24 results
The predictive role of symptoms in COVID-19 diagnostic models: A longitudinal insight
- Olivia Bird, Eva P. Galiza, David Neil Baxter, Marta Boffito, Duncan Browne, Fiona Burns, David R. Chadwick, Rebecca Clark, Catherine A. Cosgrove, James Galloway, Anna L. Goodman, Amardeep Heer, Andrew Higham, Shalini Iyengar, Christopher Jeanes, Philip A. Kalra, Christina Kyriakidou, Judy M. Bradley, Chigomezgo Munthali, Angela M. Minassian, Fiona McGill, Patrick Moore, Imrozia Munsoor, Helen Nicholls, Orod Osanlou, Jonathan Packham, Carol H. Pretswell, Alberto San Francisco Ramos, Dinesh Saralaya, Ray P. Sheridan, Richard Smith, Roy L. Soiza, Pauline A. Swift, Emma C. Thomson, Jeremy Turner, Marianne Elizabeth Viljoen, Paul T. Heath, Irina Chis Ster
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- Journal:
- Epidemiology & Infection / Volume 152 / 2024
- Published online by Cambridge University Press:
- 22 January 2024, e37
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To investigate the symptoms of SARS-CoV-2 infection, their dynamics and their discriminatory power for the disease using longitudinally, prospectively collected information reported at the time of their occurrence. We have analysed data from a large phase 3 clinical UK COVID-19 vaccine trial. The alpha variant was the predominant strain. Participants were assessed for SARS-CoV-2 infection via nasal/throat PCR at recruitment, vaccination appointments, and when symptomatic. Statistical techniques were implemented to infer estimates representative of the UK population, accounting for multiple symptomatic episodes associated with one individual. An optimal diagnostic model for SARS-CoV-2 infection was derived. The 4-month prevalence of SARS-CoV-2 was 2.1%; increasing to 19.4% (16.0%–22.7%) in participants reporting loss of appetite and 31.9% (27.1%–36.8%) in those with anosmia/ageusia. The model identified anosmia and/or ageusia, fever, congestion, and cough to be significantly associated with SARS-CoV-2 infection. Symptoms’ dynamics were vastly different in the two groups; after a slow start peaking later and lasting longer in PCR+ participants, whilst exhibiting a consistent decline in PCR- participants, with, on average, fewer than 3 days of symptoms reported. Anosmia/ageusia peaked late in confirmed SARS-CoV-2 infection (day 12), indicating a low discrimination power for early disease diagnosis.
The controlled impact of elastic plates on a quiescent water surface
- An Wang, Kit Pan Wong, Miao Yu, Kenneth T. Kiger, James H. Duncan
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- Journal:
- Journal of Fluid Mechanics / Volume 939 / 25 May 2022
- Published online by Cambridge University Press:
- 23 March 2022, A4
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The impact of flexible rectangular aluminum plates on a quiescent water surface is studied experimentally. The plates are mounted via pinned supports at the leading and trailing edges to an instrument carriage that drives the plates at constant velocity and various angles relative to horizontal into the water surface. Time-resolved measurements of the hydrodynamic normal force ($F_n$) and transverse moment ($M_{to}$), the spray root position ($\xi _r$) and the plate deflection ($\delta$) are collected during plate impacts at 25 experimental conditions for each plate. These conditions comprise a matrix of impact Froude numbers ${Fr} = V_n(gL)^{-0.5}$, plate stiffness ratios $R_D= \rho _w V_n^2 L^3D^{-1}$ and submergence time ratios $R_T= T_sT_{1w}^{-1}$. It is found that $R_D$ is the primary dimensionless ratio controlling the role of flexibility during the impact. At conditions with low $R_D$, maximum plate deflections on the order of $1$ mm occur and the records of the dimensionless form of $F_n$, $M_{to}$, $\xi _r$ and $\delta _c$ are nearly identical when plotted vs $tT_s^{-1}$. In these cases, the impact occurs over time scales substantially greater than the plate's natural period, and a quasi-static response ensues with the maximum deflection occurring approximately midway through the impact. For conditions with higher $R_D$ ($\gtrsim 1.0$), the above-mentioned dimensionless quantities depend strongly on $R_D$. These response features indicate a dynamic plate response and a two-way fluid–structure interaction in which the deformation of the plate causes significant changes in the hydrodynamic force and moment.
Food and Society at Real Alto, an Early Formative Community in Southwest Coastal Ecuador
- Deborah M. Pearsall, Neil A. Duncan, Karol Chandler-Ezell, Douglas H. Ubelaker, James A. Zeidler
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- Journal:
- Latin American Antiquity / Volume 31 / Issue 1 / March 2020
- Published online by Cambridge University Press:
- 28 January 2020, pp. 122-142
- Print publication:
- March 2020
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We investigated foodways at Real Alto, an early Formative (4400–1800 BC) Valdivia site in coastal Ecuador, using starch and phytoliths recovered from 50 stone tools from three residential and two ceremonial structures, as well as 46 human dental calculus samples, to explore how food reflects the social relationships and economy of the community. Maize was important in daily meals and ceremonial foods by the Middle Valdivia (2800–2400 BC), but it was only one component of an agricultural system that included yuca, arrowroot, llerén, canna, yam, jackbean, squash, gourd, chili, and cotton. Ceremonial and everyday foods at Real Alto did not differ: actions surrounding food were both domestic and ceremonial, depending on context. Households had equal access to annual crops and to root-tubers with longer growing seasons. Gelatinized starch was commonly recovered on tools, indicating the processing of cooked foods. Dental calculus residues confirmed common consumption of cooked foods, fruits, and root-tubers. Cultivating crops with different water and growing season requirements necessitated diverse practices, potentially including selection of short-season varieties, hand watering, and growing crops over multiple rainy seasons. The latter two practices required increased labor inputs: access to labor was likely a key element supporting the nascent social hierarchy that emerged by the Middle Valdivia.
The controlled vertical impact of an inclined flat plate on a quiescent water surface
- An Wang, James H. Duncan
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- Journal:
- Journal of Fluid Mechanics / Volume 879 / 25 November 2019
- Published online by Cambridge University Press:
- 27 September 2019, pp. 468-511
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The generation of spray during the vertical impact of a flat plate (length $L=1.22~\text{m}$, width $B=0.38~\text{m}$) on a quiescent water surface is studied experimentally. The plate is held in an orientation tilted up from horizontal by angles $\unicode[STIX]{x1D6FD}$ ranging from $10^{\circ }$ to $25^{\circ }$ about one of its long edges, which is positioned close to a vertical wall. The plate motion, which is driven by a servo motor system, is set to maintain a constant speed, $W_{0}$, until the trailing (upper) long edge of the plate passes the still water level (SWL) and then to decelerate to a stop. The impact Froude numbers $\mathit{Fr}$ ($=W_{0}/\sqrt{gB}$, where $g$ is the gravitational acceleration) range from 0.21 to 0.63. The evolution of the water surface underneath the plate and outboard of its trailing edge is measured with a cinematic laser induced fluorescence technique. As the plate’s leading (low) edge passes the SWL, the local water surface rises and develops into a thin spray sheet that travels along the plate’s lower surface toward the trailing edge. The horizontal speed of the under-plate spray tip is approximately $2.25W_{0}/\tan \unicode[STIX]{x1D6FD}$, as high as $15~\text{m}~\text{s}^{-1}$. In agreement with published similarity theory for the flow during the vertical water entry of a wedge, the under-plate surface profiles scaled by $W_{0}t$ nearly collapse on a single curve for each $\unicode[STIX]{x1D6FD}$. As the under-plate spray passes the plate’s trailing edge, it develops into the leading portion (called herein the Type I spray) of the outboard spray system. As the trailing edge of the plate passes through the local water surface, a crater develops and a large nearly vertical spray sheet (called the Type II spray) is generated from the outer edge (called the outboard spray root) of the crater. The characteristic horizontal length scale of the crater is found to expand in time following a power law with an exponent of approximately 0.77 for all conditions. A short time after its formation, the outboard spray root becomes the crest of a gravity wave whose propagation speed is of the order of $1~\text{m}~\text{s}^{-1}$ for all $\unicode[STIX]{x1D6FD}$ and $\mathit{Fr}$. The dimensionless envelope of the Type II spray profiles collapse to a single curve at high $\mathit{Fr}$ for each $\unicode[STIX]{x1D6FD}$. The connecting spray sheet between the Type I and Type II sprays tends to break up at small $\unicode[STIX]{x1D6FD}$ and large $\mathit{Fr}$.
The impact of a deep-water plunging breaker on a wall with its bottom edge close to the mean water surface
- An Wang, Christine M. Ikeda-Gilbert, James H. Duncan, Daniel P. Lathrop, Mark J. Cooker, Anne M. Fullerton
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- Journal:
- Journal of Fluid Mechanics / Volume 843 / 25 May 2018
- Published online by Cambridge University Press:
- 04 April 2018, pp. 680-721
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The impact of a deep-water plunging breaker on a finite height two-dimensional structure with a vertical front face is studied experimentally. The structure is located at a fixed horizontal position relative to a wave maker and the structure’s bottom surface is located at a range of vertical positions close to the undisturbed water surface. Measurements of the water surface profile history and the pressure distribution on the front surface of the structure are performed. As the vertical position, $z_{b}$ (the $z$ axis is positive up and $z=0$ is the mean water level), of the structure’s bottom surface is varied from one experimental run to another, the water surface evolution during impact can be categorized into three classes of behaviour. In class I, with $z_{b}$ in a range of values near $-0.1\unicode[STIX]{x1D706}_{0}$, where $\unicode[STIX]{x1D706}_{0}$ is the nominal wavelength of the breaker, the behaviour of the water surface is similar to the flip-through phenomena first described in studies with shallow water and a structure mounted on the sea bed. In the present work, it is found that the water surface between the front face of the structure and the wave crest is well fitted by arcs of circles with a decreasing radius and downward moving centre as the impact proceeds. A spatially and temporally localized high-pressure region was found on the impact surface of the structure and existing theory is used to explore the physics of this phenomenon. In class II, with $z_{b}$ in a range of values near the mean water level, the bottom of the structure exits and re-enters the water phase at least once during the impact process. These air–water transitions generate large-amplitude ripple packets that propagate to the wave crest and modify its behaviour significantly. At $z_{b}=0$, all sensors submerged during the impact record a nearly in-phase high-frequency pressure oscillation indicating possible air entrainment. In class III, with $z_{b}$ in a range of values near $0.03\unicode[STIX]{x1D706}_{0}$, the bottom of the structure remains in air before the main crest hits the bottom corner of the structure. The subsequent free surface behaviour is strongly influenced by the instantaneous momentum of the local flow just before impact and the highest wall pressures of all experimental conditions are found.
Observations of gravity–capillary lump interactions
- Naeem Masnadi, James H. Duncan
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- Journal:
- Journal of Fluid Mechanics / Volume 814 / 10 March 2017
- Published online by Cambridge University Press:
- 08 February 2017, R1
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In this experimental study, we investigate the interaction of gravity–capillary solitary waves generated by two surface pressure sources moving side by side at constant speed. The nonlinear response of a water surface to a single source moving at a speed just below the minimum phase speed of linear gravity–capillary waves in deep water ($c_{min}\approx 23~\text{cm}~\text{s}^{-1}$) consists of periodic generation of pairs of three-dimensional solitary waves (or lumps) in a V-shaped pattern downstream of the source. In the reference frame of the laboratory, these unsteady lumps propagate in a direction oblique to the motion of the source. In the present experiments, the strengths of the two sources are adjusted to produce nearly identical responses and the free-surface deformations are visualized using photography-based techniques. The first lumps generated by the two sources move in intersecting directions that make a half-angle of approximately $15^{\circ }$ and collide in the centreplane between the sources. A steep depression is formed during the collision, but this depression quickly decreases in amplitude while radiating small-amplitude radial waves. After the collision, a quasi-stable pattern is formed with several rows of localized depressions that are qualitatively similar to lumps but exhibit periodic amplitude oscillations, similar to a breather. The shape of the wave pattern and the period of oscillations depend strongly on the distance between the sources.
The generation of gravity–capillary solitary waves by a pressure source moving at a trans-critical speed
- Naeem Masnadi, James H. Duncan
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- Journal:
- Journal of Fluid Mechanics / Volume 810 / 10 January 2017
- Published online by Cambridge University Press:
- 01 December 2016, pp. 448-474
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The unsteady response of a water free surface to a localized pressure source moving at constant speed $U$ in the range $0.95c_{min}\lesssim U\leqslant 1.02c_{min}$, where $c_{min}$ is the minimum phase speed of linear gravity–capillary waves in deep water, is investigated through experiments and numerical simulations. This unsteady response state, which consists of a V-shaped pattern behind the source, and features periodic shedding of pairs of depressions from the tips of the V, was first observed qualitatively by Diorio et al. (Phys. Rev. Lett., vol. 103, 2009, 214502) and called state III. In the present investigation, cinematic shadowgraph and refraction-based techniques are utilized to measure the temporal evolution of the free-surface deformation pattern downstream of the source as it moves along a towing tank, while numerical simulations of the model equation described by Cho et al. (J. Fluid Mech., vol. 672, 2011, pp. 288–306) are used to extend the experimental results over longer times than are possible in the experiments. From the experiments, it is found that the speed–amplitude characteristics and the shape of the depressions are nearly the same as those of the freely propagating gravity–capillary lumps of inviscid potential theory. The decay rate of the depressions is measured from their height–time characteristics, which are well fitted by an exponential decay law with an order one decay constant. It is found that the shedding period of the depression pairs decreases with increasing source strength and speed. As the source speed approaches $c_{min}$, this period tends to approximately 1 s for all source magnitudes. At the low-speed boundary of state III, a new response with unsteady asymmetric shedding of depressions is found. This response is also predicted by the model equation.
Contributors
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- By Jessica Almqvist, Grace Bolton, Martin Dawidowicz, Eric De Brabandere, Katherine Del Mar, Malgosia Fitzmaurice, Duncan French, Gleider I. Hernández, Jackson Nyamuya Maogoto, Tamar Megiddo, Zohar Nevo, Alexandros X. M. Ntovas, Jadranka Petrovic, Yaël Ronen, Katja L. H. Samuel, Mohammad Shahabuddin, Kelly Stathopoulou, Charlotte Steinorth, James Summers, Mai Taha, Jure Vidmar, Jacqui Zalcberg
- Edited by Duncan French, University of Lincoln
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- Book:
- Statehood and Self-Determination
- Published online:
- 05 March 2013
- Print publication:
- 21 February 2013, pp viii-xiv
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VAST: An ASKAP Survey for Variables and Slow Transients
- Part of
- TARA MURPHY, SHAMI CHATTERJEE, DAVID L. KAPLAN, JAY BANYER, MARTIN E. BELL, HAYLEY E. BIGNALL, GEOFFREY C. BOWER, ROBERT A. CAMERON, DAVID M. COWARD, JAMES M. CORDES, STEVE CROFT, JAMES R. CURRAN, S. G. DJORGOVSKI, SEAN A. FARRELL, DALE A. FRAIL, B. M. GAENSLER, DUNCAN K. GALLOWAY, BRUCE GENDRE, ANNE J. GREEN, PAUL J. HANCOCK, SIMON JOHNSTON, ATISH KAMBLE, CASEY J. LAW, T. JOSEPH W. LAZIO, KITTY K. LO, JEAN-PIERRE MACQUART, NANDA REA, UMAA REBBAPRAGADA, CORMAC REYNOLDS, STUART D. RYDER, BRIAN SCHMIDT, ROBERTO SORIA, INGRID H. STAIRS, STEVEN J. TINGAY, ULF TORKELSSON, KIRI WAGSTAFF, MARK WALKER, RANDALL B. WAYTH, PETER K. G. WILLIAMS
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- Journal:
- Publications of the Astronomical Society of Australia / Volume 30 / 2013
- Published online by Cambridge University Press:
- 15 February 2013, e006
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The Australian Square Kilometre Array Pathfinder (ASKAP) will give us an unprecedented opportunity to investigate the transient sky at radio wavelengths. In this paper we present VAST, an ASKAP survey for Variables and Slow Transients. VAST will exploit the wide-field survey capabilities of ASKAP to enable the discovery and investigation of variable and transient phenomena from the local to the cosmological, including flare stars, intermittent pulsars, X-ray binaries, magnetars, extreme scattering events, interstellar scintillation, radio supernovae, and orphan afterglows of gamma-ray bursts. In addition, it will allow us to probe unexplored regions of parameter space where new classes of transient sources may be detected. In this paper we review the known radio transient and variable populations and the current results from blind radio surveys. We outline a comprehensive program based on a multi-tiered survey strategy to characterise the radio transient sky through detection and monitoring of transient and variable sources on the ASKAP imaging timescales of 5 s and greater. We also present an analysis of the expected source populations that we will be able to detect with VAST.
A parametric study of breaking bow waves using a 2D + T Technique
- Eric Maxeiner, Mostafa Shakeri, James H. Duncan
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- Journal:
- Journal of Fluid Mechanics / Volume 687 / 25 November 2011
- Published online by Cambridge University Press:
- 14 October 2011, pp. 540-570
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A mechanical two-dimensional wave maker with a flexible surface was used to create waves similar to those formed at the bow of a moving ship. Utilizing the two-dimensional plus time (2D + T) approximation, the wave maker was programmed so that its deformable wave board created a time sequence of shapes that simulated the line of intersection between one side of the hull of a slender ship model moving at constant speed and an imaginary vertical plane oriented normal to the ship model track. However, instead of simulating a particular ship hull, the wave maker was set to produce a parametric set of flat plate motions that represent components of typical bow shapes. The resulting surface waves were measured using a cinematic laser-induced fluorescence technique and the resulting wave profiles were analysed. A large variation of wave crest shapes was observed. An assortment of wave characteristics including the maximum contact point height, maximum wave height and plunging jet geometry were measured and related to the corresponding wave maker motion parameters. Despite the variety of wave maker motions and resulting wave crest shapes, it was observed that the gross parameters describing the wave, such as the maximum wave height, maximum contact point height and wave phase speed, correlate strongly with the wave maker velocity along the water line. Details of the crest shape at the moment of incipient breaking showed a stronger dependence on the initial acceleration of the wave board.
Resonantly forced gravity–capillary lumps on deep water. Part 2. Theoretical model
- YEUNWOO CHO, JAMES D. DIORIO, T. R. AKYLAS, JAMES H. DUNCAN
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- Journal:
- Journal of Fluid Mechanics / Volume 672 / 10 April 2011
- Published online by Cambridge University Press:
- 31 March 2011, pp. 288-306
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A theoretical model is presented for the generation of waves by a localized pressure distribution moving on the surface of deep water with speed near the minimum gravity–capillary phase speed, cmin. The model employs a simple forced–damped nonlinear dispersive equation. Even though it is not formally derived from the full governing equations, the proposed model equation combines the main effects controlling the response and captures the salient features of the experimental results reported in Diorio et al. (J. Fluid Mech., vol. 672, 2011, pp. 268–287 – Part 1 of this work). Specifically, as the speed of the pressure disturbance is increased towards cmin, three distinct responses arise: state I is confined beneath the applied pressure and corresponds to the linear subcritical steady solution; state II is steady, too, but features a steep gravity–capillary lump downstream of the pressure source; and state III is time-periodic, involving continuous shedding of lumps downstream. The transitions from states I to II and from states II to III, observed experimentally, are associated with certain limit points in the steady-state response diagram computed via numerical continuation. Moreover, within the speed range that state II is reached, the maximum response amplitude turns out to be virtually independent of the strength of the pressure disturbance, in agreement with the experiment. The proposed model equation, while ad hoc, brings out the delicate interplay between dispersive, nonlinear and viscous effects that takes place near cmin, and may also prove useful in other physical settings where a phase-speed minimum at non-zero wavenumber occurs.
Resonantly forced gravity–capillary lumps on deep water. Part 1. Experiments
- JAMES D. DIORIO, YEUNWOO CHO, JAMES H. DUNCAN, T. R. AKYLAS
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- Journal:
- Journal of Fluid Mechanics / Volume 672 / 10 April 2011
- Published online by Cambridge University Press:
- 31 March 2011, pp. 268-287
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The wave pattern generated by a pressure source moving over the free surface of deep water at speeds, U, below the minimum phase speed for linear gravity–capillary waves, cmin, was investigated experimentally using a combination of photographic measurement techniques. In similar experiments, using a single pressure amplitude, Diorio et al. (Phys. Rev. Lett., vol. 103, 2009, 214502) pointed out that the resulting surface response pattern exhibits remarkable nonlinear features as U approaches cmin, and three distinct response states were identified. Here, we present a set of measurements for four surface-pressure amplitudes and provide a detailed quantitative examination of the various behaviours. At low speeds, the pattern resembles the stationary state (U = 0), essentially a circular dimple located directly under the pressure source (called a state I response). At a critical speed, but still below cmin, there is an abrupt transition to a wave-like state (state II) that features a marked increase in the response amplitude and the formation of a localized solitary depression downstream of the pressure source. This solitary depression is steady, elongated in the cross-stream relative to the streamwise direction, and resembles freely propagating gravity–capillary ‘lump’ solutions of potential flow theory on deep water. Detailed measurements of the shape of this depression are presented and compared with computed lump profiles from the literature. The amplitude of the solitary depression decreases with increasing U (another known feature of lumps) and is independent of the surface pressure magnitude. The speed at which the transition from states I to II occurs decreases with increasing surface pressure. For speeds very close to the transition point, time-dependent oscillations are observed and their dependence on speed and pressure magnitude are reported. As the speed approaches cmin, a second transition is observed. Here, the steady solitary depression gives way to an unsteady state (state III), characterized by periodic shedding of lump-like disturbances from the tails of a V-shaped pattern.
Contributors
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- By Rose Teteki Abbey, K. C. Abraham, David Tuesday Adamo, LeRoy H. Aden, Efrain Agosto, Victor Aguilan, Gillian T. W. Ahlgren, Charanjit Kaur AjitSingh, Dorothy B E A Akoto, Giuseppe Alberigo, Daniel E. Albrecht, Ruth Albrecht, Daniel O. Aleshire, Urs Altermatt, Anand Amaladass, Michael Amaladoss, James N. Amanze, Lesley G. Anderson, Thomas C. Anderson, Victor Anderson, Hope S. Antone, María Pilar Aquino, Paula Arai, Victorio Araya Guillén, S. Wesley Ariarajah, Ellen T. Armour, Brett Gregory Armstrong, Atsuhiro Asano, Naim Stifan Ateek, Mahmoud Ayoub, John Alembillah Azumah, Mercedes L. García Bachmann, Irena Backus, J. Wayne Baker, Mieke Bal, Lewis V. Baldwin, William Barbieri, António Barbosa da Silva, David Basinger, Bolaji Olukemi Bateye, Oswald Bayer, Daniel H. Bays, Rosalie Beck, Nancy Elizabeth Bedford, Guy-Thomas Bedouelle, Chorbishop Seely Beggiani, Wolfgang Behringer, Christopher M. Bellitto, Byard Bennett, Harold V. Bennett, Teresa Berger, Miguel A. Bernad, Henley Bernard, Alan E. Bernstein, Jon L. Berquist, Johannes Beutler, Ana María Bidegain, Matthew P. Binkewicz, Jennifer Bird, Joseph Blenkinsopp, Dmytro Bondarenko, Paulo Bonfatti, Riet en Pim Bons-Storm, Jessica A. Boon, Marcus J. Borg, Mark Bosco, Peter C. Bouteneff, François Bovon, William D. Bowman, Paul S. Boyer, David Brakke, Richard E. Brantley, Marcus Braybrooke, Ian Breward, Ênio José da Costa Brito, Jewel Spears Brooker, Johannes Brosseder, Nicholas Canfield Read Brown, Robert F. Brown, Pamela K. Brubaker, Walter Brueggemann, Bishop Colin O. Buchanan, Stanley M. Burgess, Amy Nelson Burnett, J. Patout Burns, David B. Burrell, David Buttrick, James P. Byrd, Lavinia Byrne, Gerado Caetano, Marcos Caldas, Alkiviadis Calivas, William J. Callahan, Salvatore Calomino, Euan K. Cameron, William S. Campbell, Marcelo Ayres Camurça, Daniel F. Caner, Paul E. Capetz, Carlos F. Cardoza-Orlandi, Patrick W. Carey, Barbara Carvill, Hal Cauthron, Subhadra Mitra Channa, Mark D. Chapman, James H. Charlesworth, Kenneth R. Chase, Chen Zemin, Luciano Chianeque, Philip Chia Phin Yin, Francisca H. Chimhanda, Daniel Chiquete, John T. Chirban, Soobin Choi, Robert Choquette, Mita Choudhury, Gerald Christianson, John Chryssavgis, Sejong Chun, Esther Chung-Kim, Charles M. A. Clark, Elizabeth A. Clark, Sathianathan Clarke, Fred Cloud, John B. Cobb, W. Owen Cole, John A Coleman, John J. Collins, Sylvia Collins-Mayo, Paul K. Conkin, Beth A. Conklin, Sean Connolly, Demetrios J. Constantelos, Michael A. Conway, Paula M. Cooey, Austin Cooper, Michael L. Cooper-White, Pamela Cooper-White, L. William Countryman, Sérgio Coutinho, Pamela Couture, Shannon Craigo-Snell, James L. Crenshaw, David Crowner, Humberto Horacio Cucchetti, Lawrence S. Cunningham, Elizabeth Mason Currier, Emmanuel Cutrone, Mary L. Daniel, David D. Daniels, Robert Darden, Rolf Darge, Isaiah Dau, Jeffry C. Davis, Jane Dawson, Valentin Dedji, John W. de Gruchy, Paul DeHart, Wendy J. Deichmann Edwards, Miguel A. De La Torre, George E. Demacopoulos, Thomas de Mayo, Leah DeVun, Beatriz de Vasconcellos Dias, Dennis C. Dickerson, John M. Dillon, Luis Miguel Donatello, Igor Dorfmann-Lazarev, Susanna Drake, Jonathan A. Draper, N. Dreher Martin, Otto Dreydoppel, Angelyn Dries, A. J. Droge, Francis X. D'Sa, Marilyn Dunn, Nicole Wilkinson Duran, Rifaat Ebied, Mark J. Edwards, William H. Edwards, Leonard H. Ehrlich, Nancy L. Eiesland, Martin Elbel, J. Harold Ellens, Stephen Ellingson, Marvin M. Ellison, Robert Ellsberg, Jean Bethke Elshtain, Eldon Jay Epp, Peter C. Erb, Tassilo Erhardt, Maria Erling, Noel Leo Erskine, Gillian R. Evans, Virginia Fabella, Michael A. Fahey, Edward Farley, Margaret A. Farley, Wendy Farley, Robert Fastiggi, Seena Fazel, Duncan S. Ferguson, Helwar Figueroa, Paul Corby Finney, Kyriaki Karidoyanes FitzGerald, Thomas E. FitzGerald, John R. Fitzmier, Marie Therese Flanagan, Sabina Flanagan, Claude Flipo, Ronald B. Flowers, Carole Fontaine, David Ford, Mary Ford, Stephanie A. Ford, Jim Forest, William Franke, Robert M. Franklin, Ruth Franzén, Edward H. Friedman, Samuel Frouisou, Lorelei F. Fuchs, Jojo M. Fung, Inger Furseth, Richard R. Gaillardetz, Brandon Gallaher, China Galland, Mark Galli, Ismael García, Tharscisse Gatwa, Jean-Marie Gaudeul, Luis María Gavilanes del Castillo, Pavel L. Gavrilyuk, Volney P. Gay, Metropolitan Athanasios Geevargis, Kondothra M. George, Mary Gerhart, Simon Gikandi, Maurice Gilbert, Michael J. Gillgannon, Verónica Giménez Beliveau, Terryl Givens, Beth Glazier-McDonald, Philip Gleason, Menghun Goh, Brian Golding, Bishop Hilario M. Gomez, Michelle A. Gonzalez, Donald K. Gorrell, Roy Gottfried, Tamara Grdzelidze, Joel B. Green, Niels Henrik Gregersen, Cristina Grenholm, Herbert Griffiths, Eric W. Gritsch, Erich S. Gruen, Christoffer H. Grundmann, Paul H. Gundani, Jon P. Gunnemann, Petre Guran, Vidar L. Haanes, Jeremiah M. Hackett, Getatchew Haile, Douglas John Hall, Nicholas Hammond, Daphne Hampson, Jehu J. Hanciles, Barry Hankins, Jennifer Haraguchi, Stanley S. Harakas, Anthony John Harding, Conrad L. Harkins, J. William Harmless, Marjory Harper, Amir Harrak, Joel F. Harrington, Mark W. Harris, Susan Ashbrook Harvey, Van A. Harvey, R. Chris Hassel, Jione Havea, Daniel Hawk, Diana L. Hayes, Leslie Hayes, Priscilla Hayner, S. Mark Heim, Simo Heininen, Richard P. Heitzenrater, Eila Helander, David Hempton, Scott H. Hendrix, Jan-Olav Henriksen, Gina Hens-Piazza, Carter Heyward, Nicholas J. Higham, David Hilliard, Norman A. Hjelm, Peter C. Hodgson, Arthur Holder, M. Jan Holton, Dwight N. Hopkins, Ronnie Po-chia Hsia, Po-Ho Huang, James Hudnut-Beumler, Jennifer S. Hughes, Leonard M. Hummel, Mary E. Hunt, Laennec Hurbon, Mark Hutchinson, Susan E. Hylen, Mary Beth Ingham, H. Larry Ingle, Dale T. Irvin, Jon Isaak, Paul John Isaak, Ada María Isasi-Díaz, Hans Raun Iversen, Margaret C. Jacob, Arthur James, Maria Jansdotter-Samuelsson, David Jasper, Werner G. Jeanrond, Renée Jeffery, David Lyle Jeffrey, Theodore W. Jennings, David H. Jensen, Robin Margaret Jensen, David Jobling, Dale A. Johnson, Elizabeth A. Johnson, Maxwell E. Johnson, Sarah Johnson, Mark D. Johnston, F. Stanley Jones, James William Jones, John R. Jones, Alissa Jones Nelson, Inge Jonsson, Jan Joosten, Elizabeth Judd, Mulambya Peggy Kabonde, Robert Kaggwa, Sylvester Kahakwa, Isaac Kalimi, Ogbu U. Kalu, Eunice Kamaara, Wayne C. Kannaday, Musimbi Kanyoro, Veli-Matti Kärkkäinen, Frank Kaufmann, Léon Nguapitshi Kayongo, Richard Kearney, Alice A. Keefe, Ralph Keen, Catherine Keller, Anthony J. Kelly, Karen Kennelly, Kathi Lynn Kern, Fergus Kerr, Edward Kessler, George Kilcourse, Heup Young Kim, Kim Sung-Hae, Kim Yong-Bock, Kim Yung Suk, Richard King, Thomas M. King, Robert M. Kingdon, Ross Kinsler, Hans G. Kippenberg, Cheryl A. 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- Edited by Daniel Patte, Vanderbilt University, Tennessee
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- The Cambridge Dictionary of Christianity
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An experimental investigation of divergent bow waves simulated by a two-dimensional plus temporal wave maker technique – ERRATUM
- MOSTAFA SHAKERI, MOHAMMADREZA TAVAKOLINEJAD, JAMES H. DUNCAN
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- Journal of Fluid Mechanics / Volume 638 / 10 November 2009
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- 20 October 2009, p. 507
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In the published article Shakeri et al. (2009) the title should read as above (i.e. ‘wave maker technique’, not ‘wave marker technique’ as in the published article).
An experimental investigation of divergent bow waves simulated by a two-dimensional plus temporal wave marker technique
- MOSTAFA SHAKERI, MOHAMMADREZA TAVAKOLINEJAD, JAMES H. DUNCAN
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- Journal of Fluid Mechanics / Volume 634 / 10 September 2009
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- 26 August 2009, pp. 217-243
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Divergent ship bow waves were simulated experimentally with a two-dimensional wavemaker that employs a flexible wave board. The wavemaker was programmed so that the wave board created a time sequence of shapes that simulated the line of intersection between one side of the hull of a slender ship model moving at constant speed and an imaginary vertical plane oriented normal to the ship model track. The time history of the water surface shape was measured with a cinematic laser-induced fluorescence technique for eight Froude numbers (FD = U/
, where U is the forward speed of the equivalent three-dimensional ship model, g the acceleration of gravity and D the ship model draft). The waves produced ranged from small-amplitude non-breaking waves at the lowest Froude numbers to plunging breakers at the highest Froude numbers. These waves are strongly forced and at the higher Froude numbers begin breaking before leaving the wave board. The time histories of various geometric characteristics of the water surface shape including the hull contact line, the wave crest, the plunging jet and the splash zone, which is here defined as both the turbulent zone on the front face of the wave in the spilling breakers and the turbulent zone generated ahead of the jet impact point in the plunging breakers, were measured. The phase speed of the primary wave generated during each run ranged from 2.56Uwl (where Uwl is the maximum speed of the wave board at the undisturbed water level in the tank) at the lowest Froude number to about 1.7Uwl at the three highest Froude numbers. The maximum heights of the primary wave, the contact point on the wavemaker and the splash zone increased in a nearly linear fashion with increasing FD. In the cases with plunging jets, the jet tip trajectory was parabolic with a vertical acceleration ranging from 0.6g at FD = 1.467 to 0.8g at FD = 1.817 (the highest Froude number).
Preliminary evidence for progressive prefrontal abnormalities in adolescents and young adults with bipolar disorder
- JESSICA H. KALMAR, FEI WANG, LINDA SPENCER, ERIN EDMISTON, CHERYL M. LACADIE, ANDRÉS MARTIN, R. TODD CONSTABLE, JAMES S. DUNCAN, LAWRENCE H. STAIB, XENOPHON PAPADEMETRIS, HILARY P. BLUMBERG
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- Journal of the International Neuropsychological Society / Volume 15 / Issue 3 / May 2009
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- 01 May 2009, pp. 476-481
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Previous cross-sectional study of ventral prefrontal cortex (VPFC) implicated progressive volume abnormalities during adolescence in bipolar disorder (BD). In the present study, a within-subject, longitudinal design was implemented to examine brain volume changes during adolescence/young adulthood. We hypothesized that VPFC volume decreases over time would be greater in adolescents/young adults with BD than in healthy comparison adolescents/young adults. Eighteen adolescents/young adults (10 with BD I and 8 healthy comparison participants) underwent two high-resolution magnetic resonance imaging scans over approximately 2 years. Regional volume changes over time were measured. Adolescents/young adults with BD displayed significantly greater volume loss over time, compared to healthy comparison participants, in a region encompassing VPFC and rostral PFC and extending to rostral anterior cingulate cortex (p < .05). Additional areas where volume change differed between groups were observed. While data should be interpreted cautiously due to modest sample size, this study provides preliminary evidence to support the presence of accelerated loss in VPFC and rostral PFC volume in adolescents/young adults with BD. (JINS, 2009, 15, 476–481.)
An experimental study of surfactant effects on spilling breakers
- XINAN LIU, JAMES H. DUNCAN
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- Journal of Fluid Mechanics / Volume 567 / 25 November 2006
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- 19 October 2006, pp. 433-455
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The dynamics of spilling breakers in the presence of surfactants were studied experimentally. The spilling breakers were produced from Froude-scaled mechanically generated dispersively focused wave packets with average frequencies of 1.15, 1.26 and 1.42 Hz. Separate experiments were performed with the same wave-maker motions in clean water and in water with various bulk concentrations of the soluble surfactants sodium dodecyl sulfate (SDS) and Triton X-100 (TX). For nearly all surfactant conditions, the surface-pressure isotherm, equilibrium surface elasticity and surface viscosity were measured in situ in order to characterize the dynamic properties of the free surface. In clean water, all the waves considered herein break without overturning of the free surface. This breaking process begins with the formation of a bulge on the forward face of the wave crest and capillary waves upstream of the leading edge of the bulge (called the toe). After a short time, the flow separates under the toe and a turbulent flow is developed while the toe moves rapidly down the wave face. During the toe motion, a train of ripples appears between the toe and the crest and this train of ripples is swept downstream. In the presence of surfactants, the bulge shape is modified and its size generally decreases with increasing surfactant concentration. The capillary waves found upstream of the toe in the clean-water case are dramatically reduced at even the lowest concentrations of surfactants. With surfactants, the start of the breaking process is still initiated when the toe begins to move down the forward face of the wave. The pattern of ripples generated between the toe and the crest of the wave during this phase of the breaking process varies with the concentration of surfactant. It was found that the temporal history of the vertical distance between the toe and the wave crest scales with the nominal length $(\sigma_0/\rho g)^{1/2}$ while the bulge length from toe to crest scales with the nominal length $(\mu_s/\rho \sqrt{g})^{2/5}$, where $\sigma_0$ and $\mu_s$ are the ambient surface tension and the surface viscosity, respectively.
The final stage of the collapse of a cavitation bubble near a rigid wall
- Sheguang Zhang, James H. Duncan, Georges L. Chahine
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- Journal of Fluid Mechanics / Volume 257 / December 1993
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- 26 April 2006, pp. 147-181
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During the collapse of an initially spherical cavitation bubble near a rigid wall, a reentrant jet forms from the side of the bubble farthest from the wall. This re-entrant jet impacts and penetrates the bubble surface closest to the wall during the final stage of the collapse. In the present paper, this phenomenon is modelled with potential flow theory, and a numerical approach based on conventional and hypersingular boundary integral equations is presented. The method allows for the continuous simulation of the bubble motion from growth to collapse and the impact and penetration of the reentrant jet. The numerical investigations show that during penetration the bubble surface is transformed to a ring bubble that is smoothly attached to a vortex sheet. The velocity of the tip of the re-entrant jet is always directed toward the wall during penetration with a speed less than its speed before impact. A high-pressure region is created around the penetration interface. Theoretical analysis and numerical results show that the liquid-liquid impact causes a loss in the kinetic energy of the flow field. Variations in the initial distance from the bubble centre to the wall are found to cause large changes in the details of the flow field. No existing experimental data are available to make a direct comparison with the numerical predictions. However, the results obtained in this study agree qualitatively with experimental observations.
Surface ripples due to steady breaking waves
- James H. Duncan, Athanassios A. Dimas
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- Journal of Fluid Mechanics / Volume 329 / 25 December 1996
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- 26 April 2006, pp. 309-339
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Breaking waves generated by a two-dimensional hydrofoil moving near a free surface at constant speed (U∞), angle of attack and depth of submergence were studied experimentally. The measurements included the mean and fluctuating shape of the breaking wave, the surface ripples downstream of the breaker and the vertical distribution of vertical and horizontal velocity fluctuations at a single station behind the breaking waves. The spectrum of the ripples is highly peaked and shows little variation in both its peak frequency and its shape over the first three wavelengths of the wavetrain following the breaker. For a given speed, as the breaker strength is increased, the high-frequency ends of the spectra are nearly identical but the spectral peaks move to lower frequencies. A numerical instability model, in conjunction with the experimental data, shows that the ripples are generated by the shear flow developed at the breaking region. The spectrum of the vertical velocity fluctuations was also found to be highly peaked with the same peak frequency as the ripples, while the corresponding spectrum of the horizontal velocity fluctuations was found not to be highly peaked. The root-mean-square (r.m.s.) amplitude of the ripples (νrms) increases with increasing speed and with decreasing depth of submergence of the hydrofoil, and decreases as x-1/2 with increasing distance x behind the breaker. The quantity (gνrms)/(U∞Vrms) (where Vrms is the maximum r.m.s. vertical velocity fluctuation and g is the gravitational acceleration) was found to be nearly constant for all of the measurements.
The response of an incompressible, viscoelastic coating to pressure fluctuations in a turbulent boundary layer
- James H. Duncan
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- Journal of Fluid Mechanics / Volume 171 / October 1986
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- 21 April 2006, pp. 339-363
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The response of the interface between a compliant surface and a turbulent boundary-layer flow is examined theoretically. This response is forced by transient, convected, interfacial pressure pulses that represent the footprints of turbulent flow structures in the boundary layer. Calculations are presented for coatings with a wide range of damping and densities equal to the density of the flow. For coatings with moderate damping, three regimes of response are found. When the flow speed U∞ is less than about 1.2 (non-dimensionalized by the shear wave speed of the coating), the response is stable and primarily localized under the pressure pulse. For flow speeds from 1.2 to as high as 2.8, depending on the damping, the response is also stable, but it includes a wave pattern behind the pressure pulses. For flow speeds above 2.8, the response is unstable and eventually forms a two-dimensional wavetrain moving in the flow direction. At the highest stable flow velocity, the amplitude of the surface displacements reaches 4.0% of the boundary-layer displacement thickness δ* and the energy transfer from the pressure pulse reaches 5.0 × 10−4U∞2 (δ*)2. For high damping, the coating response is again stable when the flow speed is below 2.8. However, there is no wavelike response regime; the path that is traversed by the pressure pulse is covered by a scar that heals according to the viscous relaxation properties of the material. The amplitude of the response is at most 0.01δ*.