1,720,960 research outputs found
Properties of the body of a turbidity current at near‐normal conditions: 2. Effect of settling
No full textTurbidity currents are sediment-laden flows that move over a sloping surface. These flows are driven by the density difference between the sediment-laden current and the clear ambient fluid above. Here we focus on studying the process of ambient fluid entrainment at the interface between the current and the sediment-free ambient fluid and obtain a closure model for the entrainment coefficient. In particular, we extend the classical dependence of entrainment coefficient on the bulk Richardson number, by including the effect of sediment settling velocity. We focus our attention to turbidity currents under normal flow condition, where the depth-averaged streamwise velocity U is nearly a constant. We employ direct numerical simulations of temporally evolving turbidity currents. Similarly, we study the dependence of basal drag distribution on Richardson number and settling velocity. In addition, we study the turbulence structures of the flow and its relation to turbulence production.Fil: Salinas, Jorge Sebastián. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. University of Florida; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Cantero, Mariano Ignacio. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Shringarpure, M.. University of Florida; Estados UnidosFil: Selvakumar, Balachandar. University of Florida; Estados Unido
Properties of the body of a turbidity current at near-normal conditions: 1. Effect of bed slope
No full textWe study the body of turbidity currents in normal flow conditions by means of highly resolved direct numerical simulations of a homogeneous model. We focus on turbidity currents where the net amount of sediment is held fixed. We consider the sediment to be fine enough that their settling effect is neglected, and in the companion work we consider the effect of settling velocity. We consider five different shear Richardson numbers from 5 to 80. Under normal condition, basal drag and entrainment at the interface precisely balance the momentum supplied to the current from the excess weight of the sediment. The normal flow properties of a turbidity current can be fully characterized in terms of bulk Richardson number Ri and bulk Reynolds number Re. The velocity, concentration, and turbulent kinetic energy profiles take a self-similar shape when the current is at near-normal conditions. We observe the flow to display supercritical features for (Formula presented.) and to display subcritical features for (Formula presented.). From the behavior at intermediate Richardson numbers it appears that the transition between subcritical to supercritical behavior is not sharp. We observe good agreement between experimental and simulation results in both regimes. The entrainment coefficient as a function of bulk Richardson number at normal condition is in good agreement with the empirical relation and with available experimental results. We present a simple model for drag coefficient as a function of bulk Reynolds and Richardson numbers.Fil: Salinas, Jorge Sebastián. University of Florida; Estados Unidos. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Cantero, Mariano Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Shringarpure, M.. University of Florida; Estados UnidosFil: Selvakumar, Balachandar. University of Florida; Estados Unido
Mechanisms of Complete Turbulence Suppression in Turbidity Currents Driven by Mono-Disperse and Bi-Disperse Suspensions of Sediment
Get PDFTurbidity currents are submarine flows where the sediment fluid mixture (heavy current) drives along the sloping ocean floor displacing the surrounding clear fluid (light ambient). Under the influence of gravity, the suspended sediments drive the current and at the same time settle down on the ocean bed. The interplay of turbulent mixing and settling sediments leads to stable stratification of sediments in the turbidity current. In previous studies (Cantero et al. 2009b; Cantero et al., 2009a; Cantero et al., 2012a; Talling et al., 2007) it was observed that strong settling tendency (large sediment sizes) could cause complete turbulence suppression. In this study, we will analyse this process of complete turbulence suppression by means of direct numerical simulations (DNS) of turbidity currents. In wall bounded unstratified flows, it has been long established that turbulence is sustained by the process of auto-generation of near-wall hairpin like and quasi-streamwise turbulent vortical structures. It was also identified that auto-generation is possible only when the strength of the turbulent structures is greater than a threshold value (Zhou et. al., 1996). Through quadrant analysis of Reynolds stress events and visualization of turbulent vortical structures, we observe that stratification by sediments lead to damping and spatial re-distribution of turbulent vortical structures in the flow. We propose that complete turbulence suppression is brought about by a total shutdown in the auto-generation process of the existing turbulent structures in the flow. We also identify three parameters – Reynolds number (Reτ), Richardson number (Riτ) and sediment settling velocity (V˜z) that quantify the process of turbulence suppression. A criterion for complete turbulence suppression is also proposed which can be defined as a critical value for RiτV˜z. This critical value is a function of Ret and based on simulations, experiments and field observations it appears to have a logarithmic dependence on Reτ (Cantero et al. 2012). DNS of turbidity currents driven by bi-disperse suspension of sediments is also carried out and compared with the results of mono-disperse suspensions.Fil: Shringarpure, Mrugesh S.. University of Florida; Estados UnidosFil: Cantero, Mariano Ignacio. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Selvakumar, Balachandar. University of Florida; Estados Unido
Functional phenotypes of macrophages and their role in influenza A virus induced lung injury and repair
Get PDFInfluenza A Virus (IAV)-induced acute lung injury/acute respiratory distress syndrome (ALI/ARDS) is a severe complication of IAV infection in humans with often fatal outcome due to lack of effective therapeutic options. It is characterized by severe inflammation in the alveolar compartment of the lung, associated with apoptotic injury of the alveolar epithelium, resulting in loss of barrier function, edema formation and impaired gas exchange capacity with respiratory failure. Alveolar exudate macrophages (ExMa) have been shown to be key players in both driving inflammatory injury to the alveolar epithelium, but also in promoting resolution of inflammation and driving tissue repair processes, and these different functions have been suggested to be associated with the M1 versus M2 polarization phenotype of macrophages, respectively. However, to date, methods to define these phenotypes in pneumonia models in vivo have not been established, nor have the functional properties of M1 and M2ExMa and the signaling pathways or mediators associated with these functions been elucidated, particularly in the context of IAV infection.The presented data provide evidence that ExMa reveal high functional plasticity during IAV-induced ALI/ARDS. Different polarization phenotypes, M1 and M2ExMa, can be defined and separated by a newly established FACS gating strategy, allowing analyses of their gene expression profiles and correlation to their functional properties in IAV-induced lung injury. Quantitative analyses revealed that in the early, acute phase of IAV infection (D7pi), large numbers of M1ExMa infiltrate the alveolar and, to lesser extent, the interstitial space of the lung. Later on, ExMa numbers decline and increasing proportions of M2ExMa are present. By D21pi, low numbers of ExMa are present which are completely polarized towards an M2 phenotype. Of note, bone marrow chimeric mouse models and adoptive ExMa transfer studies into ExMa recruitment-deficient CCR2-/- mice demonstrated that the functional phenotype of M2ExMa is associated with both preservation and replenishment of the rAM pool depleted upon IAV infection, and with regeneration of the alveolar epithelium and improved epithelial barrier function in IAV-induced ALI/ARDS. Transcriptomic profiling of M1 versus M2ExMa revealed highly distinct gene expression profiles, with M1ExMa expressing pro-inflammatory/pro-apoptotic and host defense-associated genes, whereas M2ExMa upregulating anti-inflammatory/anti-apoptotic genes and a high number of epithelial growth factors. The most highly regulated gene in M2 versus M1ExMa was found to be Placenta-expressed transcript 1 (Plet1), a growth factor previously associated with development of epithelial layers, epithelial cell proliferation and formation of epithelial tight junctions. In vitro infection experiments using primary murine alveolar epithelial cells (mAEC) demonstrated that recombinant Plet1 prevented AEC apoptosis and IAV replication, upregulated tight junction-associated proteins and increased tightness of the AEC monolayer. Blockade of Plet1 in M2ExMa by neutralizing antibodies abolished the epithelial-protective properties of M2ExMa in IAV infection in vivo. Orotracheal treatment of IAV infected mice with recombinant Plet1 attenuated inflammation, induced AEC repair, improved alveolar barrier function and increased survival of IAV-induced ALI/ARDS. Together, these data indicate that M1 and M2ExMa are functionally distinct phenotypes evolving during IAV infection, and that M2 programming of ExMa in vivo is protective with respect to alveolar barrier function due to expression of Plet1. Moreover, therapeutic intervention using alveolar deposition of Plet1 might be a useful strategy to improve outcome after ALI/ARDS in humansDas Influenza A Virus (IAV) induzierte akute Lungenversagen/´Acute Respiratory Distress Syndrome´(ARDS) ist eine schwere Komplikation der humanen IAV Infektion mit häufig tödlichem Ausgang aufgrund fehlender effektiver therapeutischer Optionen. Es ist charakterisiert durch eine schwere Entzündung des alveolären Lungenkompartimentes mit apoptotischer Schädigung des Alveolarepithels, was zum Verlust der pulmonalen Schrankenfunktion mit Lungenödem und schwerer Gasaustauschstörung führt. Alveolär rekrutierte (Exudate) Makrophagen (ExMa) sind zentral sowohl an der inflammatorischen Gewebsschädigung des Alveolarepithels als auch an der Entzündungsauflösung und Gewebereparatur beteiligt und diese differenten Prozesse wurden jeweils einer M1 bzw. M2 Polarisation der beteiligten ExMa zugeschrieben. Bisher wurden jedoch weder Methoden etabliert, die es erlauben, diese Polarisationsphänotypen in Pneumonie Modellen in vivo zu unterscheiden, noch wurden bislang insbesondere im Kontext der IAV Infektion das funktionelle Repertoire von M1 vs. M2 polarisierten ExMa und die daran beteiligten Signalwege und Mediatoren aufgeklärt.Die in dieser Arbeit präsentierten Daten geben Hinweise darauf, dass ExMa im Verlauf des IAV-induzierten Lungenversagens/ARDS eine hohe funktionelle Plastizität aufweisen. Mit Hilfe einer neu etablierten ´FACS- Gating´ Strategie ließen sich M1 und M2 ExMa als distinkte Polarisationsphänotypen identifizieren, durchflusszytometrisch separieren und hinsichtlich ihres Genexpressionsprofils sowie ihrer Funktion im IAV-induzierten Lungenversagen charakterisieren. Quantitative Analysen zeigten, dass in der frühen akuten Phase der IAV Infektion (Tag 7 nach Infektion) M1 ExMa in großer Zahl den Alveolarraum und in geringerem Ausmaß das Lungeninterstitium infiltrieren. Später im Infektionsverlauf sinkt die Zahl der ExMa während der Anteil der ExMa mit M2 Polarisierung zunimmt. An Tag 21 nach Infektion sind nur noch wenige ExMa nachweisbar, die alle einen M2 Phänotyp aufweisen. Durch Untersuchungen in Knochenmarks-chimären Mausmodellen und adoptiven Transfer von ExMa in CCR2-/- Mäuse mit einem endogenen ExMa Rekrutierungsdefekt ließ sich zeigen, dass der funktionelle Phänotyp von M2ExMa zur Erhaltung und Regenerierung des durch die IAV Infektion depletierten Zellpools residenter Alveolarmakrophagen (rAM) beiträgt, was zur Regeneration des Alveolarepithels und verbesserter epithelialer Barrierefunktion im IAV induzierten Lungenversagen/ARDS führte. Transkriptomanalysen von M1 vs M2ExMa zeigten distinkte Genexpressionsprofile, wobei M1ExMa pro-inflammatorische/pro-apoptotische und Wirtsabwehr-assoziierte Gene exprimierten, während in M2 ExMa anti-inflammatorische/anti-apoptotische Gene sowie eine hohe Anzahl von Genen, die epitheliale Wachstumsfaktoren kodieren, hochreguliert waren. Das am stärksten in M2 versus M1ExMa hochregulierte Gen war ´Placenta-expressed transcript 1´ (Plet1), ein Wachstumsfaktor, dem bereits eine Rolle bei der Entwicklung von Epithelzellschichten, bei der Epithelzellproliferation und der Formierung von epithelialen ´Tight Junctions´ zugeschrieben worden war. In in vitro Infektionsexperimenten an primären murinen Alveolarepithelzellen (AEC) ließ sich zeigen, dass rekombinantes Plet1 die AEC Apoptose und IAV Replikation verhindert, ´Tight Junction assoziierte Proteine hochreguliert und die Dichtigkeit von AEC Monolayern erhöht. Blockade von Plet1 in M2ExMa durch neutralisierende Antikörper führte zum Verlust der Epithel-protektiven Eigenschaften von M2ExMa im Rahmen der IAV Infektion in vivo. Intratracheale Behandlung von IAV infizierten Mäusen mit rekombinantem Plet1 attenuierte die Inflammation, induzierte AEC Reparatur, verbesserte die alveoläre Barrierefunktion und erhöhte die Überlebensrate von Tieren mit IAV-induziertem ALI/ARDS. Insgesamt zeigen diese Ergebnisse, dass M1 und M2 ExMa funktionell distinkte Phänotypen im Verlauf der IAV darstellen und dass eine M2 Programmierung von ExMa durch die Expression von Plet1 in vivo protektiv für die alveoläre Barrierefunktion ist. Die alveoläre Deposition von Plet1 als therapeutische Intervention könnte deshalb eine nützliche Strategie sein, um das Behandlungsergebnis bei Patienten mit ALI/ARDS zu verbessern
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
- …
