morey, Richard D.; Province, Jordan M.

2013-01-01

Psi phenomena, such as mental telepathy, precognition, and clairvoyance, have garnered much recent attention. We reassess the evidence for psi effects from Storm, Tressoldi, and Di Risio's (2010) meta-analysis. Our analysis differs from Storm et al.'s in that we rely on Bayes factors, a Bayesian approach for stating the evidence from data for…

Instrument packages to study long-term sediment transport processes in a shallow bay

Science.gov (United States)

Strahle, William J.; Martini, Marinna A.; Davis, Ray E.

1994-01-01

Pressure and near-surface and near-bottom measurements of current, temperature, salinity and light transmission were required in Mobile Bay, a 3 m deep estuary on the Gulf of Mexico. This environment presented several obstacles to obtaining long term observations. Boat traffic, soft estuary bottom, heavy biofouling, rapid sample rates and large data storage were overcome by using instrumentation techniques that are applicable to other estuary systems. Nearly two years of continuous data was collected.

75 FR 8297 - Tongass National Forest, Thorne Bay Ranger District, Thorne Bay, AK

Science.gov (United States)

2010-02-24

..., Thorne Bay, AK AGENCY: Forest Service, USDA. ACTION: Cancellation of Notice of intent to prepare an... Roberts, Zone Planner, Thorne Bay Ranger District, Tongass National Forest, P.O. Box 19001, Thorne Bay, AK 99919, telephone: 907-828-3250. SUPPLEMENTARY INFORMATION: The 47,007-acre Kosciusko Project Area is...

77 FR 44140 - Drawbridge Operation Regulation; Sturgeon Bay Ship Canal, Sturgeon Bay, WI

Science.gov (United States)

2012-07-27

... Maple-Oregon Bridges so vehicular traffic congestion would not develop on downtown Sturgeon Bay streets... movement of vehicular traffic in Sturgeon Bay. The Sturgeon Bay Ship Canal is approximately 8.6 miles long... significant increase in vehicular and vessel traffic during the peak tourist and navigation season between...

Kink effect and noise performance in isolated-gate InAs/AlSb high electron mobility transistors

International Nuclear Information System (INIS)

Vasallo, B G; González, T; Mateos, J; Rodilla, H; Moschetti, G; Grahn, J

2012-01-01

The kink effect can spoil the otherwise excellent low noise performance of InAs/AlSb high electron mobility transistors. It has its origin in the pile-up of holes (generated by impact ionization) taking place mainly at the drain side of the buffer, which leads to a reduction of the gate-induced channel depletion and results in a drain current enhancement. Our results indicate that the generation of holes by impact ionization and their further recombination lead to fluctuations in the charge of the hole pile-up, which provoke an important increase in the drain current noise, even when the kink effect is hardly perceptible in the output characteristics. (paper)

High mobility two-dimensional hole gases in GaAs/AlGaAs heterostructures; Hochbewegliche zweidimensionale Lochsysteme in GaAs/AlGaAs Heterostrukturen

Energy Technology Data Exchange (ETDEWEB)

Gerl, Christian

2009-10-14

This thesis outlines the fabrication of high mobility two-dimensional hole-gases (2DHG) in GaAs/AlGaAs heterostructures with molecular beam epitaxy (MBE) and their characterization with magnetotransport measurements at low temperatures between 4 K and 30 mK. Here the optimization of the carrier mobility is focused. This will be achieved by introducing a novel carbon-filament doping source, with which contaminations of the MBE system and therefore in the grown layers can be reduced and by vary the band structure design to minimize scattering processes. With the help of these actions, hole mobilities above 1 E6 cm{sup 2}/Vs are achievable, what reflects an increase of factor 3 in the (001)- and factor 6.5 in the (110)- oriented transport plane compared to common 2DHGs. Furthermore states of the fractional Quantum Hall Effect can be observed in these 2DHGs, only visible in n-doped 2D systems so fare. Magnetotransport measurements on 2DHGs with aluminum gates reveal a hysteretic behavior of the carrier density with respect to the gate potential which can be attributed to the incorporation mechanisms of carbon atoms as acceptor. Temperature dependent magnetotransport measurements allow the evaluation of effective mass and quantum scattering time as well as the dependence of these parameters from the band structure design. In these experiments an aperiodic behavior of the Shubnikov-de Haas oscillations can be observed in the inverse magnetic field, which is attributed to the position of the fermi energy in the immediate vicinity of crossing regions of the complex Landau fan of 2DHGs. (orig.)

k-Space imaging of anisotropic 2D electron gas in GaN/GaAlN high-electron-mobility transistor heterostructures

OpenAIRE

Lev, L. L.; Maiboroda, I. O.; Husanu, M. -A.; Grichuk, E. S.; Chumakov, N. K.; Ezubchenko, I. S.; Chernykh, I. A.; Wang, X.; Tobler, B.; Schmitt, T.; Zanaveskin, M. L.; Valeyev, V. G.; Strocov, V. N.

2018-01-01

Nanostructures based on buried interfaces and heterostructures are at the heart of modern semiconductor electronics as well as future devices utilizing spintronics, multiferroics, topological effects and other novel operational principles. Knowledge of electronic structure of these systems resolved in electron momentum k delivers unprecedented insights into their physics. Here, we explore 2D electron gas formed in GaN/AlGaN high-electron-mobility transistor (HEMT) heterostructures with an ult...

Deployment of a Long-Term Broadband Seafloor Observatory in Monterey Bay

Science.gov (United States)

McGill, P.; Neuhauser, D.; Stakes, D.; Romanowicz, B.; Ramirez, T.; Uhrhammer, R.

2002-12-01

MOBB (Monterey bay Ocean floor Broad Band project) is a collaborative project between the Monterey Bay Aquarium Research Institute (MBARI) and the Berkeley Seismological Laboratory (BSL). Its goal is to install and operate a permanent seafloor broadband seismic station as a first step towards extending the on-shore broadband seismic network in northern California to the seaside of the North-America/Pacific plate boundary, providing better azimuthal coverage for regional earthquake and structure studies. The successful MOBB deployment took place 40km off shore at a water depth of 1000m during three dives on April 9-11, 2002. The seismometer was buried in a 60-cm deep caisson, which was later back filled with glass beads to stabilize the instrument. New tools, including a high-pressure water-jet excavator, were developed for the ROV Ventana to accomplish these tasks. The ocean-bottom MOBB station currently comprises a three-component seismometer package, a current-meter, and a recording and battery package. Data recovery dives, during which the recording and battery package will be exchanged, are planned every three months for the next three years. A differential pressure gauge (DPG) (Cox et al., 1984) will be deployed as part of the recording package during the next data recovery dive in September 2002. The station is currently recording data autonomously. Eventually, it will be linked to the planned (and recently funded) MARS (Monterey Accelerated Research System; rl {http://www.mbari.org/mars/}) cable and provide real-time, continuous seismic data to be merged with the rest of the northern California real-time seismic system. The data are archived at the NCEDC for on-line availability, as part of the Berkeley Digital Seismic Network (BDSN). This project follows the 1997 MOISE experiment, in which a three-component broadband system was deployed for a period of three months, 40km off shore in Monterey Bay. MOISE was a cooperative program sponsored by MBARI, UC

Physical processes in a coupled bay-estuary coastal system: Whitsand Bay and Plymouth Sound

Science.gov (United States)

Uncles, R. J.; Stephens, J. A.; Harris, C.

2015-09-01

Whitsand Bay and Plymouth Sound are located in the southwest of England. The Bay and Sound are separated by the ∼2-3 km-wide Rame Peninsula and connected by ∼10-20 m-deep English Channel waters. Results are presented from measurements of waves and currents, drogue tracking, surveys of salinity, temperature and turbidity during stratified and unstratified conditions, and bed sediment surveys. 2D and 3D hydrodynamic models are used to explore the generation of tidally- and wind-driven residual currents, flow separation and the formation of the Rame eddy, and the coupling between the Bay and the Sound. Tidal currents flow around the Rame Peninsula from the Sound to the Bay between approximately 3 h before to 2 h after low water and form a transport path between them that conveys lower salinity, higher turbidity waters from the Sound to the Bay. These waters are then transported into the Bay as part of the Bay-mouth limb of the Rame eddy and subsequently conveyed to the near-shore, east-going limb and re-circulated back towards Rame Head. The Simpson-Hunter stratification parameter indicates that much of the Sound and Bay are likely to stratify thermally during summer months. Temperature stratification in both is pronounced during summer and is largely determined by coastal, deeper-water stratification offshore. Small tidal stresses in the Bay are unable to move bed sediment of the observed sizes. However, the Bay and Sound are subjected to large waves that are capable of driving a substantial bed-load sediment transport. Measurements show relatively low levels of turbidity, but these respond rapidly to, and have a strong correlation with, wave height.

Suppression of surface-originated gate lag by a dual-channel AlN/GaN high electron mobility transistor architecture

International Nuclear Information System (INIS)

Deen, David A.; Storm, David F.; Scott Katzer, D.; Bass, R.; Meyer, David J.

2016-01-01

A dual-channel AlN/GaN high electron mobility transistor (HEMT) architecture is demonstrated that leverages ultra-thin epitaxial layers to suppress surface-related gate lag. Two high-density two-dimensional electron gas (2DEG) channels are utilized in an AlN/GaN/AlN/GaN heterostructure wherein the top 2DEG serves as a quasi-equipotential that screens potential fluctuations resulting from distributed surface and interface states. The bottom channel serves as the transistor's modulated channel. Dual-channel AlN/GaN heterostructures were grown by molecular beam epitaxy on free-standing hydride vapor phase epitaxy GaN substrates. HEMTs fabricated with 300 nm long recessed gates demonstrated a gate lag ratio (GLR) of 0.88 with no degradation in drain current after bias stressed in subthreshold. These structures additionally achieved small signal metrics f_t/f_m_a_x of 27/46 GHz. These performance results are contrasted with the non-recessed gate dual-channel HEMT with a GLR of 0.74 and 82 mA/mm current collapse with f_t/f_m_a_x of 48/60 GHz.

Suppression of surface-originated gate lag by a dual-channel AlN/GaN high electron mobility transistor architecture

Energy Technology Data Exchange (ETDEWEB)

Deen, David A., E-mail: david.deen@alumni.nd.edu; Storm, David F.; Scott Katzer, D.; Bass, R.; Meyer, David J. [Naval Research Laboratory, Electronics Science and Technology Division, Washington, DC 20375 (United States)

2016-08-08

A dual-channel AlN/GaN high electron mobility transistor (HEMT) architecture is demonstrated that leverages ultra-thin epitaxial layers to suppress surface-related gate lag. Two high-density two-dimensional electron gas (2DEG) channels are utilized in an AlN/GaN/AlN/GaN heterostructure wherein the top 2DEG serves as a quasi-equipotential that screens potential fluctuations resulting from distributed surface and interface states. The bottom channel serves as the transistor's modulated channel. Dual-channel AlN/GaN heterostructures were grown by molecular beam epitaxy on free-standing hydride vapor phase epitaxy GaN substrates. HEMTs fabricated with 300 nm long recessed gates demonstrated a gate lag ratio (GLR) of 0.88 with no degradation in drain current after bias stressed in subthreshold. These structures additionally achieved small signal metrics f{sub t}/f{sub max} of 27/46 GHz. These performance results are contrasted with the non-recessed gate dual-channel HEMT with a GLR of 0.74 and 82 mA/mm current collapse with f{sub t}/f{sub max} of 48/60 GHz.

Bay-annulated indigo (BAI) as an excellent electron accepting building block for high performance organic semiconductors

Science.gov (United States)

Liu, Yi; He, Bo; Pun, Andrew

2015-11-24

A novel electron acceptor based on bay-annulated indigo (BAI) was synthesized and used for the preparation of a series of high performance donor-acceptor small molecules and polymers. The resulting materials possess low-lying LUMO energy level and small HOMO-LUMO gaps, while their films exhibited high crystallinity upon thermal treatment, commensurate with high field effect mobilities and ambipolar transfer characteristics.

Mobile Marketing

OpenAIRE

竹安, 数博; Takeyasu, Kazuhiro

2005-01-01

This article deals with one of the modern trends in marketing communication, which is mobile marketing. Towards the end of 2008, several projects which use mobile phones for target marketing communication were launched. Commercial SMS´s are sent on the base of agreement or registration of the consumers on special websites, for example hellomobil.cz. The benefit for the consumers is the bonus which can have more forms - not only sending money to the account, free SMS´s/MMS´s and minutes but al...

Simulation Model of Mobile Detection Systems

International Nuclear Information System (INIS)

Edmunds, T.; Faissol, D.; Yao, Y.

2009-01-01

In this paper, we consider a mobile source that we attempt to detect with man-portable, vehicle-mounted or boat-mounted radiation detectors. The source is assumed to transit an area populated with these mobile detectors, and the objective is to detect the source before it reaches a perimeter. We describe a simulation model developed to estimate the probability that one of the mobile detectors will come in to close proximity of the moving source and detect it. We illustrate with a maritime simulation example. Our simulation takes place in a 10 km by 5 km rectangular bay patrolled by boats equipped with 2-inch x 4-inch x 16-inch NaI detectors. Boats to be inspected enter the bay and randomly proceed to one of seven harbors on the shore. A source-bearing boat enters the mouth of the bay and proceeds to a pier on the opposite side. We wish to determine the probability that the source is detected and its range from target when detected. Patrol boats select the nearest in-bound boat for inspection and initiate an intercept course. Once within an operational range for the detection system, a detection algorithm is started. If the patrol boat confirms the source is not present, it selects the next nearest boat for inspection. Each run of the simulation ends either when a patrol successfully detects a source or when the source reaches its target. Several statistical detection algorithms have been implemented in the simulation model. First, a simple k-sigma algorithm, which alarms with the counts in a time window exceeds the mean background plus k times the standard deviation of background, is available to the user. The time window used is optimized with respect to the signal-to-background ratio for that range and relative speed. Second, a sequential probability ratio test [Wald 1947] is available, and configured in this simulation with a target false positive probability of 0.001 and false negative probability of 0.1. This test is utilized when the mobile detector maintains

Simulation Model of Mobile Detection Systems

Energy Technology Data Exchange (ETDEWEB)

Edmunds, T; Faissol, D; Yao, Y

2009-01-27

In this paper, we consider a mobile source that we attempt to detect with man-portable, vehicle-mounted or boat-mounted radiation detectors. The source is assumed to transit an area populated with these mobile detectors, and the objective is to detect the source before it reaches a perimeter. We describe a simulation model developed to estimate the probability that one of the mobile detectors will come in to close proximity of the moving source and detect it. We illustrate with a maritime simulation example. Our simulation takes place in a 10 km by 5 km rectangular bay patrolled by boats equipped with 2-inch x 4-inch x 16-inch NaI detectors. Boats to be inspected enter the bay and randomly proceed to one of seven harbors on the shore. A source-bearing boat enters the mouth of the bay and proceeds to a pier on the opposite side. We wish to determine the probability that the source is detected and its range from target when detected. Patrol boats select the nearest in-bound boat for inspection and initiate an intercept course. Once within an operational range for the detection system, a detection algorithm is started. If the patrol boat confirms the source is not present, it selects the next nearest boat for inspection. Each run of the simulation ends either when a patrol successfully detects a source or when the source reaches its target. Several statistical detection algorithms have been implemented in the simulation model. First, a simple k-sigma algorithm, which alarms with the counts in a time window exceeds the mean background plus k times the standard deviation of background, is available to the user. The time window used is optimized with respect to the signal-to-background ratio for that range and relative speed. Second, a sequential probability ratio test [Wald 1947] is available, and configured in this simulation with a target false positive probability of 0.001 and false negative probability of 0.1. This test is utilized when the mobile detector maintains

Study of surface leakage current of AlGaN/GaN high electron mobility transistors

International Nuclear Information System (INIS)

Chen, YongHe; Zhang, Kai; Cao, MengYi; Zhao, ShengLei; Zhang, JinCheng; Hao, Yue; Ma, XiaoHua

2014-01-01

Temperature-dependent surface current measurements were performed to analyze the mechanism of surface conductance of AlGaN/GaN channel high-electron-mobility transistors by utilizing process-optimized double gate structures. Different temperatures and electric field dependence have been found in surface current measurements. At low electric field, the mechanism of surface conductance is considered to be two-dimensional variable range hopping. At elevated electric field, the Frenkel–Poole trap assisted emission governs the main surface electrons transportation. The extracted energy barrier height of electrons emitting from trapped state near Fermi energy level into a threading dislocations-related continuum state is 0.38 eV. SiN passivation reduces the surface leakage current by two order of magnitude and nearly 4 orders of magnitude at low and high electric fields, respectively. SiN also suppresses the Frenkel–Poole conductance at high temperature by improving the surface states of AlGaN/GaN. A surface treatment process has been introduced to further suppress the surface leakage current at high temperature and high field, which results in a decrease in surface current of almost 3 orders of magnitude at 476 K

AlGaN/GaN MISHEMTs with AlN gate dielectric grown by thermal ALD technique.

Science.gov (United States)

Liu, Xiao-Yong; Zhao, Sheng-Xun; Zhang, Lin-Qing; Huang, Hong-Fan; Shi, Jin-Shan; Zhang, Chun-Min; Lu, Hong-Liang; Wang, Peng-Fei; Zhang, David Wei

2015-01-01

Recently, AlN plasma-enhanced atomic layer deposition (ALD) passivation technique had been proposed and investigated for suppressing the dynamic on-resistance degradation behavior of high-electron-mobility transistors (HEMTs). In this paper, a novel gate dielectric and passivation technique for GaN-on-Si AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MISHEMTs) is presented. This technique features the AlN thin film grown by thermal ALD at 400°C without plasma enhancement. A 10.6-nm AlN thin film was grown upon the surface of the HEMT serving as the gate dielectric under the gate electrode and as the passivation layer in the access region at the same time. The MISHEMTs with thermal ALD AlN exhibit enhanced on/off ratio, reduced channel sheet resistance, reduction of gate leakage by three orders of magnitude at a bias of 4 V, reduced threshold voltage hysteresis of 60 mV, and suppressed current collapse degradation.

78 FR 46813 - Safety Zone; Evening on the Bay Fireworks; Sturgeon Bay, WI

Science.gov (United States)

2013-08-02

...-AA00 Safety Zone; Evening on the Bay Fireworks; Sturgeon Bay, WI AGENCY: Coast Guard, DHS. ACTION.... This temporary safety zone will restrict vessels from a portion of Sturgeon Bay due to a fireworks... hazards associated with the fireworks display. DATES: This rule is effective from 8 p.m. until 10 p.m. on...

Evaluating Ambient Concentrations and Local Emissions of Greenhouse Gases (GHGs) in the San Francisco Bay Area of California Using a Comprehensive Fixed-site and Mobile Monitoring Network

Science.gov (United States)

Guha, A.; Bower, J. P.; Martien, P. T.; Randall, S.; Young, A.; Hilken, H.; Stevenson, E.

2015-12-01

The Bay Area Air Quality Management District (hence the Air District) is the greater San Francisco Bay metropolitan region's chief air quality regulatory agency. Aligning itself with Executive Order S-3-05, the Air District has set a goal to reduce the region's GHG emissions by 80% below 1990 levels by the year 2050. The Air District's 10-point Climate Action Work Program lays out the agency's priorities, actions and coordination with regional stakeholders. The Program has three core objectives: (1) to develop a technical and monitoring program to document the region's GHG sources and related emissions, (2) to implement a policy and rule-based approach to control and regulate GHG emissions, and finally, (3) to utilize local governance, incentives and partnerships to encourage GHG emissions reductions.As part of the technical program, the Air District has set up a long term, ambient GHG monitoring network at four sites. The first site is located north and upwind of the urban core at Bodega Bay by the Pacific Coast. It mostly receives clean marine inflow and serves as the regional background site. The other three sites are strategically located at regional exit points for Bay Area plumes that presumably contain GHG enhancements from local sources. These stations are at San Martin, located south of the San Jose metropolitan area; at Patterson Pass at the cross section with California's Central Valley; and at Bethel Island at the mouth of the Sacramento-San Joaquin Delta. At all sites, carbon dioxide (CO2) and methane (CH4) are being measured continuously, along with combustion tracer CO and other air pollutants. The GHG measurements are performed with high precision and fast laser instruments (Picarro Inc). In the longer term, the network will allow the Air District to monitor ambient concentrations of GHGs and thus evaluate the effectiveness of its policy, regulation and enforcement efforts. We present data from the sites in their first few months of operation and

77 FR 38488 - Safety Zone; Alexandria Bay Chamber of Commerce, St. Lawrence River, Alexandria Bay, NY

Science.gov (United States)

2012-06-28

... 1625-AA00 Safety Zone; Alexandria Bay Chamber of Commerce, St. Lawrence River, Alexandria Bay, NY... restrict vessels from a portion of the St. Lawrence River during the Alexandria Bay Chamber of Commerce... of proposed rulemaking (NPRM) entitled Safety Zone; Alexandria Bay Chamber of Commerce, St. Lawrence...

Breakdown mechanisms in AlGaN/GaN high electron mobility transistors with different GaN channel thickness values

International Nuclear Information System (INIS)

Ma Xiao-Hua; Zhang Ya-Man; Chen Wei-Wei; Wang Xin-Hua; Yuan Ting-Ting; Pang Lei; Liu Xin-Yu

2015-01-01

In this paper, the off-state breakdown characteristics of two different AlGaN/GaN high electron mobility transistors (HEMTs), featuring a 50-nm and a 150-nm GaN thick channel layer, respectively, are compared. The HEMT with a thick channel exhibits a little larger pinch-off drain current but significantly enhanced off-state breakdown voltage (BV off ). Device simulation indicates that thickening the channel increases the drain-induced barrier lowering (DIBL) but reduces the lateral electric field in the channel and buffer underneath the gate. The increase of BV off in the thick channel device is due to the reduction of the electric field. These results demonstrate that it is necessary to select an appropriate channel thickness to balance DIBL and BV off in AlGaN/GaN HEMTs. (paper)

Enhanced two dimensional electron gas transport characteristics in Al{sub 2}O{sub 3}/AlInN/GaN metal-oxide-semiconductor high-electron-mobility transistors on Si substrate

Energy Technology Data Exchange (ETDEWEB)

Freedsman, J. J., E-mail: freedy54@gmail.com; Watanabe, A.; Urayama, Y. [Research Center for Nano-Devices and Advanced Materials, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466 8555 (Japan); Egawa, T., E-mail: egawa.takashi@nitech.ac.jp [Research Center for Nano-Devices and Advanced Materials, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466 8555 (Japan); Innovation Center for Multi-Business of Nitride Semiconductors, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466 8555 (Japan)

2015-09-07

The authors report on Al{sub 2}O{sub 3}/Al{sub 0.85}In{sub 0.15}N/GaN Metal-Oxide-Semiconductor High-Electron-Mobility Transistor (MOS-HEMT) on Si fabricated by using atomic layer deposited Al{sub 2}O{sub 3} as gate insulator and passivation layer. The MOS-HEMT with the gate length of 2 μm exhibits excellent direct-current (dc) characteristics with a drain current maximum of 1270 mA/mm at a gate bias of 3 V and an off-state breakdown voltage of 180 V for a gate-drain spacing of 4 μm. Also, the 1 μm-gate MOS-HEMT shows good radio-frequency (rf) response such as current gain and maximum oscillation cut-off frequencies of 10 and 34 GHz, respectively. The capacitance-voltage characteristics at 1 MHz revealed significant increase in two-dimensional electron gas (2DEG) density for the MOS-HEMT compared to conventional Schottky barrier HEMTs. Analyses using drain-source conductivity measurements showed improvements in 2DEG transport characteristics for the MOS-HEMT. The enhancements in dc and rf performances of the Al{sub 2}O{sub 3}/Al{sub 0.85}In{sub 0.15}N/GaN MOS-HEMT are attributed to the improvements in 2DEG characteristics.

Traveling with blindness: A qualitative space-time approach to understanding visual impairment and urban mobility.

Science.gov (United States)

Wong, Sandy

2018-01-01

This paper draws from Hägerstrand's space-time framework to generate new insights on the everyday mobilities of individuals with visual impairments in the San Francisco Bay Area. While existing research on visual impairment and mobility emphasizes individual physical limitations resulting from vision loss or inaccessible public spaces, this article highlights and bridges both the behavioral and social processes that influence individual mobility. A qualitative analysis of sit-down and mobile interview data reveals that the space-time constraints of people with visual impairments are closely linked to their access to transportation, assistive technologies, and mobile devices. The findings deepen our understandings of the relationship between health and mobility, and present intervention opportunities for improving the quality of life for people with visual impairment. Copyright © 2017 Elsevier Ltd. All rights reserved.

Performance improvement and better scalability of wet-recessed and wet-oxidized AlGaN/GaN high electron mobility transistors

Science.gov (United States)

Takhar, Kuldeep; Meer, Mudassar; Upadhyay, Bhanu B.; Ganguly, Swaroop; Saha, Dipankar

2017-05-01

We have demonstrated that a thin layer of Al2O3 grown by wet-oxidation of wet-recessed AlGaN barrier layer in an AlGaN/GaN heterostructure can significantly improve the performance of GaN based high electron mobility transistors (HEMTs). The wet-etching leads to a damage free recession of the gate region and compensates for the decreased gate capacitance and increased gate leakage. The performance improvement is manifested as an increase in the saturation drain current, transconductance, and unity current gain frequency (fT). This is further augmented with a large decrease in the subthreshold current. The performance improvement is primarily ascribed to an increase in the effective velocity in two-dimensional electron gas without sacrificing gate capacitance, which make the wet-recessed gate oxide-HEMTs much more scalable in comparison to their conventional counterpart. The improved scalability leads to an increase in the product of unity current gain frequency and gate length (fT × Lg).

Planung einer Mobile Learning Application für medizinische Lerninhalte [Planning of a mobile learning application for medical contents

Directory of Open Access Journals (Sweden)

Walther, Patrick

2013-11-01

Full Text Available [english] Due to the high popularity of mobile devices barriers for mobile learning are becoming less. Place-and time-independent access to information is part of everyday life. The number of mobile applications is steadily growing. Currently there are more than 500,000 mobile applications, so-called apps, available for the Apple iPhone/iPad which can be downloaded in the Apple iTunes Store. More than ten percent of these apps are mobile learning applications.Before starting development of a mobile app we need to analyze all requirements accurately. This is due to the fact that there is a multiplicity of different operating systems with different functionalities. This paper shows general properties of so-called native, hybrid, and web applications and advantages and disadvantages in development and use of the finished application. In addition, current software, which supports the development of a mobile application is explained.Finally the differences of the various development options are shown based on concrete mobile applications.[german] Aufgrund der hohen Verbreitung mobiler Endgeräte werden die Barrieren für das mobile Lernen immer geringer und orts- und zeitunabhängiger Zugriff auf Informationen ist längst im Alltag angekommen. Die Zahl mobiler Applikation wächst stetig an. So stehen beispielsweise aktuell mehr als 500.000 mobile Applikationen, sogenannte Apps, für das Apple iPhone/iPad, dem Nutzer über den Apple iTunes Store bereit. Hiervon sind mehr als zehn Prozent mobile Lernapplikationen.Vor der eigentlichen Entwicklung einer App muss, u.a. aufgrund der Vielzahl mobiler Betriebssysteme und Funktionen der verschiedenen mobilen Endgeräte, zuvor eine genaue Bedarfsanalyse durchgeführt werden um die passende Entwicklungsvariante zu wählen.In diesem Beitrag werden die verschiedenen Möglichkeiten (nativ, hybrid, web zur Entwicklung einer mobilen Applikation, als auch deren Vor- und Nachteile bei der Entwicklung und Nutzung der

Oxygenation variability in Mejillones Bay, off northern Chile, during the last two centuries

Science.gov (United States)

Díaz-Ochoa, J. A.; Pantoja, S.; de Lange, G. J.; Lange, C. B.; Sánchez, G. E.; Acuña, V. R.; Muñoz, P.; Vargas, G.

2011-01-01

The Peru Chile Current ecosystem is characterized by high biological productivity and important fisheries. Although this system is likely to be severely affected by climate change, its response to current global warming is still uncertain. In this paper, we analyze 10-166 year-old sediments in two cores collected from Mejillones Bay, an anoxic sedimentary setting favorable for the preservation of proxies. Based on a 166-year chronology, we used proxies of bottom-water oxygenation (Mo, V, S, and the (lycopane + n-C35)/n-C31 ratio) and surface water productivity (biogenic opal, counts of diatom valves, biogenic Ba, organic carbon, and chlorins) to reconstruct environmental variations in Mejillones Bay. During the last two centuries, a shift took place in the coastal marine ecosystem of Bahia Mejillones at decadal scales. This shift was characterized by intense ENSO-like activity, large-scale fluctuations in biological export productivity and bottom water oxygenation, and increased eolian activity (inferred from Ti/Al and Zr/Al). This short-term variability was accompanied by a gradual increase of sulfidic conditions that has intensified since the early 1960s.

Low power fluorine plasma effects on electrical reliability of AlGaN/GaN high electron mobility transistor

International Nuclear Information System (INIS)

Yang Ling; Zhou Xiao-Wei; Ma Xiao-Hua; Lv Ling; Zhang Jin-Cheng; Hao Yue; Cao Yan-Rong

2017-01-01

The new electrical degradation phenomenon of the AlGaN/GaN high electron mobility transistor (HEMT) treated by low power fluorine plasma is discovered. The saturated current, on-resistance, threshold voltage, gate leakage and breakdown voltage show that each experiences a significant change in a short time stress, and then keeps unchangeable. The migration phenomenon of fluorine ions is further validated by the electron redistribution and breakdown voltage enhancement after off-state stress. These results suggest that the low power fluorine implant ion stays in an unstable state. It causes the electrical properties of AlGaN/GaN HEMT to present early degradation. A new migration and degradation mechanism of the low power fluorine implant ion under the off-stress electrical stress is proposed. The low power fluorine ions would drift at the beginning of the off-state stress, and then accumulate between gate and drain nearby the gate side. Due to the strong electronegativity of fluorine, the accumulation of the front fluorine ions would prevent the subsequent fluorine ions from drifting, thereby alleviating further the degradation of AlGaN/GaN HEMT electrical properties. (paper)

Ospreys Use Bald Eagle Nests in Chesapeake Bay Area

OpenAIRE

Therres, Glenn D.; Chandler, Sheri K.

1993-01-01

Ospreys (Pandion haliaetus) and Bald Eagles (Haliaeetus leucocephalus) share similar breeding habitat in the Chesapeake Bay area and elsewhere. The nests of these species are similar in size and appearance. Ospreys typically build large stick nests in dead trees or on man-made structures (C.J. Henny et al. 1974, Chesapeake Sci. 15:125-133; A.F. Poole 1989, Ospreys: a natural and unnatural history, Cambridge Univ. Press, NY), while Bald Eagles usually build larger nests in live trees (P.B. Woo...

78 FR 77359 - Eighth Coast Guard District Annual Safety Zones; New Year's Eve Celebration/City of Mobile...

Science.gov (United States)

2013-12-23

...-AA00 Eighth Coast Guard District Annual Safety Zones; New Year's Eve Celebration/City of Mobile; Mobile Channel; Mobile, AL AGENCY: Coast Guard, DHS. ACTION: Temporary final rule. SUMMARY: The Coast Guard will enforce the City of Mobile New Year's Eve Celebration safety zone in the Mobile Channel, Mobile, AL from...

17th Annual ALS Users' Association Meeting

Energy Technology Data Exchange (ETDEWEB)

Robinson, Art; Tamura, Lori

2004-11-29

It's not exactly Russian roulette, but scheduling October events outdoors is not risk-free, even in usually sunny California. An overflow crowd of more than 400 registered users, ALS staff, and vendors enjoyed a full indoor program featuring science highlights and workshops spread over two and a half days from October 18 to October 20. However, a major storm, heralding the onset of the San Francisco Bay Area rainy season, posed a few weather challenges for the events on the ALS patio.

Gradient Analysis and Classification of Carolina Bay Vegetation: A Framework for Bay Wetlands Conservation and Restoration

Energy Technology Data Exchange (ETDEWEB)

Diane De Steven,Ph.D.; Maureen Tone,PhD.

1997-10-01

This report address four project objectives: (1) Gradient model of Carolina bay vegetation on the SRS--The authors use ordination analyses to identify environmental and landscape factors that are correlated with vegetation composition. Significant factors can provide a framework for site-based conservation of existing diversity, and they may also be useful site predictors for potential vegetation in bay restorations. (2) Regional analysis of Carolina bay vegetation diversity--They expand the ordination analyses to assess the degree to which SRS bays encompass the range of vegetation diversity found in the regional landscape of South Carolina's western Upper Coastal Plain. Such comparisons can indicate floristic status relative to regional potentials and identify missing species or community elements that might be re-introduced or restored. (3) Classification of vegetation communities in Upper Coastal Plain bays--They use cluster analysis to identify plant community-types at the regional scale, and explore how this classification may be functional with respect to significant environmental and landscape factors. An environmentally-based classification at the whole-bay level can provide a system of templates for managing bays as individual units and for restoring bays to desired plant communities. (4) Qualitative model for bay vegetation dynamics--They analyze present-day vegetation in relation to historic land uses and disturbances. The distinctive history of SRS bays provides the possibility of assessing pathways of post-disturbance succession. They attempt to develop a coarse-scale model of vegetation shifts in response to changing site factors; such qualitative models can provide a basis for suggesting management interventions that may be needed to maintain desired vegetation in protected or restored bays.

Metagenomic evidence for reciprocal particle exchange between the mainstem estuary and lateral bay sediments of the lower Columbia River

Directory of Open Access Journals (Sweden)

Mariya W Smith

2015-10-01

Full Text Available Lateral bays of the lower Columbia River estuary are areas of enhanced water retention that influence net ecosystem metabolism through activities of their diverse microbial communities. Metagenomic characterization of sediment microbiota from three disparate sites in two brackish lateral bays (Baker and Youngs produced approximately 100 Gbp of DNA sequence data analyzed subsequently for predicted SSU rRNA and peptide-coding genes. The metagenomes were dominated by Bacteria. A large component of Eukaryota was present in Youngs Bay samples, i.e. the inner bay sediment was enriched with the invasive New Zealand mudsnail, Potamopyrgus antipodarum, known for high ammonia production. The metagenome was also highly enriched with an archaeal ammonia oxidizer closely related to Nitrosoarchaeum limnia. Combined analysis of sequences and continuous, high-resolution time series of biogeochemical data from fixed and mobile platforms revealed the importance of large-scale reciprocal particle exchanges between the mainstem estuarine water column and lateral bay sediments. Deposition of marine diatom particles in sediments near Youngs Bay mouth was associated with a dramatic enrichment of Bacteroidetes (58% of total Bacteria and corresponding genes involved in phytoplankton polysaccharide degradation. The Baker Bay sediment metagenome contained abundant Archaea, including diverse methanogens, as well as functional genes for methylotrophy and taxonomic markers for syntrophic bacteria, suggesting that active methane cycling occurs at this location. Our previous work showed enrichments of similar anaerobic taxa in particulate matter of the mainstem estuarine water column. In total, our results identify the lateral bays as both sources and sinks of biogenic particles significantly impacting microbial community composition and biogeochemical activities in the estuary.

Daily Mobility and Residential Migrations in the Montréal Metropolitan Region

Directory of Open Access Journals (Sweden)

Gilles Sénécal

2013-06-01

Full Text Available The purpose of this article is to simultaneously examine two types of mobility by developing a model of metropolitan organization that emphasizes the axis structure of mobility. The model is based on the realities of daily mobility and long-term residential mobility. Origin−Destination study results validated the axis representation of the metropolitan structure. Furthermore, building on data from a telephone survey, we considered the interactions between the two types of mobility along the Center-North axis of Montréal’s Census Metropolitan Area (CMA. The ensuing discussion on various models of metropolitan structure and their relevance today is framed in terms of the axes of mobility defined as territorial practices that are established within the patterns of daily life and are a significant factor in residential location decisions. The study raises broader issues concerning the relevance of drawing on standard models such as Burgess’s concentric zone model, Hoyt’s sector theory, Adam’s directional bias, or recent findings from the literature to understand urban form dynamics in the CMA.

Behaviour of Bichromatic Microwave Induced Magnetoresistance Oscillations in the High Mobility GaAs/AlGaAs 2D electron System

International Nuclear Information System (INIS)

Gunawardana, Binuka; Liu, Han-Chun; Samaraweera, Rasanga L.; Mani, R.G.; Reichl, C.; Wegscheider, W

2017-01-01

Microwave radiation-induced magneto-resistance oscillations are examined under bichromatic excitation for various frequency combinations in order to obtain a better understanding of the lineshape observed in the dual excitation experiment of the high mobility GaAs/AlGaAs 2D electron system. Here, we examine superposition- or lack thereof- in the lineshape observed in the bichromatic experiment, and report a trend observed between the monochromatic and bichromatic responses of the oscillatory diagonal resistance. (paper)

Effects of waves on water dispersion in a semi-enclosed estuarine bay

Science.gov (United States)

Delpey, M. T.; Ardhuin, F.; Otheguy, P.

2012-04-01

The bay of Saint Jean de Luz - Ciboure is a touristic destination located in the south west of France on the Basque coast. This small bay is 1.5km wide for 1km long. It is semi-enclosed by breakwaters, so that the area is mostly protected from waves except in its eastern part, where wave breaking is regularly observed over a shallow rock shelf. In the rest of the area the currents are generally weak. The bay receives fresh water inflows from two rivers. During intense raining events, the rivers can introduce pollutants in the bay. The input of pollutants combined with the low level dynamic of the area can affect the water quality for several days. To study such a phenomenon, mechanisms of water dispersion in the bay are investigated. The present paper focuses on the effects of waves on bay dynamics. Several field experiments were conducted in the area, combining wave and current measurements from a set of ADCP and ADV, lagrangian difter experiments in the surfzone, salinity and temperature profile measurements. An analysis of this set of various data is provided. It reveals that the bay combines remarkable density stratification due to fresh water inflows and occasionally intense wave-induced currents in the surfzone. These currents have a strong influence on river plume dynamics when the sea state is energetic. Moreover, modifications of hydrodynamics in the bay passes are found to be remarkably correlated with sea state evolutions. This result suggests a significant impact of waves on the bay flushing. To further analyse these phenomena, a three dimensional numerical model of bay hydrodynamics is developed. The model aims at reproducing fresh water inflows combined with wind-, tide- and wave-induced currents and mixing. The model of the bay is implemented using the code MOHID , which has been modified to allow the three dimensional representation of wave-current interactions proposed by Ardhuin et al. [2008b] . The circulation is forced by the wave field modelled

Secure, Mobile, Wireless Network Technology Designed, Developed, and Demonstrated

Science.gov (United States)

Ivancic, William D.; Paulsen, Phillip E.

2004-01-01

The inability to seamlessly disseminate data securely over a high-integrity, wireless broadband network has been identified as a primary technical barrier to providing an order-of-magnitude increase in aviation capacity and safety. Secure, autonomous communications to and from aircraft will enable advanced, automated, data-intensive air traffic management concepts, increase National Air Space (NAS) capacity, and potentially reduce the overall cost of air travel operations. For the first time ever, secure, mobile, network technology was designed, developed, and demonstrated with state-ofthe- art protocols and applications by a diverse, cooperative Government-industry team led by the NASA Glenn Research Center. This revolutionary technology solution will make fundamentally new airplane system capabilities possible by enabling secure, seamless network connections from platforms in motion (e.g., cars, ships, aircraft, and satellites) to existing terrestrial systems without the need for manual reconfiguration. Called Mobile Router, the new technology autonomously connects and configures networks as they traverse from one operating theater to another. The Mobile Router demonstration aboard the Neah Bay, a U.S. Coast Guard vessel stationed in Cleveland, Ohio, accomplished secure, seamless interoperability of mobile network systems across multiple domains without manual system reconfiguration. The Neah Bay was chosen because of its low cost and communications mission similarity to low-Earth-orbiting satellite platforms. This technology was successfully advanced from technology readiness level (TRL) 2 (concept and/or application formation) to TRL 6 (system model or prototype demonstration in a relevant environment). The secure, seamless interoperability offered by the Mobile Router and encryption device will enable several new, vehicle-specific and systemwide technologies to perform such things as remote, autonomous aircraft performance monitoring and early detection and

Study on sediments from Almirantado Bay in the Antarctica continent

International Nuclear Information System (INIS)

Gomes, Marcelo da Silva; Montone, Rosalinda Carmela; Weber, Rolf Roland

1999-01-01

The Antarctic Continent is relatively free from human activities but it already comes presenting low levels of environmental contamination for anthropogenic sources. The anthropogenic contamination can be taken mainly to the continent through different manners for the marine and atmospheric currents. This work has as objective to analyze samples of sediments from Antarctic Continent in the area of Almirantado Bay, where the Brazilian Station of Resource Comandante Ferraz is located. The concentrations of ten metallic elements (Ni, Cu, Zn, Cd, Sn, Pb, U, Al, Fe and Li) were analyzed in twelve collection sites along the whole Bay. AAS and HR-ICPMS accomplished the analyses of those metallic elements. It was verified in the obtained results that a variation does not exist in the concentrations obtained among the collection sites, indicating a homogeneity in the area and there is no evidence of polluting source, at least at those obtained concentration levels. (author)

Discharge, water-quality characteristics, and nutrient loads from McKay Bay, Delaney Creek, and East Bay, Tampa, Florida, 1991-1993

Science.gov (United States)

Stoker, Y.E.; Levesque, V.A.; Fritz, E.M.

1996-01-01

Nutrient enrichment in Tampa Bay has caused a decline in water quality in the estuary. Efforts to reduce the nutrient loading to Tampa Bay have resulted in improvement in water quality from 1981 to 1991. However, Tampa Bay still is onsidered enriched with nutrients. Water quality in East Bay (located at the northeastern part of Hillsborough Bay, which is an embayment in Tampa Bay) is not improving at the same rate as the rest of the bay. East Bay is the center of shipping activity in Tampa Bay and the seventh largest port in the United States. One of the primary cargoes is phosphate ore and related products such as fertilizer. The potential for nutrient loading to East Bay from shipping activities is high and has not previously been measured. Nitrogen and phosphorus loads from East Bay to Hillsborough Bay were measured during selected time periods during June 1992 through May 1993; these data were used to estimate seasonal and annual loads. These loads were evaluated to determine whether the loss of fertilizer products from shipping activities resulted in increased nutrient loading to Hillsborough Bay. Discharge was measured, and water-quality samples were collected at the head of East Bay (exiting McKay Bay), and at the mouth of East Bay. Discharge and nitrogen and phosphorus concentrations for the period June 1992 through May 1993 were used to compute loads. Discharges from McKay Bay, Delaney Creek, and East Bay are highly variable because of the effect of tide. Flow patterns during discharge measurements generally were unidirectional in McKay Bay and Delaney Creek, but more complex, bidirectional patterns were observed at the mouth of East Bay. Tidally affected discharge data were digitally filtered with the Godin filter to remove the effects of tide so that residual, or net, discharge could be determined. Daily mean discharge from McKay Bay ranged from -1,900 to 2,420 cubic feet per second; from Delaney Creek, -3.8 to 162 cubic feet per second; and from East

46 CFR 7.20 - Nantucket Sound, Vineyard Sound, Buzzards Bay, Narragansett Bay, MA, Block Island Sound and...

Science.gov (United States)

2010-10-01

... 46 Shipping 1 2010-10-01 2010-10-01 false Nantucket Sound, Vineyard Sound, Buzzards Bay, Narragansett Bay, MA, Block Island Sound and easterly entrance to Long Island Sound, NY. 7.20 Section 7.20... Atlantic Coast § 7.20 Nantucket Sound, Vineyard Sound, Buzzards Bay, Narragansett Bay, MA, Block Island...

Breakdown voltage analysis of Al0.25Ga0.75N/GaN high electron mobility transistors with partial silicon doping in the AlGaN layer

International Nuclear Information System (INIS)

Duan Bao-Xing; Yang Yin-Tang

2012-01-01

In this paper, two-dimensional electron gas (2DEG) regions in AlGaN/GaN high electron mobility transistors (HEMTs) are realized by doping partial silicon into the AlGaN layer for the first time. A new electric field peak is introduced along the interface between the AlGaN and GaN buffer by the electric field modulation effect due to partial silicon positive charge. The high electric field near the gate for the complete silicon doping structure is effectively decreased, which makes the surface electric field uniform. The high electric field peak near the drain results from the potential difference between the surface and the depletion regions. Simulated breakdown curves that are the same as the test results are obtained for the first time by introducing an acceptor-like trap into the N-type GaN buffer. The proposed structure with partial silicon doping is better than the structure with complete silicon doping and conventional structures with the electric field plate near the drain. The breakdown voltage is improved from 296 V for the conventional structure to 400 V for the proposed one resulting from the uniform surface electric field. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

33 CFR 165.1182 - Safety/Security Zone: San Francisco Bay, San Pablo Bay, Carquinez Strait, and Suisun Bay, CA.

Science.gov (United States)

2010-07-01

... 33 Navigation and Navigable Waters 2 2010-07-01 2010-07-01 false Safety/Security Zone: San... Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED) PORTS AND WATERWAYS SAFETY... Areas Eleventh Coast Guard District § 165.1182 Safety/Security Zone: San Francisco Bay, San Pablo Bay...

Temperature dependent microwave performance of AlGaN/GaN high-electron-mobility transistors on high-resistivity silicon substrate

International Nuclear Information System (INIS)

Arulkumaran, S.; Liu, Z.H.; Ng, G.I.; Cheong, W.C.; Zeng, R.; Bu, J.; Wang, H.; Radhakrishnan, K.; Tan, C.L.

2007-01-01

The influence of temperature (- 50 deg. C to + 200 deg. C) was studied on the DC and microwave characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs) on high resistivity Si substrate for the first time. The AlGaN/GaN HEMTs exhibited a current-gain cut-off frequency (f T ) of 11.8 GHz and maximum frequency of oscillation (f max ) of 27.5 GHz. When compared to room temperature values, about 4% and 10% increase in f T and f max and 23% and 39.5% decrease in f T and f max were observed when measured at - 50 deg. C and 200 deg. C, respectively. The improvement of I D , g m f T , and f max at - 50 deg. C is due to the enhancement of 2DEG mobility and effective electron velocity. The anomalous drain current reduction in the I-V curves were observed at low voltage region at the temperature ≤ 10 deg. C but disappeared when the temperature reached ≥ 25 deg. C. A positive threshold voltage (V th ) shift was observed from - 50 deg. C to 200 deg. C. The positive shift of V th is due to the occurrence of trapping effects in the devices. The drain leakage current decreases with activation energies of 0.028 eV and 0.068 eV. This decrease of leakage current with the increase of temperature is due to the shallow acceptor initiated impact ionization

78 FR 62293 - Safety Zone, Oyster Festival 30th Anniversary Fireworks Display, Oyster Bay; Oyster Bay, NY

Science.gov (United States)

2013-10-15

... Safety Zone, Oyster Festival 30th Anniversary Fireworks Display, Oyster Bay; Oyster Bay, NY AGENCY: Coast... zone on the navigable waters of Oyster Bay near Oyster Bay, NY for the Oyster Festival 30th Anniversary... Oyster Festival 30th Anniversary Fireworks Display is scheduled for October 19, 2013 and is one of...

Diffusivities of an Al-Fe-Ni melt and their effects on the microstructure during solidification

International Nuclear Information System (INIS)

Zhang Lijun; Du Yong; Steinbach, Ingo; Chen Qing; Huang Baiyun

2010-01-01

A systematical investigation of the diffusivities in an Al-Fe-Ni melt was presented. Based on the experimental and theoretical data about diffusivities, the temperature- and composition-dependent atomic mobilities were evaluated for the elements in Al-Ni, Al-Fe, Fe-Ni and Al-Fe-Ni melts via an effective approach. Most of the reported diffusivities can be reproduced well by the obtained atomic mobilities. In particular, for the first time the ternary diffusivity of the liquid in a ternary system is described in conjunction with the established atomic mobilities. The effect of the atomic mobilities in a liquid on microstructure and microsegregation during solidification was demonstrated with one Al-Ni binary alloy. The simulation results indicate that accurate databases of mobilities in the liquid phase are much needed for the quantitative simulation of microstructural evolution during solidification by using various approaches, including DICTRA and the phase-field method.

Improved DC performance of AlGaN/GaN high electron mobility transistors using hafnium oxide for surface passivation

International Nuclear Information System (INIS)

Liu, Chang; Chor, Eng Fong; Tan, Leng Seow

2007-01-01

Improved DC performance of AlGaN/GaN high electron mobility transistors (HEMTs) have been demonstrated using reactive-sputtered hafnium oxide (HfO 2 ) thin film as the surface passivation layer. Hall data indicate a significant increase in the product of sheet carrier concentration (n s ) and electron mobility (μ n ) in the HfO 2 -passivated HEMTs, compared to the unpassivated HEMTs. This improvement in electron carrier characteristics gives rise to a 22% higher I Dmax and an 18% higher g mmax in HEMTs with HfO 2 passivation relative to the unpassivated devices. On the other hand, I gleak of the HEMTs decreases by nearly one order of magnitude when HfO 2 passivation is applied. In addition, drain current is measured in the subthreshold regime. Compared to the unpassivated HEMTs, HfO 2 -passivated HEMTs exhibit a much smaller off-state I D , indicating better turn-off characteristics

eBay.com

DEFF Research Database (Denmark)

Engholm, Ida

2014-01-01

Celebrated as one of the leading and most valuable brands in the world, eBay has acquired iconic status on par with century-old brands such as Coca-Cola and Disney. The eBay logo is now synonymous with the world’s leading online auction website, and its design is associated with the company...

Discharge between San Antonio Bay and Aransas Bay, southern Gulf Coast, Texas, May-September 1999

Science.gov (United States)

East, Jeffery W.

2001-01-01

Along the Gulf Coast of Texas, many estuaries and bays are important habitat and nurseries for aquatic life. San Antonio Bay and Aransas Bay, located about 50 and 30 miles northeast, respectively, of Corpus Christi, are two important estuarine nurseries on the southern Gulf Coast of Texas (fig. 1). According to the Texas Parks and Wildlife Department, “Almost 80 percent of the seagrasses [along the Texas Gulf Coast] are located in the Laguna Madre, an estuary that begins just south of Corpus Christi Bay and runs southward 140 miles to South Padre Island. Most of the remaining seagrasses, about 45,000 acres, are located in the heavily traveled San Antonio, Aransas and Corpus Christi Bay areas” (Shook, 2000).Population growth has led to greater demands on water supplies in Texas. The Texas Water Development Board, the Texas Parks and Wildlife Department, and the Texas Natural Resource Conservation Commission have the cooperative task of determining inflows required to maintain the ecological health of the State’s streams, rivers, bays, and estuaries. To determine these inflow requirements, the three agencies collect data and conduct studies on the need for instream flows and freshwater/ saline water inflows to Texas estuaries.To assist in the determination of freshwater inflow requirements, the U.S. Geological Survey (USGS), in cooperation with the Texas Water Development Board, conducted a hydrographic survey of discharge (flow) between San Antonio Bay and Aransas Bay during the period May–September 1999. Automated instrumentation and acoustic technology were used to maximize the amount and quality of data that were collected, while minimizing personnel requirements. This report documents the discharge measured at two sites between the bays during May–September 1999 and describes the influences of meteorologic (wind and tidal) and hydrologic (freshwater inflow) conditions on discharge between the two bays. The movement of water between the bays is

Heavy metal determination by X-rays spectrometry in superficial sediments at Havana Bay

International Nuclear Information System (INIS)

Gelen, Alina; Izquierdo, Walter; Lopez, Neivy; Corrales, Yasser; Casanova, Amaya O.; Diaz, Oscar; Manso, Maria V.; D'Alessandro, Katia; Reyes, Enma; Toledo, Carlos; Beltran, Jesus; Perez, Marlen; Ramirez, Marta; Soto, Jesus

2007-01-01

Havana Bay is a typical bag-type located in the Western-North Coast of the Republic of Cuba. Since 1980 it has been the object of a study for sea bottom rehabilitation and improvement of quality of the waters, where the final objective will be the recovery of the coastal and marine ecosystem. Thirteen surface samples of the Havana Bay (Cuba) were collected and analysed by X-Rays spectrometry. Some majority elements (Si, Ca, K, Na, S, Cl, Al, Fe, Mg, C and O) were measured by scanning electron microscopy (SEM) coupled with microanalysis to perform geomorphologic analysis. Nine elements (Ca, Fe, Ti, Mn, Cu, Zn, Sr, Zr and Pb) have been measured using an Energy Dispersive X-Ray Fluorescence (EDXRF) with a Si(Li) detector. Multivariate statistical was used for the analysis. The concentration levels showed this bay as the most polluted in Cuba. The highest contents of Cu, Zn and Pb were obtained in Atares and Marimelena Cove; these elements are indicators of urban as well as industrial pollution. (author)

Heavy metal determination by X-rays spectrometry in superficial sediments at Havana Bay

Energy Technology Data Exchange (ETDEWEB)

Gelen, Alina; Izquierdo, Walter; Lopez, Neivy; Corrales, Yasser; Casanova, Amaya O.; Diaz, Oscar; Manso, Maria V.; D' Alessandro, Katia [Institute for Applied Sciences and Technology, Havana (Cuba)], E-mail: alina@instec.cu; Reyes, Enma; Toledo, Carlos [Central Laboratory Criminology, Havana (Cuba); Beltran, Jesus; Perez, Marlen; Ramirez, Marta [Engineering Centre for Environmental Management of Bays and Coasts, Havana (Cuba)], E-mail: beltran@cimab.transnet.cu; Soto, Jesus [Universidad de Cantabria, Santander (Spain)], E-mail: sotoj@unican.es

2007-07-01

Havana Bay is a typical bag-type located in the Western-North Coast of the Republic of Cuba. Since 1980 it has been the object of a study for sea bottom rehabilitation and improvement of quality of the waters, where the final objective will be the recovery of the coastal and marine ecosystem. Thirteen surface samples of the Havana Bay (Cuba) were collected and analysed by X-Rays spectrometry. Some majority elements (Si, Ca, K, Na, S, Cl, Al, Fe, Mg, C and O) were measured by scanning electron microscopy (SEM) coupled with microanalysis to perform geomorphologic analysis. Nine elements (Ca, Fe, Ti, Mn, Cu, Zn, Sr, Zr and Pb) have been measured using an Energy Dispersive X-Ray Fluorescence (EDXRF) with a Si(Li) detector. Multivariate statistical was used for the analysis. The concentration levels showed this bay as the most polluted in Cuba. The highest contents of Cu, Zn and Pb were obtained in Atares and Marimelena Cove; these elements are indicators of urban as well as industrial pollution. (author)

The effect of iron-ore particles on the metal content of the brown alga Padina gymnospora (Espirito Santo Bay, Brazil)

International Nuclear Information System (INIS)

Nassar, C.A.G.; Salgado, L.T.; Yoneshigue-Valentin, Y.; Amado Filho, G.M.

2003-01-01

Iron ore deposits mat be the source of metals found in the brown alga Padina gymnospora. - The iron-ore particles discharged by a pellet processing plant (Espirito Santo Bay, Brazil) cover the seabed of Camburi Beach and consequently, the epibenthic community. In order to determine the importance of the contribution of the iron-ore deposits to the metal concentration in macroalgae of Espirito Santo Bay, four methods of cleaning particulate material adhered to the surface of thalli were tested prior to metal tissue analysis (Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) of Padina gymnospora. In addition, heavy metal concentrations were determined in individuals of P. gymnospora from a site (Frade Island) not affected by the iron-ore particles. The most efficient cleaning treatment, a combination of scraping and washing with an ethanol-seawater solution (NA+SC+ET) removed a number of particles on the surface of thalli 10 times higher than that observed in the control (C). Using this treatment, the total-metal concentrations were reduced by 78% for Fe and 50% for Al respect to the control. However, Fe, Al and Cu concentrations after treatment NA+SC+ET were significantly higher than those found at Frade Island. It is suggested that the iron-ore deposit might be a source for metal availability to macroalgae exposed to the dumped material at Espirito Santo Bay

Stormwater impact in Guanabara Bay (Rio de Janeiro): Evidences of seasonal variability in the dynamic of the sediment heavy metals

Science.gov (United States)

Fonseca, E. M.; Baptista Neto, J. A.; Silva, C. G.; McAlister, J. J.; Smith, B. J.; Fernandez, M. A.

2013-09-01

Guanabara Bay is one of the most prominent coastal bays in Brazil. This environment is an estuary of 91 rivers and channels, surrounded by the metropolis of Rio de Janeiro. The bay receives considerable amounts of contaminants introduced from sewage effluents, industrial discharge, urban and agricultural runoff, atmospheric fallout, and the combined inputs from the rivers, making Guanabara Bay one of the most polluted coastal environments on the Brazilian coastline. The aim of this work is to study the concentration and fractionation of the heavy metals within the sediments of the bay. In order to understand the possible seasonal influence on the heavy metal fractionation, two campaigns were carried out in two different seasons of the year (rainy and dry). Twelve stations, in four different areas, with different oceanographic characteristics, where chosen. To assess the bioavailability of the metals a selective extraction procedure was used to study the geochemical fractionation and bioavailability of Zn, Cu, Cr, Ni and Pb. The rainy season was very important with respect to variation in the total concentrations of Cr, Ni and Pb and their fractionation within different "operational" phases present in Guanabara Bay sediments. The water-soluble phase showed little importance, with respect to metal adsorption and this would suggest very low mobility of metals in the water column. Nevertheless, the potentially available metals within these sediments showed a high probability for their release and therefore cause contamination of the water column, since different parts of the bay are constantly subjected to dredging projects promoted by the harbor authorities.

Suppression of self-heating effect in AlGaN/GaN high electron mobility transistors by substrate-transfer technology using h-BN

International Nuclear Information System (INIS)

Hiroki, Masanobu; Kumakura, Kazuhide; Kobayashi, Yasuyuki; Akasaka, Tetsuya; Makimoto, Toshiki; Yamamoto, Hideki

2014-01-01

We fabricated AlGaN/GaN high electron mobility transistors (HEMTs) on h-BN/sapphire substrates and transferred them from the host substrates to copper plates using h-BN as a release layer. In current–voltage characteristics, the saturation drain current decreased by about 30% under a high-bias condition before release by self-heating effect. In contrast, after transfer, the current decrement was as small as 8% owing to improved heat dissipation: the device temperature increased to 50 °C in the as-prepared HEMT, but only by several degrees in the transferred HEMT. An effective way to improve AlGaN/GaN HEMT performance by a suppression of self-heating effect has been demonstrated

Suppression of self-heating effect in AlGaN/GaN high electron mobility transistors by substrate-transfer technology using h-BN

Energy Technology Data Exchange (ETDEWEB)

Hiroki, Masanobu, E-mail: hiroki.masanobu@lab.ntt.co.jp; Kumakura, Kazuhide; Kobayashi, Yasuyuki; Akasaka, Tetsuya; Makimoto, Toshiki; Yamamoto, Hideki [NTT Basic Research Laboratories, NTT Corporation 3-1 Morinosato Wakamiya, Atsugi-shi 243-0198 (Japan)

2014-11-10

We fabricated AlGaN/GaN high electron mobility transistors (HEMTs) on h-BN/sapphire substrates and transferred them from the host substrates to copper plates using h-BN as a release layer. In current–voltage characteristics, the saturation drain current decreased by about 30% under a high-bias condition before release by self-heating effect. In contrast, after transfer, the current decrement was as small as 8% owing to improved heat dissipation: the device temperature increased to 50 °C in the as-prepared HEMT, but only by several degrees in the transferred HEMT. An effective way to improve AlGaN/GaN HEMT performance by a suppression of self-heating effect has been demonstrated.

Classification using Hierarchical Naive Bayes models

DEFF Research Database (Denmark)

Langseth, Helge; Dyhre Nielsen, Thomas

2006-01-01

Classification problems have a long history in the machine learning literature. One of the simplest, and yet most consistently well-performing set of classifiers is the Naïve Bayes models. However, an inherent problem with these classifiers is the assumption that all attributes used to describe......, termed Hierarchical Naïve Bayes models. Hierarchical Naïve Bayes models extend the modeling flexibility of Naïve Bayes models by introducing latent variables to relax some of the independence statements in these models. We propose a simple algorithm for learning Hierarchical Naïve Bayes models...

Various Recipes of SiNx Passivated AlGaN/GaN High Electron Mobility Transistors in Correlation with Current Slump

International Nuclear Information System (INIS)

Ling, Yang; Yue, Hao; Xiao-Hua, Ma; Si, Quan; Gui-Zhou, Hu; Shou-Gao, Jiang; Li-Yuan, Yang

2009-01-01

The current slump of different recipes of SiN x passivated AlGaN/GaN high electron mobility transistors (HEMTs) is investigated. The dc and pulsed current-voltage curves of AlGaN/GaN HEMTs using different recipes are analyzed. It is found that passivation leakage has a strong relationship with NH 3 flow in the plasma-enhanced chemical vapor phase deposition process, which has impacted on the current collapse of SiN x passivated devices. We analyze the pulsed I DS – V DS characteristics of different recipes of SiN x passivation devices for different combinations of gate and drain quiescent biases (V GS0 , V DS0 ) of (0, 0), (−6, 0), (−6, 15) and (0, 15)V. The possible mechanisms are the traps in SiN x passivation capturing the electrons and the surface states at the SiN x /AlGaN interface, which can affect the channel of two-dimensional electron gas and cause the current collapse. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

75 FR 11837 - Chesapeake Bay Watershed Initiative

Science.gov (United States)

2010-03-12

... DEPARTMENT OF AGRICULTURE Commodity Credit Corporation Chesapeake Bay Watershed Initiative AGENCY...: Notice of availability of program funds for the Chesapeake Bay Watershed Initiative. SUMMARY: The... through the Chesapeake Bay Watershed Initiative for agricultural producers in the Chesapeake Bay watershed...

Urban Greening Bay Area

Science.gov (United States)

Information about the San Francisco Bay Water Quality Project (SFBWQP) Urban Greening Bay Area, a large-scale effort to re-envision urban landscapes to include green infrastructure (GI) making communities more livable and reducing stormwater runoff.

Concentration of PSP (Paralytic Shellfish Poisoning) Toxin On Shellfish From Inner Ambon Bay and Kao Bay North Halmahera

Science.gov (United States)

Pello, F. S.; Haumahu, S.; Huliselan, N. V.; Tuapattinaja, M. A.

2017-10-01

The Inner Ambon Bay and Kao Bay have potential on fisheries resources which one of them is molluscs. Molluscs especially for class bivalve have economical values and are consumed by coastal community. The research had been done to analyze saxitoxin (STX) concentration on bivalves from Kao Bay and Inner Ambon Bay. The Saxitoxin Elisa Test Kit Protocol was used to determine saxitoxin concentration. The measurement showed that the highest concentration of saxitoxin (392.42 µg STXeq/100g shellfish meat) was Gafrarium tumidum from Ambon Bay, whereas concentration of saxitoxin (321.83 µg STXeq/100g shellfish meat) was Mactra mera from Kao Bay

Marine littoral diatoms from the Gordon’s bay region of False Bay, Cape Province, South Africa

CSIR Research Space (South Africa)

Giffen, MH

1971-01-01

Full Text Available and Comic/i for Scientific and Industrial Research, Pretoria (Received: 5.2. 1970) The Gordon?s Bay region occupies the north western corner of False Bay, a large rectangular bay, bounded on the west by the Cape Peninsula ending at Cape Point...

Spatial distribution of heavy metals in surficial sediments from Guanabara Bay: Rio de Janeiro, Brazil

Science.gov (United States)

Neto, José Antônio Baptista; Gingele, Franz Xaver; Leipe, Thomas; Brehme, Isa

2006-04-01

Ninety-two surface sediment samples were collected in Guanabara Bay, one of the most prominent urban bays in SE Brazil, to investigate the spatial distribution of anthropogenic pollutants. The concentrations of heavy metals, organic carbon and particle size were examined in all samples. Large spatial variations of heavy metals and particle size were observed. The highest concentrations of heavy metals were found in the muddy sediments from the north western region of the bay near the main outlets of the most polluted rivers, municipal waste drainage systems and one of the major oil refineries. Another anomalous concentration of metals was found adjacent to Rio de Janeiro Harbour. The heavy metal concentrations decrease to the northeast, due to intact rivers and the mangrove systems in this area, and to the south where the sand fraction and open-marine processes dominate. The geochemical normalization of metal data to Li or Al has also demonstrated that the anthropogenic input of heavy metals have altered the natural sediment heavy metal distribution.

Concentrations of metals in blood and feathers of nestling ospreys (Pandion haliaetus) in Chesapeake and Delaware Bays

Science.gov (United States)

Rattner, B.A.; Golden, N.H.; Toschik, P.C.; McGowan, P.C.; Custer, T.W.

2008-01-01

In 2000, 2001, and 2002, blood and feather samples were collected from 40-45-day-old nestling ospreys (Pandion haliaetus) from Chesapeake Bay and Delaware Bay and River. Concentrations of 18 metals, metalloids, and other elements were determined in these samples by inductively coupled plasma-mass spectroscopy, and Hg concentrations were measured by cold vapor atomic absorption spectroscopy. When compared to concurrent reference areas (South, West, and Rhode Rivers), mean As and Hg concentrations in blood were greater (p nestlings from the highly industrialized Elizabeth River compared to the rural reference area. When compared to the concurrent reference area, mean Al, Ba, Hg, Mn, and Pb concentrations in feathers were substantially greater (p nestlings from northern Delaware Bay and River had greater concentrations (p nestling feathers from Delaware were frequently greater than in the Chesapeake. The present findings and those of related reproductive studies suggest that concentrations of several heavy metals (e.g., Cd, Hg, Pb) in nestling blood and feathers from Chesapeake and Delaware Bays were below toxicity thresholds and do not seem to be affecting chick survival during the nestling period.

Description of gravity cores from San Pablo Bay and Carquinez Strait, San Francisco Bay, California

Science.gov (United States)

Woodrow, Donald L.; John L. Chin,; Wong, Florence L.; Fregoso, Theresa A.; Jaffe, Bruce E.

2017-06-27

Seventy-two gravity cores were collected by the U.S. Geological Survey in 1990, 1991, and 2000 from San Pablo Bay and Carquinez Strait, California. The gravity cores collected within San Pablo Bay contain bioturbated laminated silts and sandy clays, whole and broken bivalve shells (mostly mussels), fossil tube structures, and fine-grained plant or wood fragments. Gravity cores from the channel wall of Carquinez Strait east of San Pablo Bay consist of sand and clay layers, whole and broken bivalve shells (less than in San Pablo Bay), trace fossil tubes, and minute fragments of plant material.

Oxygenation variability in Mejillones Bay, off northern Chile, during the last two centuries

Directory of Open Access Journals (Sweden)

J. A. Díaz-Ochoa

2011-01-01

Full Text Available The Peru Chile Current ecosystem is characterized by high biological productivity and important fisheries. Although this system is likely to be severely affected by climate change, its response to current global warming is still uncertain. In this paper, we analyze 10–166 year-old sediments in two cores collected from Mejillones Bay, an anoxic sedimentary setting favorable for the preservation of proxies. Based on a 166-year chronology, we used proxies of bottom-water oxygenation (Mo, V, S, and the (lycopane + n−C₃₅/n−C₃₁ ratio and surface water productivity (biogenic opal, counts of diatom valves, biogenic Ba, organic carbon, and chlorins to reconstruct environmental variations in Mejillones Bay. During the last two centuries, a shift took place in the coastal marine ecosystem of Bahia Mejillones at decadal scales. This shift was characterized by intense ENSO-like activity, large-scale fluctuations in biological export productivity and bottom water oxygenation, and increased eolian activity (inferred from Ti/Al and Zr/Al. This short-term variability was accompanied by a gradual increase of sulfidic conditions that has intensified since the early 1960s.

The Evolution of Personal Mobile Communications

Institute of Scientific and Technical Information of China (English)

I.S.Groves

1995-01-01

Within Europe the recently published Mobile Green Paper predicts a market for person-al communication services(PCS)of,perhaps,80% of the population-one connection to every adult.In the light of such a demand this paper reviews the emergence of present generation sys-tems and looks forward at vision for third generation mobile systems.

Universality of electron mobility in LaAlO₃/SrTiO₃ and bulk SrTiO₃

DEFF Research Database (Denmark)

Trier, Felix; Reich, K. V.; Christensen, Dennis Valbjørn

2017-01-01

Metallic LaAlO3/SrTiO3 (LAO/STO) interfaces attract enormous attention, but the relationship between the electron mobility and the sheet electron density, ns, is poorly understood. Here, we derive a simple expression for the three-dimensional electron density near the interface, n3D, as a function...

Highly selective and sensitive phosphate anion sensors based on AlGaN/GaN high electron mobility transistors functionalized by ion imprinted polymer.

Science.gov (United States)

Jia, Xiuling; Chen, Dunjun; Bin, Liu; Lu, Hai; Zhang, Rong; Zheng, Youdou

2016-06-09

A novel ion-imprinted electrochemical sensor based on AlGaN/GaN high electron mobility transistors (HEMTs) was developed to detect trace amounts of phosphate anion. This sensor combined the advantages of the ion sensitivity of AlGaN/GaN HEMTs and specific recognition of ion imprinted polymers. The current response showed that the fabricated sensor is highly sensitive and selective to phosphate anions. The current change exhibited approximate linear dependence for phosphate concentration from 0.02 mg L(-1) to 2 mg L(-1), the sensitivity and detection limit of the sensor is 3.191 μA/mg L(-1) and 1.97 μg L(-1), respectively. The results indicated that this AlGaN/GaN HEMT-based electrochemical sensor has the potential applications on phosphate anion detection.

Makirina bay peloid (N Dalmatia, Republic of Croatia – its potential use in balneotherapy

Directory of Open Access Journals (Sweden)

Darja Komar

2014-12-01

Full Text Available Recent marine sediments from Makirina bay are according to their organoleptic properties, treated as peloid or healing mud, already frequently used by local people and tourists as pomades. The application of peloids in balneotherapy is mainly intended for therapeutic treatment generally related to muscle-bone skin pathologies and purposes of wellness and relaxation. Recent studies point out that one of the main factors determining the final characteristics of peloids are grain size distribution, mineralogy, cation exchange capacity (CEC, elemental and microbiological composition of initial »geological material«. As reported by previous studies Makirina Bay peloid is represented mostly by sandy silt with relatively high CEC value (63.82 meq/100g. Peloid mineral composition is dominated by dolomite and quartz, followed by illite/muscovite, aragonite, halite, calcite, and pyrite. The average concentrations of potentially toxic elements (PTE in Makirina bay peloid determined in this research are: As (17.6 mg/kg, Cr (92.09 mg/kg, Cu (44.5 mg/ kg, Mo (31.8 mg/kg, Pb (28.9 mg/kg and Zn (69.2 mg/kg and are comparable to previous results. PTE contents in benthic algae Codium bursa (C. bursa are: As (8.8 mg/kg, Cr (15.7 mg/kg, Cu (5.6 mg/kg, Mo (0.7 mg/kg, Pb (3.6 mg/ kg and Zn (16.3 mg/kg. Calculated Transfer factors (TF from surficial peloid (0-5 cm to benthic algae C. bursa are <1 for all analysed PTE, indicating no PTE transfer or bioaccumulation of PTE in C. bursa. Results of microbiological research correspond to previous studies and showed no coliforms and E. coli presence in Makirina bay peloid. Our studies have shown the adequate comparability of Makirina Bay peloid with peloids already successfully used in various spa centres around the world in purposes related to wellness and therapy, but additional researches (determination of Cr and Mo mobilities are necessary before potential use of Makirina bay peloid.

75 FR 15343 - Regulated Navigation Area: Narragansett Bay, RI and Mount Hope Bay, RI and MA, Including the...

Science.gov (United States)

2010-03-29

...: Narragansett Bay, RI and Mount Hope Bay, RI and MA, Including the Providence River and Taunton River AGENCY... River and Mount Hope Bay in the vicinity of the two Brightman Street bridges have not been adopted and... Island and Mt. Hope Bay, MA.'' The notice was prompted primarily by two events: (1) The U.S. Army Corps...

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

Physisorption of functionalized gold nanoparticles on AlGaN/GaN high electron mobility transistors for sensing applications.

Science.gov (United States)

Makowski, M S; Kim, S; Gaillard, M; Janes, D; Manfra, M J; Bryan, I; Sitar, Z; Arellano, C; Xie, J; Collazo, R; Ivanisevic, A

2013-02-18

AlGaN/GaN high electron mobility transistors (HEMTs) were used to measure electrical characteristics of physisorbed gold nanoparticles (Au NPs) functionalized with alkanethiols with a terminal methyl, amine, or carboxyl functional group. Additional alkanethiol was physisorbed onto the NP treated devices to distinguish between the effects of the Au NPs and alkanethiols on HEMT operation. Scanning Kelvin probe microscopy and electrical measurements were used to characterize the treatment effects. The HEMTs were operated near threshold voltage due to the greatest sensitivity in this region. The Au NP/HEMT system electrically detected functional group differences on adsorbed NPs which is pertinent to biosensor applications.

Shaping Air Mobility Forces for Future Relevance

Science.gov (United States)

2017-01-01

King Air University Press 600 Chennault Circle, Building 1405 Maxwell AFB, AL 36112-6010 afri.aupress@us.af.mil http://aupress.au.af.mil...the congressional study’s Persian Gulf scenario.37 Later Defense Department air mobility plans continued the CMMS pat- tern of paring down air mobility

Cryptanalysis and Improvement of "A Secure Password Authentication Mechanism for Seamless Handover in Proxy Mobile IPv6 Networks".

Science.gov (United States)

Alizadeh, Mojtaba; Zamani, Mazdak; Baharun, Sabariah; Abdul Manaf, Azizah; Sakurai, Kouichi; Anada, Hiroaki; Anada, Hiroki; Keshavarz, Hassan; Ashraf Chaudhry, Shehzad; Khurram Khan, Muhammad

2015-01-01

Proxy Mobile IPv6 is a network-based localized mobility management protocol that supports mobility without mobile nodes' participation in mobility signaling. The details of user authentication procedure are not specified in this standard, hence, many authentication schemes have been proposed for this standard. In 2013, Chuang et al., proposed an authentication method for PMIPv6, called SPAM. However, Chuang et al.'s Scheme protects the network against some security attacks, but it is still vulnerable to impersonation and password guessing attacks. In addition, we discuss other security drawbacks such as lack of revocation procedure in case of loss or stolen device, and anonymity issues of the Chuang et al.'s scheme. We further propose an enhanced authentication method to mitigate the security issues of SPAM method and evaluate our scheme using BAN logic.

MOBILE LEARNING – AN ALTERNATIVE APPROACH IN HIGHER EDUCATION

OpenAIRE

Khalil Alsaadat

2017-01-01

Due to the swift proliferation of mobile technology, the use of mobile devices, like notebook computers, and mobile phones, as learning tools has offered people the flexibility and convenience to acquire new knowledge anytime and anywhere. In light of this, growing attention has been paid to the critical roles of perceived flexibility advantages in mobile and online learning (Huang et al, 2014). And because of the increasing use of mobile technologies in society and by the younger generation,...

Monitoring of bird abundance and distribution at McKinley Bay and Hutchison Bay, Northwest Territories, 1981 to 1993

Energy Technology Data Exchange (ETDEWEB)

Cornish, B J; Dickson, D L

1994-04-01

McKinley Bay has been identified as a preferred site for a harbor to support oil and gas production in the Beaufort Sea. As the bay is a molting area for several species of diving duck, a study was initiated to monitor the effect of harbor development on birds using the bay. Baseline information on the natural annual fluctuations in the number of birds were collected for nine years at McKinley Bay and eight years at neighboring Hutchinson Bay, an area chosen as the control. The final report of the predevelopment phase of the monitoring study is presented, including results of the 1993 surveys and a summary of results of all years of surveys. There were significantly more diving ducks in McKinley Bay in early August 1990 to 1993, on average, than from 1981 to 1985. No statistically significant change in total diving ducks was noted at Hutchinson Bay. Numbers of species of divers varied substantially between years at the two bays but not to the same degree. Significantly more Pacific loons, red-throated loons, and northern pintails were recorded in the 1990-1993 surveys at McKinley Bay than in earlier surveys. Potential explanations for the large between-year fluctuations in diving duck numbers are discussed. The variations may be due to bird responses to changes in the physical environment or related to the limitations of the aerial survey techniques used. Because of the large natural fluctuations in numbers of molting diving ducks using these bays in early August, it will be difficult to detect future impacts of industrial disturbance, even when sources of survey bias are minimized. It is concluded that aerial surveys of molting diving ducks in the two bays are unsuitable for monitoring the effects of industrial development. 41 refs., 7 figs., 23 tabs.

Contenido de metales en Cancer polyodon (Crustacea: Decapoda en un sistema de bahías del norte de Chile (27°S Metal contents in Cancer polyodon (Crustacea: Decapoda in a bay system of northern Chile (27°S

Directory of Open Access Journals (Sweden)

Alexis Castillo

2011-11-01

Full Text Available El contenido de Zn, Cu, Cd, Pb, Fe, Al y Ni fue analizado en tejido muscular de Cancer polyodon en las bahías de Caldera, Calderilla, Inglesa y Salada (Atacama, Chile. Los resultados fueron comparados con estudios similares desarrollados por otros autores y la normativa de carácter nacional e internacional relacionada con el contenido de metales pesados en crustáceos para consumo humano. El orden de abundancia de los metales analizados en C. polyodon fue CdThe contents of Zn, Cu, Cd, Pb, Fe, Al and Ni in the muscle tissue of Cancer polyodon from Caldera, Calderilla, Inglesa, and Salada bays (Atacama, Chile were quantified. The results were compared with similar studies by other authors and with the national and international regulatory standards for heavy metal contents in crustaceans for human consumption. In increasing order, the metal contents in C. polyodon were: Cd< Ni< Cu< Pb< ZnAl. Mean concentrations of Cd, Pb, Fe and Al were highest in Salada Bay: Cu and Ni were highest in Caldera Bay; and Zn was highest in Inglesa Bay. All the metals except Cu differed significantly (P < 0.05 among the analyzed bays. Of the seven metals analyzed, Pb, Fe, and Al concentrations in C. polyodon were higher than those reported for other coastal systems. Concentrations of Cu (except Calderilla, Cd (except Caldera and Inglesa, and Pb exceeded the threshold values indicated by the national and international standards, suggesting that the presence of these metals in C. polyodon represents a potential risk for human health.

Site Safety and Food Affect Movements of Semipalmated Sandpipers (Calidris pusilla Migrating Through the Upper Bay of Fundy

Directory of Open Access Journals (Sweden)

Ashley J. Sprague

2008-12-01

Full Text Available The upper Bay of Fundy is a critical stopover site for Semipalmated Sandpipers (Calidris pusilla during their fall migration. However, little is known about factors that influence selection of feeding and roosting sites by these birds, or the extent to which birds move between different sites during their time in the region. Using radio-telemetry, we studied movement patterns, examined habitat use, and tested hypotheses associated with factors influencing foraging and roost-site selection. Movements of radio-tagged sandpipers were tracked in the upper Bay of Fundy in August 2004 and 2005. In 2004, sandpipers from the Minas Basin, Nova Scotia and Chignecto Bay, New Brunswick and Nova Scotia, were tracked, and in 2005, sandpipers were tracked only in Chignecto Bay. Sandpipers were highly mobile in both the Minas Basin 2004 and Chignecto Bay 2005, making daily movements of up to 20 km between foraging and roosting sites, although very little movement was detected in Chignecto Bay in 2004. Migrating sandpipers appeared to select foraging sites based on relative safety, as measured by distance to cover, provided that these sites offered an adequate food supply. Similarly, roosting sandpipers preferred sites that were far from nearby trees that might offer cover to predators. This preference for safe sites became more apparent later in their stay in the Bay of Fundy, when birds were heavier and, therefore, possibly more vulnerable to predation. Semipalmated Sandpipers appear to be flexible during their time in the upper Bay of Fundy, displaying year-to-year and site-to-site variability in movement and mudflat usage. Therefore, multiple, synchronized population counts should be conducted at known roost sites in order to more accurately estimate Semipalmated Sandpiper abundance in this region. Furthermore, in a highly dynamic system where food can be variable, landscape features such as distance to cover may be important factors to consider when

Study of SiNx:Hy passivant layers for AlGaN/GaN high electron mobility transistors

International Nuclear Information System (INIS)

Redondo-Cubero, A.; Gago, R.; Romero, M.F.; Gonzalez-Posada, F.; Brana, A.F.; Munoz, E.; Jimenez, A.

2008-01-01

In this work, hydrogenated silicon nitride (SiN x :H y ) grown by chemical vapour deposition as passivant layers for high electron mobility transistors (HEMT) have been studied. The film composition and bonding structure were determined by ion beam analysis and X-ray absorption spectroscopy techniques, respectively. The effects of gas precursors (SiH 4 /N 2 and SiH 4 /NH 3 ) and film/substrate interface on the film growth have been addressed. The growth on different substrates (Si, GaN, AlGaN), and the effects of plasma pre-treatments have been studied before the growth and the film growth evolution. Results yield no significant differences in all the analysed samples. This points out the relevant role of SiHn radicals as growth precursor species and that intrinsic characteristics of the SiNx:Hy layers are not affected by the film/substrate interface. Hence, improved performance of HEMT with surface plasma pre-treatments before passivation should be related to extrinsic mechanisms (such as creation of defects in AlGaN surface, removal of the surface contamination or ion-induced roughness). (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

Default Bayes factors for ANOVA designs

NARCIS (Netherlands)

Rouder, Jeffrey N.; Morey, Richard D.; Speckman, Paul L.; Province, Jordan M.

2012-01-01

Bayes factors have been advocated as superior to p-values for assessing statistical evidence in data. Despite the advantages of Bayes factors and the drawbacks of p-values, inference by p-values is still nearly ubiquitous. One impediment to the adoption of Bayes factors is a lack of practical

77 FR 21890 - Drawbridge Operation Regulation; Sturgeon Bay Ship Canal, Sturgeon Bay, WI

Science.gov (United States)

2012-04-12

... Street and Maple-Oregon Bridges so vehicular traffic congestion would not develop on downtown Sturgeon... the efficient movement of vehicular traffic in Sturgeon Bay. The Sturgeon Bay Ship Canal is... experiences a significant increase in vehicular and vessel traffic during the peak tourist and navigation...

Ni/Au-gate In0.45Al0.55As/In0.53Ga0.47As/InAlGaAs/GaAs metamorphic high-electron-mobility transistors

International Nuclear Information System (INIS)

Lee, Ching-Sung; Hsu, Wei-Chou; Su, Ke-Hua; Huang, Jun-Chin; Huang, Dong-Hai; Chen, Yeong-Jia

2006-01-01

A δ-doped In 0.45 Al 0.55 As/In 0.53 Ga 0.47 As/InAlGaAs/GaAs metamorphic high electron mobility transistor (MHEMT) using a Ni/Au-gate electrode has been successfully fabricated and demonstrated. Compared to conventional Au-gate devices with identical structures, the proposed device improves the kink-effect-related output conductance, the gate-voltage swing, the current drive capability, the breakdown characteristics, and the device power performance. Experimentally, a high extrinsic transconductance of 309 mS/mm, a high drain-source saturation current density of 573 mA/mm, an improved gate-voltage swing of 1.05 V with a corresponding saturation current density of 314 mA/mm, a high saturated output power of 11.3 dBm, and a high power gain of 23.8 dB with a power-added efficiency of 39.2 % are obtained for a 0.65 x 200 μm 2 gate at 300 K. In addition, the measured f T and f max are 49.1 and 61.7 GHz, respectively.

Retrospective reconstruction of personal doses using mobile phones

International Nuclear Information System (INIS)

Ekendahl, Daniela

2011-01-01

Mobile phones are among objects usable for retrospective reconstruction of doses received by persons irradiated from serious radiation accidents or terrorist acts involving radioactivity. In this respect, it is an advantage of mobile phones that they are often worn close to the body and are used by the majority of population. Like other portable electronic devices, mobile phones contain electronic components which can include ceramic materials exhibiting radiation induced luminescence. Aluminium oxide (Al2O3) is an example; its layers are often used in chip resistors. This work summarizes the results of a pilot study investigating the dosimetric potential of Al2O3 measured via thermoluminescence (TL) and optically stimulated luminescence (OSL). A trial dose reconstruction performed with two mobile phones is described. It is shown that the material exhibits favourable dosimetric properties and the method is sufficiently accurate and operative for personal accident dosimetry purposes. (orig.)

Study on origin and sedimentary environment of marine sediments from Kii Channel, Hiroshima Bay and Tosa Bay

International Nuclear Information System (INIS)

Suzuki, Misaki

2008-01-01

The trace amounts of elements in the sediments of sea bottom in Kii Channel, Hiroshima Bay and Tosa Bay were determined quantitatively by the neutron activation analysis. The following facts were illustrated particularly from the quantitative analysis of scandium, rare earths, thorium and uranium: 1) It was known from Ce/La ratio that the geological feature in the west part of Japan is reflected in Kii Channel, Hiroshima Bay and Tosa Bay; 2) The rare-earth element pattern and La/Lu ratio suggest the fact that Kii Channel, Hiroshima Bay and Tosa Bay are essentially composed of the materials of which origin is land; 3) From the fact that Ce/La ratio in these sites are slightly under 1.0, these sites are considered to be affected mainly by the materials of which origin is land; 4) The sedimentary environment in the marine bottom of the Japanese coasts has been found to be mostly under a reductive state. (M.H.)

1.5-V-threshold-voltage Schottky barrier normally-off AlGaN/GaN high-electron-mobility transistors with f T/f max of 41/125 GHz

Science.gov (United States)

Hou, Bin; Ma, Xiaohua; Yang, Ling; Zhu, Jiejie; Zhu, Qing; Chen, Lixiang; Mi, Minhan; Zhang, Hengshuang; Zhang, Meng; Zhang, Peng; Zhou, Xiaowei; Hao, Yue

2017-07-01

In this paper, a normally-off AlGaN/GaN high-electron-mobility transistors (HEMT) fabricated using inductively coupled plasma (ICP) CF4 plasma recessing and an implantation technique is reported. A gate-to-channel distance of ˜10 nm and an equivalent negative fluorine sheet charge density of -1.21 × 1013 cm-2 extracted using a simple threshold voltage (V th) analytical model result in a high V th of 1.5 V, a peak transconductance of 356 mS/mm, and a subthreshold slope of 133 mV/decade. A small degradation of channel mobility leads to a high RF performance with f T/f max of 41/125 GHz, resulting in a record high f T × L g product of 10.66 GHz·µm among Schottky barrier AlGaN/GaN normally-off HEMTs with V th exceeding 1 V, to the best of our knowledge.

Cryptanalysis and Improvement of "A Secure Password Authentication Mechanism for Seamless Handover in Proxy Mobile IPv6 Networks".

Directory of Open Access Journals (Sweden)

Mojtaba Alizadeh

Full Text Available Proxy Mobile IPv6 is a network-based localized mobility management protocol that supports mobility without mobile nodes' participation in mobility signaling. The details of user authentication procedure are not specified in this standard, hence, many authentication schemes have been proposed for this standard. In 2013, Chuang et al., proposed an authentication method for PMIPv6, called SPAM. However, Chuang et al.'s Scheme protects the network against some security attacks, but it is still vulnerable to impersonation and password guessing attacks. In addition, we discuss other security drawbacks such as lack of revocation procedure in case of loss or stolen device, and anonymity issues of the Chuang et al.'s scheme. We further propose an enhanced authentication method to mitigate the security issues of SPAM method and evaluate our scheme using BAN logic.

76 FR 28309 - Drawbridge Operation Regulation; Sturgeon Bay Ship Canal, Sturgeon Bay, WI

Science.gov (United States)

2011-05-17

... vehicular traffic congestion would not develop on downtown Sturgeon Bay streets due to unscheduled bridge... schedules during the peak tourist and navigation seasons to provide for the efficient movement of vehicular... between Lake Michigan and Green Bay. The area experiences a significant increase in vehicular and vessel...

High-electric-field-stress-induced degradation of SiN passivated AlGaN/GaN high electron mobility transistors

International Nuclear Information System (INIS)

Wen-Ping, Gu; Huan-Tao, Duan; Jin-Yu, Ni; Yue, Hao; Jin-Cheng, Zhang; Qian, Feng; Xiao-Hua, Ma

2009-01-01

AlGaN/GaN high electron mobility transistors (HEMTs) are fabricated by employing SiN passivation, this paper investigates the degradation due to the high-electric-field stress. After the stress, a recoverable degradation has been found, consisting of the decrease of saturation drain current I Dsat , maximal transconductance g m , and the positive shift of threshold voltage V TH at high drain-source voltage V DS . The high-electric-field stress degrades the electric characteristics of AlGaN/GaN HEMTs because the high field increases the electron trapping at the surface and in AlGaN barrier layer. The SiN passivation of AlGaN/GaN HEMTs decreases the surface trapping and 2DEG depletion a little during the high-electric-field stress. After the hot carrier stress with V DS = 20 V and V GS = 0 V applied to the device for 10 4 sec, the SiN passivation decreases the stress-induced degradation of I Dsat from 36% to 30%. Both on-state and pulse-state stresses produce comparative decrease of I Dsat , which shows that although the passivation is effective in suppressing electron trapping in surface states, it does not protect the device from high-electric-field degradation in nature. So passivation in conjunction with other technological solutions like cap layer, prepassivation surface treatments, or field-plate gate to weaken high-electric-field degradation should be adopted. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

Mechanism of leakage of ion-implantation isolated AlGaN/GaN MIS-high electron mobility transistors on Si substrate

Science.gov (United States)

Zhang, Zhili; Song, Liang; Li, Weiyi; Fu, Kai; Yu, Guohao; Zhang, Xiaodong; Fan, Yaming; Deng, Xuguang; Li, Shuiming; Sun, Shichuang; Li, Xiajun; Yuan, Jie; Sun, Qian; Dong, Zhihua; Cai, Yong; Zhang, Baoshun

2017-08-01

In this paper, we systematically investigated the leakage mechanism of the ion-implantation isolated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors (MIS-HEMTs) on Si substrate. By means of combined DC tests at different temperatures and electric field dependence, we demonstrated the following original results: (1) It is proved that gate leakage is the main contribution to OFF-state leakage of ion-implantation isolated AlGaN/GaN MIS-HEMTs, and the gate leakage path is a series connection of the gate dielectric Si3N4 and Si3N4-GaN interface. (2) The dominant mechanisms of the leakage current through LPCVD-Si3N4 gate dielectric and Si3N4-GaN interface are identified to be Frenkel-Poole emission and two-dimensional variable range hopping (2D-VRH), respectively. (3) A certain temperature annealing could reduce the density of the interface state that produced by ion implantation, and consequently suppress the interface leakage transport, which results in a decrease in OFF-state leakage current of ion-implantation isolated AlGaN/GaN MIS-HEMTs.

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.

Ecological evaluation of proposed dredged material from St. Andrew Bay, Florida

International Nuclear Information System (INIS)

Mayhew, H.L.; Word, J.Q.; Kohn, N.P.; Pinza, M.R.; Karle, L.M.; Ward, J.A.

1993-10-01

The US Army Corps of Engineers (USACE), Mobile District, requested that the Battelle/Marine Sciences Laboratory (MSL) conduct field sampling and chemical and biological testing to determine the suitability of potential dredged material for open ocean disposal. Sediment from St. Andrew Bay was chemically characterized and evaluated for biological toxicity and bioaccumulation of contaminants. The Tier III guidance for ocean disposal testing requires tests of water column effects (following dredged material disposal), deposited sediment toxicity, and bioaccumulation of contaminants from deposited sediment (dredged material). To meet these requirements, the MSL conducted suspended-particulate-phase (SPP) toxicity tests, solid-phase toxicity tests, and bioaccumulation testing on sediment representing potential dredged material from Panama City Harbor. Physical and chemical characterization of sediment to support toxicity and bioaccumulation results was also conducted on both the test and reference sediments. The MSL collected sediment samples from five sites in St. Andrew Bay and one reference site near Lands End Peninsula. The five test sediments and the reference sediment were analyzed for physical and chemical sediment characteristics, SPP chemical contaminants, solid-phase toxicity, SPP toxicity, and bioaccumulation of contaminants

76 FR 22809 - Safety Zone; Bay Ferry II Maritime Security Exercise; San Francisco Bay, San Francisco, CA

Science.gov (United States)

2011-04-25

... DEPARTMENT OF HOMELAND SECURITY Coast Guard 33 CFR Part 165 [Docket No. USCG-2011-0196] RIN 1625-AA00 Safety Zone; Bay Ferry II Maritime Security Exercise; San Francisco Bay, San Francisco, CA AGENCY... Security Exercise; San Francisco Bay, San Francisco, CA. (a) Location. The limits of this safety zone...

Responses of upland herpetofauna to the restoration of Carolina Bays and thinning of forested Bay Margins.

Energy Technology Data Exchange (ETDEWEB)

Ledvina, Joseph A.

2008-05-01

Research on the effects of wetland restoration on reptiles and amphibians is becoming more common, but almost all of these studies have observed the colonization of recently disturbed habitats that were completely dry at the time of restoration. In a similar manner, investigations herpetofaunal responses to forest management have focused on clearcuts, and less intensive stand manipulations are not as well studied. To evaluate community and population responses of reptiles and amphibians to hydrology restoration and canopy removal in the interior of previously degraded Carolina bays, I monitored herpetofauna in the uplands adjacent to six historically degraded Carolina bays at the Savannah River Site (SRS) in South Carolina for four years after restoration. To evaluate the effects of forest thinning on upland herpetofauna, forests were thinned in the margins of three of these bays. I used repeated measures ANOVA to compare species richness and diversity and the abundance of selected species and guilds between these bays and with those at three reference bays that were not historically drained and three control bays that remained degraded. I also used Non-metric Multidimensional Scaling (NMDS) to look for community-level patterns based treatments.

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)

Impact of rounded electrode corners on breakdown characteristics of AlGaN/GaN high-electron mobility transistors

Science.gov (United States)

Yamazaki, Taisei; Asubar, Joel T.; Tokuda, Hirokuni; Kuzuhara, Masaaki

2018-05-01

We investigated the impact of rounded electrode corners on the breakdown characteristics of AlGaN/GaN high-electron mobility transistors. For standard reference devices, catastrophic breakdown occurred predominantly near the sharp electrode corners. By introducing a rounded-electrode architecture, premature breakdown at the corners was mitigated. Moreover, the rate of breakdown voltage (V BR) degradation with an increasing gate width (W G) was significantly lower for devices with rounded corners. When W G was increased from 100 µm to 10 mm, the V BR of the reference device dropped drastically, from 1,200 to 300 V, whereas that of the rounded-electrode device only decreased to a respectable value of 730 V.

A Bayes linear Bayes method for estimation of correlated event rates.

Science.gov (United States)

Quigley, John; Wilson, Kevin J; Walls, Lesley; Bedford, Tim

2013-12-01

Typically, full Bayesian estimation of correlated event rates can be computationally challenging since estimators are intractable. When estimation of event rates represents one activity within a larger modeling process, there is an incentive to develop more efficient inference than provided by a full Bayesian model. We develop a new subjective inference method for correlated event rates based on a Bayes linear Bayes model under the assumption that events are generated from a homogeneous Poisson process. To reduce the elicitation burden we introduce homogenization factors to the model and, as an alternative to a subjective prior, an empirical method using the method of moments is developed. Inference under the new method is compared against estimates obtained under a full Bayesian model, which takes a multivariate gamma prior, where the predictive and posterior distributions are derived in terms of well-known functions. The mathematical properties of both models are presented. A simulation study shows that the Bayes linear Bayes inference method and the full Bayesian model provide equally reliable estimates. An illustrative example, motivated by a problem of estimating correlated event rates across different users in a simple supply chain, shows how ignoring the correlation leads to biased estimation of event rates. © 2013 Society for Risk Analysis.

An empirical test of the 'shark nursery area concept' in Texas bays using a long-term fisheries-independent data set

Science.gov (United States)

Froeschke, John T.; Stunz, Gregory W.; Sterba-Boatwright, Blair; Wildhaber, Mark L.

2010-01-01

Using a long-term fisheries-independent data set, we tested the 'shark nursery area concept' proposed by Heupel et al. (2007) with the suggested working assumptions that a shark nursery habitat would: (1) have an abundance of immature sharks greater than the mean abundance across all habitats where they occur; (2) be used by sharks repeatedly through time (years); and (3) see immature sharks remaining within the habitat for extended periods of time. We tested this concept using young-of-the-year (age 0) and juvenile (age 1+ yr) bull sharks Carcharhinus leucas from gill-net surveys conducted in Texas bays from 1976 to 2006 to estimate the potential nursery function of 9 coastal bays. Of the 9 bay systems considered as potential nursery habitat, only Matagorda Bay satisfied all 3 criteria for young-of-the-year bull sharks. Both Matagorda and San Antonio Bays met the criteria for juvenile bull sharks. Through these analyses we examined the utility of this approach for characterizing nursery areas and we also describe some practical considerations, such as the influence of the temporal or spatial scales considered when applying the nursery role concept to shark populations.

Interface characteristics of spin-on-dielectric SiO{sub x}-buffered passivation layers for AlGaN/GaN high electron mobility transistors

Energy Technology Data Exchange (ETDEWEB)

Ko, Pil-Seok; Park, Kyoung-Seok; Yoon, Yeo-Chang [Division of Electronics and Electrical Engineering, Dongguk University, 100-715 Seoul (Korea, Republic of); Sheen, Mi-Hyang [Department of Materials Science Engineering, Seoul National University, 151-742 Seoul (Korea, Republic of); Kim, Sam-Dong, E-mail: samdong@dongguk.edu [Division of Electronics and Electrical Engineering, Dongguk University, 100-715 Seoul (Korea, Republic of)

2015-08-31

To reveal the cause for significant enhancement of dc current performance of the AlGaN/GaN high electron mobility transistors (HEMTs) with the spin-on-dielectric (SOD) SiO{sub x}-buffered passivation structure compared to the conventional Si{sub 3}N{sub 4} passivation deposited by plasma-enhanced vapor deposition (PECVD), we characterized the passivation interfaces using the cross-sectional transmission electron microscopy, cathodoluminescence, capacitance–voltage (C–V) characterizations, and Hall-effect measurements. The interface state density of PECVD Si{sub 3}N{sub 4} passivation was in the range of 10{sup 12}–10{sup 13} cm{sup −2} eV{sup −1}, which is one-order higher than that of the SOD (10{sup 11}–10{sup 12} cm{sup −2} eV{sup −1}) as measured by C–V measurements from the metal–insulator–semiconductor capacitors. Higher density of effective oxide charge density (especially dominant contribution of ionic mobile charge) was also derived from the PECVD Si{sub 3}N{sub 4} passivation. A well-resolved reduction of the electron Hall mobility of the Si{sub 3}N{sub 4} passivation compared to that of the perhydropolysilazane SOD passivation, which can be due to the higher-density interface states and trap charges, can answer the relative dc current collapse of our HEMT devices. - Highlights: • Spin-on-dielectric (SOD)-buffered passivation for AlGaN/GaN HEMTs • Characterize the charge density and interface states using the C–V measurements • SOD-buffered passivation minimizes surface states at the interface. • DC performance of SOD-buffered structure is due to the interface characteristics.

Columnar Self-Assembly of Electron-Deficient Dendronized Bay-Annulated Perylene Bisimides.

Science.gov (United States)

Gupta, Ravindra Kumar; Shankar Rao, Doddamane S; Prasad, S Krishna; Achalkumar, Ammathnadu S

2018-03-07

Three new heteroatom bay-annulated perylene bisimides (PBIs) have been synthesized by microwave-assisted synthesis in excellent yield. N-annulated and S-annulated perylene bisimides exhibited columnar hexagonal phase, whereas Se-annulated perylene bisimide exhibited low temperature columnar oblique phase in addition to the high temperature columnar hexagonal phase. The cup shaped bay-annulated PBIs pack into columns with enhanced intermolecular interactions. In comparison to PBI, these molecules exhibited lower melting and clearing temperature, with good solubility. A small red shift in the absorption was seen in the case of N-annulated PBI, whereas S- and Se-annulated PBIs exhibited blue-shifted absorption spectra. Bay-annulation increased the HOMO and LUMO levels of the N-annulated perylene bisimide, whereas a slight increase in the LUMO level and a decrease in the HOMO levels were observed in the case of S- and Se-annulated perylene bisimides, in comparison to the simple perylene bisimide. The band gaps of PBI and PBI-N were almost same, whereas an increase in the band gaps were observed in the case of S- and Se-annulated PBIs. The tendency to freeze in the ordered glassy columnar phase for PBI-N and PBI-S will help to overcome the charge traps due to crystallization, which are detrimental to one-dimensional charge carrier mobility. These solution processable electron deficient columnar semiconductors possessing good thermal stability may form an easily accessible promising class of n-type materials. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Florida Bay: A history of recent ecological changes

Science.gov (United States)

Fourqurean, J.W.; Robblee, M.B.

1999-01-01

Florida Bay is a unique subtropical estuary at the southern tip of the Florida peninsula. Recent ecological changes (seagrass die-off, algal blooms, increased turbidity) to the Florida Bay ecosystem have focused the attention of the public, commercial interests, scientists, and resource managers on the factors influencing the structure and function of Florida Bay. Restoring Florida Bay to some historic condition is the goal of resource managers, but what is not clear is what an anthropogenically-unaltered Florida Bay would look like. While there is general consensus that human activities have contributed to the changes occurring in the Florida Bay ecosystem, a high degree of natural system variability has made elucidation of the links between human activity and Florida Bay dynamics difficult. Paleoecological analyses, examination of long-term datasets, and directed measurements of aspects of the ecology of Florida Bay all contribute to our understanding of the behavior of the bay, and allow quantification of the magnitude of the recent ecological changes with respect to historical variability of the system.

Comprehensive magnetotransport characterization of two dimensional electron gas in AlGaN/GaN high electron mobility transistor structures leading to the assessment of interface roughness

Energy Technology Data Exchange (ETDEWEB)

Mishra, Manna Kumari [Solid State Physics Laboratory, Lucknow Road, Timarpur, Delhi-110054 (India); Netaji Subhas Institute of Technology, Dwarka, New Delhi-110078 (India); Sharma, Rajesh K., E-mail: rksharma@sspl.drdo.in; Manchanda, Rachna; Bag, Rajesh K.; Muralidharan, Rangarajan [Solid State Physics Laboratory, Lucknow Road, Timarpur, Delhi-110054 (India); Thakur, Om Prakash [Netaji Subhas Institute of Technology, Dwarka, New Delhi-110078 (India)

2014-09-15

Magnetotransport in two distinct AlGaN/GaN HEMT structures grown by Molecular Beam Epitaxy (MBE) on Fe-doped templates is investigated using Shubnikov de-Haas Oscillations in the temperature range of 1.8–6 K and multicarrier fitting in the temperature range of 1.8–300 K. The temperature dependence of the two dimensional electron gas mobility is extracted from simultaneous multicarrier fitting of transverse and longitudinal resistivity as a function of magnetic field and the data is utilized to estimate contribution of interface roughness to the mobility and the corresponding transport lifetime. The quantum scattering time obtained from the analysis of Shubnikov de Haas Oscillations in transverse magnetoresistance along with the transport lifetime time were used to estimate interface roughness amplitude and lateral correlation length. The results indicate that the insertion of AlN over layer deposited prior to the growth of GaN base layer on Fe doped GaN templates for forming HEMT structures reduced the parallel conduction but resulted in an increase in interface roughness.

Comprehensive magnetotransport characterization of two dimensional electron gas in AlGaN/GaN high electron mobility transistor structures leading to the assessment of interface roughness

International Nuclear Information System (INIS)

Mishra, Manna Kumari; Sharma, Rajesh K.; Manchanda, Rachna; Bag, Rajesh K.; Muralidharan, Rangarajan; Thakur, Om Prakash

2014-01-01

Magnetotransport in two distinct AlGaN/GaN HEMT structures grown by Molecular Beam Epitaxy (MBE) on Fe-doped templates is investigated using Shubnikov de-Haas Oscillations in the temperature range of 1.8–6 K and multicarrier fitting in the temperature range of 1.8–300 K. The temperature dependence of the two dimensional electron gas mobility is extracted from simultaneous multicarrier fitting of transverse and longitudinal resistivity as a function of magnetic field and the data is utilized to estimate contribution of interface roughness to the mobility and the corresponding transport lifetime. The quantum scattering time obtained from the analysis of Shubnikov de Haas Oscillations in transverse magnetoresistance along with the transport lifetime time were used to estimate interface roughness amplitude and lateral correlation length. The results indicate that the insertion of AlN over layer deposited prior to the growth of GaN base layer on Fe doped GaN templates for forming HEMT structures reduced the parallel conduction but resulted in an increase in interface roughness

Bird surveys at McKinley Bay and Hutchinson Bay, Northwest Territories, in 1990

Energy Technology Data Exchange (ETDEWEB)

Cornish, B J; Dickson, D L; Dickson, H L

1991-03-01

Monitoring surveys of bird abundance and distribution were conducted in 1990 at McKinley Bay in the Northwest Territories, the site of a winter harbour for drillships and the proposed location for a major year-round support base for oil and gas exploration. Primary objectives of the survey were to determine whether diving duck numbers had changed since the initial phase of the study from 1981-1985, and to provide additional baseline data on natural annual fluctuations in diving duck numbers. Three aerial surveys at each bay were carried out using techniques identical to those in previous years. On 5 August 1990, when survey conditions were considered best of the three surveys, more than twice as many diving ducks were found in McKinley Bay and Hutchinson Bay than on average during the five years of 1981-1985. Old squaw and scooters comprised ca 90% of the diving ducks observed, and both species showed significant increases in numbers. The increase in abundance of diving ducks was likely unrelated to industrial activity in the area since a similar increase occurred in the control area, Hutchinson Bay. Many factors, including both environmental factors such as those affecting nesting success and timing of the moult, and factors related to the survey methods, could be involved in causing the large fluctuations observed. 9 refs., 8 figs., 10 tabs.

Bird surveys at McKinley Bay and Hutchinson Bay, Northwest Territories, in 1990

International Nuclear Information System (INIS)

Cornish, B.J.; Dickson, D.L.; Dickson, H.L.

1991-01-01

Monitoring surveys of bird abundance and distribution were conducted in 1990 at McKinley Bay in the Northwest Territories, the site of a winter harbour for drillships and the proposed location for a major year-round support base for oil and gas exploration. Primary objectives of the survey were to determine whether diving duck numbers had changed since the initial phase of the study from 1981-1985, and to provide additional baseline data on natural annual fluctuations in diving duck numbers. Three aerial surveys at each bay were carried out using techniques identical to those in previous years. On 5 August 1990, when survey conditions were considered best of the three surveys, more than twice as many diving ducks were found in McKinley Bay and Hutchinson Bay than on average during the five years of 1981-1985. Old squaw and scooters comprised ca 90% of the diving ducks observed, and both species showed significant increases in numbers. The increase in abundance of diving ducks was likely unrelated to industrial activity in the area since a similar increase occurred in the control area, Hutchinson Bay. Many factors, including both environmental factors such as those affecting nesting success and timing of the moult, and factors related to the survey methods, could be involved in causing the large fluctuations observed. 9 refs., 8 figs., 10 tabs

Real-time x-ray response of biocompatible solution gate AlGaN/GaN high electron mobility transistor devices

International Nuclear Information System (INIS)

Hofstetter, Markus; Funk, Maren; Paretzke, Herwig G.; Thalhammer, Stefan; Howgate, John; Sharp, Ian D.; Stutzmann, Martin

2010-01-01

We present the real-time x-ray irradiation response of charge and pH sensitive solution gate AlGaN/GaN high electron mobility transistors. The devices show stable and reproducible behavior under and following x-ray radiation, including a linear integrated response with dose into the μGy range. Titration measurements of devices in solution reveal that the linear pH response and sensitivity are not only retained under x-ray irradiation, but an irradiation response could also be measured. Since the devices are biocompatible, and can be simultaneously operated in aggressive fluids and under hard radiation, they are well-suited for both medical radiation dosimetry and biosensing applications.

WIRELESS ADVERTISING: A STUDY OF MOBILE PHONE USERS

Directory of Open Access Journals (Sweden)

Gurau Calin

2011-07-01

Full Text Available Topic: Using a qualitative methodology, this study attempts to provide a general framework of the functions of mobile communication, and to identify the specific preferences of mobile phone users regarding the commercial messages received on their personal devices. Research objectives: (1 To identify the specific characteristics of mobile communication as perceived by mobile users; (2 to define and analyze the functions of wireless communication as perceived by mobile phone users; and (3 to investigate users preference regarding the content of commercial wireless communication. Previous research: Bauer et al. (2002 identified time, location, information and personalization as relevant acceptance factors for mobile advertising. Barwise and Strong (2002 developed a conceptual model, arguing that social norms, user's motives, mode, time, location and personal characteristics will affect the processing of mobile information by consumers. Tsang et al. (2004 evidenced the influence of entertainment, informativeness and irritation, while Bauer et al. (2005 argued that consumer attitudes are influenced by perceived information, entertainment, and social utility. In a similar study, Xu and Gutierrez (2006 tested the effect of entertainment, irritation, informativeness, credibility and personalization on the attitudes of Chinese consumers. Research methodology: First, a series of academic and practical articles and reports have been accessed in order to assess the existing knowledge on this topic. Second, five focus groups have been organized with six mobile phone users, aged between 20 and 40 years old. Each focus group comprised an equal number of male and female participants. The focus groups lasted between 45 and 60 minutes and addressed three main issues: the specific characteristics of the mobile phones as a commercial communication media, the functions of mobile phone communication, and the specific preferences of mobile phones users regarding the

Network Controlled Mobility Management with Policy Enforcement towards IMT-A

DEFF Research Database (Denmark)

Klockar, Annika; Mihovska, Albena D.; Luo, Jijun

2008-01-01

This paper introduces a framework of mobility management and call-handling based on policy en-hancement towards the IMT-A system. The function al-location and several selected mechanisms for the frame-work are described with analysis.......This paper introduces a framework of mobility management and call-handling based on policy en-hancement towards the IMT-A system. The function al-location and several selected mechanisms for the frame-work are described with analysis....

78 FR 27126 - East Bay, St. Andrews Bay and the Gulf of Mexico at Tyndall Air Force Base, Florida; Restricted...

Science.gov (United States)

2013-05-09

... DEPARTMENT OF DEFENSE Department of the Army, Corps of Engineers 33 CFR Part 334 East Bay, St. Andrews Bay and the Gulf of Mexico at Tyndall Air Force Base, Florida; Restricted Areas AGENCY: U.S. Army... read as follows: Sec. 334.665 East Bay, St. Andrews Bay and the Gulf of Mexico, Restricted Areas...

Spill management strategy for the Chesapeake Bay

International Nuclear Information System (INIS)

Butler, H.L.; Chapman, R.S.; Johnson, B.H.

1990-01-01

The Chesapeake Bay Program is a unique cooperative effort between state and Federal agencies to restore the health and productivity of America's largest estuary. To assist in addressing specific management issues, a comprehensive three-dimensional, time-varying hydrodynamic and water quality model has ben developed. The Bay modeling strategy will serve as an excellent framework for including submodules to predict the movement, dispersion, and weathering of accidental spills, such as for petroleum products or other chemicals. This paper presents sample results from the Bay application to illustrate the success of the model system in simulating Bay processes. Also, a review of model requirements for successful spill modeling in Chesapeake Bay is presented. Recommendations are given for implementing appropriate spill modules with the Bay model framework and establishing a strategy for model use in addressing management issues

A high-mobility two-dimensional electron gas at the spinel/perovskite interface of γ-Al₂O₃/SrTiO₃

DEFF Research Database (Denmark)

Chen, Yunzhong; Bovet, N.; Trier, Felix

2013-01-01

The discovery of two-dimensional electron gases at the heterointerface between two insulating perovskite-type oxides, such as LaAlO3 and SrTiO3, provides opportunities for a new generation of all-oxide electronic devices. Key challenges remain for achieving interfacial electron mobilities much...

Seismic stratigraphic architecture of the Disko Bay trough-mouth fan system, West Greenland

Science.gov (United States)

Hofmann, Julia C.; Knutz, Paul C.

2015-04-01

Spatial and temporal changes of the Greenland Ice Sheet on the continental shelf bordering Baffin Bay remain poorly constrained. Then as now, fast-flowing ice streams and outlet glaciers have played a key role for the mass balance and stability of polar ice sheets. Despite their significance for Greenland Ice Sheet dynamics and evolution, our understanding of their long-term behaviour is limited. The central West Greenland margin is characterized by a broad continental shelf where a series of troughs extend from fjords to the shelf margin, acting as focal points for trough-mouth fan (TMF) accummulations. The sea-ward bulging morphology and abrupt shelf-break of these major depositional systems is generated by prograding depocentres that formed during glacial maxima when ice streams reached the shelf edge, delivering large amounts of subglacial sediment onto the continental slope (Ó Cofaigh et al., 2013). The aim of this study is to unravel the seismic stratigraphic architecture and depositional processes of the Disko Bay TMF, aerially the largest single sedimentary system in West Greenland, using 2D and 3D seismic reflection data, seabed bathymetry and stratigraphic information from exploration well Hellefisk-1. The south-west Disko Bay is intersected by a deep, narrow trough, Egedesminde Dyb, which extends towards the southwest and links to the shallower and broader cross-shelf Disko Trough (maximum water depths of > 1000 m and a trough length of c. 370 km). Another trough-like depression (trough length of c. 120 km) in the northern part of the TMF, indicating a previous position of the ice stream, can be distinguished on the seabed topographic map and the seismic images. The Disko Bay TMF itself extends from the shelf edge down to the abyssal plain (abyssal floor depths of 2000 m) of the southern Baffin Bay. Based on seismic stratigraphic configurations relating to reflection terminations, erosive patterns and seismic facies (Mitchum et al., 1977), the TMF

Hydrography and bottom boundary layer dynamics: Influence on inner shelf sediment mobility, Long Bay, North Carolina

Science.gov (United States)

Davis, L.A.; Leonard, L.A.; Snedden, G.A.

2008-01-01

This study examined the hydrography and bottom boundary-layer dynamics of two typical storm events affecting coastal North Carolina (NC); a hurricane and the passages of two small consecutive extratropical storms during November 2005. Two upward-looking 1200-kHz Acoustic Doppler Current Profilers (ADCP) were deployed on the inner shelf in northern Long Bay, NC at water depths of less than 15 m. Both instruments profiled the overlying water column in 0.35 in bins beginning at a height of 1.35 in above the bottom (mab). Simultaneous measurements of wind speed and direction, wave and current parameters, and acoustic backscatter were coupled with output from a bottom boundary layer (bbl) model to describe the hydrography and boundary layer conditions during each event. The bbl model also was used to quantify sediment transport in the boundary layer during each storm. Both study sites exhibited similar temporal variations in wave and current magnitude, however, wave heights during the November event were higher than waves associated with the hurricane. Near-bottom mean and subtidal currents, however, were of greater magnitude during the hurricane. Peak depth-integrated suspended sediment transport during the November event exceeded transport associated with the hurricane by 25-70%. Substantial spatial variations in sediment transport existed throughout both events. During both events, along-shelf sediment transport exceeded across-shelf transport and was related to the magnitude and direction of subtidal currents. Given the variations in sediment type across the bay, complex shoreline configuration, and local bathymetry, the sediment transport rates reported here are very site specific. However, the general hydrography associated with the two storms is representative of conditions across northern Long Bay. Since the beaches in the study area undergo frequent renourishment to counter the effects of beach erosion, the results of this study also are relevant to coastal

Chesapeake Bay plume dynamics from LANDSAT

Science.gov (United States)

Munday, J. C., Jr.; Fedosh, M. S.

1981-01-01

LANDSAT images with enhancement and density slicing show that the Chesapeake Bay plume usually frequents the Virginia coast south of the Bay mouth. Southwestern (compared to northern) winds spread the plume easterly over a large area. Ebb tide images (compared to flood tide images) show a more dispersed plume. Flooding waters produce high turbidity levels over the shallow northern portion of the Bay mouth.

High quality InAsSb grown on InP substrates using AlSb/AlAsSb buffer layers

International Nuclear Information System (INIS)

Wu, B.-R.; Liao, C.; Cheng, K. Y.

2008-01-01

High quality InAsSb grown on semi-insulating InP substrates by molecular beam epitaxy was achieved using AlSb/AlAsSb structure as the buffer layer. A 1000 A InAsSb layer grown on top of 1 μm AlSb/AlAsSb buffer layer showed a room temperature electron mobility of ∼12 000 cm 2 /V s. High structural quality and low misfit defect density were also demonstrated in the InAsSb layer. This novel AlSb/AlAsSb buffer layer structure with the AlAsSb layer lattice matched to InP substrates could enhance the performance of optoelectronic devices utilizing 6.1 A family of compound semiconductor alloys

Security analysis and enhanced user authentication in proxy mobile IPv6 networks.

Directory of Open Access Journals (Sweden)

Dongwoo Kang

Full Text Available The Proxy Mobile IPv6 (PMIPv6 is a network-based mobility management protocol that allows a Mobile Node(MN connected to the PMIPv6 domain to move from one network to another without changing the assigned IPv6 address. The user authentication procedure in this protocol is not standardized, but many smartcard based authentication schemes have been proposed. Recently, Alizadeh et al. proposed an authentication scheme for the PMIPv6. However, it could allow an attacker to derive an encryption key that must be securely shared between MN and the Mobile Access Gate(MAG. As a result, outsider adversary can derive MN's identity, password and session key. In this paper, we analyze Alizadeh et al.'s scheme regarding security and propose an enhanced authentication scheme that uses a dynamic identity to satisfy anonymity. Furthermore, we use BAN logic to show that our scheme can successfully generate and communicate with the inter-entity session key.

Security analysis and enhanced user authentication in proxy mobile IPv6 networks.

Science.gov (United States)

Kang, Dongwoo; Jung, Jaewook; Lee, Donghoon; Kim, Hyoungshick; Won, Dongho

2017-01-01

The Proxy Mobile IPv6 (PMIPv6) is a network-based mobility management protocol that allows a Mobile Node(MN) connected to the PMIPv6 domain to move from one network to another without changing the assigned IPv6 address. The user authentication procedure in this protocol is not standardized, but many smartcard based authentication schemes have been proposed. Recently, Alizadeh et al. proposed an authentication scheme for the PMIPv6. However, it could allow an attacker to derive an encryption key that must be securely shared between MN and the Mobile Access Gate(MAG). As a result, outsider adversary can derive MN's identity, password and session key. In this paper, we analyze Alizadeh et al.'s scheme regarding security and propose an enhanced authentication scheme that uses a dynamic identity to satisfy anonymity. Furthermore, we use BAN logic to show that our scheme can successfully generate and communicate with the inter-entity session key.

Process-based, morphodynamic hindcast of decadal deposition (1856-1887) and erosion (1951-1983) patterns in San Pablo Bay, California

Science.gov (United States)

Wegen, M. V.; Jaffe, B. E.; Roelvink, J.

2009-12-01

The objective of the current research is to hindcast decadal morphodynamic development in San Pablo Bay, California, USA using a process-based, numerical model, Delft3D. Experience gained in the current research will be ultimately used to model future morphodynamic changes in San Pablo Bay under different scenarios of climate change. Delft3D is run in 3D mode including wind waves, salt and fresh water interaction, sand and mud fractions and applies a sophisticated morphodynamic update scheme [Roelvink (2006)]. Model outcomes are evaluated against measured bathymetric developments [Cappiella (1999), Jaffe et al (2007)] and include an extensive sensitivity analysis on model parameter settings. In the 19th century more than 250 million cubic meters of sediment was deposited in San Pablo Bay because of the increased sediment load associated with hydraulic gold mining activities. When mining stopped and dam construction regulated river flows and trapped sediment upstream early 20th century, San Pablo Bay showed an eroding trend. Focus of the hindcast is on the 1856 to 1887 depositional period and on the 1951 to 1983 erosional period. The results of the model heavily depend on parameter settings related to sediment transport, bed composition and boundary conditions schematization. A major handicap is that the (historic) values of these parameters are not known in detail. Recommendations by Ganju et al. (2008) are used to overcome this problem. The results show, however, that applying best-guess model parameter settings can predict decadal morphodynamic developments reasonably well in San Pablo Bay. From all varied settings sediment concentration, river discharge and waves have the most significant effect on deposition volumes, whereas waves have the most impact on sediment distribution within San Pablo Bay. For the depositional period Brier Skill Scores have values around 0.25 with a maximum of 0.43 (qualified as ‘good’) although higher values (up to 0.65) were

Short Term Sediment Exchange Between Marshes and Bays Using Beryllium-7 as a Tracer, Fourleague Bay, Louisiana.

Science.gov (United States)

Restreppo, G. A.; Bentley, S. J.; Xu, K.; Wang, J.

2016-12-01

Modern delta models focus on the availability and exchange of coarse sediment as one of the major factors of deltaic growth or decay. Fine-grained sediment exchange within a river's delta is relatively poorly understood, as is the impact that this exchange has on land building and land loss. To better understand the dynamics of fine grain sediment exchange between river mouth, adjacent bays, and marshland, sediment cores from Fourleague Bay, LA, were collected and analyzed for 7Be, a naturally occurring radioisotope that serves as a marker for recently deposited sediment. Time-series push cores were collected every two months at ten sites, five located across a longitudinal transect in the middle bay and five located along adjacent marshes, from May 2015 to May 2016. All sites fall within 11 to 28 km of the Atchafalaya Delta, along a gradient extending towards the open ocean. Cores were extruded in 2 cm intervals, dried, ground, and analyzed via gamma spectrometry for the presence of 7Be. Inventories of 7Be were then calculated and used to determine bimonthly sedimentation rates over the course twelve months. Sediment deposition on the bay floor and marsh surface were then compared to Atchafalaya River discharge, wind speed and direction, and wave action. Preliminary results indicate patterns of initial fluvial sediment transfer from river to bay floor, then bay floor to marsh surface, with decreasing fluvial influence towards the open ocean. Sediment transport from bay to marsh appears to be coupled with meteorological forcing that induces bay-floor sediment resuspension and the flooding of marsh surfaces. This indirect mechanism of fluvial sediment supply to wetland surfaces may extend the region of influence for sediment delivery from man-made river-sediment diversions.

Role of upper ocean parameters in the genesis, intensification and tracks of cyclones over the Bay of Bengal

Digital Repository Service at National Institute of Oceanography (India)

Maneesha, K.; Sadhuram, Y.; Prasad, K.V.S.R.

of high heat potential (>90 kj/cm2) in the western Gulf of Mexico (Goni et al. 2003, 2009; Shay et al. 2000). Further, Hurricanes Igor (tropical Atlantic) and Celia (Eastern North Pacific), Typhoon Megi (Western North Pacific) and Cyclone Phet (Arabian Sea... 2009/10 in the Gulf of Mexico and the southwestern Pacific Ocean, while there was an increase in the western Pacific Ocean, Arabian Sea and Bay of Bengal. All the above studies emphasize the importance of the UOHC in the genesis and intensification...

Investigation of high sensitivity radio-frequency readout circuit based on AlGaN/GaN high electron mobility transistor

International Nuclear Information System (INIS)

Zhang Xiao-Yu; Sun Jian-Dong; Li Xin-Xing; Zhou Yu; Lü Li; Qin Hua; Tan Ren-Bing

2015-01-01

An AlGaN/GaN high electron mobility transistor (HEMT) device is prepared by using a semiconductor nanofabrication process. A reflective radio-frequency (RF) readout circuit is designed and the HEMT device is assembled in an RF circuit through a coplanar waveguide transmission line. A gate capacitor of the HEMT and a surface-mounted inductor on the transmission line are formed to generate LC resonance. By tuning the gate voltage V g , the variations of gate capacitance and conductance of the HEMT are reflected sensitively from the resonance frequency and the magnitude of the RF reflection signal. The aim of the designed RF readout setup is to develop a highly sensitive HEMT-based detector. (paper)

Room-Temperature Quantum Ballistic Transport in Monolithic Ultrascaled Al-Ge-Al Nanowire Heterostructures.

Science.gov (United States)

Sistani, Masiar; Staudinger, Philipp; Greil, Johannes; Holzbauer, Martin; Detz, Hermann; Bertagnolli, Emmerich; Lugstein, Alois

2017-08-09

Conductance quantization at room temperature is a key requirement for the utilizing of ballistic transport for, e.g., high-performance, low-power dissipating transistors operating at the upper limit of "on"-state conductance or multivalued logic gates. So far, studying conductance quantization has been restricted to high-mobility materials at ultralow temperatures and requires sophisticated nanostructure formation techniques and precise lithography for contact formation. Utilizing a thermally induced exchange reaction between single-crystalline Ge nanowires and Al pads, we achieved monolithic Al-Ge-Al NW heterostructures with ultrasmall Ge segments contacted by self-aligned quasi one-dimensional crystalline Al leads. By integration in electrostatically modulated back-gated field-effect transistors, we demonstrate the first experimental observation of room temperature quantum ballistic transport in Ge, favorable for integration in complementary metal-oxide-semiconductor platform technology.

The association between Generalized Joint Hypermobility and shoulder mobility in young, competitive swimmers

DEFF Research Database (Denmark)

Knudsen, Hans Kromann; Junge, Tina

2016-01-01

The association between Generalized Joint Hypermobility and shoulder mobility in young, competitive swimmers. Junge, T.1, 2, 3, Henriksen, P. 2, 4, Knudsen, H.K.1, Juul-Kristensen, B.3, 4 1Institute of Regional Health Services, University of Southern Denmark, Odense, Denmark 2Department...... (Zemek et al., 1995). Increased shoulder mobility as well as Generalised Joint Hypermobility (GJH), are both suggested being predisposing risk factors for shoulder injuries (Pink et al., 2000, Zemek et al., 1995). An association between GJH and shoulder mobility among young, competitive swimmers has......) participated. GJH was evaluated by the Beighton test (BT) a 0-9 scoring system. GJH was classified at cut points ≥5/9, ≥6/9 and ≥7/9. Shoulder mobility was measured as HSA using an inclinometer in a standardized protocol format. A multiple regression analysis was used to reveal associations between GJH...

BOOK REVIEW OF "CHESAPEAKE BAY BLUES: SCIENCE, POLITICS, AND THE STRUGGLE TO SAVE THE BAY"

Science.gov (United States)

This is a book review of "Chesapeake Bay Blues: Science, Politics, and the Struggle to Save the Bay". This book is very well written and provides an easily understandable description of the political challenges faced by those proposing new or more stringent environmental regulat...

Latest results from Daya Bay

Science.gov (United States)

Vorobel, Vit; Daya Bay Collaboration

2017-07-01

The Daya Bay Reactor Neutrino Experiment was designed to measure θ 13, the smallest mixing angle in the three-neutrino mixing framework, with unprecedented precision. The experiment consists of eight functionally identical detectors placed underground at different baselines from three pairs of nuclear reactors in South China. Since Dec. 2011, the experiment has been running stably for more than 4 years, and has collected the largest reactor anti-neutrino sample to date. Daya Bay is able to greatly improve the precision on θ 13 and to make an independent measurement of the effective mass splitting in the electron antineutrino disappearance channel. Daya Bay can also perform a number of other precise measurements, such as a high-statistics determination of the absolute reactor antineutrino flux and spectrum, as well as a search for sterile neutrino mixing, among others. The most recent results from Daya Bay are discussed in this paper, as well as the current status and future prospects of the experiment.

Die Welt als Spielfeld: Mobile Serious Games mit Augmented Reality

NARCIS (Netherlands)

Klemke, Roland; Schneider, Jan; Happe, Sven; Bockelmann, Timo; Börner, Dirk; Specht, Marcus

2014-01-01

Technological innovations enable us to connect computer games with the environment they are played in: augmented reality games take the world as their playground. In this talk, the use of such technologies for mobile serious games is explored.

The attenuation of concentrations model: a new method for assessing mercury mobility in sediments

Directory of Open Access Journals (Sweden)

Julio C. Wasserman

2004-02-01

Full Text Available In this work we propose a new approach for the determination of the mobility of mercury in sediments based on spatial distribution of concentrations. We chose the Tainheiros Cove, located in the Todos os Santos Bay, Brazil, as the study area, for it has a history of mercury contamination due to a chloro-alkali plant that was active during 12 years. Twenty-six surface sediment samples were collected from the area and mercury concentrations were measured by cold vapour atomic absorption spectrophotometry. A contour map was constructed from the results, indicating that mercury accumulated in a "hot spot" where concentrations reach more than 1 µg g-1. The model is able to estimate mobility of mercury in the sediments based on the distances between iso-concentration contours that determines an attenuation of concentrations factor. Values of attenuation ranged between 0.0729 (East of the hot spot, indicating higher mobility to 0.7727 (North of the hot spot, indicating lower mobility.

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

Towards a sustainable future in Hudson Bay

International Nuclear Information System (INIS)

Okrainetz, G.

1991-01-01

To date, ca $40-50 billion has been invested in or committed to hydroelectric development on the rivers feeding Hudson Bay. In addition, billions more have been invested in land uses such as forestry and mining within the Hudson Bay drainage basin. However, there has never been a study of the possible impacts on Hudson Bay resulting from this activity. Neither has there been any federal environmental assessment on any of the economic developments that affect Hudson Bay. To fill this gap in knowledge, the Hudson Bay Program was established. The program will not conduct scientific field research but will rather scan the published literature and consult with leading experts in an effort to identify biophysical factors that are likely to be significantly affected by the cumulative influence of hydroelectric and other developments within and outside the region. An annotated bibliography on Hudson Bay has been completed and used to prepare a science overview paper, which will be circulated for comment, revised, and used as the basis for a workshop on cumulative effects in Hudson Bay. Papers will then be commissioned for a second workshop to be held in fall 1993. A unique feature of the program is its integration of traditional ecological knowledge among the Inuit and Cree communities around Hudson Bay with the scientific approach to cumulative impact assessment. One goal of the program is to help these communities bring forward their knowledge in such a way that it can be integrated into the cumulative effects assessment

POTENTIAL HAZARDS OF SEDIMENT IN KENDARI BAY, SOUTHEAST SULAWESI

Directory of Open Access Journals (Sweden)

Nur Adi Kristanto

2017-07-01

Full Text Available Kendari bay is located in front of Kendari city. There are two harbors in the inner part of bay which very important to support economic activities such as shipping and passenger transportation. The result of coastal characteristic mapping and physical oceanography survey show various coastal morphology, vegetation, weathering processes, sedimentation, currents, and water depth and sea floor morphology. Kendari bay is an enclosed bay; the area is wide in the inner part and narrow in mouth of bay (outlet, the morphology look like a bottle’s neck. Numerous mouth rivers are concentrate around the bay. The rivers load material from land since erosion on land is intensive enough. There is indication that sediment supplies from land trough river mouth not equivalent with outlet capacity. Sediment load is trapped in the inner bay caused the outlet morphology. So high sediment rate play an important role in the process of shallow of water depth in Kendari bay. This condition make the Kendari bay is a prone area of sediment hazard due to height rate of sedimentary process. Therefore, to anticipate the hazards, precaution should be taken related to the Kendari bay as the center of activities in southeast of Sulawesi. The further survey is needed such as marine geotechnique and on land environmental to collect data, which can be used as database for development planning. Key words: Potential hazard, sediment, Kendari Bay Teluk

MODELING THE 1958 LITUYA BAY MEGA-TSUNAMI, II

Directory of Open Access Journals (Sweden)

Charles L. Mader

2002-01-01

Full Text Available Lituya Bay, Alaska is a T-Shaped bay, 7 miles long and up to 2 miles wide. The two arms at the head of the bay, Gilbert and Crillon Inlets, are part of a trench along the Fairweather Fault. On July 8, 1958, an 7.5 Magnitude earthquake occurred along the Fairweather fault with an epicenter near Lituya Bay.A mega-tsunami wave was generated that washed out trees to a maximum altitude of 520 meters at the entrance of Gilbert Inlet. Much of the rest of the shoreline of the Bay was denuded by the tsunami from 30 to 200 meters altitude.In the previous study it was determined that if the 520 meter high run-up was 50 to 100 meters thick, the observed inundation in the rest of Lituya Bay could be numerically reproduced. It was also concluded that further studies would require full Navier-Stokes modeling similar to those required for asteroid generated tsunami waves.During the Summer of 2000, Hermann Fritz conducted experiments that reproduced the Lituya Bay 1958 event. The laboratory experiments indicated that the 1958 Lituya Bay 524 meter run-up on the spur ridge of Gilbert Inlet could be caused by a landslide impact.The Lituya Bay impact landslide generated tsunami was modeled with the full Navier- Stokes AMR Eulerian compressible hydrodynamic code called SAGE with includes the effect of gravity.

Impact of the Gate Width of Al0.27Ga0.73N/AlN/Al0.04Ga0.96N/GaN HEMT on Its Characteristics

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Liwei Jin

2013-01-01

Full Text Available This paper presents impact of layout sizes of Al0.27Ga0.73N/AlN/Al0.04Ga0.96N/GaN HEMT heterostructure high-mobility transistors (HEMTs on SiC substrate on its characteristics that include the threshold voltage, the maximum transconductance, characteristic frequency, and the maximum oscillation frequency. The changing parameters include the gate finger number, the gate width per finger. The measurement results based on common-source devices demonstrate that the above parameters have different effects on the threshold voltage, maximum transconductance, and frequency characteristics.

Characterization of Al2O3NP–Al2024 and AgCNP–Al2024 composites prepared by mechanical processing in a high energy ball mill

International Nuclear Information System (INIS)

Carreño-Gallardo, C.; Estrada-Guel, I.; Romero-Romo, M.; Cruz-García, R.; López-Meléndez, C.; Martínez-Sánchez, R.

2012-01-01

Graphical abstract: Mechanical alloying was used to produce two kinds of metal matrix composites based on 2024 aluminum alloy, the nanocomposites were reinforced with different percentages of Al 2 O 3 and Ag C nanoparticles. The content of nanoparticles has a role important on the mechanical properties of the nanocomposite. 10 h of milling time are enough to former the Al 2024 nanocomposites. The results obtained by differential scanning calorimeter show the temperatures of intermetallic precipitation, which were identified by X-ray diffraction. The results revealed that mechanical alloying is an excellent route to incorporate and distribute NP into Al 2024 . Highlights: ► Aluminum-based nanocomposites were synthesized bay milling process. ► An homogeneous nanoparticles dispersion was reached and mechanical properties were enhanced. ► Phase transformation during heating was characterized by XRD. - Abstract: Mechanical alloying was used to produce two kinds of metal matrix composites based on 2024 aluminum alloy. The nanocomposites were reinforced with different percentages of Al 2 O 3 and Ag C nanoparticles. The content of nanoparticles has an important role on the mechanical properties of the nanocomposites. A milling time of 10 h is enough to form the Al 2024 nanocomposites. The thermograms obtained by differential scanning calorimeter show the temperatures of phase precipitation, which were identified by X-ray diffraction. The results revealed that mechanical alloying is an excellent route for the incorporation and distribution of nanoparticles into Al 2024 .

Radionuclides in sediments from Port Phillip Bay, Australia

International Nuclear Information System (INIS)

Smith, J.D.; Tinker, R.A.; Towler, P.H.

1998-01-01

Full text: Sediment cores were collected from two sites in Port Phillip Bay, Australia, in 1994 and 1995. The concentration of 210 Pb and parameters including water content were measured. The sites chosen were near the centre of the bay where fine sediment accumulates, and towards the northern end of the bay closer to the mouth of the Yarra River. The mid-bay sediment had a high water content (about 1.8 g water per g dry sediment) and a supported 210 Pb activity of about 22 mBq per g of dry sediment. The sediments from further north in the bay were more consolidated, with a lower water content (about 0.6 g water per g dry sediment), and had a supported 210 Pb activity of about 6 mBq per g of dry sediment. Unsupported 210 Pb occurred to depths of about 10 cm in the mid-bay sediment and about 20 cm in sediment from further north in the bay. Models incorporating the water and 210 Pb contents of the sediments were used to calculate possible rates of sediment accumulation and mixing. The distribution of other radionuclides was used as an aid in understanding the sediment behaviour in Port Phillip Bay

Motivation and mobile devices: exploring the role of appropriation and coping strategies

Directory of Open Access Journals (Sweden)

Ann Jones

2007-12-01

Full Text Available There has been interest recently in how mobile devices may be motivating forces in the right contexts: for example, one of the themes for the IADIS International Conference on Mobile Learning in 2007 was ‘Affective Factors in Learning with Mobile Devices' (http://www.mlearningconf.org. The authors have previously proposed six aspects of learning with mobile devices in informal contexts that might be motivating: control over learners' goals, ownership, fun, communication, learning-in-context and continuity between contexts. How do these motivational features relate to theoretical accounts of what motivates people to use mobile devices and learn in technology- rich contexts? In this exploratory paper we consider two different candidates for such theoretical approaches. One is technology appropriation–the process by which technology or particular technological artefacts are adopted and shaped in use. Two different approaches to technology appropriation are discussed in order to explore the relationship between the different aspects of appropriation and motivation; that of Carroll et al. and that of Waycott. Both appropriation frameworks have been developed in the context of using mobile devices, but neither has a specific focus on learning. By contrast, the second theoretical approach is Järvelä et al.'s model of coping strategies, which is specifically concerned with learning with technologies, although not with mobile technologies in particular. The paper draws on case-study data in order to illustrate and discuss the extent to which these two approaches are helpful in informing our understanding of the motivating features of using mobile devices for informal learning.

Molecular beam epitaxy growth of In0.52Al0.48As/In0.53Ga0.47As metamorphic high electron mobility transistor employing growth interruption and in situ rapid thermal annealing

International Nuclear Information System (INIS)

Ihn, Soo-Ghang; Jo, Seong June; Song, Jong-In

2006-01-01

We investigated the effects of high temperature (∼700 deg. C) in situ rapid thermal annealing (RTA) carried out during growth interruption between spacer and δ-doping layers of an In 0.52 Al 0.48 As/In 0.53 Ga 0.47 As metamorphic high electron mobility transistor (MHEMT) grown on a compositionally graded InGaAlAs buffer layer. The in situ RTA improved optical and structural properties of the MHEMT without degradation of transport property, while postgrowth RTA improved the structural property of the MHEMT but significantly degraded mobility due to the defect-assisted Si diffusion. The results indicate the potential of the in situ RTA for use in the growth of high-quality metamorphic epitaxial layers for optoelectronic applications requiring improved optical and electrical properties

Gate length scaling effect on high-electron mobility transistors devices using AlGaN/GaN and AlInN/AlN/GaN heterostructures.

Science.gov (United States)

Liao, S Y; Lu, C C; Chang, T; Huang, C F; Cheng, C H; Chang, L B

2014-08-01

Compared to AlGaN/GaN HEMT with 0.15 μm T-gate length, the AlInN/AlN/GaN one exhibits much higher current density and transconductance of 1558 mA/mm at Vd = 2 V and 330 mS/mm, respectively. The high extrinsic ft and fmax of 82 GHz and 70 GHz are extracted from AlInN/AlN/GaN HEMT. Besides, we find that the transconductance roll-off is significant in AlGaN/GaN, but largely improved in AlInN/AlN/GaN HEMT, suggesting that the high carrier density and lattice-matched epitaxial heterostructure is important to reach both large RF output power and high operation frequency, especially for an aggressively gate length scaling.

Effect of OFF-state stress induced electric field on trapping in AlGaN/GaN high electron mobility transistors on Si (111)

Science.gov (United States)

Anand, M. J.; Ng, G. I.; Arulkumaran, S.; Manoj Kumar, C. M.; Ranjan, K.; Vicknesh, S.; Foo, S. C.; Syamal, B.; Zhou, X.

2015-02-01

The influence of electric field (EF) on the dynamic ON-resistance (dyn-RDS[ON]) and threshold-voltage shift (ΔVth) of AlGaN/GaN high electron mobility transistors on Si has been investigated using pulsed current-voltage (IDS-VDS) and drain current (ID) transients. Different EF was realized with devices of different gate-drain spacing (Lgd) under the same OFF-state stress. Under high-EF (Lgd = 2 μm), the devices exhibited higher dyn-RDS[ON] degradation but a small ΔVth (˜120 mV). However, at low-EF (Lgd = 5 μm), smaller dyn-RDS[ON] degradation but a larger ΔVth (˜380 mV) was observed. Our analysis shows that under OFF-state stress, the gate electrons are injected and trapped in the AlGaN barrier by tunnelling-assisted Poole-Frenkel conduction mechanism. Under high-EF, trapping spreads towards the gate-drain access region of the AlGaN barrier causing dyn-RDS[ON] degradation, whereas under low-EF, trapping is mostly confined under the gate causing ΔVth. A trap with activation energy 0.33 eV was identified in the AlGaN barrier by ID-transient measurements. The influence of EF on trapping was also verified by Silvaco TCAD simulations.

Nutrient load estimates for Manila Bay, Philippines using population data

Science.gov (United States)

Sotto, Lara Patricia A.; Beusen, Arthur H. W.; Villanoy, Cesar L.; Bouwman, Lex F.; Jacinto, Gil S.

2015-06-01

A major source of nutrient load to periodically hypoxic Manila Bay is the urban nutrient waste water flow from humans and industries to surface water. In Manila alone, the population density is as high as 19,137 people/km2. A model based on a global point source model by Morée et al. (2013) was used to estimate the contribution of the population to nitrogen and phosphorus emissions which was then used in a water transport model to estimate the nitrogen (N) and phosphorus (P) loads to Manila Bay. Seven scenarios for 2050 were tested, with varying degrees and amounts for extent of sewage treatment, and population growth rates were also included. In scenario 1, the sewage connection and treatment remains the same as 2010; in scenario 2, sewage connection is improved but the treatment is the same; in scenario 3, the sewage connection as well as treatment is improved (70% tertiary); and in scenario 4, a more realistic situation of 70% primary treatment achieved with 100% connection to pipes is tested. Scenarios 5, 6, and 7 have the same parameters as 1, 2, and 3 respectively, but with the population growth rate per province reduced to half of what was used in 1, 2, and 3. In all scenarios, a significant increase in N and P loads was observed (varying from 27% to 469% relative to 2010 values). This was found even in scenario 3 where 70% of the waste water undergoes tertiary treatment which removes 80% N and 90% P. However, the lowest increase in N and P load into the bay was achieved in scenarios 5 to 7 where population growth rate is reduced to half of 2010 values. The results suggest that aside from improving sewage treatment, the continued increase of the human population in Manila at current growth rates will be an important determinant of N and P load into Manila Bay.

Viscosity-dependent drain current noise of AlGaN/GaN high electron mobility transistor in polar liquids

International Nuclear Information System (INIS)

Fang, J. Y.; Hsu, C. P.; Kang, Y. W.; Fang, K. C.; Kao, W. L.; Yao, D. J.; Chen, C. C.; Li, S. S.; Yeh, J. A.; Wang, Y. L.; Lee, G. Y.; Chyi, J. I.; Hsu, C. H.; Huang, Y. F.; Ren, F.

2013-01-01

The drain current fluctuation of ungated AlGaN/GaN high electron mobility transistors (HEMTs) measured in different fluids at a drain-source voltage of 0.5 V was investigated. The HEMTs with metal on the gate region showed good current stability in deionized water, while a large fluctuation in drain current was observed for HEMTs without gate metal. The fluctuation in drain current for the HEMTs without gate metal was observed and calculated as standard deviation from a real-time measurement in air, deionized water, ethanol, dimethyl sulfoxide, ethylene glycol, 1,2-butanediol, and glycerol. At room temperature, the fluctuation in drain current for the HEMTs without gate metal was found to be relevant to the dipole moment and the viscosity of the liquids. A liquid with a larger viscosity showed a smaller fluctuation in drain current. The viscosity-dependent fluctuation of the drain current was ascribed to the Brownian motions of the liquid molecules, which induced a variation in the surface dipole of the gate region. This study uncovers the causes of the fluctuation in drain current of HEMTs in fluids. The results show that the AlGaN/GaN HEMTs may be used as sensors to measure the viscosity of liquids within a certain range of viscosity

A Bayes Theory-Based Modeling Algorithm to End-to-end Network Traffic

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Zhao Hong-hao

2016-01-01

Full Text Available Recently, network traffic has exponentially increasing due to all kind of applications, such as mobile Internet, smart cities, smart transportations, Internet of things, and so on. the end-to-end network traffic becomes more important for traffic engineering. Usually end-to-end traffic estimation is highly difficult. This paper proposes a Bayes theory-based method to model the end-to-end network traffic. Firstly, the end-to-end network traffic is described as a independent identically distributed normal process. Then the Bases theory is used to characterize the end-to-end network traffic. By calculating the parameters, the model is determined correctly. Simulation results show that our approach is feasible and effective.

Thermal Analysis of AlGaN/GaN High-Electron-Mobility Transistor and Its RF Power Efficiency Optimization with Source-Bridged Field-Plate Structure.

Science.gov (United States)

Kwak, Hyeon-Tak; Chang, Seung-Bo; Jung, Hyun-Gu; Kim, Hyun-Seok

2018-09-01

In this study, we consider the relationship between the temperature in a two-dimensional electron gas (2-DEG) channel layer and the RF characteristics of an AlGaN/GaN high-electron-mobility transistor by changing the geometrical structure of the field-plate. The final goal is to achieve a high power efficiency by decreasing the channel layer temperature. First, simulations were performed to compare and contrast the experimental data of a conventional T-gate head structure. Then, a source-bridged field-plate (SBFP) structure was used to obtain the lower junction temperature in the 2-DEG channel layer. The peak electric field intensity was reduced, and a decrease in channel temperature resulted in an increase in electron mobility. Furthermore, the gate-to-source capacitance was increased by the SBFP structure. However, under the large current flow condition, the SBFP structure had a lower maximum temperature than the basic T-gate head structure, which improved the device electron mobility. Eventually, an optimum position of the SBFP was used, which led to higher frequency responses and improved the breakdown voltages. Hence, the optimized SBFP structure can be a promising candidate for high-power RF devices.

Daya bay reactor neutrino experiment

International Nuclear Information System (INIS)

Cao Jun

2010-01-01

Daya Bay Reactor Neutrino Experiment is a large international collaboration experiment under construction. The experiment aims to precisely determine the neutrino mixing angle θ 13 by detecting the neutrinos produced by the Daya Bay Nuclear Power Plant. θ 13 is one of two unknown fundamental parameters in neutrino mixing. Its magnitude is a roadmap of the future neutrino physics, and very likely related to the puzzle of missing antimatter in our universe. The precise measurement has very important physics significance. The detectors of Daya Bay is under construction now. The full operation is expected in 2011. Three years' data taking will reach the designed the precision, to determine sin 2 2θ 13 to better than 0.01. Daya Bay neutrino detector is an underground large nuclear detector of low background, low energy, and high precision. In this paper, the layout of the experiment, the design and fabrication progress of the detectors, and some highlighted nuclear detecting techniques developed in the detector R and D are introduced. (author)

A Bayes-Maximum Entropy method for multi-sensor data fusion

Energy Technology Data Exchange (ETDEWEB)

Beckerman, M.

1991-01-01

In this paper we introduce a Bayes-Maximum Entropy formalism for multi-sensor data fusion, and present an application of this methodology to the fusion of ultrasound and visual sensor data as acquired by a mobile robot. In our approach the principle of maximum entropy is applied to the construction of priors and likelihoods from the data. Distances between ultrasound and visual points of interest in a dual representation are used to define Gibbs likelihood distributions. Both one- and two-dimensional likelihoods are presented, and cast into a form which makes explicit their dependence upon the mean. The Bayesian posterior distributions are used to test a null hypothesis, and Maximum Entropy Maps used for navigation are updated using the resulting information from the dual representation. 14 refs., 9 figs.

226Ra and 228Ra in the mixing zones of the Pee Dee River-Winyah Bay, Yangtze River and Delaware Bay Estuaries

International Nuclear Information System (INIS)

Elsinger, R.J.; Moore, W.S.

1984-01-01

226 Ra and 228 Ra have non-conservative excess concentrations in the mixing zones of the Pee Dee River-Winyah Bay estuary, the Yangtze River estuary, and the Delaware Bay estuary. Laboratory experiments, using Pee Dee River sediment, indicate desorption of 226 Ra to increase with increasing salinities up to 20 per mille. In Winyah Bay desorption from river-borne sediments could contribute almost all of the increases for both isotopes. Desorption adds only a portion of the excess 228 Ra measured in the Yangtze River and adjacent Shelf waters and Delaware Bay. In the Yangtze River the mixing zone extends over a considerable portion of the Continental Shelf where 228 Ra is added to the water column by diffusion from bottom sediments, while 226 Ra concentrations decrease from dilution. Diffusion of 228 Ra from bottom sediments in Delaware Bay primarily occurs in the upper part of the bay ( 228 Ra of 0.33 dpm cm -2 year was determined for Delaware Bay. (author)

Tunable electron heating induced giant magnetoresistance in the high mobility GaAs/AlGaAs 2D electron system.

Science.gov (United States)

Wang, Zhuo; Samaraweera, R L; Reichl, C; Wegscheider, W; Mani, R G

2016-12-07

Electron-heating induced by a tunable, supplementary dc-current (I dc ) helps to vary the observed magnetoresistance in the high mobility GaAs/AlGaAs 2D electron system. The magnetoresistance at B = 0.3 T is shown to progressively change from positive to negative with increasing I dc , yielding negative giant-magnetoresistance at the lowest temperature and highest I dc . A two-term Drude model successfully fits the data at all I dc and T. The results indicate that carrier heating modifies a conductivity correction σ 1 , which undergoes sign reversal from positive to negative with increasing I dc , and this is responsible for the observed crossover from positive- to negative- magnetoresistance, respectively, at the highest B.

The Neoglacial landscape and human history of Glacier Bay, Glacier Bay National Park and Preserve, southeast Alaska, USA

Science.gov (United States)

Connor, C.; Streveler, G.; Post, A.; Monteith, D.; Howell, W.

2009-01-01

The Neoglacial landscape of the Huna Tlingit homeland in Glacier Bay is recreated through new interpretations of the lower Bay's fjordal geomorphology, late Quaternary geology and its ethnographic landscape. Geological interpretation is enhanced by 38 radiocarbon dates compiled from published and unpublished sources, as well as 15 newly dated samples. Neoglacial changes in ice positions, outwash and lake extents are reconstructed for c. 5500?????"200 cal. yr ago, and portrayed as a set of three landscapes at 1600?????"1000, 500?????"300 and 300?????"200 cal. yr ago. This history reveals episodic ice advance towards the Bay mouth, transforming it from a fjordal seascape into a terrestrial environment dominated by glacier outwash sediments and ice-marginal lake features. This extensive outwash plain was building in lower Glacier Bay by at least 1600 cal. yr ago, and had filled the lower bay by 500 cal. yr ago. The geologic landscape evokes the human-described landscape found in the ethnographic literature. Neoglacial climate and landscape dynamism created difficult but endurable environmental conditions for the Huna Tlingit people living there. Choosing to cope with environmental hardship was perhaps preferable to the more severely deteriorating conditions outside of the Bay as well as conflicts with competing groups. The central portion of the outwash plain persisted until it was overridden by ice moving into Icy Strait between AD 1724?????"1794. This final ice advance was very abrupt after a prolonged still-stand, evicting the Huna Tlingit from their Glacier Bay homeland. ?? 2009 SAGE Publications.

Organic Matter Remineralization Predominates Phosphorus Cycling in the Mid-Bay Sediments in the Chesapeake Bay

Energy Technology Data Exchange (ETDEWEB)

Sunendra, Joshi R.; Kukkadapu, Ravi K.; Burdige, David J.; Bowden, Mark E.; Sparks, Donald L.; Jaisi, Deb P.

2015-05-19

The Chesapeake Bay, the largest and most productive estuary in the US, suffers from varying degrees of water quality issues fueled by both point and non–point source nutrient sources. Restoration of the bay is complicated by the multitude of nutrient sources, their variable inputs and hydrological conditions, and complex interacting factors including climate forcing. These complexities not only restrict formulation of effective restoration plans but also open up debates on accountability issues with nutrient loading. A detailed understanding of sediment phosphorus (P) dynamics enables one to identify the exchange of dissolved constituents across the sediment- water interface and aid to better constrain mechanisms and processes controlling the coupling between the sediments and the overlying waters. Here we used phosphate oxygen isotope ratios (δ18Op) in concert with sediment chemistry, XRD, and Mössbauer spectroscopy on the sediment retrieved from an organic rich, sulfidic site in the meso-haline portion of the mid-bay to identify sources and pathway of sedimentary P cycling and to infer potential feedback effect on bottom water hypoxia and surface water eutrophication. Isotope data indicate that the regeneration of inorganic P from organic matter degradation (remineralization) is the predominant, if not sole, pathway for authigenic P precipitation in the mid-bay sediments. We interpret that the excess inorganic P generated by remineralization should have overwhelmed any bottom-water and/or pore-water P derived from other sources or biogeochemical processes and exceeded saturation with respect to authigenic P precipitation. It is the first research that identifies the predominance of remineralization pathway against remobilization (coupled Fe-P cycling) pathway in the Chesapeake Bay. Therefore, these results are expected to have significant implications for the current understanding of P cycling and benthic-pelagic coupling in the bay, particularly on the

Local heteroepitaxy as an adhesion mechanism in aluminium coatings cold gas sprayed on AlN substrates

International Nuclear Information System (INIS)

Wüstefeld, Christina; Rafaja, David; Motylenko, Mykhaylo; Ullrich, Christiane; Drehmann, Rico; Grund, Thomas; Lampke, Thomas; Wielage, Bernhard

2017-01-01

Cold gas sprayed Al coatings deposited onto wurtzitic AlN substrates show excellent adhesion. As a possible adhesion mechanism, the local heteroepitaxy between Al and AlN was considered and verified experimentally in Al coatings, which were deposited using magnetron sputtering or cold gas spraying on single-crystalline and polycrystalline AlN substrates. Analysis of the local orientation relationships at the Al/AlN interfaces revealed that preferentially such lattice planes of Al align parallel with the upright lattice planes of AlN, which possess similar interplanar distances. The matching lattice planes in the Al coatings grew as continuations of the lattice planes in the AlN substrates. In all samples under study, the parallel alignment of the lattice planes {220}_A_l and {110}_A_l_N was found. Additional orientation relationships between Al and AlN arose if parallel lattice planes with similar interplanar spacing could be found in both counterparts via rotation of the lattice planes {220}_A_l around their normal direction. Still, the oriented growth of Al on AlN is only possible if Al atoms in the deposited coatings are mobile enough to rearrange along the AlN surface. Whereas the mobility of Al atoms in a magnetron sputtering process is expected to be sufficiently high, the intrinsic mobility of Al atoms in the cold gas sprayed particles is anticipated to be low. However, the auxiliary microstructure analyses have shown that local recrystallization and partial melting are two phenomena, which can facilitate the rearrangement of Al atoms within the cold gas sprayed coating.

Algae Reefs in Shark Bay, Western Australia, Australia

Science.gov (United States)

1990-01-01

Numerous algae reefs are seen in Shark Bay, Western Australia, Australia (26.0S, 113.5E) especially in the southern portions of the bay. The south end is more saline because tidal flow in and out of the bay is restricted by sediment deposited at the north and central end of the bay opposite the mouth of the Wooramel River. This extremely arid region produces little sediment runoff so that the waters are very clear, saline and rich in algae.

Optimization design on breakdown voltage of AlGaN/GaN high-electron mobility transistor

Science.gov (United States)

Yang, Liu; Changchun, Chai; Chunlei, Shi; Qingyang, Fan; Yuqian, Liu

2016-12-01

Simulations are carried out to explore the possibility of achieving high breakdown voltage of GaN HEMT (high-electron mobility transistor). GaN cap layers with gradual increase in the doping concentration from 2 × 1016 to 5 × 1019 cm-3 of N-type and P-type cap are investigated, respectively. Simulation results show that HEMT with P-doped GaN cap layer shows more potential to achieve higher breakdown voltage than N-doped GaN cap layer under the same doping concentration. This is because the ionized net negative space charges in P-GaN cap layer could modulate the surface electric field which makes more contribution to RESURF effect. Furthermore, a novel GaN/AlGaN/GaN HEMT with P-doped GaN buried layer in GaN buffer between gate and drain electrode is proposed. It shows enhanced performance. The breakdown voltage of the proposed structure is 640 V which is increased by 12% in comparison to UID (un-intentionally doped) GaN/AlGaN/GaN HEMT. We calculated and analyzed the distribution of electrons' density. It is found that the depleted region is wider and electric field maximum value is induced at the left edge of buried layer. So the novel structure with P-doped GaN buried layer embedded in GaN buffer has the better improving characteristics of the power devices. Project supported by the National Basic Research Program of China (No. 2014CB339900) and the Open Fund of Key Laboratory of Complex Electromagnetic Environment Science and Technology, China Academy of Engineering Physics (No. 2015-0214.XY.K).

AlN and Al oxy-nitride gate dielectrics for reliable gate stacks on Ge and InGaAs channels

Energy Technology Data Exchange (ETDEWEB)

Guo, Y.; Li, H.; Robertson, J. [Engineering Department, Cambridge University, Cambridge CB2 1PZ (United Kingdom)

2016-05-28

AlN and Al oxy-nitride dielectric layers are proposed instead of Al{sub 2}O{sub 3} as a component of the gate dielectric stacks on higher mobility channels in metal oxide field effect transistors to improve their positive bias stress instability reliability. It is calculated that the gap states of nitrogen vacancies in AlN lie further away in energy from the semiconductor band gap than those of oxygen vacancies in Al{sub 2}O{sub 3}, and thus AlN might be less susceptible to charge trapping and have a better reliability performance. The unfavourable defect energy level distribution in amorphous Al{sub 2}O{sub 3} is attributed to its larger coordination disorder compared to the more symmetrically bonded AlN. Al oxy-nitride is also predicted to have less tendency for charge trapping.

Modern sedimentation processes in a wave-dominated coastal embayment: Espírito Santo Bay, southeast Brazil

Science.gov (United States)

Bastos, Alex Cardoso; Costa Moscon, Daphnne Moraes; Carmo, Dannilo; Neto, José Antonio Baptista; da Silva Quaresma, Valéria

2015-02-01

Sediment dynamics in wave-dominated coastal embayments are generally controlled by seasonal meteorological conditions, storms having a particularly strong influence. In the present study, such hydrodynamic processes and associated deposits have been investigated in a coastal embayment located along the southeast coast of Brazil, i.e. Espírito Santo Bay, in the winter (June/July) of 2008. The bay has undergone a series of human interventions that have altered the local hydrodynamic processes and, consequently, the sediment transport patterns. Facies distribution and sediment dynamics were examined by acoustic seabed mapping, sediment and core sampling, hydrodynamic measurements and sand transport modelling. The results show that sediment distribution can be described in terms of nearshore and offshore zones. The offshore bay sector is predominantly composed of "palimpsest" lithoclastic medium-coarse sands deposited in the course of the early Holocene transgression that peaked about 5,000 years ago. In the inner bay or nearshore zone (up to depths of 4-8 m), these older transgressive deposits are today overlain by a thin (up to 30-cm-thick) and partly patchy blanket of younger regressive fine sand/muddy fine sands. Both coarse- and fine-grained facies are being reworked during high-energy events (Hs>1.5 m) when fine sediment is resuspended, weak tide-induced drift currents causing the sand patches to be displaced. The coarser sediment, by contrast, is mobilized as bedload to produce wave ripples with spacings of up to 1.2 m. These processes lead to a sharp spatial delimitation between a fine sand/mud facies and a rippled coarse sand facies. The fine sand patches have a relief of about 20-30 cm and reveal a typical internal tempestite depositional sequence. Fair-weather wave-induced sediment transport (Hs<1 m), supported by weak tidal currents, seems to only affect the fine sediment facies. Sediment dynamics in Espírito Santo Bay is thus essentially controlled by

Unique thermal record in False Bay

CSIR Research Space (South Africa)

Grundlingh, ML

1993-10-01

Full Text Available Over the past decade False Bay has assumed a prime position in terms of research in to large South African bays. This is manifested by investigations that cover flow conditions modelling, thermal structure, management, biology and nutrients, geology...

NUMERICAL MODELS AS TOOLS TO UNDERSTAND THE DYNAMICS IN BAYS: CASE OF STUDY CHETUMAL BAY, QUINTANA ROO

Directory of Open Access Journals (Sweden)

David Avalos-Cueva

2017-07-01

Full Text Available In this study performed the simulation of currents generated by the wind on the Bay of Chetumal, Quintana Roo through the use of a stationary shallow-water model. A homogeneous climatic wind was used for the entire Bay, with a velocity of 3m·s-1 , and directions North, South, Northeast, Northwest, East, Southeast, Southwest and West. The results showed a rather complex dynamics in Chetumal Bay, in which important turns were observed in deep areas, with speeds reaching up to 13 cm·s-1 .

Exploring Mobility Options for Children with Physical Disabilities: A Focus on Powered Mobility

Science.gov (United States)

Wiart, Lesley

2011-01-01

The study by Tefft et al. (2011, in this issue) is one of the few studies that have explored the impact of pediatric powered mobility on families. The parents who participated in their study reported increased satisfaction with their children's social and play skills, ability to move independently, sleeping patterns, and public perception of their…

A Text-Independent Speaker Authentication System for Mobile Devices

Directory of Open Access Journals (Sweden)

Florentin Thullier

2017-09-01

Full Text Available This paper presents a text independent speaker authentication method adapted to mobile devices. Special attention was placed on delivering a fully operational application, which admits a sufficient reliability level and an efficient functioning. To this end, we have excluded the need for any network communication. Hence, we opted for the completion of both the training and the identification processes directly on the mobile device through the extraction of linear prediction cepstral coefficients and the naive Bayes algorithm as the classifier. Furthermore, the authentication decision is enhanced to overcome misidentification through access privileges that the user should attribute to each application beforehand. To evaluate the proposed authentication system, eleven participants were involved in the experiment, conducted in quiet and noisy environments. Public speech corpora were also employed to compare this implementation to existing methods. Results were efficient regarding mobile resources’ consumption. The overall classification performance obtained was accurate with a small number of samples. Then, it appeared that our authentication system might be used as a first security layer, but also as part of a multilayer authentication, or as a fall-back mechanism.

76 FR 31851 - Safety Zone; Put-in-Bay Fireworks, Fox's the Dock Pier; South Bass Island, Put-in-Bay, OH

Science.gov (United States)

2011-06-02

... DEPARTMENT OF HOMELAND SECURITY Coast Guard 33 CFR Part 165 [Docket No. USCG-2011-0417] RIN 1625-AA00 Safety Zone; Put-in-Bay Fireworks, Fox's the Dock Pier; South Bass Island, Put-in-Bay, OH AGENCY.... Add Sec. 165.T09-0417 as follows: Sec. 165.T09-0417 Safety Zone; Put-In-Bay Fireworks, Fox's the Dock...

Cascading walks model for human mobility patterns.

Science.gov (United States)

Han, Xiao-Pu; Wang, Xiang-Wen; Yan, Xiao-Yong; Wang, Bing-Hong

2015-01-01

Uncovering the mechanism behind the scaling laws and series of anomalies in human trajectories is of fundamental significance in understanding many spatio-temporal phenomena. Recently, several models, e.g. the explorations-returns model (Song et al., 2010) and the radiation model for intercity travels (Simini et al., 2012), have been proposed to study the origin of these anomalies and the prediction of human movements. However, an agent-based model that could reproduce most of empirical observations without priori is still lacking. In this paper, considering the empirical findings on the correlations of move-lengths and staying time in human trips, we propose a simple model which is mainly based on the cascading processes to capture the human mobility patterns. In this model, each long-range movement activates series of shorter movements that are organized by the law of localized explorations and preferential returns in prescribed region. Based on the numerical simulations and analytical studies, we show more than five statistical characters that are well consistent with the empirical observations, including several types of scaling anomalies and the ultraslow diffusion properties, implying the cascading processes associated with the localized exploration and preferential returns are indeed a key in the understanding of human mobility activities. Moreover, the model shows both of the diverse individual mobility and aggregated scaling displacements, bridging the micro and macro patterns in human mobility. In summary, our model successfully explains most of empirical findings and provides deeper understandings on the emergence of human mobility patterns.

Chesapeake Bay under stress

Science.gov (United States)

According to extensive data obtained over its 13,000 km of shoreline, the Chesapeake Bay has been suffering a major, indeed unprecedented, reduction in submerged vegetation. Chesapeake Bay is alone in experiencing decline in submerged vegetation. Other estuary systems on the east coast of the United States are not so affected. These alarming results were obtained by the synthesis of the findings of numerous individual groups in addition to large consortium projects on the Chesapeake done over the past decade. R. J. Orth and R. A. Moore of the Virginia Institute of Marine Science pointed to the problem of the severe decline of submerged grasses on the Bay and along its tributaries. In a recent report, Orth and Moore note: “The decline, which began in the 1960's and accelerated in the 1970's, has affected all species in all areas. Many major river systems are now totally devoid of any rooted vegetation” (Science, 222, 51-53, 1983).

AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors with reduced leakage current and enhanced breakdown voltage using aluminum ion implantation

Energy Technology Data Exchange (ETDEWEB)

Sun, Shichuang [Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China); Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, Suzhou 215123 (China); Fu, Kai, E-mail: kfu2009@sinano.ac.cn, E-mail: cqchen@mail.hust.edu.cn; Yu, Guohao; Zhang, Zhili; Song, Liang; Deng, Xuguang; Li, Shuiming; Sun, Qian; Cai, Yong; Zhang, Baoshun [Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, CAS, Suzhou 215123 (China); Qi, Zhiqiang; Dai, Jiangnan; Chen, Changqing, E-mail: kfu2009@sinano.ac.cn, E-mail: cqchen@mail.hust.edu.cn [Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074 (China)

2016-01-04

This letter has studied the performance of AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors on silicon substrate with GaN buffer treated by aluminum ion implantation for insulating followed by a channel regrown by metal–organic chemical vapor deposition. For samples with Al ion implantation of multiple energies of 140 keV (dose: 1.4 × 10{sup 14} cm{sup −2}) and 90 keV (dose: 1 × 10{sup 14} cm{sup −2}), the OFF-state leakage current is decreased by more than 3 orders and the breakdown voltage is enhanced by nearly 6 times compared to the samples without Al ion implantation. Besides, little degradation of electrical properties of the 2D electron gas channel is observed where the maximum drain current I{sub DSmax} at a gate voltage of 3 V was 701 mA/mm and the maximum transconductance g{sub mmax} was 83 mS/mm.

Chondrichthyan occurrence and abundance trends in False Bay ...

African Journals Online (AJOL)

Commercial fishing in False Bay, South Africa, began in the 1600s. Today chondrichthyans are regularly taken in fisheries throughout the bay. Using a combination of catch, survey and life history data, the occurrence and long-term changes in populations of chondrichthyans in False Bay are described. Analyses of time ...

Study of the enhancement-mode AlGaN/GaN high electron mobility transistor with split floating gates

Science.gov (United States)

Wang, Hui; Wang, Ning; Jiang, Ling-Li; Zhao, Hai-Yue; Lin, Xin-Peng; Yu, Hong-Yu

2017-11-01

In this work, the charge storage based split floating gates (FGs) enhancement mode (E-mode) AlGaN/GaN high electron mobility transistors (HEMTs) are studied. The simulation results reveal that under certain density of two dimensional electron gas, the variation tendency of the threshold voltage (Vth) with the variation of the blocking dielectric thickness depends on the FG charge density. It is found that when the length sum and isolating spacing sum of the FGs both remain unchanged, the Vth shall decrease with the increasing FGs number but maintaining the device as E-mode. It is also reported that for the FGs HEMT, the failure of a FG will lead to the decrease of Vth as well as the increase of drain current, and the failure probability can be improved significantly with the increase of FGs number.

Toxic phytoplankton in San Francisco Bay

Science.gov (United States)

Rodgers, Kristine M.; Garrison, David L.; Cloern, James E.

1996-01-01

The Regional Monitoring Program (RMP) was conceived and designed to document the changing distribution and effects of trace substances in San Francisco Bay, with focus on toxic contaminants that have become enriched by human inputs. However, coastal ecosystems like San Francisco Bay also have potential sources of naturally-produced toxic substances that can disrupt food webs and, under extreme circumstances, become threats to public health. The most prevalent source of natural toxins is from blooms of algal species that can synthesize metabolites that are toxic to invertebrates or vertebrates. Although San Francisco Bay is nutrient-rich, it has so far apparently been immune from the epidemic of harmful algal blooms in the world’s nutrient-enriched coastal waters. This absence of acute harmful blooms does not imply that San Francisco Bay has unique features that preclude toxic blooms. No sampling program has been implemented to document the occurrence of toxin-producing algae in San Francisco Bay, so it is difficult to judge the likelihood of such events in the future. This issue is directly relevant to the goals of RMP because harmful species of phytoplankton have the potential to disrupt ecosystem processes that support animal populations, cause severe illness or death in humans, and confound the outcomes of toxicity bioassays such as those included in the RMP. Our purpose here is to utilize existing data on the phytoplankton community of San Francisco Bay to provide a provisional statement about the occurrence, distribution, and potential threats of harmful algae in this Estuary.

Heavy metals in superficial sediment of Algiers Bay

International Nuclear Information System (INIS)

Benamar, M.A.; Toumert, C.L.; Chaouch, L.; Bacha, L.; Tobbeche, S.

1996-01-01

Sediment samples were collected in 33 stations from the bay of Algiers for the potential sources of pollution. the analyses were made x-ray fluorescence (XRF) and atomic absorption spectrometry (AAS) the results give information about level of concentrations morphology of the bay (funnel form of bay). only Co,Mn,Fe, and Cd present a particular repartition (unrelated to the sedimentary facies). the level pollution bu heavy metals of the bottom sediments in algiers bay have been compared with those of Surkouk considered as a region with low anthropogenic activities

Hierarchical mixtures of naive Bayes classifiers

NARCIS (Netherlands)

Wiering, M.A.

2002-01-01

Naive Bayes classifiers tend to perform very well on a large number of problem domains, although their representation power is quite limited compared to more sophisticated machine learning algorithms. In this pa- per we study combining multiple naive Bayes classifiers by using the hierar- chical

Studies of movement of sediments in Santos bay

International Nuclear Information System (INIS)

Bandeira, J.V.; Aun, P.E.; Bomtempo, V.L.; Salim, L.H.; Minardi, P.S.P.; Santos, J.A.

1990-01-01

In the years of 1973, 74, 80, 81 and 85 several studies were performed at Santos bay, using radioactive tracers, with the following main objectives: to evaluate the behaviour (on the bottom and in suspension) of the mixture of silt and clay which is dredged from the estuary and from its access channel and dumped at pre-determined sites, in the bay and surrounding regions, with the objective of optimizing dredging disposal operations; to quantify the movement of sandy sediments on the bottom, in 3 areas of the bay, in summer and winter conditions, to obtain pertinent information related to the siltation of the access channel. As results of these studies, it was found that: the ancient dumping site, near Itaipu Point, in the western limit of the bay, was inadequate, since the material could return to the bay and to the estuary. The dumping site was moved to a region at the south of Moela Island, located eastwards relative to the bay, which brought substantial economies in dredging works; the bottom sediment transport was quantified, following clouds of tagged materials for about 8 months, thus obtaining important conclusions about transport rates in different regions of the bay. An analysis of the intervening hydrodynamic agents is also presented. (author) (L.J.C.)

Integrating science and resource management in Tampa Bay, Florida

Science.gov (United States)

Yates, Kimberly K.; Greening, Holly; Morrison, Gerold

2011-01-01

Tampa Bay is recognized internationally for its remarkable progress towards recovery since it was pronounced "dead" in the late 1970s. Due to significant efforts by local governments, industries and private citizens throughout the watershed, water clarity in Tampa Bay is now equal to what it was in 1950, when population in the watershed was less than one-quarter of what it is today. Seagrass extent has increased by more than 8,000 acres since the mid-1980s, and fish and wildlife populations are increasing. Central to this successful turn-around has been the Tampa Bay resource management community's long-term commitment to development and implementation of strong science-based management strategies. Research institutions and agencies, including Eckerd College, the Florida Wildlife Commission Fish and Wildlife Research Institute, Mote Marine Laboratory, National Oceanic and Atmospheric Administration, the Southwest Florida Water Management District, University of South Florida, U.S. Environmental Protection Agency, U.S. Geological Survey, local and State governments, and private companies contribute significantly to the scientific basis of our understanding of Tampa Bay's structure and ecological function. Resource management agencies, including the Tampa Bay Regional Planning Council's Agency on Bay Management, the Southwest Florida Water Management District's Surface Water Improvement and Management Program, and the Tampa Bay Estuary Program, depend upon this scientific basis to develop and implement regional adaptive management programs. The importance of integrating science with management has become fully recognized by scientists and managers throughout the region, State and Nation. Scientific studies conducted in Tampa Bay over the past 10–15 years are increasingly diverse and complex, and resource management programs reflect our increased knowledge of geology, hydrology and hydrodynamics, ecology and restoration techniques. However, a synthesis of this

Cryptanalysis and Improvement of "A Secure Password Authentication Mechanism for Seamless Handover in Proxy Mobile IPv6 Networks"

Science.gov (United States)

Alizadeh, Mojtaba; Zamani, Mazdak; Baharun, Sabariah; Abdul Manaf, Azizah; Sakurai, Kouichi; Anada, Hiroki; Keshavarz, Hassan; Ashraf Chaudhry, Shehzad; Khurram Khan, Muhammad

2015-01-01

Proxy Mobile IPv6 is a network-based localized mobility management protocol that supports mobility without mobile nodes’ participation in mobility signaling. The details of user authentication procedure are not specified in this standard, hence, many authentication schemes have been proposed for this standard. In 2013, Chuang et al., proposed an authentication method for PMIPv6, called SPAM. However, Chuang et al.’s Scheme protects the network against some security attacks, but it is still vulnerable to impersonation and password guessing attacks. In addition, we discuss other security drawbacks such as lack of revocation procedure in case of loss or stolen device, and anonymity issues of the Chuang et al.’s scheme. We further propose an enhanced authentication method to mitigate the security issues of SPAM method and evaluate our scheme using BAN logic. PMID:26580963

Whose Bay Street? Competing Narratives of Nassau's City Centre

Directory of Open Access Journals (Sweden)

Nona Patara Martin

2009-05-01

Full Text Available Bay Street has always been at the centre of commercial, cultural and political life in the Bahama Islands. It also acts as a gateway for millions of tourists who come to Nassau, the Bahamian capital, via cruise ships every year. Not surprisingly, Bahamians and non-Bahamians have widely divergent impressions of Bay Street. The need to accommodate the tourists who are critical to the Bahamian economy has meant that Bay Street, despite its deep social significance for Bahamians, has increasingly become a tourist space. With reference to the ‘sense of place’ and place attachment literature, this paper traces the transformation of Bay Street and attempts to tease out the most obvious tensions between the Bay Street that Bahamians experience and Bay Street as a port of call.

Empirical Bayes ranking and selection methods via semiparametric hierarchical mixture models in microarray studies.

Science.gov (United States)

Noma, Hisashi; Matsui, Shigeyuki

2013-05-20

The main purpose of microarray studies is screening of differentially expressed genes as candidates for further investigation. Because of limited resources in this stage, prioritizing genes are relevant statistical tasks in microarray studies. For effective gene selections, parametric empirical Bayes methods for ranking and selection of genes with largest effect sizes have been proposed (Noma et al., 2010; Biostatistics 11: 281-289). The hierarchical mixture model incorporates the differential and non-differential components and allows information borrowing across differential genes with separation from nuisance, non-differential genes. In this article, we develop empirical Bayes ranking methods via a semiparametric hierarchical mixture model. A nonparametric prior distribution, rather than parametric prior distributions, for effect sizes is specified and estimated using the "smoothing by roughening" approach of Laird and Louis (1991; Computational statistics and data analysis 12: 27-37). We present applications to childhood and infant leukemia clinical studies with microarrays for exploring genes related to prognosis or disease progression. Copyright © 2012 John Wiley & Sons, Ltd.

InAlAs/InGaAs Pseudomorphic High Eelectron Mobility Transistors Grown by Molecular Beam Epitaxy on the InP Substrate

International Nuclear Information System (INIS)

Huang Jie; Guo Tian-Yi; Zhang Hai-Ying; Xu Jing-Bo; Fu Xiao-Jun; Yang Hao; Niu Jie-Bin

2010-01-01

A novel PMMA/PMGI/ZEP520 trilayer resist electron beam lithograph (EBL) technology is successfully developed and used to fabricate the 150 nm gate-length In 0.7 Ga 0.3 As/In 0.52 Al 0.48 As Pseudomorphic HEMT on an InP substrate, of which the material structure is successfully designed and optimized. A perfect profile of T-gate is successfully obtained. These fabricated devices demonstrate excellent dc and rf characteristics: the transconductance G m , maximum saturation drain-to-source current I DSS , threshold voltage V T , maximum current gain frequency f T derived from h 21 , maximum frequency of oscillation derived from maximum available power gain/maximum stable gain and from unilateral power-gain of metamorphic InGaAs/InAlAs high electron mobility transistors (HEMTs) are 470 mS/mm, 560 mA/mm, −1.0 V, 76 GHz, 135 GHz and 436 GHz, respectively. The excellent high frequency performances promise the possibility of metamorphic HEMTs for millimeter-wave applications. (cross-disciplinary physics and related areas of science and technology)

Fecal indicator bacteria at Havana Bay

International Nuclear Information System (INIS)

Lopez Perez, Lisse; Gomez D'Angelo, Yamiris; Beltran Gonzalez, Jesus; Alvarez Valiente, Reinaldo

2013-01-01

Aims: Fecal indicator bacteria concentrations were evaluated in Havana Bay. Methods: Concentrations of traditional fecal indicator bacteria were calculated between April 2010 and February 2011, by MPN methods. Concentrations of thermo tolerant coliform (CTT), Escherichia coli, fecal streptococci (EF), intestinal enterococci (ENT) in seawater, and Clostridium perfringens in sediment surface, were determined. Results: CTT and E. coli levels were far above Cuban water quality standard for indirect contact with water, showing the negative influence of sewage and rivers on the bay. The EF and ENT were measured during sewage spills at the discharge site and they were suitable indicators of fecal contamination, but these indicators didn't show the same behavior in other selected sites. This result comes from its well-known inactivation by solar light in tropical zones and the presumable presence of humid acids in the waters of the bay. Conclusion: Fecal indicator bacteria and its statistical relationships reflect recent and chronic fecal contamination at the bay and near shores.

Heme oxygenase-1 mediates BAY 11-7085 induced ferroptosis.

Science.gov (United States)

Chang, Ling-Chu; Chiang, Shih-Kai; Chen, Shuen-Ei; Yu, Yung-Luen; Chou, Ruey-Hwang; Chang, Wei-Chao

2018-03-01

Ferroptosis is a form of oxidative cell death and has become a chemotherapeutic target for cancer treatment. BAY 11-7085 (BAY), which is a well-known IκBα inhibitor, suppressed viability in cancer cells via induction of ferroptotic death in an NF-κB-independent manner. Reactive oxygen species scavenging, relief of lipid peroxidation, replenishment of glutathione and thiol-containing agents, as well as iron chelation, rescued BAY-induced cell death. BAY upregulated a variety of Nrf2 target genes related to redox regulation, particularly heme oxygenase-1 (HO-1). Studies with specific inhibitors and shRNA interventions suggested that the hierarchy of induction is Nrf2-SLC7A11-HO-1. SLC7A11 inhibition by erastin, sulfasalazine, or shRNA interference sensitizes BAY-induced cell death. Overexperession of SLC7A11 attenuated BAY-inhibited cell viability. The ferroptotic process induced by hHO-1 overexpression further indicated that HO-1 is a key mediator of BAY-induced ferroptosis that operates through cellular redox regulation and iron accumulation. BAY causes compartmentalization of HO-1 into the nucleus and mitochondrion, and followed mitochondrial dysfunctions, leading to lysosome targeting for mitophagy. In this study, we first discovered that BAY induced ferroptosis via Nrf2-SLC7A11-HO-1 pathway and HO-1 is a key mediator by responding to the cellular redox status. Copyright © 2017 Elsevier B.V. All rights reserved.

Changing Salinity Patterns in Biscayne Bay, Florida

Science.gov (United States)

,

2004-01-01

Biscayne Bay, Fla., is a 428-square-mile (1,109-square-kilometer) subtropical estuarine ecosystem that includes Biscayne National Park, the largest marine park in the U.S. national park system (fig. 1). The bay began forming between 5,000 and 3,000 years ago as sea level rose and southern Florida was flooded. Throughout most of its history, the pristine waters of the bay supported abundant and diverse fauna and flora, and the bay was a nursery for the adjacent coral-reef and marine ecosystems. In the 20th century, urbanization of the Miami-Dade County area profoundly affected the environment of the bay. Construction of powerplants, water-treatment plants, and solid-waste sites and large-scale development along the shoreline stressed the ecosystem. Biscayne National Monument was established in 1968 to ?preserve and protect for the education, inspiration, recreation and enjoyment of present and future generations a rare combination of terrestrial, marine, and amphibious life in a tropical setting of great natural beauty? (Public Law 90?606). The monument was enlarged in 1980 and designated a national park.

Mobile eye services: Literature review with special reference to the experience of Al-Basar International Foundation

Directory of Open Access Journals (Sweden)

Adel A Rushood

2010-01-01

Full Text Available Purpose: To evaluate the concept of quality assured mobile eye services (MES in implementing the vision 2020 initiative. Materials and Methods: Literature review as well as the medical records of Al-Basar International Foundation (BIF on MES. Emphasis was focused on the causes of blindness, objectives, operation, management and the benefits of MES, a critical appraisal of MES, training for MES and the relationship with other organizations and concerned government agencies. Findings: More than 38 countries have been included in this exercise during which more than 620 eye camps have been conducted. More than two million people have benefited from the services provided including medicines and glasses in these eye camps and about 180,000 sight restoring surgeries performed for cataract, glaucoma etc. Conclusion: Quality assured MES are a very important means of tackling the problems of blindness and implementing the vision 2020 initiative. The adoption of this concept by major stake-holders in the prevention of blindness (e.g. WHO, IAPB will bring an additional momentum to the achievement of this noble goal.

Incident wave run-up into narrow sloping bays and estuaries

Science.gov (United States)

Sinan Özeren, M.; Postacioglu, Nazmi; Canlı, Umut

2015-04-01

The problem is investigated using Carrier Greenspan hodograph transformations.We perform a quasi-one-dimensional solution well into the bay, far enough of the mouth of the bay. The linearized boundary conditions at the mouth of the bay lead to an integral equation for 2-D geometry. A semi analytical optimization method has been developed to solve this integral equation. When the wavelength of the incident wave is much larger than the width of the bay, the conformalmapping of the bay and the semi infinite sea onto upper complex plane provides a solution of the integral equation in closed form. Particular emphasis is placed on the case where the frequency of the incident waves matches the real-part of the natural frequency of the oscillation of the bay. These natural frequencies are complex because of the radiation conditions imposed at the mouth of the bay. It is found that the complex part of these natural frequencies decreases with decreasing width of the bay. Thus the trapping of the waves in narrower bays leads to a strong resonance phenomenon when the frequency of the incident wave is equal to the real part of the natural frequency.

Investigation of the Vehicle Mobility in Fording

Science.gov (United States)

2016-05-29

Conference on Multibody System Dynamics May 29 – June 2, 2016, Montréal, Canada Investigation of the Vehicle Mobility in Fording Arman Pazouki1...strategy outlined has been implemented in Chrono as a dedicated add-on called Chrono::FSI [3]. Figure 1 shows a vehicle model used in a fording simulation...rigid objects. Chrono::FSI has been used for vehicle mobility in fording operations as shown in Figure 2. The computational time per simulation time

Elemental analysis of Uranouchi bay seabed sludge using PIXE

International Nuclear Information System (INIS)

Kabir, M. Hasnat; Narusawa, Tadashi; Nishiyama, Fumitaka; Sumi, Katsuhiro

2006-01-01

Elemental analyses were carried out for the seabed sludge collected from Uranouchi bay (Kochi, Japan) using Particle Induced X-ray Emission (PIXE). Seabed-sludge contamination with heavy metals as well as toxic elements becomes one of the most serious environmental problems. The aim of the present study is to investigate the polluted areas in the bay by heavy and toxic elements. As a results of analyses of samples collected from eleven different places in the bay, seventeen elements including toxic ones were detected. The results suggest that the center region of the bay is seriously contaminated by heavy and toxic elements in comparison with the other areas in the bay. (author)

Dependences of the Al thickness and annealing temperature on the structural, optical and electrical properties in ZnO/Al multilayers

International Nuclear Information System (INIS)

Hu, Y.M.; Lin, C.W.; Huang, J.C.A.

2006-01-01

High-quality (0001) oriented ZnO (300 A) film and [ZnO(100 A)/Al(t Al )] 3 (t Al = 0.6, 1.7, 2.8 A) multilayers have been established at room temperature on Al 2 O 3 (0001) substrates by ion-beam sputtering. The structural, optical and electrical properties of multilayers as functions of both the Al thickness and annealing temperature are reported. We have verified that Al thickness and annealing temperature are the key factors to optimize transparency-conducting property in ZnO/Al multilayers. The optimum Al thickness and annealing temperature for ZnO/Al multilayer of 300 A thin is 1.7 A (about one Al atomic layer) and 400 deg. C, respectively, leading to the relatively lower resistivity (2.8 x 10 -3 Ω cm) and higher Hall mobility (10 cm 2 /V.s) without suppression of the visible transmittance (above 85%)

South Bay Salt Pond Mercury Studies Project

Science.gov (United States)

Information about the SFBWQP South Bay Salt Pond Mercury Studies Project, part of an EPA competitive grant program to improve SF Bay water quality focused on restoring impaired waters and enhancing aquatic resources.

Analysis of multi cloud storage applications for resource constrained mobile devices

Directory of Open Access Journals (Sweden)

Rajeev Kumar Bedi

2016-09-01

Full Text Available Cloud storage, which can be a surrogate for all physical hardware storage devices, is a term which gives a reflection of an enormous advancement in engineering (Hung et al., 2012. However, there are many issues that need to be handled when accessing cloud storage on resource constrained mobile devices due to inherent limitations of mobile devices as limited storage capacity, processing power and battery backup (Yeo et al., 2014. There are many multi cloud storage applications available, which handle issues faced by single cloud storage applications. In this paper, we are providing analysis of different multi cloud storage applications developed for resource constrained mobile devices to check their performance on the basis of parameters as battery consumption, CPU usage, data usage and time consumed by using mobile phone device Sony Xperia ZL (smart phone on WiFi network. Lastly, conclusion and open research challenges in these multi cloud storage apps are discussed.

Lagrangian structure of flows in the Chesapeake Bay: challenges and perspectives on the analysis of estuarine flows

Directory of Open Access Journals (Sweden)

M. Branicki

2010-03-01

Full Text Available In this work we discuss applications of Lagrangian techniques to study transport properties of flows generated by shallow water models of estuarine flows. We focus on the flow in the Chesapeake Bay generated by Quoddy (see Lynch and Werner, 1991, a finite-element (shallow water model adopted to the bay by Gross et al. (2001. The main goal of this analysis is to outline the potential benefits of using Lagrangian tools for both understanding transport properties of such flows, and for validating the model output and identifying model deficiencies. We argue that the currently available 2-D Lagrangian tools, including the stable and unstable manifolds of hyperbolic trajectories and techniques exploiting 2-D finite-time Lyapunov exponent fields, are of limited use in the case of partially mixed estuarine flows. A further development and efficient implementation of three-dimensional Lagrangian techniques, as well as improvements in the shallow-water modelling of 3-D velocity fields, are required for reliable transport analysis in such flows. Some aspects of the 3-D trajectory structure in the Chesapeake Bay, based on the Quoddy output, are also discussed.

Reliability of AlGaN/GaN high electron mobility transistors on low dislocation density bulk GaN substrate: Implications of surface step edges

Energy Technology Data Exchange (ETDEWEB)

Killat, N., E-mail: Nicole.Killat@bristol.ac.uk, E-mail: Martin.Kuball@bristol.ac.uk; Montes Bajo, M.; Kuball, M., E-mail: Nicole.Killat@bristol.ac.uk, E-mail: Martin.Kuball@bristol.ac.uk [Center for Device Thermography and Reliability (CDTR), H.H. Wills Physics Laboratory, Tyndall Avenue, Bristol BS8 1TL (United Kingdom); Paskova, T. [Kyma Technologies, Inc., Raleigh, North Carolina 27617 (United States); Materials Science and Engineering Department, North Carolina State University, Raleigh, North Carolina 27695 (United States); Evans, K. R. [Kyma Technologies, Inc., Raleigh, North Carolina 27617 (United States); Leach, J. [Kyma Technologies, Inc., Raleigh, North Carolina 27617 (United States); Electrical and Computer Engineering Department, Virginia Commonwealth University, Richmond, Virginia 23284 (United States); Li, X.; Özgür, Ü.; Morkoç, H. [Electrical and Computer Engineering Department, Virginia Commonwealth University, Richmond, Virginia 23284 (United States); Chabak, K. D.; Crespo, A.; Gillespie, J. K.; Fitch, R.; Kossler, M.; Walker, D. E.; Trejo, M.; Via, G. D.; Blevins, J. D. [Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio 45433 (United States)

2013-11-04

To enable gaining insight into degradation mechanisms of AlGaN/GaN high electron mobility transistors, devices grown on a low-dislocation-density bulk-GaN substrate were studied. Gate leakage current and electroluminescence (EL) monitoring revealed a progressive appearance of EL spots during off-state stress which signify the generation of gate current leakage paths. Atomic force microscopy evidenced the formation of semiconductor surface pits at the failure location, which corresponds to the interaction region of the gate contact edge and the edges of surface steps.

Influence of the channel electric field distribution on the polarization Coulomb field scattering in In0.18Al0.82N/AlN/GaN heterostructure field-effect transistors

International Nuclear Information System (INIS)

Yu Ying-Xia; Lin Zhao-Jun; Luan Chong-Biao; Yang Ming; Wang Yu-Tang; Lü Yuan-Jie; Feng Zhi-Hong

2014-01-01

By making use of the quasi-two-dimensional (quasi-2D) model, the current–voltage (I–V) characteristics of In 0.18 Al 0.82 N/AlN/GaN heterostructure field-effect transistors (HFETs) with different gate lengths are simulated based on the measured capacitance–voltage (C–V) characteristics and I–V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas (2DEG) with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm 2 /V·s for the prepared In 0.18 Al 0.82 N/AlN/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain–source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density, the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

DEVELOP Chesapeake Bay Watershed Hydrology - UAV Sensor Web

Science.gov (United States)

Holley, S. D.; Baruah, A.

2008-12-01

The Chesapeake Bay is the largest estuary in the United States, with a watershed extending through six states and the nation's capital. Urbanization and agriculture practices have led to an excess runoff of nutrients and sediment into the bay. Nutrients and sediment loading stimulate the growth of algal blooms associated with various problems including localized dissolved oxygen deficiencies, toxic algal blooms and death of marine life. The Chesapeake Bay Program, among other stakeholder organizations, contributes greatly to the restoration efforts of the Chesapeake Bay. These stakeholders contribute in many ways such as monitoring the water quality, leading clean-up projects, and actively restoring native habitats. The first stage of the DEVELOP Chesapeake Bay Coastal Management project, relating to water quality, contributed to the restoration efforts by introducing NASA satellite-based water quality data products to the stakeholders as a complement to their current monitoring methods. The second stage, to be initiated in the fall 2008 internship term, will focus on the impacts of land cover variability within the Chesapeake Bay Watershed. Multiple student led discussions with members of the Land Cover team at the Chesapeake Bay Program Office in the DEVELOP GSFC 2008 summer term uncovered the need for remote sensing data for hydrological mapping in the watershed. The Chesapeake Bay Program expressed in repeated discussions on Land Cover mapping that significant portions of upper river areas, streams, and the land directly interfacing those waters are not accurately depicted in the watershed model. Without such hydrological mapping correlated with land cover data the model will not be useful in depicting source areas of nutrient loading which has an ecological and economic impact in and around the Chesapeake Bay. The fall 2008 DEVELOP team will examine the use of UAV flown sensors in connection with in-situ and Earth Observation satellite data. To maximize the

The mobile macro-invertebrate fauna of the Oosterschelde and the Westerschelde (SW Netherlands)

OpenAIRE

Hostens, K.; Mees, J.; Hummel, H.

2003-01-01

Abstract Both in the marine bay the Oosterschelde and in the Westerschelde estuary, the mobile macro- invertebrate fauna from sub tidal soft substrates was sampled with a three-metre beam trawl during 10 quarterly surveys between August 1999 and November 2001. A total of 35 species was recorded. In the Oosterschelde 33 species were found: 9 caridean prawns, 9 brachyuran crabs, 6 echinoderms, 3 caridean shrimps, 3 cephalopods, 2 anomuran crabs and 1 lobster. The dominating species in the Ooste...

Humboldt Bay, California Benthic Habitats 2009 Geoform

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Humboldt Bay is the largest estuary in California north of San Francisco Bay and represents a significant resource for the north coast region. Beginning in 2007 the...

Humboldt Bay, California Benthic Habitats 2009 Substrate

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Humboldt Bay is the largest estuary in California north of San Francisco Bay and represents a significant resource for the north coast region. Beginning in 2007 the...

Humboldt Bay Benthic Habitats 2009 Aquatic Setting

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Humboldt Bay is the largest estuary in California north of San Francisco Bay and represents a significant resource for the north coast region. Beginning in 2007 the...

Humboldt Bay, California Benthic Habitats 2009 Geodatabase

Data.gov (United States)

National Oceanic and Atmospheric Administration, Department of Commerce — Humboldt Bay is the largest estuary in California north of San Francisco Bay and represents a significant resource for the north coast region. Beginning in 2007 the...

Contaminant transport in Massachusetts Bay

Science.gov (United States)

Butman, Bradford

Construction of a new treatment plant and outfall to clean up Boston Harbor is currently one of the world's largest public works projects, costing about $4 billion. There is concern about the long-term impact of contaminants on Massachusetts Bay and adjacent Gulf of Maine because these areas are used extensively for transportation, recreation, fishing, and tourism, as well as waste disposal. Public concern also focuses on Stellwagen Bank, located on the eastern side of Massachusetts Bay, which is an important habitat for endangered whales. Contaminants reach Massachusetts Bay not only from Boston Harbor, but from other coastal communities on the Gulf of Maine, as well as from the atmosphere. Knowledge of the pathways, mechanisms, and rates at which pollutants are transported throughout these coastal environments is needed to address a wide range of management questions.

Bayes linear statistics, theory & methods

CERN Document Server

Goldstein, Michael

2007-01-01

Bayesian methods combine information available from data with any prior information available from expert knowledge. The Bayes linear approach follows this path, offering a quantitative structure for expressing beliefs, and systematic methods for adjusting these beliefs, given observational data. The methodology differs from the full Bayesian methodology in that it establishes simpler approaches to belief specification and analysis based around expectation judgements. Bayes Linear Statistics presents an authoritative account of this approach, explaining the foundations, theory, methodology, and practicalities of this important field. The text provides a thorough coverage of Bayes linear analysis, from the development of the basic language to the collection of algebraic results needed for efficient implementation, with detailed practical examples. The book covers:The importance of partial prior specifications for complex problems where it is difficult to supply a meaningful full prior probability specification...

Reputation-Based Internet Protocol Security: A Multilayer Security Framework for Mobile Ad Hoc Networks

Science.gov (United States)

2010-09-01

motivated research in behavior grading systems [56]. Peer-to-peer eCommerce appli- cations such as eBay, Amazon, uBid, and Yahoo have performed research that...Security in Mobile Ad Hoc Networks”. IEEE Security & Privacy , 72–75, 2008. 15. Chakeres, ID and EM Belding-Royer. “AODV Routing Protocol Implementa...Detection System”. Proceedings of IEEE Computer Society Symposium on Research in Security and Privacy , 240–250. 1992. 21. Devore, J.L. and N.R. Farnum

Terrestrially derived dissolved organic matter in the chesapeake bay and the middle atlantic bight

Science.gov (United States)

Mitra, Siddhartha; Bianchi, Thomas S.; Guo, Laodong; Santschi, Peter H.

2000-10-01

Concentrations of lignin-phenols were analyzed in high molecular weight dissolved organic matter (0.2 μm > HMW DOM > 1 kDa) isolated from surface waters of the Chesapeake Bay (C. Bay), and surface and bottom waters of the Middle Atlantic Bight (MAB). The abundance of lignin-phenols in HMW DOM was higher in the C. Bay (0.128 ± 0.06 μg L -1) compared to MAB surface waters (0.016 ± 0.004 μg L -1) and MAB bottom waters (0.005 ± 0.003 μg L -1). On an organic carbon-normalized basis, lignin-phenol abundances in the HMW DOM (i.e., Λ 6), were significantly higher ( p vanillin (Ad/Al) V in HMW DOM, indicative of lignin decay, ranged from 0.611 to 1.37 in C. Bay, 0.534 to 2.62 in MAB surface waters, and 0.435 to 1.96 in MAB bottom water. Ratios of S/V and (Ad/Al) V showed no significant differences between each environment, providing no evidence of any compositionally distinct input of terrestrial organic matter into each environment. When considering depth profiles of suspended particulate matter in the MAB, with C:N ratios, and bulk radiocarbon ages and stable carbon isotopic values in HMW DOM isolated from these areas, two scenarios present themselves regarding the sources and transport of terrestrially derived HMW DOM in the MAB. Scenario #1 assumes that a low amount of refractory terrestrial organic matter and old DOC are uniformly distributed in the oceans, both in surface and bottom waters, and that primary production in surface waters increases DOC with low lignin and younger DOC which degrades easily. In this case, many of the trends in age and biomarker composition likely reflect general patterns of Atlantic Ocean surface and bottom water circulation in the area of the MAB. Scenario 2 assumes terrestrial organic matter in bottom waters of the MAB may have originated from weathered shelf and slope sediments in nearshore areas via a combination of mechanisms (e.g., diffusion, recent resuspension events, and/or desorption of DOM from riverine POM buried deep

Reconstructing Sea Surface Conditions in the Bay of Bengal during the Mid-Pleistocene Transition

Science.gov (United States)

Lagos, A. D.; Dekens, P.; Reilly, B. T.; Selkin, P. A.; Meynadier, L.; Savian, J. F.

2017-12-01

During the Mid-Pleistocene Transition (MPT, 0.8-1.2Ma) Earth's glacial cycles transitioned from responding primarily to 41kyr obliquity cycles to responding to 100kyr eccentricity cycles. In the tropics, sea surface temperature (SST) in the eastern tropical Pacific cooled through the MPT, suggesting a strengthening of the equatorial Pacific zonal temperature gradient (Medina-Elizalde & Lea, 2005). The strong SST gradient would have intensified Walker Cell convection during the MPT and built up latent heat in the western Pacific, which could cause cold SST anomalies in the northern Indian Ocean (Liu et al., 2015). Due to a scarcity of records, it is unclear how climate and oceanic conditions evolved in the Indian Ocean during the MPT. A set of recent IODP expeditions, including 353 and 354, cored sediment from the Bay of Bengal. Several sites recovered by expedition 353 will be ideal for reconstructing monsoon intensity through time, while the expedition 354 cores from a longitudinal transect at 8°N are in a region not directly impacted by changes in freshwater input due to direct precipitation or run off. The sites are influenced by the northeastern migration of equatorial Indian Ocean water via the Southwest Monsoon Current, which supplies significant moisture to the monsoon. Expedition 354's southern Bay of Bengal sites are well situated for better understanding the link between the tropical Indian Ocean and the northern Bay of Bengal. We reconstructed sea surface conditions at IODP site 1452 (8°N, 87°E, 3670m water depth) in the distal Bengal Fan. A 3 meter long section of the core has been identified as the MPT using the Bruhnes/Matuyama, Jaramillo, and Cobb Mountain paleomagnetic reversals (France-Lanord et al., 2016). This section of site 1452 was sampled every 2cm ( 2kyr resolution). Approximately 30 G. sacculifer, a surface dwelling planktonic foraminifera, were picked from the 355-425μm size fraction. We measured Mg/Ca and δ18O on splits of the same

Long-term impacts due to sediment supply changes towards the San Francisco Bay-Delta system

Science.gov (United States)

Achete, F.; Van der Wegen, M. V.; Jaffe, B. E.

2012-12-01

The Sacramento-San Joaquin Delta and Watershed is the main source of fresh water and sediment to San Francisco Bay. Mid 19th century hydraulic mining in the catchment caused an excessive supply of sediment. After mining activities stopped, in the first part of the 20th century several hydraulic structures were built deviating fresh water and trapping sediment upstream. The main purpose of most of these structures is water storage for irrigation and/or water supply Wright and Schoellhamer (2004) show that from 1957 to 2001 the sediment load carried to San Francisco Bay has decreased by about one half. The lack of sediments may lead to a different erosion/deposition pattern in the Bay-Delta system causing problems like mud flat erosion, shift in navigation channel, land subsidence and changing habitat for endemic species. The objective of this work is to identify and quantify morphological shifts in the Bay-Delta system due to variation in fresh water and sediment supply. In this study, we couple the Delta and Bay in a unique model network (the Delta-Bay model). This coupling allows tracking of sediment from Sacramento via the Delta and Bay and through the Golden Gate, making it possible to identify erosion and deposition areas. The numerical model applied is an unstructured, process-based model (D-Flow Flexible Mesh developed by Deltares). It simulates the hydrodynamics and morphodynamics of the area on a detailed, 64000-node mesh (10-200m mesh length scale) on a timescale of minutes. The morphological impact is assessed for multiple scenarios with different input of sediment and fresh water. A statistical analysis is performed to account for uncertainty of model parameters and climate change impacts. The fresh water discharge already has a strong natural seasonal and inter-annual variation. The human impact by foreseen different water pumping strategies due to the peripheral canal will be considered. Jaffe et al. (2007) has shown that substantial morphological

Mex Bay

African Journals Online (AJOL)

user

2015-02-23

Feb 23, 2015 ... surveys to assess the vulnerability of the most important physical and eutrophication parameters along. El- Mex Bay coast. As a result of increasing population and industrial development, poorly untreated industrial waste, domestic sewage, shipping industry and agricultural runoff are being released to the.

San Francisco Bay Water Quality Improvement Fund

Science.gov (United States)

EPAs grant program to protect and restore San Francisco Bay. The San Francisco Bay Water Quality Improvement Fund (SFBWQIF) has invested in 58 projects along with 70 partners contributing to restore wetlands, water quality, and reduce polluted runoff.,

PEMANFATAN TEOREMA BAYES DALAM PENENTUAN PENYAKIT THT

Directory of Open Access Journals (Sweden)

Sri Winiarti

2008-07-01

Full Text Available Dalam konsep pelacakan dalam mencari solusi dengan pendekatan artificial inteligent, ada berbagai metode yang dapat diterapkan untuk mengatasi masalah ketidakpastian saat proses pelacakan terjadi. Salah satunya adalah teorema bayes. Adanya ketidakpastian pada proses pelacakan dapat terjadi karena adanya perubahan pengetahuan yang ada di dalam sistem. Untuk itu diperlukan adanya suatu metode untuk mengatasi permasalahan tersebut. Dalam penelitian ini telah diterapkan suatu metode untuk mengatasi ketidakpastian dengan teorema Bayes pada kasus pelacakan untuk mendiagnosa penyakit pada THT (Telinga,Hidung dan Tenggorokan. Subjek pada penelitian ini adalah proses pelacakan untuk menentukan penyakit THT dengan model penalaran forward chaining dan metode kepastiannya menggunakan teorema bayes dengan cara menghitung nilai probabilitas suatu penyakit dan membandingkan probabilitas setiap gejalanya. Model pengembangan perangkat lunak yang digunakan dalam penelitian ini adalah Waterfall. Metode Waterfall diawali dengan analisis data, perancangan sistem, pengkodean menggunakan Visual Basic 6.0, pengujian sistem dengan black box test dan alfa test. Dari penelitian yang dilakukan menghasilkan sebuah perangkat lunak yaitu yang mampu menentukan penyakit pada THT dengan menerapkan metode bayes untuk mengatasi ketidakpastian. Hasil uji coba sistem menujukkan bahwa aplikasi ini layak dan dapat digunakan. Kata kunci : Penyakit, THT, Teorema Bayes.

X-ray diffraction study of InAlAs-InGaAs on InP high electron mobility transistor structure prepared by molecular-beam epitaxy

International Nuclear Information System (INIS)

Liu, H.Y.; Kao, Y.C.; Kim, T.S.

1990-01-01

High-electron mobility transistors (HEMTs) can be prepared by growing alternating epitaxial layers of InAlAs and InGaAs on InP substrates. Lattice matched HEMTs are obtained by growing layers of IN x Al (1-x) As and In y Ga (1-y) As with x ≅ 0.5227 and y ≅ 0.5324. Varying the values of x and y by controlling the individual flux during molecular-beam epitaxial (MBE) growth, one can obtain pseudomorphic HEMTs. Pseudomorphic HEMTs may have superior electronic transport properties and larger conduction band discontinuity when compared to an unstrained one. The precise control of the composition is thus important to the properties of HEMTs. This control is however very difficult and the values of x and y may vary from run to run. The authors demonstrate in this paper the capability of a double crystal rocking curve (DCRC) on the structure characterization

Geochemistry of sediments in the Back Bay and Yellowknife Bay of the Great Slave Lake

International Nuclear Information System (INIS)

Mudroch, A.; Joshi, S.R.; Sutherland, D.; Mudroch, P.; Dickson, K.M.

1989-01-01

Gold mining activities have generated wastes with high concentrations of arsenic and zinc in the vicinity of Yellowknife, Northwest Territories, Canada. Some of the waste material has been discharged into Yellowknife Bay of Great Slave Lake. Concentrations of arsenic and zinc were determined in sediment cores collected at the depositional areas of Yellowknife Bay. Sedimentation rates were estimated using two different radiometric approaches: the depth profiles of cesium 137 and lead 210. Geochemical analysis of the sediment cores indicated input of similar material into sampling areas over the past 50 yr. Age profiles of the sediment constructed from the radionuclide measurements were used to determine historical trends of arsenic and zinc inputs into Yellowknife Bay. The historical record was in good agreement with implemented remedial actions and the usage patterns of both elements. 16 refs., 6 figs., 3 tabs

Weak acid extractable metals in Bramble Bay, Queensland, Australia: temporal behaviour, enrichment and source apportionment.

Science.gov (United States)

Brady, James P; Ayoko, Godwin A; Martens, Wayde N; Goonetilleke, Ashantha

2015-02-15

Sediment samples were taken from six sampling sites in Bramble Bay, Queensland, Australia between February and November in 2012. They were analysed for a range of heavy metals including Al, Fe, Mn, Ti, Ce, Th, U, V, Cr, Co, Ni, Cu, Zn, As, Cd, Sb, Te, Hg, Tl and Pb. Fraction analysis, Enrichment Factors and Principal Component Analysis-Absolute Principal Component Scores (PCA-APCS) were carried out in order to assess metal pollution, potential bioavailability and source apportionment. Cr and Ni exceeded the Australian Interim Sediment Quality Guidelines at some sampling sites, while Hg was found to be the most enriched metal. Fraction analysis identified increased weak acid soluble Hg and Cd during the sampling period. Source apportionment via PCA-APCS found four sources of metals pollution, namely, marine sediments, shipping, antifouling coatings and a mixed source. These sources need to be considered in any metal pollution control measure within Bramble Bay. Copyright © 2014 Elsevier Ltd. All rights reserved.

Ubiquitous Knowledge Construction: Mobile Learning Re-Defined and a Conceptual Framework

Science.gov (United States)

Peng, Hsinyi; Su, Yi-Ju; Chou, Chien; Tsai, Chin-Chung

2009-01-01

Emerging from recent mobile technologies, mobile learning, or m-learning, is beginning to offer "stunning new technical capabilities" in education (DiGiano et al., 2003). This new genre of learning is viewed as a revolutionary stage in educational technology. However, ubiquitous computing technologies have given rise to several issues. This…

Improved linearity in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistors with nonlinear polarization dielectric

International Nuclear Information System (INIS)

Gao, Tao; Xu, Ruimin; Kong, Yuechan; Zhou, Jianjun; Kong, Cen; Dong, Xun; Chen, Tangsheng

2015-01-01

We demonstrate highly improved linearity in a nonlinear ferroelectric of Pb(Zr 0.52 Ti 0.48 )-gated AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). Distinct double-hump feature in the transconductance-gate voltage (g m -V g ) curve is observed, yielding remarkable enhancement in gate voltage swing as compared to MIS-HEMT with conventional linear gate dielectric. By incorporating the ferroelectric polarization into a self-consistent calculation, it is disclosed that in addition to the common hump corresponding to the onset of electron accumulation, the second hump at high current level is originated from the nonlinear polar nature of ferroelectric, which enhances the gate capacitance by increasing equivalent dielectric constant nonlinearly. This work paves a way for design of high linearity GaN MIS-HEMT by exploiting the nonlinear properties of dielectric

Optimasi Naive Bayes Dengan Pemilihan Fitur Dan Pembobotan Gain Ratio

Directory of Open Access Journals (Sweden)

I Guna Adi Socrates

2016-03-01

Full Text Available Naïve Bayes merupakan salah satu metode data mining yang umum digunakan dalam klasifikasi dokumen berbasis text. Kelebihan dari metode ini adalah algoritma yang sederhana dengan  kompleksitas  perhitungan  yang  rendah.  Akan  tetapi,  pada  metode  Naïve  Bayes terdapat kelemahan dimana sifat independensi dari fitur Naïve Bayes tidak dapat selalu diterapkan sehingga akan berpengaruh pada tingkat akurasi perhitungan. Maka dari itu, metode Naïve Bayes perlu dioptimasi dengan cara pemberian bobot mengunakan Gain Ratio. Namun, pemberian bobot pada Naïve Bayes menimbulkan permasalahan pada penghitungan probabilitas setiap    dokumen, dimana fitur  yang tidak  merepresentasikan kelas  yang diuji banyak muncul sehingga terjadi kesalahan klasifikasi. Oleh karena itu, pembobotan Naïve Bayes   masih   belum   optimal.   Paper   ini mengusulkan  optimasi  metode   Naïve   Bayes mengunakan pembobotan Gain Ratio yang ditambahkan dengan metode pemilihan fitur pada kasus klasifikasi teks. Hasil penelitian ini menunjukkan bahwa optimasi metode Naïve Bayes menggunakan pemilihan fitur dan pembobotan menghasilkan akurasi sebesar 94%.

Illumination modelling of a mobile device environment for effective use in driving mobile apps

Science.gov (United States)

Marhoubi, Asmaa H.; Saravi, Sara; Edirisinghe, Eran A.; Bez, Helmut E.

2015-05-01

The present generation of Ambient Light Sensors (ALS) of a mobile handheld device suffer from two practical shortcomings. The ALSs are narrow angle, i.e. they respond effectively only within a narrow angle of operation and there is a latency of operation. As a result mobile applications that operate based on the ALS readings could perform sub-optimally especially when operated in environments with non-uniform illumination. The applications will either adopt with unacceptable levels of latency or/and may demonstrate a discrete nature of operation. In this paper we propose a framework to predict the ambient illumination of an environment in which a mobile device is present. The predictions are based on an illumination model that is developed based on a small number of readings taken during an application calibration stage. We use a machine learning based approach in developing the models. Five different regression models were developed, implemented and compared based on Polynomial, Gaussian, Sum of Sine, Fourier and Smoothing Spline functions. Approaches to remove noisy data, missing values and outliers were used prior to the modelling stage to remove their negative effects on modelling. The prediction accuracy for all models were found to be above 0.99 when measured using R-Squared test with the best performance being from Smoothing Spline. In this paper we will discuss mathematical complexity of each model and investigate how to make compromises in finding the best model.

GaN-on-silicon high-electron-mobility transistor technology with ultra-low leakage up to 3000 V using local substrate removal and AlN ultra-wide bandgap

Science.gov (United States)

Dogmus, Ezgi; Zegaoui, Malek; Medjdoub, Farid

2018-03-01

We report on extremely low off-state leakage current in AlGaN/GaN-on-silicon metal–insulator–semiconductor high-electron-mobility transistors (MISHEMTs) up to a high blocking voltage. Remarkably low off-state gate and drain leakage currents below 1 µA/mm up to 3 kV have been achieved owing to the use of a thick in situ SiN gate dielectric under the gate, and a local Si substrate removal technique combined with a cost effective 15-µm-thick AlN dielectric layer followed by a Cu deposition. This result establishes a manufacturable state-of-the-art high-voltage GaN-on-silicon power transistors while maintaining a low specific on-resistance of approximately 10 mΩ·cm2.

Recent results from Daya Bay

Directory of Open Access Journals (Sweden)

Chua Ming-chung

2016-01-01

Full Text Available Utilizing powerful nuclear reactors as antineutrino sources, high mountains to provide ample shielding from cosmic rays in the vicinity, and functionally identical detectors with large target volume for near-far relative measurement, the Daya Bay Reactor Neutrino Experiment has achieved unprecedented precision in measuring the neutrino mixing angle θ13 and the neutrino mass squared difference |Δm2ee|. I will report the latest Daya Bay results on neutrino oscillations and light sterile neutrino search.

77 FR 30443 - Safety Zone; Alexandria Bay Chamber of Commerce, St. Lawrence River, Alexandria Bay, NY

Science.gov (United States)

2012-05-23

...The Coast Guard proposes to establish a temporary safety zone on the St. Lawrence River, Alexandria Bay, NY. This proposed rule is intended to restrict vessels from a portion of the St. Lawrence River during the Alexandria Bay Chamber of Commerce fireworks display. The safety zone established by this proposed rule is necessary to protect spectators and vessels from the hazards associated with a fireworks display.

Holocene evolution of Apalachicola Bay, Florida

Science.gov (United States)

Osterman, L.E.; Twichell, D.C.; Poore, R.Z.

2009-01-01

A program of geophysical mapping and vibracoring was conducted to better understand the geologic evolution of Apalachicola Bay. Analyses of the geophysical data and sediment cores along with age control provided by 34 AMS 14C dates on marine shells and wood reveal the following history. As sea level rose in the early Holocene, fluvial deposits filled the Apalachicola River paleochannel, which extended southward under the central part of the bay and seaward across the continental shelf. Sediments to either side of the paleochannel contain abundant wood fragments, with dates documenting that those areas were forested at 8,000 14C years b.p. As sea level continued to rise, spits formed of headland prodelta deposits. Between ???6,400 and ???2,500 14C years b.p., an Apalachicola prodelta prograded and receded several times across the inner shelf that underlies the western part of the bay. An eastern deltaic lobe was active for a shorter time, between ???5,800 and 5,100 14C years b.p. Estuarine benthic foraminiferal assemblages occurred in the western bay as early as 6,400 14C years b.p., and indicate that there was some physical barrier to open-ocean circulation and shelf species established by that time. It is considered that shoals formed in the region of the present barrier islands as the rising sea flooded an interstream divide. Estuarine conditions were established very early in the post-glacial flooding of the bay. ?? 2009 US Government.

Long-term morphologic evolution of the Hangzhou Bay, China

Science.gov (United States)

Wen, W.; Zhijun, D.; Hualiang, X.

2013-12-01

Estuaries are the most productive ecosystems of coastal zones in the world, which are significant to mankind as places of navigation, recreation and commerce as well as extensive and diverse habitats for wildlife. However, most estuary environments in the world had occurred greatly changes in recent decades. These estuaries have suffered from impacts of forcing factors including wave climate, mean sea level change and storm surge, especial to the intensive human activities such as training wall construction, channel dredging, sand mining and dam constructions. Thus, there have been increasing concerns about estuary environment changes under effects of different factors. Riverine loads into the Changjiang Estuary have declined dramatically with the construction of Three Gorges Dam (TGD) in 2003. The morphological evolution of the Hangzhou bay that located the southern proximity of the Yangtze estuary starts to attract increasing attentions due to most material of the Hangzhou bay received from Yangtze estuary. In this paper, historical bathymetric charts were digitized and analyzed within a GIS to provide quantitative estimate of changes in volumes in different regions below 0 m elevation. The results show that Hangzhou bay has experienced a major loss in estuarine volume of about 15% with annual mean sediment deposition rate of 80 million m3/a during the last 75 years. However, there is a large-scale spatial adjustment in Hangzhou bay: Bathymetric changes of the Hangzhou bay can be rapidly shifted within the range of 8-10 classes. Volume of the Jinshanzui upstream of the Hangzhou bay has obviously decreased in the last 75 years, especially during 2003-2008. However, Volume of the southern Hangzhou bay has experienced slowly decrease with minor deposition. The northern Hangzhou bay had largely volume changes with rapidly decrease during 1931-1981, and drastically increase since 2003. Further analysis of the bathymetric data relating to possible factors indicates

Building the city with emphasis on urban mobility – examples from USA

Directory of Open Access Journals (Sweden)

Mojca Šašek Divjak

2002-01-01

Full Text Available In the last decades developed countries have tried to improve and strengthen public transport modes in urban regions, because they have established negative effects of car traffic on mobility: bottlenecks, increased investment in road infrastructure. New movements that have emerged in the nineties in USA, often coined as smart growth, emphasise efficient urban growth, which should be tied to public transport enabling rational prices of infrastructure and better spatial use. Good examples of such developments are shown, such as the San Francisco Bay area (California, Portland (Oregon and Salt Lake (Utah.

Effect of OFF-state stress induced electric field on trapping in AlGaN/GaN high electron mobility transistors on Si (111)

International Nuclear Information System (INIS)

Anand, M. J.; Ng, G. I.; Syamal, B.; Zhou, X.; Arulkumaran, S.; Manoj Kumar, C. M.; Ranjan, K.; Vicknesh, S.; Foo, S. C.

2015-01-01

The influence of electric field (EF) on the dynamic ON-resistance (dyn-R DS[ON] ) and threshold-voltage shift (ΔV th ) of AlGaN/GaN high electron mobility transistors on Si has been investigated using pulsed current-voltage (I DS -V DS ) and drain current (I D ) transients. Different EF was realized with devices of different gate-drain spacing (L gd ) under the same OFF-state stress. Under high-EF (L gd  = 2 μm), the devices exhibited higher dyn-R DS[ON] degradation but a small ΔV th (∼120 mV). However, at low-EF (L gd  = 5 μm), smaller dyn-R DS[ON] degradation but a larger ΔV th (∼380 mV) was observed. Our analysis shows that under OFF-state stress, the gate electrons are injected and trapped in the AlGaN barrier by tunnelling-assisted Poole-Frenkel conduction mechanism. Under high-EF, trapping spreads towards the gate-drain access region of the AlGaN barrier causing dyn-R DS[ON] degradation, whereas under low-EF, trapping is mostly confined under the gate causing ΔV th . A trap with activation energy 0.33 eV was identified in the AlGaN barrier by I D -transient measurements. The influence of EF on trapping was also verified by Silvaco TCAD simulations

Parameter Identification by Bayes Decision and Neural Networks

DEFF Research Database (Denmark)

Kulczycki, P.; Schiøler, Henrik

1994-01-01

The problem of parameter identification by Bayes point estimation using neural networks is investigated.......The problem of parameter identification by Bayes point estimation using neural networks is investigated....

Chesapeake Bay baseline data acquisition, toxics in the Chesapeake Bay. Final preliminary report, 1946-78

International Nuclear Information System (INIS)

1978-07-01

This report identifies researchers, research activities, and data files applicable to the Chesapeake Bay estuarine system. The identified data were generated after 1973 on the following: submerged aquatic vegetation, shellfish bed closures, eutrophication, toxics accumulation in the food chain, dredging and spoil disposal, hydrologic modifications, modification of fisheries, shoreline erosion, wetlands alterations, and the effects of boating and shipping on water quality. Major past and current program monitoring in the Bay and its tributaries are summarized according to frequency

Learning and Teaching with Mobile Devices: An Approach in Higher Secondary Education in Ghana

Science.gov (United States)

Grimus, Margarete; Ebner, Martin

2015-01-01

While many developing nations find Internet-based e-learning unsuitable for their needs mobile learning methods--specifically those involving the use of mobile-phones for both formal and informal learning--hold great promise for them (Grimus et al, 2013b). In this paper chances and challenges introduced by mobile devices to support improvement and…

Investigation of enhancement-mode AlGaN/GaN nanowire channel high-electron-mobility transistor with oxygen-containing plasma treatment

Science.gov (United States)

He, Yunlong; Wang, Chong; Mi, Minhan; Zhang, Meng; Zhu, Qing; Zhang, Peng; Wu, Ji; Zhang, Hengshuang; Zheng, Xuefeng; Yang, Ling; Duan, Xiaoling; Ma, Xiaohua; Hao, Yue

2017-05-01

A novel enhancement-mode (E-mode) AlGaN/GaN high-electron-mobility transistor (HEMT) has been fabricated, by combining nanowire channel (NC) structure fabrication and N2O (or O2) plasma treatment. A comparison of two NC-HEMTs with different plasma treatments has been made. The NC-HEMT with N2O plasma treatment shows an output current of 610 mA/mm and a peak transconductance of 450 mS/mm. The DIBL of the NC-HEMT with N2O plasma treatment is as low as 2 mV/V, and an SS of 70 mV/decade is achieved. The device exhibits an intrinsic current gain cutoff frequency f T of 19 GHz and a maximum oscillation frequency f max of 58 GHz.

Wind-Driven Waves in Tampa Bay, Florida

Science.gov (United States)

Gilbert, S. A.; Meyers, S. D.; Luther, M. E.

2002-12-01

Turbidity and nutrient flux due to sediment resuspension by waves and currents are important factors controlling water quality in Tampa Bay. During December 2001 and January 2002, four Sea Bird Electronics SeaGauge wave and tide recorders were deployed in Tampa Bay in each major bay segment. Since May 2002, a SeaGauge has been continuously deployed at a site in middle Tampa Bay as a component of the Bay Regional Atmospheric Chemistry Experiment (BRACE). Initial results for the summer 2002 data indicate that significant wave height is linearly dependent on wind speed and direction over a range of 1 to 12 m/s. The data were divided into four groups according to wind direction. Wave height dependence on wind speed was examined for each group. Both northeasterly and southwesterly winds force significant wave heights that are about 30% larger than those for northwesterly and southeasterly winds. This difference is explained by variations in fetch due to basin shape. Comparisons are made between these observations and the results of a SWAN-based model of Tampa Bay. The SWAN wave model is coupled to a three-dimensional circulation model and computes wave spectra at each model grid cell under observed wind conditions and modeled water velocity. When SWAN is run without dissipation, the model results are generally similar in wave period but about 25%-50% higher in significant wave height than the observations. The impact of various dissipation mechanisms such as bottom drag and whitecapping on the wave state is being investigated. Preliminary analyses on winter data give similar results.

Epitaxial ZnO gate dielectrics deposited by RF sputter for AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors

Science.gov (United States)

Yoon, Seonno; Lee, Seungmin; Kim, Hyun-Seop; Cha, Ho-Young; Lee, Hi-Deok; Oh, Jungwoo

2018-01-01

Radio frequency (RF)-sputtered ZnO gate dielectrics for AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs) were investigated with varying O2/Ar ratios. The ZnO deposited with a low oxygen content of 4.5% showed a high dielectric constant and low interface trap density due to the compensation of oxygen vacancies during the sputtering process. The good capacitance-voltage characteristics of ZnO-on-AlGaN/GaN capacitors resulted from the high crystallinity of oxide at the interface, as investigated by x-ray diffraction and high-resolution transmission electron microscopy. The MOS-HEMTs demonstrated comparable output electrical characteristics with conventional Ni/Au HEMTs but a lower gate leakage current. At a gate voltage of -20 V, the typical gate leakage current for a MOS-HEMT with a gate length of 6 μm and width of 100 μm was found to be as low as 8.2 × 10-7 mA mm-1, which was three orders lower than that of the Ni/Au Schottky gate HEMT. The reduction of the gate leakage current improved the on/off current ratio by three orders of magnitude. These results indicate that RF-sputtered ZnO with a low O2/Ar ratio is a good gate dielectric for high-performance AlGaN/GaN MOS-HEMTs.

Heavy metal burden in coastal marine sediments of north west coast of India in relation to pollution

Digital Repository Service at National Institute of Oceanography (India)

Rokade, M.A.

the concentrations of potentially toxic metals (Flegal and Wilhelmy, 1991; Hornberger et al., 1999). 6 Between 1850 and 1900 most of the Hg mining in the world occurred in the watershed of the San Francisco Bay. Hydraulic mining for gold mobilized sediments... to the ocean bottom water (about 0.2 8 μg/l). When anoxic diagenesis takes over, reduction of Fe also occurs with high levels of both the metals in pore waters. Several trace metals that are bound to particle surfaces are also mobilized with Mn and Fe...

Occurrence of the Spotted Sea Hare Aplysia dactylomela (Rang 1828, Aplysiidae in the Yeşilovacık Bay, Norteastern Mediterranean Coast of Turkey

Directory of Open Access Journals (Sweden)

Deniz Ayas

2017-10-01

Full Text Available The first record of the A. dactylomela from the Mediterranean Sea, in the Strait of Sicily waters was reported in 2002 (Trainito, 2003. Some reports of the A. dactylomela are given in the Mediterranean Sea in Table 1. A specimen of spotted sea hare was seen in a rock pool which was covered with algea. It was first recorded from Yeşilovacık Bay in 2017. Previous record of the species was noted in the Hatay coast of Turkey (Çinar et al. 2006. The present rapid communication reported the first record of A. dactylomela from the Yeşilovacık Bay. One specimen of A. dactylomela was photographed at the infralittoral zone of the Bay on 26 March, 2017, at a depth of 1 m in a rock pool togetter with Padina pavonica (Linnaeus and other algea.

Modeling plug-in electric vehicle charging demand with BEAM: the framework for behavior energy autonomy mobility

Energy Technology Data Exchange (ETDEWEB)

Sheppard, Colin; Waraich, Rashid; Campbell, Andrew; Pozdnukov, Alexei; Gopal, Anand R.

2017-05-01

This report summarizes the BEAM modeling framework (Behavior, Energy, Mobility, and Autonomy) and its application to simulating plug-in electric vehicle (PEV) mobility, energy consumption, and spatiotemporal charging demand. BEAM is an agent-based model of PEV mobility and charging behavior designed as an extension to MATSim (the Multi-Agent Transportation Simulation model). We apply BEAM to the San Francisco Bay Area and conduct a preliminary calibration and validation of its prediction of charging load based on observed charging infrastructure utilization for the region in 2016. We then explore the impact of a variety of common modeling assumptions in the literature regarding charging infrastructure availability and driver behavior. We find that accurately reproducing observed charging patterns requires an explicit representation of spatially disaggregated charging infrastructure as well as a more nuanced model of the decision to charge that balances tradeoffs people make with regards to time, cost, convenience, and range anxiety.

Mesozooplankton production, grazing and respiration in the Bay of Bengal: Implications for net heterotrophy

Science.gov (United States)

Fernandes, Veronica; Ramaiah, N.

2016-03-01

Mesozooplankton samples were collected from the mixed layer along a central (along 88°E) and a western transect in the Bay of Bengal during four seasons covered between 2001 and 2006 in order to investigate spatio-temporal variability in their biomass. At these stations, grazing and respiration rates were measured from live zooplankton hauled in from the surface during December 2005. Akin to the mesozooplankton "paradox" in the central and eastern Arabian Sea, biomass in the mixed layer was more or less invariant in the central and western Bay of Bengal, even as the chl a showed marginal temporal variation. By empirical equation, the mesozooplankton production rate calculated to be 70-246 mg C m- 2 d- 1 is on par with the Arabian Sea. Contrary to the conventional belief, mesozooplankton grazing impact was up to 83% on primary production (PP). Low PP coupled with very high zooplankton production (70% of PP) along with abundant bacterial production (50% of the PP; Ramaiah et al., 2009) is likely to render the Bay of Bengal net heterotrophic, especially during the spring intermonsoon. Greater estimates of fecal pellet-carbon egestion by mesozooplankton compared to the average particulate organic carbon flux in sediment traps, implies that much of the matter is recycled by heterotrophic communities in the mixed layer facilitating nutrient regeneration for phytoplankton growth. We also calculated that over a third of the primary production is channelized for basin-wide zooplankton respiration that accounts for 52 Mt C annually. In the current scenario of global warming, if low (primary) productive warm pools like the Bay of Bengal continue to be net heterotrophic, negative implications like enhanced emission of CO2 to the atmosphere, increased particulate flux to the deeper waters and greater utilization of dissolved oxygen resulting in expansion of the existing oxygen minimum zone are imminent.

Sorption and bioreduction of hexavalent uranium at a military facility by the Chesapeake Bay

International Nuclear Information System (INIS)

Dong Wenming; Xie Guibo; Miller, Todd R.; Franklin, Mark P.; Oxenberg, Tanya Palmateer; Bouwer, Edward J.; Ball, William P.; Halden, Rolf U.

2006-01-01

Directly adjacent to the Chesapeake Bay lies the Aberdeen Proving Ground, a U.S. Army facility where testing of armor-piercing ammunitions has resulted in the deposition of >70,000 kg of depleted uranium (DU) to local soils and sediments. Results of previous environmental monitoring suggested limited mobilization in the impact area and no transport of DU into the nation's largest estuary. To determine if physical and biological reactions constitute mechanisms involved in limiting contaminant transport, the sorption and biotransformation behavior of the radionuclide was studied using geochemical modeling and laboratory microcosms (500 ppb U(VI) initially). An immediate decline in dissolved U(VI) concentrations was observed under both sterile and non-sterile conditions due to rapid association of U(VI) with natural organic matter in the sediment. Reduction of U(VI) to U(IV) occurred only in non-sterile microcosms. In the non-sterile samples, intrinsic bioreduction of uranium involved bacteria of the order Clostridiales and was only moderately enhanced by the addition of acetate (41% vs. 56% in 121 days). Overall, this study demonstrates that the migration of depleted uranium from the APG site into the Chesapeake Bay may be limited by a combination of processes that include rapid sorption of U(VI) species to natural organic matter, followed by slow, intrinsic bioreduction to U(IV). - At the Aberdeen Proving Ground in Maryland, USA, migration of depleted uranium into the Chesapeake Bay is limited by rapid sorption of the radionuclide to natural organic matter followed by slow biological reduction of water-soluble U(VI) to the insoluble and less toxic U(IV) species

Physical and electrical characteristics of AlGaN/GaN metal-oxide-semiconductor high-electron-mobility transistors with rare earth Er2O3 as a gate dielectric