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Articles de revues sur le sujet "Dispersal event"
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Hooker, J. J. « A two-phase Mammalian Dispersal Event across the Paleocene–Eocene transition ». Newsletters on Stratigraphy 48, no 2 (1 avril 2015) : 201–20. http://dx.doi.org/10.1127/nos/2015/0060.
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McClenaghan, M. B., et R. N. W. DiLabio. « Ice-flow history and glacial dispersal patterns, southeastern Cape Breton Island, Nova Scotia : implications for mineral exploration ». Canadian Journal of Earth Sciences 33, no 2 (1 février 1996) : 351–62. http://dx.doi.org/10.1139/e96-026.
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Regional till sampling and stratigraphic studies were completed in southeastern Cape Breton Island, Nova Scotia, in 1990 and 1991 to document the directions and distances that successive ice-flow events have dispersed material and to document regional till geochemical patterns to aid mineral exploration in this heavily drift-covered area. Three major Wisconsinan ice-flow events affected the area: an early eastward flow, followed by a northeastward flow, and finally a southward flow. The shape and magnitude of dispersal trains in the area are the net result of the three ice-flow events, which are variable from north to south. In the north, the northeast ice flow was the dominant erosive and depositional event, producing a large northeast-trending drumlin field. Salmon River porphyry clasts and Pb- and Zn-rich till from the Yava Pb mine were dispersed more than 15 km to the northeast. In the south, eastward ice flow was the dominant erosive and depositional event, producing large east-trending till ridges. Dispersal in this area is difficult to detect because exotic red silty till in the giant till ridges masks underlying mineralized bedrock and dilutes the locally derived glacial debris. Many precious and base metal anomalies and dispersal trains were identified in the regional till samples, several of which are related to unknown mineralized sources.
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Iannucci, Alessio, et Raffaele Sardella. « What Does the “Elephant-Equus” Event Mean Today ? Reflections on Mammal Dispersal Events around the Pliocene-Pleistocene Boundary and the Flexible Ambiguity of Biochronology ». Quaternary 6, no 1 (28 février 2023) : 16. http://dx.doi.org/10.3390/quat6010016.
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The dispersal of primitive elephantines and monodactyl equids in Eurasia has long been regarded as representative of a substantial turnover in mammal faunas, denoting the spread of open environments linked to the onset of cold and dry conditions in the Northern Hemisphere. During the 1980s, this event was named the “Elephant-Equus event” and it was correlated with the Gauss-Matuyama reversal, today corresponding to the Pliocene-Pleistocene transition and the beginning of the Quaternary, dated at ~2.6 Ma. Therefore, the Elephant-Equus event became a concept of prominent biochronological and paleoecological significance, especially in western Europe. Yet, uncertainties surrounding the taxonomy and chronology of early “elephant” and “Equus”, as well as conceptual differences in adopting (or understanding) the Elephant-Equus event as an intercontinental dispersal event or as a stratigraphic datum, engendered ambiguity and debate. Here, we provide a succinct review of the Elephant-Equus event, considering separately the available evidence on the “elephant” and the “Equus”. Elephantines dispersed out of Africa during the Pliocene (Piacenzian). Their earliest calibrated occurrences from eastern Europe date at ~3.2 Ma and they are usually referred to Mammuthus rumanus, although the allocation of several samples to this species is tentative. Available dating constraints for other localities do not resolve whether the dispersal of Mammuthus was synchronous across Eurasia, but this possibility cannot be ruled out. The spread of Mammuthus was part of an intercontinental faunal exchange between Africa and Eurasia that occurred during the Piacenzian, but in this scenario, Mammuthus is quite unique in being the only genus of African origin dispersing to western Eurasia. The arrival of monodactyl equids from North America coincides with the Pliocene-Pleistocene transition, with several occurrences dated or calibrated at ~2.6 Ma and no compelling evidence prior to this age. In Europe, early monodactyl equids are often aligned to Equus livenzovensis, but the material from the type locality of this species is chronologically time-averaged and taxonomically heterogeneous, and western European samples are seldom abundant or informative. Regardless, this does not diminish the biochronological significance of the “Equus event”. Indeed, while the term “Elephant-Equus event” should no longer be used, as the appearance of elephantines in the European fossil record markedly precedes that of monodactyl equids, we endorse the use of the “Equus event” as a valid alternative to refer to the intercontinental dispersal event that characterizes the middle Villafranchian faunal turnover, epitomized by but not limited to monodactyl equids.
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Vahedian, Amin, Xun Zhou, Ling Tong, W. Nick Street et Yanhua Li. « Predicting Urban Dispersal Events : A Two-Stage Framework through Deep Survival Analysis on Mobility Data ». Proceedings of the AAAI Conference on Artificial Intelligence 33 (17 juillet 2019) : 5199–206. http://dx.doi.org/10.1609/aaai.v33i01.33015199.
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Urban dispersal events are processes where an unusually large number of people leave the same area in a short period. Early prediction of dispersal events is important in mitigating congestion and safety risks and making better dispatching decisions for taxi and ride-sharing fleets. Existing work mostly focuses on predicting taxi demand in the near future by learning patterns from historical data. However, they fail in case of abnormality because dispersal events with abnormally high demand are non-repetitive and violate common assumptions such as smoothness in demand change over time. Instead, in this paper we argue that dispersal events follow a complex pattern of trips and other related features in the past, which can be used to predict such events. Therefore, we formulate the dispersal event prediction problem as a survival analysis problem. We propose a two-stage framework (DILSA), where a deep learning model combined with survival analysis is developed to predict the probability of a dispersal event and its demand volume. We conduct extensive case studies and experiments on the NYC Yellow taxi dataset from 20142016. Results show that DILSA can predict events in the next 5 hours with F1-score of 0:7 and with average time error of 18 minutes. It is orders of magnitude better than the state-of-the-art deep learning approaches for taxi demand prediction.
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Vidal, Nicolas, Anna Azvolinsky, Corinne Cruaud et S. Blair Hedges. « Origin of tropical American burrowing reptiles by transatlantic rafting ». Biology Letters 4, no 1 (11 décembre 2007) : 115–18. http://dx.doi.org/10.1098/rsbl.2007.0531.
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Populations of terrestrial or freshwater taxa that are separated by oceans can be explained by either oceanic dispersal or fragmentation of a previously contiguous land mass. Amphisbaenians, the worm lizards (approx. 165 species), are small squamate reptiles that are uniquely adapted to a burrowing lifestyle and inhabit Africa, South America, Caribbean Islands, North America, Europe and the Middle East. All but a few species are limbless and they rarely leave their subterranean burrows. Given their peculiar habits, the distribution of amphisbaenians has been assumed to be primarily the result of two land-mass fragmentation events: the split of the supercontinent Pangaea starting 200 Myr ago, separating species on the northern land mass (Laurasia) from those on the southern land mass (Gondwana), and the split of South America from Africa 100 Myr ago. Here we show with molecular evidence that oceanic dispersal—on floating islands—played a more prominent role, and that amphisbaenians crossed the Atlantic Ocean in the Eocene (40 Myr ago) resulting in a tropical American radiation representing one-half of all known amphisbaenian species. Until now, only four or five transatlantic dispersal events were known in terrestrial vertebrates. Significantly, this is the first such dispersal event to involve a group that burrows, an unexpected lifestyle for an oceanic disperser.
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Magalhaes, Ivan L. F., Adalberto J. Santos et Martín J. Ramírez. « Incorporating Topological and Age Uncertainty into Event-Based Biogeography of Sand Spiders Supports Paleo-Islands in Galapagos and Ancient Connections among Neotropical Dry Forests ». Diversity 13, no 9 (31 août 2021) : 418. http://dx.doi.org/10.3390/d13090418.
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Event-based biogeographic methods, such as dispersal-extinction-cladogenesis, have become increasingly popular for attempting to reconstruct the biogeographic history of organisms. Such methods employ distributional data of sampled species and a dated phylogenetic tree to estimate ancestral distribution ranges. Because the input tree is often a single consensus tree, uncertainty in topology and age estimates are rarely accounted for, even when they may affect the outcome of biogeographic estimates. Even when such uncertainties are taken into account for estimates of ancestral ranges, they are usually ignored when researchers compare competing biogeographic hypotheses. We explore the effect of incorporating this uncertainty in a biogeographic analysis of the 21 species of sand spiders (Sicariidae: Sicarius) from Neotropical xeric biomes, based on a total-evidence phylogeny including a complete sampling of the genus. Using a custom R script, we account for uncertainty in ages and topology by estimating ancestral ranges over a sample of trees from the posterior distribution of a Bayesian analysis, and for uncertainty in biogeographic estimates by using stochastic maps. This approach allows for counting biogeographic events such as dispersal among areas, counting lineages through time per area, and testing biogeographic hypotheses, while not overestimating the confidence in a single topology. Including uncertainty in ages indicates that Sicarius dispersed to the Galapagos Islands when the archipelago was formed by paleo-islands that are now submerged; model comparison strongly favors a scenario where dispersal took place before the current islands emerged. We also investigated past connections among currently disjunct Neotropical dry forests; failing to account for topological uncertainty underestimates possible connections among the Caatinga and Andean dry forests in favor of connections among Caatinga and Caribbean + Mesoamerican dry forests. Additionally, we find that biogeographic models including a founder-event speciation parameter (“+J”) are more prone to suffer from the overconfidence effects of estimating ancestral ranges using a single topology. This effect is alleviated by incorporating topological and age uncertainty while estimating stochastic maps, increasing the similarity in the inference of biogeographic events between models with or without a founder-event speciation parameter. We argue that incorporating phylogenetic uncertainty in biogeographic hypothesis-testing is valuable and should be a commonplace approach in the presence of rogue taxa or wide confidence intervals in age estimates, and especially when using models including founder-event speciation.
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Mai-Prochnow, Anne, Jeremy S. Webb, Belinda C. Ferrari et Staffan Kjelleberg. « Ecological Advantages of Autolysis during the Development and Dispersal of Pseudoalteromonas tunicata Biofilms ». Applied and Environmental Microbiology 72, no 8 (août 2006) : 5414–20. http://dx.doi.org/10.1128/aem.00546-06.
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ABSTRACT In the ubiquitous marine bacterium Pseudoalteromonas tunicata, subpopulations of cells are killed by the production of an autocidal protein, AlpP, during biofilm development. Our data demonstrate an involvement of this process in two parameters, dispersal and phenotypic diversification, which are of importance for the ecology of this organism and for its survival within the environment. Cell death in P. tunicata wild-type biofilms led to a major reproducible dispersal event after 192 h of biofilm development. The dispersal was not observed with a ΔAlpP mutant strain. Using flow cytometry and the fluorescent dye DiBAC4(3), we also show that P. tunicata wild-type cells that disperse from biofilms have enhanced metabolic activity compared to those cells that disperse from ΔAlpP mutant biofilms, possibly due to nutrients released from dead cells. Furthermore, we report that there was considerable phenotypic variation among cells dispersing from wild-type biofilms but not from the ΔAlpP mutant. Wild-type cells that dispersed from biofilms showed significantly increased variations in growth, motility, and biofilm formation, which may be important for successful colonization of new surfaces. These findings suggest for the first time that the autocidal events mediated by an antibacterial protein can confer ecological advantages to the species by generating a metabolically active and phenotypically diverse subpopulation of dispersal cells.
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James, Trevor K., Michael R. Trolove et Claire A. Dowsett. « Roadside mowing spreads yellow bristle grass (Setaria pumila) seeds further than by natural dispersal ». New Zealand Plant Protection 72 (22 juillet 2019) : 153–57. http://dx.doi.org/10.30843/nzpp.2019.72.246.
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Yellow bristle grass is a highly invasive annual C4 pasture weed that has spread rapidly through many New Zealand dairying regions via seed dispersal. Seven trials were conducted on roadsides infested with yellow bristle grass to evaluate natural and mower-assisted dispersal. To trap seeds, yellow sticky traps were laid out at various intervals both perpendicular to and parallel to the road. Traps were in place for 24 h in the four natural dispersal trials but only for the event in the mowing trials. Seeds on the retrieved traps were counted and the seeds caught in the mower estimated. For natural dispersal, 90% of seeds fell within 0.5 m. When mown, 90% of the seeds fell within 2 metres in the direction of mowing and 80% within 20 cm in the perpendicular direction. More importantly, a small percentage of dispersed seeds were caught in the mower and presumably could subsequently fall off anywhere. Mowing mature yellow bristle grass on the roadside will result in accelerating seed dispersal along the roadside for many metres and potentially many kilometres.
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Skjelseth, Sigrun, Thor Harald Ringsby, Jarle Tufto, Henrik Jensen et Bernt-Erik Sæther. « Dispersal of introduced house sparrows Passer domesticus : an experiment ». Proceedings of the Royal Society B : Biological Sciences 274, no 1619 (8 mai 2007) : 1763–71. http://dx.doi.org/10.1098/rspb.2007.0338.
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An important issue concerning the introduction of non-indigenous organisms into local populations is the potential of the introduced individuals to spread and interfere both demographically and genetically with the local population. Accordingly, the potential of spatial dispersal among introduced individuals compared with local individuals is a key parameter to understand the spatial and temporal dynamics of populations after an introduction event. In addition, if the variance in dispersal rate and distance is linked to individual characteristics, this may further affect the population dynamics. We conducted a large-scale experiment where we introduced 123 house sparrows from a distant population into 18 local populations without changing population density or sex ratio. Introduced individuals dispersed more frequently and over longer distances than residents. Furthermore, females had higher probability of dispersal than males. In females, there was also a positive relationship between the wing length and the probability of dispersal and dispersal distance. These results suggest that the distribution and frequency of introduced individuals may be predicted by their sex ratio as well as their phenotypic characteristics.
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Martínez, Isabel, et Fernando González-Taboada. « Seed dispersal patterns in a temperate forest during a mast event : performance of alternative dispersal kernels ». Oecologia 159, no 2 (19 novembre 2008) : 389–400. http://dx.doi.org/10.1007/s00442-008-1218-4.
Texte intégralThèses sur le sujet "Dispersal event"
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Smith, David A. « An integrated approach to evaluating the environmental impact following a radiological dispersal event ». Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1148312072.
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Scarboro, Sarah Brashear. « The use of a thyroid uptake system for assaying internal contamination following a radioactive dispersal event ». Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22639.
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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008.Committee Chair: Nolan Hertel; Committee Member: Armin Ansari; Committee Member: Chris Wang; Committee Member: Rebecca Howell.
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Bridges, Ashby H. « Estimating the radiation dose to emergency room personnel in an event of a radiological dispersal device explosion ». Thesis, Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-08242006-142548/.
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Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2007.Dr. Armin J. Ansari, Committee Member ; Dr. Farzad Rahnema, Committee Member ; Dr. Rebecca Howell, Committee Member ; Dr. Nolan E. Hertel, Committee Chair.
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Censullo, Shaolin Meliora. « Did Alternating Dispersal and Vicariance Contribute to Increased Biodiversification During the Great Ordovician Biodiversification Event ? : A Phylogenetic Test Using Brachiopods ». Ohio University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1586947231228706.
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Teague, Kara Elizabeth. « Environmental Ramification of the Fire Ecology of Slash Pine (Pinus elliottii) : A Study of Population Dynamics and Dispersal following a Fire Event ». Scholar Commons, 2003. https://scholarcommons.usf.edu/etd/1491.
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With increasing encroachment on natural communities by anthropogenic activity, it is important to understand the functions of natural ecosystems in an effort to conserve natural areas. A first-hand study of the population dynamics of South Florida Slash Pine (P. elliottii Engelm. var. densa) following a fire event provided insight to its recovery and dispersal following a fire. A natural fire (lightning-induced) occurred in the spring of 2000 at the T. Mabry Carlton, Jr. Reserve, Sarasota County, providing an opportunity to study aspects of slash pine in relation to fire. One objective of my research was to look at dispersal/recruitment conditions and slash pine dynamics in relation to fire. I looked at the varying degrees of tree mortality due to fire at different stands of slash pines. I also looked at the stands in terms of stand composition and spatial arrangement of surviving adults. Finally, I studied how variable seedling establishment and survival was between stands. Few inferences could be drawn between fire and these individual analyses; however, all analyses revealed that at the scale of this study, pine flatwoods are patchy.
I also looked at the dispersal of slash pines following a fire event. I modeled my research after Ribbens et al. (1994) and Clark et al. (1998), who took a phenomenological approach to dispersal modeling. This approach involved using distances between adults and seeds/seedlings and fecundity of adults to create dispersal models based on maximum likelihood estimates (MLE). I found that, while I could predict a model within acceptable parameters for most of the stands, more data was needed to predict models that better fit the data. This finding, along with the fact that I recovered no seed data for analysis, suggests factors are contributing to dispersal and recruitment (e.g. cone-crop) that need to be accounted for in the future.
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Teague, Kara Elizabeth. « Environmental ramifications of the fire ecology of slash pine (Pinus elliottii) a study of population dynamics and dispersal following a fire event / ». [Tampa, Fla. : s.n.], 2003. http://purl.fcla.edu/fcla/etd/SFE0000089.
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Teague, Kara Elizabeth. « Environmental ramification of the fire ecology of slash pine (Pinus elliottii) [electronic resource] : a study of population dynamimcs and dispersal following a fire event. / by Kara Elizabeth Teague ». University of South Florida, 2003. http://purl.fcla.edu/fcla/etd/SFE0000089.
Texte intégralRésumé :
Title from PDF of title page.Document formatted into pages; contains 78 pages.
Thesis (M.S.)--University of South Florida, 2003.
Includes bibliographical references.
Text (Electronic thesis) in PDF format.
ABSTRACT: With increasing encroachment on natural communities by anthropogenic activity, it is important to understand the functions of natural ecosystems in an effort to conserve natural areas. A first-hand study of the population dynamics of South Florida Slash Pine (P. elliottii Engelm. var. densa) following a fire event provided insight to its recovery and dispersal following a fire. A natural fire (lightning-induced) occurred in the spring of 2000 at the T. Mabry Carlton, Jr. Reserve, Sarasota County, providing an opportunity to study aspects of slash pine in relation to fire. One objective of my research was to look at dispersal/recruitment conditions and slash pine dynamics in relation to fire. I looked at the varying degrees of tree mortality due to fire at different stands of slash pines.
ABSTRACT: I also looked at the stands in terms of stand composition and spatial arrangement of surviving adults. Finally, I studied how variable seedling establishment and survival was between stands. Few inferences could be drawn between fire and these individual analyses; however, all analyses revealed that at the scale of this study, pine flatwoods are patchy. I also looked at the dispersal of slash pines following a fire event. I modeled my research after Ribbens et al. (1994) and Clark et al. (1998), who took a phenomenological approach to dispersal modeling. This approach involved using distances between adults and seeds/seedlings and fecundity of adults to create dispersal models based on maximum likelihood estimates (MLE). I found that, while I could predict a model within acceptable parameters for most of the stands, more data was needed to predict models that better fit the data.
ABSTRACT: This finding, along with the fact that I recovered no seed data for analysis, suggests factors are contributing to dispersal and recruitment (e.g. cone-crop) that need to be accounted for in the future.
System requirements: World Wide Web browser and PDF reader.
Mode of access: World Wide Web.
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Dewji, Shaheen Azim. « Assessing internal contamination after a radiological dispersion device event using a 2x2-inch sodium-iodide detector ». Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28092.
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BRANDINI, STEFANIA. « Employing mitogenomes to reconstruct migration and dispersal events ». Doctoral thesis, Università degli studi di Pavia, 2017. http://hdl.handle.net/11571/1203286.
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The mitochondrial genome is organized as a small circular molecule of DNA, present in hundreds/thousands of copies per cell and characterized by a much greater evolutionary rate than the average nuclear gene. The mitochondrial DNA (mtDNA) is transmitted as a non-recombining unit only through the mother and its variability is originated only by the sequential accumulation of new mutations. During millennia, this process of molecular divergence has given rise to monophyletic units (haplogroups) that are generally restricted to specific geographic areas or population groups. The study of the geographical distribution, the internal variability and the coalescence age of each haplogroup allow us to make inferences about the demographic history of populations, such as dispersals, range expansions, or migrations.
During my PhD studies, I analysed the sequence variation of the mtDNA at the highest level of resolution, that of complete sequence (mitogenome), in order to reconstruct the migration events of both human and animal populations. In particular, I mainly focused my research activity on three projects.
The first project aimed to date the events that brought to the initial peopling in Sardinia and to clarify the genetic history of Europe. Sardinians are "outliers" in the European genetic landscape and, according to paleogenomic nuclear data, the closest to early European Neolithic farmers. To learn more about the genetic ancestry of Sardinians, we analyzed 3491 modern and 21 ancient mitogenomes from Sardinia and observed that the age estimates of three Sardinian-specific haplogroups are >7800 years, the archeologically-based upper boundary of the Neolithic in the island. This finding supports archeological evidence of a Mesolithic occupation of the island, but also reveals a dual ancestral origin of the first Sardinians. Indeed, one of the Sardinian-specific haplogroups harbors ancestral roots in Paleolithic Western Europe, but the other two are most likely of Late Paleolithic Near Eastern ancestry, and among those that are often assumed to have spread from Anatolia only with the Neolithic. Thus, their ages are compatible with the scenario of a Late Glacial recolonization of Mediterranean Europe from the Near East prior to the migration wave(s) associated with the onset of farming.
The second project aimed to further assess the mitogenome variation of Native Americans origin. Specifically, I focused on Ecuador and Peru, two geographical areas of particular interest because of their location along the Pacific coast, in order to shed light on the peopling of South America. Phylogenetic analyses encompassing both novel and previously reported mitogenomes, allowed the identification of 50 new sub-haplogroups and the finding of a number of sub-clades shared with Native Americans from North and Central America, thus increasing the number of founding mtDNA lineages that entered South America from the North. Our phylogeographic analyses confirmed that the North to South expansion was extremely rapid, and most likely occurred along both the Pacific and Atlantic coasts.
The third study was aimed to acquire information about the diffusion process of the Asian tiger mosquito Ae. albopictus by analysing the mitogenome variation of representatives from Asia, America and Europe. Phylogenetic analyses revealed five haplogroups in Asia, but population surveys showed that only three of these were involved in the recent worldwide spread. We also found out that a sub-haplogroup, which is now common in Italy, most likely arose in North America from an ancestral Japanese source.
During these three years I also contributed to two additional projects whose goals were to reconstruct the ancient migratory events involving the Arabian Peninsula and Eastern Africa by the study of a rare haplogroup named R0a and to acquire new insights on the initial events that brought to the diffusion of domestic cattle (Bos taurus) outside the Near East.
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Cardenas, Leyla. « Dispersal ability and genetic structure in Concholepas concholepas (Bruguiière, 1789) : effects of historical and contemporary events ». Paris 6, 2007. http://www.theses.fr/2007PA066405.
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Grâce à l’étude du gastéropode Concholepas concholepas, distribué le long des côtes chiliennes, cette thèse a cherché à contribué au débat concernant l’adéquation entre les structures biogéographiques et phylogéographiques et le rôle de la dispersion contemporaine dans le maintien des structures historiques. Sur un plan historique, les patrons observés, suite à l’analyse d’un fragment de l’ADNmt COI de 14 populations réparties sur 4000 km, témoignent d’un processus d’expansion démographique et géographique très rapide sur l’aire de distribution de l’espèce. Concernant les flux de gènes contemporains, l’étude de 11 microsatellites a permis de montrer que la dispersion efficace ne reflète que partiellement le potentiel de dispersion conféré par une longue phase larvaire pélagique : cette dispersion dépend des contraintes hydro-dynamiques (rétention) et d’habitats (fjords vs. Côte linéaire). Ces données permettront d’affiner les plans de gestion et conservation de C. ConcholepasBased on the study of the marine gastropod Concholepas concholepas, spread along the Chilean coasts, this thesis aimed at examining the correlation between biogeographic and phylogeography patterns and the role played by the present-day dispersal on the maintenance of the historical population structure. On an historical time scale, the analysis of sequences of a mitochondrial DNA gene (COI) on ca. 400 individuals from 14 localities along 4000 km of coastline revealed a rapid demographic and geographic expansion. On a contemporary time scale, the use of 11 microsatellites showed that the effective dispersal represents only a fraction of the potential larval ability previously hypothesized based on the pelagic larval duration: dispersal strongly vary according to hydro-dynamic patterns (retention zone) and habitats (fjords vs. Linear coasts). The results of this thesis have implications on management and conservations policy applied to C. Concholepas
Livres sur le sujet "Dispersal event"
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Martin, Colin. Wreck-Site Formation Processes. Sous la direction de Ben Ford, Donny L. Hamilton et Alexis Catsambis. Oxford University Press, 2012. http://dx.doi.org/10.1093/oxfordhb/9780199336005.013.0002.
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The environmental settings within which shipwrecks occur are matters of chance rather than of choice. It is primarily the wreck and not its physical context that is of consequence to nautical archaeologists. No two wreck-site formations are the same, since the complex and interacting variables that constitute the environmental setting, the nature of the ship, and the circumstances of its loss combine to create a set of attributes unique to each site. The dynamic phase, which begins with the event of shipwreck, is characterized by the wreck's status as an environmental anomaly. It is unstable, lacks integration with its surroundings, and is prone to further disintegration and dispersal by external influences. The chemical and physical properties of water cause reactions with the metals. Understanding these natural processes in the context of the distinctively anthropogenic inputs, this article characterizes archaeology as an essential prerequisite to the interpretation of any shipwreck.
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Dominy, Graham. Soldiers in Garrison. University of Illinois Press, 2017. http://dx.doi.org/10.5406/illinois/9780252040047.003.0007.
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This chapter examines the problem of discipline within the ranks of the Victorian army stationed at Fort Napier and how alcohol abuse sparked the mutiny of the Cape Mounted Riflemen (CMR) detachment at the Bushman's River post in 1852. Drunkenness was almost all-pervasive at Fort Napier throughout its existence as a garrison center. The abuse of alcohol provided the fuel for conflict in various incidents, both minor and major. The chapter first provides a background on the CMR, also known as the Cape Corps, in the Colony of Natal before discussing “interior life” in the garrison. It then describes the dispersal of small units across Zululand and how it exacerbated the general problems of crime and drunkenness among soldiers. It also analyzes the CMR mutiny in the context of the Eighth Frontier War (1850–53) in the eastern Cape; this event and the mutiny of the Inniskilling Fusiliers at Fort Napier in 1887 were the most pronounced episodes of indiscipline and inhumanity to occur during the seven decades of military occupation.
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McDougal, Topher L. Trade Network Splintering and Ethnic Homogenization in Liberia and Sierra Leone. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198792598.003.0005.
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In violent conflict, civilians in both urban and rural areas, depend to some extent on the function of trade networks for their welfare. This chapter then seeks to understand the ways in which trade network morphologies shift during a conflict. Analyzing unique survey data via GIS and statistical models, this chapter scrutinizes the dispersal of production networks via a multiplication of petty traders during civil wars in Sierra Leone and Liberia. First, it argues that violent events tended to splinter production networks. Second, it argues that violent events also tended to have a localizing effect on the composition of traders, making them more homogenous with respect to the populations they serve. It implies that cities become hubs of activity for numerous overlapping, but ultimately separate, radial ethnic networks serving rural areas.
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Armstrong, Chris. Against Permanent Sovereignty. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198702726.003.0007.
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The status quo within international politics is that individual nation-states enjoy extensive and for the most part exclusive rights over the resources falling within their borders. Egalitarians have often assumed that such a situation cannot be defended, but perhaps some sophisticated defences of state or national rights over natural resources which have been made in recent years prove otherwise. This chapter critically assesses these various arguments, and shows that they are not sufficient to justify the institution of ‘permanent sovereignty’ over resources. Even insofar as those arguments have some weight, they are compatible with a significant dispersal of resource rights away from individual nation-states, both downwards towards local communities, and upwards towards transnational and global agencies.
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Jacobsen, Dean, et Olivier Dangles. Organisms and diversity patterns at high altitudes. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198736868.003.0004.
Texte intégralRésumé :
Chapter 4 gives a group-by-group treatment from amphibians and fish to algae and microbes of what is known about altitudinal diversity patterns, dominant groups, and prominent species from high altitude waters around the world. This is accompanied by biogeographical considerations on dispersal, immigration, and local speciation processes. The general and well-known decrease in species richness with increasing altitude observed in the terrestrial environment is also the rule in aquatic systems. Yet, while some groups of organisms show very clear altitudinal patterns, others do not. Some groups even increase in richness towards high plateaus. Likewise, the proportion of endemics often increases with altitude. Patterns also vary globally and seem to depend on factors such as regional topography, catchment physiognomy, and palaeo-environmental and climatic history.
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Cassaniti, Julia. “Wherever You Go, There You Aren’t?”. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780190495794.003.0007.
Texte intégralRésumé :
In his highly influential book Wherever You Go, There You Are (1995) Jon Kabat-Zinn suggests a particular kind of person revealed through mindfulness: a “you” to be found wherever you go. But who are “you”? Based on long-term anthropological fieldwork in northern Thailand, this chapter demonstrates that for many people there is no “you” exposed through Buddhist mindfulness practices, but instead local articulations of ideas about anattā, or non-self. “Spirits” of the person, called khwan, are also implicated: khwan are thought to be vulnerable to dispersal due to a lack of mindfulness, resulting in possible mental disorder. Through an analysis of the multiple constructions of the person in Thailand, the chapter argues that the “you” revealed in mindfulness has less to do with what is scientifically or even religiously real, and more to do with the authority of culturally constructed claims about what that “you” looks like, wherever you go.
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Goodin, Robert E., et Kai Spiekermann. Introduction. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198823452.003.0001.
Texte intégralRésumé :
If it lacks minimal competence to track the truth, good government is impossible. Even though a lot of dispersed information is available that would help to make competent decisions, governments can fail to collect and aggregate this information. ‘Wisdom of crowds’ arguments appeal to the idea that random noise cancels so that the aggregation of many opinions leads to elimination of errors, which is epistemically valuable. This insight is formalized in Condorcet’s jury theorem. Many objections have been levelled against the theorem or its limited applicability, but we argue that the objections are often exaggerated and the usefulness of the theorem underappreciated.
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Hazarika, Manjil. Linguistic Groups. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780199474660.003.0003.
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An old-fashioned somatological analysis of the racial composition of the present-day populations of Northeast India suggested that this area was home to two major races of mankind, the Caucasoid and the Mongoloid, and modern population genetic studies now provide us with an even more fine-meshed and complex view of population prehistory. Close proximity of these populations in terms of settlements has led to exchange of genes between the two groups. This chapter provides a detailed account of the linguistic situation in Northeast India, which is relevant to our understanding of the prehistoric dispersals of linguistic groups. Various linguistic hypotheses and feasible archaeological links are discussed in this chapter. Probable routes of migration are also discussed on the basis of linguistic, ethnographical, historical, and folkloristic data.
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Schotter, Jesse. Misreading Egypt. Edinburgh University Press, 2018. http://dx.doi.org/10.3366/edinburgh/9781474424776.003.0002.
Texte intégralRésumé :
The first chapter of Hieroglyphic Modernisms exposes the complex history of Western misconceptions of Egyptian writing from antiquity to the present. Hieroglyphs bridge the gap between modern technologies and the ancient past, looking forward to the rise of new media and backward to the dispersal of languages in the mythical moment of the Tower of Babel. The contradictory ways in which hieroglyphs were interpreted in the West come to shape the differing ways that modernist writers and filmmakers understood the relationship between writing, film, and other new media. On the one hand, poets like Ezra Pound and film theorists like Vachel Lindsay and Sergei Eisenstein use the visual languages of China and of Egypt as a more primal or direct alternative to written words. But Freud, Proust, and the later Eisenstein conversely emphasize the phonetic qualities of Egyptian writing, its similarity to alphabetical scripts. The chapter concludes by arguing that even avant-garde invocations of hieroglyphics depend on narrative form through an examination of Hollis Frampton’s experimental film Zorns Lemma.
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Hardy, Duncan. Lordship and Administration. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198827252.003.0005.
Texte intégralRésumé :
The Holy Roman Empire, and especially Upper Germany, was notoriously politically fragmented in the fourteenth to sixteenth centuries. A common way to interpret this fragmentation has been to view late medieval lordships, particularly those ruled by princes, as incipient ‘territories’, or even ‘territorial states’. However, this over-simplifies and reifies structures of lordship and administration in this period, which consisted of shifting agglomerations of assets, revenues, and jurisdictions that were dispersed among and governed by interconnected networks of political actors. Seigneurial properties and rights had become separable, commoditized, and highly mobile by the later middle ages, and these included not only fiefs (Lehen) but also loan-based pledges (Pfandschaften) and offices, all of which could be sold, transferred, or even ruled or exercised by multiple parties at once, whether these were princes, nobles, or urban elites. This fostered intensive interaction between formally autonomous political actors, generating frictions and disputes.
Chapitres de livres sur le sujet "Dispersal event"
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da Silva, Fernanda Ribeiro, et Marco Aurélio Pizo. « Restoration of seed dispersal interactions in communities invaded by non-native plants. » Dans Plant invasions : the role of biotic interactions, 391–401. Wallingford : CABI, 2020. http://dx.doi.org/10.1079/9781789242171.0391.
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Abstract Restoration aims to rebuild not only species but also the tangled interactions between species that ensure communities perpetuate by themselves. In tropical forests, restoration of seed dispersal interactions is essential because most plant species depend on animals to spread their seeds. A big challenge in restoring such forests is dealing with invasion by non-native species. Non-native plant species may outcompete and eliminate native species from the community, potentially disrupting or arresting the restoration process. Once established, invasive non-native plants are usually incorporated into the local seed dispersal network, potentially causing loss of biodiversity by competition with native species. This chapter reports on a case study of a 25-year old restored forest invaded by several bird-dispersed plant species. We assessed network metrics at the species level to specifically evaluate the role performed by invasive non-native species in the structure of the bird - seed dispersal network. The removal of invasive non-native plants and the re-establishment of native plant communities should be considered for the restoration of habitats invaded by non-native plants. For this reason, we discuss the impacts of removing such non-native plants and explore the consequences for the structure of the overall network. Because restoration areas are open systems, even after the removal of invasive non-native plant species they can return via seed dispersal. So, both the control and management of invasive non-native species would be more effective if planned with a landscape perspective. We also point out relevant management aspects to avoid the negative influence of invasive non-native plants on the seed dispersal interactions occurring between native plant and bird species in restored tropical forests.
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Masini, Federico, et Danilo Torre. « Large Mammal Dispersal Events at the Beginning of the Late Villafranchian ». Dans European Neogene Mammal Chronology, 131–38. Boston, MA : Springer US, 1990. http://dx.doi.org/10.1007/978-1-4899-2513-8_9.
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Venter, Gary. « A Mortality Model for Pandemics and Other Contagion Events ». Dans Springer Actuarial, 75–94. Cham : Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-78334-1_5.
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AbstractThe crisis caused by COVID-19 has had various impacts on the mortality of different sexes, age groups, ethnic and socio-economic backgrounds and requires improved mortality models. Here a very simple model extension is proposed: add a proportional jump to mortality rates that is a constant percent increase across the ages and cohorts but which varies by year. Thus all groups are affected, but the higher-mortality groups get the biggest increases in number dying. Every year gets a jump factor, but these can be vanishingly small for the normal years. Statistical analysis reveals that even before considering pandemic effects, mortality models are often missing systemic risk elements which could capture unusual or even extreme population events. Adding a provision for annual jumps, stochastically dispersed enough to include both tiny and pandemic risks, improves the results and incorporates the systemic risk in projection distributions. Here the mortality curves across the age, cohort, and time parameters are fitted using regularised smoothing splines, and cross-validation criteria are used for fit quality. In this way, we get more parsimonious models with better predictive properties. Performance of the proposed model is compared to standard mortality models existing in the literature.
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Coffin, Jack. « Plateaus and Afterglows : Theorizing the Afterlives of Gayborhoods as Post-Places ». Dans The Life and Afterlife of Gay Neighborhoods, 371–89. Cham : Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-66073-4_16.
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AbstractA number of commentators have acknowledged the decline of gayborhoods and the concomitant emergence of non-heteronormative diasporas in societies where sexual and gender diversity is normalized (Ghaziani 2015; Nash and Gorman-Murray 2017; Bitterman 2020). Academic studies tend to focus on the new lives that are being led beyond the gayborhood and the diminished distinctiveness of the territories left behind (e.g. Ghaziani 2014). In contrast, this chapter explores the possibility that gayborhoods can continue to influence sociospatial dynamics, even after their physical presence has diminished or disappeared altogether. Individuals and collectives may still be inspired by the memories, representations, and imaginaries previously provided by these erstwhile places. Indeed, the metaphor of a non-heteronormative diaspora relies on an ‘origin’ from which a cultural network has dispersed. In this sense gayborhoods can continue to function as post-places, as symbolic anchors of identity that operate even if they no longer exist in a material form, even if they are used simply as markers of ‘how far the diaspora has come’. The proposition that gayborhoods are becoming post-places could be more fully theorized in a number of ways, but the approach here is to adapt Deleuze and Guattari’s (1987: 22) notion of plateaus, which denote a “region of intensities whose development avoids any orientation towards a culmination point or external end”. From this perspective gayborhoods are not spatial phenomena that reach a climax of concentration and then disappear through dissipation. Instead, they can be described as becoming more intense and concrete in the latter half of the twentieth century before gradually fading after the new millennium as they disperse gradually into a diaspora as memories, habits, and so forth. Put another way, non-climactic gayborhoods leave ‘afterglows’, affects that continue to exert geographical effects in the present and near future. This conceptualization is consequential for theory, practice, and political activism, and ends the main body of this edited volume on a more ambitious note.
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Schiocchet, Leonardo. « Palestinian Diaspora or Exile ? Affective and Experiential Dimensions of (Im)mobility ». Dans Embodied Violence and Agency in Refugee Regimes, 71–108. Bielefeld, Germany : transcript Verlag, 2022. http://dx.doi.org/10.14361/9783839458020-005.
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Many authors working on Palestinian displacement stand by the use of the term »diaspora«, and their reasoning is not easily dismissed. Yet, this chapter explains why I prefer to use the term »exile«, and why this is tied to questions about refugee regimes and refugee agency. It argues that we must problematize how even the academic discussion on refugee regimes may be embedded in, and often unintentionally may help to reinforce, mechanisms of refugee control. To achieve this goal, the chapter first considers the Palestinian global dispersal and social belonging subjectivity as a background for a debate around conceptualizations of the term »diaspora«. This discussion about the term diaspora then informs my arguments on how (un)fitting this term may be for the Palestinian case, and what it may leave out of the picture.
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Sripathy, K. V., et Steven P. C. Groot. « Seed Development and Maturation ». Dans Seed Science and Technology, 17–38. Singapore : Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-19-5888-5_2.
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AbstractIn plants, a fascinating set of post-fertilization events result in the development of a dispersal unit known as a seed. During the maturation phase, seeds accumulate storage reserves and acquire desiccation tolerance, followed by an increase in seed vigour during maturation drying. Physiological (or mass) maturity may be attributed to the stage of seed maturation when maximum seed dry matter accumulation has occurred, marking the end of the seed-filling phase. The stage of maturity at harvest is one of the most important factors that can influence the quality of seeds. Recent studies established that seed vigour and longevity continue to increase even after physiological maturity, signifying the importance of the late maturation phase for maximizing seed quality. Among the plant hormones, abscisic acid (ABA) has been studied extensively for its role during seed development and maturation. Apart from ABA, gibberellic acid (GA), cytokinin and auxin also play a critical role during the development of seeds. Desiccation tolerance in seeds begins much before the attainment of physiological maturity. Acquisition of desiccation tolerance is associated with embryo accumulation of oligosaccharides of the raffinose family, low molecular weight antioxidants, late embryogenesis abundant proteins and heat shock proteins coupled with structural changes at the cellular level. To obtain seeds of maximum quality (in terms of germination, vigour and longevity), harvesting needs to be performed at or slightly after harvest maturity a period at which seed moisture content stabilizes with environmental factors. In this chapter, an attempt has been made to present the current understanding of seed development and maturation concentrating on various aspects viz. phases of seed development, the role of plant hormones, other factors affecting seed development, concepts of seed maturity, and its relevance to seed quality, maturity indices in crop plants and acquisition of desiccation tolerance in seeds.
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Ranganathan, Umarani, et Steven P. C. Groot. « Seed Longevity and Deterioration ». Dans Seed Science and Technology, 91–108. Singapore : Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-19-5888-5_5.
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AbstractThe fundamental deteriorative processes that lead to loss of seed viability contrastingly vary between desiccation insensitive (orthodox) and desiccation sensitive seeds (recalcitrant). Orthodox seeds which undergo maturation drying are bestowed with protective mechanisms which guard the seeds against deterioration. They include the accumulation of antioxidants, non-reducing sugars, protective proteins such as late embryogenesis abundant proteins, heat-shock proteins, lipocalins, hormones and chemical protectants (raffinose family oligosaccharides, flavonoids, lignins, vitamin E). The nuclear DNA is packed denser and chlorophyll is degraded. Besides, the cytoplasm is capable of transitioning between liquid and glassy state depending on the moisture content of the seeds aiding in the maintenance of seed viability potential. In the dry seeds, the glassy state of the cytoplasm ensures the stabilization of cellular components by arresting cell metabolism. However, even with low moisture content and a glassy state of cytoplasm, reactive oxygen species generated due to the presence of oxygen in the storage atmosphere may cause the ageing of seed. As the seed moisture content increases, mitochondrial respiration gets activated, also leading to increased production of reactive oxygen species, owing to inefficient mitochondrial activity. The reactive oxygen species lead to the oxidation of essential molecules such as DNA, RNA, proteins and lipids. Further, mitochondrial membranes also get oxidized, leading to reduced aerobic respiration potential. When the damage is not substantial, orthodox seeds are capable of repairing the molecular damages that accumulate during storage, enabling the seeds to partially overcome the damages and extend their longevity. This includes activation of repair of cell membranes, DNA, RNA, proteins and mitochondria as the seeds imbibe water.Unlike the orthodox seeds, the recalcitrant seeds are largely devoid of protective mechanisms which guard the seeds against rapid deterioration. The recalcitrant seeds are shed from the mother tree at high moisture content while they are metabolically active. After dispersal, the seeds undergo deteriorative changes during drying due to the damage to the cytoskeleton (physical damage), besides reactive oxygen species-induced damage due to lack of antioxidant activity (metabolism-induced damage). Even when maintained under high moisture content, seeds exhibit dysfunction of the cell organelles and extensive vacuolization predisposing the seeds to deterioration. Thus, recalcitrant seeds are prone to deterioration either under low or high moisture content.
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Bostoen, Koen. « The Bantu Expansion ». Dans Language Dispersal, Diversification, and Contact, 227–39. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198723813.003.0013.
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The Bantu Expansion, the foremost linguistic, cultural, and demographic event in Late Holocene Africa, has sparked a fervent interdisciplinary debate, especially regarding its driving forces. As is often the case with hotly debated issues, certain ‘factoids’ bearing little relation to factual evidence emerge. Two such factoids are that (1) the Bantu Expansion would have been a single migratory macro-event and (2) it would have been driven by agriculture. These two widely held beliefs are critically assessed here. Regarding (1), the chapter argues that the Bantu Expansion did involve the actual migration of Bantu speakers but that backward and forward migration occurred after the initial spread and that Bantu languages also expanded through adoption by autochthonous hunter-gatherers. As for (2), the chapter argues that the earliest Bantu speakers had their own archeologically visible culture, but they were not farmers. Therefore, the Bantu Expansion is not a textbook example of a farming/language dispersal.
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Peace, Alexander L., et Jordan J. J. Phethean. « The African continental divide : Indian versus Atlantic Ocean spreading during Gondwana dispersal ». Dans In the Footsteps of Warren B. Hamilton : New Ideas in Earth Science. Geological Society of America, 2022. http://dx.doi.org/10.1130/2021.2553(07).
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ABSTRACT It is well established that plate-tectonic processes operate on a global scale and that spatially separate but temporally coincident events may be linked. However, identifying such links in the geological record and understanding the mechanisms involved remain speculative. This is particularly acute during major geodynamic events, such as the dispersal of supercontinents, where multiple axes of breakup may be present as well as coincidental collisional events. To explore this aspect of plate tectonics, we present a detailed analysis of the temporal variation in the mean half rate of seafloor spreading in the Indian and Atlantic Oceans, as well as plate-kinematic attributes extracted from global plate-tectonic models during the dispersal of Gondwana since ca. 200 Ma. Our analysis shows that during the ~20 m.y. prior to collision between India and Asia at ca. 55 Ma, there was an increase in the mean rate of seafloor spreading in the Indian Ocean. This manifests as India rapidly accelerating toward Asia. This event was then followed by a prompt deceleration in the mean rate of Indian Ocean seafloor spreading after India collided with Asia at ca. 55 Ma. Since inception, the mean rate of seafloor spreading in the Indian Ocean has been generally greater than that in the Atlantic Ocean, and the period of fastest mean half spreading rate in the Indian Ocean was coincident with a slowdown in mean half seafloor spreading rate in the competing Atlantic Ocean. We hypothesize that faster and hotter seafloor spreading in the Indian Ocean resulted in larger ridge-push forces, which were transmitted through the African plate, leading to a slowdown in Atlantic Ocean spreading. Following collision between India and Asia, and a slowdown of Indian Ocean spreading, Atlantic spreading rates consequently increased again. We conclude that the processes in the Indian and Atlantic Oceans have likely remained coupled throughout their existence, that their individual evolution has influenced each other, and that, more generally, spreading in one basin inevitably influences proximal regions. While we do not believe that ridge push is the main cause of plate motions, we consider it to have played a role in the coupling of the kinematic evolution of these oceans. The implication of this observation is that interaction and competition between nascent ocean basins and ridges during supercontinent dispersal exert a significant control on resultant continental configuration.
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Ewers-Saucedo, Christine, et John P. Wares. « Population Connectivity and Phylogeography of Crustaceans ». Dans Evolution and Biogeography, 440–63. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780190637842.003.0017.
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Crustacea display diverse life histories and occur in all marine habitats. This makes them particularly useful when thinking about how we can predict geographical distribution from life history and ecology. As would be expected from such diversity, crustaceans exhibit various population connectivity patterns, from panmictic, well-connected populations to small and isolated populations. Here we ask first what can be learned from exploring crustacean phylogeography and connectivity around well-understood vicariance events with known ages. We find that vicariance events are generally useful in calibrating molecular rates of evolution, but that there is substantial variation between taxa. This variation can be linked, on the one hand, to habitat differences (which determine when gene flow between populations actually ceased) and, on the other hand, to population size differences (which determine how fast genetic differences accumulate). In a few instances, populations must have diverged much earlier or later than the hypothesized vicariance event, providing evidence of earlier or later dispersal or more ancient separation. Second, we ask when comparative studies of multiple taxa show consistent results, predictable from their similar life history, and when not. For example, species that disperse little, such as brooding peracarids, have smaller, more isolated populations than species with planktonic larvae, such as decapods. Less consistent are the patterns across biogeographic breaks. While gene flow is clearly limited across such breaks in some species, other species do not seem to perceive them. This to-date-unexplained variation challenges our understanding of marine phylogeography.
Actes de conférences sur le sujet "Dispersal event"
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Sheffield, Sarah, Adriane R. Lam et Nicholas J. Matzke. « ESTIMATING DISPERSAL AND EVOLUTIONARY DYNAMICS IN DIPLOPORAN BLASTOZOANS (ECHINODERMATA) ACROSS THE GREAT ORDOVICIAN BIODIVERSIFICATION EVENT ». Dans GSA 2020 Connects Online. Geological Society of America, 2020. http://dx.doi.org/10.1130/abs/2020am-355924.
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Brown, Alexander L., et Kurt E. Metzinger. « Computational Test Design for High-Speed Liquid Impact and Dispersal ». Dans ASME/JSME 2011 8th Thermal Engineering Joint Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajtec2011-44422.
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Transportation accidents frequently involve liquids dispersing in the atmosphere. An example is that of aircraft impacts, which often result in spreading fuel and a subsequent fire. Predicting the resulting environment is of interest for design, safety, and forensic applications. This environment is challenging for many reasons, one among them being the disparate time and length scales that must be resolved for an accurate physical representation of the problem. A recent computational method appropriate for this class of problems has been developed for modeling the impact and subsequent liquid spread. This involves coupling a structural dynamics code to a turbulent computational fluid mechanics reacting flow code. Because the environment intended to be simulated with this capability is difficult to instrument and costly to test, the existing validation data are of limited scope, relevance, and quality. A rocket sled test is being performed where a scoop moving through a water channel is being used to brake a pusher sled. We plan to instrument this test to provide appropriate scale data for validating the new modeling capability. The intent is to get high fidelity data on the break-up and evaporation of the water that is ejected from the channel as the sled is braking. These two elements are critical to fireball formation for this type of event involving fuel in the place of water. We demonstrate our capability in this paper by describing the pre-test predictions which are used to locate instrumentation for the actual test. We also present a sensitivity analysis to understand the implications of length scale assumptions on the prediction results.
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Censullo, Shaolin Meliora, et Alycia L. Stigall. « DID ALTERNATING DISPERSAL AND VICARIANCE DRIVE BIODIVERSITY INCREASE DURING THE GREAT ORDOVICIAN BIODIVERSIFICATION EVENT ? A PHYLOGENETIC TEST USING BRACHIOPODS ». Dans GSA Annual Meeting in Phoenix, Arizona, USA - 2019. Geological Society of America, 2019. http://dx.doi.org/10.1130/abs/2019am-333129.
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Xiang, K. L., A. S. Erst, T. V. Erst et W. Wang. « Phylogenetic systematics and biogeography of Coptis (Ranunculaceae), an eastern Asian and North American genus ». Dans Problems of studying the vegetation cover of Siberia. TSU Press, 2020. http://dx.doi.org/10.17223/978-5-94621-927-3-2020-52.
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The goldthread genus Coptis includes 15 species disjunctly distributed in eastern Asia and North America. Here, we provide a dated phylogeny for the genus with all 15 species. Our results indicate that Coptis contains two strongly supported clades (I and II). Clade I consists of subg. Coptis and sect. Japonocoptis of subg. Metacoptis; clade II composes sect. Japonocoptis of subg. Metacoptis. Central leaflet base, sepal shape, and petal blade carry a strong phylogenetic signal in Coptis, while leaf type, sepal and petal color, and petal shape exhibit relatively higher levels of evolutionary flexibility. Our dating and biogeographic analyses indicate that a vicariance event between Japan-North America occurred in the middle Miocene, resulting in the split of Coptis and its sister group. Subsequently, a colonization event occurred at 9.55 Ma from Japan to mainland China. Both vicariance and dispersal events have played important roles in shaping the current distribution and endemism of Coptis, likely resulting from eustatic sea-level changes, mountain formation processes and an increasing drier and cooler climate from the middle Miocene onwards.
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Kretzschmar, Frank. « Onset of Gas Blowthrough During Melt Expulsion From a Hole in a RPV : Numerical Analysis Using the SIMMER Code ». Dans ASME 2006 2nd Joint U.S.-European Fluids Engineering Summer Meeting Collocated With the 14th International Conference on Nuclear Engineering. ASMEDC, 2006. http://dx.doi.org/10.1115/fedsm2006-98205.
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In the case of a severe accident in a nuclear power plant there is a residual risk, that the Reactor Pressure Vessel (RPV) does not withstand the thermal attack of the molten core material, of which the temperature can be about 3000 K. For the analysis of the processes governing melt dispersal and heating up of the containment atmosphere of a nuclear power plant in the case of such an event, it is important to know the time of the onset of gas blowthrough during the melt expulsion through the hole in the bottom of the RPV. In the test facility DISCO-C (Dispersion of Simulant Corium-Cold) at the FZK /6/, experiments were performed to furnish data for modeling Direct Containment Heating (DCH) processes in computer codes that will be used to extrapolate these results to the reactor case. DISCO-C models the RPV, the Reactor Coolant System (RCS), cavity and the annular subcompartments of a large European reactor in a scale 1:18. The liquid type, the initial liquid mass, the type of the driving gas and the size of the hole were varied in these experiments. We present results for the onset of the gas blowthrough that were reached by numerical analysis with the Multiphase-Code SIMMER. We compare the results with the experimental results from the DISCO-C experiments and with analytical correlations, given by other authors.
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Cowan, Ellen, Sarah Zellers, Maureen H. Walczak, Gina Marie Carney, Oscar E. Romero et Beth Caissie. « SOURCES AND DISPERSAL OF ICE RAFTED SIKU EVENTS IN THE NE PACIFIC ». Dans GSA Connects 2021 in Portland, Oregon. Geological Society of America, 2021. http://dx.doi.org/10.1130/abs/2021am-369250.
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Soni, Sankalp, Bakhtier Farouk et Charles N. Haas. « Simulation of Contaminant Dispersal in an Apartment Building ». Dans ASME 2004 Heat Transfer/Fluids Engineering Summer Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/ht-fed2004-56379.
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Bio-terrorism events (like the 2001 anthrax attacks) accentuate the importance of countering these incidents. In order to develop reliable countermeasures for these events, it is essential to understand the associated transport processes. The transport processes involved pose challenges as they occur over wide ranges of spatial and temporal scales. CONTAMW, a multi zone indoor air quality and ventilation analysis program is used to predict the contaminant dispersal in an apartment building. Detailed simulation results and analysis of controlled release of propylene within a generic apartment building is presented. A zonal analysis is carried out for the entire apartment building (using CONTAMW) to obtain time histories of propylene concentration in different zones. The simulations provide the dispersion, transport and contaminant concentration within each zone of the apartment. This study also considers the effect of flow obstructions and ventilation rates on contaminant dispersal. The results are validated with the experimental results reported in Cybyk et al. (1999). We have also simulated propylene transport in the apartment with FDS, a large eddy simulation model.
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Zhao, X. T., S. R. Yang, Z. M. Xu, J. G. Wang et Z. P. Song. « A HEAT PERCOLATION MODEL IN DISPERSE SYETEM OF EVEN PELLETS ». Dans International Heat Transfer Conference 11. Connecticut : Begellhouse, 1998. http://dx.doi.org/10.1615/ihtc11.4210.
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Yang, Yong, Jie Lan et Xiaochun Li. « Ultrasonic-Based Fabrication of Bulk Aluminum Matrix Nanocomposite ». Dans ASME 2004 International Mechanical Engineering Congress and Exposition. ASMEDC, 2004. http://dx.doi.org/10.1115/imece2004-59632.
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Lightweight metal matrix nano-composites (MMNCs) (metal matrix with nano-sized ceramic particles) can be of significance for automobile, aerospace and numerous other applications. However, it is extremely difficult to disperse nano-sized ceramic particles uniformly in molten metal for casting. This paper presents a fabrication method for casting of bulk aluminum MMNCs by use of ultrasonic nonlinear effects, namely transient cavitation and acoustic streaming. Nano-sized SiC particles have been dispersed in molten aluminum alloy A356 for casting. Microstructural study was carried out and it validates a good distribution and dispersion of nano-sized SiC in aluminum alloy matrix. Hardness of the as-cast MMNCs have been improved significantly even with a low weight fraction of nano-sized SiC. The ultrasonic fabrication methodology is promising to produce a wide range of other MMNCs.
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Lalouani, Wassila, Mohamed Younis, Mohamed El-Amine Chergui et Nadjib Badache. « Load-Balanced and Energy-Efficient Coverage of Dispersed Events Using Mobile Sensor/Actuator Nodes ». Dans GLOBECOM 2015 - 2015 IEEE Global Communications Conference. IEEE, 2014. http://dx.doi.org/10.1109/glocom.2014.7417482.
Texte intégralRapports d'organisations sur le sujet "Dispersal event"
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Seamans, Thomas, et Allen Gosser. Bird dispersal techniques. U.S. Department of Agriculture, Animal and Plant Health Inspection Service, août 2016. http://dx.doi.org/10.32747/2016.7207730.ws.
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Conflicts between humans and birds likely have existed since agricultural practices began. Paintings from ancient Greek, Egyptian, and Roman civilizations depict birds attacking crops. In Great Britain, recording of efforts at reducing bird damage began in the 1400s, with books on bird control written in the 1600s. Even so, the problem persists. Avian damage to crops remains an issue today, but we also are concerned with damage to homes, businesses, and aircraft, and the possibility of disease transmission from birds to humans or livestock. Bird dispersal techniques are a vital part of safely and efficiently reducing bird conflicts with humans. The bird must perceive a technique as a threat if it is to be effective. No single technique can solve all bird conflicts, but an integrated use of multiple techniques, each enhancing the other, generally provides relief.
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Böhm, Franziska, Ingrid Jerve Ramsøy et Brigitte Suter. Norms and Values in Refugee Resettlement : A Literature Review of Resettlement to the EU. Malmö University, 2021. http://dx.doi.org/10.24834/isbn.9789178771776.
Texte intégralRésumé :
As a result of the refugee reception crisis in 2015 the advocacy for increasing resettlement numbers in the overall refugee protection framework has gained momentum, as has research on resettlement to the EU. While the UNHCR purports resettlement as a durable solution for the international protection of refugees, resettlement programmes to the European Union are seen as a pillar of the external dimension of the EU’s asylum and migration policies and management. This paper presents and discusses the literature regarding the value transmissions taking place within these programmes. It reviews literature on the European resettlement process – ranging from the selection of refugees to be resettled, the information and training they receive prior to travelling to their new country of residence, their reception upon arrival, their placement and dispersal in the receiving state, as well as programs of private and community sponsorship. The literature shows that even if resettlement can be considered an external dimension of European migration policy, this process does not end at the border. Rather, resettlement entails particular forms of reception, placement and dispersal as well as integration practices that refugees are confronted with once they arrive in their resettlement country. These practices should thus be understood in the context of the resettlement regime as a whole. In this paper we map out where and how values (here understood as ideas about how something should be) and norms (expectations or rules that are socially enforced) are transmitted within this regime. ‘Value transmission’ is here understood in a broad sense, taking into account the values that are directly transmitted through information and education programmes, as well as those informing practices and actors’ decisions. Identifying how norms and values figure in the resettlement regime aid us in further understanding decision making processes, policy making, and the on-the-ground work of practitioners that influence refugees’ lives. An important finding in this literature review is that vulnerability is a central notion in international refugee protection, and even more so in resettlement. Ideas and practices regarding vulnerability are, throughout the resettlement regime, in continuous tension with those of security, integration, and of refugees’ own agency. The literature review and our discussion serve as a point of departure for developing further investigations into the external dimension of value transmission, which in turn can add insights into the role of norms and values in the making and un-making of (external) boundaries/borders.
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Pérez, Alex, et Juan Sebastián Vélez-Velásquez. Price Dispersion and Wholesale Costs Shocks in the Colombian Retail Gasoline Markets. Banco de la República Colombia, décembre 2022. http://dx.doi.org/10.32468/be.1220.
Texte intégralRésumé :
Price dispersion is a prevalent feature even of markets where, arguably, homogeneous good are traded. At the heart of the causes of price dispersion lie the firms' strategic interactions with their customers and rivals. Consumers' eagerness and ability to search for lower prices tends to reduce dispersion because it enhances competition. Firms inability to sustain tacit collusion, on the other hand, increases price dispersion. Wholesale costs shock can impact both. We use data on retail gasoline markets from Colombia to assess whether changes in price dispersion following wholesale cost shocks are explained by consumer searching or by firms breaking away from collusive equilibria. We also explore the role played by market structure on the extent of price dispersion. Our findings suggest that changes in price dispersion following wholesale cost shocks are driven by consumers searching more intensely for lower prices. We also find a positive relationship between the number of service stations in a market and how disperse prices are. Our results are robust to alternative ways of measuring price dispersion and alternative ways of defining relevant markets.
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Heifetz, Yael, et Michael Bender. Success and failure in insect fertilization and reproduction - the role of the female accessory glands. United States Department of Agriculture, décembre 2006. http://dx.doi.org/10.32747/2006.7695586.bard.
Texte intégralRésumé :
The research problem. Understanding of insect reproduction has been critical to the design of insect pest control strategies including disruptions of mate-finding, courtship and sperm transfer by male insects. It is well known that males transfer proteins to females during mating that profoundly affect female reproductive physiology, but little is known about the molecular basis of female mating response and no attempts have yet been made to interfere with female post-mating responses that directly bear on the efficacy of fertilization. The female reproductive tract provides a crucial environment for the events of fertilization yet thus far those events and the role of the female tract in influencing them are poorly understood. For this project, we have chosen to focus on the lower reproductive tract because it is the site of two processes critical to reproduction: sperm management (storage, maintenance, and release from storage) and fertilization. E,fforts during this project period centered on the elucidation of mating responses in the female lower reproductive tract The central goals of this project were: 1. To identify mating-responsive genes in the female lower reproductive tract using DNA microarray technology. 2. In parallel, to identify mating-responsive genes in these tissues using proteomic assays (2D gels and LC-MS/MS techniques). 3. To integrate proteomic and genomic analyses of reproductive tract gene expression to identify significant genes for functional analysis. Our main achievements were: 1. Identification of mating-responsive genes in the female lower reproductive tract. We identified 539 mating-responsive genes using genomic and proteomic approaches. This analysis revealed a shift from gene silencing to gene activation soon after mating and a peak in differential gene expression at 6 hours post-mating. In addition, comparison of the two datasets revealed an expression pattern consistent with the model that important reproductive proteins are pre-programmed for synthesis prior to mating. This work was published in Mack et al. (2006). Validation experiments using real-time PCR techniques suggest that microarray assays provide a conservativestimate of the true transcriptional activity in reproductive tissues. 2.lntegration of proteomics and genomics data sets. We compared the expression profiles from DNA microarray data with the proteins identified in our proteomic experiments. Although comparing the two data sets poses analyical challenges, it provides a more complete view of gene expression as well as insights into how specific genes may be regulated. This work was published in Mack et al. (2006). 3. Development of primary reproductive tract cell cultures. We developed primary cell cultures of dispersed reproductive tract cell types and determined conditions for organ culture of the entire reproductive tract. This work will allow us to rapidly screen mating-responsive genes for a variety of reproductive-tract specifi c functions. Scientific and agricultural significance. Together, these studies have defined the genetic response to mating in a part of the female reproductive tract that is critical for successful fertllization and have identified alarge set of mating-responsive genes. This work is the first to combine both genomic and proteomic approaches in determining female mating response in these tissues and has provided important insights into insect reproductive behavior.
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Meidan, Rina, et Robert Milvae. Regulation of Bovine Corpus Luteum Function. United States Department of Agriculture, mars 1995. http://dx.doi.org/10.32747/1995.7604935.bard.
Texte intégralRésumé :
The main goal of this research plan was to elucidate regulatory mechanisms controlling the development, function of the bovine corpus luteum (CL). The CL contains two different sterodigenic cell types and therefore it was necessary to obtain pure cell population. A system was developed in which granulosa and theca interna cells, isolated from a preovulatory follicle, acquired characteristics typical of large (LL) and small (SL) luteal cells, respectively, as judged by several biochemical and morphological criteria. Experiments were conducted to determine the effects of granulosa cells removal on subsequent CL function, the results obtained support the concept that granulosa cells make a substaintial contribution to the output of progesterone by the cyclic CL but may have a limited role in determining the functional lifespan of the CL. This experimental model was also used to better understand the contribution of follicular granulosa cells to subsequent luteal SCC mRNA expression. The mitochondrial cytochrome side-chain cleavage enzyme (SCC), which converts cholesterol to pregnenolone, is the first and rate-limiting enzyme of the steroidogenic pathway. Experiments were conducted to characterize the gene expression of P450scc in bovine CL. Levels of P450scc mRNA were higher during mid-luteal phase than in either the early or late luteal phases. PGF 2a injection decreased luteal P450scc mRNA in a time-dependent manner; levels were significantly reduced by 2h after treatment. CLs obtained from heifers on day 8 of the estrous cycle which had granulosa cells removed had a 45% reduction in the levels of mRNA for SCC enzymes as well as a 78% reduction in the numbers of LL cells. To characterize SCC expression in each steroidogenic cell type we utilized pure cell populations. Upon luteinization, LL expressed 2-3 fold higher amounts of both SCC enzymes mRNAs than SL. Moreover, eight days after stimulant removal, LL retained their P4 production capacity, expressed P450scc mRNA and contained this protein. In our attempts to establish the in vitro luteinization model, we had to select the prevulatory and pre-gonadotropin surge follicles. The ratio of estradiol:P4 which is often used was unreliable since P4 levels are high in atretic follicles and also in preovulatory post-gonadotropin follicles. We have therefore examined whether oxytocin (OT) levels in follicular fluids could enhance our ability to correctly and easily define follicular status. Based on E2 and OT concentrations in follicular fluids we could more accurately identify follicles that are preovulatory and post gonadotropin surge. Next we studied OT biosynthesis in granulosa cells, cells which were incubated with forskolin contained stores of the precursor indicating that forskolin (which mimics gonadotropin action) is an effective stimulator of OT biosynthesis and release. While studying in vitro luteinization, we noticed that IGF-I induced effects were not identical to those induced by insulin despite the fact that megadoses of insulin were used. This was the first indication that the cells may secrete IGF binding protein(s) which regonize IGFs and not insulin. In a detailed study involving several techniques, we characterized the species of IGF binding proteins secreted by luteal cells. The effects of exogenous polyunsaturated fatty acids and arachidonic acid on the production of P4 and prostanoids by dispersed bovine luteal cells was examined. The addition of eicosapentaenoic acid and arachidonic acid resulted in a dose-dependent reduction in basal and LH-stimulated biosynthesis of P4 and PGI2 and an increase in production of PGF 2a and 5-HETE production. Indomethacin, an inhibitor of arachidonic acid metabolism via the production of 5-HETE was unaffected. Results of these experiments suggest that the inhibitory effect of arachidonic acid on the biosynthesis of luteal P4 is due to either a direct action of arachidonic acid, or its conversion to 5-HETE via the lipoxgenase pathway of metabolism. The detailed and important information gained by the two labs elucidated the mode of action of factors crucially important to the function of the bovine CL. The data indicate that follicular granulosa cells make a major contribution to numbers of large luteal cells, OT and basal P4 production, as well as the content of cytochrome P450 scc. Granulosa-derived large luteal cells have distinct features: when luteinized, the cell no longer possesses LH receptors, its cAMP response is diminished yet P4 synthesis is sustained. This may imply that maintenance of P4 (even in the absence of a Luteotropic signal) during critical periods such as pregnancy recognition, is dependent on the proper luteinization and function of the large luteal cell.