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David R. Smith

Bio: David R. Smith is an academic researcher from Duke University. The author has contributed to research in topics: Metamaterial & Antenna (radio). The author has an hindex of 110, co-authored 881 publications receiving 91683 citations. Previous affiliations of David R. Smith include Brunel University London & Princeton University.


Papers
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Journal ArticleDOI
TL;DR: In this article, the authors investigated how vegetation composition and CO2 fluxes vary spatially in response to the pattern of drainage features in Molinia caerulea-dominated peatlands.
Abstract: Peatlands are recognized as important carbon stores; despite this, many have been drained for agricultural improvement. Drainage has been shown to lower water tables and alter vegetation composition, modifying primary productivity and decomposition, potentially initiating peat loss. To quantify CO2 fluxes across whole landscapes, it is vital to understand how vegetation composition and CO2 fluxes vary spatially in response to the pattern of drainage features. However, Molinia caerulea-dominated peatlands are poorly understood despite their widespread extent. Photosynthesis (PG600) and ecosystem respiration (REco) were modelled (12 °C, 600 µmol photons m−2 s−1, greenness excess index of 60) using empirically derived parameters based on closed-chamber measurements collected over a growing season. Partitioned below-ground fluxes were also collected. Plots were arranged ⅛, ¼ and ½ the distance between adjacent ditches in two catchments located in Exmoor National Park, southwest England. Water table depths were deepest closest to the ditch and non-significantly (p = 0·197) shallower further away. Non-Molinia species coverage and the Simpson diversity index significantly decreased with water table depth (p < 0·024) and increased non-significantly (p < 0·083) away from the ditch. No CO2 fluxes showed significant spatial distribution in response to drainage ditches, arguably due to insignificant spatial distribution of water tables and vegetation composition. Whilst REco showed no significant spatial variation, PG600 varied significantly between sites (p = 0·012), thereby controlling the spatial distribution of net ecosystem exchange between sites. As PG600 significantly co-varied with water table depths (p = 0·034), determining the spatial distribution of water table depths may enable CO2 fluxes to be estimated across M. caerulea-dominated landscapes. © 2015 The Authors. Ecohydrology published by John Wiley & Sons, Ltd.

27 citations

Journal ArticleDOI
TL;DR: In this article, the authors considered a beamed WPT scheme based on a dynamically reconfigurable source aperture transferring power to receiving devices within the Fresnel (near-zone) region.
Abstract: Wireless power transfer (WPT) has been an active topic of research, with a number of WPT schemes implemented in the near-field (coupling) and far-field (radiation) regimes. Here, we consider a beamed WPT scheme based on a dynamically reconfigurable source aperture transferring power to receiving devices within the Fresnel (near-zone) region. In this context, the dynamic aperture resembles a reconfigurable lens capable of focusing power to a well-defined spot, whose dimension can be related to a point spread function (PSF). Near-zone focusing can be achieved by generating different amplitude or phase profiles over the aperture, which can be realized using traditional architectures, such as phased arrays. Alternatively, metasurface guided-wave apertures can achieve dynamic focusing, with potentially lower cost implementations. We present an initial tradeoff analysis of the near-zone WPT concept, relating key parameters such as spot size, aperture size, wavelength, focal distance, and availability of sources. We find that approximate design formulas derived from the Gaussian optics approximation provide useful estimates of system performance, including transfer efficiency and coverage volume. The accuracy of these formulas is confirmed using numerical calculations.

26 citations

Journal ArticleDOI
TL;DR: The SUBM with its smaller, more manoeuvrable probe handpiece and a wider scanning field was more accurate in detecting muscle insertions compared with HUBM.
Abstract: Aim The ultrasound biomicroscope (UBM) can accurately locate an extraocular muscle (EOM) insertion. The authors compared the accuracy of the Sonomed UBM (SUBM), a new ‘wide-field ultrasound biomicroscope’, with the older model Humphrey UBM (HUBM) in localising EOM insertions and compared their ranges of detection of muscle insertions. Methods Prospective, double-masked, observational study of 27 patients undergoing primary (n=40 muscles) or repeat (n=10 muscles) horizontal or vertical rectus muscle surgery. EOM insertional distances were measured with SUBM, and then intraoperatively with callipers. A Bland–Altman analysis and intraclass correlation coefficient were used to compare the SUBM and surgical data. Results For all muscles, the differences between SUBM and surgery measurements were less than 1.0 mm. The mean of the SUBM insertion distances was 6.67 mm (SD 1.65 mm) versus 6.7 mm (SD 1.6 mm) at surgery. The intraclass correlation coefficient showed ‘excellent’ correlation between the two sets of data and was higher than that reported with HUBM. The image quality with the SUBM was superior to the HUBM, and its range of field was much larger (14×18 mm vs 5×6 mm). Conclusion The SUBM with its smaller, more manoeuvrable probe handpiece and a wider scanning field was more accurate in detecting muscle insertions compared with HUBM.

26 citations

Journal ArticleDOI
TL;DR: In this article, the dependence on density gradient is studied through the observation of a large density gradient variation in the core induced by an edge localized mode (ELM) event, where they found the first clear experimental evidence of density gradient stabilization of electron-gyro scale turbulence in a fusion plasma.
Abstract: Electron-scale turbulence is predicted to drive anomalous electron thermal transport. However, experimental study of its relation with transport is still in its early stage. On the National Spherical Tokamak Experiment (NSTX), electron-scale density fluctuations are studied with a novel tangential microwave scattering system with high radial resolution of ±2 cm. Here, we report a study of parametric dependence of electron-scale turbulence in NSTX H-mode plasmas. The dependence on density gradient is studied through the observation of a large density gradient variation in the core induced by an edge localized mode (ELM) event, where we found the first clear experimental evidence of density gradient stabilization of electron-gyro scale turbulence in a fusion plasma. This observation, coupled with linear gyro-kinetic calculations, leads to the identification of the observed instability as toroidal electron temperature gradient (ETG) modes. It is observed that longer wavelength ETG modes, k⊥ρs≲10 (ρs is the i...

26 citations

Journal ArticleDOI
Stanley Kaye1, Tyler Abrams1, Joon-Wook Ahn2, Jean Paul Allain3, R. Andre1, Daniel Andruczyk3, R. Barchfeld4, D. J. Battaglia1, Amitava Bhattacharjee1, F. Bedoya3, R.E. Bell1, Elena Belova1, John Berkery5, Lee A. Berry2, Nicola Bertelli1, Peter Beiersdorfer6, J.M. Bialek5, R. Bilato7, J.A. Boedo8, P.T. Bonoli9, Allen H. Boozer5, Alessandro Bortolon10, M. D. Boyer1, Dennis Boyle1, Dylan Brennan11, J. Breslau1, Jeffrey N. Brooks12, R. J. Buttery13, Angela M. Capece1, John Canik2, Choong-Seock Chang1, Neal Crocker14, D. S. Darrow1, W. Davis1, L. F. Delgado-Aparicio1, Ahmed Diallo1, D.A. D'Ippolito, Calvin Domier4, F. Ebrahimi11, Stephane Ethier1, Todd Evans13, Nathaniel Ferraro13, J.R. Ferron13, Michael Finkenthal15, R.J. Fonck16, E.D. Fredrickson1, Guoyong Fu1, David Gates1, S.P. Gerhardt1, A. H. Glasser17, Nikolai Gorelenkov1, M. Gorelenkova1, I.R. Goumiri11, T.K. Gray2, D. L. Green2, W. Guttenfelder1, R. W. Harvey18, Ahmed Hassanein12, William Heidbrink19, Yoshiki Hirooka20, E. B. Hooper6, J. Hosea1, D.A. Humphreys13, E. F. Jaeger, Thomas Jarboe17, Stephen Jardin1, Michael Jaworski1, Robert Kaita1, C.E. Kessel1, Kimin Kim1, Bruce E. Koel11, Egemen Kolemen1, G. J. Kramer1, Seung-Hoe Ku1, S. Kubota14, R. J. Lahaye13, L.L. Lao13, B.P. LeBlanc1, Fred Levinton, D. W. Liu19, J. Lore11, M. Lucia3, Neville C. Luhmann14, R. Maingi1, Richard Majeski1, D.K. Mansfield1, R.J. Maqueda, George McKee16, S. S. Medley1, E.T. Meier6, Jonathan Menard1, D. Mueller1, Tobin Munsat21, Christopher Muscatello4, J.R. Myra, Brian Nelson17, J.H. Nichols1, M. Ono1, T.H. Osborne13, Jinseop Park1, W. A. Peebles14, Rory Perkins1, C. K. Phillips1, Mario Podesta1, Francesca Poli1, Roger Raman17, Yang Ren1, J.P. Roszell11, Clarence W. Rowley11, D. A. Russell, David N. Ruzic3, P.M. Ryan2, S.A. Sabbagh5, Eugenio Schuster22, Filippo Scotti6, Y. Sechrest21, Ker-Chung Shaing16, Tatyana Sizyuk12, Valeryi Sizyuk3, C.H. Skinner1, David R. Smith16, P. B. Snyder13, W. M. Solomon1, C. Sovenic16, Vlad Soukhanovskii6, Edward A. Startsev1, D.P. Stotler1, B. Stratton1, Dan Stutman15, Chase N. Taylor12, G. Taylor1, Kevin Tritz15, M.L. Walker13, W. X. Wang1, Zhehui Wang1, Roscoe White1, James R. Wilson1, Brian D. Wirth10, John Wright9, X. Yuan1, Howard Yuh, Leonid E. Zakharov1, Stewart Zweben1 
TL;DR: The National Spherical Torus Experiment (NSTX) is currently being upgraded to operate at twice the toroidal field and plasma current (up to 1 T and 2 MA), with a second, more tangentially aimed neutral beam (NB) for current and rotation control, allowing for pulse lengths up to 5 s as mentioned in this paper.
Abstract: The National Spherical Torus Experiment (NSTX) is currently being upgraded to operate at twice the toroidal field and plasma current (up to 1 T and 2 MA), with a second, more tangentially aimed neutral beam (NB) for current and rotation control, allowing for pulse lengths up to 5 s. Recent NSTX physics analyses have addressed topics that will allow NSTX-Upgrade to achieve the research goals critical to a Fusion Nuclear Science Facility. These include producing stable, 100% non-inductive operation in high-performance plasmas, assessing plasma–material interface (PMI) solutions to handle the high heat loads expected in the next-step devices and exploring the unique spherical torus (ST) parameter regimes to advance predictive capability. Non-inductive operation and current profile control in NSTX-U will be facilitated by co-axial helicity injection (CHI) as well as radio frequency (RF) and NB heating. CHI studies using NIMROD indicate that the reconnection process is consistent with the 2D Sweet–Parker theory. Full-wave AORSA simulations show that RF power losses in the scrape-off layer (SOL) increase significantly for both NSTX and NSTX-U when the launched waves propagate in the SOL. Toroidal Alfven eigenmode avalanches and higher frequency Alfven eigenmodes can affect NB-driven current through energy loss and redistribution of fast ions. The inclusion of rotation and kinetic resonances, which depend on collisionality, is necessary for predicting experimental stability thresholds of fast growing ideal wall and resistive wall modes. Neutral beams and neoclassical toroidal viscosity generated from applied 3D fields can be used as actuators to produce rotation profiles optimized for global stability. DEGAS-2 has been used to study the dependence of gas penetration on SOL temperatures and densities for the MGI system being implemented on the Upgrade for disruption mitigation. PMI studies have focused on the effect of ELMs and 3D fields on plasma detachment and heat flux handling. Simulations indicate that snowflake and impurity seeded radiative divertors are candidates for heat flux mitigation in NSTX-U. Studies of lithium evaporation on graphite surfaces indicate that lithium increases oxygen surface concentrations on graphite, and deuterium–oxygen affinity, which increases deuterium pumping and reduces recycling. In situ and test-stand experiments of lithiated graphite and molybdenum indicate temperature-enhanced sputtering, although that test-stand studies also show the potential for heat flux reduction through lithium vapour shielding. Non-linear gyro kinetic simulations have indicated that ion transport can be enhanced by a shear-flow instability, and that non-local effects are necessary to explain the observed rapid changes in plasma turbulence. Predictive simulations have shown agreement between a microtearing-based reduced transport model and the measured electron temperatures in a microtearing unstable regime. Two Alfven eigenmode-driven fast ion transport models have been developed and successfully benchmarked against NSTX data. Upgrade construction is moving on schedule with initial physics research operation of NSTX-U planned for mid-2015.

26 citations


Cited by
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Journal ArticleDOI

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

28 Jul 2005
TL;DR: PfPMP1)与感染红细胞、树突状组胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作�ly.
Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1(PfPMP1)与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用,在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员,通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

18,940 citations

Journal ArticleDOI
TL;DR: A review of gold nanoparticles can be found in this article, where the most stable metal nanoparticles, called gold colloids (AuNPs), have been used for catalysis and biology applications.
Abstract: Although gold is the subject of one of the most ancient themes of investigation in science, its renaissance now leads to an exponentially increasing number of publications, especially in the context of emerging nanoscience and nanotechnology with nanoparticles and self-assembled monolayers (SAMs). We will limit the present review to gold nanoparticles (AuNPs), also called gold colloids. AuNPs are the most stable metal nanoparticles, and they present fascinating aspects such as their assembly of multiple types involving materials science, the behavior of the individual particles, size-related electronic, magnetic and optical properties (quantum size effect), and their applications to catalysis and biology. Their promises are in these fields as well as in the bottom-up approach of nanotechnology, and they will be key materials and building block in the 21st century. Whereas the extraction of gold started in the 5th millennium B.C. near Varna (Bulgaria) and reached 10 tons per year in Egypt around 1200-1300 B.C. when the marvelous statue of Touthankamon was constructed, it is probable that “soluble” gold appeared around the 5th or 4th century B.C. in Egypt and China. In antiquity, materials were used in an ecological sense for both aesthetic and curative purposes. Colloidal gold was used to make ruby glass 293 Chem. Rev. 2004, 104, 293−346

11,752 citations

Journal ArticleDOI
14 Aug 2003-Nature
TL;DR: By altering the structure of a metal's surface, the properties of surface plasmons—in particular their interaction with light—can be tailored, which could lead to miniaturized photonic circuits with length scales that are much smaller than those currently achieved.
Abstract: Surface plasmons are waves that propagate along the surface of a conductor. By altering the structure of a metal's surface, the properties of surface plasmons--in particular their interaction with light--can be tailored, which offers the potential for developing new types of photonic device. This could lead to miniaturized photonic circuits with length scales that are much smaller than those currently achieved. Surface plasmons are being explored for their potential in subwavelength optics, data storage, light generation, microscopy and bio-photonics.

10,689 citations

Journal ArticleDOI
01 Apr 1988-Nature
TL;DR: In this paper, a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) is presented.
Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

9,929 citations