Academic literature on the topic 'Dune patterns'
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Journal articles on the topic "Dune patterns"
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Gadal, C., C. Narteau, S. Courrech du Pont, O. Rozier, and P. Claudin. "Periodicity in fields of elongating dunes." Geology 48, no. 4 (2020): 343–47. http://dx.doi.org/10.1130/g46987.1.
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Abstract Dune fields are commonly associated with periodic patterns that are among the most recognizable landscapes on Earth and other planetary bodies. However, in zones of limited sediment supply, where periodic dunes elongate and align in the direction of the resultant sand flux, there has been no attempt to explain the emergence of such a regular pattern. Here, we show, by means of numerical simulations, that the elongation growth mechanism does not produce a pattern with a specific wavelength. Periodic elongating dunes appear to be a juxtaposition of individual structures, the arrangement of which is due to regular landforms at the border of the field acting as boundary conditions. This includes, among others, dune patterns resulting from bed instability, or the crestline reorganization induced by dune migration. The wavelength selection in fields of elongating dunes therefore reflects the interdependence of dune patterns over the course of their evolution.
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Els, A., S. Merlo, and J. Knight. "Comparison of two Satellite Imaging Platforms for Evaluating Sand Dune Migration in the Ubari Sand Sea (Libyan Fazzan)." ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences XL-7/W3 (April 30, 2015): 1375–80. http://dx.doi.org/10.5194/isprsarchives-xl-7-w3-1375-2015.
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Sand dunes can change location, form or dimensions depending on wind direction and strength. Sand dune movements can be effectively monitored through the comparison of multi-temporal satellite images. However, not all remote sensing platforms are suitable to study sand dunes. This study compares coarse (Landsat) and fine (Worldview) resolution platforms, specifically focussing on sand dunes within the Ubari Sand Sea (Libya). Sand dune features (crest line, dune ridge basal outlines) were extracted from Landsat and Worldview 2 imagery in order to construct geomorphic maps. These geomorphic maps were then compared using image overlay and differencing, and the Root Mean Squared Error (RMSE) was used to determine if the mapped dune patterns were significantly different. It was found that Landsat is a sufficient data source when studying dune patterns within a regional sand sea, but smaller dunes identified from Worldview data were not capable of being extracted in the data sourced from Landsat. This means that for studies concerned with the dune patterns and movements within sand seas, Landsat is sufficient. But in studies where the specific dynamics of specific dunes are required, a finer resolution is required; platforms such as Worldview are needed in order to gain more detailed insight and to link the past and present day climate and environmental change.
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Bar Kutiel, Pua, and Michael Dorman. "The Importance of Annual Plants and Multi-Scalar Analysis for Understanding Coastal Dune Stabilization Process in the Mediterranean." Applied Sciences 11, no. 6 (2021): 2821. http://dx.doi.org/10.3390/app11062821.
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Since ecological phenomena and patterns vary with scale, scalar analysis is a developing practice in ecology. Scalar analysis is most valuable in heterogeneous environments, since habitat heterogeneity is a key factor in determining biodiversity. One such case can be seen in the changes in annual vegetation in coastal sand dune systems. Most studies in these environments are carried out at the dune scale, comparing dunes at different stabilization states. However, a broader understanding of dune stabilization processes requires analyses at the finer scales of dune slope aspects (directions of exposure to wind) and patches (under and between woody perennial species). Here, we present the results of a study that combines the three scales (dune, slope, and patch) in the Mediterranean coastal dune systems in Israel. Through this multi-scalar analysis, we are able to describe processes at the finer patch and aspect scale and explain how they shape patterns at the dune scale. The results indicate that the dune scale exposes the differences in annual plant characteristics between mobile and fixed dunes, their slopes and patches and the reorganization and spatial distribution of annual plants within mobile and fixed dunes during the stabilization process.
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Lü, Ping, Clément Narteau, Zhibao Dong, et al. "Direct validation of dune instability theory." Proceedings of the National Academy of Sciences 118, no. 17 (2021): e2024105118. http://dx.doi.org/10.1073/pnas.2024105118.
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Modern dune fields are valuable sources of information for the large-scale analysis of terrestrial and planetary environments and atmospheres, but their study relies on understanding the small-scale dynamics that constantly generate new dunes and reshape older ones. Here, we designed a landscape-scale experiment at the edge of the Gobi desert, China, to quantify the development of incipient dunes under the natural action of winds. High-resolution topographic data documenting 42 mo of bedform dynamics are examined to provide a spectral analysis of dune pattern formation. We identified two successive phases in the process of dune growth, from the initial flat sand bed to a meter-high periodic pattern. We focus on the initial phase, when the linear regime of dune instability applies, and measure the growth rate of dunes of different wavelengths. We identify the existence of a maximum growth rate, which readily explains the mechanism by which dunes select their size, leading to the prevalence of a 15-m wavelength pattern. We quantitatively compare our experimental results with the prediction of the dune instability theory using transport and flow parameters independently measured in the field. The remarkable agreement between theory and observations demonstrates that the linear regime of dune growth is permanently expressed on low-amplitude bed topography, before larger regular patterns and slip faces eventually emerge. Our experiment underpins existing theoretical models for the early development of eolian dunes, which can now be used to provide reliable insights into atmospheric and surface processes on Earth and other planetary bodies.
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Poppema, Daan, Kathelijne Wijnberg, Jan Mulder, and Suzanne Hulscher. "THE EFFECT OF BUILDING GEOMETRY ON AEOLIAN DEPOSITION AND EROSION PATTERNS: A FIELD EXPERIMENT." Coastal Engineering Proceedings, no. 36v (December 28, 2020): 21. http://dx.doi.org/10.9753/icce.v36v.sediment.21.
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Buildings at the beach-dune interface, such as restaurants and (holiday) houses, affect wind-driven sand transport in their surroundings. Hereby they shape the development of the beach-dune system. This can have implications for the flood protection offered by dunes. Therefore, this research aims to understand the effect of buildings at the beach-dune interface on beach-dune morphology. In this contribution we present the results of a field experiment which focused on the effect of building size and geometry on the size and location of the deposition patterns directly around buildings.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/hlcMP7Ev1m0
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McArthur, E., and Stewart Sanderson. "Great Sand Dunes National Monument Vegetation Patterns." UW National Parks Service Research Station Annual Reports 15 (January 1, 1991): 185–89. http://dx.doi.org/10.13001/uwnpsrc.1991.3019.
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This project is designed to chacterize and map the vegetation of the Great Sand Dunes National Monument, Colorado (GSDNM) and to determine if the vegetated areas in the dune field are permanent, temporary, or migratory. It is not known if the vegetation around the dunes is encroaching on the dunes, being replaced by the dunes or is stable. There are also concerns about the possible effect a proposed water export project adjacent to GSDNM would have on the dunes and their vegetation.
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Honrado, J., J. Vicente, A. Lomba, et al. "Fine-scale patterns of vegetation assembly in the monitoring of changes in coastal sand-dune landscapes." Web Ecology 10, no. 1 (2010): 1–14. http://dx.doi.org/10.5194/we-10-1-2010.
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Abstract. Understanding dune ecosystem responses to multi-scale environmental changes can provide the framework for reliable forecasts and cost-efficient protocols for detecting shifts in prevailing coastal dynamics. Based on the hypothesis that stress and disturbance interact as primary community controls in coastal dunes, we studied the fine-scale floristic assembly of foredune vegetation, in its relation to topography, along regional and local environmental gradients in the 200 km long coastline of northern Portugal, encompassing a major biogeographic transition in western Europe. Thirty topographic profiles perpendicular to the shoreline were recorded at ten sites along the regional climate gradient, and vegetation was sampled by recording the frequency of plant species along those profiles. Quantitative topographic attributes of vegetated dune profiles (e.g. length or height) exhibited wide variations relatable to differences in prevailing coastal dynamics. Metrics of taxonomic diversity (e.g. total species richness and its additive beta component) and of the functional composition of vegetation were highly correlated to attributes of dune topography. Under transgressive dynamics, vegetation profiles have fewer species, increased dominance, lower turnover rates, and lower total vegetation cover. These changes may drive a decrease in structural and functional diversity, with important consequences for resistance, resilience and other ecosystem properties. Moreover, differences in both vegetation assembly (in meta-stable dunes) and response to increased disturbance (in eroding dunes) between distinct biogeographic contexts highlight a possible decline in facilitation efficiency under extreme physical stress (i.e. under Mediterranean climate) and support the significance of functional approaches in the study of local ecosystem responses to disturbance along regional gradients. Our results strongly suggest that assessing fine-scale community assembly can provide insights on the relation between dune vegetation, environmental filters and ecosystem processes. A combination of cost-efficient indicators from dune topography and vegetation is thus suggested as a promising approach to survey, forecast and monitor changes in coastal dune ecosystems.
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Bishop, Steven R., Hiroshi Momiji, Ricardo Carretero-González, and Andrew Warren. "Modelling desert dune fields based on discrete dynamics." Discrete Dynamics in Nature and Society 7, no. 1 (2002): 7–17. http://dx.doi.org/10.1080/10260220290013462.
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A mathematical formulation is developed to model the dynamics of sand dunes. The physical processes display strong non-linearity that has been taken into account in the model. When assessing the success of such a model in capturing physical features we monitor morphology, dune growth, dune migration and spatial patterns within a dune field. Following recent advances, the proposed model is based on a discrete lattice dynamics approach with new features taken into account which reflect physically observed mechanisms.
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Carson, M. A., and P. A. MacLean. "Development of hybrid aeolian dunes: the William River dune field, northwest Saskatchewan, Canada." Canadian Journal of Earth Sciences 23, no. 12 (1986): 1974–90. http://dx.doi.org/10.1139/e86-183.
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Observations have been made on the structure, morphology, and pattern of sand movement on large-scale, roughly elongate, northwest–southeast-aligned aeolian sand dunes in a desert area of northern Saskatchewan, Canada. Transverse profiles show steeper northeast flanks, the lower parts of which are covered with psammophilous grasses. Dune structure is dominated by northeast-dipping accretion laminae, and 14C dates of organic material trapped between such exposed laminae on the southwest flank indicate migration to the northeast at about 0.5 m/year in the last few centuries. On the other hand, there is a progressive increase in height, bulk, symmetry, and peakedness of the dunes from northwest to southeast, suggestive of substantial along-dune sand movement. The present-day wind regime shows a potential resultant sand-transport vector to the southeast, virtually parallel to the dune axis; winds from the north-northeast and northeast dominate the first 6 months of the year, followed by winds from the west-southwest in the latter half. Field evidence of airflow and sand-movement patterns upon the surfaces of two dunes also indicates a strong along-dune component. The dunes are interpreted as hybrid landforms reflecting both transverse and longitudinal processes acting at the present time. Of particular sedimentological significance is the discordance between dune stratigraphy and the wind regime. Dune structure is controlled by a southwest–northeast imbalance in sand movement assumed to result from an asymmetric distribution of sand-trapping vegetation and from a seasonal contrast in sand mobility that partly correlates with seasonality in the wind regime. Both factors promote northeast migration normal to the potential resultant of effective winds.
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Zorndt, Anna Christina, Andreas Wurpts, Torsten Schlurmann, Nino Ohle, and Thomas Strotmann. "DUNE MIGRATION AND SAND TRANSPORT RATES IN TIDAL ESTUARIES: THE EXAMPLE OF THE RIVER ELBE." Coastal Engineering Proceedings 1, no. 32 (2011): 38. http://dx.doi.org/10.9753/icce.v32.sediment.38.
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Large parts of the tidal estuary of river Elbe (Germany) are characterized by regular patterns of sand dunes. They are presumed to evolve due to complex sand transport mechanisms and show multi-faceted migration patterns. Direction and magnitude of their migration are influenced by hydrodynamic boundary conditions such as river runoff and tides. Dune Migration can lead to residual sand transport rates, depending on its direction and magnitude and the dune’s characteristics. The understanding of dune migration patterns and associated sand transport is the basis of an effective sediment management as well as an important requirement for planning offshore structures. This study focuses on methods for computing migration and sand transport rates in automated ways. In a comparison and validation of different approaches, a cross-correlation technique was found to produce best results. From a unique data set of up to six annual bathymetrical multi-beam soundings between 1995 and 2010, dune characteristics and migration rates were processed and analysed autonomously. The findings show that in a long perspective, average dune migration and sand transport rates in the present study reach are directed upstream.
Dissertations / Theses on the topic "Dune patterns"
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Livingstone, I. "The dynamics of sand transport on a Namib linear dune." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375978.
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Kirkwood, Donovan. "Establishment patterns of thicket and forest species in coastal dune landscapes of the southern Cape." Thesis, University of Cape Town, 1993. http://hdl.handle.net/11427/26396.
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Joubert, Eugene Christiaan. "A computational fluid dynamics study of the near surface wind patterns over a desert dune and the effect on seed dispersion." Thesis, Stellenbosch : Stellenbosch University, 2010. http://hdl.handle.net/10019.1/4357.
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Thesis (MScEng)--Stellenbosch University, 2010.<br>ENGLISH ABSTRACT: This project originated when a team of scientists at the Gobabeb training and research and centre
observed seed accumulation sites on the slope of sand dunes in the Namib Desert. Seeds that
accumulate on the slip face of a sand dune provide food for small desert creatures that in turn
attract larger animals, resulting in a small ecosystem on the side of the dune. Since wind is the
primary transport of seeds throughout the Namib Desert it is of interest to investigate wind
patterns over the dune. In this project it is therefore desired to look at seed dynamics and
deposition as a result of near surface wind patterns around a three-dimensional dune geometry
using computational fluid dynamics. The project is a joint venture between the University of
Stellenbosch and the University of Namibia. This document presents the South African MScEng
thesis part.
The literature review shows the dominant winds in the Namib Desert to be from the south to
westerly direction. Previous studies on air flow over dunes focussed on sand movement and were
often limited to simplified two-dimensional geometries and steady state simulations. From these
studies the basic flow features associated with dunes can be identified. Lastly, factors that
influence particle dynamics around dune geometries are looked at. These particle studies mostly
involve the movement of sand rather than seeds but still provide valuable insight.
The project methodology is explained and includes the equipment used, the considerations taken
into account, the simplifications made as well as the procedure followed when conducting field
work and simulations. A section of an actual Namibian linear dune is mapped in order to obtain
a geometry for the simulations. Flow measurements are carried out with a wind mast to obtain
velocity profile inlet conditions for the simulations. Furthermore, seed sampling is done by the
collaborating Namibian team of which the data is used to obtain an effective seed particle model.
Lastly, simulations are carried out using primarily OpenFOAM-1.5. The simulations look at
general near surface wind patterns, time dependant flow features and particle movement and seed
deposition around and on the linear dune.
The results show different wind profiles for different wind direction. It is also possible to see
how the profile changes as the flow accelerates up the dune slope. Two-dimensional results
provide the opportunity to compare results with previous studies as well as to provide the basis
for looking at aspects such as differencing schemes, turbulence models and parallel computing
before three-dimensional simulations are carried out. The importance of higher order
differencing schemes are confirmed in the two-dimensional results. The turbulence models,
however, produce very similar results. The results from the two- and three-dimensional results
show typical flow features associated with dunes. Transient flow features and separation vortex
structures can be identified from time dependant simulations. Furthermore, particle simulations
reveal how particles tend to be trapped in the recirculation regions.
The conclusions explain how the project objectives were achieved and provide recommendations
for future studies related to this project.<br>AFRIKAANSE OPSOMMING: Die projek het ontstaan toe naforsers areas van saad akumulasie op die hellings van duine in
Namibë opgelet het. Hierdie akumulasie van plant materiaal verskaf die voedsel vir klein diere
op die duin wat ‘n klein ekosisteem tot gevolg het. Aaangesien die primêre vervoermiddel vir
sade in die woestyn wind is beoog die projek om deur die wind patrone oor die duin beter te
verstaan die saad verspreiding te beskryf. Die doel is dus om saad verspreiding en akumulasie te
beskryf deur die wind patrone te bekyk wat die verspreiding tot gevolg het deur gebruik te maak
van numeriese vloei dinamika. Die projek is ‘n saamgestelde projek tussen die Universiteit van
Stellenbosch en die Universiteit van Namibië. Hierdie dokument behels die Suid Afrikaanse
MScIng gedeelte van die projek.
Deur die hersiening van literatuur word daar gesien dat die domineerende wind rigtings as suid
tot wes beskryf kan word. Vorige studies wat verband hou met wind vloei oor duine wys dat die
meeste op twee-dimensionele eenvoudige geometrië gefokus het met tyd onafhankike simulasies.
Dit is egter moontlik om die resultate te gebruik om karakteristieke vloei patrone te identifiseer
wat met duin wind patrone geassosieer kan word. Laastens word daar gekyk na die faktore wat
partikel beweeging beïnvloed, maar hierdie studies sluit hoofsaaklik sand partikels in eerder as
sade.
Die motodologie beskryf die toerusting, oorwegings en prosedures wat gevolg is tydens veld
werk asook simulasies. Tydens die veld werk is ‘n gedeelte van ‘n Namib lineêre duin gemeet en
so gebruik om ‘n geometrie te maak wat vir simulasie doeleindes gebruik kan word. Daar is ook
wind meetings gedoen met ‘n wind mas om wind profiele vir inlaat kondisies vir die simulasies te
kry. Verder het saad bestudeering die nodige data verskaf om ‘n voledige saad partikel model op
te stel wat in die simulasies gebruik kan word. Laastens kyk die simulasies veral na algemene
vloei patrone, tyd afhanklike vloei effekte en ook partikel beweging in die vloei veld.
Die resultate wys hoe wind profiele verskil wat van verskillende rigtings af waai. Dit is ook
moontlik on te wys hoe die wind profiele verander soos die wind versnel teen die duin op. Tweedimensionele
simulasies verskaf die geleentheid om te kyk na die effek van verkillende
numeriese modelle, turbulensie modelle en ook multi-prosesseerder verwerking. Tydens die
twee-dimensionele simulasies is die belangrikheid van hoër orde numeriese metodes besef. Die
verkillende turbulensie modelle het egter klein verkille gewys. Alby die twee- en driedimensionele
resultate wys karakteristieke vloei patrone wat met duine geasosieer kan word.
Verder het tyd afhanklike simulasies gewys hoe wind patrone verander met tyd. Die partikel
simulasies wys ook die beweging van partikels deur die wind en hoe dit neig om te akumuleer in
die hersirkulasie gebied agter die duin.
Die gevolgtrekkings wys dat al die doelstellings bereik is en maak voorstelle vir toekomstige
studies wat met hierdie studie verband hou.
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McConnachie, Lauren Bernyse. "Morphology, patterns and processes in the Oyster Bay headland bypass dunefield, South Africa." Thesis, Rhodes University, 2013. http://hdl.handle.net/10962/d1001904.
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Studies of the dunefield systems crossing the Cape St. Francis headland in the Eastern Cape have focused on the role that wind plays in sediment transfer in coastal dunefield systems, with limited consideration of the role of water. The aim of this study was to improve understanding of the morphology, processes and patterns within the Oyster Bay HBD system, focussing particularly on surface water and groundwater interactions and the role of surface water in sediment transfer across the dunefield system. An extensive field survey was conducted, to collect related data, complimented by spatial and temporal analysis of the study area using GIS. The key findings from this research were the apparent differences between the western and eastern regions of the dunefield with regard to specific drivers and the respective processes and responses. Wind is the major driver of change up to and across the crest of the dunefield. In the eastern region water (ground water, surface water and the Sand River System) is the primary agent of sediment flux through processes of aggregation and slumping as well as episodic events including debris flows. This study has highlighted a need for further quantitative studies that investigate the movement of sediment through dunefield systems such as this (where water is at or near the land surface). The paradigm that sediment flux is entirely due to wind is almost certainly simplistic, and deeper understanding of these systems is needed<br>Maiden name: Elkington, Lauren
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Hays, Allison Whitney. "Determining the impacts of beach restoration on loggerhead (Caretta caretta) and green turtle (Chelonia mydas) nesting patterns and reproductive success along Florida's Atlantic coast." Master's thesis, University of Central Florida, 2012. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5295.
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Artificial beach nourishment, the most common method to mitigate coastal erosion in the United States, is also considered the most ecologically friendly alternative for shoreline stabilization. However, this habitat alteration has the potential to impact nesting marine turtles and developing hatchlings. The first objective of this study was to determine how nourishing beaches with two different design templates affects loggerhead (Caretta caretta) and green turtle (Chelonia mydas) nesting success, the ratio of nests to the total number of nests and non-nesting emergences, and reproductive success, the ratio of hatched and emerged hatchlings to the total number of eggs deposited. Two types of restoration designs exist along the southern Brevard County, FL coastline, which supports some of the highest density loggerhead and green turtle nesting worldwide. Since 2005, approximately 35 kilometers of beach have undergone 1) full-scale restoration (typically called nourishment), where sand was added above and below the mean high tide line (2005, 2010) or 2) dune restoration, where sand was placed on the dune (2005, 2006, 2008, 2009). To quantify the effects of these restoration types, we used a Before-After-Control-Impact-Paired Series (BACIPS) model, which tests for significance between the difference in nesting success rates at the impact (engineered) and control sites (natural beach) before and after restoration ([delta]). For loggerheads, there was a significant difference in [delta] after dune restoration during the years of construction (2005, 2006, 2008, and 2009; p<0.001) and one year post-construction (2007; p<0.05 and 2010; p<0.001). After full-scale restoration, there was a significant difference in [delta] during the years of construction (2005 and 2010; p <0.001) and one year post-construction (2006; p<0.001). For green turtles, there was a significant difference in [delta] after dune restoration during two of the four years of construction (2006; p<0.05 and 2008; p<0.01) and one of the two one-year post-construction years (2010; p<0.05). After full-scale restoration, the significant difference in [delta] lasted every season (2005-2010; p<0.001). There were no significant differences in [delta] for loggerhead or green turtle reproductive success rates after either type of restoration. The second objective was to use the different restoration designs to study what beach characteristics function as loggerhead nesting cues to explain why altering the beach decreases nesting success rates. We examined beach elevation and slope, sand moisture content, sand grain size, beach width, and distance traveled. Logistic regression model selection found all variables were important (R2=0.75). Further examination of trends, with each crawl divided into quarters, found beach slope served as a nesting cue. In all study sites except one, when turtles false crawled, the beach flattened out in the final quarter of the crawl. Conversely, in nesting emergences, the final quarter rose at a steeper slope than the previous quarter. Additionally, model selection found variables important in nest site selection were also important in hatching (R2=0.44) and emergence (R2=0.45) success. These results offer new insight into how and why marine turtle nesting patterns change after artificial nourishment, providing information necessary to nourish beaches in a more “turtle-friendly” manner.<br>ID: 031001543; System requirements: World Wide Web browser and PDF reader.; Mode of access: World Wide Web.; Adviser: John Weishampel.; Co-adviser: Llewellyn Ehrhart.; Title from PDF title page (viewed August 22, 2013).; Thesis (M.S.)--University of Central Florida, 2012.; Includes bibliographical references (p. 84-90).<br>M.S.<br>Masters<br>Biology<br>Sciences<br>Biology
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Diniega, Serina. "Modeling Aeolian Dune and Dune Field Evolution." Diss., The University of Arizona, 2010. http://hdl.handle.net/10150/195665.
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sand hops and bounces -see the dunes grow, run, collide -form the field's pattern.Aeolian sand dune morphologies and sizes are strongly connected to the environmental context and physical processes active since dune formation. As such, the patterns and measurable features found within dunes and dune fields can be interpreted as records of environmental conditions. Using mathematical models of dune and dune field evolution, it should be possible to quantitatively predict dune field dynamics from current conditions or to determine past field conditions based on present-day observations.In this dissertation, we focus on the construction and quantitative analysis of a continuum dune evolution model. We then apply this model towards interpretation of the formative history of terrestrial and martian dunes and dune fields. Our first aim is to identify the controls for the characteristic lengthscales seen in patterned dune fields. Variations in sand flux, binary dune interactions, and topography are evaluated with respect to evolution of individual dunes. Through the use of both quantitative and qualitative multiscale models, these results are then extended to determine the role such processes may play in (de)stabilization of the dune field. We find that sand flux variations and topography generally destabilize dune fields, while dune collisions can yield more similarly-sized dunes. We construct and apply a phenomenological macroscale dune evolution model to then quantitatively demonstrate how dune collisions cause a dune field to evolve into a set of uniformly-sized dunes. Our second goal is to investigate the influence of reversing winds and polar processes in relation to dune slope and morphology. Using numerical experiments, we investigate possible causes of distinctive morphologies seen in Antarctic and martian polar dunes. Finally, we discuss possible model extensions and needed observations that will enable the inclusion of more realistic physical environments in the dune and dune field evolution models.By elucidating the qualitative and quantitative connections between environmental conditions, physical processes, and resultant dune and dune field morphologies, this research furthers our ability to interpret spacecraft images of dune fields, and to use present-day observations to improve our understanding of past terrestrial and martian environments.
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Savage, Christopher Jon. "Implications of Dune Pattern Analysis for Titan's Surface History." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/3077.
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Analyzing dune parameters such as dune width and spacing can be useful in determining the reaction of dunes to changes in atmospheric and sedimentary conditions currently and in the recent geologic past. Dune parameters, dune width and spacing, were measured for linear dunes in regions across Saturn's moon Titan from images T21, 23, 28, 44 and 48 collected by Synthetic Aperture RADAR aboard the Cassini spacecraft in order to reconstruct the surface history of Titan. Dunes in the five study swaths are all linear in form, but lack superimposed or flanking dunes. They have a mean width of 1.3 km and mean crest spacing of 2.7 km, wider and farther apart on average than similar terrestrial dunes in the Namib and Agneitir Sand Seas though larger linear dunes exist on Earth. Because of the lack of superimposed and flanking dunes and their size, Titan's dunes are classified as very large simple linear dunes. The large size, spacing and uniform morphology are all indicators that Titan's dunes are very mature and long-lived features. The ratio of dune width to spacing for Titan's dunes is similar to that found in terrestrial dunes in that dune spacing tends to be twice dune width. In addition to being similar in size, this is further evidence that terrestrial dunes can be used as analogues for Titan's dunes and vice versa and that the essential dune-forming processes are the same on both bodies. Dune width and spacing decrease northward, which is attributed to, but not limited to, increased maturity of dune fields to the south or increased sediment stabilization to the north. Sediment stabilization may be caused by Titan's asymmetric seasons and a net transport of moisture from south to north. The majority of dunes have spacings consistent with an upper limit of 2 to 4 km established by the atmospheric boundary layer, further evidence they are mature. Dunes are more widely spaced in the south are evidence they have been growing toward a steady state for a longer period of time than those in the north. Titan's large linear dunes have long reconstitution times. This is in part due to the fact that winds sufficient for saltation are reached only near the Titan equinox every 14 Earth years. Based on rates for similar terrestrial dunes the reconstitution time for Titan's dune is 600,000 Earth years or more, and therefore substantial changes in dune form should not be observable over Cassini's lifetime. Cumulative probability plots of dune parameters measured at different locations across Titan indicate there is a single population of dunes on Titan. This suggests that, unlike analogous dunes in the Namib and Agneitir Sand Seas, dune-forming conditions that currently exist on Titan are either the only dune-friendly conditions in the moon's history, or the current conditions have been stable and active long enough to erase any evidence of past conditions.
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Mello, Raquel Gewehr de. "Reconstrução dos paleoventos do Gonduana no Juro-cretáceo." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/173583.
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A passagem de um padrão monsoonal para um padrão de circulação atmosférica zonal ocorreu durante o Cretáceo devido à fragmentação do Supercontinente Gonduana. Essa mudança na direção dos paleoventos é registrada no mergulho de estratos cruzados de dunas eólicas acumuladas em várias bacias de Gonduana. Três mapas de reconstrução de paleoventos foram construídos com a integração de dados paleocorrentes compilados de bacias Fanerozoicas brasileiras, Bacia de Neuquén na Argentina e bacias do Congo e Huab na África. O Gonduana foi dominado por ventos do nordeste ao norte e ventos do sudoeste ao sul, deslocando, assim, a Zona de Convergência Intertropical para 15º a 20 sul do equador durante o Jurássico Tardio até o início do Cretáceo. Por sua vez, os ventos apresentaram uma tendência geral para o oeste-noroeste em latitudes baixas e médias no Gonduana no final do Cretáceo Inical. Esses resultados apontam para a existência de um padrão monsoonal durante o Jurássico Tardio até o início do Cretáceo Inicial e a entrada do padrão zonal no final do Cretáceo Inicial, associado à fragmentação de Gonduana.<br>The passage of a monsoonal pattern to a zonal atmospheric circulation pattern occurred during the Cretaceous due to fragmentation of Gondwana Supercontinent. This change in the paleowind direction is recorded in crossstrata dip directions of eolian dunes accumulated in various basins of Gondwana. Three maps of paleowind reconstruction were built with integration of compiled paleocurrent data from Phanerozoic basins in Brazil, Neuquén Basin in Argentina and Congo Basin and Huab Basin in Africa. Gondwana was dominated by northeast winds to the north and southwest winds to the south, thus shifting the Intertropical Convergence Zone to 15º to 20⁰ south of the equator during Late Jurassic to the beginning of the Cretaceous. In turn, winds had a general tendency towards west-northwest at low and mid-latitudes in Gondwana at the end of Early Cretaceous. These results point to the existence of a monsoonal pattern during the Late Jurassic to the beginning of Early Cretaceous and the entry of zonal pattern at the end of Early Cretaceous, associated with fragmentation of Gondwana.
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Pierce, Shirley M. "Pattern and process in South Coast dune fynbos : population, community and landscape level studies." Doctoral thesis, University of Cape Town, 1990. http://hdl.handle.net/11427/8422.
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Includes bibliographies.<br>The study aimed to explain vegetation dynamics in response to disturbance in a dune landscape comprising a mosaic and admixture of grassland, fynbos and thicket. A hierarchical approach directed investigations at the landscape, community and population levels, with emphasis on seed banks. The study concentrated on fynbos, the predominant vegetation type. At the landscape-level, pattern was attributed to successional processes rather than abiotic factors. Each vegetation was maintained under defined disturbance regimes of fire, grazing and bushcutting. In the absence of disturbance, succession proceeded from grassland, through fynbos, to thicket. The study contributed to existing theory on the effects of disturbance on seed bank size, and the relationship between seed bank composition and its above-ground vegetation. No single model for successional pathways and mechanisms was supported: these differed amongst vegetation types and within fynbos communities.
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Wiebe, Joshua Daniel. "Time and patterns of development of dunes subjected to sudden changes in flow depth." Thesis, Kingston, Ont. : [s.n.], 2007. http://hdl.handle.net/1974/706.
Full textBooks on the topic "Dune patterns"
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Guldan, Mary Duke. A woodcarver's workbook: Carving animals with Mary Duke Guldan. 2nd ed. Fox Chapel, 1992.
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Downing, Laura J., and Al Mtenje. Tonal Phonology: Lexical Tone Patterns. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198724742.003.0006.
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Like the vast majority of Bantu languages, Chichewa is a tone language. The chapter begins with a brief introduction to the Chichewa tone system. The lexical tone patterns for noun and verb stems are taken up next. Lexical tones do not always surface on their input sponsor syllable due to the application of tone processes such as tone doubling, tone plateauing, and final retraction. These processes, all conditioned by phrase penult lengthening, are defined and illustrated in detail in this chapter, along with the OCP-motivated process, Meeussen’s Rule. The tonal properties of clitics and clitic-like nominal modifiers are shown to motivate the process of tone shift. The phonetics of tone and the accentual properties of the Chichewa tone system are discussed in the concluding sections.
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Rankin, Watson S. James Buchanan Duke: A Great Pattern Of Hard Work, Wisdom And Benevolence. Kessinger Publishing, LLC, 2006.
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Glanville, Peter John. Reflexive marking. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198792734.003.0004.
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Chapter 4 examines the semantics of Arabic reflexive verbs formed in pattern VII, which produces anticausative verbs, and pattern VIII, associated with the middle voice. It argues that these patterns result from the conversion of full reflexive pronouns into reflexive affixes, and considers the difference between them in the framework of an agency continuum. It then offers an analysis of reflexive verbs that do not participate in a verb alternation. The chapter argues that once a reflexive verb pattern comes about due to affixation, it becomes a morpheme paired with a reflexive semantic structure, and is then no longer restricted to producing verbs that alternate with an unmarked base verb. The chapter shows that verbs marked with this morpheme may be derived from a variety of base nouns and adjectives, or may not be derived at all, but simply marked because they construe a reflexive action.
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Lippiatt, G. E. M. Duke of Narbonne and Count of Toulouse. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198805137.003.0007.
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Simon’s dynamism failed just as his crusade reached its zenith in the acquisition of the county of Toulouse. Though Simon’s introduction of French feudal patterns and antiheretical policies stood in stark contrast to the government of his Raymondine predecessors, their dynastic eminence offered more incentive to maintain iconographic continuity and cultivate ties with traditionally favoured abbeys. As in the viscounties, cultivation of local nobles, appointment of French followers to key posts, preservation of urban liberties, and patronage of Cistercians and bishops all undergirded Simon’s regime. But even with this broad base of support, Simon was finally undone by the southern resurgence that focused on the fatal exception to his characteristic urban lenience: Toulouse. His inability to accommodate the independence of his ostensible capital allowed it to serve as a rallying point for the disaffected aristocracy of the region, and it was before its walls that Simon met his bloody end.
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Badenhorst, Shaw. The zooarchaeology of Iron Age farmers from southern Africa. Edited by Umberto Albarella, Mauro Rizzetto, Hannah Russ, Kim Vickers, and Sarah Viner-Daniels. Oxford University Press, 2017. http://dx.doi.org/10.1093/oxfordhb/9780199686476.013.29.
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The Iron Age of southern Africa covers the spread and occupation of Bantu-speaking farmers during the last 1,500 years. Archaeological research of these farmers was heavily influenced by the Central Cattle Pattern, a settlement model which, as one of its main concepts, argued that cattle were the most important domestic animal since the first farmers settled in southern Africa during the first millennium ad. Various arguments have been presented to support this view, including the presence of cattle dung, cattle herd sizes, informants and ethnography, and weights of livestock, as well as ageing and skeletal part data. These arguments have been challenged recently, and new interpretations offered. New interpretations unrestricted by the Central Cattle Pattern have focused on descent patterns of farmers. Changes in identification methodology and measures of changes of livestock over time have played a major role in these new interpretations.
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Zsiga, Elizabeth C., and One Tlale Boyer. Sebirwa in Contact with Setswana. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780190256340.003.0015.
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Setswana, spoken by about 4.5 million people throughout Botswana, is well-known in the literature for “post-nasal devoicing,” in which /b/ and /l/ become [p] and [t] after nasals, contra the expected, phonetically-grounded pattern of post-nasal voicing. Sebirwa, in contrast, has at most 15,000 speakers concentrated in the far eastern corner of the country. Sebirwa is being overwhelmed by Setswana, and in a process of “massive Tswananization,” has borrowed some aspects of post-nasal devoicing. Our analysis, based on fieldwork in the village of Molalatau, shows that the Sebirwa pattern is doubly unexpected: only /b/ devoices, not /d/ and /g/. We attribute the asymmetry to frequency effects from Setswana, where, due to a skewed voicing inventory, the majority of lexical items that exhibit the alternation have underlying /b/. We discuss the implications of this type of borrowing, both for the typology of alternations, and for patterns of language loss.
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Kasprzak, Jaroslaw D., Anita Sadeghpour, and Ruxandra Jurcut. Doppler echocardiography. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780198726012.003.0003.
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Doppler examination is an integral part of the echocardiogram. Current systems are equipped with spectral Doppler in continuous wave mode (offering measurements of high velocities with limited spatial specificity due to integration of signal along the scan line), pulsed wave mode (high spatial specificity with maximal recordable velocity reduced by the Nyquist limit), and colour Doppler flow mapping (allowing rapid identification of flow pattern within a cross-sectional B-mode sector). Tissue Doppler echocardiography emerged as a basic tool for sampling regional myocardial velocities, in pulsed wave or colour velocity mapping mode. Finally, three-dimensional systems improve spatial presentation of flow phenomena by integrating Doppler-derived flow patterns in three-dimensional datasets.
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Klemenhagen, Kristen C., Franklin R. Schneier, Abby J. Fyer, H. Blair Simpson, and René Hen. Adult Hippocampal Neurogenesis, Pattern Separation, and Generalization. Edited by Israel Liberzon and Kerry J. Ressler. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780190215422.003.0006.
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Almost one-third of adult Americans will have an anxiety disorder in their lifetime, with enormous personal, societal, and financial costs. Among the most disabling of these disorders are post-traumatic stress disorder (PTSD), obsessive-compulsive disorder (OCD), social anxiety disorder, generalized anxiety disorder, and panic disorder. Although there are evidence-based treatments for these disorders, as many as 50% of patients do not respond, and there is a considerable need for new therapies. This chapter proposes that the excessive generalization seen in patients with pathological anxiety is due to impaired hippocampal functioning, specifically a deficit in the neural process of pattern separation, which relies upon the dentate gyrus and is sensitive to neurogenesis. Preclinical findings indicate that stimulating DG neurogenesis improves pattern separation and reduces anxiety behaviors in mice. As a result the authors hypothesize that pharmacological or environmental manipulations aimed at stimulating neurogenesis will be beneficial for the treatment of anxiety disorders.
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Litell, John M., and Nathan I. Shapiro. Pathophysiology of septic shock. Oxford University Press, 2016. http://dx.doi.org/10.1093/med/9780199600830.003.0297.
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The pathophysiology of sepsis is the result of a dysregulated host response to infection. Interactions between conserved pathogenic signals and host recognition systems initiate a systemic reaction to local infection. Pro- and anti-inflammatory intermediates and associated coagulatory abnormalities lead to altered macrovascular, microvascular, and mitochondrial function. Uncorrected, these processes yield similar patterns of failure in multiple organ systems. Mortality increases with successive organ failures. Although commonly thought to be a manifestation of impaired renal circulation, septic acute kidney injury may be due primarily to non-haemodynamic factors. Pulmonary parenchymal dysfunction in sepsis also contributes to failures in other organ systems. Sepsis involves complex alterations in myocardial function, vascular tone, and capillary integrity, which are mediated by elevated concentrations of inflammatory cytokines, inducible nitric oxide, and reactive oxygen species, among others. Gut hypomotility and translocation of enteric flora likely contribute to a persistent inflammatory response. This perpetuates the pathophysiological pattern of sepsis, and can lead to the delayed onset of these features in patients with other types of critical illness. The neurological manifestations of sepsis include acquired delirium, which is also probably due to circulatory and inflammatory abnormalities, as well as alterations in cerebral amino acid metabolism. Critical illness-related corticosteroid insufficiency and derangements in glucose metabolism are among the endocrine abnormalities commonly seen in septic patients. Restoration of homeostasis requires early haemodynamic resuscitation and aggressive infectious source control.
Book chapters on the topic "Dune patterns"
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Hargitai, Henrik. "Dune-Field Patterns (Aeolian)." In Encyclopedia of Planetary Landforms. Springer New York, 2014. http://dx.doi.org/10.1007/978-1-4614-9213-9_165-1.
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Hargitai, Henrik. "Dune-Field Patterns (Aeolian)." In Encyclopedia of Planetary Landforms. Springer New York, 2015. http://dx.doi.org/10.1007/978-1-4614-3134-3_165.
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Piotrowska, H. "The dynamics of the dune vegetation on the Polish Baltic coast." In Temporal and Spatial Patterns of Vegetation Dynamics. Springer Netherlands, 1988. http://dx.doi.org/10.1007/978-94-009-2275-4_18.
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Recoder, Renato Sousa, and Miguel Trefaut Rodrigues. "Diversification Processes in Lizards and Snakes from the Middle São Francisco River Dune Region, Brazil." In Neotropical Diversification: Patterns and Processes. Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-31167-4_26.
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San Roque, Lila. "Chapter 13. Egophoric patterns in Duna verbal morphology." In Typological Studies in Language. John Benjamins Publishing Company, 2018. http://dx.doi.org/10.1075/tsl.118.13san.
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Kumar, Vinay V., Supriya Ebenezer, and Andreas Thor. "Bone Augmentation Procedures in Implantology." In Oral and Maxillofacial Surgery for the Clinician. Springer Singapore, 2021. http://dx.doi.org/10.1007/978-981-15-1346-6_19.
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AbstractSuccessful implant dentistry mandates implants to be placed in an appropriate three-dimensional manner that supports the prosthesis adequately. Due to the resorption patterns of edentulous jaws, the ideal position of implants required varying amounts of bone augmentation. Commonly carried out bone-augmentation procedures are Guided Bone Regeneration, onlay bone grafting and sinus floor elevation. This chapter discusses the resorption pattern of edentulous jaws, the biology of alveolar bone of relevance to the maxillofacial surgeon, the biomaterials used for augmentation and the commonly carried out augmentation procedures.
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Kato., Naoyuki, and Tomowo Hirasawa. "The Variation of Stresses due to Aseismic Sliding and its Effect on Seismic Activity." In Seismicity Patterns, their Statistical Significance and Physical Meaning. Birkhäuser Basel, 1999. http://dx.doi.org/10.1007/978-3-0348-8677-2_12.
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Ma, Shihan, and Andrei Kirilenko. "How Reliable Is Social Media Data? Validation of TripAdvisor Tourism Visitations Using Independent Data Sources." In Information and Communication Technologies in Tourism 2021. Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-65785-7_26.
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AbstractSocial media data has been rapidly applied as alternative data source for tourism statistics and measurement in recent years due to its availability, easy collection, good spatial coverage at multiple scales, and rich content. However, frequent criticism towards the social media is the bias towards the population of social media users leading to unknown representativeness of the entire population. The purpose of this study is to cross-validate the reliability and validity of visitation pattern of tourist destinations retrieved from the social media using alternative independent data sources. The primary social media data is TripAdvisor reviews of Florida attraction points, restaurants, and hotels. The inferred visitation pattern was validated against two independent datasets: cellphone tracking data and official visitor surveys. The validity was explored in tourist origins, destinations, and travel flows. Repetitively, travel patterns inferred from the social media were found strongly correlated to those from cellphone tracking and surveys. The visitation data obtained from social media was concluded to be reliable and representative.
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Agbehadji, Israel Edem, Richard Millham, Surendra Thakur, Hongji Yang, and Hillar Addo. "Visualization of Frequently Changed Patterns Based on the Behaviour of Dung Beetles." In Communications in Computer and Information Science. Springer Singapore, 2018. http://dx.doi.org/10.1007/978-981-13-3441-2_18.
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Sutherland, Grant R., and Robert I. Richards. "Unusual Inheritance Patterns Due to Dynamic Mutation in Fragile X Syndrome." In Ciba Foundation Symposium 197 - Variation in the Human Genome. John Wiley & Sons, Ltd., 2007. http://dx.doi.org/10.1002/9780470514887.ch7.
Full textConference papers on the topic "Dune patterns"
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Lancaster, Nicholas, David LeBlanc, George Bebis, and Mircea Nicolescu. "AUTOMATED CREST-LINE DETECTION AND ANALYSIS OF SAND DUNE PATTERNS." In GSA Annual Meeting in Denver, Colorado, USA - 2016. Geological Society of America, 2016. http://dx.doi.org/10.1130/abs/2016am-283599.
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HALL, KRISTEN. "ASSESSMENT OF DECADAL AND ANNUAL BEACH WIDTH AND DUNE HEIGHT PATTERNS ON MASONBORO ISLAND, NORTH CAROLINA." In Coastal Sediments 2015. WORLD SCIENTIFIC, 2015. http://dx.doi.org/10.1142/9789814689977_0015.
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Dai, Y., T. S. Khan, M. S. Alshehhi, and L. Khezzar. "Experimental Investigation on Particle Deposition Patterns From Turbulent Pipe Flow." In ASME 2015 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/imece2015-51729.
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This paper reports an experimental study on sand particles deposition pattern in a horizontal circular pipe for several air flow rates and particle - air volumetric loading ratios. The experiments are conducted in a horizontal circular pipe with air - sand particles flow to simulate the solid particles movement in turbulent flow. A 50 mm diameter pipe was used in the current study while the averaged sand particles size used is around 100 μm. The particles are injected into the fully developed turbulent air flow. Digital cameras are used to capture the images of scaled test sections. The time dependent deposition layer properties including the geometry of deposition layers and the agglomeration pitch are studied. Hence, the average velocity of dune movement could also be calculated. The experimental results show that, in general, the deposition layer is continuous near the injection point, while small agglomerates are observed at the remote end. For the low air flow rate, striped-like dunes were found near injection point. For relatively higher air flow rates, the dunes became longer in size. Similarly, the length of agglomerates increased and the area fraction occupied by the agglomerates increased. Small aggregates are re-entrained from the frontal dunes of the deposition layer, and new agglomerates were gradually formed behind the next dune. The free flight length of solid particles for a range of air flow rates with different solid loading ratios was studied. It is found that for a given solid loading ratio, decreasing air velocity decreased the free-flight length of particles.
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Cornachione, Harriet S., Tammy M. Rittenour, and Michelle S. Nelson. "CHRONOSTRATIGRAPHY OF TWO DUNE FIELDS IN SOUTHERN UTAH - IMPLICATIONS FOR DROUGHT PATTERNS IN THE CENTRAL COLORADO PLATEAU." In Joint 70th Annual Rocky Mountain GSA Section / 114th Annual Cordilleran GSA Section Meeting - 2018. Geological Society of America, 2018. http://dx.doi.org/10.1130/abs/2018rm-314190.
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Hansen, Edward, Brian P. Yurk, Brian E. Bodenbender, Thomas Smyth, Randall Schaetzl, and Suzanne DeVries-zimmerman. "WINDFLOW PATTERNS AND SEDIMENT TRANSPORT ON THE LEE SLOPE OF A LARGE PARABOLIC DUNE, SOUTHEASTERN SHORE OF LAKE MICHIGAN." In GSA Annual Meeting in Phoenix, Arizona, USA - 2019. Geological Society of America, 2019. http://dx.doi.org/10.1130/abs/2019am-335631.
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Nossair, Ahmed Mohamed, Peter Rodgers, and Afshin Goharzadeh. "Influence of Pipeline Inclination on Hydraulic Conveying of Sand Particles." In ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-93199.
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The understanding of sand particle transport by fluids in pipelines is of importance for the drilling of horizontal and inclined hydrocarbon production wells, topside process facilities, infield pipelines, and trunk lines. Previous studies on hydraulic conveying of sand particles in pipelines have made significant contributions to the understanding of multiphase flow patterns, pressure drop and particle transport rate in horizontal pipelines. However, due to the complexity of the flow structure resulting from liquid-sand interactions, the mechanisms responsible for bed-load transport flow for hydraulic conveying of sand particles have not been extensively studied in inclined pipelines. This paper presents an experimental investigation of hydraulic conveying of sand particles resulting from a stationary flat bed in both horizontal and +3.6 degree upward inclined pipelines. The characteristics of sand transportation by saltation from an initial sand bed are experimentally visualized using a transparent Plexiglas pipeline and high-speed digital photography. The dune formation process is assessed as a function of pipeline orientation. Based on the visualized dune morphology, pipeline inclination is found to have a significant influence on hydraulic conveying of sand dune dynamics (i.e., dune velocity), as well as sand dune geometry (i.e., dune pitch and characteristic dune angles).
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Saha, Sourabh K., and Martin L. Culpepper. "Predicting the Quality of One-Dimensional Periodic Micro and Nano Structures Fabricated via Wrinkling." In ASME 2012 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/imece2012-87081.
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Wrinkling of thin films due to buckling-based surface instabilities is a fast and inexpensive technique for template-free fabrication of periodic micro/nano scale structures. Although one-dimensional (1-D) periodic micro and nano structures have been fabricated via wrinkling in the past, wrinkling is not yet appropriate for a manufacturing environment. This is because it is currently not possible to predict and control the quality of the fabricated patterns. Pattern quality is quantified in terms of the uniformity of the pattern, i.e., defect density within the patterned area. Herein, we (i) identify the process parameters that affect pattern quality, (ii) model the effect of these parameters on wrinkling quality and (iii) quantify the feasible operating region for a target pattern quality. During wrinkling, dislocation defects are observed due to local geometric imperfections such as voids or variations in the material properties. We have developed a finite element model of the wrinkling process that accounts for voids in the material. The wavelength and amplitude predictions of this model were found to be within ∼13% of the experimental observations. Also, it was found that below a threshold void size, the non-uniformity in the pattern due to voids decays with an increase in the applied compressive strain. This provides a practical means to minimize the non-uniformity in 1-D wrinkled patterns by increasing the compression. However, the defect density due to surface cracks increases with an increase in the compressive strains. Our analysis enables one to identify and predict the feasible operating region within which uniform 1-D patterns can be obtained, thereby improving manufacturability via wrinkling.
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Aladahalli, Chandankumar, Jonathan Cagan, and Kenji Shimada. "Objective Function Based Pattern Search: A Computationally Efficient Algorithm for 3D Component Layout." In ASME 2004 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/detc2004-57429.
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A new class of pattern search algorithms called Objective Function-based Pattern Search is proposed for 3D Layout. These algorithms are driven by decreasing expected change in objective function rather than by decreasing step size. Current pattern search algorithms rely on decreasing step size of all patterns at the same rate. Also, all translation and rotation patterns are active at all step sizes of patterns. The new class of algorithms decreases the step sizes of the patterns based on the expected change in objective function value due to that pattern. Also, whether a pattern is active or inactive at a particular step size is decided by the expected change in objective function due to that pattern at that step size. The new algorithm is found to be up to 50% faster in runtime compared to previous pattern search based algorithms.
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Wang, Cheng-Hua, and David A. Bourne. "Compact 2D Pattern Development From 3D Polygonal Surfaces." In ASME 1996 Design Engineering Technical Conferences and Computers in Engineering Conference. American Society of Mechanical Engineers, 1996. http://dx.doi.org/10.1115/96-detc/dfm-1292.
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Abstract Pattern development involves mapping 3D surfaces into 2D flat patterns. To reduce the complexity of patterns, approximations of the surfaces into polygonal surfaces such as quadrilateral or triangular facets are usually necessary. This paper is concerned with the pattern development of polygonal surfaces with a special reference to bent sheet metal parts. The development process needs to consider the unfoldability of 2D patterns. The unfoldability requires that the 2D pattern does not overlap itself, and the faces of the part do not distort during bending. For some designs, there are multiple 2D patterns that can all be bent into the same 3D shape. The compact pattern is usually selected due to better stock utilization in cutting and nesting and ease of handling during bending. We show that the development of the compact 2D pattern can be converted into a minimum cost spanning tree problem. This approach has been implemented using an A* search algorithm and several examples are presented.
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Day, Mackenzie D., and Gary Kocurek. "HOW PERFECT IS PERFECT IN A DUNE-FIELD PATTERN?" In GSA Annual Meeting in Seattle, Washington, USA - 2017. Geological Society of America, 2017. http://dx.doi.org/10.1130/abs/2017am-294798.
Full textReports on the topic "Dune patterns"
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Brodie, Katherine, Ian Conery, Nicholas Cohn, Nicholas Spore, and Margaret Palmsten. Spatial variability of coastal foredune evolution, part A : timescales of months to years. Engineer Research and Development Center (U.S.), 2021. http://dx.doi.org/10.21079/11681/41322.
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Coastal foredunes are topographically high features that can reduce vulnerability to storm-related flooding hazards. While the dominant aeolian, hydrodynamic, and ecological processes leading to dune growth and erosion are fairly well-understood, predictive capabilities of spatial variations in dune evolution on management and engineering timescales (days to years) remain relatively poor. In this work, monthly high-resolution terrestrial lidar scans were used to quantify topographic and vegetation changes over a 2.5 year period along a micro-tidal intermediate beach and dune. Three-dimensional topographic changes to the coastal landscape were used to investigate the relative importance of environmental, ecological, and morphological factors in controlling spatial and temporal variability in foredune growth patterns at two 50 m alongshore stretches of coast. Despite being separated by only 700 m in the alongshore, the two sites evolved differently over the study period. The northern dune retreated landward and lost volume, whereas the southern dune prograded and vertically accreted. The largest differences in dune response between the two sections of dunes occurred during the fall storm season, when each of the systems’ geomorphic and ecological properties modulated dune growth patterns. These findings highlight the complex eco-morphodynamic feedback controlling dune dynamics across a range of spatial scales.
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Day, Christopher M., Hiromal Premachandra, and Darcy M. Bullock. Characterizing the Impacts of Phasing, Environment, and Temporal Factors on Pedestrian Demand at Traffic Signals. Purdue University, 2011. http://dx.doi.org/10.5703/1288284317352.
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There is a need for more and higher quality data on pedestrian demand patterns for a number of applications in planning, transportation engineering, public health, and other areas. It is particularly desirable to better characterize the influence of daily, weekly, and annual variations; the impact of weather and special events; and the effects of changes in pedestrian phasing. This paper proposes and demonstrates a methodology for quantifying the relative demand for pedestrian service at a signalized intersection by using the percent of signal cycles per hour in which the pedestrian phase was actuated. Although this performance measure does not by itself provide a pedestrian count, it can be used as a surrogate to characterize how pedestrian volumes vary due to operating conditions. More importantly, since this technique does not require new sensors, the data can be collected at thousands of intersections across the nation where pedestrian push buttons are in use. This paper documents findings from over a year of data collection at a signalized intersection on a college campus. The effects of daily/weekly/annual variations, special events, weather (temperature and precipitation), seasonal changes in activity patterns, and changes in pedestrian signal phasing are documented. A Tobit model is used to account for the influences of these variables and understand how they co-influence pedestrian activity. The implementation of an exclusive pedestrian phase is associated with a 9% increase in pedestrian phase utilization at the intersection. This change is associated with a decrease in user cost relative to performing midblock crossings. The modeled impact of snowfall events adds further insight by showing that as the user cost of making midblock crossings increases, pedestrian activity at the intersection increases.
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de Caritat, Patrice, Brent McInnes, and Stephen Rowins. Towards a heavy mineral map of the Australian continent: a feasibility study. Geoscience Australia, 2020. http://dx.doi.org/10.11636/record.2020.031.
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Heavy minerals (HMs) are minerals with a specific gravity greater than 2.9 g/cm3. They are commonly highly resistant to physical and chemical weathering, and therefore persist in sediments as lasting indicators of the (former) presence of the rocks they formed in. The presence/absence of certain HMs, their associations with other HMs, their concentration levels, and the geochemical patterns they form in maps or 3D models can be indicative of geological processes that contributed to their formation. Furthermore trace element and isotopic analyses of HMs have been used to vector to mineralisation or constrain timing of geological processes. The positive role of HMs in mineral exploration is well established in other countries, but comparatively little understood in Australia. Here we present the results of a pilot project that was designed to establish, test and assess a workflow to produce a HM map (or atlas of maps) and dataset for Australia. This would represent a critical step in the ability to detect anomalous HM patterns as it would establish the background HM characteristics (i.e., unrelated to mineralisation). Further the extremely rich dataset produced would be a valuable input into any future machine learning/big data-based prospectivity analysis. The pilot project consisted in selecting ten sites from the National Geochemical Survey of Australia (NGSA) and separating and analysing the HM contents from the 75-430 µm grain-size fraction of the top (0-10 cm depth) sediment samples. A workflow was established and tested based on the density separation of the HM-rich phase by combining a shake table and the use of dense liquids. The automated mineralogy quantification was performed on a TESCAN® Integrated Mineral Analyser (TIMA) that identified and mapped thousands of grains in a matter of minutes for each sample. The results indicated that: (1) the NGSA samples are appropriate for HM analysis; (2) over 40 HMs were effectively identified and quantified using TIMA automated quantitative mineralogy; (3) the resultant HMs’ mineralogy is consistent with the samples’ bulk geochemistry and regional geological setting; and (4) the HM makeup of the NGSA samples varied across the country, as shown by the mineral mounts and preliminary maps. Based on these observations, HM mapping of the continent using NGSA samples will likely result in coherent and interpretable geological patterns relating to bedrock lithology, metamorphic grade, degree of alteration and mineralisation. It could assist in geological investigations especially where outcrop is minimal, challenging to correctly attribute due to extensive weathering, or simply difficult to access. It is believed that a continental-scale HM atlas for Australia could assist in derisking mineral exploration and lead to investment, e.g., via tenement uptake, exploration, discovery and ultimately exploitation. As some HMs are hosts for technology critical elements such as rare earth elements, their systematic and internally consistent quantification and mapping could lead to resource discovery essential for a more sustainable, lower-carbon economy.
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Gaines, Roger, Stephen Sanborn, William McAnally, and Christopher Wallen. Mississippi River Adaptive Hydraulics model development and evaluation, Commerce to New Madrid, Missouri, Reach. Engineer Research and Development Center (U.S.), 2020. http://dx.doi.org/10.21079/11681/39519.
Full textAbstract:
A numerical, two-dimensional hydrodynamic model of the Mississippi River, from Thebes, IL, to Tiptonville, TN (128 miles/206 km), was developed using the Adaptive Hydraulics model. The study objective assessed current patterns and flow distributions and their possible impacts on navigation due to Birds Point New Madrid Floodway (BPNMF) operations and the Len Small (LS) levee break. The model was calibrated to stage, discharge, and velocity data for the 2011, 2015–2016, and 2017 floods. The calibrated model was used to run four scenarios, with the BPNMF and the LS breach alternately active/open and inactive/closed. Effects from the LS breach being open are increased river velocities upstream of the breach, decreased velocities from the breach to Thompson Landing, no effects on velocity below the confluence, and cross-current velocities greater than 3.28 ft/s (1.0 m/s) within 1186.8 ft (60 m) of the bankline revetment. Effects from BPNMF operation are increased river velocities above the confluence, decreased velocities from the BPNMF upper inflow crevasse (Upper Fuseplug) to New Madrid, cross-current velocities greater than 1.5 ft/s (0.5 m/s) only near the right bank where flow re-enters the river from the BPNMF lower inflow/outflow crevasse Number 2 (Lower Fuseplug) and St. Johns Bayou.
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Duch, Michael. Performing Hanne Darboven's Opus 17a and long duration minimalist music. Norges Musikkhøgskole, 2018. http://dx.doi.org/10.22501/nmh-ar.481276.
Full textAbstract:
Hanne Darboven’s (1941-2009) Opus 17a is a composition for solo double bass that is rarely performed due to the physical and mental challenges involved in its performance. It is one of four opuses from the composers monumental 1008 page Wünschkonzert (1984), and was composed during her period of making “mathematical music” based on mathematical systems where numbers were assigned to certain notes and translated to musical scores. It can be described as large-scale minimalism and it is highly repetitive, but even though the same notes and intervals keep repeating, the patterns slightly change throughout the piece. This is an attempt to unfold the many challenges of both interpreting, preparing and performing this 70 minute long solo piece for double bass consisting of a continuous stream of eight notes. It is largely based on my own experiences of preparing, rehearsing and performing Opus 17a, but also on interviews I have conducted with fellow bass players Robert Black and Tom Peters, who have both made recordings of this piece as well as having performed it live. One is met with few instrumental technical challenges such as fingering, string crossing and bowing when performing Opus 17a, but because of its long duration what one normally would take for granted could possibly prove to be challenging.
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Bedoya-Maya, Felipe, Lynn Scholl, Orlando Sabogal-Cardona, and Daniel Oviedo. Who uses Transport Network Companies?: Characterization of Demand and its Relationship with Public Transit in Medellín. Inter-American Development Bank, 2021. http://dx.doi.org/10.18235/0003621.
Full textAbstract:
Transport Network Companies (TNCs) have become a popular alternative for mobility due to their ability to provide on-demand flexible mobility services. By offering smartphone-based, ride-hailing services capable of satisfying specific travel needs, these modes have transformed urban mobility worldwide. However, to-date, few studies have examined the impacts in the Latin American context. This analysis is a critical first step in developing policies to promote efficient and sustainable transport systems in the Latin-American region. This research examines the factors affecting the adoption of on-demand ride services in Medellín, Colombia. It also explores whether these are substituting or competing with public transit. First, it provides a descriptive analysis in which we relate the usage of platform-based services with neighborhood characteristics, socioeconomic information of individuals and families, and trip-level details. Next, factors contributing to the election of platform-based services modeled using discrete choice models. The results show that wealthy and highly educated families with low vehicle availability are more likely to use TNCs compared to other groups in Medellín. Evidence also points at gender effects, with being female significantly increasing the probability of using a TNC service. Finally, we observe both transit complementary and substitution patterns of use, depending on the context and by whom the service is requested.
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Thompson, John, Thompson, John, Njuguna Ndung’u, Miguel Albacete, Abid Q. Suleri, Junaid Zahid, and Rubab Aftab. The Impact of Covid-19 on Livelihoods and Food Security. Institute of Development Studies (IDS), 2021. http://dx.doi.org/10.19088/core.2021.002.
Full textAbstract:
Studies of livelihoods and food systems since the start of the global pandemic in 2020 have shown a consistent pattern: the primary risks to food and livelihood security are at the household level. Covid-19 is having a major impact on households’ production and access to quality, nutritious food, due to losses of income, combined with increasing food prices, and restrictions to movements of people, inputs and products. The studies included in this Research for Policy and Practice Report and supported by the Covid-19 Responses for Equity (CORE) Programme span several continents and are coordinated by leading research organisations with a detailed understanding of local food system dynamics and associated equity and livelihood issues in their regions: (1) the impact of the Covid-19 pandemic on livelihoods in sub-Saharan Africa; (2) supporting small and medium enterprises, food security, and evolving social protection mechanisms to deal with Covid-19 in Pakistan; and (3) impact of Covid-19 on family farming and food security in Latin America: evidence-based public policy responses.
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Thompson, John, Thompson, John, Njuguna Ndung’u, Miguel Albacete, Abid Q. Suleri, Junaid Zahid, and Rubab Aftab. The Impact of Covid-19 on Livelihoods and Food Security. Institute of Development Studies (IDS), 2021. http://dx.doi.org/10.19088/core.2021.001.
Full textAbstract:
Studies of livelihoods and food systems since the start of the global pandemic in 2020 have shown a consistent pattern: the primary risks to food and livelihood security are at the household level. Covid-19 is having a major impact on households’ production and access to quality, nutritious food, due to losses of income, combined with increasing food prices, and restrictions to movements of people, inputs and products. The studies included in this Research for Policy and Practice Report and supported by the Covid-19 Responses for Equity (CORE) Programme span several continents and are coordinated by leading research organisations with a detailed understanding of local food system dynamics and associated equity and livelihood issues in their regions: (1) the impact of the Covid-19 pandemic on livelihoods in sub-Saharan Africa; (2) supporting small and medium enterprises, food security, and evolving social protection mechanisms to deal with Covid-19 in Pakistan; and (3) impact of Covid-19 on family farming and food security in Latin America: evidence-based public policy responses.
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Matsuo, Hideko, and Koen Matthijs. The life course and subjective well-being across generations – an analysis based on cross-national surveys (2002–2016). Verlag der Österreichischen Akademie der Wissenschaften, 2021. http://dx.doi.org/10.1553/populationyearbook2021.res4.2.
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This paper identifies subjective well-being trajectories through happiness measures as influenced by time, socio-economic, demographic and behavioural determinants. Hierarchical age-period-cohort models are applied to European Social Survey (2002–2016) data on the population aged 30 and older in 10 countries. A U-shaped relationship between age and happiness is found for some countries, but a rather flat pattern and considerable diversity beyond age 80 are detected for other countries. Lower happiness levels are found for baby boomers (1945–1964) than for preboomers and post-boomers, and also for late boomers (1955–1964) than for early boomers (1945–1954). Women, highly educated and native people are shown to have higher happiness levels than men, less educated and non-native people, respectively. Moreover, a positive assessment of income, having a partner, and being a parent, in good health, employed and socially active are all found to have a positive impact on happiness levels. We find evidence of gaps in happiness levels due to differences in socio-economic characteristics over the life course in some, but not in all of the countries analysed.
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Tabinskyy, Yaroslav. VISUAL CONCEPTS OF PHOTO IN THE MEDIA (ON THE EXAMPLE OF «UKRAINER» AND «REPORTERS»). Ivan Franko National University of Lviv, 2021. http://dx.doi.org/10.30970/vjo.2021.50.11099.
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The article is devoted to the analysis of the main forms of visualization in the media related to photo. The thematic visual concepts are described in accordance with the content of electronic media, which consider the impact of modern technologies on the development of media space. The researches of the Ukrainian and foreign educational institutions concerning the main features of modern photo is classificate. Modifications and new visual forms in the media are singled out. The main objective of the article is to study the visual concepts of modern photo and identify ideological and thematic priorities in photo projects. To achieve the main objective in the article a certain methodology were used. Due to the historical-theoretical description it was possible to substantiate the study of visual concepts. The conceptual-system method was used to study the subject of media photo projects. The main results of the research are the definition of visual concepts of photo on the example of electronic media and the identification of the main thematic features in the process of visual filling of the media space. Based on the study, we can conclude that today the information field needs quality visual content. For successful creation of visual concepts it is necessary to single out thematic features of modern photo and to carry out classifications on ideological and semantic signs. Given the rapid development of digital technologies, the topic of the scientific article we offer is relevant for scientists, journalists, media researchers, visual journalism experts and photojournalists. Modern space is filled with a large number of pictorial materials, which in most cases form specific images, patterns or stereotypes in the mind of the reader (viewer). Also important is the classification of photo used in journalistic publications. That is why there is a need to explore the content and principles of distribution of ideological priorities of photo in the media. The substantiation of scientists about the important place of photography in the modern media space and the future development of visual technologies, which already use artificial intelligence, is relevant.