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29 results on '"David A. Cullen"'

2. Atomically dispersed iron sites with a nitrogen–carbon coating as highly active and durable oxygen reduction catalysts for fuel cells

Author

Shengwen Liu, Chenzhao Li, Michael J. Zachman, Yachao Zeng, Haoran Yu, Boyang Li, Maoyu Wang, Jonathan Braaten, Jiawei Liu, Harry M. Meyer, Marcos Lucero, A. Jeremy Kropf, E. Ercan Alp, Qing Gong, Qiurong Shi, Zhenxing Feng, Hui Xu, Guofeng Wang, Deborah J. Myers, Jian Xie, David A. Cullen, Shawn Litster, and Gang Wu

Subjects
Fuel Technology, Renewable Energy, Sustainability and the Environment, Energy Engineering and Power Technology, Electronic, Optical and Magnetic Materials
Published
2022

3. Unveiling mechanism of surface-guided platinum nanowire growth

Author

Zhiqiang Xie, Shule Yu, Can Cui, Haoran Yu, Kui Li, Lei Ding, Weitian Wang, David A. Cullen, Harry M. Meyer, Jefferey S. Baxter, Pu-Xian Gao, and Feng-Yuan Zhang

Subjects
Mechanics of Materials, Mechanical Engineering, General Materials Science
Published
2022

4. Grooved electrodes for high-power-density fuel cells

Author

ChungHyuk Lee, Wilton J. M. Kort-Kamp, Haoran Yu, David A. Cullen, Brian M. Patterson, Tanvir Alam Arman, Siddharth Komini Babu, Rangachary Mukundan, Rod L. Borup, and Jacob S. Spendelow

Subjects
Fuel Technology, Renewable Energy, Sustainability and the Environment, Energy Engineering and Power Technology, Electronic, Optical and Magnetic Materials
Published
2023

5. Efficient conversion of low-concentration nitrate sources into ammonia on a Ru-dispersed Cu nanowire electrocatalyst

Author

Feng-Yang Chen, Zhen-Yu Wu, Srishti Gupta, Daniel J. Rivera, Sten V. Lambeets, Stephanie Pecaut, Jung Yoon Timothy Kim, Peng Zhu, Y. Zou Finfrock, Debora Motta Meira, Graham King, Guanhui Gao, Wenqian Xu, David A. Cullen, Hua Zhou, Yimo Han, Daniel E. Perea, Christopher L. Muhich, and Haotian Wang

Subjects
Nitrates, Ammonia, Nanowires, Biomedical Engineering, General Materials Science, Bioengineering, Wastewater, Electrical and Electronic Engineering, Condensed Matter Physics, Atomic and Molecular Physics, and Optics, Water Purification
Abstract

Electrochemically converting nitrate ions, a widely distributed nitrogen source in industrial wastewater and polluted groundwater, into ammonia represents a sustainable route for both wastewater treatment and ammonia generation. However, it is currently hindered by low catalytic activities, especially under low nitrate concentrations. Here we report a high-performance Ru-dispersed Cu nanowire catalyst that delivers an industrial-relevant nitrate reduction current of 1 A cm

Published
2022

8. 20%-efficient polycrystalline Cd(Se,Te) thin-film solar cells with compositional gradient near the front junction

Author

Deng-Bing Li, Sandip S. Bista, Rasha A. Awni, Sabin Neupane, Abasi Abudulimu, Xiaoming Wang, Kamala K. Subedi, Manoj K. Jamarkattel, Adam B. Phillips, Michael J. Heben, Jonathan D. Poplawsky, David A. Cullen, Randy J. Ellingson, and Yanfa Yan

Subjects
Multidisciplinary, General Physics and Astronomy, General Chemistry, General Biochemistry, Genetics and Molecular Biology
Abstract

Bandgap gradient is a proven approach for improving the open-circuit voltages (VOCs) in Cu(In,Ga)Se2 and Cu(Zn,Sn)Se2 thin-film solar cells, but has not been realized in Cd(Se,Te) thin-film solar cells, a leading thin-film solar cell technology in the photovoltaic market. Here, we demonstrate the realization of a bandgap gradient in Cd(Se,Te) thin-film solar cells by introducing a Cd(O,S,Se,Te) region with the same crystal structure of the absorber near the front junction. The formation of such a region is enabled by incorporating oxygenated CdS and CdSe layers. We show that the introduction of the bandgap gradient reduces the hole density in the front junction region and introduces a small spike in the band alignment between this and the absorber regions, effectively suppressing the nonradiative recombination therein and leading to improved VOCs in Cd(Se,Te) solar cells using commercial SnO2 buffers. A champion device achieves an efficiency of 20.03% with a VOC of 0.863 V.

Published
2022

9. General synthesis of single-atom catalysts with high metal loading using graphene quantum dots

Author

Dongxing Zheng, Graham King, Chuan Xia, Peng Li, Husam N. Alshareef, Emilio Heredia, David A. Cullen, Peng Zhu, Haotian Wang, Peixin Cui, Xiao Zhang, Yunrui Qiu, Jung Yoon Timothy Kim, Zhen-Yu Wu, Yang Xia, Yongfeng Hu, and Mohsen Shakouri

Subjects
General method, 010405 organic chemistry, Graphene, Chemistry, General Chemical Engineering, Inorganic chemistry, General Chemistry, Carbon matrix, 010402 general chemistry, Electrochemistry, 01 natural sciences, 0104 chemical sciences, law.invention, Catalysis, Metal, law, Quantum dot, visual_art, Atom, visual_art.visual_art_medium
Abstract

Transition-metal single-atom catalysts present extraordinary activity per metal atomic site, but suffer from low metal-atom densities (typically less than 5 wt% or 1 at.%), which limits their overall catalytic performance. Here we report a general method for the synthesis of single-atom catalysts with high transition-metal-atom loadings of up to 40 wt% or 3.8 at.%, representing several-fold improvements compared to benchmarks in the literature. Graphene quantum dots, later interweaved into a carbon matrix, were used as a support, providing numerous anchoring sites and thus facilitating the generation of high densities of transition-metal atoms with sufficient spacing between the metal atoms to avoid aggregation. A significant increase in activity in electrochemical CO2 reduction (used as a representative reaction) was demonstrated on a Ni single-atom catalyst with increased Ni loading. Transition-metal single-atom catalysts display excellent activity per metal atom site, but suffer from low metal atom densities (typically less than 5 wt% or 1 at.%), which limits their overall catalytic performance. Now, the use of a graphene-quantum-dot primary support, later interweaved into a carbon matrix, has enabled the synthesis of single-atom catalysts with high transition-metal atom loadings of up to 40 wt% or 3.84 at.%.

Published
2021

10. Chemical vapour deposition of Fe–N–C oxygen reduction catalysts with full utilization of dense Fe–N4 sites

Author

Moulay Tahar Sougrati, Deborah J. Myers, Qingying Jia, Sichen Zhong, Jingkun Li, Magali Ferrandon, Fan Yang, Yu Huang, Sanjeev Mukerjee, Li Jiao, Qiang Sun, Ershuai Liu, Thomas Stracensky, David A. Cullen, Hui Xu, Jaehyung Park, Frédéric Jaouen, Lynne Larochelle Richard, Zipeng Zhao, Northeastern University [Boston], Institut Charles Gerhardt Montpellier - Institut de Chimie Moléculaire et des Matériaux de Montpellier (ICGM ICMMM), Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM)-Centre National de la Recherche Scientifique (CNRS)-Université de Montpellier (UM)-Université Montpellier 1 (UM1)-Université Montpellier 2 - Sciences et Techniques (UM2)-Institut de Chimie du CNRS (INC), and Argonne National Laboratory [Lemont] (ANL)

Subjects
Inorganic chemistry, chemistry.chemical_element, Proton exchange membrane fuel cell, 02 engineering and technology, Chemical vapor deposition, 010402 general chemistry, 01 natural sciences, Redox, Catalysis, General Materials Science, biology, Mechanical Engineering, Substrate (chemistry), Active site, [CHIM.MATE]Chemical Sciences/Material chemistry, [CHIM.CATA]Chemical Sciences/Catalysis, General Chemistry, 021001 nanoscience & nanotechnology, Condensed Matter Physics, Oxygen reduction, 0104 chemical sciences, chemistry, Mechanics of Materials, biology.protein, 0210 nano-technology, Platinum
Abstract

Replacing scarce and expensive platinum (Pt) with metal–nitrogen–carbon (M–N–C) catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells has largely been impeded by the low oxygen reduction reaction activity of M–N–C due to low active site density and site utilization. Herein, we overcome these limits by implementing chemical vapour deposition to synthesize Fe–N–C by flowing iron chloride vapour over a Zn–N–C substrate at 750 °C, leading to high-temperature trans-metalation of Zn–N4 sites into Fe–N4 sites. Characterization by multiple techniques shows that all Fe–N4 sites formed via this approach are gas-phase and electrochemically accessible. As a result, the Fe–N–C catalyst has an active site density of 1.92 × 1020 sites per gram with 100% site utilization. This catalyst delivers an unprecedented oxygen reduction reaction activity of 33 mA cm−2 at 0.90 V (iR-corrected; i, current; R, resistance) in a H2–O2 proton exchange membrane fuel cell at 1.0 bar and 80 °C. Replacing platinum with metal–nitrogen–carbon catalysts for the oxygen reduction reaction in proton exchange membrane fuel cells has been impeded by low activity. These limitations have now been overcome by the trans-metalation of Zn–N4 sites into Fe–N4 sites.

Published
2021

11. Author Correction: P-block single-metal-site tin/nitrogen-doped carbon fuel cell cathode catalyst for oxygen reduction reaction

Author

Fang Luo, Aaron Roy, Luca Silvioli, David A. Cullen, Andrea Zitolo, Moulay Tahar Sougrati, Ismail Can Oguz, Tzonka Mineva, Detre Teschner, Stephan Wagner, Ju Wen, Fabio Dionigi, Ulrike I. Kramm, Jan Rossmeisl, Frédéric Jaouen, and Peter Strasser

Subjects
Mechanics of Materials, Mechanical Engineering, General Materials Science, General Chemistry, Condensed Matter Physics
Published
2022

12. Atomically dispersed manganese catalysts for oxygen reduction in proton-exchange membrane fuel cells

Author

Maoyu Wang, Chao Lei, Sooyeon Hwang, Zhen-Bo Wang, David A. Cullen, Hanguang Zhang, Dong Su, Marcos Lucero, Kexi Liu, Karren L. More, Jiazhan Li, Guofeng Wang, Stavros Karakalos, Boyang Li, Hui Xu, Gang Wu, Mengjie Chen, George E. Sterbinsky, and Zhenxing Feng

Subjects
inorganic chemicals, Process Chemistry and Technology, chemistry.chemical_element, Proton exchange membrane fuel cell, Bioengineering, 02 engineering and technology, Manganese, 010402 general chemistry, 021001 nanoscience & nanotechnology, 01 natural sciences, Biochemistry, Catalysis, 0104 chemical sciences, Metal, Membrane, chemistry, Chemical engineering, visual_art, visual_art.visual_art_medium, Reversible hydrogen electrode, 0210 nano-technology, Dispersion (chemistry), Carbon
Abstract

Platinum group metal (PGM)-free catalysts that are also iron free are highly desirable for the oxygen reduction reaction (ORR) in proton-exchange membrane fuel cells, as they avoid possible Fenton reactions. Here we report an efficient ORR catalyst that consists of atomically dispersed nitrogen-coordinated single Mn sites on partially graphitic carbon (Mn-N-C). Evidence for the embedding of the atomically dispersed MnN4 moieties within the carbon surface-exposed basal planes was established by X-ray absorption spectroscopy and their dispersion was confirmed by aberration-corrected electron microscopy with atomic resolution. The Mn-N-C catalyst exhibited a half-wave potential of 0.80 V versus the reversible hydrogen electrode, approaching that of Fe-N-C catalysts, along with significantly enhanced stability in acidic media. The encouraging performance of the Mn-N-C catalyst as a PGM-free cathode was demonstrated in fuel cell tests. First-principles calculations further support the MnN4 sites as the origin of the ORR activity via a 4e− pathway in acidic media. Platinum group metal- and iron-free catalysts are highly desirable for the oxygen reduction reaction in proton-exchange membrane fuel cells. Now, Wu and co-workers show a carbon catalyst with atomically dispersed single Mn sites as an efficient catalyst with enhanced stability in acidic media.

Published
2018

13. Improved electrochemical cycling stability of intercalation battery electrodes via control of material morphology

Author

Karren L. More, Mallory Clites, David A. Cullen, Bryan W. Byles, and Ekaterina Pomerantseva

Subjects
Nanostructure, Materials science, General Chemical Engineering, Intercalation (chemistry), General Engineering, Nanowire, General Physics and Astronomy, 02 engineering and technology, Crystal structure, Electrolyte, 010402 general chemistry, 021001 nanoscience & nanotechnology, Electrochemistry, 01 natural sciences, 0104 chemical sciences, Chemical engineering, Electrode, General Materials Science, 0210 nano-technology, Contact area
Abstract

Using a model tunnel manganese oxide with the todorokite crystal structure (T-MnO2), we demonstrate that controlling the morphology of the active material can improve the cycling stability of intercalation battery electrodes. The T-MnO2 structure is built from tunnels that provide spacious 1D diffusion channels for charge-carrying ions. Taking advantage of the unique ability to synthesize T-MnO2 in the form of both highly crystalline two-dimensional (2D) nanoplatelets and one-dimensional (1D) nanowires through a facile hydrothermal growth method, we investigated the effect of nanoscale particle dimensions on reversible battery cycling. Insertion of ions into the tunnels results in anisotropic expansion of the structure, making T-MnO2 with different morphologies an excellent model platform to understand how intercalation-induced volume change, typically leading to the deterioration of the electrode performance over extended cycling, can be controlled through synthesis of targeted morphologies. T-MnO2 nanowires showed not only significantly improved capacity retention but also substantially higher specific capacity than the T-MnO2 nanoplatelets. The enhanced electrochemical properties of the nanowire electrodes could be attributed to the larger surface-to-volume ratio than that of nanoplatelets, resulting in higher contact area with electrolyte for the nanowires. Moreover, due to the smaller cross-sectional area of the nanowires, volume expansion and contraction perpendicular to the structural tunnels induced by reversible ion intercalation occurs in a more facile fashion. This work shows that chemically controlling morphology and producing particles with nanostructure dimensionality replicating that of atomic structure (i.e., 1D morphology and 1D structure) makes it possible to enhance material performance.

Published
2018

14. Geometry-Induced Spatial Variation of Microstructure Evolution During Selective Electron Beam Melting of Rene-N5

Author

David A. Cullen, Michael M. Kirka, Edwin J. Schwalbach, Austin Staub, Curtis Lee Frederick, S. Suresh Babu, Michael Haines, and Alex Plotkowski

Subjects
010302 applied physics, Materials science, Structural material, Precipitation (chemistry), Alloy, Metals and Alloys, chemistry.chemical_element, Geometry, 02 engineering and technology, Welding, engineering.material, 021001 nanoscience & nanotechnology, Condensed Matter Physics, Microstructure, 01 natural sciences, law.invention, Nickel, Cracking, chemistry, Mechanics of Materials, law, 0103 physical sciences, Heat transfer, engineering, 0210 nano-technology
Abstract

High gamma prime (γ′) nickel-based alloys produced by selective electron beam melting are of interest to the turbine industry which requires control of microstructure in relation to loading conditions within complex component geometry. Welding literature predicts cracking and microstructure evolution as a function of alloy composition and process parameters in this class of alloys. In addition, Additive manufacturing causes variations in the above conditions due to the interaction of geometry on processing and heat transfer. The influence of geometry on processing conditions was explored for alloy Rene N5 by characterizing the solidification grain microstructure and solid-state precipitation. A Semi-Analytical Heat Transfer Model was employed to explain the resulting variation in solidification grain morphology that occurred due to the part geometry. The as-built precipitation structure was found to vary as a function of build height and had no correlation to the solidification grain structure or the layer geometry.

Published
2018

15. Characterization of Al-Mg Alloy Aged at Low Temperatures

Author

Kenneth C. Littrell, Gaosong Yi, William Golumbfskie, Erik Sundberg, David A. Cullen, and Michael L. Free

Subjects
010302 applied physics, Materials science, Metallurgy, Alloy, Metals and Alloys, 02 engineering and technology, Neutron scattering, Intergranular corrosion, engineering.material, 021001 nanoscience & nanotechnology, Condensed Matter Physics, 01 natural sciences, Mechanics of Materials, Phase (matter), 0103 physical sciences, Scanning transmission electron microscopy, engineering, Grain boundary, 0210 nano-technology, Spectroscopy, Electron backscatter diffraction
Abstract

Long-term aged [343 K (70 °C) for 30 months and natural exposure for over 10 years] Al 5456 H116 samples were characterized using electron backscatter diffraction (EBSD), scanning transmission electron microscopy (STEM), state-of-the-art energy-dispersive X-ray spectroscopy (EDS) systems, and small-angle neutron scattering (SANS). ASTM G-67 mass loss tests of the sensitized Al 5456 alloy samples were conducted. Intragranular Mg-rich precipitates, such as Guinier–Preston (GP) zones, were confirmed in Al 5456 H116 aged at 343 K (70 °C) for 30 months, and the volume of these precipitates is 1.39 pct. β′ phase is identified at the grain boundary of a navy ship sample, while high-resolution STEM results reveal no intragranular precipitates. Intergranular corrosion (IGC) of Al 5456 was found to be related to the continuity of intergranular precipitates.

Published
2017

16. Distinct photoluminescence and Raman spectroscopy signatures for identifying highly crystalline WS2 monolayers produced by different growth methods

Author

Victor Carozo, Bernd Kabius, David A. Cullen, Mauricio Terrones, Nestor Perea-Lopez, Ayse Berkdemir, Amber McCreary, Ana Laura Elías, Kazunori Fujisawa, Junjie Wang, Thomas E. Mallouk, Minh An T. Nguyen, and Jun Zhu

Subjects
Photoluminescence, Materials science, Mechanical Engineering, Nanotechnology, 02 engineering and technology, 010402 general chemistry, 021001 nanoscience & nanotechnology, Condensed Matter Physics, 01 natural sciences, 0104 chemical sciences, symbols.namesake, Crystallinity, Transition metal, Mechanics of Materials, Chemical physics, Monolayer, symbols, General Materials Science, 0210 nano-technology, Raman spectroscopy, Luminescence
Abstract

Transition metal dichalcogenides such as WS2 show exciting promise in electronic and optoelectronic applications. Significant variations in the transport, Raman, and photoluminescence (PL) can be found in the literature, yet it is rarely addressed why this is. In this report, Raman and PL of monolayered WS2 produced via different methods are studied and distinct features that indicate the degree of crystallinity of the material are observed. While the intensity of the LA(M) Raman mode is found to be a useful indicator to assess the crystallinity, PL is drastically more sensitive to the quality of the material than Raman spectroscopy. We also show that even exfoliated crystals, which are usually regarded as the most pristine material, can contain large amounts of defects that would not be apparent without Raman and PL measurements. These findings can be applied to the understanding of other two-dimensional heterostructured systems.

Published
2016

17. Evaluation of Al3Mg2 Precipitates and Mn-Rich Phase in Aluminum-Magnesium Alloy Based on Scanning Transmission Electron Microscopy Imaging

Author

Soumya Kar, Yakun Zhu, Lawrence F. Allard, Michael P Free, and David A. Cullen

Subjects
Equiaxed crystals, Materials science, Precipitation (chemistry), Metallurgy, Alloy, Metals and Alloys, Intergranular corrosion, engineering.material, Condensed Matter Physics, Mechanics of Materials, Scanning transmission electron microscopy, engineering, Grain boundary, Magnesium alloy, Dislocation
Abstract

Scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS) were used to observe intergranular and intragranular β-phase (Al3Mg2) formation and growth in as-received sample and long-term (~1 year) thermally treated samples of 5083-H131 alloy. Rod-shaped and equiaxed particles rich in Mn, Fe, and Cr were present in the as-received and heat treated samples. The β-phase precipitated along grain boundaries as well as around and between preexisting Mn-Fe-Cr rich particles. The measured thickness of β-phase along grain boundaries was lower than Zener–Hillert diffusion model predicted value and the potential reasons were theoretically analyzed. Dislocation networks, grain boundaries, and different preexisting particles were observed to contribute to Mg diffusion and β-phase precipitation.

Published
2012

18. Fuel Cells Catalyst for Start-Up and Shutdown Conditions: Electrochemical, XPS, and STEM Evaluation of Sputter-Deposited Ru, Ir, and Ti on Pt-Coated Nanostructured Thin Film Supports

Author

Gregory M. Haugen, David A. Cullen, Liliana Atanasoska, Radoslav Atanasoski, Karren L. More, and George D. Vernstrom

Subjects
X-ray photoelectron spectroscopy, chemistry, Electrolysis of water, Chemical engineering, Electrochemistry, Analytical chemistry, Proton exchange membrane fuel cell, chemistry.chemical_element, Overpotential, Thin film, Platinum, Electrode potential, Catalysis
Abstract

Minute amounts of Ru, Ir, and Ti (2 and 10 μg/cm2) sputter-deposited over 3M Pt-coated nanostructured thin film (NSTF) substrate were evaluated as oxygen evolution reaction (OER) catalysts in a polymer electrolyte membrane (PEM) environment. The purpose of the study was to explore the suitability of these elements for modifying both the anode and the cathode catalysts in order to lower the overpotential for the oxidation of water during transient conditions. By keeping the electrode potential as close as possible to the thermodynamic potential for OER, other components in the fuel cell, such as platinum, the gas diffusion layer, and the bipolar plates, will be less prone to degradation. While Ru and Ir were chosen due to their high OER activity in aqueous environment, Ti was also included due to its ability to stabilize the OER catalysts. The 3M Pt-NSTF was selected as a stable, carbon-free substrate. The surface chemistry and the morphology of OER catalysts on Pt-NSTF were examined by X-ray photoelectron spectroscopy and scanning transmission electron microscopy. The OER catalytic activity of Ru and Ir in PEMs compares well with their behavior in aqueous environment. It was found that Ru is more active than Ir, that Ir is considerably more stable, while the mass activity of both is higher in comparison with similar OER catalysts.

Published
2012

19. Exploration of Ellsworth Subglacial Lake: a concept paper on the development, organisation and execution of an experiment to explore, measure and sample the environment of a West Antarctic subglacial lake

Author

Mark A. Sephton, John C. Priscu, David C. Cullen, John Parnell, Stephen A. Bowden, Mark R. Sims, Dominic A. Hodgson, Richard C. A. Hindmarsh, Martin J. Siegert, Gary S. Wilson, Henry F. Lamb, Cynan Ellis-Evans, Hugh F. J. Corr, John Woodward, Jemma L. Wadham, David Blake, A. Ellery, Edward C. King, Charles S. Cockell, David A. Pearce, Keith Makinson, Andrés Rivera, Poul Christoffersen, Martyn Tranter, Howell G. M. Edwards, L. Lane, Andrew Smith, Michael J. Bentley, Gwyn Griffiths, A. Behar, and Matthew C. Mowlem

Subjects
Environmental Engineering, Ecology, Borehole, Climate change, Pollution, Applied Microbiology and Biotechnology, Water column, Shelf ice, Geophysical survey, Subglacial lake, Lake Vostok, Bathymetry, Physical geography, Waste Management and Disposal, Geology
Abstract

Antarctic subglacial lakes have, over the past few years, been hypothesised to house unique forms of life and hold detailed sedimentary records of past climate change. Testing this hypothesis requires in situ examinations. The direct measurement of subglacial lakes has been considered ever since the largest and best-known lake, named Lake Vostok, was identified as having a deep water-column. The Subglacial Antarctic Lake Environments (SALE) programme, set up by the Scientific Committee on Antarctic Research (SCAR) to oversee subglacial lakes research, state that prior exploration of smaller lakes would be a “prudent way forward”. Over 145 subglacial lakes are known to exist in Antarctica, but one lake in West Antarctica, officially named Ellsworth Subglacial Lake (referred to hereafter as Lake Ellsworth), stands out as a candidate for early exploration. A consortium of over 20 scientists from seven countries and 14 institutions has been assembled to plan the exploration of Lake Ellsworth. An eight-year programme is envisaged: 3 years for a geophysical survey, 2 years for equipment development and testing, 1 year for field planning and operation, and 2 years for sample analysis and data interpretation. The science experiment is simple in concept but complex in execution. Lake Ellsworth will be accessed using hot water drilling. Once lake access is achieved, a probe will be lowered down the borehole and into the lake. The probe will contain a series of instruments to measure biological, chemical and physical characteristics of the lake water and sediments, and will utilise a tether to the ice surface through which power, communication and data will be transmitted. The probe will pass through the water column to the lake floor. The probe will then be pulled up and out of the lake, measuring its environment continually as this is done. Once at the ice surface, any water samples collected will be taken from the probe for laboratory analysis (to take place over subsequent years). The duration of the science mission, from deployment of the probe to its retrieval, is likely to take between 24 and 36 h. Measurements to be taken by the probe will provide data about the following: depth, pressure, conductivity and temperature; pH levels; biomolecules (using life marker chips); anions (using a chemical analyzer); visualisation of the environment (using cameras and light sources); dissolved gases (using chromatography); and morphology of the lake floor and sediment structures (using sonar). After the probe has been retrieved, a sediment corer may be dropped into the lake to recover material from the lake floor. Finally, if time permits, a thermistor string may be left in the lake water to take time-dependent measurements of the lake’s water column over subsequent years. Given that the comprehensive geophysical survey of the lake will take place in two seasons during 2007–2009, a two-year instrument and logistic development phase from 2008 (after the lake’s bathymetry has been assessed) makes it possible that the exploration of Lake Ellsworth could take place at the beginning of the next decade.

Published
2006

20. [Untitled]

Author

David L. Cullen, Lopa V. Desai, John A. Shelnutt, and Marc Zimmer

Subjects
Plane (geometry), chemistry.chemical_element, Dihedral angle, Condensed Matter Physics, Measure (mathematics), Porphyrin, Crystallography, chemistry.chemical_compound, chemistry, Principal component analysis, Cluster (physics), Molecule, Physical and Theoretical Chemistry, Cobalt
Abstract

Principal component analysis, cluster analysis, and various structural parameters have been used to differentiate the nonplanar deformations of cobalt(III) porphyrins. The results were compared with normal-coordinate structural decomposition analysis. Cobalt(III) porphyrins discussed in this paper do not undergo large wav, dom, and pro deformations and they were not considered in our analysis. The cis Cα-N-N-Cα dihedral angle is the best structural measure of ruffling and it is the only structural parameter that does not overestimate the extent of ruffling due to the presence of saddling. The average distance between the Cβ carbons and the plane comprising the four nitrogens, the four meso carbons and the cobalt ion is the best structural measure of saddling. No structural parameters were found that could be used in principal component analysis to find PC's that quantified the nonplanar deformations in cobalt(III) porphyrins. Cluster analysis was able to separate the sad, ruf, and planar structures, however, the preparation and symmetry adaptation of all the structures was complicated and was no more informative than the use of some of the univarient structural parameters. The NSD deformations are related to the vibrational energies and motions of the macrocycle and are thus the preferred description, but the more easily obtained structural parameters are useful measures of the normal coordinate deformations whenever a full NSD analysis is not possible.

Published
2001

21. [Untitled]

Author

Adama M. Sesay and David C. Cullen

Subjects
Investigation methods, Chromatography, Chemistry, Environmental chemistry, General Medicine, Estrone-3-glucuronide, Management, Monitoring, Policy and Law, Pollution, Laundry detergent, General Environmental Science
Abstract

The ubiquitous presence of chemicals, both natural andsynthetic, in the environment with the potential to mimichormones that may in turn interfere with the endocrinesystem in both wildlife and humans has in the last decadebecome a major international concern. Hormone mimics orendocrine disrupting compounds (EDCs) are especiallyprevalent in surface and waste-waters and therefore, thereis a need for an at-source or at-line analytical device forthe monitoring of EDC levels.We have incorporated a miniature integrated surface plasmonresonance (SPR) liquid sensor from Texas Instruments into afield analyser and developed a competition/inhibition assayfor a model estrogenic compound in aqueous samples. Theanalyser has the potential for in situ and semi-continuous analysis of EDCs. A novel regeneration schemeemploying the use of a domestic laundry detergent has beenused to remove immobilised assay components between eachassay cycle. The resultant re-usable sensor has beendemonstrated using estrone-3-glucuronide (E3G) as a modelEDC and an anti-E3G antibody producing a current detectionrange of 10 to 150 ng mL-1.

Published
2001

22. Contributory presentations/posters

Author

N. Manoj, V. R. Srinivas, A. Surolia, M. Vijayan, K. Suguna, R. Ravishankar, R. Schwarzenbacher, K. Zeth, null Diederichs, G. M. Kostner, A. Gries, P. Laggner, R. Prassl, null Madhusudan, Pearl Akamine, Nguyen-huu Xuong, Susan S. Taylor, M. Bidva Sagar, K. Saikrishnan, S. Roy, K. Purnapatre, P. Handa, U. Varshney, B. K. Biswal, N. Sukumar, J. K. Mohana Rao, A. Johnson, Vasantha Pattabhi, S. Sri Krishna, Mira Sastri, H. S. Savithri, M. R. N. Murthy, Bindu Pillai, null Kannan, M. V. Hosur, Mukesh Kumar, Swati Patwardhan, K. K. Kannan, B. Padmanabhaa, S. Sasaki-Sugio, M. Nukaga, T. Matsuzaki, S. Karthikevan, S. Sharma, A. K. Sharma, M. Paramasivam, P. Kumar, J. A. Khan, S. Yadav, A. Srinivasan, T. P. Singh, S. Gourinath, Neelima Alam, A. Srintvasan, Vikas Chandra, Punit Kaur, Ch. Betzel, S. Ghosh, A. K. Bera, S. Bhattacharya, S. Chakraborty, A. K. Pal, B. P. Mukhopadhyay, I. Dey, U. Haldar, Asok Baneriee, Jozef Sevcik, Adriana Solovicova, K. Sekar, M. Sundaralingam, N. Genov, Dong-cai Liang, Tao Jiang, Ji-ping Zhang, Wen-rui Chang, Wolfgang Jahnke, Marcel Blommers, S. C. Panchal, R. V. Hosur, Bindu Pillay, Puniti Mathur, S. Srivatsun, Ratan Mani Joshi, N. R. Jaganathan, V. S. Chauhan, H. S. Atreya, S. C. Sahu, K. V. R. Chary, Girjesh Govil, Elisabeth Adjadj, Éric Quinjou, Nadia Izadi-Pruneyre, Yves Blouquit, Joël Mispelter, Bernadette Heyd, Guilhem Lerat, Philippe Milnard, Michel Desmadreil, Y. Lin, B. D. Nageswara Rao, Vidva Raghunathan, Mei H. Chau, Prashant Pesais, Sudha Srivastava, Evans Coutinho, Anil Saran, Leizl F. Sapico, Jayson Gesme, Herbert Lijima, Raymond Paxton, Thamarapu Srikrishnan, C. R. Grace, G. Nagenagowda, A. M. Lynn, Sudha M. Cowsik, Sarata C. Sahu, S. Chauhan, A. Bhattacharya, G. Govil, Anil Kumar, Maurizio Pellecchia, Erik R. P. Zuiderweg, Keiichi Kawano, Tomoyasu Aizawa, Naoki Fujitani, Yoichi Hayakawa, Atsushi Ohnishi, Tadayasu Ohkubo, Yasuhiro Kumaki, Kunio Hikichi, Katsutoshi Nitta, V. Rani Parvathy, R. M. 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Fromherz, K. N. Rao, S. M. Gaikwad, M. I. Khan, C. G. Suresh, P. Kaliannan, M. Elanthiraiyan, K. Chadha, J. Payne, J. L. Ambrus, M. P. N. Nair, Madhavan P. N. Nair, S. Mahajan, K. C. Chadha, R. Hewitt, S. A. Schwartz, J. Bourguignon, M. Faure, C. Cohen-Addad, M. Neuburger, R. Ober, L. Sieker, D. Macherel, R. Douce, D. S. Gurumurthy, S. Velmurugan, Z. Lobo, Ratna S. Phadke, Prashant Desai, I. M. Guseinova, S. Yu. Suleimanov, I. S. Zulfugarov, S. N. Novruzova, J. A. Aliev, M. A. Ismayilov, T. V. Savchenko, D. R. Alieva, Petr Ilík, Roman Kouřil, Hana Bartošková, Jan Nauš, Jvoti U. Gaikwad, Sarah Thomas, P. B. Vidyasagar, G. Garab, I. Simidjiev, S. Rajagopal, Zs. Várkonyi, S. Stoylova, Z. Cseh, E. Papp, L. Mustárdy, A. Holzenburg, R. Bruder, U. K. Genick, T. T. Woo, D. P. Millar, K. Gerwert, E. D. Getzoff, Tamás Jávorfí, Győző Garab, K. Razi Naqvi, Md. Kalimullah, Jyoti Gaikwad, Manoj Semwal, Roman Kouril, Petr Ilik, Man Naus, István Pomozi, Gábor Horváth, Rüdiger Wehner, Gary D. Bernard, Ana Damjanović, Thorsten Ritz, Klaus Schulten, Wang Jushuo, Shan Jixiu, Gong Yandao, Kuang Tingyun, Zhao Nanming, Arvi Freiberg, Kõu Timpmann, Rein Ruus, Neal W. Woodbury, E. V. Nemtseva, N. S. Kudryasheva, A. G. Sizykh, V. N. Shikhov, T. V. Nesterenko, A. A. Tikhomirov, Giorgio Forti, Giovanni Finazzi, Alberto Furia, Romina Paola Barbagallo, S. Iskenderova, R. Agalarov, R. Gasanov, Miyashita Osamu, G. O. Nobuhiro, R. K. Soni, M. Ramrakhiani, Hiromasa Yagi, Kacko Tozawa, Nobuaki Sekino, Tomoyuki Iwabuchi, Masasuke Yoshida, Hideo Akutsu, A. V. Avetisyan, A. D. Kaulen, V. P. Skulachev, B. A. Feniouk, Cécile Breyton, Werner Kühlbrandt, Maria Assarsson, Astrid Gräslund, G. Horváth, B. Libisch, Z. Gombos, N. V. Budagovskaya, N. Kudryasheva, Erisa Harada, Yuki Fukuoka, Tomoaki Ohmura, Arima Fukunishi, Gota Kawai, Kimitsuna Watanabe, Jure Derganc, Bojan Božič, Saša Svetina, Boštjan Žekš, J. F. Y. Hoh, Z. B. Li, G. H. Rossmanith, E. L. de Beer, B. W. Treijtel, P. L. T. M. Frederix, T. Blangè, S. Hénon, F. Galtet, V. Laurent, E. Planus, D. Isabey, L. S. Rath, P. K. Dash, M. K. Raval, C. Ramakrishnan, R. Balaram, Milan Randic, Subhash C. Basak, Marjan Vracko, Ashesh Nandy, Dragan Amic, Drago Beslo, Sonja Nikolic, Nenad Trinajstic, J. Walahaw, Marc F. J. Lensink, Boojala V. B. Reddy, Ilya N. Shindylov, Philip E. Bourne, M. C. Donnamaria, J. de Xammar Oro, J. R. Grigera, Monica Neagu, Adrian Neagu, Matej Praprotnik, Dušanka Janežič, Pekka Mark, Lennart Nilsson, L. La Fata, Laurent E. Dardenne, Araken S. Werneck, Marçal de O. Neto, N. Kannan, S. Vishveshwara, K. Veluraja, Gregory D. Grunwald, Alexandra T. Balaban, Kanika Basak, Brian D. Gute, Denise Mills, David Opitz, Krishnan Balasubramanian, G. I. Mihalas, Diana Lungeanu, G. Macovievici, Raluca Gruia, C. Cortez-Maghelly, B. Dalcin, E. P. Passos, S. Blesic, M. Ljubisavljevic, S. Milosevic, D. J. Stratimirovic, Nandita Bachhawat, Shekhar C. Mande, A. Nandy, Ayumu Saito, Koichi Nishigaki, Mohammed Naimuddin, Takatsugu Hirokawa, Mitsuo Ono, Hirotomo Takaesu, M. I. El Gohary, Abdalla S. Ahmed, A. M. Eissa, Hiroshi Nakashima, G. P. S. Raghava, N. Kurgalvuk, O. Goryn, Bernard S. Gerstman, E. V. Gritsenko, N. N. Remmel, O. M. Maznyak, V. A. Kratasyuk, E. N. Esimbekova, D. Tchitchkan, S. Koulchitsky, A. Tikhonov, A. German, Y. Pesotskaya, S. Pashkevich, S. Pletnev, V. Kulchitsky, Umamaheswar Duvvuri, Sridhar Charagundla, Rahim Rizi, John S. Leigh, Ravinder Reddy, Mahesh Kumar, O. Coshic, P. K. Julka, O. K. Rath, NR. Jagannathan, Karina Roxana Iliescu, Maria Sajin, Nicolcta Moisoi, Ileana Petcu, A. I. Kuzmenko, R. P. Morozova, I. A. Nikolenko, G. V. Donchenko, M. K. Rahman, M. M. Ahmed, Takehiro Watanabe, Y. Rubin, H. Gilboa, R. Sharony, R. Ammar, G. Uretzky, M. Khubchandani, H. N. Mallick, V. Mohan Kumar, Arijitt Borthakur, Erik M. Shapiro, M. Gulnaz Begum, Mahaveer N. Degaonkar, S. Govindasamy, Ivan Dimitrov, T. A. Kumosani, W. Bild, I. Stefanescu, G. Titescu, R. Iliescu, C. Lupusoru, V. Nastasa, I. Haulica, Gopal Khetawat, N. Faraday, M. Nealen, S. Noga, P. F. Bray, T. V. Ananieva, E. A. Lycholat, MV. Kosevich, S. G. Stepanyan, S. V. Antonyuk, R. Khachatryan, H. Arakelian, A. Kumar, S. Ayrapetyan, V. Mkheyan, S. Agadjanyan, A. Khachatryan, S. S. Rajan, V. Kabaleeswaran, Geetha Gopalakrishnan, T. R. Govindachari, Meera Ramrakhiani, Phillip Lowe, Andrew Badley, David C. Cullen, H. Hermel, W. Schmahl, H. Möhwald, Nirmalya Majumdar, Joydip Das, András Dér, Loránd Kelemen, László Oroszi, András Hámori, Jeremy J. Ramsden, Pál Ormos, D. Savitri, Chanchal K. Mitra, Toshio Yanagida, Seiji Esaki, Yuji Kimura, Tomoyuki Nishida, Yosiyuki Sowa, M. Radu, V. K. Koltover, Ya. I. Estrin, L. A. Kasumova, V. P. Bubnov, E. E. Laukhina, Rajiv Dotta, M. Degaonkar, P. Raghunathan, Rama Jayasundar, Pavel Novák, Milan Marko, Ivan Zahradník, Hiroaki Hirata, Hidetake Miyata, J. Balaji, P. Sengupta, S. Maiti, M. Gonsalves, A. L. Barker, J. V. Macpherson, D. O’Hare, C. P. Winlove, P. R. Unwin, R. Phillip, S. Banerjee, G. Ravindra Kumar, K. Nagayaka, R. Danev, S. Sugitani, K. Murata, Michael Gősch, H. Blom, P. Thyberg, Z. Földes-Papp, G. Björk, J. Holm, T. Heino, Masashi Yokochi, Fuyuhiko Inagaki, Masami Kusunoki, E. K. Matthews, J. Pines, Yu. P. Chukova, Vitaly K. Koltover, Geetanjali Bansal, Uma Singh, M. P. Bansal, Kotoko Nakata, Tastuya Nakano, Tsuguchika Kaminuma, B. P. S. Kang, U. Singh, Bonn Kirn, Neja Potocnik, Vito Stare, Latal Shukla, V. Natarajan, T. P. A. Devasagayam, M. D. Sastry, P. C. Kesavan, R. Sayfutdinov, V. V. Adamovich, D. Yu. Rogozin, A. G. Degermendzhy, C. L. Khetrapal, G. A. Nagana Gowda, Kedar Nath Ghimire, Ishida Masaru, H. Fujita, S. Ishiwata, Y. Kishimoto, S. Kawahara, M. Suzuki, H. Mori, M. Mishina, Y. Kirino, H. Ohshima, A. S. Dukhin, V. N. Shilov, P. J. Goetz, and R. K. Mishra

Subjects
0303 health sciences, biology, General Medicine, 010402 general chemistry, 01 natural sciences, Horseradish peroxidase, General Biochemistry, Genetics and Molecular Biology, 0104 chemical sciences, 03 medical and health sciences, Biochemistry, Manganese porphyrin, biology.protein, Enzyme reconstitution, General Agricultural and Biological Sciences, 030304 developmental biology
Published
1999

23. The Effects of Device Dimension, Substrate Temperature, and Gate Metallization on the Reliability of AlGaN/GaN High Electron Mobility Transistors

Author

David J. Smith, Erica A. Douglas, Stephen J. Pearton, Lin Zhou, Li Liu, Fan Ren, Chien-Fong Lo, Tsung-Sheng Kang, C. Y. Chang, and David A. Cullen

Subjects
Materials science, business.industry, Transistor, Biasing, Substrate (electronics), High-electron-mobility transistor, law.invention, law, Electric field, Optoelectronics, Breakdown voltage, business, AND gate, Voltage
Abstract

The effects of source field plates on AlGaN/GaN High Electron Mobility Transistor reliability under off-state stress conditions were investigated using step-stress cycling. The source field plate enhanced the drain breakdown voltage from 55V to 155V and the critical voltage for off-state gate stress from 40V to 65V, relative to devices without the field plate. Transmission electron microscopy was used to examine the degradation of the gate contacts. The presence of cracking that appeared on both source and drain side of the gate edges was attributed to the inverse piezoelectric effect. In addition, a thin oxide layer was observed between the Ni gate contact and the AlGaN layer, and both Ni and oxygen had diffused into the AlGaN layer. The critical degradation voltage of AlGaN/GaN High Electron Mobility Transistors during off-state electrical stress was determined as a function of Ni/Au gate dimensions (0.1-0.17μm). Devices with different gate length and gate-drain distances were found to exhibit the onset of degradation at different source-drain biases but similar electric field strengths, showing that the degradation mechanism is primarily field-driven. The temperature dependence of sub-threshold drain current versus gate voltage at a constant drain bias voltage were used to determine the trap densities in AlGaN/GaN high electron mobility transistors (HEMTs) before and after the off-state stress. Two different trap densities were obtained for the measurements conducted at 300-493K and 493-573K, respectively.

Published
2012

24. Thin Film Bulk Acoustic Wave Resonators for Continuous Monitoring in the Physical, Chemical and Biological Realms

Author

Paul B. Kirby, David C. Cullen, Jack Luo, Greg Ashley, and T. Butler

Subjects
Resonator, Transducer, Materials science, Orders of magnitude (temperature), Acoustics, Continuous monitoring, Sensitivity (control systems), Thin film, Biosensor, Microwave
Abstract

A transducer that can act as a highly sensitive and reliable universal sensor capable of detecting and continuously monitoring changes in the physical, chemical and biological domains is a potentially useful scientific tool. The Thin Film Bulk Acoustic Wave Resonator (FBAR) is a microwave device that is becoming increasingly recognised as a universal transduction platform with the added advantage of potential integration into CMOS architecture and array-like formats. This work shows preliminary results on FBAR where a continuous monitoring arrangement demonstrated the capability of FBAR to respond to changes in physical parameters such as temperature and light levels, the work goes on further to show the ability of FBAR to respond to changes in humidity in a gas flow and can have sensitivity increased with the addition of hygroscopic polymers on its surface and finally how FBAR can be adapted to act as a biosensor in the form of an immunosensor with sensitivity some orders of magnitude greater than traditional lower frequency bulk acoustic wave platforms.

Published
2009

25. The cardiovascular responses to the addition of nitrous oxide to diethyl ether in man

Author

David J. Cullen, George A. Gregory, Bruce F. Cullen, Edmond I. EceR, and N. Ty Smith

Subjects
Adult, Male, medicine.medical_specialty, Nitrous Oxide, Blood Pressure, Cardiovascular System, Body Temperature, Electrocardiography, chemistry.chemical_compound, Heart Rate, medicine, Humans, Cardiac Output, Gynecology, business.industry, Phonocardiography, Arteries, General Medicine, Carbon Dioxide, Hydrogen-Ion Concentration, Oxygen, Ethyl Ethers, Anesthesiology and Pain Medicine, chemistry, Regional Blood Flow, Anesthesia, Arm, Vascular Resistance, Diethyl ether, Anesthesia, Inhalation, business, Blood Flow Velocity
Abstract

Chez des jeunes sujets en bonne sante, on a etudie oe qui se produit si on ajoute a une anesthesie a 1’ether bien etablie 70 pour cent de protoxyde d’azote ou d’azote. Le fait de changer la concentration d’oxygene en ajoutant de l’azote a 4.5 pour cent d’ether n’affecta que le rythme cardiaque, qui s’est legerement accelere. Le protoxyde d’azote ajoute a 3 pour cent d’ether ne produisit aucun effet, rnais ajoute a 4.5 pour cent d’ether, il augmenta la pression arterieUe moyenne, la resistance vasculaire systemique, le travail minute du ventricule gauche et l’index de tension. Les pupilles furent legerement dilatees. Ainsi, le protoxyde d’azote avec l’ether a produit des signes de stimulation du recepteur alpha-adrenergique, semblables a ceux qu’on observe avec l’halothane, mais ne presenta pas les effets beta qu’on observe avec le fluroxene

Published
1972

26. 'Two-way Stretch' of Sialic Crust and Plate Tectonics in the South-west Pacific

Author

David J. Cullen

Subjects
Plate tectonics, Paleontology, Multidisciplinary, Trough (geology), Crust, Convergent boundary, Structural basin, Geology
Abstract

ANALYSES of seismic and continuous gravity measurements over the northern Tasman Sea1 have confirmed the existence of “quasi-continental” crust (20–26 km thick) beneath the parallel ridges—Norfolk Ridge, Lord Howe Rise and Dampier Ridge—that extend north-westward from New Zealand (Fig. 1). The intervening major trough, New Caledonia Basin, is shown to have a floor of true oceanic thickness (9 km).

Published
1970

27. Bioturbation of Superficial Marine Sediments by Interstitial Meiobenthos

Author

David J. Cullen

Subjects
geography, Multidisciplinary, geography.geographical_feature_category, Oceanography, Meiobenthos, Bioturbation, Channel (geography), Geology
Abstract

IN a recently completed series of laboratory studies, lebensspuren were produced by individual macrobenthic organisms on a variety of marine sand and mud substrates (freshly collected from depths down to 30 m in the Bristol Channel), from which all other macrofauna had been removed by passing it through a 1.0 mm mesh. But the resultant tracks, trails and burrows gradually disappeared when the aquarium tanks containing them were left undisturbed after the termination of the experiments.

Published
1973

28. Mantle Convection and Sea-floor Spreading in the South-west Pacific

Author

David J. Cullen

Subjects
Convection, Multidisciplinary, Mantle convection, Hotspot (geology), Island arc, Geophysics, Seafloor spreading, Geology
Abstract

THE interpretation of south-west Pacific structure recently proposed by Summerhayes1 is, in many respects, in agreement with suggestions previously made by myself2. Both emphasize the importance of sub-crustal convection and sea-floor spreading in determining the structure of the region, and both recognize the development of island arc structures to the north and south of New Zealand.

Published
1967

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